[ { "text": "Herschel survey of brown dwarf disks in Rho Ophiuchi: Recent observations of the Rho Ophiuchi cluster with the Herschel Space\nObservatory allow us to probe the spectral energy distribution (SED) of the\nbrown dwarf population in the far-IR, where the disk emission peaks. We\nperformed aperture photometry at 70, 100, and 160 micron, and constructed SEDs\nfor all previously known brown dwarfs detected. These were complemented with\nancillary photometry at shorter wavelengths. We compared the observed SEDs to a\ngrid of synthetic disks produced with the radiative transfer code MCFOST, and\nused the relative figure of merit estimated from the Bayesian inference of each\ndisk parameter to analyse the structural properties. We detected 12 Class II\nbrown dwarfs with Herschel, which corresponds to one-third of all currently\nknown brown dwarf members of Rho Ophiuchi. We do not detect any of the known\nClass III brown dwarfs. Comparison to models reveals that the disks are best\ndescribed by an inner radius between 0.01 and 0.07 AU, and a flared disk\ngeometry with a flaring index between 1.05 and 1.2. Furthermore, we can exclude\nvalues of the disk scale-height lower than 10 AU (measured at a fiducial radius\nof 100 AU). We combined the Herschel data with recent ALMA observations of the\nbrown dwarf GY92 204 (ISO-Oph 102), and by comparing its SED to the same grid\nof disk models, we derived an inner disk radius of 0.035 AU, a scale height of\n15 AU with a flaring index of beta~1.15, an exponent for dust settling of -1.5,\nand a disk mass of 0.001 MSun. This corresponds to a disk-to-central object\nmass ratio of ~1%. The structural parameters constrained by the extended SED\ncoverage (inner radius and flaring index) show a narrow distribution for the 11\nyoung brown dwarfs detected in Rho Ophiuchi, suggesting that these objects\nshare the same disk evolution and, perhaps, formation.", "category": "astro-ph_GA" }, { "text": "Fuzzy dark matter dynamics in tidally perturbed dwarf spheroidal galaxy\n satellites: Fuzzy dark matter (FDM) has dynamical properties that differ significantly\nfrom cold dark matter (CDM). These dynamical differences are strongly\nmanifested on the spatial scale of dwarf spheroidal galaxies (dSphs), which\nroughly corresponds to the de Broglie wavelength of a canonical mass FDM\nparticle. We study simulations of a dSph satellite which is tidally perturbed\nby its host galaxy, in order to identify dynamical signatures that are unique\nto FDM, and to quantify the imprints of such perturbations on an observable\nstellar tracer population. We find that a perturbed FDM soliton develops a\nlong-standing breathing mode, whereas for CDM such a breathing mode quickly\nphase-mixes and disappears. We also demonstrate that such signatures become\nimprinted on the dynamics of a stellar tracer population, making them\nobservable with sufficiently precise astrometric measurements.", "category": "astro-ph_GA" }, { "text": "Power-law models of totally anisotropic scattering: The interstellar scattering responsible for pulsar parabolic arcs, and for\nintra-day variability of compact radio quasars, is highly anisotropic in some\ncases. We numerically simulate these observed phenomena using totally\nanisotropic, power-law models for the electron density fluctuations which cause\nthe scattering. By comparing our results to the scattered image of PSR B0834+06\nand, independently, to dual-frequency light curves of the quasar PKS1257-326,\nwe constrain the nature of the scattering media on these lines of sight. We\nfind that models with spectral indices slightly below \\beta=3, including the\none-dimensional Kolmogorov model, are broadly consistent with both data sets.\nWe confirm that a single physical model suffices for both sources, with the\nscattering medium simply being more distant in the case of B0834+06. This\nreinforces the idea that intra-day variability and parabolic arcs have a common\ncause in a type of interstellar structure which, though obscure, is\ncommonplace. However, the implied gas pressure fluctuations are large compared\nto typical interstellar pressures, and the magnetic stresses are much larger\nstill. Thus while these scattering media may be commonplace, their underlying\ndynamics appear quite extraordinary.", "category": "astro-ph_GA" }, { "text": "Effects of feedback on galaxies in the VELA simulations: elongation,\n clumps and compaction: The evolution of star-forming galaxies at high redshifts is very sensitive to\nthe strength and nature of stellar feedback. Using two sets of cosmological,\nzoom-in simulations from the VELA suite, we compare the effects of two\ndifferent models of feedback: with and without kinetic feedback from the\nexpansion of supernovae shells and stellar winds. At a fixed halo mass and\nredshift, the stellar mass is reduced by a factor of 1-3 in the models with\nstronger feedback, so the stellar-mass-halo-mass relation is in better\nagreement with abundance matching results. On the other hand, the\nthree-dimensional shape of low-mass galaxies is elongated along a major axis in\nboth models. At a fixed stellar mass, Ms<10^10 Msun, galaxies are more\nelongated in the strong-feedback case. More massive, star-forming discs with\nhigh surface densities form giant clumps. However, the population of round,\ncompact, old (age_c > 300 Myr), quenched, stellar (or gas-poor) clumps is\nabsent in the model with strong feedback. On the other hand, giant star-forming\nclumps with intermediate ages (age_c= 100 - 300 Myr) can survive for several\ndisc dynamical times, independently of feedback strength. The evolution through\ncompaction followed by quenching in the plane of central surface density and\nspecific star-formation rate is similar under the two feedback models.", "category": "astro-ph_GA" }, { "text": "Is there a relationship between AGN and star formation in IR-bright\n AGNs?: We report the relationship between the luminosities of active galactic nuclei\n(AGNs) and the rates of star formation (SF) for a sample of 323 far-infrared\n(FIR)-detected AGNs. This sample has a redshift range of 0.2 $< z <$ 2.5, and\nspans three orders of magnitude in luminosity, ${\\rm L_{X} \\sim\n10^{42-45}}$erg$s^{-1}$. We find that in AGN hosts, the total IR luminosity\n(8-1000$\\mu$m) has a significant AGN contribution (average$\\sim$20%), and we\nsuggest using the FIR luminosity (30-1000 $\\mu$m) as a more reliable star\nformation rate (SFR) estimator. We also conclude that monochromatic\nluminosities at 60 and 100\\,$\\mu$\\,m are also good SFR indicators with\nnegligible AGN contributions, and are less sensitive than integrated infrared\nluminosities to the shape of the AGN SED, which is uncertain at\n$\\lambda>$100\\micron. Significant bivariate $L_{\\rm X}$-$L_{\\rm IR}$\ncorrelations are found, which remain significant in the combined sample when\nusing residual partial correlation analysis to account for the inherent\nredshift dependence. No redshift or mass dependence is found for the ratio\nbetween SFR and black hole accretion rate (BHAR), which has a mean and scatter\nof log (SFR/BHAR) $=3.1 \\pm$ 0.5, agreeing with the local mass ratio between\nsupermassive black hole and host galaxies. The large scatter in this ratio and\nthe strong AGN-SF correlation found in these IR-bright AGNs are consistent with\nthe scenario of an AGN-SF dependence on a common gas supply, regardless of the\nevolutionary model.", "category": "astro-ph_GA" }, { "text": "CHANG-ES XIII: Transport processes and the magnetic fields of NGC 4666 -\n indication of a reversing disk magnetic field: We analyze the magnetic field geometry and the transport processes of the\ncosmic rays of the edge-on spiral starburst galaxy NGC 4666 from CHANG-ES radio\ncontinuum data in two frequencies; 6 GHz (C-band) and 1.5 GHz (L-band).\nSupplementary X-ray data are used to investigate the hot gas in NGC 4666. We\ndetermine the radio scale heights of total power emission at both frequencies\nfor this galaxy. We show the magnetic field orientations derived from the\npolarization data. Using rotation measure (RM) synthesis we further study the\nbehavior of the RM values along the disk in C-band to investigate the\nlarge-scale magnetic-field pattern. We use the revised equipartition formula to\ncalculate a map of the magnetic field strength. Furthermore, we model the\nprocesses of cosmic-ray transport into the halo with the 1D SPINNAKER model.\nThe extended radio halo of NGC 4666 is box-shaped and is probably produced by\nthe previously observed supernova-driven superwind. This is supported by our\nfinding of an advective cosmic-ray transport such as that expected for a\ngalactic wind. The scaleheight analysis revealed an asymmetric halo above and\nbelow the disk as well as between the two sides of the major axis. A central\npoint source as well as a bubble structure is seen in the radio data for the\nfirst time. Our X-ray data show a box-shaped hot halo around NGC 4666 and\nfurthermore confirm the AGN nature of the central source. NGC 4666 has a\nlarge-scale X-shaped magnetic field in the halo, as has been observed in other\nedge-on galaxies. The analysis furthermore revealed that the disk of NGC 4666\nshows hints of field reversals along its radius, which is the first detection\nof this phenomenon in an external galaxy.", "category": "astro-ph_GA" }, { "text": "ALMA reveals sequential high-mass star formation in the G9.62+0.19\n complex: Stellar feedback from high-mass stars (e.g., H{\\sc ii} regions) can strongly\ninfluence the surrounding interstellar medium and regulate star formation. Our\nnew ALMA observations reveal sequential high-mass star formation taking place\nwithin one sub-virial filamentary clump (the G9.62 clump) in the G9.62+0.19\ncomplex. The 12 dense cores (MM 1-12) detected by ALMA are at very different\nevolutionary stages, from starless core phase to UC H{\\sc ii} region phase.\nThree dense cores (MM6, MM7/G, MM8/F) are associated with outflows. The\nmass-velocity diagrams of outflows associated with MM7/G and MM8/F can be well\nfitted with broken power laws. The mass-velocity diagram of SiO outflow\nassociated with MM8/F breaks much earlier than other outflow tracers (e.g., CO,\nSO, CS, HCN), suggesting that SiO traces newly shocked gas, while the other\nmolecular lines (e.g., CO, SO, CS, HCN) mainly trace the ambient gas\ncontinuously entrained by outflow jets. Five cores (MM1, MM3, MM5, MM9, MM10)\nare massive starless core candidates whose masses are estimated to be larger\nthan 25 M$_{\\sun}$, assuming a dust temperature of $\\leq$ 20 K. The shocks from\nthe expanding H{\\sc ii} regions (\"B\" \\& \"C\") to the west may have great impact\non the G9.62 clump through compressing it into a filament and inducing core\ncollapse successively, leading to sequential star formation. Our findings\nsuggest that stellar feedback from H{\\sc ii} regions may enhance the star\nformation efficiency and suppress the low-mass star formation in adjacent\npre-existing massive clumps.", "category": "astro-ph_GA" }, { "text": "The galaxy counterpart of the high-metallicity and 16 kpc impact\n parameter DLA towards Q0918+1636 - a challenge to galaxy formation models?: The quasar Q0918+1636 (z=3.07) has an intervening high-metallicity Damped\nLyman-alpha Absorber (DLA) along the line of sight, at a redshift of z=2.58.\nThe DLA is located at a large impact parameter of 16.2 kpc, and has an almost\nsolar metallicity. It is shown, that a novel type of cosmological galaxy\nformation models, invoking a new SNII feedback prescription, the Haardt & Madau\n(2012) UVB field and explicit treatment of UVB self-shielding, can reproduce\nthe observed characteristics of the DLA. UV radiation from young stellar\npopulations in the galaxy, in particular in the photon energy range 10.36-13.61\neV (relating to Sulfur II abundance), are also considered in the analysis. It\nis found that a) for L~L* galaxies (at z=2.58), about 10% of the sight-lines\nthrough the galaxies at impact parameter 16.2 kpc will display a Sulfur II\ncolumn density N(SII)$>$ 10$^{15.82}$ cm$^{-2}$ (the observed value for the\nDLA), and b) considering only cases where a near-solar metallicity will be\ndetected at 16.2 kpc impact parameter, the probability distribution of galaxy\nSFR peaks near the value observed for the DLA galaxy counterpart of ~27\nMsun/yr. It is argued, that the bulk of the alpha-elements, like Sulfur, traced\nby the high metal column density, b=16.2 kpc absorption lines, were produced by\nevolving young stars in the inner galaxy, and later transported outward by\ngalactic winds.", "category": "astro-ph_GA" }, { "text": "Stripped elliptical galaxies as probes of ICM physics: II. Stirred, but\n mixed? Viscous and inviscid gas stripping of the Virgo elliptical M89: Elliptical galaxies moving through the intra-cluster medium (ICM) are\nprogressively stripped of their gaseous atmospheres. X-ray observations reveal\nthe structure of galactic tails, wakes, and the interface between the galactic\ngas and the ICM. This fine-structure depends on dynamic conditions (galaxy\npotential, initial gas contents, orbit in the host cluster), orbital stage\n(early infall, pre-/post-pericenter passage), as well as on the still\nill-constrained ICM plasma properties (thermal conductivity, viscosity,\nmagnetic field structure). Paper I describes flow patterns and stages of\ninviscid gas stripping. Here we study the effect of a Spitzer-like temperature\ndependent viscosity corresponding to Reynolds numbers, Re, of 50 to 5000 with\nrespect to the ICM flow around the remnant atmosphere. Global flow patterns are\nindependent of viscosity in this Reynolds number range. Viscosity influences\ntwo aspects: In inviscid stripping, Kelvin-Helmholtz instabilities (KHIs) at\nthe sides of the remnant atmosphere lead to observable horns or wings.\nIncreasing viscosity suppresses KHIs of increasing length scale, and thus\nobservable horns and wings. Furthermore, in inviscid stripping, stripped\ngalactic gas can mix with the ambient ICM in the galaxy's wake. This mixing is\nsuppressed increasingly with increasing viscosity, such that viscously stripped\ngalaxies have long X-ray bright, cool wakes. We provide mock X-ray images for\ndifferent stripping stages and conditions. While these qualitative results are\ngeneric, we tailor our simulations to the Virgo galaxy M89 (NGC 4552), where\nRe~ 50 corresponds to a viscosity of 10% of the Spitzer level. Paper III\ncompares new deep Chandra and archival XMM-Newton data to our simulations.", "category": "astro-ph_GA" }, { "text": "The Dragon-II simulations -- II. Formation mechanisms, mass, and spin of\n intermediate-mass black holes in star clusters with up to 1 million stars: The processes that govern the formation of intermediate-mass black holes\n(IMBHs) in dense stellar clusters are still unclear. Here, we discuss the role\nof stellar mergers, star-BH interactions and accretion, as well as BH binary\n(BBH) mergers in seeding and growing IMBHs in the \\textsc{Dragon-II} simulation\ndatabase, a suite of 19 direct $N$-body models representing dense clusters with\nup to $10^6$ stars. \\textsc{Dragon-II} IMBHs have typical masses of $m_{\\rm\nIMBH} = (100-380)$ M$_\\odot$ and relatively large spins $\\chi_{\\rm IMBH} >\n0.6$. We find a link between the IMBH formation mechanism and the cluster\nstructure. In clusters denser than $3\\times 10^5$ M$_\\odot$ pc$^{-3}$, the\ncollapse of massive star collision products represents the dominant IMBH\nformation process, leading to the formation of heavy IMBHs ($m_{\\rm IMBH} >\n200$ M$_\\odot$), possibly slowly rotating, that form over times $<5$ Myr and\ngrow further via stellar accretion and mergers in just $<30$ Myr. BBH mergers\nare the dominant IMBH formation channel in less dense clusters, for which we\nfind that the looser the cluster, the longer the formation time ($10-300$ Myr)\nand the larger the IMBH mass, although remaining within $200$ M$_\\odot$. Strong\ndynamical scatterings and relativistic recoil efficiently eject all IMBHs in\n\\textsc{Dragon-II} clusters, suggesting that IMBHs in this type of cluster are\nunlikely to grow beyond a few $10^2$ M$_\\odot$.", "category": "astro-ph_GA" }, { "text": "Probing the origin of the two-component structure of broad line region\n by reverberation mapping of an extremely variable quasar: The physical origins of quasar components, such as the broad line region\n(BLR) and dust torus, remain under debate. To gain insights into them, we\nfocused on Changing-State Quasars (CSQs) which provide a unique perspective\nthrough structural changes associated with accretion disk state transitions. We\ntargeted SDSS J125809.31+351943.0, an extremely variable CSQ, to study its\ncentral core structure and kinematics. We conducted reverberation mapping with\noptical spectroscopy to explore the structure of the BLR and estimate the black\nhole mass. The results from H$\\beta$ reverberation mapping indicated a black\nhole mass of $10^{9.64^{+0.11}_{-0.20}}\\rm{M_\\odot}$. Additionally, we analyzed\nvariations in the optical to X-ray spectral indices, $\\alpha_{\\rm{ox}}$, before\nand after the state transition, to investigate the accretion disk. These\nvariations in $\\alpha_{\\rm{ox}}$ and the Eddington ratio (from 0.4 \\% to 2.4\n\\%) exhibitied behavior similar to state transitions observed in X-ray binary\nsystems. Spectral analysis of H$\\beta$ revealed a predominantly double-peaked\nprofile during dim periods, transitioning to include a single-peaked component\nas the quasar brightened, suggesting that H$\\beta$ contains a mixture of two\ncomponents. Each of these components has its distinct characteristics: the\nfirst is a double-peaked profile that remains stable despite changes in the\naccretion rate, while the second is a variable single-peaked profile. Using\ntime lags from reverberation mapping, we estimated the spatial relationships\nbetween these BLR components, the accretion disk, and the dust torus. Our\nresults suggest that the BLR consists of two distinct components, each\ndiffering in location and origin.", "category": "astro-ph_GA" }, { "text": "Unraveling the Complex Structure of AGN-driven Outflows. VI. Strong\n Ionized Outflows in Type 1 AGNs and the Outflow Size-Luminosity Relation: We present spatially resolved gas kinematics, ionization, and energetics of\n11 type 1 and 5 type 2 active galactic nuclei (AGNs) with strong ionized gas\noutflows at z $<0.3$ using Gemini Multi-Object Spectrograph Integral Field Unit\n(GMOS-IFU) data. We find a strongly blueshifted region in [OIII] velocity maps,\nrepresenting an approaching cone in biconical outflows, and blueshifted and\nredshifted regions in H$\\alpha$ velocity maps, which show gravitationally\nrotating kinematics. AGN photoionization is dominant in the central region of\nmost targets, and some of them also show ring-like structures of LINER or\ncomposite that surround the AGN-dominated center. Following our previous\nstudies, we kinematically determine outflow sizes by the ratio between [OIII]\nand stellar velocity dispersion. Outflow sizes of type 1 AGNs follow the same\nkinematic outflow size-[OIII] luminosity relation obtained from the type 2 IFU\nsample in Kang & Woo and Luo (updated slope $0.29\\pm0.04$), while they are\nlimited to the central kpc scales, indicating the lack of global impact of\noutflows on the interstellar medium. Small mass outflow rates and large star\nformation rates of the combined sample support that there is no evidence of\nrapid star formation quenching by outflows, which is consistent with the\ndelayed AGN feedback.", "category": "astro-ph_GA" }, { "text": "MAHALO Deep Cluster Survey II. Characterizing massive forming galaxies\n in the Spiderweb protocluster at z=2.2: This paper is the second in a series presenting the results of our deep\nH$\\alpha$-line survey towards protoclusters at $z>2$, based on narrow-band\nimaging with the Subaru Telescope. This work investigates massive galaxies in a\nprotocluster region associated with a radio galaxy (PKS 1138$-$262), the\nSpiderweb galaxy, at $z=2.2$. Our 0.5 mag deeper narrow-band imaging than\nprevious surveys collects a total of 68 H$\\alpha$ emitters (HAE). 17 out of the\n68 are newly discovered protocluster members. First, a very high characteristic\nstellar mass of M$_\\star^\\ast=10^{11.73}$ M$_\\odot$ is measured from a\nSchechter function fit to the mass distribution of HAEs. Together with the\nChandra X-ray data, we find that four out of six massive HAEs\n(M$_\\star>10^{11}$ M$_\\odot$) show bright X-ray emission, suggesting that they\nhost active galactic nuclei (AGNs). Their mass estimates, therefore, would be\naffected by the nuclear emission from AGNs. Notably, the X-ray detected HAEs\nare likely positioned near the boundary between star-forming and quiescent\npopulations in the rest-frame $UVJ$ plane. Moreover, our deep narrow-band data\nsucceed in probing the bright H$\\alpha$ (+[Nii]) line nebula of the Spiderweb\ngalaxy extending over $\\sim100$ physical kpc. These results suggest that the\nmassive galaxies in the Spiderweb protocluster are on the way to becoming the\nbright red sequence objects seen in local galaxy clusters, where AGNs might\nplay an essential role in their quenching processes. Though a more statistical\ndatabase is needed to build a general picture.", "category": "astro-ph_GA" }, { "text": "Molecular Emission from a Galaxy Associated with a z~2.2 Damped\n Lyman-alpha Absorber: Using the Atacama Large Millimeter/sub-millimeter Array, we have detected\nCO(3-2) line and far-infrared continuum emission from a galaxy associated with\na high-metallicity ([M/H] = -0.27) damped Ly-alpha absorber (DLA) at z\n=2.19289. The galaxy is located 3.5\" away from the quasar sightline,\ncorresponding to a large impact parameter of 30 kpc at the DLA redshift. We use\narchival Very Large Telescope-SINFONI data to detect Halpha emission from the\nassociated galaxy, and find that the object is dusty, with a dust-corrected\nstar formation rate of 110 +60 -30 Msun/yr. The galaxy's molecular mass is\nlarge, Mmol = (1.4 +- 0.2) x 10^11 x (\\alpha_CO/4.3) x (0.57/r_31) Msun,\nsupporting the hypothesis that high-metallicity DLAs arise predominantly near\nmassive galaxies. The excellent agreement in redshift between the CO(3-2) line\nemission and low-ion metal absorption (~40 km/s) disfavors scenarios whereby\nthe gas probed by the DLA shows bulk motion around the galaxy. We use Giant\nMetrewave Radio Telescope HI 21cm absorption spectroscopy to find that the HI\nalong the DLA sightline must be warm, with a stringent lower limit on the spin\ntemperature of T_s > 1895 x (f/0.93) K. The detection of CI absorption in the\nDLA, however, also indicates the presence of cold neutral gas. To reconcile\nthese results requires that the cold components in the DLA contribute little to\nthe HI column density, yet contain roughly 50% of the metals of the absorber,\nunderlining the complex multi-phase nature of the gas surrounding high-z\ngalaxies.", "category": "astro-ph_GA" }, { "text": "Where stars form: inside-out growth and coherent star formation from HST\n Halpha maps of 2676 galaxies across the main sequence at z~1: We present Ha maps at 1kpc spatial resolution for star-forming galaxies at\nz~1, made possible by the WFC3 grism on HST. Employing this capability over all\nfive 3D-HST/CANDELS fields provides a sample of 2676 galaxies. By creating deep\nstacked Halpha (Ha) images, we reach surface brightness limits of\n1x10^-18\\erg\\s\\cm^2\\arcsec^2, allowing us to map the distribution of ionized\ngas out to >10kpc for typical L* galaxies at this epoch. We find that the\nspatial extent of the Ha distribution increases with stellar mass as\nr(Ha)[kpc]=1.5(Mstars/10^10Msun)^0.23. Furthermore, the Ha emission is more\nextended than the stellar continuum emission, consistent with inside-out\nassembly of galactic disks. This effect, however, is mass dependent with\nr(Ha)/r(stars)=1.1(M/10^10Msun)^0.054, such that at low masses r(Ha)~r(stars).\nWe map the Ha distribution as a function of SFR(IR+UV) and find evidence for\n`coherent star formation' across the SFR-M plane: above the main sequence, Ha\nis enhanced at all radii; below the main sequence, Ha is depressed at all\nradii. This suggests that at all masses the physical processes driving the\nenhancement or suppression of star formation act throughout the disks of\ngalaxies. It also confirms that the scatter in the star forming main sequence\nis real and caused by variations in the star formation rate at fixed mass. At\nhigh masses (10^10.5 30 km/s, and about\n29% or all globular clusters formed at redshifts z > 7. These results further\nstrengthen the notion that globular cluster formation was an important mode of\nstar formation in high-redshift galaxies and likely played a significant role\nin the reionization of the intergalactic medium", "category": "astro-ph_GA" }, { "text": "A massive mess: When a large dwarf and a Milky Way-like galaxy merge: Circa 10 billion years ago the Milky Way merged with a massive satellite,\nGaia-Enceladus. To gain insight into the properties of its debris we analyse in\ndetail the suite of simulations from Villalobos & Helmi (2008), which includes\nan experiment that produces a good match to the kinematics of nearby halo stars\ninferred from Gaia data. We compare the kinematic distributions of stellar\nparticles in the simulations and study the distribution of debris in orbital\nangular momentum, eccentricity and energy, and its relation to the mass-loss\nhistory of the simulated satellite. We confirm that Gaia-Enceladus probably\nfell in on a retrograde, 30$^\\circ$ inclination orbit. We find that while 75%\nof the debris in our preferred simulation has large eccentricity ($> 0.8$),\nroughly 9% has eccentricity smaller than 0.6. Star particles lost early have\nlarge retrograde motions, and a subset of these have low eccentricity. Such\nstars would be expected to have lower metallicities as they stem from the\noutskirts of the satellite, and hence naively they could be confused with\ndebris associated with a separate system. These considerations seem to apply to\nsome of the stars from the postulated Sequoia galaxy. When a massive discy\ngalaxy merges, it leaves behind debris with a complex phase-space structure, a\nlarge range of orbital properties, and a range of chemical abundances.\nObservationally, this results in substructures with very different properties,\nwhich can be misinterpreted as implying independent progeny. Detailed chemical\nabundances of large samples of stars and tailored hydrodynamical simulations\nare critical to resolving such conundrums.", "category": "astro-ph_GA" }, { "text": "Correlations of gas, dust and young stellar populations in the spiral\n galaxy NGC 7331: Molecular clouds (MCs) in galaxies are complex places with many phases. It\nis, therefore, essential to study the physics and kinematics of the MCs using\nmultiple emission lines. We probe the physics of the molecular gas and dust in\nthe nearby spiral galaxy NGC 7331 using multiple emission lines, i.e. carbon\nmonoxide (CO), 24{\\mu}m and far-ultraviolet (FUV) data. 14 positions were\ntargeted across the gaseous disc of NGC 7331. We found that CO intensities, gas\nmass, gas surface density, and 24{\\mu}m-to-FUV flux ratio (i.e. the extinction)\nincrease up to about 40 arcsec from the centre and then start to decrease.\nThere is a positive correlation between most of the pair of parameters studied\n(except FUV flux density). The beam-averaged physical parameters on the eastern\nside of the disc show higher median values than those on the western side. Our\nresults indicate that the star formation activity, stellar populations and\noverall physical properties of the ISM are different on either side of the\ndisc. Our study provides notable insights into the complex nature of the\ninterstellar medium (ISM) in galaxies and has the potential to provoke future\nhigher-resolution studies yet to come.", "category": "astro-ph_GA" }, { "text": "Kinematics of the Atomic ISM in M33 on 80 pc scales: We present new L-band ($1\\mbox{--}2$ GHz) observations of the nearby spiral\ngalaxy M33 with 80 pc resolution obtained with the Karl G. Jansky Very Large\nArray. The HI observations, combined with HI measurements from the Green Bank\nTelescope, improve the spectral resolution and sensitivity ($2.8$ K rms noise\nin a $0.2$ km s$^{-1}$ channel) compared to previous observations. We find\nindividual profiles are usually non-Gaussian, harbouring line wings, multiple\ncomponents, and asymmetries. Given this spectral complexity, we quantify the\nmotions in the atomic ISM through moment analysis of the spectra and fits to\naligned, stacked profiles. The measured value of the HI line width depends\nstrongly on the method used, with the velocity stacked profiles aligned to the\npeak velocity giving the minimum value of $\\sigma = 7$ km s$^{-1}$ and all\nother methods giving higher values ($\\sigma\\sim10$ km s$^{-1}$). All\nmeasurements of the line width show a shallow radial trend, with $\\sigma$\ndecreasing by $\\sim2$ km s$^{-1}$ from $R_{\\rm gal}=0$ to $R_{\\rm gal}=8$ kpc.\nWe consider a number of energy sources that might maintain the line width\nagainst turbulent dissipation, but no single source is adequate. We find excess\nemission relative to a Gaussian in the stacked profile line wings, ranging from\n9% to 26% depending on how the spectra are aligned. By splitting the line wings\ninto symmetric and asymmetric components, we find that the lagging rotational\ndisk accounts for one-third of the line wing flux. We also find emission far\nfrom the rotation axis of the galaxy in multiple discrete HI clouds, including\na filament with a projected length of $\\sim8$ kpc.", "category": "astro-ph_GA" }, { "text": "A 2-3 mm high-resolution molecular line survey towards the centre of the\n nearby spiral galaxy NGC 6946: The complex physical, kinematic, and chemical properties of galaxy centres\nmake them interesting environments to examine with molecular line emission. We\npresent new $2-4$\" (${\\sim}75{-}150$ pc at $7.7$ Mpc) observations at 2 and 3\nmm covering the central $50$\" (${\\sim}1.9$ kpc) of the nearby double-barred\nspiral galaxy NGC 6946 obtained with the IRAM Plateau de Bure Interferometer.\nWe detect spectral lines from ten molecules: CO, HCN, HCO$^+$, HNC, CS,\nHC$_3$N, N$_2$H$^+$, C$_2$H, CH$_3$OH, and H$_2$CO. We complemented these with\npublished 1mm CO observations and 33 GHz continuum observations to explore the\nstar formation rate surface density ${\\Sigma_{\\mathrm{SFR}}}$ on 150 pc scales.\nIn this paper, we analyse regions associated with the inner bar of NGC 6946 $-$\nthe nuclear region (NUC), the northern (NBE), and southern inner bar end (SBE)\nand we focus on short-spacing corrected bulk (CO) and dense gas tracers (HCN,\nHCO$^+$, and HNC). We find that HCO$^+$ correlates best with\n${\\Sigma_{\\mathrm{SFR}}}$, but the dense gas fraction ($f_{\\mathrm{dense}}$)\nand star formation efficiency of the dense gas (${\\mathrm{SFE_{dense}}}$) fits\nshow different behaviours than expected from large-scale disc observations.The\nSBE has a higher ${\\Sigma_{\\mathrm{SFR}}}$, $f_{\\mathrm{dense}}$, and shocked\ngas fraction than the NBE. We examine line ratio diagnostics and find a higher\nCO(2-1)/CO(1-0) ratio towards NBE than for the NUC. Moreover, comparison with\nexisting extragalactic datasets suggests that using the HCN/HNC ratio to probe\nkinetic temperatures is not suitable on kiloparsec and sub-kiloparsec scales in\nextragalactic regions. Lastly, our study shows that the HCO$^+$/HCN ratio might\nnot be a unique indicator to diagnose AGN activity in galaxies.", "category": "astro-ph_GA" }, { "text": "Is a recently discovered HI cloud near M94 a starless dark matter halo?: Observations with the Five-Hundred-Meter Aperture Spherical Telescope have\nrevealed the presence of a marginally-resolved source of 21 cm emission from a\nlocation $\\sim50'$ from the M94 galaxy, without a stellar counterpart down to\nthe surface brightness limit of the DESI Imaging Legacy Survey ($\\sim29.15$ mag\narcsec$^{-2}$ in the $g$ band). The system (hereafter Cloud-9) has round column\ndensity isocontours and a line width consistent with thermal broadening from\ngas at $T\\sim2\\times10^4$ $K$. These properties are unlike those of previously\ndetected dark HI clouds and similar to the expected properties of\nREionization-Limited-HI Cloud (RELHICs), namely, starless dark matter (DM)\nhalos filled with gas in hydrostatic equilibrium and in thermal equilibrium\nwith the cosmic ultraviolet background. At the distance of M94, $d\\sim4.7$ Mpc,\nwe find that Cloud-9 is consistent with being a RELHIC inhabiting a\nNavarro-Frenk-White (NFW) DM halo of mass, $M_{200}\\sim5\\times10^{9}$\n$M_{\\odot}$, and concentration, $c_{\\rm NFW}\\sim13$. Although the agreement\nbetween the model and observations is good, Cloud-9 appears to be slightly, but\nsystematically, more extended than expected for $\\Lambda$CDM RELHICs. This may\nimply either that Cloud-9 is much closer than implied by its recessional\nvelocity, $v_{\\rm CL9}\\sim300$ km s$^{-1}$, or that its halo density profile is\nflatter than NFW, with a DM mass deficit greater than a factor of $10$ at radii\n$r\\lesssim1$ kpc. Further observations may aid in constraining these scenarios\nbetter and help elucidate whether Cloud-9 is the first ever observed RELHIC, a\ncornerstone prediction of the $\\Lambda$CDM model on the smallest scales.", "category": "astro-ph_GA" }, { "text": "The Galaxy in Context: Structural, Kinematic and Integrated Properties: Our Galaxy, the Milky Way, is a benchmark for understanding disk galaxies. It\nis the only galaxy whose formation history can be studied using the full\ndistribution of stars from white dwarfs to supergiants. The oldest components\nprovide us with unique insight into how galaxies form and evolve over billions\nof years. The Galaxy is a luminous (L-star) barred spiral with a central\nbox/peanut bulge, a dominant disk, and a diffuse stellar halo. Based on global\nproperties, it falls in the sparsely populated \"green valley\" region of the\ngalaxy colour-magnitude diagram. Here we review the key integrated, structural\nand kinematic parameters of the Galaxy, and point to uncertainties as well as\ndirections for future progress. Galactic studies will continue to play a\nfundamental role far into the future because there are measurements that can\nonly be made in the near field and much of contemporary astrophysics depends on\nsuch observations.", "category": "astro-ph_GA" }, { "text": "A Uniformly Selected, Southern-Sky 6dF, Optical AGN Catalog: We have constructed a catalog of active galactic nuclei (AGNs) with $z <\n0.13$, based on optical spectroscopy, from the parent sample of galaxies in the\n6dF galaxy survey (Final Release of 6dFGS), a census of the Southern\nhemisphere. This work is an extension of our all sky AGN catalog \\citet [ZCF,\nhere after]{ZCF19}. The ZCF is based on 43,533 galaxies with $\\rm K_s \\leq$\n11.75 ($z \\leq 0.09$) in the 2MASS Redshift Survey (2MRS). The parent catalog\nof this work, the 6dF catalog, consists of 136,304 publicly available digital\nspectra for 125,071 galaxies with $\\rm Dec \\leq 0^\\circ$ and $\\rm K_s \\leq\n12.65$ (median $z = 0.053$). Our AGN catalog consists of 3109 broad line AGNs\nand 12,156 narrow line AGNs which satisfy the \\citet{Kauffmann03} criteria, of\nwhich 3865 also satisfy the \\citet{Kewley01} criteria. We also provide emission\nline widths, fluxes, flux errors, and signal-to-noise ratios of all the\ngalaxies in our spectroscopic sample, allowing users to customize the selection\ncriteria. In addition, we provide AGN likelihood for the rest of galaxies based\non the availability and quality of their spectra. These likelihood values can\nbe used for rigorous statistical analyses.", "category": "astro-ph_GA" }, { "text": "Effects of baryonic and dark matter substructure on the Pal 5 stream: Gravitational encounters between small-scale dark matter substructure and\ncold stellar streams in the Milky Way halo lead to density perturbations in the\nlatter, making streams an effective probe for detecting dark matter\nsubstructure. The Pal 5 stream is one such system for which we have some of the\nbest data. However, Pal 5 orbits close to the center of the Milky Way and has\npassed through the Galactic disk many times, where its structure can be\nperturbed by baryonic structures such as the Galactic bar and giant molecular\nclouds (GMCs). In order to understand how these baryonic structures affect Pal\n5's density, we present a detailed study of the effects of the Galactic bar,\nspiral structure, GMCs, and globular clusters on the Pal 5 stream. We estimate\nthe effect of each perturber on the stream density by computing its power\nspectrum and comparing it to the power induced by a CDM-like population of dark\nmatter subhalos. We find that the bar and GMCs can each individually create\npower that is comparable to the observed power on large scales, leaving little\nroom for dark matter substructure, while spirals are subdominant on all scales.\nOn degree scales, the power induced by the bar is small, but GMCs create\nsmall-scale density variations that are similar in amplitude to the dark-matter\ninduced variations but otherwise indistinguishable from it. These results\ndemonstrate that Pal 5 is a poor system for constraining the dark matter\nsubstructure fraction and that observing streams further out in the halo will\nbe necessary to confidently detect dark matter subhalos.", "category": "astro-ph_GA" }, { "text": "Probing $z \\gtrsim 6$ massive black holes with gravitational waves: We investigate the coalescence of massive black hole ($M_{\\rm BH}\\gtrsim\n10^{6}~\\rm M_{\\odot}$) binaries (MBHBs) at $63 \\sigma$) overdense regions ($M_h\\sim 10^{12}~\\rm M_{\\odot}$ dark\nmatter halos at $z = 6$) of the Universe. We first analyse the impact of\ndifferent resolutions and AGN feedback prescriptions on the merger rate,\nassuming instantaneous mergers. Then, we compute the halo bias correction\nfactor due to the overdense simulated region. Our simulations predict merger\nrates that range between 3 - 15 $\\rm yr^{-1}$ at $z\\sim 6$, depending on the\nrun considered, and after correcting for a bias factor of $\\sim 20-30$.\n For our fiducial model, we further consider the effect of delay in the MBHB\ncoalescence due to dynamical friction. We find that 83 per cent of MBHBs will\nmerge within the Hubble time, and 21 per cent within 1 Gyr, namely the age of\nthe Universe at $z > 6$. We finally compute the expected properties of the\ngravitational wave (GW) signals and find the fraction of LISA detectable events\nwith high signal-to-noise ratio (SNR $>$ 5) to range between 66-69 per cent.\nHowever, identifying the electro-magnetic counterpart of these events remains\nchallenging due to the poor LISA sky localization that, for the loudest signals\n($\\mathcal M_c\\sim 10^6~\\rm M_{\\odot}$ at $z=6$), is around 10 $\\rm deg^2$.", "category": "astro-ph_GA" }, { "text": "The impact of black hole feedback on the UV luminosity and stellar mass\n assembly of high-redshift galaxies: We employ the Delphi semi-analytical model to study the impact of black hole\ngrowth on high-redshift galaxies, both in terms of the observed UV luminosity\nand of the star formation rate. To do this, firstly, we assess the contribution\nof AGN to the total galaxy UV luminosity as a function of stellar mass and\nredshift. We find that for $M_{UV} < -24$ mag and $z \\approx 5 - 6$ the\ngalaxies for which the black hole UV luminosity outshines the stellar UV\nemission become the majority, and we estimate their duty cycle. Secondly, we\nstudy the evolution of the AGN and stellar luminosity functions (LFs), finding\nthat it is driven both by changes in their characteristic luminosities (i.e.\nevolution of the intrinsic brightness of galaxies) and in their normalizations\n(i.e. evolution of the number densities of galaxies), depending on the\nluminosity range considered. Finally, we follow the mass assembly history for\nthree different halo mass bins, finding that the magnitude of AGN-driven\noutflows depends on the host halo mass. We show that AGN feedback is most\neffective when the energy emitted by the accreting black hole is approximately\n$1\\%$ of the halo binding energy, and that this condition is met in galaxies in\nhalos with $M_h \\sim 10^{11.75} M_\\odot$ at $z=4$. In such cases, AGN feedback\ncan drive outflows that are up to 100 times more energetic than SN-driven\noutflows, and the star formation rate is a factor of three lower than for\ngalaxies of the same mass without black hole activity.", "category": "astro-ph_GA" }, { "text": "Restoration of the Tully-Fisher Relation by Statistical Rectification: I employ the Lucy rectification algorithm to recover the\ninclination-corrected distribution of local disk galaxies in the plane of\nabsolute magnitude ($M_i$) and HI velocity width ($W_{20}$). By considering the\ninclination angle as a random variable with a known probability distribution,\nthe novel approach eliminates one major source of uncertainty in studies of the\nTully-Fisher relation: inclination angle estimation from axial ratio.\nLeveraging the statistical strength derived from the entire sample of 28,264\nHI-selected disk galaxies at $z < 0.06$ from the Arecibo Legacy Fast ALFA\n(ALFALFA) survey, I show that the restored distribution follows a sharp\ncorrelation that is approximately a power law between $-16 > M_i > -22$: $M_i =\nM_0 - 2.5\\beta \\ [\\log(W_{\\rm 20}/250 {\\rm km/s})]$, with $M_0 = -19.77\\pm0.04$\nand $\\beta = 4.39\\pm0.06$. At the brighter end ($M_i < -22$), the slope of the\ncorrelation decreases to $\\beta \\approx 3.3$, confirming previous results.\nBecause the method accounts for measurement errors, the intrinsic dispersion of\nthe correlation is directly measured: $\\sigma(\\log W_{20}) \\approx 0.06$ dex\nbetween $-17 > M_i > -23$, while $\\sigma(M_i)$ decreases from $\\sim$0.8 in slow\nrotators to $\\sim$0.4 in fast rotators. The statistical rectification method\nholds significant potential, especially in the studies of\nintermediate-to-high-redshift samples, where limited spatial resolution hinders\nprecise measurements of inclination angles.", "category": "astro-ph_GA" }, { "text": "Magnetized Kelvin-Helmholtz instability in the presence of a radiation\n field: The purpose of this study is to analyze the dynamical role of a radiation\nfield on the growth rate of the unstable Kelvin - Helmholtz (KH) perturbations.\nAs a first step toward this purpose, the analyze is done in a general way,\nirrespective of applying the model to a specific astronomical system. The\ntransition zone between the two layers of the fluid is ignored. Then, we\nperform a linear analysis and by imposing suitable boundary conditions and\nconsidering a radiation field, we obtain appropriate dispersion relation.\nUnstable modes are studied by solving the dispersion equation numerically, and\nthen growth rates of them are obtained. By analyzing our dispersion relation,\nwe show that for a wide range of the input parameters, the radiation field has\na destabilizing effect on KH instability. In eruptions of the galaxies or\nsupermassive stars, the radiation field is dynamically important and because of\nthe enhanced KH growth rates in the presence of the radiation; these eruptions\ncan inject more momentum and energy into their environment and excite more\nturbulent motions.", "category": "astro-ph_GA" }, { "text": "A 10,000 Years Old Explosion in DR21: Sensitive high angular resolution ($\\sim$ 2$\"$) CO(2-1) line observations\nmade with the Submillimeter Array (SMA) of the flow emanating from the\nhigh-mass star forming region DR21 located in the Cygnus X molecular cloud are\npresented. These new interferometric observations indicate that this well known\nenigmatic outflow appears to have been produced by an explosive event that took\nplace about 10,000 years ago, and that might be related with the disintegration\nof a massive stellar system, as the one that occurred in Orion BN/KL 500 years\nago, but about 20 times more energetic. This result therefore argues in favor\nof the idea that the disintegration of young stellar systems perhaps is a\nfrequent phenomenon present during the formation of the massive stars. However,\nmany more theoretical and observational studies are still needed to confirm our\nhypothesis.", "category": "astro-ph_GA" }, { "text": "Constraints on Spin of a Supermassive Black Hole in Quasars with Big\n Blue Bump: We determined the spin value of supermassive black hole (SMBH) in active\ngalactic nuclei (AGN) with investigated ultraviolet-to-optical spectral energy\ndistribution, presented in the sample of Shang et al. (2005). The estimates of\nthe spin values have been produced at the base of the standard geometrically\nthin accretion disk model and with using the results of the polarimetric\nobservations. The polarimetric observations are very important for determining\nthe inclination angle of AGN disk. We presented the results of our\ndeterminations of the radiation efficiency of the accretion flow and values of\nthe spins of SMBHs, that derives the coefficient of radiation efficiency. The\nmajority of SMBHs of AGNs from Shang et al. (2005) sample are to be the Kerr\nblack holes with the high spin value.", "category": "astro-ph_GA" }, { "text": "$\u03a9_{\\rm bar}$ in NGC 5597 from VLA HI 21 cm Observations: We report Very Large Array B-configuration observations of the atomic\nhydrogen 21 cm line emission from the barred disk galaxy NGC 5597 at an angular\nresolution of 7.1\" x 4.2\". Using the resonance method, and assuming the ratio\nof the corotation radius to the semi-major axis of the stellar bar is unity\n($\\mathcal{R} \\equiv R_{\\rm CR}/a_{\\rm bar} = 1$), we estimate the angular\npattern speed of the stellar bar to be, $\\Omega_{{\\rm bar}} \\sim 15.3$ km\ns$^{-1}$ kpc$^{-1}$. This constant value for $\\Omega_{\\rm bar}$ crosses\n$\\Omega_{\\rm gas} + \\kappa(R)/4$ at a distance $\\sim 6.73$ kpc which would\ncorrespond to the spatial location of the north spiral structure near an outer\nm=4 resonance. This value of $\\Omega_{\\rm bar}$ is similar to the values\nestimated for other bright nearby barred galaxies that exhibit circumnuclear\nrings (near ILR) or outer rings (near OLR).", "category": "astro-ph_GA" }, { "text": "Hidden giants in JWST's PEARLS: An ultra-massive z=4.26 sub-millimeter\n galaxy that is invisible to HST: We present a multi-wavelength analysis using SMA, JCMT, NOEMA, JWST, HST, and\nSST of two dusty strongly star-forming galaxies, 850.1 and 850.2, seen through\nthe massive cluster lens A1489. These SMA-located sources both lie at z=4.26\nand have bright dust continuum emission, but 850.2 is a UV-detected Lyman-break\ngalaxy, while 850.1 is undetected at <2um, even with deep JWST/NIRCam\nobservations. We investigate their stellar, ISM, and dynamical properties,\nincluding a pixel-level SED analysis to derive sub-kpc-resolution stellar-mass\nand Av maps. We find that 850.1 is one of the most massive and highly obscured,\nAv~5, galaxies known at z>4 with M*~10^11.8 Mo (likely forming at z>6), and\n850.2 is one of the least massive and least obscured, Av~1, members of the z>4\ndusty star-forming population. The diversity of these two dust-mass-selected\ngalaxies illustrates the incompleteness of galaxy surveys at z>3-4 based on\nimaging at <2um, the longest wavelengths feasible from HST or the ground. The\nresolved mass map of 850.1 shows a compact stellar mass distribution,\nRe(mass)~1kpc, but its expected evolution to z~1.5 and then z~0 matches both\nthe properties of massive, quiescent galaxies at z~1.5 and ultra-massive\nearly-type galaxies at z~0. We suggest that 850.1 is the central galaxy of a\ngroup in which 850.2 is a satellite that will likely merge in the near future.\nThe stellar morphology of 850.1 shows arms and a linear bar feature which we\nlink to the active dynamical environment it resides within.", "category": "astro-ph_GA" }, { "text": "The better half -- Asymmetric star-formation due to ram pressure in the\n EAGLE simulations: We use the EAGLE simulations to study the effects of the intra-cluster medium\n(ICM) on the spatially resolved star-formation activity in galaxies. We study\nthree cases of galaxy asymmetry dividing each galaxy in two halves using the\nplane (i) perpendicular to the $\\rm \\texttt{velocity}$ direction,\ndifferentiating the galaxy part approaching to the cluster center, hereafter\ndubbed as the \"leading half\", and the opposite one \"trailing half\", (ii)\nperpendicular to the $\\rm \\texttt{radial}$ position of the satellite to the\ncentre of the cluster, (iii) that maximizes the star-formation rate ($\\rm SFR$)\ndifference between the two halves. For (i), we find an enhancement of the $\\rm\nSFR$, star formation efficiency ($\\rm SFE$), and interstellar medium pressure\nin the leading half with respect to the trailing one and normal star-forming\ngalaxies in the EAGLE simulation, and a clear overabundance of gas particles in\ntheir trailing. These results suggest that ram pressure (RP) is boosting the\nstar formation by gas compression in the leading half, and transporting the gas\nto the trailing half. This effect is more pronounced in satellites of\nintermediate stellar masses $\\rm 10^{9.5-10.5} M_{\\odot}$, with gas masses\nabove $\\rm 10^{9} M_{\\odot}$, and located within one virial radius or in the\nmost massive clusters. In (iii) we find an alignment between the velocity and\nthe vector perpendicular to the plane that maximizes the $\\rm SFR$ difference\nbetween the two halves. It suggests that finding this plane in real galaxies\ncan provide insights into the velocity direction.", "category": "astro-ph_GA" }, { "text": "The TREX Survey: Kinematical Complexity Throughout M33's Stellar Disk\n and Evidence for a Stellar Halo: We present initial results from a large spectroscopic survey of stars\nthroughout M33's stellar disk. We analyze a sample of 1667 red giant branch\n(RGB) stars extending to projected distances of $\\sim 11$ kpc from M33's center\n($\\sim 18$ kpc, or $\\sim 10$ scale lengths, in the plane of the disk). The\nline-of-sight velocities of RGB stars show the presence of two kinematical\ncomponents. One component is consistent with rotation in the plane of M33's HI\ndisk and has a velocity dispersion ($\\sim 19$ km s$^{-1}$) consistent with that\nobserved in a comparison sample of younger stars, while the second component\nhas a significantly higher velocity dispersion. A two-component fit to the RGB\nvelocity distribution finds that the high dispersion component has a velocity\ndispersion of $59.3^{+2.6}_{-2.5}$ km s$^{-1}$ and rotates very slowly in the\nplane of the disk (consistent with no rotation at the $<1.5\\sigma$ level),\nwhich favors interpreting it as a stellar halo rather than a thick disk\npopulation. A spatial analysis indicates that the fraction of RGB stars in the\nhigh-velocity-dispersion component decreases with increasing radius over the\nrange covered by the spectroscopic sample. Our spectroscopic sample establishes\nthat a significant high-velocity-dispersion component is present in M33's RGB\npopulation from near M33's center to at least the radius where M33's HI disk\nbegins to warp at 30$'$ ($\\sim 7.5$ kpc) in the plane of the disk. This is the\nfirst detection and spatial characterization of a kinematically hot stellar\ncomponent throughout M33's inner regions.", "category": "astro-ph_GA" }, { "text": "CO Multi-line Imaging of Nearby Galaxies (COMING). III. Dynamical effect\n on molecular gas density and star formation in the barred spiral galaxy NGC\n 4303: We present the results of $^{12}$CO($J$=1-0) and $^{13}$CO($J$=1-0)\nsimultaneous mappings toward the nearby barred spiral galaxy NGC 4303 as a part\nof the CO Multi-line Imaging of Nearby Galaxies (COMING) project. Barred spiral\ngalaxies often show lower star-formation efficiency (SFE) in their bar region\ncompared to the spiral arms. In this paper, we examine the relation between the\nSFEs and the volume densities of molecular gas $n(\\rm{H}_2)$ in the eight\ndifferent regions within the galactic disk with CO data combined with archival\nfar-ultraviolet and 24 $\\mu$m data. We confirmed that SFE in the bar region is\nlower by 39% than that in the spiral arms. Moreover, velocity-alignment\nstacking analysis was performed for the spectra in the individual regions. The\nintegrated intensity ratios of $^{12}$CO to $^{13}$CO ($R_{12/13}$) range from\n10 to 17 as the results of stacking. Fixing a kinetic temperature of molecular\ngas, $n(\\rm{H}_2)$ was derived from $R_{12/13}$ via non-local thermodynamic\nequilibrium (non-LTE) analysis. The density $n(\\rm{H}_2)$ in the bar is lower\nby 31-37% than that in the arms and there is a rather tight positive\ncorrelation between SFEs and $n(\\rm{H}_2)$, with a correlation coefficient of\n$\\sim 0.8$. Furthermore, we found a dependence of $n(\\rm{H}_2)$ on the velocity\ndispersion of inter-molecular clouds ($\\Delta V/ \\sin i$). Specifically,\n$n(\\rm{H}_2)$ increases as $\\Delta V/ \\sin i$ increases when $\\Delta V/ \\sin i\n< 100$ km s$^{-1}$. On the other hand, $n(\\rm{H}_2)$ decreases as $\\Delta V/\n\\sin i$ increases when $\\Delta V/ \\sin i > 100$ km s$^{-1}$. These relations\nindicate that the variations of SFE could be caused by the volume densities of\nmolecular gas, and the volume densities could be governed by the dynamical\ninfluence such as cloud-cloud collisions, shear and enhanced inner-cloud\nturbulence.", "category": "astro-ph_GA" }, { "text": "Photometric and kinematical analysis of Koposov 12 and Koposov 43 open\n clusters: We present a photometric and kinematical analysis of two and poorly studied\nopen clusters; Koposov 12 (FSR 802) and Koposov 43 (FSR 848) by using\ncross-matched data from PPMXL and Gaia DR2 catalog. We use astrometric\nparameters to identify 285 and 310 cluster members for Koposov 12 and Koposov\n43, respectively. Using the extracted member candidates and isochrone fitting\nto near-infrared (J, H, Ks) and Gaia DR2 bands (G, GBP, GRP), and Color\nMagnitude Diagrams (CMDs), we have estimated ages: log (age/yr) = 9.00 +/- 0.20\nand 9.50 +/- 0.20, and distances d = 1850 +/- 43 pc and 2500 +/- 50 pc for\nKoposov 12 and Koposov 43, respectively, assuming Solar metallicity (Z=0.019).\nThe estimated masses of the cluster derived using initial mass function and\nsynthetic CMD are 364 +/- 19 M_sun and 352 +/- 19 M_sun. We have also computed\ntheir velocity ellipsoid parameters based on (3x3) matrix elements (mu_ij).", "category": "astro-ph_GA" }, { "text": "Observations contradict galaxy size and surface brightness predictions\n that are based on the expanding universe hypothesis: In a non-expanding universe surface brightness is independent of distance or\nredshift, while in an expanding universe it decreases rapidly with both.\nSimilarly, for objects of the same luminosity, the angular radius of an object\nin a non-expanding universe declines with redshift, while in an expanding\nuniverse this radius increases for redshifts z>1.25. The author and colleagues\nhave previously shown that data for the surface brightness of disk galaxies are\ncompatible with a static universe with redshift linearly proportional to\ndistance at all z (SEU hypothesis). In this paper we examine the more\nconventional hypothesis that the universe is expanding, but that the actual\nradii of galaxies of a given luminosity increase with time (decrease with z),\nas others have proposed. We show that the radii data for both disk and\nelliptical galaxies are incompatible with any of the published size-evolution\npredictions based on an expanding universe. We find that all the physical\nmechanisms proposed for size evolution, such as galaxy mergers, lead to\npredictions that are in quantitative contradiction with either the radius data\nor other data sets, such as the observed rate of galaxy mergers. In addition,\nwe find that when the effect of telescope resolution is taken into account, the\nr-z relationships for disk and elliptical galaxies are identical. Both are\nexcellently fit by SEU predictions. An overall comparison of cosmological\nmodels requires examining all available data-sets, but for this data-set there\nis a clear contradiction of predictions based on an expanding universe\nhypothesis.", "category": "astro-ph_GA" }, { "text": "Semi-Supervised Domain Adaptation for Cross-Survey Galaxy Morphology\n Classification and Anomaly Detection: In the era of big astronomical surveys, our ability to leverage artificial\nintelligence algorithms simultaneously for multiple datasets will open new\navenues for scientific discovery. Unfortunately, simply training a deep neural\nnetwork on images from one data domain often leads to very poor performance on\nany other dataset. Here we develop a Universal Domain Adaptation method\nDeepAstroUDA, capable of performing semi-supervised domain alignment that can\nbe applied to datasets with different types of class overlap. Extra classes can\nbe present in any of the two datasets, and the method can even be used in the\npresence of unknown classes. For the first time, we demonstrate the successful\nuse of domain adaptation on two very different observational datasets (from\nSDSS and DECaLS). We show that our method is capable of bridging the gap\nbetween two astronomical surveys, and also performs well for anomaly detection\nand clustering of unknown data in the unlabeled dataset. We apply our model to\ntwo examples of galaxy morphology classification tasks with anomaly detection:\n1) classifying spiral and elliptical galaxies with detection of merging\ngalaxies (three classes including one unknown anomaly class); 2) a more\ngranular problem where the classes describe more detailed morphological\nproperties of galaxies, with the detection of gravitational lenses (ten classes\nincluding one unknown anomaly class).", "category": "astro-ph_GA" }, { "text": "Near-infrared spectroscopy of 5 ultra-massive galaxies at 1.7 < z < 2.7: We present the results of a pilot near-infrared (NIR) spectroscopic campaign\nof five very massive galaxies ($\\log(\\text{M}_\\star/\\text{M}_\\odot)>11.45$) in\nthe range of $1.74$ enhanced SF rate\nrelative to a control sample of non-interacting galaxies which are $\\pm 0.2$\ndex in stellar mass and $\\pm 1$ in $T$-type. Starbursts are mainly early-type\n($T\\lesssim 5$), massive spiral galaxies ($M_{\\ast}\\gtrsim 10^{10}M_{\\odot}$)\nthat are not necessarily interacting. For a given stellar mass bin, starbursts\nare characterised by lower gas depletion times, similar gas fractions, and\nlarger central stellar mass concentrations than non-starburst galaxies. The\nglobal distributions of gas fraction and gas depletion time are not\nstatistically different for interacting and non-interacting galaxies. However,\nin the case of currently merging galaxies, the median gas depletion time is a\nfactor of $0.4 \\pm 0.2$ that of control sample galaxies, and their SF rates are\na factor of $1.9 \\pm 0.5$ enhanced, even though the median gas fraction is\nsimilar. Starbursts present long-lasting SF in the circumnuclear regions that\ncauses an enhancement of the central stellar density at $z\\approx0$ in both\ninteracting and non-interacting systems. Starbursts have low gas depletion\ntimescales, yet similar gas fractions as normal main-sequence galaxies. Galaxy\nmergers cause a moderate enhancement of the SF efficiency (Abridged).", "category": "astro-ph_GA" }, { "text": "Towards a complete stellar mass function of the Hyades. I. Pan-STARRS1\n optical observations of the low-mass stellar content: The Hyades cluster is an ideal target to study the dynamical evolution of a\nstar cluster over the entire mass range due to its intermediate age and\nproximity to the Sun. We wanted to extend the Hyades mass function towards\nlower masses down to 0.1 Msol and to use the full three-dimensional spatial\ninformation to characterize the dynamical evolution of the cluster. We\nperformed a kinematic and photometric selection using the PPMXL and Pan-STARRS1\nsky surveys, to search for cluster members up to 30 pc from the cluster centre.\nWe determined our detection efficiency and field star contamination rate to\nderive the cluster luminosity and mass functions down to masses of 0.1 Msol.\nThe thorough astrometric and photometric constraints minimized the\ncontamination. A minimum spanning tree algorithm was used to quantify the mass\nsegregation. We discovered 43 new Hyades member candidates with velocity\nperpendicular to the Hyades motion up to 2 km/s. They have mass estimates\nbetween 0.43 and 0.09 Msol, for a total mass of 10 Msol. This doubles the\nnumber of Hyades candidates with masses smaller than 0.15 Msol. We provide an\nadditional list of 11 possible candidates with velocity perpendicular to the\nHyades motion up to 4 km/s. The cluster is significantly mass segregated. The\nextension of the mass function towards lower masses provided an even clearer\nsignature than estimated in the past. We also identified as likely Hyades\nmember an L0 dwarf previously assumed to be a field dwarf. Finally we question\nthe membership of a number of previously published candidates, including a\nL2.5-type dwarf.", "category": "astro-ph_GA" }, { "text": "Physical Model of Dust Polarization by Radiative Torque Alignment and\n Disruption and Implications for Grain Internal Structures: Dust polarization depends on the physical and mechanical properties of dust,\nas well as the properties of local environments. To understand how dust\npolarization varies with grain mechanical properties and the local environment,\nin this paper, we model the wavelength-dependence polarization of starlight and\npolarized dust emission by aligned grains by simultaneously taking into account\ngrain alignment and rotational disruption by radiative torques (RATs). We\nexplore a wide range of the local radiation field and grain mechanical\nproperties characterized by tensile strength. We find that the maximum\npolarization and the peak wavelength shift to shorter wavelengths as the\nradiation strength $U$ increases due to the enhanced alignment of small grains.\nGrain rotational disruption by RATs tends to decrease the optical-near infrared\npolarization but increases the ultraviolet polarization of starlight due to the\nconversion of large grains into smaller ones. In particular, we find that the\nsubmillimeter (submm) polarization degree at $850~\\mu \\rm m$ ($P_{850}$) does\nnot increase monotonically with the radiation strength or grain temperature\n($T_{d}$), but it depends on the tensile strength of grain materials. Our\nphysical model of dust polarization can be tested with observations toward\nstar-forming regions or molecular clouds irradiated by a nearby star, which\nhave higher radiation intensity than the average interstellar radiation field.\nFinally, we compare our predictions of the $P_{850}-T_{d}$ relationship with\n{\\it Planck} data and find that the observed decrease of $P_{850}$ with $T_{d}$\ncan be explained when grain disruption by RATs is accounted for, suggesting\nthat interstellar grains unlikely to have a compact structure but perhaps a\ncomposite one. The variation of the submm polarization with U (or $T_{d}$) can\nprovide a valuable constraint on the internal structures of cosmic dust.", "category": "astro-ph_GA" }, { "text": "A Submillimeter Perspective on the GOODS Fields (SUPER GOODS). V. Deep\n 450 Micron Imaging: We present deep SCUBA-2 450 micron imaging of the two GOODS fields, achieving\na central rms of 1.14 mJy for the GOODS-N and 1.86 mJy for the GOODS-S. For\neach field, we give a catalog of >4-sigma detections (79 and 16 sources,\nrespectively). We construct the 450 micron number counts, finding excellent\nagreement with others from the literature. We match the 450 micron sources to\n20 cm data (both fields) and ALMA 870 micron data (GOODS-S) to gauge the\naccuracy of the 450 micron positions. We use the extensive redshift information\navailable on the fields to test how well redshift can be estimated from simple\nflux ratios (450 micron/850 micron and 20 cm/850 micron), finding tight\ncorrelations. We provide a catalog of candidate high-redshift submillimeter\ngalaxies. We look for evolution in dust temperature with redshift by fitting\nthe spectral energy distributions of the sources, but we do not find any\nsignificant redshift evolution after accounting for the far-infrared\nluminosity. We do not find evidence for 450 micron selection picking out warmer\nsources than 850 micron selection. We find that a 450 micron selected sample\nonly adds low-redshift (z<1.5) galaxies beyond an 850 micron sample.", "category": "astro-ph_GA" }, { "text": "A new strong-lensing galaxy at z=0.066: Another elliptical galaxy with a\n lightweight IMF: We report the discovery of a new low-redshift galaxy-scale gravitational\nlens, identified from a systematic search of publicly available MUSE\nobservations. The lens galaxy, 2MASXJ04035024-0239275, is a giant elliptical at\n$z$ = 0.06604 with a velocity dispersion of $\\sigma$ = 314 km s$^{-1}$. The\nlensed source has a redshift of 0.19165 and forms a pair of bright images\neither side of the lens centre. The Einstein radius is 1.5 arcsec, projecting\nto 1.8 kpc, which is just one quarter of the galaxy effective radius. After\ncorrecting for an estimated 19 per cent dark matter contribution, we find that\nthe stellar mass-to-light ratio from lensing is consistent with that expected\nfor a Milky Way initial mass function (IMF). Combining the new system with\nthree previously-studied low-redshift lenses of similar $\\sigma$, the derived\nmean mass excess factor (relative to a Kroupa IMF) is $\\langle\\alpha\\rangle$ =\n1.09$\\pm$0.08. With all four systems, the intrinsic scatter in $\\alpha$ for\nmassive elliptical galaxies can be limited to $<0.32$, at 90 per cent\nconfidence.", "category": "astro-ph_GA" }, { "text": "Spectrophotometric Redshifts In The Faint Infrared Grism Survey: Finding\n Overdensities Of Faint Galaxies: We improve the accuracy of photometric redshifts by including low-resolution\nspectral data from the G102 grism on the Hubble Space Telescope, which assists\nin redshift determination by further constraining the shape of the broadband\nSpectral Energy Disribution (SED) and identifying spectral features. The\nphotometry used in the redshift fits includes near-IR photometry from\nFIGS+CANDELS, as well as optical data from ground-based surveys and HST ACS,\nand mid-IR data from Spitzer. We calculated the redshifts through the\ncomparison of measured photometry with template galaxy models, using the EAZY\nphotometric redshift code. For objects with F105W $< 26.5$ AB mag with a\nredshift range of $0 < z < 6$, we find a typical error of $\\Delta z = 0.03 *\n(1+z)$ for the purely photometric redshifts; with the addition of FIGS spectra,\nthese become $\\Delta z = 0.02 * (1+z)$, an improvement of 50\\%. Addition of\ngrism data also reduces the outlier rate from 8\\% to 7\\% across all fields.\nWith the more-accurate spectrophotometric redshifts (SPZs), we searched the\nFIGS fields for galaxy overdensities. We identified 24 overdensities across the\n4 fields. The strongest overdensity, matching a spectroscopically identified\ncluster at $z=0.85$, has 28 potential member galaxies, of which 8 have previous\nspectroscopic confirmation, and features a corresponding X-ray signal. Another\ncorresponding to a cluster at $z=1.84$ has 22 members, 18 of which are\nspectroscopically confirmed. Additionally, we find 4 overdensities that are\ndetected at an equal or higher significance in at least one metric to the two\nconfirmed clusters.", "category": "astro-ph_GA" }, { "text": "Physical Properties of Massive Compact Starburst Galaxies with Extreme\n Outflows: We present results on the nature of extreme ejective feedback episodes and\nthe physical conditions of a population of massive ($\\rm M_* \\sim 10^{11}\nM_{\\odot}$), compact starburst galaxies at z = 0.4-0.7. We use data from\nKeck/NIRSPEC, SDSS, Gemini/GMOS, MMT, and Magellan/MagE to measure rest-frame\noptical and near-IR spectra of 14 starburst galaxies with extremely high star\nformation rate surface densities (mean $\\rm \\Sigma_{SFR} \\sim 3000 \\,M_{\\odot}\nyr^{-1} kpc^{-2}$) and powerful galactic outflows (maximum speeds v$_{98} \\sim$\n1000-3000 km s$^{-1}$). Our unique data set includes an ensemble of both\nemission [OII]$\\lambda\\lambda$3726,3729, H$\\beta$,\n[OIII]$\\lambda\\lambda$4959,5007, H$\\alpha$, [NII]$\\lambda\\lambda$6548,6583, and\n[SII]$\\lambda\\lambda$6716,6731) and absorption MgII$\\lambda\\lambda$2796,2803,\nand FeII$\\lambda$2586) lines that allow us to investigate the kinematics of the\ncool gas phase (T$\\sim$10$^4$ K) in the outflows. Employing a suite of line\nratio diagnostic diagrams, we find that the central starbursts are\ncharacterized by high electron densities (median n$_e \\sim$ 530 cm$^{-3}$), and\nhigh metallicity (solar or super-solar). We show that the outflows are most\nlikely driven by stellar feedback emerging from the extreme central starburst,\nrather than by an AGN. We also present multiple intriguing observational\nsignatures suggesting that these galaxies may have substantial Lyman continuum\n(LyC) photon leakage, including weak [SII] nebular emission lines. Our results\nimply that these galaxies may be captured in a short-lived phase of extreme\nstar formation and feedback where much of their gas is violently blown out by\npowerful outflows that open up channels for LyC photons to escape.", "category": "astro-ph_GA" }, { "text": "The Effect of Many Minor Mergers on the Size Growth of Compact Quiescent\n Galaxies: Massive galaxies with a half-mass radius <~ 1kpc are observed in the early\nuniverse (z~>2), but not in the local universe. In the local universe\nsimilar-mass (within a factor of two) galaxies tend to be a factor of 4 to 5\nlarger. Dry minor mergers are known to drive the evolution of the size of a\ngalaxy without much increasing the mass, but it is unclear if the growth in\nsize is sufficient to explain the observations. We test the hypothesis that\ngalaxies grow through dry minor mergers by simulating merging galaxies with\nmass ratios of q=1:1 (equal mass) to q=1:160. In our N-body simulations the\ntotal mass of the parent galaxy doubles. We confirm that major mergers do not\ncause a sufficient growth in size. The observation can be explained with\nmergers with a mass ratio of q=1:5--1:10. Smaller mass ratios cause a more\ndramatic growth in size, up to a factor of ~17 for mergers with a mass ratio of\n1:80. For relatively massive minor mergers q ~> 1:20 the mass of the incoming\nchild galaxies tend to settle in the halo of the parent galaxy. This is caused\nby the tidal stripping of the child galaxies by the time they enter the central\nportion of the parent. When the accretion of minor galaxies becomes more\ncontinuous, when q <~ 1:40, the foreign mass tends to concentrate more in the\ncentral region of the parent galaxy. We speculate that this is caused by\ndynamic interactions between the child galaxies inside the merger remnant and\nthe longer merging times when the difference in mass is larger. These\ninteractions cause dynamical heating which results in accretion of mass inside\nthe galaxy core and a reduction of the parent's circular velocity and density.", "category": "astro-ph_GA" }, { "text": "The Abell 85 BCG: a nucleated, core-less galaxy: New high-resolution r band imaging of the brightest cluster galaxy (BCG) in\nAbell 85 (Holm 15A) was obtained using the Gemini Multi Object Spectrograph.\nThese data were taken with the aim of deriving an accurate surface brightness\nprofile of the BCG of Abell 85, in particular its central region. The new\nGemini data show clear evidence of a previously unreported nuclear emission\nthat is evident as a distinct light excess in the central kiloparsec of the\nsurface brightness profile. We find that the light profile is never flat nor\ndoes it present a downward trend towards the center of the galaxy. That is, the\nnew Gemini data show a different physical reality from the featureless,\n\"evacuated core\" recently claimed for the Abell 85 BCG. After trying different\nmodels, we find that the surface brightness profile of the BCG of Abell 85 is\nbest fit by a double Sersic model.", "category": "astro-ph_GA" }, { "text": "Resolved neutral carbon emission in nearby galaxies: [CI] Lines as Total\n Molecular Gas Tracers: We present maps of atomic carbon [CI](1-0) and [CI](2-1) at a linear\nresolution ~1kpc scale for a sample of one HII, six LINER, three Seyfert and\nfive starburst galaxies observed with Herschel. We compare spatial\ndistributions of two [CI] lines with that of CO(1-0) emission, and find that\nboth [CI] lines distribute similarly to CO(1-0) emission in most galaxies. We\npresent luminosity ratio maps of L'_[CI](1-0)/L'_CO(1-0),\nL'_[CI](2-1)/L'_CO(1-0), L'_[CI](2-1)/L'_[CI](1-0) (hereafter R_[CI]) and\nf_70/f_160. L'_[CI](2-1)/L'_CO(1-0), R_[CI] and f_70/f_160 are centrally peaked\nin starbursts; whereas remain relatively constant in LINERs, indicating that\nstar-forming activity can enhance carbon emission, especially for [CI](2-1). We\nexplore the correlations between the luminosities of CO(1-0) and [CI] lines,\nand find that L'_CO(1-0) correlates tightly and almost linearly with both\nL'_[CI](1-0) and L'_[CI](2-1), suggesting that [CI] lines, similar as CO(1-0),\ncan trace total molecular gas in our resolved galaxies on kpc scales. We\ninvestigate the dependence of L'_[CI](1-0)/L'_CO(1-0), L'_[CI](2-1)/L'_CO(1-0)\nand [CI] excitation temperature T_ex on dust temperature T_dust, and find\nnon-correlation, a weak and modest correlation, respectively. The ratio of\nL'_[CI](1-0)/L'_CO(1-0) stays smooth distribution in most galaxies, indicating\nthat the conversion factor of [CI](1-0) luminosity to H_2 mass (X_[CI](1-0))\nchanges with CO(1-0) conversion factor (\\alpha_CO) proportionally. Under\noptically thin and LTE assumptions, we derive a galaxy-wide average carbon\nexcitation temperature T_ex ~ 19.7 \\pm 0.5K and an average neutral carbon\nabundance X[CI]/X[H_2] ~2.5 \\pm 1.0 * 10^{-5} in our resolved sample, which is\ncomparable to the usually adopted value of 3*10^{-5}, but ~3 times lower than\nthe carbon abundance in local (U)LIRGs. We conclude that the carbon abundance\nvaries in different galaxy types.", "category": "astro-ph_GA" }, { "text": "The Impact of an AGN on PAH Emission in Galaxies: the Case of Ring\n Galaxy NGC 4138: We present a focused study of radially-resolved varying PAH emission in the\nlow-luminosity AGN-host NGC 4138 using deep Spitzer/IRS spectral maps. Using\nnew model PAH spectra, we investigate whether these variations could be\nassociated with changes to the PAH grain size distribution due to\nphotodestruction by the AGN. Separately, we model the effects of the varying\nradiation field within NGC 4138, and we use this model to predict the\ncorresponding changes in the PAH emission spectrum. We find that PAH band\nratios are strongly variable with radius in this galaxy with short-to-long\nwavelength band ratios peaking in the starburst ring. The changing mix of\nstarlight appears to have a considerable effect on the trends in these band\nratios, and our radiation model predicts the shapes of these trends. However,\nthe amplitude of observed variation is ~2.5 times larger than predicted for\nsome ratios. A cutoff of small grains in the PAH size distribution, as has been\nsuggested for AGN, together with changes in PAH ionization fraction could\nexplain the behavior of the shorter bands, but this model fails to reproduce\nlonger band behaviors. Additionally, we find that short-to-long wavelength PAH\nband ratios increase slightly within ~270pc of the center, suggesting that the\nAGN may directly influence PAH emission there.", "category": "astro-ph_GA" }, { "text": "Green Bank Telescope Observations of ${\\bf ^3He^{\\bf +}}$: Planetary\n Nebulae: We use the Green Bank Telescope to search for $^3He^+$ emission from a sample\nof four Galactic planetary nebulae: NGC 3242, NGC 6543, NGC 6826, and NGC 7009.\nDuring the era of primordial nucleosynthesis the light elements $^2H$, $^3He$,\n$^4He$, and $^7Li$ were produced in significant amounts and these abundances\nhave since been modified primarily by stars. Observations of $^3He^+$ in H II\nregions located throughout the Milky Way disk reveal very little variation in\nthe $^3He/H$ abundance ratio -- the \"$^3He$ Plateau\" -- indicating that the net\neffect of $^3He$ production in stars is negligible. This is in contrast to much\nhigher $^3He/H$ abundance ratios reported for some planetary nebulae. This\ndiscrepancy is known as the \"$^3He$ Problem\". We use radio recombination lines\nobserved simultaneously with the $^3He^+$ transition to make a robust\nassessment of the spectral sensitivity that these observations achieve. We\ndetect spectral lines at $\\sim$ 1 -- 2 mK intensities, but at these levels\ninstrumental effects compromise our ability to measure accurate spectral line\nparameters. We do not confirm reports of previous detections of $^3He^+$ in NGC\n3242 nor do we detect $^3He^+$ emission from any of our sources. This result\ncalls into question all reported detections of $^3He^+$ emission from any\nplanetary nebula. The $^3He/H$ abundance upper limit we derive here for NGC\n3242 is inconsistent with standard stellar production of $^3He$ and thus\nrequires that some type of extra mixing process operates in low-mass stars.", "category": "astro-ph_GA" }, { "text": "Realistic galaxy images and improved robustness in machine learning\n tasks from generative modelling: We examine the capability of generative models to produce realistic galaxy\nimages. We show that mixing generated data with the original data improves the\nrobustness in downstream machine learning tasks. We focus on three different\ndata sets; analytical S\\'ersic profiles, real galaxies from the COSMOS survey,\nand galaxy images produced with the SKIRT code, from the IllustrisTNG\nsimulation. We quantify the performance of each generative model using the\nWasserstein distance between the distributions of morphological properties\n(e.g. the Gini-coefficient, the asymmetry, and ellipticity), the surface\nbrightness distribution on various scales (as encoded by the power-spectrum),\nthe bulge statistic and the colour for the generated and source data sets. With\nan average Wasserstein distance (Fr\\'echet Inception Distance) of $7.19 \\times\n10^{-2}\\, (0.55)$, $5.98 \\times 10^{-2}\\, (1.45)$ and $5.08 \\times 10^{-2}\\,\n(7.76)$ for the S\\'ersic, COSMOS and SKIRT data set, respectively, our best\nmodels convincingly reproduce even the most complicated galaxy properties and\ncreate images that are visually indistinguishable from the source data. We\ndemonstrate that by supplementing the training data set with generated data, it\nis possible to significantly improve the robustness against domain-shifts and\nout-of-distribution data. In particular, we train a convolutional neural\nnetwork to denoise a data set of mock observations. By mixing generated images\ninto the original training data, we obtain an improvement of $11$ and $45$ per\ncent in the model performance regarding domain-shifts in the physical pixel\nsize and background noise level, respectively.", "category": "astro-ph_GA" }, { "text": "Boron Abundances in Diffuse Interstellar Clouds: We present a comprehensive survey of B abundances in diffuse interstellar\nclouds from HST/STIS observations along 56 Galactic sight lines. Our sample is\nthe result of a complete search of archival STIS data for the B II resonance\nline at 1362 angstroms, with each detection confirmed by the presence of\nabsorption from other dominant ions at the same velocity. The data probe a\nrange of astrophysical environments including both high-density regions of\nmassive star formation as well as low-density paths through the Galactic halo,\nallowing us to clearly define the trend of B depletion onto interstellar grains\nas a function of gas density. Many extended sight lines exhibit complex\nabsorption profiles that trace both local gas and gas associated with either\nthe Sagittarius-Carina or Perseus spiral arm. Our analysis indicates a higher\nB/O ratio in the inner Sagittarius-Carina spiral arm than in the vicinity of\nthe Sun, which may suggest that B production in the current epoch is dominated\nby a secondary process. The average gas-phase B abundance in the warm diffuse\nISM is consistent with the abundances determined for a variety of Galactic disk\nstars, but is depleted by 60 percent relative to the solar system value. Our\nsurvey also reveals sight lines with enhanced B abundances that potentially\ntrace recent production of B-11 either by cosmic-ray or neutrino-induced\nspallation. Such sight lines will be key to discerning the relative importance\nof the two production routes for B-11 synthesis.", "category": "astro-ph_GA" }, { "text": "Ultraviolet and optical view of galaxies in the Coma Supercluster: The Coma supercluster (100 Mpc) offers an unprecedented contiguous range of\nenvironments in the nearby Universe. In this paper we present a catalogue of\nspectroscopically confirmed galaxies in the Coma supercluster detected in the\nultraviolet (UV) wavebands. We use the arsenal of UV and optical data for\ngalaxies in the Coma supercluster covering ~ 500 square degrees on the sky to\nstudy their photometric and spectroscopic properties as a function of\nenvironment at various scales. We identify the different components of the\ncosmic-web: large-scale filaments and voids using Discrete Persistent\nStructures Extractor, and groups and clusters using Hierarchical Density-based\nspatial clustering of applications with noise, respectively. We find that in\nthe Coma supercluster the median emission in Halpha inclines, while the g-r and\nFUV-NUV colours of galaxies become bluer moving further away from the spine of\nthe filaments out to a radius of around 1 Mpc. On the other hand, an opposite\ntrend is observed as the distance between the galaxy and centre of the nearest\ncluster or group decreases. Our analysis supports the hypothesis that\nproperties of galaxies are not just defined by its stellar mass and large-scale\ndensity, but also by the environmental processes resulting due to the\nintrafilament medium whose role in accelerating galaxy transformations needs to\nbe investigated thoroughly using multi-wavelength data.", "category": "astro-ph_GA" }, { "text": "Water vapour masers in long-period variable stars II. The semi-regular\n variables R Crt and RT Vir: Within the 'Medicina/Effelsberg H2O maser monitoring program' we have\nobserved the maser emission of R Crt and RT Vir for more than two decades. To\nget insight in the distribution and longevity of maser spots in the\ncircumstellar envelopes, we have collected interferometric data, taken in the\nsame period, from the literature.\n We confirm short-time variations of individual maser features on timescales\nof months to up to 1.5 years. Also decade-long variations of the general\nbrightness level independent from individual features were seen in both stars.\nThese are due to brightness variations occurring independently from each other\nin selected velocity ranges, and are independent of the optical lightcurves.\nExpected drifts in velocity of individual features are usually masked by\nblending. However, in RT Vir we found an exceptional case of a feature with a\nconstant velocity over 7.5 years (<0.06 km/s/yr).\n We attribute the long-term brightness variations to the presence of regions\nwith higher-than-average density in the stellar wind, which host several clouds\nwhich emit maser radiation on the short time scales. These regions typically\nneed ~20 years to cross the H2O maser shell, where the right conditions to\nexcite H2O masers are present. The constant velocity feature (11 km/s) is\nlikely to come from a single maser cloud, which moved through about half of RT\nVir's H2O maser shell without changing velocity. From this we infer that its\npath was located in the outer part of the H2O maser shell, where RT Vir's\nstellar wind apparently has already reached its terminal outflow velocity. This\nconclusion is corroborated by the observation that the highest H2O maser\noutflow velocity in RT Vir approaches the terminal outflow velocity as given by\nOH and CO observations. This is generally not observed in other semi-regular\nvariable stars.", "category": "astro-ph_GA" }, { "text": "NGC 1261: an $r$-process enhanced globular cluster from the\n Gaia-Enceladus event: Our Milky Way (MW) has witnessed a series of major accretion events. One of\nthe later additions, Gaia-Enceladus, has contributed a considerable mass to the\ninner Galaxy, but also generously donated to the outer halo. So far,\nassociations with present-day MW globular clusters (GCs) have been chiefly\nbased on their kinematics and ages. Here, we present a chemical abundance study\nof the outer halo (R$_{\\rm GC}$=18 kpc) GC NGC 1261, which has been suggested\nto be an accreted object. We measured 31 species of 29 elements in two stars\nfrom high-resolution Magellan/MIKE spectra and find that the cluster is\nmoderately metal poor, at [Fe/H]=-1.26. NGC 1261 is moderately\n$\\alpha$-enhanced to the 0.3-dex level. While from the small sample alone it is\ndifficult to assert any abundance correlations, the light elements Na,O,Mg, and\nAl differ significantly between the two stars in contrast to the majority of\nother elements with smaller scatter; this argues in favour of multiple\ngenerations of stars coexisting in this GC. Intriguingly for its metallicity,\nNGC 1261 shows heavy element abundances that are consistent with $r$-process\nnucleosynthesis and we discuss their origin in various sites. In particular the\nEu overabundance quantitatively suggests that one single $r$-process event,\nsuch as a neutron-star neutron-star merger or a rare kind of supernova, can be\nresponsible for the stellar enhancement or even the enrichment of the cluster\nwith the excess $r$-material. Its heavy element pattern makes NGC 1261 resemble\nthe moderately enhanced r-I stars that are commonly found in the halo and have\nbeen detected in Gaia-Enceladus as well. Therefore, combining all kinematical,\nage, and chemical evidence we conclude that NGC 1261 is a chemically intriguing\nGC that was born in Gaia-Enceladus and has been subsequently accreted into the\nMW halo. [abridged]", "category": "astro-ph_GA" }, { "text": "Stellar Black Hole Binary Mergers in Open Clusters: In this paper we study the evolution of a primordial black hole binary (BHB)\nin a sample of over 1500 direct-summation $N-$body simulations of small-and\nintermediate-size isolated star clusters as proxies of galactic open clusters.\nThe BHBs have masses in the range of the first LIGO/Virgo detections. Some of\nour models show a significant hardening of the BHB in a relatively short time.\nSome of them merge within the cluster, while ejected binaries, typically, have\nexceedingly long merger timescales. The perturbation of stars around BHB\nsystems is key to induce their coalescence. The BHBs which merge in the cluster\ncould be detected with a delay of a few years between space detectors, as\nfuture LISA, and ground-based ones, due to their relatively high eccentricity.\nUnder our assumptions, we estimate a BHB merger rate of $R_{\\rm mrg} \\sim 2$\nyr$^{-1}$ Gpc$^{-3}$. We see that in many cases the BHB triggers tidal\ndisruption events which, however, are not linked to the GW emission. Open\ncluster-like systems are, hence, a promising environment for GWs from BHBs and\ntidal disruptions.", "category": "astro-ph_GA" }, { "text": "The Sheet of Giants: Unusual Properties of the Milky Way's Immediate\n Neighbourhood: We quantify the shape and overdensity of the galaxy distribution in the\n`Local Sheet' within a sphere of $R=8$ Mpc, and compare these properties with\nthe expectations of the $\\Lambda$CDM model. We measure ellipsoidal axis ratios\nof $c/a\\approx0.16$ and $b/a\\approx0.79$, indicating that the distribution of\ngalaxies in the Local Volume can be approximated by a flattened oblate\nellipsoid, consistent with the `sheet'-like configuration noted in previous\nstudies. In contrast with previous estimates that the Local Sheet has a density\nclose to average, we find that the number density of faint and bright galaxies\nin the Local Volume is $\\approx1.7$ and $\\approx5.2$ times denser,\nrespectively, than the mean number density of galaxies of the same luminosity.\nComparison with simulations shows that the number density contrasts of bright\nand faint galaxies within $8$ Mpc alone make the Local Volume a $\\approx\n2.5\\sigma$ outlier in the $\\Lambda$CDM cosmology. Our results indicate that the\ncosmic neighbourhood of the Milky Way may be unusual for galaxies of similar\nluminosity. The impact of the peculiar properties of our neighbourhood on the\nproperties of the Milky Way and other nearby galaxies is not yet understood and\nwarrants further study.", "category": "astro-ph_GA" }, { "text": "Nuclear regions as seen with LOFAR international baselines: A\n high-resolution study of the recurrent activity: Radio galaxies dominate the radio sky and are essential to the galaxy\nevolution puzzle. High-resolution studies of statistical samples of radio\ngalaxies are expected to shed light on the triggering mechanisms of the AGN,\nalternating between the phases of activity and quiescence. In this work, we\nfocus on the sub-arcsec radio structures in the central regions of the 35 radio\ngalaxies over 6.6 $deg^2$ of the Lockman Hole region. These sources were\npreviously classified as active, remnant, and candidate restarted radio\ngalaxies using 150 MHz LOFAR observations. We examine the morphologies and\nstudy the spectral properties of their central regions to explore their\nevolutionary stages and revise the criteria used to select the initial sample.\nWe use the newly available LOFAR 150 MHz image obtained using international\nbaselines, achieving 0.38'' x 0.30'' resolution, making this the first\nsystematic study of the nuclear regions at high resolution and low frequency.\nWe use publicly available images from the FIRST survey at 1.4 GHz and the Karl\nG. Jansky VLA Sky Survey at 3 GHz to achieve our goals. In addition, for one\nrestarted candidate we present new dedicated observations with the VLA at 3\nGHz. We have found various morphologies of the central regions of the radio\ngalaxies in our sample, some resembling miniature double-double radio galaxies.\nWe also see the beginnings of active jets or distinct detections unrelated to\nthe large-scale structure. Furthermore, we have found diverse radio spectra in\nour sample - flat, steep, or peaked between 150 MHz and 3 GHz, indicative of\nthe different life-cycle phases. Based on these analyses, we confirm five of\nsix previously considered restarted candidates and identify three more from the\nactive sample, supporting previous results suggesting that the restarted phase\ncan occur after a relatively short remnant phase (i.e. a few tens of millions\nof years).", "category": "astro-ph_GA" }, { "text": "Quantifying the suppression of the (un)-obscured star formation in\n galaxy cluster cores at 0.2$\\lesssim$$z$$\\lesssim$0.9: We quantify the star formation (SF) in the inner cores\n($\\mathcal{R}$/$R_{200}$$\\leq$0.3) of 24 massive galaxy clusters at\n0.2$\\lesssim$$z$$\\lesssim$0.9 observed by the $Herschel$ Lensing Survey and the\nCluster Lensing and Supernova survey with $Hubble$. These programmes, covering\nthe rest-frame ultraviolet to far-infrared regimes, allow us to accurately\ncharacterize stellar mass-limited ($\\mathcal{M}_{*}$$>$$10^{10}$ $M_{\\odot}$)\nsamples of star-forming cluster members (not)-detected in the mid- and/or\nfar-infrared. We release the catalogues with the photometry, photometric\nredshifts, and physical properties of these samples. We also quantify the SF\ndisplayed by comparable field samples from the Cosmic Assembly Near-infrared\nDeep Extragalactic Legacy Survey. We find that in intermediate-$z$ cluster\ncores, the SF activity is suppressed with respect the field in terms of both\nthe fraction ($\\mathcal{F}$) of star-forming galaxies (SFG) and the rate at\nwhich they form stars ($\\mathcal{SFR}$ and $s\\mathcal{SFR} =\n\\mathcal{SFR}/\\mathcal{M}_{*}$). On average, the $\\mathcal{F}$ of SFGs is a\nfactor $\\sim$$2$ smaller in cluster cores than in the field. Furthermore, SFGs\npresent average $\\mathcal{SFR}$ and $s\\mathcal{SFR}$ typically $\\sim$0.3 dex\nsmaller in the clusters than in the field along the whole redshift range\nprobed. Our results favour long time-scale quenching physical processes as the\nmain driver of SF suppression in the inner cores of clusters since\n$z$$\\sim$0.9, with shorter time-scale processes being very likely responsible\nfor a fraction of the missing SFG population.", "category": "astro-ph_GA" }, { "text": "A galactic-scale origin for stellar clustering: We recently presented a model for the cluster formation efficiency (CFE),\ni.e. the fraction of star formation occurring in bound stellar clusters. It\nutilizes the idea that the formation of stars and stellar clusters occurs\nacross a continuous spectrum of ISM densities. Bound stellar clusters naturally\narise from the high-density end of this density spectrum. Due to short\nfree-fall times, these high-density regions can achieve high star formation\nefficiencies (SFEs) and can be unaffected by gas expulsion. Lower-density\nregions remain gas-rich and substructured, and are unbound upon gas expulsion.\nThe model enables the CFE to be calculated using galactic-scale observables. I\npresent a brief summary of the model physics, assumptions and caveats, and show\nthat it agrees well with observations. Fortran and IDL routines for calculating\nthe CFE are publicly available at http://www.mpa-garching.mpg.de/cfe.", "category": "astro-ph_GA" }, { "text": "One, Two, Three ... An Explosive Outflow in IRAS 12326$-$6245 revealed\n by ALMA: In the last years there has been a substantial increase in the number of the\nreported massive and luminous star-forming regions with related explosive\noutflows thanks to the superb sensitivity and angular resolution provided by\nthe new radio, infrared, and optical facilities. Here, we report one more\nexplosive outflow related with the massive and bright star-forming region IRAS\n12326$-$6245 using Band 6 sensitive and high angular resolution ($\\sim$0.2$\"$)\nAtacama Large Millimeter/Submillimeter Array (ALMA) observations. We find over\n10 molecular and collimated well-defined streamers, with Hubble-Lemaitre like\nexpansion motions, and pointing right to the center of a dusty and molecular\nshell (reported for the first time here) localized in the northern part of the\nUCHII region known as G301.1A. The estimated kinematic age, and energy for the\nexplosion are $\\sim$700 yrs, and 10$^{48}$ erg, respectively. Taking into\naccount the recently reported explosive outflows together with IRAS\n12326$-$6245, we estimate an event rate of once every 90 yr in our Galaxy,\nsimilar to the formation rate of massive stars.", "category": "astro-ph_GA" }, { "text": "The nature of the Milky Way's stellar halo revealed by the three\n integrals of motion: We developed a new selection method of halo stars in the phase-space\ndistribution defined by the three integrals of motion in an axisymmetric\nGalactic potential, ($E$, $L_z$, $I_3$), where $I_3$ is the third integral of\nmotion. The method is used to explore the general chemo-dynamical structure of\nthe halo based on stellar samples from SDSS-SEGUE DR7 and DR16-APOGEE, matched\nwith Gaia-DR2. We found, (a) halo stars can be separated from disk stars by\nselecting over (1) $0 < L_z < 1500$ \\kpckms, $(2I_3)^{1/2} > 1000$ \\kpckms\n(orbital angle $\\theta_{\\rm orb}$ $>$ 15-20 deg), and $E < -1.5 \\times 10^5$\nkm$^2$ s$^{-2}$, and (2) $L_z < 0$ \\kpckms. These selection criteria are free\nfrom kinematical biases introduced by the simple high-velocity cuts adopted in\nrecent literature; (b) the averaged, or {\\it coarse-grained}, halo phased-space\ndistribution shows a monotonic exponential decrease with increasing $E$ and\n$I_3$ like the Michie-Bodenheimer models; (c) the inner stellar halo described\nin \\citet{carollo2007,carollo2010} is found to comprise a combination of Gaia\nEnceladus debris (GE; \\citealt{helmi2018}), lowest-$E$ stars (likely in-situ\nstars), as well as metal-poor prograde stars missed by the high velocity cuts\nselection; (d) the very metal poor outer halo, ([Fe/H] $< -$2.2), exhibits both\nretrograde and prograde rotation, with an asymmetric $L_z$ distribution towards\nhigh retrograde motions, and larger $\\theta_{\\rm orb}$ than those possessed by\nthe GE dominated inner halo; (e) the Sgr dSph galaxy could induce a long-range\ndynamical effect on local halo stars. Implication for the formation of the\nstellar halo are also discussed.", "category": "astro-ph_GA" }, { "text": "Photoionization Modelling of the Giant Broad-Line Region in NGC 3998: Prior high angular resolution spectroscopic observations of the\nLow-ionization nuclear emission-line region (Liner) in NGC 3998 obtained with\nthe Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space\nTelescope (HST) revealed a rich UV-visible spectrum consisting of broad\npermitted and broad forbidden emission lines. The photoionization code XSTAR is\nemployed together with reddening-insensitive emission line diagnostics to\nconstrain a dynamical model for the broad-line region (BLR) in NGC 3998. The\nBLR is modelled as a large H$^+$ region ${\\sim}$ 7 pc in radius consisting of\ndust-free, low density ${\\sim}$ 10$^4$ cm$^{-3}$, low metallicity ${\\sim}$ 0.01\n$Z/Z_\\odot$ gas. Modelling the shape of the broad H${\\alpha}$ emission line\nsignificantly discriminates between two independent measures of the black hole\nmass, favouring the estimate of de Francesco et al. (2006). Interpreting the\nbroad H${\\alpha}$ emission line in terms of a steady-state spherically\nsymmetric inflow leads to a mass inflow rate of 1.4 ${\\times}$ 10$^{-2}$\nM$_\\odot$/yr, well within the present uncertainty of calculations that attempt\nto explain the observed X-ray emission in terms of an advection-dominated\naccretion flow (ADAF). Collectively, the model provides an explanation for the\nshape of the H${\\alpha}$ emission line, the relative intensities and\nluminosities for the H Balmer, [O III], and potentially several of the broad UV\nemission lines, as well as refining the initial conditions needed for future\nmodelling of the ADAF.", "category": "astro-ph_GA" }, { "text": "Molecular-Cloud-Scale Chemical Composition III: Constraints of Average\n Physical Properties through Chemical Models: It is important to understand the origin of molecular line intensities and\nchemical composition in the molecular-cloud scale in the Galactic sources\nbecause it serves as a benchmark to compare with the chemical compositions of\nextragalactic sources. Recent observations of the 3-mm spectra averaged over\nthe 10-pc scale show similar spectral pattern among sources for molecular lines\nHCN, HCO$^+$, CCH, HNC, HNCO, c-C$_3$H$_2$, CS, SO, N$_2$H$^+$, and CN. To\nconstrain the average physical property emitting such spectral pattern, we\nmodel molecular spectra using a time-dependent gas-grain chemical model\nfollowed by a radiative transfer calculation. We use a grid of physical\nparameters such as the density $n=3 \\times 10^2 - 3\\times 10^4$ cm$^{-3}$, the\ntemperature, $T=10-30$ K, the visual extinction $A_{\\rm V} = 2,4,10$ mag, the\ncosmic-ray ionization rate $\\zeta = 10^{-17} - 10^{-16}$ s$^{-1}$, and the\nsulfur elemental abundance $S/H = 8\\times 10^{-8} - 8\\times 10^{-7}$.\nComparison with the observed spectra indicates that spectra are well reproduced\nwith the relatively low density of $n=(1-3) \\times 10^3\\,$cm$^{-3}$, $T=10\\,$K,\n$\\zeta = 10^{-17}$ s$^{-1}$, and the short chemistry timescale of $10^5$ yrs.\nThis short chemistry timescale may indicate that molecular clouds are\nconstantly affected by the turbulence, and exposed to low-density, low $A_{\\rm\nV}$ regions that \"refreshes\" the chemical clock by UV radiation. The relatively\nlow density obtained is orders of magnitude lower than the commonly-quoted\ncritical density in the optically thin case. Meanwhile, this range of density\nis consistent with results from recent observational analysis of\nmolecular-cloud-scale mapping.", "category": "astro-ph_GA" }, { "text": "Spontaneous Formation of Outflows Powered by Rotating Magnetized\n Accretion Flows in a Galactic Center: We investigate how magnetically driven outflows are powered by a rotating,\nweakly magnetized accretion flow onto a supermassive black hole using\naxisymmetric magnetohydrodynamic simulations. Our proposed model focuses on the\naccretion dynamics on an intermediate scale between the Schwarzschild radius\nand the galactic scale, which is $\\sim$1-100 pc. We demonstrate that a rotating\ndisk formed on a parsec-scale acquires poloidal magnetic fields via accretion\nand this produces an asymmetric bipolar outflow at some point. The formation of\nthe outflow was found to follow the growth of strongly magnetized regions\naround disk surfaces (magnetic bubbles). The bipolar outflow grew continuously\ninside the expanding bubbles. We theoretically derived the growth condition of\nmagnetic bubbles for our model that corresponds to a necessary condition for\noutflow growth. We found that the north-south asymmetric structure of the\nbipolar outflow originates from the complex motions excited by accreting flows\naround the outer edge of the disk. The bipolar outflow comprises multiple\nmini-outflows and downflows (failed outflows). The mini-outflows emanate from\nthe magnetic concentrations (magnetic patches). The magnetic patches exhibit\ninward drifting motions, thereby making the outflows unsteady. We demonstrate\nthat the inward drift can be modeled using a simple magnetic patch model that\nconsiders magnetic angular momentum extraction. This study could be helpful for\nunderstanding how asymmetric and non-steady outflows with complex substructures\nare produced around supermassive black holes without the help of strong\nradiation from accretion disks or entrainment by radio jets such as molecular\noutflows in radio-quiet active galactic nuclei, NGC 1377.", "category": "astro-ph_GA" }, { "text": "Simulations of the star-forming molecular gas in an interacting M51-like\n galaxy: cloud population statistics: To investigate how molecular clouds react to different environmental\nconditions at a galactic scale, we present a catalogue of giant molecular\nclouds resolved down to masses of $\\sim 10$~M$_{\\odot}$ from a simulation of\nthe entire disc of an interacting M51-like galaxy and a comparable isolated\ngalaxy. Our model includes time-dependent gas chemistry, sink particles for\nstar formation and supernova feedback, meaning we are not reliant on star\nformation recipes based on threshold densities and can follow the physics of\nthe cold molecular phase. We extract giant molecular clouds at a given timestep\nof the simulations and analyse their properties. In the disc of our simulated\ngalaxies, spiral arms seem to act merely as snowplows, gathering gas and clouds\nwithout dramatically affecting their properties. In the centre of the galaxy,\non the other hand, environmental conditions lead to larger, more massive\nclouds. While the galaxy interaction has little effect on cloud masses and\nsizes, it does promote the formation of counter-rotating clouds. We find that\nthe identified clouds seem to be largely gravitationally unbound at first\nglance, but a closer analysis of the hierarchical structure of the molecular\ninterstellar medium shows that there is a large range of virial parameters with\na smooth transition from unbound to mostly bound for the densest structures.\nThe common observation that clouds appear to be virialised entities may\ntherefore be due to CO bright emission highlighting a specific level in this\nhierarchical binding sequence. The small fraction of gravitationally bound\nstructures found suggests that low galactic star formation efficiencies may be\nset by the process of cloud formation and initial collapse.", "category": "astro-ph_GA" }, { "text": "The nature of sub-millimetre galaxies II: an ALMA comparison of SMG dust\n heating mechanisms: We compare the contribution of Active Galactic Nuclei (AGN) and\nstar-formation towards dust heating in sub-mm galaxies (SMGs). We have used\nALMA at $0.\"1$ resolution to image a complete flux-limited sample of seven\nsub-mm sources previously shown to have spectral energy distributions (SEDs)\nthat were as well-fitted by obscured AGN as star-forming galaxy templates.\nIndeed, two sub-mm sources were known to be quasars from their absorbed X-ray\nemission. We find the sub-mm sizes of all SMGs to be small ($\\approx1-2$kpc)\nand generally $\\sim3$ times smaller than any host detected in the\nNear-Infra-Red (NIR). In all cases, the five SMGs are comparable in sub-mm size\nto the two known quasars and four $z\\approx6$ quasars, also observed with ALMA.\nWe detect no evidence of diffuse spiral arms in this complete sample. We then\nconvert the Far-Infra-Red (FIR) luminosities to star-formation rate (SFR)\nsurface densities and find that the SMGs occupy the same range as the known\nquasars in our sample. We conclude that in terms of sub-mm size, extent\nrelative to host and SFR density as well as luminosity and Mid-IR (MIR) colour,\nthere is little distinction between the SMGs and sub-mm bright quasars.\nFinally, we present preliminary evidence that SMGs with higher MIR luminosities\nand sub-mm loud quasars tend to have dust components that range to hotter\ntemperatures than their less luminous SMG counterparts. In light of these\nresults, we continue to suggest that luminous SMGs may host dust-absorbed\nquasars that may simultaneously dominate the FIR and hard X-ray backgrounds.", "category": "astro-ph_GA" }, { "text": "Subaru FOCAS IFU observations of two z=0.12 strong-lensing elliptical\n galaxies from SDSS MaNGA: We present new observations of two z=0.12 strong-lensing elliptical galaxies,\noriginally discovered from the SDSS-IV MaNGA survey, using the new FOCAS IFU\nspectrograph on the Subaru Telescope. For J1436+4943, our observations confirm\nthe identification of this system as a multiple-image lens, in a cusp\nconfiguration, with Einstein radius $\\theta_{Ein}$=2.0 arcsec. For J1701+3722,\nthe improved data confirm earlier hints of a complex source plane, with\ndifferent configurations evident in different emission lines. The new\nobservations reveal a previously unseen inner counter-image to the [OIII] arc\nfound from MaNGA, leading to a smaller revised Einstein radius of\n$\\theta_{Ein}$=1.6 arcsec. The inferred projected masses within the Einstein\napertures (3.7-4.7kpc) are consistent with being dominated by stars with an\ninitial mass function (IMF) similar to that of the Milky Way, and a dark matter\ncontribution of ~35 per cent as supported from cosmological simulations. These\nresults are consistent with `pure lensing' analyses of lower-redshift lenses,\nbut contrast with claims for heavier IMFs from combined lensing-and-dynamical\nstudies of more distant early-type galaxies.", "category": "astro-ph_GA" }, { "text": "The Black Hole in the Compact, High-dispersion Galaxy NGC 1271: Located in the Perseus cluster, NGC 1271 is an early-type galaxy with a small\neffective radius of 2.2 kpc and a large stellar velocity dispersion of 276 km/s\nfor its K-band luminosity of 8.9x10^{10} L_sun. We present a mass measurement\nfor the black hole in this compact, high-dispersion galaxy using observations\nfrom the integral field spectrograph NIFS on the Gemini North telescope\nassisted by laser guide star adaptive optics, large-scale integral field unit\nobservations with PPAK at the Calar Alto Observatory, and Hubble Space\nTelescope WFC3 imaging observations. We are able to map out the stellar\nkinematics on small spatial scales, within the black hole sphere of influence,\nand on large scales that extend out to four times the galaxy's effective\nradius. We find that the galaxy is rapidly rotating and exhibits a sharp rise\nin the velocity dispersion. Through the use of orbit-based stellar dynamical\nmodels, we determine that the black hole has a mass of (3.0^{+1.0}_{-1.1}) x\n10^9 M_sun and the H-band stellar mass-to-light ratio is 1.40^{+0.13}_{-0.11}\nM_sun/L_sun (1-sigma uncertainties). NGC 1271 occupies the sparsely-populated\nupper end of the black hole mass distribution, but is very different from the\nBrightest Cluster Galaxies (BCGs) and giant elliptical galaxies that are\nexpected to host the most massive black holes. Interestingly, the black hole\nmass is an order of magnitude larger than expectations based on the galaxy's\nbulge luminosity, but is consistent with the mass predicted using the galaxy's\nbulge stellar velocity dispersion. More compact, high-dispersion galaxies need\nto be studied using high spatial resolution observations to securely determine\nblack hole masses, as there could be systematic differences in the black hole\nscaling relations between these types of galaxies and the BCGs/giant\nellipticals, thereby implying different pathways for black hole and galaxy\ngrowth.", "category": "astro-ph_GA" }, { "text": "A Catalog of Globular Cluster Systems: What Determines the Size of a\n Galaxy's Globular Cluster Population?: We present a catalog of 422 galaxies with published measurements of their\nglobular cluster (GC) populations. Of these, 248 are E galaxies, 93 are S0\ngalaxies, and 81 are spirals or irregulars. Among various correlations of the\ntotal number of GCs with other global galaxy properties, we find that N_GC\ncorrelates well though nonlinearly with the dynamical mass of the galaxy bulge\nM_dyn = 4 \\sigma_e^2 R_e /G, where \\sigma_e is the central velocity dispersion\nand R_e the effective radius of the galaxy light profile. We also present\nupdated versions of the GC specific frequency S_N and specific mass S_M versus\nhost galaxy luminosity and baryonic mass. These graphs exhibit the previously\nknown U-shape: highest S_N or S_M values occur for either dwarfs or\nsupergiants, but in the midrange of galaxy size (10^9 - 10^10 L_Sun) the GC\nnumbers fall along a well defined baseline value of S_N ~ 1 or S_M ~ 0.1,\nsimilar among all galaxy types. Along with other recent discussions, we suggest\nthat this trend may represent the effects of feedback, which systematically\ninhibited early star formation at either very low or very high galaxy mass, but\nwhich had its minimum effect for intermediate masses. Our results strongly\nreinforce recent proposals that GC formation efficiency appears to be most\nnearly proportional to the galaxy halo mass M_halo. The mean \"absolute\"\nefficiency ratio for GC formation that we derive from the catalog data is\nM_GCS/M_halo = 6 \\times 10^-5. We suggest that the galaxy-to-galaxy scatter\naround this mean value may arise in part because of differences in the relative\ntiming of GC formation versus field-star formation. Finally, we find that an\nexcellent empirical predictor of total GC population for galaxies of all\nluminosities is N_GC \\sim (R_e \\sigma_e)^1.3$, a result consistent with\nFundamental Plane scaling relations.", "category": "astro-ph_GA" }, { "text": "The SEDIGISM survey: a search for molecular outflows: Context. The formation processes of massive stars are still unclear but a\npicture is emerging involving accretion disks and molecular outflows in what\nappears to be a scaled-up version of low-mass star formation. A census of\noutflow activity towards massive star-forming clumps in various evolutionary\nstages has the potential to shed light on massive star formation (MSF).\n Aims. We conducted an outflow survey towards ATLASGAL clumps using SEDIGISM\ndata and aimed to obtain a large sample of clumps exhibiting outflows in\ndifferent evolutionary stages.\n Methods. We identify the high-velocity wings of the 13CO lines toward\nATLASGAL clumps by (1) extracting the simultaneously observed 13CO and C18O\nspectra from SEDIGISM, and (2) subtracting Gaussian fits to the scaled C18O\nfrom the 13CO, line after considering opacity broadening.\n Results. We have detected high-velocity gas towards 1192 clumps out of a\ntotal sample of 2052, giving an overall detection rate of 58%. Outflow activity\nhas been detected in the earliest quiescent clumps (i.e., 70$\\mu$m weak), to\nthe most evolved HII region stages i.e., 8$\\mu$m bright with MSF tracers. The\ndetection rate increases as a function of evolution (quiescent=51%,\nprotostellar=47%, YSO=57%, UCHII regions=76%).\n Conclusion. Our sample is the largest outflow sample identified so far. The\nhigh-detection rate from this large sample is consistent with previous results\nand supports that outflows are a ubiquitous feature of MSF. The lower detection\nrate in early evolutionary stages may be due to that outflows in the early\nstages are weak and difficult to detect. We obtain a statistically significant\nsample of outflow clumps for every evolutionary stage, especially for outflow\nclumps in the 70$\\mu$m dark stage. This suggests that the absence of 70$\\mu$m\nemission is not a robust indicator of starless/pre-stellar cores.", "category": "astro-ph_GA" }, { "text": "Identification of filamentary structures in the environment of\n superclusters of galaxies in the Local Universe: The characterization of the internal structure of the superclusters of\ngalaxies (walls, filaments and knots where the clusters are located) is\nparamount for understanding the formation of the Large Scale Structure and for\noutlining the environment where galaxies evolved in the last Gyr. (i) To detect\nthe compact regions of high relative density (clusters and rich groups of\ngalaxies); (ii) to map the elongated structures of low relative density\n(filaments, bridges and tendrils of galaxies); (iii) to characterize the galaxy\npopulations on filaments and study the environmental effects they are subject\nto. We employed optical galaxies with spectroscopic redshifts from the\nSDSS-DR13 inside rectangular boxes encompassing the volumes of a sample of 46\nsuperclusters of galaxies, up to z=0.15. Our methodology implements different\nclassical pattern recognition and machine learning techniques pipelined in the\nGalaxy Systems-Finding algorithm and the Galaxy Filaments-Finding algorithm. We\ndetected in total 2,705 galaxy systems (clusters and groups, of which 159 are\nnew) and 144 galaxy filaments in the 46 superclusters of galaxies. The\nfilaments we detected have a density contrast above 3, with a mean value around\n10, a radius of about 2.5 Mpc and lengths between 9 and 130 Mpc. Correlations\nbetween the galaxy properties (mass, morphology and activity) and the\nenvironment in which they reside (systems, filaments and the dispersed\ncomponent) suggest that galaxies closer to the skeleton of the filaments are\nmore massive by up to 25% compared to those in the dispersed component; 70 % of\nthe galaxies in the filament region present early type morphologies and the\nfractions of active galaxies (both AGN and SF) seem to decrease as galaxies\napproach the filament. These results suggest that preprocessing in large scale\nfilaments could have significant effects on galaxy evolution.", "category": "astro-ph_GA" }, { "text": "Stellar Kinematics and Metallicities in the Ultra-Faint Dwarf Galaxy\n Reticulum II: We present Magellan/M2FS, VLT/GIRAFFE, and Gemini South/GMOS spectroscopy of\nthe newly discovered Milky Way satellite Reticulum II. Based on the spectra of\n25 Ret II member stars selected from Dark Energy Survey imaging, we measure a\nmean heliocentric velocity of 62.8 +/- 0.5 km/s and a velocity dispersion of\n3.3 +/- 0.7 km/s. The mass-to-light ratio of Ret II within its half-light\nradius is 470 +/- 210 Msun/Lsun, demonstrating that it is a strongly dark\nmatter-dominated system. Despite its spatial proximity to the Magellanic\nClouds, the radial velocity of Ret II differs from that of the LMC and SMC by\n199 and 83 km/s, respectively, suggesting that it is not gravitationally bound\nto the Magellanic system. The likely member stars of Ret II span 1.3 dex in\nmetallicity, with a dispersion of 0.28 +/- 0.09 dex, and we identify several\nextremely metal-poor stars with [Fe/H] < -3. In combination with its\nluminosity, size, and ellipticity, these results confirm that Ret II is an\nultra-faint dwarf galaxy. With a mean metallicity of [Fe/H] = -2.65 +/- 0.07,\nRet II matches Segue~1 as the most metal-poor galaxy known. Although Ret II is\nthe third-closest dwarf galaxy to the Milky Way, the line-of-sight integral of\nthe dark matter density squared is log J = 18.8 +/- 0.6 Gev^2/cm^5 within 0.2\ndegrees, indicating that the predicted gamma-ray flux from dark matter\nannihilation in Ret II is lower than that of several other dwarf galaxies.", "category": "astro-ph_GA" }, { "text": "Large scale clustering measurements with photometric redshifts:\n comparing the dark matter halos of X-ray AGN, star-forming and passive\n galaxies at z~1: We combine multiwavelength data in the AEGIS-XD and C-COSMOS surveys to\nmeasure the typical dark matter halo mass of X-ray selected AGN\n[Lx(2-10keV)>1e42 erg/s] in comparison with far-infrared selected star-forming\ngalaxies detected in the Herschel/PEP survey (PACS Evolutionary Probe; Lir>1e11\nsolar) and quiescent systems at z~1. We develop a novel method to measure the\nclustering of extragalactic populations that uses photometric redshift\nProbability Distribution Functions in addition to any spectroscopy. This is\nadvantageous in that all sources in the sample are used in the clustering\nanalysis, not just the subset with secure spectroscopy. The method works best\nfor large samples. The loss of accuracy because of the lack of spectroscopy is\nbalanced by increasing the number of sources used to measure the clustering. We\nfind that X-ray AGN, far-infrared selected star-forming galaxies and passive\nsystems in the redshift interval 0.6500 km/s) characteristic of young, ejecta-dominated SNRs like Cas\nA; instead, most if not all appear to be middle-aged SNRs. The general\nproperties of the SNRs, size distribution and spectral characteristics,\nresemble those in other nearby spiral galaxies, notably M33, M83, and NGC6946,\nwhere similar samples exist. However, the spectroscopically observed [N\nII]:H{\\alpha} ratios appear to be significantly higher than in any of these\nother galaxies. Although we have explored various ideas to explain the high\nratios in M51, none of the explanations appears to be satisfactory.", "category": "astro-ph_GA" }, { "text": "Strongly lensed candidates from the HSC transient survey: We present a lensed quasar search based on the variability of lens systems in\nthe HSC transient survey. Starting from 101,353 variable objects with i-band\nphotometry in the HSC transient survey, we used a variability-based lens search\nmethod measuring the spatial extent in difference images to select potential\nlensed quasar candidates. We adopted conservative constraints in this\nvariability selection and obtained 83,657 variable objects as possible lens\ncandidates. We then ran CHITAH, a lens search algorithm based on the image\nconfiguration, on those 83,657 variable objects, and 2,130 variable objects\nwere identified as potential lensed objects. We visually inspected the 2,130\nvariable objects, and seven of them are our final lensed quasar candidates.\nAdditionally, we found one lensed galaxy candidate as a serendipitous\ndiscovery. Among the eight final lensed candidates, one is the only known\nquadruply lensed quasar in the survey field, HSCJ095921+020638. None of the\nother seven lensed candidates have been previously classified as a lens nor a\nlensed candidate. Three of the five final candidates with available HST images,\nincluding HSCJ095921+020638, show clues of a lensed feature in the HST images.\nA tightening of variability selection criteria might result in the loss of\npossible lensed quasar candidates, especially the lensed quasars with faint\nbrightness or narrow separation, without efficiently eliminating the non-lensed\nobjects; CHITAH is therefore important as an advanced examination to improve\nthe lens search efficiency through the object configuration. The recovery of\nHSCJ095921+020638 proves the effectiveness of the variability-based lens search\nmethod, and this lens search method can be used in other cadenced imaging\nsurveys, such as the upcoming Rubin Observatory Legacy Survey of Space and\nTime.", "category": "astro-ph_GA" }, { "text": "The extreme luminosity states of Sagittarius A*: We discuss mm-wavelength radio, 2.2-11.8um NIR and 2-10 keV X-ray light\ncurves of the super massive black hole (SMBH) counterpart of Sagittarius A*\n(SgrA*) near its lowest and highest observed luminosity states. The luminosity\nduring the low state can be interpreted as synchrotron emission from a\ncontinuous or even spotted accretion disk. For the high luminosity state SSC\nemission from THz peaked source components can fully account for the flux\ndensity variations observed in the NIR and X-ray domain. We conclude that at\nnear-infrared wavelengths the SSC mechanism is responsible for all emission\nfrom the lowest to the brightest flare from SgrA*. For the bright flare event\nof 4 April 2007 that was covered from the radio to the X-ray domain, the SSC\nmodel combined with adiabatic expansion can explain the related peak\nluminosities and different widths of the flare profiles obtained in the NIR and\nX-ray regime as well as the non detection in the radio domain.", "category": "astro-ph_GA" }, { "text": "The Three Hundred: $M_{sub}-V_{circ}$ relation: In this study, we investigate a recent finding based on strong lensing\nobservations, which suggests that the sub-halos observed in clusters exhibit\ngreater compactness compared to those predicted by $\\Lambda$CDM simulations. To\naddress this discrepancy, we performed a comparative analysis by comparing the\ncumulative mass function of sub-halos and the\n$M_{\\text{sub}}$-$V_{\\text{circ}}$ relation between observed clusters and 324\nsimulated clusters from The Three Hundred project, focusing on re-simulations\nusing GADGET-X and GIZMO-SIMBA baryonic models. The sub-halos' cumulative mass\nfunction of the GIZMO-SIMBA simulated clusters agrees with observations, while\nthe GADGET-X simulations exhibit discrepancies in the lower sub-halo mass range\npossibly due to its strong SuperNova feedback. Both GADGET-X and GIZMO-SIMBA\nsimulations demonstrate a redshift evolution of the sub-halo mass function and\nthe $V_{max}$ function, with slightly fewer sub-halos observed at lower\nredshifts. Neither the GADGET-X nor GIZMO-SIMBA(albeit a little closer)\nsimulated clusters' predictions for the $M_{\\text{sub}}$-$V_{\\text{circ}}$\nrelation align with the observational result. Further investigations on the\ncorrelation between sub-halo/halo properties and the discrepancy in the\n$M_{\\text{sub}}$-$V_{\\text{circ}}$ relation reveals that the sub-halo's half\nmass radius and galaxy stellar age, the baryon fraction and sub-halo distance\nfrom the cluster's centre, as well as the halo relaxation state play important\nroles on this relation. Nevertheless, we think it is still challenging in\naccurately reproducing the observed $M_{\\text{sub}}$-$V_{\\text{circ}}$ relation\nin our current hydrodynamic cluster simulation under the standard $\\Lambda$CDM\ncosmology.", "category": "astro-ph_GA" }, { "text": "The Origin of the 300 km s$^{-1}$ Stream Near Segue 1: We present a search for new members of the 300 km s$^{-1}$ stream (300S) near\nthe dwarf galaxy Segue 1 using wide-field survey data. We identify 11\npreviously unknown bright stream members in the APOGEE-2 and SEGUE-1 and 2\nspectroscopic surveys. Based on the spatial distribution of the high-velocity\nstars, we confirm for the first time that this kinematic structure is\nassociated with a 24$^{\\circ}$-long stream seen in SDSS and Pan-STARRS imaging\ndata. The 300S stars display a metallicity range of $-2.17 < {\\rm [Fe/H]} <\n-1.24$, with an intrinsic dispersion of 0.21$_{-0.09}^{+0.12}$ dex. They also\nhave chemical abundance patterns similar to those of Local Group dwarf\ngalaxies, as well as that of the Milky Way halo. Using the open-source code\ngalpy to model the orbit of the stream, we find that the progenitor of the\nstream passed perigalacticon about 70 Myr ago, with a closest approach to the\nGalactic Center of about 4.1 kpc. Using Pan-STARRS DR1 data, we obtain an\nintegrated stream luminosity of $4 \\times 10^3$ L$_{\\odot}$. We conclude that\nthe progenitor of the stream was a dwarf galaxy that is probably similar to the\nsatellites that were accreted to build the present-day Milky Way halo.", "category": "astro-ph_GA" }, { "text": "Can X-rays provide a solution to the abundance discrepancy problem in\n photoionised nebulae?: We re-examine the well-known discrepancy between ionic abundances determined\nvia the analysis of recombination lines (RLs) and collisionally excited lines\n(CELs). We show that abundance variations can be mimicked in a {\\it chemically\nhomogeneous} medium by the presence of dense X-ray irradiated regions which\npresent different ionisation and temperature structures from those of the more\ndiffuse medium they are embedded in, which is predominantly ionised by\nextreme-ultraviolet radiation. The presence of X-ray ionised dense clumps or\nfilaments also naturally explains the lower temperatures often measured from O\n{\\sc ii} recombination lines and from the Balmer jump when compared to\ntemperatures determined by CELs. We discuss the implications for abundances\ndetermined via the analysis of CELs and RLs and provide a simple analytical\nprocedure to obtain upwards corrections for CEL-determined abundance. While we\nshow that the abundance discrepancy factor (ADF) and the Balmer Jump\ntemperature determined from observations of the Orion Nebula can simultaneously\nbe reproduced by this model (implying upward corrections for CELs by a factor\nof 1.15), we find that the required X-ray fluxes exceed the known Orion's\nstellar and diffuse X-ray budget, if we assume that the clumps are located at\nthe edge of the blister. We propose, however, that spatially resolved\nobservations may be used to empirically test the model, and we outline how the\nframework developed in this letter may be applied in the future to objects with\nbetter constrained geometries (e.g. planetary nebulae).", "category": "astro-ph_GA" }, { "text": "A catalogue of 74 new open clusters found in Gaia Data-Release 2: Based on astrometric data from Gaia DR2, we employ an unsupervised machine\nlearning method to blindly search for open star clusters in the Milky Way\nwithin the Galactic latitude range of |b| < 20 degrees. In addition to 2,080\nknown clusters, 74 new open cluster candidates are found. In this work, we\npresent the positions, apparent radii, parallaxes, proper motions and member\nstars of these candidates\n(https://cdsarc.u-strasbg.fr/ftp/vizier.submit//new_OC/). Meanwhile, to obtain\nthe physical parameters of each candidate cluster, stellar isochrones are fit\nto the photometric data. The results show that the apparent radii and the\nobserved proper motion dispersions of these new candidates are consistent with\nthose of open clusters previously identified in Gaia DR2.", "category": "astro-ph_GA" }, { "text": "Radiation pressure acting on the neutral He atoms in the Heliosphere: The Interstellar Neutral Helium (ISN He) is an important source of\ninformation on the physical state of the Local Interstellar Medium. Radiation\npressure acting on the neutral helium atoms in the heliosphere has always been\nneglected, its effect has been considered insignificant compared to\ngravitational force. The most advanced numerical models of ISN He take into\naccount more and more subtle effects, therefore it is important to check if the\neffect of radiation pressure is still negligible. In this paper, we use the\nmost up-to-date version of the Warsaw Test Particle Model (WTPM) to calculate\nthe expected helium distribution in the heliosphere, and simulate the flux of\nISN He observed by the Interstellar Boundary Explorer (IBEX) and in the future\nby the Interstellar Mapping and Acceleration Probe (IMAP). We compare results\ncalculated with and without radiation pressure during low and high solar\nactivity. The results show that in the analysis of IBEX-Lo observations the\nradiation pressure acting on typical helium causes flux differences at a level\nof 1-4% and is comparable to the observational errors. For the more sensitive\nIMAP-Lo instrument, there are some regions in the considered observations\nconfigurations where radiation pressure causes potentially statistically\nsignificant changes in the calculated fluxes. The effect can be up to 9% for\nthe indirect beam and is likely to be higher than the estimated errors.\nTherefore, we claim that in the future analysis of the IMAP-Lo observations\nradiation pressure acting on ISN He should be considered.", "category": "astro-ph_GA" }, { "text": "Are rotating planes of satellite galaxies ubiquitous?: We compare the dynamics of satellite galaxies in the Sloan Digital Sky Survey\nto simple models in order to test the hypothesis that a large fraction of\nsatellites co-rotate in coherent planes. We confirm the previously-reported\nexcess of co-rotating satellite pairs located near diametric opposition with\nrespect to the host, but show that this signal is unlikely to be due to\nrotating discs (or planes) of satellites. In particular, no overabundance of\nco-rotating satellites pairs is observed within $\\sim 20^{\\circ}-50^{\\circ}$ of\ndirect opposition, as would be expected for planar distributions inclined\nrelative to the line-of-sight. Instead, the excess co-rotation for satellite\npairs within $\\sim 10^{\\circ}$ of opposition is consistent with random noise\nassociated with undersampling of an underlying isotropic velocity distribution.\nWe conclude that at most $10\\%$ of the hosts in our sample harbor co-rotating\nsatellite planes (as traced by the luminous satellite population).", "category": "astro-ph_GA" }, { "text": "Predicting resolved galaxy properties from photometric images using\n convolutional neural networks: Multi-band images of galaxies reveal a huge amount of information about their\nmorphology and structure. However, inferring properties of the underlying\nstellar populations such as age, metallicity or kinematics from those images is\nnotoriously difficult. Traditionally such information is best extracted from\nexpensive spectroscopic observations. Here we present the $Painting\\,\nIntrinsiC\\, Attributes\\, onto\\, SDSS\\, Objects$ (PICASSSO) project and test the\ninformation content of photometric multi-band images of galaxies. We train a\nconvolutional neural network on 27,558 galaxy image pairs to establish a\nconnection between broad-band images and the underlying physical stellar and\ngaseous galaxy property maps. We test our machine learning (ML) algorithm with\nSDSS $ugriz$ mock images for which uncertainties and systematics are exactly\nknown. We show that multi-band galaxy images contain enough information to\nreconstruct 2d maps of stellar mass, metallicity, age and gas mass, metallicity\nas well as star formation rate. We recover the true stellar properties on a\npixel by pixel basis with only little scatter, $\\lesssim20\\%$ compared to\n$\\sim50\\%$ statistical uncertainty from traditional mass-to-light-ratio based\nmethods. We further test for any systematics of our algorithm with image\nresolution, training sample size or wavelength coverage. We find that galaxy\nmorphology alone constrains stellar properties to better than $\\sim20\\%$ thus\nhighlighting the benefits of including morphology into the parameter\nestimation. The machine learning approach can predict maps of high resolution,\nonly limited by the resolution of the input bands, thus achieving higher\nresolution than IFU observations. The network architecture and all code is\npublicly available on GitHub.", "category": "astro-ph_GA" }, { "text": "First laboratory detection of vibration-rotation transitions of CH$^+$\n and $^{13}$CH$^+$ and improved measurement of their rotational transition\n frequencies: The long-searched C-H stretches of the fundamental ions CH$^+$ and\n$^{13}$CH$^+$ have been observed for the first time in the laboratory. For\nthis, the state-dependent attachment of He atoms to these ions at cryogenic\ntemperatures has been exploited to obtain high-resolution rovibrational data.\nIn addition, the lowest rotational transitions of CH$^+$, $^{13}$CH$^+$ and\nCD$^+$ have been revisited and their rest frequency values improved\nsubstantially.", "category": "astro-ph_GA" }, { "text": "Fossil group origins X. Velocity segregation in fossil systems: We want to study how the velocity segregation and the radial profile of the\nvelocity dispersion depend on the prominence of the brightest cluster galaxies\n(BCGs). We divide a sample of 102 clusters and groups of galaxies into four\nbins of magnitude gap between the two brightest cluster members. We then\ncompute the velocity segregation in bins of absolute and relative magnitudes.\nMoreover, for each bin of magnitude gap we compute the radial profile of the\nvelocity dispersion. When using absolute magnitudes, the segregation in\nvelocity is limited to the two brightest bins and no significant difference is\nfound for different magnitude gaps. However, when we use relative magnitudes, a\ntrend appears in the brightest bin: the larger the magnitude gap, the larger\nthe velocity segregation. We also show that this trend is mainly due to the\npresence, in the brightest bin, of satellite galaxies in systems with small\nmagnitude gaps: in fact, if we study separately central galaxies and\nsatellites, this trend is mitigated and central galaxies are more segregated\nthan satellites for any magnitude gap. A similar result is found in the radial\nvelocity dispersion profiles: a trend is visible in central regions (where the\nBCGs dominate) but, if we analyse the profile using satellites alone, the trend\ndisappears. In the latter case, the shape of the velocity dispersion profile in\nthe centre of systems with different magnitude gaps show three types of\nbehaviours: systems with the smallest magnitude gaps have an almost flat\nprofile from the centre to the external regions; systems with the largest\nmagnitude gaps show a monothonical growth from the low values of the central\npart to the flat ones in the external regions; finally, systems with $1.0 <\n\\Delta m_{12} \\le 1.5$ show a profile that peaks in the centres and then\ndecreases towards the external regions. We suggest that two mechanisms could be\nrespons....", "category": "astro-ph_GA" }, { "text": "High-Dimensional Dust Mapping: Galactic interstellar dust has a profound impact not only on our observations\nof objects throughout the Universe, but also on the morphology, star formation,\nand chemical evolution of the Galaxy. The advent of massive imaging and\nspectroscopic surveys (particularly in the infrared) places us on the threshold\nof being able to map the properties and dynamics of dust and the interstellar\nmedium (ISM) in three dimensions throughout the Milky Way disk and bulge. These\ndevelopments will enable a fundamentally new understanding of dust properties,\nincluding how grains respond to their local environment and how those\nenvironments affect dust attenuation of background objects of interest.\nDistance-resolved maps of dust motion also hold great promise for tracing the\nflow of interstellar material throughout the Galaxy on a variety of scales,\nfrom bar-streaming motions to the collapse and dissolution of individual\nmolecular clouds. These advances require optical and infrared imaging of stars\nthroughout the Galactic midplane, stretching many kiloparsecs from the Sun,\nmatched with very dense spectroscopic coverage to probe the ISM's fine-grained\nstructure.", "category": "astro-ph_GA" }, { "text": "Formation of Dark Matter Torii Around Supermassive Black Holes Via The\n Eccentric Kozai-Lidov Mechanism: We explore the effects of long term secular perturbations on the distribution\nof dark matter particles around Supermassive Black Hole (BH) binaries. We show\nthat in the hierarchical (in separation) three-body problem, one of the BHs and\na dark matter particle form an inner binary. Gravitational perturbations from\nthe BH companion, on a much wider orbit, can cause the dark matter particle to\nreach extremely high eccentricities and even get accreted onto the BH, by what\nis known as the Eccentric Kozai-Lidov (EKL) mechanism. We show that this may\nproduce a torus-like configuration for the dark matter distribution around the\nless massive member of the BH binary. We first consider an Intermediate BH\n(IMBH) in the vicinity of our Galactic Center, which may be a relic of a past\nminor merger. We show that if the IMBH is close enough (i.e., near the stellar\ndisk) the EKL mechanism is very efficient in exciting the eccentricity of dark\nmatter particles in near-polar configurations to extremely high values where\nthey are accreted by the IMBH. We show that this mechanism is even more\neffective if the central BH grows in mass, where we have assumed adiabatic\ngrowth. Since near-polar configurations are disrupted, a torus-like shape is\nformed. We also show that this behavior is also likely to be relevant for\nSupermassive BH binaries. We suggest that if the BHs are spinning, the accreted\ndark matter particles may linger in the ergosphere and thereby may generate\nself-annihilations and produce an indirect signature of potential interest.", "category": "astro-ph_GA" }, { "text": "SDSS-IV MaNGA: Spatially resolved star-formation histories and the\n connection to galaxy physical properties: A key task of observational extragalactic astronomy is to determine where --\nwithin galaxies of diverse masses and morphologies -- stellar mass growth\noccurs, how it depends on galaxy properties and what processes regulate star\nformation. Using spectroscopic indices derived from the stellar continuum at\n$\\sim 4000$\\AA, we determine the spatially resolved star-formation histories of\n980000 spaxels in 2404 galaxies in the SDSS-IV MaNGA IFU survey. We examine the\nspatial distribution of star-forming, quiescent, green valley, starburst and\npost-starburst spaxels as a function of stellar mass and morphology to see\nwhere and in what types of galaxy star formation is occurring. The spatial\ndistribution of star-formation is dependent primarily on stellar mass, with a\nnoticeable change in the distribution at \\mstar$>10^{10}$\\msun. Galaxies above\nthis mass have an increasing fraction of regions that are forming stars with\nincreasing radius, whereas lower mass galaxies have a constant fraction of star\nforming regions with radius. Our findings support a picture of inside-out\ngrowth and quenching at high masses. We find that morphology (measured via\nconcentration) correlates with the fraction of star-forming spaxels, but not\nwith their radial distribution. We find (post-)starburst regions are more\ncommon outside of the galaxy centre, are preferentially found in asymmetric\ngalaxies, and have lower gas-phase metallicity than other regions, consistent\nwith interactions triggering starbursts and driving low metallicity gas into\nregions at $<1.5R_e$.", "category": "astro-ph_GA" }, { "text": "Revisiting the Mass-Excitation (MEx) diagram using the MaNGA dataset: The diagram comparing the flux ratio of the [OIII] and H$\\beta$ emission\nlines with the total stellar mass of galaxies (also known as the\nmass-excitation diagram, MEx) has been widely used to classify the ionization\nmechanism in high redshift galaxies between star formation and active galactic\nnuclear ones. This diagram was mainly derived using single-fiber spectroscopy\nfrom the SDSS-DR7 survey. In this study, we revise this diagram using the\ncentral and integrated spectral measurement from the entire Integral Field\nSpectroscopic MaNGA sample. Our results suggest that along with the physical\nparameters of this diagram, the equivalent width of the H$\\alpha$ emission line\nis also required to constrain the ionization mechanism of a high-redshifted\ngalaxy. Furthermore, the location of a galaxy in the excitation-mass diagram\nvaries depending on the use of central or integrated properties.", "category": "astro-ph_GA" }, { "text": "Dynamic Localised Turbulent Diffusion and its Impact on the Galactic\n Ecosystem: Modelling the turbulent diffusion of thermal energy, momentum, and metals is\nrequired in all galaxy evolution simulations due to the ubiquity of turbulence\nin galactic environments. The most commonly employed diffusion model, the\nSmagorinsky model, is known to be over-diffusive due to its strong dependence\non the fluid velocity shear. We present a method for dynamically calculating a\nmore accurate, locally appropriate, turbulent diffusivity: the dynamic\nlocalised Smagorinsky model. We investigate a set of standard\nastrophysically-relevant hydrodynamical tests, and demonstrate that the dynamic\nmodel curbs over-diffusion in non-turbulent shear flows and improves the\ndensity contrast in our driven turbulence experiments. In galactic discs, we\nfind that the dynamic model maintains the stability of the disc by preventing\nexcessive angular momentum transport, and increases the metal-mixing timescale\nin the interstellar medium. In both our isolated Milky Way-like galaxies and\ncosmological simulations, we find that the interstellar and circumgalactic\nmedia are particularly sensitive to the treatment of turbulent diffusion. We\nalso examined the global gas enrichment fractions in our cosmological\nsimulations, to gauge the potential effect on the formation sites and\npopulation statistics of Population III stars and supermassive black holes,\nsince they are theorised to be sensitive to the metallicity of the gas out of\nwhich they form. The dynamic model is, however, not for galaxy evolution\nstudies only. It can be applied to all astrophysical hydrodynamics simulations,\nincluding those modelling stellar interiors, planetary formation, and star\nformation.", "category": "astro-ph_GA" }, { "text": "Trans-cis molecular photoswitching in interstellar Space: As many organic molecules, formic acid (HCOOH) has two conformers (trans and\ncis). The energy barrier to internal conversion from trans to cis is much\nhigher than the thermal energy available in molecular clouds. Thus, only the\nmost stable conformer (trans) is expected to exist in detectable amounts. We\nreport the first interstellar detection of cis-HCOOH. Its presence in\nultraviolet (UV) irradiated gas exclusively (the Orion Bar photodissociation\nregion), with a low trans-to-cis abundance ratio of 2.8+-1.0, supports a\nphotoswitching mechanism: a given conformer absorbs a stellar photon that\nradiatively excites the molecule to electronic states above the interconversion\nbarrier. Subsequent fluorescent decay leaves the molecule in a different\nconformer form. This mechanism, which we specifically study with ab initio\nquantum calculations, was not considered in Space before but likely induces\nstructural changes of a variety of interstellar molecules submitted to UV\nradiation.", "category": "astro-ph_GA" }, { "text": "Extracting galaxy merger timescales I: Tracking haloes with WhereWolf\n and spinning orbits with OrbWeaver: Hierarchical models of structure formation predict that dark matter halo\nassembly histories are characterised by episodic mergers and interactions with\nother haloes. An accurate description of this process will provide insights\ninto the dynamical evolution of haloes and the galaxies that reside in them.\nUsing large cosmological N-body simulations, we characterise halo orbits to\nstudy the interactions between substructure haloes and their hosts, and how\ndifferent evolutionary histories map to different classes of orbits. We use two\nnew software tools - WhereWolf, which uses halo group catalogues and merger\ntrees to ensure that haloes are tracked accurately in dense environments, and\nOrbWeaver, which quantifies each halo's orbital parameters. We demonstrate how\nWhereWolf improves the accuracy of halo merger trees, and we use OrbWeaver to\nquantify orbits of haloes. We assess how well analytical prescriptions for the\nmerger timescale from the literature compare to measured merger timescales from\nour simulations and find that existing prescriptions perform well, provided the\nratio of substructure-to-host mass is not too small. In the limit of small\nsubstructure-to-host mass ratio, we find that the prescriptions can\noverestimate the merger timescales substantially, such that haloes are\npredicted to survive well beyond the end of the simulation. This work\nhighlights the need for a revised analytical prescription for the merger\ntimescale that more accurately accounts for processes such as catastrophic\ntidal disruption.", "category": "astro-ph_GA" }, { "text": "HST imaging of the brightest z~8-9 galaxies from UltraVISTA: the extreme\n bright end of the UV luminosity function: We report on the discovery of three especially bright candidate $z_{phot}\n\\gtrsim 8$ galaxies. Five sources were targeted for follow-up with HST/WFC3,\nselected from a larger sample of 16 bright ($24.8 \\lesssim H\\lesssim25.5$~mag)\ncandidate $z\\gtrsim 8$ LBGs identified over the 1.6 degrees$^2$ of the\nCOSMOS/UltraVISTA field. These were identified as Y and J dropouts by\nleveraging the deep (Y-to-$K_{S} \\sim 25.3-24.8$~mag, $5\\sigma$) NIR data from\nthe UltraVISTA DR3 release, deep ground based optical imaging from the CFHTLS\nand Subaru Suprime Cam programs and Spitzer/IRAC mosaics combining observations\nfrom the SMUVS and SPLASH programs. Through the refined spectral energy\ndistributions, which now also include new HyperSuprime Cam g, r, i, z and Y\nband data, we confirm that 3/5 galaxies have robust $z_{phot}\\sim8.0-8.7$,\nconsistent with the initial selection. The remaining 2/5 galaxies have a\nnominal $z_{phot}\\sim2$. However, if we use the HST data alone, these objects\nhave increased probability of being at $z\\sim9$. Furthermore, we measure mean\nUV continuum slopes $\\beta=-1.91\\pm0.26$ for the three $z\\sim8-9$ galaxies,\nmarginally bluer than similarly luminous $z\\sim4-6$ in CANDELS but consistent\nwith previous measurements of similarly luminous galaxies at $z\\sim7$. The\ncircularized effective radius for our brightest source is $0.9\\pm0.2$ kpc,\nsimilar to previous measurements for a bright $z\\sim11$ galaxy and bright\n$z\\sim7$ galaxies. Finally, enlarging our sample to include the six brightest\n$z\\sim8$ LBGs identified over UltraVISTA (i.e., including three other sources\nfrom Labbe et al. 2017, in prep.) we estimate for the first time the volume\ndensity of galaxies at the extreme bright ($M_{UV}\\sim-22$~mag) end of the\n$z\\sim8$ UV LF. Despite this exceptional result, the still large statistical\nuncertainties do not allow us to discriminate between a Schechter and a double\npower-law form.", "category": "astro-ph_GA" }, { "text": "The chemical evolution of local star forming galaxies: Radial profiles\n of ISM metallicity, gas mass, and stellar mass and constraints on galactic\n accretion and winds: The radially averaged metallicity distribution of the ISM and the young\nstellar population of a sample of 20 disk galaxies is investigated by means of\nan analytical chemical evolution model which assumes constant ratios of\ngalactic wind mass loss and accretion mass gain to star formation rate. Based\non this model the observed metallicities and their gradients can be described\nsurprisingly well by the radially averaged distribution of the ratio of stellar\nmass to ISM gas mass. The comparison between observed and model predicted\nmetallicity is used to constrain the rate of mass loss through galactic wind\nand accretion gain in units of the star formation rate. Three groups of\ngalaxies are found: galaxies with either mostly winds and only weak accretion,\nor mostly accretion and only weak winds, and galaxies where winds are roughly\nbalanced by accretion. The three groups are distinct in the properties of their\ngas disks. Galaxies with approximately equal rates of mass-loss and accretion\ngain have low metallicity, atomic hydrogen dominated gas disks with a flat\nspatial profile. The other two groups have gas disks dominated by molecular\nhydrogen out to 0.5 to 0.7 isophotal radii and show a radial exponential\ndecline, which is on average steeper for the galaxies with small accretion\nrates. The rates of accretion (<1.0 x SFR) and outflow (<2.4 x SFR) are\nrelatively low. The latter depend on the calibration of the zero point of the\nmetallicity determination from the use of HII region strong emission lines.", "category": "astro-ph_GA" }, { "text": "Study of rotation curves of spiral galaxies with a scalar field dark\n matter model: In this work we study rotation curves of spiral galaxies using a model of\ndark matter based on a scalar-tensor theory of gravity. We show how to estimate\nthe scalar field dark matter parameters using a sample of observed rotation\ncurves.", "category": "astro-ph_GA" }, { "text": "Understanding inverse metallicity gradients in galactic discs as a\n consequence of inside-out formation: The early stages of a galaxy's evolution leave an imprint on its metallicity\ndistribution. We discuss the origins and evolution of radial metallicity\ngradients in discs of spiral galaxies using an analytical chemical evolution\nmodel. We explain how radial metallicity gradients in stellar populations are\ndetermined by three factors: the radial metallicity profile of the star-forming\nISM, radial changes in the star-formation history (in particular inside-out\nformation), and radial mixing of stars. Under reasonable assumptions,\ninside-out formation steepens the negative ISM metallicity gradient, but\ncontributes positively to the stellar metallicity gradient, up to inverting the\nmetallicity profile to a positive d[Fe/H]/dR. This reconciles steep negative\nd[Fe/H]/dR in some high redshift galaxies to generally flatter gradients in\nlocal observations.\n We discuss the evidence for inverse radial metallicity gradients (positive\nd[X/H]/dR) at high redshifts and the inverse relationship between azimuthal\nvelocity and the metallicity (positive dV_{\\phi}/d[Fe/H]) of stars for the\nMilky Way's thick disc. The former can be achieved by high central gas-loss\nrates and re-distribution processes, e.g. re-accretion of enriched material in\nconjunction with inside-out formation, and near-disc galactic fountaining. For\nthe Milky Way thick disc, we show that the positive dV_{\\phi}/d[Fe/H]\ncorrelation points to comparable timescales for inside-out formation, initial\nmetal enrichment and SNIa enrichment. We argue that the original ISM\nmetallicity gradient could be inferred with better data from the\nhigh-metallicity tail of the alpha enhanced population. Including inside-out\nformation in our models changes the local vertical metallicity gradient by\nabout -0.2dex/kpc, in line with local measurements.", "category": "astro-ph_GA" }, { "text": "The ACS Nearby Galaxy Survey Treasury: The ACS Nearby Galaxy Survey Treasury (ANGST) is a systematic survey to\nestablish a legacy of uniform multi-color photometry of resolved stars for a\nvolume-limited sample of nearby galaxies (D<4 Mpc). The survey volume\nencompasses 69 galaxies in diverse environments, including close pairs, small &\nlarge groups, filaments, and truly isolated regions. The galaxies include a\nnearly complete range of morphological types spanning a factor of ~10^4 in\nluminosity and star formation rate. The survey data consists of images taken\nwith ACS on HST, supplemented with archival data and new WFPC2 imaging taken\nafter the failure of ACS. Survey images include wide field tilings covering the\nfull radial extent of each galaxy, and single deep pointings in uncrowded\nregions of the most massive galaxies in the volume. The new wide field imaging\nin ANGST reaches median 50% completenesses of m_F475W=28.0 mag, m_F606W=27.3\nmag, and m_F814W=27.3 mag, several magnitudes below the tip of the red giant\nbranch (TRGB). The deep fields reach magnitudes sufficient to fully resolve the\nstructure in the red clump. The resulting photometric catalogs are publicly\naccessible and contain over 34 million photometric measurements of >14 million\nstars. In this paper we present the details of the sample selection, imaging,\ndata reduction, and the resulting photometric catalogs, along with an analysis\nof the photometric uncertainties (systematic and random), for both the ACS and\nWFPC2 imaging. We also present uniformly derived relative distances measured\nfrom the apparent magnitude of the TRGB.", "category": "astro-ph_GA" }, { "text": "Stellar masses, sizes, and radial profiles for 465 nearby early-type\n galaxies: an extension to the Spitzer Survey of Stellar Structure in Galaxies\n (S$^{4}$G): The Spitzer Survey of Stellar Structure in Galaxies (S$^{4}$G) is a detailed\nstudy of over 2300 nearby galaxies in the near-infrared (NIR), which has been\ncritical to our understanding of the detailed structures of nearby galaxies.\nBecause the sample galaxies were selected only using radio-derived velocities,\nhowever, the survey favored late-type disk galaxies over lenticulars and\nellipticals. A follow-up Spitzer survey was conducted to rectify this bias,\nadding 465 early-type galaxies (ETGs) to the original sample, to be analyzed in\na manner consistent with the initial survey. We present the data release of\nthis ETG extension, up to the third data processing pipeline (P3): surface\nphotometry. We produce curves of growth and radial surface brightness profiles\n(with and without inclination corrections) using reduced and masked Spitzer\nIRAC 3.6$\\mu$m and 4.5$\\mu$m images produced through Pipelines 1 and 2,\nrespectively. From these profiles, we derive the following integrated\nquantities: total magnitudes, stellar masses, concentration parameters, and\ngalaxy size metrics. We showcase NIR scaling relations for ETGs among these\nquantities. We examine general trends across the whole S$^{4}$G and ETG\nextension among our derived parameters, highlighting differences between ETGs\nand late-type galaxies (LTGs). ETGs are, on average, more massive and more\nconcentrated than LTGs, and also show subtle distinctions among ETG\nmorphological sub-types. We also derive the following scaling relations and\ncompare with previous results in visible light: mass--size (both half-light and\nisophotal), mass--concentration, mass--surface brightness (central, effective,\nand within 1 kpc), and mass--color. We find good agreement with previous works,\nthough some relations (e.g., mass--central surface brightness) will require\nmore careful multi-component decompositions to be fully understood.", "category": "astro-ph_GA" }, { "text": "The quasar main sequence and its potential for cosmology: The main sequence offers a method for the systematization of quasar spectral\nproperties. Extreme FeII emitters (or extreme Population A, xA) are believed to\nbe sources accreting matter at very high rates. They are easily identifiable\nalong the quasar main sequence, in large spectroscopic surveys over a broad\nredshift range. The very high accretion rate makes it possible that massive\nblack holes hosted in xA quasars radiate at a stable, extreme\nluminosity-to-mass ratio. After reviewing the basic interpretation of the main\nsequence, we report on the possibility of identifying virial broadening\nestimators from low-ionization line widths, and provide evidence of the\nconceptual validity of redshift-independent luminosities based on virial\nbroadening for a known luminosity-to-mass ratio.", "category": "astro-ph_GA" }, { "text": "Two sequences of spiral galaxies with different shapes of the\n metallicity gradients: We considered two sequences of spiral galaxies with different shapes of the\nradial gas-phase oxygen abundance distributions from the galaxies in the MaNGA\nsurvey: (1) Galaxies in which the gradient is well approximated by a single\nlinear relation across the whole disc, that is, galaxies with an S (slope)\ngradients, (2) galaxies in which the metallicity in the inner region of the\ndisc is at a nearly constant level and the gradient is negative at larger\nradii, that is, galaxies with level-slope (LS) gradients. We also selected\ngalaxies with a nearly uniform oxygen abundance across the whole galaxy, that\nis, galaxies with level (L) gradients that can be the final evolutionary stage\nof the two galaxy sequences described above. The radial nitrogen abundance\ndistributions in galaxies with LS oxygen abundance distributions also show\nbreaks at radii smaller than the O/H distribution breaks. The observed\nbehaviour of the oxygen and nitrogen abundances with radius in these galaxies\ncan be explained by the time delay between the nitrogen and oxygen enrichment\ntogether with the variation in the star formation history along the radius.\nThese galaxies clearly show the effect of the inside-out disc evolution model.\nWe find that the shape of the radial abundance distribution in a galaxy is not\nrelated to its macroscopic characteristics (rotation velocity, stellar mass,\nisophotal radius, and star formation rate). The correlations between the\ngradient slopes and macroscopic characteristics of galaxies are weak in the\nsense that the scatter of the points in each diagram is large. We also examined\nthe properties of the Milky Way in the context of the considered galaxy\nsamples.", "category": "astro-ph_GA" }, { "text": "New constraints on the 1.4 GHz source number counts and luminosity\n functions in the Lockman Hole field: We present a study of the 1173 sources brighter than $S_{1.4\\,\\rm GHz}=\n120\\,\\mu$Jy detected over an area of $\\simeq 1.4\\,\\hbox{deg}^{2}$ in the\nLockman Hole field. Exploiting the multi-band information available in this\nfield for $\\sim$79% of the sample, sources have been classified into radio loud\n(RL) active galactic nuclei (AGNs), star forming galaxies (SFGs) and radio\nquiet (RQ) AGNs, using a variety of diagnostics available in the literature.\nExploiting the observed tight anti-correlations between IRAC band 1 or band 2\nand the source redshift we could assign a redshift to 177 sources missing a\nspectroscopic measurement or a reliable photometric estimate. A Monte Carlo\napproach was used to take into account the spread around the mean relation. The\nderived differential number counts and luminosity functions at several\nredshifts of each population show a good consistency with models and with\nearlier estimates made using data from different surveys and applying different\napproaches. Our results confirm that below $\\sim300\\,\\mu$Jy SFGs$+$RQ AGNs\novertake RL AGNs that dominate at brighter flux densities. We also confirm\nearlier indications of a similar evolution of RQ AGNs and SFGs. Finally, we\ndiscuss the angular correlation function of our sources and highlight its\nsensitivity to the criteria used for the classification.", "category": "astro-ph_GA" }, { "text": "The Abundance Inhomogeneity in the Northern Rim of the Cygnus Loop: We observed the northern rim of the Cygnus Loop with the \\textit{Suzaku}\nobservatory in 5 pointings (P21-P25). From the spatially resolved analysis, all\nthe spectra are well fitted by the single component of the non-equilibrium\nionization plasma model. From the best-fit parameters, we found that the\nabundances of the heavy elements are significantly lower than the solar values\nexcept those at the outermost edge in P21 and P22. The origin of the depleted\nmetal abundances is still unclear while such deficiencies have been reported\nfrom many other rim observations of the Loop. To explain these depletion at the\nrim regions, we considered the several possibilities. The effects of the\nresonance-line-scattering and the grain condensation lower the values of the\nabundances. However, these are not sufficient to account for the abundance\ndepletion observed.\n We found that the abundances at the outermost edge in P21 and P22 are higher\nthan those at the other regions. From the morphological point of view, it is\nreasonable to consider that this abundance inhomogeneity is derived from the\nbreakout or the thinness of the cavity wall of the Loop.", "category": "astro-ph_GA" }, { "text": "Mapping the stellar population and gas excitation of MaNGA galaxies with\n MEGACUBES. Results for AGN versus control sample: We present spaxel-by-spaxel stellar population fits for the $\\sim$10 thousand\nMaNGA datacubes. We provide multiple extension fits files, nominated as\nMEGACUBES, with maps of several properties as well as emission-line profiles\nthat are provided for each spaxel. All the MEGACUBES are available through a\nweb interface (\\url{https://manga.linea.org.br/} or\n\\url{http://www.if.ufrgs.br/~riffel/software/megacubes/}). We also defined a\nfinal Active Galactic Nuclei (AGN) sample, as well as a control sample matching\nthe AGN host galaxy properties. We have analysed the stellar populations and\nspatially resolved emission-line diagnostic diagrams of these AGNs and compared\nthem with the control galaxies sample. We find that the relative fractions of\nyoung ($t \\leq $56 Myr) and intermediate-age (100 Myr $\\leq t \\leq$ 2 Gyr) show\npredominantly a positive gradient for both AGNs and controls. The relative\nfraction of intermediate-age stellar population is higher in AGN hosts when\ncompared to the control sample, and this difference becomes larger for higher\n[O III] luminosity AGNs. We attribute this to the fact that extra gas is\navailable in these more luminous sources and that it most likely originates\nfrom mass-loss from the intermediate-age stars. The spatially resolved\ndiagnostic diagrams reveal that the AGN emission is concentrated in the inner\n0.5 $R_e$ (effective radius) region of the galaxies, showing that the AGN\nclassification is aperture dependent and that emission-line ratios have to be\ntaken together with the H$\\alpha$ equivalent width for proper activity\nclassification. We present a composite ``BPT+WHAN\" diagram that produces a more\ncomprehensive mapping of the gas excitation.", "category": "astro-ph_GA" }, { "text": "Chemical evolution in the early phases of massive star formation II:\n Deuteration: The chemical evolution in high-mass star-forming regions is still poorly\nconstrained. Studying the evolution of deuterated molecules allows to\ndifferentiate between subsequent stages of high-mass star formation regions due\nto the strong temperature dependence of deuterium isotopic fractionation. We\nobserved a sample of 59 sources including 19 infrared dark clouds, 20 high-mass\nprotostellar objects, 11 hot molecular cores and 9 ultra-compact HII regions in\nthe (3-2) transitions of the four deuterated molecules, DCN, DNC, DCO+ and N2D+\nas well as their non-deuterated counterpart. The overall detection fraction of\nDCN, DNC and DCO+ is high and exceeds 50% for most of the stages. N2D+ was only\ndetected in a few infrared dark clouds and high-mass protostellar objects. It\ncan be related to problems in the bandpass at the frequency of the transition\nand to low abundances in the more evolved, warmer stages. We find median D/H\nratios of ~0.02 for DCN, ~0.005 for DNC, ~0.0025 for DCO+ and ~0.02 for N2D+.\nWhile the D/H ratios of DNC, DCO+ and N2D+ decrease with time, DCN/HCN peaks at\nthe hot molecular core stage. We only found weak correlations of the D/H ratios\nfor N2D+ with the luminosity of the central source and the FWHM of the line,\nand no correlation with the H2 column density. In combination with a previously\nobserved set of 14 other molecules (Paper I) we fitted the calculated column\ndensities with an elaborate 1D physico-chemical model with time-dependent\nD-chemistry including ortho- and para-H2 states. Good overall fits to the\nobserved data have been obtained the model. It is one of the first times that\nobservations and modeling have been combined to derive chemically based\nbest-fit models for the evolution of high-mass star formation including\ndeuteration.", "category": "astro-ph_GA" }, { "text": "VLT/X-Shooter Survey of BAL Quasars: Large Distance Scale and AGN\n Feedback: We conducted a survey of quasar outflows using the VLT/X-shooter\nspectrograph. When choosing the 14 BAL and mini-BALs comprising this sample,\nthe data did not cover the S IV and S IV* troughs, whose ratio can be used to\ndetermine the distance of the outflows from the central source (R). Therefore,\nthis \"Blind Survey\" is unbiased towards a particular distance scale. Out of the\neight outflows where R can be measured, six have R > 100 pc (spanning the range\n100-4500 pc), one has R > 10 pc, and only one (at R < 60 pc) is compatible with\na much smaller R scale. At least two of the outflows have a kinetic luminosity\ngreater than 0.5% of their Eddington luminosity, implying that they are able to\nprovide significant AGN feedback. The outflows span a range of 0 to -10000 km\ns$^{-1}$ in velocity; total column density between 10$^{20}$ - 10$^{22.5}$\ncm$^{-2}$ ; ionization parameter ($U_H$ ) in the range 0.01 - 1; and electron\nnumber density between 10$^3$ - 10$^{5.5}$ cm$^{-3}$ , with one upper and one\nlower limit. The results of this survey can be extrapolated to the majority of\nBAL outflows, implying that most of these outflows are situated far away from\nthe AGN accretion disk; and that a significant portion of them can contribute\nto AGN feedback processes.", "category": "astro-ph_GA" }, { "text": "The discovery of lensed radio and X-ray sources behind the Frontier\n Fields cluster MACS J0717.5+3745 with the JVLA and Chandra: We report on high-resolution JVLA and Chandra observations of the HST\nFrontier Cluster MACS J0717.5+3745. MACS J0717.5+3745 offers the largest\ncontiguous magnified area of any known cluster, making it a promising target to\nsearch for lensed radio and X-ray sources. With the high-resolution 1.0-6.5 GHz\nJVLA imaging in A and B configuration, we detect a total of 51 compact radio\nsources within the area covered by the HST imaging. Within this sample we find\n7 lensed sources with amplification factors larger than $2$. None of these\nsources are identified as multiply-lensed. Based on the radio luminosities, the\nmajority of these sources are likely star forming galaxies with star formation\nrates of 10-50 M$_\\odot$ yr$^{-1}$ located at $1 \\lesssim z \\lesssim 2$. Two of\nthe lensed radio sources are also detected in the Chandra image of the cluster.\nThese two sources are likely AGN, given their $2-10$ keV X-ray luminosities of\n$\\sim 10^{43-44}$ erg s$^{-1}$. From the derived radio luminosity function, we\nfind evidence for an increase in the number density of radio sources at\n$0.6 2.5) don't have a broad light curve width and the SNe Ia which appeared\nin blue host galaxies (u - r < 2.0) have a variety of light curve widths. The\nKolmogorov-Smirnov test shows that the colour distribution of SNe Ia appeared\nin red / blue host galaxies is different (significance level of 99.9%). We also\ninvestigate the extinction law of host galaxy dust. As a result, we find the\nvalue of Rv derived from SNe Ia with medium light curve width is consistent\nwith the standard Galactic value. On the other hand, the value of Rv derived\nfrom SNe Ia that appeared in red host galaxies becomes significantly smaller.\nThese results indicate that there may be two types of SNe Ia with different\nintrinsic colours, and they are obscured by host galaxy dust with two different\nproperties.", "category": "astro-ph_GA" }, { "text": "Comparing semi-analytic particle tagging and hydrodynamical simulations\n of the Milky Way's stellar halo: Particle tagging is an efficient, but approximate, technique for using\ncosmological N-body simulations to model the phase-space evolution of the\nstellar populations predicted, for example, by a semi-analytic model of galaxy\nformation. We test the technique developed by Cooper et al. (which we call\nSTINGS here) by comparing particle tags with stars in a smooth particle\nhydrodynamic (SPH) simulation. We focus on the spherically averaged density\nprofile of stars accreted from satellite galaxies in a Milky Way (MW)-like\nsystem. The stellar profile in the SPH simulation can be recovered accurately\nby tagging dark matter (DM) particles in the same simulation according to a\nprescription based on the rank order of particle binding energy. Applying the\nsame prescription to an N-body version of this simulation produces a density\nprofile differing from that of the SPH simulation by <10 per cent on average\nbetween 1 and 200 kpc. This confirms that particle tagging can provide a\nfaithful and robust approximation to a self-consistent hydrodynamical\nsimulation in this regime (in contradiction to previous claims in the\nliterature). We find only one systematic effect, likely due to the\ncollisionless approximation, namely that massive satellites in the SPH\nsimulation are disrupted somewhat earlier than their collisionless\ncounterparts. In most cases this makes remarkably little difference to the\nspherically averaged distribution of their stellar debris. We conclude that,\nfor galaxy formation models that do not predict strong baryonic effects on the\npresent-day DM distribution of MW-like galaxies or their satellites,\ndifferences in stellar halo predictions associated with the treatment of star\nformation and feedback are much more important than those associated with the\ndynamical limitations of collisionless particle tagging.", "category": "astro-ph_GA" }, { "text": "Isolating signatures of major cloud-cloud collisions using\n position-velocity diagrams: Collisions between giant molecular clouds are a potential mechanism for\ntriggering the formation of massive stars, or even super star clusters. The\ntrouble is identifying this process observationally and distinguishing it from\nother mechanisms. We produce synthetic position-velocity diagrams from models\nof: cloud-cloud collisions, non-interacting clouds along the line of sight,\nclouds with internal radiative feedback and a more complex cloud evolving in a\ngalactic disc, to try and identify unique signatures of collision. We find that\na broad bridge feature connecting two intensity peaks, spatially correlated but\nseparated in velocity, is a signature of a high velocity cloud-cloud collision.\nWe show that the broad bridge feature is resilient to the effects of radiative\nfeedback, at least to around 2.5Myr after the formation of the first massive\n(ionising) star. However for a head on 10km/s collision we find that this will\nonly be observable from 20-30 per cent of viewing angles. Such broad-bridge\nfeatures have been identified towards M20, a very young region of massive star\nformation that was concluded to be a site of cloud-cloud collision by Torii et\nal (2011), and also towards star formation in the outer Milky Way by Izumi et\nal (2014).", "category": "astro-ph_GA" }, { "text": "The role of AGN on the structure, kinematics and evolution of ETGs in\n the Horizon simulations: Feedback processes play a fundamental role in the regulation of the star\nformation (SF) activity in galaxies and, in particular, in the quenching of\nearly-type galaxies (ETGs) as has been inferred by observational and numerical\nstudies of Lambda CDM models. At z = 0, ETGs exhibit well-known fundamental\nscaling relations, but the connection between them and the physical processes\nshaping ETG evolution remains unknown.This work aims at studying the impact of\nthe energetic feedback due to active galactic nuclei (AGN) on the formation and\nevolution of ETGs.We focus on assessing the impact of AGN feedback on the\nevolution of the mass-plane and the fundamental plane (FP, defined by using\nmass surface density) as well as on morphology, kinematics, and stellar age\nacross the FP.The Horizon-AGN and Horizon-noAGN cosmological hydrodynamical\nsimulations were performed with identical initial conditions and including the\nsame physical processes except for the activation of the AGN feedback in the\nformer. We select a sample of central ETGs from both simulations using the same\ncriteria and exhaustively study their SF activity, kinematics, and scaling\nrelations for z <= 3. We find that Horizon-AGN ETGs identified at z = 0 follow\nthe observed fundamental scaling relations (mass-plane, FP, mass-size relation)\nand qualitatively reproduce kinematic features albeit conserving a rotational\ninner component with a mass fraction regulated by the AGN feedback. AGN\nfeedback seems to be required to reproduce the bimodality in the spin parameter\ndistribution reported by observational works and the mass-size relation (with\nmore massive galaxies having older stellar populations (SPs), larger sizes, and\nbeing slower rotators). We study the evolution of the fundamental relations\nwith redshift, finding .Abridged", "category": "astro-ph_GA" }, { "text": "The Hector Survey: integral field spectroscopy of 100,000 galaxies: In March 2013, the Sydney--AAO Multi-object Integral field spectrograph\n(SAMI) began a major survey of 3400 galaxies at the AAT, the largest of its\nkind to date. At the time of writing, over a third of the targets have been\nobserved and the scientific impact has been immediate. The Manga galaxy survey\nhas now started at the SDSS telescope and will target an even larger sample of\nnearby galaxies. In Australia, the community is now gearing up to deliver a\nmajor new facility called Hector that will allow integral field spectroscopy of\n100 galaxies observed simultaneously. By the close of the decade, it will be\npossible to obtain integral field spectroscopy of 100,000 galaxies over 3000\nsquare degrees of sky down to r=17 (median). Many of these objects will have HI\nimaging from the new ASKAP radio surveys. We discuss the motivation for such a\nsurvey and the use of new cosmological simulations that are properly matched to\nthe integral field observations. The Hector survey will open up a new and\nunique parameter space for galaxy evolution studies.", "category": "astro-ph_GA" }, { "text": "An enduring puzzle: the width variations of the 2175 Angstrom extinction\n band: Graphene, a single infinite, planar, sheet of graphite, has the same\ndielectric resonances as bulk graphite, but solid state theory indicates that\nits features are about half as wide. Based on this theory, the dielectric\nfunctions of mono- and multi-layer graphenes are deduced and compared with\nthose of terrestrial graphite. The resonance width of an ordered stack of\ngraphenes is found to increase with the number of layers while the central\nfrequency stays constant. This is the basis of the polycrystalline model of the\ncarrier of the 2175 Angstrom interstellar extinction band. In this model, the\ncarrier dust grains derive from parent hydrocarbon grains. As a grain ages in\nthe IS medium, the light atoms are expelled, hexagonal carbon rings lump\ntogether into compact planar clusters, which then assemble into stacks of\nparallel, equidistant, graphene-like layers. This so-called graphitization is\nwell known to occur in the earth or under strong heating. As the number of\nlayers in each stack increases and their relative orientational order improves,\nthe pi resonance width increases asymptotically towards that of terrestrial\ngraphite. Because of the initial random structure of the parent grains, many\nrandomly oriented stacks may coexist in the same grain. Calculations of the\ndielectric response of this composite medium show that, for such a grain, the\nwidth of the extinction efficiency peak follows the same trend as the pi\nresonance of the average stack, and thus covers the observed range of IS\nfeature widths, at very nearly constant peak frequency.", "category": "astro-ph_GA" }, { "text": "Extreme High-velocity Outflows from High-redshift BOSS Quasars: It is common to assume that all narrow absorption lines (NALs) at extreme\nhigh-velocity shifts form in cosmologically intervening gas or galaxies\nunrelated to quasars. However, previous detailed studies of individual quasars\nhave shown that some NALs at these large velocity shifts do form in high-speed\nquasar ejecta. We search for extreme high-velocity NAL outflows (with speeds\n$\\sim$0.1-0.2c) based on relationships with associated absorption lines (AALs)\nand broad absorption-line (BAL) outflows. We find that high-velocity NALs are\nstrongly correlated with AALs, BALs, and radio loudness, indicating that a\nsignificant fraction of high-velocity systems are either ejected from the\nquasars or form in material swept up by the radio jets (and are not unrelated\nintervening gas). We also consider line-locked C IV doublets as another\nindicator of high-velocity NALs formed in outflows. The fact that line-locked\nNALs are highly ionized and correlated with BAL outflows and radio-loud quasars\nimplies that physical line locking due to radiative forces is both common and\nreal, which provides indirect evidence that a significant fraction of\nhigh-velocity NALs are intrinsic to quasars.", "category": "astro-ph_GA" }, { "text": "Detection of anhydrous hydrochloric acid, HCl, in IRC+10216 with the\n Herschel SPIRE and PACS spectrometers: We report on the detection of anhydrous hydrochloric acid (hydrogen chlorine,\nHCl) in the carbon-rich star IRC+10216 using the spectroscopic facilities\nonboard the Herschel satellite. Lines from J=1-0 up to J=7-6 have been\ndetected. From the observed intensities, we conclude that HCl is produced in\nthe innermost layers of the circumstellar envelope with an abundance relative\nto H2 of 5x10^-8 and extends until the molecules reach its photodissociation\nzone. Upper limits to the column densities of AlH, MgH, CaH, CuH, KH, NaH, FeH,\nand other diatomic hydrides have also been obtained.", "category": "astro-ph_GA" }, { "text": "Velocity dispersion measurements of dwarf galaxies in the Coma cluster -\n implications for the structure of the fundamental plane: We present intermediate-resolution spectroscopic data for a set of dwarf and\ngiant galaxies in the Coma Cluster, with -20.6 < M_R < -15.7. The photometric\nand kinematic properties of the brighter galaxies can be cast in terms of\nparameters which present little scatter with respect to a set of scaling\nrelations known as the Fundamental Plane. To determine the form of these\nfundamental scaling relations at lower luminosities, we have measured velocity\ndispersions for a sample comprising 69 galaxies on the border of the dwarf and\ngiant regime. Combining these data with our photometric survey, we find a tight\ncorrelation of luminosity and velocity dispersion, L \\propto \\sigma^{2.0},\nsubstantially flatter than the Faber-Jackson relation characterising giant\nelliptical galaxies. In addition, the variation of mass-to-light ratio with\nvelocity dispersion is quite weak in our dwarf sample: M/L \\propto\n\\sigma^{0.2}. Our overall results are consistent with theoretical models\ninvoking large-scale mass removal and subsequent structural readjustment, e.g.,\nas a result of galactic winds.", "category": "astro-ph_GA" }, { "text": "X-ray Shadowing Experiments Toward Infrared Dark Clouds: We searched for X-ray shadowing toward two infrared dark clouds (IRDCs) using\nthe MOS detectors on XMM-Newton to learn about the Galactic distribution of\nX-ray emitting plasma. IRDCs make ideal X-ray shadowing targets of 3/4 kev\nphotons due to their high column densities, relatively large angular sizes, and\nknown kinematic distances. Here we focus on two clouds near 30 deg. Galactic\nlongitude at distances of 2 and 5 kpc from the Sun. We derive the foreground\nand background column densities of molecular and atomic gas in the direction of\nthe clouds. We find that the 3/4 kev emission must be distributed throughout\nthe Galactic disk. It is therefore linked to the structure of the cooler\nmaterial of the ISM, and to the birth of stars.", "category": "astro-ph_GA" }, { "text": "E(B-V), N(H I) and N(H_2): We consider the structure of the N(H I) - E(B-V) relationship when H I is\nmeasured in the 21 cm radio line and \\EBV\\ is defined by far-IR dust-derived\nmeasures. We derive reddening-dependent corrections to N(H I) based on\ninterferometric absorption measurements over the past 30 years that follow a\nsingle power-law relationship $\\int \\tau(H I) dv = 14.07 ~\\kms\\ $\\EBV$^{1.074}$\nat 0.02 $\\la$ \\EBV\\ $\\la$ 3 mag. Corrections to 21cm line-derived H I column\ndensities are too small to have had any effect on the ratio N(H I)/\\EBV\\ $= 8.3\n\\times 10^{21}\\pcc$ mag$^{-1}$ we derived at 0.015 $\\la$ \\EBV\\ $\\la$ 0.075 mag\nand \\absb\\ $\\ge$ 20\\degr; they are also too small to explain the break in the\nslope of the N(H I) - \\EBV\\ relation at \\EBV\\ $\\ga$ 0.1 mag that we\ndemonstrated around the Galaxy at \\absb $\\ge 20$\\degr. The latter must\ntherefore be attributed to the onset of \\HH-formation and we show that models\nof \\HH\\ formation in a low density diffuse molecular gas can readily explain\nthe inflected N(H I)- \\EBV\\ relationship. Below \\absb\\ = 20\\degr\\ N(H I)/\\EBV\\\nmeasured at 0.015 $\\la$ \\EBV\\ $\\la$ 0.075 mag increases steadily down to \\absb\\\n= 8\\degr\\ where sightlines with small \\EBV\\ no longer occur.\n By contrast, the ratio N(H I)/\\EBV\\ measured over all \\EBV\\ declines to N(H\nI)/\\EBV\\ $= 5-6 \\times 10^{21}\\pcc$ mag$^{-1}$ at \\absb\\ $\\la 30$\\degr, perhaps\nproviding an explanation of the difference between our results and the\ngas/reddening ratios measured previously using stellar spectra.", "category": "astro-ph_GA" }, { "text": "Dissipation of AGN jets in a clumpy interstellar medium: Accreting supermassive black holes (SMBHs) frequently power jets that\ninteract with the interstellar/circumgalactic medium (ISM/CGM), regulating\nstar-formation in the galaxy. Highly supersonic jets launched by active\ngalactic nuclei (AGN) power a cocoon that confines them and shocks the ambient\nmedium. We build upon the models of narrow conical jets interacting with a\nsmooth ambient medium, to include the effect of dense clouds that are an\nessential ingredient of a multiphase ISM. The key physical ingredient of this\nmodel is that the clouds along the supersonic jet-beam strongly decelerate the\njet-head, but the subsonic cocoon easily moves around the clouds without much\nresistance. We propose scalings for important physical quantities -- cocoon\npressure, head & cocoon speed, and jet radius. We obtain, for the first time,\nthe analytic condition on clumpiness of the ambient medium for the jet to\ndissipate within the cocoon and verify it with numerical simulations of conical\njets interacting with a uniform ISM with embedded spherical clouds. A jet is\ndefined to be dissipated when the cocoon speed exceeds the speed of the\njet-head. We compare our models to more sophisticated numerical simulations,\ndirect observations of jet-ISM interaction (e.g., quasar J1316+1753), and\ndiscuss implications for the Fermi/eROSITA bubbles. Our work also motivates\neffective subgrid models for AGN jet feedback in a clumpy ISM unresolved by the\npresent generation of cosmological galaxy formation simulations.", "category": "astro-ph_GA" }, { "text": "NIR spectroscopic observation of massive galaxies in the protocluster at\n z = 3.09: We present the results of near-infrared spectroscopic observations of the\n$K$-band selected candidate galaxies in the protocluster at $z=3.09$ in the\nSSA22 field. We observed 67 candidates with $K_{\\rm AB}<24$ and confirmed\nredshifts of the 39 galaxies at $2.0< z_{\\rm spec}< 3.4$. Of the 67 candidates,\n24 are certainly protocluster members with $3.04\\leq z_{\\rm spec}\\leq 3.12$,\nwhich are massive red galaxies those have been unidentified in previous optical\nobservations of the SSA22 protocluster. Many distant red galaxies (DRGs;\n$J-K_{\\rm AB}>1.4$), hyper extremely red objects (HEROs; $J-K_{\\rm AB}>2.1$),\n{\\it Spitzer} MIPS 24 $\\mu$m sources, active galactic nuclei (AGNs) as well as\nthe counterparts of Ly$\\alpha$ blobs and the AzTEC/ASTE 1.1-mm sources in the\nSSA22 field are also found to be the protocluster members. The mass of the\nSSA22 protocluster is estimated to be $\\sim2-5\\times10^{14}~M_{\\odot}$ and this\nsystem is plausibly a progenitor of the most massive clusters of galaxies in\nthe current Universe. The reddest ($J-K_{\\rm AB}\\geq 2.4$) protocluster\ngalaxies are massive galaxies with $M_{\\rm star}\\sim10^{11}~M_{\\odot}$ showing\nquiescent star formation activities and plausibly dominated by old stellar\npopulations. Most of these massive quiescent galaxies host moderately luminous\nAGNs detected by X-ray. There are no significant differences in the\n[O{\\footnotesize III}] $\\lambda$5007/H$\\beta$ emission line ratios, and\n[O{\\footnotesize III}] $\\lambda$5007 line widths and spatial extents of the\nprotocluster galaxies from those of massive galaxies at $z\\sim2-3$ in the\ngeneral field.", "category": "astro-ph_GA" }, { "text": "ngVLA: Astrometry and Long Baseline Science: Recent advances in VLBI have led to astrometric accuracy exceeding that of\nthe Gaia mission goals. This chapter describes some important astrophysical\nproblems that can be addressed with sub-milliarcsecond imaging and\nmicro-arcsecond astrometry using the ngVLA with long baselines.", "category": "astro-ph_GA" }, { "text": "A $Gaia$ EDR3 search for tidal tails in disintegrating open clusters: We carry out a search for tidal tails in a sample of open clusters with known\nrelatively elongated morphology. We identify the member stars of these clusters\nfrom the precise astrometric and deep photometric data from $Gaia$ Early Data\nRelease 3 using the robust membership determination algorithm, ML-MOC. We\nidentify 46 open clusters having a stellar corona beyond the tidal radius, 20\nof which exhibit extended tails aligned with the cluster orbit direction in\ngalactocentric coordinates. Notably we find NGC 6940 (at a distance of $\\sim1$\nkpc) is the furthest open cluster exhibiting tidal tails that are $\\sim50$ pc\nfrom its center, while also identifying $\\sim40$ pc long tidal tails for the\nnearby Pleiades. Using the minimum spanning tree length for the most massive\nstars relative to all cluster members, we obtain the mass segregation ratio\n($\\rm\\lambda_{MSR}$) profiles as a function of the number of massive stars in\neach cluster. From these profiles, we can classify the open clusters into four\nclasses based on the degree of mass segregation experienced by the clusters. We\nfind that clusters in the most mass segregated classes are the oldest on\naverage and have the flattest mass function slope. Of the 46 open clusters\nstudied in this work, 41 exhibit some degree of mass segregation. Furthermore,\nwe estimate the initial masses (M$\\rm_{i}$) of these open clusters finding that\nsome of them, having M$\\rm_{i}\\gtrsim 10^{4} M_{\\odot}$, could be the\ndissolving remnants of Young Massive Clusters.", "category": "astro-ph_GA" }, { "text": "Resolving the shocked gas in HH54 with Herschel: CO line mapping at high\n spatial and spectral resolution: The HH54 shock is a Herbig-Haro object, located in the nearby Chamaeleon II\ncloud. Observed CO line profiles are due to a complex distribution in density,\ntemperature, velocity, and geometry. Resolving the HH54 shock wave in the\nfar-infrared cooling lines of CO constrain the kinematics, morphology, and\nphysical conditions of the shocked region. We used the PACS and SPIRE\ninstruments on board the Herschel space observatory to map the full FIR\nspectrum in a region covering the HH54 shock wave. Complementary Herschel-HIFI,\nAPEX, and Spitzer data are used in the analysis as well. The observed features\nin the line profiles are reproduced using a 3D radiative transfer model of a\nbow-shock, constructed with the Line Modeling Engine code (LIME). The FIR\nemission is confined to the HH54 region and a coherent displacement of the\nlocation of the emission maximum of CO with increasing J is observed. The peak\npositions of the high-J CO lines are shifted upstream from the lower J CO lines\nand coincide with the position of the spectral feature identified previously in\nCO(10-9) profiles with HIFI. This indicates a hotter molecular component in the\nupstream gas with distinct dynamics. The coherent displacement with increasing\nJ for CO is consistent with a scenario where IRAS12500-7658 is the exciting\nsource of the flow, and the 180 K bow-shock is accompanied by a hot (800 K)\nmolecular component located upstream from the apex of the shock and blueshifted\nby -7 km s$^{-1}$. The spatial proximity of this knot to the peaks of the\natomic fine-structure emission lines observed with Spitzer and PACS ([OI]63,\n145 $\\mu$m) suggests that it may be associated with the dissociative shock as\nthe jet impacts slower moving gas in the HH54 bow-shock.", "category": "astro-ph_GA" }, { "text": "Surface density effects in quenching: cause or effect?: There are very strong observed correlations between the specific\nstar-formation rates (sSFR) of galaxies and their mean surface mass densities,\n{\\Sigma}, as well as other aspects of their internal structure. These strong\ncorrelations have often been taken to indicate that the internal structure of a\ngalaxy must play a major physical role, directly or indirectly, in the control\nof star-formation. In this paper we show by means of a very simple toy model\nthat these correlations can arise naturally without any such physical role once\nthe observed evolution of the size-mass relation for star-forming galaxies is\ntaken into account. In particular, the model reproduces the sharp threshold in\n{\\Sigma} between galaxies that are star-forming and those that are quenched,\nand the evolution of this threshold with redshift. Similarly, it produces\niso-quenched-fraction contours in the ${f_Q(m,R_e)}$ plane that are almost\nexactly parallel to lines of constant {\\Sigma} for centrals and shallower for\nsatellites. It does so without any dependence on quenching on size or {\\Sigma},\nand without invoking any differences between centrals and satellites, beyond\nthe different mass-dependences of their quenching laws. The toy-model also\nreproduces several other observations, including the sSFR gradients within\ngalaxies and the appearance of inside-out build-up of passive galaxies.\nFinally, it is shown that curvature in the Main Sequence sSFR-mass relation can\nproduce curvature in the apparent B/T ratios with mass. Our analysis therefore\nsuggests that many of the strong correlations that are observed between galaxy\nstructure and sSFR may well be a consequence of things unrelated to quenching\nand should not be taken as evidence of the physical processes that drive\nquenching.", "category": "astro-ph_GA" }, { "text": "The pride of lions around Messier 105: We undertook a search for new dwarf galaxies in the Leo-I group using the\ndata from the DECaLS digital sky survey. Five new presumed members of this\ngroup have been found in a wide vicinity of ${\\rm M}\\,105 ({\\rm NGC}\\,3379$).\nCurrently, the group has a population of $83$ galaxies, $33$ of which have\nmeasured radial velocities. More than half of the group members belong to early\ntypes with no signs of ongoing star formation. About a quarter of the galaxies\nare outside the group's virial radius, $R_v = 385$~kpc. The presence of\nmultiple systems with a size of about 15~kpc is evident in the group, but there\nare no noticeable global flat or filamentary substructures. The luminosity\nfunction of the group looks to be deficient in galaxies with absolute\nmagnitudes in the interval $M_B = [-18, -15]$ mag. The ${\\rm M}\\,105$ group is\ncharacterized by a radial velocity dispersion of $136$~km~s$^{-1}$, orbital\nmass estimate $(5.76\\pm1.32)\\times 10^{12}~M_{\\odot}$, and the total\nmass-to-K-band-luminosity ratio $(17.8\\pm4.1) M_\\odot/L_\\odot$. The neighboring\ngroup of galaxies around ${\\rm M}\\,66 ({\\rm NGC}\\,3627$) has a similar virial\nradius, $390$~kpc, velocity dispersion, $135$~km~s$^{-1}$, and total\nmass-to-luminosity ratio, $(15.6\\pm3.9) M_\\odot/L_\\odot$. Both groups in the\nLeo constellation are approaching the Local Group with a velocity of about\n100~km~s$^{-1}$. In the background of the ${\\rm M}\\,105$ group, we noted a\ngroup of 6 galaxies with an unusually low virial mass-to-luminosity ratio,\n$M_T/L_K = (4.1\\pm2.2) M_\\odot/L_\\odot$.", "category": "astro-ph_GA" }, { "text": "Dark matter deficient galaxies in the Illustris flat-$\u039b$CDM model\n structure formation simulation: Surveying dark matter deficient galaxies (those with dark matter mass to\nstellar mass ratio $M_{\\rm dm}/M_{\\rm star}<1$) in the Illustris simulation of\nstructure formation in the flat-$\\Lambda$CDM cosmogony, we find $M_{\\rm star}\n\\approx 2 \\times 10^8\\, M_\\sun$ galaxies that have properties similar to those\nascribed by \\citet{vanDokkumetal2018a} to the ultra-diffuse galaxy NGC1052-DF2.\nThe Illustris simulation also contains more luminous dark matter deficient\ngalaxies. Illustris galaxy subhalo 476171 is a particularly interesting\noutlier, a massive and very compact galaxy with $M_{\\rm star} \\approx 9 \\times\n10^{10}\\, M_\\sun$ and $M_{\\rm dm}/M_{\\rm star} \\approx 0.1$ and a\nhalf-stellar-mass radius of $\\approx 2$ kpc. If the Illustris simulation and\nthe $\\Lambda$CDM model are accurate, there are a significant number of dark\nmatter deficient galaxies, including massive luminous compact ones. It will be\ninteresting to observationally discover these galaxies, and to also more\nclearly understand how they formed, as they are likely to provide new insight\ninto and constraints on models of structure formation and the nature of dark\nmatter.", "category": "astro-ph_GA" }, { "text": "Simulating MOS science on the ELT: Ly$\u03b1$ forest tomography: Mapping of the large-scale structure through cosmic time has numerous\napplications in the studies of cosmology and galaxy evolution. At $z > 2$, the\nstructure can be traced by the neutral intergalactic medium (IGM) by way of\nobserving the Ly$\\alpha$, forest towards densely-sampled lines-of-sight of\nbright background sources, such as quasars and star forming galaxies. We\ninvestigate the scientific potential of MOSAIC, a planned multi-object\nspectrograph on the European Extremely Large Telescope (ELT), for the 3D\nmapping of the IGM at $z \\gtrsim 3$. We simulate a survey of $3 \\lesssim z\n\\lesssim 4$ galaxies down to a limiting magnitude of $m_{r}\\sim 25.5$ mag in an\narea of 1 degree$^2$ in the sky. Galaxies and their spectra (including the\nline-of-sight Ly$\\alpha$ absorption) are taken from the lightcone extracted\nfrom the Horizon-AGN cosmological hydrodynamical simulation. The quality of the\nreconstruction of the original density field is studied for different spectral\nresolutions and signal-to-noise ratios of the spectra. We demonstrate that the\nminimum $S/N$ (per resolution element) of the faintest galaxies that such\nsurvey has to reach is $S/N = 4$. We show that a survey with such sensitivity\nenables a robust extraction of cosmic filaments and the detection of the\ntheoretically-predicted galaxy stellar mass and star-formation rate gradients\ntowards filaments. By simulating the realistic performance of MOSAIC we obtain\n$S/N(T_{\\rm obs}, R, m_{r})$ scaling relations. We estimate that $\\lesssim\n35~(65)$ nights of observation time are required to carry out the survey with\nthe instrument's high multiplex mode and with the spectral resolution of\n$R=1000~(2000)$. A survey with a MOSAIC-concept instrument on the ELT is found\nto enable the mapping of the IGM at $z > 3$ on Mpc scales, and as such will be\ncomplementary to and competitive with other planned IGM tomography surveys.\n[abridged]", "category": "astro-ph_GA" }, { "text": "The H2O southern Galactic Plane Survey(HOPS): NH3 (1,1) and (2,2)\n catalogues: The H2O Southern Galactic Plane Survey (HOPS) has mapped a 100 degree strip\nof the Galactic plane (-70deg > l > 30deg, |b| < 0.5deg) using the 22-m Mopra\nantenna at 12-mm wavelengths. Observations were conducted in on-the-fly mode\nusing the Mopra spectrometer (MOPS), targeting water masers, thermal molecular\nemission and radio-recombination lines. Foremost among the thermal lines are\nthe 23 GHz transitions of NH3 J,K = (1,1) and (2,2), which trace the densest\nparts of molecular clouds (n > 10^4 cm^{-3}). In this paper we present the NH3\n(1,1) and (2,2) data, which have a resolution of 2 arcmin and cover a velocity\nrange of +/-200 km/s. The median sensitivity of the NH3 data-cubes is sigma_Tmb\n= 0.20 +/1 0.06 K. For the (1,1) transition this sensitivity equates to a 3.2\nkpc distance limit for detecting a 20 K, 400 Msun cloud at the 5-sigma level.\nSimilar clouds of mass 5,000 Msun would be detected as far as the Galactic\ncentre, while 30,000 Msun clouds would be seen across the Galaxy. We have\ndeveloped an automatic emission finding procedure based on the ATNF DUCHAMP\nsoftware and have used it to create a new catalogue of 669 dense molecular\nclouds. The catalogue is 100 percent complete at the 5-sigma detection limit\n(Tmb = 1.0 K). A preliminary analysis of the ensemble cloud properties suggest\nthat the near kinematic distances are favoured. The cloud positions are\nconsistent with current models of the Galaxy containing a long bar. Combined\nwith other Galactic plane surveys this new molecular-line dataset constitutes a\nkey tool for examining Galactic structure and evolution. Data-cubes, spectra\nand catalogues are available to the community via the HOPS website.", "category": "astro-ph_GA" }, { "text": "Understanding the X-ray spectral curvature of Mkn 421 using broadband\n AstroSat observations: We present a time-resolved X-ray spectral study of the high energy peaked\nblazar Mkn 421 using simultaneous broadband observations from the LAXPC and SXT\ninstruments on-board AstroSat. The ~ 400 ksec long observation taken during 3-8\nJanuary, 2017 was divided into segments of 10 ksecs. Each segment was fitted\nusing synchrotron emission from particles whose energy distribution was\nrepresented by a log-parabola model. We also considered particle energy\ndistribution models where (i) the radiative cooling leads to a maximum energy\n({\\xi} max model), (ii) the system has energy dependent diffusion (EDD) and\n(iii) has energy dependent acceleration (EDA). We found that all these models\ndescribe the spectra, although the EDD and EDA models were marginally better.\nTime resolved spectral analysis allowed for studying the correlation between\nthe spectral parameters for different models. In the simplest and direct\napproach, the observed correlations are not compatible with the predictions of\nthe {\\xi} max model. While the EDD and EDA models do predict the correlations,\nthe values of the inferred physical parameters are not compatible with the\nmodel assumptions. Thus, we show that spectrally degenerate models, can be\ndistinguished based on spectral parameter correlations (especially those\nbetween the model normalization and spectral shape ones) making time-resolved\nspectroscopy a powerful tool to probe the nature of these systems.", "category": "astro-ph_GA" }, { "text": "The physical properties of z>2 Lyman limit systems: new constraints for\n feedback and accretion models: We study the physical properties of a homogeneous sample of 157\noptically-thick absorption line systems at redshifts ~1.8-4.4, selected from a\nhigh-dispersion spectroscopic survey of Lyman limit systems (LLSs). By means of\nmultiple ionisation models and Bayesian techniques, we derive the posterior\nprobability distribution functions for the density, metallicity, temperature,\nand dust content of the absorbing gas. We find that z>2 LLSs are highly ionised\nwith ionisation parameters between -32 are characterised by a broad\nunimodal distribution over >4 orders of magnitude, with a peak at log\nZ/Zsun~-2. LLSs are metal poor, significantly less enriched than DLAs, with\n~70% of the metallicity PDF below log Z/Zsun<-1.5. The median metallicity of\nsuper LLSs with log N(HI)>19 rapidly evolves with redshift, with a ten-fold\nincrease between z~2.1-3.6 (~1.5 Gyr). Based on this sample, we find that LLSs\nat z=2.5-3.5 account for ~15% of all the metals produced by UV-selected\ngalaxies. The implications for theories of cold gas accretion and metal\nejection from galaxies are also discussed.", "category": "astro-ph_GA" }, { "text": "Extended narrow-line region in Seyfert galaxies: We present our recent results about the extended narrow-line region (ENLR) of\ntwo nearby Seyfert 2 galaxies (IC 5063 and NGC 7212) obtained by modelling the\nobserved line profiles and spectra with composite models\n(photoionization+shocks) in the different regions surrounding the AGN. Then, we\ncompare the Seyfert 2 ENLRs with the very extended one recently discovered in\nthe narrow-line Seyfert 1 (NLS1) galaxy Mrk 783. We have found several\nevidences of interaction between the ISM of the galaxies and their radio jets,\nsuch as a) the contribution of shocks in ionizing the high velocity gas, b) the\ncomplex kinematics showed by the profile of the emission lines, c) the high\nfragmentation of matter, etc. The results suggest that the ENLR of IC 5063 have\na hollow bi-conical shape, with one edge aligned to the galaxy disk, which may\ncause some kind of dependence on velocity of the ionization parameter.\nRegarding the Mrk 783 properties, it is found that the extension of the optical\nemission is almost twice the size of the radio one and it seems due to the AGN\nactivity, although there is contamination by star formation around 12 arcsec\nfrom the nucleus. Diagnostic diagrams excluded the contribution of star\nformation in IC 5063 and NGC 7212, while the shock contribution was used to\nexplain the spectra emitted by their high velocity gas.", "category": "astro-ph_GA" }, { "text": "SDSS J0159 as an outlier in the Mbh-sigma space: further clues to\n support a central tidal disruption event?: In this Letter, properties of black hole (BH) mass are well checked for the\ninteresting object SDSS J0159, a changing-look AGN and also a host galaxy of a\ntidal disruption event (TDE). Through spectral absorption features, the stellar\nvelocity dispersion of SDSS J0159 can be well measured as $\\sigma\\sim81~{\\rm\nkm/s}$, leading to SDSS J0159 being an apparent outlier in the \\msig space,\nbecause of the BH mass estimated through the \\msig relation about two\nmagnitudes lower than the reported virial BH mass of about $10^8~{\\rm\nM_\\odot}$. After considerations of contributions of stellar debris from the\ncentral TDE to broad line emission clouds, the over-estimated virial BH mass\ncould be well explained in SDSS J0159. Therefore, over-estimated virial BH\nmasses through broad line properties in the \\msig space could be treated as\ninteresting clues to support central TDEs.", "category": "astro-ph_GA" }, { "text": "Herschel SPIRE and PACS observations of the red supergiant VY CMa:\n analysis of the molecular line spectra: We present an analysis of the far-infrared and submillimetre molecular\nemission line spectrum of the luminous M-supergiant VY CMa, observed with the\nSPIRE and PACS spectrometers aboard the Herschel Space Observatory. Over 260\nemission lines were detected in the 190-650-micron SPIRE FTS spectra, with\none-third of the observed lines being attributable to H2O. Other detected\nspecies include CO, 13CO, H2^18O, SiO, HCN, SO, SO2, CS, H2S, and NH3. Our\nmodel fits to the observed 12CO and 13CO line intensities yield a 12C/13C ratio\nof 5.6+-1.8, consistent with measurements of this ratio for other M\nsupergiants, but significantly lower than previously estimated for VY CMa from\nobservations of lower-J lines. The spectral line energy distribution for twenty\nSiO rotational lines shows two temperature components: a hot component at 1000\nK, which we attribute to the stellar atmosphere and inner wind, plus a cooler\n~200 K component, which we attribute to an origin in the outer circumstellar\nenvelope. We fit the line fluxes of 12CO, 13CO, H2O and SiO, using the SMMOL\nnon-LTE line transfer code, with a mass-loss rate of 1.85x10^-4 Msun yr^-1\nbetween 9 R* and 350 R*. To fit the observed line fluxes of 12CO, 13CO, H2O and\nSiO with SMMOL non-LTE line radiative transfer code, along with a mass-loss\nrate of 1.85x10^-4 Msun yr^-1.\n To fit the high rotational lines of CO and H2O, the model required a rather\nflat temperature distribution inside the dust condensation radius, attributed\nto the high H2O opacity. Beyond the dust condensation radius the gas\ntemperature is fitted best by an r^-0.5 radial dependence, consistent with the\ncoolant lines becoming optically thin. Our H2O emission line fits are\nconsistent with an ortho:para ratio of 3 in the outflow.", "category": "astro-ph_GA" }, { "text": "The First VLBI Detection of a Spiral DRAGN Core: The existence of spiral DRAGNs challenges standard galaxy formation theories.\nWe present the first observation of 0313$-$192, the archetypal spiral DRAGN, at\nVLBI resolutions. Spiral DRAGNs are Double Radio Sources Associated with\nGalactic Nuclei (DRAGNs) that are hosted by spiral galaxies. 0313$-$192 is an\nedge-on spiral galaxy that appears to host a 360 kpc double-lobed radio source.\nThe core of this galaxy is clearly detected at L, S, and X-bands using the\nVLBA, signifying an ongoing active nucleus in the galaxy. This rules out the\npossibility that the spiral DRAGN is merely a chance alignment. The radio core\nhas L$_{1.4\\,GHz} \\sim 3.0 \\times 10^{23}$W Hz$^{-1}$. Radio components are\ndetected to the South-West of the core, but there are no detections of a\ncounterjet. Assuming a symmetric, relativistic jet, we estimate an upper limit\nto the inclination angle of $\\theta \\lesssim 72$ degrees. The VLBI-detected\nradio jet components are extremely well-aligned with the larger-scale radio\nsource suggesting little to no jet disruption or interaction with the ISM of\nthe host galaxy.", "category": "astro-ph_GA" }, { "text": "The mass-metallicity relation of local active galaxies: We systematically measure the gas-phase metallicities and the\nmass-metallicity relation of a large sample of local active galaxies for the\nfirst time. Observed emission-line fluxes from the Sloan Digital Sky Survey\n(SDSS) are compared to a four-dimensional grid of photoionization models using\nthe Bayesian parameter estimation code NebulaBayes. For the first time we take\ninto account arbitrary mixing between HII region and narrow-line region (NLR)\nemission, and the models are also varied with metallicity, ionization parameter\nin the NLR, and the gas pressure. The active galactic nucleus (AGN) oxygen\nabundance is found to increase by $\\Delta {\\rm O/H} \\sim 0.1$ dex as a function\nof host galaxy stellar mass over the range $10.1 < \\log M_* / M_\\odot < 11.3$.\nWe also measure the metallicity and ionization parameter of 231000 star-forming\ngalaxies for comparison with the sample of 7670 Seyfert 2 galaxies. A\nsystematic offset in oxygen abundance of 0.09 dex is observed between the\nmass-metallicity relations of the star-forming and active galaxies. We\ninvestigate potential causes of the offset, including sample selection and the\ntreatment in the models of diffuse ionized gas, pressure, and ionization\nparameter. We cannot identify the major cause(s), but suspect contributions due\nto deficiencies in modeling the ionizing spectra and the treatment of dust\nphysics. Optical diagnostic diagrams are presented with the star-forming and\nSeyfert data colored by the inferred oxygen abundance, ionization parameter and\ngas pressure, clearly illustrating the trends in these quantities.", "category": "astro-ph_GA" }, { "text": "On the possible common origin of M16 and M17: It has been suggested that the well-studied giant HII regions M16 and M17 may\nhave had a common origin, being an example of large-scale triggered star\nformation. While some features of the distribution of the interstellar medium\nin the region support this interpretation, no definitive detection of an\nearlier population of massive stars responsible for the triggering has been\nmade thus far. We have carried out observations looking for red supergiants in\nthe area covered by a giant shell seen in HI and CO centered on galactic\ncoordinates $l \\sim 14^\\circ 5$, $b\\sim +1^\\circ$ that peaks near the same\nradial velocity as the bulk of the emission from both giant HII regions, which\nare located along the shell. Red supergiants have ages in the range expected\nfor the parent association whose most massive members could have triggered the\nformation of the shell and of the giant HII regions along its rim. Out of a\nsample of 37 bright red stars, we identify four red supergiants that confirm\nthe existence of massive stars in the age range between $\\sim 10$ and $\\sim\n30$~Myr in the area. At least three of them have Gaia DR2 parallaxes consistent\nwith them being at the same distance as M16 and M17. The evidence of past\nmassive star formation within the area of the gaseous shell lends support to\nthe idea that it was formed by the combined action of stellar winds and\nionizing radiation of the precursors of the current red supergiants. These\ncould be the remnants of a richer population, whose most massive members have\nexploded already as core-collapse supernovae. The expansion of the shell\nagainst the surrounding medium, perhaps combined with the overrun of\npreexisting clouds, is thus a plausible trigger of the formation of a second\ngeneration of stars currently responsible for the ionization of M16 and M17.", "category": "astro-ph_GA" }, { "text": "A Number of Nearby Moving Groups may be Fragments of Dissolving Open\n Clusters: We propose that fourteen co-moving groups of stars uncovered by Kounkel &\nCovey (2019) may be related to known nearby moving groups and bridge those and\nnearby open clusters with similar ages and space velocities. This indicates\nthat known nearby moving groups may be spatially much more extended than\npreviously though, and some of them might be parts of tidal tails around the\ncores of known open clusters, reminiscent of those recently found around the\nHyades and a handful of other nearby clusters. For example, we find that both\nthe nearby Carina and Columba associations may be linked to Theia 208 from\nKounkel & Covey (2019) and together form parts of a large tidal tail around the\nPlatais 8 open cluster. The AB Doradus moving group and Theia 301 may form a\ntrailing tidal tail behind the Pleiades open cluster, with hints of a possible\nleading tidal tail in Theia 369. We similarly find that IC 2391 and its tidal\ntails identified by Meingast et al. (2021) may be extended by the nearby Argus\nassociation and are possibly further extended by Theia 115. The nearby Octans\nand Octans-Near associations, as well as Theia 94 and 95, may form a large\ntidal tail leading the poorly studied Platais 5 open cluster candidate. While a\npreliminary analysis of Gaia color-magnitude sequences hint that these\nstructures are plausibly related, more observational evidence is still required\nto corroborate their consistent ages and space velocities. These observations\nmay change our current understanding of nearby moving groups and the different\npathways through which they can form. While some moving groups may have formed\nloosely in extended star-formation events with rich spatial structure, others\nmay in fact correspond to the tidal tails of nearby open clusters.", "category": "astro-ph_GA" }, { "text": "The Behavior of Selected Diffuse Interstellar Bands with Molecular\n Fraction in Diffuse Atomic and Molecular Clouds: We study the behavior of eight diffuse interstellar bands (DIBs) in different\ninterstellar environments, as characterized by the fraction of hydrogen in\nmolecular form [$f$(H$_2$)], with comparisons to the corresponding behavior of\nvarious known atomic and molecular species. The equivalent widths of the five\n\"normal\" DIBs ($\\lambda\\lambda$5780.5, 5797.1, 6196.0, 6283.8, and 6613.6),\nnormalized to $E(B-V)$, show a \"Lambda-shaped\" behavior: they increase at low\n$f$(H$_2$), peak at $f$(H$_2$) ~ 0.3, and then decrease. The similarly\nnormalized column densities of Ca, Ca$^+$, Ti$^+$, and CH$^+$ also decline for\n$f$(H$_2$) > 0.3. In contrast, the normalized column densities of Na, K, CH,\nCN, and CO increase monotonically with $f$(H$_2$), and the trends exhibited by\nthe three C$_2$ DIBs ($\\lambda\\lambda$4726.8, 4963.9, and 4984.8) lie between\nthose two general behaviors. These trends with $f$(H$_2$) are accompanied by\ncosmic scatter, the dispersion at any given $f$(H$_2$) being significantly\nlarger than the individual errors of measurement. The Lambda-shaped trends\nsuggest the balance between creation and destruction of the DIB carriers\ndiffers dramatically between diffuse atomic and diffuse molecular clouds;\nadditional processes besides ionization and shielding are needed to explain\nthose observed trends. Except for several special cases, the highest\n$W$(5780)/$W$(5797) ratios, characterizing the so-called \"sigma-zeta effect\",\noccur only at $f$(H$_2$) < 0.2. We propose a sequence of DIBs based on trends\nin their pair-wise strength ratios with increasing $f$(H$_2$). In order of\nincreasing environmental density, we find the $\\lambda$6283.8 and\n$\\lambda$5780.5 DIBs, the $\\lambda$6196.0 DIB, the $\\lambda$6613.6 DIB, the\n$\\lambda$5797.1 DIB, and the C$_2$ DIBs.", "category": "astro-ph_GA" }, { "text": "Photon-Dominated Region Modeling of the [C I],[C II], and CO Line\n Emission from a Boundary in the Taurus Molecular Cloud: We present [Ci] and [Cii] observations of a linear edge region in the Taurus\nmolecular cloud, and model this region as a cylindrically symmetric PDR exposed\nto a low-intensity UV radiation field. The sharp, long profile of the linear\nedge makes it an ideal case to test PDR models and determine cloud parameters.\nWe compare observations of the [C i], 3P1 -> 3P0 (492 GHz), [C i] 3P2 -> 3P1\n(809 GHz), and [Cii] 2P3/2 -> 2P1/2 (1900 GHz) transitions, as well as the\nlowest rotational transitions of 12CO and 13CO, with line intensities produced\nby the RATRAN radiative transfer code from the results of the Meudon PDR code.\nWe constrain the density structure of the cloud by fitting a cylindrical\ndensity function to visual extinction data. We study the effects of variation\nof the FUV field, 12C/13C isotopic abundance ratio, sulfur depletion, cosmic\nray ionization rate, and inclination of the filament relative to the sky-plane\non the chemical network of the PDR model and resulting line emission. We also\nconsider the role of suprathermal chemistry and density inhomogeneities. We\nfind good agreement between the model and observations, and that the integrated\nline intensities can be explained by a PDR model with an external FUV field of\n0.05 G0, a low ratio of 12C to 13C ~ 43, a highly depleted sulfur abundance (by\na factor of at least 50), a cosmic ray ionization rate (3 - 6) x 10-17 s^-1,\nand without significant effects from inclination, clumping or suprathermal\nchemistry.", "category": "astro-ph_GA" }, { "text": "Constraining nuclear star cluster formation using MUSE-AO observations\n of the early-type galaxy FCC47: Nuclear star clusters (NSCs) are found in at least 70% of all galaxies, but\ntheir formation path is still unclear. In the most common scenarios, NSCs form\nin-situ from the galaxy's central gas reservoir, through merging of globular\nclusters (GCs), or through a combination of the two. As the scenarios pose\ndifferent expectations for angular momentum and stellar population properties\nof the NSC in comparison to the host galaxy and the GC system, it is necessary\nto characterise the stellar light, NSC and GCs simultaneously. The large NSC\n(r$_\\rm{eff} = 66$ pc) and rich GC system of the early-type Fornax cluster\ngalaxy FCC47 (NGC1336) render this galaxy an ideal laboratory to constrain NSC\nformation. Using MUSE science verification data assisted by adaptive optics, we\nobtained maps for the stellar kinematics and for stellar-population properties\nof FCC47. We extracted the spectra of the central NSC and determined\nline-of-sight velocities of 24 GCs and metallicities of five. FCC47 shows two\ndecoupled components (KDCs): a rotating disk and the NSC. Our orbit-based\ndynamical Schwarzschild model revealed that the NSC is a distinct kinematic\nfeature and it constitutes the peak of metallicity and old ages in the galaxy.\nThe main body consists of two counter-rotating populations and is dominated by\na more metal-poor population. The GC system is bimodal with a dominant\nmetal-poor population and the total GC system mass is $\\sim 17\\%$ of the NSC\nmass ($\\sim$ 7 $\\times$ $10^8 M_\\odot$). The rotation, high metallicity and\nhigh mass of the NSC cannot be uniquely explained by GC-inspiral and most\nlikely requires additional, but quickly quenched, in-situ formation. The\npresence of two KDCs most probably are evidence of a major merger that has\naltered the structure of FCC47 significantly, indicating the important role of\ngalaxy mergers in forming the complex kinematics in the galaxy-NSC system.", "category": "astro-ph_GA" }, { "text": "A 95 GHz Methanol Emission Survey Toward Eight Small Supernova Remnants: We report on a 95 GHz ($8_0-7_1$ A$^{+}$) methanol (CH$_3$OH) emission survey\nwith the Purple Mountain Observatory Delingha 13.7 m telescope. Eight supernova\nremnants (SNRs) with angular size $\\lesssim$ 10' were observed, but emission\nwas only detected in three SNRs near the Galactic center (Sgr A East, G\n0.1-0.1, and G 359.92-0.09). CH$_3$OH emission mainly surrounds the SNRs and\ncan be decomposed into nine spatial peaks with velocity range of eight peaks\nbeing (-30, 70) km s$^{-1}$, and the other (70, 120) km s$^{-1}$. They are\nprobably excited by interaction with these SNRs and adjacent molecular gas in\nthe central molecular zone (CMZ), although star formation may play an important\nrole in exciting CH$_3$OH emission in some regions of CMZ. We infer that tidal\naction is unlikely to be an excitation source for CH$_3$OH emission.", "category": "astro-ph_GA" }, { "text": "A sharp rise in the detection rate of broad absorption line variations\n in a quasar SDSS J141955.26+522741.1: We present an analysis of the variability of broad absorption lines (BALs) in\na quasar SDSS J141955.26+522741.1 at $z=2.145$ with 72 observations from the\nSloan Digital Sky Survey Data Release 16 (SDSS DR16). The strong correlation\nbetween the equivalent widths of BAL and the continuum luminosity, reveals that\nthe variation of BAL trough is dominated by the photoionization. The\nphotoionization model predicts that when the time interval $\\Delta T$ between\ntwo observations is longer than the recombination timescale $t_{\\rm rec}$, the\nBAL variations can be detected. This can be characterized as a \"sharp rise\" in\nthe detection rate of BAL variation at $\\Delta T=t_{\\rm rec}$. For the first\ntime, we detect such a \"sharp rise\" signature in the detection rate of BAL\nvariations. As a result, we propose that the $t_{\\rm rec}$ can be obtained from\nthe \"sharp rise\" of the detection rate of BAL variation. It is worth mentioning\nthat the BAL variations are detected at the time-intervals less than the\n$t_{\\rm rec}$ for half an order of magnitude in two individual troughs. This\nresult indicates that there may be multiple components with different $t_{\\rm\nrec}$ but the same velocity in an individual trough.", "category": "astro-ph_GA" }, { "text": "Chemical abundances in Seyfert galaxies -- V. The discovery of shocked\n emission outside the AGN ionization axis: We present maps for the electron temperature in the inner kpc of three\nluminous Seyfert galaxies: Mrk 79, Mrk 348, and Mrk 607 obtained from Gemini\nGMOS-IFU observations at spatial resolutions of 110-280 pc. We study the\ndistributions of electron temperature in active galaxies and find temperatures\nvarying in the range from 8000 to >30000 K. Shocks due to gas outflows play an\nimportant role in the observed temperature distributions of Mrk 79 and Mrk 348,\nwhile standard photoionization models reproduce the derived temperature values\nfor Mrk 607. In Mrk 79 and Mrk 348, we find direct evidence for\nshock-ionization with overall orientation orthogonal to the ionization axis,\nwhere shocks can be easily observed as the AGN radiation field is shielded by\nthe nuclear dusty torus. This also indicates that even when the ionization\ncones are narrow, the shocks can be much wider-angle.", "category": "astro-ph_GA" }, { "text": "Mapping kiloparsec-scale structures in the extended HI disc of the\n galaxy UGC 00439 by HI 21-cm absorption: We study the properties of HI gas in the outer regions (~2r_25) of a spiral\ngalaxy, UGC 00439 (z = 0.01769), using HI 21-cm absorption towards different\ncomponents of an extended background radio source, J0041$-$0043 (z = 1.679).\nThe radio source exhibits a compact core coincident with the optical quasar and\ntwo lobes separated by ~7 kpc, all at an impact parameter ~25 kpc. The HI 21-cm\nabsorption detected towards the southern lobe is found to extend over ~2 kpc^2.\nThe absorbing gas shows sub-kpc-scale structures with the line-of-sight\nvelocities dominated by turbulent motions. Much larger optical depth variations\nover 4-7 kpc-scale are revealed by the non-detection of HI 21-cm absorption\ntowards the radio core and the northern lobe, and the detection of NaI and CaII\nabsorption towards the quasar. This could reflect a patchy distribution of cold\ngas in the extended HI disc. We also detect HI 21-cm emission from UGC 00439\nand two other galaxies within ~150 kpc to it, that probably form an interacting\ngroup. However, no HI 21-cm emission from the absorbing gas is detected.\nAssuming a linear extent of ~4 kpc, as required to cover both the core and the\nsouthern lobe, we constrain the spin temperature <~300 K for the absorbing gas.\nThe kinematics of the gas and the lack of signatures of any ongoing in situ\nstar formation are consistent with the absorbing gas being at the kinematical\nminor axis and corotating with the galaxy. Deeper HI 21-cm observations would\nhelp to map in greater detail both the large- and small-scale structures in the\nHI gas associated with UGC 00439.", "category": "astro-ph_GA" }, { "text": "IMF radial gradients in most massive early-type galaxies: Using new long-slit spectroscopy obtained with X-Shooter at ESO-VLT, we\nstudy, for the first time, radial gradients of optical and Near-Infrared\nIMF-sensitive features in a representative sample of galaxies at the very\nhigh-mass end of the galaxy population. The sample consists of seven early-type\ngalaxies (ETGs) at $z\\sim0.05$, with central velocity dispersion in the range\n$300<\\sigma<350$km/s. Using state-of-art stellar population synthesis models,\nwe fit a number of spectral indices, from different chemical species (including\nTiO's and Na indices), to constrain the IMF slope (i.e. the fraction of\nlow-mass stars), as a function of galactocentric distance, over a radial range\nout to $\\sim4$kpc. ETGs in our sample show a significant correlation of IMF\nslope and surface mass density. The bottom-heavy population (i.e. an excess of\nlow-mass stars in the IMF) is confined to central galaxy regions with surface\nmass density above $\\sim 10^{10} M_\\odot kpc^{-2}$, or, alternatively, within a\ncharacteristic radius of $\\sim2$~kpc. Radial distance, in physical units, and\nsurface mass density, are the best correlators to IMF variations, with respect\nto other dynamical (e.g. velocity dispersion) and stellar population (e.g.\nmetallicity) properties. Our results for the most massive galaxies suggest that\nthere is no single parameter} that fully explains variations in the stellar\nIMF, but IMF radial profiles at z$\\sim$0 rather result from the complex\nformation and mass accretion history of galaxy inner and outer regions.", "category": "astro-ph_GA" }, { "text": "The density variance -- Mach number relation in supersonic, isothermal\n turbulence: We examine the relation between the density variance and the mean-square Mach\nnumber in supersonic, isothermal turbulence, assumed in several recent analytic\nmodels of the star formation process. From a series of calculations of\nsupersonic, hydrodynamic turbulence driven using purely solenoidal Fourier\nmodes, we find that the `standard' relationship between the variance in the log\nof density and the Mach number squared, i.e., sigma^2_(ln rho/rhobar)=ln (1+b^2\nM^2), with b = 1/3 is a good fit to the numerical results in the supersonic\nregime up to at least Mach 20, similar to previous determinations at lower Mach\nnumbers. While direct measurements of the variance in linear density are found\nto be severely underestimated by finite resolution effects, it is possible to\ninfer the linear density variance via the assumption of log-normality in the\nProbability Distribution Function. The inferred relationship with Mach number,\nconsistent with sigma_(rho/rhobar) ~ b M with b=1/3, is, however, significantly\nshallower than observational determinations of the relationship in the Taurus\nMolecular Cloud and IC5146 (both consistent with b~ 0.5), implying that\nadditional physics such as gravity is important in these clouds and/or that\nturbulent driving in the ISM contains a significant compressive component.\nMagnetic fields are not found to change this picture significantly, in general\nreducing the measured variances and thus worsening the discrepancy with\nobservations.", "category": "astro-ph_GA" }, { "text": "A Robust Measure of Dark Matter Halo Ellipticities: In simulations of the standard cosmological model (LCDM), dark matter halos\nare aspherical. However, so far the asphericity of an individual galaxy's halo\nhas never been robustly established. We use the Jeans equations to define a\nquantity which robustly characterizes a deviation from rotational symmetry.\nThis quantity is essentially the gravitational torque and it roughly provides\nthe ellipticity projected along the line of sight. We show that the Thirty\nMeter Telescope (TMT), with a single epoch of observations combined with those\nof the Gaia space telescope, can distinguish the LCDM value of the torque from\nzero for each Sculptor-like dwarf galaxy with a confidence between 0 and 5\nsigma, depending on the orientation of each halo. With two epochs of\nobservations, TMT will achieve a 5 sigma discovery of torque and so asphericity\nfor most such galaxies, and so will provide a new and powerful test of the LCDM\nmodel.", "category": "astro-ph_GA" }, { "text": "A binning-free method reveals a continuous relationship between\n galaxies' AGN power and offset from main sequence: Studies investigating the relationship between AGN power and the star\nformation rates (SFRs) of their host galaxies often rely on averaging\ntechniques -- such as stacking -- to incorporate information from\nnon-detections. However, averages, and especially means, can be strongly\naffected by outliers and can therefore give a misleading indication of the\n\"typical\" case. Recently, a number of studies have taken a step further by\nbinning their sample in terms of AGN power (approximated by the 2-10keV\nluminosity of the AGN), and investigating how the SFR distribution differs\nbetween these bins. These bin thresholds are often weakly motivated, and\nbinning implicitly assumes that sources within the same bin have similar (or\neven identical) properties. In this paper, we investigate whether the\ndistribution of host SFRs -- relative to the locus of the star-forming main\nsequence (i.e., $R_{\\rm MS}$) -- changes continuously as a function of AGN\npower. We achieve this by using a hierarchical Bayesian model that completely\nremoves the need to bin in AGN power. In doing so, we find strong evidence that\nthe $R_{\\rm MS}$ distribution changes with 2-10keV X-ray luminosity. The\nresults suggest that higher X_ray luminosity AGNs have a tighter physical\nconnection to the star-forming process than lower X-ray luminosity AGNs, at\nleast within the $0.8 < z < 1.2$ redshift range considered here.", "category": "astro-ph_GA" }, { "text": "Schwarzschild dynamical model of the Fornax dwarf spheroidal galaxy: We present a full dynamical model of the Fornax dwarf spheroidal galaxy\nobtained with the spherically symmetric Schwarzschild orbit superposition\nmethod applied to the largest kinematic data set presently available. We\nmodelled the total mass content of the dwarf with the mass-to-light ratio\n$\\Upsilon$ varying with radius and found that Fornax is with high probability\nembedded in a massive and extended dark matter halo. We estimated the total\nmass contained within 1$\\,$kpc to be $M(<1\\,$kpc$)=1.25^{+0.06}_{-0.13} \\times\n10^8\\,$M$_{\\odot}$. The data are consistent with the constant mass-to-light\nratio, i.e. the mass-follows-light model, only at 3$\\sigma$ level, but still\nrequire a high value of $\\Upsilon \\approx 11.2\\,$M$_{\\odot}/$L$_{\\odot}$. Our\nresults are in general agreement with previous estimates of the dynamical mass\nprofile of Fornax. As the Schwarzschild method does not require any assumptions\non the orbital anisotropy of the stars, we obtained a profile of the anisotropy\nparameter $\\beta$ as an output of our modelling. The derived anisotropy is\nclose to zero in the centre of the galaxy and decreases with radius, but\nremains consistent with isotropic orbits at all radii at 1$\\sigma$ confidence\nlevel.", "category": "astro-ph_GA" }, { "text": "Symplectic coarse graining approach to the dynamics of spherical\n self-gravitating systems: We investigate the evolution of the phase-space distribution function around\nslightly perturbed stationary states and the process of violent relaxation in\nthe context of the dissipationless collapse of an isolated spherical\nself-gravitating system. By means of the recently introduced symplectic coarse\ngraining technique, we obtain an effective evolution equation that allows us to\ncompute the scaling of the frequencies around a stationary state, as well as\nthe damping times of Fourier modes of the distribution function, with the\nmagnitude of the Fourier $k-$vectors themselves. We compare our analytical\nresults with $N$-body simulations.", "category": "astro-ph_GA" }, { "text": "Common origin for Hercules-Aquila and Virgo Clouds in Gaia DR2: We use a sample of ~350 RR Lyrae stars with radial velocities and Gaia DR2\nproper motions to study orbital properties of the Hercules-Aquila Cloud (HAC)\nand Virgo Over-density (VOD). We demonstrate that both structures are dominated\nby stars on highly eccentric orbits, with peri-centres around ~1 kpc and\napo-centres between 15 and 25 kpc from the Galactic centre. Given that the\nstars in the HAC and the VOD occupy very similar regions in the space spanned\nby integrals of motion, we conclude that these diffuse debris clouds are part\nof the same accretion event. More precisely, these inner halo sub-structures\nlikely represent two complementary not-fully-mixed portions of an ancient\nmassive merger, also known as the \"sausage\" event.", "category": "astro-ph_GA" }, { "text": "Studying the late evolution of a radio-loud AGN in a galaxy group with\n LOFAR: Feedback by radio-loud active galactic nuclei (AGN) in galaxy groups is not\nfully understood. Open questions include the duty cycle of the AGN, the spatial\nextent of the radio lobes, the effect they have on the intragroup medium, and\nthe fate of the cosmic rays. We present the discovery of a 650 kpc-radio galaxy\nembedded in steep diffuse emission at $z = 0.18793 \\pm 5 \\times 10^{-5}$\nlocated at the center of the galaxy group MaxBCG J199.31832+51.72503 using an\nobservation from the LOFAR Two-meter Sky Survey (LoTSS) at the central\nfrequency of 144 MHz. Subsequently, we performed a GMRT observation at the\ncentral frequency of 607 MHz to study the spectral properties of the source.\nThe observations reveal a radio galaxy with a total radio power $P_{\\rm tot,\n1.4} \\sim 2.1 \\times 10^{24}$ W Hz$^{-1}$, exhibiting two asymmetrical jets and\nlobes. The derived spectral index map shows a steepening toward the inner\nregions and a steep-spectrum core region. We model the integrated radio\nspectrum, providing two possible interpretations: the radio source is evolved\nbut still active or it is just at the end of its active phase. Finally, in the\nsame field of view we have discovered Mpc-sized emission surrounding a close\npair of AGN located at a redshift $z = 0.0587 \\pm 2 \\times 10^{-4}$ (SDSS\nJ131544.56+521213.2 and SDSS J131543.99+521055.7) which could be a radio\nremnant source.", "category": "astro-ph_GA" }, { "text": "Circum-galactic medium in the halo of quasars: The properties of circum-galactic gas in the halo of quasar host galaxies are\ninvestigated analyzing Mg II 2800 and C IV 1540 absorption-line systems along\nthe line of sight close to quasars. We used optical spectroscopy of closely\naligned pairs of quasars (projected distance $\\leq$ 200 kpc, but at very\ndifferent redshift) obtained at the VLT and Gran Telescopio Canarias to\ninvestigate the distribution of the absorbing gas for a sample of quasars at\nz$\\sim$1. Absorption systems of EW $\\geq$ 0.3 $\\rm{\\AA}$ associated with the\nforeground quasars are revealed up to 200 kpc from the centre of the host\ngalaxy, showing that the structure of the absorbing gas is patchy with a\ncovering fraction quickly decreasing beyond 100 kpc. In this contribution we\nuse optical and near-IR images obtained at VLT to investigate the relations\nbetween the properties of the circum-galactic medium of the host galaxies and\nof the large scale galaxy environments of the foreground quasars.", "category": "astro-ph_GA" }, { "text": "The dimensionality of stellar chemical space using spectra from the\n Apache Point Observatory Galactic Evolution Experiment: Chemical tagging of stars based on their similar compositions can offer new\ninsights about the star formation and dynamical history of the Milky Way. We\ninvestigate the feasibility of identifying groups of stars in chemical space by\nforgoing the use of model derived abundances in favour of direct analysis of\nspectra. This facilitates the propagation of measurement uncertainties and does\nnot presuppose knowledge of which elements are important for distinguishing\nstars in chemical space. We use ~16,000 red-giant and red-clump H-band spectra\nfrom the Apache Point Observatory Galactic Evolution Experiment and perform\npolynomial fits to remove trends not due to abundance-ratio variations. Using\nexpectation maximized principal component analysis, we find principal\ncomponents with high signal in the wavelength regions most important for\ndistinguishing between stars. Different subsamples of red-giant and red-clump\nstars are all consistent with needing about 10 principal components to\naccurately model the spectra above the level of the measurement uncertainties.\nThe dimensionality of stellar chemical space that can be investigated in the\nH-band is therefore $\\lesssim 10$. For APOGEE observations with typical\nsignal-to-noise ratios of 100, the number of chemical space cells within which\nstars cannot be distinguished is approximately $10^{10\\pm2} \\times (5\\pm\n2)^{n-10}$ with $n$ the number of principal components. This high\ndimensionality and the fine-grained sampling of chemical space are a promising\nfirst step towards chemical tagging based on spectra alone.", "category": "astro-ph_GA" }, { "text": "The Astrochemical Impact of Cosmic Rays in Protoclusters I: Molecular\n Cloud Chemistry: We present astrochemical photo-dissociation region models in which cosmic ray\nattenuation has been fully coupled to the chemical evolution of the gas. We\nmodel the astrochemical impact of cosmic rays, including those accelerated by\nprotostellar accretion shocks, on molecular clouds hosting protoclusters. Our\nmodels with embedded protostars reproduce observed ionization rates. We study\nthe imprint of cosmic ray attenuation on ions for models with different surface\ncosmic ray spectra and different star formation efficiencies. We find that\nabundances, particularly ions, are sensitive to the treatment of cosmic rays.\nWe show the column densities of ions are under predicted by the `classic'\ntreatment of cosmic rays by an order of magnitude. We also test two common\nchemistry approximations used to infer ionization rates. We conclude that the\napproximation based on the H$_3^+$ abundance under predicts the ionization rate\nexcept in regions where the cosmic rays dominate the chemistry. Our models\nsuggest the chemistry in dense gas will be significantly impacted by the\nincreased ionization rates, leading to a reduction in molecules such as NH$_3$\nand causing H$_2$-rich gas to become [C II] bright.", "category": "astro-ph_GA" }, { "text": "Angular momentum evolution of bulge stars in disc galaxies in NIHAO: We study the origin of bulge stars and their angular momentum (AM) evolution\nin 10 spiral galaxies with baryonic masses above $10^{10}$M$_\\odot$ in the\nNIHAO galaxy formation simulations. The simulated galaxies are in good\nagreement with observations of the relation between specific AM and mass of the\nbaryonic component and the stellar bulge-to-total ratio ($B/T$). We divide the\nstar particles at $z=0$ into disc and bulge components using a hybrid\nphotometric/kinematic decomposition method that identifies all central mass\nabove an exponential disc profile as the `bulge'. By tracking the bulge star\nparticles back in time, we find that on average 95\\% of the bulge stars formed\n{\\it in situ}, 3\\% formed {\\it ex situ} in satellites of the same halo, and\nonly 2\\% formed {\\it ex situ} in external galaxies. The evolution of the AM\ndistribution of the bulge stars paints an interesting picture: the higher the\nfinal $B/T$ ratio, the more the specific AM remains preserved during the bulge\nformation. In all cases, bulge stars migrate significantly towards the central\nregion, reducing their average galactocentric radius by roughly a factor 2,\nindependently of the final $B/T$ value. However, in the higher $B/T$\n($\\gtrsim0.2$) objects, the velocity of the bulge stars increases and the AM of\nthe bulge is almost conserved, whereas at lower $B/T$ values, the velocity of\nthe bulge stars decreases and the AM of bulge reduces. The correlation between\nthe evolution of the AM and $B/T$ suggests that bulge and disc formation are\nclosely linked and cannot be treated as independent processes.", "category": "astro-ph_GA" }, { "text": "Herschel-PACS spectroscopy of the intermediate mass protostar NGC7129\n FIRS 2: Aims: We present preliminary results of the first Herschel spectroscopic\nobservations of NGC7129 FIRS2, an intermediate mass star-forming region. We\nattempt to interpret the observations in the framework of an in-falling\nspherical envelope. Methods: The PACS instrument was used in line spectroscopy\nmode (R=1000-5000) with 15 spectral bands between 63 and 185 microns. This\nprovided good detections of 26 spectral lines seen in emission, including lines\nof H2O, CO, OH, O I, and C II. Results: Most of the detected lines,\nparticularly those of H2O and CO, are substantially stronger than predicted by\nthe spherical envelope models, typically by several orders of magnitude. In\nthis paper we focus on what can be learned from the detected CO emission lines.\nConclusions: It is unlikely that the much stronger than expected line emission\narises in the (spherical) envelope of the YSO. The region hot enough to produce\nsuch high excitation lines within such an envelope is too small to produce the\namount of emission observed. Virtually all of this high excitation emission\nmust arise in structures such as as along the walls of the outflow cavity with\nthe emission produced by a combination of UV photon heating and/or\nnon-dissociative shocks.", "category": "astro-ph_GA" }, { "text": "Star Cluster Classification using Deep Transfer Learning with PHANGS-HST: Currently available star cluster catalogues from HST imaging of nearby\ngalaxies heavily rely on visual inspection and classification of candidate\nclusters. The time-consuming nature of this process has limited the production\nof reliable catalogues and thus also post-observation analysis. To address this\nproblem, deep transfer learning has recently been used to create neural network\nmodels which accurately classify star cluster morphologies at production scale\nfor nearby spiral galaxies (D < 20 Mpc). Here, we use HST UV-optical imaging of\nover 20,000 sources in 23 galaxies from the Physics at High Angular Resolution\nin Nearby GalaxieS (PHANGS) survey to train and evaluate two new sets of\nmodels: i) distance-dependent models, based on cluster candidates binned by\ngalaxy distance (9-12 Mpc, 14-18 Mpc, 18-24 Mpc), and ii) distance-independent\nmodels, based on the combined sample of candidates from all galaxies. We find\nthat the overall accuracy of both sets of models is comparable to previous\nautomated star cluster classification studies (~60-80 per cent) and show\nimprovement by a factor of two in classifying asymmetric and multi-peaked\nclusters from PHANGS-HST. Somewhat surprisingly, while we observe a weak\nnegative correlation between model accuracy and galactic distance, we find that\ntraining separate models for the three distance bins does not significantly\nimprove classification accuracy. We also evaluate model accuracy as a function\nof cluster properties such as brightness, colour, and SED-fit age. Based on the\nsuccess of these experiments, our models will provide classifications for the\nfull set of PHANGS-HST candidate clusters (N ~ 200,000) for public release.", "category": "astro-ph_GA" }, { "text": "Chemodynamical evolution of the Milky Way disk II: Variations with\n Galactic radius and height above the disk plane: [Abridge] In the first paper of this series (paper I) we presented a new\napproach for studying the chemo-odynamical evolution in disk galaxies, focusing\non the Milky Way. Here we extend these results to different distances from the\nGalactic center, looking for variations of observables that can be related to\non-going and future spectroscopic surveys. By separating the effects of\nkinematic heating and radial migration, we show that migration is much more\nimportant, even for the oldest and hottest stellar population. The\ndistributions of stellar birth guiding radii and final guiding radii\n(signifying contamination from migration and heating, respectively) widen with\nincreasing distance from the Galactic center. As a result, the slope in the\nage-metallicity relation flattens significantly at Galactic radii larger than\nsolar. The radial metallicity and [Mg/Fe] gradients in our model show\nsignificant variations with height above the plane due to changes in the\nmixture of stellar ages. An inversion in the radial metallicity gradient is\nfound from negative to weakly positive (at r<10 kpc), and from positive to\nnegative for the [Mg/Fe] gradient, with increasing distance from the disk\nplane. We relate this to the combined effect of (i) the predominance of young\nstars close to the disk plane and old stars away from it, (ii) the more\nconcentrated older stellar component, and (iii) the flaring of mono-age disk\npopulations. We also investigate the effect of recycled gas flows on the mean\n[Fe/H] and find that in the region 4 50%\ncompleteness in order to minimize these systematics, we still find that the\nfaint-end slope is steep and getting steeper with redshift, though with\nslightly shallower (less negative) values ($\\alpha=-1.55\\pm0.06$,\n$-1.69\\pm0.07$ and $-1.79\\pm0.08$ for $z\\sim1.3$, 1.9 and 2.6, respectively).\nFinally, we conclude that the faint star-forming galaxies with UV magnitudes of\n$-18.5}{\\sim}\\;$}} 20$),\nat least in AzTEC/C159. The mass decompositions of the rotation curves show\nthat both galaxies are highly baryon-dominated with gas masses of $\\approx\n10^{11}M_{\\odot}$, which, for J1000+0234, is significantly higher than previous\nestimates. We show that these high-$z$ galaxies overlap with $z=0$ massive ETGs\nin the ETG analogue of the stellar-mass Tully-Fisher relation once their gas is\nconverted into stars. This provides dynamical evidence of the connection\nbetween massive high-$z$ starbursts and ETGs, although the transformation\nmechanism from fast rotating to nearly pressure-supported systems remains\nunclear.", "category": "astro-ph_GA" }, { "text": "HST/WFC3 Observations of Low-Mass Globular Clusters AM 4 and Palomar 13:\n Physical Properties and Implications for Mass Loss: We investigate the loss of low-mass stars in two of the faintest globular\nclusters known, AM 4 and Palomar 13 (Pal 13), using HST/WFC3 F606W and F814W\nphotometry. To determine the physical properties of each cluster --- age, mass,\nmetallicity, extinction, present day mass function (MF) --- we use the maximum\nlikelihood color-magnitude diagram (CMD) fitting program MATCH and the\nDartmouth, Padova and BaSTI stellar evolution models. For AM 4, the Dartmouth\nmodels provide the best match to the CMD and yield an age of >13 Gyr,\nmetallicity log Z/Z_solar = -1.68 +/- 0.08, a distance modulus (m-M)_V = 17.47\n+/- 0.03 and reddening A_V = 0.19 +/- 0.02. For Pal 13 the Dartmouth models\ngive an age of 13.4 +/- 0.5 Gyr, log Z/Z_solar = -1.55 +/- 0.06, (m-M)_V =\n17.17 +/- 0.02 and A_V = 0.43 +/- 0.01. We find that the systematic\nuncertainties due to choice in assumed stellar model greatly exceed the random\nuncertainties, highlighting the importance of using multiple stellar models\nwhen analyzing stellar populations. Assuming a single-sloped power law MF, we\nfind that AM 4 and Pal 13 have spectral indices alpha = +0.68 +/- 0.34 and\nalpha = -1.67 +/- 0.25 (where a Salpeter MF has alpha = +1.35), respectively.\nComparing our derived slopes with literature measurements of cluster integrated\nmagnitude (M_V) and MF slope indicates that AM 4 is an outlier. Its MF slope is\nsubstantially steeper than clusters of comparable luminosity, while Pal 13 has\na MF in line with the general trend. We discuss both primordial and dynamical\norigins for the unusual MF slope of AM 4 and tentatively favor the dynamical\nscenario. However, MF slopes of more low luminosity clusters are needed to\nverify this hypothesis.", "category": "astro-ph_GA" }, { "text": "A sensitive search for predicted methanol maser transitions with the\n Australia Telescope Compact Array: We have used the Australia Telescope Compact Array (ATCA) to search for a\nnumber of centimetre wavelength methanol transitions which are predicted to\nshow weak maser emission towards star formation regions. Sensitive, high\nspatial and spectral resolution observations towards four high-mass star\nformation regions which show emission in a large number of class II methanol\nmaser transitions did not result in any detections. From these observations we\nare able to place an upper limit of <~1300K on the brightness temperature of\nany emission from the $3_1$A$^+$-$3_1$A$^-$, $17_{-2}$-$18_{-3}$E ($v_t=1$),\n$12_4$-$13_3$A$^-$, $12_4$-$13_3$A$^+$ and $4_1$A$^+$-$4_1$A$^-$ transitions of\nmethanol in these sources on angular scales of 2 arcseconds. This upper limit\nis consistent with current models for class II methanol masers in high-mass\nstar formation regions and better constraints than those provided here will\nlikely require observations with next-generation radio telescopes.", "category": "astro-ph_GA" }, { "text": "Two Mass Distributions in the L 1641 Molecular Clouds: The Herschel\n connection of Dense Cores and Filaments in Orion A: We present the Herschel Gould Belt survey maps of the L1641 molecular clouds\nin Orion A. We extracted both the filaments and dense cores in the region. We\nidentified which of dense sources are proto- or pre-stellar, and studied their\nassociation with the identified filaments. We find that although most (71%) of\nthe pre-stellar sources are located on filaments there is still a significant\nfraction of sources not associated with such structures. We find that these two\npopulations (on and off the identified filaments) have distinctly different\nmass distributions. The mass distribution of the sources on the filaments is\nfound to peak at 4 Solar masses and drives the shape of the CMF at higher\nmasses, which we fit with a power law of the form dN/dlogM \\propto\nM^{-1.4+/-0.4}. The mass distribution of the sources off the filaments, on the\nother hand, peaks at 0.8 Solar masses and leads to a flattening of the CMF at\nmasses lower than ~4 Solar masses. We postulate that this difference between\nthe mass distributions is due to the higher proportion of gas that is available\nin the filaments, rather than in the diffuse cloud.", "category": "astro-ph_GA" }, { "text": "Interstellar and Circumgalactic Properties of an Unseen $z=6.84$ Galaxy:\n Abundances, Ionization, and Heating in the Earliest Known Quasar Absorber: We analyze relative abundances and ionization conditions in a strong\nabsorption system at z=6.84, seen in the spectrum of the z=7.54 background\nquasar ULAS J134208.10+092838.61. Singly ionized C, Si, Fe, Mg, and Al\nmeasurements are consistent with a warm neutral medium that is metal-poor but\nnot chemically pristine. Firm non-detections of C IV and Si IV imply that any\nwarm ionized phase of the IGM or CGM has not yet been enriched past the\nultra-metal-poor regime (<0.001Z_{solar}), unlike lower redshift DLAs where\nthese lines are nearly ubiquitous. Relative abundances of the heavy elements\n794 Myr after the Big Bang resemble those of metal-poor damped Lyman Alpha\nsystems at intermediate redshift and Milky Way halo stars, and show no evidence\nof enhanced [alpha/Fe], [C/Fe] or other signatures of yields dominated by\nmassive stars. A detection of the CII* fine structure line reveals local\nsources of excitation from heating, beyond the level of photo-excitation\nsupplied by the CMB. We estimate the total and [CII] cooling rates, balancing\nagainst ISM heating sources to develop an heuristic two-phase model of the\nneutral medium. The implied heating requires a surface density of star\nformation slightly exceeding that of the Milky Way but not at the level of a\nstrong starburst. For a typical (assumed) NHI=10^{20.6}, an abundance of\n[Fe/H]=-2.2 matches the columns of species in the neutral phase. To remain\nundetected in C IV, a warm ionized phase would either need much lower\n[C/H]<-4.2 over an absorption path of 1 kpc, or else a very small absorption\npath (a few pc). While still speculative, these results suggest a significant\nreduction in heavy element enrichment outside of neutral star forming regions\nof the ISM, as would be expected in early stages of galactic chemical\nevolution.", "category": "astro-ph_GA" }, { "text": "Chandra Study of the Massive and Distant Galaxy Cluster SDSS J0150-1005: In this work, we present a high spatial resolution study of a fossil cluster,\nSDSS J0150-1005 ($z \\simeq 0.364$), based on the imaging spectroscopic analysis\nof \\chandra\\ observation. The \\chandra\\ X-ray image shows a relax and symmetric\nmorphology, which indicates SDSS J0150-1005 is a well-developed galaxy cluster\nwith no sign of recent merger. Its global gas temperature is 5.73 $\\pm$ 0.80\nkeV, and the virial mass is 6.23 $\\pm$ 1.34 $\\times 10^{14} $ M$_{\\odot}$\naccording to the isothermal model. Compared with polytropic temperature model,\nthe mass calculated based on isothermal model overestimates 49 $\\pm$ 11%. The\ncentral gas entropy, $S_{0.1r_{200}} = 143.9 \\pm 18.3$ keV cm$^2$, is\nsignificantly lower than average value of the normal galaxy clusters with\nsimilar temperatures. Our results indicate the early formation epoch of SDSS\nJ0150-1005.", "category": "astro-ph_GA" }, { "text": "\u039b CDM is Consistent with SPARC Radial Acceleration Relation: Recent analysis \\citep{McGaugh2016} of the SPARC galaxy sample found a\nsurprisingly tight relation between the radial acceleration inferred from the\nrotation curves, and the acceleration due to the baryonic components of the\ndisc. It has been suggested that this relation may be evidence for new physics,\nbeyond $\\Lambda CDM$. In this letter we show that 32 galaxies from the MUGS2\nmatch the SPARC acceleration relation. These cosmological simulations of star\nforming, rotationally supported discs were simulated with a {\\sc WMAP3}\n$\\Lambda CDM$ cosmology, and match the SPARC acceleration relation with less\nscatter than the observational data. These results show that this acceleration\nrelation is a consequence of dissipative collapse of baryons, rather than being\nevidence for exotic dark-sector physics or new dynamical laws.", "category": "astro-ph_GA" }, { "text": "Estimating the mass of galactic components using machine learning\n algorithms: The estimation of the bulge and disk massses, the main baryonic components of\na galaxy, can be performed using various approaches, but their implementation\ntend to be challenging as they often rely on strong assumptions about either\nthe baryon dynamics or the dark matter model. In this work, we present an\nalternative method for predicting the masses of galactic components, including\nthe disk, bulge, stellar and total mass, using a set of machine learning\nalgorithms: KNN-neighbours (KNN), Linear Regression (LR), Random Forest (RF)\nand Neural Network (NN). The rest-frame absolute magnitudes in the\nugriz-photometric system were selected as input features, and the training was\nperformed using a sample of spiral galaxies hosting a bulge from Guo's mock\ncatalogue \\citep{Guo-Catalog} derived from the Millennium simulation. In\ngeneral, all the algorithms provide good predictions for the galaxy's mass\ncomponents ranging from $10^9\\,M_\\odot$ to $10^{11}\\,M_\\odot$, corresponding to\nthe central region of the training mass domain; however, the NN give rise to\nthe most precise predictions in comparison to other methods. Additionally, to\ntest the performance of the NN architecture, we used a sample of observed\ngalaxies from the SDSS survey whose mass components are known. We found that\nthe NN can predict the luminous masses of disk-dominant galaxies within the\nsame range of magnitudes that for the synthetic sample up to a $99\\%$ level of\nconfidence, while mass components of galaxies hosting larger bulges are well\npredicted up to $95\\%$ level of confidence. The NN algorithm can also bring up\nscaling relations between masses of different components and magnitudes.", "category": "astro-ph_GA" }, { "text": "A giant Ly$\u03b1$ nebula in the core of an X-ray cluster at $z=1.99$:\n implications for early energy injection: We present the discovery of a giant $\\gtrsim$100~kpc Ly$\\alpha$ nebula\ndetected in the core of the X-ray emitting cluster CL~J1449+0856 at $z=1.99$\nthrough Keck/LRIS narrow-band imaging. This detection extends the known\nrelation between Ly$\\alpha$ nebulae and overdense regions of the Universe to\nthe dense core of a $5-7\\times10^{13}$ M$_{\\odot}$ cluster. The most plausible\ncandidates to power the nebula are two Chandra-detected AGN host cluster\nmembers, while cooling from the X-ray phase and cosmological cold flows are\ndisfavored primarily because of the high Ly$\\alpha$ to X-ray luminosity ratio\n($L_{\\mathrm{Ly\\alpha}}/L_{\\mathrm{X}} \\approx0.3$, $\\gtrsim10-1000\\times$\nhigher than in local cool-core clusters) and by current modeling. Given the\nphysical conditions of the Ly$\\alpha$-emitting gas and the possible interplay\nwith the X-ray phase, we argue that the Ly$\\alpha$ nebula would be short-lived\n($\\lesssim10$ Myr) if not continuously replenished with cold gas at a rate of\n$\\gtrsim1000$ M$_{\\odot}$ yr$^{-1}$. We investigate the possibility that\ncluster galaxies supply the required gas through outflows and we show that\ntheir total mass outflow rate matches the replenishment necessary to sustain\nthe nebula. This scenario directly implies the extraction of energy from\ngalaxies and its deposition in the surrounding intracluster medium, as required\nto explain the thermodynamic properties of local clusters. We estimate an\nenergy injection of the order of $\\thickapprox2$ keV per particle in the\nintracluster medium over a $2$ Gyr interval. In our baseline calculation AGN\nprovide up to $85$% of the injected energy and 2/3 of the mass, while the rest\nis supplied by supernovae-driven winds.", "category": "astro-ph_GA" }, { "text": "Evidence for extended gaseous reservoirs around AGN at cosmic noon from\n ALMA CO(3-2) observations: Gaseous outflows are key phenomena in the evolution of galaxies, as they\naffect star formation (either positively or negatively), eject gas from the\ncore or disk, and directly cause mixing of pristine and processed material.\nActive outflows may be detected through searches for broad spectral line\nemission or high-velocity gas, but it is also possible to determine the\npresence of past outflows by searching for extended reservoirs of chemically\nenriched molecular gas in the circumgalactic medium (CGM) around galaxies. In\nthis work, we examine the CO(3-2) emission of a set of seven z~2.0-2.5 AGN host\ngalaxies, as observed with ALMA. Through a three-dimensional stacking analysis\nwe find evidence for extended CO emission of radius r~13kpc. We extend this\nanalysis to the HST/ACS i-band images of the sample galaxies, finding a complex\nsmall-scale (r<10kpc) morphology but no robust evidence for extended emission.\nIn addition, the dust emission (traced by rest-frame FIR emission) shows no\nevidence for significant spatial extension. This indicates that the diffuse CO\nemission revealed by ALMA is morphologically distinct from the stellar\ncomponent, and thus traces an extended reservoir of enriched gas. The presence\nof a diffuse, enriched molecular reservoir around this sample of AGN host\ngalaxies at cosmic noon hints at a history of AGN-driven outflows that likely\nhad strong effects on the star formation history of these objects.", "category": "astro-ph_GA" }, { "text": "Do halos that form early, have high concentration, are part of a pair,\n or contain a central galaxy potential host more pronounced planes of\n satellite galaxies?: The Milky Way, the Andromeda galaxy, and Centaurus A host flattened\ndistributions of satellite galaxies which exhibits coherent velocity trends\nindicative of rotation. Comparably extreme satellite structures are very rare\nin cosmological LCDM simulations, giving rise to the `satellite plane problem'.\nAs a possible explanation it has been suggested that earlier-forming, higher\nconcentration host halos contain more flattened and kinematically coherent\nsatellite planes. We have tested for such a proposed correlation between the\nsatellite plane and host halo properties in the ELVIS suite of simulations. We\nfind evidence neither for a correlation of plane flattening with halo\nconcentration or formation time, nor for a correlation of kinematic coherence\nwith concentration. The height of the thinnest sub-halo planes does correlate\nwith the host virial radius and with the radial extent of the sub-halo system.\nThis can be understood as an effect of not accounting for differences in the\nradial distribution of sub-halos, and selecting them from different volumes\nthan covered by the actual observations. Being part of a halo pair like the\nLocal Group does not result in more narrow or more correlated satellite planes\neither. Additionally, using the PhatELVIS simulations we show that the presence\nof a central galaxy potential does not favor more narrow or more correlated\nsatellite planes, it rather leads to slightly wider planes. Such a central\npotential is a good approximation of the dominant effect baryonic physics in\ncosmological simulations has on a sub-halo population. This suggests that, in\ncontrast to other small-scale problems, the planes of satellite galaxies issue\nis made worse by accounting for baryonic effects.", "category": "astro-ph_GA" }, { "text": "Simulations of the star-forming molecular gas in an interacting M51-like\n galaxy: We present here the first of a series of papers aimed at better understanding\nthe evolution and properties of giant molecular clouds (GMCs) in a galactic\ncontext. We perform high resolution, three-dimensional {\\sc arepo} simulations\nof an interacting galaxy inspired by the well-observed M51 galaxy. Our fiducial\nsimulations include a non-equilibrium, time-dependent, chemical network that\nfollows the evolution of atomic and molecular hydrogen as well as carbon and\noxygen self-consistently. Our calculations also treat gas self-gravity and\nsubsequent star formation (described by sink particles), and coupled supernova\nfeedback. In the densest parts of the simulated interstellar medium (ISM) we\nreach sub-parsec resolution, granting us the ability to resolve individual GMCs\nand their formation and destruction self-consistently throughout the galaxy. In\nthis initial work we focus on the general properties of the ISM with a\nparticular focus on the cold star-forming gas. We discuss the role of the\ninteraction with the companion galaxy in generating cold molecular gas and\ncontrolling stellar birth. We find that while the interaction drives\nlarge-scale gas flows and induces spiral arms in the galaxy, it is of secondary\nimportance in determining gas fractions in the different ISM phases and the\noverall star-formation rate. The behaviour of the gas on small GMC scales\ninstead is mostly controlled by the self-regulating property of the ISM driven\nby coupled feedback.", "category": "astro-ph_GA" }, { "text": "Super-Eddington accretion of dusty gas onto seed black holes:\n metallicity-dependent efficiency of mass growth: The super-Eddington accretion onto intermediate seed BHs is a potential\nformation mode of supermassive black holes exceeding $10^9~M_\\odot$ in the\nearly universe. We here investigate how such rapid accretion may occur with\nfinite amounts of heavy elements contained in the gas and dust. In our 1D\nradiation-hydrodynamics simulations, the radiative transfer is solved for both\nthe direct UV lights emitted by an accretion disk and the diffuse IR lights\nthermally emitted by dust grains. Our results show that the radiative force by\nthe IR lights causes a strong feedback to regulate the mass accretion. The\nresulting mean accretion rate is lower with the higher metallicity, and there\nis the critical metallicity $Z \\sim 10^{-2}~Z_\\odot$, above which the\nsuper-Eddington accretion is prevented by the radiation pressure of the IR\nlights. With this taken into account, we examine if the dusty super-Eddington\naccretion occurs in young galaxies using a simple model. We show that a\nsufficient number of galaxies at $z \\gtrsim 10$ can be such potential sites if\nBHs accrete the cold dense gas with $T \\sim 10^2$ K, approximately the thermal\nequilibrium value at $Z = 10^{-2}~Z_\\odot$. We argue that the efficiency of the\nBH growth via the rapid accretion depends on the metallicity, and that the\nmetallicity slightly lower than $10^{-2}~Z_\\odot$ provides a chance for the\nmost efficient growth.", "category": "astro-ph_GA" }, { "text": "The MAGIC project. III. Radial and azimuthal Galactic abundance\n gradients using classical Cepheids: Radial abundance gradients provide sound constraints for chemo-dynamical\nmodels of galaxies. Azimuthal variations of abundance ratios are solid\ndiagnostics to understand their chemical enrichment. In this paper we\ninvestigate azimuthal variations of abundances in the Milky Way using Cepheids.\nWe provide the detailed chemical composition (25 elements) of 105 Classical\nCepheids from high-resolution SALT spectra observed by the MAGIC project.\nNegative abundance gradients, with abundances decreasing from the inner to the\nouter disc, have been reported both in the Milky Way and in external galaxies,\nand our results are in full agreement with literature results. We find\nazimuthal variations of the oxygen abundance [O/H]. While a large number of\nexternal spirals show negligible azimuthal variations, the Milky Way seems to\nbe one of the few galaxies with noticeable [O/H] azimuthal asymmetries. They\nreach ~0.2 dex in the inner Galaxy and in the outer disc, where they are the\nlargest, thus supporting similar findings for nearby spiral galaxies as well as\nrecent 2D chemo-dynamical models.", "category": "astro-ph_GA" }, { "text": "Rotational signature of the Milky Way stellar halo: We measure the rotation of the Milky Way stellar halo on two samples of Blue\nHorizontal Branch (BHB) field halo stars from the Sloan Digital Sky Survey\n(SDSS) with four different methods. The two samples comprise 1582 and 2563\nstars respectively and reach out to ~50 kpc in galactocentric distance. Two of\nthe methods to measure rotation rely exclusively on line-of-sight velocities,\nnamely the popular double power-law model and a direct estimate of the\nde-projected l.o.s. velocity. The other two techniques use the full 3D motions:\nthe radial velocity based rotation estimator of Sch\\\"onrich, Binney & Asplund\n(2012) and a simple 3D azimuthal velocity mean. In this context we a) critique\nthe popular model and b) assess the reliability of the estimators. All four\nmethods agree on a weakly prograde or non-rotating halo. Further, we observe no\nduality in the rotation of sub-samples with different metallicities or at\ndifferent radii. We trace the rotation gradient across metallicity measured by\nDeason et al. (2011) on a similar sample of BHB stars back to the inclusion of\nregions in the apparent magnitude-surface gravity plane known to be\ncontaminated. In the spectroscopically selected sample of Xue et al. (2011), we\nflag ~500 hot metal-poor stars for their peculiar kinematics w.r.t. to both\ntheir cooler metal-poor counter-parts and to the metal-rich stars in the same\nsample. They show a seemingly retrograde behaviour in line-of-sight velocities,\nwhich is not confirmed by the 3D estimators. Their anomalous vertical motion\nhints at either a pipeline problem or a stream-like component rather than a\nsmooth retrograde population.", "category": "astro-ph_GA" }, { "text": "Massive Quiescent Galaxies at z>3 in The Millennium Simulation Populated\n by A Semi-analytic Galaxy Formation Model: We take advantage of the statistical power of the large-volume\ndark-matter-only Millennium simulation, combined with a sophisticated\nsemi-analytic galaxy formation model, to explore whether the recently reported\n$z=3.7$ quiescent galaxy ZF-COSMOS-20115 (ZF; Glazebrook et al. 2017) can be\naccommodated in current galaxy formation models. In our model, a population of\nquiescent galaxies (QGs) with stellar masses and star formation rates\ncomparable to those of ZF naturally emerges at redshifts $z<4$. There are two\nand five ZF analogues at the redshift $3.86$ and $3.58$ in the Millennium\nsimulation volume, respectively. We demonstrate that, while the $z>3.5$ massive\nQGs are rare (about 2\\% of the galaxies with the similar stellar masses), the\nexisting AGN feedback model implemented in the semi-analytic galaxy formation\nmodel can successfully explain the formation of the high-redshift QGs as it\ndoes on their lower redshift counterparts.", "category": "astro-ph_GA" }, { "text": "Constraints from Faraday rotation on the magnetic field structure in the\n Galactic halo: We examine the constraints imposed by Faraday rotation measures of\nextragalactic point sources on the structure of the magnetic field in the halo\nof our Galaxy. Guided by radio polarization observations of external spiral\ngalaxies, we look in particular into the possibility that field lines in the\nGalactic halo have an X shape. We employ the analytical models of spiraling,\npossibly X-shape magnetic fields derived in a previous paper to generate\nsynthetic all-sky maps of the Galactic Faraday depth, which we fit to an\nobservational reference map with the help of Markov Chain Monte Carlo\nsimulations. We find that the magnetic field in the Galactic halo is slightly\nmore likely to be bisymmetric (azimuthal wavenumber, $m = 1$) than axisymmetric\n($m = 0$). If it is indeed bisymmetric, it must appear as X-shaped in radio\npolarization maps of our Galaxy seen edge-on from outside, but if it is\nactually axisymmetric, it must instead appear as nearly parallel to the\nGalactic plane.", "category": "astro-ph_GA" }, { "text": "A high resolution VLT/FLAMES study of individual stars in the centre of\n the Fornax dwarf spheroidal galaxy: For the first time we show the detailed late-stage chemical evolution history\nof small nearby dwarf spheroidal galaxy in the Local Group. We present the\nresults of a high resolution (R$\\sim$20000) FLAMES/GIRAFFE abundance study at\nESO/VLT of 81 photometrically selected red giant branch stars in the central\n25$'$ of the Fornax dwarf spheroidal galaxy. We present abundances of \\alfe\\\n(Mg, Si, Ca and Ti), iron-peak elements (Fe, Ni and Cr) and heavy elements (Y,\nBa, La, Nd and Eu). Our sample was randomly selected, and is clearly dominated\nby the younger and more metal rich component of Fornax which represents the\nmajor fraction of stars in the central region. This means that the majority of\nour stars are 1$-$4 Gyr old, and thus represent the end phase of chemical\nevolution in this system. Our sample of stars has unusually low [$\\alpha$/Fe],\n[Ni/Fe] and [Na/Fe] compared to the Milky Way stellar populations at the same\n[Fe/H]. The particularly important role of stellar winds from low metallicity\nAGB stars in the creation of s-process elements is clearly seen from the high\n[Ba/Y]. Furthermore, we present evidence for an s-process contribution to Eu.", "category": "astro-ph_GA" }, { "text": "New candidates for extremely metal-poor emission-line galaxies in the\n SDSS/BOSS DR10: We present a spectroscopic study of eight extremely low-metallicity candidate\nemission-line galaxies with oxygen abundances possibly below 12 +log O/H =\n7.35. These galaxies were selected from Data Release 10 of the Sloan Digital\nSky Survey/Baryon Oscillation Spectroscopic Survey (SDSS/BOSS DR10). We will\ncall these extremely metal-deficient galaxies XMD galaxies. The electron\ntemperature-sensitive emission line [O~{\\sc iii}] $\\lambda$4363 is detected in\nthree galaxies and marginally detected in two galaxies, allowing for abundance\ndetermination by a \"direct\" method. Because of large uncertainties in the [O\n{\\sc iii}]$\\lambda$4363\\AA\\ line fluxes, we also calculated oxygen abundance in\nthese galaxies together with the remaining three galaxies using a strong-line\nsemi-empirical method. This method gives oxygen abundances higher than 7.35 for\nthree galaxies with detected [O {\\sc iii}]$\\lambda$4363\\AA\\ line and lower than\n7.35 for the remaining five objects of the sample. The newly-discovered\ngalaxies represent excellent targets for follow-up spectroscopic observations\nwith the largest telescopes to improve the oxygen abundance determination and\nto increase the number of these very rare low-metallicity objects. The extreme\nlocation of the most massive and luminous XMD galaxies and XMD candidates in\nthe stellar mass-metallicity diagram implies that these galaxies may be genuine\nyoung objects.\n With stellar masses of up to $\\sim$ 10$^7$ - 10$^8$$M_{\\odot}$, the galaxies\nare not chemically enriched and strongly deviate to lower metallicity as\ncompared to the relation obtained for a large sample of low-redshift,\nstar-forming galaxies.", "category": "astro-ph_GA" }, { "text": "Star Cluster Formation and Survival in the First Galaxies: Using radiation-hydrodynamic cosmological simulations, we present a detailed\n($0.1$ pc resolution), physically motivated portrait of a typical-mass dwarf\ngalaxy before the epoch of reionization, resolving the formation and evolution\nof star clusters into individual $10\\:\\mathrm{M_{\\odot}}$ star particles. In\nthe rest-frame UV, the galaxy has an irregular morphology with no bulge or\ngalactic disk, dominated by light emitted from numerous, compact, and\ngravitationally-bound star clusters. This is especially interesting in light of\nrecent HST and JWST observations that -- aided by the magnifying power of\ngravitational lenses -- have imaged, at parsec-scale resolution, individual\nyoung star clusters in the process of forming in similar galaxies at $z>6$.\nBecause of their low metallicities and high temperatures, star-forming gas\nclouds in this galaxy have densities $\\sim 100$ times higher than typical giant\nmolecular clouds; hence, their star formation efficiencies are high enough\n($f_*\\sim10-70$ per cent) to produce a sizeable population of potential\nglobular cluster progenitors but typically smaller (between a few $100\\:-\\:\n2\\times10^4\\:\\mathrm{M_{\\odot}}$, sizes of $0.1-3$ pc) and of lower\nmetallicities ($10^{-3.5}-10^{-2.5}\\:\\mathrm{Z_{\\odot}}$). The initial mass\nfunction of the star-forming clouds is log-normal while the bound star cluster\nmass function is a power-law with a slope that depends mainly on $f_*$ but also\non the temporal proximity to a major starburst. We find slopes between $-0.5$\nand $-2.5$ depending on the assumed sub-grid $f_*$. Star formation is\nself-regulated on galactic scales; however, the multi-modal metallicity\ndistribution of the star clusters and the fraction of stars locked into\nsurviving bound star clusters depends on $f_*$.", "category": "astro-ph_GA" }, { "text": "The Milky Way Halo in Action Space: We analyse the structure of the local stellar halo of the Milky Way using\n$\\sim$ 60000 stars with full phase space coordinates extracted from the\nSDSS--{\\it Gaia} catalogue. We display stars in action space as a function of\nmetallicity in a realistic axisymmetric potential for the Milky Way Galaxy. The\nmetal-rich population is more distended towards high radial action $J_R$ as\ncompared to azimuthal or vertical action, $J_\\phi$ or $J_z$. It has a mild\nprograde rotation $(\\langle v_\\phi \\rangle \\approx 25$ km s$^{-1}$), is\nradially anisotropic and highly flattened with axis ratio $q \\approx 0.6 -\n0.7$. The metal-poor population is more evenly distributed in all three\nactions. It has larger prograde rotation $(\\langle v_\\phi \\rangle \\approx 50$\nkm s$^{-1}$), a mild radial anisotropy and a roundish morphology ($q\\approx\n0.9$). We identify two further components of the halo in action space. There is\na high energy, retrograde component that is only present in the metal-rich\nstars. This is suggestive of an origin in a retrograde encounter, possibly the\none that created the stripped dwarf galaxy nucleus, $\\omega$Centauri. Also\nvisible as a distinct entity in action space is a resonant component, which is\nflattened and prograde. It extends over a range of metallicities down to [Fe/H]\n$\\approx -3$. It has a net outward radial velocity $\\langle v_R \\rangle \\approx\n12$ km s$^{-1}$ within the Solar circle at $|z| <3.5$ kpc. The existence of\nresonant stars at such extremely low metallicities has not been seen before.", "category": "astro-ph_GA" }, { "text": "Distinct core and halo stellar populations and the formation history of\n the bright Coma cluster early-type galaxy NGC 4889: We study the stellar population far into the halo of one of the two brightest\ngalaxies in the Coma cluster, NGC 4889, based on deep medium resolution\nspectroscopy with FOCAS at the Subaru 8.2m telescope. We fit single stellar\npopulation models to the measured line-strength (Lick) indices (Hbeta, Mgb,\n[MgFe]' and ). Combining with literature data, we construct radial profiles\nof metallicity, [alpha/Fe] element abundance ratio and age for NGC 4889, from\nthe center out to ~60 kpc (~4Re). We find evidence for different chemical and\nstar formation histories for stars inside and outside 1.2Re = 18 kpc radius.\nThe inner regions are characterized by a steep [Z/H] gradient and high\n[alpha/Fe] at ~2.5 times solar value. In the halo, between 18 and 60 kpc, the\n[Z/H] is near-solar with a shallow gradient, while [alpha/Fe] shows a strong\nnegative gradient, reaching solar values at ~60 kpc. We interpret these data in\nterms of different formation histories for both components. The data for the\ninner galaxy are consistent with a rapid, quasi-monolithic, dissipative merger\norigin at early redshifts, followed by one or at most a few dry mergers. Those\nfor the halo argue for later accretion of stars from old systems with more\nextended star formation histories. The half-light radius of the inner component\nalone is estimated as ~6 kpc, suggesting a significantly smaller size of this\ngalaxy in the past. This may be the local stellar population signature of the\nsize evolution found for early-type galaxies from high-redshift observations.", "category": "astro-ph_GA" }, { "text": "MOSEL Survey: Extremely weak outflows in EoR analogues at z=3-4: This paper presents deep K-band spectroscopic observations of galaxies at\nz=3-4 with composite photometric rest-frame Hb+[OIII] equivalent widths\nEW_0>600A, comparable to the EW of galaxies observed during the epoch of\nreionisation (EoR, z>6). The typical spectroscopic [OIII] EW_0 and stellar mass\nof our targets is ~ 700A and log(M_star/M_sun)=8.98. By stacking the [OIII]\nemission profiles, we find evidence of a weak broad component with\nF_broad/F_narrow ~ 0.2 and velocity width sigma_{broad} ~ 170 km/s. The\nstrength and velocity width of the broad component does not change\nsignificantly with stellar mass and [OIII] EW_0 of the stacked sample. Assuming\nsimilar broad component profiles for [OIII] and Halpha emission, we estimate a\nmass loading factor ~0.2, similar to low stellar mass galaxies at z>1 even if\nthe star formation rates of our sample is 10 times higher. We hypothesize that\neither the multi-phase nature of supernovae driven outflows or the suppression\nof winds in the extreme star-forming regime is responsible for the weak\nsignature of outflows in the EoR analogues.", "category": "astro-ph_GA" }, { "text": "ALMA Observations of Multiple-CO and C Lines Toward the Active Galactic\n Nucleus of NGC 7469: X-Ray-dominated Region Caught in the Act: We used the Atacama Large Millimeter/submillimeter Array (ALMA) to map\n$^{12}$CO($J$ = 1-0), $^{12}$CO($J$ = 2-1), $^{12}$CO($J$ = 3-2), $^{13}$CO($J$\n= 2-1), and [CI]($^3P_1$-$^3P_0$) emission lines around the type 1 active\ngalactic nucleus (AGN) of NGC 7469 ($z = 0.0164$) at $\\sim 100$ pc resolutions.\nThe CO lines are bright both in the circumnuclear disk (central $\\sim 300$ pc)\nand the surrounding starburst (SB) ring ($\\sim 1$ kpc diameter), with two\nbright peaks on either side of the AGN. By contrast, the [CI]($^3P_1$-$^3P_0$)\nline is strongly peaked on the AGN. Consequently, the brightness temperature\nratio of [CI]($^3P_1$-$^3P_0$) to $^{13}$CO(2-1) is $\\sim 20$ at the AGN, as\ncompared to $\\sim 2$ in the SB ring. Our local thermodynamic equilibrium (LTE)\nand non-LTE models indicate that the enhanced line ratios (or CI enhancement)\nare due to an elevated C$^0$/CO abundance ratio ($\\sim 3-10$) and temperature\n($\\sim 100-500$ K) around the AGN as compared to the SB ring (abundance ratio\n$\\sim 1$, temperature $\\lesssim 100$ K), which accords with the picture of the\nX-ray-dominated Region (XDR). Based on dynamical modelings, we also provide\nCO(1-0)-to- and [CI]($^3P_1$-$^3P_0$)-to-molecular mass conversion factors at\nthe central $\\sim 100$ pc of this AGN as $\\alpha_{\\rm CO} = 4.1$ and\n$\\alpha_{\\rm CI} = 4.4~M_\\odot$ (K km s$^{-1}$ pc$^2$)$^{-1}$, respectively.\nOur results suggest that the CI enhancement is potentially a good marker of\nAGNs that could be used in a new submillimeter diagnostic method toward dusty\nenvironments.", "category": "astro-ph_GA" }, { "text": "Radiation Hydrodynamical Simulations of the First Quasars: Supermassive black holes (SMBHs) are the central engines of luminous quasars\nand are found in most massive galaxies today. But the recent discoveries of\nULAS J1120+0641, a $2 \\times 10^9$ M$_{\\odot}$ BH at $z =$ 7.1, and ULAS\nJ1342+0928, a $8.0 \\times 10^{8}$ M$_{\\odot}$ BH at $z =$ 7.5, now push the era\nof quasar formation up to just 690 Myr after the Big Bang. Here we report new\ncosmological simulations of SMBHs with X-rays fully coupled to primordial\nchemistry and hydrodynamics that show that J1120 and J1342 can form from direct\ncollapse black holes (DCBHs) if their growth is fed by cold, dense accretion\nstreams, like those thought to fuel rapid star formation in some galaxies at\nlater epochs. Our models reproduce all of the observed properties of J1120: its\nmass, luminosity, and H II region as well as star formation rates and\nmetallicities in its host galaxy. They also reproduce the dynamical mass of the\ninnermost 1.5 kpc of its emission region recently measured by ALMA and J-band\nmagnitudes that are in good agreement with those found by the VISTA Hemisphere\nSurvey.", "category": "astro-ph_GA" }, { "text": "The Arecibo Galaxy Environment Survey IX: The Isolated Galaxy Sample: We have used the Arecibo L-band Feed Array to map three regions, each of 5\nsquare degrees, around the isolated galaxies NGC 1156, UGC 2082, and NGC 5523.\nIn the vicinity of these galaxies we have detected two dwarf companions: one\nnear UGC 2082, previously discovered by ALFALFA, and one near NGC 1156,\ndiscovered by this project and reported in an earlier paper. This is\nsignificantly fewer than the 15.4 $^{+1.7}_{-1.5}$ that would be expected from\nthe field HI mass function from ALFALFA or the 8.9 $\\pm$ 1.2 expected if the HI\nmass function from the Local Group applied in these regions. The number of\ndwarf companions detected is, however, consistent with a flat or declining HI\nmass function as seen by a previous, shallower, HI search for companions to\nisolated galaxies.We attribute this difference in Hi mass functions to the\ndifferent environments in which they are measured. This agrees with the general\nobservation that lower ratios of dwarf to giant galaxies are found in lower\ndensity environments.", "category": "astro-ph_GA" }, { "text": "The mass--metallicity relation AKARI-FMOS infrared galaxies at\n $z\\sim0.88$ in the AKARI North Ecliptic Pole Deep Survey Field: Mass, metallicity, and star formation rate (SFR) of a galaxy are crucial\nparameters in understanding galaxy formation and evolution. However, the\nrelation among these is still a matter of debate for luminous infrared\ngalaxies, which carry a bulk of SFR budget of the universe at $z\\sim1$. We have\ninvestigated the relation among stellar mass, gas-phase oxygen abundance, and\nSFR of AKARI-detected mid-IR galaxies at $z\\sim0.88$ in the AKARI NEP deep\nfield. We observed about 350 AKARI sources with Subaru/FMOS NIR spectrograph,\nand detected secure and expected H$\\alpha$ emission lines from 25 and 44\ngalaxies, respectively. The SFR of our sample is almost constant ($\\sim\n25M_{\\odot}/yr$) over the stellar mass range of our sample. Compared with\nmain-sequence (MS) galaxies at a similar redshift range, the average SFR of our\ndetected sample is comparable for massive galaxies\n($\\sim10^{10.58}~M_{\\odot}$), while higher by $\\sim$0.6dex for less massive\ngalaxies ($\\sim 10^{10.05}~M_{\\odot}$). We measure metallicities from the\n[NII]/H$\\alpha$ emission line ratio.\n We find that the mass-metallicity relation of our individually measured\nsources agrees with that for optical-selected star-forming galaxies at\n$z\\sim0.1$, while metallicities of stacked spectra agree with that of MS\ngalaxies at $z\\sim0.78$. Considering high SFR of individually measured sources,\nFMR of the IR galaxies is different from that at $z\\sim0.1$. However, on the\nmass-metallicity plane, they are consistent with the MS galaxies, highlighting\nhigher SFR of the IR galaxies. This suggests the evolutionary path of our IR\ngalaxies is different from that of MS galaxies. A possible physical\ninterpretation includes that the star-formation activities of IR galaxies at\n$z\\sim0.88$ in our sample are enhanced by interaction and/or merger of\ngalaxies, but the inflow of metal-poor gas is not yet induced, keeping the\nmetallicity intact.", "category": "astro-ph_GA" }, { "text": "The SPLASH Survey: A Spectroscopic Analysis of the Metal-Poor,\n Low-Luminosity M31 dSph Satellite Andromeda X: Andromeda X (And X) is a newly discovered low-luminosity M31 dwarf spheroidal\ngalaxy (dSph) found by Zucker et al. (2007) in the Sloan Digital Sky Survey\n(SDSS - York et al. 2000). In this paper, we present the first spectroscopic\nstudy of individual red giant branch stars in And X, as a part of the SPLASH\nSurvey (Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo).\nUsing the Keck II telescope and multiobject DEIMOS spectrograph, we target two\nspectroscopic masks over the face of the galaxy and measure radial velocities\nfor ~100 stars with a median accuracy of sigma_v ~ 3 km/s. The velocity\nhistogram for this field confirms three populations of stars along the sight\nline: foreground Milky Way dwarfs at small negative velocities, M31 halo red\ngiants over a broad range of velocities, and a very cold velocity ``spike''\nconsisting of 22 stars belonging to And X with v_rad = -163.8 +/- 1.2 km/s. By\ncarefully considering both the random and systematic velocity errors of these\nstars (e.g., through duplicate star measurements), we derive an intrinsic\nvelocity dispersion of just sigma_v = 3.9 +/- 1.2 km/s for And X, which for its\nsize, implies a minimum mass-to-light ratio of M/L =37^{+26}_{-19} assuming the\nmass traces the light. Based on the clean sample of member stars, we measure\nthe median metallicity of And X to be [Fe/H] = -1.93 +/- 0.11, with a slight\nradial metallicity gradient. The dispersion in metallicity is large,\nsigma([Fe/H]) = 0.48, possibly hinting that the galaxy retained much of its\nchemical enrichment products. We discuss the potential for better understanding\nthe formation and evolution mechanisms for M31's system of dSphs through\n(current) kinematic and chemical abundance studies, especially in relation to\nthe Milky Way sample. (abridged version)", "category": "astro-ph_GA" }, { "text": "Effect of turbulent velocity on the \\HI intensity fluctuation power\n spectrum from spiral galaxies: We use numerical simulations to investigate effect of turbulent velocity on\nthe power spectrum of \\HI intensity from external galaxies when (a) all\nemission is considered, (b) emission with velocity range smaller than the\nturbulent velocity dispersion is considered. We found that for case (a) the\nintensity fluctuation depends directly only on the power spectrum of the column\ndensity, whereas for case (b) it depends only on the turbulent velocity\nfluctuation. We discuss the implications of this result in real observations of\n\\HI fluctuations.", "category": "astro-ph_GA" }, { "text": "A Newborn AGN in a Starforming Galaxy: We report on the finding of a newborn AGN, i.e. current AGN activity in a\ngalaxy previously classified as non-active, and characterize its evolution.\nBlack hole ignition event candidates were selected from a parent sample of\nspectrally classified non-active galaxies (2.394.312 objects), that currently\nshow optical flux variability indicative of a type I AGN, according to the\nALeRCE light curve classifier. A second epoch spectrum for a sample of\ncandidate newborn AGN were obtained with the SOAR telescope to search for new\nAGN features. We present spectral results for the most convincing case of new\nAGN activity, for a galaxy with a previous star-forming optical classification,\nwhere the second epoch spectrum shows the appearance of prominent, broad Balmer\nlines without significant changes in the narrow line flux ratios. Long term\noptical lightcurves show a steady increase in luminosity starting 1.5 years\nafter the SDSS spectrum was taken and continuing for at least 7 years. MIR\ncolors from the WISE catalog have also evolved from typical non active galaxy\ncolors to AGN-like colors and recent X-ray flux detections confirm its AGN\nnature.", "category": "astro-ph_GA" }, { "text": "Linking High- and Low-Mass Star Formation: Observation-Based Continuum\n Modelling and Physical Conditions: Astronomers have yet to establish whether high-mass protostars form from\nhigh-mass prestellar cores, similar to their lower-mass counterparts, or from\nlower-mass fragments at the heart of a pre-protostellar cluster undergoing\nlarge-scale collapse. Part of the uncertainty is due to a shortage of envelope\nstructure data on protostars of a few tens of solar masses, where we expect to\nsee a transition from intermediate-mass star formation to the high-mass\nprocess. We sought to derive the masses, luminosities, and envelope density\nprofiles for eight sources in Cygnus-X, whose mass estimates in the literature\nplaced them in the sampling gap. Combining these sources with similarly evolved\nsources in the literature enabled us to perform a meta-analysis of protostellar\nenvelope parameters over six decades in source luminosity. We performed\nspectral energy distribution (SED) fitting on archival broadband photometric\ncontinuum data from 1.2 to 850 $\\mu$m, to derive bolometric luminosities for\nour eight sources plus initial mass and radius estimates for modelling density\nand temperature profiles with the radiative transfer package Transphere. The\nenvelope masses, densities at 1000 AU, outer envelope radii, and density power\nlaw indices as functions of bolometric luminosity all follow established trends\nin the literature spanning six decades in luminosity. Most of our sources\noccupy an intermediate to moderately high range of masses and luminosities,\nwhich helps to more firmly establish the continuity between low- and high-mass\nstar formation mechanisms. Our density power law indices are consistent with\nobserved values in literature, which show no discernible trends with\nluminosity. Finally, we show that the trends in all of the envelope parameters\nfor high-mass protostars are statistically indistinguishable from trends in the\nsame variables for low- and intermediate-mass protostars.", "category": "astro-ph_GA" }, { "text": "Laboratory Rotational Spectra of Silyl Isocyanide: The rotational spectrum of silyl isocyanide (SiH$_3$NC), an isomer of the\nwell studied silyl cyanide (SiH$_3$CN), has been detected in the laboratory in\na supersonic molecular beam, and the identification was confirmed by\nobservations of the corresponding rotational transitions in the rare isotopic\nspecies SiH$_3$$^{15}$NC and SiH$_3$N$^{13}$C. Spectroscopic constants derived\nfrom 19 transitions between $11 - 35$~GHz in the three lowest harmonically\nrelated rotational transitions in the $K = 0 ~{\\rm{and}}~1$ ladders of the\nnormal isotopic species including the nitrogen nuclear quadrupole hyperfine\nconstant, allow the principal astronomical transitions of SiH$_3$NC to be\ncalculated to an uncertainty of about 4~km~s$^{-1}$ in equivalent radial\nvelocity, or within the FWHM of narrow spectral features in the inner region of\nIRC+10216 near 200~GHz. The concentration of SiH$_3$NC in our molecular beam is\nthree times less than SiH$_3$CN, or about the same as the corresponding ratio\nof the isomeric pair SiNC and SiCN produced under similar conditions. Silyl\nisocyanide is an excellent candidate for astronomical detection, because the\nspectroscopic and chemical properties are very similar to SiH$_3$CN which was\nrecently identified in the circumstellar envelope of IRC+10216 by\n\\citet{cernicharo_discovery_2017} and of SiNC and SiCN in the same source.", "category": "astro-ph_GA" }, { "text": "Signatures of Kinematic Substructure in the Galactic Stellar Halo: Tidal debris from infalling satellites can leave observable structure in the\nphase-space distribution of the Galactic halo. Such substructure can be\nmanifest in the spatial and/or velocity distributions of the stars in the halo.\nThis paper focuses on a class of substructure that is purely kinematic in\nnature, with no accompanying spatial features. To study its properties, we use\na simulated stellar halo created by dynamically populating the Via Lactea II\nhigh-resolution N-body simulation with stars. A significant fraction of the\nstars in the inner halo of Via Lactea share a common speed and metallicity,\ndespite the fact that they are spatially diffuse. We argue that this kinematic\nsubstructure is a generic feature of tidal debris from older mergers and may\nexplain the detection of radial-velocity substructure in the inner halo made by\nthe Sloan Extension for Galactic Understanding and Exploration. The GAIA\nsatellite, which will provide the proper motions of an unprecedented number of\nstars, should further characterize the kinematic substructure in the inner\nhalo. Our study of the Via Lactea simulation suggests that the stellar halo can\nbe used to map the speed distribution of the local dark-matter halo, which has\nimportant consequences for dark-matter direct-detection experiments.", "category": "astro-ph_GA" }, { "text": "Discerning the Form of the Dense Core Mass Function: We investigate the ability to discern between lognormal and powerlaw forms\nfor the observed mass function of dense cores in star forming regions. After\ntesting our fitting, goodness-of-fit, and model selection procedures on\nsimulated data, we apply our analysis to 14 datasets from the literature.\nWhether the core mass function has a powerlaw tail or whether it follows a pure\nlognormal form cannot be distinguished from current data. From our simulations\nit is estimated that datasets from uniform surveys containing more than\napproximately 500 cores with a completeness limit below the peak of the mass\ndistribution are needed to definitively discern between these two functional\nforms. We also conclude that the width of the core mass function may be more\nreliably estimated than the powerlaw index of the high mass tail and that the\nwidth may also be a more useful parameter in comparing with the stellar initial\nmass function to deduce the statistical evolution of dense cores into stars.", "category": "astro-ph_GA" }, { "text": "LABOCA mapping of the infrared dark cloud MSXDC G304.74+01.32: Infrared dark clouds (IRDCs) likely represent very early stages of high-mass\nstar/star cluster formation. In this study, we aim to determine the physical\nproperties and spatial distribution of dense clumps in the IRDC MSXDC\nG304.74+01.32 (G304.74), and bring these characteristics into relation to\ntheories concerning the origin of IRDCs and their fragmentation into clumps and\nstar-forming cores. G304.74 was mapped in the 870 $\\mu$m dust continuum with\nthe LABOCA bolometer on APEX. Archival MSX and IRAS infrared data were used to\nstudy the nature and properties of the submillimetre clumps within the cloud.\nThere are 8 clumps within G304.74 which are not associated with mid-infrared\n(MIR) emission. Some of them are candidates for being/harbouring high-mass\nstarless cores (HMSCs). We compared the clump masses and their spatial\ndistribution in G304.74 with those in several other recently studied IRDCs.\nThere is a high likelihood that the clump mass distributions in G304.74 and in\nseveral other IRDCs represent the samples of the same parent distribution. In\nmost cases the spatial distributions of clumps in IRDCs do not deviate\nsignificantly from random distributions. This is consistent with the idea that\nthe origin of IRDCs, and their further sub-fragmentation down to scales of\nclumps is caused by supersonic turbulence in accordance with results from giant\nmolecular clouds.", "category": "astro-ph_GA" }, { "text": "Planck Early Results: All sky temperature and dust optical depth from\n Planck and IRAS: Constraints on the \"dark gas\" in our galaxy: We construct an all-sky map of the apparent temperature and optical depth of\nthermal dust emission using the Planck-HFI and IRAS data. The optical depth\nmaps are correlated to tracers of the atomic and molecular gas. The correlation\nis linear in the lowest column density regions at high galactic latitudes. At\nhigh NH, the correlation is consistent with that of the lowest NH. In the\nintermediate NH range, we observe departure from linearity, with the dust\noptical depth in excess to the correlation. We attribute this excess emission\nto thermal emission by dust associated with a Dark-Gas phase, undetected in the\navailable HI and CO measurements. We show the 2D spatial distribution of the\nDark-Gas in the solar neighborhood and show that it extends around known\nmolecular regions traced by CO. The average dust emissivity in the HI phase in\nthe solar neighborhood follows roughly a power law distribution with beta = 1.8\nall the way down to 3 mm, although the SED flattens slightly in the millimetre.\nThe threshold for the existence of the Dark-Gas is found at NH = (8.0\\pm 0.58)\n10^{20} Hcm-2. Assuming the same dust emissivity at high frequencies for the\ndust in the atomic and molecular phases leads to an average XCO = (2.54\\pm0.13)\n10^{20} H2cm-2/(K km s-1). The mass of Dark-Gas is found to be 28% of the\natomic gas and 118% of the CO emitting gas in the solar neighborhood. A\npossible origin for the Dark-Gas is the existence of a dark molecular phase,\nwhere H2 survives photodissociation but CO does not. The observed transition\nfor the onset of this phase in the solar neighborhood (AV = 0.4 mag) appears\nconsistent with recent theoretical predictions. We also discuss the possibility\nthat up to half of the Dark-Gas could be in atomic form, due to optical depth\neffects in the HI measurements.", "category": "astro-ph_GA" }, { "text": "The density structure of the L1157 molecular outflow: We present a multiline CS survey towards the brightest bow-shock B1 in the\nprototypical chemically active protostellar outflow L1157. We made use of\n(sub-)mm data obtained in the framework of the Chemical HErschel Surveys of\nStar forming regions (CHESS) and Astrochemical Surveys at IRAM (ASAI) key\nscience programs. We detected $^{12}$C$^{32}$S, $^{12}$C$^{34}$S,\n$^{13}$C$^{32}$S, and $^{12}$C$^{33}$S emissions, for a total of 18\ntransitions, with $E_{\\rm u}$ up to $\\sim$ 180 K. The unprecedented sensitivity\nof the survey allows us to carefully analyse the line profiles, revealing\nhigh-velocity emission, up to 20 km s$^{-1}$ with respect to the systemic. The\nprofiles can be well fitted by a combination of two exponential laws that are\nremarkably similar to what previously found using CO. These components have\nbeen related to the cavity walls produced by the $\\sim$ 2000 yr B1 shock and\nthe older ($\\sim$ 4000 yr) B2 shock, respectively. The combination of low- and\nhigh-excitation CS emission was used to properly sample the different physical\ncomponents expected in a shocked region. Our CS observations show that this\nmolecule is highlighting the dense, $n_{\\rm H_2}$ = 1--5 $\\times$ 10$^{5}$\ncm$^{-3}$, cavity walls produced by the episodic outflow in L1157. In addition,\nthe highest excitation (E$_u$ $\\geq$ 130 K) CS lines provide us with the\nsignature of denser (1--5 $\\times$ 10$^{6}$ cm$^{-3}$) gas, associated with a\nmolecular reformation zone of a dissociative J-type shock, which is expected to\narise where the precessing jet impacting the molecular cavities. The CS\nfractional abundance increases up to $\\sim$ 10$^{-7}$ in all the kinematical\ncomponents. This value is consistent with what previously found for\nprototypical protostars and it is in agreement with the prediction of the\nabundances obtained via the chemical code Astrochem.", "category": "astro-ph_GA" }, { "text": "Supernova-driven outflows and chemical evolution of dwarf spheroidal\n galaxies: We present a general phenomenological model for the metallicity distribution\n(MD) in terms of [Fe/H] for dwarf spheroidal galaxies (dSphs). These galaxies\nappear to have stopped accreting gas from the intergalactic medium and are\nfossilized systems with their stars undergoing slow internal evolution. For a\nwide variety of infall histories of unprocessed baryonic matter to feed star\nformation, most of the observed MDs can be well described by our model. The key\nrequirement is that the fraction of the gas mass lost by supernova-driven\noutflows is close to unity. This model also predicts a relationship between the\ntotal stellar mass and the mean metallicity for dSphs in accord with properties\nof their dark matter halos. The model further predicts as a natural consequence\nthat the abundance ratios [E/Fe] for elements such as O, Mg, and Si decrease\nfor stellar populations at the higher end of the [Fe/H] range in a dSph. We\nshow that for infall rates far below the net rate of gas loss to star formation\nand outflows, the MD in our model is very sharply peaked at one [Fe/H] value,\nsimilar to what is observed in most globular clusters. This suggests that\nglobular clusters may be end members of the same family as dSphs.", "category": "astro-ph_GA" }, { "text": "Star Clusters in Tidal Debris: We present results of a Hubble Space Telescope (HST) UBVI-band study of star\nclusters in tidal tails, using new WFC3 and ACS imaging to complement existing\nWFPC2 data. We survey 12 tidal tails across seven merging systems, deriving\nages and masses for 425 star cluster candidates (SCCs). The stacked mass\ndistribution across all systems follows a power law of the form $dN/dM \\propto\nM^{\\beta}$, with $\\beta = -2.02 \\pm 0.15$, consistent with what is seen in\nother star forming environments. GALEX and Swift UV imaging provide star\nformation rates (SFRs) for our tidal tails, which when compared with ages and\nmasses of our SCCs, allows for a determination of the cluster formation\nefficiency (CFE). We find the CFE increases with increasing SFR surface\ndensity, matching the theoretical model. We confirm this fit down at SFR\ndensities lower than previously measured (log $\\Sigma_\\text{SFR} \\:\n(\\text{M}_\\odot \\: \\text{yr}^{-1} \\: \\text{kpc}^{-2}) \\approx -4.2$), as\nrelated to the CFE. We determine the half-light radii for a refined sample of\n57 SCCs with our HST WFC3 and ACS imaging, and calculate their dynamical age,\nfinding the majority of them to be gravitationally bound. We also provide\nevidence of only low-mass ($< 10^4 \\: \\text{M}_\\odot$) cluster formation in our\nnearest galaxy, NGC 1487, consistent with the theory that this system is a\ndwarf merger.", "category": "astro-ph_GA" }, { "text": "A dark matter disc in the Milky Way: Predicting the local flux of dark matter particles is vital for dark matter\ndirect detection experiments. To date, such predictions have been based on\nsimulations that model the dark matter alone. Here we include the influence of\nthe baryonic matter for the first time. We use two different approaches.\nFirstly, we use dark matter only simulations to estimate the expected merger\nhistory for a Milky Way mass galaxy, and then add a thin stellar disc to\nmeasure its effect. Secondly, we use three cosmological hydrodynamic\nsimulations of Milky Way mass galaxies. In both cases, we find that a\nstellar/gas disc at high redshift (z~1) causes merging satellites to be\npreferentially dragged towards the disc plane. This results in an accreted dark\nmatter disc that contributes ~0.25 - 1 times the non-rotating halo density at\nthe solar position. An associated thick stellar disc forms with the dark disc\nand shares a similar velocity distribution. If these accreted stars can be\nseparated from those that formed in situ, future astronomical surveys will be\nable to infer the properties of the dark disc from these stars. The dark disc,\nunlike dark matter streams, is an equilibrium structure that must exist in disc\ngalaxies that form in a hierarchical cosmology. Its low rotation lag with\nrespect to the Earth significantly boosts WIMP capture in the Earth and Sun,\nincreases the likelihood of direct detection at low recoil energy, boosts the\nannual modulation signal, and leads to distinct variations in the flux as a\nfunction of recoil energy that allow the WIMP mass to be determined (see\ncontribution from T. Bruch this volume).", "category": "astro-ph_GA" }, { "text": "NuSTAR J033202-2746.8: direct constraints on the Compton reflection in a\n heavily obscured quasar at z~2: We report NuSTAR observations of NuSTAR J033202-2746.8, a heavily obscured,\nradio-loud quasar detected in the Extended Chandra Deep Field-South, the\ndeepest layer of the NuSTAR extragalactic survey (~400 ks, at its deepest).\nNuSTAR J033202-2746.8 is reliably detected by NuSTAR only at E>8 keV and has a\nvery flat spectral slope in the NuSTAR energy band (Gamma=0.55^{+0.62}_{-0.64};\n3-30 keV). Combining the NuSTAR data with extremely deep observations by\nChandra and XMM-Newton (4 Ms and 3 Ms, respectively), we constrain the\nbroad-band X-ray spectrum of NuSTAR J033202-2746.8, indicating that this source\nis a heavily obscured quasar (N_H=5.6^{+0.9}_{-0.8}x10^23 cm^-2) with\nluminosity L_{10-40 keV}~6.4x10^44 erg s^-1. Although existing optical and\nnear-infrared (near-IR) data, as well as follow-up spectroscopy with the Keck\nand VLT telescopes, failed to provide a secure redshift identification for\nNuSTAR J033202-2746.8, we reliably constrain the redshift z=2.00+/-0.04 from\nthe X-ray spectral features (primarily from the iron K edge). The NuSTAR\nspectrum shows a significant reflection component (R=0.55^{+0.44}_{-0.37}),\nwhich was not constrained by previous analyses of Chandra and XMM-Newton data\nalone. The measured reflection fraction is higher than the R~0 typically\nobserved in bright radio-loud quasars such as NuSTAR J033202-2746.8, which has\nL_{1.4 GHz}~10^27 W Hz^-1. Constraining the spectral shape of AGN, including\nbright quasars, is very important for understanding the AGN population, and can\nhave a strong impact on the modeling of the X-ray background. Our results show\nthe importance of NuSTAR in investigating the broad-band spectral properties of\nquasars out to high redshift.", "category": "astro-ph_GA" }, { "text": "Generation of mock tidal streams: In this paper we discuss a method for the generation of mock tidal streams.\nUsing an ensemble of simulations in an isochrone potential where the actions\nand frequencies are known, we derive an empirical recipe for the evolving\nsatellite mass and the corresponding mass loss rate, and the ejection\nconditions of the stream material. The resulting stream can then be quickly\ngenerated either with direct orbital integration, or by using the action-angle\nformalism. The model naturally produces streaky features within the stream.\nThese are formed due to the radial oscillation of the progenitor and the bursts\nof stars emitted near pericenter, rather than clumping at particular\noscillation phases as sometimes suggested. When detectable, these streaky\nfeatures are a reliable diagnostic for the stream's direction of motion and\nencode other information on the progenitor and its orbit. We show several tests\nof the recipe in alternate potentials, including a case with a chaotic\nprogenitor orbit which displays a marked effect on the width of the stream.\nAlthough the specific ejection recipe may need adjusting when elements such as\nthe orbit or satellite density profile are changed significantly, our examples\nsuggest that model tidal streams can be quickly and accurately generated by\nmodels of this general type for use in Bayesian sampling.", "category": "astro-ph_GA" }, { "text": "The structural properties of multiple populations in the dynamically\n young globular cluster NGC 2419: NGC 2419 is likely the globular cluster (GC) with the lowest dynamical age in\nthe Galaxy. This makes it an extremely interesting target for studying the\nproperties of its multiple populations (MPs), as they have been likely affected\nonly modestly by long-term dynamical evolution effects. Here we present for the\nfirst time a detailed analysis of the structural and morphological properties\nof the MPs along the whole extension of this remote and massive GC by combining\nhigh-resolution HST and wide-field ground-based data. In agreement with\nformation models predicting that second population (SP) stars form in the inner\nregions of the first population (FP) system, we find that the SP is more\ncentrally concentrated than the FP. This may provide constraints on the\nrelative concentrations of MPs in the cluster early stages of the evolutionary\nphase driven by two-body relaxation. In addition, we find that the fraction of\nFP stars is larger than expected from the general trend drawn by Galactic GCs.\nIf, as suggested by a number of studies, NGC 2419 formed in the Sagittarius\ndwarf galaxy and was later accreted by the Milky Way, we show that the observed\nFP fraction may be explained as due to the transition of NGC 2419 to a weaker\ntidal field (its current Galactocentric distance is d_gc~95 kpc) and\nconsequently to a reduced loss rate of FP stars.", "category": "astro-ph_GA" }, { "text": "High-Fidelity VLA Imaging of the Radio Structure of 3C273: 3C273, the nearest bright quasar, comprises a strong nuclear core and a\nbright, one-sided jet extending ~ 23 arcseconds to the SW. The source has been\nthe subject of imaging campaigns in all wavebands. Extensive observations of\nthis source have been made with the Very Large Array and other telescopes as\npart of a campaign to understand the jet emission mechanisms. Partial results\nfrom the VLA radio campaign have been published, but to date, the complete set\nof VLA imaging results has not been made available. We have utilized the VLA to\ndetermine the radio structure of 3C273 in Stokes I, Q, and U, over the widest\npossible frequency and resolution range. The VLA observed the source in all\nfour of its configurations, and with all eight of its frequency bands, spanning\n73.8 MHz to 43 GHz. The data were taken in a pseudo-spectral line mode to\nminimize the VLA's correlator errors, and were fully calibrated with subsequent\nself-calibration techniques to maximise image fidelity. Images in Stokes\nparameters I, Q, and U, spanning a resolution range from 6 arcseconds to 88\nmilliarcseconds are presented. Spectral index images, showing the evolution of\nthe jet component are shown. Polarimetry demonstrates the direction of the\nmagnetic fields responsible for the emission, and rotation measure maps show\nthe RM to be very small with no discernible trend along or across the jet. This\npaper presents a small subset of these images to demonstrate the major\ncharacteristics of the source emission. A library of all ~500 images has been\nmade available for open, free access by interested parties.", "category": "astro-ph_GA" }, { "text": "Rings and Halos in the Mid-Infrared: The Planetary Nebulae NGC 7354 and\n NGC 3242: We present images of the planetary nebulae (PNe) NGC 7354 and NGC 3242 in\nfour mid-infrared (MIR) photometric bands centred at 3.6, 4.5, 5.8 and 8.0\nmicrons; the results of observations undertaken using the Spitzer Space\nTelescope (SST). The resulting images show the presence of a halo and rings in\nNGC 3242, as previously observed through narrow band imaging at visual\nwavelengths, as well as evidence for a comparable halo and ring system in NGC\n7354. This is the first time that a halo and rings have been observed in the\nlatter source.\n We have analysed the formation of halos as a result of radiatively\naccelerated mass loss in the AGB progenitors. Although the models assume that\ndust formation occurs in C-rich environments, we note that qualitatively\nsimilar results would be expected for O-rich progenitors as well. The model\nfall-offs in halo density are found to result in gradients in halo surface\nbrightness which are similar to those observed in the visible and MIR.", "category": "astro-ph_GA" }, { "text": "Influence of galactic arm scale dynamics on the molecular composition of\n the cold and dense ISM II. Molecular oxygen abundance: Molecular oxygen has been the subject of many observational searches as\nchemical models predicted it to be a reservoir of oxygen. Although it has been\ndetected in two regions of the interstellar medium, its rarity is a challenge\nfor astrochemical models. In this paper, we have combined the physical\nconditions computed with smoothed particle hydrodynamics (SPH) simulations with\nour full gas-grain chemical model Nautilus, to study the predicted O2 abundance\nin interstellar material forming cold cores. We thus follow the chemical\nevolution of gas and ices in parcels of material from the diffuse interstellar\nconditions to the cold dense cores. Most of our predicted O2 abundances are\nbelow 1e-8 (with respect to the total proton density) and the predicted column\ndensities in simulated cold cores is at maximum a few 1e14 cm-2, in agreement\nwith the non detection limits. This low O2 abundance can be explained by the\nfact that, in a large fraction of the interstellar material, the atomic oxygen\nis depleted onto the grain surface (and hydrogenated to form H2O) before O2 can\nbe formed in the gas-phase and protected from UV photo-dissociations. We could\nachieve this result only because we took into account the full history of the\nevolution of the physical conditions from the diffuse medium to the cold cores.", "category": "astro-ph_GA" }, { "text": "Supernovae and their host galaxies - IV. The distribution of supernovae\n relative to spiral arms: Using a sample of 215 supernovae (SNe), we analyze their positions relative\nto the spiral arms of their host galaxies, distinguishing grand-design (GD)\nspirals from non-GD (NGD) galaxies. We find that: (1) in GD galaxies, an offset\nexists between the positions of Ia and core-collapse (CC) SNe relative to the\npeaks of arms, while in NGD galaxies the positions show no such shifts; (2) in\nGD galaxies, the positions of CC SNe relative to the peaks of arms are\ncorrelated with the radial distance from the galaxy nucleus. Inside (outside)\nthe corotation radius, CC SNe are found closer to the inner (outer) edge. No\nsuch correlation is observed for SNe in NGD galaxies nor for SNe Ia in either\ngalaxy class; (3) in GD galaxies, SNe Ibc occur closer to the leading edges of\nthe arms than do SNe II, while in NGD galaxies they are more concentrated\ntowards the peaks of arms. In both samples of hosts, the distributions of SNe\nIa relative to the arms have broader wings. These observations suggest that\nshocks in spiral arms of GD galaxies trigger star formation in the leading\nedges of arms affecting the distributions of CC SNe (known to have short-lived\nprogenitors). The closer locations of SNe Ibc vs. SNe II relative to the\nleading edges of the arms supports the belief that SNe Ibc have more massive\nprogenitors. SNe Ia having less massive and older progenitors, have more time\nto drift away from the leading edge of the spiral arms.", "category": "astro-ph_GA" }, { "text": "Probing Self-interacting Dark Matter with Disk Galaxies in Cluster\n Environments: Self-Interacting Dark Matter (SIDM) has long been proposed as a solution to\nsmall scale problems posed by standard Cold Dark Matter (CDM). We use numerical\nsimulations to study the effect of dark matter interactions on the morphology\nof disk galaxies falling into galaxy clusters. The effective drag force on dark\nmatter leads to offsets of the stellar disk with respect to the surrounding\nhalo, causing distortions in the disk. For anisotropic scattering\ncross-sections of 0.5 and 1.0$\\,\\textrm{cm}^{2}\\textrm{g}^{-1}$, we show that\npotentially observable warps, asymmetries, and thickening of the disk occur in\nsimulations. We discuss observational tests of SIDM with galaxy surveys and\nmore realistic simulations needed to obtain detailed predictions.", "category": "astro-ph_GA" }, { "text": "The Neutron Star Born in the Antlia Supernova Remnant: Among all known young nearby neutron stars, we search for the neutron star\nthat was born in the same supernova event that formed the Antlia supernova\nremnant (SNR). We also look for a runaway star that could have been the former\ncompanion to the neutron star (if it exists) and then got ejected due to the\nsame supernova. We find the pulsar PSR J0630-2834 to be the best candidate for\na common origin with the Antlia SNR. In that scenario the SNR is ~1.2 Myr old\nand is presently located at a distance of ~138 pc. We consider the runaway star\nHIP 47155 a former companion candidate to PSR J0630-2834. The encounter time\nand place is consistent with both stars being ejected from the Antlia SNR. We\nmeasured the radial velocity of HIP 47155 as 32.42 +/- 0.70km/s.", "category": "astro-ph_GA" }, { "text": "Dust in the Torus of the AGN Unified Model: These proceedings are based on an invited review talk at the 7th Meeting on\nCosmic Dust. The scope of the meeting was broad, covering dust-related topics\nin areas from comets to debris disks and high-redshift galaxies. This is\ntherefore intended to be an accessible, introductory overview of the dusty\ntorus of the AGN unified model, aimed at summarizing our current understanding\nof the torus and with some emphasis on the solid-state spectral features\nobserved.", "category": "astro-ph_GA" }, { "text": "Major Substructure in the M31 Outer Halo: Distances and Metallicities\n along the Giant Stellar Stream: We present a renewed look at M31's Giant Stellar Stream along with the nearby\nstructures Stream C and Stream D, exploiting a new algorithm capable of fitting\nto the red giant branch (RGB) of a structure in both colour and magnitude\nspace. Using this algorithm, we are able to generate probability distributions\nin distance, metallicity and RGB width for a series of subfields spanning these\nstructures. Specifically, we confirm a distance gradient of approximately 20\nkpc per degree along a 6 degree extension of the Giant Stellar Stream, with the\nfarthest subfields from M31 lying ~ 120 kpc more distant than the inner-most\nsubfields. Further, we find a metallicity that steadily increases from\n-0.7^{+0.1}_{-0.1} dex to -0.2^{+0.2}_{-0.1} dex along the inner half of the\nstream before steadily dropping to a value of -1.0^{+0.2}_{-0.2} dex at the\nfarthest reaches of our coverage. The RGB width is found to increase rapidly\nfrom 0.4^{+0.1}_{-0.1} dex to 1.1^{+0.2}_{-0.1} dex in the inner portion of the\nstream before plateauing and decreasing marginally in the outer subfields of\nthe stream. In addition, we estimate Stream C to lie at a distance between 794\nand 862 kpc and Stream D between 758 kpc and 868 kpc. We estimate the median\nmetallicity of Stream C to lie in the range -0.7 to -1.6 dex and a metallicity\nof -1.1^{+0.3}_{-0.2} dex for Stream D. RGB widths for the two structures are\nestimated to lie in the range 0.4 to 1.2 dex and 0.3 to 0.7 dex respectively.\nIn total, measurements are obtained for 19 subfields along the Giant Stellar\nStream, 4 along Stream C, 5 along Stream D and 3 general M31 spheroid fields\nfor comparison. We thus provide a higher resolution coverage of the structures\nin these parameters than has previously been available in the literature.", "category": "astro-ph_GA" }, { "text": "The Intracluster Light and its Link with the Dynamical State of the Host\n Group/Cluster: the Role of the Halo Concentration: We investigate on the role of the halo concentration in the formation of the\nintra-cluster light (ICL) in galaxy groups and clusters, as predicted by a\nstate-of-art semi-analytic model of galaxy formation, coupled with a set of\nhigh-resolution dark matter only simulations. The analysis focuses on how the\nfraction of ICL correlates with halo mass, concentration and fraction of\nearly-type galaxies (ETGs) in a large sample of groups and clusters with\n$13.0\\leq \\log M_{halo} \\leq 15.0$. The fraction of ICL follows a normal\ndistribution, a consequence of the stochastic nature of the physical processes\nresponsible for the formation of the diffuse light. The fractional budget of\nICL depends on both halo mass (very weakly) until group scales, and\nconcentration (remarkably). More interestingly, the ICL fraction is higher in\nmore concentrated objects, a result of the stronger tidal forces acting in the\ninnermost regions of the haloes where the concentration is the quantity playing\nthe most relevant role. Our model predictions do not show any dependence\nbetween the ICL and ETGs fractions and so, we instead suggest the concentration\nrather than the mass, as recently claimed, to be the main driver of the ICL\nformation. The diffuse light starts to form in groups via stellar stripping and\nmergers and later assembled in more massive objects. However, the formation and\nassembly keep going on group/cluster scales at lower redshift through the same\nprocesses, mainly via stellar stripping in the vicinity of the central regions\nwhere tidal forces are stronger.", "category": "astro-ph_GA" }, { "text": "Dynamical cloud formation traced by atomic and molecular gas: Context: Atomic and molecular cloud formation is a dynamical process.\nHowever, kinematic signatures of these processes are still observationally\npoorly constrained. Methods: Targeting the cloud-scale environment of the\nprototypical infrared dark cloud G28.3, we employ spectral line imaging\nobservations of the two atomic lines HI and [CI] as well as molecular lines\nobservations in 13CO in the 1--0 and 3--2 transitions. The analysis comprises\ninvestigations of the kinematic properties of the different tracers, estimates\nof the mass flow rates, velocity structure functions, a Histogram of Oriented\nGradients (HOG) study as well as comparisons to simulations. Results: The\ncentral IRDC is embedded in a more diffuse envelope of cold neutral medium\n(CNM) traced by HI self-absorption (HISA) and molecular gas. The spectral line\ndata as well as the HOG and structure function analysis indicate a possible\nkinematic decoupling of the HI from the other gas compounds. Spectral analysis\nand position-velocity diagrams reveal two velocity components that converge at\nthe position of the IRDC. Estimated mass flow rates appear rather constant from\nthe cloud edge toward the center. The velocity structure function analysis is\nconsistent with gas flows being dominated by the formation of hierarchical\nstructures. Conclusions: The observations and analysis are consistent with a\npicture where the IRDC G28 is formed at the center of two converging gas flows.\nWhile the approximately constant mass flow rates are consistent with a\nself-similar, gravitationally driven collapse of the cloud, external\ncompression by, e.g., spiral arm shocks or supernovae explosions cannot be\nexcluded yet. Future investigations should aim at differentiating the origin of\nsuch converging gas flows.", "category": "astro-ph_GA" }, { "text": "PSR J1841-0500: a radio pulsar that mostly is not there: In a search for radio pulsations from the magnetar 1E 1841-045, we have\ndiscovered the unrelated pulsar J1841-0500, with rotation period P=0.9 s and\ncharacteristic age 0.4 Myr. One year after discovery with the Parkes telescope\nat 3 GHz, radio emission ceased from this bright pulsar. After 580 days,\nemission resumed as before. The P-dot during both on states is 250% of the\naverage in the off state. PSR J1841-0500 is a second example of an extremely\nintermittent pulsar, although with a much longer off period and larger ratio of\nspin-down rates than PSR B1931+24. The new pulsar is hugely scattered by the\nISM, with a fitted timescale referenced to 1 GHz of tau_1=2 s. Based on\npolarimetric observations at 5 GHz with the Green Bank Telescope, the intrinsic\npulse profile has not obviously changed between the two on states observed so\nfar, although relatively small variations cannot be excluded. The magnitude of\nits rotation measure is the largest known, RM=-3000 rad/m^2, and with a\ndispersion measure DM=532 pc/cc implies a large electron-weighted average\nmagnetic field strength along the line of sight, 7 microG.", "category": "astro-ph_GA" }, { "text": "The Extension of the Transition Temperature Plasma into the Lower\n Galactic Halo: Column densities for H I, Al III, Si IV, C IV, and O VI toward 109 stars and\n30 extragalactic objects have been assembled to study the extensions of these\nspecies away from the Galactic plane into the Galactic halo. H I and Al III\nmostly trace the warm neutral and warm ionized medium, respectively, while Si\nIV, C IV and O VI trace a combination of warm photoionized and collisionally\nionized plasmas. The much larger object sample compared to previous studies\nallows us to consider and correct for the effects of the sample bias that has\naffected earlier but smaller surveys of the gas distributions. We find Si IV\nand C IV have similar exponential scale heights of 3.2(+1.0, -0.6) and\n3.6(+1.0, -0.8) kpc. The scale height of O VI is marginally smaller with h =\n2.6+/- 0.6 kpc. The transition temperature gas is ~3 times more extended than\nthe warm ionized medium traced by Al III with h = 0.90(+0.62, -0.33) kpc and\n~12 times more extended than the warm neutral medium traced by H I with h =\n0.24 +/- 0.06 kpc. There is a factor of 2 decrease in the dispersion of the log\nof the column density ratios for transition temperature gas for lines of sight\nin the Galactic disk compared to extragalactic lines of sight through the\nentire halo. The observations are compared to the predictions of the various\nmodels for the production of the transition temperature gas in the halo. The\nappendix presents a revision to the electron scale height proposed by Gaensler\net al. (2008) based on electron dispersion measures.", "category": "astro-ph_GA" }, { "text": "MusE GAs FLOw and Wind (MEGAFLOW) VII. A NOEMA pilot program to probe\n molecular gas in galaxies with measured circumgalactic gas flows: We present a pilot program using IRAM's NOrthern Extended Millimeter Array\n(NOEMA) to probe the molecular gas reservoirs of six $z=0.6-1.1$ star-forming\ngalaxies whose circumgalactic medium has been observed in absorption along\nquasar lines-of-sight as part of the MusE GAs FLOw and Wind (MEGAFLOW) survey\nand for which we have estimates of either the accretion or the outflow rate.\nThis program is motivated by testing the quasi equilibrium model and the\ncompaction scenario describing the evolution of galaxies along the main\nsequence of star formation, which imply tight relations between the gas\ncontent, the star formation activity, and the amount of gas flowing in and out.\nWe report individual carbon monoxide CO(4-3), CO(3-2) and dust continuum upper\nlimits, as well as stacked CO detections over the whole sample and the three\ngalaxies identified with outflows. The resulting molecular gas fractions and\ndepletion times are compatible with published scaling relations established\nwithin a mass-selected sample, indicating that galaxies selected through their\nabsorption follow similar relations on average. We further detect the dust\ncontinuum of three of the quasars and a strong emission line in one of them,\nwhich we identify as CO(4-3). Extending the sample to more galaxies and deeper\nobservations will enable to quantify how the molecular gas fraction and\ndepletion time depend on the inflow and ouflow rates.", "category": "astro-ph_GA" }, { "text": "Preliminary results on SiO v=3 J=1-0 maser emission from AGB stars: We present the results of SiO maser observations at 43GHz toward two AGB\nstars using the VLBA. Our preliminary results on the relative positions of the\ndifferent J=1-0 SiO masers (v=1,2 and 3) indicate that the current ideas on SiO\nmaser pumping could be wrong at some fundamental level. A deep revision of the\nSiO pumping models could be necessary.", "category": "astro-ph_GA" }, { "text": "From the Convergence of Filaments to Disk-Outflow Accretion:\n Massive-Star Formation in W33A: Interferometric observations of the W33A massive star-formation region,\nperformed with the Submillimeter Array (SMA) and the Very Large Array (VLA) at\nresolutions from 5 arcsec (0.1 pc) to 0.5 arcsec (0.01 pc) are presented. Our\nthree main findings are: (1) parsec-scale, filamentary structures of cold\nmolecular gas are detected. Two filaments at different velocities intersect in\nthe zone where the star formation is occurring. This is consistent with\ntriggering of the star-formation activity by the convergence of such filaments,\nas predicted by numerical simulations of star formation initiated by converging\nflows. (2) The two dusty cores (MM1 and MM2) at the intersection of the\nfilaments are found to be at different evolutionary stages, and each of them is\nresolved into multiple condensations. MM1 and MM2 have markedly different\ntemperatures, continuum spectral indices, molecular-line spectra, and masses of\nboth stars and gas. (3) The dynamics of the \"hot-core\" MM1 indicates the\npresence of a rotating disk in its center (MM1-Main) around a faint free-free\nsource. The stellar mass is estimated to be approximately 10 Msun. A massive\nmolecular outflow is observed along the rotation axis of the disk.", "category": "astro-ph_GA" }, { "text": "Prospects for detecting CII emission during the Epoch of Reionization: We produce simulations of emission of the atomic CII line in large sky fields\nin order to determine the current prospects for mapping this line during the\nhigh redshift Epoch of Reionization. We estimate the CII line intensity,\nredshift evolution and spatial fluctuations using observational relations\nbetween CII emission and the SFR in a galaxy for the frequency range of 200 GHz\nto 300 GHz. We obtained a frequency averaged intensity of CII emission of ${\\rm\nI_{\\rm CII}=(4 \\pm 2)\\times10^{2}\\, Jy\\, \\rm sr^{-1}}$ in the redshift range\n$z\\, \\sim\\, 5.3\\, -\\, 8.5$. Observations of CII emission in this frequency\nrange will suffer contamination from emission lines at lower redshifts, in\nparticular from the CO rotation lines. For the relevant frequency range we\nestimated the CO contamination (originated in emission from galaxies at $z\\,\n<\\, 2.5$), using simulations, to be ${\\rm I_{\\rm CO} \\approx 10^{3}\\, Jy \\,\nsr^{-1}}$ and independently confirmed the result based in observational\nrelations. We generated maps as a function of angle and frequency using\ndetailed simulations of the CII and CO emission across several redshifts in\norder to properly take into account the observational pipeline and light cone\neffects. In order to reduce the foreground contamination we found that we\nshould mask galaxies below redshifts $\\sim 2.5$ with a CO flux in one of the\nCO(J:2-1) to CO(J:6-5) lines higher than ${\\rm 5\\times 10^{-22}\\, W\\ m^{-2}}$\nor a AB magnitude lower than ${\\rm m_{\\rm K}\\, =\\, 22}$. We estimate that the\nadditional continuum contamination is of the order of ${\\rm 10^{5}\\, Jy\\,\nsr^{-1}}$. It is also considered the possibility of cross correlating\nforeground lines with galaxies in order to probe the intensity of the\nforegrounds.", "category": "astro-ph_GA" }, { "text": "The Lives of Stars: Insights From the TGAS-RAVE-LAMOST Dataset: In this paper we investigate how the chemical and kinematic properties of\nstars vary as a function of age. Using data from a variety of photometric,\nastrometric and spectroscopic surveys, we calculate the ages, phase space\ninformation and orbits for $\\sim$125,000 stars covering a wide range of stellar\nparameters.\n We find indications that the inner regions of the disk reached high levels of\nenrichment early, while the outer regions were more substantially enriched in\nintermediate and recent epochs. We consider these enrichment histories through\ncomparison of the ages of stars, their metallicities, and kinematic properties,\nsuch as their angular momentum in the solar neighborhood (which is a proxy for\norbital radius). We calculate rates at which the velocity dispersions evolve,\ninvestigate the Oort constants for different aged populations (finding a\nslightly negative $\\partial V_{C} / \\partial R$ and $\\partial V_{R} / \\partial\nR$ for all ages, being most negative for the oldest stars), as well as examine\nthe behavior of the velocity vertex deviation angle as a function of age (which\nwe find to fall from $\\sim$15 degrees for the 2 Gyr aged population to $\\sim$6\ndegrees at around 6.5 Gyr of age, after which it remains unchanged). We find\nevidence for stellar churning, and find that the churned stars have a slightly\nyounger age distribution than the rest of the data.", "category": "astro-ph_GA" }, { "text": "An Outer Arm in the Second Galactic Quadrant: Structure: The lack of arm tracers, especially the remote tracers, is one of the most\ndifficult problems preventing us from studying the structure of the Milky Way.\nFortunately, with its high-sensitivity CO survey, the Milky Way Imaging Scroll\nPainting (MWISP) project offers such an opportunity. Since completing about\none-third of its mission, an area of l=[100,150] deg, b=[-3,5] deg has nearly\nbeen covered. The Outer arm of the Milky Way first clearly revealed its shape\nin the second galactic quadrant in the form of molecular gas --- this is the\nfirst time that the Outer arm has been reported in such a large-scale mapping\nof molecular gas. Using the 115 GHz 12CO(1-0) data of MWISP at the LSR velocity\n~= [-100,-60] km s^-1 and in the area mentioned above, we have detected 481\nmolecular clouds in total, and among them 332 (about 69\\%) are newly detected\nand 457 probably belong to the Outer arm. The total mass of the detected Outer\narm clouds is ~ 3.1*10^6 M_sun. Assuming that the spiral arm is a logarithmic\nspiral, the pitch angle is fitted as ~ 13.1 deg. Besides combining both the CO\ndata from MWISP and the 21 cm HI data from the Canadian Galactic Plane Survey\n(CGPS), the gas distribution, warp, and thickness of the Outer arm are also\nstudied.", "category": "astro-ph_GA" }, { "text": "X-ray galaxies selected from HyperLEDA database: We cross-matched the 4XMM-DR10 catalog with the HyperLEDA database and\nobtained the new sample of galaxies that contain X-ray sources. Excluding\nduplicate observations and false matches, we present a total of 7759 galaxies\nwith X-ray sources. In the current work, we present general properties of the\nsample: namely the distribution in equatorial coordinates, radial velocity\ndistribution, morphological type, and X-ray fluxes. The sample includes\nmorphological classification for 5241 galaxies with X-ray emission, almost half\nof which, 42\\%, are elliptical (E, E-S0). Most galaxies in the sample have\nnuclear X-ray emission (6313 or 81\\%), and the remaining 1443 (19\\%) present\nX-ray emission from the host galaxy. This sample can be used for future deep\nstudies of multi wavelengths properties of the galaxies with X-ray emission.", "category": "astro-ph_GA" }, { "text": "Fragmentation in a Primordial Accretion Flow: Under rapid cooling from molecular hydrogen, the accretion disks around\nPopulation III (PopIII) stars are believed to fragment, resulting in multiple\naccreting cores. In this paper, we build a theoretical framework for\ncalculating the optical depth of H$_2$ ro-vibrational line cooling based on the\nvertical structure in these accretion disks. Applying this physically motivated\nprescription for the optical depth, we find that cooling in the inner disk with\n$r \\lesssim 10 {\\rm\\ AU}$ is attenuated significantly as a result of high\nsurface density; $PdV$ heating becomes more efficient than cooling, which\nprevents fragmentation in the inner disk. Despite this, cooling becomes\ndynamically important in the outer disk, favoring fragmentation. We argue that\nmost of the resultant fragments are initially at the outer disk, and that any\nsurviving fragment has to migrate slower than the disk-scale photo-evaporation\nprocess. Since type I migration is fast, migration slows down as a result of\ngap-opening in the disk structure. Two possible processes for gap-opening are\nstudied: (1) through a massive, densely-cored ($\\rho \\gtrsim 10^{-8} {\\rm\\ g\\\ncm^{-3}}$) clump able to radiate away the excess gravitational potential\nenergy, and (2) through a fast-growing central star, with $\\dot{M} \\gtrsim 2\n\\times 10^{-3} \\, M_\\odot {\\rm\\ yr^{-1}}$, whose gravity dominates the\nstar-disk system and favors gap opening.", "category": "astro-ph_GA" }, { "text": "A Deep Near-Infrared [Fe II]+[Si I] Emission Line Image of the Supernova\n Remnant Cassiopeia A: We present a long-exposure (~10 hr) image of the supernova (SN) remnant\nCassiopeia A (Cas A) obtained with the UKIRT 3.8-m telescope using a narrow\nband filter centered at 1.644 um emission. The passband contains [Fe II] 1.644\num and [Si I] 1.645 um lines, and our `deep [Fe II]+[Si I] image' provides an\nunprecedented panoramic view of Cas A, showing both shocked and unshocked SN\nejecta together with shocked circumstellar medium at subarcsec (~0.7 arcsec or\n0.012 pc) resolution. The diffuse emission from the unshocked SN ejecta has a\nform of clumps, filaments, and arcs, and their spatial distribution correlates\nwell with that of the Spitzer [Si II] infrared emission, suggesting that the\nemission is likely due to [Si I] line not [Fe II] line as in shocked material.\nThe structure of the optically-invisible western area of Cas A is clearly seen\nfor the first time. The area is filled with many Quasi-Stationary Flocculi\n(QSFs) and fragments of the disrupted ejecta shell. We suggest that the\nanomalous radio properties in this area could be due to the increased number of\nsuch dense clumps. We identified 309 knots in the deep [Fe II]+[Si I] image and\nclassified them into QSFs and fast-moving knots (FMKs). The total H+He mass of\nQSFs is ~0.23 Msun, implying that the mass fraction of dense clumps in the\nprogenitor's red-supergiant wind is 4--13%. The spatial distribution of QSFs\nsuggests that there had been a highly asymmetric mass loss $10^4$--$10^5$ yr\nbefore the SN explosion. The mass of the [Fe II] line-emitting, shocked dense\nFe ejecta is ~3x$10^{-5}$ Msun. The comparison with the ionic S-line dominated\nHubble Space Telescope WFC3/IR image suggests that the outermost FMKs in the\nsoutheastern area are Fe-rich.", "category": "astro-ph_GA" }, { "text": "Entropy-Conserving Scheme for Modeling Nonthermal Energies in Fluid\n Dynamics Simulations: We compare the performance of energy-based and entropy-conserving schemes for\nmodeling nonthermal energy components, such as unresolved turbulence and cosmic\nrays, using idealized fluid dynamics tests and isolated galaxy simulations.\nWhile both methods are aimed to model advection and adiabatic compression or\nexpansion of different energy components, the energy-based scheme numerically\nsolves the nonconservative equation for the energy density evolution, while the\nentropy-conserving scheme uses a conservative equation for modified entropy.\nUsing the standard shock tube and Zel'dovich pancake tests, we show that the\nenergy-based scheme results in a spurious generation of nonthermal energy on\nshocks, while the entropy-conserving method evolves the energy adiabatically to\nmachine precision. We also show that, in simulations of an isolated $L_\\star$\ngalaxy, switching between the schemes results in $\\approx 20-30\\%$ changes of\nthe total star formation rate and a significant difference in morphology,\nparticularly near the galaxy center. We also outline and test a simple method\nthat can be used in conjunction with the entropy-conserving scheme to model the\ninjection of nonthermal energies on shocks. Finally, we discuss how the\nentropy-conserving scheme can be used to capture the kinetic energy dissipated\nby numerical viscosity into the subgrid turbulent energy implicitly, without\nexplicit source terms that require calibration and can be rather uncertain. Our\nresults indicate that the entropy-conserving scheme is the preferred choice for\nmodeling nonthermal energy components, a conclusion that is equally relevant\nfor Eulerian and moving-mesh fluid dynamics codes.", "category": "astro-ph_GA" }, { "text": "A Catalog of Galaxies in the Direction of the Perseus Cluster: We present a catalog of 5437 morphologically classified sources in the\ndirection of the Perseus galaxy cluster core, among them 496 early-type\nlow-mass galaxy candidates. The catalog is primarily based on V-band imaging\ndata acquired with the William Herschel Telescope, which we used to conduct\nautomated source detection and to derive photometry. We additionally reduced\narchival Subaru multiband imaging data in order to measure aperture colors and\nto perform a morphological classification, benefiting from 0.5 arcsec seeing\nconditions in the r-band data. Based on morphological and color properties, we\nextracted a sample of early-type low-mass galaxy candidates with absolute\nV-band magnitudes in the range of -10 to -20 mag. In the color-magnitude\ndiagram the galaxies are located where the red sequence for early-type cluster\ngalaxies is expected, and they lie on the literature relation between absolute\nmagnitude and S\\'{e}rsic index. We classified the early-type dwarf candidates\ninto nucleated and nonnucleated galaxies. For the faint candidates, we found a\ntrend of increasing nucleation fraction toward brighter luminosity or higher\nsurface brightness, similar to what is observed in other nearby galaxy\nclusters. We morphologically classified the remaining sources as likely\nbackground elliptical galaxies, late-type galaxies, edge-on disk galaxies, and\nlikely merging systems and discussed the expected contamination fraction\nthrough non-early-type cluster galaxies in the magnitude-size surface\nbrightness parameter space. Our catalog reaches its 50 per cent completeness\nlimit at an absolute V-band luminosity of -12 mag and a V-band surface\nbrightness of 26 mag arcsec$^{-2}$. This makes it to the largest and deepest\ncatalog with coherent coverage compared to previous imaging studies of the\nPerseus cluster.", "category": "astro-ph_GA" }, { "text": "Turbulent magnetic reconnection in 2D and 3D: Magnetic field embedded in a perfectly conducting fluid preserves its\ntopology for all time. Although ionized astrophysical objects, like stars and\ngalactic disks, are almost perfectly conducting, they show indications of\nchanges in topology, `magnetic reconnection', on dynamical time scales.\nReconnection can be observed directly in the solar corona, but can also be\ninferred from the existence of large scale dynamo activity inside stellar\ninteriors. Solar flares and gamma ray busts are usually associated with\nmagnetic reconnection. Previous work has concentrated on showing how\nreconnection can be rapid in plasmas with very small collision rates. Here we\npresent numerical evidence, based on three dimensional simulations, that\nreconnection in a turbulent fluid occurs at a speed comparable to the rms\nvelocity of the turbulence, regardless of the value of the resistivity. In\nparticular, this is true for turbulent pressures much weaker than the magnetic\nfield pressure so that the magnetic field lines are only slightly bent by the\nturbulence. These results are consistent with the proposal by Lazarian and\nVishniac (1999) that reconnection is controlled by the stochastic diffusion of\nmagnetic field lines, which produces a broad outflow of plasma from the\nreconnection zone. This work implies that reconnection in a turbulent fluid\ntypically takes place in approximately a single eddy turnover time, with broad\nimplications for dynamo activity and particle acceleration throughout the\nuniverse. In contrast, the reconnection in 2D configurations in the presence of\nturbulence depends on resistivity, i.e. is slow.", "category": "astro-ph_GA" }, { "text": "High abundance ratio of $^{13}$CO to C$^{18}$O toward photon-dominated\n regions in the Orion-A giant molecular cloud: Aims. We derive physical properties such as the optical depths and the column\ndensities of $^{13}$CO and C$^{18}$O to investigate the relationship between\nthe far ultraviolet (FUV) radiation and the abundance ratios between $^{13}$CO\nand C$^{18}$O.\n Method. We have carried out wide-field (0.4 deg$^2$) observations with an\nangular resolution of 25.8 arcsec ($\\sim$ 0.05 pc) in $^{13}$CO ($J$=1--0) and\nC$^{18}$O ($J$=1--0) toward the Orion-A giant molecular cloud using the\nNobeyama 45 m telescope in the on-the-fly mode.\n Results. Overall distributions and velocity structures of the $^{13}$CO and\nC$^{18}$O emissions are similar to those of the $^{12}$CO ($J$=1--0) emission.\nThe optical depths of the $^{13}$CO and C18O emission lines are estimated to be\n0.05 $<$ $\\tau_{\\rm ^{13}CO}$ $<$ 1.54 and 0.01 $<$ $\\tau_{\\rm C^{18}O}$ $<$\n0.18, respectively. The column densities of the $^{13}$CO and C$^{18}$O\nemission lines are estimated to be 0.2 $\\times$ 10$^{16}$ $<$ $N_{\\rm ^{13}CO}$\n$<$ 3.7 $\\times$ 10$^{17}$ cm$^{-2}$ and 0.4 $\\times$ 10$^{15}$ $<$ $N_{\\rm\nC^{18}O}$ $<$ 3.5 $\\times$ 10$^{16}$ cm$^{-2}$, respectively. The abundance\nratios between $^{13}$CO and C$^{18}$O, $X_{\\rm ^{13}CO}$/$X_{\\rm C^{18}O}$,\nare found to be 5.7 - 33.0. The mean value of $X_{\\rm ^{13}CO}$/$X_{\\rm\nC^{18}O}$ in the nearly edge-on photon-dominated regions is found to be 16.47\n$\\pm$ 0.10, which is a third larger than that the solar system value of 5.5.\nThe mean value of $X_{\\rm ^{13}CO}$/$X_{\\rm C^{18}O}$ in the other regions is\nfound to be 12.29 $\\pm$ 0.02. The difference of the abundance ratio is most\nlikely due to the selective FUV photodissociation of C$^{18}$O.", "category": "astro-ph_GA" }, { "text": "The optical variability of SDSS quasars from multi-epoch spectroscopy.\n II. color variation: We investigated the optical/ultraviolet (UV) color variations for a sample of\n2169 quasars based on multi-epoch spectroscopy in the Sloan Digital Sky Survey\n(SDSS) data release seven (DR7) and data release nine (DR9). To correct the\nsystematic difference between DR7 and DR9 due to the different instrumental\nsetup, we produced a correction spectrum by using a sample of F-stars observed\nboth in DR7 and DR9. The correction spectrum was then applied to quasars when\ncomparing the spectra of DR7 with DR9. In each object, the color variation was\nexplored by comparing the spectral index of the continuum power-law fit on the\nbrightest spectrum with the faintest one, and also by the shape of their\ndifference spectrum. In 1876 quasars with consistent color variations from two\nmethods, we found that most sources (1755, $\\sim 94\\%$) show\nbluer-when-brighter (BWB) trend, and the redder-when-brighter (RWB) trend is\nonly detected in 121 objects ($\\sim 6\\%$). The common BWB trend is supported by\nthe bluer composite spectrum constructed from bright spectra than that from\nfaint spectra, and also by the blue composite difference spectrum. The\ncorrection spectrum is proved to be highly reliable by comparing the composite\nspectrum from corrected DR9 and original DR7 spectra. Assuming that the\noptical/UV variability is triggered by fluctuations, RWB trend can likely be\nexplained if the fluctuations occur firstly at outer disk region, and the inner\ndisk region has not fully responded yet when the fluctuation being propagated\ninward. In contrast, the common BWB trend implies that the fluctuations are\nlikely more often happening firstly in inner disk region.", "category": "astro-ph_GA" }, { "text": "JCMT Mapping of CO(3-2) in the Circumnuclear Region of M31: We present a survey of CO(3-2) molecular line emission in the circumnuclear\nregion of M31 with the James Clerk Maxwell Telescope (JCMT), aiming to explore\nthe physical conditions of the molecular gas. Significant CO(3-2) lines are\ndetected primarily along the so-called nuclear spiral, out to a projected\ngalactocentric radius of 700 pc at a linear resolution of ~50 pc. We find that\nthe velocity field of the molecular gas is in rough agreement with that of the\nionized gas previously determined from optical observations. Utilizing existed\nCO(2-1) and CO(1-0) measurements in selected regions of the nuclear spiral, we\nderive characteristic intensity ratios of CO(3-2)/CO(2-1) and CO(3-2)/CO(1-0),\nwhich are both close to unity and are significantly higher than the typical\nintensity ratios in the disk. Such line ratios suggest high kinetic\ntemperatures of the gas, which might be due to strong interstellar shocks\nprevalent in the circumnuclear region.", "category": "astro-ph_GA" }, { "text": "Seeds of Life in Space SOLIS. IX. Chemical segregation of $\\rm SO_2$ and\n SO toward the low-mass protostellar shocked region of L1157: We present observations of SO and $\\rm SO_2$ lines toward the shocked regions\nalong the L1157 chemically rich outflow, taken in the context of the Seeds Of\nLife In Space IRAM-NOrthern Extended Millimeter Array Large Program, and\nsupported by data from Submillimeter Array and IRAM-30 m telescope at 1.1--3.6\nmm wavelengths. We simultaneously analyze, for the first time, all of the\nbrightest shocks in the blueshifted lobe, namely, B0, B1, and B2. We found the\nfollowing. (1) SO and $\\rm SO_2$ may trace different gas, given that the\nlarge(-scale) velocity gradient analysis indicates for $\\rm SO_2$ a volume\ndensity ($\\rm 10^5\\text{--}10^6\\,cm^{-3}$) denser than that of the gas emitting\nin SO by a factor up to an order of magnitude. (2) Investigating the 0.1 pc\nscale field of view, we note a tentative gradient along the path of the\nprecessing jet. More specifically, $\\rm \\chi({SO/SO_2})$ decreases from the\nB0-B1 shocks to the older B2. (3) At a linear resolution of 500--1400 au, a\ntentative spatial displacement between the two emitting molecules is detected,\nwith the SO peak closer (with respect to $\\rm SO_2$) to the position where the\nrecent jet is impinging on the B1 cavity wall. Our astrochemical modeling shows\nthat the SO and $\\rm SO_2$ abundances evolve on timescales less than about 1000\nyears. Furthermore, the modeling requires high abundances ($2\\times10^{-6}$) of\nboth $\\rm H_2S/H$ and S/H injected in the gas phase due to the shock\noccurrence, so pre-frozen OCS only is not enough to reproduce our new\nobservations.", "category": "astro-ph_GA" }, { "text": "Tips learned from panchromatic modeling of AGNs: I will review the tips learned from panchromatic modeling of active galactic\nnuclei (AGNs), based on our recent work to study the relationship between AGN\nand star formation (SF). Several AGN SED models are compared, and signifficant\nAGN contribution is found in the IR luminosities and corresponding star\nformation rate (SFR). I will review the AGN-SF relation and how different\nparameters and sample selections affect the observed correlation. I will then\nreport on the constant ratio discovered between the SFR and the black hole mass\naccretion rate (BHAR), and their implications on the gas supply and galaxy\nformation history of these systems. Caveats and important questions to answer\nare summarized at the end.", "category": "astro-ph_GA" }, { "text": "Detailed chemical abundances of distant RR Lyrae stars in the Virgo\n Stellar Stream: We present the first detailed chemical abundances for distant RR Lyrae stars\nmembers of the Virgo Stellar Stream (VSS), derived from X-Shooter\nmedium-resolution spectra. Sixteen elements from carbon to barium have been\nmeasured in six VSS RR Lyrae stars, sampling all main nucleosynthetic channels.\nFor the first time we will be able to compare in detail the chemical evolution\nof the VSS progenitor with those of Local Group dwarf spheroidal galaxies (LG\ndSph) as well as the one of the smooth halo.", "category": "astro-ph_GA" }, { "text": "Testing the universality of the IMF with Bayesian statistics: young\n clusters: The universality of the stellar initial mass function (IMF) is tested using\nBayesian statistics with a sample of eight young Galactic stellar clusters (IC\n348, ONC, NGC 2024, NGC 6611, NGC 2264, $\\rho$ Ophiuchi, Chameleon I, and\nTaurus). We infer the posterior probability distribution function (pPDF) of the\nIMF parameters when the likelihood function is described by a tapered power law\nfunction, a lognormal distribution at low masses coupled to a power law at\nhigher masses, and a multi-component power law function. The inter-cluster\ncomparison of the pPDFs of the IMF parameters for each likelihood function\nshows that these distributions do not overlap within the $1\\sigma$ uncertainty\nlevel. Furthermore, the most probable values of the IMF parameters for most of\nthe clusters deviate substantially from their values for the Galactic field\nstellar IMF. We also quantify the effects of taking into account the\ncompleteness correction as well as the uncertainties on the measured masses.\nThe inclusion of the former affects the inferred pPDFs of the slope of the IMF\nat the low mass end while considering the latter affects the pPDFs of the slope\nof the IMF in the intermediate- to high mass regime. As variations are observed\nin all of the IMF parameters at once and for each of the considered likelihood\nfunctions, even for completeness corrected samples, we argue that the observed\nvariations are real and significant, at least for the sample of eight clusters\nconsidered in this work. The results presented here clearly show that the IMF\nis not universal.", "category": "astro-ph_GA" }, { "text": "The Milky Way's Shell Structure Reveals the Time of a Radial Collision: We identify shell structures in the Milky Way for the first time. We find 2\nshells in the Virgo Overdensity (VOD) region and 2 shells in the Hercules\nAquila Cloud (HAC) region using Sloan Digital Sky Survey, Gaia, and LAMOST\ndata. These shell stars are a subset of the substructure previously identified\nas the Virgo Radial Merger (VRM). Timing arguments for these shells indicate\nthat their progenitor dwarf galaxy passed through the Galactic center 2.7 +/-\n0.2 Gyr ago. Based on the time of collision, it is also possible that the VRM\nis related to the phenomenon that created phase-space spirals in the vertical\nmotion of the disk and/or the Splash, and could have caused a burst of star\nformation in the inner disk.\n We analyze phase mixing in a collection of radial merger N-body simulations,\nand find that shell structure similar to that observed in Milky Way data\ndisappears by 5 Gyr after collision with the Galactic center. The method used\nto calculate the merger time of the VRM was able to reliably recover the\ncorrect merger times for these simulations.\n Previous work supports the idea that the VRM and the Gaia\nSausage/Gaia-Enceladus Merger are the same. However, the Gaia Sausage is widely\nbelieved to be 8--11 Gyr old. The disparate ages could be reconciled if the\nlarger age is associated with an infall time when the progenitor crossed the\nvirial radius; we do not constrain the time at which the progenitor became\nbound to the Milky Way. Alternatively, the Gaia Sausage could be younger than\npreviously thought.", "category": "astro-ph_GA" }, { "text": "The relationship between IGM Lyman-alpha opacity and galaxy density near\n the end of reionization: Observed scatter in the Lyman-alpha opacity of quasar sightlines at $z<6$ has\nmotivated measurements of the correlation between Ly$\\alpha$ opacity and galaxy\ndensity, as models that predict this scatter make strong and sometimes opposite\npredictions for how they should be related. Our previous work associated two\nhighly opaque Ly$\\alpha$ troughs at $z\\sim5.7$ with a deficit of Lyman-$\\alpha$\nemitting galaxies (LAEs). In this work, we survey two of the most highly\ntransmissive lines of sight at this redshift, towards the $z=6.02$ quasar SDSS\nJ1306+0356 and the $z=6.17$ quasar PSO J359-06. We find that both fields are\nunderdense in LAEs within 10 $h^{-1}$ Mpc of the quasar sightline, somewhat\nless extensive than underdensities associated with Ly$\\alpha$ troughs. We\ncombine our observations with three additional fields from the literature, and\nfind that while fields with extreme opacities are generally underdense,\nmoderate opacities span a wider density range. The results at high opacities\nare consistent with models that invoke UV background fluctuations and/or late\nreionization to explain the observed scatter in IGM Ly$\\alpha$ opacities. There\nis tension at low opacities, however, as the models tend to associate lower IGM\nLy$\\alpha$ opacities with higher densities. Although the number of fields\nsurveyed is still small, the low-opacity results may support a scenario in\nwhich the ionizing background in low-density regions increases more rapidly\nthan some models suggest after becoming ionized. Elevated gas temperatures from\nrecent reionization may also be making these regions more transparent.", "category": "astro-ph_GA" }, { "text": "Aromatic cycles are widespread in cold clouds: We report the detection of large hydrocarbon cycles toward several cold dense\nclouds. We observed four sources (L1495B, Lupus-1A, L483, and L1527) in the Q\nband (31-50 GHz) using the Yebes 40m radiotelescope. Using the line stack\ntechnique, we find statistically significant evidence of benzonitrile\n(C$_6$H$_5$CN) in L1495B, Lupus-1A, and L483 at levels of 31.8$\\,\\sigma$,\n15.0$\\,\\sigma$, and 17.2$\\,\\sigma$, respectively, while there is no hint of\nC$_6$H$_5$CN in the fourth source, L1527. The column densities derived are in\nthe range (1.7-3.8)$\\,\\times\\,10^{11}$ cm$^{-2}$, which is somewhat below the\nvalue derived toward the cold dense cloud TMC-1. When we simultaneously analyze\nall the benzonitrile abundances derived toward cold clouds in this study and in\nthe literature, a clear trend emerges in that the higher the abundance of\nHC$_7$N, the more abundant C$_6$H$_5$CN is. This indicates that aromatic cycles\nare especially favored in those interstellar clouds where long carbon chains\nare abundant, which suggests that the chemical processes that are responsible\nfor the formation of linear carbon chains are also behind the synthesis of\naromatic rings. We also searched for cycles other than benzonitrile, and found\nevidence of indene (C$_9$H$_8$), cyclopentadiene (C$_5$H$_6$), and 1-cyano\ncyclopentadiene (1-C$_5$H$_5$CN) at levels of 9.3$\\,\\sigma$, 7.5$\\,\\sigma$, and\n8.4$\\,\\sigma$, respectively, toward L1495B, which shows the strongest signal\nfrom C$_6$H$_5$CN. The relative abundances between the various cycles detected\nin L1495B are consistent -- within a factor of three -- with those previously\nfound in TMC-1. It is therefore likely that not only C$_6$H$_5$CN but also\nother large aromatic cycles are abundant in clouds rich in carbon chains.", "category": "astro-ph_GA" }, { "text": "Gas kinematics, morphology, and angular momentum in the FIRE simulations: We study the z=0 gas kinematics, morphology, and angular momentum content of\nisolated galaxies in a suite of cosmological zoom-in simulations from the FIRE\nproject spanning $M_{\\star}=10^{6-11}M_{\\odot}$. Gas becomes increasingly\nrotationally supported with increasing galaxy mass. In the lowest-mass galaxies\n($M_{\\star}<10^{8}M_{\\odot}$), gas fails to form a morphological disk and is\nprimarily dispersion and pressure supported. At intermediate masses\n($M_{\\star}=10^{8-10}M_{\\odot}$), galaxies display a wide range of gas\nkinematics and morphologies, from thin, rotating disks, to irregular spheroids\nwith negligible net rotation. All the high-mass\n($M_{\\star}=10^{10-11}M_{\\odot}$) galaxies form rotationally supported gas\ndisks. Many of the halos whose galaxies fail to form disks harbor high angular\nmomentum gas in their circumgalactic medium. The ratio of the specific angular\nmomentum of gas in the central galaxy to that of the dark-matter halo increases\nsignificantly with galaxy mass, from $j_{\\rm gas}/j_{\\rm DM}\\sim0.1$ at\n$M_{\\star}=10^{6-7}M_{\\odot}$ to $j_{\\rm gas}/j_{\\rm DM}\\sim2$ at\n$M_{\\star}=10^{10-11}M_{\\odot}$. The reduced rotational support in the\nlowest-mass galaxies owes to (a) stellar feedback and the UV background\nsuppressing the accretion of high-angular momentum gas at late times, and (b)\nstellar feedback driving large non-circular gas motions. We broadly reproduce\nthe observed scaling relations between galaxy mass, gas rotation velocity,\nsize, and angular momentum, but may somewhat underpredict the incidence of\ndisky, high-angular momentum galaxies at the lowest observed masses\n($M_{\\star}=(10^{6}-2\\times10^{7})M_{\\odot}$). In our simulations, stars are\nuniformly less rotationally supported than gas. The common assumption that\nstars follow the same rotation curve as gas thus substantially overestimates\ngalaxies' stellar angular momentum, particularly at low masses.", "category": "astro-ph_GA" }, { "text": "The Initial Conditions of Clustered Star Formation III. The Deuterium\n Fractionation of the Ophiuchus B2 Core: We present N2D+ 3-2 (IRAM) and H2D+ 1_11 - 1_10 and N2H+ 4-3 (JCMT) maps of\nthe small cluster-forming Ophiuchus B2 core in the nearby Ophiuchus molecular\ncloud. In conjunction with previously published N2H+ 1-0 observations, the N2D+\ndata reveal the deuterium fractionation in the high density gas across Oph B2.\nThe average deuterium fractionation R_D = N(N2D+)/N(N2H+) ~ 0.03 over Oph B2,\nwith several small scale R_D peaks and a maximum R_D = 0.1. The mean R_D is\nconsistent with previous results in isolated starless and protostellar cores.\nThe column density distributions of both H2D+ and N2D+ show no correlation with\ntotal H2 column density. We find, however, an anticorrelation in deuterium\nfractionation with proximity to the embedded protostars in Oph B2 to distances\n>= 0.04 pc. Destruction mechanisms for deuterated molecules require gas\ntemperatures greater than those previously determined through NH3 observations\nof Oph B2 to proceed. We present temperatures calculated for the dense core gas\nthrough the equating of non-thermal line widths for molecules (i.e., N2D+ and\nH2D+) expected to trace the same core regions, but the observed complex line\nstructures in B2 preclude finding a reasonable result in many locations. This\nmethod may, however, work well in isolated cores with less complicated velocity\nstructures. Finally, we use R_D and the H2D+ column density across Oph B2 to\nset a lower limit on the ionization fraction across the core, finding a mean\nx_e, lim >= few x 10^{-8}. Our results show that care must be taken when using\ndeuterated species as a probe of the physical conditions of dense gas in\nstar-forming regions.", "category": "astro-ph_GA" }, { "text": "Cepheid Kinematics and the Galactic Warp: The space velocities of 200 long-period ($P>5$ days) classical Cepheids with\nknown proper motions and line-of-sight velocities whose distances were\nestimated from the period--luminosity relation have been analyzed. The linear\nOgorodnikov-Milne model has been applied, with the Galactic rotation having\nbeen excluded from the observed velocities in advance. Two significant\ngradients have been found in the Cepheid velocities,\n $\\partial W/\\partial Y=-2.1\\pm0.7$ km s$^{-1}$ kpc$^{-1}$ and\n $\\partial V/\\partial Z= 27\\pm10 $ km s$^{-1}$ kpc$^{-1}$.\n In such a case, the angular velocity of solid-body rotation around the\nGalactic $X$ axis directed to the Galactic center is $-15\\pm5$ km s$^{-1}$\nkpc$^{-1}$.", "category": "astro-ph_GA" }, { "text": "The interaction of a large-scale nuclear wind with the high velocity HII\n region G0.17+0.15: We investigate the nature of a Galactic center source, G0.17+0.15, lying\nalong the northern extension of the Radio Arc near l~0.2deg. G0.17+0.15 is an\nHII region located toward the eastern edge of the radio bubble, embedded within\nthe highly polarized Galactic center eastern Lobe where a number of radio\nfilaments appear to cross through the HII region. We report the detection of\nhydrogen and helium recombination lines with a radial velocity exceeding 140\nkm/s based on GBT and VLA observations. The morphology of G0.17+0.15, aided by\nkinematics, and spectral index characteristics, suggests the presence of an\nexternal pressure dragging and shredding the ionized gas. We argue that this\nionized cloud is interacting with a bundle of radio filaments and is entrained\nby the ram pressure of the radio bubble, which itself is thought to be produced\nby cosmic-ray driven outflows at the Galactic center. In this interpretation,\nthe gas streamers on the western side of G0.17+0.15 are stripped, accelerated\nfrom 0 to deltav~35 km/s, over a time scale roughly 8x10^4 years, implying that\nablating ram pressure is ~700 eV cm-3, comparable to the ~10^3 eV cm-3\ncosmic-ray driven wind pressure in the Galactic center region.", "category": "astro-ph_GA" }, { "text": "NGC 3628-UCD1: A possible $\u03c9$ Cen Analog Embedded in a Stellar\n Stream: Using Subaru/Suprime-Cam wide-field imaging and both Keck/ESI and LBT/MODS\nspectroscopy, we identify and characterize a compact star cluster, which we\nterm NGC 3628-UCD1, embedded in a stellar stream around the spiral galaxy NGC\n3628. The size and luminosity of UCD1 are similar to $\\omega$ Cen, the most\nluminous Milky Way globular cluster, which has long been suspected to be the\nstripped remnant of an accreted dwarf galaxy. The object has a magnitude of\n$i=19.3$ mag (${\\rm L}_{\\rm i}=1.4\\times10^{6}~{\\rm L}_{\\odot}$). UCD1 is\nmarginally resolved in our ground-based imaging, with a half-light radius of\n$\\sim10$ pc. We measure an integrated brightness for the stellar stream of\n$i=13.1$ mag, with $(g-i)=1.0$. This would correspond to an accreted dwarf\ngalaxy with an approximate luminosity of ${\\rm L}_i\\sim4.1\\times10^{8}~{\\rm\nL}_{\\odot}$. Spectral analysis reveals that UCD1 has an age of $6.6$ Gyr ,\n$[\\rm{Z}/\\rm{H}]=-0.75$, an $[{\\alpha}/\\rm{Fe}]=-0.10$. We propose that UCD1 is\nan example of an $\\omega$ Cen-like star cluster possibly forming from the\nnucleus of an infalling dwarf galaxy, demonstrating that at least some of the\nmassive star cluster population may be created through tidal stripping.", "category": "astro-ph_GA" }, { "text": "Persistent Non-Gaussian Structure in the Image of Sagittarius A* at 86\n GHz: Observations of the Galactic Center supermassive black hole Sagittarius A*\n(Sgr A*) with very long baseline interferometry (VLBI) are affected by\ninterstellar scattering along our line of sight. At long radio observing\nwavelengths ($\\gtrsim1\\,$cm), the scattering heavily dominates image\nmorphology. At 3.5 mm (86 GHz), the intrinsic source structure is no longer\nsub-dominant to scattering, and thus the intrinsic emission from Sgr A* is\nresolvable with the Global Millimeter VLBI Array (GMVA). Long-baseline\ndetections to the phased Atacama Large Millimeter/submillimeter Array (ALMA) in\n2017 provided new constraints on the intrinsic and scattering properties of Sgr\nA*, but the stochastic nature of the scattering requires multiple observing\nepochs to reliably estimate its statistical properties. We present new\nobservations with the GMVA+ALMA, taken in 2018, which confirm non-Gaussian\nstructure in the scattered image seen in 2017. In particular, the ALMA-GBT\nbaseline shows more flux density than expected for an anistropic Gaussian\nmodel, providing a tight constraint on the source size and an upper limit on\nthe dissipation scale of interstellar turbulence. We find an intrinsic source\nextent along the minor axis of $\\sim100\\,\\mu$as both via extrapolation of\nlonger wavelength scattering constraints and direct modeling of the 3.5 mm\nobservations. Simultaneously fitting for the scattering parameters, we find an\nat-most modestly asymmetrical (major-to-minor axis ratio of $1.5\\pm 0.2$)\nintrinsic source morphology for Sgr A*.", "category": "astro-ph_GA" }, { "text": "A Magnified Compact Galaxy at Redshift 9.51 with Strong Nebular Emission\n Lines: Ultraviolet light from early galaxies is thought to have ionized gas in the\nintergalactic medium. However, there are few observational constraints on this\nepoch because of the faintness of those galaxies and the redshift of their\noptical light into the infrared. We report the observation, in JWST imaging, of\na distant galaxy that is magnified by gravitational lensing. JWST spectroscopy\nof the galaxy, at rest-frame optical wavelengths, detects strong nebular\nemission lines that are attributable to oxygen and hydrogen. The measured\nredshift is z = 9.51 +- 0.01, corresponding to 510 million years after the Big\nBang. The galaxy has a radius of 16.2+4.6-7.2 parsecs, which is substantially\nmore compact than galaxies with equivalent luminosity at z = 6 to 8, leading to\na high star formation rate surface density.", "category": "astro-ph_GA" }, { "text": "An HST/COS survey of molecular hydrogen in DLAs & sub-DLAs at z < 1:\n Molecular fraction and excitation temperature: We present the results of a systematic search for molecular hydrogen (H2) in\nlow redshift ($ 0.05 \\lesssim z \\lesssim 0.7$) DLAs and sub-DLAs with $N(HI)\n\\gtrsim 10^{19.0}$ cm$^{-2}$, in the archival HST/COS spectra. Our core sample\nis comprised of 27 systems with a median $\\log N(HI) = 19.6$. On the average,\nour survey is sensitive down to $\\log N(H2) = 14.4$ corresponding to a\nmolecular fraction of $\\log f_{H2} = -4.9$ at the median $N(HI)$. H2 is\ndetected in 10 cases (3/5 DLAs and 7/22 sub-DLAs) down to this $f_{H2}$ limit.\nThe H2 detection rate of $50^{+25}_{-12}$ percent seen in our sample, is a\nfactor of $\\gtrsim 2$ higher than that of the high-$z$ sample of Noterdaeme et\nal. (2008), for systems with $N(H2) > 10^{14.4}$ cm$^{-2}$. In spite of having\n$N(HI)$ values typically lower by a factor of 10, low-$z$ H2 systems show\nmolecular fractions ($\\log f_{H2}=-1.93\\pm0.63$) that are comparable to the\nhigh-$z$ sample. The rotational excitation temperatures ($T_{01} = 133\\pm55$\nK), as measured in our low-$z$ sample, are typically consistent with high-$z$\nmeasurements. Simple photoionization models favour a radiation field much\nweaker than the mean Galactic ISM field for a particle density in the range 10\n- 100 cm$^{-3}$. The impact parameters of the identified host-galaxy candidates\nare in the range $10 \\lesssim \\rho$ (kpc) $\\lesssim 80$. We, therefore,\nconjecture that the low-$z$ H2 bearing gas is not related to star-forming disks\nbut stems from self-shielded, tidally stripped or ejected disk-material in the\nextended halo.", "category": "astro-ph_GA" }, { "text": "Globular Cluster Intrinsic Iron Abundance Spreads: II. Protocluster\n Metallicities and the Age-Metallicity Relations of Milky Way Progenitors: Intrinsic iron abundance spreads in globular clusters, although usually\nsmall, are very common, and are signatures of self enrichment: some stars\nwithin the cluster have been enriched by supernova ejecta from other stars\nwithin the same cluster. We use the Bailin (2018) self enrichment model to\npredict the relationship between properties of the protocluster -- its mass and\nthe metallicity of the protocluster gas cloud -- and the final observable\nproperties today -- its current metallicity and the internal iron abundance\nspread. We apply this model to an updated catalog of Milky Way globular\nclusters where the initial mass and/or the iron abundance spread is known to\nreconstruct their initial metallicities. We find that with the exception of the\nknown anomalous bulge cluster Terzan 5 and three clusters strongly suspected to\nbe nuclear star clusters from stripped dwarf galaxies, the model provides a\ngood lens for understanding their iron spreads and initial metallicities. We\nthen use these initial metallicities to construct age-metallicity relations for\nkinematically-identified major accretion events in the Milky Way's history. We\nfind that using the initial metallicity instead of the current metallicity does\nnot alter the overall picture of the Milky Way's history, since the difference\nis usually small, but does provide information that can help distinguish which\naccretion event some individual globular clusters with ambiguous kinematics\nshould be associated with, and points to potential complexity within the\naccretion events themselves.", "category": "astro-ph_GA" }, { "text": "The Lifecycle of Clusters in Galaxies: We review many of the basic properties of star cluster systems, and focus in\nparticular on how they relate to their host galaxy properties and ambient\nenvironment. The cluster mass and luminosity functions are well approximated by\npower-laws of the form $Ndm \\propto M^{\\alpha}dm$, with $\\alpha\\sim-2$ over\nmost of the observable range. However, there is now clear evidence that both\nbecome steeper at high masses/luminosities, with the value of the downward turn\ndependent on environment. The host galaxy properties also appear to affect the\ncluster formation efficiency ($\\Gamma$ - i.e., the fraction of stars that form\nin bound clusters), with higher star-formation rate density galaxies having\nhigher $\\Gamma$ values. Within individual galaxies, there is evidence for\n$\\Gamma$ to vary by a factor of 3-4, likely following the molecular gas surface\ndensity, in agreement with recent predictions. Finally, we discuss cluster\ndisruption and its effect on the observed properties of a population, focussing\non the age distribution of clusters. We briefly discuss the expectations of\ntheoretical and numerical studies, and also the observed distributions in a\nnumber of galaxies. Most observational studies now find agreement with\ntheoretical expectations, namely nearly a constant cluster age distribution for\nages up to ~100 Myr (i.e. little disruption), and a drastic steepening above\nthis value caused by a combination of cluster disruption and incompleteness.\nRapid cluster disruption for clusters with ages < 100 Myr is ruled out for most\ngalaxies.", "category": "astro-ph_GA" }, { "text": "Bar-driven evolution and quenching of spiral galaxies in cosmological\n simulations: We analyse the output of the hi-res cosmological zoom-in simulation ErisBH to\nstudy self-consistently the formation of a strong stellar bar in a Milky\nWay-type galaxy and its effect on the galactic structure, on the central gas\ndistribution and on star formation. The simulation includes radiative cooling,\nstar formation, SN feedback and a central massive black hole which is\nundergoing gas accretion and is heating the surroundings via thermal AGN\nfeedback. A large central region in the ErisBH disk becomes bar-unstable after\nz~1.4, but a clear bar-like structure starts to grow significantly only after\nz~0.4, possibly triggered by the interaction with a massive satellite. At z~0.1\nthe bar reaches its maximum radial extent of l~2.2 kpc. As the bar grows, it\nbecomes prone to buckling instability, which we quantify based on the\nanisotropy of the stellar velocity dispersion. The actual buckling event is\nobservable at z~0.1, resulting in the formation of a boxy-peanut bulge clearly\ndiscernible in the edge-on view of the galaxy at z=0. The bar in ErisBH does\nnot dissolve during the formation of the bulge but remains strongly\nnon-axisymmetric down to the resolution limit of ~100 pc at z=0. During its\nearly growth, the bar exerts a strong torque on the gas within its extent and\ndrives gas inflows that enhance the nuclear star formation on sub-kpc scales.\nLater on the infalling gas is nearly all consumed into stars and, to a lesser\nextent, accreted onto the central black hole, leaving behind a gas-depleted\nregion within the central ~2 kpc. Observations would more likely identify a\nprominent, large-scale bar at the stage when the galactic central region has\nalready been quenched. Bar-driven quenching may play an important role in\ndisk-dominated galaxies at all redshift. [Abridged]", "category": "astro-ph_GA" }, { "text": "Stirring up an embedded star cluster with a moving gas filament: We perform simulations to test the effects of a moving gas filament on a\nyoung star cluster (i.e. the \"Slingshot\" Model). We model Orion Nebula\nCluster-like clusters as Plummer spheres and the Integral Shaped Filament gas\nas a cylindrical potential. We observe that in a static filament, an initially\nspherical cluster evolves naturally into an elongated distribution of stars.\nFor sinusoidal moving filaments, we observe different remnants, and classify\nthem into 4 categories.%: 3 different objects and one transition object.\n\"Healthy\" clusters, where almost all the stars stay inside the filament and the\ncluster; \"destroyed\" clusters are the opposite case, with almost no particles\nin the filament or near the centre of density of the clusters; \"ejected\"\nclusters, where a large fraction of stars are close to the centre of density of\nthe stars , but almost none of them in the filament; and \"transition\" clusters,\nwhere roughly the same number of particles is ejected from the cluster and from\nthe filament. An {{Orion Nebula Cluster-like}} cluster might stay inside the\nfilament or be ejected, but it will not be destroyed.", "category": "astro-ph_GA" }, { "text": "Possible routes for the Formation of Prebiotic Molecules in the\n Horsehead Nebula: This article presents the results of a study concerning interstellar\nmolecules which are useful for the bookkeeping of the organic content of the\nuniverse and for providing a glimpse into prebiotic conditions on Earth and in\nother environments in the universe. We explored production channels for\nastrobiological relevant nitrogen-bearing cyclic molecules (N-heterocycles), e.\ng. pyrrole and pyridine. The present simulations demonstrate how the\nexploration of a few possible routes of production of N-heterocycles resulted\nin significant abundances for these species. One particularly efficient class\nof channels for the production of N-heterocycles incorporates polycyclic\naromatic hydrocarbons (PAHs) as catalysts. Thereby, an exploration of a variety\nof production paths should reveal more species to be target of astrophysical\nobservations.", "category": "astro-ph_GA" }, { "text": "Medium-resolution Spectroscopy of Red Giant Branch Stars in $\u03c9$\n Centauri: We present [Fe/H] and [Ca/Fe] of $\\sim600$ red giant branch (RGB) members of\nthe globular cluster $\\omega$ Centauri. We collect medium-resolution\n($R\\sim2000$) spectra using the Blanco 4 m telescope at the Cerro Tololo\nInter-American Observatory equipped with Hydra, the fiber-fed multi-object\nspectrograph. We demonstrate that blending of stellar light in optical fibers\nseverely limits the accuracy of spectroscopic parameters in the crowded central\nregion of the cluster. When photometric temperatures are taken in the\nspectroscopic analysis, our kinematically selected cluster members, excluding\nthose that are strongly affected by flux from neighboring stars, include\nrelatively fewer stars at intermediate metallicity ([Fe/H]$\\sim-1.5$) than seen\nin the previous high-resolution survey for brighter giants in Johnson &\nPilachowski. As opposed to the trend of increasing [Ca/Fe] with [Fe/H] found by\nthose authors, our [Ca/Fe] estimates, based on Ca II H & K measurements, show\nessentially the same mean [Ca/Fe] for most of the metal-poor and\nmetal-intermediate populations in this cluster, suggesting that mass- or\nmetallicity-dependent SN II yields may not be necessary in their proposed\nchemical evolution scenario. Metal-rich cluster members in our sample show a\nlarge spread in [Ca/Fe], and do not exhibit a clear bimodal distribution in\n[Ca/Fe]. We also do not find convincing evidence for a radial metallicity\ngradient among RGB stars in $\\omega$ Centauri.", "category": "astro-ph_GA" }, { "text": "Exemplary Merging Clusters: Weak-lensing and X-ray Analysis of the\n Double Radio Relic Merging Galaxy Clusters MACS 1752.0+4440 and ZWCL\n 1856.8+6616: The investigation of merging galaxy clusters that exhibit radio relics is\nstrengthening our understanding of the formation and evolution of galaxy\nclusters, the nature of dark matter, the intracluster medium, and astrophysical\nparticle acceleration. Each merging cluster provides only a single view of the\ncluster formation process and the variety of merging clusters is vast. Clusters\nhosting double radio relics are rare and extremely important because they allow\ntight constraints on the merger scenario. We present a weak-lensing and X-ray\nanalysis of MACSJ1752.0+4440 ($z$=0.365) and ZWCL1856.8+6616 ($z$=0.304), two\ndouble radio relic clusters. Our weak-lensing mass estimates show that each\ncluster is a major merger with approximately 1:1 mass ratio. The total mass of\nMACSJ1752.0+4440 (ZWCL1856.8+6616) is $M_{200}=14.7^{+3.8}_{-3.3}\\times10^{14}\\\n$M$_\\odot$ ($M_{200}=2.4^{+0.9}_{-0.7}\\times10^{14}\\ $M$_\\odot$). We find that\nthese two clusters have comparable features in their weak-lensing and gas\ndistributions, even though the systems have vastly different total masses. From\nthe likeness of the X-ray morphologies and the remarkable symmetry of the radio\nrelics, we propose that both systems underwent nearly head-on collisions.\nHowever, revelations from the hot-gas features and our multiwavelength data\nanalysis suggest that ZWCL1856.8+6618 is likely at a later merger phase than\nMACSJ1752.0+4440. We postulate that the SW radio relic in MACSJ1752.0+4440 is a\nresult of particle re-acceleration.", "category": "astro-ph_GA" }, { "text": "Low-frequency radio spectra of submillimetre galaxies in the Lockman\n Hole: We investigate the radio properties of a sample of 53 sources selected at 850\n$\\mu$m from the SCUBA-2 Cosmology Legacy Survey using new deep, low-frequency\nradio imaging of the Lockman Hole field from the Low Frequency Array. Combining\nthese data with additional radio observations from the GMRT and the JVLA, we\nfind a variety of radio spectral shapes and luminosities within our sample\ndespite their similarly bright submillimetre flux densities. We characterise\ntheir spectral shapes in terms of multi-band radio spectral indices. Finding\nstrong spectral flattening at low frequencies in ~20% of sources, we\ninvestigate the differences between sources with extremely flat low-frequency\nspectra and those with `normal' radio spectral indices. As there are no other\nstatistically significant differences between the two subgroups of our sample\nas split by the radio spectral index, we suggest that any differences are\nundetectable in galaxy-averaged properties that we can observe with our\nunresolved images, and likely relate to galaxy properties that we cannot\nresolve, on scales $\\lesssim$ 1 kpc. We attribute the observed spectral\nflattening in the radio to free-free absorption, proposing that those sources\nwith significant low-frequency spectral flattening have a clumpy distribution\nof star-forming gas. We estimate an average spatial extent of absorbing\nmaterial of at most several hundred parsecs to produce the levels of absorption\nobserved in the radio spectra. This estimate is consistent with the\nhighest-resolution observations of submillimetre galaxies in the literature,\nwhich find examples of non-uniform dust distributions on scales of ~100 pc,\nwith evidence for clumps and knots in the interstellar medium. Additionally, we\nfind two bright (> 6 mJy) submm sources undetected at all other wavelengths. We\nspeculate that these objects may be very high redshift sources, likely residing\nat z > 4.", "category": "astro-ph_GA" }, { "text": "Zooming in on the circumgalactic medium: resolving small-scale gas\n structure with the GIBLE cosmological simulations: We introduce Project GIBLE (Gas Is Better resoLved around galaxiEs), a suite\nof cosmological zoom-in simulations where gas in the circumgalactic medium\n(CGM) is preferentially simulated at ultra-high numerical resolution. Our\ninitial sample consists of eight galaxies, all selected as Milky Way-like\ngalaxies at $z=0$ from the TNG50 simulation. Using the same galaxy formation\nmodel as IllustrisTNG, and the moving-mesh code AREPO, we re-simulate each of\nthese eight galaxies maintaining a resolution equivalent to TNG50-2\n($m_{\\rm{gas}}$ $\\sim$ $8 \\times 10^5 {\\rm M}_{\\odot}$). However, we use our\nsuper-Lagrangian refinement scheme to more finely resolve gas in the CGM around\nthese galaxies. Our highest resolution runs achieve 512 times better mass\nresolution ($\\sim$ $10^3 {\\rm M}_{\\odot}$). This corresponds to a median\nspatial resolution of $\\sim$ $75$ pc at $0.15~R_{\\rm{200,c}}$, which coarsens\nwith increasing distance to $\\sim$ $700$ pc at the virial radius. We make\npredictions for the covering fractions of several observational tracers of\nmulti-phase CGM gas: HI, MgII, CIV and OVII. We then study the impact of\nimproved resolution on small scale structure. While the abundance of the\nsmallest cold, dense gas clouds continues to increase with improving\nresolution, the number of massive clouds is well converged. We conclude by\nquantifying small scale structure with the velocity structure function and the\nauto-correlation function of the density field, assessing their resolution\ndependence. The GIBLE cosmological hydrodynamical simulations enable us to\nimprove resolution in a computationally efficient manner, thereby achieving\nnumerical convergence of a subset of key CGM gas properties and observables.", "category": "astro-ph_GA" }, { "text": "Unfolding the Laws of Star Formation: The Density Distribution of\n Molecular Clouds: The formation of stars shapes the structure and evolution of entire galaxies.\nThe rate and efficiency of this process are affected substantially by the\ndensity structure of the individual molecular clouds in which stars form. The\nmost fundamental measure of this structure is the probability density function\nof volume densities (rho-PDF), which determines the star formation rates\npredicted with analytical models. This function has remained unconstrained by\nobservations. We have developed an approach to quantify rho-PDFs and establish\ntheir relation to star formation. The rho-PDFs instigate a density threshold of\nstar formation and allow us to quantify the star formation efficiency above it.\nThe rho-PDFs provide new constraints for star formation theories and correctly\npredict several key properties of the star-forming interstellar medium.", "category": "astro-ph_GA" }, { "text": "The Effects of Stellar Population and Gas Covering Fraction on the\n Emergent Lyman Alpha Emission of High-Redshift Galaxies: We perform joint modeling of the composite rest-frame far-UV (FUV) and\noptical spectra of redshift 1.85~ 1.5.", "category": "astro-ph_GA" }, { "text": "High resolution elemental abundance analysis of the Hyades Supercluster: The existence of a kinematically defined moving group of stars centred at U =\n-40, V = -17 km/s referred to as the Hyades Supercluster, has been suggested as\nthe debris of an originally large star forming event, with its core being the\npresent day Hyades open cluster. Using high-resolution UVES spectra, we present\nelemental abundances for a range of alpha, Fe-peak and neutron-capture elements\nfor 26 proposed supercluster stars. Our results show that the sample stars\ndisplay a heterogeneous abundance distribution, with a clump around [Fe/H] =\n+0.15. We also calculate stellar radial velocities and U,V,W space velocities.\nEnforcing a strict chemical and kinematical membership criteria, we find 4\nsupercluster stars share the Hyades open cluster abundances and kinematics,\nwhile many of the remaining stars fit the disc field kinematics and abundance\nrange. We discuss our findings in the context of the Hyades supercluster being\na dispersed star-forming remnant, a stellar stream of purely dynamical origin\nor a result of several processes.", "category": "astro-ph_GA" }, { "text": "Gaseous-phase metallicities and stellar populations in the centres of\n barred galaxies: Numerical simulations predict that bars represent a very important agent for\ntriggering gas inflows, which in turn could lead to central star formation.\nBars thus are thought to contribute to the formation of the bulge.This changes\nboth, the gaseous-phase and stellar-phase metallicities in the centres of\ngalaxies. With the aim of quantifying the importance of this process we present\na comparative study of the gaseous-phase and stellar-phase metallicities in the\ncentres of members of a sample of barred and unbarred galaxies from SDSS. We do\nnot find a significant difference in the metallicity (neither gaseous nor\nstellar) of barred and unbarred galaxies, but we find different trends in the\nmetallicities of early- and late- type galaxies, with larger differences in the\nmetallicity in the early-type subsample. Our results contradict some previous\nresearch in this field, but we find a possible origin of the discrepancies\nbetween previous works and our results.", "category": "astro-ph_GA" }, { "text": "Enhanced tidal disruption rates from massive black hole binaries: \"Hard\" massive black hole (MBH) binaries embedded in steep stellar cusps can\nshrink via three-body slingshot interactions. We show that this process will\ninevitably be accompanied by a burst of stellar tidal disruptions, at a rate\nthat can be several orders of magnitude larger than that appropriate for a\nsingle MBH. Our numerical scattering experiments reveal that: 1) a significant\nfraction of stars initially bound to the primary hole are scattered into its\ntidal disruption loss cone by gravitational interactions with the secondary\nhole, an enhancement effect that is more pronounced for very unequal-mass\nbinaries; 2) about 25% (40%) of all strongly interacting stars are tidally\ndisrupted by a MBH binary of mass ratio q=1/81 (q=1/243) and eccentricity 0.1;\nand 3) two mechanisms dominate the fueling of the tidal disruption loss cone, a\nKozai non-resonant interaction that causes the secular evolution of the stellar\nangular momentum in the field of the binary, and the effect of close encounters\nwith the secondary hole that change the stellar orbital parameters in a chaotic\nway. For a hard MBH binary of 10^7 solar masses and mass ratio 0.01, embedded\nin an isothermal stellar cusp of velocity dispersion sigma*=100 km/s, the tidal\ndisruption rate can be as large as 1/yr. This is 4 orders of magnitude higher\nthan estimated for a single MBH fed by two-body relaxation. When applied to the\ncase of a putative intermediate-mass black hole inspiraling onto Sgr A*, our\nresults predict tidal disruption rates ~0.05-0.1/yr.", "category": "astro-ph_GA" }, { "text": "A highly magnified gravitationally lensed red quasar at z = 2.5 with\n significant flux anomaly: Uncovering a missing population: We present the discovery of a gravitationally lensed dust-reddened QSO at\n$z=2.517$ discovered in a survey for red QSOs by infrared selection.\n$Hubble~Space~Telescope$ imaging in the WFC3/IR F160W and F125W filters reveals\na quadruply lensed system in a cusp configuration. We find that compared to the\ncentral image of the cusp, the nearby, brightest image is anomalous by a factor\nof $\\sim7-11$. Although the source is extremely bright in the mid-infrared, a\nmagnification by a factor of $\\sim50-120$ places an upper limit of 1.35 mJy on\nthe intrinsic mid-infrared brightness, well below the $WISE~W4$ detection limit\nof 6 mJy. We find that this QSO is moderately reddened, with $E(B-V)=0.7$ and\nthat $\\sim1\\%$ of the intrinsic spectrum is leaked back into the line of sight\nresulting in an upturn in its UV spectrum. We conclude that the QSO's reddening\nis intrinsic and not due to the lens. Consistent with previous red quasar\nsamples, this source exhibits outflows in its spectrum as well as morphological\nproperties suggestive of it being in a merger-driven transitional phase.\nDepending on how $L_{\\rm bol}$ is computed, the quasar's accretion rate may be\nas high as $0.26~L_{\\rm Edd}$. We detect two Lyman limit systems, at $z=2.102$\nand $z=2.431$, with absorption by metal lines likely at small impact parameter\nto the QSO, and a putative lens redshift of $z=0.599$. Given the rarity of quad\nlenses, the discovery of this source allows detailed study of a less luminous,\nmore typical infrared-selected quasar at high redshift.", "category": "astro-ph_GA" }, { "text": "The Green Bank Ammonia Survey (GAS): First Results of NH3 mapping the\n Gould Belt: We present an overview of the first data release (DR1) and first-look science\nfrom the Green Bank Ammonia Survey (GAS). GAS is a Large Program at the Green\nBank Telescope to map all Gould Belt star-forming regions with $A_V \\gtrsim 7$\nmag visible from the northern hemisphere in emission from NH$_3$ and other key\nmolecular tracers. This first release includes the data for four regions in\nGould Belt clouds: B18 in Taurus, NGC 1333 in Perseus, L1688 in Ophiuchus, and\nOrion A North in Orion. We compare the NH$_3$ emission to dust continuum\nemission from Herschel, and find that the two tracers correspond closely.\nNH$_3$ is present in over 60\\% of lines-of-sight with $A_V \\gtrsim 7$ mag in\nthree of the four DR1 regions, in agreement with expectations from previous\nobservations. The sole exception is B18, where NH$_3$ is detected toward ~ 40\\%\nof lines-of-sight with $A_V \\gtrsim 7$ mag. Moreover, we find that the NH$_3$\nemission is generally extended beyond the typical 0.1 pc length scales of dense\ncores. We produce maps of the gas kinematics, temperature, and NH$_3$ column\ndensities through forward modeling of the hyperfine structure of the NH$_3$\n(1,1) and (2,2) lines. We show that the NH$_3$ velocity dispersion,\n${\\sigma}_v$, and gas kinetic temperature, $T_K$, vary systematically between\nthe regions included in this release, with an increase in both the mean value\nand spread of ${\\sigma}_v$ and $T_K$ with increasing star formation activity.\nThe data presented in this paper are publicly available.", "category": "astro-ph_GA" }, { "text": "Solving the puzzle of discrepant quasar variability on monthly\n time-scales implied by SDSS and CRTS data sets: We present an improved photometric error analysis for the 7,100 CRTS\n(Catalina Real-Time Transient Survey) optical light curves for quasars from the\nSDSS (Sloan Digital Sky Survey) Stripe 82 catalogue. The SDSS imaging survey\nhas provided a time-resolved photometric data set which greatly improved our\nunderstanding of the quasar optical continuum variability: Data for monthly and\nlonger time-scales are consistent with a damped random walk (DRW). Recently,\nnewer data obtained by CRTS provided puzzling evidence for enhanced\nvariability, compared to SDSS results, on monthly time-scales. Quantitatively,\nSDSS results predict about 0.06 mag root-mean-square (rms) variability for\nmonthly time-scales, while CRTS data show about a factor of 2 larger rms, for\nspectroscopically confirmed SDSS quasars. Our analysis has successfully\nresolved this discrepancy as due to slightly underestimated photometric\nuncertainties from the CRTS image processing pipelines. As a result, the\ncorrection for observational noise is too small and the implied quasar\nvariability is too large. The CRTS photometric error correction factors,\nderived from detailed analysis of non-variable SDSS standard stars that were\nre-observed by CRTS, are about 20-30%, and result in reconciling quasar\nvariability behaviour implied by the CRTS data with earlier SDSS results. An\nadditional analysis based on independent light curve data for the same objects\nobtained by the Palomar Transient Factory provides further support for this\nconclusion. In summary, the quasar variability constraints on weekly and\nmonthly time-scales from SDSS, CRTS and PTF surveys are mutually compatible, as\nwell as consistent with DRW model.", "category": "astro-ph_GA" }, { "text": "Understanding Galaxy Mergers & AGN Feedback with UVIT: Simulations expect an enhanced star-formation and active galactic nuclei\n(AGN) activity during galaxy mergers, which can lead to formation of\nbinary/dual AGN. AGN feedback can enhance or suppress star-formation. We have\ncarried out a pilot study of a sample of 10 dual nuclei galaxies with\nAstroSat's Ultraviolet Imaging Telescope (UVIT). Here, we present the initial\nresults for two sample galaxies (Mrk 739, ESO 509) and deep multi-wavelength\ndata of another galaxy (Mrk 212). UVIT observations have revealed signatures of\npositive AGN feedback in Mrk 739 and Mrk 212, and negative feedback in ESO 509.\nDeeper UVIT observations have recently been approved; these will provide better\nconstraints on star-formation as well as AGN feedback in these systems.", "category": "astro-ph_GA" }, { "text": "Investigating 16 Open Clusters in the Kepler/K2-Gaia DR3 field. I.\n Membership, Binary, and Rotation: Using data from the Gaia Data Release 3 (Gaia DR3) and Kepler/K2, we present\na catalog of 16 open clusters with ages ranging from 4 to 4000 Myr, which\nprovides detailed information on membership, binary systems, and rotation. We\nassess the memberships in 5D phase space, and estimate the basic parameters of\neach cluster. Among the 20,160 members, there are 4,381 stars identified as\nbinary candidates and 49 stars as blue straggler stars. The fraction of\nbinaries vary in each cluster, and the range between 9% to 44%. We obtain the\nrotation periods of 5,467 members, of which 4,304 are determined in this work.\nTo establish a benchmark for the rotation-age-color relation, we construct\ncolor-period diagrams. We find that the rotational features of binaries are\nsimilar to that of single stars, while features for binaries are more scattered\nin the rotation period. Moreover, the morphology of the color-period\nrelationship is already established for Upper Scorpius at the age of 19 Myr,\nand some stars of varying spectral types (i.e. FG-, K-, and M-type) show\ndifferent spin-down rates after the age of ~110 Myr. By incorporating the\neffects of stalled spin-down into our analysis, we develop an empirical\nrotation-age-color relation, which is valid with ages between 700 - 4000 Myr\nand colors corresponding to a range of 0.5 < (G_BP-G_RP)0 < 2.5 mag.", "category": "astro-ph_GA" }, { "text": "Searching for shocks in high-mass starless clump candidates: In order to search for shocks in the very early stage of star formation, we\nperformed single-point surveys of SiO J=1-0, 2-1 and 3-2 lines and the H$_2$CO\n$2_{12}-1_{11}$ line toward a sample of 100 high-mass starless clump candidates\n(SCCs) by using the Korean VLBI Network (KVN) 21-m radio telescopes. The\ndetection rates of the SiO J=1-0, 2-1, 3-2 lines and the H$_2$CO line are\n$31.0\\%$, $31.0\\%$, $19.5\\%$ and $93.0\\%$, respectively. Shocks seem to be\ncommon in this stage of massive star formation. The widths of the observed SiO\nlines (full width at zero power (FWZP)) range from 3.4 to 55.1 km s$^{-1}$. A\nsignificant fraction ($\\sim29\\%$) of the detected SiO spectra have broad line\nwidths (FWZP $>20~km~s^{-1}$), which are very likely associated with fast\nshocks driven by protostellar outflows. This result suggests that about one\nthird of the SiO-detected SCCs are not really starless but protostellar. On the\nother hand, about 40$\\%$ of the detected SiO spectra show narrow line widths\n(FWZP<10 $km~s^{-1}$) probably associated with low-velocity shocks which are\nnot necessarily protostellar in origin. The estimated SiO column densities are\nmostly $0.31-4.32\\times10^{12}~cm^{-2}$. Comparing the SiO column densities\nderived from SiO J=1-0 and 2-1 lines, we suggest that the SiO molecules in the\nSCCs may be in the non-LTE condition. The SiO abundances to H$_2$ are usually\n$0.20-10.92\\times10^{-10}$.", "category": "astro-ph_GA" }, { "text": "Properties of the Circumgalactic Medium in Cosmic Ray-Dominated Galaxy\n Halos: We investigate the impact of cosmic rays (CRs) on the circumgalactic medium\n(CGM) in FIRE-2 simulations, for ultra-faint dwarf through Milky Way (MW)-mass\nhalos hosting star-forming (SF) galaxies. Our CR treatment includes injection\nby supernovae, anisotropic streaming and diffusion along magnetic field lines,\ncollisional and streaming losses, with constant parallel diffusivity\n$\\kappa\\sim3\\times10^{29}\\,\\mathrm{cm^2\\ s^{-1}}$ chosen to match $\\gamma$-ray\nobservations. With this, CRs become more important at larger halo masses and\nlower redshifts, and dominate the pressure in the CGM in MW-mass halos at\n$z\\lesssim 1-2$. The gas in these \"CR-dominated\" halos differs significantly\nfrom runs without CRs: the gas is primarily cool (a few $\\sim10^{4}\\,$K), and\nthe cool phase is volume-filling and has a thermal pressure below that needed\nfor virial or local thermal pressure balance. Ionization of the \"low\" and \"mid\"\nions in this diffuse cool gas is dominated by photo-ionization, with O VI\ncolumns $\\gtrsim 10^{14.5}\\,\\mathrm{cm^{-2}}$ at distances $\\gtrsim\n150\\,\\mathrm{kpc}$. CR and thermal gas pressure are locally anti-correlated,\nmaintaining total pressure balance, and the CGM gas density profile is\ndetermined by the balance of CR pressure gradients and gravity. Neglecting CRs,\nthe same halos are primarily warm/hot ($T\\gtrsim 10^{5}\\,$K) with thermal\npressure balancing gravity, collisional ionization dominates, O VI columns are\nlower and Ne VIII higher, and the cool phase is confined to dense filaments in\nlocal thermal pressure equilibrium with the hot phase.", "category": "astro-ph_GA" }, { "text": "Preliminary results on SiO v=3 J=1-0 maser emission from AGB stars: We present the results of SiO maser observations at 43GHz toward two AGB\nstars using the VLBA. Our preliminary results on the relative positions of the\ndifferent J=1-0 SiO masers (v=1,2 and 3) indicate that the current ideas on SiO\nmaser pumping could be wrong at some fundamental level. A deep revision of the\nSiO pumping models could be necessary.", "category": "astro-ph_GA" }, { "text": "Lyman-$\u03b1$ emission from a WISE-selected optically faint powerful\n radio galaxy M151304.72-252439.7 at $z$ = 3.132: We report the detection of a large ($\\sim90$ kpc) and luminous\n$\\mathrm{Ly\\alpha}$ nebula [$L\\mathrm{_{Ly\\alpha}}$ = $(6.80\\pm0.08)\\times\n10^{44}$] $\\rm{\\,erg\\,s^{-1}}$ around an optically faint (r$>23$ mag) radio\ngalaxy M1513-2524 at $z\\mathrm{_{em}}$=3.132. The double-lobed radio emission\nhas an extent of 184 kpc, but the radio core, i.e., emission associated with\nthe active galactic nucleus (AGN) itself, is barely detected. This object was\nfound as part of our survey to identify high-$z$ quasars based on Wide-field\nInfrared Survey Explorer (WISE) colors. The optical spectrum has revealed\n$\\mathrm{Ly\\alpha}$, NV, CIV and HeII emission lines with a very weak\ncontinuum. Based on long-slit spectroscopy and narrow band imaging centered on\nthe $\\mathrm{Ly\\alpha}$ emission, we identify two spatial components: a\n\"compact component\" with high velocity dispersion ($\\sim\n1500$$\\rm{\\,km\\,s^{-1}}$) seen in all three lines, and an \"extended component\",\nhaving low velocity dispersion (i.e., 700-1000$\\rm{\\,km\\,s^{-1}}$). The\nemission line ratios are consistent with the compact component being in\nphotoionization equilibrium with an AGN. We also detect spatially extended\nassociated $\\mathrm{Ly\\alpha}$ absorption, which is blue-shifted within\n250-400$\\rm{\\,km\\,s^{-1}}$ of the $\\mathrm{Ly\\alpha}$ peak. The probability of\n$\\mathrm{Ly\\alpha}$ absorption detection in such large radio sources is found\nto be low ($\\sim$10%) in the literature. M1513-2524 belongs to the top few\npercent of the population in terms of $\\mathrm{Ly\\alpha}$ and radio\nluminosities. Deep integral field spectroscopy is essential for probing this\ninteresting source and its surroundings in more detail.", "category": "astro-ph_GA" }, { "text": "A Characteristic Mass Scale in the Mass-Metallicity Relation of Galaxies: We study the shape of the gas-phase mass-metallicity relation (MZR) of a\ncombined sample of present-day dwarf and high-mass star-forming galaxies using\nIZI, a Bayesian formalism for measuring chemical abundances presented in Blanc\net al. 2015. We observe a characteristic stellar mass scale at $M_* \\simeq\n10^{9.5}$M$_{\\odot}$, above which the ISM undergoes a sharp increase in its\nlevel of chemical enrichment. In the $10^{6}-10^{9.5}$M$_{\\odot}$ range the MZR\nfollows a shallow power-law ($Z\\propto M^{\\alpha}_*$) with slope\n$\\alpha=0.14\\pm0.08$. At approaching $M_* \\simeq 10^{9.5}$M$_{\\odot}$ the MZR\nsteepens significantly, showing a slope of $\\alpha=0.37\\pm0.08$ in the\n$10^{9.5}-10^{10.5}$M$_{\\odot}$ range, and a flattening towards a constant\nmetallicity at higher stellar masses. This behavior is qualitatively different\nfrom results in the literature that show a single power-law MZR towards the low\nmass end. We thoroughly explore systematic uncertainties in our measurement,\nand show that the shape of the MZR is not induced by sample selection, aperture\neffects, a changing N/O abundance, the adopted methodology used to construct\nthe MZR, secondary dependencies on star formation activity, nor diffuse ionized\ngas (DIG) contamination, but rather on differences in the method used to\nmeasure abundances. High resolution hydrodynamical simulations can\nqualitatively reproduce our result, and suggest a transition in the ability of\ngalaxies to retain their metals for stellar masses above this threshold. The\nMZR characteristic mass scale also coincides with a transition in the scale\nheight and clumpiness of cold gas disks, and a typical gas fraction below which\nthe efficiency of star formation feedback for driving outflows is expected to\ndecrease sharply.", "category": "astro-ph_GA" }, { "text": "The creation and persistence of a misaligned gas disc in a simulated\n early-type galaxy: Massive early-type galaxies commonly have gas discs which are kinematically\nmisaligned with the stellar component. These discs feel a torque from the stars\nand the angular momentum vectors are expected to align quickly. We present\nresults on the evolution of a misaligned gas disc in a cosmological simulation\nof a massive early-type galaxy from the Feedback In Realistic Environments\nproject. This galaxy experiences a merger which, together with a strong\ngalactic wind, removes most of the original gas disc. The galaxy subsequently\nreforms a gas disc through accretion of cold gas, but it is initially 120\ndegrees misaligned with the stellar rotation axis. This misalignment persists\nfor about 2 Gyr before the gas-star misalignment angle drops below 20 degrees.\nThe time it takes for the gaseous and stellar components to align is much\nlonger than previously thought, because the gas disc is accreting a significant\namount of mass for about 1.5 Gyr after the merger, during which the angular\nmomentum change induced by accreted gas dominates over that induced by stellar\ntorques. Once the gas accretion rate has decreased sufficiently, the gas disc\ndecouples from the surrounding halo gas and realigns with the stellar component\nin about 6 dynamical times. During the late evolution of the misaligned gas\ndisc, the centre aligns faster than the outskirts, resulting in a warped disc.\nWe discuss the observational consequences of the long survival of our\nmisaligned gas disc and how our results can be used to calibrate merger rate\nestimates from observed gas misalignments.", "category": "astro-ph_GA" }, { "text": "Milky Way's Thick and Thin disk: Is there distinct thick disk?: This article is based on our discussion session on Milky Way models at the\n592 WE-Heraeus Seminar, Reconstructing the Milky Way's History: Spectroscopic\nSurveys, Asteroseismology and Chemodynamical models. The discussion focused on\nthe following question: \"Are there distinct thick and thin disks?\". The answer\nto this question depends on the definition one adopts for thin and thick disks.\nThe participants of this discussion converged to the idea that there are at\nleast two different types of disks in the Milky Way. However, there are still\nimportant open questions on how to best define these two types of disks\n(chemically, kinematically, geometrically or by age?). The question of what is\nthe origin of the distinct disks remains open. The future Galactic surveys\nwhich are highlighted in this conference should help us answering these\nquestions. The almost one-hour debate involving researchers in the field\nrepresenting different modelling approaches (Galactic models such as TRILEGAL,\nBesancon and Galaxia, chemical evolution models, extended distribution\nfunctions method, chemodynamics in the cosmological context, and\nself-consistent cosmological simulations) illustrated how important is to have\nall these parallel approaches. All approaches have their advantages and\nshortcomings (also discussed), and different approaches are useful to address\nspecific points that might help us answering the more general question above.", "category": "astro-ph_GA" }, { "text": "Galaxy to cloud scales: Simulations from the scales of isolated galaxies to clouds have been\ninstrumental in informing us about molecular cloud formation and evolution.\nSimulations are able to investigate the roles of gravity, feedback, turbulence,\nheating and cooling, and magnetic fields on the physics of the interstellar\nmedium, and star formation. Compared to simulations of individual clouds,\ngalactic and sub-galactic scale simulations can include larger galactic scale\nprocesses such as spiral arms, bars, and larger supernovae bubbles, which may\ninfluence star formation. Simulations show cloud properties and lifetimes in\nbroad agreement with observations. Gravity and spiral arms are required to\nproduce more massive GMCs, whilst stellar feedback, likely photoionisation,\nleads to relatively short cloud lifetimes. On larger scales, supernovae may be\nmore dominant in driving the structure and dynamics, but photoionisation may\nstill have a role. In terms of the dynamics, feedback is probably the main\ndriver of velocity dispersions, but large scale processes such as gravity and\nspiral arms may also be significant. Magnetic fields are generally found to\ndecrease star formation on galaxy or cloud scales, and simulations are ongoing\nto study whether clouds are sub or supercritical on different scales in galaxy\nscale simulations. Simulations on subgalactic scales, or zoom in simulations,\nallow better resolution of feedback processes, filamentary structure within\nclouds, and the study of stellar clusters.", "category": "astro-ph_GA" }, { "text": "A population of galaxy-scale jets discovered using LOFAR: The effects of feedback from high luminosity radio-loud AGN have been\nextensively discussed in the literature, but feedback from low-luminosity\nradio-loud AGN is less well understood. The advent of high sensitivity, high\nangular resolution, large field of view telescopes such as LOFAR is now\nallowing wide-area studies of such faint sources for the first time. Using the\nfirst data release of the LOFAR Two Metre Sky Survey (LoTSS) we report on our\ndiscovery of a population of 195 radio galaxies with 150 MHz luminosities\nbetween $3\\times10^{22}$ and $1.5\\times10^{25}\\text{ W Hz}^{-1}$ and total\nradio emission no larger than 80 kpc. These objects, which we term galaxy-scale\njets (GSJ), are small enough to be directly influencing the evolution of the\nhost on galaxy scales. We report upon the typical host properties of our\nsample, finding that 9 per cent are hosted by spirals with the remainder being\nhosted by elliptical galaxies. Two of the spiral-hosted GSJ are highly unusual\nwith low radio luminosities and FRII-like morphology. The host properties of\nour GSJ show that they are ordinary AGN observed at a stage in their life\nshortly after the radio emission has expanded beyond the central regions of the\nhost. Based on our estimates, we find that about half of our GSJ have internal\nradio lobe energy within an order of magnitude of the ISM energy so that, even\nignoring any possible shocks, GSJ are energetically capable of affecting the\nevolution of the host. The current sample of GSJ will grow in size with future\nreleases of LoTSS and can also form the basis for further studies of feedback\nfrom low-luminosity radio sources.", "category": "astro-ph_GA" }, { "text": "The VVV Open Cluster Project. Near-infrared sequences of NGC6067,\n NGC6259, NGC4815, Pismis18, Trumpler23, and Trumpler20: Open clusters are central elements of our understanding of the Galactic disk\nevolution, as an accurate determination of their parameters leads to an\nunbiased picture of our Galaxy's structure. Extending the analysis towards\nfainter magnitudes in cluster sequences has a significant impact on the derived\nfundamental parameters, such as extinction and total mass. We perform a\nhomogeneous analysis of six open stellar clusters in the Galactic disk using\nkinematic and photometric information from the Gaia DR2 and VVV surveys:\nNGC6067, NGC6259, NGC4815, Pismis18, Trumpler23, and Trumpler20. We implement\ntwo coarse-to-fine characterization methods: first, we employ Gaussian mixture\nmodels to tag fields around each open cluster in the proper motion space, and\nthen we apply an unsupervised machine learning method to make the membership\nassignment to each cluster. For the studied clusters, with ages in the\n$\\sim$120-1900 Myr range, we report an increase of $\\sim$45 % new member\ncandidates on average in our sample. The data-driven selection approach of\ncluster members makes our catalog a valuable resource for testing stellar\nevolutionary models and for assessing the cluster low-to-intermediate mass\npopulations. This study is the first of a series intended to homogeneously\nreveal open cluster near-infrared sequences.", "category": "astro-ph_GA" }, { "text": "Massive Galaxies Impede Massive Outflows: A set of 66 3D hydrodynamical simulations explores how galactic stellar mass\naffects three-phase, starburst-driven outflows. Simulated velocities are\ncompared to two basic analytic models: with (Johnson \\& Axford 1971) and\nwithout (Chevalier \\& Clegg 1985) a gravitational potential. For stellar mass\n$<10^{10}$ solar masses, simulated velocities match those of both analytical\nmodels and are unaffected by the potential; above they reduce significantly as\nexpected from the analytic model with gravity. Gravity also affects total\noutflow mass and each of the three phases differently. Outflow mass in the hot,\nwarm, and cold phases each scale with stellar mass as $\\log M_*=$ -0.25, -0.97,\nand -1.70, respectively. Thus, the commonly used Chevalier \\& Clegg analytic\nmodel should be modified to include gravity when applied to higher mass\ngalaxies. In particular, using M82 as the canonical galaxy to interpret\nhydrodynamical simulations of starburst-driven outflows from higher mass\ngalaxies will underestimate the retarding effect of gravity. Using the analytic\nmodel of Johnson \\& Axford with realistic thermalization efficiency and mass\nloading I find that only galaxy masses that are less than $\\sim10^{11.5}$ solar\nmasses can outflow.", "category": "astro-ph_GA" }, { "text": "Structural parameters and possible association of the Ultra-Faint Dwarfs\n Pegasus III and Pisces II from deep Hubble Space Telescope photometry: We present deep Hubble Space Telescope (HST) photometry of the ultra-faint\ndwarf (UFD) galaxies Pegasus III (Peg III) and Pisces II (Psc II), two of the\nmost distant satellites in the halo of the Milky Way (MW). We measure the\nstructure of both galaxies, derive mass-to-light ratios with newly determined\nabsolute magnitudes, and compare our findings to expectations from UFD-mass\nsimulations. For Peg III, we find an elliptical half-light radius of\n$a_h=1.88^{+0.42}_{-0.33}$ arcminutes ($118^{+31}_{-30}$ pc) and\n$M_V{=}{-4.17}^{+0.19}_{-0.22}$; for Psc II, we measure\n$a_h{=}1.31^{+0.10}_{-0.09}$ arcminutes ($69\\pm8$ pc) and\n$M_V{=}{-4.28}^{+0.19}_{-0.16}$. We do not find any morphological features that\nindicate a significant interaction between the two has occurred, despite their\nclose separation of only $\\sim$40 kpc. Using proper motions (PMs) from Gaia\nearly Data Release 3, we investigate the possibility of any past association by\nintegrating orbits for the two UFDs in a MW-only and a combined MW and Large\nMagellanic Cloud (LMC) potential. We find that including the gravitational\ninfluence of the LMC is crucial, even for these outer-halo satellites, and that\na possible orbital history exists where Peg III and Psc II experienced a close\n($\\sim$10-20 kpc) passage about each other just over $\\sim$1 Gyr ago, followed\nby a collective passage around the LMC ($\\sim$30-60 kpc) just under $\\sim$1 Gyr\nago. Considering the large uncertainties on the PMs and the restrictive priors\nimposed to derive them, improved PM measurements for Peg III and Psc II will be\nnecessary to clarify their relationship. This would add to the rare findings of\nconfirmed pairs of satellites within the Local Group.", "category": "astro-ph_GA" }, { "text": "Selection bias in dynamically-measured supermassive black hole samples:\n Scaling relations and correlations between residuals in semi-analytic galaxy\n formation models: Recent work has confirmed that the masses of supermassive black holes,\nestimated from scaling relations with global properties such as the stellar\nmasses of their host galaxies, may be biased high. Much of this may be caused\nby the requirement that the gravitational sphere of influence of the black hole\nmust be resolved for the black-hole mass to be reliably estimated. We revisit\nthis issue by using a comprehensive galaxy evolution semi-analytic model, which\nself-consistently evolves supermassive black holes from high-redshift seeds via\ngas accretion and mergers, and also includes AGN feedback. Once tuned to\nreproduce the (mean) correlation of black-hole mass with velocity dispersion,\nthe model is unable to also account for the correlation with stellar mass. This\nbehaviour is independent of the model's parameters, thus suggesting an internal\ninconsistency in the data. The predicted distributions, especially at the\nlow-mass end, are also much broader than observed. However, if selection\neffects are included, the model's predictions tend to align with the\nobservations. We also demonstrate that the correlations between the residuals\nof the local scaling relations are more effective than the scaling relations\nthemselves at constraining AGN feedback models. In fact, we find that our\nsemi-analytic model, while in apparent broad agreement with the scaling\nrelations when accounting for selection biases, yields very weak correlations\nbetween their residuals at fixed stellar mass, in stark contrast with\nobservations. This problem persists when changing the AGN feedback strength,\nand is also present in the $z\\sim 0$ outputs of the hydrodynamic cosmological\nsimulation Horizon-AGN, which includes state-of-the-art treatments of AGN\nfeedback. This suggests that current AGN feedback models may be too weak or are\nsimply not capturing the effect of the black hole on the stellar velocity\ndispersion.", "category": "astro-ph_GA" }, { "text": "Tracing the Local Volume galaxy halo-to-stellar mass ratio with\n satellite kinematics: Rapid advance has been made recently in accurate distance measurements for\nnearby ($D < 11$ Mpc) galaxies based on the magnitude of the tip of red giant\nbranch stars resolved with the Hubble Space Telescope. We use observational\nproperties of galaxies presented in the last version of Updated Nearby Galaxy\nCatalog to derive a halo mass of luminous galaxies via orbital motion of their\ncompanions. Our sample contains 298 assumed satellites with known radial\nvelocities around 25 Milky Way-like massive galaxies and 65 assumed satellites\naround 47 fainter dominant galaxies. The average total mass-to-$K$-band\nluminosity ratio is $31\\pm6 M_\\odot/L_\\odot$ for the luminous galaxies,\nincreasing up to $\\sim200 M_\\odot/L_\\odot$ toward dwarfs. The bulge-dominated\nluminous galaxies are characterized with $\\langle{}M_T/L_K\\rangle = 73\\pm15\nM_\\odot/L_\\odot$, while the disc-dominated spirals have\n$\\langle{}M_T/L_K\\rangle = 17.4\\pm2.8 M_\\odot/L_\\odot$. We draw attention to a\nparticular subsample of luminous spiral galaxies with signs of declining\nrotation curve, which have a radial velocity dispersion of satellites less than\n55 km/s and a poor dark matter halo with $\\langle{}M_T/L_K\\rangle = 5.5\\pm1.1\nM_\\odot/L_\\odot$. We note that a fraction of quenched (dSph, dE) companions\naround Milky Way-like galaxies decreases with their linear projected separation\nas $0.75 \\exp(-R_p/350\\,\\mathrm{kpc})$.", "category": "astro-ph_GA" }, { "text": "A law of motion for spherical shells in special relativity: Self-similar solutions to the problem of a special relativistic law of motion\nfor thin shells of matter are calculated. These solutions represent the special\nrelativistic generalization of momentum conservation for the thin layer\napproximation in classical physics. The analytical and numerical results are\napplied to Supernova Remnant 1987 A.", "category": "astro-ph_GA" }, { "text": "A z=2.5 protocluster associated with the radio galaxy MRC 2104-242: star\n formation and differing mass functions in dense environments: We present results from a narrow-band survey of the field around the high\nredshift radio galaxy MRC 2104-242. We have selected Halpha emitters in a\n7sq.arcmin field and compared the measured number density with that of a field\nsample at similar redshift. We find that MRC 2104-242 lies in an overdensity of\ngalaxies that is 8.0 +/- 0.8 times the average density of a blank field,\nsuggesting it resides in a large-scale structure that may eventually collapse\nto form a massive cluster. We find that there is more dust obscured star\nformation in the protocluster galaxies than in similarly selected control field\ngalaxies and there is tentative evidence of a higher fraction of starbursting\ngalaxies in the denser environment. However, on average we do not find a\ndifference between the star formation rate (SFR)-mass relations of the\nprotocluster and field galaxies and so conclude that the SFR of these galaxies\nat z~2.5 is governed predominantly by galaxy mass and not the host environment.\nWe also find that the stellar mass distribution of the protocluster galaxies is\nskewed towards higher masses and there is a significant lack of galaxies at M <\n10^10Msun within our small field of view. Based on the level of overdensity we\nexpect to find ~22 star forming galaxies below 10^10Msun in the protocluster\nand do not detect any. This lack of low mass galaxies affects the level of\noverdensity which we detect. If we only consider high mass (M > 10^10.5Msun)\ngalaxies, the density of the protocluster field increases to ~55 times the\ncontrol field density.", "category": "astro-ph_GA" }, { "text": "Lessons from Comparisons between the Nuclear Region of the Milky Way &\n Those in Nearby Spirals: The Milky Way appears is a typical barred spiral, and comparisons can be made\nbetween its nuclear region and those of structurally similar nearby spirals.\nMaffei 2, M83, IC 342 and NGC 253 are nearby systems whose nuclear region\nproperties contrast with those of the Milky Way. Stellar masses derived from\nNIR photometery, molecular gas masses and star formation rates allow us to\nassess the evolutionary states of this set of nuclear regions. These data\nsuggest similarities between nuclear regions in terms of their stellar content\nwhile highlighting significant differences in current star formation rates. In\nparticular current star formation rates appear to cover a larger range than\nexpected based on the molecular gas masses. This behavior is consistent with\nnuclear region star formation experiencing episodic variations. Under this\nhypothesis the Milky Way's nuclear region currently may be in a low star\nformation rate phase.", "category": "astro-ph_GA" }, { "text": "Radio Jet Feedback and Star Formation in Heavily Obscured Quasars at\n Redshifts ~0.3-3, I: ALMA Observations: We present ALMA 870 micron (345 GHz) data for 49 high redshift (0.476$ where H I cannot be observed. Observational\nconsiderations have limited such studies to a small number of sightlines, with\nmost surveys at $z>6$ focused upon the statistical properties of individual\nions such as Mg II or C IV. Here we compare high- and low-ionization absorption\nwithin 69 intervening systems at $z>5$, including 16 systems at $z>6$, from\nMagellan/FIRE spectra of 47 quasars together with a Keck/HIRES spectrum of the\n`ultraluminous' $z=6.3$ quasar SDSSJ010013.02+280225.8. The highest redshift\nabsorbers increasingly exhibit low-ionization species alone, consistent with\nprevious single-ion surveys that show the frequency of Mg II is unchanging with\nredshift while C IV absorption drops markedly toward $z=6$. We detect no C IV\nor Si IV in half of all metal-line absorbers at $z>5.7$, with stacks not\nrevealing any slightly weaker C IV just below our detection threshold, and most\nof the other half have $N_\\mathrm{CII}>N_\\mathrm{CIV}$. In contrast, only 20\\%\nof absorbers at 5.0--5.7 lack high-ionization gas, and a search of 25 HIRES\nsightlines at $z\\sim3$ yielded zero such examples. We infer these\nlow-ionization high-redshift absorption systems may be analogous to metal-poor\nDamped Lyman-$\\alpha$ systems ($\\sim1\\%$ of the absorber population at\n$z\\sim3$), based on incidence rates and absolute and relative column densities.\nSimple photoionization models suggest that circumgalactic matter at redshift\nsix has systematically lower chemical abundances and experiences a softer\nionizing background relative to redshift three.", "category": "astro-ph_GA" }, { "text": "Chemical Diversity in the Ultra-faint Dwarf Galaxy Tucana II: We present the first detailed chemical abundance study of the ultra-faint\ndwarf galaxy Tucana II based on high-resolution Magellan/MIKE spectra of four\nred giant stars. The metallicity of these stars ranges from [Fe/H] = -3.2 to\n-2.6, and all stars are low in neutron-capture abundances ([Sr/Fe] and [Ba/Fe]\n< -1). However, a number of anomalous chemical signatures are present. Three\nstars are carbon-enhanced, including the most metal-rich star. This star\n([Fe/H]=-2.6) shows [Na,$\\alpha$,Sc/Fe] < 0, suggesting an extended star\nformation history with contributions from AGB stars and Type Ia supernovae. The\nother carbon-enhanced stars have [Fe/H] < -3 and may be consistent with\nenrichment by faint supernovae, if such supernovae can produce neutron-capture\nelements. A fourth star with [Fe/H] = -3 is carbon-normal, and exhibits\ndistinct light element abundance ratios from the carbon-enhanced stars. The\ncarbon-normal star implies that at least two distinct nucleosynthesis sources,\nboth possibly associated with Population III stars, contributed to the early\nchemical enrichment of this galaxy. Despite its very low luminosity, Tucana II\nshows a diversity of chemical signatures that preclude it from being a simple\n\"one-shot\" first galaxy, but still provide a window to star and galaxy\nformation in the early universe.", "category": "astro-ph_GA" }, { "text": "Water emission from the high-mass star-forming region IRAS 17233-3606.\n High water abundances at high velocities: We investigate the physical and chemical processes at work during the\nformation of a massive protostar based on the observation of water in an\noutflow from a very young object previously detected in H2 and SiO in the IRAS\n17233-3606 region. We estimated the abundance of water to understand its\nchemistry, and to constrain the mass of the emitting outflow. We present new\nobservations of shocked water obtained with the HIFI receiver onboard Herschel.\nWe detected water at high velocities in a range similar to SiO. We\nself-consistently fitted these observations along with previous SiO data\nthrough a state-of-the-art, one-dimensional, stationary C-shock model. We found\nthat a single model can explain the SiO and H2O emission in the red and blue\nwings of the spectra. Remarkably, one common area, similar to that found for H2\nemission, fits both the SiO and H2O emission regions. This shock model\nsubsequently allowed us to assess the shocked water column density,\nN(H2O)=1.2x10^{18} cm^{-2}, mass, M(H2O)=12.5 M_earth, and its maximum\nfractional abundance with respect to the total density, x(H2O)=1.4x10^{-4}. The\ncorresponding water abundance in fractional column density units ranges between\n2.5x10^{-5} and 1.2x10^{-5}, in agreement with recent results obtained in\noutflows from low- and high-mass young stellar objects.", "category": "astro-ph_GA" }, { "text": "TREX: Kinematic Characterisation of a High-Dispersion Intermediate-Age\n Stellar Component in M33: The dwarf galaxy Triangulum (M33) presents an interesting testbed for\nstudying stellar halo formation: it is sufficiently massive so as to have\nlikely accreted smaller satellites, but also lies within the regime where\nfeedback and other \"in-situ\" formation mechanisms are expected to play a role.\nIn this work, we analyse the line-of-sight kinematics of stars across M33 from\nthe TREX survey with a view to understanding the origin of its halo. We split\nour sample into two broad populations of varying age, comprising 2032 \"old\" red\ngiant branch (RGB) stars, and 671 \"intermediate-age\" asymptotic giant branch\n(AGB) and carbon stars. We find decisive evidence for two distinct kinematic\ncomponents in both old and intermediate-age populations: a low-dispersion (~22\nkm/s) disk-like component co-rotating with M33's HI gas, and a significantly\nhigher-dispersion component (~50-60 km/s) which does not rotate in the same\nplane as the gas and is thus interpreted as M33's stellar halo. While\nkinematically similar, the fraction of stars associated with the halo component\ndiffers significantly between the two populations: this is consistently ~10%\nfor the intermediate age population, but decreases from ~34% to ~10% as a\nfunction of radius for the old population. We additionally find evidence that\nthe intermediate-age halo population is systematically offset from the systemic\nvelocity of M33 by ~25 km/s, with a preferred central LOS velocity of ~-155\nkm/s. This is the first detection and characterisation of an intermediate-age\nhalo in M33, and suggests in-situ formation mechanisms, as well as potentially\ntidal interactions, have helped shaped it.", "category": "astro-ph_GA" }, { "text": "Self-similarity in the chemical evolution of galaxies and the delay time\n distribution of SNe Ia: Recent improvements in the age dating of stellar populations and single stars\nallow us to study the ages and abundance of stars and galaxies with\nunprecedented accuracy. We here compare the relation between age and\n\\alpha-element abundances for stars in the solar neighborhood to that of local,\nearly-type galaxies. We find both relations to be very similar. Both fall into\ntwo regimes with a flat slope for ages younger than ~9 Gyr and a steeper slope\nfor ages older than that value. This quantitative similarity seems surprising,\ngiven the different types of galaxies and scales involved. For the sample of\nearly-type galaxies we also show that the data are inconsistent with literature\ndelay time distributions of either single or double Gaussian shape. The data\nare consistent with a power law delay time distribution. We thus confirm that\nthe delay time distribution inferred for the Milky Way from chemical evolution\narguments also must apply to massive early-type galaxies. We also offer a\ntentative explanation for the seeming universality of the age-[\\alpha/Fe]\nrelation as the manifestation of averaging of different stellar populations\nwith varying chemical evolution histories.", "category": "astro-ph_GA" }, { "text": "Line shapes in narrow-line Seyfert 1 galaxies: a tracer of physical\n properties?: Line profiles can provide fundamental information on the physics of active\ngalactic nuclei (AGN). In the case of narrow-line Seyfert 1 galaxies (NLS1s)\nthis is of particular importance since past studies revealed how their\npermitted line profiles are well reproduced by a Lorentzian function instead of\na Gaussian. This has been explained with different properties of the broad-line\nregion (BLR), which may present a more pronounced turbulent motions in NLS1s\nwith respect to other AGN. We investigated the line profiles in a recent large\nNLS1 sample classified using SDSS, and we divided the sources into two\nsubsamples according to their line shapes, Gaussian or Lorentzian. The line\nprofiles clearly separate all the properties of NLS1s. Black hole mass,\nEddington ratio, [O III], and Fe II strength are all very different in the\nLorentzian and Gaussian samples. We interpret this in terms of evolution within\nthe class of NLS1s. The Lorentzian sources may be the youngest objects, while\nGaussian profiles may be typically associated to more evolved objects. Further\ndetailed spectroscopic studies are needed to fully confirm our hypothesis.", "category": "astro-ph_GA" }, { "text": "Inferring the star formation histories of the most massive and passive\n early-type galaxies at z<0.3: Massive galaxies are key probes to understand how the baryonic matter evolves\nwithin the dark matter halos. We use the \"archaeological\" approach to infer the\nstellar population properties and star formation histories of the most massive\n(M > 10^10.75 Msun) and passive early-type galaxies (ETGs) at 0 < z < 0.3,\nbased on stacked, high signal to noise ratio (SNR), Sloan Digital Sky Survey\nspectra. We exploit the information present in the full-spectrum by means of\nthe STARLIGHT public code to retrieve the ETGs evolutionary properties, such as\nage, metallicity and star formation history. We find that the stellar\nmetallicities are slightly supersolar (Z ~ 0.027 +/- 0.002) and do not depend\non redshift. Dust extinction is very low, with a mean of Av ~ 0.08 +/- 0.03\nmag. The ETGs show an anti-hierarchical evolution (downsizing) where more\nmassive galaxies are older. The SFHs can be approximated by a parametric\nfunction of the form SFR(t) \\propto \\tau^-(c+1) t^(c) exp(-t/\\tau), with\ntypical short e-folding times of \\tau ~ 0.6 - 0.8 Gyr (and a dispersion of +/-\n0.1 Gyr) and c ~ 0.1 (and a dispersion of +/- 0.05). The inferred SFHs are also\nused to place constraints on the properties and evolution of the ETG\nprogenitors. In particular, the ETGs of our samples should have formed most\nstars through a phase of vigorous star formation (SFRs > 350-400 Msun yr^-1) at\nz ~ 4 - 5, and are quiescent by z ~ 1.5 -2. Our results represent an attempt to\ndemonstrate quantitatively the evolutionary link between the most massive ETGs\nat z < 0.3 and the properties of suitable progenitors at high redshifts, also\nshowing that the full-spectrum fitting is a powerful approach to reconstruct\nthe star formation histories of massive quiescent galaxies.", "category": "astro-ph_GA" }, { "text": "A Search For Supernova Remnants in The Nearby Spiral Galaxy M74 (NGC\n 628): We have identified nine new SNR candidates in M74 with [S II]/H$\\alpha$\n$\\geq$ 0.4 as the basic criterion. We obtain [S II]/H$\\alpha$ ratio in the\nrange from 0.40 to 0.91 and H$\\alpha$ intensities from 2.8 $\\times$ $10^{-15}$\nerg cm$^{-2}$ s$^{-1}$ to 1.7 $\\times$ $10^{-14}$ erg cm$^{-2}$ s$^{-1}$. We\nalso present spectral follow-up observations of the SNR candidates and can\nconfirm only three of them (SNR2, SNR3, and SNR5). The lack of confirmation for\nthe rest might be due to the contamination by the nearby H II emission regions\nas well as due to the inaccurate positioning of the long slit on these objects.\nIn addition, we search the $Chandra$ Observatory archival data for the X-ray\ncounterparts to the optically identified candidates. We find positional\ncoincidence with only three SNR candidates, SNR1, SNR2, and SNR8. The spectrum\nof SNR2 yields a shock temperature of 10.8 keV with an ionization timescale of\n1.6 $\\times$ 10$^{10}$ s cm$^{-3}$ indicating a relatively young remnant in an\nearly Sedov phase which is not supported by our optical wavelength analysis.\nGiven the high luminosity of 10$^{39}$ erg s$^{-1}$ and the characteristics of\nthe X-ray spectrum, we favor an Ultra Luminous X-ray Source interpretation for\nthis source associated with an SNR. We calculate an X-ray flux upper limit of\n9.0 $\\times$ $10^{-15}$ erg cm$^{-2}$ s$^{-1}$ for the rest of the SNRs\nincluding spectroscopically identified SNR3 and SNR5.", "category": "astro-ph_GA" }, { "text": "Abundance gradients in spiral disks: is the gradient inversion at high\n redshift real?: We compute the abundance gradients along the disk of the Milky Way by means\nof the two-infall model: in particular, the gradients of oxygen and iron and\ntheir temporal evolution. First, we explore the effects of several physical\nprocesses which influence the formation and evolution of abundance gradients.\nThey are: i) the inside-out formation of the disk, ii) a threshold in the gas\ndensity for star formation, iii) a variable star formation efficiency along the\ndisk, iv) radial flows and their speed, and v) different total surface mass\ndensity (gas plus stars) distributions for the halo. We are able to reproduce\nat best the present day gradients of oxygen and iron if we assume an inside-out\nformation, no threshold gas density, a constant efficiency of star formation\nalong the disk and radial gas flows. It is particularly important the choice of\nthe velocity pattern for radial flows and the combination of this velocity\npattern with the surface mass density distribution in the halo. Having selected\nthe best model, we then explore the evolution of abundance gradients in time\nand find that the gradients in general steepen in time and that at redshift z~3\nthere is a gradient inversion in the inner regions of the disk, in the sense\nthat at early epochs the oxygen abundance decreases toward the Galactic center.\nThis effect, which has been observed, is naturally produced by our models if an\ninside-out formation of the disk and and a constant star formation efficiency\nare assumed. The inversion is due to the fact that in the inside-out formation\na strong infall of primordial gas, contrasting chemical enrichment, is present\nin the innermost disk regions at early times. The gradient inversion remains\nalso in the presence of radial flows, either with constant or variable speed in\ntime, and this is a new result.", "category": "astro-ph_GA" }, { "text": "Impact of turbulence intensity and fragmentation velocity on dust\n particle size evolution and non-ideal magnetohydrodynamics effects: We investigate the influence of dust particle size evolution on non-ideal\nmagnetohydrodynamic effects during the collapsing phase of star-forming cores,\ntaking both the turbulence intensity in the collapsing cloud core and the\nfragmentation velocity of dust particles as parameters. When the turbulence\nintensity is small, the dust particles do not grow significantly, and the\nnon-ideal MHD effects work efficiently in high-density regions. The dust\nparticles rapidly grow in a strongly turbulent environment, while the\nefficiency of non-ideal MHD effects in such an environment depends on the\nfragmentation velocity of the dust particles. When the fragmentation velocity\nis small, turbulence promotes coagulation growth and collisional fragmentation\nof dust particles, producing small dust particles. In this case, the adsorption\nof charged particles on the dust particle surfaces becomes efficient and the\nabundance of charged particles decreases, making non-ideal MHD effects\neffective at high densities. On the other hand, when the fragmentation velocity\nis high, dust particles are less likely to fragment, even if the turbulence is\nstrong. In this case, the production of small dust particles become inefficient\nand non-ideal MHD effects become less effective. We also investigate the effect\nof the dust composition on the star and disk formation processes. We constrain\nthe turbulence intensity of a collapsing core and the fragmentation velocity of\ndust for circumstellar disk formation due to the dissipation of the magnetic\nfield.", "category": "astro-ph_GA" }, { "text": "Stellar Dynamics and Stellar Phenomena Near A Massive Black Hole: Most galactic nuclei harbor a massive black hole (MBH), whose birth and\nevolution are closely linked to those of its host galaxy. The unique conditions\nnear the MBH: high velocity and density in the steep potential of a massive\nsingular relativistic object, lead to unusual modes of stellar birth,\nevolution, dynamics and death. A complex network of dynamical mechanisms,\noperating on multiple timescales, deflect stars to orbits that intercept the\nMBH. Such close encounters lead to energetic interactions with observable\nsignatures and consequences for the evolution of the MBH and its stellar\nenvironment. Galactic nuclei are astrophysical laboratories that test and\nchallenge our understanding of MBH formation, strong gravity, stellar dynamics,\nand stellar physics. I review from a theoretical perspective the wide range of\nstellar phenomena that occur near MBHs, focusing on the role of stellar\ndynamics near an isolated MBH in a relaxed stellar cusp.", "category": "astro-ph_GA" }, { "text": "The angular momentum of disc galaxies at z=1: We investigate the relation between stellar mass and specific stellar angular\nmomentum, or `Fall relation', for a sample of 17 isolated, regularly rotating\ndisc galaxies at z=1. All galaxies have a) rotation curves determined from\nHalpha emission-line data; b) HST imaging in optical and infrared filters; c)\nrobust determinations of their stellar masses. We use HST images in f814w and\nf160w filters, roughly corresponding to rest-frames B and I bands, to extract\nsurface brightness profiles for our systems. We robustly bracket the specific\nangular momentum by assuming that rotation curves beyond the outermost Halpha\nrotation point stay either flat or follow a Keplerian fall-off. By comparing\nour measurements with those determined for disc galaxies in the local Universe,\nwe find no evolution in the Fall relation in the redshift range 01\\sigma$)\ndifference between these two CCFs. We also compare mass-metallicity relations\n(MZRs) of the EMPGs and those of galaxies at $z\\sim$ 0--4 with a steady\nchemical evolution model and find that the EMPG MZR is comparable with the\nmodel prediction on average. These clustering and chemical properties of EMPGs\nare explained by a scenario of stochastic metal-poor gas accretion on\nmetal-rich galaxies showing metal-poor star formation. Extending the broadband\ncolor-excess technique to a high-$z$ EMPG search, we select 17 candidates of\n$z\\sim$ 4--5 EMPGs with the deep ($\\simeq30$ mag) near-infrared JWST/NIRCam\nimages obtained by ERO and ERS programs. We find galaxy candidates with\nnegligible {\\sc[Oiii]}$\\lambda\\lambda$4959,5007 emission weaker than the local\nEMPGs and known high-$z$ galaxies, suggesting that some of these candidates may\nfall in 0--0.01 $Z_\\odot$, which potentially break the lowest metallicity limit\nknown to date.", "category": "astro-ph_GA" }, { "text": "Fullerenes in circumstellar and interstellar environments: In recent years, the fullerene species C60 (and to a lesser extent also C70)\nhas been reported in the mid-IR spectra of various astronomical objects. Cosmic\nfullerenes form in the circumstellar material of evolved stars, and survive in\nthe interstellar medium (ISM). It is not entirely clear how they form or what\ntheir excitation mechanism is.", "category": "astro-ph_GA" }, { "text": "Reconciling the emission mechanism discrepancy in Mira's tail, and its\n evolution in an interface with shear: GALEX observations of the Mira AB binary system revealed a surrounding\nstructure that has been successfully hydrodynamically interpreted as a bow\nshock and tail of ram-pressure-stripped material. Even the narrow tail,\ninitially difficult to model, has been understood as the effect of the passage\nof Mira from a warm neutral medium into a hot, low-density medium, postulated\nto be the Local Bubble. However, no model to date has explained the observed\nkink and associated general curvature of the tail. We test the hypothesis that\nbefore entering the Local Bubble, Mira was travelling through a shear flow with\napproximately 1/3 Mira's own velocity at an angle of ~30degrees to Mira's\nproper motion. The hypothesis reproduces the kinked nature of Mira's tail and\npredicts recompression and reheating of the tail material to the same or\ngreater levels of density and temperature predicted in the shock. This provides\na heat source for the FUV emission, allowing for an extended lifetime of the\nFUV emission in line with other estimates of the age of the tail. The\nuniqueness of Mira's situation implies that the chances of observing other FUV\ntails behind AGB stars is highly unlikely.", "category": "astro-ph_GA" }, { "text": "BiPoS1 -- a computer programme for the dynamical processing of the\n initial binary star population: The first version of the Binary Population Synthesizer (BiPoS1) is made\npublicly available. It allows to efficiently calculate binary distribution\nfunctions after the dynamical processing of a realistic population of binary\nstars during the first few Myr in the hosting embedded star cluster. Instead of\ntime-consuming N-body simulations, BiPoS1 uses a stellar dynamical operator\nwhich determines the fraction of surviving binaries depending on the binding\nenergy of the binaries. The stellar dynamical operator depends on the initial\nstar cluster density as well as the time until the residual gas of the star\ncluster is expelled. BiPoS1 has also a galactic-field mode, in order to\nsynthesize the stellar population of a whole galaxy. At the time of gas\nexpulsion, the dynamical processing of the binary population is assumed to\nefficiently end due to the subsequent expansion of the star cluster. While\nBiPoS1 $has been used previously unpublished, here we demonstrate its use in\nthe modelling of the binary populations in the Orion Nebula Cluster, in OB\nassociations and as an input for simulations of globular clusters.", "category": "astro-ph_GA" }, { "text": "A universal, turbulence-regulated star formation law: from Milky Way\n clouds to high-redshift disk and starburst galaxies: Whilst the star formation rate (SFR) of molecular clouds and galaxies is key\nin understanding galaxy evolution, the physical processes which determine the\nSFR remain unclear. This uncertainty about the underlying physics has resulted\nin various different star formation laws, all having substantial intrinsic\nscatter. Extending upon previous works that define the column density of star\nformation (Sigma_SFR) by the gas column density (Sigma_gas), we develop a new\nuniversal star formation (SF) law based on the multi-freefall prescription of\ngas. This new SF law relies predominantly on the probability density function\n(PDF) and on the sonic Mach number of the turbulence in the star-forming\nclouds. By doing so we derive a relation where the star formation rate (SFR)\ncorrelates with the molecular gas mass per multi-freefall time, whereas\nprevious models had used the average, single-freefall time. We define a new\nquantity called maximum (multi-freefall) gas consumption rate (MGCR) and show\nthat the actual SFR is only about 0.4% of this maximum possible SFR, confirming\nthe observed low efficiency of star formation. We show that placing\nobservations in this new framework (Sigma_SFR vs. MGCR) yields a significantly\nimproved correlation with 3-4 times reduced scatter compared to previous SF\nlaws and a goodness-of-fit parameter R^2=0.97. By inverting our new\nrelationship, we provide sonic Mach number predictions for kpc-scale\nobservations of Local Group galaxies as well as unresolved observations of\nlocal and high-redshift disk and starburst galaxies that do not have\nindependent, reliable estimates for the turbulent cloud Mach number.", "category": "astro-ph_GA" }, { "text": "The THESAN project: Lyman-alpha emitter luminosity function calibration: The observability of Lyman-alpha emitting galaxies (LAEs) during the Epoch of\nReionization can provide a sensitive probe of the evolving neutral hydrogen gas\ndistribution, thus setting valuable constraints to distinguish different\nreionization models. In this study, we utilize the new THESAN suite of\nlarge-volume (95.5 cMpc) cosmological radiation-hydrodynamic simulations to\ndirectly model the Ly$\\alpha$ emission from individual galaxies and the\nsubsequent transmission through the intergalactic medium. THESAN combines the\nAREPO-RT radiation-hydrodynamic solver with the IllustrisTNG galaxy formation\nmodel and includes high- and medium-resolution simulations designed to\ninvestigate the impacts of halo-mass-dependent escape fractions, alternative\ndark matter models, and numerical convergence. We find important differences in\nthe Ly$\\alpha$ transmission based on reionization history, bubble morphology,\nfrequency offset from line centre, and galaxy brightness. For a given global\nneutral fraction, Ly$\\alpha$ transmission reduces when low mass haloes dominate\nreionization over high mass haloes. Furthermore, the variation across\nsightlines for a single galaxy is greater than the variation across all\ngalaxies. This collectively affects the visibility of LAEs, directly impacting\nobserved Ly$\\alpha$ luminosity functions (LFs). We employ Gaussian Process\nRegression using SWIFTEmulator to rapidly constrain an empirical model for dust\nescape fractions and emergent spectral line profiles to match observed LFs. We\nfind that dust strongly impacts the Ly$\\alpha$ transmission and covering\nfractions of $M_{UV} < -19$ galaxies in $M_{vir} > 10^{11} {\\rm M}_{\\odot}$\nhaloes, such that the dominant mode of removing Ly$\\alpha$ photons in non-LAEs\nchanges from low IGM transmission to high dust absorption around $z \\sim 7$.", "category": "astro-ph_GA" }, { "text": "Morphological evolution in situ: Disk-dominated cluster red sequences at\n z ~ 1.25: We have carried out a joint photometric and structural analysis of red\nsequence galaxies in four clusters at a mean redshift of z ~ 1.25 using optical\nand near-IR HST imaging reaching to at least 3 magnitudes fainter than $M^*$.\nAs expected, the photometry and overall galaxy sizes imply purely passive\nevolution of stellar populations in red sequence cluster galaxies. However, the\nmorphologies of red sequence cluster galaxies at these redshifts show\nsignificant differences to those of local counterparts. Apart from the most\nmassive galaxies, the high redshift red sequence galaxies are significantly\ndiskier than their low redshift analogues. These galaxies also show significant\ncolour gradients, again not present in their low redshift equivalents, most\nstraightforwardly explained by radial age gradients. A clear implication of\nthese findings is that red sequence cluster galaxies originally arrive on the\nsequence as disk-dominated galaxies whose disks subsequently fade or evolve\nsecularly to end up as high S\\'ersic index early-type galaxies (classical S0s\nor possibly ellipticals) at lower redshift. The apparent lack of growth seen in\na comparison of high and low redshift red sequence galaxies implies that any\nevolution is internal and is unlikely to involve significant mergers. While\nsignificant star formation may have ended at high redshift, the cluster red\nsequence population continues to evolve (morphologically) for several Gyrs\nthereafter.", "category": "astro-ph_GA" }, { "text": "Seeking the growth of the first black hole seeds with JWST: In this paper we provide predictions for the BH population that would be\nobservable with planned JWST surveys at $5 \\le z \\le 15$. We base our study on\nthe recently developed Cosmic Archaeology Tool (CAT), which allows us to model\nBH seeds formation and growth, while being consistent with the general\npopulation of AGNs and galaxies observed at $4 \\le z \\le 7$. We find that JWST\nplanned surveys will provide a complementary view on active BHs at $z > 5$,\nwith JADES-Medium/-Deep being capable of detecting the numerous BHs that\npopulate the faint-end of the distribution, COSMOS-Web sampling a large enough\narea to detect the rarest brightest systems, and CEERS/PRIMER bridging the gap\nbetween these two regimes. The relatively small field of view of the above\nsurveys preferentially selects BHs with masses $6 \\leq {\\rm Log} (M_{\\rm\nBH}/M_\\odot) < 8$ at $7 \\le z < 10$, residing in relatively metal poor (${\\rm\nLog} (Z/Z_\\odot) \\ge -2$) and massive ($8\\leq {\\rm Log} (M_*/M_\\odot) < 10$)\ngalaxies. At $z \\ge 10$, only JADES-Deep will have the sensitivity to detect\ngrowing BHs with masses $4 \\leq {\\rm Log} (M_{\\rm BH}/M_\\odot) < 6$, hosted by\nmore metal poor ($-3 \\leq {\\rm Log} (Z/Z_\\odot) < -2$) and less massive ($6\n\\leq {\\rm Log} (M_*/M_\\odot) < 8$) galaxies. In our model, the latter\npopulation corresponds to heavy BH seeds formed by the direct collapse of\nsuper-massive stars in their earliest phases of mass growth. Detecting these\nsystems would provide invaluable insights on the nature and early growth of the\nfirst BH seeds.", "category": "astro-ph_GA" }, { "text": "Mapping the Galactic Halo VIII: Quantifying substructure: We have measured the amount of kinematic substructure in the Galactic halo\nusing the final data set from the Spaghetti project, a pencil-beam high\nlatitude sky survey. Our sample contains 101 photometrically selected and\nspectroscopically confirmed giants with accurate distance, radial velocity and\nmetallicity information. We have developed a new clustering estimator: the\n\"4distance\" measure, which when applied to our data set leads to the\nidentification of 1 group and 7 pairs of clumped stars. The group, with 6\nmembers, can confidently be matched to tidal debris of the Sagittarius dwarf\ngalaxy. Two pairs match the properties of known Virgo structures. Using models\nof the disruption of Sagittarius in Galactic potentials with different degrees\nof dark halo flattening, we show that this favors a spherical or prolate halo\nshape, as demonstrated by Newberg et al. (2007) using SDSS data. One additional\npair can be linked to older Sagittarius debris. We find that 20% of the stars\nin the Spaghetti data set are in substructures. From comparison with random\ndata sets we derive a very conservative lower limit of 10% to the amount of\nsubstructure in the halo. However, comparison to numerical simulations shows\nthat our results are also consistent with a halo entirely built up from\ndisrupted satellites, provided the dominating features are relatively broad due\nto early merging or relatively heavy progenitor satellites.", "category": "astro-ph_GA" }, { "text": "Radio Jet Feedback and Star Formation in Heavily Obscured Quasars at\n Redshifts ~0.3-3, I: ALMA Observations: We present ALMA 870 micron (345 GHz) data for 49 high redshift (0.470.5\"$), suggesting that\nthe gas is dynamically settled and suitable for dynamically deriving the mass\nof its central source. As is expected from X-ray dominated region (XDR) effects\nthat dramatically increase an atomic carbon abundance by dissociating CO\nmolecules, we suggest that the atomic [CI](1-0) emission is a better probe of\nSMBH masses than CO emission in AGNs. Our dynamical model using the ${\\rm\n[CI]}$(1-0) kinematics yields a $M_{\\rm\nBH}=1.78^{+2.69}_{-1.10}\\times10^7$M$_\\odot$ and $M/L_{\\rm\nF547M}=2.25^{+0.40}_{-0.43}$ (M$_\\odot$/L$_\\odot$). The model using the CO(1-0)\nkinematics also gives a consistent $M_{\\rm BH}$ with a larger uncertainty, up\nto an order of magnitude, i.e.\\ $M_{\\rm\nBH}=1.60^{+11.52}_{-1.45}\\times10^7$M$_\\odot$. This newly dynamical $M_{\\rm\nBH}$ is $\\approx$ 2 times higher than the mass determined from the\nreverberation mapped (RM) method using emissions arising in the unresolved\nbroad-line region (BLR). Given this new $M_{\\rm BH}$, we are able to constrain\nthe specific RM dimensionless scaling factor of $f=7.2^{+4.2}_{-3.4}$ for the\nAGN BLR in NGC7469. The gas within the unresolved BLR thus has a Keplerian\nvirial velocity component and the inclination of\n$i\\approx11.0^\\circ$$_{-2.5}^{+2.2}$, confirming its face-on orientation in a\nSeyfert 1 AGN by assuming a geometrically thin BLR model.", "category": "astro-ph_GA" }, { "text": "Chemical abundances of distant extremely metal-poor unevolved stars: Aims: The purpose of our study is to determine the chemical composition of a\nsample of 16 candidate Extremely Metal-Poor (EMP) dwarf stars, extracted from\nthe Sloan Digital Sky Survey (SDSS). There are two main purposes: in the first\nplace to verify the reliability of the metallicity estimates derived from the\nSDSS spectra; in the second place to see if the abundance trends found for the\nbrighter nearer stars studied previously also hold for this sample of fainter,\nmore distant stars. Methods: We used the UVES at the VLT to obtain\nhigh-resolution spectra of the programme stars. The abundances were determined\nby an automatic analysis with the MyGIsFOS code, with the exception of lithium,\nfor which the abundances were determined from the measured equivalent widths of\nthe Li I resonance doublet. Results: All candidates are confirmed to be EMP\nstars, with [Fe/H]<= -3.0. The chemical composition of the sample of stars is\nsimilar to that of brighter and nearer samples. We measured the lithium\nabundance for 12 stars and provide stringent upper limits for three other\nstars, for a fourth star the upper limit is not significant, owing to the low\nsignal-to noise ratio of the spectrum. The \"meltdown\" of the Spite plateau is\nconfirmed, but some of the lowest metallicity stars of the sample lie on the\nplateau. Conclusions: The concordance of the metallicities derived from\nhigh-resolution spectra and those estimated from the SDSS spectra suggests that\nthe latter may be used to study the metallicity distribution of the halo. The\nabundance pattern suggests that the halo was well mixed for all probed\nmetallicities and distances. The fact that at the lowest metallicities we find\nstars on the Spite plateau suggests that the meltdown depends on at least\nanother parameter, besides metallicity. (abridged)", "category": "astro-ph_GA" }, { "text": "Ionised gas structure of 100 kpc in an over-dense region of the galaxy\n group COSMOS-Gr30 at z ~ 0.7: We report the discovery of a 10^4 kpc^2 gaseous structure detected in [OII]\nin an over-dense region of the COSMOS-Gr30 galaxy group at z~0.725 thanks to\ndeep MUSE Guaranteed Time Observations. We estimate the total amount of diffuse\nionised gas to be of the order of (~5+-3)x10^10 Msun and explore its physical\nproperties to understand its origin and the source(s) of the ionisation. The\nMUSE data allow the identification of a dozen of group members embedded in this\nstructure from emission and absorption lines. We extracted spectra from small\napertures defined for both the diffuse ionised gas and the galaxies. We\ninvestigated the kinematics and ionisation properties of the various galaxies\nand extended gas regions thanks to line diagnostics (R23, O32 and\n[OIII]/H\\beta) available within the MUSE wavelength range. We compared these\ndiagnostics to photo-ionisation models and shock models. The structure is\ndivided in two kinematically distinct sub-structures. The most extended\nsub-structure of ionised gas is likely rotating around a massive galaxy and\ndisplays filamentary patterns linking some galaxies. The second sub-structure\nlinks another massive galaxy hosting an Active Galactic Nucleus to a low mass\ngalaxy but also extends orthogonally to the AGN host disk over ~35 kpc. This\nextent is likely ionised by the AGN itself. The location of small diffuse\nregions in the R23 vs. O32 diagram is compatible with photo-ionisation.\nHowever, the location of three of these regions in this diagram (low O32, high\nR23) can also be explained by shocks, which is supported by their large\nvelocity dispersions. One edge-on galaxy shares the same properties and may be\na source of shocks. Whatever the hypothesis, the extended gas seems to be non\nprimordial. We favour a scenario where the gas has been extracted from galaxies\nby tidal forces and AGN triggered by interactions between at least the two\nsub-structures.", "category": "astro-ph_GA" }, { "text": "Discovery of inverse-Compton X-ray emission and estimate of the\n volume-averaged magnetic field in a galaxy group: Observed in a significant fraction of clusters and groups of galaxies,\ndiffuse radio synchrotron emission reveals the presence of relativistic\nelectrons and magnetic fields permeating large-scale systems of galaxies.\nAlthough these non-thermal electrons are expected to upscatter cosmic microwave\nbackground photons up to hard X-ray energies, such inverse-Compton (IC) X-ray\nemission has so far not been unambiguously detected on cluster/group scales.\nUsing deep, new proprietary XMM-Newton observations ($\\sim$200 ks of clean\nexposure), we report a 4.6$\\sigma$ detection of extended IC X-ray emission in\nMRC 0116+111, an extraordinary group of galaxies at $z = 0.131$. Assuming a\nspectral slope derived from low-frequency radio data, the detection remains\nrobust to systematic uncertainties. Together with low-frequency radio data from\nGMRT, this detection provides an estimate for the volume-averaged magnetic\nfield of $(1.9 \\pm 0.3)$ $\\mu$G within the central part of the group. This\nvalue can serve as an anchor for studies of magnetic fields in the largest\ngravitationally bound systems in the Universe.", "category": "astro-ph_GA" }, { "text": "The PAU Survey: Close galaxy pairs identification and analysis: Galaxy pairs constitute the initial building blocks of galaxy evolution,\nwhich is driven through merger events and interactions. Thus, the analysis of\nthese systems can be valuable in understanding galaxy evolution and studying\nstructure formation. In this work, we present a new publicly available\ncatalogue of close galaxy pairs identified using photometric redshifts provided\nby the Physics of the Accelerating Universe Survey (PAUS). To efficiently\ndetect them we take advantage of the high-precision photo$-z$ ($\\sigma_{68} <\n0.02$) and apply an identification algorithm previously tested using simulated\ndata. This algorithm considers the projected distance between the galaxies\n($r_p < 50$ kpc), the projected velocity difference ($\\Delta V < 3500$ km/s)\nand an isolation criterion to obtain the pair sample. We applied this technique\nto the total sample of galaxies provided by PAUS and to a subset with\nhigh-quality redshift estimates. Finally, the most relevant result we achieved\nwas determining the mean mass for several subsets of galaxy pairs selected\naccording to their total luminosity, colour and redshift, using galaxy-galaxy\nlensing estimates. For pairs selected from the total sample of PAUS with a mean\n$r-$band luminosity $10^{10.6} h^{-2} L_\\odot$, we obtain a mean mass of\n$M_{200} = 10^{12.2} h^{-1} M_\\odot$, compatible with the mass-luminosity ratio\nderived for elliptical galaxies. We also study the mass-to-light ratio $M/L$ as\na function of the luminosity $L$ and find a lower $M/L$ (or steeper slope with\n$L$) for pairs than the one extrapolated from the measurements in groups and\ngalaxy clusters.", "category": "astro-ph_GA" }, { "text": "Update on HI data collection from GBT, Parkes and Arecibo telescopes for\n the Cosmic Flows project: Cosmic Flows is an international multi-element project with the goal to map\nmotions of galaxies in the Local Universe. Kinematic information from\nobservations in the radio HI line and photometry at optical or near-infrared\nbands are acquired to derive the large majority of distances that are obtained\nthrough the luminosity-linewidth or Tully-Fisher relation. This paper gathers\nadditional observational radio data, frequently unpublished, retrieved from the\narchives of Green Bank, Parkes and Arecibo telescopes. Extracted HI profiles\nare consistently processed to produce linewidth measurements. Our current\n\"All-Digital HI Catalog\" contains a total of 20,343 HI spectra for 17,738\ngalaxies with 14,802 galaxies with accurate linewidth measurement useful for\nTully-Fisher galaxy distances. This addition of 4,117 new measurements\nrepresents an augmentation of 34\\% compared to our last release.", "category": "astro-ph_GA" }, { "text": "Constraints on the temperature inhomogeneity in quasar accretion discs\n from the ultraviolet-optical spectral variability: The physical mechanisms of the quasar ultraviolet (UV)-optical variability\nare not well understood despite the long history of observations. Recently,\nDexter & Agol presented a model of quasar UV-optical variability, which assumes\nlarge local temperature fluctuations in the quasar accretion discs. This\ninhomogeneous accretion disc model is claimed to describe not only the\nsingle-band variability amplitude, but also microlensing size constraints and\nthe quasar composite spectral shape. In this work, we examine the validity of\nthe inhomogeneous accretion disc model in the light of quasar UV-optical\nspectral variability by using five-band multi-epoch light curves for nearly 9\n000 quasars in the Sloan Digital Sky Survey (SDSS) Stripe 82 region. By\ncomparing the values of the intrinsic scatter $\\sigma_{\\text{int}}$ of the\ntwo-band magnitude-magnitude plots for the SDSS quasar light curves and for the\nsimulated light curves, we show that Dexter & Agol's inhomogeneous accretion\ndisc model cannot explain the tight inter-band correlation often observed in\nthe SDSS quasar light curves. This result leads us to conclude that the local\ntemperature fluctuations in the accretion discs are not the main driver of the\nseveral years' UV-optical variability of quasars, and consequently, that the\nassumption that the quasar accretion discs have large localized temperature\nfluctuations is not preferred from the viewpoint of the UV-optical spectral\nvariability.", "category": "astro-ph_GA" }, { "text": "Molecular hydrogen in absorption at high redshifts. Science cases for\n CUBES: Absorption lines from molecular hydrogen ($\\rm H_2$) in the spectra of\nbackground sources are a powerful probe of the physical conditions in\nintervening cold neutral medium. At high redshift, $z>2$, $\\rm H_2$ lines are\nconveniently shifted in the optical domain, allowing the use of ground-based\ntelescopes to perform high-resolution spectroscopy, which is essential for a\nproper analysis of the cold gas. We describe recent observational progress,\nbased on the development of efficient pre-selection techniques in\nlow-resolution spectroscopic surveys such as the Sloan Digital Sky Survey\n(SDSS). The next generation of spectrographs with high blue-throughput, such as\nCUBES, will certainly significantly boost the efficiency and outcome of\nfollow-up observations. In this paper, we discuss high priority science cases\nfor CUBES, building on recent $\\rm H_2$ observations at high-z: probing the\nphysical conditions in the cold phase of regular galaxies and outflowing gas\nfrom active galactic nucleus.", "category": "astro-ph_GA" }, { "text": "Mapping Spatial Variations of HI Turbulent Properties in the Small and\n Large Magellanic Cloud: We developed methods for mapping spatial variations of the spatial power\nspectrum (SPS) and structure function (SF) slopes, with a goal of connecting\nneutral hydrogen (HI) statistical properties with the turbulent drivers. The\nnew methods were applied on the HI observations of the Small and Large\nMagellanic Clouds (SMC and LMC). In the case of the SMC, we find highly uniform\nturbulent properties of HI, with no evidence for local enhancements of\nturbulence due to stellar feedback. Such properties could be caused by a\nsignificant turbulent driving on large-scales. Alternatively, a significant\nline-of-sight depth of the SMC could be masking out localized regions with a\nsteeper SPS slope caused by stellar feedback. In contrast to the SMC, the LMC\nHI shows a large diversity in terms of its turbulent properties. Across most of\nthe LMC, the small-scale SPS slope is steeper than the large-scale slope due to\nthe presence of the HI disk. On small spatial scales, we find several areas of\nlocalized steepening of the SPS slope around major HII regions, with the 30\nDoradus region being the most prominent. This is in agreement with predictions\nfrom numerical simulations which suggest steepening of the SPS slope due to\nstellar feedback eroding and destroying interstellar clouds. We also find\nlocalized steepening of the large-scale SPS slope in the outskirts of the LMC.\nThis is likely caused by the flaring of the HI disk, or alternatively\nram-pressure stripping of the LMC disk due to the interactions with the\nsurrounding halo gas.", "category": "astro-ph_GA" }, { "text": "New Insights into the Evolution of Massive Stars and Their Effects on\n Our Understanding of Early Galaxies: The observable characteristics and subsequent evolution of young stellar\npopulations is dominated by their massive stars. As our understanding of those\nmassive stars and the factors affecting their evolution improves, so our\ninterpretation of distant, unresolved stellar systems can also advance. As\nobservations increasingly probe the distant Universe, and the rare low\nmetallicity starbursts nearby, so the opportunity arises for these two fields\nto complement one another, and lead to an improved conception of both stars and\ngalaxies. Here we review the current state of the art in modelling of massive\nstar dominated stellar populations, and discuss their applications and\nimplications for interpreting the distant Universe. Our principle findings\ninclude:\n - Binary evolutionary pathways must be included to understand the stellar\npopulations in early galaxies.\n - Observations constraining the extreme ultraviolet spectrum of early\ngalaxies are showing that current models are incomplete. The best current guess\nis that some form of accretion onto compact remnants is required.\n - The evolution and fates of very massive stars, of the order of 100Msun and\nabove, may be key to fully understand aspects of early galaxies.", "category": "astro-ph_GA" }, { "text": "The physics and modes of star cluster formation: simulations: We review progress in numerical simulations of star cluster formation. These\nsimulations involve the bottom-up assembly of clusters through hierarchical\nmergers, which produces a fractal stellar distribution at young (~0.5 Myr)\nages. The resulting clusters are predicted to be mildly aspherical and highly\nmass-segregated, except in the immediate aftermath of mergers. The upper\ninitial mass function within individual clusters is generally somewhat flatter\nthan for the aggregate population. Recent work has begun to clarify the factors\nthat control the mean stellar mass in a star-forming cloud and also the\nefficiency of star formation. The former is sensitive to the thermal properties\nof the gas while the latter depends both on the magnetic field and the initial\ndegree of gravitational boundedness of the natal cloud. Unmagnetized clouds\nthat are initially bound undergo rapid collapse, which is difficult to reverse\nby ionization feedback or stellar winds.", "category": "astro-ph_GA" }, { "text": "Herschel/HIFI search for H2-17O and H2-18O in IRC+10216: constraints on\n models for the origin of water vapor: We report the results of a sensitive search for the minor isotopologues of\nwater, H2-17O and H2-18O, toward the carbon-rich AGB star IRC+10216 (a.k.a. CW\nLeonis) using the HIFI instrument on the Herschel Space Observatory. This\nsearch was motivated by the fact that any detection of isotopic enhancement in\nthe H2-17O and H2-18O abundances would have strongly implicated CO\nphotodissociation as the source of the atomic oxygen needed to produce water in\na carbon-rich circumstellar envelope. Our observations place an upper limit of\n1/470 on the H2-17O/H2-16O abundance ratio. Given the isotopic 17O/16O ratio of\n1/840 inferred previously for the photosphere of IRC+10216, this result places\nan upper limit of a factor 1.8 on the extent of any isotope-selective\nenhancement of H2-17O in the circumstellar material, and provides an important\nconstraint on any model that invokes CO photodissociation as the source of O\nfor H2O production. In the context of the clumpy photodissociation model\nproposed previously for the origin of water in IRC+10216, our limit implies\nthat 12C-16O (not 13C-16O or SiO) must be the dominant source of 16O for H2O\nproduction, and that the effects of self-shielding can only have reduced the\n12C-16O photodissociation rate by at most a factor ~ 2.", "category": "astro-ph_GA" }, { "text": "Young Galaxy Candidates in the Hubble Frontier Fields - III.\n MACSJ0717.5+3745: In this paper we present the results of our search for and study of $z\n\\gtrsim 6$ galaxy candidates behind the third Frontier Fields (FF) cluster,\nMACSJ0717.5+3745, and its parallel field, combining data from Hubble and\nSpitzer. We select 39 candidates using the Lyman Break technique, for which the\nclear non-detection in optical make the extreme mid-$z$ interlopers hypothesis\nunlikely. We also take benefit from $z \\gtrsim 6$ samples selected using\nprevious Frontier Fields datasets of Abell 2744 and MACS0416 to improve the\nconstraints on the properties of very high-redshift objects. We compute the\nredshift and the physical properties, such emission lines properties, star\nformation rate, reddening, and stellar mass for all Frontier Fields objects\nfrom their spectral energy distribution using templates including nebular\nemission lines. We study the relationship between several physical properties\nand confirm the trend already observed in previous surveys for evolution of\nstar formation rate with galaxy mass, and between the size and the UV\nluminosity of our candidates. The analysis of the evolution of the UV\nLuminosity Function with redshift seems more compatible with an evolution of\ndensity. Moreover, no robust $z\\ge$8.5 object is selected behind the cluster\nfield, and few $z$$\\sim$9 candidates have been selected in the two previous\ndatasets from this legacy survey, suggesting a strong evolution in the number\ndensity of galaxies between $z$$\\sim$8 and 9. Thanks to the use of the lensing\ncluster, we study the evolution of the star formation rate density produced by\ngalaxies with L$>$0.03L$^{\\star}$, and confirm the strong decrease observed\nbetween $z$$\\sim$8 and 9.", "category": "astro-ph_GA" }, { "text": "ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): A Hot Corino\n Survey toward Protostellar Cores in the Orion Cloud: The presence of complex organic molecules (COMs) in the interstellar medium\n(ISM) is of great interest since it may link to the origin and prevalence of\nlife in the universe. Aiming to investigate the occurrence of COMs and their\npossible origins, we conducted a chemical census toward a sample of\nprotostellar cores as part of the ALMA Survey of Orion Planck Galactic Cold\nClumps (ALMASOP) project. We report the detection of 11 hot corino sources,\nwhich exhibit compact emissions from warm and abundant COMs, among 56 Class 0/I\nprotostellar cores. All the hot corino sources discovered are likely Class 0\nand their sizes of the warm region ($>$ 100 K) are comparable to 100 au. The\nluminosity of the hot corino sources exhibits positive correlations with the\ntotal number of methanol and the extent of its emissions. Such correlations are\nconsistent with the thermal desorption picture for the presence of hot corino\nand suggest that the lower luminosity (Class 0) sources likely have a smaller\nregion with COMs emissions. With the same sample selection method and detection\ncriteria being applied, the detection rates of the warm methanol in the Orion\ncloud (15/37) and the Perseus cloud (28/50) are statistically similar when the\ncloud distances and the limited sample size are considered. Observing the same\nset of COM transitions will bring a more informative comparison between the\ncloud properties.", "category": "astro-ph_GA" }, { "text": "The HI Gas Disk Thickness of the Ultra-diffuse Galaxy AGC 242019: Ultra-diffuse galaxies (UDGs) are as faint as dwarf galaxies but whose sizes\nare similar to those of spiral galaxies. A variety of formation mechanisms have\nbeen proposed, some of which could result in different disk thicknesses. In\nthis study, we measure the radial profile of the HI scale height (h_g) and\nflaring angle (h_g/R) of AGC 242019 through the joint Poisson-Boltzmann\nequation based on its well spatially-resolved HI gas maps. The mean HI scale\nheight of AGC 242019 is \\approx 537.15 \\pm 89.4 pc, and the mean flaring\nangle is \\approx 0.19 \\pm 0.03. As a comparison, we also derive the\ndisk thickness for a sample of 14 dwarf irregulars. It is found that the HI\ndisk of AGC 242019 has comparable thickness to dwarfs. This suggests that AGC\n242019 is unlikely to experience much stronger stellar feedback than dwarf\ngalaxies, which otherwise leads to a thicker disk for this galaxy.", "category": "astro-ph_GA" }, { "text": "The Spitzer Space Telescope Survey of the Orion A and B Molecular Clouds\n II: the Spatial Distribution and Demographics of Dusty Young Stellar Objects: We analyze the spatial distribution of dusty young stellar objects (YSOs)\nidentified in the Spitzer Survey of the Orion Molecular clouds, augmenting\nthese data with Chandra X-ray observations to correct for incompleteness in\ndense clustered regions. We also devise a scheme to correct for spatially\nvarying incompleteness when X-ray data are not available. The local surface\ndensities of the YSOs range from 1 pc$^{-2}$ to over 10,000 pc$^{-2}$, with\nprotostars tending to be in higher density regions. This range of densities is\nsimilar to other surveyed molecular clouds with clusters, but broader than\nclouds without clusters. By identifying clusters and groups as continuous\nregions with surface densities $\\ge10$ pc$^{-2}$, we find that 59% of the YSOs\nare in the largest cluster, the Orion Nebular Cluster (ONC), while 13% of the\nYSOs are found in a distributed population. A lower fraction of protostars in\nthe distributed population is evidence that it is somewhat older than the\ngroups and clusters. An examination of the structural properties of the\nclusters and groups show that the peak surface densities of the clusters\nincrease approximately linearly with the number of members. Furthermore, all\nclusters with more than 70 members exhibit asymmetric and/or highly elongated\nstructures. The ONC becomes azimuthally symmetric in the inner 0.1 pc,\nsuggesting that the cluster is only $\\sim 2$ Myr in age. We find the star\nformation efficiency (SFE) of the Orion B cloud is unusually low, and that the\nSFEs of individual groups and clusters are an order of magnitude higher than\nthose of the clouds. Finally, we discuss the relationship between the young low\nmass stars in the Orion clouds and the Orion OB 1 association, and we determine\nupper limits to the fraction of disks that may be affected by UV radiation from\nOB stars or by dynamical interactions in dense, clustered regions.", "category": "astro-ph_GA" }, { "text": "Dust temperature uncertainties hamper the inference of dust and\n molecular gas masses from the dust continuum emission of quiescent\n high-redshift galaxies: Single flux density measurements at observed-frame sub-millimeter and\nmillimeter wavelengths are commonly used to probe dust and gas masses in\ngalaxies. In this Letter, we explore the robustness of this method to infer\ndust mass, focusing on quiescent galaxies, using a series of controlled\nexperiments on four massive haloes from the Feedback in Realistic Environments\n(FIRE) project. Our starting point is four star-forming, central galaxies at\nseven redshifts between z=1.5 and z=4.5. We generate modified quiescent\ngalaxies that have been quenched for 100Myr, 500Myr, or 1Gyr prior to each of\nthe studied redshifts by re-assigning stellar ages. We derive spectral energy\ndistributions for each fiducial and modified galaxy using radiative transfer.\nWe demonstrate that the dust mass inferred is highly dependent on the assumed\ndust temperature, T_dust, which is often unconstrained observationally.\nMotivated by recent work on quiescent galaxies that assumed T_dust~25K, we show\nthat the ratio between dust mass and 1.3mm flux density can be higher than\ninferred by up to an order of magnitude, due to the considerably lower dust\ntemperatures seen in non star-forming galaxies. This can lead to an\nunderestimation of dust mass (and, when sub-mm flux density is used as a proxy\nfor molecular gas content, gas mass). This underestimation is most severe at\nhigher redshifts, where the observed-frame 1.3mm flux density probes rest-frame\nwavelengths far from the Rayleigh-Jeans regime, and hence depends\nsuper-linearly on dust temperature. We fit relations between ratios of\nrest-frame far-infrared flux densities and mass-weighted dust temperature that\ncan be used to constrain dust temperatures from observations and hence derive\nmore reliable dust and molecular gas masses.", "category": "astro-ph_GA" }, { "text": "Galactic fountains and the rotation of disc-galaxy coronae: In galaxies like the Milky Way, cold (~ 10^4 K) gas ejected from the disc by\nstellar activity (the so-called galactic-fountain gas) is expected to interact\nwith the virial-temperature (~ 10^6 K) gas of the corona. The associated\ntransfer of momentum between cold and hot gas has important consequences for\nthe dynamics of both gas phases. We quantify the effects of such an interaction\nusing hydrodynamical simulations of cold clouds travelling through a hot medium\nat different relative velocities. Our main finding is that there is a velocity\nthreshold between clouds and corona, of about 75 km/s, below which the hot gas\nceases to absorb momentum from the cold clouds. It follows that in a disc\ngalaxy like the Milky Way a static corona would be rapidly accelerated: the\ncorona is expected to rotate and to lag, in the inner regions, by ~ 80-120 km/s\nwith respect to the cold disc. We also show how the existence of this velocity\nthreshold can explain the observed kinematics of the cold extra-planar gas.", "category": "astro-ph_GA" }, { "text": "Evolution of dust grain size distribution and grain porosity in galaxies: The radiative properties of interstellar dust are affected not only by the\ngrain size distribution but also by the grain porosity. We develop a model for\nthe evolution of size-dependent grain porosity and grain size distribution over\nthe entire history of galaxy evolution. We include stellar dust production,\nsupernova dust destruction, shattering, coagulation, and accretion. Coagulation\nis {assumed to be} the source of grain porosity. We use a one-zone model with a\nconstant dense gas fraction ($\\eta_\\mathrm{dense}$), which regulates the\nbalance between shattering and coagulation. We find that porosity develops\nafter small grains are sufficiently created by the interplay between shattering\nand accretion (at age $t\\sim 1$ Gyr for star formation time-scale\n$\\tau_\\mathrm{SF}=5$ Gyr) and are coagulated. The filling factor drops down to\n0.3 at grain radii $\\sim 0.03~\\mu$m for $\\eta_\\mathrm{dense}=0.5$. The grains\nare more porous for smaller $\\eta_\\mathrm{dense}$ because small grains, from\nwhich porous coagulated grains form, are more abundant. We also calculate the\nextinction curves based on the above results. The porosity steepens the\nextinction curve significantly for silicate, but not much for amorphous carbon.\nThe porosity also increases the collisional cross-sections and produces\nslightly more large grains through the enhanced coagulation; however, the\nextinction curve does not necessarily become flatter because of the steepening\neffect by porosity. We also discuss the implication of our results for the\nMilky Way extinction curve.", "category": "astro-ph_GA" }, { "text": "The Galactic Center Lobe Filled with Thermal Plasma: An observational result of a radio continuum and H92$\\alpha$ radio\nrecombination line of the Galactic Center Lobe (GCL), using the Yamaguchi 32 m\nradio telescope, is reported. The obtained spatial intensity distribution of\nthe radio recombination line shows two distinctive ridge-like structures\nextending from the galactic plane vertically to the north at the eastern and\nwestern sides of the galactic center, which are connected to each other at a\nlatitude of $1.2^{\\circ}$ to form a loop-like structure as a whole. This\nsuggests that most of the radio continuum emission of the GCL is free-free\nemission, and that the GCL is filled with thermal plasma. The east ridge of the\nGCL observed with the radio recombination line separates 30 pc from the radio\narc, which has been considered as a part of the GCL, but coincides with a ridge\nof the radio continuum at a galactic longitude of $0^{\\circ}$. The radial\nvelocity of the radio recombination line is found to be between $-4$ and $+10$\nkm s$^{-1}$ across the GCL. This velocity is much smaller than the one expected\nfrom the galactic rotation, and hence indicates that the GCL exists apart from\nthe galactic center. These characteristics of the GCL suggest that the\nlong-standing hypothesis that the GCL was created by an explosive activity in\nthe galactic center is unlikely, but favor that the GCL is a giant HII region.", "category": "astro-ph_GA" }, { "text": "VVV Survey Microlensing: the Galactic Longitude Dependence: We completed the search for microlensing events in the zero latitude area of\nthe Galactic bulge using the VVV Survey near-IR data obtained between 2010 and\n2015. We have now a total sample of N = 630 events Using the near-IR\nColor-Magnitude Diagram we selected the Red Clump sources to analyze the\nlongitude dependence of microlensing across the central region of the Galactic\nplane. The events show a homogeneous distribution, smoothly increasing in\nnumbers towards the Galactic centre, as predicted by different models. We find\na slight asymmetry, with a larger number of events toward negative longitudes\nthan positive longitudes. This asymmetry is seen both in the complete sample\nand the subsample of red clump giant sources, and it is possibly related with\nthe inclination of the bar along the line of sight. The timescale distribution\nis fairly symmetric with a peak in 17.4 $\\pm$ 1.0 days for the complete sample\n(N = 630 events), and 20.7 $\\pm$ 1.0 days for the Red Clump stars (N = 291\nevents), in agreement with previous results.", "category": "astro-ph_GA" }, { "text": "Is there a maximum mass for black holes in galactic nuclei?: The largest observed supermassive black holes (SMBHs) have a mass of M_BH ~\n10^{10} M_sun, nearly independent of redshift, from the local (z~0) to the\nearly (z>6) Universe. We suggest that the growth of SMBHs above a few 10^{10}\nM_sun is prevented by small-scale accretion physics, independent of the\nproperties of their host galaxies or of cosmology. Growing more massive BHs\nrequires a gas supply rate from galactic scales onto a nuclear region as high\nas >10^3 M_sun/yr. At such a high accretion rate, most of the gas converts to\nstars at large radii (~10-100 pc), well before reaching the BH. We adopt a\nsimple model (Thompson et al. 2005) for a star-forming accretion disk, and find\nthat the accretion rate in the sub-pc nuclear region is reduced to the smaller\nvalue of at most a few M_sun/yr. This prevents SMBHs from growing above\n~10^{11} M_sun in the age of the Universe. Furthermore, once a SMBH reaches a\nsufficiently high mass, this rate falls below the critical value at which the\naccretion flow becomes advection dominated. Once this transition occurs, BH\nfeeding can be suppressed by strong outflows and jets from hot gas near the BH.\nWe find that the maximum SMBH mass, given by this transition, is between\nM_{BH,max} ~ (1-6) * 10^{10} M_sun, depending primarily on the efficiency of\nangular momentum transfer inside the galactic disk, and not on other properties\nof the host galaxy.", "category": "astro-ph_GA" }, { "text": "A refined search for high-velocity gas in the Cygnus Loop supernova\n remnant: We present the results of a sensitive search for high-velocity gas in\ninterstellar absorption lines associated with the Cygnus Loop supernova remnant\n(SNR). We examine high-resolution, high signal-to-noise ratio optical spectra\nof six stars in the Cygnus Loop region with distances greater than ~700 pc. All\nstars show low-velocity Na I and Ca II absorption. However, only one star, HD\n198301, exhibits high-velocity Ca II absorption components, at velocities of\n+62, +82, and +96 km/s. The distance to this star of ~870 pc helps to constrain\nthe distance to the receding edge of the Cygnus Loop's expanding shock front.\nOne of our targets, HD 335334, was previously thought to exhibit high positive\nand high negative velocity interstellar Na I and Ca II absorption. This was one\nfactor leading Fesen et al. to derive a distance to the Cygnus Loop of 725 pc.\nHowever, we find that HD 335334 is in fact a double-line spectroscopic binary\nand shows no evidence of high-velocity interstellar absorption. As such, the\ndistance to HD 335334 cannot be used to constrain the distance to the Cygnus\nLoop. Our detection of Ca II absorption approaching 100 km/s toward HD 198301\nis the first conclusive detection of high-velocity absorption from a low\nionization species associated with the Cygnus Loop SNR. A large jump in the Na\nI column density toward BD+31 4218, a star located beyond the northwestern\nboundary of the Cygnus Loop, helps to constrain the distance to a large\nmolecular cloud complex with which the Cygnus Loop is evidently interacting.", "category": "astro-ph_GA" }, { "text": "Ly-alpha Radiative Transfer: A Stokes Vector Approach to Ly-alpha\n Polarization: Ly-alpha emitting galaxies and giant Ly-alpha blobs (LABs) have been\nextensively observed to study the formation history of galaxies. However, the\norigin of their extended Ly-alpha emission, especially of LABs, remains\ncontroversial. Polarization signals from some LABs have been discovered, and\nthis is commonly interpreted as strong evidence supporting that the extended\nLy-alpha emission originates from the resonance scattering. The Monte Carlo\nLy-alpha radiative transfer code LaRT is updated to investigate the\npolarization of Ly-alpha using the Stokes vector formalism. We apply LaRT to a\nfew models to explore the fundamental polarization properties of Ly-alpha.\nInterestingly, individual Ly-alpha photon packets are found to be almost\ncompletely polarized by a sufficient number of scatterings (N_scatt > 10^4-10^5\nin a static medium) or Doppler shifts induced by gas motion, even starting from\nunpolarized light. It is also found that the polarization pattern can exhibit a\nnon-monotonically increasing pattern in some cases, besides the commonly-known\ntrend that the polarization monotonically increases with radius. The\npolarization properties are primarily determined by the degree of polarization\nof individual photon packets and the anisotropy of the Ly-alpha radiation\nfield, which are eventually controlled by the medium's optical depth and\nvelocity field. If once Ly-alpha photon packets achieve ~100% polarization, the\nradial profile of polarization appears to correlate with the surface brightness\nprofile. A steep surface brightness profile tends to yield a rapid increase of\nthe linear polarization near the Ly-alpha source location. In contrast, a\nshallow surface brightness profile gives rise to a slowly increasing\npolarization pattern.", "category": "astro-ph_GA" }, { "text": "No Evidence for [O III] Variability in Mrk 142: Using archival data from the 2008 Lick AGN Monitoring Project, Zhang & Feng\n(2016) claimed to find evidence for flux variations in the narrow [O III]\nemission of the Seyfert 1 galaxy Mrk 142 over a two-month time span. If\ncorrect, this would imply a surprisingly compact size for the narrow-line\nregion. We show that the claimed [O III] variations are merely the result of\nrandom errors in the overall flux calibration of the spectra. The data do not\nprovide any support for the hypothesis that the [O III] flux was variable\nduring the 2008 monitoring period.", "category": "astro-ph_GA" }, { "text": "New Limits on an Intermediate Mass Black Hole in Omega Centauri: I.\n Hubble Space Telescope Photometry and Proper Motions: We analyze data from the Hubble Space Telescope's Advanced Camera for Surveys\nof the globular cluster Omega Cen. We construct a photometric and proper-motion\ncatalog using the GO-9442, GO-10252, and GO-10775 data sets. The 2.5- to 4-year\nbaseline between observations yields a catalog of some 10^5 proper motions,\nwith 53,382 high-quality measurements in a central field. We determine the\ncluster center to ~1-arcsecond accuracy using two different star-count methods,\nand a completely independent method using 2MASS images. We also determine the\nkinematical center of the proper motions, which agrees with the star-count\ncenter to within its uncertainty. The proper-motion dispersion of the cluster\nincreases gradually inwards, but there is no variation in kinematics with\nposition within the central ~15 arcsec: there is no dispersion cusp and no\nstars with unusually high velocities. We measure for the first time in any\nglobular cluster the variation in proper-motion dispersion with mass along the\nmain sequence, and find the cluster not yet to be in equipartition. Our\nproper-motion results do not confirm the arguments put forward by Noyola,\nGebhardt & Bergmann to suspect an intermediate-mass black hole (IMBH) in Omega\nCen. In Paper II we present new dynamical models for the high-quality data\npresented here, with the aim of putting quantitative contraints on the mass of\nany possible IMBH.", "category": "astro-ph_GA" }, { "text": "SAMI-HI: The HI view of the H$\u03b1$ Tully-Fisher relation and data\n release: We present SAMI-HI, a survey of the atomic hydrogen content of 296 galaxies\nwith integral field spectroscopy available from the SAMI Galaxy Survey. The\nsample spans nearly 4 dex in stellar mass ($M_\\star = 10^{7.4}-10^{11.1}~ \\rm\nM_\\odot$), redshift $z<0.06$, and includes new Arecibo observations of 153\ngalaxies, for which we release catalogues and HI spectra. We use these data to\ncompare the rotational velocities obtained from optical and radio observations\nand to show how systematic differences affect the slope and scatter of the\nstellar-mass and baryonic Tully-Fisher relations. Specifically, we show that\nH$\\alpha$ rotational velocities measured in the inner parts of galaxies (1.3\neffective radii in this work) systematically underestimate HI global\nmeasurements, with HI/H$\\alpha$ velocity ratios that increase at low stellar\nmasses, where rotation curves are typically still rising and H$\\alpha$\nmeasurements do not reach their plateau. As a result, the H$\\alpha$ stellar\nmass Tully-Fisher relation is steeper (when $M_\\star$ is the independent\nvariable) and has larger scatter than its HI counterpart. Interestingly, we\nconfirm the presence of a small fraction of low-mass outliers of the H$\\alpha$\nrelation that are not present when HI velocity widths are used and are not\nexplained by \"aperture effects\". These appear to be highly disturbed systems\nfor which H$\\alpha$ widths do not provide a reliable estimate of the rotational\nvelocity. Our analysis reaffirms the importance of taking into account\ndifferences in velocity definitions as well as tracers used when interpreting\noffsets from the Tully-Fisher relation, at both low and high redshifts and when\ncomparing with simulations.", "category": "astro-ph_GA" }, { "text": "Another Look at the EBS: A Stellar Debris Stream and a Possible\n Progenitor: Using the Sloan Digital Sky Survey Data Release 7, we reexamine the Eastern\nBanded Structure (EBS), a stellar debris stream first discovered in Data\nRelease 5 and more recently detected in velocity space by Schlaufman et al. The\nvisible portion of the stream is 18 degrees long, lying roughly in the Galactic\nAnticenter direction and extending from Hydra to Cancer. At an estimated\ndistance of 9.7 kpc, the stream is approximately 170 pc across on the sky. The\ncurvature of the stream implies a fairly eccentric box orbit that passes close\nto both the Galactic center and to the sun, making it dynamically distinct from\nthe nearby Monoceros, Anticenter, and GD-1 streams. Within the stream is a\nrelatively strong, 2 degree-wide concentration of stars with a very similar\ncolor-magnitude distribution that we designate Hydra I. Given its prominence\nwithin the stream and its unusual morphology, we suggest that Hydra I is the\nlast vestige of the EBS's progenitor, possibly already unbound or in the final\nthroes of tidal dissolution. Though both Hydra I and the EBS have a relatively\nhigh velocity dispersion, given the comparatively narrow width of the stream\nand the high frequency of encounters with the bulge and massive constituents of\nthe disk that such an eccentric orbit would entail, we suggest that the\nprogenitor was likely a globular cluster, and that both it and the stream have\nundergone significant heating over time.", "category": "astro-ph_GA" }, { "text": "Toward an Empirical Theory of Pulsar Emission. IX. On the Peculiar\n Properties and Geometric Regularity of Lyne & Manchester's \"Partial Cone\"\n Pulsars: Lyne & Manchester (1988) identified a group of some 50 pulsars they called\n\"partial cones\" which they found difficult to classify and interpret. They were\nnotable for their asymmetric average profiles and asymmetric polarization\nposition-angle (PPA) traverses, wherein the steepest gradient (SG) point fell\ntoward one edge of the total intensity profile. Over the last two decades, this\npopulation of pulsars has raised cautions regarding the core/cone model of the\nradio pulsar-emission beam which implies a high degree of order, symmetry and\ngeometric regularity. In this paper we reinvestigate this population \"partial\ncone\" pulsars on the basis of new single pulse polarimetric observations of 39\nof them, observed with the Giant Meterwave Radio Telescope in India and the\nArecibo Observatory in Puerto Rico. These highly sensitive observations help us\nto establish that most of these \"partial cones\" exhibit a core/cone structure\njust as did the \"normal\" pulsars studied in the earlier papers of this series.\nIn short, we find that many of these \"partial cones\" are partial in the sense\nthat the emission above different areas of their polar caps can be (highly)\nasymmetric. However, when studied closely we find that their emission\ngeometries are overall identical to core/double cone structure encountered\nearlier-that is, with specific conal dimensions scaling as the polar cap size.", "category": "astro-ph_GA" }, { "text": "Predicting Images for the Dynamics Of stellar Clusters (\u03c0-DOC): a\n deep learning framework to predict mass, distance and age of globular\n clusters: Dynamical mass estimates of simple systems such globular clusters (GCs) still\nsuffer from up to a factor of 2 uncertainty. This is primarily due to the\noversimplifications of standard dynamical models that often neglect the effects\nof the long-term evolution of GCs. Here, we introduce a new approach to measure\nthe dynamical properties of GCs, based on the combination of a deep-learning\nframework and the large amount of data from direct $N$-body simulations. Our\nalgorithm, $\\texttt{$\\pi$-DOC}$ ($\\textit{Predicting Images for the Dynamics Of\nstellar Clusters}$) is composed of two convolutional networks, trained to learn\nthe non-trivial transformation between an observed GC luminosity map and its\nassociated mass distribution, age, and distance. The training set is made of\nV-band luminosity and mass maps constructed as mock observations from $N$-body\nsimulations. The tests on $\\texttt{$\\pi$-DOC}$ demonstrate that we can predict\nthe mass distribution with a mean error per pixel of 27%, and the age and\ndistance with an accuracy of 1.5 Gyr and 6 kpc, respectively. In turn, we\nrecover the shape of the mass-to-light profile and its global value with a mean\nerror of 12%, which implies that we efficiently trace mass segregation. A\npreliminary comparison with observations indicates that our algorithm is able\nto predict the dynamical properties of GCs within the limits of the training\nset. These encouraging results demonstrate that our deep-learning framework and\nits forward modelling approach can offer a rapid and adaptable tool competitive\nwith standard dynamical models.", "category": "astro-ph_GA" }, { "text": "First [NII]122$\u03bc$m line detection in a QSO-SMG pair BRI 1202-0725 at\n $z=4.69$: We report the first detection obtained with ALMA of the [N II] 122$\\mu$m line\nemission from a galaxy group BRI 1202-0725 at $z=4.69$ consisting of a QSO and\na submilimeter-bright galaxy (SMG). Combining with a detection of [N II]\n205$\\mu$m line in both galaxies, we constrain the electron densities of the\nionized gas based on the line ratio of [NII]122/205. The derived electron\ndensities are $26^{+12}_{-11}$ and $134^{+50}_{-39}$ cm$^{-3}$ for the SMG and\nthe QSO, respectively. The electron density of the SMG is similar to that of\nthe Galactic Plane and to the average of the local spirals. Higher electron\ndensities by up to a factor of three could, however, be possible for systematic\nuncertainties of the line flux estimates. The electron density of the QSO is\ncomparable to high-$z$ star-forming galaxies at $z=1.5-2.3$, obtained using\nrest-frame optical lines and with the lower limits suggested from stacking\nanalysis on lensed starbursts at $z=1-3.6$ using the same tracer of [NII]. Our\nresults suggest a large scatter of electron densities in global scale at fixed\nstar formation rates for extreme starbursts. The success of the [N II]\n122$\\mu$m and 205$\\mu$m detections at $z=4.69$ demonstrates the power of future\nsystematic surveys of extreme starbursts at $z>4$ for probing the ISM\nconditions and the effects on surrounding environments.", "category": "astro-ph_GA" }, { "text": "The role of the Galactic bar in the chemical evolution of the Milky Way: In the absence of an interaction, central bars might be the most effective\nmechanism for radial motions of gas in barred spiral galaxies, which represent\ntwo-thirds of disc galaxies. The dynamical effects induced by bars in the first\nfew kpc of discs might play an important role in the disc profiles in this\nregion. In this work, a chemical evolution model with radial gas flows is\nproposed in order to mimic the effects of the Milky Way bar in the bulge and\ninner disc. The model is an update of a chemical evolution model with the\ninclusion of radial gas flows in the disc and bulge. The exchange of gas\nbetween the cylindrical concentric regions that form the Galaxy is modelled\nconsidering the flows of gas from and to the adjacent cylindrical regions. The\nmost recent data for the bulge metallicity distribution are reproduced by means\nof a single and longer bulge collapse time-scale (2 Gyr) than other chemical\nevolution models predict. The model is able to reproduce the peak in the\npresent star formation rate at 4 kpc and the formation of the molecular gas\nring. The model with a bar predicts a flattening of the oxygen radial gradient\nof the disc. Additionally, models with radial gas flows predict a higher star\nformation rate during the formation of the bulge. This is in agreement with the\nmost recent observations of the star formation rate at the centre of massive\nbarred spiral galaxies.", "category": "astro-ph_GA" }, { "text": "The impact of stripped Nuclei on the Super-Massive Black Hole number\n density in the local Universe: The recent discovery of super-massive black holes (SMBHs) in the centers of\nhigh-mass ultra compact dwarf galaxies (UCDs) suggests that at least some UCDs\nare the stripped nuclear star clusters of lower mass galaxies. Tracing these\nformer nuclei of stripped galaxies provides a unique way to track the assembly\nhistory of a galaxy or galaxy cluster. In this paper we present a new method to\nestimate how many UCDs host an SMBH in their center and thus are stripped\ngalaxy nuclei. We revisit the dynamical mass measurements that suggest many\nUCDs have more mass than expected from stellar population estimates, which\nrecent observations have shown is due to the presence of an SMBH. We revise the\nstellar population mass estimates using a new empirical relation between the\nmass-to-light ratio (M/L) and metallicity, and use this to predict which UCDs\nare most likely to host an SMBH. This enables us to calculate the fraction of\nUCDs that host SMBHs across their entire luminosity range for the first time.\nWe then apply the SMBH occupation fraction to the observed luminosity function\nof UCDs and estimate that in the Fornax and Virgo cluster alone there should be\n$69^{+32}_{-25}$ stripped nuclei with SMBHs. This analysis shows that stripped\nnuclei with SMBHs are almost as common in clusters as present-day galaxy\nnuclei. We estimate the local SMBH number density in stripped nuclei to\n$3-8\\times10^{-3}Mpc^{-3}$, which represents a significant fraction (10-40\\%)\nof the SMBH density in the local Universe. These SMBHs hidden in stripped\nnuclei will increase expected event rates for tidal disruption events and\nSMBH-SMBH and SMBH-BH mergers. The existence of numerous stripped nuclei with\nSMBHs are a direct consequence of hierarchical galaxy formation, but until now\ntheir impact on the SMBH density had not been quantified.", "category": "astro-ph_GA" }, { "text": "Gas accretion onto the disc of a simulated Milky Way-mass galaxy: In the standard paradigm of galaxy formation and evolution, the baryonic\ncomponent of galaxies forms from the collapse and condensation of gas within\ndark matter haloes, and later grows from continuous accretion of gaseous mass,\nboth in diffuse form and in mergers with other systems. After a first period of\nrapid and violent halo growth, the gas settles into a rotationally-supported\nstructure, eventually giving rise to the formation of a stellar disc. Stars\nevolve and return chemically-processed gas and energy to the interstellar\nmedium, mainly through Type II supernova explosions. In the disc region, the\ncosmological accretion of gas combines with the outflows resulting from\nsupernovae, affecting the hydrodynamical and structural properties of the disc\nand producing gas flows in the vertical and radial directions. In this work, we\nuse a simulation of the Auriga Project, a suite of magneto-hydrodynamical,\nzoom-in cosmological simulations of Milky Way-like galaxies, to study the\ntemporal and radial dependencies of gas accretion onto the disc. We also\ninvestigate the disc evolution, focusing on the inside-out disc formation\nscenario, which is one of the fundamental hypotheses of chemical evolution\nmodels of the Galaxy.", "category": "astro-ph_GA" }, { "text": "Hierarchical Bayesian inference of the Initial Mass Function in\n Composite Stellar Populations: The initial mass function (IMF) is a key ingredient in many studies of galaxy\nformation and evolution. Although the IMF is often assumed to be universal,\nthere is continuing evidence that it is not universal. Spectroscopic studies\nthat derive the IMF of the unresolved stellar populations of a galaxy often\nassume that this spectrum can be described by a single stellar population\n(SSP). To alleviate these limitations, in this paper we have developed a unique\nhierarchical Bayesian framework for modelling composite stellar populations\n(CSPs). Within this framework we use a parameterized IMF prior to regulate a\ndirect inference of the IMF. We use this new framework to determine the number\nof SSPs that is required to fit a set of realistic CSP mock spectra. The CSP\nmock spectra that we use are based on semi-analytic models and have an IMF that\nvaries as a function of stellar velocity dispersion of the galaxy. Our results\nsuggest that using a single SSP biases the determination of the IMF slope to a\nhigher value than the true slope, although the trend with stellar velocity\ndispersion is overall recovered. If we include more SSPs in the fit, the\nBayesian evidence increases significantly and the inferred IMF slopes of our\nmock spectra converge, within the errors, to their true values. Most of the\nbias is already removed by using two SSPs instead of one. We show that we can\nreconstruct the variable IMF of our mock spectra for signal-to-noise ratios\nexceeding $\\sim$75.", "category": "astro-ph_GA" }, { "text": "Reproducing sub-millimetre galaxy number counts with cosmological\n hydrodynamic simulations: Matching the number counts of high-$z$ sub-millimetre-selected galaxies\n(SMGs) has been a long standing problem for galaxy formation models. In this\npaper, we use 3D dust radiative transfer to model the sub-mm emission from\ngalaxies in the SIMBA cosmological hydrodynamic simulations, and compare\npredictions to the latest single-dish observational constraints on the\nabundance of 850$\\mathrm{\\mu m}$-selected sources. We find good agreement with\nthe shape of the integrated 850$\\mathrm{\\mu m}$ luminosity function, and the\nnormalisation is within 0.25 dex at $> 3 \\; \\mathrm{mJy}$, unprecedented for a\nfully cosmological hydrodynamic simulation, along with good agreement in the\nredshift distribution of bright SMGs. The agreement is driven primarily by\nSIMBA's good match to infrared measures of the star formation rate (SFR)\nfunction between $z = 2-4$ at high SFRs. Also important is the self-consistent\non-the-fly dust model in SIMBA, which predicts, on average, higher dust masses\n(by up to a factor of 2.5) compared to using a fixed dust-to-metals ratio of\n0.3. We construct a lightcone to investigate the effect of far-field blending,\nand find that 52% of sources are blends of multiple components, which makes a\nsmall contribution to the normalisation of the bright-end of the number counts.\nWe provide new fits to the 850$\\mathrm{\\mu m}$ luminosity as a function of SFR\nand dust mass. Our results demonstrate that exotic solutions to the discrepancy\nbetween sub-mm counts in simulations and observations, such as a top-heavy IMF,\nare unnecessary, and that sub-millimetre-bright phases are a natural\nconsequence of massive galaxy evolution.", "category": "astro-ph_GA" }, { "text": "A High Resolution Study of the Atomic Hydrogen in CO-Rich Early-Type\n Galaxies: We present an analysis of new and archival VLA HI observations of a sample of\neleven early-type galaxies rich in CO, with detailed comparisons of CO and HI\ndistributions and kinematics. The early-type sample consists of both lenticular\nand elliptical galaxies in a variety of environments. A range of morphologies\nand environments were selected in order to give a broader understanding of the\norigins, distribution, and fate of the cold gas in early-type galaxies. Six of\nthe eleven galaxies in the sample are detected in both HI and CO. The H$_{2}$\nto HI mass ratios for this sample range from 0.2-120. The HI morphologies of\nthe sample are consistent with that of recent HI surveys of early-type galaxies\nwhich also find a mix of HI morphologies and masses, low HI peak surface\ndensities, and a lack of HI in early-type galaxies which reside in high density\nenvironments. The HI-detected galaxies have a wide range of HI masses\n(1.4$\\times10^{6}$ to 1.1$\\times10^{10}$ M$_{\\odot}$). There does not appear to\nbe any correlation between the HI mass and morphology (E versus S0). When HI is\ndetected, it is centrally peaked - there are no central kpc-scale central HI\ndepressions like those observed for early-type spiral galaxies at similar\nspatial resolutions and scales. A kinematic comparison between the HI and CO\nindicates that both cold gas components share the same origin. The primary goal\nof this and a series of future papers is to better understand the relationship\nbetween the atomic and molecular gas in early-type galaxies, and to compare the\nobserved relationships with those of spiral galaxies where this relationship\nhas been studied in depth.", "category": "astro-ph_GA" }, { "text": "Herschel Spectroscopy of the Taffy Galaxies (UGC 12914/12915 = VV 254):\n Enhanced [C II] emission in the collisionally-formed bridge: Using the PACS and SPIRE spectrometers on-board Herschel, we obtained\nobservations of the Taffy galaxies (UGC 12914/12915) and bridge. The Taffy\nsystem is believed to be the result of a face-on collision between two gas-rich\ngalaxies, in which the stellar disks passed through each other, but the gas was\ndispersed into a massive H I and molecular bridge between them. Emission is\ndetected and mapped in both galaxies and the bridge in the [C II]157.7 $\\mu$m\nand [O I]63.2 $\\mu$m fine-structure lines. Additionally, SPIRE FTS spectroscopy\ndetects the [C I] $^3$P$_2$$\\rightarrow$$^3$P$_1$(809.3 GHz) and [C I]\n$^3$P$_1$$\\rightarrow$$3$P$_0$(492.2 GHz) neutral carbon lines, and weakly\ndetects high-J CO transitions in the bridge. These results indicate that the\nbridge is composed of a warm multi-phase medium consistent with shock and\nturbulent heating. Despite low star formation rates in the bridge, the [C II]\nemission appears to be enhanced, reaching [C II]/FIR ratios of 3.3% in parts of\nthe bridge. Both the [C II] and [O I] lines show broad intrinsic\nmulti-component profiles, similar to those seen in previous CO 1-0 and H I\nobservations. The [C II] emission shares similar line profiles with both the\ndouble-peaked H I profiles and shares a high-velocity component with\nsingle-peaked CO profiles in the bridge, suggesting that the [C II] emission\noriginates in both the neutral and molecular phases. We show that it is\nfeasible that a combination of turbulently heated H$_2$ and high column-density\nH I, resulting from the galaxy collision, is responsible for the enhanced [C\nII] emission.", "category": "astro-ph_GA" }, { "text": "No evidence for large-scale outflows in the extended ionised halo of\n ULIRG Mrk273: We present deep new GTC/OSIRIS narrow-band images and optical WHT/ISIS\nlong-slit spectroscopy of the merging system Mrk273 that show a spectacular\nextended halo of warm ionised gas out to a radius of $\\sim45$ kpc from the\nsystem nucleus. Outside of the immediate nuclear regions (r > 6 kpc), there is\nno evidence for kinematic disturbance in the ionised gas: in the extended\nregions covered by our spectroscopic slits the emission lines are relatively\nnarrow (FWHM $\\lesssim$ 350 km$\\rm s^{-1}$) and velocity shifts small\n(|$\\Delta$V| $\\lesssim{} $250 km$\\rm s^{-1}$). This is despite the presence of\npowerful near-nuclear outflows (FWHM > 1000 km$\\rm s^{-1}$; |$\\Delta$V| > 400\nkm$\\rm s^{-1}$; r < 6 kpc). Diagnostic ratio plots are fully consistent with\nSeyfert 2 photo-ionisation to the NE of the nuclear region, however to the SW\nthe plots are more consistent with low-velocity radiative shock models. The\nkinematics of the ionised gas, combined with the fact that the main structures\nare aligned with low-surface-brightness tidal continuum features, are\nconsistent with the idea that the ionised halo represents tidal debris left\nover from a possible triple-merger event, rather than a reservoir of outflowing\ngas.", "category": "astro-ph_GA" }, { "text": "Differences in Halo-Scale Environments between Type 1 and Type 2 AGNs at\n Low Redshift: Using low-redshift (z<0.09) samples of AGNs, normal galaxies and groups of\ngalaxies selected from the Sloan Digital Sky Survey (SDSS), we study the\nenvironments of type 1 and type 2 AGNs both on small and large scales.\nComparisons are made for galaxy samples matched in redshift, $r$-band\nluminosity, [OIII] luminosity, and also the position in groups (central or\nsatellite). We find that type 2 AGNs and normal galaxies reside in similar\nenvironments. Type 1 and type 2 AGNs have similar clustering properties on\nlarge scales ($\\gtrsim1$Mpc), but at scales smaller than 100 kpc, type 2s have\nsignificant more neighbors than type 1s ($3.09\\pm0.69$ times more for central\nAGNs at $\\lesssim30$kpc). These results suggest that type 1 and type 2 AGNs are\nhosted by halos of similar masses, as is also seen directly from the mass\ndistributions of their host groups ($\\sim10^{12}h^{-1} M_{\\odot}$ for centrals\nand $\\sim10^{13}h^{-1} M_{\\odot}$ for satellites). Type~2s have significantly\nmore satellites around them, and the distribution of their satellites is also\nmore centrally concentrated. The host galaxies of both types of AGNs have\nsimilar optical properties, but their infrared colors are significantly\ndifferent. Our results suggest that the simple unified model based solely on\ntorus orientation is not sufficient, but that galaxy interactions in dark\nmatter halos must have played an important role in the formation of the dust\nstructure that obscures AGNs.", "category": "astro-ph_GA" }, { "text": "HI absorption spectra for Supernova Remnants in the VGPS survey: The set of supernova remnants (SNR) from Green's SNR catalog which are found\nin the VLA Galactic Plane Survey (VGPS) are the objects considered in this\nstudy. For these SNR, we extract and analyse HI absorption spectra in a uniform\nway and construct a catalogue of absorption spectra and distance\ndeterminations.", "category": "astro-ph_GA" }, { "text": "Outflows, Accretion, and Clustered Protostellar Cores around a Forming O\n Star: We present a Submillimeter Array study in the 1.3 mm waveband of the NGC 7538\nIRS 1--3 massive star-forming region. The brightest core in the mm continuum\nmap, MM1, harbors the IRS 1 young O star. The core has a gas temperature of\nabout 245 K and shows spatially unresolved emission in complex organic\nmolecules, all typical of a hot molecular core. Toward MM1, redshifted\nabsorption is seen in molecular lines with different energies above the ground\nstate. This absorption probes inward motion of the dense gas toward the central\nyoung O star, and the estimated mass accretion rate reaches 10^{-3} Msun/yr.\nMultiple outflows are seen in the CO and 13CO maps. The gas mass of 50 Msun and\nmass outflow rate of 2.5 by 10^{-3} Msun/yr measured in CO line wings are\ndominated by the MM1 outflow, which is most likely driven by a fast wide-angle\nwind. Apart from MM1, we discover eight new dusty cores, MM2--9, within a\nprojected distance of 0.35 pc from MM1. These cores show no counterpart in\ninfrared or radio continuum emission, while seven of them appear to be forming\nintermediate- to high-mass stars. This manifests a deeply embedded star-forming\ncomponent of the parent cloud of IRS 1--3. Apparently we are observing a\nTrapezium system in formation, and the system is presumably surrounded by a\ncluster of lower mass stars.", "category": "astro-ph_GA" }, { "text": "Stochastic 2-D Models of Galaxy Disk Evolution. The Galaxy M33: We have developed a fast numerical 2-D model of galaxy disk evolution\n(resolved along the galaxy radius and azimuth) by adopting a scheme of\nparameterized stochastic self-propagating star formation. We explore the\nparameter space of the model and demonstrate its capability to reproduce 1-D\nradial profiles of the galaxy M33: gas surface density, surface brightness in\nthe i and GALEX FUV passbands, and metallicity.", "category": "astro-ph_GA" }, { "text": "On the Helium fingers in the intracluster medium: In this paper we investigate the convection phenomenon in the intracluster\nmedium (the weakly-collisional magnetized inhomogeneous plasma permeating\ngalaxy clusters) where the concentration gradient of the Helium ions is not\nignorable. To this end, we build upon the general machinery employed to study\nthe salt finger instability found in the oceans. The salt finger instability is\na form of double diffusive convection where the diffusions of two physical\nquantities---heat and salt concentrations---occur with different diffusion\nrates. The analogous instability in the intracluster medium may result owing to\nthe magnetic field mediated anisotropic diffusions of the heat and the Helium\nions (in the sea of the Hydrogen ions and the free electrons). These two\ndiffusions have inherently different diffusion rates. Hence the convection\ncaused by the onset of this instability is an example of double diffusive\nconvection in the astrophysical settings. A consequence of this instability is\nthe formation of the vertical filamentary structures having more concentration\nof the Helium ions with respect to the immediate neighbourhoods of the\nfilaments. We term these structures as Helium fingers in analogy with the salt\nfingers found in the case of the salt finger instability. Here we show that the\nwidth of a Helium finger scales as one-fourth power of the radius of the inner\nregion of the intracluster medium in the supercritical regime. We also\ndetermine the explicit mathematical expression of the criterion for the onset\nof the heat-flux-driven buoyancy instability modified by the presence of\ninhomogeneously distributed Helium ions.", "category": "astro-ph_GA" }, { "text": "The Galactic bar and the large scale velocity gradients in the Galactic\n disk: Aims: We investigate whether the cylindrical (galactocentric) radial velocity\ngradient of ~ -3 km/s/kpc, directed radially from the Galactic center and\nrecently observed in the stars of the solar neighborhood with the RAVE survey,\ncan be explained by the resonant effects of the bar near the solar\nneighborhood.\n Methods: We compared the results of test particle simulations of the Milky\nWay with a potential that includes a rotating bar with observations from the\nRAVE survey. To this end we applied the RAVE selection function to the\nsimulations and convolved these with the characteristic RAVE errors. We\nexplored different \"solar neighborhoods\" in the simulations, as well as\ndifferent bar models\n Results: We find that the bar induces a negative radial velocity gradient at\nevery height from the Galactic plane, outside the outer Lindblad resonance and\nfor angles from the long axis of the bar compatible with the current estimates.\nThe selection function and errors do not wash away the gradient, but often make\nit steeper, especially near the Galactic plane, because this is where the RAVE\nsurvey is less radially extended. No gradient in the vertical velocity\nispresent in our simulations, from which we may conclude that this cannot be\ninduced by the bar.", "category": "astro-ph_GA" }, { "text": "Taking apart the dynamical clock. Fat-tailed dynamical kicks shape the\n blue-straggler star bimodality: In globular clusters, blue straggler stars are heavier than the average star,\nso dynamical friction strongly affects them. The radial distribution of BSS,\nnormalized to a reference population, appears bimodal in a fraction of Galactic\nGCs, with a density peak in the core, a prominent zone of avoidance at\nintermediate radii, and again higher density in the outskirts. The zone of\navoidance appears to be located at larger radii the more relaxed the host\ncluster, acting as a sort of dynamical clock. We use a new method to compute\nthe evolution of the BSS radial distribution under dynamical friction and\ndiffusion. We evolve our BSS in the mean cluster potential under dynamical\nfriction plus a random fluctuating force, solving the Langevin equation with\nthe Mannella quasi symplectic scheme. This amounts to a new simulation method\nwhich is much faster and simpler than direct N-body codes but retains their\nmain feature: diffusion powered by strong, if infrequent, kicks. We compute the\nradial distribution of initially unsegregated BSS normalized to a reference\npopulation as a function of time. We trace the evolution of its minimum,\ncorresponding to the zone of avoidance. We compare the evolution under kicks\nextracted from a Gaussian distribution to that obtained using a Holtsmark\ndistribution. The latter is a fat tailed distribution which correctly models\nthe effects of close gravitational encounters. We find that the zone of\navoidance moves outwards over time, as expected based on observations, only\nwhen using the Holtsmark distribution. Thus the correct representation of near\nencounters is crucial to reproduce the dynamics of the system. We confirm and\nextend earlier results that showed how the dynamical clock indicator depends\nboth on dynamical friction and effective diffusion powered by dynamical\nencounters.", "category": "astro-ph_GA" }, { "text": "Radio--Far infrared correlation in \"blue cloud\" galaxies with 0300). The observed radio spectrum\nof PSO J191$+$86 shows a possible turnover around $\\sim$1 GHz (i.e., $\\sim$6\nGHz in the rest frame), making it a Gigahertz-Peaked Spectrum (GPS) source.\nHowever, variability could affect the real shape of the radio spectrum, since\nthe data in hand have been taken $\\sim$25 years apart. By assuming a peak of\nthe observed radio spectrum between 1 and 2 GHz (i.e. $\\sim$ 6 and 13 GHz in\nthe rest-frame) we found a linear size of the source of $\\sim$10-30 pc and a\ncorresponding kinetic age of 150-460 yr. This would make PSO J191$+$86 a newly\nborn radio source. However, the large X-ray luminosity (5.3$\\times$10$^{45}$\nerg s$^{-1}$), the flat X-ray photon index ($\\Gamma_X$=1.32) and the\noptical-X-ray spectral index ($\\tilde{\\alpha_{ox}}$=1.329) are typical of\nblazars. This could indicate that the non-thermal emission of PSO J191$+$86 is\nDoppler boosted. Further radio observations (both on arcsec and parsec scales)\nare necessary to better investigate the nature of this powerful radio QSO.", "category": "astro-ph_GA" }, { "text": "VII Zw 403: HI Structure in a Blue Compact Dwarf Galaxy: We present optical (UBVJ), ultraviolet (FUV, NUV), and high resolution atomic\nhydrogen (HI) observations of the nearby blue compact dwarf (BCD), VII Zw 403.\nWe find that VII Zw 403 has a relatively high HI mass-to-light ratio for a BCD.\nThe rotation velocity is nominally 10-15 km/s, but rises to ~20 km/s after\ncorrection for the ~8-10 km/s random motions present in the gas. The velocity\nfield is complex; including a variation in the position angle of the major axis\ngoing from the NE to the SW parts of the galaxy. Our high resolution HI maps\nreveal structure in the central gas, including a large, low-density HI\ndepression or hole between the southern and northern halves of the galaxy,\ncoincident with an unresolved x-ray source. Although interactions have been\nproposed as the triggering mechanism for the vigorous star formation occurring\nin BCDs, VII Zw 403 does not seem to have been tidally triggered by an external\ninteraction, as we have found no nearby possible perturbers. It also doesn't\nappear to fall in the set of galaxies that exhibit a strong central mass\ndensity concentration, as its optical scale length is large in comparison to\nsimilar systems. However, there are some features that are compatible with an\naccretion event: optical/HI axis misalignment, a change in position angle of\nthe kinematic axis, and a complex velocity field.", "category": "astro-ph_GA" }, { "text": "Chemical Cartography. I. A Carbonicity Map of the Galactic Halo: We present the first map of carbonicity, [C/Fe], for the halo system of the\nMilky Way, based on a sample of over 100,000 main-sequence turnoff stars with\navailable spectroscopy from the Sloan Digital Sky Survey. This map, which\nexplores distances up to 15 kpc from the Sun, reveals clear evidence for the\ndual nature of the Galactic halo, based on the spatial distribution of stellar\ncarbonicity. The metallicity distribution functions of stars in the inner- and\nouter-halo regions of the carbonicity map reproduce those previously argued to\narise from contributions of the inner- and outer-halo populations, with peaks\nat [Fe/H] = -1.5 and -2.2, respectively. From consideration of the absolute\ncarbon abundances for our sample, A(C), we also confirm that the\ncarbon-enhanced metal-poor (CEMP) stars in the outer-halo region exhibit a\nhigher frequency of CEMP-no stars (those with no overabundances of heavy\nneutron-capture elements) than of CEMP-s stars (those with strong\noverabundances of elements associated with the s-process), whereas the stars in\nthe inner-halo region exhibit a higher frequency of CEMP-s stars. We argue that\nthe contrast in the behavior of the CEMP-no and CEMP-s fractions in these\nregions arises from differences in the mass distributions of the mini-halos\nfrom which the stars of the inner- and outer-halo populations formed, which\ngives rise in turn to the observed dichotomy of the Galactic halo.", "category": "astro-ph_GA" }, { "text": "ALMA observations of the archetypal \"hot core\" that isn't: Orion KL: We present sensitive high angular resolution ($\\sim$ 0.1$''$ -- 0.3$''$)\ncontinuum ALMA (The Atacama Large Millimeter/Submillimeter Array) observations\nof the archetypal hot core located in Orion-KL. The observations were made in\nfive different spectral bands (bands 3, 6, 7, 8, and 9) covering a very broad\nrange of frequencies (149 -- 658 GHz). Apart of the well-know millimeter\nemitting objects located in this region (Orion Source I and BN), we report the\nfirst submillimeter detection of three compact continuum sources (ALMA 1-3) in\nthe vicinities of the Orion-KL hot molecular core. These three continuum\nobjects have spectral indices between 1.47 to 1.56, and brightness temperatures\nbetween 100 to 200 K at 658 GHz suggesting that we are seeing moderate\noptically thick dust emission with possible grain growth. However, as these\nobjects are not associated with warm molecular gas, and some of them are\nfarther out from the molecular core, we thus conclude that they cannot heat the\nmolecular core. This result favours the hypothesis that the hot molecular core\nin Orion-KL core is heated externally.", "category": "astro-ph_GA" }, { "text": "Comparison of distance measurements to dust clouds using GRB X-ray halos\n and 3D dust extinction: X-ray photons from energetic sources such as gamma-ray bursts (GRBs) can be\nscattered on dust clouds in the Milky Way, creating a time-evolving halo around\nthe GRB position. X-ray observations of such halos allow the measurement of\ndust clouds distances in the Galaxy on which the scattering occurs. We present\nthe first systematic comparison of the distances to scattering regions derived\nfrom GRB halos with the 3D dust distribution derived from recently published\noptical-to-near infrared extinction maps. GRB halos were observed around 7\nsources by the Swift XRT and the XMM-Newton EPIC instruments, namely GRB\n031203, GRB 050713A, GRB 050724, GRB 061019, GRB 070129, GRB 160623A and GRB\n221009A. We used four 3D extinction maps that exploit photometric data from\ndifferent surveys and apply diverse algorithms for the 3D mapping of\nextinction, and compared the X-ray halo-derived distances with the local maxima\nin the 3D extinction density distribution. We found that in all GRBs we can\nfind at least one local maximum in the 3D dust extinction map that is in\nagreement with the dust distance measured from X-ray rings. For GRBs with\nmultiple X-ray rings, the dust distance measurements coincide with at least 3\nmaxima in the extinction map for GRB 160623A, and 5 maxima for GRB 221009A. The\nagreement of these independent distance measurements shows that the methods\nused to create dust extinction maps may potentially be optimized by the X-ray\nhalo observations from GRBs.", "category": "astro-ph_GA" }, { "text": "The Sixteenth Data Release of the Sloan Digital Sky Surveys: First\n Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra: This paper documents the sixteenth data release (DR16) from the Sloan Digital\nSky Surveys; the fourth and penultimate from the fourth phase (SDSS-IV). This\nis the first release of data from the southern hemisphere survey of the Apache\nPoint Observatory Galactic Evolution Experiment 2 (APOGEE-2); new data from\nAPOGEE-2 North are also included. DR16 is also notable as the final data\nrelease for the main cosmological program of the Extended Baryon Oscillation\nSpectroscopic Survey (eBOSS), and all raw and reduced spectra from that project\nare released here. DR16 also includes all the data from the Time Domain\nSpectroscopic Survey (TDSS) and new data from the SPectroscopic IDentification\nof ERosita Survey (SPIDERS) programs, both of which were co-observed on eBOSS\nplates. DR16 has no new data from the Mapping Nearby Galaxies at Apache Point\nObservatory (MaNGA) survey (or the MaNGA Stellar Library \"MaStar\"). We also\npreview future SDSS-V operations (due to start in 2020), and summarize plans\nfor the final SDSS-IV data release (DR17).", "category": "astro-ph_GA" }, { "text": "The influence of magnetic field on the CNM mass fraction and its\n alignment with density structures: To contribute to the understanding of the magnetic field's influence on the\nsegregation of CNM in the solar neighbourhood we analyse MHD simulations which\ninclude the main physical characteristics of the local neutral atomic ISM. The\nsimulations have a continuous solenoidal Fourier forcing in a periodic box of\n100 pc per side and an initial uniform magnetic field ($\\vec{B_0}$) with\nintensities ranging between $\\sim 0.4$ $\\mu$G and $\\sim 8$ $\\mu$G. Our main\nresults are: i) the CNM mass fraction diminishes with the increase in magnetic\nfield intensity. ii) There is a preferred alignment between CNM structures and\n$\\vec{B}$ in all our $B_0$ range but the preference weakens as $B_{0}$\nincreases. It is worth noticing that this preference is also present in\ntwo-dimensional projections making an extreme angle ($0$ or $\\pi / 2$) with\nrespect to $\\vec{B_0}$ and it is only lost for the strongest magnetic field\nwhen the angle of projection is perpendicular to $\\vec{B_0}$. iii) The\naforementioned results are prevalent despite the inclusion of self-gravity in\nour continuously forced simulations with a mean density similar to the average\nvalue of the solar neighbourhood. iv) Given a fixed $B_0$ and slightly higher\nmean densities, up to double, the effects of self-gravity are still not\nqualitatively significant.", "category": "astro-ph_GA" }, { "text": "Optical Imaging & Spectral Study of FR-I Type Radio Galaxy:CTD 086 (B2\n 1422+26B): We present optical imaging and spectroscopic studies of the Fanaroff \\& Riley\nclass I (FR I) radio galaxy CTD 086 based on Hubble Space Telescope (HST) and\nSloan Digital Sky Survey (SDSS) observations. We use isophote shape analysis to\nshow that there is no stellar disk component within CTD 086 and further that\nthe morphological class of the galaxy is most likely E2. Optical spectroscopy\nof this galaxy reveals the presence of narrow emission lines only, and thus it\nqualifies to be termed as a narrow-line radio galaxy (type 2 AGN). We also\nextract stellar kinematics from the absorption-line spectra of CTD 086 using\nPenalized Pixel-Fitting method and derive the black hole mass MBH to be equal\nto (8.8\\pm2.4)\\times10^{7} Msun.", "category": "astro-ph_GA" }, { "text": "Direct observations of the atomic-molecular phase transition in the\n Milky Way's nuclear wind: Hundreds of high-velocity atomic gas clouds exist above and below the\nGalactic Centre, with some containing a molecular component. However, the\norigin of these clouds in the Milky Way's wind is unclear. This paper presents\nnew high-resolution MeerKAT observations of three atomic gas clouds and studies\nthe relationship between the atomic and molecular phases at $\\sim 1$ pc scales.\nThe clouds' atomic hydrogen column densities, $N_{\\mathrm{HI}}$, are less than\na $\\mbox{few}\\times 10^{20}$ cm$^{-2}$, but the two clouds closest to the\nGalactic Centre nonetheless have detectable CO emission. This implies the\npresence of H$_{2}$ at levels of $N_{\\mathrm{HI}}$ at least a factor of ten\nlower than in the typical Galactic interstellar medium. For the cloud closest\nto the Galactic Centre, there is little correlation between the\n$N_{\\mathrm{HI}}$ and the probability that it will harbour detectable CO\nemissions. In contrast, for the intermediate cloud, detectable CO is heavily\nbiased toward the highest values of $N_{\\mathrm{HI}}$. The cloud most distant\nfrom the Galactic Centre has no detectable CO at similar $N_{\\mathrm{HI}}$\nvalues. Moreover, we find that the two clouds with detectable CO are too\nmolecule-rich to be in chemical equilibrium, given the depths of their atomic\nshielding layers, which suggests a scenario whereby these clouds consist of\npre-existing molecular gas from the disc that the Galactic wind has swept up,\nand that is dissociating into atomic hydrogen as it flows away from the Galaxy.\nWe estimate that entrained molecular material of this type has a $\\sim\n\\mathrm{few}-10$ Myr lifetime before photodissociating.", "category": "astro-ph_GA" }, { "text": "Rotation Curves in z~1-2 Star-Forming Disks: Evidence for Cored Dark\n Matter Distributions: We report high quality, Halpha or CO rotation curves (RCs) to several Re for\n41 large, massive, star-forming disk galaxies (SFGs), across the peak of cosmic\ngalaxy evolution (z~0.67-2.45), taken with the ESO-VLT, the LBT and IRAM-NOEMA.\nMost RC41 SFGs have reflection symmetric RCs plausibly described by equilibrium\ndynamics. We fit the major axis position-velocity cuts with beam-convolved,\nforward modeling with a bulge, a turbulent rotating disk, and a dark matter\n(DM) halo. We include priors for stellar and molecular gas masses, optical\nlight effective radii and inclinations, and DM masses from abundance matching\nscaling relations. Two-thirds or more of the z>1.2 SFGs are baryon dominated\nwithin a few Re of typically 5.5 kpc, and have DM fractions less than maximal\ndisks (=0.12). At lower redshift (z<1.2) that fraction is less than\none-third. DM fractions correlate inversely with the baryonic angular momentum\nparameter, baryonic surface density and bulge mass. Inferred low DM fractions\ncannot apply to the entire disk & halo but more plausibly reflect a flattened,\nor cored, inner DM density distribution. The typical central 'DM deficit' in\nthese cores relative to NFW distributions is ~30% of the bulge mass. The\nobservations are consistent with rapid radial transport of baryons in the first\ngeneration massive gas rich halos forming globally gravitationally unstable\ndisks, and leading to efficient build-up of massive bulges and central black\nholes. A combination of heating due to dynamical friction and AGN feedback may\ndrive DM out of the initial cusps.", "category": "astro-ph_GA" }, { "text": "The Local Cluster Survey II: Disk-Dominated Cluster Galaxies with\n Suppressed Star Formation: We investigate the role of dense environments in suppressing star formation\nby studying $\\rm \\log_{10}(M_\\star/M_\\odot) > 9.7$ star-forming galaxies in\nnine clusters from the Local Cluster Survey ($0.0137 < z < 0.0433$) and a large\ncomparison field sample drawn from the Sloan Digital Sky Survey. We compare the\nstar-formation rate (SFR) versus stellar mass relation as a function of\nenvironment and morphology. After carefully controlling for mass, we find that\nin all environments, the degree of SFR suppression increases with increasing\nbulge-to-total (B/T) ratio. In addition, the SFRs of cluster and infall\ngalaxies at a fixed mass are more suppressed than their field counterparts at\nall values of B/T. These results suggest a quenching mechanism that is linked\nto bulge growth that operates in all environments and an additional mechanism\nthat further reduces the SFRs of galaxies in dense environments. We limit the\nsample to $B/T < 0.3$ galaxies to control for the trends with morphology and\nfind that the excess population of cluster galaxies with suppressed SFRs\npersists. We model the timescale associated with the decline of SFRs in dense\nenvironments and find that the observed SFRs of the cluster core galaxies are\nconsistent with a range of models including: a mechanism that acts slowly and\ncontinuously over a long (2-5 Gyr) timescale, and a more rapid ($<1$ Gyr)\nquenching event that occurs after a delay period of 1-6 Gyr. Quenching may\ntherefore start immediately after galaxies enter clusters.", "category": "astro-ph_GA" }, { "text": "Shadows around Sgr A* and M87* as a tool to test gravity theories: In the framework of Randall -- Sundrum theory with extra dimension Reissner\n-- Nordstr\\\"om black hole solutions with a tidal charge have been found. The\nshadow around the supermassive black hole in M87 was reconstructed in 2019\nbased on observations with the Event Horizon Telescope (EHT) in April 2017. In\nMay 2022 the EHT Collaboration presented results of a shadow reconstruction for\nour Galactic Center. Earlier, for Reissner -- Nordstr\\\"om metric we derived\nanalytical expressions for shadow size as a function of charge and later\ngeneralized these results for a tidal charge case. We discuss opportunities to\nevaluate parameters of alternative theories of gravity with shadow size\nestimates done by the EHT Collaboration, in particular, a tidal charge could be\nestimated from these observations.", "category": "astro-ph_GA" }, { "text": "First sample of $\\rm N_2H^+$ nitrogen isotopic ratio measurements in\n low-mass protostars: Context. The nitrogen isotopic ratio is considered an important diagnostic\ntool of the star formation process, and $N_2H^+$ is particularly important\nbecause it is directly linked to molecular nitrogen $N_2$. However, theoretical\nmodels still lack to provide an exhaustive explanation for the observed\n$^{14}N/^{15}N$ values.\n Aims. Recent theoretical works suggest that the $^{14}N/^{15}N$ behaviour is\ndominated by two competing reactions that destroy $ N_2H^+$: dissociative\nrecombination and reaction with CO. When CO is depleted from the gas phase, if\n$N_2H^+$ recombination rate is lower with respect to the $N^{15}NH^+$ one, the\nrarer isotopologue is destroyed faster. This implies that the $N_2H^+$ isotopic\nratio in protostars should be lower than the one in prestellar cores, and\nconsistent with the elemental value of ~440. We aim to test this hypothesis,\nproducing the first sample of $N_2H^+ / N^{15}NH^+$ measurements in low mass\nprotostars.\n Methods. We observe the $N_2H^+$ and $N^{15}NH^+$ lowest rotational\ntransition towards six young stellar objects in Perseus and Taurus molecular\nclouds. We model the spectra with a custom python code using a constant\n$T_{ex}$ approach to fit the observations. We discuss in appendix the validity\nof this hypothesis. The derived column densities are used to compute the\nnitrogen isotopic ratio.\n Results. Our analysis yields an average of $\\rm ^{14}N/^{15}N|_{pro} = 420\n\\pm 15$ in the protostellar sample. This is consistent with the protosolar\nvalue of 440, and significantly lower than the average value previously\nobtained in a sample of prestellar objects. Conclusions. Our results are in\nagreement with the hypothesis that, when CO is depleted from the gas-phase,\ndissociative recombinations with free electrons destroy $N^{15}NH^+$ faster\nthan $N_2H^+$, leading to high isotopic ratios in prestellar cores, where CO is\nfrozen on dust grains.", "category": "astro-ph_GA" }, { "text": "The origin of low-surface-brightness galaxies in the dwarf regime: Low-surface-brightness galaxies (LSBGs) -- defined as systems that are\nfainter than the surface-brightness limits of past wide-area surveys -- form\nthe overwhelming majority of galaxies in the dwarf regime (M* < 10^9 MSun).\nUsing NewHorizon, a high-resolution cosmological simulation, we study the\norigin of LSBGs and explain why LSBGs at similar stellar mass show the large\nobserved spread in surface brightness. New Horizon galaxies populate a\nwell-defined locus in the surface brightness -- stellar mass plane, with a\nspread of ~3 mag arcsec^-2, in agreement with deep SDSS Stripe data. Galaxies\nwith fainter surface brightnesses today are born in regions of higher\ndark-matter density. This results in faster gas accretion and more intense star\nformation at early epochs. The stronger resultant supernova feedback flattens\ngas profiles at a faster rate which, in turn, creates shallower stellar\nprofiles (i.e. more diffuse systems) more rapidly. As star formation declines\ntowards late epochs (z<1), the larger tidal perturbations and ram pressure\nexperienced by these systems (due to their denser local environments)\naccelerate the divergence in surface brightness, by increasing their effective\nradii and reducing star formation respectively. A small minority of dwarfs\ndepart from the main locus towards high surface brightnesses, making them\ndetectable in past wide surveys. These systems have anomalously high\nstar-formation rates, triggered by recent, fly-by or merger-driven starbursts.\nWe note that objects considered extreme/anomalous at the depth of current\ndatasets, e.g. `ultra-diffuse galaxies', actually dominate the predicted dwarf\npopulation and will be routinely visible in future surveys like LSST.", "category": "astro-ph_GA" }, { "text": "30 GHz monitoring of broad absorption line (BAL) quasars: Broad absorption line (BAL) quasars have been studied for over thirty years.\nYet it is still unclear why and when we observe broad absorption lines in\nquasars. Is this phenomenon caused by geometry or is it connected with the\nevolution process? Variability of the BAL quasars, if present, can give us\ninformation about their orientation, namely it can indicate whether they are\noriented more pole-on. Using the Torun 32-metre dish equipped with the One\nCentimetre Receiver Array (OCRA) we have started a monitoring campaign of a\nsample of compact radio-loud BAL quasars. This 30 GHz variability monitoring\nprogram supplements the high-resolution interferometric observations of these\nobjects we have carried out with the EVN and VLBA.", "category": "astro-ph_GA" }, { "text": "COSMOS2020: Investigating the AGN-obscured accretion phase at $z\\sim 1$\n via [NeV] selection: We investigated the properties of 94 [NeV]3426AA-selected type 2 AGN in\nCOSMOS at z=0.6-1.2, performing optical-to-far-infrared spectral energy\ndistribution fitting. In addition, we analyze the X-ray spectra of the\nX-ray-detected sources to obtain reliable values of the AGN obscuration and\nintrinsic luminosity.\n We found that more than two-thirds of our sample is composed of very obscured\nsources, with about 20% of the sources being candidate CT-AGN and half being\nAGNs in a strong phase of accretion. With respect to non-active galaxies, we\nfind a higher fraction of sources within the main sequence and little evidence\nfor AGNs quenching the SF. The comparison with the prediction from the in situ\nco-evolution model suggests that [NeV] is an effective tool for selecting\ngalaxies in the obscured growth phase of the BH-galaxy co-evolution paradigm.\nWe find that the \"quenching phase\" is still to come for most of the sample and\nonly few galaxies show evidence of quenched SF activity.", "category": "astro-ph_GA" }, { "text": "Atomic and Molecular Absorption in Redshifted Radio Sources: We report on a survey for associated HI 21-cm and OH 18-cm absorption with\nthe Giant Metrewave Radio Telescope at redshifts z = 0.2-0.4. Although the low\nredshift selection ensures that our targets are below the critical ultra-violet\nluminosity, which is hypothesised to ionise all of the neutral gas in the host\ngalaxy, we do not obtain any detections in the six sources searched. Analysing\nthese in context of the previous surveys, in addition to the anti-correlation\nwith the ultra-violet luminosity (ionising photon rate), we find a correlation\nbetween the strength of the absorption and the blue -- near-infrared colour, as\nwell as the radio-band turnover frequency. We believe that these are due to the\nphoto-ionisation of the neutral gas, an obscured sight-line being more\nconducive to the presence of cold gas and the compact radio emission being\nbetter intercepted by the absorbing gas, maximising the flux coverage,\nrespectively. Regarding the photo-ionisation, the compilation of the previous\nsurveys increases the significance of the critical ionising photon rate, above\nwhich all of the gas in the host galaxy is hypothesised to be ionised, to >5\nsigma. This reaffirms that this is an ubiquitous effect, which has profound\nimplications for the detection of neutral gas in these objects with the Square\nKilometre Array.", "category": "astro-ph_GA" }, { "text": "Probing the hot circumgalactic medium of external galaxies in X-ray\n absorption II: a luminous spiral galaxy at $z\\approx 0.225$: The circumgalactic medium (CGM) is the most massive baryonic component of a\nspiral galaxy, shock heated to about $10^6$K for an $\\rm L^{\\star}$ galaxy. The\nCGM of the Milky Way has been well-characterized through X-ray absorption line\nspectroscopy. However, the paucity of bright background sources makes it\nchallenging to probe the CGM of external galaxies. Previously, using broad OVI\nabsorption as a signpost, we successfully detected the CGM of one galaxy in\nX-rays. Here we report on the detection of the OVII $K\\alpha$ absorption line\nat the redshift of a spiral galaxy at $z\\approx0.225$ using 1.2 Ms of Chandra\nobservations. This is a robust detection, clearly showing the presence of the\nhot gas. The mass in the hot phase is at least an order of magnitude larger\nthan that in the cooler phases detected in the UV. The presence of hot gas\n$116h^{-1}$kpc from the center of this galaxy provides credence to the\nexistence of the extended CGM of the Milky Way. There has been a report of the\ndetection of OVII absorption from the warm-hot intergalactic medium in this\nsightline using stacking analysis on an older dataset. We argue that the\nabsorption line is from the CGM of the $z\\approx0.225$ galaxy instead.", "category": "astro-ph_GA" }, { "text": "Galactic nebular lines in the fiber spectra of background QSOs: Reaching\n a hundred QSO-galaxy pairs with spectroscopic and photometric measurements: We present photometric and spectroscopic measurements of 53 QSO-galaxy pairs\nfrom the Sloan Digital Sky Survey, where nebular emission lines from a 0 10^44 erg/s, among\ngalaxies in the redshift range 4\n10%.", "category": "astro-ph_GA" }, { "text": "Compton Thick AGN in the 70 Month Swift-BAT All-Sky Hard X-ray Survey: a\n Bayesian approach: The 70-month Swift/BAT catalogue provides a sensitive view of the\nextragalactic X-ray sky at hard energies (>10 keV) containing about 800 Active\nGalactic Nuclei. We explore its content in heavily obscured, Compton-thick AGN\nby combining the BAT (14-195 keV) with the lower energy XRT (0.3-10 keV) data.\nWe apply a Bayesian methodology using Markov chains to estimate the exact\nprobability distribution of the column density for each source. We find 53\npossible Compton-thick sources (with probability 3 to 100%) translating to a\n~7% fraction of the AGN in our sample. We derive the first parametric\nluminosity function of Compton-thick AGN. The unabsorbed luminosity function\ncan be represented by a double power-law with a break at $L_{\\star} 2 \\times\n10^{42}$ $\\rm ergs~s^{-1}$ in the 20-40 keV band.", "category": "astro-ph_GA" }, { "text": "Differences and similarities of stellar populations in LAEs and LBGs at\n $z\\sim$ 3.4 - 6.8: The differences between the inherent stellar populations (SPs) of LAEs and\nLBGs are a key factor in understanding early galaxy formation and evolution. We\nhave run a set of SP burst-like models for a sample of 1,558 sources at\n$3.4 100 A) cannot be explained by our model,\nand we need to invoke additional mechanisms. We find that LAEs and LBGs span a\nvery similar dynamical range, but bright LAEs are about 4 times rarer than LBGs\nin massive halos. Moreover, massive halos mainly contain weak LAEs in our\nmodel, which might introduce a bias towards low-mass halos in surveys which\nselect sources with high EW cuts. Overall, our results are consistent with the\nidea that LAEs and LBGs make a very similar galaxy population. Their apparent\ndifferences seem mainly due to EW selections, UV detection limits, and a\ndecreasing Lya-to-UV escape fraction ratio in high SFR galaxies.", "category": "astro-ph_GA" }, { "text": "A multiwavelength study of the star forming region IRAS 18544+0112: This work aims at investigating the molecular and infrared components in the\nmassive young stellar object (MYSO) candidate IRAS 18544+0112. The purpose is\nto determine the nature and the origin of this infrared source. To analyze the\nmolecular gas towards IRAS 18544+0112, we have carried out observations in a\n90\" x 90\" region around l = 34.69, b = -0.65, using the Atacama Submillimeter\nTelescope Experiment (ASTE) in the 12CO J=3-2, 13CO J=3-2, HCO+ J=4-3 and CS\nJ=7-6 lines with an angular resolution of 22\". The infrared emission in the\narea has been analyzed using 2MASS and Spitzer public data. From the molecular\nanalysis, we find self-absorbed 12CO J=3-2 profiles, which are typical in star\nforming regions, but we do not find any evidence of outflow activity. Moreover,\nwe do not detect either HCO+ J=4-3 or CS J=7-6 in the region, which are species\nnormally enhanced in molecular outflows and high density envelopes. The 12CO\nJ=3-2 emission profile suggests the presence of expanding gas in the region.\nThe Spitzer images reveal that the infrared source has a conspicuous extended\nemission bright at 8 um with an evident shell-like morphology of ~ 1.5 arcmin\nin size (~ 1.4 pc at the proposed distance of 3 kpc) that encircles the 24 um\nemission. The non-detection of ionized gas related to IRAS 18544+0112, together\nwith the fact that it is still embedded in a molecular clump suggest that IRAS\n18544+0112, has not reached the UCHII region stage yet. Based on near infrared\nphotometry we search for YSO candidates in the region and propos that 2MASS\n18565878+0116233 is the infrared point source associated with IRAS 18544+0112.\nFinally, we suggest that the expansion of a larger nearby HII region,\nG034.8-0.7, might be related to the formation of IRAS 18544+0112.", "category": "astro-ph_GA" }, { "text": "A thorough view of the nuclear region of NGC 253 - Combined Herschel,\n SOFIA and APEX dataset: We present a large set of spectral lines detected in the $40\"$ central region\nof the starburst galaxy NGC 253. Observations were obtained with the three\ninstruments SPIRE, PACS and HIFI on board the Herschel Space Observatory,\nupGREAT on board of the SOFIA airborne observatory, and the ground based APEX\ntelescope. Combining the spectral and photometry products of SPIRE and PACS we\nmodel the dust continuum Spectral Energy Distribution (SED) and the most\ncomplete $^{12}$CO Line SED reported so far toward the nuclear region of NGC\n253. Properties and excitation of the molecular gas were derived from a\nthree-component non-LTE radiative transfer model, using the SPIRE $^{13}$CO\nlines and ground based observations of the lower-$J$ $^{13}$CO and HCN lines,\nto constrain the model parameters. Three dust temperatures were identified from\nthe continuum emission, and three components are needed to fit the full CO\nLSED. Only the third CO component (fitting mostly the HCN and PACS $^{12}$CO\nlines) is consistent with a shock/mechanical heating scenario. A hot core\nchemistry is also argued as a plausible scenario to explain the high-$J$\n$^{12}$CO lines detected with PACS. The effect of enhanced cosmic ray\nionization rates, however, cannot be ruled out, and is expected to play a\nsignificant role in the diffuse and dense gas chemistry. This is supported by\nthe detection of ionic species like OH$^+$ and H$_2$O$^+$, as well as the\nenhanced fluxes of the OH lines with respect to those of H$_2$O lines detected\nin both PACS and SPIRE spectrum.", "category": "astro-ph_GA" }, { "text": "Mid and Far-Infrared Color-Color Relations within Local Galaxies: We present an extensive archival analysis of a sample of local galaxies,\ncombining multi-wavelength data from GALEX, Spitzer and Herschel to investigate\n\"blue-side\" mid-infrared (MIR) and \"red-side\" far-infrared (FIR) color-color\ncorrelations within the observed infrared spectral energy distributions (IR\nSEDs). Our sample largely consists of the KINGFISH galaxies, with the important\naddition of a select few including NGC5236 (M83) and NGC4449. With data from\nthe far-ultraviolet FUV (${\\sim}0.15$ $\\mu$m) through 500 $\\mu$m convolved to\ncommon angular resolution, we measure photometry of $kpc$-scale star-forming\nregions 36$\"\\times$36$\"$ in size. Star formation rates (SFRs), stellar masses\nand metallicity distributions are derived throughout our sample. Focusing on\nthe $f_{70}/f_{500}$ \"FIR\" and $f_{8}/f_{24}$ \"MIR\" flux density ratios\n(colors), we find that a sub-sample of galaxies demonstrate a strong IR\ncolor-color correlation within their star-forming regions, while others\ndemonstrate uncorrelated colors. This division is driven by two main effects:\n1) the local strength of star formation (SF) and 2) the metal content of the\ninterstellar medium (ISM). Galaxies uniformly dominated by high surface\ndensities of SF (e.g. NGC5236) demonstrate strong IR color-color correlations,\nwhile galaxies that exhibit lower levels of SF and mixed environments (e.g.\nNGC5457) demonstrate weaker or no correlation--explained by the increasing\neffect of varying ISM heating and metal content on the IR colors, specifically\nin the MIR. We find large dispersion in the SFR-$L_{8}$ (8 $\\mu$m luminosity)\nrelation that is traced by the metallicity distributions, consistent with\nextant studies, highlighting its problematic use as a SFR indicator across\ndiverse systems/samples.", "category": "astro-ph_GA" }, { "text": "The Case Against Dark Matter and Modified Gravity: Flat Rotation Curves\n Are a Rigorous Requirement in Rotating Self-Gravitating Newtonian Gaseous\n Disks: By solving analytically the various types of Lane-Emden equations with\nrotation, we have discovered two new coupled fundamental properties of\nrotating, self-gravitating, gaseous disks in equilibrium: Isothermal disks\nmust, on average, exhibit strict power-law density profiles in radius $x$ on\ntheir equatorial planes of the form $A x^{k-1}$, where $A$ and $k-1$ are the\nintegration constants, and \"flat\" rotation curves precisely such as those\nobserved in spiral galaxy disks. Polytropic disks must, on average, exhibit\nstrict density profiles of the form $\\left[\\ln(A x^k)\\right]^n$, where $n$ is\nthe polytropic index, and \"flat\" rotation curves described by square roots of\nupper incomplete gamma functions. By \"on average,\" we mean that, irrespective\nof the chosen boundary conditions, the actual profiles must oscillate around\nand remain close to the strict mean profiles of the analytic singular\nequilibrium solutions. We call such singular solutions the \"intrinsic\"\nsolutions of the differential equations because they are demanded by the\nsecond-order equations themselves with no regard to the Cauchy problem. The\nresults are directly applicable to gaseous galaxy disks that have long been\nknown to be isothermal and to protoplanetary disks during the extended\nisothermal and adiabatic phases of their evolution. In galactic gas dynamics,\nthey have the potential to resolve the dark matter--modified gravity\ncontroversy in a sweeping manner, as they render both of these hypotheses\nunnecessary. In protoplanetary disk research, they provide observers with\npowerful new probing tool, as they predict a clear and simple connection\nbetween the radial density profiles and the rotation curves of self-gravitating\ndisks in their very early (pre-Class 0 and perhaps the youngest Class Young\nStellar Objects) phases of evolution.", "category": "astro-ph_GA" }, { "text": "Radio-Loud and Radio-Quiet BAL Quasars: A Detailed Ultraviolet\n Comparison: Studies of radio-loud (RL) broad absorption line (BAL) quasars indicate that\npopular orientation-based BAL models fail to account for all observations. Are\nthese results extendable to radio-quiet (RQ) BAL quasars? Comparisons of RL and\nRQ BAL quasars show that many of their properties are quite similar. Here we\nextend these analyses to the rest-frame ultraviolet (UV) spectral properties,\nusing a sample of 73 RL and 473 RQ BAL quasars selected from the Sloan Digital\nSky Survey (SDSS). Each RQ quasar is individually matched to a RL quasar in\nboth redshift (over the range $1.5 < z < 3.5$) and continuum luminosity. We\ncompare several continuum, emission line, and absorption line properties, as\nwell as physical properties derived from these measurements. Most properties in\nthe samples are statistically identical, though we find slight differences in\nthe velocity structure of the BALs that cause apparent differences in CIV\nemission line properties. Differences in the velocities may indicate an\ninteraction between the radio jets and the absorbing material. We also find\nthat UV FeII emission is marginally stronger in RL BAL quasars. All of these\ndifferences are subtle, so in general we conclude that RL and RQ BAL QSOs are\nnot fundamentally different objects, except in their radio properties. They are\ntherefore likely to be driven by similar physical phenomena, suggesting that\nresults from samples of RL BAL quasars can be extended to their RQ\ncounterparts.", "category": "astro-ph_GA" }, { "text": "Lyman-alpha spectroscopy of extreme [OIII] emitting galaxies at\n $z\\simeq2-3$: Implications for Ly$\u03b1$ visibility and LyC leakage at $z>6$: Spectroscopic observations of massive $z>7$ galaxies selected to have\nextremely large [OIII]+H$\\beta$ equivalent width (EW $\\sim1500$ \\r{A}) have\nrecently revealed large Ly$\\alpha$ detection rates, in contrast to the weak\nemission seen in the general population. Why these systems are uniquely visible\nin Ly$\\alpha$ at redshifts where the IGM is likely significantly neutral is not\nclear. With the goal of better understanding these results, we have begun a\ncampaign with MMT and Magellan to measure Ly$\\alpha$ in galaxies with similar\n[OIII]+H$\\beta$ EWs at $z\\simeq2-3$. At these redshifts, the IGM is highly\nionized, allowing us to clearly disentangle how the Ly$\\alpha$ properties\ndepend on the [OIII]+H$\\beta$ EW. Here we present Ly$\\alpha$ EWs of $49$\ngalaxies at $z=2.2-3.7$ with intense [OIII]+H$\\beta$ line emission (EW\n$=300-3000$ \\r{A}). Our results demonstrate that strong Ly$\\alpha$ emission (EW\n$>20$ \\r{A}) becomes more common in galaxies with larger [OIII]+H$\\beta$ EW,\nreflecting a combination of increasingly efficient ionizing photon production\nand enhanced transmission of Ly$\\alpha$. Among the galaxies with the most\nextreme [OIII]+H$\\beta$ emission (EW $\\sim1500$ \\r{A}), we find that strong\nLy$\\alpha$ emission is not ubiquitous, with only $50$ per cent of our\npopulation showing Ly$\\alpha$ EW $>20$ \\r{A}. Our data suggest that the range\nof Ly$\\alpha$ strengths is related to the observed ellipticity, with those\nsystems that appear edge-on or elongated having weaker Ly$\\alpha$ emission. We\nuse these results to interpret the anomalous Ly$\\alpha$ properties seen in\n$z>7$ galaxies with extreme [OIII]+H$\\beta$ emission and discuss implications\nfor the escape of ionizing radiation from these extreme line emitting galaxies.", "category": "astro-ph_GA" }, { "text": "The formation of cosmic fullerenes from arophatic clusters: Fullerenes have recently been identified in space and they may play a\nsignificant role in the gas and dust budget of various astrophysical objects\nincluding planetary nebulae (PNe), reflection nebulae (RNe) and H II regions.\nThe tenuous nature of the gas in these environments precludes the formation of\nfullerene materials following known vaporization or combustion synthesis routes\neven on astronomical timescales. We have studied the processing of hydrogenated\namorphous carbon (a-C:H or HAC) nano-particles and their specific derivative\nstructures, which we name \"arophatics\", in the circumstellar environments of\nyoung, carbon-rich PNe. We find that UV-irradiation of such particles can\nresult in the formation of fullerenes, consistent with the known physical\nconditions in PNe and with available timescales.", "category": "astro-ph_GA" }, { "text": "Stream Members Only: Data-Driven Characterization of Stellar Streams\n with Mixture Density Networks: Stellar streams are sensitive probes of the Milky Way's gravitational\npotential. The mean track of a stream constrains global properties of the\npotential, while its fine-grained surface density constrains galactic\nsubstructure. A precise characterization of streams from potentially noisy data\nmarks a crucial step in inferring galactic structure, including the dark\nmatter, across orders of magnitude in mass scales. Here we present a new method\nfor constructing a smooth probability density model of stellar streams using\nall of the available astrometric and photometric data. To characterize a\nstream's morphology and kinematics, we utilize mixture density networks to\nrepresent its on-sky track, width, stellar number density, and kinematic\ndistribution. We model the photometry for each stream as a single-stellar\npopulation, with a distance track that is simultaneously estimated from the\nstream's inferred distance modulus (using photometry) and parallax distribution\n(using astrometry). We use normalizing flows to characterize the distribution\nof background stars. We apply the method to the stream GD-1, and the tidal\ntails of Palomar 5. For both streams we obtain a catalog of stellar membership\nprobabilities that are made publicly available. Importantly, our model is\ncapable of handling data with incomplete phase-space observations, making our\nmethod applicable to the growing census of Milky Way stellar streams. When\napplied to a population of streams, the resulting membership probabilities from\nour model form the required input to infer the Milky Way's dark matter\ndistribution from the scale of the stellar halo down to subhalos.", "category": "astro-ph_GA" }, { "text": "Infall of nearby galaxies into the Virgo cluster as traced with HST: We measured the Tip of the Red Giant Branch distances to nine galaxies in the\ndirection to the Virgo cluster using the Advanced Camera for Surveys on the\nHubble Space Telescope. These distances put seven galaxies: GR 34, UGC 7512,\nNGC 4517, IC 3583, NGC 4600, VCC 2037 and KDG 215 in front of the Virgo, and\ntwo galaxies: IC 3023, KDG 177 likely inside the cluster. Distances and radial\nvelocities of the galaxies situated between us and the Virgo core clearly\nexhibit the infall phenomenon toward the cluster. In the case of spherically\nsymmetric radial infall we estimate the radius of the \"zero-velocity surface\"\nto be (7.2+-0.7) Mpc that yields the total mass of the Virgo cluster to be\n(8.0+-2.3) X 10^{14} M_sun in good agreement with its virial mass estimates. We\nconclude that the Virgo outskirts does not contain significant amounts of dark\nmatter beyond its virial radius.", "category": "astro-ph_GA" }, { "text": "FSR 1716: A new Milky Way Globular Cluster confirmed using VVV RR Lyrae\n stars: We use deep multi-epoch near-IR images of the VISTA Variables in the V\\'ia\nL\\'actea (VVV) Survey to search for RR Lyrae stars towards the Southern\nGalactic plane. Here we report the discovery of a group of RR Lyrae stars close\ntogether in VVV tile d025. Inspection of the VVV images and PSF photometry\nreveals that most of these stars are likely to belong to a globular cluster,\nthat matches the position of the previously known star cluster FSR\\,1716. The\nstellar density map of the field yields a $>100$ sigma detection for this\ncandidate globular cluster, that is centered at equatorial coordinates\n$RA_{J2000}=$16:10:30.0, $DEC_{J2000}=-$53:44:56; and galactic coordinates\n$l=$329.77812, $b=-$1.59227. The color-magnitude diagram of this object reveals\na well populated red giant branch, with a prominent red clump at $K_s=13.35 \\pm\n0.05$, and $J-K_s=1.30 \\pm 0.05$. We present the cluster RR Lyrae positions,\nmagnitudes, colors, periods and amplitudes. The presence of RR Lyrae indicates\nan old globular cluster, with age $>10$ Gyr. We classify this object as an\nOosterhoff type I globular cluster, based on the mean period of its RR Lyrae\ntype ab, $

=0.540$ days, and argue that this is a relatively metal-poor\ncluster with $[Fe/H] = -1.5 \\pm 0.4$ dex. The mean extinction and reddening for\nthis cluster are $A_{K_s}=0.38 \\pm 0.02$, and $E(J-K_s)=0.72 \\pm 0.02$ mag,\nrespectively, as measured from the RR Lyrae colors and the near-IR\ncolor-magnitude diagram. We also measure the cluster distance using the RR\nLyrae type ab stars. The cluster mean distance modulus is $(m-M)_0 = 14.38 \\pm\n0.03$ mag, implying a distance $D = 7.5 \\pm 0.2$ kpc, and a Galactocentric\ndistance $R_G=4.3$ kpc.", "category": "astro-ph_GA" }, { "text": "Physical conditions in high$-$z optically thin C III absorbers: Origin\n of cloud sizes and associated correlations: We present detailed photoionization models of well aligned optically thin C\nIII absorption components at $2.1 < z < 3.4$. Using our models we estimate\ndensity ($n_{\\rm \\tiny H}$), metallicity ($[C/H]$), total hydrogen column\ndensity and line-of-sight thickness ($L$) in each C III components. We estimate\nthe systematic errors in these quantities contributed by the allowed range of\nthe quasar spectral index used in the ultraviolet background radiation\ncalculations. Our inferred $n_{\\rm \\tiny H}$ and overdensity ($\\Delta$) are\nmuch higher than the measurements available in the literature and favor the\nabsorption originating from gas associated with circumgalactic medium and\nprobably not in hydrostatic equilibrium. We also notice $n_{\\rm \\tiny H}$, $L$\nand $[C/H]$ associated with C III components show statistically significant\nredshift evolution. To some extent, these redshift evolutions are driven by the\nappearance of compact, high $n_{\\rm \\tiny H}$ and high $[C/H]$ components only\nin the low$-z$ end. We find more than 5$\\sigma$ level correlation between\n$[C/H]$ and $L$, $L$ and neutral hydrogen column density (N (HI)), N (HI) and\n$[C/H]$. We show $L$ versus $[C/H]$ correlation can be well reproduced if $L$\nis governed by the product of gas cooling time and sound speed as expected in\nthe case of cloud fragmentation under thermal instabilities. This allows us to\nexplain other observed correlations by simple photoionization considerations.\nStudying the optically thin C III absorbers over a large $z$ range and probably\ncorrelating their $z$ evolution with global star formation rate density\nevolution can shed light into the physics of cold clump formation and their\nevolution in the circumgalactic medium.", "category": "astro-ph_GA" }, { "text": "Nature of shocks revealed by SOFIA OI observations in the Cepheus E\n protostellar outflow: Protostellar jets and outflows are key features of the star-formation\nprocess, and primary processes of the feedback of young stars on the\ninterstellar medium. Understanding the underlying shocks is necessary to\nexplain how jets and outflows are launched, and to quantify their chemical and\nenergetic impacts on the surrounding medium. We performed a high-spectral\nresolution study of the [OI]$_{\\rm 63 \\mu m}$ emission in the outflow of the\nintermediate-mass Class 0 protostar Cep E-mm. We present observations of the OI\n$^3$P$_1 \\rightarrow$ $^3$P$_2$, OH between $^2\\Pi_{1/2}$ $J = 3/2$ and $J =\n1/2$ at 1837.8 GHz, and CO (16-15) lines with SOFIA-GREAT at three positions in\nthe Cep E outflow: mm (the driving protostar), BI (in the southern lobe), and\nBII (the terminal position in the southern lobe). The CO line is detected at\nall three positions. The OI line is detected in BI and BII, whereas the OH line\nis not detected. In BII, we identify three kinematical components in OI and CO,\nalready detected in CO: the jet, the HH377 terminal bow-shock, and the outflow\ncavity. The OI column density is higher in the outflow cavity than in the jet,\nwhich itself is higher than in the terminal shock. The terminal shock is where\nthe abundance ratio of OI to CO is the lowest (about 0.2), whereas the jet\ncomponent is atomic (ratio $\\sim$2.7). In the jet, we compare the OI\nobservations with shock models that successfully fit the integrated intensity\nof 10 CO lines: these models do not fit the OI data. The high intensity of OI\nemission points towards the propagation of additional dissociative or\nalternative FUV-irradiated shocks, where the illumination comes from the shock\nitself. From the sample of low-to-high mass protostellar outflows where similar\nobservations have been performed, the effects of illumination seem to increase\nwith the mass of the protostar.", "category": "astro-ph_GA" }, { "text": "The SEDIGISM survey: a search for molecular outflows: Context. The formation processes of massive stars are still unclear but a\npicture is emerging involving accretion disks and molecular outflows in what\nappears to be a scaled-up version of low-mass star formation. A census of\noutflow activity towards massive star-forming clumps in various evolutionary\nstages has the potential to shed light on massive star formation (MSF).\n Aims. We conducted an outflow survey towards ATLASGAL clumps using SEDIGISM\ndata and aimed to obtain a large sample of clumps exhibiting outflows in\ndifferent evolutionary stages.\n Methods. We identify the high-velocity wings of the 13CO lines toward\nATLASGAL clumps by (1) extracting the simultaneously observed 13CO and C18O\nspectra from SEDIGISM, and (2) subtracting Gaussian fits to the scaled C18O\nfrom the 13CO, line after considering opacity broadening.\n Results. We have detected high-velocity gas towards 1192 clumps out of a\ntotal sample of 2052, giving an overall detection rate of 58%. Outflow activity\nhas been detected in the earliest quiescent clumps (i.e., 70$\\mu$m weak), to\nthe most evolved HII region stages i.e., 8$\\mu$m bright with MSF tracers. The\ndetection rate increases as a function of evolution (quiescent=51%,\nprotostellar=47%, YSO=57%, UCHII regions=76%).\n Conclusion. Our sample is the largest outflow sample identified so far. The\nhigh-detection rate from this large sample is consistent with previous results\nand supports that outflows are a ubiquitous feature of MSF. The lower detection\nrate in early evolutionary stages may be due to that outflows in the early\nstages are weak and difficult to detect. We obtain a statistically significant\nsample of outflow clumps for every evolutionary stage, especially for outflow\nclumps in the 70$\\mu$m dark stage. This suggests that the absence of 70$\\mu$m\nemission is not a robust indicator of starless/pre-stellar cores.", "category": "astro-ph_GA" }, { "text": "Can we believe the strong-line abundances in giant HII regions and\n emission-line galaxies?: This review is not a compendium of strong-line methods to derive abundances\nin giant HII regions. It is mostly intended for readers who wish to use such\nmethods but do not have a solid background on the physics of HII regions. It is\nalso meant to encourage those using abundance results published in the\nliterature to think more thoroughly about the validity of these results.", "category": "astro-ph_GA" }, { "text": "Spectroscopy of the three distant Andromedan satellites Cassiopeia III,\n Lacerta I, and Perseus I: We present Keck II/DEIMOS spectroscopy of the three distant dwarf galaxies of\nM31 Lacerta I, Cassiopeia III, and Perseus I, recently discovered within the\nPan-STARRS1 3\\pi imaging survey. The systemic velocities of the three systems\n(v_{r,helio} = -198.4 +/- 1.1 km/s, -371.6 +/- 0.7 km/s, and -326 +/- 3 km/s,\nrespectively) confirm that they are satellites of M31. In the case of Lacerta I\nand Cassiopeia III, the high quality of the data obtained for 126 and 212\nmember stars, respectively, yields reliable constraints on their global\nvelocity dispersions (\\sigma_{vr} = 10.3 +/- 0.9 km/s and 8.4 +/- 0.6 km/s,\nrespectively), leading to dynamical-mass estimates for both of ~4x10^7 Msun\nwithin their half-light radius. These translate to V-band mass-to-light ratios\nof 15^{+12}_{-9} and 8^{+9}_{-5} in solar units. We also use our spectroscopic\ndata to determine the average metallicity of the 3 dwarf galaxies ([Fe/H] =\n-2.0 +/- 0.1, -1.7 +/- 0.1, and -2.0 +/- 0.2, respectively). All these\nproperties are typical of dwarf galaxy satellites of Andromeda with their\nluminosity and size.", "category": "astro-ph_GA" }, { "text": "Models of turbulent dissipation regions in the diffuse interstellar\n medium: Supersonic turbulence is a large reservoir of suprathermal energy in the\ninterstellar medium. Its dissipation, because it is intermittent in space and\ntime, can deeply modify the chemistry of the gas. We further explore a hybrid\nmethod to compute the chemical and thermal evolution of a magnetized\ndissipative structure, under the energetic constraints provided by the observed\nproperties of turbulence in the cold neutral medium. For the first time, we\nmodel a random line of sight by taking into account the relative duration of\nthe bursts with respect to the thermal and chemical relaxation timescales of\nthe gas. The key parameter is the turbulent rate of strain \"a\" due to the\nambient turbulence. With the gas density, it controls the size of the\ndissipative structures, therefore the strength of the burst. For a large range\nof rates of strain and densities, the models of turbulent dissipation regions\n(TDR) reproduce the CH+ column densities observed in the diffuse medium and\ntheir correlation with highly excited H2. They do so without producing an\nexcess of CH. As a natural consequence, they reproduce the abundance ratios of\nHCO+/OH and HCO+/H2O, and their dynamic range of about one order of magnitude\nobserved in diffuse gas. Large C2H and CO abundances, also related to those of\nHCO+, are another outcome of the TDR models that compare well with observed\nvalues. The abundances and column densities computed for CN, HCN and HNC are\none order of magnitude above PDR model predictions, although still\nsignificantly smaller than observed values.", "category": "astro-ph_GA" }, { "text": "Does the galaxy NGC1052-DF2 falsify Milgromian dynamics?: A great challenge in present-day physics is to understand whether the\nobserved internal dynamics of galaxies is due to dark matter matter or due to a\nmodification of the law of gravity. Recently, van Dokkum et al. reported that\nthe ultra-diffuse dwarf galaxy NGC1052-DF2 lacks dark matter, and they claimed\nthat this would -- paradoxically -- be problematic for modified gravity\ntheories like Milgromian dynamics (MOND). However, NGC1052-DF2 is not isolated,\nso that a valid prediction of its internal dynamics in MOND cannot be made\nwithout properly accounting for the external gravitational fields from\nneighbouring galaxies. Including this external field effect following Haghi et\nal. shows that NGC1052-DF2 is consistent with MOND.", "category": "astro-ph_GA" }, { "text": "A 500 pc filamentary gas wisp in the disk of the Milky Way: Star formation occurs in molecular gas. In previous studies, the structure of\nthe molecular gas has been studied in terms of molecular clouds, but has been\noverlooked beyond the cloud scale. We present an observational study of the\nmolecular gas at 49.5 degree = 500 pc) filamentary gas\nwisp. This has a large physical extent and a velocity dispersion of ~5 km/s.\nThe eastern part of the filamentary gas wisp is located ~130 pc above the\nGalactic disk (which corresponds to 1.5-4 e-folding scale-heights), and the\ntotal mass of the gas wisp is >= 1 X 10^5 M_sun. It is composed of two\nmolecular clouds and an expanding bubble. The velocity structure of the gas\nwisp can be explained as a smooth quiescent component disturbed by the\nexpansion of a bubble. That the length of the gas wisp exceeds by much the\nthickness of the molecular disk of the Milky Way is consistent with the\ncloud-formation scenario in which the gas is cold prior to the formation of\nmolecular clouds. Star formation in the filamentary gas wisp occurs at the edge\nof a bubble (G52L nebula), which is consistent with some models of triggered\nstar formation.", "category": "astro-ph_GA" }, { "text": "The potential of tracing the star formation history with HI 21-cm in\n intervening absorption systems: Unlike the neutral gas density, which remains largely constant over redshifts\nof 0 < z < 5, the star formation density exhibits a strong redshift dependence,\nincreasing from the present day before peaking at a redshift of z ~ 2.5. Thus,\nthere is a stark contrast between the star formation rate and the abundance of\nraw material available to fuel it. However, using the ratio of the strength of\nthe HI 21-cm absorption to the total neutral gas column density to quantify the\nspin temperature of the gas, it has recently been shown that its reciprocal may\ntrace the star formation density. This would be expected on the grounds that\nthe cloud of gas must be sufficiently cool to collapse under its own gravity.\nThis, however, relies on very limited data and so here we explore the potential\nof applying the above method to absorbers for which individual column densities\nare not available (primarily MgII absorption systems). By using the mean value\nas a proxy to the column density of the gas at a given redshift, we do, again,\nfind that 1/T (degenerate with the absorber-emitter size ratio) traces the SF\ndensity. If confirmed by higher redshift data, this could offer a powerful tool\nfor future surveys for cool gas throughout the Universe with the Square\nKilometre Array.", "category": "astro-ph_GA" }, { "text": "On planet formation around supermassive black holes and the grain\n disruption barriers by radiative torques: It has recently been suggested that planets can form by dust coagulation in\nthe torus of active galactic nuclei (AGN) with low luminosity of $L_{\\rm\nbol}\\lesssim 10^{42} erg s^{-1}$, constituting a new class of exoplanets\norbiting the supermassive black hole called \\textit{blanets}. However, large\ndust grains in the AGN torus may be rotationally disrupted by the Radiative\nTorque Disruption (RATD) mechanism due to AGN radiation feedback, which would\nprevent the blanet formation. To test this scenario, we adopt the simple smooth\nand clumpy dust/gas distribution inside the torus region to study the effect of\nRATD on the evolution of composite dust grains in the midplane of the torus. We\nfound that grain growth and then blanet formation are possible in the smooth\ntorus model. However, in the clumpy torus model, grain growth will be strongly\nconstrained by RATD, assuming the gas density distribution as adopted in Wada\net al. We also found that icy grain mantles inside clumps are quickly detached\nfrom the grain core by rotational desorption, reducing the sticking coefficient\nbetween icy grains and coagulation efficiency. The grain rotational disruption\nand ice desorption occur on timescales much shorter than the growth time up to\na factor of $\\sim 10^{4}$, which are the new barriers that grain growth must\novercome to form blanets. Further studies with more realistic AGN models are\nrequired to better constrain the effect of RATD on grain growth and blanet\nformation hypothesis around low luminosity AGN.", "category": "astro-ph_GA" }, { "text": "Resolved Near-infrared Stellar Photometry from the Magellan Telescope\n for 13 Nearby Galaxies: JAGB Method Distances: We present near-infrared JHK photometry for the resolved stellar populations\nin 13 nearby galaxies: NGC 6822, IC 1613, NGC 3109, Sextans B, Sextans A, NGC\n300, NGC 55, NGC 7793, NGC 247, NGC 5253, Cen A, NGC 1313, and M83, acquired\nfrom the 6.5m Baade-Magellan telescope. We measure distances to each galaxy\nusing the J-region asymptotic giant branch (JAGB) method, a new standard candle\nthat leverages the constant luminosities of color-selected, carbon-rich AGB\nstars. While only single-epoch, random-phase photometry is necessary to derive\nJAGB distances, our photometry is time-averaged over multiple epochs, thereby\ndecreasing the contribution of the JAGB stars' intrinsic variability to the\nmeasured dispersions in their observed luminosity functions. To cross-validate\nthese distances, we also measure near-infrared tip of the red giant branch\n(TRGB) distances to these galaxies. The residuals obtained from subtracting the\ndistance moduli from the two methods yield an RMS scatter of $\\sigma_{JAGB -\nTRGB}= \\pm 0.07$ mag. Therefore, all systematics in either the JAGB method and\nTRGB method (e.g., crowding, differential reddening, star formation histories)\nmust be contained within these $\\pm0.07$ mag bounds for this sample of galaxies\nbecause the JAGB and TRGB distance indicators are drawn from entirely distinct\nstellar populations, and are thus affected by these systematics independently.\nFinally, the composite JAGB star luminosity function formed from this diverse\nsample of galaxies is well-described by a Gaussian function with a modal value\nof $M_J = -6.20 \\pm 0.003$ mag (stat), indicating the underlying JAGB star\nluminosity function of a well-sampled full star formation history is highly\nsymmetric and Gaussian, based on over 6,700 JAGB stars in the composite sample.", "category": "astro-ph_GA" }, { "text": "The MUSE-Wide survey: A measurement of the Ly$\u03b1$ emitting fraction\n among $z>3$ galaxies: We present a measurement of the fraction of Lyman $\\alpha$ (Ly$\\alpha$)\nemitters ($X_{\\rm{Ly} \\alpha}$) amongst HST continuum-selected galaxies at\n$31 3CR Radio Galaxies and QSOs: From Proto-Clusters\n to Clusters of Galaxies?: We study the cluster environment for a sample of 21 radio loud AGN from the\n3CR catalog at z>1, 12 radio galaxies and 9 quasars with HST images in the\noptical and IR. We use two different approaches to determine cluster\ncandidates. We identify the early type galaxies (ETGs) in every field by\nmodeling each of the sources within a 40\" radius of the targets with a Sersic\nprofile. Using a simple passive evolution model, we derive the expected\nlocation of the ETGs on the red sequence (RS) in the color-magnitude diagram\nfor each of the fields of our sources. For seven targets, the model coincides\nwith the position of the ETGs. A second approach involves a search for over\ndensities. We compare the object densities of the sample as a whole and\nindividually against control fields taken from the GOODS-S region of 3D-HST\nsurvey. With this method we determine the fields of 10 targets to be cluster\ncandidates. Four cluster candidates are found by both methods. The two methods\ndisagree in some cases, depending on the specific properties of each field. For\nthe most distant radio galaxy in the 3CR catalog (3C257 at z = 2.47), we\nidentify a population of bluer ETGs that lie on the expected location of the RS\nmodel for that redshift. This appears to be the general behavior of ETGs in our\nfields and it is possibly a signature of the evolution of such galaxies. Our\nresults are consistent with half of the z > 1 radio galaxies being located in\ndense, rapidly evolving environments.", "category": "astro-ph_GA" }, { "text": "MHD Simulation of The Inner Galaxy with Radiative Cooling and Heating: We investigate the role of magnetic field on the gas dynamics in the Galactic\nbulge region by three dimensional simulations with radiative cooling and\nheating. While high-temperature corona with $T>10^6\\ {\\rm K}$ is formed in the\nhalo regions, the temperature near the Galactic plane is $\\lesssim 10^4\\ {\\rm\nK}$ following the thermal equilibrium curve determined by the radiative cooling\nand heating. Although the thermal energy of the interstellar gas is lost by\nradiative cooling, the saturation level of the magnetic field strength does not\nsignificantly depend on the radiative cooling and heating. The magnetic field\nstrength is amplified to $10\\ {\\rm \\mu G}$ on average, and reaches several\nhundred ${\\rm \\mu G}$ locally. We find the formation of magnetically dominated\nregions at mid-latitudes in the case with the radiative cooling and heating,\nwhich is not seen in the case without radiative effect. The vertical thickness\nof the mid-latitude regions is $50-150\\ {\\rm pc}$ at the radial location of\n$0.4-0.8 \\ {\\rm kpc}$ from the Galactic center, which is comparable to the\nobserved vertical distribution of neutral atomic gas. When we take the average\nof different components of energy density integrated over the Galactic bulge\nregion, the magnetic energy is comparable to the thermal energy. We conclude\nthat the magnetic field plays a substantial role in controlling the dynamical\nand thermal properties of the Galactic bulge region.", "category": "astro-ph_GA" }, { "text": "High Resolution Near-Infrared Survey of the Pipe Nebula I: A Deep\n Infrared Extinction Map of Barnard 59: We present our analysis of a fully sampled, high resolution dust extinction\nmap of the Barnard 59 complex in the Pipe Nebula. The map was constructed with\nthe infrared color excess technique applied to a photometric catalog that\ncombines data from both ground and space based observations. The map resolves\nfor the first time the high density center of the main core in the complex,\nthat is associated with the formation of a small cluster of stars. We found\nthat the central core in Barnard 59 shows an unexpected lack of significant\nsubstructure consisting of only two significant fragments. Overall, the\nmaterial appears to be consistent with being a single, large core with a\ndensity profile that can be well fit by a King model. A series of NH$_3$\npointed observations towards the high column density center of the core appear\nto show that the core is still thermally dominated, with sub-sonic non-thermal\nmotions. The stars in the cluster could be providing feedback to support the\ncore against collapse, but the relatively narrow radio lines suggest that an\nadditional source of support, for example a magnetic field, may be required to\nstabilize the core. Outside the central core our observations reveal the\nstructure of peripheral cores and resolve an extended filament into a handful\nof significant substructures whose spacing and masses appear to be consistent\nwith Jeans fragmentation.", "category": "astro-ph_GA" }, { "text": "The origin of high velocity stars from Gaia and LAMOST: Based on the second Gaia data (Gaia DR2) and spectroscopy from the LAMOST\nData Release 5, we defined the high-velocity (HiVel) stars sample as those\nstars with $v_{\\mathrm{gc}} > 0.85 v_{\\mathrm{esc}}$, and derived the final\nsample of 24 HiVel stars with stellar astrometric parameters and radial\nvelocities. Most of the HiVel stars are metal-poor and $\\alpha$-enhanced. In\norder to further explore the origin of these HiVel stars, we traced the\nbackwards orbits of each HiVel star in the Galactic potential to derive\nprobability parameters which are used to classify these HiVel stars. Of these,\n5 stars are from the tidal debris of disrupted dwarf galaxy and 19 stars are\nrunaway-star candidates which originate from the stellar disk.", "category": "astro-ph_GA" }, { "text": "Time-delay measurement of MgII broad line response for the\n highly-accreting quasar HE 0413-4031: Implications for the MgII-based\n radius-luminosity relation: We present the monitoring of the AGN continuum and MgII broad line emission\nfor the quasar HE 0413-4031 ($z=1.38$) based on the six-year monitoring by the\nSouth African Large Telescope (SALT). We managed to estimate a time-delay of\n$302.6^{+28.7}_{-33.1}$ days in the rest frame of the source using seven\ndifferent methods: interpolated cross-correlation function (ICCF), discrete\ncorrelation function (DCF), $z$-transformed DCF, JAVELIN, two estimators of\ndata regularity (Von Neumann, Bartels), and $\\chi^2$ method. This time-delay is\nbelow the value expected from the standard radius-luminosity relation. However,\nbased on the monochromatic luminosity of the source and the SED modelling, we\ninterpret this departure as the shortening of the time-delay due to the higher\naccretion rate of the source, with the inferred Eddington ratio of $\\sim 0.4$.\nThe MgII line luminosity of HE 0413-4031 responds to the continuum variability\nas $L_{\\rm line}\\propto L_{\\rm cont}^{0.43\\pm 0.10}$, which is consistent with\nthe light-travel distance of the location of MgII emission at $R_{\\rm out} \\sim\n10^{18}\\,{\\rm cm}$. Using the data of 10 other quasars, we confirm the\nradius-luminosity relation for broad MgII line, which was previously determined\nfor broad H$\\beta$ line for lower-redshift sources. In addition, we detect a\ngeneral departure of higher-accreting quasars from this relation in analogy to\nH$\\beta$ sample. After the accretion-rate correction of the light-travel\ndistance, the MgII-based radius-luminosity relation has a small scatter of only\n$0.10$ dex.", "category": "astro-ph_GA" }, { "text": "Driven Multifluid MHD Molecular Cloud Turbulence: It is believed that turbulence may have a significant impact on star\nformation and the dynamics and evolution of the molecular clouds in which this\noccurs. It is also known that non-ideal magnetohydrodynamic effects influence\nthe nature of this turbulence. We present the results of a numerical study of\n4-fluid MHD turbulence in which the dynamics of electrons, ions, charged dust\ngrains and neutrals and their interactions are followed. The parameters\ndescribing the fluid being simulated are based directly on observations of\nmolecular clouds. We find that the velocity and magnetic field power spectra\nare strongly influenced by multifluid effects on length-scales at least as\nlarge as 0.05 pc. The PDFs of the various species in the system are all found\nto be close to log-normal, with charged species having a slightly less\nplatykurtic (flattened) distribution than the neutrals. We find that the\nintroduction of multifluid effects does not significantly alter the structure\nfunctions of the centroid velocity increment.", "category": "astro-ph_GA" }, { "text": "Plasma dark matter direct detection: Dark matter in spiral galaxies like the Milky Way may take the form of a dark\nplasma. Hidden sector dark matter charged under an unbroken $U(1)'$ gauge\ninteraction provides a simple and well defined particle physics model realising\nthis possibility. The assumed $U(1)'$ neutrality of the Universe then implies\n(at least) two oppositely charged dark matter components with self-interactions\nmediated via a massless \"dark photon\" (the $U(1)'$ gauge boson). In addition to\nnuclear recoils such dark matter can give rise to keV electron recoils in\ndirect detection experiments. In this context, the detailed physical properties\nof the dark matter plasma interacting with the Earth is required. This is a\ncomplex system, which is here modelled as a fluid governed by the\nmagnetohydrodynamic equations. These equations are numerically solved for some\nillustrative examples, and implications for direct detection experiments\ndiscussed. In particular, the analysis presented here leaves open the\nintriguing possibility that the DAMA annual modulation signal is due primarily\nto electron recoils (or even a combination of electron recoils and nuclear\nrecoils). The importance of diurnal modulation (in addition to annual\nmodulation) as a means of probing this kind of dark matter is also emphasised.", "category": "astro-ph_GA" }, { "text": "A systematic DECam search for RR Lyrae in the outer halo of the Milky\n Way: The discovery of very distant stars in the halo of the Milky Way provides\nvaluable tracers on the Milky Way mass and its formation. Beyond 100 kpc from\nthe Galactic center, most of the stars are likely to be in faint dwarf galaxies\nor tidal debris from recently accreted dwarfs, making the outer reaches of the\nGalaxy important for understanding the Milky Way's accretion history. However,\ndistant stars in the halo are scarce. In that context, RR Lyrae are ideal\nprobes of the distant halo as they are intrinsically bright and thus can be\nseen at large distances, follow well-known period-luminosity relations that\nenable precise distance measurements, and are easily identifiable in\ntime-series data. Therefore, a detailed study of RR Lyrae will help us\nunderstand the accreted outskirts of the Milky Way. In this contribution, we\npresent the current state of our systematic search for distant RR Lyrae stars\nin the halo using the DECam imager at the 4m telescope on Cerro Tololo (Chile).\nThe total surveyed area consists of more than 110 DECam fields (~ 350 sq. deg)\nand includes two recent independent campaigns carried out in 2017 and 2018 with\nwhich we have detected > 650 candidate RR Lyrae stars. Here we describe the\nmethodology followed to analyze the two latest campaigns. Our catalog contains\na considerable number of candidate RR Lyrae beyond 100 kpc, and reaches out up\nto ~ 250 kpc. The number of distant RR Lyrae found is consistent with recent\nstudies of the outer halo. These stars provide a set of important probes of the\nmass of the Milky Way, the nature of the halo, and the accretion history of the\nGalactic outskirts.", "category": "astro-ph_GA" }, { "text": "From the Outside Looking in: What can Milky Way Analogues Tell us About\n the Star Formation Rate of Our Own Galaxy?: The Milky Way has been described as an anaemic spiral, but is its star\nformation rate (SFR) unusually low when compared to its peers? To answer this\nquestion, we define a sample of Milky Way Analogues (MWAs) based on stringent\ncuts on the best literature estimates of non-transient structural features for\nthe Milky Way. This selection yields only 176 galaxies from the whole of the\nSDSS DR7 spectroscopic sample which have morphological classifications in GZ2,\nfrom which we infer SFRs from two separate indicators. The mean SFRs found are\n$\\log(\\rm{SFR}_{SED}/\\rm{M}_{\\odot}~\\rm{yr}^{-1})=0.53$ with a standard\ndeviation of 0.23 dex from SED fits, and\n$\\log(\\rm{SFR}_{W4}/\\rm{M}_{\\odot}~\\rm{yr}^{-1})=0.68$ with a standard\ndeviation of 0.41 dex from a mid-infrared calibration. The most recent estimate\nfor the Milky Way's star formation rate of\n$\\log(\\rm{SFR}_{MW}/\\rm{M}_{\\odot}~\\rm{yr}^{-1})=0.22$ fits well within\n2$\\sigma$ of these values, where $\\sigma$ is the standard deviation of each of\nthe SFR indicator distributions. We infer that the Milky Way, while being a\ngalaxy with a somewhat low SFR, is not unusual when compared to similar\ngalaxies.", "category": "astro-ph_GA" }, { "text": "An Intensity Mapping Detection of Aggregate CO Line Emission at 3 mm: We present a detection of molecular gas emission at $z\\sim1-5$ using the\ntechnique of line intensity mapping. We make use of a pair of 3 mm\ninterferometric data sets, the first from the ALMA Spectroscopic Survey in the\nHubble Ultra Deep Field (ASPECS), and the second from a series of Atacama\nCompact Array (ACA) observations conducted between 2016 and 2018, targeting the\nCOSMOS field. At 100 GHz, we measure non-zero power at 97.8% and 99.9%\nconfidence in the ACA and ALMA data sets, respectively. In the joint result, we\nreject the zero-power hypothesis at 99.99% confidence, finding\n$\\tilde{I}^{2}_{s}(\\nu)=770\\pm210\\ \\mu\\textrm{K}^2\\ \\textrm{Hz}\\ \\textrm{sr}$.\nAfter accounting for sample variance effects, the estimated spectral shot power\nis $\\tilde{I}^{2}_{s}(\\nu)=1010_{-390}^{+550}\\ \\mu\\textrm{K}^2\\ \\textrm{Hz}\\\n\\textrm{sr}$. We derive a model for the various line species our measurement is\nexpected to be sensitive to, and estimate the shot power to be\n$120_{-40}^{+80}\\ \\mu\\textrm{K}^2\\ h^{-3}\\,\\textrm{Mpc}^{3}$,\n$200^{+120}_{-70}\\ \\mu\\textrm{K}^2\\ h^{-3}\\,\\textrm{Mpc}^{3}$, and\n$90^{+70}_{-40}\\ \\mu\\textrm{K}^2\\ h^{-3}\\,\\textrm{Mpc}^{3}$ for CO(2-1) at\n$z=1.3$, CO(3-2) at $z=2.5$, and CO(4-3) at $z=3.6$, respectively. Using line\nratios appropriate for high-redshift galaxies, we find these results to be in\ngood agreement with those from the CO Power Spectrum Survey (COPSS). Adopting\n$\\alpha_{\\rm CO}=3.6\\ M_{\\odot}\\ (\\textrm{K}\\ \\textrm{km}\\ \\textrm{s}^{-1}\\\n\\textrm{pc}^{2})^{-1}$, we estimate a cosmic molecular gas density of\n$\\rho_{\\textrm{H}_2}(z)\\sim 10^{8}\\ M_{\\odot}\\ \\textrm{Mpc}^{-3}$ between\n$z=1-3$.", "category": "astro-ph_GA" }, { "text": "A Search For Supernova Remnants in The Nearby Spiral Galaxy M74 (NGC\n 628): We have identified nine new SNR candidates in M74 with [S II]/H$\\alpha$\n$\\geq$ 0.4 as the basic criterion. We obtain [S II]/H$\\alpha$ ratio in the\nrange from 0.40 to 0.91 and H$\\alpha$ intensities from 2.8 $\\times$ $10^{-15}$\nerg cm$^{-2}$ s$^{-1}$ to 1.7 $\\times$ $10^{-14}$ erg cm$^{-2}$ s$^{-1}$. We\nalso present spectral follow-up observations of the SNR candidates and can\nconfirm only three of them (SNR2, SNR3, and SNR5). The lack of confirmation for\nthe rest might be due to the contamination by the nearby H II emission regions\nas well as due to the inaccurate positioning of the long slit on these objects.\nIn addition, we search the $Chandra$ Observatory archival data for the X-ray\ncounterparts to the optically identified candidates. We find positional\ncoincidence with only three SNR candidates, SNR1, SNR2, and SNR8. The spectrum\nof SNR2 yields a shock temperature of 10.8 keV with an ionization timescale of\n1.6 $\\times$ 10$^{10}$ s cm$^{-3}$ indicating a relatively young remnant in an\nearly Sedov phase which is not supported by our optical wavelength analysis.\nGiven the high luminosity of 10$^{39}$ erg s$^{-1}$ and the characteristics of\nthe X-ray spectrum, we favor an Ultra Luminous X-ray Source interpretation for\nthis source associated with an SNR. We calculate an X-ray flux upper limit of\n9.0 $\\times$ $10^{-15}$ erg cm$^{-2}$ s$^{-1}$ for the rest of the SNRs\nincluding spectroscopically identified SNR3 and SNR5.", "category": "astro-ph_GA" }, { "text": "An HST/COS Observation of Broad Ly$\u03b1$ Emission and Associated\n Absorption Lines of the BL Lacertae Object H 2356-309: Weak spectral features in BL Lacertae objects (BL Lac) often provide a unique\nopportunity to probe the inner region of this rare type of active galactic\nnucleus. We present a Hubble Space Telescope/Cosmic Origins Spectrograph\nobservation of the BL Lac H 2356-309. A weak Ly$\\alpha$ emission line was\ndetected. This is the fourth detection of a weak Ly$\\alpha$ emission feature in\nthe ultraviolet (UV) band in the so-called \"high energy peaked BL Lacs\", after\nStocke et al. Assuming the line-emitting gas is located in the broad line\nregion (BLR) and the ionizing source is the off-axis jet emission, we constrain\nthe Lorentz factor ($\\Gamma$) of the relativistic jet to be $\\geq 8.1$ with a\nmaximum viewing angle of 3.6$^\\circ$. The derived $\\Gamma$ is somewhat larger\nthan previous measurements of $\\Gamma \\approx 3 - 5$, implying a covering\nfactor of $\\sim$ 3% of the line-emitting gas. Alternatively, the BLR clouds\ncould be optically thin, in which case we constrain the BLR warm gas to be\n$\\sim 10^{-5}\\rm\\ M_{\\odot}$. We also detected two HI and one OVI absorption\nlines that are within $|\\Delta v| < 150\\rm\\ km\\ s^{-1}$ of the BL Lac object.\nThe OVI and one of the HI absorbers likely coexist due to their nearly\nidentical velocities. We discuss several ionization models and find a\nphotoionization model where the ionizing photon source is the BL Lac object can\nfit the observed ion column densities with reasonable physical parameters. This\nabsorber can either be located in the interstellar medium of the host galaxy,\nor in the BLR.", "category": "astro-ph_GA" }, { "text": "Element Abundances in a Gas-rich Galaxy at z = 5: Clues to the Early\n Chemical Enrichment of Galaxies: Element abundances in high-redshift quasar absorbers offer excellent probes\nof the chemical enrichment of distant galaxies, and can constrain models for\npopulation III and early population II stars. Recent observations indicate that\nthe sub-damped Lyman-alpha (sub-DLA) absorbers are more metal-rich than DLA\nabsorbers at redshifts 0$<$$z$$<$3. It has also been suggested that the DLA\nmetallicity drops suddenly at $z$$>$4.7. However, only 3 DLAs at $z$$>$4.5 and\nnone at $z$$>$3.5 have \"dust-free\" metallicity measurements of undepleted\nelements. We report the first quasar sub-DLA metallicity measurement at\n$z$$>$3.5, from detections of undepleted elements in high-resolution data for a\nsub-DLA at $z$=5.0. We obtain fairly robust abundances of C, O, Si, and Fe,\nusing lines outside the Lyman-alpha forest. This absorber is metal-poor, with\nO/H]=-2.00$\\pm$0.12, which is $\\gtrsim$4$\\sigma$ below the level expected from\nextrapolation of the trend for $z$$<$3.5 sub-DLAs. The C/O ratio is\n1.8$^{+0.4}_{-0.3}$ times lower than in the Sun. More strikingly, Si/O is\n3.2$^{+0.6}_{-0.5}$ times lower than in the Sun, while Si/Fe is nearly\n(1.2$^{+0.4}_{-0.3}$ times) solar. This absorber does not display a clear\nalpha/Fe enhancement. Dust depletion may have removed more Si from the gas\nphase than is common in the Milky Way interstellar medium, which may be\nexpected if high-redshift supernovae form more silicate-rich dust. C/O and Si/O\nvary substantially between different velocity components, indicating spatial\nvariations in dust depletion and/or early stellar nucleosynethesis (e.g.,\npopulation III star initial mass function). The higher velocity gas may trace\nan outflow enriched by early stars.", "category": "astro-ph_GA" }, { "text": "Unravelling the nature of the dual AGN in the galaxy pair system IRAS\n 05589+2828 and 2MASX J06021107+2828382: We have studied the nuclear region of the previously detected dual AGN system\nin the galaxy pair IRAS 05589+2828 and 2MASX J06021107+2828382 through new\noptical spectroscopy observations, along with radio and X-ray archival data.\nOur multiwavelength data strongly suggest that the Sy1 \\iras\\,\n(z=0.0330$\\pm$0.0002) conforms to a dual AGN system with the Sy2 \\twomas\\,\n(z=0.0334$\\pm$0.0001) with a projected separation obtained from the radio data\nof 20.08\\arcsec\\, ($\\sim$13.3\\,kpc). Analysis of the optical spectra reveals a\nfaint narrow extended emission from H$\\alpha$ and [OIII] amidst the two AGN,\nsupporting evidence for an ongoing merger. \\iras\\, is a double component narrow\nemission line AGN, with complex broad Balmer emission line profiles that\nclearly show a strong red-peaklet with a velocity shift of\n$\\sim$3500\\,km\\,s$^{-1}$. The black hole mass estimates of \\iras\\, and\n\\twomas\\, are log\\,M$\\rm_{BH}$\\,=\\,8.59\\,$\\pm$\\,0.14 (M$_\\odot$) and\nlog\\,M$\\rm_{BH}$\\,=\\,8.21$\\pm$0.2 (M$_\\odot$), respectively. In the X-ray\nbands, \\iras\\, is compatible with a Type 1 object, showing both spectral and\nflux variability. \\chandra\\, data of 2MASX\\,J06021107+2828382 allowed us to\nmeasure a high hardness ratio in this source, providing evidence for a Type 2\nAGN. The 22 GHz image obtained with the {\\it Karl G. Jansky Very Large Array}\nhas revealed that both AGN are compact radio objects with spectral indices\n-0.26$\\pm$0.03 and -0.70$\\pm$0.11, confirming for the first time its dual AGN\nnature in the radio bands.", "category": "astro-ph_GA" }, { "text": "New Maser Emission from Nonmetastable Ammonia in NGC 7538. III.\n Detection of the (10,6) Transition and a Velocity Gradient: We present the first astronomical detection of the 14NH3 (J,K) = (10,6) line:\nnonthermal emission at several velocities in the Galactic star-forming region\nNGC 7538. Using the VLA we have imaged the (10,6) and (9,6) ammonia masers at\nseveral positions within NGC 7538 IRS 1. The individual sources have angular\nsizes < 0.1 arcseconds corresponding to brightness temperatures T_B > 1E6 K. We\napply the pumping model of Brown & Cragg, confirming the conjecture that\nmultiple ortho-ammonia masers can occur with the same value of K. The positions\nand velocities of the (10,6) and (9,6) masers are modeled as motion in a\npossible disk or torus and are discussed in the context of recent models of the\nregion.", "category": "astro-ph_GA" }, { "text": "Mixing and transport of metals by gravitational instability-driven\n turbulence in galactic discs: Metal production in galaxies traces star formation, and is highly\nconcentrated toward the centers of galactic discs. This suggests that galaxies\nshould have inhomogeneous metal distributions with strong radial gradients, but\nobservations of present-day galaxies show only shallow gradients with little\nazimuthal variation, implying the existence of a redistribution mechanism. We\nstudy the role of gravitational instability-driven turbulence as a mixing\nmechanism by simulating an isolated galactic disc at high resolution, including\nmetal fields treated as passive scalars. Since any cylindrical field can be\ndecomposed into a sum of Fourier-Bessel basis functions, we set up initial\nmetal fields characterized by these functions and study how different modes\nmix. We find both shear and turbulence contribute to mixing, but the mixing\nstrongly depends on the symmetries of the mode. Non-axisymmetric modes have\ndecay times smaller than the galactic orbital period because shear winds them\nup to small spatial scales, where they are erased by turbulence. The decay\ntimescales for axisymmetric modes are much greater, though for all but the\nlargest-scale inhomogeneities the mixing timescale is still short enough to\nerase chemical inhomogeneities over cosmological times. These different\ntimescales provide an explanation for why galaxies retain metallicity gradients\nwhile there is almost no variation at a fixed radius. Moreover, the\ncomparatively long timescales required for mixing axisymmetric modes may\nexplain the greater diversity of metallicity gradients observed in high\nredshift galaxies as compared to local ones: these systems have not yet reached\nequilibrium between metal production and diffusion.", "category": "astro-ph_GA" }, { "text": "Revisiting the bulge-halo conspiracy I: Dependence on galaxy properties\n and halo mass: We carry out a systematic investigation of the total mass density profile of\nmassive (Mstar>2e11 Msun) early-type galaxies and its dependence on galactic\nproperties and host halo mass with the aid of a variety of lensing/dynamical\ndata and large mock galaxy catalogs. The latter are produced via semi-empirical\nmodels that, by design, are based on just a few basic input assumptions.\nGalaxies, with measured stellar masses, effective radii and S\\'{e}rsic indices,\nare assigned, via abundance matching relations, host dark matter halos\ncharacterized by a typical LCDM profile. Our main results are as follows: (i)\nIn line with observational evidence, our semi-empirical models naturally\npredict that the total, mass-weighted density slope at the effective radius\ngamma' is not universal, steepening for more compact and/or massive galaxies,\nbut flattening with increasing host halo mass. (ii) Models characterized by a\nSalpeter or variable initial mass function and uncontracted dark matter\nprofiles are in good agreement with the data, while a Chabrier initial mass\nfunction and/or adiabatic contractions/expansions of the dark matter halos are\nhighly disfavored. (iii) Currently available data on the mass density profiles\nof very massive galaxies (Mstar>1e12 Msun), with Mhalo>3e14 Msun, favor instead\nmodels with a stellar profile flatter than a S\\'{e}rsic one in the very inner\nregions (r<3-5 kpc), and a cored NFW or Einasto dark matter profile with median\nhalo concentration a factor of ~2 or <1.3, respectively, higher than those\ntypically predicted by N-body numerical simulations.", "category": "astro-ph_GA" }, { "text": "Precipitation-Regulated Star Formation in Galaxies: Galaxy growth depends critically on the interplay between radiative cooling\nof cosmic gas and the resulting energetic feedback that cooling triggers. This\ninterplay has proven exceedingly difficult to model, even with large\nsupercomputer simulations, because of its complexity. Nevertheless, real\ngalaxies are observed to obey simple scaling relations among their primary\nobservable characteristics. Here we show that a generic emergent property of\nthe interplay between cooling and feedback can explain the observed scaling\nrelationships between a galaxy's stellar mass, its total mass, and its chemical\nenrichment level, as well as the relationship between the average orbital\nvelocity of its stars and the mass of its central black hole. These\nrelationships naturally result from any feedback mechanism that strongly heats\na galaxy's circumgalactic gas in response to precipitation of colder clouds out\nof that gas, because feedback then suspends the gas in a marginally\nprecipitating state.", "category": "astro-ph_GA" }, { "text": "The Galaxy's Veil of Excited Hydrogen: Many of the baryons in our Galaxy probably lie outside the well known disk\nand bulge components. Despite a wealth of evidence for the presence of some gas\nin galactic halos, including absorption line systems in the spectra of quasars,\nhigh velocity neutral hydrogen clouds in our Galaxy halo, line emitting ionised\nhydrogen originating from galactic winds in nearby starburst galaxies, and the\nX-ray coronas surrounding the most massive galaxies, accounting for the gas in\nthe halo of any galaxy has been observationally challenging primarily because\nof its low density in the expansive halo. The most sensitive measurements come\nfrom detecting absorption by the intervening gas in the spectra of distant\nobjects such as quasars or distant halo stars, but these have typically been\nlimited to a few lines of sight to sufficiently bright objects. Massive\nspectroscopic surveys of millions of objects provide an alternative approach to\nthe problem. Here, we present the first evidence for a widely distributed,\nneutral, excited hydrogen component of the Galaxy's halo. It is observed as the\nslight, (0.779 $\\pm$ 0.006)\\%, absorption of flux near the rest wavelength of\nH$\\alpha$ in the combined spectra of hundreds of thousands of galaxy spectra\nand is ubiquitous in high latitude lines of sight. This observation provides an\navenue to tracing, both spatially and kinematically, the majority of the gas in\nthe halo of our Galaxy.", "category": "astro-ph_GA" }, { "text": "Discovery of H2O Megamasers in Obscured Active Galactic Nuclei: Recently a new method to discover obscured active galactic nuclei (AGNs) by\nutilizing X-ray and Infrared data has been developed. We carried out a survey\nof H2O maser emission toward ten obscured AGNs with the Nobeyama 45-m\ntelescope. We newly detected the maser emission with the signal-noise-ratio\n(SNR) of above 4 from two AGNs, NGC 1402 and NGC 7738. We also found a\ntentative detection with its SNR > 3 in NGC 5037. The detection rate of 20% is\nhigher than those of previous surveys (usually several percents).", "category": "astro-ph_GA" }, { "text": "The Ionized Gas in Nearby Galaxies as Traced by the [NII] 122 and 205\n \u03bcm Transitions: The [NII] 122 and 205 \\mu m transitions are powerful tracers of the ionized\ngas in the interstellar medium. By combining data from 21 galaxies selected\nfrom the Herschel KINGFISH and Beyond the Peak surveys, we have compiled 141\nspatially resolved regions with a typical size of ~1 kiloparsec, with\nobservations of both [NII] far-infrared lines. We measure [NII] 122/205 line\nratios in the ~0.6-6 range, which corresponds to electron gas densities\n$n_e$~1-300 cm$^{-3}$, with a median value of $n_e$=30 cm$^{-3}$. Variations in\nthe electron density within individual galaxies can be as a high as a factor of\n~50, frequently with strong radial gradients. We find that $n_e$ increases as a\nfunction of infrared color, dust-weighted mean starlight intensity, and star\nformation rate surface density ($\\Sigma_{SFR}$). As the intensity of the [NII]\ntransitions is related to the ionizing photon flux, we investigate their\nreliability as tracers of the star formation rate (SFR). We derive relations\nbetween the [NII] emission and SFR in the low-density limit and in the case of\na log-normal distribution of densities. The scatter in the correlation between\n[NII] surface brightness and $\\Sigma_{SFR}$ can be understood as a property of\nthe $n_e$ distribution. For regions with $n_e$ close to or higher than the\n[NII] line critical densities, the low-density limit [NII]-based SFR\ncalibration systematically underestimates the SFR since [NII] emission is\ncollisionally quenched. Finally, we investigate the relation between [NII]\nemission, SFR, and $n_e$ by comparing our observations to predictions from the\nMAPPINGS-III code.", "category": "astro-ph_GA" }, { "text": "Revealing a detailed mass distribution of a high-density core\n MC27/L1521F in Taurus with ALMA: We present the results of ALMA observations of dust continuum emission and\nmolecular rotational lines toward a dense core MC27 (aka L1521F) in Taurus,\nwhich is considered to be at a very early stage of star formation. The detailed\ncolumn density distribution on size scales from a few tens AU to ~10,000 AU\nscale are revealed by combining the ALMA (12 m array + 7 m array) data with the\npublished/unpublished single-dish data. The high angular resolution\nobservations at 0.87 mm with a synthesized beam size of ~0.\"74 x 0.\"32 reveal\nthat a protostellar source, MMS-1, is not spatially resolved and lacks\nassociated gas emission, while a starless high-density core, MMS-2, has\nsubstructures both in dust and molecular emission. The averaged radial column\ndensity distribution of the inner part of MC27/L1521F (r $\\lesssim$ 3000 AU) is\nN(H2) ~r$^{-0.4}$, clearly flatter than that of the outer part, ~r$^{-1.0}$.\nThe complex velocity/spatial structure obtained with previous ALMA observations\nis located inside the inner flatter region, which may reflect the dynamical\nstatus of the dense core.", "category": "astro-ph_GA" }, { "text": "Constraints on Individual Supermassive Black Hole Binaries from Pulsar\n Timing Array Limits on Continuous Gravitational Waves: Pulsar timing arrays (PTAs) are placing increasingly stringent constraints on\nthe strain amplitude of continuous gravitational waves emitted by supermassive\nblack hole binaries on subparsec scales. In this paper, we incorporate\nindependent information about the dynamical masses $M_{bh}$ of supermassive\nblack holes in specific galaxies at known distances and use this additional\ninformation to further constrain whether or not those galaxies could host a\ndetectable supermassive black hole binary. We estimate the strain amplitudes\nfrom individual binaries as a function of binary mass ratio for two samples of\nnearby galaxies: (1) those with direct dynamical measurements of $M_{bh}$ in\nthe literature, and (2) the 116 most massive early-type galaxies (and thus\nlikely hosts of the most massive black holes) within 108 Mpc from the MASSIVE\nSurvey. Our exploratory analysis shows that the current PTA upper limits on\ncontinuous waves (as a function of angular position in the sky) can already\nconstrain the mass ratios of hypothetical black hole binaries in many galaxies\nin our samples. The constraints are stronger for galaxies with larger $M_{bh}$\nand at smaller distances. For the black holes with $M_{bh} \\gtrsim 5\\times 10^9\nM_\\odot$ at the centers of NGC 1600, NGC 4889, NGC 4486 (M87) and NGC 4649\n(M60), any binary companion in orbit within the PTA frequency bands would have\nto have a mass ratio of a few percent or less.", "category": "astro-ph_GA" }, { "text": "ALMA Deep Field in SSA22: Survey Design and Source Catalog of a 20\n arcmin^2 Survey at 1.1mm: To search for dust-obscured star-formation activity in the early Universe, it\nis essential to obtain a deep and wide submillimeter/millimeter map. The advent\nof the Atacama Large Millimeter/submillimeter Array (ALMA) has enabled us to\nobtain such maps at sufficiently high spatial resolution to be free from source\nconfusion. We present a new 1.1mm map obtained by ALMA in the SSA22 field.\nSSA22 contains a remarkable proto-cluster at z=3.09 and is therefore an ideal\nregion to investigate the role of large-scale cosmic web on dust-obscured star\nformation. The typical 1sigma depth of our map is 73 uJy/beam at a 0.5\nresolution; combined with earlier, archived observations, we map an area of 20\narcmin^2 (71 comoving Mpc^2 at z=3.09). Within the combined survey area we have\ndetected 35 sources at a signal-to-noise ratio (S/N) >5, with flux densities,\nS1.1mm=0.43--5.6 mJy, equivalent to star-formation rates of >=100--1000 Msun/yr\nat z=3.09, for a Chabrier initial mass function; of these, 17 are new\ndetections. The cumulative number counts show a factor 3--5x excess compared to\nblank fields. The excess suggests enhanced dust-enshrouded star-formation\nactivity in the proto-cluster on a 10 comoving Mpc scale, indicating\naccelerated galaxy evolution in this overdense region.", "category": "astro-ph_GA" }, { "text": "Selecting accreted populations: metallicity, elemental abundances, and\n ages of the Gaia-Sausage-Enceladus and Sequoia populations: Identifying stars found in the Milky Way as having formed in situ or accreted\ncan be a complex and uncertain undertaking. We use Gaia kinematics and APOGEE\nelemental abundances to select stars belonging to the Gaia-Sausage-Enceladus\n(GSE) and Sequoia accretion events. These samples are used to characterize the\nGSE and Sequoia population metallicity distribution functions, elemental\nabundance patterns, age distributions, and progenitor masses. We find that the\nGSE population has a mean [Fe/H] $\\sim -1.15$ and a mean age of $10-12$ Gyr.\nGSE has a single sequence in [Mg/Fe] vs [Fe/H] consistent with the onset of SN\nIa Fe contributions and uniformly low [Al/Fe] of $\\sim -0.25$ dex. The derived\nproperties of the Sequoia population are strongly dependent on the kinematic\nselection. We argue the selection with the least contamination is\n$J_{\\phi}/J_{\\mbox{tot}} < -0.6$ and $(J_z - J_R)/J_{\\mbox{tot}} < 0.1$. This\nresults in a mean [Fe/H] $\\sim -1.3$ and a mean age of $12-14$ Gyr. The Sequoia\npopulation has a complex elemental abundance distribution with mainly high\n[Mg/Fe] stars. We use the GSE [Al/Fe] vs [Mg/H] abundance distribution to\ninform a chemically-based selection of accreted stars, which is used to remove\npossible contaminant stars from the GSE and Sequoia samples.", "category": "astro-ph_GA" }, { "text": "Temperature structure and kinematics of the IRDC G035.39-00.33: Aims. Infrared dark clouds represent the earliest stages of high-mass star\nformation. Detailed observations of their physical conditions on all physical\nscales are required to improve our understanding of their role in fueling star\nformation.\n Methods. We investigate the large-scale structure of the IRDC G035.39-00.33,\nprobing the dense gas with the classical ammonia thermometer. This allows us to\nput reliable constraints on the temperature of the extended, pc-scale dense gas\nreservoir and to probe the magnitude of its non-thermal motions. Available\nfar-infrared observations can be used in tandem with the observed ammonia\nemission to estimate the total gas mass contained in G035.39-00.33.\n Results. We identify a main velocity component as a prominent filament,\nmanifested as an ammonia emission intensity ridge spanning more than 6 pc,\nconsistent with the previous studies on the Northern part of the cloud. A\nnumber of additional line-of-sight components are found, and a large scale,\nlinear velocity gradient of ~0.2 km s$^{-1}$ pc$^{-1}$ is found along the ridge\nof the IRDC. In contrast to the dust temperature map, an ammonia-derived\nkinetic temperature map, presented for the entirety of the cloud, reveals local\ntemperature enhancements towards the massive protostellar cores. We show that\nwithout properly accounting for the line of sight contamination, the dust\ntemperature is 2-3 K larger than the gas temperature measured with NH$_3$.\n Conclusions. While both the large scale kinematics and temperature structure\nare consistent with that of starless dark filaments, the kinetic gas\ntemperature profile on smaller scales is suggestive of tracing the heating\nmechanism coincident with the locations of massive protostellar cores.", "category": "astro-ph_GA" }, { "text": "A Change of Rotation Profile in the Envelope in the HH 111 Protostellar\n System: A Transition to a Disk?: The HH 111 protostellar system consists of two Class I sources (VLA 1 and 2)\nwith putative disks deeply embedded in a flattened envelope at a distance of\n400 pc. Here is a follow-up study of this system in C18O (J=2-1), SO (N_J =\n5_6-4_5), and 1.33 mm continuum at ~ 1\" (400 AU) resolution, and it may show\nfor the first time how a rotationally supported disk can be formed inside an\ninfalling envelope. The 1.33 mm continuum emission is seen arisen from both\nsources, likely tracing the dusty putative disks around them. In particular,\nthe emission around the VLA 1 source is elongated in the equatorial plane with\na radius of ~ 300 AU. The envelope is well seen in C18O, extending to ~ 7000 AU\nout from the VLA 1 source, with the innermost part overlapping with the dusty\ndisk. It has a differential rotation, with the outer part (~ 2000-7000 AU)\nbetter described by a rotation that has constant specific angular momentum and\nthe inner part (~ 60-2000 AU) by a Keplerian rotation. The envelope seems to\nalso have some infall motion that is smaller than the rotation motion. Thus,\nthe material in the outer part of the envelope seems to be slowly spiraling\ninward with its angular momentum and the rotation can indeed become Keplerian\nin the inner part. A compact SO emission is seen around the VLA 1 source with a\nradius of ~ 400 AU and it may trace a shock such as an (inner) accretion shock\naround the disk.", "category": "astro-ph_GA" }, { "text": "The location of the dust causing internal reddening of active galactic\n nuclei: We use the Balmer decrements of the broad-line regions (BLRs) and narrow-line\nregions (NLRs) of active galactic nuclei (AGNs) as reddening indicators to\ninvestigate the location of the dust for four samples of AGNs with reliable\nestimates of the NLR contribution to the Balmer lines. Intercomparison of the\nNLR and BLR Balmer decrements indicates that the reddening of the NLR sets a\nlower limit to the reddening of the BLR. Almost no objects have high NLR\nreddening but low BLR reddening. The reddening of the BLR is often\nsubstantially greater than the reddening of the NLR. The BLR reddening is\ncorrelated with the equivalent widths of [O III] lines and the intensity of the\n[O III] lines relative to broad H\\beta. We find these relationships to be\nconsistent with the predictions of a simple model where the additional dust\nreddening the BLR is interior to the NLR. We thus conclude that the dust\ncausing the additional reddening of the accretion disc and BLR is mostly\nlocated at a smaller radius than the NLR.", "category": "astro-ph_GA" }, { "text": "Radio continuum emission and water masers towards CB 54: We present high angular resolution observations of water masers at 1.3 cm and\nradio continuum emission at 1.3, 3.6 and 6 cm towards the Bok globule CB 54\nusing the Very Large Array. At 1.3 cm, with subarsecond angular resolution, we\ndetect a radio continuum compact source located to the south-west of the\nglobule and spatially coincident with a mid-infrared embedded object (MIR-b).\nThe spectral index derived between 6 and 1.3 cm (alpha=0.3+/-0.4) is flat,\nconsistent with optically thin free-free emission from ionized gas. We propose\nthe shock-ionization scenario as a viable mechanism to produce the radio\ncontinuum emission observed at cm frequencies. Water masers are detected at two\ndifferent positions separated by 2.3'', and coincide spatially with two\nmid-infrared sources: MIR-b and MIR-c. The association of these mid-IR sources\nwith water masers confirms that they are likely protostars undergoing\nmass-loss, and they are the best candidate as driving sources of the molecular\noutflows in the region.", "category": "astro-ph_GA" }, { "text": "The origin of carbon: Low-mass stars and an evolving, initially\n top-heavy IMF?: Multi-zone chemical evolution models (CEMs), differing in the nucleosynthesis\nprescriptions (yields) and prescriptions of star formation, have been computed\nfor the Milky Way. All models fit the observed O/H and Fe/H gradients well and\nreproduce the main characteristics of the gas distribution, but they are also\ndesigned to do so. For the C/H gradient the results are inconclusive with\nregards to yields and star formation. The C/Fe and O/Fe vs. Fe/H, as well as\nC/O vs. O/H trends predicted by the models for the solar neighbourhood zone\nwere compared with stellar abundances from the literature. For O/Fe vs. Fe/H\nall models fit the data, but for C/O vs. O/H, only models with increased carbon\nyields for zero-metallicity stars or an evolving initial mass function provide\ngood fits. Furthermore, a steep star formation threshold in the disc can be\nruled out since it predicts a steep fall-off in all abundance gradients beyond\na certain galactocentric distance (~ 13 kpc) and cannot explain the possible\nflattening of the C/H and Fe/H gradients in the outer disc seen in\nobservations. Since in the best-fit models the enrichment scenario is such that\ncarbon is primarily produced in low-mass stars, it is suggested that in every\nenvironment where the peak of star formation happened a few Gyr back in time,\nwinds of carbon-stars are responsible for most of the carbon enrichment.\nHowever, a significant contribution by zero-metallicity stars, especially at\nvery early stages, and by winds of high-mass stars, which are increasing in\nstrength with metallicity, cannot be ruled out by the CEMs presented here. In\nthe solar neighbourhood, as much as 80%, or as little as 40% of the carbon may\nhave been injected to the interstellar medium by low- and intermediate-mass\nstars. The stellar origin of carbon remains an open question, although\nproduction in low- and intermediate-mass stars appears to be the simplest\nexplanation of observed carbon abundance trends.", "category": "astro-ph_GA" }, { "text": "Optical photometry and basic parameters of 10 unstudied open clusters: We present BVI CCD photometry of 10 northern open clusters, Berkeley 43,\nBerkeley 45, Berkeley 47, NGC 6846, Berkeley 49, Berkeley 51, Berkeley 89,\nBerkeley 91, Tombaugh 4 and Berkeley 9, and estimate their fundamental\nparameters. Eight of the clusters are located in the first galactic quadrant\nand 2 are in the second. This is the first optical photometry for 8 clusters.\nAll of them are embedded in rich galactic fields and have large reddening\ntowards them (E(B-V) = 1.0 - 2.3 mag). There is a possibility that some of\nthese difficult-to-study clusters may be asterisms rather than physical\nsystems, but assuming they are physical clusters, we find that 8 of them are\nlocated beyond 2 kpc, and 6 clusters (60% of the sample) are located well above\nor below the Galactic plane. Seven clusters have ages 500 Myr or less and the\nother 3 are 1 Gyr or more in age. This sample of clusters has increased the\noptical photometry of clusters in the second half of the first galactic\nquadrant, beyond 2 kpc, from 10 to 15. NGC 6846 is found to be one of the most\ndistant clusters in this region of the Galaxy.", "category": "astro-ph_GA" }, { "text": "Doubly substituted isotopologues of HCCCN in TMC-1: Detection of\n D13CCCN, DC13CCN, DCC13CN, DCCC15N, H13C13CCN, H13CC13CN, HC13C13CN,\n HCC13C15N, and HC13CC15N: We report the first detection in space of a complete sample of nine doubly\nsubstituted isotopologues of HCCCN towards the cyanopolyyne peak of TMC-1 using\nobservations of the QUIJOTE line survey taken with the Yebes 40 m telescope. We\ndetected D13CCCN, DC13CCN, DCC13CN, DCCC15N, H13C13CCN, H13CC13CN, HC13C13CN,\nHCC13C15N, and HC13CC15N through their J=4-3 and J=5-4 lines in the 7 mm\nwindow. In addition, we present an extensive analysis of the emission of HCCCN\nand its singly substituted isotopologues through a large velocity gradient\nmodel of the lines detected at 7 mm and 3 mm using the Yebes 40 m and the IRAM\n30 m telescopes, respectively. The derived column densities for all the\nisotopologues are consistent in the two spectral bands for an H2 volume density\nof 1e4 cm-3 and a kinetic temperature of 10 K. Whereas we observed a 13C\nfractionation for HCC13CN and other double isotopologues with a 13C atom\nadjacent to the nitrogen atom, we derived similar C/13C abundance ratios for\nthe three 13C substituted species of DCCCN. This suggests additional chemical\ndiscrimination for deuterated isotopologues of HCCCN. Finally, we present the\nspatial distribution of the J=4-3 and J=5-4 lines from the singly substituted\nspecies observed with the Yebes 40 m telescope. The emission peak of the\nspatial distribution of DCCCN appears to be displaced by 40'' with respect to\nthat of HCCCN and the 13C and 15N isotopologues. In addition to a different\nformation route for the deuterated species, we could also expect that this\ndifferentiation owing to the deuterium fractionation is more efficient at low\ntemperatures, and therefore, that deuterated species trace a colder region of\nthe cloud.", "category": "astro-ph_GA" }, { "text": "Mapping the Polarization of the Radio-Loud Ly$\u03b1$ Nebula B3\n J2330+3927: Lya nebulae, or \"Lya blobs\", are extended (up to ~100 kpc), bright (L[Lya] >\n10^43 erg/s) clouds of Lya emitting gas that tend to lie in overdense regions\nat z ~ 2--5. The origin of the Lya emission remains unknown, but recent\ntheoretical work suggests that measuring the polarization might discriminate\namong powering mechanisms. Here we present the first narrowband, imaging\npolarimetry of a radio-loud Lya nebula, B3 J2330+3927 at z=3.09, with an\nembedded active galactic nucleus (AGN). The AGN lies near the blob's Lya\nemission peak and its radio lobes align roughly with the blob's major axis.\nWith the SPOL polarimeter on the 6.5m MMT telescope, we map the total (Lya +\ncontinuum) polarization in a grid of circular apertures of radius 0.6\"\n(4.4kpc), detecting a significant (>2sigma) polarization fraction P in nine\napertures and achieving strong upper-limits (as low as 2%) elsewhere. P\nincreases from <2% at ~5kpc from the blob center to ~17% at ~15-25kpc. The\ndetections are distributed asymmetrically, roughly along the nebula's major\naxis. The polarization angles theta are mostly perpendicular to this axis.\nComparing the Lya flux to that of the continuum, and conservatively assuming\nthat the continuum is highly polarized (20-100%) and aligned with the total\npolarization, we place lower limits on the polarization of the Lya emission\nP(Lya) ranging from no significant polarization at ~5 kpc from the blob center\nto ~ 3--17% at 10--25kpc. Like the total polarization, the Lya polarization\ndetections occur more often along the blob's major axis.", "category": "astro-ph_GA" }, { "text": "Ionized and molecular gas kinematics in a z=1.4 star-forming galaxy: We present deep observations of a $z=1.4$ massive, star-forming galaxy in\nmolecular and ionized gas at comparable spatial resolution (CO 3-2, NOEMA;\nH$\\alpha$, LBT). The kinematic tracers agree well, indicating that both gas\nphases are subject to the same gravitational potential and physical processes\naffecting the gas dynamics. We combine the one-dimensional velocity and\nvelocity dispersion profiles in CO and H$\\alpha$ to forward-model the galaxy in\na Bayesian framework, combining a thick exponential disk, a bulge, and a dark\nmatter halo. We determine the dynamical support due to baryons and dark matter,\nand find a dark matter fraction within one effective radius of $f_{\\rm\nDM}(\\leq$$R_{e})=0.18^{+0.06}_{-0.04}$. Our result strengthens the evidence for\nstrong baryon-dominance on galactic scales of massive $z\\sim1-3$ star-forming\ngalaxies recently found based on ionized gas kinematics alone.", "category": "astro-ph_GA" }, { "text": "The Next Generation Virgo cluster Survey (NGVS). XXVI. The issues of\n photometric age and metallicity estimates for globular clusters: Large samples of globular clusters (GC) with precise multi-wavelength\nphotometry are becoming increasingly available and can be used to constrain the\nformation history of galaxies. We present the results of an analysis of Milky\nWay (MW) and Virgo core GCs based on five optical-near-infrared colors and ten\nsynthetic stellar population models. For the MW GCs, the models tend to agree\non photometric ages and metallicities, with values similar to those obtained\nwith previous studies. When used with Virgo core GCs, for which photometry is\nprovided by the Next Generation Virgo cluster Survey (NGVS), the same models\ngenerically return younger ages. This is a consequence of the systematic\ndifferences observed between the locus occupied by Virgo core GCs and models in\npanchromatic color space. Only extreme fine-tuning of the adjustable parameters\navailable to us can make the majority of the best-fit ages old. Although we\ncannot exclude that the formation history of the Virgo core may lead to more\nconspicuous populations of relatively young GCs than in other environments, we\nemphasize that the intrinsic properties of the Virgo GCs are likely to differ\nsystematically from those assumed in the models. Thus, the large wavelength\ncoverage and photometric quality of modern GC samples, such as used here, is\nnot by itself sufficient to better constrain the GC formation histories. Models\nmatching the environment-dependent characteristics of GCs in multi-dimensional\ncolor space are needed to improve the situation.", "category": "astro-ph_GA" }, { "text": "Giant molecular clouds in M 33: are they susceptible to dynamical\n friction?: Most of giant molecular clouds (GMCs) in M 33 are connected with spiral-like\ngaseous arms (filaments) with the exception of the inner 2 kpc region where the\nlink between the arms and GMCs disappears (see Tosaki et al. 2011). We check\nwhether it may be caused by the dynamic friction retarding the clouds. Using\nsemi-analytical model for this galaxy we calculate the dynamics of GMCs of\ndifferent masses situated at different initial galactocentric distances in the\ndisk plane. We demonstrate that the dynamical friction may really change the\norbits of GMCs in the central 2 kpc-size region. However in this case the\ntypical lifetimes of GMCs should be close to or greater than $10^8$~yr, which\nis larger than the usually accepted values.", "category": "astro-ph_GA" }, { "text": "Chemistry of massive young stellar objects with a disk-like structure: Our goal is to take an inventory of complex molecules in three well-known\nhigh-mass protostars for which disks or toroids have been claimed and to study\nthe similarities and differences with a sample of massive YSOs without evidence\nof such flattened disk-like structures. With a disk-like geometry, UV radiation\ncan escape more readily and potentially affect the ice and gas chemistry on\nhot-core scales. A partial submillimeter line survey, targeting CH3OH, H2CO,\nC2H5OH, HCOOCH3, CH3OCH3, CH3CN, HNCO, NH2CHO, C2H5CN, CH2CO, HCOOH, CH3CHO,\nand CH3CCH, was made toward three massive YSOs with disk-like structures,\nIRAS20126+4104, IRAS18089-1732, and G31.41+0.31. Rotation temperatures and\ncolumn densities were determined by the rotation diagram method, as well as by\nindependent spectral modeling. The molecular abundances were compared with\nprevious observations of massive YSOs without evidence of any disk structure,\ntargeting the same molecules with the same settings and using the same analysis\nmethod. Consistent with previous studies, different complex organic species\nhave different characteristic rotation temperatures and can be classified\neither as warm (>100 K) or cold (<100 K). The excitation temperatures and\nabundance ratios are similar from source to source and no significant\ndifference can be established between the two source types. Acetone, CH3COCH3,\nis detected for the first time in G31.41+0.31 and IRAS18089-1732. Temperatures\nand abundances derived from the two analysis methods generally agree within\nfactors of a few. The lack of chemical differentiation between massive YSOs\nwith and without observed disks suggest either that the chemical complexity is\nalready fully established in the ices in the cold prestellar phase or that the\nmaterial experiences similar physi- cal conditions and UV exposure through\noutflow cavities during the short embedded lifetime.", "category": "astro-ph_GA" }, { "text": "Understanding the Structural Scaling Relations of Early-Type Galaxies: We use a large suite of hydrodynamical simulations of binary galaxy mergers\nto construct and calibrate a physical prescription for computing the effective\nradii and velocity dispersions of spheroids. We implement this prescription\nwithin a semi-analytic model embedded in merger trees extracted from the\nBolshoi Lambda-CDM N-body simulation, accounting for spheroid growth via major\nand minor mergers as well as disk instabilities. We find that without disk\ninstabilities, our model does not predict sufficient numbers of intermediate\nmass early-type galaxies in the local universe. Spheroids also form earlier in\nmodels with spheroid growth via disk instabilities. Our model correctly\npredicts the normalization, slope, and scatter of the low-redshift size-mass\nand Fundamental Plane relations for early type galaxies. It predicts a degree\nof curvature in the Faber-Jackson relation that is not seen in local\nobservations, but this could be alleviated if higher mass spheroids have more\nbottom-heavy initial mass functions. The model also correctly predicts the\nobserved strong evolution of the size-mass relation for spheroids out to higher\nredshifts, as well as the slower evolution in the normalization of the\nFaber-Jackson relation. We emphasize that these are genuine predictions of the\nmodel since it was tuned to match hydrodynamical simulations and not these\nobservations.", "category": "astro-ph_GA" }, { "text": "Discovery of two new hypervelocity stars from the LAMOST spectroscopic\n surveys: We report the discovery of two new unbound hypervelocity stars (HVSs) from\nthe LAMOST spectroscopic surveys. They are respectively a B2V type star of ~ 7\nM$_{\\rm \\odot}$ with a Galactic rest-frame radial velocity of 502 km/s at a\nGalactocentric radius of ~ 21 kpc and a B7V type star of ~ 4 M$_{\\rm \\odot}$\nwith a Galactic rest-frame radial velocity of 408 km/s at a Galactocentric\nradius of ~ 30 kpc. The origins of the two HVSs are not clear given their\ncurrently poorly measured proper motions. However, the future data releases of\nGaia should provide proper motion measurements accurate enough to solve this\nproblem. The ongoing LAMOST spectroscopic surveys are expected to yield more\nHVSs to form a statistical sample, providing vital constraint on understanding\nthe nature of HVSs and their ejection mechanisms.", "category": "astro-ph_GA" }, { "text": "Why Simple Stellar Population models do not reproduce the colours of\n Galactic open clusters: (...) We search for an explanation of the disagreement between the observed\nintegrated colours of 650 local Galactic clusters and the theoretical colours\nof present-day SSP models. We check the hypothesis that the systematic offsets\nbetween observed and theoretical colours, which are $(B$$-$$V)\\approx 0.3$ and\n$(J$$-$$K_s)\\approx 0.8$, are caused by neglecting the discrete nature of the\nunderlying mass function. Using Monte Carlo simulations, we construct\nartificial clusters of coeval stars taken from a mass distribution defined by\nan Salpeter initial mass function (IMF) and compare them with corresponding\n\"continuous-IMF\" SSP models. If the discreteness of the IMF is taken into\naccount, the model fits the observations perfectly and is able to explain\nnaturally a number of red \"outliers\" observed in the empirical colour-age\nrelation. We find that the \\textit{systematic} offset between the continuous-\nand discrete-IMF colours reaches its maximum of about 0.5 in $(B$$-$$V)$ for a\ncluster mass $M_c=10^2 m_\\odot$ at ages $\\log t\\approx 7$, and diminishes\nsubstantially but not completely to about one hundredth of a magnitude at $\\log\nt >7.9$ at cluster masses $M_c> 10^5 m_\\odot$. At younger ages, it is still\npresent even in massive clusters, and for $M_c \\leqslant 10^4 m_\\odot$ it is\nlarger than 0.1 mag in $(B$$-$$V)$. Only for very massive clusters ($M_c>10^6\nm_\\odot$) with ages $\\log t< 7.5$ is the offset small (of the order of 0.04\nmag) and smaller than the typical observational error of colours of\nextragalactic clusters.", "category": "astro-ph_GA" }, { "text": "The Initial Mass Function of the Orion Nebula Cluster across the\n H-burning limit: We present a new census of the Orion Nebula Cluster (ONC) over a large field\nof view (>30'x30'), significantly increasing the known population of stellar\nand substellar cluster members with precisely determined properties. We develop\nand exploit a technique to determine stellar effective temperatures from\noptical colors, nearly doubling the previously available number of objects with\neffective temperature determinations in this benchmark cluster. Our technique\nutilizes colors from deep photometry in the I-band and in two medium-band\nfilters at lambda~753 and 770nm, which accurately measure the depth of a\nmolecular feature present in the spectra of cool stars. From these colors we\ncan derive effective temperatures with a precision corresponding to better than\none-half spectral subtype, and importantly this precision is independent of the\nextinction to the individual stars. Also, because this technique utilizes only\nphotometry redward of 750nm, the results are only mildly sensitive to optical\nveiling produced by accretion. Completing our census with previously available\ndata, we place some 1750 sources in the Hertzsprung-Russel diagram and assign\nmasses and ages down to 0.02 solar masses. At faint luminosities, we detect a\nlarge population of background sources which is easily separated in our\nphotometry from the bona fide cluster members. The resulting initial mass\nfunction of the cluster has good completeness well into the substellar mass\nrange, and we find that it declines steeply with decreasing mass. This suggests\na deficiency of newly formed brown dwarfs in the cluster compared to the\nGalactic disk population.", "category": "astro-ph_GA" }, { "text": "Precision measurement of magnetic field from near to far, from fine to\n large scales in ISM: Magnetic fields have important or dominant effects in many areas of\nastrophysics, but have been very difficult to quantify. Spectropolarimetry from\nGround State Alignment (GSA) has been suggested as a direct tracer of magnetic\nfield in interstellar diffuse medium. Owing to the long life of the atoms on\nground states the Larmor precession in an external magnetic field imprints the\ndirection of the field onto the polarization of absorbing species. This\nprovides a unique tool for studies of sub-gauss magnetic fields using\npolarimetry of UV, optical and radio lines. Many spectral lines with strong\nsignals from GSA are in the UV band. By discerning magnetic fields in gas with\ndifferent dynamical properties, high spectral resolution measurement of\nspectral polarization will allow the study of 3D magnetic field distribution\nand interstellar turbulence. GSA provides also a unique chance to map 3D\ndirection of magnetic field on small scales, e.g., disks, where grain alignment\nis unreliable. The range of objects suitable for studies is extremely wide and\nincludes magnetic fields in the interplanetary medium, in the interstellar\nmedium, and in circumstellar regions as well as diffuse media in extragalactic\nobjects.", "category": "astro-ph_GA" }, { "text": "The Influence of Orbital Eccentricity on Tidal Radii of Star Clusters: We have performed N-body simulations of star clusters orbiting in a\nspherically symmetric smooth galactic potential. The model clusters cover a\nrange of initial half-mass radii and orbital eccentricities in order to test\nthe historical assumption that the tidal radius of a cluster is imposed at\nperigalacticon. The traditional assumption for globular clusters is that since\nthe internal relaxation time is larger than its orbital period, the cluster is\ntidally stripped at perigalacticon. Instead, our simulations show that a\ncluster with an eccentric orbit does not need to fully relax in order to\nexpand. After a perigalactic pass, a cluster re-captures previously unbound\nstars, and the tidal shock at perigalacticon has the effect of energizing inner\nregion stars to larger orbits. Therefore, instead of the limiting radius being\nimposed at perigalacticon, it more nearly traces the instantaneous tidal radius\nof the cluster at any point in the orbit. We present a numerical correction\nfactor to theoretical tidal radii calculated at perigalacticon which takes into\nconsideration both the orbital eccentricity and current orbital phase of the\ncluster.", "category": "astro-ph_GA" }, { "text": "Photon and neutrino emission from active galactic nuclei: Supermassive black holes in the centers of galaxies are very common. They are\nknown to rotate, accrete, spin down and eject highly relativistic jets; those\njets pointed at us all seem to show a spectrum with two strong bumps, one in\nthe TeV photon range, and one in X-rays - ordered by the emission frequency of\nthe first bump this constitutes the blazar sequence. Here we wish to explain\nthis sequence as the combined interaction of electrons and protons with the\nmagnetic field and radiation field at the first strong shockwave pattern in the\nrelativistic jet. With two key assumptions on particle scattering, this concept\npredicts that the two basic maximum peak frequencies scale with the mass of the\ncentral black hole as $M_{BH}^{-1/2}$, have a ratio of $(m_p/m_e)^{3}$, and the\nluminosities with the mass itself $M_{BH}$. Due to strong losses of the\nleptons, the peak luminosities are generally the same, but with large\nvariations around equality. This model predicts large fluxes in ultra high\nenergy cosmic rays, and also large neutrino luminosities.", "category": "astro-ph_GA" }, { "text": "Photometry and Kinematics of Self-Gravitating Eccentric Nuclear Disks: The Andromeda Galaxy hosts an elongated nucleus with (at least) two distinct\nbrightness peaks. The double nucleus can be explained by the projection of a\nthick, apsidally-aligned eccentric nuclear disk of stars in orbit about the\ncentral black hole. Several nearby early-type galaxies have similar asymmetric\nnuclear features, indicating the possible presence of eccentric nuclear disks.\nWe create simulated photometric (surface density) and kinematic (line-of-sight\nvelocity) maps of eccentric nuclear disks using N-body simulations. We image\nour simulations from various lines of sight in order to classify them as double\nnuclei, offset nuclei, and centered nuclei. We explore the effects of mass\nsegregation on the photometric maps, finding that heavier stars are\nconcentrated in the brighter peak. The average line-of-sight velocity values\nare lower in an eccentric nuclear disk than for a circular ring about the\nsupermassive black hole. The velocity dispersion values are higher and peak at\nthe position of the supermassive black hole, which does not typically match the\npeak in photometry.", "category": "astro-ph_GA" }, { "text": "Infrared Contributions of X-Ray Selected Active Galactic Nuclei in Dusty\n Star-Forming Galaxies: We investigate the infrared contribution from supermassive black hole\nactivity versus host galaxy emission in the mid to far-infrared (IR) spectrum\nfor a large sample of X-ray bright active galactic nuclei (AGN) residing in\ndusty, star-forming host galaxies. We select 703 AGN with L_X = 10^42-46 ergs/s\nat 0.1 < z < 5 from the Chandra XBootes X-ray Survey with rich multi-band\nobservations in the optical to far-IR. This is the largest sample to date of\nX-ray AGN with mid and far-IR detections that uses spectral energy distribution\n(SED) decomposition to determine intrinsic AGN and host galaxy infrared\nluminosities. We determine weak or nonexistent relationships when averaging\nstar-formation activity as a function of AGN activity, but see stronger\npositive trends when averaging L_X in bins of star-forming activity for AGN at\nlow redshifts. We estimate an average dust covering factor of 33% based on\ninfrared SEDs and bolometric AGN luminosity, corresponding to a Type 2 AGN\npopulation of roughly a third. We also see a population of AGN that challenge\nthe inclination based unification model with individual dust covering factors\nthat contradict the nuclear obscuration expected from observed X-ray hardness\nratios. We see no strong connection between AGN fractions in the IR and\ncorresponding total infrared, 24 um, or X-ray luminosities. The average\nrest-frame AGN contribution as a function of IR wavelength shows significant\n(~80%) contributions in the mid-IR that trail off at lambda > 30 um.\nAdditionally, we provide a relation between observed L_X and pure AGN IR output\nfor high-z AGN allowing future studies to estimate AGN infrared contribution\nusing only observed X-ray flux density estimates.", "category": "astro-ph_GA" }, { "text": "Photoemission of spin-polarized electrons from aligned grains and chiral\n symmetry breaking: The unique biosignature of life on Earth is the homochirality of organic\ncompounds such as amino acids, proteins, and sugars. The origin of this\nhomochirality has remained a mystery for over a century. While high-energy\nspin-polarized (spin-up or spin-down) electrons (SPEs) from the $\\beta$ decay\nof radioactive nuclei discovered by Lee and Yang (1956) and Wu et al. (1957)\nhave been proposed as a potential source of symmetry breaking, their exact role\non homochirality is much debated. Here we suggest magnetically aligned dust\ngrains as a new source of SPEs due to photoemission of electrons having aligned\nspins by the Barnett effect. For the interstellar UV radiation field of\nstrength $G_{\\rm UV}$, we found that the SPE emission rate is $\\Gamma_{\\rm\npe}^{\\rm SPE}\\sim 10^{-14}G_{\\rm UV}$ electrons per second per H, the fraction\nof spin-polarized to total photoelectrons is $\\sim 10\\%$, and the SPE yield\n(photoelectron number per UV photon) can reach $\\sim 1\\%$, using the modern\ntheory of grain alignment. Low-energy SPEs from aligned grains would cause\nchiral symmetry breaking of interstellar chiral molecules due to spin-selective\n(dipole-dipole) interactions. Finally, we suggest magnetically aligned grains\nas chiral agents that facilitate and enrich the chiral asymmetry of chiral\nmolecules. Our proposed mechanism might explain the detection of chiral\nasymmetry in the ISM, comets, and meteorites due to the ubiquitous UV radiation\nand magnetically aligned grains, paving the way for understanding the origin\nand distribution of life in the universe. This mechanism based on magnetic\ngrain alignment implies the role of magnetic fields on chirality symmetry\nbreaking.", "category": "astro-ph_GA" }, { "text": "Direct $N$-body simulations of globular clusters - II. Palomar 4: We use direct $N$-body calculations to study the evolution of the unusually\nextended outer halo globular cluster Palomar 4 (Pal~4) over its entire lifetime\nin order to reproduce its observed mass, half-light radius, velocity dispersion\nand mass function slope at different radii.\n We find that models evolving on circular orbits, and starting from a non-mass\nsegregated, canonical initial mass function (IMF) can reproduce neither Pal 4's\noverall mass function slope nor the observed amount of mass segregation.\nIncluding either primordial mass segregation or initially flattened IMFs does\nnot reproduce the observed amount of mass segregation and mass function\nflattening simultaneously. Unresolved binaries cannot reconcile this\ndiscrepancy either. We find that only models with both a flattened IMF and\nprimordial segregation are able to fit the observations. The initial (i.e.\nafter gas expulsion) mass and half-mass radius of Pal~4 in this case are about\n57000 M${\\odot}$ and 10 pc, respectively. This configuration is more extended\nthan most globular clusters we observe, showing that the conditions under which\nPal~4 formed must have been significantly different from that of the majority\nof globular clusters. We discuss possible scenarios for such an unusual\nconfiguration of Pal~4 in its early years.", "category": "astro-ph_GA" }, { "text": "Profiling filaments: comparing near-infrared extinction and\n submillimetre data in TMC-1: Interstellar filaments are an important part of star formation. To understand\nthe structure of filaments, cross-section profiles are often fitted with\nPlummer profiles. This profiling is often done with submm studies, such as\nHerschel. It would be convenient if filament properties could also be studied\nusing groundbased NIR data. We compare the filament profiles obtained by NIR\nextinction and submm observations to find out if reliable profiles can be\nderived using NIR data. We use J-, H-, and K-band data of a filament north of\nTMC-1 to derive an extinction map from colour excesses of background stars. We\ncompare the Plummer profiles obtained from extinction maps with Herschel dust\nemission maps. We present 2 methods to estimate profiles from NIR: Plummer\nprofile fits to median Av of stars or directly to the Av of individual stars.\nWe compare the methods by simulations. In simulations extinction maps and the\nnew methods give correct results to within ~10-20 for modest densities. Direct\nfit to data on individual stars gives more accurate results than extinction\nmap, and can work in higher density. In profile fits to real observations,\nvalues of Plummer parameters are generally similar to within a factor of ~2.\nAlthough parameter values can vary significantly, estimates of filament mass\nusually remain accurate to within some tens of per cent. Our results for TMC-1\nare in agreement with earlier results. High resolution NIR data give more\ndetails, but 2MASS data can be used to estimate profiles. NIR extinction can be\nused as an alternative to submm observations to profile filaments. Direct fits\nof stars can also be a valuable tool. Plummer profile parameters are not always\nwell constrained, and caution should be taken when making fits. In the\nevaluation of Plummer parameters, one can use the independence of dust emission\nand NIR data and the difference in the shapes of the confidence regions.", "category": "astro-ph_GA" }, { "text": "A photometric and astrometric study of the open clusters NGC 1664 and\n NGC 6939: This study calculated astrophysical parameters, as well as kinematic and\ngalactic orbital parameters, of the open clusters NGC 1664 and NGC 6939. The\nwork is based on CCD UBV and Gaia photometric and astrometric data from ground\nand space-based observations. Considering Gaia Early Data Release 3 (EDR3)\nastrometric data, we determined membership probabilities of stars located in\nboth of the clusters. We used two-color diagrams to determine $E(B-V)$ color\nexcesses for NGC 1664 and NGC 6939 as $0.190 \\pm 0.018$ and $0.380 \\pm 0.025$\nmag, respectively. Photometric metallicities for the two clusters were\nestimated as [Fe/H] = $-0.10 \\pm 0.02$ dex for NGC 1664 and as [Fe/H] = $-0.06\n\\pm 0.01$ dex for NGC 6939. Using the reddening and metallicity calculated in\nthe study, we obtained distance moduli and ages of the clusters by fitting\nPARSEC isochrones to the color-magnitude diagrams based on the most likely\nmember stars. Isochrone fitting distances are $1289 \\pm 47$ pc and $1716 \\pm\n87$ pc, which coincide with ages of $675 \\pm 50$ Myr and $1.5 \\pm 0.2$ Gyr for\nNGC 1664 and NGC 6939, respectively. We also derived the distances to the\nclusters using Gaia trigonometric parallaxes and compared these estimates with\nthe literature. We concluded that the results are in good agreement with those\ngiven by the current study. Present day mass function slopes were calculated as\n$\\Gamma=-1.22\\pm0.33$ and $\\Gamma=-1.18\\pm0.21$ for NGC 1664 and NGC 6939,\nrespectively, which are compatible with the Salpeter (1955) slope. Analyses\nshowed that both of clusters are dynamically relaxed. The kinematic and dynamic\norbital parameters of the clusters were calculated, indicating that the\nbirthplaces of the clusters are outside the solar circle.", "category": "astro-ph_GA" }, { "text": "COOL-LAMPS I. An Extraordinarily Bright Lensed Galaxy at Redshift 5.04: We report the discovery of COOL J1241+2219, a strongly-lensed galaxy at\nredshift $z$=5.043$\\pm$0.002 with observed magnitude $z_{AB}=20.47$, lensed by\na moderate-mass galaxy cluster at $z$=1.001$\\pm$0.001. COOL J1241+2219 is the\nbrightest lensed galaxy currently known at optical and near-infrared\nwavelengths at $z$ $\\gtrsim$ 5; it is $\\sim$5 times brighter than the prior\nrecord-holder lensed galaxy, and several magnitudes brighter than the brightest\nunlensed galaxies known at these redshifts. It was discovered as part of\nCOOL-LAMPS, a collaboration initiated to find strongly lensed systems in recent\npublic optical imaging data. We characterise the lensed galaxy, as well as the\ncentral galaxy of the lensing cluster using ground-based $griz$JH imaging and\noptical spectroscopy. We report model-based magnitudes, and derive stellar\nmasses, dust content, metallicity and star-formation rates via\nstellar-population synthesis modeling. Our lens mass modeling, based on\nground-based imaging, implies a median source magnification of $\\sim$30, which\nputs the stellar mass and star formation rate (in the youngest age bin, closest\nto the epoch of observation) at logM$_{*}$ = $10.11^{+0.21}_{-0.26}$ and SFR =\n$27^{+13}_{-9}$ M$_{\\odot}$/yr, respectively. We constrain a star formation\nhistory for COOL J1241+2219 consistent with constant star formation across\n$\\sim$1 Gyr of cosmic time, and that places this galaxy on the high-mass end of\nthe star-forming main sequence. COOL J1241+2219 is 2-4 times more luminous than\na galaxy with the characteristic UV luminosity at these redshifts. The UV\ncontinuum slope $\\beta$= -2.2$\\pm$0.2 places this galaxy on the blue side of\nthe observed distribution of galaxies at $z$=5, although the lack of Ly$\\alpha$\nemission indicates dust sufficient to suppress this emission.", "category": "astro-ph_GA" }, { "text": "Alignment of dense molecular core morphology and velocity gradients with\n ambient magnetic fields: Studies of dense core morphologies and their orientations with respect to gas\nflows and the local magnetic field have been limited to only a small sample of\ncores with spectroscopic data. Leveraging the Green Bank Ammonia Survey\nalongside existing sub-millimeter continuum observations and Planck dust\npolarization, we produce a cross-matched catalogue of 399 dense cores with\nestimates of core morphology, size, mass, specific angular momentum, and\nmagnetic field orientation. Of the 399 cores, 329 exhibit 2D\n$\\mathrm{v}_\\mathrm{LSR}$ maps that are well fit with a linear gradient,\nconsistent with rotation projected on the sky. We find a best-fit specific\nangular momentum and core size relationship of $J/M \\propto R^{1.82 \\pm 0.10}$,\nsuggesting that core velocity gradients originate from a combination of solid\nbody rotation and turbulent motions. Most cores have no preferred orientation\nbetween the axis of core elongation, velocity gradient direction, and the\nambient magnetic field orientation, favouring a triaxial and weakly magnetized\norigin. We find, however, strong evidence for a preferred anti-alignment\nbetween the core elongation axis and magnetic field for protostellar cores,\nrevealing a change in orientation from starless and prestellar populations that\nmay result from gravitational contraction in a magnetically-regulated (but not\ndominant) environment. We also find marginal evidence for anti-alignment\nbetween the core velocity gradient and magnetic field orientation in the L1228\nand L1251 regions of Cepheus, suggesting a preferred orientation with respect\nto magnetic fields may be more prevalent in regions with locally ordered\nfields.", "category": "astro-ph_GA" }, { "text": "Variability-selected Active Galactic Nuclei in the VST-SUDARE/VOICE\n Survey of the COSMOS Field: Optical variability has proven to be an effective way of detecting AGNs in\nimaging surveys, lasting from weeks to years. In the present work we test its\nuse as a tool to identify AGNs in the VST multi-epoch survey of the COSMOS\nfield, originally tailored to detect supernova events. We make use of the\nmulti-wavelength data provided by other COSMOS surveys to discuss the\nreliability of the method and the nature of our AGN candidates. Our selection\nreturns a sample of 83 AGN candidates; based on a number of diagnostics, we\nconclude that 67 of them are confirmed AGNs (81% purity), 12 are classified as\nsupernovae, while the nature of the remaining 4 is unknown. For the subsample\nof AGNs with some spectroscopic classification, we find that Type 1 are\nprevalent (89%) compared to Type 2 AGNs (11%). Overall, our approach is able to\nretrieve on average 15% of all AGNs in the field identified by means of\nspectroscopic or X-ray classification, with a strong dependence on the source\napparent magnitude. In particular, the completeness for Type 1 AGNs is 25%,\nwhile it drops to 6% for Type 2 AGNs. The rest of the X-ray selected AGN\npopulation presents on average a larger r.m.s. variability than the bulk of non\nvariable sources, indicating that variability detection for at least some of\nthese objects is prevented only by the photometric accuracy of the data. We\nshow how a longer observing baseline would return a larger sample of AGN\ncandidates. Our results allow us to assess the usefulness of this AGN selection\ntechnique in view of future wide-field surveys.", "category": "astro-ph_GA" }, { "text": "Gaseous Spiral Structure and Mass Drift in Spiral Galaxies: We use hydrodynamic simulations to investigate nonlinear gas responses to an\nimposed stellar spiral potential in disk galaxies. The gaseous medium is\nassumed to be infinitesimally thin, isothermal, and unmagnetized. We consider\nvarious spiral-arm models with differing strength and pattern speed. We find\nthat the extent and shapes of gaseous arms as well as the related mass drift\nrate depend rather sensitively on the arm pattern speed. In models where the\narm pattern is rotating slow, the gaseous arms extend across the corotation\nresonance (CR) all the way to the outer boundary, with a pitch angle slightly\nsmaller than that of the stellar counterpart. In models with a fast rotating\npattern, on the other hand, spiral shocks are much more tightly wound than the\nstellar arms, and cease to exist in the regions near and outside the CR where\n$\\mathcal{M}_\\perp/{\\rm sin} p_* \\ge 25-40$, with $\\mathcal{M}_\\perp$ denoting\nthe perpendicular Mach number of a rotating gas relative to the arms with pitch\nangle $p_*$. Inside the CR, the arms drive mass inflows at a rate of $\\sim\n0.05-3.0 {\\rm M}_\\odot {\\rm yr}^{-1}$ to the central region, with larger values\ncorresponding to stronger and slower arms. The contribution of the shock\ndissipation, external torque, and self-gravitational torque to the mass inflow\nis roughly 50%, 40%, and 10%, respectively. We demonstrate that the\ndistributions of line-of-sight velocities and spiral-arm densities can be a\nuseful diagnostic tool to distinguish if the spiral pattern is rotating fast or\nslow.", "category": "astro-ph_GA" }, { "text": "Following the Cosmic Evolution of Pristine Gas II: The search for Pop\n III-Bright Galaxies: Direct observational searches for Population III (Pop III) stars at high\nredshift are faced with the question of how to select the most promising\ntargets for spectroscopic follow-up. To help answer this, we use a large-scale\ncosmological simulation, augmented with a new subgrid model that tracks the\nfraction of pristine gas, to follow the evolution of high-redshift galaxies and\nthe Pop III stars they contain. We generate rest-frame ultraviolet (UV)\nluminosity functions for our galaxies and find that they are consistent with\ncurrent $z \\ge 7 $ observations. Throughout the redshift range $7 \\le z \\le 15$\nwe identify \"Pop III-bright\" galaxies as those with at least 75% of their flux\ncoming from Pop III stars. While less than 1% of galaxies brighter than $m_{\\rm\nUV, AB} = 31.4$ mag are Pop III--bright in the range $7\\leq z \\leq8$, roughly\n17% of such galaxies are Pop III--bright at $z=9$, immediately before\nreionization occurs in our simulation. Moving to $z=10$, $m_{\\rm UV, AB} =\n31.4$ mag corresponds to larger, more luminous galaxies and the Pop III-bright\nfraction falls off to 5%. Finally, at the highest redshifts, a large fraction\n(29% at $z=14$ and 41% at $z=15)$ of all galaxies are Pop III-bright regardless\nof magnitude. While $m_{\\rm UV, AB} = 31.4$ mag galaxies are extremely rare\nduring this epoch, we find that 13% of galaxies at $z = 14$ are Pop III-bright\nwith $m_{\\rm UV, AB} \\le 33$ mag, an intrisic magnitude within reach of the\nJames Webb Space Telescope using lensing. Thus, we predict that the best\nredshift to search for luminous Pop III--bright galaxies is just before\nreionization, while lensing surveys for fainter galaxies should push to the\nhighest redshifts possible.", "category": "astro-ph_GA" }, { "text": "High-precision astrometry with VVV -- II. A near-infrared extension of\n Gaia into the Galactic plane: Aims. We use near-infrared, ground-based data from the VISTA Variables in the\nVia Lactea (VVV) survey to indirectly extend the astrometry provided by the\nGaia catalog to objects in heavily-extincted regions towards the Galactic bulge\nand plane that are beyond Gaia's reach. Methods. We make use of the\nstate-of-the-art techniques developed for high-precision astrometry and\nphotometry with the Hubble Space Telescope to process the VVV data. We employ\nempirical, spatially-variable, effective point-spread functions and local\ntransformations to mitigate the effects of systematic errors, like residual\ngeometric distortion and image motion, and to improve measurements in crowded\nfields and for faint stars. We also anchor our astrometry to the absolute\nreference frame of the Gaia Data Release 3. Results. We measure between 20 and\n60 times more sources than Gaia in the region surrounding the Galactic center,\nobtaining an single-exposure precision of about 12 mas and a proper-motion\nprecision of better than 1 mas yr$^{-1}$ for bright, unsaturated sources. Our\nastrometry provides an extension of Gaia into the Galactic center. We publicly\nrelease the astro-photometric catalogs of the two VVV fields considered in this\nwork, which contain a total of $\\sim$ 3.5 million sources. Our catalogs cover\n$\\sim$ 3 sq. degrees, about 0.5% of the entire VVV survey area.", "category": "astro-ph_GA" }, { "text": "What Makes Quadruply Lensed Quasars Quadruple?: Among known strongly lensed quasar systems, ~25% have gravitational\npotentials sufficiently flat (and sources sufficiently well aligned) to produce\nfour images rather than two. The projected flattening of the lensing galaxy and\ntides from neighboring galaxies both contribute to the potential's quadrupole.\nWitt's hyperbola and Wynne's ellipse permit determination of the overall\nquadrupole from the positions of the quasar images. The position of the lensing\ngalaxy resolves the distinct contributions of intrinsic ellipticity and tidal\nshear to that quadrupole. Among 31 quadruply lensed quasars systems with\nstatistically significant decompositions, 15 are either reliably ($2\\sigma$) or\nprovisionally ($1\\sigma$) shear-dominated and 11 are either reliably or\nprovisionally ellipticity-dominated. For the remaining 8, the two effects make\nroughly equal contributions to the combined cross section (newly derived here)\nfor quadruple lensing. This observational result is strongly at variance with\nthe ellipticity-dominated forecast of Oguri & Marshall (2010).", "category": "astro-ph_GA" }, { "text": "Formation and Evolution of the Disk System of the Milky Way: [alpha/Fe]\n Ratios and Kinematics of the SEGUE G-Dwarf Sample: We employ measurements of the [alpha/Fe] ratio derived from low-resolution\n(R~2000) spectra of 17,277 G-type dwarfs from the SEGUE survey to separate them\ninto likely thin- and thick-disk subsamples. Both subsamples exhibit strong\ngradients of orbital rotational velocity with metallicity, of opposite signs,\n-20 to -30 km/s/dex for the thin-disk and +40 to +50 km/s/dex for the\nthick-disk population. The rotational velocity is uncorrelated with\nGalactocentric distance for the thin-disk subsample, and exhibits a small trend\nfor the thick-disk subsample. The rotational velocity decreases with distance\nfrom the plane for both disk components, with similar slopes (-9.0 {\\pm} 1.0\nkm/s/kpc). Thick-disk stars exhibit a strong trend of orbital eccentricity with\nmetallicity (about -0.2/dex), while the eccentricity does not change with\nmetallicity for the thin-disk subsample. The eccentricity is almost independent\nof Galactocentric radius for the thin-disk population, while a marginal\ngradient of the eccentricity with radius exists for the thick-disk population.\nBoth subsamples possess similar positive gradients of eccentricity with\ndistance from the Galactic plane. The shapes of the eccentricity distributions\nfor the thin- and thick-disk populations are independent of distance from the\nplane, and include no significant numbers of stars with eccentricity above 0.6.\nAmong several contemporary models of disk evolution we consider, radial\nmigration appears to have played an important role in the evolution of the\nthin-disk population, but possibly less so for the thick disk, relative to the\ngas-rich merger or disk heating scenarios. We emphasize that more physically\nrealistic models and simulations need to be constructed in order to carry out\nthe detailed quantitative comparisons that our new data enable.", "category": "astro-ph_GA" }, { "text": "HSCO$^+$ and DSCO$^+$: a multi-technique approach in the laboratory for\n the spectroscopy of interstellar ions: Protonated molecular species have been proven to be abundant in the\ninterstellar gas. This class of molecules is also pivotal for the determination\nof important physical parameters for the ISM evolution (e.g. gas ionisation\nfraction) or as tracers of non-polar, hence not directly observable, species.\nThe identification of these molecular species through radioastronomical\nobservations is directly linked to a precise laboratory spectral\ncharacterisation. The goal of the present work is to extend the laboratory\nmeasurements of the pure rotational spectrum of the ground electronic state of\nprotonated carbonyl sulfide (HSCO$^+$) and its deuterium substituted isotopomer\n(DSCO$^+$). At the same time, we show how implementing different laboratory\ntechniques allows the determination of different spectroscopical properties of\nasymmetric-top protonated species. Three different high-resolution experiments\nwere involved to detected for the first time the $b-$type rotational spectrum\nof HSCO$^+$, and to extend, well into the sub-millimeter region, the $a-$type\nspectrum of the same molecular species and DSCO$^+$. The electronic\nground-state of both ions have been investigated in the 273-405 GHz frequency\nrange, allowing the detection of 60 and 50 new rotational transitions for\nHSCO$^+$ and DSCO$^+$, respectively. The combination of our new measurements\nwith the three rotational transitions previously observed in the microwave\nregion permits the rest frequencies of the astronomically most relevant\ntransitions to be predicted to better than 100 kHz for both HSCO$^+$ and\nDSCO$^+$ up to 500 GHz, equivalent to better than 60 m/s in terms of equivalent\nradial velocity. The present work illustrates the importance of using different\nlaboratory techniques to spectroscopically characterise a protonated species at\nhigh frequency, and how a similar approach can be adopted when dealing with\nreactive species.", "category": "astro-ph_GA" }, { "text": "Photoinduced polycyclic aromatic hydrocarbon dehydrogenation: The\n competition between H- and H2-loss: PAHs constitute a major component of the interstellar medium carbon budget,\nlocking up to 10--20% of the elemental carbon. Sequential fragmentation induced\nby energetic photons leads to the formation of new species, including\nfullerenes. However, the exact chemical routes involved in this process remain\nlargely unexplored. In this work, we focus on the first photofragmentation\nsteps, which involve the dehydrogenation of these molecules. For this, we\nconsider a multidisciplinary approach, taking into account the results from\nexperiments, DFT calculations, and modeling using dedicated Monte-Carlo\nsimulations. By considering the simplest isomerization pathways --- i.e.,\nhydrogen roaming along the edges of the molecule --- we are able to\ncharacterize the most likely photodissociation pathways for the molecules\nstudied here. These comprise nine PAHs with clearly different structural\nproperties. The formation of aliphatic-like side groups is found to be critical\nin the first fragmentation step and, furthermore, sets the balance of the\ncompetition between H- and H2-loss. We show that the presence of trio\nhydrogens, especially in combination with bay regions in small PAHs plays an\nimportant part in the experimentally established variations in the odd-to-even\nH-atom loss ratios. In addition, we find that, as PAH size increases, H2\nformation becomes dominant, and sequential hydrogen loss only plays a marginal\nrole. We also find disagreements between experiments and calculations for\nlarge, solo containing PAHs, which need to be accounted for. In order to match\ntheoretical and experimental results, we have modified the energy barriers and\nrestricted the H-hopping to tertiary atoms. The formation of H2 in large PAHs\nupon irradiation appears to be the dominant fragmentation channel, suggesting\nan efficient formation path for molecular hydrogen in PDRs.", "category": "astro-ph_GA" }, { "text": "The local standard of rest and the well in the velocity distribution: It is now recognised that the traditional method of calculating the LSR\nfails. We find an improved estimate of the LSR by making use of the larger and\nmore accurate database provided by XHIP and repeating our preferred analysis\nfrom Francis & Anderson (2009a). We confirm an unexpected high value of $U_0$\nby calculating the mean for stars with orbits sufficiently inclined to the\nGalactic plane that they do not participate in bulk streaming motions. Our best\nestimate of the solar motion with respect to the LSR $(U_0, V_0, W_0) = (14.1\n\\pm 1.1, 14.6 \\pm 0.4, 6.9 \\pm 0.1)$ km\\ s$^{-1}$.", "category": "astro-ph_GA" }, { "text": "Environmental Quenching of Low Surface Brightness Galaxies near Milky\n Way mass Hosts: Low Surface Brightness Galaxies (LSBGs) are excellent probes of quenching and\nother environmental processes near massive galaxies. We study an extensive\nsample of LSBGs near massive hosts in the local universe that are distributed\nacross a diverse range of environments. The LSBGs with surface-brightness\n$\\mu_{\\rm eff,g}> $24.2 mag arcsec$^{-2}$ are drawn from the Dark Energy Survey\nYear 3 catalog while the hosts with masses $9.0< log(M_{\\star}/M_{\\odot})<\n11.0$ comparable to the Milky Way and the Large Magellanic Cloud are selected\nfrom the z0MGS sample. We study the projected radial density profiles of LSBGs\nas a function of their color and surface brightness around hosts in both the\nrich Fornax-Eridanus cluster environment and the low-density field. We detect\nan overdensity with respect to the background density, out to 2.5 times the\nvirial radius for both hosts in the cluster environment and the isolated field\ngalaxies. When the LSBG sample is split by $g-i$ color or surface brightness\n$\\mu_{\\rm eff,g}$, we find the LSBGs closer to their hosts are significantly\nredder and brighter, like their high surface-brightness counterparts. The LSBGs\nform a clear 'red sequence' in both the cluster and isolated environments that\nis visible beyond the virial radius of the hosts. This suggests a\npre-processing of infalling LSBGs and a quenched backsplash population around\nboth host samples. However, the relative prominence of the 'blue cloud' feature\nimplies that pre-processing is ongoing near the isolated hosts compared to the\ncluster hosts.", "category": "astro-ph_GA" }, { "text": "Hot gas in massive halos drives both mass quenching and environment\n quenching: Observations indicate that galaxies with high stellar masses or in dense\nenvironments have low specific star formation rates, i.e. they are quenched.\nBased on cosmological hydrodynamic simulations that include a prescription\nwhere quenching occurs in regions dominated by hot (>10^5 K) gas, we argue that\nthis hot gas quenching in halos >10^12 Msun drives both mass quenching (i.e.\ncentral quenching) and environment quenching (i.e. satellite quenching). These\nsimulations reproduce a broad range of locally observed trends among quenching,\nhalo mass, stellar mass, environment, and distance to halo center. We show that\nmass quenching is independent of environment because 10^12-10^13 Msun\n\"quenching halos\" -- those where most mass quenching occurs -- inhabit a large\nrange of environments. On the other hand, environment quenching is independent\nof stellar mass because galaxies of all stellar masses may live in dense\nenvironments as satellites of groups and clusters. Furthermore, satellite\ngalaxies show signs of mass quenching independent of halo mass because massive\nsatellites at z=0 have typically been mass quenched as centrals in their own\nhot halos at higher z -- a kind of pre-processing. As in observations, the\nfraction of quenched satellites increases with halo mass and decreases with\ndistance to the center of the group or cluster. We investigate quenched\ncentrals in low-mass halos (<10^12 Msun), and show that most of these are\nejected former satellites of groups or clusters, while about 20 per cent were\nnever satellites but are enveloped in hot gas that extends up to 3 Rvir from\nthe centers of clusters. The agreement of our model with key observational\ntrends suggests that hot gas in massive halos plays a leading role in quenching\nlow-redshift galaxies.", "category": "astro-ph_GA" }, { "text": "OH 18 cm Transition as a Thermometer for Molecular Clouds: We have observed the four hyperfine components of the 18 cm OH transition\ntoward the translucent cloud eastward of Heiles Cloud 2 (HCL2E), the cold dark\ncloud L134N, and the photodissociation region of the $\\rho$-Ophiuchi molecular\ncloud with the Effelsberg 100 m telescope. We have found intensity anomalies\namongst the hyperfine components in all three regions. In particular, an\nabsorption feature of the 1612 MHz satellite line against the cosmic microwave\nbackground has been detected toward HCL2E and two positions of the\n$\\rho$-Ophiuchi molecular cloud. On the basis of statistical equilibrium\ncalculations, we find that the hyperfine anomalies originate from the non-LTE\npopulation of the hyperfine levels, and can be used to determine the kinetic\ntemperature of the gas over a wide range of H$_2$ density (10$^2$ - 10$^7$\ncm$^{-3}$). Toward the center of HCL2E, the gas kinetic temperature is\ndetermined to be 53$\\pm$1 K, and it increases toward the cloud peripheries\n($\\sim$ 60 K). The ortho-to-para ratio of H$_2$ is determined to be 3.5 $\\pm$\n0.9 from the averaged spectrum for the 8 positions. In L134N, a similar\nincrease of the temperature is also seen toward the periphery. In the\n$\\rho$-Ophiuchi molecular cloud, the gas kinetic temperature decreases as a\nfunction of the distance from the exciting star HD147889. These results\ndemonstrate a new aspect of the OH 18 cm line as a good thermometer of\nmolecular cloud envelopes. The OH 18 cm line can be used to trace a new class\nof warm molecular gas surrounding a molecular cloud, which is not well traced\nby emission of CO and its isotopologues.", "category": "astro-ph_GA" }, { "text": "A New Concept of Transonic Galactic Outflows in a Cold Dark Matter Halo\n with a Central Super-Massive Black Hole: We study fundamental properties of isothermal, steady and spherically\nsymmetric galactic outflow in the gravitational potential of a cold dark matter\nhalo and a central super-massive black hole. We find that there are two\ntransonic solutions having different properties: each solution is mainly\nproduced by the dark matter halo and the super-massive black hole,\nrespectively. Furthermore, we apply our model to the Sombrero galaxy. In this\ngalaxy, Chandra X-ray observatory detected the diffuse hot gas as the trace of\ngalactic outflows while the star-formation rate is low and the observed gas\ndensity distribution presumably indicates the hydrostatic equilibrium. To solve\nthis discrepancy, we propose a solution that this galaxy has a transonic\noutflow, however, the transonic point forms in a very distant region from the\ngalactic center (?$\\sim$ 127 kpc). In this slowly accelerated transonic\noutflow, the outflow velocity is less than the sound velocity for most of the\ngalactic halo. Since the gas density distribution in this subsonic region is\nsimilar to the hydrostatic one, it is difficult to distinguish the wide\nsubsonic region from hydrostatic state. Such galactic outflows are dfferent\nfrom the conventional supersonic outflows observed in star-forming galaxies.", "category": "astro-ph_GA" }, { "text": "LBT/MODS spectroscopy of globular clusters in the irregular galaxy NGC\n 4449: We present intermediate-resolution (R$\\sim$1000) spectra in the\n$\\sim$3500-10,000 A range of 14 globular clusters in the magellanic irregular\ngalaxy NGC 4449 acquired with the Multi Object Double Spectrograph on the Large\nBinocular Telescope. We derived Lick indices in the optical and the\nCaII-triplet index in the near-infrared in order to infer the clusters' stellar\npopulation properties. The inferred cluster ages are typically older than\n$\\sim$9 Gyr, although ages are derived with large uncertainties. The clusters\nexhibit intermediate metallicities, in the range\n$-1.2\\lesssim$[Fe/H]$\\lesssim-0.7$, and typically sub-solar [$\\alpha/Fe$]\nratios, with a peak at $\\sim-0.4$. These properties suggest that i) during the\nfirst few Gyrs NGC 4449 formed stars slowly and inefficiently, with galactic\nwinds having possibly contributed to the expulsion of the $\\alpha$-elements,\nand ii) globular clusters in NGC 4449 formed relatively \"late\", from a medium\nalready enriched in the products of type Ia supernovae. The majority of\nclusters appear also under-abundant in CN compared to Milky Way halo globular\nclusters, perhaps because of the lack of a conspicuous N-enriched,\nsecond-generation of stars like that observed in Galactic globular clusters.\nUsing the cluster velocities, we infer the dynamical mass of NGC 4449 inside\n2.88 kpc to be M($<$2.88 kpc)=$3.15^{+3.16}_{-0.75} \\times 10^9~M_\\odot$. We\nalso report the serendipitous discovery of a planetary nebula within one of the\ntargeted clusters, a rather rare event.", "category": "astro-ph_GA" }, { "text": "Stellar Over-densities in the Outer Halo of the Milky Way: This study presents a tomographic survey of a subset of the outer halo (10-40\nkpc) drawn from the Sloan Digital Sky Survey Data Release 6. Halo substructure\non spatial scales of $>3$ degrees is revealed as an excess in the local density\nof sub-giant stars. With an appropriate assumption of a model stellar isochrone\nit is possible for us to then derive distances to the sub-giant population. We\ndescribe three new candidate halo substructures; the 160- and 180-degree\nover-densities (at distances of 17 and 19 kpc respectively and radii of 1.3 and\n1.5 kpc respectively) and an extended feature at 28 kpc that covers at least\n162 square degrees, the Virgo Equatorial Stream. In addition, we recover the\nSagittarius dwarf galaxy (Sgr) leading arm material and the Virgo Over-density.\n The derived distances, together with the number of sub-giant stars associated\nwith each substructure, enables us to derive the integrated luminosity for the\nfeatures. The tenuous, low surface brightness of the features strongly suggests\nan origin from the tidal disruption of an accreted galaxy or galaxies. Given\nthe dominance of the tidal debris of Sgr in this region of the sky we\ninvestigate if our observations can be accommodated by tidal disruption models\nfor Sgr. The clear discordance between observations and model predictions for\nknown Sgr features means it is difficult to tell unambiguously if the new\nsubstructures are related to Sgr or not. Radial velocities in the stellar\nover-densities will be critical in establishing their origins.", "category": "astro-ph_GA" }, { "text": "An HI study of NGC 3521 - a galaxy with a slow-rotating halo: A study is presented of HI line observations of the nearby spiral galaxy NGC\n3521 observed with the VLA as part of The HI Nearby Galaxy Survey. Clearly\nevident in the HI data cube is the presence of an anomalous HI component that\nis both diffuse and slow-rotating. The data cube is dynamically decomposed into\nregular and anomalous HI components. A mass of M_HI=1.5 x 10^9 Msun is\nestimated for the anomalous HI - 20 per cent of the total HI mass. Standard HI\ndata products and rotation curves are produced for each dynamical component. In\nterms of circular rotation speed, the anomalous HI is found to lag the regular\nHI by ~25 - 125 km/s. Three-dimensional models are generated and used to\ndetermine the possible location of the anomalous HI. The results strongly\nsuggest it to be distributed in a thick disc with a scale-height of a few kpc\n(~3.5 kpc). It is concluded that the anomalous HI in NGC 3521 constitutes a\nslow-rotating halo gas component, consistent with similar findings for other\nnearby galaxies. A study of the radial distribution of the anomalous HI shows\nit to be spatially coincident with the inner regions of the stellar disc where\nthe star formation rate is highest. It is most likely a galactic fountain that\nhas deposited gas from the disc of the galaxy into the halo.", "category": "astro-ph_GA" }, { "text": "SiO maser emission from red supergiants across the Galaxy: I. Targets in\n massive star clusters: Aims. Red supergiants (RSGs) are among the most luminous of all stars, easily\ndetectable in external galaxies, and may ideally serve as kinematic tracers of\nGalactic structure. Some RSGs are surrounded by circumstellar envelopes\ndetectable by their dust and molecular and, in particular, maser emission. This\nstudy consists of a search for maser emission from silicon monoxide (SiO)\ntoward a significant number of RSGs that are members of massive stellar\nclusters, many of which have only recently been discovered. Further, we aim to\nrelate the occurrence of maser action to properties of the host stars.\n Methods. Using the IRAM 30 meter telescope, we searched for maser emission in\nthe J = 2 - 1 rotational transition within the first vibrationally excited\nstate of SiO toward a sample of 88 RSGs.\n Results. With an average rms noise level of 0.25 Jy, we detected maser\nemission in 15% of the sample, toward most of the sources for the first time in\nthis transition. The peak of the emission provides accurate radial velocities\nfor the RSGs. The dependence of the detection rate on infrared colors supports\na radiative pumping mechanism for the SiO masers.", "category": "astro-ph_GA" }, { "text": "Constraints on the Shape of the Milky Way Dark Matter Halo from Jeans\n Equations Applied to SDSS Data: We search for evidence of dark matter in the Milky Way by utilizing the\nstellar number density distribution and kinematics measured by the Sloan\nDigital Sky Survey (SDSS) to heliocentric distances exceeding ~10 kpc. We\nemploy the cylindrically symmetric form of Jeans equations and focus on the\nmorphology of the resulting acceleration maps, rather than the normalization of\nthe total mass as done in previous, mostly local, studies. Jeans equations are\nfirst applied to a mock catalog based on a cosmologically derived N-body + SPH\nsimulation, and the known acceleration (gradient of gravitational potential) is\nsuccessfully recovered. The same simulation is also used to quantify the impact\nof dark matter on the total acceleration. We use Galfast, a code designed to\nquantitatively reproduce SDSS measurements and selection effects, to generate a\nsynthetic stellar catalog. We apply Jeans equations to this catalog and produce\ntwo-dimensional maps of stellar acceleration. These maps reveal that in a\nNewtonian framework, the implied gravitational potential cannot be explained by\nvisible matter alone. The acceleration experienced by stars at galactocentric\ndistances of ~20 kpc is three times larger than what can be explained by purely\nvisible matter. The application of an analytic method for estimating the dark\nmatter halo axis ratio to SDSS data implies an oblate halo with q_DM = 0.47 +/-\n0.14 within the same distance range. These techniques can be used to map the\ndark matter halo to much larger distances from the Galactic center using\nupcoming deep optical surveys, such as LSST.", "category": "astro-ph_GA" }, { "text": "One hundred SMUDGes in S-PLUS: ultra-diffuse galaxies flourish in the\n field: We present the first systematic study of the stellar populations of\nultra-diffuse galaxies (UDGs) in the field, integrating the large area search\nand characterization of UDGs by the SMUDGes survey with the twelve-band optical\nphotometry of the S-PLUS survey. Based on Bayesian modeling of the optical\ncolors of UDGs, we determine the ages, metallicities and stellar masses of 100\nUDGs distributed in an area of $\\sim 330$ deg$^2$ in the Stripe 82 region. We\nfind that the stellar masses and metallicities of field UDGs are similar to\nthose observed in clusters and follow the trends previously defined in studies\nof dwarf and giant galaxies. However, field UDGs have younger\nluminosity-weighted ages than do UDGs in clusters. We interpret this result to\nmean that field UDGs have more extended star formation histories, including\nsome that continue to form stars at low levels to the present time. Finally, we\nexamine stellar population scaling relations that show that UDGs are, as a\npopulation, similar to other low-surface brightness galaxies.", "category": "astro-ph_GA" }, { "text": "Distances to PHANGS Galaxies: New Tip of the Red Giant Branch\n Measurements and Adopted Distances: PHANGS-HST is an ultraviolet-optical imaging survey of 38 spiral galaxies\nwithin ~20 Mpc. Combined with the PHANGS-ALMA, PHANGS-MUSE surveys and other\nmultiwavelength data, the dataset will provide an unprecedented look into the\nconnections between young stars, HII regions, and cold molecular gas in these\nnearby star-forming galaxies. Accurate distances are needed to transform\nmeasured observables into physical parameters (e.g., brightness to luminosity,\nangular to physical sizes of molecular clouds, star clusters and associations).\nPHANGS-HST has obtained parallel ACS imaging of the galaxy halos in the F606W\nand F814W bands. Where possible, we use these parallel fields to derive tip of\nthe red giant branch (TRGB) distances to these galaxies. In this paper, we\npresent TRGB distances for 11 galaxies from ~4 to ~15 Mpc, based on the first\nyear of PHANGS-HST observations. Five of these represent the first published\nTRGB distance measurements (IC 5332, NGC 2835, NGC 4298, NGC 4321, and NGC\n4328), and eight of which are the best available distances to these targets. We\nalso provide a compilation of distances for the 118 galaxies in the full PHANGS\nsample, which have been adopted for the first PHANGS-ALMA public data release.", "category": "astro-ph_GA" }, { "text": "Nebular spectroscopy: A guide on H II regions and planetary nebulae: We present a tutorial on the determination of the physical conditions and\nchemical abundances in gaseous nebulae. We also include a brief review of\nrecent results on the study of gaseous nebulae, their relevance for the study\nof stellar evolution, galactic chemical evolution, and the evolution of the\nuniverse. One of the most important problems in abundance determinations is the\nexistence of a discrepancy between the abundances determined with collisionally\nexcited lines and those determined by recombination lines, this is called the\nADF (abundance discrepancy factor) problem; we review results related to this\nproblem. Finally, we discuss possible reasons for the large t$^2$ values\nobserved in gaseous nebulae.", "category": "astro-ph_GA" }, { "text": "The oldest stars of the bulge: new information on the ancient Galaxy: Recently the search for the oldest stars have started to focus on the Bulge\nregion. The Galactic bulge hosts extremely old stars, with ages compatible with\nthe ages of the oldest halo stars. The data coming from these recent\nobservations present new chemical signatures and therefore provide\ncomplementary constraints to those already found in the halo. So, the study of\nthe oldest bulge stars can improve dramatically the constraints on the nature\nof first stars and how they polluted the pristine ISM of our Galaxy. We present\nour first results regarding the light elements (CNO) and the neutron capture\nelements. Our findings in the oldest bulge stars support the scenario where the\nfirst stellar generations have been fast rotators.", "category": "astro-ph_GA" }, { "text": "Tidal Limit of Stellar Systems in Two-Power Density Models: As the generalization of gravitational effects on the point mass systems, we\nwant to study the tidal effect exerted on an extended stellar system using\nspherical and axisymmetric elliptical models. Considering the Isochrone and\nPlummer models for a passing extended stellar system, the tidal distance and\nthe equipotential surface are calculated. The corresponding critical surfaces\nand maps are plotted in different cases. There are different results some of\nthem may be used in describing stellar systems deformation", "category": "astro-ph_GA" }, { "text": "Supernova enhanced cosmic ray ionization and induced chemistry in a\n molecular cloud of W51C: Cosmic rays pervade the Galaxy and are thought to be accelerated in supernova\nshocks. The interaction of cosmic rays with dense interstellar matter has two\nimportant effects: 1) high energy (>1 GeV) protons produce {\\gamma}-rays by\n{\\pi}0-meson decay; 2) low energy (< 1 GeV) cosmic rays (protons and electrons)\nionize the gas. We present here new observations towards a molecular cloud\nclose to the W51C supernova remnant and associated with a recently discovered\nTeV {\\gamma}-ray source. Our observations show that the cloud ionization degree\nis highly enhanced, implying a cosmic ray ionization rate ~ 10-15 s-1, i.e. 100\ntimes larger than the standard value in molecular clouds. This is consistent\nwith the idea that the cloud is irradiated by an enhanced flux of freshly\naccelerated low-energy cosmic rays. In addition, the observed high cosmic ray\nionization rate leads to an instability in the chemistry of the cloud, which\nkeeps the electron fraction high, ~ 10-5, in a large fraction (Av \\geq 6mag) of\nthe cloud and low, ~ 10-7, in the interior. The two states have been predicted\nin the literature as high- and low-ionization phases (HIP and LIP). This is the\nobservational evidence of their simultaneous presence in a cloud.", "category": "astro-ph_GA" }, { "text": "Cosmic evolution of supermassive black holes: A view into the next two\n decades: The discoveries made over the past 20 years by Chandra and XMM-Newton surveys\nin conjunction with multiwavelength imaging and spectroscopic data available in\nthe same fields have significantly changed the view of the supermassive black\nhole (SMBH) and galaxy connection. These discoveries have opened up several\nexciting questions that are beyond the capabilities of current X-ray telescopes\nand will need to be addressed by observatories in the next two decades. As new\nobservatories peer into the early Universe, we will begin to understand the\nphysics and demographics of SMBH infancy (at $z>6$) and investigate the\ninfluence of their accretion on the formation of the first galaxies ($\\S$ 2.1).\nWe will also be able to understand the accretion and evolution over the cosmic\nhistory (at $z\\sim$1-6) of the full population of black holes in galaxies,\nincluding low accretion rate, heavily obscured AGNs at luminosities beyond the\nreach of current X-ray surveys ($\\S$2.2 and $\\S$2.3), enabling us to resolve\nthe connection between SMBH growth and their environment.", "category": "astro-ph_GA" }, { "text": "HST and Ground-Based Spectroscopy of Quasar Outflows: From Mini-BALs to\n BALs: Quasar outflows have been posited as a mechanism to couple super-massive\nblack holes to evolution in their host galaxies. We use multi-epoch spectra\nfrom the Hubble Space Telescope and ground-based observatories to study the\noutflows in seven quasars that have CIV outflow lines ranging from a classic\nBAL to weaker/narrower \"mini-BALs\" across rest wavelengths of at least 850\n$\\AA$ to 1650 $\\AA$. The CIV outflow lines all varied within a time frame of\n$\\leq$ 1.9 yrs (rest). This includes equal occurrences of strengthening and\nweakening plus the emergence of a new BAL system at $-$38,800 km/s accompanied\nby dramatic strengthening in a mini-BAL at $-$22,800 km/s. We infer from\n$\\sim$1:1 doublet ratios in PV and other lines that the BAL system is highly\nsaturated with line-of-sight covering fractions ranging from 0.27 to 0.80 in\nthe highest to lowest column density regions, respectively. Three of the\nmini-BALs also provide evidence for saturation and partial covering based on\n$\\sim$1:1 doublet ratios. We speculate that the BALs and mini-BALs form in\nsimilar clumpy/filamentary outflows, with mini-BALs identifying smaller or\nfewer clumps along our lines of sight. If we attribute the line variabilities\nto clumps crossing our lines of sight at roughly Keplerian speeds, then a\ntypical variability time in our study, $\\sim$1.1 yrs, corresponds to a distance\n$\\sim$2 pc from the central black hole. Combining this with the speed and\nminimum total column density inferred from the PV BAL, $N_H \\gtrsim$\n2.5$\\times$10$^{22}$ cm$^{-2}$, suggests that the BAL outflow kinetic energy is\nin the range believed to be sufficient for feedback to galaxy evolution.", "category": "astro-ph_GA" }, { "text": "Cold gas in the early Universe. Survey for neutral atomic-carbon in GRB\n host galaxies at 1 < z < 6 from optical afterglow spectroscopy: We present a survey for neutral atomic-carbon (CI) along gamma-ray burst\n(GRB) sightlines, which probes the shielded neutral gas-phase in the\ninterstellar medium (ISM) of GRB host galaxies at high redshift. We compile a\nsample of 29 medium- to high-resolution GRB optical afterglow spectra spanning\na redshift range through most of cosmic time from $1 < z < 6$. We find that\nseven ($\\approx 25\\%$) of the GRBs entering our statistical sample have CI\ndetected in absorption. It is evident that there is a strong excess of cold gas\nin GRB hosts compared to absorbers in quasar sightlines. We investigate the\ndust properties of the GRB CI absorbers and find that the amount of neutral\ncarbon is positively correlated with the visual extinction, $A_V$, and the\nstrength of the 2175 \\AA\\ dust extinction feature, $A_{\\mathrm{bump}}$. GRBs\nwith CI detected in absorption are all observed above a certain threshold of\n$\\log N$(HI)$/\\mathrm{cm}^{-2}$ + [X/H] > 20.7 and a dust-phase iron column\ndensity of $\\log N$(Fe)$_{\\mathrm{dust}}/\\mathrm{cm}^{-2}$ > 16.2. In contrast\nto the SED-derived dust properties, the strength of the CI absorption does not\ncorrelate with the depletion-derived dust properties. This indicates that the\nGRB CI absorbers trace dusty systems where the dust composition is dominated by\ncarbon-rich dust grains. The observed higher metal and dust column densities of\nthe GRB CI absorbers compared to H$_2$- and CI-bearing quasar absorbers is\nmainly a consequence of how the two absorber populations are selected, but is\nalso required in the presence of intense UV radiation fields in actively\nstar-forming galaxies.", "category": "astro-ph_GA" }, { "text": "MCMC-based Voigt Profile fitting to a Mini-BAL System in the Quasar\n UM675: We introduce a Bayesian approach coupled with a Markov Chain Monte Carlo\n(MCMC) method and the maximum likelihood statistic for fitting the profiles of\nnarrow absorption lines (NALs) in quasar spectra. This method also incorporates\noverlap between different absorbers. We illustrate and test this method by\nfitting models to a \"mini-broad\" (mini-BAL) and six NAL profiles in four\nspectra of the quasar UM675 taken over a rest-frame interval of 4.24 years. Our\nfitting results are consistent with past results for the mini-BAL system in\nthis quasar by Hamann et al. (1997b). We also measure covering factors ($C_{\\rm\nf}$) for two narrow components in the CIV and NV mini-BALs and their overlap\ncovering factor with the broad component. We find that $C_{\\rm f}$(NV) is\nalways larger than $C_{\\rm f}$(CIV) for the broad component, while the opposite\nis true for the narrow components in the mini-BAL system. This could be\nexplained if the broad and narrow components originated in gas at different\nradial distances, but it seems more likely to be due to them produced by gas at\nthe same distance but with different gas densities (i.e., ionization states).\nThe variability detected only in the broad absorption component in the mini-BAL\nsystem is probably due to gas motion since both $C_{\\rm f}$(CIV) and $C_{\\rm\nf}$(NV) vary. We determine for the first time that multiple absorbing clouds\n(i.e., a broad and two narrow components) overlap along our line of sight. We\nconclude that the new method improves fitting results considerably compared to\nprevious methods.", "category": "astro-ph_GA" }, { "text": "History of the gas fuelling star formation in eagle galaxies: Theory predicts that cosmological gas accretion plays a fundamental role\nfuelling star formation in galaxies. However, a detailed description of the\naccretion process to be used when interpreting observations is still lacking.\nUsing the state-of-the-art cosmological hydrodynamical simulation eagle, we\nwork out the chemical inhomogeneities arising in the disk of galaxies due to\nthe randomness of the accretion process. In low-mass systems and outskirts of\nmassive galaxies, low metallicity regions are associated with enhanced\nstar-formation, a trend that reverses in the centers of massive galaxies. These\npredictions agree with the relation between surface density of star formation\nrate and metallicity observed in the local spiral galaxies from the MaNGA\nsurvey. Then, we analyse the origin of the gas that produces stars at two key\nepochs, z simeq 0 and z simeq 2. The main contribution comes from gas already\nin the galaxy about 1 Gyr before stars are formed, with a share from external\ngas that is larger at high redshift. The accreted gas may come from major and\nminor mergers, but also as gravitationally unbound gas and from mergers with\ndark galaxies (i.e., haloes where more than 95 % of the baryon mass is in gas).\nWe give the relative contribution of these sources of gas as a function of\nstellar mass (8 < log Mstar < 11). Even at z = 0, some low-mass galaxies form a\nsignificant fraction of their total stellar mass during the last Gyr from\nmergers with dark galaxies.", "category": "astro-ph_GA" }, { "text": "Witnessing a Galaxy Cluster Merger with JWST and a Chandra X-ray\n Temperature Map: The first James Webb Space Telescope (JWST) image released was of galaxy\ncluster SMACSJ0723.3- 7327, a lensing cluster at z=0.39 showing detail only\nJWST can provide. While the majority of the focus has been on the brilliantly\nlensed galaxies at redshifts far beyond it, there is more to the story than it\nbeing just a lensing cluster. The Chandra X-ray temperature map tells a tale of\na merging cluster with a significant subcluster leaving a wake in the\nintracluster medium (ICM). This paper presents a high fidelity temperature map\nof SMACSJ0723.3-7327 using adaptive circular binning, overlaid with the JWST\nimage, showing clear signs of merger activity. As the ICM extends well past the\nboundaries of the JWST imagery, and no low-frequency radio observations are yet\npublished, a fuller story of this cluster remains to be told. This new X-ray\ntemperature map reveals new details of a moderately distant actively merging\ncluster.", "category": "astro-ph_GA" }, { "text": "LoCuSS: Exploring the selection of faint blue background galaxies for\n cluster weak-lensing: Cosmological constraints from galaxy clusters rely on accurate measurements\nof the mass and internal structure of clusters. An important source of\nsystematic uncertainty in cluster mass and structure measurements is the secure\nselection of background galaxies that are gravitationally lensed by clusters.\nThis issue has been shown to be particular severe for faint blue galaxies. We\ntherefore explore the selection of faint blue background galaxies, by reference\nto photometric redshift catalogs derived from the COSMOS survey and our own\nobservations of massive galaxy clusters at z~0.2. We show that methods relying\non photometric redshifts of galaxies in/behind clusters based on observations\nthrough five filters, and on deep 30-band COSMOS photometric redshifts are both\ninadequate to identify safely faint blue background galaxies. This is due to\nthe small number of filters used by the former, and absence of massive galaxy\nclusters at redshifts of interest in the latter. We therefore develop a\npragmatic method to combine both sets of photometric redshifts to select a\npopulation of blue galaxies based purely on photometric analysis. This sample\nyields stacked weak-lensing results consistent with our previously published\nresults based on red galaxies. We also show that the stacked clustercentric\nnumber density profile of these faint blue galaxies is consistent with\nexpectations from consideration of the lens magnification signal of the\nclusters. Indeed, the observed number density of blue background galaxies\nchanges by ~10-30 per cent across the radial range over which other surveys\nassume it to be flat.", "category": "astro-ph_GA" }, { "text": "Cold galaxies: We use 350 mu angular diameter estimates from Planck to test the idea that\nsome galaxies contain exceptionally cold (10-13 K) dust, since colder dust\nimplies a lower surface brightness radiation field illuminating the dust, and\nhence a greater physical extent for a given luminosity. The galaxies identified\nfrom their spectral energy distributions as containing cold dust do indeed show\nthe expected larger 350 mu diameters. For a few cold dust galaxies where\nHerschel data are available we are able to use submillimetre maps or surface\nbrightness profiles to locate the cold dust, which as expected generally lies\noutside the optical galaxy.", "category": "astro-ph_GA" }, { "text": "Potential Importance of Binary Evolution in UV-Optical Spectral Fitting\n of Early-Type Galaxies: Binaries are very common in galaxies, and more than half of Galactic hot\nsubdwarf stars, which are thought as a possible origin of UV-upturn of old\nstellar populations, are found in binaries. Previous works showed that binary\nevolution can make the spectra of binary star populations significantly\ndifferent from those of single star populations. However, the effect of binary\nevolution has not been taken into account in most works of spectral fitting of\ngalaxies. This paper studies the role of binary evolution in spectral fitting\nof early-type galaxies, via a stellar population synthesis model including both\nsingle and binary star populations. Spectra from ultraviolet to optical band\nare fitted to determine a few parameters of galaxies. The results show that the\ninclusion of binaries in stellar population models may lead to obvious change\nin the determination of some galaxy parameters and therefore it is potentially\nimportant for spectral studies. In particular, the ages of young components of\ncomposite stellar populations become much older when using binary star\npopulation models instead of single star population models. This implies that\nbinary star population models will measure significantly different star\nformation histories (SFHs) for galaxies compared to single star population\nmodels. In addition, stellar population models with binary interactions measure\nlarger dust extinctions than single star population models on average. It\nsuggests that when using binary star population models instead of single star\npopulation models, negative extinctions are possibly unnecessary in spectral\nfitting of early-type galaxies.", "category": "astro-ph_GA" }, { "text": "The Far-Infrared-Radio Correlation in MS0451-03: We present a multi-wavelength analysis of star-forming galaxies in the\nmassive cluster MS0451.6-0305 at z $\\sim$ 0.54 to shed new light on the\nevolution of the far-infrared-radio relationship in distant rich clusters. We\nhave derived total infrared luminosities for a spectroscopically confirmed\nsample of cluster and field galaxies through an empirical relation based on\n$Spitzer$ MIPS 24 $\\mu$m photometry. The radio flux densities were measured\nfrom deep Very Large Array 1.4 GHz radio continuum observations. We find the\nratio of far-infrared to radio luminosity for galaxies in an intermediate\nredshift cluster to be $q_{\\rm FIR}$ = 1.80$\\pm$0.15 with a dispersion of 0.53.\nDue to the large intrinsic dispersion, we do not find any observable change in\nthis value with either redshift or environment. However, a higher percentage of\ngalaxies in this cluster show an excess in their radio fluxes when compared to\nlow redshift clusters ($27^{+23}_{-13}\\%$ to $11\\%$), suggestive of a cluster\nenhancement of radio-excess sources at this earlier epoch. In addition, the\nfar-infrared-radio relationship for blue galaxies, where $q_{\\rm FIR}$ =\n2.01$\\pm$0.14 with a dispersion of 0.35, is consistent with the predicted value\nfrom the field relationship, although these results are based on a sample from\na single cluster.", "category": "astro-ph_GA" }, { "text": "Extremely metal-poor galaxies with HST/COS: laboratories for models of\n low-metallicity massive stars and high-redshift galaxies: Ultraviolet (UV) observations of local star-forming galaxies have begun to\nestablish an empirical baseline for interpreting the rest-UV spectra of\nreionization-era galaxies. However, existing high-ionization emission line\nmeasurements at $z>6$ ($\\mathrm{W_{C IV, 0}} \\gtrsim 20$ {\\AA}) are uniformly\nstronger than observed locally ($\\mathrm{W_{C IV, 0}} \\lesssim 2$ {\\AA}),\nlikely due to the relatively high metallicities ($Z/Z_\\odot > 0.1$) typically\nprobed by UV surveys of nearby galaxies. We present new HST/COS spectra of six\nnearby ($z<0.01$) extremely metal-poor galaxies (XMPs, $Z/Z_\\odot \\lesssim\n0.1$) targeted to address this limitation and provide constraints on the\nhighly-uncertain ionizing spectra powered by low-metallicity massive stars. Our\ndata reveal a range of spectral features, including one of the most prominent\nnebular C IV doublets yet observed in local star-forming systems and strong He\nII emission. Using all published UV observations of local XMPs to-date, we find\nthat nebular C IV emission is ubiquitous in very high specific star formation\nrate systems at low metallicity, but still find equivalent widths smaller than\nthose measured in individual lensed systems at $z>6$. Our moderate-resolution\nHST/COS data allow us to conduct an analysis of the stellar winds in a local\nnebular C IV emitter, which suggests that some of the tension with $z>6$ data\nmay be due to existing local samples not yet probing sufficiently high\n$\\mathrm{\\alpha/Fe}$ abundance ratios. Our results indicate that C IV emission\ncan play a crucial role in the JWST and ELT era by acting as an accessible\nsignpost of very low metallicity ($Z/Z_\\odot < 0.1$) massive stars in\nassembling reionization-era systems.", "category": "astro-ph_GA" }, { "text": "Generating Images of the M87* Black Hole Using GANs: In this paper, we introduce a novel data augmentation methodology based on\nConditional Progressive Generative Adversarial Networks (CPGAN) to generate\ndiverse black hole (BH) images, accounting for variations in spin and electron\ntemperature prescriptions. These generated images are valuable resources for\ntraining deep learning algorithms to accurately estimate black hole parameters\nfrom observational data. Our model can generate BH images for any spin value\nwithin the range of [-1, 1], given an electron temperature distribution. To\nvalidate the effectiveness of our approach, we employ a convolutional neural\nnetwork to predict the BH spin using both the GRMHD images and the images\ngenerated by our proposed model. Our results demonstrate a significant\nperformance improvement when training is conducted with the augmented dataset\nwhile testing is performed using GRMHD simulated data, as indicated by the high\nR2 score. Consequently, we propose that GANs can be employed as cost effective\nmodels for black hole image generation and reliably augment training datasets\nfor other parameterization algorithms.", "category": "astro-ph_GA" }, { "text": "CARMA CO Observations of Three Extremely Metal-Poor, Star-Forming\n Galaxies: We present sensitive CO (J = 1 - 0) emission line observations of three\nmetal-poor dwarf irregular galaxies Leo P (Z ~ 3% Z_Solar), Sextans A (Z ~ 7.5%\nZ_Solar), and Sextans B (Z ~ 7.5% Z_Solar), all obtained with the Combined\nArray for Millimeter-wave Astronomy (CARMA) interferometer. While no CO\nemission was detected, the proximity of the three systems allows us to place\nvery stringent (4 sigma) upper limits on the CO luminosity (L_CO) in these\nmetal-poor galaxies. We find the CO luminosities to be L_CO < 2900 K km/s pc^2\nfor Leo P, L_CO < 12400 K km/s pc^2 for Sextans A, and L_CO < 9700 K km/s pc^2\nfor Sextans B. Comparison of our results with recent observational estimates of\nthe factor for converting between L_CO and the mass of molecular hydrogen, as\nwell as theoretical models, provides further evidence that either the CO-to-H_2\nconversion factor increases sharply as metallicity decreases, or that stars are\nforming in these three galaxies very efficiently, requiring little molecular\nhydrogen.", "category": "astro-ph_GA" }, { "text": "Globular clusters in the stellar stream surrounding the Milky Way analog\n NGC 5907: We study the globular clusters (GCs) in the spiral galaxy NGC~5907 well-known\nfor its spectacular stellar stream -- to better understand its origin. Using\nwide-field Subaru/Suprime-Cam $gri$ images and deep Keck/DEIMOS multi-object\nspectroscopy, we identify and obtain the kinematics of several GCs superimposed\non the stellar stream and the galaxy disk. We estimate the total number of\nglobular clusters in NGC 5907 to be $154\\pm44$, with a specific frequency of\n$0.73\\pm0.21$. Our analysis also reveals a significant, new population of young\nstar cluster candidates found mostly along the outskirts of the stellar disk.\nUsing the properties of the stream GCs, we estimate that the disrupted galaxy\nhas a stellar mass similar to the Sagittarius dwarf galaxy accreted by the\nMilky Way, i.e. $\\sim10^8~M_\\odot$.", "category": "astro-ph_GA" }, { "text": "Two-component outer ring and the Galactic spiral structure: Model of the Galaxy with the ring R1R2' can explain some large-scale\nmorphological features of the Galactic spiral structure. The Carina-Sagittarius\narm can consist of two ascending segments of the outer rings R1 and R2 which\nalmost touch each other near the Carina region. The Perseus and Crux arms can\nbe partially identified with the descending segments of the ring R2. Model of\nthe two-component outer ring can also explain the existence of some maxima in\ndiagrams (l, VLSR) which are supposed to correspond to the directions\ntangential to the spiral arms. On the basis of numerical simulations we propose\ntwo sketches of the ring structure of the Galaxy which include the bar, two\nouter rings, the inner ring, and the nuclear gas condensation, that may be a\nnuclear ring. Both sketches can explain the position of the Carina-Sagittarius\narm with respect to the Sun.", "category": "astro-ph_GA" }, { "text": "The structure of molecular gas associated with NGC2264: wide-field 12CO\n and H2 imaging: We present wide-field, high-resolution imaging observations in 12CO 3-2 and\nH2 1-0 S(1) towards a ~1 square degree region of NGC2264. We identify 46 H2\nemission objects, of which 35 are new discoveries. We characterize several\ncores as protostellar, reducing the previously observed ratio of\nprestellar/protostellar cores in the NGC2264 clusters. The length of H2 jets\nincreases the previously reported spatial extent of the clusters. In each\ncluster, <0.5% of cloud material has been perturbed by outflow activity. A\nprincipal component analysis of the 12CO data suggests that turbulence is\ndriven on scales >2.6 pc, which is larger than the extent of the outflows. We\nobtain an exponent alpha=0.74 for the size-linewidth relation, possibly due to\nthe high surface density of NGC2264. In this very active, mixed-mass star\nforming region, our observations suggest that protostellar outflow activity is\nnot injecting energy and momentum on a large enough scale to be the dominant\nsource of turbulence.", "category": "astro-ph_GA" }, { "text": "Dynamic role of dust in formation of molecular clouds: Dust is the usual minor component of the interstellar medium. Its dynamic\nrole in the contraction of the diffuse gas into molecular clouds is commonly\nassumed to be negligible because of the small mass fraction, $f \\simeq 0.01$.\nHowever, as shown in this study, the collective motion of dust grains with\nrespect to the gas may considerably contribute to the destabilisation of the\nmedium on scales $\\lambda \\lesssim \\lambda_J$, where $\\lambda_J$ is the Jeans\nlength-scale. The linear perturbations of the uniform self-gravitating gas at\nrest are marginally stable at $\\lambda \\simeq \\lambda_J$, but as soon as the\ndrift of grains is taken into account, they begin growing at a rate\napproximately equal to $(f \\tau)^{1/3} t^{-1}_{ff}$, where $\\tau$ is the\nstopping time of grains expressed in units of the free fall time of the cloud,\n$t_{ff}$. The physical mechanism responsible for such a weak dependence of the\ngrowth rate on $f$ is the resonance of heavy sound waves stopped by the\nself-gravity of gas with weak gravitational attraction caused by perturbations\nof the dust fraction. Once there is stationary subsonic bulk drift of the dust,\nthe growing gas-dust perturbations at $\\lambda < \\lambda_J$ become waves\npropagating with the drift velocity projected onto the wavevector. Their growth\nhas a resonant nature as well and the growth rate is substantially larger than\nthat of the recently discovered resonant instability of gas-dust mixture in the\nabsence of self-gravity. The new instabilities can facilitate gravitational\ncontraction of cold interstellar gas into clouds and additionally produce dusty\ndomains of sub-Jeans size at different stages of molecular cloud formation and\nevolution.", "category": "astro-ph_GA" }, { "text": "A New Challenge for Dark Matter Models: Cold dark matter (CDM) has faced a number of challenges mainly at small\nscales, such as the too-big-to-fail problem, and core-cusp density profile of\ndwarf galaxies. Such problems were argued to have a solution either in the\nbaryonic physics sector or in modifying the nature of dark matter to be\nself-interacting, or self-annihilating, or ultra-light. Here we present a new\nchallenge for CDM by showing that two of Milky Way's satellites (Horologium I,\nand Tucana II) are too dense, requiring the formation masses and redshifts of\nhalos in CDM not compatible with being a satellite. These\ntoo-dense-to-be-satellite systems are dominated by dark matter and exhibit a\nsurface density above mean dark energy cosmic surface density\n$\\sim\\Omega_{\\Lambda} \\rho_c c/H_0\\approx 600~\\rm M_{\\odot}/pc^2$. This value\ncorresponds to dark matter pressure of $\\approx 10^{-9}{\\rm erg/cm^3}$. Along\nwith the recently reported excess in small-scale substructures found in\ncluster-lenses, this problem, unlike other issues facing CDM, has no solution\nin the baryonic sector and none of the current alternatives of dark matter can\naccount for it. The too-dense-to-be-satellite problem presented in this work\nprovides a new clue for the nature of dark matter, never accounted for before.\nWe note that Horologium I and Tucana II have only been discovered in the past\n$\\sim6$ years with DES, and future surveys (such as those done by Vera C. Rubin\nObservatory) may uncover a broader population of such galaxies. Moreover, we\nfind that a number of MW's satellite require formation halo masses below the\natomic cooling limit which by itself is another challenging observation to\naccount for in CDM.", "category": "astro-ph_GA" }, { "text": "Infrared appearance of wind-blown bubbles around young massive stars: Thousands of ring-like bubbles appear on infrared images of the Galaxy plane.\nMost of these infrared bubbles form during expansion of HII regions around\nmassive stars. However, the physical effects that determine their morphology\nare still under debate. Namely, the absence of the infrared emission toward the\ncentres of the bubbles can be explained by pushing the dust grains by stellar\nradiation pressure. At the same time, small graphite grains and PAHs are not\nstrongly affected by the radiation pressure and must be removed by another\nprocess. Stellar ultraviolet emission can destroy the smallest PAHs but the\nphotodestruction is ineffective for the large PAHs. Meanwhile, the stellar wind\ncan evacuate all types of grains from HII regions. In the frame of our\nchemo-dynamical model we vary parameters of the stellar wind and illustrate\ntheir influence on the morphology and synthetic infrared images of the bubbles.", "category": "astro-ph_GA" }, { "text": "A Long Time Ago in a Galaxy Far, Far Away: A Candidate z ~ 12 Galaxy in\n Early JWST CEERS Imaging: We report the discovery of a candidate galaxy with a photo-z of z~12 in the\nfirst epoch of the JWST Cosmic Evolution Early Release Science (CEERS) Survey.\nFollowing conservative selection criteria we identify a source with a robust\nz_phot = 11.8^+0.3_-0.2 (1-sigma uncertainty) with m_F200W=27.3, and >7-sigma\ndetections in five filters. The source is not detected at lambda < 1.4um in\ndeep imaging from both HST and JWST, and has faint ~3-sigma detections in JWST\nF150W and HST F160W, which signal a Ly-alpha break near the red edge of both\nfilters, implying z~12. This object (Maisie's Galaxy) exhibits F115W-F200W >\n1.9 mag (2-sigma lower limit) with a blue continuum slope, resulting in 99.6%\nof the photo-z PDF favoring z > 11. All data quality images show no artifacts\nat the candidate's position, and independent analyses consistently find a\nstrong preference for z > 11. Its colors are inconsistent with Galactic stars,\nand it is resolved (r_h = 340 +/- 14 pc). Maisie's Galaxy has log M*/Msol ~ 8.5\nand is highly star-forming (log sSFR ~ -8.2 yr^-1), with a blue rest-UV color\n(beta ~ -2.5) indicating little dust though not extremely low metallicity.\nWhile the presence of this source is in tension with most predictions, it\nagrees with empirical extrapolations assuming UV luminosity functions which\nsmoothly decline with increasing redshift. Should followup spectroscopy\nvalidate this redshift, our Universe was already aglow with galaxies less than\n400 Myr after the Big Bang.", "category": "astro-ph_GA" }, { "text": "Ultra-diffuse galaxies: the high-spin tail of the abundant dwarf galaxy\n population: Recent observations have revealed the existence of an abundant population of\nfaint, low surface brightness (SB) galaxies, which appear to be numerous and\nubiquitous in nearby galaxy clusters, including the Virgo, Coma and Fornax\nclusters. With median stellar masses of dwarf galaxies, these ultra-diffuse\ngalaxies (UDGs) have unexpectedly large sizes, corresponding to a mean SB of\n$24\\lesssim\\langle\\mu_e\\rangle_r\\ {\\rm mag}^{-1} {\\rm arcsec}^2\\lesssim27$\nwithin the effective radius. We show that the UDG population represents the\ntail of galaxies formed in dwarf-sized haloes with higher-than-average angular\nmomentum. By adopting the standard model of disk formation -- in which the size\nof galaxies is set by the spin of the halo -- we recover both the abundance of\nUDGs as a function of the host cluster mass and the distribution of sizes\nwithin the UDG population. According to this model, UDGs are not failed $L_*$\ngalaxies, but genuine dwarfs, and their low SB is not uniquely connected to the\nharsh cluster environment. We therefore expect a correspondingly abundant\npopulation of UDGs in the field, with likely different morphologies and\ncolours.", "category": "astro-ph_GA" }, { "text": "The Physical Properties of Galaxies with Unusually Red Mid-Infrared\n Colours: The goal of this paper is to investigate the physical nature of galaxies in\nthe redshift range $0.021000$ km s$^{-1}$) Ly$\\alpha$\nemission lines. We derive the Ly$\\alpha$ (UV) LF over 2 orders of magnitude\ncovering bright galaxies and AGN in $\\log\nL_\\mathrm{Ly\\alpha}/\\mathrm{[erg~s^{-1}]}=43.3-45.5$ ($-27-21$) type 1\nAGN increases from $z\\sim2$ to $z\\sim0$ as opposed to the evolution of bright\n($M_\\mathrm{UV}<-21$) type 1 AGN, suggesting the AGN downsizing in the\nrest-frame UV luminosity.", "category": "astro-ph_GA" }, { "text": "Stratified Distribution of Organic Molecules at the Planet-Formation\n Scale in the HH 212 Disk Atmosphere: Formamide (NH2CHO) is considered an important prebiotic molecule because of\nits potential to form peptide bonds. It was recently detected in the atmosphere\nof the HH 212 protostellar disk on the Solar-System scale where planets will\nform. Here we have mapped it and its potential parent molecules HNCO and H2CO,\nalong with other molecules CH3OH and CH3CHO, in the disk atmosphere, studying\nits formation mechanism. Interestingly, we find a stratified distribution of\nthese molecules, with the outer emission radius increasing from ~ 24 au for\nNH2CHO and HNCO, to 36 au for CH3CHO, to 40 au for CH3OH, and then to 48 au for\nH2CO. More importantly, we find that the increasing order of the outer emission\nradius of NH2CHO, CH3OH, and H2CO is consistent with the decreasing order of\ntheir binding energies, supporting that they are thermally desorbed from the\nice mantle on dust grains. We also find that HNCO, which has much lower binding\nenergy than NH2CHO, has almost the same spatial distribution, kinematics, and\ntemperature as NH2CHO, and is thus more likely a daughter species of desorbed\nNH2CHO. On the other hand, we find that H2CO has a more extended spatial\ndistribution with different kinematics from NH2CHO, thus questioning whether it\ncan be the gas-phase parent molecule of NH2CHO.", "category": "astro-ph_GA" }, { "text": "On the Virialization of Disk Winds: Implications for the Black Hole Mass\n Estimates in AGN: Estimating the mass of a supermassive black hole (SMBH) in an active galactic\nnucleus (AGN) usually relies on the assumption that the broad line region (BLR)\nis virialized. However, this assumption seems invalid in BLR models that\nconsists of an accretion disk and its wind. The disk is likely Keplerian and\ntherefore virialized. However, the wind material must, beyond a certain point,\nbe dominated by an outward force that is stronger than gravity. Here, we\nanalyze hydrodynamic simulations of four different disk winds: an isothermal\nwind, a thermal wind from an X-ray heated disk, and two line-driven winds, one\nwith and the other without X-ray heating and cooling. For each model, we check\nwhether gravity governs the flow properties, by computing and analyzing the\nvolume-integrated quantities that appear in the virial theorem: internal,\nkinetic, and gravitational energies, We find that in the first two models, the\nwinds are non-virialized whereas the two line-driven disk winds are virialized\nup to a relatively large distance. The line-driven winds are virialized because\nthey accelerate slowly so that the rotational velocity is dominant and the wind\nbase is very dense. For the two virialized winds, the so-called projected\nvirial factor scales with inclination angle as $1/ \\sin^2{i}$. Finally, we\ndemonstrate that an outflow from a Keplerian disk becomes unvirialized more\nslowly when it conserves the gas specific angular momentum -- as in the models\nconsidered here, than when it conserves the angular velocity -- as in the\nso-called magneto-centrifugal winds.", "category": "astro-ph_GA" }, { "text": "The ALPINE-ALMA [CII] Survey: Multi-Wavelength Ancillary Data and Basic\n Physical Measurements: We present the ancillary data and basic physical measurements for the\ngalaxies in the ALMA Large Program to Investigate C+ at Early Times (ALPINE)\nsurvey - the first large multi-wavelength survey which aims at characterizing\nthe gas and dust properties of 118 main-sequence galaxies at redshifts 4.4 < z\n< 5.9 via the measurement of [CII]-emission at 158 micro-meter (64% at\n>3.5$\\sigma$) and the surrounding far-infrared (FIR) continuum in conjunction\nwith a wealth of optical and near-infrared data. We outline in detail the\nspectroscopic data and selection of the galaxies as well as the ground- and\nspace-based imaging products. In addition, we provide several basic\nmeasurements including stellar masses, star formation rates (SFR), rest-frame\nultra-violet (UV) luminosities, UV continuum slopes ($\\beta$), and absorption\nline redshifts, as well as H-alpha emission derived from Spitzer colors. We\nfind that the ALPINE sample is representative of the 4 < z < 6 galaxy\npopulation selected by photometric methods and only slightly biased towards\nbluer colors ($\\Delta\\beta$ ~ 0.2). Using [CII] as tracer of the systemic\nredshift (confirmed for one galaxy at z=4.5 out of 118 for which we obtained\noptical [OII]$\\lambda$3727A emission), we confirm red shifted Ly-alpha emission\nand blue shifted absorption lines similar to findings at lower redshifts. By\nstacking the rest-frame UV spectra in the [CII] rest-frame we find that the\nabsorption lines in galaxies with high specific SFR are more blue shifted,\nwhich could be indicative of stronger winds and outflows.", "category": "astro-ph_GA" }, { "text": "A Deep Chandra ACIS Survey of M83: We have obtained a series of deep X-ray images of the nearby galaxy M83 using\nChandra, with a total exposure of 729 ks. Combining the new data with earlier\narchival observations totaling 61 ks, we find 378 point sources within the D25\ncontour of the galaxy. We find 80 more sources, mostly background AGN, outside\nof the D25 contour. Of the X-ray sources, 47 have been detected in a new radio\nsurvey of M83 obtained using the Australia Telescope Compact Array. Of the\nX-ray sources, at least 87 seem likely to be supernova remnants (SNRs), based\non a combination of their properties in X-rays and at other wavelengths. We\nattempt to classify the point source population of M83 through a combination of\nspectral and temporal analysis. As part of this effort, we carry out an initial\nspectral analysis of the 29 brightest X-ray sources. The soft X-ray sources in\nthe disk, many of which are SNRs, are associated with the spiral arms, while\nthe harder X-ray sources, mostly X-ray binaries (XRBs), do not appear to be.\nAfter eliminating AGN, foreground stars and identified SNRs from the sample, we\nconstruct the cumulative luminosity function (CLF) of XRBs brighter than 8\n10$^{35}$ ergs/s. Despite M83's relatively high star formation rate, the CLF\nindicates that most of the XRBs in the disk are low mass XRBs.", "category": "astro-ph_GA" }, { "text": "Fundamental plane of elliptical galaxies in $f(R)$ gravity: the role of\n luminosity: The global properties of elliptical galaxies are connected through the\nso-called fundamental plane of ellipticals, which is an empirical relation\nbetween their parameters: effective radius, central velocity dispersion and\nmean surface brightness within the effective radius. We investigated the\nrelation between the parameters of the fundamental plane equation and the\nparameters of modified gravity potential $f(R)$. With that aim, we compared\ntheoretical predictions for circular velocity in $f(R)$ gravity with the\ncorresponding values from a large sample of observed elliptical galaxies.\nBesides, we consistently reproduced the values of coefficients of the\nfundamental plane equation as deduced from observations, showing that the\nphotometric quantities like mean surface brightness are related to\ngravitational parameters. We show that this type of modified gravity,\nespecially its power-law version - $R^n$, is able to reproduce the stellar\ndynamics in elliptical galaxies. Also, it is shown that $R^n$ gravity fits the\nobservations very well, without need for a dark matter.", "category": "astro-ph_GA" }, { "text": "Photodissociation Region Diagnostics Across Galactic Environments: We present three-dimensional astrochemical simulations and synthetic\nobservations of magnetised, turbulent, self-gravitating molecular clouds. We\nexplore various galactic interstellar medium environments, including cosmic-ray\nionization rates in the range of $\\zeta_{\\rm CR}=10^{-17}$-$10^{-14}\\,{\\rm\ns}^{-1}$, far-UV intensities in the range of $G_0=1$-$10^3$ and metallicities\nin the range of $Z=0.1$-$2\\,{\\rm Z}_{\\odot}$. The simulations also probe a\nrange of densities and levels of turbulence, including cases where the gas has\nundergone recent compression due to cloud-cloud collisions. We examine: i) the\ncolumn densities of carbon species across the cycle of CII, CI and CO, along\nwith OI, in relation to the HI-to-H$_2$ transition; ii) the velocity-integrated\nemission of [CII]~$158\\mu$m, [$^{13}$CII]~$158\\mu$m, [CI]~$609\\mu$m and\n$370\\mu$m, [OI]~$63\\mu$m and $146\\mu$m, and of the first ten $^{12}$CO\nrotational transitions; iii) the corresponding Spectral Line Energy\nDistributions; iv) the usage of [CII] and [OI]~$63\\mu$m to describe the\ndynamical state of the clouds; v) the behavior of the most commonly used ratios\nbetween transitions of CO and [CI]; and vi) the conversion factors for using CO\nand CI as H$_2$-gas tracers. We find that enhanced cosmic-ray energy densities\nenhance all aforementioned line intensities. At low metallicities, the emission\nof [CII] is well connected with the H$_2$ column, making it a promising new\nH$_2$ tracer in metal-poor environments. The conversion factors of $X_{\\rm CO}$\nand $X_{\\rm CI}$ depend on metallicity and the cosmic-ray ionization rate, but\nnot on FUV intensity. In the era of ALMA, SOFIA and the forthcoming CCAT-prime\ntelescope, our results can be used to understand better the behaviour of\nsystems in a wide range of galactic and extragalactic environments.", "category": "astro-ph_GA" }, { "text": "The fate of the pre-main sequence-rich clusters Collinder197 and vdB92:\n dissolution?: We investigate the nature and possible evolution of the young Galactic star\nclusters Collinder 197 (Cr 197) and vdB 92. The colour-magnitude diagrams\n(CMDs) are basically characterised by a poorly-populated MS and a dominant\nfraction ($\\ga75%$) of PMS stars, and the combined MS and PMS CMD morphology in\nboth clusters consistently constrains the age to within $5\\pm4$ Myr, with a\n$\\sim10$ Myr spread in the star formation process. The MS$ + $PMS stellar\nmasses are $\\approx660^{+102}_{-59} \\ms$ (Cr 197) and $\\approx750^{+101}_{-51}\n\\ms$ (vdB 92). Cr 197 and vdB 92 appear to be abnormally large, when compared\nto clusters within the same age range. They have irregular stellar radial\ndensity distributions (RDPs) with a marked excess in the innermost region, a\nfeature that, at less than 10 Myr, is more likely related to the star formation\nand/or molecular cloud fragmentation than to age-dependent dynamical effects.\nThe velocity dispersion of both clusters, derived from proper motions, is in\nthe range $\\sim15 - 22 \\kms$. Both clusters appear to be in a super-virial\nstate, with velocity dispersions higher than those expected of\nnearly-virialised clusters of similar mass and size. A possible interpretation\nis that Cr 197 and vdB 92 deviate critically from dynamical equilibrium, and\nmay dissolve into the field. We also conclude that early cluster dissolution\nleaves detectable imprints on RDPs of clusters as massive as several $10^2\n\\ms$. Cr 197 and vdB 92 may be the link between embedded clusters and young\nstellar associations.", "category": "astro-ph_GA" }, { "text": "PROBES-I: A Compendium of Deep Rotation Curves and Matched multiband\n Photometry: We present the Photometry and Rotation Curve Observations from Extragalactic\nSurveys (PROBES) compendium of extended rotation curves for 3163 late-type\nspirals, with matching homogeneous multiband photometry for 1677 of them.\nPROBES rotation curves originally extracted from Halpha long-slit spectra and\naperture synthesis HI (21cm) velocity maps typically extend out to a median\n2R_e (or 1R_{23.5, r}). Our uniform photometry takes advantage of GALEX,\nDESI-LIS, and WISE images and the software AutoProf to yield multiband\nazimuthally averaged surface brightness profiles that achieve depths greater\nthan 25 mag/arcsec^2 (FUV, NUV), 27 mag/arcsec^2 (g, r), and 26 mag/arcsec^2\n(z, W1, W2). With its library of spatially resolved profiles and an extensive\ntable of structural parameters, the versatile PROBES data set will benefit\nstudies of galaxy structure and formation.", "category": "astro-ph_GA" }, { "text": "Spiral Structure in Scale-free, Thin Discs: Rigid Rotation: In this paper we suggest the existence in the central regions of spiral\ngalaxies of collisionless, scale-free, rigidly rotating, self-gravitating discs\nwith spiral symmetry. Such discs must be truncated at a finite radius, and they\nmust be stabilized and rendered self-similar by a suitable halo. The halo and\nthe rotating disc share the self-similar class and must form together to arrive\nat the suggested state. We make comparisons with the well-known rigidly\nrotating, Kalnajs discs; one of which is axi-symmetric and finite while the\nother is infinite and decomposed into spiral modes. We find the\nself-consistent, self-similar, distribution functions in one and two dimensions\nin a rigidly rotating, collisionless system. In the case of two dimensions we\ndeduce the self-consistency condition for discrete spiral arms.\n We give an estimate of the disturbance created in the halo by the presence of\nthe disc, and argue that the halo itself should be close to self-similarity. A\nvery weak cusp in the halo may be necessary. The necessary spatial coincidence\nof the halo results in a kind of disc-halo `conspiracy'. Finally the disc\nequations are formulated in `spiral' coordinates, and the passage to an\napproximately discrete `line spiral' is given as an example. Although in two\ndimensions the collisionless particles enter and leave the arms in non-linear\nepicycles, they move approximately parallel to the arms in the line spiral\nlimit. The spiral pattern is however in rigid rotation. Aperiodic spiral arms\nare suggested wherein discontinuities may be coarse-grained to appear as\ncollisionless shocks.", "category": "astro-ph_GA" }, { "text": "Lagrangian statistics of a shock-driven turbulent dynamo in decaying\n turbulence: Small-scale fluctuating magnetic fields of order $n$G are observed in\nsupernova shocks and galaxy clusters, where its amplification is likely caused\nby the Biermann battery mechanism. However, these fields cannot be amplified\nfurther without the turbulent dynamo, which generates magnetic energy through\nthe stretch-twist-fold (STF) mechanism. Thus, we present here novel\nthree-dimensional magnetohydrodynamic (MHD) simulations of a laser-driven shock\npropagating into a stratified, multiphase medium, to investigate the post-shock\nturbulent magnetic field amplification via the turbulent dynamo. The\nconfiguration used here is currently being tested in the shock tunnel at the\nNational Ignition Facility (NIF). In order to probe the statistical properties\nof the post-shock turbulent region, we use $384 \\times 512 \\times 384$ tracers\nto track its evolution through the Lagrangian framework, thus providing a\nhigh-fidelity analysis of the shocked medium. Our simulations indicate that the\ngrowth of the magnetic field, which accompanies the near-Saffman kinetic energy\ndecay ($E_{\\textrm{kin}} \\propto t^{-1.15})$ without turbulence driving,\nexhibits slightly different characteristics as compared to periodic box\nsimulations. Seemingly no distinct phases exist in its evolution, because the\nshock passage and time to observe the magnetic field amplification during the\nturbulence decay are very short ($\\sim\\!0.3$ of a turbulent turnover time).\nYet, the growth rate is still consistent with those expected for compressive\n(curl-free) turbulence driving in subsonic, compressible turbulence.\nPhenomenological understanding of the dynamics of the magnetic and velocity\nfields are also elucidated via Lagrangian frequency spectra, which are\nconsistent with the expected inertial range scalings in the Eulerian-Lagrangian\nbridge.", "category": "astro-ph_GA" }, { "text": "On the Dispersal of Young Stellar Hierarchies: Hierarchical structure in young star fields has been demonstrated in a\nvariety of ways, including two point correlation functions (TPCFs) that are\npower laws for spatial scales up to at least several hundred parsecs. As the\nstars age, this power law decreases in slope until it becomes nearly flat at\n~100 Myr, at which point the hierarchical structure has disappeared. The fact\nthat the TPCF remains nearly a power law during this time implies that the\ndispersal mechanism is somewhat independent of scale. This rules out dispersal\nby random stellar motions at either the local gas turbulent speed or a constant\nspeed, because in both cases the hierarchy would disappear at small scales\nfirst, causing the TPCF to bend over. Destruction by shear has the right\nproperty as the shear rate in a galaxy is independent of scale for kpc-size\nregions, but shear converts the hierarchy into an azimuthal stream which still\nhas a power-law TPCF. What does explain the observation is the overlapping of\nseveral independent hierarchies from successive generations of star formation\nin the same region. If stellar age is determined from magnitude intervals on\nthe main sequence of a color-magnitude diagram, or if clusters ages are grouped\ntogether logarithmically into bins, then multiple generations will overlap more\nand more as the grouped populations age, and this overlap will lower the\nspatial correlations between group members. Models of these processes\nillustrate their relative roles in removing the appearance of young stellar\nhierarchies.", "category": "astro-ph_GA" }, { "text": "Robust statistical tools for identifying multiple stellar populations in\n globular clusters in the presence of measurement errors. A case study: NGC\n 2808: The finding of multiple stellar populations (MP), defined by patterns in the\nstellar element abundances, is nowadays considered a distinctive feature of\nglobular clusters. However, while data availability and quality improved in\nlast decades, this is not always true for the techniques adopted to their\nanalysis, rising problems of objectivity of the claims and reproducibility.\nUsing NGC 2808 as test case we show the use of well established statistical\nclustering methods. We focus the analysis to the RGB phase, where two data sets\nare available from recent literature for low- and high-resolution spectroscopy.\nWe adopt both hierarchical clustering and partition methods. We explicitly\naddress the usually neglected problem of measurement errors. The results of the\nclustering algorithms were subjected to silhouette width analysis to compare\nthe performance of the split into different number of MP. For both data sets\nthe results are at odd with those reported in the literature. Two MP are\ndetected for both data sets, while the literature reports five and four MP from\nhigh- and low-resolution spectroscopy respectively. The silhouette analysis\nsuggests that the population sub-structure is reliable for high-resolution\nspectroscopy data, while the actual existence of MP is questionable for the\nlow-resolution spectroscopy data. The discrepancy with literature claims is\nexplainable due to the difference of methods adopted to MP characterisation. By\nmeans of Monte Carlo simulations and multimodality statistical tests we show\nthat the often adopted study of the histogram of the differences in some key\nelements is prone to multiple false positive findings. The adoption of\nstatistically grounded methods, which adopt all the available information to\nsubset the data and explicitly address the problem of data uncertainty, is of\nparamount importance to present more robust and reproducible researches.", "category": "astro-ph_GA" }, { "text": "ALMA sub-/millimeter sources among $Spitzer$ SMUVS galaxies at $z>2$ in\n the COSMOS field: Sub-millimeter observations reveal the star-formation activity obscured by\ndust in the young Universe. It still remains unclear how galaxies detected at\nsub-millimeter wavelengths are related to ultraviolet/optical-selected galaxies\nin terms of their observed quantities, physical properties, and evolutionary\nstages. Deep near- and mid-infrared observational data are crucial to\ncharacterize the stellar properties of galaxies detected with sub-millimeter\nemission. In this study, we make use of a galaxy catalog from the $Spitzer$\nMatching Survey of the UltraVISTA ultra-deep Stripes. By cross-matching with a\nsub-millimeter source catalog constructed with the archival data of the Atacama\nLarge Millimeter/submillimeter Array (ALMA), we search for galaxies at $z>$ 2\nwith a sub-millimeter detection in our galaxy catalog. We find that the\nALMA-detected galaxies at $z>$ 2 are systematically massive and have redder\n$K_s$-[4.5] colors than the non-detected galaxies. The redder colors are\nconsistent with the larger dust reddening values of the ALMA-detected galaxies\nobtained from SED fitting. We also find that the ALMA-detected galaxies tend to\nhave brighter 4.5 $\\mu$m magnitudes. This may suggest that they tend to have\nsmaller mass-to-light ratios, and thus, to be younger than star-forming\ngalaxies fainter at sub-millimeter wavelengths with similar stellar masses. We\nidentify starburst galaxies with high specific star-formation rates among both\nALMA-detected and non-detected SMUVS sources. Irrespective of their brightness\nat sub-millimeter wavelengths, these populations have similar dust reddening\nvalues, which may suggest a variety of dust SED shapes among the starburst\ngalaxies at $z>2$.", "category": "astro-ph_GA" }, { "text": "Simulated Galaxy Interactions as Probes of Merger Spectral Energy\n Distributions: We present the first systematic comparison of ultraviolet-millimeter spectral\nenergy distributions (SEDs) of observed and simulated interacting galaxies. Our\nsample is drawn from the Spitzer Interacting Galaxy Survey, and probes a range\nof galaxy interaction parameters. We use 31 galaxies in 14 systems which have\nbeen observed with Herschel, Spitzer, GALEX, and 2MASS. We create a suite of\nGADGET-3 hydrodynamic simulations of isolated and interacting galaxies with\nstellar masses comparable to those in our sample of interacting galaxies.\nPhotometry for the simulated systems is then calculated with the SUNRISE\nradiative transfer code for comparison with the observed systems. For most of\nthe observed systems, one or more of the simulated SEDs match reasonably well.\nThe best matches recover the infrared luminosity and the star formation rate of\nthe observed systems, and the more massive systems preferentially match SEDs\nfrom simulations of more massive galaxies. The most morphologically distorted\nsystems in our sample are best matched to simulated SEDs close to coalescence,\nwhile less evolved systems match well with SEDs over a wide range of\ninteraction stages, suggesting that an SED alone is insufficient to identify\ninteraction stage except during the most active phases in strongly interacting\nsystems. This result is supported by our finding that the SEDs calculated for\nsimulated systems vary little over the interaction sequence.", "category": "astro-ph_GA" }, { "text": "EVN observations of 6.7 GHz methanol maser polarization in massive\n star-forming regions. V. Completion of the flux-limited sample: Although the role of magnetic fields in launching molecular outflows in\nmassive YSOs has been convincingly demonstrated by theoretical arguments,\nobservationally, the alignment of the magnetic field lines with the molecular\noutflows is still under debate. We aim to complete the measurements of the\ndirection of the magnetic fields at mas resolution around a sample of massive\nstar-forming regions (MSFRs) to determine whether the magnetic field and\noutflows are aligned. In 2012, we started a large VLBI campaign with the EVN to\nmeasure the magnetic field orientation and strength toward a sample of 31 MSFRs\n(the flux-limited sample) by analyzing the polarized emission of 6.7GHz CH3OH\nmasers. In the previous papers of the series, we have presented 80% of the\nsample. Here, we report the linearly and circularly polarized emission of\n6.7GHz CH3OH masers toward the last five MSFRs of the flux-limited sample. The\nsources are G30.70-0.07, G30.76-0.05, G31.28+0.06, G32.03+0.06, and\nG69.52-0.97. We detected a total of 209 masers, 15% of which show linearly\npolarized emission (0.07%-16.7%), and 2% of which show circularly polarized\nemission (0.2%-4.2%). Zeeman splitting was measured toward G30.70-0.07,\nG32.03+0.06, and G69.52-0.97. The statistical analysis of the entire\nflux-limited sample shows that the observations are consistent with a bimodal\ndistribution in the difference between the 3D magnetic field direction and the\noutflow axis, with half the magnetic field directions being perpendicular and\nthe other half being parallel to the outflow. In addition, we determined that\ntypical values of the linear and circular polarization fractions for 6.7 GHz\nCH3OH masers are Pl=1.0%-2.5% and Pv=0.5%-0.75%, respectively. We found that a\ntypical Zeeman splitting is in the range between 0.5 m/s and 2.0 m/s. This\nwould correspond to 9 mG<$|B_{||}|$<40 mG if F=3->4 is the most favored\nhyperfine transition.", "category": "astro-ph_GA" }, { "text": "A rogues gallery of Andromeda's dwarf galaxies II. Precise Distances to\n 17 Faint Satellites: We present new horizontal branch (HB) distance measurements to 17 of the\nfaintest known M31 satellites ($-6 \\lesssim M_{V} \\lesssim -13$) based on deep\nHubble Space Telescope (HST) imaging. The color-magnitude diagrams extend\n$\\sim$1-2 magnitudes below the HB, which provides for well-defined HBs, even\nfor faint galaxies in which the tip of the red giant branch (TRGB) is sparsely\npopulated. We determine distances across the sample to an average precision of\n4% ($\\sim 30$~kpc at $800$~kpc). We find that the majority of these galaxies\nare in good agreement, though slightly farther (0.1-0.2 mag) when compared to\nrecent ground-based TRGB distances. Two galaxies (And~IX and And~XVII) have\ndiscrepant HST and ground-based distances by $\\sim 0.3$ mag ($\\sim 150$~kpc),\nwhich may be due to contamination from Milky Way foreground stars and/or M31\nhalo stars in sparsely populated TRGB regions. We use the new distances to\nupdate the luminosities and structural parameters for these 17 M31 satellites.\nThe new distances do not substantially change the spatial configuration of the\nM31 satellite system. We comment on future prospects for precise and accurate\nHB distances for faint galaxies in the Local Group and beyond.", "category": "astro-ph_GA" }, { "text": "Analysing surveys of our Galaxy I: basic astrometric data: We consider what is the best way to extract science from large surveys of the\nMilky Way galaxy. The diversity of data gathered in these surveys, together\nwith our position within the Galaxy, imply that science must be extracted by\nfitting dynamical models to the data in the space of the observables. Models\nbased on orbital tori promise to be superior for this task than traditional\ntypes of models, such as N-body models and Schwarzschild models. A formalism\nthat allows such models to be fitted to data is developed and tested on\npseudodata of varying richness.", "category": "astro-ph_GA" }, { "text": "Age bimodality in the central region of pseudobulges in S0 galaxies: We present evidence for bimodal stellar age distribution of pseudobulges of\nS0 galaxies as probed by the $D_n(4000)$ index. We do not observe any\nbimodality in age distribution for pseudobulges in spiral galaxies. Our sample\nis flux limited and contains 2067 S0 and 2630 spiral galaxies drawn from the\nSloan Digital Sky Survey. We identify pseudobulges in S0 and spiral galaxies,\nbased on the position of the bulge on the Kormendy diagram and their central\nvelocity dispersion. Dividing the pseudobulges of S0 galaxies into those\ncontaining old and young stellar populations, we study the connection between\nglobal star formation and pseudobulge age on the $u-r$ color-mass diagram. We\nfind that most old pseudobulges are hosted by passive galaxies while majority\nof young bulges are hosted by galaxies which are star forming. Dividing our\nsample of S0 galaxies into early-type S0s and S0/a galaxies, we find that old\npseudobulges are mainly hosted by early-type S0 galaxies while most of the\npseudobulges in S0/a galaxies are young. We speculate that morphology plays a\nstrong role in quenching of star formation in the disc of these S0 galaxies,\nwhich stops the growth of pseudobulges, giving rise to old pseudobulges and the\nobserved age bimodality.", "category": "astro-ph_GA" }, { "text": "Chemical abundances of giant stars in the Crater stellar system: We obtained spectra for two giants of Crater (Crater J113613-105227 and\nCrater J113615-105244) using X-Shooter at the VLT. The spectra have been\nanalysed with the MyGIsFoS code using a grid of synthetic spectra computed from\none dimensional, Local Thermodynamic Equilibrium (LTE) model atmospheres.\nEffective temperature and surface gravity have been derived from photometry\nmeasured from images obtained by the Dark Energy Survey. The radial velocities\nare 144.3+-4.0 km/s for Crater J113613-105227 and and 134.1+-4.0 km/s for\nCrater J113615-105244. The metallicities are [Fe/H]=-1.73 and [Fe/H]=-1.67,\nrespectively. Beside the iron abundance we could determine abundances for nine\nelements: Na, Mg, Ca, Ti, V, Cr, Mn, Ni and Ba. For Na and Ba we took into\naccount deviations from LTE, since the corrections are significant. The\nabundance ratios are similar in the two stars and resemble those of Galactic\nstars of the same metallicity. On the deep photometric images we could detect\nseveral stars that lie to the blue of the turn-off. conclusions heading\n(optional), leave it empty if necessary The radial velocities imply that both\nstars are members of the Crater stellar system. The difference in velocity\nbetween the two taken at face value, implies a velocity dispersion > 3.7 km/s\nat 95% confidence level. Our spectroscopic metallicities are in excellent\nagreement with that determined by previous investigations using photometry. Our\ndeep photometry and the spectroscopic metallicity imply an age of 7 Gyr for the\nmain population of the system. The stars to the blue of the turn-off can be\ninterpreted as a younger population, of the same metallicity and an age of 2.2\nGyr. Finally, spatial and kinematical parameters support the idea that this\nsystem is associated to the galaxies Leo~IV and Leo~V. All the observations\nfavour the interpretation of Crater as a dwarf galaxy. (Abridged).", "category": "astro-ph_GA" }, { "text": "Long period variable stars in NGC 147 and NGC 185. I. Their star\n formation histories: NGC 147 and NGC 185 are two of the most massive satellites of the Andromeda\ngalaxy (M 31). Close together in the sky, of similar mass and morphological\ntype dE, they possess different amounts of interstellar gas and tidal\ndistortion. The question therefore is, how do their histories compare? Here we\npresent the first reconstruction of the star formation histories of NGC 147 and\nNGC 185 using long-period variable stars. These represent the final phase of\nevolution of low- and intermediate-mass stars at the asymptotic giant branch,\nwhen their luminosity is related to their birth mass. Combining near-infrared\nphotometry with stellar evolution models, we construct the mass function and\nhence the star formation history. For NGC 185 we found that the main epoch of\nstar formation occurred 8.3 Gyr ago, followed by a much lower, but relatively\nconstant star formation rate. In the case of NGC 147, the star formation rate\npeaked only 7 Gyr ago, staying intense until ~ 3 Gyr ago, but no star formation\nhas occurred for at least 300 Myr. Despite their similar masses, NGC 147 has\nevolved more slowly than NGC 185 initially, but more dramatically in more\nrecent times. This is corroborated by the strong tidal distortions of NGC 147\nand the presence of gas in the centre of NGC 185.", "category": "astro-ph_GA" }, { "text": "Redshift and stellar mass dependence of intrinsic shapes of\n disc-dominated galaxies from COSMOS observations below $z = 1.0$: The high abundance of disc galaxies without a large central bulge challenges\npredictions of current hydrodynamic simulations of galaxy formation. We aim to\nshed light on the formation of these objects by studying the redshift and mass\ndependence of their intrinsic 3D shape distributions in the COSMOS galaxy\nsurvey below redshift $z=1.0$. This distribution is inferred from the observed\ndistribution of 2D shapes, using a reconstruction method which we test using\nhydrodynamic simulations. Our tests reveal a moderate bias for the inferred\naverage disc circularity and relative thickness, but a large bias on the\ndispersion of these quantities. Applying the reconstruction method on COSMOS\ndata, we find variations of the average disc circularity and relative thickness\nwith redshift of around $\\sim1\\%$ and $\\sim10\\%$ respectively, which is\ncomparable to the error estimates on these quantities. The average relative\ndisc thickness shows a significant mass dependence which can be accounted for\nby the scaling of disc radius with galaxy mass. We conclude that our data\nprovides no evidence for a strong dependence of the average circularity and\nabsolute thickness of disc-dominated galaxies on redshift and mass that is\nsignificant with respect to the statistical uncertainties in our analysis.\nThese findings are expected in the absence of disruptive merging or feedback\nevents that would affect galaxy shapes. They hence support a scenario where\npresent-day discs form early ($z>1.0$) and subsequently undergo a tranquil\nevolution in isolation. However, more data and a better understanding of\nsystematics are needed to reaffirm our results.", "category": "astro-ph_GA" }, { "text": "Molecular cloud determination in the Northern Galactic Plane: The Exeter FCRAO CO Galactic Plane Survey consists of 12CO and 13CO (J=1-0)\nobservations over the galactic plane covering 55 degrees <= l <= 102 degrees,\n|b| >= 1 degree and 141 degrees <= l <= 195 degrees, -3.5 degrees <= b <= 5.5\ndegrees with a spatial resolution of ~45\" and a spectral resolution of\n~0.15km/s. We will present the methodology of a threshold-based cloud and clump\ndetermination method which retains hierarchical information, then discuss\nassociating sources with clouds in the catalogue. Once complete, this catalogue\nof clouds and clumps will encompass the majority of the Northern Galactic\nPlane, providing knowledge of the molecular structure of the galaxy and the\nstarting point for studies of the variation in star formation efficiency. In\naddition, it will allow us to identify clouds that have no or little star\nformation taking place inside them, which are often overlooked in the study of\nthe conditions required for star formation to take place.", "category": "astro-ph_GA" }, { "text": "Extremely Low Molecular Gas Content in the Vicinity of a Red Nugget\n Galaxy at $z=1.91$: We present Atacama Large Millimeter/submillimeter Array (ALMA) Band 5\nobservations of a galaxy at $z=1.91$, GDS24569, in search of molecular gas in\nits vicinity via the [C I] $^3$P$_1$-$^3$P$_0$ line. GDS24569 is a massive\n($\\log M_*/M_\\odot=11$) passively evolving galaxy, and characterized by compact\nmorphology with an effective radius of $\\sim0.5$ kpc. We apply two blind\ndetection algorithms to the spectral data cubes, and find no promising\ndetection in or around GDS24569 out to projected distance of $\\sim320$ kpc,\nwhile a narrow tentative line ($4.1 \\sigma$) is identified at $+1200$ km/s by\none of the algorithms. From the non-detection of [C I], we place a $3\\sigma$\nupper limit on molecular hydrogen mass, $\\sim 7.1 \\times 10^9 M_\\odot$, which\nconverts to an extremely low gas-to-stellar mass fraction, $< 5 \\%$. We conduct\na spectral energy distribution modeling by including optical-to-far-infrared\ndata, and find a considerably high ($\\sim0.1\\%$) dust-to-stellar mass ratio,\n$\\sim10$-$100\\times$ higher than those of local early-type galaxies. In\ncombination with a previous result of an insufficient number of surrounding\nsatellite galaxies, it is suggested that GDS24569 is unlikely to experience\nsignificant size evolution via satellite mergers. We discuss possible physical\nmechanisms that quenched GDS24569.", "category": "astro-ph_GA" }, { "text": "Dust Reverberation Mapping of Z229-15: We report results of the dust reverberation mapping (DRM) on the Seyfert 1\ngalaxy Z229-15 at z = 0.0273. Quasi-simultaneous photometric observations for a\ntotal of 48 epochs were acquired during the period 2017 July to 2018 December\nin B, V, J, H and Ks bands. The calculated spectral index ({\\alpha}) between B\nand V bands for each epoch was used to correct for the accretion disk (AD)\ncomponent present in the infrared light curves. The observed {\\alpha} ranges\nbetween -0.99 and 1.03. Using cross correlation function analysis we found\nsignificant time delays between the optical V and the AD corrected J, H and Ks\nlight curves. The lags in the rest frame of the source are 12.52 (+10.00/-9.55)\ndays (between V and J), 15.63 (+5.05/-5.11) days (between V and H) and 20.36\n(+5.82/-5.68) days (between V and Ks). Given the large error bars, these lags\nare consistent with each other. However, considering the lag between V and Ks\nbands to represent the inner edge of the dust torus, the torus in Z229-15 lies\nat a distance of 0.017 pc from the central ionizing continuum. This is smaller\nthan that expected from the radius luminosity (R-L) relationship known from\nDRM. Using a constant {\\alpha} = 0.1 to account for the AD component, as is\nnormally done in DRM, the deduced radius (0.025 pc) lies close to the expected\nR-L relation. However, usage of constant {\\alpha} in DRM is disfavoured as the\n{\\alpha} of the ionizing continuum changes with the flux of the source.", "category": "astro-ph_GA" }, { "text": "The formation and evolution of Andromeda IX: Local Group (LG), the nearest and most complete galactic environment,\nprovides valuable information on the formation and evolution of the Universe.\nStudying galaxies of different sizes, morphologies, and ages can provide this\ninformation. For this purpose, we chose the And\\,IX dSph galaxy, which is one\nof the observational targets of the Isaac Newton Telescope (INT) survey. A\ntotal of 50 long-period variables (LPVs) were found in And\\,IX in two filters,\nSloan $i'$ and Harris $V$ at a half-light radius of 2.5 arcmin. The And\\,IX's\nstar formation history (SFH) was constructed with a maximum star formation rate\n(SFR) of about $0.00082\\pm0.00031$ M$_\\odot$ yr$^{-1}$, using LPVs as a tracer.\nThe total mass return rate of LPVs was calculated based on the spectral energy\ndistribution (SED) of about $2.4\\times10^{-4}$ M$_\\odot$ yr$^{-1}$. The\ndistance modulus of $24.56_{-0.15}^{+0.05}$ mag was estimated based on the tip\nof the red giant branch (TRGB).", "category": "astro-ph_GA" }, { "text": "The Si+SO$_2$ collision and an extended network of neutral-neutral\n reactions between silicon and sulphur bearing species: The Si+SO$_2$ reaction is investigated to verify its impact on the abundances\nof molecules with astrochemical interest, such as SiS, SiO, SO and others.\nAccording to our results Si($^3$P) and SO$_2$ react barrierlessly yielding only\nthe monoxides SO and SiO as products. No favourable pathway has been found\nleading to other products, and this reaction should not contribute to SiS\nabundance. Furthermore, it is predicted that SiS is stable in collisions with\nO$_2$, and that S($^3$P)+SiO$_2$ and O($^3$P)+OSiS will also produce SO+SiO.\nUsing these results and gathering further experimental and computational data\nfrom the literature, we provide an extended network of neutral-neutral\nreactions involving Si- and S-bearing molecules. The effects of these reactions\nwere examined in a protostellar shock model, using the Nautilus gas-grain code.\nThis consisted in simulating the physicochemical conditions of a shocked gas\nevolving from $i.$ primeval cold core, $ii.$ the shock region itself, $iii.$\nand finally the gas bulk conditions after the passage of the shock. Emphasising\non the cloud ages and including systematically these chemical reactions, we\nfound that [SiS/H$_2$] can be of the order of $\\sim$ 10$^{-8}$ in shocks that\nevolves from clouds of $t=1\\times 10^6$ yr, whose values are mostly affected by\nthe SiS+O $\\longrightarrow$SiO+S reaction. Perspectives on further models along\nwith observations are discussed in the context of sources harbouring molecular\noutflows.", "category": "astro-ph_GA" }, { "text": "The SSA22 HI Tomography Survey (SSA22-HIT). I. Data Set and Compiled\n Redshift Catalog: We conducted a deep spectroscopic survey, named SSA22-HIT, in the SSA22 field\nwith the DEep Imaging MultiObject Spectrograph (DEIMOS) on the Keck telescope,\ndesigned to tomographically map high-z HI gas through analysis of Lya\nabsorption in background galaxies' spectra. In total, 198 galaxies were\nspectroscopically confirmed at 2.5 < z < 6 with a few low-z exceptions in the\n26 x 15 arcmin^2 area, of which 148 were newly determined in this study. Our\nredshift measurements were merged with previously confirmed redshifts available\nin the 34 x 27 arcmin^2 area of the SSA22 field. This compiled catalog\ncontaining 730 galaxies of various types at z > 2 is useful for various\napplications, and it is made publicly available. Our SSA22-HIT survey has\nincreased by approximately twice the number of spectroscopic redshifts of\nsources at z > 3.2 in the observed field. From a comparison with publicly\navailable redshift catalogs, we show that our compiled redshift catalog in the\nSSA22 field is comparable to those among major extragalactic survey fields in\nterms of a combination of wide area and high surface number density of objects\nat z > 2. About 40 % of the spectroscopically confirmed objects in SSA22-HIT\nshow reasonable quality of spectra in the wavelengths shorter than Lya when a\nsufficient amount of smoothing is adopted. Our data set enables us to make the\nHI tomographic map at z > 3, which we present in a parallel study.", "category": "astro-ph_GA" }, { "text": "A Census of Protostellar Outflows in Nearby Molecular Clouds: We adopt the deep learning method CASI-3D (Convolutional Approach to\nStructure Identification-3D) to systemically identify protostellar outflows in\n12CO and 13CO observations of the nearby molecular clouds, Ophiuchus, Taurus,\nPerseus and Orion. The total outflow masses are 267 Msun, 795 Msun, 1305 Msun\nand 6332 Msun for Ophiuchus, Taurus, Perseus and Orion, respectively. We show\nthe outflow mass in each cloud is linearly proportional to the total number of\nyoung stellar objects. The estimated total 3D deprojected outflow energies are\n9e45 ergs, 6e46 ergs, 1.2e47 ergs and 6e47 ergs for Ophiuchus, Taurus, Perseus\nand Orion, respectively. The energy associated with outflows is sufficient to\noffset turbulent dissipation at the current epoch for all four clouds. All\nclouds also exhibit a break point in the spatial power spectrum of the outflow\nprediction map, which likely corresponds to the typical outflow mass and energy\ninjection scale.", "category": "astro-ph_GA" }, { "text": "ALMA-IMF. V. Prestellar and protostellar core populations in the W43\n cloud complex: The origin of the stellar initial mass function (IMF) and its relation with\nthe core mass function (CMF) are actively debated issues with important\nimplications in astrophysics. Recent observations in the W43 molecular complex\nof top-heavy CMFs, with an excess of high-mass cores compared to the canonical\nmass distribution, raise questions about our understanding of the star\nformation processes and their evolution in space and time. We aim to compare\npopulations of protostellar and prestellar cores in three regions imaged in the\nALMA-IMF Large Program. We created an homogeneous core catalogue in W43,\ncombining a new core extraction in W43-MM1 with the catalogue of W43-MM2&MM3\npresented in a previous work. Our detailed search for protostellar outflows\nenabled us to identify between 23 and 30 protostellar cores out of 127 cores in\nW43-MM1 and between 42 and 51 protostellar cores out of 205 cores in\nW43-MM2&MM3. Cores with neither outflows nor hot core emission are classified\nas prestellar candidates. We found a similar fraction of cores which are\nprotostellar in the two regions, about 35%. This fraction strongly varies in\nmass, from 15-20% at low mass, between 0.8 and 3$M_{\\odot} $ up to about 80%\nabove 16$M_{\\odot}$. Protostellar cores are found to be, on average, more\nmassive and smaller in size than prestellar cores. Our analysis also revealed\nthat the high-mass slope of the prestellar CMF in W43,\n$\\alpha=-1.46_{-0.19}^{+0.12}$, is consistent with the Salpeter slope, and thus\nthe top-heavy form measured for the global CMF, $\\alpha=-0.96$, is due to the\nprotostellar core population. Our results could be explained by clump-fed\nmodels in which cores grow in mass, especially during the protostellar phase,\nthrough inflow from their environment. The difference between the slopes of the\nprestellar and protostellar CMFs moreover implies that high-mass cores grow\nmore in mass than low-mass cores.", "category": "astro-ph_GA" }, { "text": "The Evolution of Magellanic-like Galaxy Pairs and The Production of\n Magellanic Stream Analogues in Simulations with Tides, Ram Pressure, and\n Stellar Feedback: We present a series of chemodynamical simulations of Magellanic-like systems\nconsisting of two interacting, equal-mass dwarf galaxies orbiting a massive\nhost galaxy, including feedback and star formation, tides, and ram pressure. We\nstudy the star formation and chemical enrichment history of the dwarfs, and the\nproduction of a Magellanic Stream analogue. The dwarfs interact with each other\nthrough tidal forces, distorting their morphologies and triggering star\nformation. A stream is naturally produced as outflows, induced by feedback and\ninteractions, are stretched by tidal forces. Counter to some recent\nsimulations, we find that the leading arm persists even in the presence of ram\npressure from the host galaxy. Interactions between the dwarfs and the host\ngalaxies produce multiple kinematic components in the stream, as observed. A\ncombination of ongoing star-formation and entrained low-metallicity gas causes\nthe stream to have a complex chemical structure, with an average metallicity\nthat is generally lower than that of the dwarfs.", "category": "astro-ph_GA" }, { "text": "Surface Brightness Evolution of Galaxies in the CANDELS GOODS Fields up\n to $z \\sim 6$: High-z Galaxies are Unique or Remain Undetected: We investigate the rest-frame Ultraviolet (UV, $\\lambda\\sim2000$\\AA) surface\nbrightness (SB) evolution of galaxies up to $z\\sim6$ using a variety of deep\nHubble Space Telescope imaging. UV SB is a measure of the density of emission\nfrom mostly young stars and correlates with an unknown combination of star\nformation rate, initial mass function, cold gas mass density, dust attenuation,\nand the size evolution of galaxies. In addition to physical effects, the SB is,\nunlike magnitude, a more direct way in which a galaxy's detectability is\ndetermined. We find a very strong evolution in the intrinsic SB distribution\nwhich declines as $(1+z)^{3}$, decreasing by 4-5 mag arcsec$^{-2}$ between\n$z=6$ to $z=1$. This change is much larger than expected in terms of the\nevolution in UV luminosity, sizes or dust extinction and we demonstrate that\nthis evolution is 'unnatural' and due to selection biases. We also find no\nstrong correlation between mass and UV SB. Thus, deep HST imaging is unable to\ndiscover all of the most massive galaxies in the distant universe. Through\nsimulations we show that only $\\sim15$\\% of galaxies that we can detect at\n$z=2$ would be detected at high-$z$. We furthermore explore possible origins of\nhigh SB galaxies at high-$z$ by investigating the relationship between\nintrinsic SB and star formation rates. We conclude that ultra-high SB galaxies\nare produced by very gas rich dense galaxies which are in a unique phase of\nevolution, possibly produced by mergers. Analogues of such galaxies do not\nexist in the relatively nearby universe.", "category": "astro-ph_GA" }, { "text": "Stellar Mass Black Holes in Young Galaxies: We explore the potential cumulative energy production of stellar mass black\nholes in early galaxies. Stellar mass black holes may accrete substantially\nfrom the higher density interstellar media of primordial galaxies, and their\nenergy release would be distributed more uniformly over the galaxy, perhaps\nproviding a different mode of energy feedback into young galaxies than central\nsupermassive black holes. We construct a model for the production and growth of\nstellar mass black holes over the first few gigayears of a young galaxy. With\nthe simplifying assumption of a constant density of the ISM, n ~ 10^4 - 10^5\nper cubic centimeter, we estimate the number of accreting stellar mass black\nholes to be ~ 10^6 and the potential energy production to be as high as 10^61\nergs over several billion years. For densities less than 10^5 per cubic\ncentimeter, stellar mass black holes are unlikely to reach their Eddington\nlimit luminosities. The framework we present could be incorporated in numerical\nsimulations to compute the feedback from stellar-mass black holes with\ninhomogeneous, evolving interstellar media.", "category": "astro-ph_GA" }, { "text": "What determines the formation and characteristics of protoplanetary\n discs?: Planets form in protoplanetary discs. Their masses, distribution, and orbits\nsensitively depend on the structure of the protoplanetary discs. However, what\nsets the initial structure of the discs in terms of mass, radius and accretion\nrate is still unknown. We perform non-ideal MHD numerical simulations using the\nadaptive mesh refinement code Ramses, of a collapsing, one solar mass,\nmolecular core to study the disc formation and early, up to 100 kyr, evolution,\npaying great attention to the impact of numerical resolution and accretion\nscheme. We found that while the mass of the central object is almost\nindependent of the numerical parameters such as the resolution and the\naccretion scheme onto the sink particle, the disc mass, and to a lower extent\nits size, heavily depend on the accretion scheme, which we found, is itself\nresolution dependent. This implies that the accretion onto the star and through\nthe disc are largely decoupled. For a relatively large domain of initial\nconditions (except at low magnetisation), we found that the properties of the\ndisc do not change too significantly. In particular both the level of initial\nrotation and turbulence do not influence the disc properties provide the core\nis sufficiently magnetized. After a short relaxation phase, the disc settles in\na stationary state. It then slowly grows in size but not in mass. The disc\nitself is weakly magnetized but its immediate surrounding is on the contrary\nhighly magnetized. Our results show that the disc properties directly depend on\nthe inner boundary condition, i.e. the accretion scheme onto the central\nobject, suggesting that the disc mass is eventually controlled by the small\nscale accretion process, possibly the star-disc interaction. Because of\nambipolar diffusion and its significant resistivity, the disc diversity remains\nlimited and except for low magnetisation, their properties are (abridged).", "category": "astro-ph_GA" }, { "text": "New Optical Reddening Maps of the Large and Small Magellanic Clouds: We present new reddening maps of the SMC and LMC based on the data of the\nthird phase of the Optical Gravitational Lensing Experiment (OGLE III). We have\nused two different methods to derive optical reddening maps. We adopt a\ntheoretical mean unreddened colour for the red clump in the SMC and LMC,\nrespectively. We subdivide the photometric data for both Clouds into subfields\nand calculate the difference between the observed red clump position and the\ntheoretical value for each field, which provides us with the reddening value in\n(V-I). Furthermore reddening values are obtained for 13490 LMC RR Lyrae ab and\n1529 SMC RR Lyrae ab stars covering the whole OGLE III region of the MCs. The\nobserved colours (V-I) of the RR Lyrae stars are compared with the colour from\nthe absolute magnitudes. The absolute magnitude of each RR Lyrae star is\ncomputed using its period and metallicity derived from Fourier decomposition of\nits lightcurve. In general we find a low and uniform reddening distribution in\nboth Magellanic Clouds. The red clump method indicates a mean reddening of the\nLMC of E(V-I) = 0.09 +/- 0.07 mag, while for the SMC E(V-I) = 0.04 +/- 0.06 mag\nis obtained. With RR Lyrae stars a median value of E(V-I) = 0.11 +/- 0.06 mag\nfor the LMC and E(V-I) = 0.07 +/- 0.06 mag for the SMC is found. The LMC shows\nvery low reddening in the bar region, whereas the reddening in the star-forming\nleading edge and 30 Doradus is considerably higher. In the SMC three pronounced\nregions with higher reddening are visible. Two are located along the bar, while\nthe highest reddening is found in the star-forming wing of the SMC. In general\nthe regions with higher reddening are in good spatial agreement with infrared\nreddening maps as well as with reddening estimations of other studies. The\nposition-dependent reddening values from the red clump method are available via\nthe Virtual Observatory interface.", "category": "astro-ph_GA" }, { "text": "Constraining the physical properties of the first lensed $z\\sim10-16$\n galaxy candidates with JWST: The first deep-field observations of the JWST have immediately yielded a\nsurprisingly large number of very high redshift candidates, pushing the\nfrontier of observability well beyond $z\\gtrsim10$. We here present a detailed\nSED-fitting analysis of the 15 gravitationally lensed $z\\sim10-16$ galaxy\ncandidates detected behind the galaxy cluster SMACS J0723.3-7327 in Atek et al.\n(2022) using the BEAGLE tool. Our analysis makes use of dynamical\nconsiderations to place limits on the ages of these galaxies and of all three\npublished SL models of the cluster to account for lensing systematics. We find\nthese galaxies to have relatively low stellar masses\n$M_{\\star}\\sim10^7-10^8\\,\\mathrm{M}_{\\odot}$ and young ages\n$t_{\\mathrm{age}}\\sim10-100$\\,Myr. Due to their very blue UV-slopes, down to\n$\\beta\\sim-3$, all of the galaxies in our sample have extremely low dust\nattenuations $A_V\\lesssim0.02$. Placing the measured parameters into relation,\nwe find a very shallow $M_{\\star}-M_{\\mathrm{UV}}$-slope and high sSFRs above\nthe main sequence of star-formation with no significant redshift-evolution in\neither relation. This is in agreement with the bright UV luminosities measured\nfor these objects and indicates that we are naturally selecting galaxies that\nare currently undergoing a star-bursting episode at the time they are observed.\nFinally, we discuss the robustness of our high-redshift galaxy sample regarding\nlow-redshift interlopers and conclude that low-redshift solutions can safely be\nruled out for roughly half of the sample, including the highest-redshift\ngalaxies at $z\\sim12-16$. These objects represent compelling targets for\nspectroscopic follow-up observations with JWST and ALMA.", "category": "astro-ph_GA" }, { "text": "Spectroscopic investigation of a reionized galaxy overdensity at z=7: We present deep spectroscopic follow-up observations of the Bremer Deep Field\n(BDF) where the two $z\\sim$7 bright Ly$\\alpha$ emitters (LAE) BDF521 and\nBDF3299 were previously discovered by Vanzella et al. (2011) and where a factor\nof $\\sim$3-4 overdensity of faint LBGs has been found by Castellano et al.\n(2016). We confirm a new bright Ly$\\alpha$ emitter, BDF2195, at the same\nredshift of BDF521, $z=7.008$, and at only $\\sim$90 kpc physical distance from\nit, confirming that the BDF area is likely an overdense, reionized region. A\nquantitative assessment of the Ly$\\alpha$ fraction shows that the number of\ndetected bright emitters is much higher than the average found at z$\\sim$7,\nsuggesting a high Ly$\\alpha$ transmission through the inter-galactic medium\n(IGM). However, the line visibility from fainter galaxies is at odds with this\nfinding, since no Ly$\\alpha$ emission is found in any of the observed\ncandidates with $M_{UV}>$-20.25. This discrepancy can be understood either if\nsome mechanism prevents Ly$\\alpha$ emission from fainter galaxies within the\nionized bubbles from reaching the observer, or if faint galaxies are located\noutside the reionized area and bright LAEs are solely responsible for the\ncreation of their own HII regions. A thorough assessment of the nature of the\nBDF region and of its sources of re-ionizing radiation will be made possible by\nJWST spectroscopic capabilities.", "category": "astro-ph_GA" }, { "text": "The Stellar-to-Halo Mass Ratios of Passive and Star-Forming Galaxies at\n z~2-3 from the SMUVS survey: In this work, we use measurements of galaxy stellar mass and two-point\nangular correlation functions to constrain the stellar-to-halo mass ratios\n(SHMRs) of passive and \\np\\ galaxies at $z\\sim2-3$, as identified in the\n\\emph{Spitzer} Matching Survey of the UltraVISTA ultra-deep Stripes (SMUVS). We\nadopt a sophisticated halo modeling approach to statistically divide our two\npopulations into central and satellite galaxies. For central galaxies, we find\nthat the normalization of the SHMR is greater for our passive population.\nThrough the modeling of $\\Lambda$ cold dark matter halo mass accretion\nhistories, we show that this can only arise if the conversion of baryons into\nstars was more efficient at higher redshifts and additionally that passive\ngalaxies can be plausibly explained as residing in halos with the highest\nformation redshifts (i.e., those with the lowest accretion rates) at a given\nhalo mass. At a fixed stellar mass, satellite galaxies occupy host halos with a\ngreater mass than central galaxies, and we find further that the fraction of\npassive galaxies that are satellites is higher than for the combined\npopulation. This, and our derived satellite quenching timescales, combined with\nearlier estimates from the literature, support dynamical/environmental\nmechanisms as the dominant process for satellite quenching at $z\\lesssim3$.", "category": "astro-ph_GA" }, { "text": "Modelling the CO streamers in the explosive ejection of Orion BN/KL\n region: We present reactive gasdynamic, axisymmetric simulations of dense, high\nvelocity clumps for modelling the CO streamers observed in Orion BN/KL. We have\nconsidered 15 chemical species, a cooling function for atomic and molecular\ngas, and heating through cosmic rays. Our numerical simulations explore\ndifferent ejection velocities, interstellar medium density configurations, and\nCO content. Using the CO density and temperature, we have calculated the CO\n($J=2\\to1$) emissivity, and have built CO maps and spatially resolved line\nprofiles, allowing us to see the CO emitting regions of the streamers and to\nobtain position velocity diagrams to compare with observations. We find that in\norder to reproduce the images and line profiles of the BN/KL CO streamers and\nH$_2$ fingers, we need to have clumps that first travel within a dense cloud\ncore, and then emerge into a lower-density environment.", "category": "astro-ph_GA" }, { "text": "Recognizing Blazars Using Radio Morphology from the VLA Sky Survey: Blazars are radio-loud Active Galactic Nuclei (AGN) whose jets have a very\nsmall angle to our line of sight. Observationally, the radio emission are\nmostly compact or a compact-core with a 1-sided jet. With 2.5$^{\\prime\\prime}$\nresolution at 3 GHz, the Very Large Array Sky Survey (VLASS) enables us to\nresolve the structure of some blazar candidates in the sky north of Decl. $-40$\ndeg. We introduce an algorithm to classify radio sources as either blazar-like\nor non-blazar-like based on their morphology in the VLASS images. We apply our\nalgorithm to three existing catalogs, including one of known blazars\n(Roma-BzCAT) and two of blazar candidates identified by WISE colors and radio\nemission (WIBRaLS, KDEBLLACS). We show that in all three catalogs, there are\nobjects with morphology inconsistent with being blazars. Considering all the\ncatalogs, more than 12% of the candidates are unlikely to be blazars, based on\nthis analysis. Notably, we show that 3% of the Roma-BzCAT \"confirmed\" blazars\ncould be a misclassification based on their VLASS morphology. The resulting\ntable with all sources and their radio morphological classification is\navailable online.", "category": "astro-ph_GA" }, { "text": "Probing the initial conditions of high-mass star formation -- IV. Gas\n dynamics and NH$_2$D chemistry in high-mass precluster and protocluster\n clumps: The initial stage of star formation is a complex area study because of its\nhigh density and low temperature. Under such conditions, many molecules become\ndepleted from the gas phase by freezing out onto dust grains. However, the\ndeuterated species could remain gaseous and are thus ideal tracers. We\ninvestigate the gas dynamics and NH$_2$D chemistry in eight massive\npre/protocluster clumps. We present NH$_2$D 1$_{11}$-1$_{01}$ (at 85.926 GHz),\nNH$_3$ (1, 1) and (2, 2) observations in the eight clumps using the PdBI and\nthe VLA, respectively. We find that the distribution between deuterium\nfractionation and kinetic temperature shows a number density peak at around\n$T_{\\rm kin}=16.1$ K, and the NH$_2$D cores are mainly located at a temperature\nrange of 13.0 to 22.0 K. We detect seven instances of extremely high deuterium\nfractionation of $1.0 \\leqslant D_{\\rm frac} \\leqslant 1.41$. We find that the\nNH$_2$D emission does not appear to coincide exactly with either dust continuum\nor NH$_3$ peak positions, but often surrounds the star-formation active\nregions. This suggests that the NH$_{2}$D has been destroyed by the central\nyoung stellar object (YSO) due to its heating. The detected NH$_2$D lines are\nvery narrow with a median width of $\\rm 0.98\\pm0.02 km/s$. The extracted\nNH$_2$D cores are gravitationally bound ($\\alpha_{\\rm vir} < 1$), are likely\nprestellar or starless, and can potentially form intermediate-mass or high-mass\nstars. Using NH$_3$ (1, 1) as a dynamical tracer, we find very complicated\ndynamical movement, which can be explained by a combined process with outflow,\nrotation, convergent flow, collision, large velocity gradient, and rotating\ntoroids. High deuterium fractionation strongly depends on the temperature\ncondition. NH$_2$D is a poor evolutionary indicator of high-mass star formation\nin evolved stages, but a useful tracer in the starless and prestellar cores.", "category": "astro-ph_GA" }, { "text": "The numbers of z~2 star-forming and passive galaxies in 2.5 square\n degrees of deep CFHT imaging: We use an adaptation of the BzKs technique to select ~40,000 z~2 galaxies (to\nK(AB) = 24), including ~5,000 passively evolving (PE) objects (to K(AB) = 23),\nfrom 2.5 deg^2 of deep CFTH imaging. The passive galaxy luminosity function\nexhibits a clear peak at R = 22 and a declining faint-end slope ({\\alpha} = -\n0.12 [+0.16 -0.14]),while that of star-forming galaxies is characterized by a\nsteep faint-end slope ({\\alpha} = -1.43 +- [0.02] (systematic) [+0.05 -0.04]\n(random)). The details of the LFs are somewhat sensitive (at <25% level) to\ncosmic variance even in these large(~0.5 deg^2) fields, with the D2 field\n(located in the COSMOS field) most discrepant from the mean. The shape of the z\n~ 2 stellar mass function of passive galaxies is remarkably similar to that at\nz ~ 0.9, save for a factor of ~4 lower number density. This similarity suggests\nthat the same mechanism may be responsible for the formation of passive\ngalaxies seen at both these epochs. This same formation mechanism may also\noperate down to z ~ 0 if the local PE galaxy mass function, known to be\ntwo-component, contains two distinct galaxy populations. This scenario is\nqualitatively in agreement with recent phenomenological mass-quenching models\nand extends them to span more than three quarters of the history of the\nUniverse.", "category": "astro-ph_GA" }, { "text": "The dragonfly nearby galaxies survey. Iv. A giant stellar disk in ngc\n 2841: Neutral gas is commonly believed to dominate over stars in the outskirts of\ngalaxies, and investigations of the disk-halo interface are generally\nconsidered to be in the domain of radio astronomy. This may simply be a\nconsequence of the fact that deep HI observations typically probe to a lower\nmass surface density than visible wavelength data. This paper presents low\nsurface brightness optimized visible wavelength observations of the extreme\noutskirts of the nearby spiral galaxy NGC 2841. We report the discovery of an\nenormous low-surface brightness stellar disk in this object. When azimuthally\naveraged, the stellar disk can be traced out to a radius of $\\sim$70 kpc (5\n$R_{25}$ or 23 inner disk scale lengths). The structure in the stellar disk\ntraces the morphology of HI emission and extended UV emission. Contrary to\nexpectations, the stellar mass surface density does not fall below that of the\ngas mass surface density at any radius. In fact, at all radii greater than\n$\\sim$20 kpc, the ratio of the stellar to gas mass surface density is a\nconstant 3:1. Beyond $\\sim$30 kpc, the low surface brightness stellar disk\nbegins to warp, which may be an indication of a physical connection between the\noutskirts of the galaxy and infall from the circumgalactic medium. A\ncombination of stellar migration, accretion and in-situ star formation might be\nresponsible for building up the outer stellar disk, but whatever mechanisms\nformed the outer disk must also explain the constant ratio between stellar and\ngas mass in the outskirts of this galaxy.", "category": "astro-ph_GA" }, { "text": "Toward an Empirical Theory of Pulsar Emission. X. On the Precursor and\n Postcursor Emission: Precursors and postcursors (PPCs) are rare emission components detected in a\nhandful of pulsars that appear beyond the main pulse emission, in some cases\nfar away from it. In this paper we attempt to characterize the PPC emission in\nrelation to the pulsar main pulse geometry. In our analysis we find that PPC\ncomponents have properties very different from that of outer conal emission.\nThe separation of the PPC components from the main pulse center remains\nconstant with frequency. In addition the beam opening angles corresponding to\nthe separation of PPC components from the pulsar center are much larger than\nthe largest encountered in conal emission. Pulsar radio emission is believed to\noriginate within the magnetic polar flux tubes due to the growth of\ninstabilities in the outflowing relativistic plasma. Observationally, there is\nstrong evidence that the main pulse emission originates at altitudes of about\n50 neutron star radii for a canonical pulsar. Currently, the most plausible\nradio emission model that can explain main pulse emission is the coherent\ncurvature radiation mechanism, wherein relativistic charged solitons are formed\nin a non-stationary electron-positron-pair plasma. The wider beam opening\nangles of PPC require the emission to emanate from larger altitudes as compared\nto the main pulse, if both these components originate by the same emission\nmechanism. We explore this possibility and find that this emission mechanism is\nprobably inapplicable at the height of the PPC emission. We propose that the\nPPC emission represents a new type of radiation from pulsars with a mechanism\ndifferent from that of the main pulse.", "category": "astro-ph_GA" }, { "text": "ALMA unveils a triple merger and gas exchange in a hyper-luminous radio\n galaxy at z=2: the Dragonfly Galaxy (II): The Dragonfly Galaxy (MRC0152-209), at redshift z~2, is one of the most\nvigorously star-forming radio galaxies in the Universe. What triggered its\nactivity? We present ALMA Cycle 2 observations of cold molecular CO(6-5) gas\nand dust, which reveal that this is likely a gas-rich triple merger. It\nconsists of a close double nucleus (separation ~4 kpc) and a weak CO-emitter at\n~10 kpc distance, all of which have counterparts in HST/NICMOS imagery. The\nhyper-luminous starburst and powerful radio-AGN were triggered at this\nprecoalescent stage of the merger. The CO(6-5) traces dense molecular gas in\nthe central region, and complements existing CO(1-0) data, which revealed more\nwidespread tidal debris of cold gas. We also find ~10$^{10}$ M(sun) of\nmolecular gas with enhanced excitation at the highest velocities. At least\n20-50% of this high-excitation, high-velocity gas shows kinematics that\nsuggests it is being displaced and redistributed within the merger, although\nwith line-of-sight velocities of |v| < 500 km/s, this gas will probably not\nescape the system. The processes that drive the redistribution of cold gas are\nlikely related to either the gravitational interaction between two kpc-scale\ndiscs, or starburst/AGN-driven outflows. We estimate that the rate at which the\nmolecular gas is redistributed is at least ~1200 +- 500 M(sun)/yr, and could\nperhaps even approach the star formation rate of ~3000 +- 800 M(sun)/yr. The\nfact that the gas depletion and gas redistribution timescales are similar\nimplies that dynamical processes can be important in the evolution of massive\nhigh-z galaxies.", "category": "astro-ph_GA" }, { "text": "ATLASGAL --- properties of compact HII regions and their natal clumps: We present a complete sample of molecular clumps containing compact and\nultra-compact (UC) HII regions between \\ell=10\\degr and 60\\degr\\ and\n$|b|<1\\degr, identified by combining the the ATLASGAL submm and CORNISH radio\ncontinuum surveys with visual examination of archival infrared data. Our sample\nis complete to optically thin, compact and UCHII regions driven by a zero age\nmain sequence star of spectral type B0 or earlier embedded within a 1,000 Msun\nclump. In total we identify 213 compact and UCHII regions, associated with 170\nclumps. Unambiguous kinematic distances are derived for these clumps and used\nto estimate their masses and physical sizes, as well as the Lyman continuum\nfluxes and sizes of their embedded HII regions. We find a clear lower envelope\nfor the surface density of molecular clumps hosting massive star formation of\n0.05 g cm^{-2}, which is consistent with a similar sample of clumps associated\nwith 6.7 GHz masers. The mass of the most massive embedded stars is closely\ncorrelated with the mass of their natal clump. Young B stars appear to be\nsignificantly more luminous in the ultraviolet than predicted by current\nstellar atmosphere models. The properties of clumps associated with compact and\nUCHII regions are very similar to those associated with 6.7 GHz methanol masers\nand we speculate that there is little evolution in the structure of the\nmolecular clumps between these two phases. Finally, we identify a significant\npeak in the surface density of compact and UCHII regions associated with the\nW49A star-forming complex, noting that this complex is truly one of the most\nmassive and intense regions of star formation in the Galaxy.", "category": "astro-ph_GA" }, { "text": "A phase-space view of cold-gas properties of Virgo-cluster galaxies:\n multiple quenching processes at work?: We investigate the cold-gas properties of massive Virgo galaxies ($>10^9$\nM$_\\odot$) at $<3R_{200}$ ($R_{200}$ is the radius where the mean interior\ndensity is 200 times the critical density) on the projected phase-space diagram\n(PSD) with the largest archival dataset to date to understand the environmental\neffect on galaxy evolution in the Virgo cluster. We find: lower HI and H$_2$\nmass fractions and higher star-formation efficiencies (SFEs) from HI and H$_2$\nin the Virgo galaxies than the field galaxies for matched stellar masses; the\nVirgo galaxies generally follow the field relationships between the offset from\nthe main sequence of the star-forming galaxies [$\\Delta$(MS)] with gas\nfractions and SFEs but slightly offset to lower gas fractions or higher SFEs\nthan field galaxies at $\\Delta({\\rm MS})< 0$; lower gas fractions in galaxies\nwith smaller clustocentric distance and velocity; lower gas fractions in the\ngalaxies in the W cloud, a substructure of the Virgo cluster. Our results\nsuggest the cold-gas properties of some Virgo galaxies are affected by their\nenvironment at least at $3 R_{200}$ maybe via strangulation and/or\npre-processes and HI and H$_2$ in some galaxies are removed by ram pressure at\n$<1.5 R_{200}$. Our data cannot rule the possibility of the other processes\nsuch as strangulation and galaxy harassment accounting for the gas reduction in\nsome galaxies at $<1.5 R_{200}$. Future dedicated observations of a\nmass-limited complete sample are required for definitive conclusions.", "category": "astro-ph_GA" }, { "text": "Unresolved z~8 point sources and their impact on the bright end of the\n galaxy luminosity function: The distribution and properties of the first galaxies and quasars are\ncritical pieces of the puzzle in understanding galaxy evolution and cosmic\nreionization. Previous studies have often excluded unresolved sources as\npotential low redshift interlopers. We combine broadband color and photometric\nredshift analysis with morphological selections to identify a robust sample of\ncandidates consistent with unresolved point sources at redshift $z\\sim8$ using\ndeep Hubble Space Telescope images. We also examine G141 grism spectroscopic\ndata to identify and eliminate dwarf star contaminants. From these analyses, we\nidentify three, bright ($M_{UV}\\lesssim-22$ ABmag) dropout point sources at\n$7.5 11$, but also demonstrates\nthat another candidate with suggested $z\\approx 16$ instead has $z = 4.9$, with\nan unusual combination of nebular line emission and dust reddening that mimics\nthe colors expected for much more distant objects. These results reinforce\nevidence for the early, rapid formation of remarkably luminous galaxies, while\nalso highlighting the necessity of spectroscopic verification. The large\nabundance of bright, early galaxies may indicate shortcomings in current galaxy\nformation models, or deviation from physical properties (such as the stellar\ninitial mass function) that are generally believed to hold at later times.", "category": "astro-ph_GA" }, { "text": "Spatially-resolved spectroscopy of narrow-line Seyfert 1 host galaxies: We present optical integral field spectroscopy for five $z<0.062$ narrow-line\nSeyfert 1 galaxies (NLS1s) host galaxies, probing their host galaxies at\n$\\gtrsim 2-3$ kpc scales. Emission lines in the nuclear AGN spectra and the\nlarge-scale host galaxy are analyzed separately, based on an AGN-host\ndecomposition technique. The host galaxy gas kinematics indicates large-scale\ngas rotation in all five sources. At the probed scales of $\\gtrsim 2-3$ kpc,\nthe host galaxy gas is found to be predominantly ionized by star formation\nwithout any evidence of a strong AGN contribution. None of the five objects\nshows specific star formation rates exceeding the main sequence of low-redshift\nstar forming galaxies. The specific star formation rates for MCG-05-01-013 and\nWPVS 007 are roughly consistent with the main sequence, while ESO 399-IG20, MS\n22549-3712, and TON S180 show lower specific star formation rates, intermediate\nto the main sequence and red quiescent galaxies. The host galaxy metallicities,\nderived for the two sources with sufficient data quality (ESO 399-IG20 and\nMCG-05-01-013), indicate central oxygen abundances just below the low-redshift\nmass-metallicity relation. Based on this initial case study, we outline a\ncomparison of AGN and host galaxy parameters as a starting point for future\nextended NLS1 studies with similar methods.", "category": "astro-ph_GA" }, { "text": "An infrared view of AGN feedback in a type-2 quasar: the case of the\n Teacup galaxy: We present near-infrared integral field spectroscopy data obtained with\nVLT/SINFONI of \"the Teacup galaxy\". The nuclear K-band (1.95-2.45 micron)\nspectrum of this radio-quiet type-2 quasar reveals a blueshifted broad\ncomponent of FWHM~1600-1800 km/s in the hydrogen recombination lines\n(Pa$\\alpha$, Br$\\delta$, and Br$\\gamma$) and also in the coronal line [Si\nVI]$\\lambda$1.963 micron. Thus the data confirm the presence of the nuclear\nionized outflow previously detected in the optical and reveal its coronal\ncounterpart. Both the ionized and coronal nuclear outflows are resolved, with\nseeing-deconvolved full widths at half maximum of 1.1$\\pm$0.1 and 0.9$\\pm$0.1\nkpc along PA$\\sim$72-74 deg. This orientation is almost coincident with the\nradio axis (PA=77 deg), suggesting that the radio jet could have triggered the\nnuclear outflow. In the case of the H$_2$ lines we do not require a broad\ncomponent to reproduce the profiles, but the narrow lines are blueshifted by\n~50 km/s on average from the galaxy systemic velocity. This could be an\nindication of the presence of a nuclear molecular outflow, although the bulk of\nthe H$_2$ emission in the inner ~2 arcsec (~3 kpc) of the galaxy follows a\nrotation pattern. We find evidence for kinematically disrupted gas (FWHM>250\nkm/s) at up to 5.6 kpc from the AGN, which can be naturally explained by the\naction of the outflow. The narrow component of [Si VI] is redshifted with\nrespect to the systemic velocity, unlike any other emission line in the K-band\nspectrum. This indicates that the region where the coronal lines are produced\nis not co-spatial with the narrow line region.", "category": "astro-ph_GA" }, { "text": "Chemical Evolution of R-process Elements in Stars (CERES). I. Stellar\n parameters and chemical abundances from Na to Zr: Aims. The Chemical Evolution of R-process Elements in Stars (CERES) project\naims to provide a homogeneous analysis of a sample of metal-poor stars\n([Fe/H]<-1.5). We present the stellar parameters and the chemical abundances of\nelements up to Zr for a sample of 52 giant stars.Methods. We relied on a sample\nof high signal-to-noise UVES spectra. We determined stellar parameters from\nGaia photometry and parallaxes. Chemical abundances were derived using spectrum\nsynthesis and model atmospheres.Results. We determined chemical abundances of\n26 species of 18 elements: Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni,\nCu, Zn, Sr, Y, and Zr. For several stars, we were able to measure both neutral\nand ionised species, including Si, Sc, Mn, and Zr. We have roughly doubled the\nnumber of measurements of Cu for stars at [Fe/H] <= -2.5. The homogeneity of\nthe sample made it possible to highlight the presence of two Zn-rich stars\n([Zn/Fe]~+0.7), one r-rich and the other r-poor. We report the existence of two\nbranches in the [Zn/Fe] versus [Ni/Fe] plane and suggest that the high [Zn/Fe]\nbranch is the result of hypernova nucleosynthesis. We discovered two stars with\npeculiar light neutron-capture abundance patterns: CES1237+1922 (also known as\nBS 16085-0050), which is ~1 dex underabundant in Sr, Y, and Zr with respect to\nthe other stars in the sample, and CES2250-4057 (also known as HE 2247-4113),\nwhich shows a ~1 dex overabundance of Sr with respect to Y and Zr.Conclusions.\nThe high quality of our dataset allowed us to measure hardly detectable ions.\nThis can provide guidance in the development of line formation computations\nthat take deviations from local thermodynamic equilibrium and hydrodynamical\neffects into account.", "category": "astro-ph_GA" }, { "text": "Spectral scaling laws in MHD turbulence simulations and in the solar\n wind: The question is addressed to what extent incompressible magnetohydrodynamics\n(MHD) can describe random magnetic and velocity fluctuations measured in the\nsolar wind. It is demonstrated that distributions of spectral indices for the\nvelocity, magnetic field, and total energy obtained from high resolution\nnumerical simulations are qualitatively and quantitatively similar to solar\nwind observations at 1 AU. Both simulations and observations show that in the\ninertial range the magnetic field spectrum E_b is steeper than the velocity\nspectrum E_v with E_b >~ E_v and that the residual energy E_R = E_b-E_v\ndecreases nearly following a k_perp^-2 scaling.", "category": "astro-ph_GA" }, { "text": "An uncertainty principle for star formation -- III. The characteristic\n emission time-scales of star formation rate tracers: We recently presented a new statistical method to constrain the physics of\nstar formation and feedback on the cloud scale by reconstructing the underlying\nevolutionary timeline. However, by itself this new method only recovers the\nrelative durations of different evolutionary phases. To enable observational\napplications, it therefore requires knowledge of an absolute 'reference\ntime-scale' to convert relative time-scales into absolute values. The logical\nchoice for this reference time-scale is the duration over which the star\nformation rate (SFR) tracer is visible because it can be characterised using\nstellar population synthesis (SPS) models. In this paper, we calibrate this\nreference time-scale using synthetic emission maps of several SFR tracers,\ngenerated by combining the output from a hydrodynamical disc galaxy simulation\nwith the SPS model SLUG2. We apply our statistical method to obtain\nself-consistent measurements of each tracer's reference time-scale. These\ninclude H${\\alpha}$ and 12 ultraviolet (UV) filters (from GALEX, Swift, and\nHST), which cover a wavelength range 150-350 nm. At solar metallicity, the\nmeasured reference time-scales of H${\\alpha}$ are ${4.32^{+0.09}_{-0.23}}$ Myr\nwith continuum subtraction, and 6-16 Myr without, where the time-scale\nincreases with filter width. For the UV filters we find 17-33 Myr, nearly\nmonotonically increasing with wavelength. The characteristic time-scale\ndecreases towards higher metallicities, as well as to lower star formation rate\nsurface densities, owing to stellar initial mass function sampling effects. We\nprovide fitting functions for the reference time-scale as a function of\nmetallicity, filter width, or wavelength, to enable observational applications\nof our statistical method across a wide variety of galaxies.", "category": "astro-ph_GA" }, { "text": "WALLABY Early Science - III. An HI Study of the Spiral Galaxy NGC 1566: This paper reports on the atomic hydrogen gas (HI) observations of the spiral\ngalaxy NGC 1566 using the newly commissioned Australian Square Kilometre Array\nPathfinder (ASKAP) radio telescope. We measure an integrated HI flux density of\n$180.2$ Jy km s$^{-1}$ emanating from this galaxy, which translates to an HI\nmass of $1.94\\times10^{10}$M$_\\circ$ at an assumed distance of $21.3$ Mpc. Our\nobservations show that NGC 1566 has an asymmetric and mildly warped HI disc.\nThe HI-to-stellar mass fraction of NGC 1566 is $0.29$, which is high in\ncomparison with galaxies that have the same stellar mass\n($10^{10.8}$M$_\\circ$). We also derive the rotation curve of this galaxy to a\nradius of $50$ kpc and fit different mass models to it. The NFW, Burkert and\npseudo-isothermal dark matter halo profiles fit the observed rotation curve\nreasonably well and recover dark matter fractions of $0.62$, $0.58$ and $0.66$,\nrespectively. Down to the column density sensitivity of our observations\n($N_{HI} = 3.7\\times10^{19}$ cm$^{-2}$), we detect no HI clouds connected to,\nor in the nearby vicinity of, the HI disc of NGC 1566 nor nearby interacting\nsystems. We conclude that, based on a simple analytic model, ram pressure\ninteractions with the IGM can affect the HI disc of NGC 1566 and is possibly\nthe reason for the asymmetries seen in the HI morphology of NGC 1566.", "category": "astro-ph_GA" }, { "text": "Red Clump stars from LAMOST II: the outer disc of the Milky Way: We present stellar density maps of the Galactic outer disc with red clump\nstars from the LAMOST data. These samples are separated into younger (mean age\n~ 2.7 Gyr) and older (mean age ~ 4.6 Gyr) populations so that they can trace\nthe variation of the structures with ages in the range of the Galactocentric\nradius R from 9 to 13.5 kpc. We show that both the scale heights for the two\npopulations increase with R and display radial gradients of 48 +/- 6 and 40 +/-\n4 pc/kpc for the older and younger populations, respectively. This is evident\nthat the flaring occurs in the thin disc populations with a wide range of ages.\nMoreover, the intensity of flaring seems not significantly related to the age\nof the thin disc populations. On the other hand, the scale lengths of the\nradial surface density profiles are 4.7 +/- 0.5 kpc for the younger and 3.4 +/-\n0.2 kpc for the older population, meaning that the younger disc population is\nmore radially extended than the older one. Although the fraction of the younger\npopulation mildly increases from 28% at R ~ 9 to about 35% at R ~ 13 kpc, the\nolder population is prominent with the fraction no less than 65% in the outer\ndisc.", "category": "astro-ph_GA" }, { "text": "A comparison of the distribution of satellite galaxies around Andromeda\n and the results of $\u039b$CDM simulations: Ibata et al. (2013) recently reported the existence of a vast thin plane of\ndwarf galaxies (VTPD) orbiting around Andromeda. We investigate whether such a\nconfiguration can be reproduced within the standard cosmological framework and\nsearch for similar planes of co-rotating satellite galaxies around\nAndromeda-like host haloes in data from the Millennium II simulation combined\nwith a semi-analytic galaxy formation model. We apply a baryonic mass cut of\n$2.8\\times 10^4 \\text{M}_{\\text{sun}}$ for the satellite haloes and restrict\nthe data to a PAndAS like field. If we include the so-called orphan galaxies in\nour analysis, we find that planes with a rms lower than the VTPD are common in\nMillennium II. This is partially due to the strongly radially concentrated\ndistribution of orphan galaxies. Excluding part of the orphan galaxies brings\nthe radial distributions of Millennium II satellites into better agreement with\nthe satellite distribution of Andromeda while still producing a significant\nfraction of planes with a lower rms than the VTPD. We also find haloes in\nMillennium II with an equal or higher number of co-rotating satellites than the\nVTPD. This demonstrates that the VTPD is not in conflict with the standard\ncosmological framework, although a definite answer of this question might\nrequire higher resolution cosmological simulations that do not have to consider\norphan galaxies. Our results finally show that satellite planes in Millennium\nII are not stable structures, hence the VTPD might only be a statistical\nfluctuation of an underlying more spherical galaxy distribution.", "category": "astro-ph_GA" }, { "text": "High velocity stars from the interaction of a globular cluster and a\n massive black hole binary: High velocity stars are stars moving at velocities so high to require an\nacceleration mechanism involving binary systems or the presence of a massive\ncentral black hole. In the frame of a galaxy hosting a supermassive black hole\nbinary (of total mass $10^8$ M$_\\odot$), we investigated a mechanism for the\nproduction of high velocity stars due to the close interaction between a\nmassive and orbitally decayed globular cluster and the super massive black hole\nbinary. Some stars of the cluster acquire high velocities by conversion of\ngravitational energy into kinetic energy deriving from their interaction with\nthe black hole binary. After the interaction, few stars reach a velocity\nsufficient to overcome the galactic gravitational well, while some of them are\njust stripped from the globular cluster and start orbiting around the galactic\ncentre.", "category": "astro-ph_GA" }, { "text": "The Optical to Mid-Infrared Extinction Law Based on the APOGEE, Gaia\n DR2, Pan-STARRS1, SDSS, APASS, 2MASS and WISE Surveys: A precise interstellar dust extinction law is critically important to\ninterpret observations. There are two indicators of extinction: the color\nexcess ratio (CER) and the relative extinction. Compared to the CER, the\nwavelength-dependent relative extinction is more challenging to be determined.\nIn this work, we combine spectroscopic, astrometric, and photometric data to\nderive high-precision CERs and relative extinction from optical to mid-infrared\n(IR) bands. A group of 61,111 red clump (RC) stars are selected as tracers by\nstellar parameters from APOGEE survey. The multiband photometric data are\ncollected from Gaia, APASS, SDSS, Pan-STARRS1, 2MASS, and WISE surveys. For the\nfirst time, we calibrate the curvature of CERs in determining CERs\nE(lambda-GRP)/E(GBP-GRP) from color excess--color excess diagrams. Through\nelaborate uncertainty analysis, we conclude that the precision of our CERs is\nsignificantly improved (sigma < 0.015). With parallaxes from Gaia DR2, we\ncalculate the relative extinction A_GBP/A_GRP for 5051 RC stars. By combining\nthe CERs with the A_GBP/A_GRP, the optical--mid-IR extinction A_lambda/A_GRP\nhas been determined in a total of 21 bands. Given no bias toward any specific\nenvironment, our extinction law represents the average extinction law with the\ntotal-to-selective extinction ratio Rv=3.16+-0.15. Our observed extinction law\nsupports an adjustment in parameters of the CCM Rv=3.1 curve, together with the\nnear-IR power-law index alpha=2.07+-0.03. The relative extinction values of HST\nand JWST near-IR bandpasses are predicted in 2.5% precision. As the observed\nreddening/extinction tracks are curved, the curvature correction needs to be\nconsidered when applying extinction correction.", "category": "astro-ph_GA" }, { "text": "Dark Matter In Disk Galaxies II: Density Profiles as Constraints on\n Feedback Scenarios: The disparity between the density profiles of galactic dark matter haloes\npredicted by dark matter only cosmological simulations and those inferred from\nrotation curve decomposition, the so-called cusp-core problem, suggests that\nbaryonic physics has an impact on dark matter density in the central regions of\ngalaxies. Feedback from black holes, supernovae and massive stars may each play\na role by removing matter from the centre of the galaxy on shorter timescales\nthan the dynamical time of the dark matter halo. Our goal in this paper is to\ndetermine constraints on such feedback scenarios based on the observed\nproperties of a set of nearby galaxies.\n Using a Markov Chain Monte Carlo (MCMC) analysis of galactic rotation curves,\nvia a method developed in a previous paper, we constrain density profiles and\nan estimated minimum radius for baryon influence, $r_1$, which we couple with a\nfeedback model to give an estimate of the fraction of matter within that radius\nthat must be expelled to produce the presently observed halo profile. We show\nthat in the case of the gas rich dwarf irregular galaxy DDO 154, an outflow\nfrom a central source (e.g. a black hole or star forming region) could produce\nsufficient feedback on the halo without removing the disk gas.\n We examine the rotation curves of 8 galaxies taken from the THINGS data set\nand determine constraints on the radial density profiles of their dark matter\nhaloes. For some of the galaxies, both cored haloes and cosmological $\\rho\n\\propto r^{-1}$ cusps are excluded. These intermediate central slopes require\nbaryonic feedback to be finely tuned. We also find for galaxies which exhibit\nextended cores in their haloes (e.g. NGC 925), the use of a split power-law\nhalo profile yields models without the unphysical, sharp features seen in\nmodels based on the Einasto profile.", "category": "astro-ph_GA" }, { "text": "Gaia FGK Benchmark Stars - Metallicity: To calibrate automatic pipelines that determine atmospheric parameters of\nstars, one needs a sample of stars -- ``benchmark stars'' -- with well defined\nparameters to be used as a reference We provide a detailed documentation of the\ndetermination of the iron abundance of the 34 FGK-type benchmark stars selected\nto be the pillars for calibration of the one billion Gaia stars. They cover a\nwide range of temperatures, surface gravities and metallicities. Up to seven\ndifferent methods were used to analyze an observed spectral library of high\nresolution and high signal-to-noise ratio. The metallicity was determined\nassuming a value of effective temperature and surface gravity obtained from\nfundamental relations, i.e. these parameters were known a priori independently\nfrom the spectra. We present a set of metallicity values obtained in a\nhomogeneous way for our sample of Benchmark Stars. In addition to this value,\nwe provide a detailed documentation of the associated uncertainties. Finally,\nwe report for the first time a value of the metallicity of the cool giant psi\nPhe.", "category": "astro-ph_GA" }, { "text": "A Bayesian Approach to the Vertical Structure of the Disk of the Milky\n Way: This work investigates the vertical profile of the stars in the disk of the\nMilky Way. The models investigated are of the form $sech^{2/n}(nz/(2H))$ where,\nsetting $\\alpha = 2/n$, the three functions of the sequence $\\alpha = 0,1,2$\ncorrespond to exponential, $sech$, $sech^2$ functions. We consider symmetric\nmodels and asymmetric models, above and below the plane. The study uses the\nlarge sample of K and M stars of Ferguson et al. (2017) and applies the methods\nof Bayesian model comparison to discriminate between the 6 models. Two\ninconsistencies in Ferguson et al. (2017), concerning the vertical height cut\nand the model continuity across the plane, are noted and addressed. We find\nthat (1) in the Milky Way the symmetric disc models are decisively ruled out,\nwith northern thin disc scale heights $\\sim25\\%$ larger than southern, (2)\nthere is moderate evidence for the exponential and $sech$ models over the\n$sech^2$ model, though a sample extending further into the Galactic mid-plane\nis needed to strengthen this result, (3) the photometric distances used by\nFerguson et al. underestimate the GAIA distances by a factor of roughly 1.16,\nand (4) the increase of scale height with Galactic latitude observed by\nFerguson et al. is due to incorrect cuts to the data.", "category": "astro-ph_GA" }, { "text": "Denoising Diffusion Probabilistic Models to Predict the Density of\n Molecular Clouds: We introduce the state-of-the-art deep learning Denoising Diffusion\nProbabilistic Model (DDPM) as a method to infer the volume or number density of\ngiant molecular clouds (GMCs) from projected mass surface density maps. We\nadopt magnetohydrodynamic simulations with different global magnetic field\nstrengths and large-scale dynamics, i.e., noncolliding and colliding GMCs. We\ntrain a diffusion model on both mass surface density maps and their\ncorresponding mass-weighted number density maps from different viewing angles\nfor all the simulations. We compare the diffusion model performance with a more\ntraditional empirical two-component and three-component power-law fitting\nmethod and with a more traditional neural network machine learning approach\n(CASI-2D). We conclude that the diffusion model achieves an order of magnitude\nimprovement on the accuracy of predicting number density compared to that by\nother methods. We apply the diffusion method to some example astronomical\ncolumn density maps of Taurus and the Infrared Dark Clouds (IRDCs) G28.37+0.07\nand G35.39-0.33 to produce maps of their mean volume densities.", "category": "astro-ph_GA" }, { "text": "Resolved Star Formation on Sub-galactic Scales in a Merger at z=1.7: We present a detailed analysis of Hubble Space Telescope (HST), Wide Field\nCamera 3 (WFC3) G141 grism spectroscopy for seven star-forming regions of the\nhighly magnified lensed starburst galaxy RCSGA 032727-132609 at z=1.704. We\nmeasure the spatial variations of the extinction in RCS0327 through the\nobserved H$\\gamma$/H$\\beta$ emission line ratios, finding a constant average\nextinction of $\\mathrm{E(B-V)_{gas}}=0.40\\pm0.07$. We infer that the star\nformation is enhanced as a result of an ongoing interaction, with measured star\nformation rates derived from demagnified, extinction-corrected H$\\beta$ line\nfluxes for the individual star-forming clumps falling >1-2 dex above the star\nformation sequence. When combining the HST/WFC3 [OIII]$\\lambda$5007/H$\\beta$\nemission line ratio measurements with [NII]/H$\\alpha$ line ratios from Wuyts et\na. (2014), we find that the majority of the individual star-forming regions\nfall along the local \"normal\" abundance sequence. With the first detections of\nthe He I $\\lambda$5876 and He II $\\lambda$4686 recombination lines in a distant\ngalaxy, we probe the massive-star content of the star-forming regions in\nRCS0327. The majority of the star-forming regions have a He I $\\lambda$5876 to\nH$\\beta$ ratio consistent with the saturated maximum value, which is only\npossible if they still contain hot O-stars. Two regions have lower ratios,\nimplying that their last burst of new star formation ended ~5 Myr ago.\nTogether, the He I $\\lambda$5876 and He II $\\lambda$4686 to H$\\beta$ line\nratios provide indirect evidence for the order in which star formation is\nstopping in individual star-forming knots of this high redshift merger. We\nplace the spatial variations of the extinction, star formation rate and\nionization conditions in the context of the star formation history of RCS0327.", "category": "astro-ph_GA" }, { "text": "The Spitzer Space Telescope Survey of the Orion A and B Molecular Clouds\n II: the Spatial Distribution and Demographics of Dusty Young Stellar Objects: We analyze the spatial distribution of dusty young stellar objects (YSOs)\nidentified in the Spitzer Survey of the Orion Molecular clouds, augmenting\nthese data with Chandra X-ray observations to correct for incompleteness in\ndense clustered regions. We also devise a scheme to correct for spatially\nvarying incompleteness when X-ray data are not available. The local surface\ndensities of the YSOs range from 1 pc$^{-2}$ to over 10,000 pc$^{-2}$, with\nprotostars tending to be in higher density regions. This range of densities is\nsimilar to other surveyed molecular clouds with clusters, but broader than\nclouds without clusters. By identifying clusters and groups as continuous\nregions with surface densities $\\ge10$ pc$^{-2}$, we find that 59% of the YSOs\nare in the largest cluster, the Orion Nebular Cluster (ONC), while 13% of the\nYSOs are found in a distributed population. A lower fraction of protostars in\nthe distributed population is evidence that it is somewhat older than the\ngroups and clusters. An examination of the structural properties of the\nclusters and groups show that the peak surface densities of the clusters\nincrease approximately linearly with the number of members. Furthermore, all\nclusters with more than 70 members exhibit asymmetric and/or highly elongated\nstructures. The ONC becomes azimuthally symmetric in the inner 0.1 pc,\nsuggesting that the cluster is only $\\sim 2$ Myr in age. We find the star\nformation efficiency (SFE) of the Orion B cloud is unusually low, and that the\nSFEs of individual groups and clusters are an order of magnitude higher than\nthose of the clouds. Finally, we discuss the relationship between the young low\nmass stars in the Orion clouds and the Orion OB 1 association, and we determine\nupper limits to the fraction of disks that may be affected by UV radiation from\nOB stars or by dynamical interactions in dense, clustered regions.", "category": "astro-ph_GA" }, { "text": "Searching for new observational signatures of the dynamical evolution of\n star clusters: We present a numerical study, based on Monte Carlo simulations, aimed at\ndefining new empirical parameters measurable from observations and able to\ntrace the different phases of star cluster dynamical evolution. As expected, a\ncentral density cusp, deviating from the King model profile, develops during\nthe core collapse (CC) event. Although the slope varies during the post-CC\noscillations, the cusp remains a stable feature characterizing the central\nportion of the density profile in all post-CC stages. We then investigate the\nnormalized cumulative radial distribution (nCRD) drawn by all the cluster stars\nincluded within one half the tridimensional half-mass radius (R<0.5 rh),\nfinding that its morphology varies in time according to the cluster's dynamical\nstage. To quantify these changes we defined three parameters: A5, the area\nsubtended by the nCRD within 5% of the half-mass radius, P5, the value of the\nnCRD measured at the same distance, and S2.5, the slope of the straight line\ntangent to the nCRD measured at R=2.5% rh. The three parameters evolve\nsimilarly during the cluster's dynamical evolution: after an early phase in\nwhich they are essentially constant, their values rapidly increase, reaching\ntheir maximum at the CC epoch and slightly decreasing in the post-CC phase,\nwhen their average value remains significantly larger than the initial one, in\nspite of some fluctuations. The results presented in the paper suggest that\nthese three observable parameters are very promising empirical tools to\nidentify the star cluster's dynamical stage from observational data.", "category": "astro-ph_GA" }, { "text": "N-body simulations of the Carina dSph in MOND: The classical dwarf spheroidals (dSphs) provide a critical test for Modified\nNewtonian Dynamics (MOND) because they are observable satellite galactic\nsystems with low internal accelerations and low, but periodically varying,\nexternal acceleration. This varying external gravitational field is not\ncommonly found acting on systems with low internal acceleration. Using Jeans\nmodelling, Carina in particular has been demonstrated to require a V-band\nmass-to-light ratio greater than 5, which is the nominal upper limit for an\nancient stellar population. We run MOND N-body simulations of a Carina-like\ndSph orbiting the Milky Way to test if dSphs in MOND are stable to tidal forces\nover the Hubble time and if those same tidal forces artificially inflate their\nvelocity dispersions and therefore their apparent mass-to-light ratio. We run\nmany simulations with various initial total masses for Carina, and\nGalactocentric orbits (consistent with proper motions), and compare the\nsimulation line of sight velocity dispersions (losVDs) with the observed losVDs\nof Walker et al. (2007). We find that the dSphs are stable, but that the tidal\nforces are not conducive to artificially inflating the losVDs. Furthermore, the\nrange of mass-to-light ratios that best reproduces the observed line of sight\nvelocity dispersions of Carina is 5.3 to 5.7 and circular orbits are preferred\nto plunging orbits. Therefore, some tension still exists between the required\nmass-to-light ratio for the Carina dSph in MOND and those expected from stellar\npopulation synthesis models. It remains to be seen whether a careful treatment\nof the binary population or triaxiality might reduce this tension.", "category": "astro-ph_GA" }, { "text": "High-velocity stars in the cores of globular clusters: The illustrative\n case of NGC 2808: We report the detection of five high-velocity stars in the core of the\nglobular cluster NGC 2808. The stars lie on the the red giant branch and show\ntotal velocities between 40 and 45 km/s. For a core velocity dispersion sigma_c\n= 13.4 km/s, this corresponds to up to 3.4 sigma_c. These velocities are close\nto the estimated escape velocity (~ 50 km/s) and suggest an ejection from the\ncore. Two of these stars have been confirmed in our recent integral field\nspectroscopy data and we will discuss them in more detail here. These two red\ngiants are located at a projected distance of ~ 0.3 pc from the center.\nAccording to their positions on the color magnitude diagram, both stars are\ncluster members. We investigate several possible origins for the high\nvelocities of the stars and conceivable ejection mechanisms. Since the\nvelocities are close to the escape velocity, it is not obvious whether the\nstars are bound or unbound to the cluster. We therefore consider both cases in\nour analysis. We perform numerical simulations of three-body dynamical\nencounters between binaries and single stars and compare the resulting velocity\ndistributions of escapers with the velocities of our stars. We compare the\npredictions for a single dynamical encounter with a compact object with those\nof a sequence of two-body encounters due to relaxation. If the stars are\nunbound, the encounter must have taken place recently, when the stars were\nalready in the giant phase. After including binary fractions and black-hole\nretention fractions, projection effects, and detection probabilities from\nMonte-Carlo simulations, we estimate the expected numbers of detections for all\nthe different scenarios. Based on these numbers, we conclude that the most\nlikely scenario is that the stars are bound and were accelerated by a single\nencounter between a binary of main-sequence stars and a ~ 10 M_sun black hole.", "category": "astro-ph_GA" }, { "text": "Tracing the Milky Way Nuclear Wind with 21cm Atomic Hydrogen Emission: There is evidence in 21cm HI emission for voids several kpc in size centered\napproximately on the Galactic centre, both above and below the Galactic plane.\nThese appear to map the boundaries of the Galactic nuclear wind. An analysis of\nHI at the tangent points, where the distance to the gas can be estimated with\nreasonable accuracy, shows a sharp transition at Galactic radii $R\\lesssim 2.4$\nkpc from the extended neutral gas layer characteristic of much of the Galactic\ndisk, to a thin Gaussian layer with FWHM $\\sim 125$ pc. An anti-correlation\nbetween HI and $\\gamma$-ray emission at latitudes $10^{\\circ} \\leq |b| \\leq\n20^{\\circ}$ suggests that the boundary of the extended HI layer marks the walls\nof the Fermi Bubbles. With HI we are able to trace the edges of the voids from\n$|z| > 2$ kpc down to $z\\approx0$, where they have a radius $\\sim 2$ kpc. The\nextended HI layer likely results from star formation in the disk, which is\nlimited largely to $R \\gtrsim 3$ kpc, so the wind may be expanding into an area\nof relatively little HI. Because the HI kinematics can discriminate between gas\nin the Galactic center and foreground material, 21cm HI emission may be the\nbest probe of the extent of the nuclear wind near the Galactic plane.", "category": "astro-ph_GA" }, { "text": "The formation of the Milky Way halo and its dwarf satellites: a NLTE-1D\n abundance analysis. IV. Segue 1, Triangulum II, and Coma Berenices UFDs: We present atmospheric parameters and abundances for chemical elements from\ncarbon to barium in metal-poor stars in Segue 1 (seven stars), Coma Berenices\n(three stars), and Triangulum II (one star) ultra-faint dwarf galaxies (UFDs).\nThe effective temperatures rely on new photometric observations in the visible\nand infra-red bands, obtained with the 2.5 m telescope of the SAI MSU Caucasian\nobservatory. Abundances of up to fourteen chemical elements were derived under\nthe non-local thermodynamic equilibrium (NLTE) line formation, and LTE\nabundances were obtained for up to five more elements. For the first time we\npresent abundance of oxygen in Seg 1 S1 and S4, silicon in ComaBer S2 and Tri\nII S40, potassium in Seg 1 S1-S6 and ComaBer S1-S3, and barium in Seg 1 S7.\nThree stars in Segue 1, two stars in Coma Berenices, and Triangulum II star\nhave very low [Na/Mg] of -1.08 to -1.67 dex, which is usually attributed in the\nliterature to an odd-even effect produced by nucleosynthesis in massive\nmetal-free stars. We interpret this chemical property as a footprint of first\nstars, which is not blurred due to a small number of nucleosynthesis events\nthat contributed to chemical abundance patterns of the sample stars. Our NLTE\nabundances of Sr and Ba in Coma Berenices, Segue 1, and Triangulum II report on\nlower [Sr/Ba] abundance ratio in the UFDs compared to that in classical dwarf\nspheroidal galaxies and the Milky Way halo. However, in UFDs, just as in\nmassive galaxies, [Sr/Ba] is not constant and it can be higher than the pure\nr-process ratio. We suggest a hypothesis of Sr production in metal-poor\nbinaries at the earliest epoch of galactic evolution.", "category": "astro-ph_GA" }, { "text": "Radio Imaging of the NGC 2024 FIR 5/6 Region: a Hypercompact H II Region\n Candidate in Orion: The NGC 2024 FIR 5/6 region was observed in the 6.9 mm continuum with an\nangular resolution of about 1.5 arcsec. The 6.9 mm continuum map shows four\ncompact sources, FIR 5w, 5e, 6c, and 6n, as well as an extended structure of\nthe ionization front associated with the optical nebulosity. FIR 6c has a\nsource size of about 0.4 arcsec or 150 AU. The spectral energy distribution\n(SED) of FIR 6c is peculiar: rising steeply around 6.9 mm and flat around 1 mm.\nThe possibility of a hypercompact H II region is explored. If the millimeter\nflux of FIR 6c comes from hot ionized gas heated by a single object at the\ncenter, the central object may be a B1 star of about 5800 solar luminosities\nand about 13 solar masses. The 6.9 mm continuum of FIR 6n may be a mixture of\nfree-free emission and dust continuum emission. Archival data show that both\nFIR 6n and 6c exhibit water maser activity, suggesting the existence of shocked\ngas around them. The 6.9 mm continuum emission from FIR 5w has a size of about\n1.8 arcsec or 760 AU. The SEDs suggest that the 6.9 mm emission of FIR 5w and\n5e comes from dust, and the masses of the dense molecular gas are about 0.6 and\n0.5 solar masses, respectively.", "category": "astro-ph_GA" }, { "text": "Properties of dense molecular gas along the major axis of M 82: Dense gas is important for galaxy evolution and star formation.\nOptically-thin dense-gas tracers, such as isotopologues of HCN, HCO+, etc., are\nvery helpful to diagnose excitation conditions of dense molecular gas. However,\nprevious studies of optically-thin dense-gas tracers were mostly focusing on\naverage properties of galaxies as a whole, due to limited sensitivity and\nangular resolution. M82, a nearby prototype starburst galaxy, offers a unique\ncase for spatially-resolved studies with single-dish telescopes. With the IRAM\n30-m telescope, we observed the J = 1 - 0 transition of H13CN, HC15N, H13CO+,\nHN13C, H15NC, and SiO J = 2 - 1, HC3N J= 10 - 9, H2CO J = 2 - 1 toward five\npositions along the major axis of M82. The intensity ratios of I(HCN)/I(H13CN)\nand I(HCO+)/I(H13CO+) show a significant spatial variation along the major\naxis, with lower values in the central region than those on the disk,\nindicating higher optical depths in the central region. The optical depths of\nHCO+ lines are found to be systematically higher than those of HCN lines at all\npositions. Futhermore, we find that the 14N/15N ratios have an increasing\ngradient from the center to the outer disk.", "category": "astro-ph_GA" }, { "text": "VINTERGATAN III: how to reset the metallicity of the Milky Way: Using the cosmological zoom simulation VINTERGATAN, we present a new scenario\nfor the onset of star formation at the metal-poor end of the low-[$\\alpha$/Fe]\nsequence in a Milky Way-like galaxy. In this scenario, the galaxy is fueled by\ntwo distinct gas flows. One is enriched by outflows from massive galaxies, but\nnot the other. While the former feeds the inner galactic region, the latter\nfuels an outer gas disk, inclined with respect to the main galactic plane, and\nwith a significantly poorer chemical content. The first passage of the last\nmajor merger galaxy triggers tidal compression in the outer disk, which\nincreases the gas density and eventually leads to star formation, at a\nmetallicity 0.75 dex lower than the inner galaxy. This forms the first stars of\nthe low-[$\\alpha$/Fe] sequence. These in situ stars have halo-like kinematics,\nsimilarly to what is observed in the Milky Way, due to the inclination of the\nouter disk which eventually aligns with the inner one via gravitational\ntorques. We show that this tilting disk scenario is likely to be common in\nMilky-Way like galaxies. This process implies that the low-[$\\alpha$/Fe]\nsequence is populated in situ, simultaneously from two formation channels, in\nthe inner and the outer galaxy, with distinct metallicities. This contrasts\nwith purely sequential scenarios for the assembly of the Milky Way disk and\ncould be tested observationally.", "category": "astro-ph_GA" }, { "text": "Effects of radial flows on the chemical evolution of the Milky Way disk: The majority of chemical evolution models assume that the Galactic disk forms\nby means of infall of gas and divide the disk into several independent rings\nwithout exchange of matter between them. However, if gas infall is important,\nradial gas flows should be taken into account as a dynamical consequence of\ninfall. The aim of this paper is to test the effect of radial gas flows on\ndetailed chemical evolution models (one-infall and two-infall) for the Milky\nWay disk with different prescriptions for the infall law and star formation\nrate. We found, that with a gas radial inflow of constant speed the metallicity\ngradient tends to steepen. Taking into account a constant time scale for the\ninfall rate along the Galaxy disk and radial flows with a constant speed, we\nobtained a too flat gradient, at variance with data, implying that an\ninside-out formation and/or a variable gas flow speed are required. To\nreproduce the observed gradients the gas flow should increase in modulus with\nthe galactocentric distance, both in the one-infall and two-infall models.\nHowever, the inside-out disk formation coupled with a threshold in the gas\ndensity (only in the two-infall model) for star formation and/or a variable\nefficiency of star formation with galactocentric distance can also reproduce\nthe observed gradients without radial flows. We showed that the radial flows\ncan be the most important process in reproducing abundance gradients but only\nwith a variable gas speed. Finally, one should consider that uncertainties in\nthe data concerning gradients prevent us to draw firm conclusions. Future more\ndetailed data will help to ascertain whether the radial flows are a necessary\ningredient in the formation and evolution of the Galactic disk and disks in\ngeneral.", "category": "astro-ph_GA" }, { "text": "Galactic disk winds driven by cosmic ray pressure: Cosmic ray pressure gradients transfer energy and momentum to extraplanar gas\nin disk galaxies, potentially driving significant mass loss as galactic winds.\nThis may be particularly important for launching high-velocity outflows of\n\"cool\" (T < 10^4 K) gas. We study cosmic-ray driven disk winds using a\nsimplified semi-analytic model assuming streamlines follow the large-scale\ngravitational potential gradient. We consider scaled Milky Way-like potentials\nincluding a disk, bulge, and halo with a range of halo velocities V_H = 50-300\nkm/s, and streamline footpoints with radii in the disk R_0=1-16 kpc at height 1\nkpc. Our solutions cover a wide range of footpoint gas velocity u_0,\nmagnetic-to-cosmic-ray pressure ratio, gas-to-cosmic-ray pressure ratio, and\nangular momentum. Cosmic ray streaming at the Alfv\\'en speed enables the\neffective sound speed C_eff to increase from the footpoint to a critical point\nwhere C_eff,c = u_c ~ V_H; this differs from thermal winds in which C_eff\ndecreases outward. The critical point is typically at a height of 1-6 kpc from\nthe disk, increasing with V_H, and the asymptotic wind velocity exceeds the\nescape speed of the halo. Mass loss rates are insensitive to the footpoint\nvalues of the magnetic field and angular momentum. In addition to numerical\nparameter space exploration, we develop and compare to analytic scaling\nrelations. We show that winds have mass loss rates per unit area up to ~ Pi_0\nV_H^-5/3 u_0^2/3 where Pi_0 is the footpoint cosmic ray pressure and u_0 is set\nby the upwelling of galactic fountains. The predicted wind mass-loss rate\nexceeds the star formation rate for V_H < 200 km/s and u_0 = 50 km/s, a typical\nfountain velocity.", "category": "astro-ph_GA" }, { "text": "VERA astrometry toward the Perseus arm gap: The Perseus arm has a gap in Galactic longitudes (l) between 50 and 80 deg\n(hereafter the Perseus arm gap) where the arm has little star formation\nactivity. To better understand the gap, we conducted astrometric observations\nwith VERA and analyzed archival H I data. We report on parallax and proper\nmotion results from four star-forming regions, of which G050.28-00.39 and\nG070.33+01.59 are likely associated with the gap. The measured parallaxes are\n0.140+/-0.018 (mas), 0.726+/-0.038 (mas), 0.074+/-0.037 (mas), and\n0.118+/-0.035 (mas) for G050.28-00.39, G053.14+00.07, G070.33+01.59, and\nG079.08+01.33, respectively. Since the fractional parallax error of\nG070.33+01.59 is large (0.5), we estimated a 3D kinematic distance of the\nsource to be 7.7+/-1.0 kpc using both the LSR velocity (VLSR) and the measured\nproper motion. Perseus-arm sources G049.41+00.32 and G050.28-00.39 lag relative\nto a Galactic rotation by 77+/-17 km/s and 31+/-10 km/s, respectively. The\nnoncircular motion of G049.41+00.32 cannot be explained by the gravitational\npotential of the Perseus arm. We discovered rectangular holes with integrated\nbrightness temperatures of < 30 K arcdeg in l vs. VLSR of the H I data. One of\nthe holes is centered near (l, VLSR) = (47 deg, -15 km/s), and G049.41+00.32 is\nassociated with the rim of the hole. However, G050.28-00.39 is not associated\nwith the hole. We found extended H I emission on one side of the Galactic plane\nwhen integrating the H I data over the velocity range covering the hole (i.e.,\nVLSR = [-25, -5] km/s). G049.41+00.32 and G050.28-00.39 are moving toward the\nemission. The Galactic H I disk at the same velocity range showed an arc\nstructure, indicating that the disk was pushed from the lower side of the disk.\nAll the observational results might be explained by a cloud collision with the\nGalactic disk.", "category": "astro-ph_GA" }, { "text": "Universes without the Weak Force: Astrophysical Processes with Stable\n Neutrons: We investigate a class of universes in which the weak interaction is not in\noperation. We consider how astrophysical processes are altered in the absence\nof weak forces, including Big Bang Nucleosynthesis (BBN), galaxy formation,\nmolecular cloud assembly, star formation, and stellar evolution. Without weak\ninteractions, neutrons no longer decay, and the universe emerges from its early\nepochs with a mixture of protons, neutrons, deuterium, and helium. The\nbaryon-to-photon ratio must be smaller than the canonical value in our universe\nto allow free nucleons to survive the BBN epoch without being incorporated into\nheavier nuclei. At later times, the free neutrons readily combine with protons\nto make deuterium in sufficiently dense parts of the interstellar medium, and\nprovide a power source before they are incorporated into stars. Almost all of\nthe neutrons are incorporated into deuterium nuclei before stars are formed. As\na result, stellar evolution proceeds primarily through strong interactions,\nwith deuterium first burning into helium, and then helium fusing into carbon.\nLow-mass deuterium-burning stars can be long-lived, and higher mass stars can\nsynthesize the heavier elements necessary for life. Although somewhat different\nfrom our own, such universes remain potentially habitable.", "category": "astro-ph_GA" }, { "text": "Star Formation in CALIFA survey perturbed galaxies. I. Effects of Tidal\n Interactions: We explore the effects of tidal interactions on star formation (SF) by\nanalysing a sample of CALIFA survey galaxies. The sample consists of tidally\nand non-tidally perturbed galaxies, paired at the closest stellar mass\ndensities for the same galaxy type between subsamples. They are then compared,\nboth on the resolved Star Formation Main Sequence (SFMS) plane and in annular\nproperty profiles. Star-forming regions in tidally perturbed galaxies exhibit\nflatter SFMS slopes compared to star-forming regions in non-tidally perturbed\ngalaxies. Despite that the annular profiles show star-forming regions in\ntidally perturbed galaxies as being mostly older, their SF properties are never\nreduced against those ones proper of non-tidally perturbed galaxies.\nStar-forming regions in non-tidally perturbed galaxies are better candidates\nfor SF suppression (quenching). The lowered SF with increasing stellar mass\ndensity in tidally perturbed galaxies may suggest a lower dependence of SF on\nstellar mass. Though the SFMS slopes, either flatter or steeper, are found\nindependent of stellar mass density, the effect of global stellar mass can not\nbe ignored when distinguishing among galaxy types. Since a phenomenon or\nproperty other than local/global stellar mass may be taking part in the\nmodulation of SF, the integrated SF properties are related to the tidal\nperturbation parameter. We find weak, but detectable, positive correlations for\nperturbed galaxies suggesting that tidal perturbations induced by close\ncompanions increase the gas accretion rates of these objects.", "category": "astro-ph_GA" }, { "text": "Tracing the general structure of Galactic molecular clouds using Planck\n data: I. The Perseus region as a test case: We present an analysis of probability distribution functions (pdfs) of column\ndensity in different zones of the star-forming region Perseus and its diffuse\nenvironment based on the map of dust opacity at 353 GHz available from the\nPlanck archive. The pdf shape can be fitted by a combination of a lognormal\nfunction and an extended power-law tail at high densities, in zones centred at\nthe molecular cloud Perseus. A linear combination of several lognormals fits\nvery well the pdf in rings surrounding the cloud or in zones of its diffuse\nneighbourhood. The slope of the mean density scaling law $\\langle\\rho\\rangle_L\n\\propto L^\\alpha$ is steep ($\\alpha=-1.93$) in the former case and rather\nshallow ($\\alpha=-0.77\\pm0.11$) in the rings delineated around the cloud. We\ninterpret these findings as signatures of two distinct physical regimes: i) a\ngravoturbulent one which is characterized by nearly linear scaling of mass and\npractical lack of velocity scaling; and ii) a predominantly turbulent one which\nis best described by steep velocity scaling and by invariant for compressible\nturbulence $\\langle\\rho\\rangle_L u_L^3/L$, describing a scale-independent flux\nof the kinetic energy per unit volume through turbulent cascade. The\ngravoturbulent spatial domain can be identified with the molecular cloud\nPerseus while a relatively sharp transition to predominantly turbulent regime\noccurs in its vicinity.", "category": "astro-ph_GA" }, { "text": "Galactic planetary nebulae in the AKARI far-infrared surveyor bright\n source catalog: We present the results of our preliminary study of all known Galactic PNe\n(included in the Kerber 2003 catalog) which are detected by the AKARI/FIS\nAll-Sky Survey as identified in the AKARI/FIS Bright Source Catalog (BSC)\nVersion Beta-1.", "category": "astro-ph_GA" }, { "text": "Predicting the hypervelocity star population in Gaia: Hypervelocity stars (HVSs) are amongst the fastest objects in our Milky Way.\nThese stars are predicted to come from the Galactic center (GC) and travel\nalong unbound orbits across the Galaxy. In the coming years, the ESA satellite\nGaia will provide the most complete and accurate catalogue of the Milky Way,\nwith full astrometric parameters for more than $1$ billion stars. In this\npaper, we present the expected sample size and properties (mass, magnitude,\nspatial, velocity distributions) of HVSs in the Gaia stellar catalogue. We\nbuild three Gaia mock catalogues of HVSs anchored to current observations,\nexploring different ejection mechanisms and GC stellar population properties.\nIn all cases, we predict hundreds to thousands of HVSs with precise proper\nmotion measurements within a few tens of kpc from us. For stars with a relative\nerror in total proper motion below $10 \\%$, the mass range extends to ~$10\nM_{\\odot}$ but peaks at ~$1$ $M_\\odot$. The majority of Gaia HVSs will\ntherefore probe a different mass and distance range compared to the current\nnon-Gaia sample. In addition, a subset of a few hundreds to a few thousands of\nHVSs with $M$ ~ $3$ $M_\\odot$ will be bright enough to have a precise\nmeasurement of the three-dimensional velocity from Gaia alone. Finally, we show\nthat Gaia will provide more precise proper motion measurements for the current\nsample of HVS candidates. This will help identifying their birthplace narrowing\ndown their ejection location, and confirming or rejecting their nature as HVSs.\nOverall, our forecasts are extremely encouraging in terms of quantity and\nquality of HVS data that can be exploited to constrain both the Milky Way\npotential and the GC properties.", "category": "astro-ph_GA" }, { "text": "The Faint Satellite System of NGC 253: Insights into Low-Density\n Environments and No Satellite Plane: We have conducted a systematic search around the Milky Way (MW) analog NGC\n253 (D=3.5 Mpc), as a part of the Panoramic Imaging Survey of Centaurus and\nSculptor (PISCeS) - a Magellan+Megacam survey to identify dwarfs and other\nsubstructures in resolved stellar light around MW-mass galaxies outside of the\nLocal Group. In total, NGC 253 has five satellites identified by PISCeS within\n100 kpc with an absolute V-band magnitude $M_V<-7$. We have additionally\nobtained deep Hubble Space Telescope imaging of four reported candidates beyond\nthe survey footprint: Do III, Do IV, and dw0036m2828 are confirmed to be\nsatellites of NGC 253, while SculptorSR is found to be a background galaxy. We\nfind no convincing evidence for the presence of a plane of satellites\nsurrounding NGC 253. We construct its satellite luminosity function, which is\ncomplete down to $M_V$$\\lesssim$$-8$ out to 100 kpc and $M_V$$\\lesssim$$-9$ out\nto 300 kpc, and compare it to those calculated for other Local Volume galaxies.\nExploring trends in satellite counts and star-forming fractions among satellite\nsystems, we find relationships with host stellar mass, environment, and\nmorphology, pointing to a complex picture of satellite formation, and a\nsuccessful model has to reproduce all of these trends.", "category": "astro-ph_GA" }, { "text": "Optical Properties of High-Frequency Radio Sources from the Australia\n Telescope 20 GHz (AT20G) Survey: Our current understanding of radio-loud AGN comes predominantly from studies\nat frequencies of 5 GHz and below. With the recent completion of the Australia\nTelescope 20 GHz (AT20G) survey, we can now gain insight into the\nhigh-frequency radio properties of AGN. This paper presents supplementary\ninformation on the AT20G sources in the form of optical counterparts and\nredshifts. Optical counterparts were identified using the SuperCOSMOS database\nand redshifts were found from either the 6dF Galaxy survey or the literature.\nWe also report 144 new redshifts. For AT20G sources outside the Galactic plane,\n78.5% have optical identifications and 30.9% have redshift information. The\noptical identification rate also increases with increasing flux density.\nTargets which had optical spectra available were examined to obtain a spectral\nclassification.\n There appear to be two distinct AT20G populations; the high luminosity\nquasars that are generally associated with point-source optical counterparts\nand exhibit strong emission lines in the optical spectrum, and the lower\nluminosity radio galaxies that are generally associated with passive galaxies\nin both the optical images and spectroscopic properties. It is suggested that\nthese different populations can be associated with different accretion modes\n(cold-mode or hot-mode). We find that the cold-mode sources have a steeper\nspectral index and produce more luminous radio lobes, but generally reside in\nsmaller host galaxies than their hot-mode counterparts. This can be attributed\nto the fact that they are accreting material more efficiently. Lastly, we\ncompare the AT20G survey with the S-cubed semi-empirical (S3-SEX) models and\nconclude that the S3-SEX models need refining to correctly model the compact\ncores of AGN. The AT20G survey provides the ideal sample to do this.", "category": "astro-ph_GA" }, { "text": "Aligned Grains and Scattered Light Found in Gaps of Planet-Forming Disk: Polarized (sub)millimeter emission from dust grains in circumstellar disks\nwas initially thought to be due to grains aligned with the magnetic field.\nHowever, higher resolution multi-wavelength observations along with improved\nmodels found that this polarization is dominated by self-scattering at shorter\nwavelengths (e.g., 870 $\\mu$m) and by grains aligned with something other than\nmagnetic fields at longer wavelengths (e.g., 3 mm). Nevertheless, the\npolarization signal is expected to depend on the underlying substructure, and\nobservations hitherto have been unable to resolve polarization in multiple\nrings and gaps. HL Tau, a protoplanetary disk located 147.3 $\\pm$ 0.5 pc away,\nis the brightest Class I or Class II disk at millimeter/submillimeter\nwavelengths. Here we show deep, high-resolution 870 $\\mu$m polarization\nobservations of HL Tau, resolving polarization in both the rings and gaps. We\nfind that the gaps have polarization angles with a significant azimuthal\ncomponent and a higher polarization fraction than the rings. Our models show\nthat the disk polarization is due to both scattering and emission from aligned\neffectively prolate grains. The intrinsic polarization of aligned dust grains\nis likely over 10%, which is much higher than what was expected in low\nresolution observations (~1%). Asymmetries and dust features are revealed in\nthe polarization observations that are not seen in non-polarimetric\nobservations.", "category": "astro-ph_GA" }, { "text": "The destruction and survival of dust in the shell around SN 2008S: SN 2008S erupted in early 2008 in the grand design spiral galaxy NGC 6946.\nThe progenitor was detected by Prieto et al. in Spitzer Space Telescope images\ntaken over the four years prior to the explosion, but was not detected in deep\noptical images, from which they inferred a self-obscured object with a mass of\nabout 10 Msun. We obtained Spitzer observations of SN 2008S five days after its\ndiscovery, as well as coordinated Gemini and Spitzer optical and infrared\nobservations six months after its outburst.\n We have constructed radiative transfer dust models for the object before and\nafter the outburst, using the same r^-2 density distribution of pre-existing\namorphous carbon grains for all epochs and taking light-travel time effects\ninto account for the early post-outburst epoch. We rule out silicate grains as\na significant component of the dust around SN 2008S. The inner radius of the\ndust shell moved outwards from its pre-outburst value of 85 AU to a\npost-outburst value of 1250 AU, attributable to grain vaporisation by the light\nflash from SN 2008S. Although this caused the circumstellar extinction to\ndecrease from Av = 15 before the outburst to 0.8 after the outburst, we\nestimate that less than 2% of the overall circumstellar dust mass was\ndestroyed.\n The total mass-loss rate from the progenitor star is estimated to have been\n(0.5-1.0)x10^-4 Msun yr^-1. The derived dust mass-loss rate of 5x10^-7 Msun\nyr^-1 implies a total dust injection into the ISM of up to 0.01 Msun over the\nsuggested duration of the self-obscured phase. We consider the potential\ncontribution of objects like SN 2008S to the dust enrichment of galaxies.", "category": "astro-ph_GA" }, { "text": "Constraints on the assembly history of the Milky Way's smooth, diffuse\n stellar halo from the metallicity-dependent, radially-dominated velocity\n anisotropy profiles probed with K giants and BHB stars using LAMOST,\n SDSS/SEGUE, and Gaia: We analyze the anisotropy profile of the Milky Way's smooth, diffuse stellar\nhalo using SDSS/SEGUE blue horizontal branch stars and SDSS/SEGUE and LAMOST K\ngiants. These intrinsically luminous stars allow us to probe the halo to\napproximately 100 kpc from the Galactic center. Line-of-sight velocities,\ndistances, metallicities, and proper motions are available for all stars via\nSDSS/SEGUE, LAMOST, and Gaia, and we use these data to construct a full 7D set\nconsisting of positions, space motions, and metallicity. We remove substructure\nfrom our samples using integrals of motion based on the method of Xue et al. We\nfind radially dominated kinematic profiles with nearly constant anisotropy\nwithin 20 kpc, beyond which the anisotropy profile gently declines although\nremains radially dominated to the furthest extents of our sample. Independent\nof star type or substructure removal, the anisotropy depends on metallicity,\nsuch that the orbits of the stars become less radial with decreasing\nmetallicity. For $-1.7<$ [Fe/H] $<-1$, the smooth, diffuse halo anisotropy\nprofile begins to decline at Galactocentric distances $\\sim20$ kpc, from\n$\\beta\\sim0.9$ to 0.7 for K giants and from $\\beta\\sim0.8$ to 0.1 for blue\nhorizontal branch stars. For [Fe/H] $<-1.7$, the smooth, diffuse halo\nanisotropy remains constant along all distances with $0.2<\\beta<0.7$ depending\non the metallicity range probed, although independent on star type. These\nsamples are ideal for estimating the total Galactic mass as they represent the\nvirialized stellar halo system.", "category": "astro-ph_GA" }, { "text": "Kiloparsec-scale jets in three radio-loud narrow-line Seyfert 1 galaxies: We have discovered kiloparsec-scale extended radio emission in three\nnarrow-line Seyfert 1 galaxies (NLS1s) in sub-arcsecond resolution 9 GHz images\nfrom the Karl G. Jansky Very Large Array (VLA). We find all sources show\ntwo-sided, mildly core-dominated jet structures with diffuse lobes dominated by\ntermination hotspots. These span 20-70 kpc with morphologies reminiscent of FR\nII radio galaxies, while the extended radio luminosities are intermediate\nbetween FR I and FR II sources. In two cases the structure is linear, while a\n$45^{\\circ}$ bend is apparent in the third. Very Long Baseline Array images at\n7.6 GHz reveal parsec-scale jet structures, in two cases with extended\nstructure aligned with the inner regions of the kiloparsec-scale jets. Based on\nthis alignment, the ratio of the radio core luminosity to the optical\nluminosity, the jet/counter-jet intensity and extension length ratios, and\nmoderate core brightness temperatures ($\\lesssim10^{10}$ K), we conclude these\njets are mildly relativistic ($\\beta\\lesssim0.3$, $\\delta\\sim1$-$1.5$) and\naligned at moderately small angles to the line of sight (10-15$^{\\circ}$). The\nderived kinematic ages of $\\sim10^6$-$10^7$ y are much younger than radio\ngalaxies but comparable to other NLS1s. Our results increase the number of\nradio-loud NLS1s with known kiloparsec-scale extensions from seven to ten and\nsuggest that such extended emission may be common, at least among the brightest\nof these sources.", "category": "astro-ph_GA" }, { "text": "AlFoCS + Fornax3D: resolved star formation in the Fornax cluster with\n ALMA and MUSE: We combine data from ALMA and MUSE to study the resolved (~300 pc scale) star\nformation relation (star formation rate vs. molecular gas surface density) in\ncluster galaxies. Our sample consists of 9 Fornax cluster galaxies, including\nspirals, ellipticals, and dwarfs, covering a stellar mass range of ~10^8.8 -\n10^11 M_Sun. CO(1-0) and extinction corrected Halpha were used as tracers for\nthe molecular gas mass and star formation rate, respectively. We compare our\nresults with Kennicutt (1998) and Bigiel et al. (2008). Furthermore, we create\ndepletion time maps to reveal small-scale variations in individual galaxies. We\nexplore these further in FCC290, using the 'uncertainty principle for star\nformation' (Kruijssen & Longmore, 2014a) to estimate molecular cloud lifetimes,\nwhich we find to be short (<10 Myr) in this galaxy. Galaxy-averaged depletion\ntimes are compared with other parameters such as stellar mass and\ncluster-centric distance. We find that the star formation relation in the\nFornax cluster is close to those from Kennicutt (1998) and Bigiel et al.\n(2008}), but overlaps mostly with the shortest depletion times predicted by\nBigiel et al. (2008). This slight decrease in depletion time is mostly driven\nby dwarf galaxies with disturbed molecular gas reservoirs close to the virial\nradius. In FCC90, a dwarf galaxy with a molecular gas tail, we find that\ndepletion times are a factor >~10 higher in its tail than in its stellar body.", "category": "astro-ph_GA" }, { "text": "Molecular outflows in local ULIRGs: energetics from multi-transition OH\n analysis: We report on the energetics of molecular outflows in 14 local Ultraluminous\nInfrared Galaxies (ULIRGs) that show unambiguous outflow signatures (P-Cygni\nprofiles or high-velocity absorption wings) in the far-infrared lines of OH\nmeasured with the Herschel/PACS spectrometer. Detection of both ground-state\n(at 119 and 79 um) and one or more radiatively-excited (at 65 and 84 um) lines\nallows us to model the nuclear gas (<~300 pc) as well as the more extended\ncomponents using spherically symmetric radiative transfer models. The highest\nmolecular outflow velocities are found in buried sources, in which slower but\nmassive expansion of the nuclear gas is also observed. With the exception of a\nfew outliers, the outflows have momentum fluxes of (2-5)xL_IR/c and mechanical\nluminosities of (0.1-0.3)% of L_IR. The moderate momentum boosts in these\nsources (<~3) suggest that the outflows are mostly momentum-driven by the\ncombined effects of AGN and nuclear starbursts, as a result of radiation\npressure, winds, and supernovae remnants. In some sources (~20%), however,\npowerful (10^{10.5-11} Lsun) AGN feedback and (partially) energy-conserving\nphases are required, with momentum boosts in the range 3-20. These outflows\nappear to be stochastic strong-AGN feedback events that occur throughout the\nmerging process. In a few sources, the outflow activity in the innermost\nregions has subsided in the last ~1 Myr. While OH traces the molecular outflows\nat sub-kpc scales, comparison of the masses traced by OH with those previously\ninferred from tracers of more extended outflowing gas suggests that most mass\nis loaded (with loading factors of Mdot/SFR=1-10) from the central galactic\ncores (a few x 100 pc). Outflow depletion timescales are <10^8 yr, shorter than\nthe gas consumption timescales by factors of 1.1-15, and are anti-correlated\nwith the AGN luminosity.", "category": "astro-ph_GA" }, { "text": "The anti-correlation between the hard X-ray photon index and the\n Eddington ratio in LLAGNs: We find a significant anti-correlation between the hard X-ray photon index\nand the Eddington ratio L_Bol/L_Edd for a sample of Low-Ionization Nuclear\nEmission-line Regions (LINERs) and local Seyfert galaxies, compiled from\nliteratures with Chandra or XMM-Newton observations. This result is in contrast\nwith the positive correlation found in luminous active galactic nuclei (AGNs),\nwhile it is similar to that of X-ray binaries (XRBs) in low/hard state. Our\nresult is qualitatively consistent with the spectra produced from advection\ndominated accretion flows (ADAFs). It implies that the X-ray emission of\nlow-luminosity active galactic nuclei (LLAGNs) may originate from the\nComptonization process in ADAF, and the accretion process in LLAGNs may be\nsimilar to that of XRBs in the low/hard state, which is different from that in\nluminous AGNs.", "category": "astro-ph_GA" }, { "text": "Missing dark matter in dwarf galaxies?: We use cosmological hydrodynamical simulations of the APOSTLE project along\nwith high-quality rotation curve observations to examine the fraction of\nbaryons in {\\Lambda}CDM haloes that collect into galaxies. This 'galaxy\nformation efficiency' correlates strongly and with little scatter with halo\nmass, dropping steadily towards dwarf galaxies. The baryonic mass of a galaxy\nmay thus be used to place a lower limit on total halo mass and, consequently,\non its asymptotic maximum circular velocity. A number of observed dwarfs seem\nto violate this constraint, having baryonic masses up to ten times higher than\nexpected from their rotation speeds, or, alternatively, rotating at only half\nthe speed expected for their mass. Taking the data at face value, either these\nsystems have formed galaxies with extraordinary efficiency - highly unlikely\ngiven their shallow potential wells - or their dark matter content is much\nlower than expected from {\\Lambda}CDM haloes. This 'missing dark matter' is\nreminiscent of the inner mass deficit of galaxies with slowly-rising rotation\ncurves, but cannot be explained away by star formation-induced 'cores' in the\ndark mass profile, since the anomalous deficit applies to regions larger than\nthe luminous galaxies themselves. We argue that explaining the structure of\nthese galaxies would require either substantial modification of the standard\nLambda cold dark matter paradigm or else significant revision to the\nuncertainties in their inferred mass profiles, which should be much larger than\nreported. Systematic errors in inclination may provide a simple resolution to\nwhat would otherwise be a rather intractable problem for the current paradigm.", "category": "astro-ph_GA" }, { "text": "GASP XXXIII. The ability of spatially resolved data to distinguish among\n the different physical mechanisms affecting galaxies in low-density\n environments: Galaxies inhabit a wide range of environments and therefore are affected by\ndifferent physical mechanisms. Spatially resolved maps combined with the\nknowledge of the hosting environment are very powerful to classify galaxies by\nphysical process. In the context of the GAs Stripping Phenomena in galaxies\n(GASP), we present a study of 27 non-cluster galaxies: 24 of them were selected\nfor showing asymmetries and disturbances in the optical morphology, suggestive\nof gas stripping, three of them are passive galaxies and were included to\ncharacterize the final stages of galaxy evolution. We therefore provide a\npanorama of the different processes taking place in low-density environments.\nThe analysis of VLT/MUSE data allows us to separate galaxies into the following\ncategories: Galaxy-galaxy interactions (2 galaxies), mergers (6), ram pressure\nstripping (4), cosmic web stripping (2), cosmic web enhancement (5), gas\naccretion (3), starvation (3). In one galaxy we identify the combination of\nmerger and ram pressure stripping. Only 6/27 of these galaxies have just a\ntentative classification. We then investigate where these galaxies are located\non scaling relations determined for a sample of undisturbed galaxies. Our\nanalysis shows the successes and limitations of a visual optical selection in\nidentifying the processes that deplete galaxies of their gas content and probes\nthe power of IFU data in pinning down the acting mechanism.", "category": "astro-ph_GA" }, { "text": "Mass and Magnetic distributions in Self Gravitating Super Alfvenic\n Turbulence with AMR: In this work, we present the mass and magnetic distributions found in a\nrecent Adaptive Mesh Refinement (AMR) MHD simulation of supersonic, \\sa, self\ngravitating turbulence. Powerlaw tails are found in both volume density and\nmagnetic field probability density functions, with $P(\\rho) \\propto\n\\rho^{-1.67}$ and $P(B)\\propto B^{-2.74}$. A power law is also found between\nmagnetic field strength and density, with $B\\propto \\rho^{0.48}$, throughout\nthe collapsing gas. The mass distribution of gravitationally bound cores is\nshown to be in excellent agreement with recent observation of prestellar cores.\nThe mass to flux distribution of cores is also found to be in excellent\nagreement with recent Zeeman splitting measurements.", "category": "astro-ph_GA" }, { "text": "Constraining the Galactic millisecond pulsar population using Fermi\n Large Area Telescope: The Fermi Large Area Telescope (Fermi-LAT) has recently revealed a large\npopulation of gamma-ray emitting millisecond pulsars (MSPs) in our Galaxy. We\naim to infer the properties of the Galactic population of gamma-ray emitting\nMSPs from the samples detected by the Fermi-LAT. We developed a Monte Carlo\nmodel to predict the spatial and gamma-ray luminosity distribution of the\nGalactic MSP population. Based on the estimated detection sensitivity of\nFermi-LAT, we split the model population into detectable and undetectable\nsamples of MSPs. Using a maximum likelihood method, we compared the detectable\nsample to a set of 36 MSPs detected by Fermi-LAT, and we derived the parameters\nof the spatial distribution and the total number of gamma-ray emitting MSPs in\nthe Galaxy. The corresponding undetectable sample provided us with an estimate\nfor the expected diffuse emission from unresolved MSPs in the Milky Way. We\nalso applied our method to an extended sample of 66 MSPs that combines firmly\ndetected MSPs and gamma-ray sources that show characteristics reminiscent of\nMSPs. For the first time our analysis provides gamma-ray based constraints on\nthe Galactic population of MSPs. The radial scale length and vertical scale\nheight of the population is consistent with estimates based on radio data. Our\nanalysis suggests that MSPs do not provide any significant contribution to the\nisotropic diffuse gamma-ray background emission.", "category": "astro-ph_GA" }, { "text": "Hierarchical structures in the Large and Small Magellanic Clouds: We investigate the degree of spatial correlation among extended structures in\nthe LMC and SMC. To this purpose we work with sub-samples characterised by\ndifferent properties such as age and size, taken from the updated catalogue of\nBica et al. or gathered in the present work. The structures are classified as\nstar clusters or non-clusters (basically, nebular complexes and their stellar\nassociations). The radius distribution functions follow power-laws\n($dN/dR\\propto R^{-\\alpha}$) with slopes and maximum radius ($R_{max}$) that\ndepend on object class (and age). Non-clusters are characterised by\n$\\alpha\\approx1.9$ and $R_{max}\\la472$ pc, while young clusters (age $\\la10$\nMyr) have $\\alpha\\approx3.6$ and $R_{max}\\la15$ pc, and old ones (age $\\ga600$\nMyr) have $\\alpha\\approx2.5$ and $R_{max}\\la40$ pc. Young clusters present a\nhigh degree of spatial self-correlation and, especially, correlate with\nstar-forming structures, which does not occur with the old ones. This is\nconsistent with the old clusters having been heavily mixed up, since their ages\ncorrespond to several LMC and SMC crossing times. On the other hand, with ages\ncorresponding to fractions of the respective crossing times, the young clusters\nstill trace most of their birthplace structural pattern. Also, small clusters\n($R<10$ pc), as well as small non-clusters ($R<100$ pc), are spatially\nself-correlated, while their large counterparts of both classes are not. The\nabove results are consistent with a hierarchical star-formation scenario for\nthe LMC and SMC.", "category": "astro-ph_GA" }, { "text": "New insights from deep VLA data on the potentially recoiling black hole\n CID-42 in the COSMOS field: We present deep 3 GHz VLA observations of the potentially recoiling black\nhole CID-42 in the COSMOS field. This galaxy shows two optical nuclei in the\nHST/ACS image and a large velocity offset of ~ 1300 km/s between the broad and\nnarrow H beta emission line although the spectrum is not spacially resolved\n(Civano et al. 2010). The new 3 GHz VLA data has a bandwidth of 2 GHz and to\ncorrectly interpret the flux densities imaging was done with two different\nmethods: multi-scale multi-frequency synthesis and spectral windows stacking.\nThe final resolutions and sensitivities of these maps are 0.7\" with rms = 4.6\nmuJy/beam and 0.9\" with rms = 4.8 muJy/beam respectively. With a 7 sigma\ndetection we find that the entire observed 3 GHz radio emission can be\nassociated with the South-Eastern component of CID-42, coincident with the\ndetected X-ray emission. We use our 3 GHz data combined with other radio data\nfrom the literature ranging from 320 MHz to 9 GHz, which include the VLA, VLBA\nand GMRT data, to construct a radio synchrotron spectrum of CID-42. The radio\nspectrum suggests a type I unobscured radio-quiet flat-spectrum AGN in the\nSouth-Eastern component which may be surrounded by a more extended region of\nold synchrotron electron population or shocks generated by the outflow from the\nsupermassive black hole. Our data are consistent with the recoiling black hole\npicture but cannot rule out the presence of an obscured and radio-quiet SMBH in\nthe North-Western component.", "category": "astro-ph_GA" }, { "text": "The Catalogue for Astrophysical Turbulence Simulations (CATS): Turbulence is a key process in many fields of astrophysics. Advances in\nnumerical simulations of fluids over the last several decades have\nrevolutionized our understanding of turbulence and related processes such as\nstar formation and cosmic ray propagation. However, data from numerical\nsimulations of astrophysical turbulence are often not made public. We introduce\na new simulation-oriented database for the astronomical community: The\nCatalogue for Astrophysical Turbulence Simulations (CATS), located at\nwww.mhdturbulence.com. CATS includes magnetohydrodynamic (MHD) turbulent box\nsimulation data products generated by the public codes athena++, arepo, enzo,\nand flash. CATS also includes several synthetic observational data sets, such\nas turbulent HI data cubes. We also include measured power spectra and 3-point\ncorrelation functions from some of these data. We discuss the importance of\nopen source statistical and visualization tools for the analysis of turbulence\nsimulations such as those found in CATS.", "category": "astro-ph_GA" }, { "text": "Exploring the Galactic Anticenter substructure with LAMOST & Gaia DR2: We characterize the kinematic and chemical properties of 589 Galactic\nAnticenter Substructure Stars (GASS) with K-/M- giants in Integrals-of-Motion\nspace. These stars likely include members of previously identified\nsubstructures such as Monoceros, A13, and the Triangulum-Andromeda cloud\n(TriAnd). We show that these stars are on nearly circular orbits on both sides\nof the Galactic plane. We can see velocity($V_{Z}$) gradient along Y-axis\nespecially for the south GASS members. Our GASS members have similar energy and\nangular momentum distributions to thin disk stars. Their location in\n[$\\alpha$/M] vs. [M/H] space is more metal poor than typical thin disk stars,\nwith [$\\alpha$/M] \\textbf{lower} than the thick disk. We infer that our GASS\nmembers are part of the outer metal-poor disk stars, and the outer-disk extends\nto 30 kpc. Considering the distance range and $\\alpha$-abundance features, GASS\ncould be formed after the thick disk was formed due to the molecular cloud\ndensity decreased in the outer disk where the SFR might be less efficient than\nthe inner disk.", "category": "astro-ph_GA" }, { "text": "The GLASS James Webb Space Telescope Early Release Science Program. I.\n Survey Design and Release Plans: The GLASS James Webb Space Telescope Early Release Science (hereafter\nGLASS-JWST-ERS) Program will obtain and make publicly available the deepest\nextragalactic data of the ERS campaign. It is primarily designed to address two\nkey science questions, namely, \"what sources ionized the universe and when?\"\nand \"how do baryons cycle through galaxies?\", while also enabling a broad\nvariety of first look scientific investigations. In primary mode, it will\nobtain NIRISS and NIRSpec spectroscopy of galaxies lensed by the foreground\nHubble Frontier Field cluster, Abell 2744. In parallel, it will use NIRCam to\nobserve two fields that are offset from the cluster center, where lensing\nmagnification is negligible, and which can thus be effectively considered blank\nfields. In order to prepare the community for access to this unprecedented\ndata, we describe the scientific rationale, the survey design (including target\nselection and observational setups), and present pre-commissioning estimates of\nthe expected sensitivity. In addition, we describe the planned public releases\nof high-level data products, for use by the wider astronomical community.", "category": "astro-ph_GA" }, { "text": "The effect of primordial mass segregation on the size scale of globular\n clusters: We use direct $N$-body calculations to investigate the impact of primordial\nmass segregation on the size scale and mass-loss rate of star clusters in a\ngalactic tidal field. We run a set of simulations of clusters with varying\ndegrees of primordial mass segregation at various galactocentric radii and show\nthat, in primordially segregated clusters, the early, impulsive mass-loss from\nstellar evolution of the most massive stars in the innermost regions of the\ncluster leads to a stronger expansion than for initially non-segregated\nclusters. Therefore, models in stronger tidal fields dissolve faster due to an\nenhanced flux of stars over the tidal boundary. Throughout their lifetimes, the\nsegregated clusters are more extended by a factor of about 2, suggesting that\n(at least) some of the very extended globular clusters in the outer halo of the\nMilky Way may have been born with primordial mass segregation. We finally\nderive a relation between star-cluster dissolution time, $T_{diss}$, and\ngalactocentric radius, $R_G$, and show how it depends on the degree of\nprimordial mass segregation.", "category": "astro-ph_GA" }, { "text": "Gas expulsion in massive star clusters? Constraints from observations of\n young and gas-free objects: Gas expulsion is a central concept in some of the models for multiple\npopulations and the light-element anticorrelations in globular clusters. If the\nstar formation efficiency was around 30 per cent and the gas expulsion happened\non the crossing timescale, this process could expel preferentially stars born\nwith the chemical composition of the proto-cluster gas, while stars with\nspecial composition born in the centre would remain bound. Recently, a sample\nof extragalactic, gas-free, young massive clusters has been identified that has\nthe potential to test the conditions for gas expulsion. We compute a large\nnumber of thin shell models, and calculate if the Rayleigh-Taylor instability\nis able to disrupt the shell before it reaches the escape speed. We show that\nthe success of gas expulsion depends on the compactness index of a star cluster\nC5, proportionate to stellar mass over half-mass radius. For given C5, a\ncertain critical, local star formation efficiency is required to remove the\nrest of the gas. Common stellar feedback processes may not lead to gas\nexpulsion with significant loss of stars above C5 = 1. Considering pulsar winds\nand hypernovae, the limit increases to C5 = 30. If successful, gas expulsion\ngenerally takes place on the crossing timescale. Some observed young massive\nclusters have 1 < C5 < 10 and are gas-free at 10 Myr. This suggests that gas\nexpulsion does not affect their stellar mass significantly, unless powerful\npulsar winds and hypernovae are common in such objects. By comparison to\nobservations, we show that C5 is a better predictor for the expression of\nmultiple populations than stellar mass. The best separation between star\nclusters with and without multiple populations is achieved by a stellar\nwinds-based gas expulsion model, where gas expulsion would occur exclusively in\nstar clusters without multiple populations.", "category": "astro-ph_GA" }, { "text": "Polarization, Polarizing Efficiency, and Grain alignment towards the\n direction of the cluster NGC 2345: We have investigated the grain alignment and dust properties towards the\ndirection of the cluster NGC 2345 using the multi-band optical polarimetric\nobservations. For the majority of the stars, the observed polarization is found\nto be due to the interstellar medium with average values of maximum\npolarization and wavelength corresponding to it as 1.55% and 0.58 $\\mu m$,\nrespectively. This reveals a similar size distribution of dust grains to that\nin the general interstellar medium in the direction of NGC 2345. Alteration of\ndust properties near the distance of 1.2 kpc towards the direction of NGC 2345\nhas been noticed. The dust grains located beyond this distance are found to be\naligned with the Galactic magnetic field, whereas a dispersion in orientation\nof the dust grains lying in the foreground of this distance is found.\nPolarizing efficiency of grains in this direction is found to be close to the\naverage efficiency for our Galaxy. The decreased grain size along with the\nincreased polarizing efficiency towards the core region of the cluster\nindicates the local radiation field is higher within the cluster which is\nresponsible for the increased alignment efficiency of small grains. The\nwavelength of maximum polarization (associated with the average size of aligned\ngrains) is also found to increase with extinction and reduces with the increase\nin polarizing efficiency, which can be explained by the radiative torque\nalignment mechanism.", "category": "astro-ph_GA" }, { "text": "The rapid transition from star-formation to AGN dominated rest-frame UV\n light at z ~ 4: With the advent of deep optical-to-near-infrared extragalactic imaging on the\ndegree scale, samples of high-redshift sources are being selected that contain\nboth bright star-forming (SF) galaxies and faint active galactic nuclei (AGN).\nIn this study we investigate the transition between SF and AGN-dominated\nsystems at $z \\simeq 4$ in the rest-frame UV. We find a rapid transition to\nAGN-dominated sources bright-ward of $M_{\\rm UV} \\simeq -23.2$. The effect is\nobserved in the rest-frame UV morphology and size-luminosity relation, where\nextended clumpy systems become point-source dominated, and also in the\navailable spectra for the sample. These results allow us to derive the\nrest-frame UV luminosity function for the SF and AGN-dominated sub-samples. We\nfind the SF-dominated LF is best fit with a double-power law, with a lensed\nSchechter function being unable to explain the existence of extremely luminous\nSF galaxies at $M_{\\rm UV} \\simeq -23.5$. If we identify AGN-dominated sources\naccording to a point-source morphology criterion we recover the relatively flat\nfaint-end slope of the AGN LF determined in previous studies. If we instead\nseparate the LF according to the current spectroscopic AGN fraction, we find a\nsteeper faint-end slope of $\\alpha = -1.83 \\pm 0.11$. Using a simple model to\npredict the rest-frame AGN LF from the $z = 4 $ galaxy LF we find that the\nincreasing impact of host galaxy light on the measured morphology of faint AGN\ncan explain our observations.", "category": "astro-ph_GA" }, { "text": "Evidence for photoionization-driven variability in narrow absorption\n lines: In this Letter, we report the discovery of a strong correlation between the\nvariability of narrow absorption lines (NALs) and the ionizing continuum from a\ntwo-epoch spectra sample of 40 quasars containing 52 variable C iv\n{\\lambda}{\\lambda}1548; 1551 absorption doublets. According to the concordance\nindex, this sample is classified into two subsamples. Subsample I shows an\nanti-correlation between the variations of absorption lines and the continuum,\nwhile Subsample II exhibits a positive correlation. These results imply that\nthese variable C iv {\\lambda}{\\lambda}1548; 1551 absorption doublets are\nintrinsic to the corresponding quasars and that their variations are caused\nprimarily by the fluctuations of the ionizing continuum. Based on our analysis,\nwe propose that there might be two kinds of absorption gas: one that is very\nsensitive to the continuum variations, the another that is not. In addition, we\nsuggest that in many cases the emergence or disappearance of NALs is caused by\nfluctuations of the ionizing continuum.", "category": "astro-ph_GA" }, { "text": "Local Stability of Galactic Discs in Modified Dynamics: The local stability of stellar and fluid discs, under a new modified\ndynamical model, is surveyed by using WKB approximation. The exact form of the\nmodified Toomre criterion is derived for both types of systems and it is shown\nthat the new model is, in all situations, more locally stable than Newtonian\nmodel. In addition, it has been proved that the central surface density of the\ngalaxies plays an important role in the local stability in the sense that LSB\ngalaxies are more stable than HSBs. Furthermore, the growth rate in the new\nmodel is found to be lower than the Newtonian one. We found that, according to\nthis model, the local instability is related to the ratio of surface density of\nthe disc to a critical surface density $\\Sigma^{crit}$. We provide\nobservational evidence to support this result based on star formation rate in\nHSBs and LSBs.", "category": "astro-ph_GA" }, { "text": "Multivariate Approaches to Classification in Extragalactic Astronomy: Clustering objects into synthetic groups is a natural activity of any\nscience. Astrophysics is not an exception and is now facing a deluge of data.\nFor galaxies, the one-century old Hubble classification and the Hubble tuning\nfork are still largely in use, together with numerous mono-or bivariate\nclassifications most often made by eye. However, a classification must be\ndriven by the data, and sophisticated multivariate statistical tools are used\nmore and more often. In this paper we review these different approaches in\norder to situate them in the general context of unsupervised and supervised\nlearning. We insist on the astrophysical outcomes of these studies to show that\nmultivariate analyses provide an obvious path toward a renewal of our\nclassification of galaxies and are invaluable tools to investigate the physics\nand evolution of galaxies.", "category": "astro-ph_GA" }, { "text": "Systematic variations of interstellar linear polarization and growth of\n dust grains: A quantitative interpretation of the observed relation between the\ninterstellar linear polarization curve parameters $K$ and $\\lambda_{\\max}$\ncharacterizing the width and the wavelength of a polarization maximum,\nrespectively, is given. The observational data available for 57 stars located\nin the dark clouds in Taurus, Chamaeleon, around the stars $\\rho$ Oph and R CrA\nare considered. The spheroidal particle model of interstellar dust grains\nearlier applied to simultaneously interpret the interstellar extinction and\npolarization curves in a wide spectral range is utilized. The observed trend $K\n\\approx 1.7 \\lambda_{\\max}$ is shown to be most likely related to a growth of\ndust grains due to coagulation rather than mantle accretion. The relation of\nthe parameters $K$ and $\\lambda_{\\max}$ with an average size of silicate dust\ngrains is discussed.", "category": "astro-ph_GA" }, { "text": "Detecting the effect of non-thermal sources on the warm-hot Galactic\n halo: We report the first detection of non-thermal broadening of OVII lines in the\nwarm-hot $\\approx 10^6$ K circumgalactic medium (CGM) of the Milky Way. We use\n$z$=0 absorption of OVII K$\\alpha$, OVII K$\\beta$, and OVIII K$\\alpha$ lines in\narchival grating data of $b>$15$^\\circ$ quasar sightlines from $Chandra$ and\n$XMM$-$Newton$. Non-thermal line broadening is evident in two-third of the\nsightlines considered, and on average is constrained at 4.6$\\sigma$\nsignificance. Non-thermal line broadening dominates over thermal broadening. We\nextensively test whether the appearance of non-thermal line broadening could\ninstead be because of multiple thermally broadened velocity components and\nrobustly rule it out. Non-thermal line broadening is more evident toward\nsightlines at lower galactic latitude indicating the Galactic disk origin of\nthe nonthermal sources. There is weak/no correlation between non-thermal line\nbroadening and the angular separation of sightlines from the Galactic center,\nindicating that the nuclear region might not be a major source of non-thermal\nfactors.", "category": "astro-ph_GA" }, { "text": "Dust-depletion sequences in damped Ly-\u03b1 absorbers II. The\n composition of cosmic dust, from low-metallicity systems to the Galaxy: We aim at assessing what are the most dominant dust species or types,\nincluding silicate and iron oxide grains present in the ISM, by using recent\nobservations of dust depletion of galaxies at various evolutionary stages. We\nuse the observed elemental abundances in dust of several metals (O, S, Si, Mg,\nand Fe) in different environments, considering systems with different\nmetallicities and dust content, namely damped Lyman-{\\alpha} absorbers (DLAs)\ntowards quasars and the Galaxy. We derive a possible dust composition by\ncomputationally finding the statistically expected elemental abundances in dust\nassuming a set of key dust species with the iron content as a free parameter.\nCarbonaceous dust is not considered in the present study. Metallic iron (likely\nin the form of inclusions in silicate grains) and iron oxides is an important\ncomponent of the mass composition of carbon-free dust. Iron oxides make up a\nsignificant mass fraction (~1/4 in some cases) of the oxygen-bearing dust and\nthere are good reasons to believe that metallic iron constitutes a similar mass\nfraction of dust. W\\\"ustite (FeO) could be a simple explanation for the\ndepletion of iron and oxygen because it is easily formed. There appears to be\nno silicate species clearly dominating the silicate mass, but rather a mix of\niron-poor as well as iron-rich olivine and pyroxene. To what extent sulphur\ndepletion is due to sulfides remains unclear. In general, there seems to be\nlittle evolution of the dust composition (not considering carbonaceous dust)\nfrom low-metallicity systems to the Galaxy.", "category": "astro-ph_GA" }, { "text": "Galaxy Zoo: constraining the origin of spiral arms: Since the discovery that the majority of low-redshift galaxies exhibit some\nlevel of spiral structure, a number of theories have been proposed as to why\nthese patterns exist. A popular explanation is a process known as swing\namplification, yet there is no observational evidence to prove that such a\nmechanism is at play. By using a number of measured properties of galaxies, and\nscaling relations where there are no direct measurements, we model samples of\nSDSS and S$^4$G spiral galaxies in terms of their relative halo, bulge and disc\nmass and size. Using these models, we test predictions of swing amplification\ntheory with respect to directly measured spiral arm numbers from Galaxy Zoo 2.\nWe find that neither a universal cored or cuspy inner dark matter profile can\ncorrectly predict observed numbers of arms in galaxies. However, by invoking a\nhalo contraction/expansion model, a clear bimodality in the spiral galaxy\npopulation emerges. Approximately 40 per cent of unbarred spiral galaxies at $z\n\\lesssim 0.1$ and $\\mathrm{M_*} \\gtrsim 10^{10} \\mathrm{M_\\odot}$ have spiral\narms that can be modelled by swing amplification. This population display a\nsignificant correlation between predicted and observed spiral arm numbers,\nevidence that they are swing amplified modes. The remainder are dominated by\ntwo-arm systems for which the model predicts significantly higher arm numbers.\nThese are likely driven by tidal interactions or other mechanisms.", "category": "astro-ph_GA" }, { "text": "Gas Dynamics in the Galaxy: Total Mass Distribution and the Bar Pattern\n Speed: Gas morphology and kinematics in the Milky Way contain key information for\nunderstanding the formation and evolution of our Galaxy. We present a high\nresolution hydrodynamical simulation based on a realistic barred Milky Way\npotential constrained by recent observations. Our model can reproduce most\nfeatures in the observed longitude-velocity diagram, including the Central\nMolecular Zone, the Near and Far 3-kpc arms, the Molecular Ring, and the spiral\narm tangents. It can also explain the non-circular motions of masers obtained\nby the recent BeSSeL2 survey. The central gas kinematics are consistent with a\nmass of $6.9\\times10^8\\; {\\rm M}_{\\odot}$ in the Nuclear Stellar Disk. Our\nmodel predicts the formation of an elliptical gaseous ring surrounding the bar,\nwhich is composed of the 3-kpc arms, Norma arm, and the bar-spiral interfaces.\nThis ring is similar to those \"inner\" rings in some Milky Way analogs with a\nboxy/peanut-shaped bulge. The kinematics of gas near the solar neighbourhood\nare governed by the Local arm, which is induced by the four major stellar\nspiral arms. The bar pattern speed constrained by our gas model is $37.5-40\\;\n{\\rm km}\\;{\\rm s}^{-1}\\;{\\rm kpc}^{-1}$, corresponding to a corotation radius\nof $R_{\\rm CR}=6.0-6.4\\;{\\rm kpc}$. The rotation curve of our model rises\ngently within the central $\\sim5\\;{\\rm kpc}$, which is significantly less steep\nthan those predicted by modern zoom-in cosmological simulations such as Auriga.", "category": "astro-ph_GA" }, { "text": "Rapid Black Hole Growth under Anisotropic Radiation Feedback: Discovery of high-redshift (z > 6) supermassive black holes (BHs) may\nindicate that the rapid (or super-Eddington) gas accretion has aided their\nquick growth. Here, we study such rapid accretion of the primordial gas on to\nintermediate-mass (10^2 - 10^5 M_sun) BHs under anisotropic radiation feedback.\nWe perform two-dimensional radiation hydrodynamics simulations that solve the\nflow structure across the Bondi radius, from far outside of the Bondi radius\ndown to a central part which is larger than a circum-BH accretion disc. The\nradiation from the unresolved circum-BH disc is analytically modeled\nconsidering self-shadowing effect. We show that the flow settles into a steady\nstate, where the flow structure consists of two distinct parts: (1) bipolar\nionized outflowing regions, where the gas is pushed outward by thermal gas\npressure and super-Eddington radiation pressure, and (2) an equatorial neutral\ninflowing region, where the gas falls toward the central BH without affected by\nradiation feedback. The resulting accretion rate is much higher than that in\nthe case of isotropic radiation, far exceeding the Eddington-limited rate to\nreach a value slightly lower than the Bondi one. The opening angle of the\nequatorial inflowing region is determined by the luminosity and directional\ndependence of the central radiation. We find that photoevaporation from its\nsurfaces set the critical opening angle of about ten degrees below which the\naccretion to the BH is quenched. We suggest that the shadowing effect allows\neven stellar-remnant BHs to grow rapidly enough to become high-redshift\nsupermassive BHs.", "category": "astro-ph_GA" }, { "text": "Spectroscopic confirmation of the dwarf spheroidal galaxy d0944+71 as a\n member of the M81 group of galaxies: We use Keck/DEIMOS spectroscopy to measure the first velocity and metallicity\nof a dwarf spheroidal (dSph) galaxy beyond the Local Group using resolved\nstars. Our target, d0944+71, is a faint dSph found in the halo of the massive\nspiral galaxy M81 by Chiboucas et al. We coadd the spectra of 27 individual\nstars and measure a heliocentric radial velocity of $-38\\pm10$~km/s. This\nvelocity is consistent with d0944+71 being gravitationally bound to M81. We\ncoadd the spectra of the 23 stars that are consistent with being red giant\nbranch stars and measure an overall metallicity of ${\\rm [Fe/H]}=-1.3 \\pm 0.3$\nbased on the calcium triplet lines. This metallicity is consistent with\nd0944+71 following the metallicity$-$luminosity relation for Local Group dSphs.\nWe investigate several potential sources of observational bias but find that\nour sample of targeted stars is representative of the metallicity distribution\nfunction of d0944+71 and any stellar contamination due to seeing effects is\nnegligible. The low ellipticity of the galaxy and its position in the\nmetallicity$-$luminosity relation suggest that d0944+71 has not been affected\nby strong tidal stripping.", "category": "astro-ph_GA" }, { "text": "The Relation Between [OIII]/H$\u03b2$ and Specific Star Formation Rate in\n Galaxies at $z \\sim 2$: Recent surveys have identified a seemingly ubiquitous population of galaxies\nwith elevated [OIII]/H$\\beta$ emission line ratios at $z > 1$, though the\nnature of this phenomenon continues to be debated. The [OIII]/H$\\beta$ line\nratio is of interest because it is a main component of the standard diagnostic\ntools used to differentiate between active galactic nuclei (AGN) and\nstar-forming galaxies, as well as the gas-phase metallicity indicators $O_{23}$\nand $R_{23}$. Here, we investigate the primary driver of increased\n[OIII]/H$\\beta$ ratios by median-stacking rest-frame optical spectra for a\nsample of star-forming galaxies in the 3D-HST survey in the redshift range\n$z\\sim1.4-2.2$. Using $N = 4220$ star-forming galaxies, we stack the data in\nbins of mass and specific star formation rates (sSFR) respectively. After\naccounting for stellar Balmer absorption, we measure\n[OIII]$\\lambda5007$\\AA/H$\\beta$ down to $\\mathrm{M} \\sim 10^{9.2} \\\n\\mathrm{M_\\odot}$ and sSFR $\\sim 10^{-9.6} \\ \\mathrm{yr}^{-1}$, more than an\norder of magnitude lower than previous work at similar redshifts. We find an\noffset of $0.59\\pm0.05$ dex between the median ratios at $z\\sim2$ and $z\\sim0$\nat fixed stellar mass, in agreement with existing studies. However, with\nrespect to sSFR, the $z \\sim 2$ stacks all lie within 1$\\sigma$ of the median\nSDSS ratios, with an average offset of only $-0.06\\pm 0.05$. We find that the\nexcitation properties of galaxies are tightly correlated with their sSFR at\nboth $z\\sim2$ and $z\\sim0$, with a relation that appears to be roughly constant\nover the last 10 Gyr of cosmic time.", "category": "astro-ph_GA" }, { "text": "JWST Reveals Widespread AGN-Driven Neutral Gas Outflows in Massive z ~ 2\n Galaxies: We use deep JWST/NIRSpec R~1000 slit spectra of 113 galaxies at 1.7 < z <\n3.5, selected from the mass-complete Blue Jay survey, to investigate the\nprevalence and typical properties of neutral gas outflows at cosmic noon. We\ndetect excess Na I D absorption (beyond the stellar contribution) in 46% of\nmassive galaxies ($\\log$ M$_*$/M$_\\odot >$ 10), with similar incidence rates in\nstar-forming and quenching systems. Half of the absorption profiles are\nblueshifted by at least 100 km/s, providing unambiguous evidence for neutral\ngas outflows. Galaxies with strong Na I D absorption are distinguished by\nenhanced emission line ratios consistent with AGN ionization. We conservatively\nmeasure mass outflow rates of 3 - 100 $M_\\odot$ yr$^{-1}$; comparable to or\nexceeding ionized gas outflow rates measured for galaxies at similar stellar\nmass and redshift. The outflows from the quenching systems\n(log(sSFR)[yr$^{-1}$] $\\lesssim$ -10) have mass loading factors of 4 - 360, and\nthe energy and momentum outflow rates exceed the expected injection rates from\nsupernova explosions, suggesting that these galaxies could possibly be caught\nin a rapid blowout phase powered by the AGN. Our findings suggest that\nAGN-driven ejection of cold gas may be a dominant mechanism for fast quenching\nof star formation at z~2.", "category": "astro-ph_GA" }, { "text": "SDSS-IV MaNGA: the indispensable role of bars in enhancing the central\n star formation of low-$z$ galaxies: We analyse two-dimensional maps and radial profiles of EW(H$\\alpha$),\nEW(H$\\delta_A$), and D$_n$(4000) of low-redshift galaxies using integral field\nspectroscopy from the MaNGA survey. Out of $\\approx1400$ nearly face-on\nlate-type galaxies with a redshift $z<0.05$, we identify 121 \"turnover\"\ngalaxies that each have a central upturn in EW(H$\\alpha$), EW(H$\\delta_A$)\nand/or a central drop in D$_n$(4000), indicative of ongoing/recent star\nformation. The turnover features are found mostly in galaxies with a stellar\nmass above $\\sim$10$^{10}$ M$_{\\odot}$ and NUV-$r$ colour less than $\\approx5$.\nThe majority of the turnover galaxies are barred, with a bar fraction of\n89$\\pm$3\\%. Furthermore, for barred galaxies the radius of the central turnover\nregion is found to tightly correlate with one third of the bar length.\nComparing the observed and the inward extrapolated star formation rate surface\ndensity, we estimate that the central SFR have been enhanced by an order of\nmagnitude. Conversely, only half of the barred galaxies in our sample have a\ncentral turnover feature, implying that the presence of a bar is not sufficient\nto lead to a central SF enhancement. We further examined the SF enhancement in\npaired galaxies, as well as the local environment, finding no relation. This\nimplies that environment is not a driving factor for central SF enhancement in\nour sample. Our results reinforce both previous findings and theoretical\nexpectation that galactic bars play a crucial role in the secular evolution of\ngalaxies by driving gas inflow and enhancing the star formation and bulge\ngrowth in the center.", "category": "astro-ph_GA" }, { "text": "Constraints on interstellar dust models from extinction and\n spectro-polarimetry: We present polarisation spectra of seven stars in the lines-of-sight towards\nthe Sco OB1 association. Our spectra were obtained within the framework of the\nLarge Interstellar Polarization Survey carried out with the FORS instrument of\nthe ESO VLT. We have modelled the wavelength-dependence of extinction and\nlinear polarisation with a dust model for the diffuse interstellar medium which\nconsists of a mixture of particles with size ranging from the molecular domain\nof 0.5 nm up to 350 nm. We have included stochastically heated small dust\ngrains with radii between 0.5 and 6 nm made of graphite and silicate, as well\nas polycyclic aromatic hydrocarbon molecules (PAHs), and we have assumed that\nlarger particles are prolate spheroids made of amorphous carbon and silicate.\nOverall, a dust model with eight free parameters best reproduces the\nobservations. Reducing the number of free parameters leads to results that are\ninconsistent with cosmic abundance constraints. We found that aligned silicates\nare the dominant contributor to the observed polarisation, and that the\npolarisation spectra are best-fit by a lower limit of the equivolume sphere\nradius of aligned grains of 70 - 200nm.", "category": "astro-ph_GA" }, { "text": "Sub-arcsecond imaging of the water emission in Arp 220: Extragalactic observations of water emission can provide valuable insights\ninto the excitation of the interstellar medium. In addition, extragalactic\nmegamasers are powerful probes of kinematics close to active nuclei. Therefore,\nit is paramount to determine the true origin of the water emission, whether it\nis excited by processes close to an AGN or in star-forming regions. We use ALMA\nBand 5 science verification observations to analyse the emission of the 183 GHz\nwater line in Arp 220 on sub-arcsecond scales, in conjunction with new ALMA\nBand 7 data at 325 GHz. Specifically, the nature of the process leading to the\nexcitation of emission at these water lines is studied in this context.\nSupplementary 22 GHz VLA observations are used to better constrain the\nparameter space in the excitation modelling of the water lines. We detect 183\nGHz H2O and 325 GHz water emission towards the two compact nuclei at the center\nof Arp 220, being brighter in Arp 220 West. The emission at these two\nfrequencies is compared to previous single-dish data and does not show evidence\nof variability. The 183 and 325 GHz lines show similar spectra and kinematics,\nbut the 22 GHz profile is significantly different in both nuclei due to a blend\nwith an NH3 absorption line. Our findings suggest that the most likely scenario\nto cause the observed water emission in Arp 220 is a large number of\nindependent masers originating from numerous star-forming regions.", "category": "astro-ph_GA" }, { "text": "KMOS LENsing Survey (KLENS) : morpho-kinematic analysis of star-forming\n galaxies at $z \\sim 2$: We present results from the KMOS lensing survey-KLENS which is exploiting\ngravitational lensing to study the kinematics of 24 star forming galaxies at\n$1.410$). We derive a $\\rm M_\\star-\\sigma_0$ relation, using\nthe Tully-Fisher relation, which highlights that a different evolution of the\nvelocity dispersion is expected depending on the stellar mass, with lower\nvelocity dispersions for lower masses, and an increase for higher masses,\nstronger at higher redshift. The observed velocity dispersions from this work\nand from comparison samples spanning $02$), where we observe higher velocity dispersions\nfor low masses ($\\rm log(M_\\star/M_\\odot)\\sim 9.6$) and lower velocity\ndispersions for high masses ($\\rm log(M_\\star/M_\\odot)\\sim 10.9$) than\nexpected. This discrepancy could, for instance, suggest that galaxies at\nhigh-$z$ do not satisfy the stability criterion, or that the adopted\nparametrisation of the specific star formation rate and molecular properties\nfail at high redshift.", "category": "astro-ph_GA" }, { "text": "Radio Loud and Radio Quiet Quasars: We discuss 6 GHz JVLA observations covering a volume-limited sample of 178\nlow redshift ($0.2 < z < 0.3$) optically selected QSOs. Our 176 radio\ndetections fall into two clear categories: (1) About $20$\\% are radio-loud QSOs\n(RLQs) having spectral luminosities $L_6 \\gtrsim 10^{\\,23.2}\n\\mathrm{~W~Hz}^{-1}$ primarily generated in the active galactic nucleus (AGN)\nresponsible for the excess optical luminosity that defines a \\emph{bona fide}\nQSO. (2) The radio-quiet QSOs (RQQs) have $10^{\\,21} \\lesssim L_6 \\lesssim\n10^{\\,23.2} \\mathrm{~W~Hz}^{-1}$ and radio sizes $\\lesssim 10 \\mathrm{~kpc}$,\nand we suggest that the bulk of their radio emission is powered by star\nformation in their host galaxies. \"Radio silent\" QSOs ($L_6 \\lesssim 10^{\\,21}\n\\mathrm{~W~Hz}^{-1}$) are rare, so most RQQ host galaxies form stars faster\nthan the Milky Way; they are not \"red and dead\" ellipticals. Earlier radio\nobservations did not have the luminosity sensitivity $L_6 \\lesssim 10^{\\,21}\n\\mathrm{~W~Hz}^{-1}$ needed to distinguish between such RLQs and RQQs. Strong,\ngenerally double-sided, radio emission spanning $\\gg 10 \\mathrm{~kpc}$ was\nfound associated with 13 of the 18 RLQ cores having peak flux densities\n$S_\\mathrm{p} > 5 \\mathrm{~mJy~beam}^{-1}$ ($log(L) \\gtrsim 24$). The radio\nluminosity function of optically selected QSOs and the extended radio emission\nassociated with RLQs are both inconsistent with simple \"unified\" models that\ninvoke relativistic beaming from randomly oriented QSOs to explain the\ndifference between RLQs and RQQs. Some intrinsic property of the AGNs or their\nhost galaxies must also determine whether or not a QSO appears radio loud.", "category": "astro-ph_GA" }, { "text": "Molecular gas and a new young stellar cluster in the far outer Galaxy: We investigate the star-formation ocurring in the region towards\nIRAS07527-3446 in the molecular cloud [MAB97]250.63-3.63, in the far outer\nGalaxy. We report the discovery of a new young stellar cluster, and describe\nits properties and those of its parent molecular cloud. Near-infrared JHKS\nimages were obtained with VLT/ISAAC, and millimetre line CO spectra were\nobtained with the SEST telescope. VLA archive date were also used. The cloud\nand cluster are located at a distance of 10.3 kpc and a Galactocentric distance\nof 15.4 kpc, in the far outer Galaxy. Morphologically, IRAS 07527-3446 appears\nas a young embedded cluster of a few hundred stars seen towards the position of\nthe IRAS source, extending for about 2-4 pc and exhibiting sub-clustering. The\ncluster contains low and intermediate-mass young reddened stars, a large\nfraction having cleared the inner regions of their circumstellar discs\nresponsible for (H-Ks) colour excess. The observations are compatible with a <\n5 Myr cluster with variable spatial extinction of between Av = 5 and Av = 11.\nDecomposition of CO emission in clumps, reveals a clump clearly associated with\nthe cluster position, of mass 3.3 x 10^3 M(solar). Estimates of the slopes of\nthe Ks-band luminosity function and of the star-formation efficiency yield\nvalues similar to those seen in nearby star-formation sites. These findings\nreinforce previous results that the distant outer Galaxy continues to be active\nin the production of new and rich stellar clusters, with the physical\nconditions required for the formation of rich clusters continuing to be met in\nthe very distant environment of the outer Galactic disc.", "category": "astro-ph_GA" }, { "text": "The impact of baryonic physics on the subhalo mass function and\n implications for gravitational lensing: We investigate the impact of baryonic physics on the subhalo population by\nanalyzing the results of two recent hydrodynamical simulations (EAGLE and\nIllustris), which have very similar configuration, but a different model of\nbaryonic physics. We concentrate on haloes with a mass between $10^{12.5}$ and\n$10^{14}M_{\\odot}h^{-1}$ and redshift between 0.2 and 0.5, comparing with\nobservational results and subhalo detections in early-type galaxy lenses. We\ncompare the number and the spatial distribution of subhaloes in the fully hydro\nruns and in their dark matter only counterparts, focusing on the differences\nbetween the two simulations. We find that the presence of baryons reduces the\nnumber of subhaloes, especially at the low mass end ($\\leq\n10^{10}M_{\\odot}h^{-1}$), by different amounts depending on the model. The\nvariations in the subhalo mass function are strongly dependent on those in the\nhalo mass function, which is shifted by the effect of stellar and AGN feedback.\nFinally, we search for analogues of the observed lenses (SLACS) in the\nsimulations, selecting them in velocity dispersion and dynamical properties. We\nuse the selected galaxies to quantify detection expectations based on the\nsubhalo populations in the different simulations, calculating the detection\nprobability and the predicted values for the projected dark matter fraction in\nsubhaloes $f_{DM}$ and the slope of the mass function $\\alpha$. We compare\nthese values with those derived from subhalo detections in observations and\nconclude that the dark-matter-only and hydro EAGLE runs are both compatible\nwith observational results, while results from the hydro Illustris run do not\nlie within the errors.", "category": "astro-ph_GA" }, { "text": "Unlocking the Full Potential of Extragalactic Ly$\u03b1$ through Its\n Polarization Properties: Lyman-$\\alpha$ (Ly$\\alpha$) is a powerful astrophysical probe. Not only is it\nubiquitous at high redshifts, it is also a resonant line, making Ly$\\alpha$\nphotons scatter. This scattering process depends on the physical conditions of\nthe gas through which Ly$\\alpha$ propagates, and these conditions are imprinted\non observables such as the Ly$\\alpha$ spectrum and its surface brightness\nprofile. In this work, we focus on a less-used observable capable of probing\nany scattering process: polarization. We implement the density matrix formalism\nof polarization into the Monte Carlo radiative transfer code tlac. This allows\nus to treat it as a quantum mechanical process where single photons develop and\nlose polarization from scatterings in arbitrary gas geometries. We explore\nstatic and expanding ellipsoids, biconical outflows, and clumpy multiphase\nmedia. We find that photons become increasingly polarized as they scatter and\ndiffuse into the wings of the line profiles, making scattered Ly$\\alpha$\npolarized in general. The degree and orientation of Ly$\\alpha$ polarization\ndepends on the kinematics and distribution of the scattering HI gas. We find\nthat it generally probes spatial or velocity space asymmetries and aligns\nitself tangentially to the emission source. We show that the mentioned\nobservables, when studied separately, can leave similar signatures for\ndifferent source models. We conclude by revealing how a joint analysis of the\nLy$\\alpha$ spectra, surface brightness profiles, and polarization can break\nthese degeneracies and help us extract unique physical information on galaxies\nand their environments from their strongest, most prominent emission line.", "category": "astro-ph_GA" }, { "text": "The Evolution of Environmental Quenching Timescales to $z\\sim1.6$: Using a sample of 4 galaxy clusters at $1.35 < z < 1.65$ and 10 galaxy\nclusters at $0.85 < z < 1.35$, we measure the environmental quenching\ntimescale, $t_Q$, corresponding to the time required after a galaxy is accreted\nby a cluster for it to fully cease star formation. Cluster members are selected\nby a photometric-redshift criterion, and categorized as star-forming,\nquiescent, or intermediate according to their dust-corrected rest-frame colors\nand magnitudes. We employ a \"delayed-then-rapid\" quenching model that relates a\nsimulated cluster mass accretion rate to the observed numbers of each type of\ngalaxy in the cluster to constrain $t_Q$. For galaxies of mass $M_* \\gtrsim\n10^{10.5}~ \\mathrm{M}_\\odot$, we find a quenching timescale of $t_Q=$ 1.24 Gyr\nin the $z\\sim1.5$ cluster sample, and $t_Q=$ 1.50 Gyr at $z\\sim1$. Using values\ndrawn from the literature, we compare the redshift evolution of $t_Q$ to\ntimescales predicted for different physical quenching mechanisms. We find $t_Q$\nto depend on host halo mass such that quenching occurs over faster timescales\nin clusters relative to groups, suggesting that properties of the host halo are\nresponsible for quenching high-mass galaxies. Between $z=0$ and $z=1.5$, we\nfind that $t_Q$ evolves faster than the molecular gas depletion timescale and\nslower than an SFR-outflow timescale, but is consistent with the evolution of\nthe dynamical time. This suggests that environmental quenching in these\ngalaxies is driven by the motion of satellites relative to the cluster\nenvironment, although due to uncertainties in the atomic gas budget at high\nredshift, we cannot rule out quenching due to simple gas depletion.", "category": "astro-ph_GA" }, { "text": "Science with an ngVLA: Understanding Massive Star Formation through\n Maser Imaging: Imaging the bright maser emission produced by several molecular species at\ncentimeter wavelengths is an essential tool for understanding the process of\nmassive star formation because it provides a way to probe the kinematics of\ndense molecular gas at high angular resolution. Unimpeded by the high dust\noptical depths that affect shorter wavelength observations, the high brightness\ntemperature of these emission lines offers a way to resolve accretion and\noutflow motions down to scales as fine as $\\sim$1-10 au in deeply embedded\nGalactic star-forming regions, and at sub-pc scales in nearby galaxies. The\nNext Generation Very Large Array will provide the capabilities needed to fully\nexploit these powerful tracers.", "category": "astro-ph_GA" }, { "text": "Spatial variations of magnetic field along active galactic nuclei jets\n on sub-pc to Mpc scales: We report the systematic analysis of knots, hotspots, and lobes in 57 active\ngalactic nuclei (AGNs) to investigate the variation of the magnetic field along\nwith the jet from the sub-pc base to the terminus in kpc-to-Mpc scales.\nExpanding the number of radio/X-ray samples in Kataoka & Stawarz (2005), we\nanalyzed the data in 12 FR I and 30 FR II radio galaxies, 12 quasars, and 3 BL\nLacs that contained 76 knots, 42 hotspots, and 29 radio lobes. We first derived\nthe equipartition magnetic fields in the cores and then estimated those in\nvarious jet components by assuming $B_{\\rm est}$ $\\propto$ $d^{-1}$, where $d$\nis the distance from the jet base. On the other hand, the magnetic field in\nlarge-scale jets (knots, hotspots, and lobes), $B_{\\rm eq}$, can be estimated\nfrom the observed flux and spatial extent under the equipartition hypothesis.\nWe show that the magnetic field decreases as the distance along the jet\nincreases, but generally gentler than $\\propto d^{-1}$. The increase in $B_{\\rm\neq}/B_{\\rm est}$ at a larger $d$ may suggest the deceleration of the jet around\nthe downstream, but there is no difference between FR I and FR II jets.\nMoreover, the magnetic fields in the hotspots are systematically larger than\nthose of knots and lobes. Finally, we applied the same analysis to knots and\nlobes in Centaurus A to check whether the above discussion will hold even in a\nsingle jet source.", "category": "astro-ph_GA" }, { "text": "Disruption of the Orion Molecular Core 1 by the stellar wind of the\n massive star $\u03b8^1$ Ori C: Massive stars inject mechanical and radiative energy into the surrounding\nenvironment, which stirs it up, heats the gas, produces cloud and intercloud\nphases in the interstellar medium, and disrupts molecular clouds (the birth\nsites of new stars). Stellar winds, supernova explosions and ionization by\nultraviolet photons control the lifetimes of molecular clouds. Theoretical\nstudies predict that momentum injection by radiation should dominate that by\nstellar winds, but this has been difficult to assess observationally.\nVelocity-resolved large-scale images in the fine-structure line of ionized\ncarbon ([C II]) provide an observational diagnostic for the radiative energy\ninput and the dynamics of the interstellar medium around massive stars. Here we\nreport observations of a one-square-degree region (about 7 parsecs in diameter)\nof Orion molecular core -- the region nearest to Earth that exhibits\nmassive-star formation -- at a resolution of 16 arcseconds (0.03 parsecs) in\nthe [C II] line at 1.9 terahertz (158 micrometres). The results reveal that the\nstellar wind originating from the massive star ${\\theta}^{1}$ Orionis C has\nswept up the surrounding material to create a bubble roughly four parsecs in\ndiameter with a 2,600-solar-mass shell, which is expanding at 13 kilometres per\nsecond. This finding demonstrates that the mechanical energy from the stellar\nwind is converted very efficiently into kinetic energy of the shell and causes\nmore disruption of the Orion molecular core 1 than do photo-ionization and\nevaporation or future supernova explosions.", "category": "astro-ph_GA" }, { "text": "Probabilities for Solar Siblings: We have shown previously (Bobylev et al 2011) that some of the stars in the\nSolar neighborhood today may have originated in the same star cluster as the\nSun, and could thus be called Solar Siblings. In this work we investigate the\nsensitivity of this result to Galactic models and to parameters of these\nmodels, and also extend the sample of orbits. There are a number of good\ncandidates for the Sibling category, but due to the long period of orbit\nevolution since the break-up of the birth cluster of the Sun, one can only\nattach probabilities of membership. We find that up to 10% (but more likely\naround 1 %) of the members of the Sun's birth cluster could be still found\nwithin 100 pc from the Sun today.", "category": "astro-ph_GA" }, { "text": "The Optically Unbiased Gamma-Ray Burst Host (TOUGH) Survey. VII. The\n Host Galaxy Luminosity Function: Probing the Relationship Between GRBs and\n Star Formation to Redshift $\\sim6$: Gamma-ray bursts (GRBs) offer a route to characterizing star-forming galaxies\nand quantifying high-$z$ star formation that is distinct from the approach of\ntraditional galaxy surveys: GRB selection is independent of dust and probes\neven the faintest galaxies that can evade detection in flux-limited surveys.\nHowever, the exact relation between the GRB rate and the star formation rate\n(SFR) throughout all redshifts is controversial. The Optically Unbiased GRB\nHost (TOUGH) survey includes observations of all GRB hosts (69) in an optically\nunbiased sample of Swift GRBs and we utilize these to constrain the evolution\nof the UV GRB-host-galaxy luminosity function (LF) between $z=0$ and $z=4.5$,\nand compare this with LFs derived from both Lyman-break galaxy (LBG) surveys\nand simulation modeling. At all redshifts we find the GRB hosts to be most\nconsistent with a luminosity function derived from SFR weighted models\nincorporating GRB production via both metallicity-dependent and independent\nchannels with a relatively high level of bias toward low metallicity hosts. In\nthe range $1 10^{10}$).\nThey lay mainly on the red sequence and live in relatively isolated\nenvironments similar to that of the field and loose groups. We use our 2D\nphotometric decomposition to define the size and photometric properties of the\nbulges, as well as their location within the galaxies. We perform mock\nspectroscopic simulations mimicking our observed galaxies to quantify the\nimpact of the underlying disc on our bulge kinematic measurements ($\\lambda$\nand $v/\\sigma$). We compare our bulge corrected kinematic measurements with the\nresults from Schwarzschild dynamical modelling. The good agreement confirms the\nrobustness of our results and allows us to use bulge reprojected values of\n$\\lambda$ and $v/\\sigma$. We find that the photometric ($n$ and $B/T$) and\nkinematic ($v/\\sigma$ and $\\lambda$) properties of our field S0 bulges are not\ncorrelated. We demonstrate that this morpho-kinematic decoupling is intrinsic\nto the bulges and it is not due to projection effects. We conclude that\nphotometric diagnostics to separate different types of bulges (disc-like vs\nclassical) might not be useful for S0 galaxies. The morpho-kinematics\nproperties of S0 bulges derived in this paper suggest that they are mainly\nformed by dissipation processes happening at high redshift, but dedicated\nhigh-resolution simulations are necessary to better identify their origin.", "category": "astro-ph_GA" }, { "text": "Evidence for gravitational quadrupole moment variations in the companion\n of PSR J2051-0827: We have conducted radio timing observations of the eclipsing millisecond\nbinary pulsar J2051-0827 with the European Pulsar Timing Array network of\ntelescopes and the Parkes radio telescope, spanning over 13 years. The\nincreased data span allows significant measurements of the orbital\neccentricity, e = (6.2 {\\pm} 1.3) {\\times} 10^{-5} and composite proper motion,\n{\\mu}_t = 7.3 {\\pm} 0.4 mas/yr. Our timing observations have revealed secular\nvariations of the projected semi-major axis of the pulsar orbit which are much\nmore extreme than those previously published; and of the orbital period of the\nsystem. Investigation of the physical mechanisms producing such variations\nconfirm that the variations of the semi-major axis are most probably caused by\nclassical spin-orbit coupling in the binary system, while the variations in\norbital period are most likely caused by tidal dissipation leading to changes\nin the gravitational quadrupole moment of the companion.", "category": "astro-ph_GA" }, { "text": "Simulating radio synchrotron emission in star-forming galaxies:\n small-scale magnetic dynamo and the origin of the far infrared-radio\n correlation: In star-forming galaxies, the far-infrared (FIR) and radio-continuum\nluminosities obey a tight empirical relation over a large range of\nstar-formation rates (SFR). We examine magneto-hydrodynamic galaxy simulations\nwith cosmic rays (CRs), accounting for their advective and anisotropic\ndiffusive transport. We show that gravitational collapse of the proto-galaxy\ngenerates a corrugated accretion shock, which injects turbulence and drives a\nsmall-scale magnetic dynamo. As the shock propagates outwards and the\nassociated turbulence decays, the large velocity shear between the\nsupersonically rotating cool disc with respect to the (partially)\npressure-supported hot circumgalactic medium excites Kelvin-Helmholtz surface\nand body modes. Those inject turbulence and drive multiple small-scale dynamos,\nwhich exponentially amplify magnetic fields. They grow in scale to reach\nequipartition with thermal and CR energies in Milky Way-mass galaxies. In small\ngalaxies, the magnetic energy saturates at the turbulent energy while it fails\nto reach equipartition with thermal and CR energies. We solve for steady-state\nspectra of CR protons, secondary electrons/positrons from hadronic CR-proton\ninteractions with the interstellar medium, and primary shock-accelerated\nelectrons at supernovae. The radio-synchrotron emission is dominated by primary\nelectrons, irradiates the magnetised disc, bulge, and bubble-shaped\nmagnetically-loaded outflows of our simulated Milky Way-mass galaxy. Our\nstar-forming and star-bursting galaxies with saturated magnetic fields match\nthe global FIR-radio correlation (FRC) across four orders of magnitude. Its\nintrinsic scatter arises due to (i) different magnetic saturation levels that\nresult from different seed magnetic fields, (ii) different radio synchrotron\nluminosities for different specific SFRs at fixed SFR and (iii) a varying radio\nintensity with galactic inclination. (abridged)", "category": "astro-ph_GA" }, { "text": "The effect of the deforming dark matter haloes of the Milky Way and the\n Large Magellanic Cloud on the Orphan-Chenab stream: It has recently been shown that the Large Magellanic Cloud (LMC) has a\nsubstantial effect on the Milky Way's stellar halo and stellar streams. Here,\nwe explore how deformations of the Milky Way and LMC's dark matter haloes\naffect stellar streams, and whether these effects are observable. In\nparticular, we focus on the Orphan-Chenab (OC) stream which passes particularly\nclose to the LMC, and spans a large portion of the Milky Way's halo. We\nrepresent the Milky Way--LMC system using basis function expansions that\ncapture their evolution in an $N$-body simulation. We present the properties of\nthis system, such as the evolution of the densities and force fields of each\ngalaxy. The OC stream is evolved in this time-dependent, deforming potential,\nand we investigate the effects of the various moments of the Milky Way and the\nLMC. We find that the simulated OC stream is strongly influenced by the\ndeformations of both the Milky Way and the LMC, and that this effect is much\nlarger than current observational errors. In particular, the Milky Way dipole\nhas the biggest impact on the stream, followed by the evolution of the LMC's\nmonopole, and the LMC's quadrupole. Detecting these effects would confirm a key\nprediction of collisionless, cold dark matter, and would be a powerful test of\nalternative dark matter and alternative gravity models.", "category": "astro-ph_GA" }, { "text": "Note on fundamental physics tests from black hole imaging: Comment on\n \"Hunting for extra dimensions in the shadow of Sagittarius A$^*$\": Several works over the past years have discussed the possibility of testing\nfundamental physics using Very Long Baseline Interferometry horizon-scale black\nhole (BH) images, such as the Event Horizon Telescope (EHT) images of M87$^*$\nand Sagittarius A$^*$ (Sgr A$^*$), using the size $r_{\\rm sh}$ and deviation\nfrom circularity $\\Delta \\mathcal{C}$ of the BH shadow. For the case of the EHT\nimage of Sgr A$^*$, limits on $\\Delta \\mathcal{C}$ are not available due to the\nsparse interferometric coverage of the 2017 observations, alongside the short\nvariability timescale of Sgr A$^*$ compared to M87$^*$. Concerning this point,\nwe comment on the results of a recent preprint which purports to have derived\nnew limits on extra dimensions using the deviation from circularity of Sgr\nA$^*$'s shadow. The latter is quoted to be $\\lesssim 10\\%$ as with M87$^*$,\nbased on the \"similarity\" of the two shadows: however, this is an incorrect\nassumption, invalidating the subsequent results. In the immediate future, the\nsimplest tests of fundamental physics from Sgr A$^*$'s image will therefore\nmostly have to rely on $r_{\\rm sh}$, whereas additional observables such as the\nphoton ring and azimuthal angle lapse should soon be available and allow for\nnovel tests.", "category": "astro-ph_GA" }, { "text": "Comparing Simulated Emission from Molecular Clouds Using Experimental\n Design: We propose a new approach to comparing simulated observations that enables us\nto determine the significance of the underlying physical effects. We utilize\nthe methodology of experimental design, a subfield of statistical analysis, to\nestablish a framework for comparing simulated position-position-velocity data\ncubes to each other. We propose three similarity metrics based on methods\ndescribed in the literature: principal component analysis, the spectral\ncorrelation function, and the Cramer multi-variate two sample similarity\nstatistic. Using these metrics, we intercompare a suite of mock observational\ndata of molecular clouds generated from magnetohydrodynamic simulations with\nvarying physical conditions. Using this framework, we show that all three\nmetrics are sensitive to changing Mach number and temperature in the simulation\nsets, but cannot detect changes in magnetic field strength and initial velocity\nspectrum. We highlight the shortcomings of one-factor-at-a-time designs\ncommonly used in astrophysics and propose fractional factorial designs as a\nmeans to rigorously examine the effects of changing physical properties while\nminimizing the investment of computational resources.", "category": "astro-ph_GA" }, { "text": "Discovery of the elusive thioketenylium, HCCS+, in TMC-1: We report the detection in TMC-1 of the cation HCCS+ (3Sigma-), which is the\nprotonated form of the widespread radical CCS. This is the first time that a\nprotonated radical has been detected in a cold dark cloud. Twenty-six hyperfine\ncomponents from twelve rotational transitions have been observed with the Yebes\n40m and IRAM 30m radio telescopes. We confidently assign the characteristic\nrotational spectrum pattern to HCCS+ based on the good agreement between the\nastronomical and theoretical spectroscopic parameters. The column density of\nHCCS+ is (1.1+/-0.1)e12 cm-2, and the CCS/HCCS+ abundance ratio is 50+/-10,\nwhich is very similar to that of CS/HCS+ (35+/-8) and CCCS/HCCCS+ (65+/-20).\nFrom a state-of-the-art gas-phase chemical model, we conclude that HCCS+ is\nmostly formed by reactions of proton transfer from abundant cations such as\nHCO+, H3O+, and H3+ to the radical CCS.", "category": "astro-ph_GA" }, { "text": "A New Multi-Tracer Approach to Defining the Spiral arm width in the\n Milky Way: We analyze recent observations of the spiral arm width in the Milky Way, as a\nfunction of the galactic radius, and we compare this relation with the\nprediction from the density wave theory. We use the following method: in each\nspiral arm, we concentrate on the separation (or offset) between the\nstarforming region (radio masers) near the shock front of a density wave, and\nthe aged star region (diffuse CO gas) near the potential minimum of a density\nwave; we take this separation between these two tracers as the arm width.\n New results: we find a typical separation (maser to diffuse CO gas) near 250\n+/- 50 pc, and an increase of this separation with galactic radius of about 25\n+/- 5 pc per kpc. We note that, as expected, this separation is somewhat\nsmaller than that found earlier between the dust lane and the aged star region.\nOverall, these results supports the basics of a density wave.", "category": "astro-ph_GA" }, { "text": "History and destiny of an emerging early-type galaxy: New IFU insights\n on the major-merger remnant NGC7252: NGC7252, which is one of the nearest major-merger galaxy remnants, is an\nideal laboratory to study the processes inherent to the transformation of disc\ngalaxies to ellipticals as observed about ~1Gyr after the collision. We\nobtained wide-field IFU spectroscopy with the VLT-VIMOS integral-field\nspectrograph covering the central 50\"x50\" of NGC7252 to map the stellar and\nionised gas kinematics, and the distribution and conditions of the ionised gas,\nrevealing the extent of ongoing star formation and recent star formation\nhistory. We find that the inner gas disc is not counter-rotating with respect\nto the stars and that the stellar kinematics appear complex with a clear\nindication of a prolate-like rotation component suggesting a polar merger\nconfiguration. The ongoing star formation rate is 2.2+-0.6 M_sun/yr and implies\na typical depletion time of 2Gyr given the molecular gas content. Furthermore,\nthe spatially-resolved star formation history suggests a slight radial\ndependence, moving outwards at later times. We confirm a large AGN-ionised gas\ncloud previously discovered 5kpc south of the nucleus, and find higher\nionisation also at the galaxy centre relative to the surrounding gas disc.\nAlthough the higher ionisation towards the centre is potentially degenerate\nwithin the central star forming ring, it may be associated with a\nlow-luminosity AGN. Although NGC7252 has been classified as post-starburst\ngalaxy at the centre, the elliptical-like major-merger remnant still appears\nvery active. A central kpc-scale gas disc has presumably re-formed quickly\nwithin the last 100Myr after final coalescence. The disc features ongoing star\nformation, implying Gyr long timescale to reach the red sequence through gas\nconsumption alone. While NGC7252 is useful to probe the transformation from\ndiscs to ellipticals, it is not well-suited to study the transformation from\nblue to red at this point.", "category": "astro-ph_GA" }, { "text": "Tightening the belt: Constraining the mass and evolution in SDC335: Recent ALMA observations identified one of the most massive star-forming\ncores yet observed in the Milky Way; SDC335-MM1, within the infrared dark cloud\nSDC335.579-0.292. Along with an accompanying core MM2, SDC335 appears to be in\nthe early stages of its star formation process. In this paper we aim to\nconstrain the properties of the stars forming within these two massive\nmillimetre sources. Observations of SDC335 at 6, 8, 23 and 25GHz were made with\nthe ATCA. We report the results of these continuum measurements, which combined\nwith archival data, allow us to build and analyse the spectral energy\ndistributions (SEDs) of the compact sources in SDC335. Three HCHII regions\nwithin SDC335 are identified, two within the MM1 core. For each HCHII region, a\nfree-free emission curve is fit to the data allowing the derivation of the\nsources' emission measure, ionising photon flux and electron density. Using\nthese physical properties we assign each HCHII region a ZAMS spectral type,\nfinding two protostars with characteristics of spectral type B1.5 and one with\na lower limit of B1-B1.5. Ancillary data from infrared to mm wavelength are\nused to construct free-free component subtracted SEDs for the mm-cores,\nallowing calculation of the bolometric luminosities and revision of the\nprevious gas mass estimates. The measured luminosities for the two mm-cores are\nlower than expected from accreting sources displaying characteristics of the\nZAMS spectral type assigned to them. The protostars are still actively\naccreting, suggesting that a mechanism is limiting the accretion luminosity, we\npresent the case for two different mechanisms capable of causing this. Finally,\nusing the ZAMS mass values as lower limit constraints, a final stellar\npopulation for SDC335 was synthesised finding SDC335 is likely to be in the\nprocess of forming a stellar cluster comparable to the Trapezium Cluster and\nNGC6334 I(N).", "category": "astro-ph_GA" }, { "text": "Modeling and Analysis of a Spectrum of the Globular Cluster NGC 2419: NGC 2419 is the most distant massive globular cluster in the outer Galactic\nhalo. It is unusual also due to the chemical peculiarities found in its red\ngiant stars in recent years. We study the stellar population of this unusual\nobject using spectra obtained at the 1.93-m telescope of the Haute-Provence\nObservatory. At variance with commonly used methods of high-resolution\nspectroscopy applicable only to bright stars, we employ spectroscopic\ninformation on the integrated light of the cluster. We carry out population\nsynthesis modeling of medium-resolution spectra using synthetic stellar\natmosphere models based on a theoretical isochrone corresponding accurately to\nthe observed color-magnitude diagram. We study the influence of non-Local\nThermodynamic Equilibrium for some chemical elements on our results. The\nderived age (12.6 Gyr), [Fe/H]=-2.25 dex, helium content Y=0.25, and abundances\nof 12 other chemical elements are in a good qualitative agreement with\npublished high-resolution spectroscopy estimates for red giant members in the\ncluster. On the other hand, the derived element abundance, [alpha/Fe]=0.13 dex\n(the mean of [O/Fe], [Mg/Fe] and [Ca/Fe]), differs from the published one\n([alpha/Fe] =0.4 dex) for selected red giants in the cluster and may be\nexplained by a large dispersion in the alpha-element abundances recently\ndiscovered in NGC2419. We suggest that studies of the {\\it integrated} light in\nthe cluster using high-resolution spectrographs in different wavelength regions\nwill help to understand the nature of these chemical anomalies.", "category": "astro-ph_GA" }, { "text": "NGDEEP Epoch 1: Spatially Resolved H$\u03b1$ Observations of Disk and\n Bulge Growth in Star-Forming Galaxies at $z \\sim$ 0.6-2.2 from JWST NIRISS\n Slitless Spectroscopy: We study the H$\\alpha$ equivalent width, EW(H$\\alpha$), maps of 19 galaxies\nat $0.6 < z < 2.2$ in the Hubble Ultra Deep Field (HUDF) derived from NIRISS\nslitless spectroscopy as part of the Next Generation Deep Extragalactic\nExploratory Public (NGDEEP) Survey. Our galaxies mostly lie on the\nstar-formation main sequence with a stellar mass range of $\\mathrm{10^9 -\n10^{11} M_\\odot}$, characterized as \"typical\" star-forming galaxies at these\nredshifts. Leveraging deep HST and JWST broad-band images, spanning 0.4-4.8\n$\\mu$m, we perform spatially-resolved fitting of the spectral energy\ndistributions (SEDs) for these galaxies and construct specific star formation\nrate (sSFR) and stellar-mass-weighted age maps with a spatial resolution of\n$\\sim$1 kpc. The pixel-to-pixel EW(H$\\alpha$) increases with increasing sSFR\nand with decreasing age. The average trends are slightly different from the\nrelations derived from integrated fluxes of galaxies from the literature,\nsuggesting complex evolutionary trends within galaxies. We quantify the radial\nprofiles of EW(H$\\alpha$), sSFR, and age. The majority (84%) of galaxies show\npositive EW(H$\\alpha$) gradients in line with the inside-out quenching\nscenario. A few galaxies (16%) show inverse (and flat) trends possibly due to\nmerging or starbursts. We compare the distributions of EW(H$\\alpha$) and sSFR\nto the star formation history models (SFHs) as a function of galactocentric\nradius. We argue that the central regions of galaxies have experienced, at\nleast one, rapid star-formation episodes, which leads to the formation of the\nbulge, while their outer regions (e.g., disks) grow via more smoothly varying\nSFHs. These results demonstrate the ability to study resolved star formation in\ndistant galaxies with JWST NIRISS.", "category": "astro-ph_GA" }, { "text": "The chemical structure of young high-mass star-forming clumps: (II)\n parsec-scale CO depletion and deuterium fraction of $\\rm HCO^+$: The physical and chemical properties of cold and dense molecular clouds are\nkey to understanding how stars form. Using the IRAM 30 m and NRO 45 m\ntelescopes, we carried out a Multiwavelength line-Imaging survey of the 70\n$\\mu$m dark and bright clOuds (MIAO). At a linear resolution of 0.1--0.5 pc,\nthis work presents a detailed study of parsec-scale CO depletion and $\\rm\nHCO^+$ deuterium (D-) fractionation toward four sources (G11.38+0.81,\nG15.22-0.43, G14.49-0.13, and G34.74-0.12) included in our full sample. In each\nsource with $\\rm T<20$ K and $n_{\\rm H}\\rm\\sim10^4$--$\\rm 10^5 cm^{-3}$, we\ncompared pairs of neighboring 70 $\\mu$m bright and dark clumps and found that\n(1) the $\\rm H_2$ column density and dust temperature of each source show\nstrong spatial anticorrelation; (2) the spatial distribution of CO isotopologue\nlines and dense gas tracers, such as 1--0 lines of $\\rm H^{13}CO^+$ and $\\rm\nDCO^+$, are anticorrelated; (3) the abundance ratio between $\\rm C^{18}O$ and\n$\\rm DCO^+$ shows a strong correlation with the source temperature; (4) both\nthe $\\rm C^{18}O$ depletion factor and D-fraction of $\\rm HCO^+$ show a robust\ndecrease from younger clumps to more evolved clumps by a factor of more than 3;\nand (5) preliminary chemical modeling indicates chemical ages of our sources\nare ${\\sim}8\\times10^4$ yr, which is comparable to their free-fall timescales\nand smaller than their contraction timescales, indicating that our sources are\nlikely dynamically and chemically young.", "category": "astro-ph_GA" }, { "text": "Revisiting the alignment of radio galaxies in the ELAIS-N1 field: Aims. Previous studies reported an alignment of the major axes of radio\ngalaxies on various angular scales. Here, we study the alignment of radio\ngalaxies in the ELAIS-N1 Low Frequency ARray (LOFAR) deep field, which covers\nan area of 25 $\\rm deg^2$. \\newline Methods. The low noise level of about 20$\n\\rm ~ \\mu Jy/beam$ of the LOFAR deep field observations at 150 MHz enabled the\nidentification of 447 extended ($> 30 \\rm ''$) radio galaxies for which we have\nmeasured the major axis position angle. We found that 95\\% of these sources\nhave either photometric or spectroscopic redshifts, which we then used for a\nthree-dimensional analysis. \\newline Results. We show the distribution of the\nposition angles of radio galaxies in the ELAIS-N1 field and perform multiple\nstatistical tests to check whether the radio galaxies are randomly oriented. We\nfound that the distribution of position angles is consistent with being\nuniform. Two peaks around position angles of 50 and 140$\\rm~ deg$ are spurious\nand are not caused by an alignment, as shown by a 3D analysis. In conclusion,\nour results do not support a 2D or 3D alignment of radio galaxies on scales\nsmaller than $\\sim 4 \\rm ~ deg$.", "category": "astro-ph_GA" }, { "text": "The Thirteenth Data Release of the Sloan Digital Sky Survey: First\n Spectroscopic Data from the SDSS-IV Survey MApping Nearby Galaxies at Apache\n Point Observatory: The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) began\nobservations in July 2014. It pursues three core programs: APOGEE-2, MaNGA, and\neBOSS. In addition, eBOSS contains two major subprograms: TDSS and SPIDERS.\nThis paper describes the first data release from SDSS-IV, Data Release 13\n(DR13), which contains new data, reanalysis of existing data sets and, like all\nSDSS data releases, is inclusive of previously released data. DR13 makes\npublicly available 1390 spatially resolved integral field unit observations of\nnearby galaxies from MaNGA, the first data released from this survey. It\nincludes new observations from eBOSS, completing SEQUELS. In addition to\ntargeting galaxies and quasars, SEQUELS also targeted variability-selected\nobjects from TDSS and X-ray selected objects from SPIDERS. DR13 includes new\nreductions of the SDSS-III BOSS data, improving the spectrophotometric\ncalibration and redshift classification. DR13 releases new reductions of the\nAPOGEE-1 data from SDSS-III, with abundances of elements not previously\nincluded and improved stellar parameters for dwarf stars and cooler stars. For\nthe SDSS imaging data, DR13 provides new, more robust and precise photometric\ncalibrations. Several value-added catalogs are being released in tandem with\nDR13, in particular target catalogs relevant for eBOSS, TDSS, and SPIDERS, and\nan updated red-clump catalog for APOGEE. This paper describes the location and\nformat of the data now publicly available, as well as providing references to\nthe important technical papers that describe the targeting, observing, and data\nreduction. The SDSS website, http://www.sdss.org, provides links to the data,\ntutorials and examples of data access, and extensive documentation of the\nreduction and analysis procedures. DR13 is the first of a scheduled set that\nwill contain new data and analyses from the planned ~6-year operations of\nSDSS-IV.", "category": "astro-ph_GA" }, { "text": "Is there a maximum mass for black holes in galactic nuclei?: The largest observed supermassive black holes (SMBHs) have a mass of M_BH ~\n10^{10} M_sun, nearly independent of redshift, from the local (z~0) to the\nearly (z>6) Universe. We suggest that the growth of SMBHs above a few 10^{10}\nM_sun is prevented by small-scale accretion physics, independent of the\nproperties of their host galaxies or of cosmology. Growing more massive BHs\nrequires a gas supply rate from galactic scales onto a nuclear region as high\nas >10^3 M_sun/yr. At such a high accretion rate, most of the gas converts to\nstars at large radii (~10-100 pc), well before reaching the BH. We adopt a\nsimple model (Thompson et al. 2005) for a star-forming accretion disk, and find\nthat the accretion rate in the sub-pc nuclear region is reduced to the smaller\nvalue of at most a few M_sun/yr. This prevents SMBHs from growing above\n~10^{11} M_sun in the age of the Universe. Furthermore, once a SMBH reaches a\nsufficiently high mass, this rate falls below the critical value at which the\naccretion flow becomes advection dominated. Once this transition occurs, BH\nfeeding can be suppressed by strong outflows and jets from hot gas near the BH.\nWe find that the maximum SMBH mass, given by this transition, is between\nM_{BH,max} ~ (1-6) * 10^{10} M_sun, depending primarily on the efficiency of\nangular momentum transfer inside the galactic disk, and not on other properties\nof the host galaxy.", "category": "astro-ph_GA" }, { "text": "Machine Learning for Galactic Archaeology: A chemistry-based neural\n network method for identification of accreted disc stars: We develop a method ('Galactic Archaeology Neural Network', GANN) based on\nneural network models (NNMs) to identify accreted stars in galactic discs by\nonly their chemical fingerprint and age, using a suite of simulated galaxies\nfrom the Auriga Project. We train the network on the target galaxy's own local\nenvironment defined by the stellar halo and the surviving satellites. We\ndemonstrate that this approach allows the detection of accreted stars that are\nspatially mixed into the disc. Two performance measures are defined - recovery\nfraction of accreted stars, and the probability that a star with a positive\n(accreted) classification is a true-positive result, P(TP). As the NNM output\nis akin to an assigned probability, we are able to determine positivity based\non flexible threshold values that can be adjusted easily to refine the\nselection of presumed-accreted stars. We find that GANN identifies accreted\ndisc stars within simulated galaxies, with high recovery fraction and/or high\nP(TP). We also find that stars in Gaia-Enceladus-Sausage (GES) mass systems are\nover 50% recovered by our NNMs in the majority (18/24) of cases. Additionally,\nnearly every individual source of accreted stars is detected at 10% or more of\nits peak stellar mass in the disc. We also demonstrate that a conglomerated\nNNM, trained on the halo and satellite stars from all of the Auriga galaxies\nprovides the most consistent results, and could prove to be an intriguing\nfuture approach as our observational capabilities expand.", "category": "astro-ph_GA" }, { "text": "A population of ultraviolet-dim protoclusters detected in absorption: Galaxy protoclusters, which will eventually grow into the massive clusters we\nsee in the local universe, are usually traced by locating overdensities of\ngalaxies. Large spectroscopic surveys of distant galaxies now exist, but their\nsensitivity depends mainly on a galaxy's star formation activity and dust\ncontent rather than its mass. Tracers of massive protoclusters that do not rely\non their galaxy constituents are therefore needed. Here we report observations\nof Lyman-$\\alpha$ absorption in the spectra of a dense grid of background\ngalaxies, which we use to locate a substantial number of candidate\nprotoclusters at redshifts 2.2-2.8 via their intergalactic gas. We find that\nthe structures producing the most absorption, most of which were previously\nunknown, contain surprisingly few galaxies compared to the dark matter content\nof their analogs in cosmological simulations. Nearly all are expected to be\nprotoclusters, and we infer that half of their expected galaxy members are\nmissing from our survey because they are unusually dim at rest-frame\nultraviolet wavelengths. We attribute this to an unexpectedly strong and early\ninfluence of the protocluster environment on the evolution of these galaxies\nthat reduced their star formation or increased their dust content.", "category": "astro-ph_GA" }, { "text": "Two step ejection of massive stars and the issue of their formation in\n isolation: In this paper we investigate the combined effect of massive binary ejection\nfrom star clusters and a second acceleration of a massive star during a\nsubsequent supernova explosion. We call this the \"two-step-ejection\" scenario.\nThe main results are: i) Massive field stars produced via the two-step-ejection\nprocess can not in the vast majority of cases be traced back to their parent\nstar clusters. These stars can be mistakenly considered as massive stars formed\nin isolation. ii) The expected O star fraction produced via the\ntwo-step-ejection process is of the order of 1-4 per cent, in quantitative\nagreement with the observed fraction of candidates for isolated-O-star\nformation. iii) Stars ejected via the two-step-ejection process can get a\nhigher final velocity (up to 1.5-2 times higher) than the pre-supernova\nvelocity of the massive-star binary.", "category": "astro-ph_GA" }, { "text": "The chemical evolution of galaxies with a variable IGIMF: Standard analytical chemical evolution modelling of galaxies has been\nassuming the stellar initial mass function (IMF) to be invariant and fully\nsampled allowing fractions of massive stars to contribute even in dwarf\ngalaxies with very low star formation rates (SFRs). Recent observations show\nthe integrated galactic initial mass function (IGIMF) of stars, i.e. the\ngalaxy-wide IMF, to become systematically top-heavy with increasing SFR. This\nhas been predicted by the IGIMF theory, which is here used to develop the\nanalytical theory of the chemical evolution of galaxies. This theory is\nnon-linear and requires the iterative solution of implicit integral equations\ndue to the dependence of the IGIMF on the metallicity and on the SFR. It is\nshown that the mass-metallicity relation of galaxies emerges naturally,\nalthough at low masses the theoretical predictions overestimate the\nobservations by 0.3--0.4 dex. A good agreement with the observation can be\nobtained only if gas flows are taken into account. In particular, we are able\nto reproduce the mass--metallicity relation observed by Lee et al. (2006) with\nmodest amounts of infall and with an outflow rate which decreases as a function\nof the galactic mass. The outflow rates required to fit the data are\nconsiderably smaller than required in models with invariant IMFs.", "category": "astro-ph_GA" }, { "text": "Galaxy stellar mass assembly: the difficulty matching observations and\n semi-analytical predictions: Semi-analytical models (SAMs) are currently the best way to understand the\nformation of galaxies within the cosmic dark-matter structures. While they\nfairly well reproduce the local stellar mass functions, correlation functions\nand luminosity functions, they fail to match observations at high redshift (z >\n3) in most cases, particularly in the low-mass range. The inconsistency between\nmodels and observations indicates that the history of gas accretion in\ngalaxies, within their host dark-matter halo, and the transformation of gas\ninto stars, are not well followed. Hereafter, we briefly present a new version\nof the GalICS semi-analytical model. We explore the impacts of classical\nmechanisms, such as supernova feedback or photoionization, on the evolution of\nthe stellar mass assembly. Even with a strong efficiency, these two processes\ncannot explain the observed stellar mass function and star formation rate\ndistribution and some other relations. We thus introduce an ad-hoc modification\nof the standard paradigm, based on the presence of a \\textit{no-star-forming}\ngas component, and a concentration of the star-forming gas in galaxy discs. The\nmain idea behind the existence of the no-star-forming gas reservoir is that\nonly a fraction of the total gas mass in a galaxy is available to form stars.\nThe reservoir generates a delay between the accretion of the gas and the star\nformation process. This new model is in much better agreement with the\nobservations of the stellar mass function in the low-mass range than the\nprevious models, and agrees quite well with a large set of observations,\nincluding the redshift evolution of the specific star formation rate. However,\nit predicts a large fraction of no-star-forming baryonic gas, potentially\nlarger than observed, even if its nature has still to be examined in the\ncontext of the missing baryon problem.", "category": "astro-ph_GA" }, { "text": "A First Look at Galaxy Flyby Interactions. II. Do Flybys matter?: In the second paper of this series, we present results from cosmological\nsimulations on the demographics of flyby interactions to gauge their potential\nimpact on galaxy evolution. In a previous paper, we demonstrated that flybys --\nan interaction where two independent halos inter-penetrate but detach at a\nlater time and do not merge -- occur much more frequently than previously\nbelieved. In particular, we found that the frequency of flybys increases at low\nredshift and is comparable to or even greater than the frequency of mergers for\nhalos $\\gtrsim 10^{11} M_\\odot/h$. In this paper, we classify flybys according\nto their orbits and the level of perturbation exacted on both the halos\ninvolved. We find that the majority of flybys penetrate deeper than $\\sim\nR_{half}$ of the primary and have an initial relative speed $\\sim 1.6\\times\nV_{vir}$ of the primary. The typical flyby mass-ratio is $\\sim 0.1$ at high $z$\nfor all halos, while at low $z$, massive primary halos undergo flybys with\nsmall secondary halos. We estimate the perturbation from the flyby on both the\nprimary and the secondary and find that a typical flyby is mostly\nnon-perturbative for the primary halo. However, since a massive primary\nexperiences so many flybys at any given time, they are nearly continually a\nvictim of a perturbative event. In particular, we find flybys that cause $\\sim\n1\\%$ change in the binding energy of a primary halo occurs $\\gtrsim 1 $\nGyr$^{-1}$ for halos $> 10^{10} M_\\odot/h$ for $z \\lesssim 4$. Secondary halos,\non the other hand, are highly perturbed by the typical encounter, experiencing\na change in binding energy of nearly order unity. Our results imply that flybys\ncan drive a significant part of galaxy transformation at moderate to lower\nredshifts ($z \\lesssim 4$). We touch on implications for observational surveys,\nmass-to-light ratios, and galaxy assembly bias.", "category": "astro-ph_GA" }, { "text": "Relativistic dynamics of stars near a supermassive black hole: General relativistic precession limits the ability of gravitational\nencounters to increase the eccentricity $e$ of orbits near a supermassive black\nhole (SBH). This \"Schwarzschild barrier\" (SB) has been shown to play an\nimportant role in the orbital evolution of stars like the galactic center\nS-stars. However, the evolution of orbits below the SB, $e>e_\\mathrm{SB}$, is\nnot well understood; the main current limitation is the computational\ncomplexity of detailed simulations. Here we present an $N$-body algorithm that\nallows us to efficiently integrate orbits of test stars around a SBH including\ngeneral relativistic corrections to the equations of motion and interactions\nwith a large ($\\gtrsim 10^3$) number of field stars. We apply our algorithm to\nthe S-stars and extract diffusion coefficients describing the evolution in\nangular momentum $L$. We identify three angular momentum regimes, in which the\ndiffusion coefficients depend in functionally different ways on $L$. Regimes of\nlowest and highest $L$ are well-described in terms of non-resonant relaxation\n(NRR) and resonant relaxation (RR), respectively. In addition, we find a new\nregime of \"anomalous relaxation\" (AR). We present analytic expressions, in\nterms of physical parameters, that describe the diffusion coefficients in all\nthree regimes, and propose a new, empirical criterion for the location of the\nSB in terms of the $L$-dependence of the diffusion coefficients. Subsequently\nwe apply our results to obtain the steady-state distribution of angular\nmomentum for orbits near a SBH.", "category": "astro-ph_GA" }, { "text": "Statistical association between the candidate repeating FRB 20200320A\n and a galaxy group: We present results from angular cross-correlations between select samples of\nCHIME/FRB repeaters and galaxies in three photometric galaxy surveys, which\nhave shown correlations with the first CHIME/FRB catalog containing repeating\nand nonrepeating sources: WISE$\\times$SCOS, DESI-BGS, and DESI-LRG. We find a\nstatistically significant correlation ($p$-value $<0.001$, after accounting for\nlook-elsewhere factors) between a sample of repeaters with extragalactic\ndispersion measure DM $>395$ pc cm$^{-3}$ and WISE$\\times$SCOS galaxies with\nredshift $z>0.275$. We demonstrate that the correlation arises surprisingly\nbecause of a statistical association between FRB 20200320A (extragalactic DM\n$\\approx550$ pc cm$^{-3}$) and a galaxy group in the same dark matter halo at\nredshift $z\\approx0.32$. We estimate that the host halo, along with an\nintervening halo at redshift $z\\approx0.12$, accounts for at least $\\sim$$30\\%$\nof the extragalactic DM. Our results strongly motivate incorporating galaxy\ngroup and cluster catalogs into direct host association pipelines for FRBs with\n$\\lesssim$$1'$ localization precision, effectively utilizing the two-point\ninformation to constrain FRB properties such as their redshift and DM\ndistributions. In addition, we find marginal evidence for a negative\ncorrelation at 99.4% CL between a sample of repeating FRBs with baseband data\n(median extragalactic DM $=354$ pc cm$^{-3}$) and DESI-LRG galaxies with\nredshift $0.3\\le z<0.45$, suggesting that the repeaters might be more prone\nthan apparent nonrepeaters to propagation effects in FRB-galaxy correlations\ndue to intervening free electrons over angular scales\n$\\sim$$0\\mbox{$.\\!\\!^\\circ$}5$.", "category": "astro-ph_GA" }, { "text": "Spatial Decorrelation of Young Stars and Dense Gas as a Probe of the\n Star Formation-Feedback Cycle in Galaxies: The spatial decorrelation of dense molecular gas and young stars observed on\n$\\lesssim 1$ kiloparsec scales in nearby galaxies indicates rapid dispersal of\nstar-forming regions by stellar feedback. We explore the sensitivity of this\ndecorrelation to different processes controlling the structure of the\ninterstellar medium, the abundance of molecular gas, star formation, and\nfeedback in a suite of simulations of an isolated dwarf galaxy with structural\nproperties similar to NGC300 that self-consistently model radiative transfer\nand molecular chemistry. Our fiducial simulation reproduces the magnitude of\ndecorrelation and its scale dependence measured in NGC300, and we show that\nthis agreement is due to different aspects of feedback, including H$_2$\ndissociation, gas heating by the locally variable UV field, early mechanical\nfeedback, and supernovae. In particular, early radiative and mechanical\nfeedback affects the correlation on $\\lesssim 100$ pc scales, while supernovae\nplay a significant role on $\\gtrsim 100$ pc scales. The correlation is also\nsensitive to the choice of the local star formation efficiency per freefall\ntime, $\\epsilon_{\\rm ff}$, which provides a strong observational constraint on\n$\\epsilon_{\\rm ff}$ when the global star formation rate is independent of its\nvalue. Finally, we explicitly show that the degree of correlation between the\npeaks of molecular gas and star formation density is directly related to the\ndistribution of the lifetimes of star-forming regions.", "category": "astro-ph_GA" }, { "text": "NOEMA spatially resolved view of the multi-phase outflow in\n IRAS17020+4544: a shocked wind in action?: The Narrow Line Seyfert 1 Galaxy IRAS17020+4544 is one of the few AGN where a\ngalaxy-scale energy-conserving outflow was revealed. This paper reports on\nNOEMA observations addressed to constrain the spatial scale of the CO emission\nin outflow. The molecular outflowing gas is resolved in five components tracing\napproaching and receding gas, all located at a distance of 2-3~kpc on the West\nand East side of the active nucleus. This high velocity gas (up to v_out=~1900\nkm/s) is not coincident with the rotation pattern of the CO gas in the host\ngalaxy disk. The estimated mass outflow rate shows that with a global mass\noutput of $\\dot{M}_{H_2}$=~139$\\pm$20$~M_\\odot$~yr$^{-1}$, this powerful\ngalaxy-scale outflow is consistent with the wind conserving its energy, and\nwith a momentum rate boost of a factor of ~30 compared to the momentum rate of\nthe nuclear X-ray wind. Preliminary results from ancillary X-ray (Chandra) and\nradio images (e-MERLIN) are reported. While the nature of the radio source is\nnot conclusive, the Chandra image may tentatively trace extended emission, as\nexpected by an expanding bubble of hot X-ray gas. The outcome of the NOEMA\nanalysis and of past and ongoing publications dedicated to the description of\nthe outflow multi-band phenomenology in IRAS17020+4544 concur to provide\ncompelling reasons to postulate that an outflow shocking with the galaxy\ninterstellar medium is driving the multi-phase wind in this peculiar AGN.", "category": "astro-ph_GA" }, { "text": "Subaru Hyper Suprime-Cam Survey of Cygnus OB2 Complex -- I:\n Introduction, Photometry and Source Catalog: Low mass star formation inside massive clusters is crucial to understand the\neffect of cluster environment on processes like circumstellar disk evolution,\nplanet and brown dwarf formation. The young massive association of Cygnus OB2,\nwith a strong feedback from massive stars, is an ideal target to study the\neffect of extreme environmental conditions on its extensive low-mass\npopulation. We aim to perform deep multi-wavelength studies to understand the\nrole of stellar feedback on the IMF, brown dwarf fraction and circumstellar\ndisk properties in the region. We introduce here, the deepest and widest\noptical photometry of 1.5$^\\circ$ diameter region centred at Cygnus OB2 in\nr$_{2}$, i$_{2}$, z and Y-filters using Subaru Hyper Suprime-Cam (HSC). This\nwork presents the data reduction, source catalog generation, data quality\nchecks and preliminary results about the pre-main sequence sources. We obtain\n713,529 sources in total, with detection down to $\\sim$ 28 mag, 27 mag, 25.5\nmag and 24.5 mag in r$_{2}$, i$_{2}$, z and Y-band respectively, which is\n$\\sim$ 3 - 5 mag deeper than the existing Pan-STARRS and GTC/OSIRIS photometry.\nWe confirm the presence of a distinct pre-main sequence branch by statistical\nfield subtraction of the central 18$^\\prime$ region. We find the median age of\nthe region as $\\sim$ 5 $\\pm$ 2 Myrs with an average disk fraction of $\\sim$\n9$\\%$. At this age, combined with A$_V$ $\\sim$ 6 - 8 mag, we detect sources\ndown to a mass range $\\sim$ 0.01 - 0.17 M$_\\odot$. The deep HSC catalog will\nserve as the groundwork for further studies on this prominent active young\ncluster.", "category": "astro-ph_GA" }, { "text": "Constraints on the non-thermal desorption of methanol in the cold core\n LDN 429-C: Cold cores are an early step of star formation, characterized by densities >\n10$^4$ cm$^{-3}$, low temperatures (< 15 K), and very low external UV\nradiation. We investigate the physico-chemical processes at play to tracing the\norigin of molecules that are predominantly formed via reactions on dust grain\nsurfaces. We observed the cold core LDN 429-C with the NOEMA interferometer and\nthe IRAM 30m single dish telescope in order to obtain the gas-phase abundances\nof key species, including CO and CH$_3$OH. Comparing the observed gas phase of\nmethanol to its solid phase previously observed with Spitzer allows us to put\nquantitative constraints on the efficiency of the non-thermal desorption of\nthis species. With physical parameters determined from available Herschel data,\nwe computed abundance maps of 11 detected molecules with a non-local thermal\nequilibrium radiative transfer model. These observations allowed us to probe\nthe molecular abundances as a function of density and visual extinction, with\nthe variation in temperature being restrained between 12 and 18 K. We then\ncompared the observed abundances to the predictions of the Nautilus\nastrochemical model. We find that all molecules have lower abundances at high\ndensities and visual extinctions with respect to lower density regions, except\nfor methanol. Comparing these observations with a grid of chemical models based\non the local physical conditions, we were able to reproduce these observations,\nallowing only the parameter time to vary. Comparing the observed gas-phase\nabundance of methanol with previous measurements of the methanol ice, we\nestimate a non-thermal desorption efficiency between 0.002% and 0.09%,\nincreasing with density. The apparent increase in the desorption efficiency\ncannot be reproduced by our model unless the yield of cosmic-ray sputtering is\naltered due to the ice composition varying as a function of density.", "category": "astro-ph_GA" }, { "text": "Low-Redshift Lyman Limit Systems as Diagnostics of Cosmological Inflows\n and Outflows: We use cosmological hydrodynamic simulations with stellar feedback from the\nFIRE project to study the physical nature of Lyman limit systems (LLSs) at z<1.\nAt these low redshifts, LLSs are closely associated with dense gas structures\nsurrounding galaxies, such as galactic winds, dwarf satellites, and cool\ninflows from the intergalactic medium. Our analysis is based on 14 zoom-in\nsimulations covering the halo mass range M_h~10^9-10^13 Msun at z=0, which we\nconvolve with the dark matter halo mass function to produce cosmological\nstatistics. We find that the majority of cosmologically-selected LLSs are\nassociated with halos in the mass range 10^10 < M_h < 10^12 Msun. The incidence\nand HI column density distribution of simulated absorbers with columns 10^16.2\n< N_HI < 2x10^20 cm^-2 are consistent with observations. High-velocity outflows\n(with radial velocity exceeding the halo circular velocity by a factor >~2)\ntend to have higher metallicities ([X/H] ~ -0.5) while very low metallicity\n([X/H] < -2) LLSs are typically associated with gas infalling from the\nintergalactic medium. However, most LLSs occupy an intermediate region in\nmetallicity-radial velocity space, for which there is no clear trend between\nmetallicity and radial kinematics. Metal-enriched inflows arise in the FIRE\nsimulations as a result of galactic winds that fall back onto galaxies at low\nredshift. The overall simulated LLS metallicity distribution has a mean\n(standard deviation) [X/H] = -0.9 (0.4) and does not show significant evidence\nfor bimodality, in contrast to recent observational studies but consistent with\nLLSs arising from halos with a broad range of masses and metallicities.", "category": "astro-ph_GA" }, { "text": "Detection of Cosmic Fullerenes in the Almahata Sitta Meteorite: Are They\n an Interstellar Heritage?: Buckminsterfullerene, C60 , is the largest molecule observed to date in\ninterstellar and circumstellar environments. The mechanism of formation of this\nmolecule is actively debated. Despite targeted searches in primitive\ncarbonaceous chondrites, no unambiguous detection of C60 in a meteorite has\nbeen reported to date. Here we report the first firm detection of fullerenes,\nfrom C30 to at least C100 , in the Almahata Sitta (AhS) polymict ureilite\nmeteorite. This detection was achieved using highly sensitive laser desorption\nlaser ionization mass spectrometry. Fullerenes have been unambiguously detected\nin seven clasts of AhS ureilites. Molecular family analysis shows that\nfullerenes are from a different reservoir compared to the polycyclic aromatic\nhydrocarbons detected in the same samples. The fullerene family correlates best\nwith carbon clusters, some of which may have been formed by the destruction of\nsolid carbon phases by the impacting laser. We show that the detected\nfullerenes are not formed in this way. We suggest that fullerenes are an\nintrinsic component of a specific carbon phase that has yet to be identified.\nThe nondetection of fullerenes in the Murchison and Allende bulk samples, while\nusing the same experimental conditions, suggests that this phase is absent or\nless abundant in these primitive chondrites. The former case would support the\nformation of fullerenes by shock-wave processing of carbonaceous phases in the\nureilite parent body. However, there are no experimental data to support this\nscenario. This leaves open the possibility that fullerenes are an interstellar\nheritage and a messenger of interstellar processes.", "category": "astro-ph_GA" }, { "text": "Luminous Quasars Do Not Live in the Most Overdense Regions of Galaxies\n at z~4: We present the cross-correlation between 151 luminous quasars ($M_{\n\\mathrm{UV}} < -26$) and 179 protocluster candidates at $z \\sim 3.8$, extracted\nfrom the Wide imaging survey ($ \\sim 121~ $deg$^2$) performed with a part of\nthe Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). We find that only two\nout of 151 quasars reside in regions that are more overdense compared to the\naverage field at $ > 4 \\sigma $. The distributions of the distance between\nquasars and the nearest protoclusters and the significance of the overdensity\nat the position of quasars are statistically identical to those found for\n$g$-dropout galaxies, suggesting that quasars tend to reside in almost the same\nenvironment as star-forming galaxies at this redshift. Using stacking analysis,\nwe find that the average density of $g$-dropout galaxies around quasars is\nslightly higher than that around $g$-dropout galaxies on $1.0 - 2.5$ pMpc\nscales, while at $ < 0.5$ pMpc that around quasars tends to be lower. We also\nfind that quasars with higher UV-luminosity or with more massive black holes\ntend to avoid the most overdense regions, and that the quasar near zone sizes\nare anti-correlated with overdensity. These findings are consistent with a\nscenario in which the luminous quasar at $z \\sim4 $ resides in structures that\nare less massive than those expected for the progenitors of today's rich\nclusters of galaxies, and possibly that luminous quasars may be suppressing\nstar formation in their close vicinity.", "category": "astro-ph_GA" }, { "text": "Galaxies M32 and NGC 5102 Confirm a Near-infrared Spectroscopic\n Chronometer: We present near infrared (NIR) IRTF/SpeX spectra of the intermediate-age\ngalaxy M32 and the post-starburst galaxy NGC 5102. We show that features from\nthermally-pulsing asymptotic giant branch (TP-AGB) and main sequence turn-off\n(MSTO) stars yield similar ages to those derived from optical spectra. The\nTP-AGB can dominate the NIR flux of a coeval stellar population between ~0.1\nand ~2 Gyr, and the strong features of (especially C-rich) TP-AGB stars are\nuseful chronometers in integrated light studies. Likewise, the Paschen series\nin MSTO stars is stongly dependent on age and is an indicator of a young\nstellar component in integrated spectra. We define four NIR spectroscopic\nindices to measure the strength of absorption features from both C-rich TP-AGB\nstars and hydrogen features in main sequence stars, in a preliminary effort to\nconstruct a robust chronometer that probes the contributions from stars in\ndifferent evolutionary phases. By comparing the values of the indices measured\nin M32 and NGC 5102 to those in the Maraston (2005) stellar population\nsynthesis models for various ages and metallicities, we show that model\npredictions for the ages of the nuclei of M32 and NGC 5102 agree with previous\nresults obtained from integrated optical spectroscopy and CMD analysis of the\ngiant branches. The indices discriminate between an intermediate age population\nof ~3-4 Gyr, a younger population of <1 Gyr, and can also detect the signatures\nof very young (<100 Myr) populations.", "category": "astro-ph_GA" }, { "text": "EMPRESS. VI. Outflows Investigated in Low-Mass Galaxies with\n $M_*=10^4-10^7~M_\\odot$: Weak Feedback in Low-Mass Galaxies?: We study emission line profiles of 21 nearby low-mass\n($M_*=10^4-10^7~M_\\odot$) galaxies in deep medium-high resolution spectra taken\nwith Magellan/MagE. These low-mass galaxies are actively star-forming systems\nwith high specific star-formation rates of\n$\\mathrm{sSFR}\\sim100-1000~\\mathrm{Gyr}^{-1}$ that are well above the\nstar-formation main sequence and its extrapolation. We identify broad-line\ncomponents of H$\\alpha$ and [OIII]$\\lambda 5007$ emission in 14 out of the 21\ngalaxies that cannot be explained by the MagE instrumental profile or the\nnatural broadening of line emission. We conduct double Gaussian profile fitting\nto the emission of the 14 galaxies, and find that the broad-line components\nhave line widths significantly larger than those of the narrow-line components,\nindicative of galactic outflows. The board-line components have moderately\nlarge line widths of $\\sim 100$ km s$^{-1}$. We estimate the maximum outflow\nvelocities $v_\\mathrm{max}$ and obtain values of $\\simeq 60-200$ km s$^{-1}$,\nwhich are found to be comparable to or slightly larger than the escape\nvelocities. Positive correlations of $v_\\mathrm{max}$ with star-formation\nrates, stellar masses, and circular velocities, extend down into this low-mass\nregime. Broad- to narrow-line flux ratios BNRs are generally found to be\nsmaller than those of massive galaxies. The small $v_\\mathrm{max}$ and BNRs\nsuggest that the mass loading factors $\\eta$ can be as small as 0.1 - 1 or\nbelow, in contrast to the large $\\eta$ of energy-driven outflows predicted by\nnumerical simulations.", "category": "astro-ph_GA" }, { "text": "Dynamics of Starbursting Dwarf Galaxies. III. A HI study of 18 nearby\n objects: We investigate the dynamics of starbursting dwarf galaxies, using both new\nand archival HI observations. We consider 18 nearby galaxies that have been\nresolved into single stars by HST observations, providing their star formation\nhistory and total stellar mass. We find that 9 objects have a\nregularly-rotating HI disk, 7 have a kinematically disturbed HI disk, and 2\nshow unsettled HI distributions. Two galaxies (NGC 5253 and UGC 6456) show a\nvelocity gradient along the minor axis of the HI disk, that we interpret as\nstrong radial motions. For galaxies with a regularly rotating disk we derive\nrotation curves, while for galaxies with a kinematically disturbed disk we\nestimate the rotation velocities in their outer parts. We derive baryonic\nfractions within about 3 optical scale lengths and find that, on average,\nbaryons constitute at least 30$\\%$ of the total mass. Despite the star\nformation having injected $\\sim$10$^{56}$ ergs in the ISM in the last $\\sim$500\nMyr, these starbursting dwarfs have both baryonic and gas fractions similar to\nthose of typical dwarf irregulars, suggesting that they did not eject a large\namount of gas out of their potential wells.", "category": "astro-ph_GA" }, { "text": "The Velocity Statistics of Turbulent Clouds in the Presence of Gravity,\n Magnetic fields, Radiation, and Outflow Feedback: The interaction of turbulence, magnetic fields, self-gravity, and stellar\nfeedback within molecular clouds is crucial for understanding star formation.\nWe study the effects of self-gravity and outflow feedback on the properties of\nthe turbulent velocity via the structure function over length scales from\n$\\sim$ 0.01 pc to 2 pc. We analyze a series of three-dimensional,\nmagnetohydrodynamical (MHD) simulations of star cluster formation. We find\noutflow feedback can change the scaling of velocity fluctuations but still\nroughly being in between Kolmogorov and Burgers turbulence. We observe that\nself-gravity and protostellar outflows increase the velocity fluctuations over\nall length scales. Outflows can amplify the velocity fluctuations by up to a\nfactor of $\\sim$7 on scales $\\sim$ 0.01 - 0.2 pc and drive turbulence up to a\nscale of $\\sim$ 1 pc. The amplified velocity fluctuations provide more support\nagainst gravity and enhance fragmentation on small scales. The self-gravity's\neffect is more significant on smaller dense clumps and it increases the\nfraction of the compressive velocity component up to a scale of $\\sim$ 0.2 pc.\nHowever, outflow feedback drives both solenoidal and compressive modes, but it\ninduces a higher fraction of solenoidal modes relative to compressive modes.\nThus, with outflows, the dense core ends up with a slightly higher fraction of\nsolenoidal modes. We find that the compressible fraction is fairly constant\nwith about 1/3 on scales $\\sim$ 0.1 - 0.2 pc. The combined effect of enhanced\nvelocity dispersion and reduced compressive fraction contributes to a reduction\nin the star formation rate.", "category": "astro-ph_GA" }, { "text": "General spherical anisotropic Jeans models of stellar kinematics:\n including proper motions and radial velocities: Cappellari (2008) presented a flexible and efficient method to model the\nstellar kinematics of anisotropic axisymmetric and spherical stellar systems.\nThe spherical formalism could be used to model the line-of-sight velocity\nsecond moments allowing for essentially arbitrary radial variation in the\nanisotropy and general luminous and total density profiles. Here we generalize\nthe spherical formalism by providing the expressions for all three components\nof the projected second moments, including the two proper motion components. A\nreference implementation is now included in the public JAM package available at\nhttp://purl.org/cappellari/software", "category": "astro-ph_GA" }, { "text": "Formation channels of slowly rotating early-type galaxies: We study the evidence for a diversity of formation processes in early-type\ngalaxies by presenting the first complete volume-limited sample of slow\nrotators with both integral-field kinematics from the ATLAS3D Project and high\nspatial resolution photometry from the Hubble Space Telescope. Analysing the\nnuclear surface brightness profiles of 12 newly imaged slow rotators, we\nclassify their light profiles as core-less, and place an upper limit to the\ncore size of ~10 pc. Considering the full magnitude and volume-limited ATLAS3D\nsample, we correlate the presence or lack of cores with stellar kinematics,\nincluding the proxy for the stellar angular momentum and the velocity\ndispersion within one half-light radius, stellar mass, stellar age,\n$\\alpha$-element abundance, and age and metallicity gradients. More than half\nof the slow rotators have core-less light profiles, and they are all less\nmassive than $10^{11}$ Msun. Core-less slow rotators show evidence for\ncounter-rotating flattened structures, have steeper metallicity gradients, and\na larger dispersion of gradient values than core slow rotators. Our results\nsuggest that core and core-less slow rotators have different assembly\nprocesses, where the former are the relics of massive dissipation-less merging\nin the presence of central supermassive black holes. Formation processes of\ncore-less slow rotators are consistent with accretion of counter-rotating gas\nor gas-rich mergers of special orbital configurations, which lower the final\nnet angular momentum of stars, but support star formation. We also highlight\ncore fast rotators as galaxies that share properties of core slow rotators and\ncore-less slow rotators. Formation processes similar to those for core-less\nslow rotators can be invoked to explain the assembly of core fast rotators,\nwith the distinction that these processes form or preserve cores.[Abridged]", "category": "astro-ph_GA" }, { "text": "Polarised radio filaments outside the Galactic plane: We used data from the \\wmap satellite at 23, 33 and 41 GHz to study the\ndiffuse polarised emission over the entire sky. The emission originates mostly\nfrom filamentary structures with well-ordered magnetic fields. Some of these\nstructures have been known for decades in radio continuum maps. Their origin is\nnot clear and there are many filaments that are visible for the first time. We\nhave identified and studied 11 filaments. The polarisation fraction of some of\nthem can be as high as 40\\%, which is a signature of a well ordered magnetic\nfield. The polarisation spectral indices, averaged over 18 regions in the sky\nis $\\beta = -3.06 \\pm 0.02$, consistent with synchrotron radiation. There are\nsignificant variations in $\\beta$ over the sky ($\\Delta\\beta\\approx0.2$).\n We explore the link between the large-scale filaments and the local ISM,\nusing the model of an expanding shell in the solar vicinity. We compared\nobserved polarisation angles with the predictions from the model and found good\nagreement. This strongly suggests that many large scale filaments and loops are\nnearby structures. This is important in the context of the Galactic magnetic\nfield as these structures are normally included in global models, neglecting\nthe fact that they might be local. We also studied the level of contamination\nadded by the diffuse filaments to the CMB polarisation power spectra. We\nconclude that, even though these filaments present low radio brightness, a\ncareful removal will be necessary for future all-sky CMB polarisation analysis.", "category": "astro-ph_GA" }, { "text": "The KMOS Cluster Survey (KCS) I: The fundamental plane and the formation\n ages of cluster galaxies at redshift $1.44\\times10^{10} M_{\\odot}$) in 3\nknown overdensities at $1.3911$) in our sample, we translate the FP zero-point\nevolution into a mass-to-light-ratio $M/L$ evolution finding $\\Delta \\log\nM/L_{B}=(-0.46\\pm0.10)z$, $\\Delta \\log M/L_{B}=(-0.52\\pm0.07)z$, to $\\Delta\n\\log M/L_{B}=(-0.55\\pm0.10)z$, respectively. We assess the potential\ncontribution of the galaxies structural and stellar velocity dispersion\nevolution to the evolution of the FP zero-point and find it to be $\\sim$6-35 %\nof the FP zero-point evolution. The rate of $M/L$ evolution is consistent with\ngalaxies evolving passively. By using single stellar population models, we find\nan average age of $2.33^{+0.86}_{-0.51}$ Gyr for the $\\log\nM_{\\star}/M_{\\odot}>11$ galaxies in our massive and virialized cluster at\n$z=1.39$, $1.59^{+1.40}_{-0.62}$ Gyr in a massive but not virialized cluster at\n$z=1.46$, and $1.20^{+1.03}_{-0.47}$ Gyr in a protocluster at $z=1.61$. After\naccounting for the difference in the age of the Universe between redshifts, the\nages of the galaxies in the three overdensities are consistent within the\nerrors, with possibly a weak suggestion that galaxies in the most evolved\nstructure are older.", "category": "astro-ph_GA" }, { "text": "Deuterium fractionation of nitrogen hydrides: detections of NHD and\n ND$_2$: Although ammonia is an abundant molecule commonly observed towards the dense\ninterstellar medium, it has not yet been established whether its main formation\nroute is from gas-phase ion-molecule reactions or grain-surface hydrogen\nadditions on adsorbed nitrogen atoms. Deuterium fractionation can be used as a\ntool to constrain formation mechanisms. High abundances of deuterated molecules\nare routinely observed in the dense interstellar medium, with the ratio between\ndeuterated molecules and the main isotopologue enhanced by several orders of\nmagnitude with respect to the elemental D/H ratio. In the case of ammonia, the\ndetection of its triply deuterated isotopologue hints at high abundances of the\ndeuterated intermediate nitrogen radicals, ND, NHD and ND$_2$. So far however,\nonly ND has been detected in the interstellar medium. In this paper, to\nconstrain the formation of ammonia, we aim at determining the NHD/NH$_2$ and\nND$_2$/NHD abundance ratios, and compare them with the predictions of both pure\ngas-phase and grain-surface chemical models. We searched for the fundamental\nrotational transitions of NHD and ND$_2$ towards the class 0 protostar\nIRAS16293-2422, towards which NH, NH$_2$ and ND had been previously detected.\nBoth NHD and ND$_2$ are detected in absorption towards the source. The relative\nabundance ratios NH$_2$ : NHD : ND$_2$ are close to 8 : 4 : 1. These ratios can\nbe reproduced by our gas-phase chemical model within a factor of two-three.\nStatistical ratios as expected from grain-surface chemistry are also consistent\nwith our data. Further investigations of the ortho-to-para ratio in ND$_2$ ,\nboth theoretical and observational, could bring new constraints to better\nunderstand nitrogen hydride chemistry.", "category": "astro-ph_GA" }, { "text": "NGC5694: another extra-galactic globular cluster: We discuss the chemical composition of six giant stars of the outer Halo\nglobular cluster NGC5694, through the analysis of UVES@FLAMES high-resolution\nspectra. The cluster has an average iron content [Fe/H]=--1.83+-0.01,\nsolar-scaled [alpha/Fe] ratios and a very low Ba abundance\n([Ba/Fe]=--0.71+-0.06). These anomalous abundance patterns are different from\nthose observed in other Halo globular clusters but similar to those of the\nmetal-poor stars in typical dwarf spheroidal galaxies. These findings suggest\nan extra-galactic origin for NGC5694, likely from a dwarf spheroidal galaxy.", "category": "astro-ph_GA" }, { "text": "Polarisation properties of Milky-Way-like galaxies: (Abridged) We study the polarisation properties, magnetic field strength, and\nsynchrotron emission scale-height of Milky-Way-like galaxies in comparison with\nother spiral galaxies. We use our 3D-emission model of the Milky Way Galaxy for\nviewing the Milky Way from outside at various inclinations as spiral galaxies\nare observed. When seen edge-on the synchrotron emission from the Milky Way has\nan exponential scale-height of about 0.74 kpc, which is much smaller than the\nvalues obtained from previous models. We find that current analysis methods\noverestimate the scale-height of synchrotron emission of galaxies by about 10%\nat an inclination of 80 degree and about 40% at an inclination of 70 degree\nbecause of contamination from the disk. The observed RMs for face-on galaxies\nderived from high-frequency polarisation measurements approximate to the\nFaraday depths (FDs) when scaled by a factor of two. For edge-on galaxies, the\nobserved RMs are indicative of the orientation of the large-scale magnetic\nfield, but are not well related with the FDs. Assuming energy equipartition\nbetween the magnetic field and particles for the Milky Way results in an\naverage magnetic-field strength, which is about two times larger than the\nintrinsic value for a K factor of 100. The number distribution of the\nintegrated polarisation percentages of a large sample of unresolved\nMilky-Way-like galaxies peaks at about 4.2% at 4.8 GHz and at about 0.8% at\n1.4GHz. Integrated polarisation angles rotated by 90 degree align very well\nwith the position angles of the major axes, implying that unresolved galaxies\ndo not have intrinsic RMs.", "category": "astro-ph_GA" }, { "text": "Intrinsic shapes of Brightest Cluster Galaxies: We discuss the statistical distribution of galaxy shapes and viewing angles\nunder the assumption of triaxiality by deprojecting observed Surface Brightness\n(SB) profiles of 56 Brightest Cluster Galaxies coming from a recently published\nlarge deep-photometry sample. For the first time, we address this issue by\ndirectly measuring axis ratio profiles without limiting ourselves to a\nstatistical analysis of average ellipticities. We show that these objects are\nstrongly triaxial, with triaxiality parameters 0.39 $ \\leq T \\leq $ 0.72, have\non average axis ratios $< p(r) > = $ 0.84 and $< q(r) > =$ 0.68, and are more\nspherical in the central regions but flatten out at large radii. Measured\nshapes in the outskirts agree well with the shapes found for simulated massive\ngalaxies and their dark matter halos from both the IllustrisTNG and the\nMagneticum simulations, possibly probing the nature of dark matter. In\ncontrast, both simulations fail to reproduce the observed inner regions of\nBCGs, producing too flattened objects.", "category": "astro-ph_GA" }, { "text": "Slingshot Mechanism for Clusters: Gas Density Regulates Star Density in\n the Orion Nebula Cluster (M42): We characterize the stellar and gas volume density, potential, and\ngravitational field profiles in the central $\\sim$ 0.5 pc of the Orion Nebula\nCluster (ONC), the nearest embedded star cluster (or rather, proto-cluster)\nhosting massive star formation available for detailed observational scrutiny.\nWe find that the stellar volume density is well characterized by a Plummer\nprofile $\\rho_{stars}(r) = 5755\\,{\\rm M}_{\\odot}\\,{\\rm\npc}^{-3}\\,(1+(r/a)^2)^{-5/2}$, where $a = 0.36$ pc. The gas density follows a\ncylindrical power law $\\rho_{gas}(R) = 25.9\\,{\\rm M}_{\\odot}\\,{\\rm\npc}^{-3}\\,(R/{\\rm pc})^{-1.775}$. The stellar density profile dominates over\nthe gas density profile inside $r\\,\\sim\\,1$ pc. The gravitational field is\ngas-dominated at all radii, but the contribution to the total field by the\nstars is nearly equal to that of the gas at $r\\,\\sim\\,a$. This fact alone\ndemonstrates that the proto-cluster cannot be considered a gas-free system or a\nvirialized system dominated by its own gravity. The stellar proto-cluster core\nis dynamically young, with an age of $\\sim$ 2-3 Myr, a 1D velocity dispersion\nof $\\sigma_{\\rm obs} = 2.6$ km s$^{-1}$, and a crossing time of $\\sim$ 0.55\nMyr. This timescale is almost identical to the gas filament oscillation\ntimescale estimated recently by Stutz & Gould (2016). This provides strong\nevidence that the proto-cluster structure is regulated by the gas filament. The\nproto-cluster structure may be set by tidal forces due to the oscillating\nfilamentary gas potential. Such forces could naturally suppress low density\nstellar structures on scales $\\gtrsim\\,a$. The analysis presented here leads to\na new suggestion that clusters form by an analog of the \"slingshot mechanism\"\npreviously proposed for stars.", "category": "astro-ph_GA" }, { "text": "Gas contents of galaxy groups from thermal Sunyaev-Zel'dovich effects: A matched filter technique is applied to the Planck all-sky Compton\ny-parameter map to measure the thermal Sunyaev-Zel'dovich (tSZ) effect produced\nby galaxy groups of different halo masses selected from large redshift surveys\nin the low-z Universe. Reliable halo mass estimates are available for all the\ngroups, which allows us to bin groups of similar halo masses to investigate how\nthe tSZ effect depends on halo mass over a large mass range. Filters are\nsimultaneously matched for all groups to minimize projection effects. We find\nthat the integrated y-parameter and the hot gas content it implies are\nconsistent with the predictions of the universal pressure profile model only\nfor massive groups above $10^{14}\\,{\\rm M}_\\odot$, but much lower than the\nmodel prediction for low-mass groups. The halo mass dependence found is in good\nagreement with the predictions of a set of simulations that include strong AGN\nfeedback, but simulations including only supernova feedback significantly over\npredict the hot gas contents in galaxy groups. Our results suggest that hot gas\nin galaxy groups is either effectively ejected or in phases much below the\nvirial temperatures of the host halos.", "category": "astro-ph_GA" }, { "text": "Statistical properties and correlation length in star-forming molecular\n clouds: II. Gravitational potential and virial parameter: In the first article of this series, we have used the ergodic theory to\nassess the validity of a statistical approach to characterize various\nproperties of star-forming molecular clouds (MCs) from a limited number of\nobservations or simulations. This allows the proper determination of confidence\nintervals for various volumetric averages of statistical quantities obtained\nform observations or numerical simulations.\n In this joint paper, we apply the same formalism to a different kind of\n(observational or numerical) study of MCs. Indeed, as observations cannot fully\nunravel the complexity of the inner density structure of star forming clouds,\nit is important to know whether global observable estimates, such as the total\nmass and size of the cloud, can give an accurate estimation of various key\nphysical quantities that characterize the dynamics of the cloud. Of prime\nimportance is the correct determination of the total gravitational (binding)\nenergy and virial parameter of a cloud. We show that, whereas for clouds that\nare not in a too advanced stage of star formation, such as Polaris or Orion B,\nthe knowledge of only their mass and size is sufficient to yield an accurate\ndetermination of the aforementioned quantities from observations (i.e. in real\nspace). In contrast, we show that this is no longer true for numerical\nsimulations in a periodic box. We derive a relationship for the ratio of the\nvirial parameter in these two respective cases.", "category": "astro-ph_GA" }, { "text": "Proper Motions of Stellar Streams Discovered in the Dark Energy Survey: We cross-match high-precision astrometric data from Gaia DR2 with accurate\nmulti-band photometry from the Dark Energy Survey (DES) DR1 to confidently\nmeasure proper motions for nine stellar streams in the DES footprint: Aliqa\nUma, ATLAS, Chenab, Elqui, Indus, Jhelum, Phoenix, Tucana III, and Turranburra.\nWe determine low-confidence proper motion measurements for four additional\nstellar streams: Ravi, Wambelong, Willka Yaku, and Turbio. We find evidence for\na misalignment between stream tracks and the systemic proper motion of streams\nthat may suggest a systematic gravitational influence from the Large Magellanic\nCloud. These proper motions, when combined with radial velocity measurements,\nwill allow for detailed orbit modeling which can be used to constrain\nproperties of the LMC and its affect on nearby streams, as well as global\nproperties of the Milky Way's gravitational potential.", "category": "astro-ph_GA" }, { "text": "The Ties that Bind? Galactic Magnetic Fields and Ram Pressure Stripping: One process affecting gas-rich cluster galaxies is ram pressure stripping,\ni.e. the removal of galactic gas through direct interaction with the\nintracluster medium. Galactic magnetic fields may have an important impact on\nthe stripping rate and tail structure. We run the first magnetohydrodynamic\nsimulations of ram pressure stripping that include a galactic magnetic field,\nusing 159 pc resolution throughout our entire domain in order to resolve mixing\nthroughout the tail. We find very little difference in the total amount of gas\nremoved from the unmagnetized and magnetized galaxies, although a magnetic\nfield with a radial component will initially accelerate stripped gas more\nquickly. In general, we find that magnetic fields in the disk lead to slower\nvelocities in the stripped gas near the disk and faster velocities farther from\nthe disk. We also find that magnetic fields in the galactic gas lead to larger\nunmixed structures in the tail. Finally, we discuss whether ram pressure\nstripped tails can magnetize the ICM. We find that the total magnetic energy\ndensity grows as the tail lengthens, likely through turbulence. There are\nmicroGauss-strength fields in the tail in all of our MHD runs, which survive to\nat least 100 kpc from the disk (the edge of our simulated region), indicating\nthat the area-filling factor of magnetized tails in a cluster could be large.", "category": "astro-ph_GA" }, { "text": "Time Variation of Fine-Structure Constant Constrained by [O III]\n Emission-Lines at 1.1 2\nR_200 from the cluster center when FRB observations with the Square Kilometre\nArray (SKA) become available. The temperature can be derived out to r~ 1.5\nR_200, and the radius is limited by the current sensitivity of SZ observations.", "category": "astro-ph_GA" }, { "text": "New Determination of Fundamental Properties of Palomar 5 Using Deep DESI\n Imaging Data: The legacy imaging surveys for the Dark Energy Spectroscopic Instrument\nproject provides multiplecolor photometric data, which are about 2 mag deeper\nthan the SDSS. In this study, we redetermine the fundamental properties for an\nold halo globular cluster of Palomar 5 based on these new imaging data,\nincluding structure parameters, stellar population parameters, and luminosity\nand mass functions. These characteristics, together with its tidal tails, are\nkey for dynamical studies of the cluster and constraining the mass model of the\nMilky Way. By fitting the King model to the radial surface density profile of\nPalomar 5, we derive the core radius of $r_c$ = 2.96' $\\pm$ 0.11', tidal radius\nof $r_t$ = 17.99' $\\pm$ 1.49', and concentration parameter of $c$ = 0.78 $\\pm$\n0.04. We apply a Bayesian analysis method to derive the stellar population\nproperties and get an age of 11.508 $\\pm$ 0.027 Gyr, metallicity of [Fe/H] =\n-1.798 $\\pm$ 0.014, reddening of $E(B-V)$ = 0.0552 $\\pm$ 0.0005, and distance\nmodulus of $(m-M)_0$ = 16.835 $\\pm$ 0.006. The main-sequence luminosity and\nmass functions for both the cluster center, and tidal tails are investigated.\nThe luminosity and mass functions at different distances from the cluster\ncenter suggest that there is obvious spatial mass segregation. Many faint\nlow-mass stars have been evaporated at the cluster center and the tidal tails\nare enhanced by low-mass stars. Both the concentration and relaxation times\nsuggest that Palomar 5 is a totally relaxed system.", "category": "astro-ph_GA" }, { "text": "Magnetic field structure in the Flattened Envelope and Jet in the young\n protostellar system HH 211: HH 211 is a young Class 0 protostellar system, with a flattened envelope, a\npossible rotating disk, and a collimated jet. We have mapped it with the\nSubmillimeter Array in 341.6 GHz continuum and SiO J=8-7 at ~ 0.6 resolution.\nThe continuum traces the thermal dust emission in the flattened envelope and\nthe possible disk. Linear polarization is detected in the continuum in the\nflattened envelope. The field lines implied from the polarization have\ndifferent orientations, but they are not incompatible with current\ngravitational collapse models, which predict different orientation depending on\nthe region/distance. Also, we might have detected for the first time polarized\nSiO line emission in the jet due to the Goldreich-Kylafis effect. Observations\nat higher sensitivity are needed to determine the field morphology in the jet.", "category": "astro-ph_GA" }, { "text": "The Distance and Peculiar Velocity of the Norma cluster (ACO 3627) using\n the Near-Infrared $J$ and $K_s$-band Fundamental Plane Relations: We report distance measurements for the Norma cluster based on the\nnear-infrared $J$- and $K_s$-band Fundamental Plane (FP) relations. Our\nsimultaneous $J$ and $K_s$-band photometry analyses were performed using 31\nearly-type galaxies in the nearby Norma cluster obtained using the 1.4 m\nInfraRed Survey Facility (IRSF) at the South African Astronomical Observatory.\nOur final $K_s$-band FP sample consists of 41 early-type galaxies from the\nNorma cluster observed using the IRSF and the New Technology Telescope (NTT) at\nthe European Southern Observatory. This is the largest cluster sample used for\npeculiar velocity studies in the Great Attractor region to date. From the\n$K_s$-band FP, we find a distance to the Norma cluster of $4915 \\pm 121$ km\ns$^{-1}$. The implied peculiar velocity for Norma is $44 \\pm 151$ km s$^{-1}$\nwhich further supports a small peculiar velocity for the Norma cluster.", "category": "astro-ph_GA" }, { "text": "The evolution of the galaxy content of dark matter haloes: We use the halo occupation distribution (HOD) framework to characterise the\npredictions from two independent galaxy formation models for the galactic\ncontent of dark matter haloes and its evolution with redshift. Our galaxy\nsamples correspond to a range of fixed number densities defined by stellar mass\nand span $0 \\le z \\le 3$. We find remarkable similarities between the model\npredictions. Differences arise at low galaxy number densities which are\nsensitive to the treatment of heating of the hot halo by active galactic\nnuclei. The evolution of the form of the HOD can be described in a relatively\nsimple way, and we model each HOD parameter using its value at $z=0$ and an\nadditional evolutionary parameter. In particular, we find that the ratio\nbetween the characteristic halo masses for hosting central and satellite\ngalaxies can serve as a sensitive diagnostic for galaxy evolution models. Our\nresults can be used to test and develop empirical studies of galaxy evolution\nand can facilitate the construction of mock galaxy catalogues for future\nsurveys.", "category": "astro-ph_GA" }, { "text": "A Multi-Scale Study of Star Formation in Messier 33: For the Local Group Scd galaxy M 33 this paper presents a multi-scale study\nof the relationship between the monochromatic star formation rate (SFR)\nestimator based on 12 $\\mu$m emission and the total SFR estimator based on a\ncombination of far-ultraviolet and 24 $\\mu$m emission. We show the 12 $\\mu$m\nemission to be a linear estimator of total SFR on spatial scales from 782 pc\ndown to 49 pc, over almost four magnitudes in SFR. These results therefore\nextend to sub-kpc length scales the analogous results from other studies for\nglobal length scales. We use high-resolution HI and $^{12}\\mathrm{CO}(J=2-1)$\nimage sets from the literature to compare the star formation to the neutral\ngas. For the full range of length scales we find well-defined power-law\nrelationships between 12 $\\mu$m-derived SFR surface densities and neutral gas\nsurface densities. For the H$_\\mathrm{2}$ gas component almost all correlations\nare consistent with being linear. No evidence is found for a breakdown in the\nstar formation law at small length scales in M 33 reported by other authors. We\nshow that the average star formation efficiency in M 33 is roughly $10^{-9}$\nyr$^{-1}$ and that it remains constant down to giant molecular cloud length\nscales. Toomre and shear-based models of the star formation threshold are shown\nto inaccurately account for the star formation activity in the inner disc of M\n33. Finally, we clearly show that the HI saturation limit of $\\approx 9$\nM$_{\\odot}$ pc$^{-2}$ reported in the literature for other galaxies is not an\nintrinsic property of M 33 - it is systematically introduced as an artefact of\nspatially smoothing the data.", "category": "astro-ph_GA" }, { "text": "Gravitational Encounters and the Evolution of Galactic Nuclei. IV.\n Captures Mediated by Gravitational-Wave Energy Loss: Direct numerical integrations of the two-dimensional Fokker-Planck equation\nare carried out for compact objects orbiting a supermassive black hole (SBH) at\nthe center of a galaxy. As in Papers I-III, the diffusion coefficients\nincorporate the effects of the lowest-order post-Newtonian corrections to the\nequations of motion. In addition, terms describing the loss of orbital energy\nand angular momentum due to the 5/2-order post-Newtonian terms are included. In\nthe steady state, captures are found to occur in two regimes that are clearly\ndifferentiated in terms of energy, or semimajor axis; these two regimes are\nnaturally characterized as \"plunges\" (low binding energy) and \"EMRIs,\" or\nextreme-mass-ratio inspirals (high binding energy). The capture rate, and the\ndistribution of orbital elements of the captured objects, are presented for two\nsteady-state models based on the Milky Way: one with a relatively high density\nof remnants and one with a lower density. In both models, but particularly in\nthe second, the steady-state energy distribution and the distribution of\norbital elements of the captured objects are substantially different than if\nthe Bahcall-Wolf energy distribution were assumed. The ability of classical\nrelaxation to soften the blocking effects of the Schwarzschild barrier is\nquantified.These results, together with those of Papers I-III, suggest that a\nFokker-Planck description can adequately represent the dynamics of collisional\nloss cones in the relativistic regime.", "category": "astro-ph_GA" }, { "text": "The SAMI Galaxy Survey: the third and final data release: We have entered a new era where integral-field spectroscopic surveys of\ngalaxies are sufficiently large to adequately sample large-scale structure over\na cosmologically significant volume. This was the primary design goal of the\nSAMI Galaxy Survey. Here, in Data Release 3 (DR3), we release data for the full\nsample of 3068 unique galaxies observed. This includes the SAMI cluster sample\nof 888 unique galaxies for the first time. For each galaxy, there are two\nprimary spectral cubes covering the blue (370-570nm) and red (630-740nm)\noptical wavelength ranges at spectral resolving power of R=1808 and 4304\nrespectively. For each primary cube, we also provide three spatially binned\nspectral cubes and a set of standardized aperture spectra. For each galaxy, we\ninclude complete 2D maps from parameterized fitting to the emission-line and\nabsorption-line spectral data. These maps provide information on the gas\nionization and kinematics, stellar kinematics and populations, and more. All\ndata are available online through Australian Astronomical Optics (AAO) Data\nCentral.", "category": "astro-ph_GA" }, { "text": "Stellar population synthesis based modelling of the Milky Way using\n asteroseismology of dwarfs and subgiants from Kepler: Early attempts to apply asteroseismology to study the Galaxy have already\nshown unexpected discrepancies for the mass distribution of stars between the\nGalactic models and the data; a result that is still unexplained. Here, we\nrevisit the analysis of the asteroseismic sample of dwarf and subgiant stars\nobserved by Kepler and investigate in detail the possible causes for the\nreported discrepancy. We investigate two models of the Milky Way based on\nstellar population synthesis, Galaxia and TRILEGAL. In agreement with previous\nresults, we find that TRILEGAL predicts more massive stars compared to Galaxia,\nand that TRILEGAL predicts too many blue stars compared to 2MASS observations.\nBoth models fail to match the distribution of the stellar sample in $(\\log\ng,T_{\\rm eff})$ space, pointing to inaccuracies in the models and/or the\nassumed selection function. When corrected for this mismatch in $(\\log g,T_{\\rm\neff})$ space, the mass distribution calculated by Galaxia is broader and the\nmean is shifted toward lower masses compared to that of the observed stars.\nThis behaviour is similar to what has been reported for the Kepler red giant\nsample. The shift between the mass distributions is equivalent to a change of\n2\\% in $\\nu_{\\rm max}$, which is within the current uncertainty in the\n$\\nu_{\\rm max}$ scaling relation. Applying corrections to the $\\Delta \\nu$\nscaling relation predicted by the stellar models makes the observed mass\ndistribution significantly narrower, but there is no change to the mean.", "category": "astro-ph_GA" }, { "text": "Note on fundamental physics tests from black hole imaging: Comment on\n \"Hunting for extra dimensions in the shadow of Sagittarius A$^*$\": Several works over the past years have discussed the possibility of testing\nfundamental physics using Very Long Baseline Interferometry horizon-scale black\nhole (BH) images, such as the Event Horizon Telescope (EHT) images of M87$^*$\nand Sagittarius A$^*$ (Sgr A$^*$), using the size $r_{\\rm sh}$ and deviation\nfrom circularity $\\Delta \\mathcal{C}$ of the BH shadow. For the case of the EHT\nimage of Sgr A$^*$, limits on $\\Delta \\mathcal{C}$ are not available due to the\nsparse interferometric coverage of the 2017 observations, alongside the short\nvariability timescale of Sgr A$^*$ compared to M87$^*$. Concerning this point,\nwe comment on the results of a recent preprint which purports to have derived\nnew limits on extra dimensions using the deviation from circularity of Sgr\nA$^*$'s shadow. The latter is quoted to be $\\lesssim 10\\%$ as with M87$^*$,\nbased on the \"similarity\" of the two shadows: however, this is an incorrect\nassumption, invalidating the subsequent results. In the immediate future, the\nsimplest tests of fundamental physics from Sgr A$^*$'s image will therefore\nmostly have to rely on $r_{\\rm sh}$, whereas additional observables such as the\nphoton ring and azimuthal angle lapse should soon be available and allow for\nnovel tests.", "category": "astro-ph_GA" }, { "text": "Ultra-compact Embedded Clusters in the Galactic Plane: We have identified a previously unrecognized population of very compact,\nembedded low-mass Galactic stellar clusters. These tight (r$ \\approx $0.14 pc)\ngroupings appear as bright singular objects at the few arcsec resolution of the\nSpitzer Space Telescope at 8 and 24 $\\mu$m but become resolved in the\nsub-arcsecond UKIDSS images. They average six stars per cluster surrounded by\ndiffuse infrared emission and coincide with 100 -- 300 M$_{\\sun}$ clumps of\nmolecular material within a larger molecular cloud. The magnitudes of the\nbrightest stars are consistent with mid- to early-B stars anchoring $\\sim$80\nM$_{\\sun}$ star clusters. Their evolutionary descendants are likely to be\nHerbig Ae/Be pre-main sequence clusters. These ultra-compact embedded clusters\n(UCECs) may fill part of the low-mass void in the embedded cluster mass\nfunction. We provide an initial catalog of 18 UCECs drawn from infrared\nGalactic Plane surveys.", "category": "astro-ph_GA" }, { "text": "Collisional excitation of methyl (iso)cyanide by He atoms: rate\n coefficients and isomerism effects: Among all closed-shell species observed in molecular clouds, molecules with\nC$_{3v}$ symmetry play a crucial role, as their rotational spectroscopy allows\nthem to behave as a gas thermometer. In the interstellar medium, methyl cyanide\n(CH$_3$CN) is the second most abundant of those (after ammonia, NH$_3$). Its\nisomer, methyl isocyanide (CH$_3$NC) is less abundant but has been detected in\nmany astrophysical sources. In order to assess their absolute and relative\nabundances, it is essential to understand their collisional excitation\nproperties. This paper reports the calculation of rate coefficients for\nrotational excitation of CH$_3$CN and CH$_3$NC molecules with He atoms, from\nlow (5 K) to moderate (100 K) temperatures. We include the first 74 and 66\nrotational states of both $para$ and $ortho$ symmetries of CH$_3$CN and\nCH$_3$NC, respectively. A propensity for $\\Delta j=2$ transitions is observed\nin the case of CH$_3$CN-He collisions, whereas in the case of CH$_3$NC-He a\npropensity for $\\Delta j=1$ is observed for transitions involving low values of\n$j$ and at low temperatures, while a propensity for $\\Delta j=2$ is observed\nfor higher values of $j$ and at high temperatures. A comparison of rate\ncoefficients shows differences up to a factor of 3, depending on temperature\nand on the $ortho$/$para$ symmetries for dominant transitions. This confirms\nthe importance of having specific collisional data for each isomer. We also\nexamined the effect of these new rates on the CH$_3$CN and CH$_3$NC excitation\nin molecular clouds by performing radiative transfer calculations of the\nexcitation and brightness temperatures for several detected lines.", "category": "astro-ph_GA" }, { "text": "Delving deep: a population of extremely dusty dwarfs observed by JWST: We take advantage of the NIRCam photometric observations available as part of\nthe Cosmic Evolution Early Release Science survey (CEERS) to identify and\nanalyse very red sources in an effort to discover very dusty star forming\ngalaxies. We select red galaxies as objects with a S/N>3 at 4.4 $\\mu$m and a\nS/N<2 in all JWST and HST filters at $\\lambda\\leq2\\mu$m, which corresponds to\n[F200W]-[F444W]>1.2 considering CEERS depths. This selection is ideal to\nidentify very dusty (Av>1 mag) galaxies with stellar masses between $10^6$ to\n$10^{10}\\, \\rm M_{\\odot}$ at z<5, more massive dusty galaxies at z=5-18 and\ngalaxies at z>18 due to the Lyman absorption, independently of their dust\nextinction. Our sample of F200W-dropouts contains no strong candidates at\nz>6.5, instead it consists almost completely (~81%) of z<2 low-mass galaxies,\nwith a median stellar mass of $10^{7.3} \\rm M_{\\odot}$. These galaxies show an\nexceptional dust extinction with median value of Av=4.9 mag, completely\nunexpected given their low stellar mass. The remaining galaxies, which are at\nz<6.5, show similar large dust extinction (Av>1), but they are generally more\nmassive $>10^{7.5}\\rm M_{\\odot}$.", "category": "astro-ph_GA" }, { "text": "Spin Temperature and Density of Cold and Warm HI in the Galactic Disk -\n Hidden HI -: We present a method to determine the spin temperature $T_{\\rm S}$ and volume\ndensity $n$ of HI gas simultaneously along the tangent-point circle of galactic\nrotation in the Milky Way by using the least-$\\chi^2$ method. The best-fit\n$T_{\\rm S}$ is shown to range either in $T_{\\rm S}=100-120$ K or in $1000-3000$\nK, indicating that the gas is either in cold HI phase with high density and\nlarge optical depth, or in warm HI with low density and small optical depth.\nAveraged values at $3\\le R \\le 8$ kpc are obtained to be $T_{\\rm S}=106.7 \\pm\n16.0$ K and $n=1.53\\pm 0.86$ H cm$^{-3}$ for cold HI, and $1720 \\pm 1060$ K and\n$0.38 \\pm 0.10$ H cm$^{-3}$ for warm HI, where $R=8\\ |\\sin \\ l|$ kpc is the\ngalacto-centric distance along the tangent-point circle. The cold HI appears in\nspiral arms and rings, whereas warm HI in the inter-arm regions. The cold HI is\ndenser by a factor of $\\sim 4$ than warm HI. The present analysis has revealed\nthe hidden HI mass in cold and optically thick phase in the galactic disk. The\ntotal HI mass inside the solar circle is shown to be greater by a factor of $2\n- 2.5$ than the current estimation by optically thin assumption.", "category": "astro-ph_GA" }, { "text": "Rotation Curve Anomaly and Galactic Warp in M51: We revisit the anomaly of rotation curve in the nearly face-on galaxy M51\nthat shows an apparently faster decrease of rotation velocity than the\nKeplerian law in the outer disk, further showing apparent counter rotation in\nthe outermost HI disk. We interpret this anomaly as due to warping of the\ngalactic disk, and determined the warping structure of M51's disk using the\ntilted-ring method, assuming that the intrinsic rotation curve is normal. It is\nshown that the disk is nearly flat in the inner disk at a constant inclination\nangle, but the disk suddenly bends at radius 7.5 kpc by about 27$\\deg$. The\ninclination angle, then, decreases monotonically outward reaching a perfect\nface-on ring at 18 kpc, beyond which the disk is warped in the opposite sense\nto the inner disk, resulting in apparent counter rotation.", "category": "astro-ph_GA" }, { "text": "No correlation of the Lyman continuum escape fraction with spectral\n hardness: The properties that govern the production and escape of hydrogen ionizing\nphotons (Lyman continuum, LyC; with energies >13.6 eV) in star-forming galaxies\nare still poorly understood, but they are key to identifying and characterizing\nthe sources that reionized the Universe. Here we empirically explore the\nrelationship between the hardness of ionizing radiation and the LyC leakage in\na large sample of low-$z$ star-forming galaxies from the recent Hubble Space\nTelescope Low-$z$ Lyman Continuum Survey. Using Sloan Digital Sky Survey stacks\nand deep XShooter observations, we investigate the hardness of the ionizing\nspectra ($Q_{\\rm He^+}/Q_{\\rm H}$) between 54.4 eV (He$^{+}$) and 13.6 eV (H)\nfrom the optical recombination lines HeII 4686A and H$\\beta$ 4861A for galaxies\nwith LyC escape fractions spanning a wide range, $f_{\\rm esc} \\rm (LyC) \\simeq\n0 - 90\\%$. We find that the observed intensity of HeII/H$\\beta$ is primarily\ndriven by variations in the metallicity, but is not correlated with LyC\nleakage. Both very strong ($ \\simeq 0.5$) and nonleakers\n($ < f_{\\rm esc} \\rm (LyC) > \\simeq 0$) present similar observed intensities of\nHeII/H$\\beta$ at comparable metallicity, between $\\simeq 0.01$ and $\\simeq\n0.02$ for $12 + \\log({\\rm O/H}) > 8.0$ and $<8.0$, respectively. Our results\ndemonstrate that $Q_{\\rm He^+}/Q_{\\rm H}$ does not correlate with $f_{\\rm esc}\n\\rm (LyC)$, which implies that strong LyC emitters do not show harder ionizing\nspectra than nonleakers at similar metallicity.", "category": "astro-ph_GA" }, { "text": "Evolution of spatio-kinematic structures in star-forming regions: are\n Friends of Friends worth knowing?: The Friends of Friends algorithm identifies groups of objects with similar\nspatial and kinematic properties, and has recently been used extensively to\nquantify the distributions of gas and stars in young star-forming regions. We\napply the Friends of Friends algorithm to $N$-body simulations of the dynamical\nevolution of subvirial (collapsing) and supervirial (expanding) star-forming\nregions. We find that the algorithm picks out a wide range of groups (1 -- 25)\nfor statistically identical initial conditions, and cannot distinguish between\nsubvirial and supervirial regions in that we obtain similar mode and median\nvalues for the number of groups it identifies. We find no correlation between\nthe number of groups identified initially and either the initial or subsequent\nspatial and kinematic tracers of the regions' evolution, such as the amount of\nspatial substructure, dynamical mass segregation, or velocity dispersion. We\ntherefore urge caution in using the Friends of Friends algorithm to quantify\nthe initial conditions of star formation.", "category": "astro-ph_GA" }, { "text": "Testing PDR models against ISO fine structure line data for\n extragalactic sources: Far-infrared [C ii] 158 micron, [O i] 145 micron and [O i] 63 micron fine\nstructure emission line fluxes were measured from archival Infrared Space\nObservatory Long Wavelength Spectrometer spectra of 46 extragalactic sources,\nwith 28 sources providing detections in all three lines. For 12 of the sources,\nthe contribution to the [C ii] 158 micron line flux from H ii regions could be\nestimated from their detected [N ii] 122 micron line fluxes. The measured [C\nii]/[O i] and [O i] 63/145 micron line flux ratios were compared with those\nfrom a grid of PDR models previously computed using the UCL PDR code.\nPersistent offsets between the observed and modelled line ratios could be\npartly attributed to the effects of [O i] 63 micron self-absorption. Using the\nSMMOL code, we calculated model [O i] line profiles and found that the strength\nof the [O i] 63 micron line was reduced by 20-80%, depending on the PDR\nparameters. We conclude that high PDR densities and radiation field strengths,\ncoupled with the effects of [O i] 63 micron self-absorption, are likely to\nprovide the best match to the observed line flux ratios.", "category": "astro-ph_GA" }, { "text": "Spatially resolved observations of outflows in the radio loud AGN of UGC\n 8782: We use optical Integral Field Spectroscopy (IFU) to study the gas emission\nstructure and kinematics in the inner 3.4$\\times$4.9 kpc$^2$ region of the\ngalaxy UGC 8782 (3C 293), host of a radio loud Active Galactic Nucleus (AGN).\nThe observations were performed with the GMOS-IFU on the Gemini North\ntelescope, resulting in a spatial resolution of $\\sim725$ pc at the distance of\nthe galaxy. While the stars present ordered rotation following the orientation\nof the large scale disc, the gas shows a disturbed kinematics. The\nemission-line profiles present two kinematic components: a narrow\n($\\sigma\\lesssim200$ km s$^{-1}$) component associated with the gas in the disc\nof the galaxy and a broad ($\\sigma\\gtrsim200$ km s$^{-1}$) component produced\nby gas outflows. Emission-line ratio diagrams indicate that the gas in the disc\nis excited by the AGN radiation field, while the emission of the outflow\nincludes additional contribution of shock excitation due to the interaction of\nthe radio jet with the environment gas. Deviations from pure rotation, of up to\n30 km s$^{-1}$, are observed in the disc component and likely produced by a\nprevious merger event. The broad component is blueshifted by $\\sim150-500$ km\ns$^{-1}$ relative to the systemic velocity of the galaxy in all locations. We\nconstruct radial profiles of the mass outflow rate and kinetic power of the\nionized gas outflows, which have the maximum values at $\\sim1$ kpc from the\nnucleus with peak values of $\\dot{M}_{\\rm out,\\Delta R}=0.5\\pm0.1$ M$_\\odot$\nyr$^{-1}$ and $\\dot{K}_{\\rm out,\\Delta R} =$(6.8$\\pm$1.1)$\\times$10$^{41}$ erg\ns$^{-1}$. The kinetic coupling efficiency of these outflows is in the range of\n1$-$3 per cent, indicating that they could be powerful enough to affect the\nstar formation in the host galaxy as predicted by theoretical simulations.", "category": "astro-ph_GA" }, { "text": "Studies of Anomalous Microwave Emission (AME) with the SKA: In this chapter, we will outline the scientific motivation for studying\nAnomalous Microwave Emission (AME) with the SKA. AME is thought to be due to\nelectric dipole radiation from small spinning dust grains, although thermal\nfluctuations of magnetic dust grains may also contribute. Studies of this\nmysterious component would shed light on the emission mechanism, which then\nopens up a new window onto the interstellar medium (ISM). AME is emitted mostly\nin the frequency range $\\sim 10$--100\\,GHz, and thus the SKA has the potential\nof measuring the low frequency side of the AME spectrum, particularly in band\n5. Science targets include dense molecular clouds in the Milky Way, as well as\nextragalactic sources. We also discuss the possibility of detecting rotational\nline emission from Poly-cyclic Aromatic Hydrocarbons (PAHs), which could be the\nmain carriers of AME. Detecting PAH lines of a given spacing would allow for a\ndefinitive identification of specific PAH species.", "category": "astro-ph_GA" }, { "text": "A Carbon-rich Mira variable in a globular cluster: A stellar merger: The membership of Matsunaga's variable 1, a carbon-rich, mass-losing, Mira\nvariable, in the globular cluster Lynga 7 is discussed on the basis of radial\nvelocities. We conclude that it is a member, the first known C-Mira in a\nglobular cluster. Since such a variable is expected to have an age of $\\sim\n1-2$ Gyr and an initial mass of $\\sim 1.5$ solar masses, we conclude that this\nstar must be the product of a stellar merger.", "category": "astro-ph_GA" }, { "text": "Extraplanar gas in Edge-on Galaxies traced by SOFIA observations of [C\n II]: Bursts of localized star formation in galaxies can levitate material from\ntheir midplanes. Spiral galaxies that are edge-on allow clear distinction of\nmaterial that is levitated off the galaxies' midplanes. We used SOFIA to\nmeasure the vertical distribution of [C II] 157.7 micron line emission for two\nnearby, edge-on galaxies, NGC 891 and NGC 5907. We find that for the central\nregion and actively-star-forming regions in the northern portion of NGC 891,\nand for NGC 5907, a thin (0.3 kpc) disk is supplemented by a thick disk with an\nexponential scale height of about 2 kpc. The [C II] is far more extended than\nmid-infrared emission (0.1 kpc, tracing present-day massive star formation) but\nnot as extended as the H I (100 kpc, tracing low-metallicity\ncircum/inter-galactic matter). The extraplanar [C II] may arise in walls of\nchimneys that connect the disk to the halo.", "category": "astro-ph_GA" }, { "text": "The Mass-Concentration Relation and the Stellar-to-Halo Mass Ratio in\n the CFHT Stripe 82 Survey: We present a new measurement of the mass-concentration relation and the\nstellar-to-halo mass ratio over the halo mass range $5\\times 10^{12}$ to\n$2\\times 10^{14}M_{\\odot}$. To achieve this, we use weak lensing measurements\nfrom the CFHT Stripe 82 Survey (CS82), combined with the central galaxies from\nthe redMaPPer cluster catalogue and the LOWZ/CMASS galaxy sample of the Sloan\nDigital Sky Survey-III Baryon Oscillation Spectroscopic Survey Tenth Data\nRelease. The stacked lensing signals around these samples are modelled as a sum\nof contributions from the central galaxy, its dark matter halo, and the\nneighboring halos, as well as a term for possible centering errors. We measure\nthe mass-concentration relation: $c_{200c}(M)=A(\\frac{M_{200c}}{M_0})^{B}$ with\n$A=5.24\\pm1.24, B=-0.13\\pm0.10$ for $0.26$\nwith the AGN contribution (driven by $M_{bh}>10^6 {\\rm M_\\odot}$ black holes in\n$M_* > 10^9 {\\rm M_\\odot}$ galaxies) dominating at lower redshifts; (ii) AGN\nonly contribute $10-25\\%$ to the cumulative ionizing emissivity by $z=4$ for\nthe models that match the observed reionization constraints; (iii) if the\nstellar mass dependence of $\\langle f_{\\rm esc}^{\\rm sf} \\rangle$ is shallower\nthan $f_{\\rm esc}^{\\rm bh}$, at $z<7$ a transition stellar mass exists above\nwhich AGN dominate the escaping ionizing photon production rate; (iv) the\ntransition stellar mass decreases with decreasing redshift. While AGN dominate\nthe escaping emissivity above the knee of the stellar mass function at $z \\sim\n6.8$, they take-over at stellar masses that are a tenth of the knee mass by\n$z=4$.", "category": "astro-ph_GA" }, { "text": "Exploring the SDSS Photometric Galaxies with Clustering Redshifts: We apply clustering-based redshift inference to all extended sources from the\nSloan Digital Sky Survey photometric catalogue, down to magnitude r = 22. We\nmap the relationships between colours and redshift, without assumption of the\nsources' spectral energy distributions (SED). We identify and locate\nstar-forming, quiescent galaxies, and AGN, as well as colour changes due to\nspectral features, such as the 4000 \\AA{} break, redshifting through specific\nfilters. Our mapping is globally in good agreement with colour-redshift tracks\ncomputed with SED templates, but reveals informative differences, such as the\nneed for a lower fraction of M-type stars in certain templates. We compare our\nclustering-redshift estimates to photometric redshifts and find these two\nindependent estimators to be in good agreement at each limiting magnitude\nconsidered. Finally, we present the global clustering-redshift distribution of\nall Sloan extended sources, showing objects up to z ~ 0.8. While the overall\nshape agrees with that inferred from photometric redshifts, the clustering\nredshift technique results in a smoother distribution, with no indication of\nstructure in redshift space suggested by the photometric redshift estimates\n(likely artifacts imprinted by their spectroscopic training set). We also infer\na higher fraction of high redshift objects. The mapping between the four\nobserved colours and redshift can be used to estimate the redshift probability\ndistribution function of individual galaxies. This work is an initial step\ntowards producing a general mapping between redshift and all available\nobservables in the photometric space, including brightness, size,\nconcentration, and ellipticity.", "category": "astro-ph_GA" }, { "text": "OMEGA: OSIRIS Mapping of Emission-Line Galaxies in A901/2: This work presents the first results from an ESO Large Programme carried out\nusing the OSIRIS instrument on the 10m GTC telescope (La Palma). We have\nobserved a large sample of galaxies in the region of the Abell 901/902 system\n(z ~ 0.165) which has been extensively studied as part of the STAGES project.\nWe have obtained spectrally and spatially resolved H-alpha and [NII] emission\nmaps for a very large sample of galaxies covering a broad range of\nenvironments. The new data are combined with extensive multi-wavelength\nobservations which include HST, COMBO-17, Spitzer, Galex and XMM imaging to\nstudy star formation and AGN activity as a function of environment and galaxy\nproperties such as luminosity, mass and morphology. The ultimate goal is to\nunderstand, in detail, the effect of the environment on star formation and AGN\nactivity.", "category": "astro-ph_GA" }, { "text": "Testing the evolutionary pathways of galaxies and their supermassive\n black holes and the impact of feedback from Active Galactic Nuclei via large\n multiwavelength datasets: It is still a matter of intense debate how supermassive black holes (SMBH)\ngrow, and the role played by feedback from active galactic nuclei (AGN) in the\nco-evolution of SMBHs and galaxies. To test the coevolution proposed by\ntheoretical models, we compile a large AGN sample of 5639 X-ray detected AGN,\nover a wide redshift range, spanning nearly three orders of magnitude in X-ray\nluminosity. The AGN have been detected in the {\\it{COSMOS-Legacy}}, the Bo$\\rm\n\\ddot{o}$tes, the XMM-{\\it{XXL}} and the eFEDS fields. Using the specific star\nformation rate estimates, we split the AGN host galaxies into star forming\n(SF), starburst (SB) and quiescent (Q). Our results show that the AGN accretion\nis increased in SB systems compared to SF and Q. Our analysis reveals a mild\nincrease of L$_X$ with M$_*$. The L$_X$/SFR ratio has a weak dependence on\nM$_*$, and at fixed M$_*$ it is highest in Q systems. The latter trend is\nmostly driven by the significant drop in SFR in the Q state. The measured\nstrong variations in SFR from the SB/SF to Q mirror those predicted in merger\nmodels with AGN feedback. However, the observed mild variations in L$_X$ are at\nvariance with the same models. We also study the evolution of SFR for a galaxy\ncontrol sample and found that it is very similar to that of X-ray AGN. This\nsuggests that either AGN play a minor role in the star formation quenching, or\nthe relative timescales of the two processes are different.", "category": "astro-ph_GA" }, { "text": "Practical application of KAM theory to galactic dynamics: II.\n Application to weakly chaotic orbits in barred galaxies: Owing to the pioneering work of Contopoulos, a strongly barred galaxy is\nknown to have irregular orbits in the vicinity of the bar. By definition,\nirregular orbits can not be represented by action-angle tori everywhere in\nphase space. This thwarts perturbation theory and complicates our understanding\nof their role in galaxy structure and evolution. This paper provides a\nqualitative introduction to a new method based on KAM theory for investigating\nthe morphology of regular and irregular orbits based on direct computation of\ntori described in Paper 1 and applies it to a galaxy disc bar. Using this\nmethod, we find that much of the phase space inside of the bar radius becomes\nchaotic for strong bars, excepting a small region in phase space between the\nILR and corotation resonances for orbits of moderate ellipticity. This helps\nexplain the preponderance of moderately eccentric bar-supporting orbits as the\nbar strength increases. This also suggests that bar strength may be limited by\nchaos! The chaos results from stochastic layers that form around primary\nresonances owing to separatrix splitting. Most investigations of orbit\nregularity are performed using numerical computation of Lyapunov exponents or\nrelated indices. We show that Lyapunov exponents poorly diagnose the degree of\nstochasticity in this problem; the island structure in the stochastic sheaths\nallow orbit to change morphology while presenting anomalously small Lyapunov\nexponent values (i.e. weak chaos). For example, a weakly chaotic orbit may\nappear to change its morphology spontaneously, while appearing regular except\nduring the change itself. The numerical KAM approach sensitively detects these\ndynamics and provides a model Hamiltonian for further investigation. It may\nunderpredict the number of broken tori for strong perturbations.", "category": "astro-ph_GA" }, { "text": "Can the observed E/B ratio for dust galactic foreground be explained by\n sub-Alfvenic turbulence?: Recent Planck observations of dust polarization in the Galaxy have revealed\nthat the power in $E$ mode is twice that in $B$ mode. Caldwell et. al. have\nformulated a theoretical model in the context of magnetohydrodynamic (MHD)\nturbulence and found it problematic to account for this result. In particular,\nthey concluded that there is a very narrow range of theoretical parameters that\ncould account for the observation. This poses a problem of whether the accepted\ndescription of MHD turbulence can apply to the interstellar medium. We revisit\nthe problem and demonstrate that MHD turbulence corresponding to the high\ngalactic latitudes range of Alfv\\'en Mach numbers, i.e. $M_A\\lesssim 0.5$, can\nsuccessfully explain the available results for the $E$ to $B$ mode ratio.", "category": "astro-ph_GA" }, { "text": "LeMMINGs. III. The e-MERLIN Legacy Survey of the Palomar sample.\n Exploring the origin of nuclear radio emission in active and inactive\n galaxies through the [O III] -- radio connection: What determines the nuclear radio emission in local galaxies? We combine\noptical [O III] line emission, robust black hole (BH) mass estimates, and\nhigh-resolution e-MERLIN 1.5-GHz data, from the LeMMINGs survey, of a\nstatistically-complete sample of 280 nearby, optically active (LINER and\nSeyfert) and inactive HII and Absorption line galaxies [ALG]) galaxies. Using\n[O III] luminosity ($L_{\\rm [O~III]}$) as a proxy for the accretion power,\nlocal galaxies follow distinct sequences in the optical-radio planes of BH\nactivity, which suggest different origins of the nuclear radio emission for the\noptical classes. The 1.5-GHz radio luminosity of their parsec-scale cores\n($L_{\\rm core}$) is found to scale with BH mass ($M_{\\rm BH}$) and [O~III]\nluminosity. Below $M_{\\rm BH} \\sim$10$^{6.5}$ M$_{\\odot}$, stellar processes\nfrom non-jetted HII galaxies dominate with $L_{\\rm core} \\propto M_{\\rm\nBH}^{0.61\\pm0.33}$ and $L_{\\rm core} \\propto L_{\\rm [O~III]}^{0.79\\pm0.30}$.\nAbove $M_{\\rm BH} \\sim$10$^{6.5}$ M$_{\\odot}$, accretion-driven processes\ndominate with $L_{\\rm core} \\propto M_{\\rm BH}^{1.5-1.65}$ and $L_{\\rm core}\n\\propto L_{\\rm [O~III]}^{0.99-1.31}$ for active galaxies: radio-quiet/loud\nLINERs, Seyferts and jetted HII galaxies always display (although low)\nsignatures of radio-emitting BH activity, with $L_{\\rm 1.5\\,\nGHz}\\gtrsim$10$^{19.8}$ W Hz$^{-1}$ and $M_{\\rm BH}\\gtrsim10^{7}$ M$_{\\odot}$,\non a broad range of Eddington-scaled accretion rates ($\\dot{m}$). Radio-quiet\nand radio-loud LINERs are powered by low-$\\dot{m}$ discs launching\nsub-relativistic and relativistic jets, respectively. Low-power slow jets and\ndisc/corona winds from moderately high to high-$\\dot{m}$ discs account for the\ncompact and edge-brightened jets of Seyferts, respectively. Jetted HII galaxies\nmay host weakly active BHs. Fuel-starved BHs and recurrent activity account for\nALG properties. [abridged]", "category": "astro-ph_GA" }, { "text": "3D Asymmetrical motions of the Galactic outer disk with LAMOST K giant\n stars: We present a three dimensional velocity analysis of Milky Way disk kinematics\nusing LAMOST K giant stars and the GPS1 proper motion catalogue. We find that\nGalactic disk stars near the anticenter direction (in the range of\nGalactocentric distance between $R=8$ and $13$ kpc and vertical position\nbetween $Z=-2$ and $2$ kpc) exhibit asymmetrical motions in the Galactocentric\nradial, azimuthal, and vertical components. Radial motions are not zero, thus\ndeparting from circularity in the orbits; they increase outwards within\n$R\\lesssim 12$ kpc, show some oscillation in the northern ($0 < Z < 2$ kpc)\nstars, and have north-south asymmetry in the region corresponding to a\nwell-known nearby northern structure in the velocity field. There is a clear\nvertical gradient in azimuthal velocity, and also an asymmetry that shifts from\na larger azimuthal velocity above the plane near the solar radius to faster\nrotation below the plane at radii of 11-12 kpc. Stars both above and below the\nplane at $R\\gtrsim 9$ kpc exhibit net upward vertical motions. We discuss some\npossible mechanisms that might create the asymmetrical motions, such as\nexternal perturbations due to dwarf galaxy minor mergers or dark matter\nsub-halos, warp dynamics, internal processes due to spiral arms or the Galactic\nbar, and (most likely) a combination of some or all of these components.", "category": "astro-ph_GA" }, { "text": "XGAPS: a sub-arcsecond cross-match of Galactic Plane Surveys: We present a sub-arcsecond cross-match of Gaia Data Release 3 (DR3) against\nthe INT Galactic Plane Surveys (IGAPS) and the United Kingdom Infrared Deep Sky\nSurvey (UKIDSS). The resulting cross-match of Galactic Plane Surveys (XGAPS)\nprovides additional precise photometry ($U_{RGO}$, $g$, $r$, $i$, H$\\alpha$,\n$J$, $H$ and $K$) to the Gaia photometry. In building the catalogue, proper\nmotions given in Gaia DR3 are wound back to match the epochs of the IGAPS\nconstituent surveys (INT Photometric \\ha Survey of the Northern Galactic Plane,\nIPHAS, and the UV-Excess Survey of the northern Galactic plane, UVEX) and\nUKIDSS, ensuring high proper motion objects are appropriately cross-matched.\nThe catalogue contains 33,987,180 sources. The requirement of $>3\\sigma$\nparallax detection for every included source means that distances out to 1--1.5\nkpc are well covered. In producing XGAPS we have also trained a Random Forest\nclassifier to discern targets with problematic astrometric solutions. Selection\ncuts based on the classifier results can be used to clean colour-magnitude and\ncolour-colour diagrams in a controlled and justified manner, as well as\nproducing subsets of astrometrically reliable targets. We provide XGAPS as a\n111 column table. Uses of the catalogue include the selection of Galactic\ntargets for multi-object spectroscopic surveys as well as identification of\nspecific Galactic populations.", "category": "astro-ph_GA" }, { "text": "An origin of narrow extended structure in the interstellar medium: an\n interstellar contrail created by a fast-moving massive object: We investigate the thermal condensation caused by a massive object that\npasses through the interstellar medium with high velocity, and propose a\nmechanism for creating a filamentary gaseous object, or interstellar contrail.\nOur main result shows that a long interstellar contrail can form with a certain\nparameter; a compact object more massive than $10^4\\ {\\rm M_\\odot}$ can make a\nfilament whose length is larger than $100\\ {\\rm pc}$. Observation of\ninterstellar contrails may provide information on the number, masses, and\nvelocities of fast-moving massive objects, and can be a new method for probing\ninvisible gravitating sources such as intermediate-mass black holes.", "category": "astro-ph_GA" }, { "text": "Invisible Active Galactic Nuclei. II Radio Morphologies & Five New HI 21\n cm Absorption Line Detections: We have selected a sample of 80 candidates for obscured radio-loud active\ngalactic nuclei and presented their basic optical/near-infrared (NIR)\nproperties in Paper 1. In this paper, we present both high-resolution radio\ncontinuum images for all of these sources and HI 21cm absorption spectroscopy\nfor a few selected sources in this sample. A-configuration 4.9 and 8.5 GHz VLA\ncontinuum observations find that 52 sources are compact or have substantial\ncompact components with size <0.5\" and flux density >0.1 Jy at 4.9 GHz. The\nmost compact 36 sources were then observed with the VLBA at 1.4 GHz. One\ndefinite and 10 candidate Compact Symmetric Objects (CSOs) are newly\nidentified, a detection rate of CSOs ~3 times higher than the detection rate\npreviously found in purely flux-limited samples. Based on possessing compact\ncomponents with high flux densities, 60 of these sources are good candidates\nfor absorption-line searches. Twenty seven sources were observed for HI 21cm\nabsorption at their photometric or spectroscopic redshifts with only 6\ndetections made (one detection is tentative). However, five of these were from\na small subset of six CSOs with pure galaxy optical/NIR spectra and for which\naccurate spectroscopic redshifts place the redshifted 21cm line in a RFI-free\nspectral window. It is likely that the presence of ubiquitous RFI and the\nabsence of accurate spectroscopic redshifts preclude HI detections in similar\nsources (only one detection out of the remaining 22 sources observed, 14 of\nwhich have only photometric redshifts). Future searches for highly-redshifted\nHI and molecular absorption can easily find more distant CSOs among bright,\nblank field' radio sources but will be severely hampered by an inability to\ndetermine accurate spectroscopic redshifts for them due to their lack of\nrest-frame UV continuum.", "category": "astro-ph_GA" }, { "text": "Chemically tagging the Hyades stream: Does it partly originate from the\n Hyades cluster?: The Hyades stream has long been thought to be a dispersed vestige of the\nHyades cluster. However, recent analyses of the parallax distribution, of the\nmass function, and of the action-space distribution of stream stars have shown\nit to be rather composed of orbits trapped at a resonance of a density\ndisturbance. This resonant scenario should leave a clearly different signature\nin the element abundances of stream stars than the dispersed cluster scenario,\nsince the Hyades cluster is chemically homogeneous. Here, we study the\nmetalllicty as well as the element abundances of Li, Na, Mg, Fe, Zr, Ba, La,\nCe, Nd, and Eu for a random sample of stars belonging to the Hyades stream, and\ncompare them with those of stars from the Hyades cluster. From this analysis:\n(i) we independently confirm that the Hyades stream cannot be solely composed\nof stars originating in the Hyades cluster; (ii) we show that some stars from\nthe Hyades stream nevertheless have abundances compatible with an origin in the\ncluster; (iii) we emphasize that the use of Li as a chemical tag of the cluster\norigin of main-sequence stars is very efficient in the range 5500 - 6200 K,\nsince the Li sequence in the Hyades cluster is very tight; (iv) we show that,\nwhile this evaporated population has a metallicity excess of ~0.2 dex w.r.t.\nthe local thin disk population, identical to that of the Hyades cluster, the\nremainder of the Hyades stream population has still a metallicity excess of\n~0.06 to 0.15 dex, consistent with an origin in the inner Galaxy; (v) we show\nthat the Hyades stream can be interpreted as an inner 4:1 resonance of the\nspiral pattern: this then also reproduces an orbital family compatible with the\nSirius stream, and places the origin of the Hyades stream up to 1 kpc inwards\nfrom the solar radius, which might explain the observed metallicity excess of\nthe stream population.", "category": "astro-ph_GA" }, { "text": "Non-similar collapse of singular isothermal spherical molecular cloud\n cores with nonzero initial velocities: Theoretically, stars have been formed from the collapse of cores in the\nmolecular clouds. Historically, the core had been assumed as an singular\nisothermal sphere (SIS), and the collapse had been investigated by a\nself-similar manner. This is while the rotation and magnetic field lead to\nnon-symmetric collapse so that a spheroid shape may be occurred. Here, the\nresultant of the centrifugal force and magnetic field gradient is assumed to be\nin the normal direction of the rotational axis, and its components are supposed\nto be a fraction $\\beta$ of the local gravitational force. In this research, a\ncollapsing SIS core is considered to find the importance of the parameter\n$\\beta$ for oblateness of the mass shells which are above the head of the\nexpansion wave. We apply the Adomian decomposition method to solve the system\nof nonlinear partial differential equations because the collapse does not occur\nin a spherical symmetry with self-similar behavior. In this way, we obtain a\nsemi-analytical relation for the mass infall rate $\\dot{M}$ of the shells at\nthe envelope. Near the rotational axis, the $\\dot{M}$ decreases with increasing\nof the non-dimensional radius $\\xi$, while a direct relation is observed\nbetween $\\dot{M}$ and $\\xi$ in the equatorial regions. Also, the values of\n$\\dot{M}$ in the polar regions are greater than the equatorial values, and this\ndifference is more often at smaller values of $\\xi$. Overall, the results show\nthat before reaching the head of expansion wave, the visible shape of the\nmolecular cloud cores can evolve to oblate spheroids. The ratio of major to\nminor axes of oblate cores increases with increasing the parameter $\\beta$, and\nits value can approach to the apparently observed elongated shapes of cores in\nthe maps of molecular clouds such as Taurus and Perseus.", "category": "astro-ph_GA" }, { "text": "Relations Between Central Black Hole Mass and Total Galaxy Stellar Mass\n in the Local Universe: Scaling relations between central black hole (BH) mass and host galaxy\nproperties are of fundamental importance to studies of BH and galaxy evolution\nthroughout cosmic time. Here we investigate the relationship between BH mass\nand host galaxy total stellar mass using a sample of 262 broad-line active\ngalactic nuclei (AGN) in the nearby Universe (z < 0.055), as well as 79\ngalaxies with dynamical BH masses. The vast majority of our AGN sample is\nconstructed using Sloan Digital Sky Survey spectroscopy and searching for\nSeyfert-like narrow-line ratios and broad H-alpha emission. BH masses are\nestimated using standard virial techniques. We also include a small number of\ndwarf galaxies with total stellar masses M_stellar < 10^9.5 Msun and a\nsub-sample of the reverberation-mapped AGNs. Total stellar masses of all 341\ngalaxies are calculated in the most consistent manner feasible using\ncolor-dependent mass-to-light ratios. We find a clear correlation between BH\nmass and total stellar mass for the AGN host galaxies, with M_BH proportional\nto M_stellar, similar to that of early-type galaxies with dynamically-detected\nBHs. However, the relation defined by the AGNs has a normalization that is\nlower by more than an order of magnitude, with a BH-to-total stellar mass\nfraction of M_BH/M_stellar ~ 0.025% across the stellar mass range 10^8 <\nM_stellar/Msun < 10^12. This result has significant implications for studies at\nhigh redshift and cosmological simulations in which stellar bulges cannot be\nresolved.", "category": "astro-ph_GA" }, { "text": "Trigonometric Parallaxes of Four Star-forming Regions in the Distant\n Inner Galaxy: We have measured trigonometric parallaxes for four water masers associated\nwith distant massive young stars in the inner regions of the Galaxy using the\nVLBA as part of the BeSSeL Survey. G026.50$+$0.28. is located at the near end\nof the Galactic bar, perhaps at the origin of the Norma spiral arm.\nG020.77$-$0.05 is in the Galactic Center region and is likely associated with a\nfar-side extension of the Scutum arm. G019.60$-$0.23 and G020.08$-$0.13 are\nlikely associated and lie well past the Galactic Center. These sources appear\nto be in the Sagittarius spiral arm, but an association with the Perseus arm\ncannot be ruled out.", "category": "astro-ph_GA" }, { "text": "First laboratory detection of vibration-rotation transitions of CH$^+$\n and $^{13}$CH$^+$ and improved measurement of their rotational transition\n frequencies: The long-searched C-H stretches of the fundamental ions CH$^+$ and\n$^{13}$CH$^+$ have been observed for the first time in the laboratory. For\nthis, the state-dependent attachment of He atoms to these ions at cryogenic\ntemperatures has been exploited to obtain high-resolution rovibrational data.\nIn addition, the lowest rotational transitions of CH$^+$, $^{13}$CH$^+$ and\nCD$^+$ have been revisited and their rest frequency values improved\nsubstantially.", "category": "astro-ph_GA" }, { "text": "On the lack of correlation between Mg II 2796, 2803 Angstrom and Lyman\n alpha emission in lensed star-forming galaxies: We examine the Mg II 2796, 2803 Angstrom, Lyman alpha, and nebular line\nemission in five bright star-forming galaxies at 1.66 9.6 for any mass fraction or S/N, due to\nthe similarity of SED shapes for those ages. In terms of the recovery of age\nspreads, we find that the derived age spreads are often larger than the real\nones, especially for log(age/yr) < 8.0 and high mass fractions of SSP1.\nIncreasing the age gap in the mock clusters improves the derived parameters,\nbut Age (SSP2) is still overestimated for the younger ages.", "category": "astro-ph_GA" }, { "text": "An ensemble study of turbulence in extended QSO nebulae at\n $z\\approx0.5$--1: Turbulent motions in the circumgalactic medium (CGM) play a critical role in\nregulating the evolution of galaxies, yet their detailed characterization\nremains elusive. Using two-dimensional velocity maps constructed from\nspatially-extended [OII] and [OIII] emission, Chen et al. (2023b) measured the\nvelocity structure functions (VSFs) of four quasar nebulae at\n$z\\approx\\!0.5$--1.1. One of these exhibits a spectacular Kolmogorov relation.\nHere we carry out an ensemble study using an expanded sample incorporating four\nnew nebulae from three additional QSO fields. The VSFs measured for all eight\nnebulae are best explained by subsonic turbulence revealed by the line-emitting\ngas, which in turn strongly suggests that the cool gas ($T\\!\\sim\\!10^4$ K) is\ndynamically coupled to the hot ambient medium. Previous work demonstrates that\nthe largest nebulae in our sample reside in group environments with clear signs\nof tidal interactions, suggesting that environmental effects are vital in\nseeding and enhancing turbulence within the gaseous halos, ultimately promoting\nthe formation of the extended nebulae. No discernible differences are observed\nin the VSF properties between radio-loud and radio-quiet QSO fields. We\nestimate the turbulent heating rate per unit volume, $Q_{\\rm turb}$, in the QSO\nnebulae to be $\\sim 10^{-26}$--$10^{-22}$ erg cm$^{-3}$ s$^{-1}$ for the cool\nphase and $\\sim 10^{-28}$--$10^{-25}$ erg cm$^{-3}$ s$^{-1}$ for the hot phase.\nThis range aligns with measurements in the intracluster medium and star-forming\nmolecular clouds but is $\\sim10^3$ times higher than the $Q_{\\rm turb}$\nobserved inside cool gas clumps on scales $\\lesssim1$ kpc using absorption-line\ntechniques. We discuss the prospect of bridging the gap between emission and\nabsorption studies by pushing the emission-based VSF measurements to below\n$\\approx\\!10$ kpc.", "category": "astro-ph_GA" }, { "text": "A technique to select the most obscured galaxy nuclei: Compact obscured nuclei (CONs) are mainly found in local U/LIRGs. In the\nlocal Universe, these sources are generally selected through the detection of\nthe HCN-vib (3-2) emission line at submillimetre wavelengths. In this work, we\npresent a diagnostic method to select deeply buried nuclei based on\nmid-infrared (mid-IR) polycyclic aromatic hydrocarbons (PAHs) and continuum\nratios. Using Spitzer/IRS spectra of a representative sample of local ULIRGs\n(z<0.27), we examine their PAH and underlying continuum emission ratios. For\ndeeply embedded sources, we find that the 9.7 micron silicate absorption band\nhas a particularly pronounced effect on the 11.3 micron PAH feature. The low\nflux level in the nuclear silicate absorption band enhances the 11.3 micron PAH\nfeature contrast (high PAH equivalent width) compared to that of the other PAH\nfeatures. The technique has been extended to include the use of the continuum\nratios. However, the latter are affected both by the extinction coming from the\nhost galaxy as well as the nuclear region, whereas the foreground extinction is\ncancelled out when using the PAH equivalent width ratios. We apply our method\nto the HERUS and GOALS samples and classify as CON candidates 14 ULIRGs and 10\nLIRGs, corresponding to 30% of ULIRGs and 7% of LIRGs from these samples. We\nfind that the observed continuum ratios of CON-dominated sources can be\nexplained by assuming torus models with a tapered disk geometry and a smooth\ndust distribution. This suggests that the nuclear dusty structure of CONs has\nan extremely high dust coverage. We also demonstrate that the use of mid-IR\ncolor-color diagrams is an effective way to select CON-dominated sources at\ndifferent redshifts. In particular, the combination of filters of the JWST/MIRI\nwill enable the selection of CONs out to z~1.5. This will allow extending the\nselection of CONs to high redshifts where U/LIRGs are more numerous.", "category": "astro-ph_GA" }, { "text": "The Korean 1592--1593 Record of a Guest Star: An `impostor' of the\n Cassiopeia A Supernova?: The missing historical record of the Cassiopeia A (Cas A) supernova (SN)\nevent implies a large extinction to the SN, possibly greater than the\ninterstellar extinction to the current SN remnant. Here we investigate the\npossibility that the guest star that appeared near Cas A in 1592--1593 in\nKorean history books could have been an `impostor' of the Cas A SN, i.e., a\nluminous transient that appeared to be a SN but did not destroy the progenitor\nstar, with strong mass loss to have provided extra circumstellar extinction. We\nfirst review the Korean records and show that a spatial coincidence between the\nguest star and Cas A cannot be ruled out, as opposed to previous studies. Based\non modern astrophysical findings on core-collapse SN, we argue that Cas A could\nhave had an impostor and derive its anticipated properties. It turned out that\nthe Cas A SN impostor must have been bright ($M_V =-14.7 \\pm 2.2$ mag) and an\namount of dust with visual extinction of $\\ge 2.8\\pm 2.2 $ mag should have\nformed in the ejected envelope and/or in a strong wind afterwards. The mass\nloss needs to have been spherically asymmetric in order to see the light echo\nfrom the SN event but not the one from the impostor event.", "category": "astro-ph_GA" }, { "text": "Some optical properties of graphite from IR to millimetric wavelengths: Far infrared(FIR) data on the optical properties of graphite are presently\nlacking. An important step towards filling this gap was taken by Kuzmenko et\nal. (2008) who measured, on HOPG (Highly Oriented Pyrolitic Graphite) at normal\nincidence and from 10 to 300 K, the in-plane dielectric functions from 0.3 to\n200 mum, and the reflectance between 0.3 and about 300 mum. We show here how,\nusing recent developments of the electron theory of graphene, extended to\ngraphite, it is possible to properly extrapolate the data farther even than\n1000 mum, in effect all the way to Direct Current. The plasma frequency as well\nas the scattering rate of free electrons are shown to both decrease with T, but\nlevel off near 0 K, in agreement with theory. Along the way, we noticed\nsignificant discrepancies with the well-known and often used derivation of\nPhilipp (1977) at room temperature, and also with previous data on temperature\ndependence and absorbance of graphitic material samples in different physical\nforms. Possible reasons for these discrepancies are discussed. Finally, the\nabsorption efficiency of small graphitic spheres is deduced for the spectral\nrange from 0.3 to 10000 mum. This may contribute to the discussion on model\ndust candidates for recently observed astronomical far infrared emissions.", "category": "astro-ph_GA" }, { "text": "Anomalous compressible mode generation by global frame projections of\n pure Alfven mode: Alfven wave is the single most important physical phenomenon of\nmagneto-hydrodynamic turbulence and has far-reaching impact to almost all\nstudies related to astrophysical magnetic field. Yet the restoration of the\nAlfven wave fluctuations from a given magnetic field, aka the local Alfven wave\nproblem, is never properly addressed in literature albeit its importance.\nPrevious works model the Alfven wave fluctuation as the perturbation along a\nstraight-line, constant magnetic field. However, Lazarian & Pogosyan (2012)\nsuggested that the decomposition of Alfven wave along a straight line, aka. the\nglobal frame decomposition, has a factor of discrepancy to the true local\nAlfven wave fluctuation. Here we provide a geometric interpretation on how the\nlocal Alfven wave is related to the global frame through the use of vector\nframe formulation. We prove both analytically and numerically that the local\nframe Alfven wave is an orthogonal transformation of that of the global frame\nand related by the local Alfvenic Mach number. In other words, when we observe\nAlfven wave in the global frame of reference, some of the Alfven wave will be\nmistaken as compressible waves. The importance of frame choices have a\nfar-reaching impact to the analytical studies of MHD turbulence. Combining the\nframe formalism and the new techniques we can have accurate measurement to some\nof the fundamental turbulence properties like the inclination angle of mean\nmagnetic field relative to the line of sight.", "category": "astro-ph_GA" }, { "text": "Aperture and Resolution Effects on Ultraviolet Star-Forming Properties:\n Insights from Local Galaxies and Implications for High-Redshift Observations: We present an analysis of the effects of spectral resolution and aperture\nscales on derived galaxy properties using far-ultraviolet (FUV) spectra of\nlocal star-forming galaxies from the International Ultraviolet Explorer (R~250,\nFOV~10\"x20\") and Cosmic Origins Spectrograph on the Hubble Space Telescope\n(R~15,000, FOV~2.5\"). Using these spectra, we measured FUV luminosities,\nspectral slopes, dust attenuation, and equivalent widths. We find that galaxies\nwith one dominant stellar cluster have FUV properties that are independent of\naperture size, while galaxies with multiple bright clusters are sensitive to\nthe total light fraction captured by the aperture. Additionally, we find\nsignificant correlations between the strength of stellar and interstellar\nabsorption-lines and metallicity, indicating metallicity-dependent line-driven\nstellar winds and interstellar macroscopic gas flows shape the stellar and\ninterstellar spectral lines, respectively. The observed line-strength versus\nmetallicity relation of stellar-wind lines agrees with the prediction of\npopulation synthesis models for young starbursts. In particular, measurements\nof the strong stellar CIV 1548,1550 line provide an opportunity to determine\nstellar abundances as a complement to gas-phase abundances. We provide a\nrelation between the equivalent width of the CIV line and the oxygen abundance\nof the galaxy. We discuss this relation in terms of the stellar-wind properties\nof massive stars. As the driving lines in stellar winds are mostly ionized iron\nspecies, the CIV line may eventually offer a method to probe\nalpha-element-to-iron ratios in star-forming galaxies once consistent models\nwith non-solar abundance ratios are available. These results have important\nimplications for the galaxy-scale, low-resolution observations of high-redshift\ngalaxies from JWST (R~100-3,500).", "category": "astro-ph_GA" }, { "text": "An Analysis of the Shapes of Interstellar Extinction Curves. VI. The\n Near-IR Extinction Law: We combine new HST/ACS observations and existing data to investigate the\nwavelength dependence of NIR extinction. Previous studies suggest a power-law\nform, with a \"universal\" value of the exponent, although some recent\nobservations indicate that significant sight line-to-sight line variability may\nexist. We show that a power-law model provides an excellent fit to most NIR\nextinction curves, but that the value of the power, beta, varies significantly\nfrom sight line-to-sight line. Therefore, it seems that a \"universal NIR\nextinction law\" is not possible. Instead, we find that as beta decreases, R(V)\n[=A(V)/E(B-V)] tends to increase, suggesting that NIR extinction curves which\nhave been considered \"peculiar\" may, in fact, be typical for different R(V)\nvalues. We show that the power law parameters can depend on the wavelength\ninterval used to derive them, with the beta increasing as longer wavelengths\nare included. This result implies that extrapolating power law fits to\ndetermine R(V) is unreliable. To avoid this problem, we adopt a different\nfunctional form for NIR extinction. This new form mimics a power law whose\nexponent increases with wavelength, has only 2 free parameters, can fit all of\nour curves over a longer wavelength baseline and to higher precision, and\nproduces R(V) values which are consistent with independent estimates and\ncommonly used methods for estimating R(V). Furthermore, unlike the power law\nmodel, it gives R(V)'s that are independent of the wavelength interval used to\nderive them. It also suggests that the relation R(V) = -1.36 E(K-V)/E(B-V) -\n0.79 can estimate R(V) to +/-0.12. Finally, we use model extinction curves to\nshow that our extinction curves are in accord with theoretical expectations.", "category": "astro-ph_GA" }, { "text": "The Interstellar Medium toward the Galactic Center Source 2MASS\n J17470898-2829561: We describe and discuss remarkable infrared spectra, covering key portions of\nthe $2-5$ $\\mu$m wavelength interval, of the probable OH/IR supergiant 2MASS\nJ17470898$-$2829561 (2M1747), located in direction of the Sgr B molecular cloud\ncomplex within the Central Molecular Zone (CMZ) of the Galaxy. This star was\noriginally singled out for examination based on its suitability for\nspectroscopy of lines of H$_3^+$ in the CMZ. Analysis of the spectra shows that\n2M1747 is deeply embedded within Sgr B1, with A$_V$ $\\gtrsim$ 100 mag, making\nit the only star within Sgr B for which infrared spectra have been obtained at\npresent, and thereby a unique infrared probe of the dense interstellar medium\nwithin the CMZ. Despite the high extinction, spectra of 2M1747 reveal a veiled\nphotosphere in the $K$ band and circumstellar gas in the $M$ band, giving clues\nas to its nature. Its $ 3.5-4.0$ $\\mu$m spectrum contains the strongest\nabsorption lines of H$_3^+$ observed toward any object to date. The $4.5-4.8$\n$\\mu$m spectrum has impressively deep and wide absorption lines of interstellar\nCO, most of which arise in dense gas within Sgr B1. The $3-5$ $\\mu$m spectrum\nalso contains several solid state absorption features, which are characteristic\nof both dense and diffuse clouds, and which raise questions about the\nidentifications of some of these features. We discuss the nature of the star,\nthe extinction to it, the extinction law for dust in the CMZ, and the\nidentifications of the various solid-state features and where they are produced\nalong this complex line of sight.", "category": "astro-ph_GA" }, { "text": "Magnetic Fields, Star Formation Rates and Gas Densities at Sub-kpc\n Scales in a Pilot Sample of Nearby Galaxies: We have estimated the magnetic field strengths of a sample of seven galaxies\nusing their non-thermal synchrotron radio emission at metre wavelengths, and\nassuming energy equipartition between magnetic fields and cosmic ray particles.\nSpatially resolved star formation rates (SFR) were estimated for the seven\ngalaxies along with five galaxies studied previously. For the combined sample\nof twelve galaxies, the equipartition magnetic fields (B$_\\textrm{eq}$) are\ncorrelated with the SFR surface densities ($\\Sigma_\\textrm{SFR}$) at sub-kpc\nscales with B$_\\textrm{eq}$ $\\propto$ $\\Sigma_\\textrm{SFR}^ {0.31\\pm0.06}$,\nconsistent with model predictions. We estimated gas densities\n($\\rho_\\textrm{gas}$) for a sub-sample of seven galaxies using archival\nobservations of the carbon monoxide (CO) rotational transitions and the atomic\nhydrogen (HI) 21 cm line and studied the spatially-resolved correlation between\nthe magnetic fields and $\\rho_\\textrm{gas}$. Magnetic fields and gas densities\nare found to be correlated at sub-kpc scale as B$_\\textrm{eq}$ $\\propto$\n$\\rho_\\textrm{gas}^{0.40\\pm0.09}$. This is broadly consistent with models,\nwhich typically predict B $\\propto$ $\\rho_\\textrm{gas}^{0.5}$.", "category": "astro-ph_GA" }, { "text": "Herschel SPIRE-FTS Observations of Excited CO and [CI] in the Antennae\n (NGC 4038/39): Warm and Cold Molecular Gas: We present Herschel SPIRE-FTS observations of the Antennae (NGC 4038/39), a\nwell studied, nearby ($22$ Mpc) ongoing merger between two gas rich spiral\ngalaxies. We detect 5 CO transitions ($J=4-3$ to $J=8-7$), both [CI]\ntransitions and the [NII]$205\\mu m$ transition across the entire system, which\nwe supplement with ground based observations of the CO $J=1-0$, $J=2-1$ and\n$J=3-2$ transitions, and Herschel PACS observations of [CII] and [OI]$63\\mu m$.\nUsing the CO and [CI] transitions, we perform both a LTE analysis of [CI], and\na non-LTE radiative transfer analysis of CO and [CI] using the radiative\ntransfer code RADEX along with a Bayesian likelihood analysis. We find that\nthere are two components to the molecular gas: a cold ($T_{kin}\\sim 10-30$ K)\nand a warm ($T_{kin} \\gtrsim 100$ K) component. By comparing the warm gas mass\nto previously observed values, we determine a CO abundance in the warm gas of\n$x_{CO} \\sim 5\\times 10^{-5}$. If the CO abundance is the same in the warm and\ncold gas phases, this abundance corresponds to a CO $J=1-0$ luminosity-to-mass\nconversion factor of $\\alpha_{CO} \\sim 7 \\ M_{\\odot}{pc^{-2} \\ (K \\ km \\\ns^{-1})^{-1}}$ in the cold component, similar to the value for normal spiral\ngalaxies. We estimate the cooling from H$_2$, [CII], CO and [OI]$63\\mu m$ to be\n$\\sim 0.01 L_{\\odot}/M_{\\odot}$. We compare PDR models to the ratio of the flux\nof various CO transitions, along with the ratio of the CO flux to the\nfar-infrared flux in NGC 4038, NGC 4039 and the overlap region. We find that\nthe densities recovered from our non-LTE analysis are consistent with a\nbackground far-ultraviolet field of strength $G_0\\sim 1000$. Finally, we find\nthat a combination of turbulent heating, due to the ongoing merger, and\nsupernova and stellar winds are sufficient to heat the molecular gas.", "category": "astro-ph_GA" }, { "text": "Disentangling the near infrared continuum spectral components of the\n inner 500 pc of Mrk 573: two-dimensional maps: We present a near infrared study of the spectral components of the continuum\nin the inner 500$\\times$500 pc$^2$ of the nearby Seyfert galaxy Mrk573 using\nadaptive optics near-infrared integral field spectroscopy with the instrument\nNIFS of the Gemini North Telescope at a spatial resolution of $\\sim$50 pc. We\nperformed spectral synthesis using the {\\sc starlight} code and constructed\nmaps for the contributions of different age components of the stellar\npopulation: young ($age\\leq100$ Myr), young-intermediate ($1002$ Gyr) to the\nnear-IR K-band continuum, as well as their contribution to the total stellar\nmass. We found that the old stellar population is dominant within the inner 250\npc, while the intermediate age components dominate the continuum at larger\ndistances. A young stellar component contributes up to $\\sim$20% within the\ninner $\\sim$70 pc, while hot dust emission and featureless continuum components\nare also necessary to fit the nuclear spectrum, contributing up to 20% of the\nK-band flux there. The radial distribution of the different age components in\nthe inner kiloparsec of Mrk573 is similar to those obtained by our group for\nthe Seyfert galaxies Mrk1066, Mrk1157 and NGC1068 in previous works using a\nsimilar methodology. Young stellar populations ($\\leq$100 Myr) are seen in the\ninner 200-300 pc for all galaxies contributing with $\\ge$20% of the K-band\nflux, while the near-IR continuum is dominated by the contribution of\nintermediate-age stars ($t=$100 Myr-2 Gyr) at larger distances. Older stellar\npopulations dominate in the inner 250 pc.", "category": "astro-ph_GA" }, { "text": "A southern hemisphere survey of the 5780 and 6284 \u00c5 diffuse\n interstellar bands: correlation with the extinction: We present a new database of 5780.5 and 6283.8 {\\AA} DIB measurements and\nalso study their correlation with the reddening. The database is based on\nhigh-resolution, high-quality spectra of early-type nearby stars located in the\nsouthern hemisphere at an average distance of 300 pc. Equivalent widths of the\ntwo DIBs were determined by means of a realistic continuum fitting and\nsynthetic atmospheric transmissions. For all stars that possess a precise\nmeasurement of their color excess, we compare the DIBs and the extinction. We\nfind average linear relationships of the DIBS and the color excess that agree\nwell with those of a previous survey of northern hemisphere stars closer than\n550 pc. This similarity shows that there is no significant spatial dependence\nof the average relationship in the solar neighborhood within $\\simeq$ 600 pc. A\nnoticeably different result is our higher degree of correlation of the two DIBs\nwith the extinction. We demonstrate that it is simply due to the lower\ntemperature and intrinsic luminosity of our targets. Using cooler target stars\nreduces the number of outliers, especially for nearby stars, confirming that\nthe radiation field of UV bright stars has a significant influence on the DIB\nstrength. We have used the cleanest data to compute updated DIB shapes.", "category": "astro-ph_GA" }, { "text": "CO luminosity function from Herschel-selected galaxies and the\n contribution of AGN: We derive the CO luminosity function (LF) for different rotational\ntransitions (i.e. (1-0), (3-2), (5-4)) starting from the Herschel LF by\nGruppioni et al. and using appropriate $L'_{\\rm CO} - L_{\\rm IR}$ conversions\nfor different galaxy classes. Our predicted LFs fit the data so far available\nat $z\\approx0$ and $2$. We compare our results with those obtained by\nsemi-analytical models (SAMs): while we find a good agreement over the whole\nrange of luminosities at $z\\approx0$, at $z\\approx1$ and $z\\approx2$ the\ntension between our LFs and SAMs in the faint and bright ends increases. We\nfinally discuss the contribution of luminous AGN\n($L_{X}>10^{44}\\,\\rm{erg\\,s^{-1}}$) to the bright end of the CO LF concluding\nthat they are too rare to reproduce the actual CO luminosity function at\n$z\\approx2$.", "category": "astro-ph_GA" }, { "text": "ATCA observations of SiO masers in the Galactic center: We present the Australia Telescope Compact Array (ATCA) observations of the\nSiO masers in the Galactic center in transitions of v=1, J=2--1 at 86 GHz and\nv=1, J=1--0 at 43 GHz. Two 86-GHz SiO masers were detected within the central\nparsec, and they are associated with IRS 10EE and IRS 15NE, respectively. We\ndetected eighteen 43-GHz SiO masers within a projected separation of <2 pc from\nSagittarius A* (Sgr A*), among which seven masers are newly discovered from our\nobservations. This raises the total number of 43-GHz SiO masers within the\ncentral 4 parsecs of the GC region to 22. Simultaneous observations at 86 and\n43 GHz showed that the intensity of 43-GHz SiO maser is ~3 times higher than\nthat of 86-GHz maser in IRS 10EE (an OH/IR star), while the integrated flux of\nthe SiO maser emission at 43 GHz is comparable with that at 86~GHz in IRS~15NE\n(an ordinary Mira variable). These results are consistent with previous\nobservations of massive late-type stars in the Galaxy in which the 86-GHz SiO\nmaser is in general weaker than the 43-GHz SiO maser in OH/IR stars, while the\ntwo transitions are comparably strong in Mira stars.", "category": "astro-ph_GA" }, { "text": "Star clusters near and far; tracing star formation across cosmic time: Star clusters are fundamental units of stellar feedback and unique tracers of\ntheir host galactic properties. In this review, we will first focus on their\nconstituents, i.e.\\ detailed insight into their stellar populations and their\nsurrounding ionised, warm, neutral, and molecular gas. We, then, move beyond\nthe Local Group to review star cluster populations at various evolutionary\nstages, and in diverse galactic environmental conditions accessible in the\nlocal Universe. At high redshift, where conditions for cluster formation and\nevolution are more extreme, we are only able to observe the integrated light of\na handful of objects that we believe will become globular clusters. We\ntherefore discuss how numerical and analytical methods, informed by the\nobserved properties of cluster populations in the local Universe, are used to\ndevelop sophisticated simulations potentially capable of disentangling the\ngenetic map of galaxy formation and assembly that is carried by globular\ncluster populations.", "category": "astro-ph_GA" }, { "text": "Ionized gas in the NGC 3077 galaxy: The nearby dwarf galaxy NGC 3077 is known for its peculiar morphology, which\nincludes numerous dust lanes and emission-line regions. The interstellar medium\nin this galaxy is subject to several perturbing factors. These are primarily\nthe central starburst and tidal structures in the M 81 group. We present a\ncomprehensive study of the state of ionization, kinematics, and chemical\ncomposition of ionized gas in NGC 3077, including both star-forming regions and\ndiffuse ionized gas (DIG) at the periphery. We study gas motions in the\nH$\\alpha$ line via high-resolution ($R\\approx15\\,000$) 3D spectroscopy with the\nscanning Fabry-Perot interferometer installed into SCORPIO-2 instrument\nattached to the 6-m telescope of the SAO RAS. Images in the main optical\nemission lines were acquired with MaNGaL photometer with a tunable filter at\nthe 2.5-m telescope of the Caucasian Mountain Observatory of SAI MSU. We also\nused SCORPIO-2 to perform long-slit spectroscopy of the galaxy with a\nresolution of $R\\approx1\\,000$. Our estimate of the gas metallicity,\n$Z=0.6Z_\\odot$, is significantly lower than the earlier determination, but\nagrees with the \"luminosity--metallicity\" dependence. Spatially resolved\ndiagnostic diagrams of the emission-line ratios do not show correlations\nbetween the gas ionization state and its velocity dispersion, and this is most\nlikely due to strong ionization by young stars, whereas the contribution of\nshocks to the excitation of emission lines is less important. We also studied\nthe locations of multicomponent H$\\alpha$ profiles and provide arguments\nsuggesting that they are mostly associated with individual kinematic components\nalong the line of sight and not with expanding shells as it was believed\nearlier. We also observe there a combination of wind outflow from star-forming\nregions and accretion from interstellar gas clouds in the M 81 group.", "category": "astro-ph_GA" }, { "text": "A comprehensive view of the Virgo Stellar Stream: Radial velocities and metallicities have been measured for 82 RR Lyrae\nidentified by the QUEST survey in the direction of the Virgo constellation.\nDistributed over 90 sq. deg. of the sky, they lie from 4 to 23 kpc from the\nSun. Using an algorithm for finding groups in phase space and modeling the\nsmooth halo component in the region, we identified the 5 most significant RRLS\ngroups. We have examined the SEKBO and the Catalina catalog of RRLS (Prior et\nal. 2009, and Drake et al. 2013), as well as the bright QUEST RRLS sample\n(Vivas et al. in prep.), the catalogs of Blue Horizontal Branch stars compiled\nby Sirko et al (2004) and Brown et al (2008, 2010) and the catalog of Red Giant\nstars from the Spaghetti survey, for stars that may be related to the QUEST\nRRLS groups. The most significant group of RRLS is the Virgo Stellar Stream\n(VSS, Duffau et al 2006), group A, which is composed of at least 10 RRLS and 3\nBHB stars. It has a mean distance of 19.6 kpc and a mean radial velocity Vgsr =\n128 km/s, as estimated from its RRLS members. With the revised velocities\nreported here, there is no longer an offset in velocity between the RRLS in the\nVSS and the prominent peak in the velocities of main-sequence turnoff stars\nreported by Newberg et al (2007) in the same direction and at a similar\ndistance (S297+63-20.5). The location in phase space of two other groups (F,H)\nsuggests a possible connection with the VSS, which cannot be discarded at this\npoint, although the turnoff colors of the VSS and group H, as identified from\nNewberg et al. (2007), suggest they might be composed of different populations.\nTwo more groups (B,D), are found at mean distances of 19 and 5.7 kpc, and mean\nradial velocities of -94 and 32 km/s. None of our groups seems to relate to Sgr\nstreams. The excess of stars observed in Virgo appears to be composed of\nseveral halo substructures along the same line of sight.", "category": "astro-ph_GA" }, { "text": "NGDEEP Epoch 1: Spatially Resolved H$\u03b1$ Observations of Disk and\n Bulge Growth in Star-Forming Galaxies at $z \\sim$ 0.6-2.2 from JWST NIRISS\n Slitless Spectroscopy: We study the H$\\alpha$ equivalent width, EW(H$\\alpha$), maps of 19 galaxies\nat $0.6 < z < 2.2$ in the Hubble Ultra Deep Field (HUDF) derived from NIRISS\nslitless spectroscopy as part of the Next Generation Deep Extragalactic\nExploratory Public (NGDEEP) Survey. Our galaxies mostly lie on the\nstar-formation main sequence with a stellar mass range of $\\mathrm{10^9 -\n10^{11} M_\\odot}$, characterized as \"typical\" star-forming galaxies at these\nredshifts. Leveraging deep HST and JWST broad-band images, spanning 0.4-4.8\n$\\mu$m, we perform spatially-resolved fitting of the spectral energy\ndistributions (SEDs) for these galaxies and construct specific star formation\nrate (sSFR) and stellar-mass-weighted age maps with a spatial resolution of\n$\\sim$1 kpc. The pixel-to-pixel EW(H$\\alpha$) increases with increasing sSFR\nand with decreasing age. The average trends are slightly different from the\nrelations derived from integrated fluxes of galaxies from the literature,\nsuggesting complex evolutionary trends within galaxies. We quantify the radial\nprofiles of EW(H$\\alpha$), sSFR, and age. The majority (84%) of galaxies show\npositive EW(H$\\alpha$) gradients in line with the inside-out quenching\nscenario. A few galaxies (16%) show inverse (and flat) trends possibly due to\nmerging or starbursts. We compare the distributions of EW(H$\\alpha$) and sSFR\nto the star formation history models (SFHs) as a function of galactocentric\nradius. We argue that the central regions of galaxies have experienced, at\nleast one, rapid star-formation episodes, which leads to the formation of the\nbulge, while their outer regions (e.g., disks) grow via more smoothly varying\nSFHs. These results demonstrate the ability to study resolved star formation in\ndistant galaxies with JWST NIRISS.", "category": "astro-ph_GA" }, { "text": "Spectro-photometric decomposition of galaxy structural components: Galaxies are complex systems made up of different structural components such\nas bulges, discs, and bars. Understanding galaxy evolution requires unveiling,\nindependently, their history of stellar mass and metallicity assembly. We\nintroduce C2D, a new algorithm to perform spectro-photometric multi-component\ndecompositions of integral field spectroscopy (IFS) datacubes. The galaxy\nsurface-brightness distribution at each wavelength (quasi-monochromatic image)\nis fitted using GASP2D, a 2D photometric decomposition code. As a result, C2D\nprovides both a characteristic one-dimensional spectra and a full datacube with\nall the spatial and spectral information for every component included in the\nfit. We show the basic steps of the C2D spectro-photometric fitting procedure,\ntests on mock datacubes demonstrating its reliability, and a first application\nof C2D to a sample of three early-type galaxies (ETGs) observed within the\nCALIFA survey. The resulting datacubes from C2D are processed through the\nPIPE3D pipeline obtaining both the stellar populations and ionised gas\nproperties of bulges and discs. This paper presents an overview of the\npotential of C2D+PIPE3D to unveil the formation and evolution of galaxies.", "category": "astro-ph_GA" }, { "text": "Angular Momentum of Dwarf Galaxies: We present measurements of baryonic mass Mb and specific angular momentum\n(sAM) jb in 14 rotating dwarf Irregular (dIrr) galaxies from the LITTLE THINGS\nsample. These measurements, based on 21cm kinematic data from the Very Large\nArray and stellar mass maps from the Spitzer Space Telescope, extend previous\nAM measurements by more than two orders of magnitude in Mb. The dwarf galaxies\nshow systematically higher jb values than expected from the jb~Mb^{2/3} scaling\nof spiral galaxies, representative of a scale-free galaxy formation scenario.\nThis offset can be explained by decreasing baryon mass fractions fM=Mb Mdyn\n(where Mdyn is the dynamical mass) with decreasing Mb (for Mb<10^{11}Msun). We\nfind that the sAM of neutral atomic hydrogen HI alone is about 2.5 times higher\nthan that of the stars. The M-j relation of HI is significantly steeper than\nthat of the stars, as a direct consequence of the systematic variation of the\nHI fraction with Mb.", "category": "astro-ph_GA" }, { "text": "The Imprint of Reionization on the Star Formation Histories of Dwarf\n Galaxies: We explore the impact of cosmic reionization on nearby isolated dwarf\ngalaxies using a compilation of SFHs estimated from deep HST data and a\ncosmological hydrodynamical simulation of the Local Group. The nearby dwarfs\nshow a wide diversity of star formation histories; from ancient systems that\nhave largely completed their star formation $\\sim 10$ Gyr ago to young dwarfs\nthat have formed the majority of their stars in the past $\\sim 5$ Gyr to\ntwo-component systems characterized by the overlap of comparable numbers of old\nand young stars. Taken as an ensemble, star formation in nearby dwarfs dips to\nlower-than-average rates at intermediate times ($412$ or $\\log M_{Halo}>14$, the difference between the true value\nand the one extracted from the $M_{ICL}-M_{BCG+ICL}$ relation ranges between\n$\\pm$30\\%. We therefore suggest this relation as a reliable test for\nobservational works aiming to isolate the ICL from the BCG, for systems hosted\nby haloes on cluster scale.", "category": "astro-ph_GA" }, { "text": "The DiskMass Survey. VIII. On the Relationship Between Disk Stability\n and Star Formation: We study the relationship between the stability level of late-type galaxy\ndisks and their star-formation activity using integral-field gaseous and\nstellar kinematic data. Specifically, we compare the two-component (gas+stars)\nstability parameter from Romeo & Wiegert (Q_RW), incorporating stellar\nkinematic data for the first time, and the star-formation rate estimated from\n21cm continuum emission. We determine the stability level of each disk\nprobabilistically using a Bayesian analysis of our data and a simple dynamical\nmodel. Our method incorporates the shape of the stellar velocity ellipsoid\n(SVE) and yields robust SVE measurements for over 90% of our sample. Averaging\nover this subsample, we find a meridional shape of sigma_z/sigma_R =\n0.51^{+0.36}_{-0.25} for the SVE and, at 1.5 disk scale lengths, a stability\nparameter of Q_RW = 2.0 +/- 0.9. We also find that the disk-averaged\nstar-formation-rate surface density (Sigma-dot_e,*) is correlated with the\ndisk-averaged gas and stellar mass surface densities (Sigma_e,g and Sigma_e,*)\nand anti-correlated with Q_RW. We show that an anti-correlation between\nSigma-dot_e,* and Q_RW can be predicted using empirical scaling relations, such\nthat this outcome is consistent with well-established statistical properties of\nstar-forming galaxies. Interestingly, Sigma-dot_e,* is not correlated with the\ngas-only or star-only Toomre parameters, demonstrating the merit of calculating\na multi-component stability parameter when comparing to star-formation\nactivity. Finally, our results are consistent with the Ostriker et al. model of\nself-regulated star-formation, which predicts\nSigma-dot_e,*/Sigma_e,g/sqrt(Sigma_e,*). Based on this and other theoretical\nexpectations, we discuss the possibility of a physical link between disk\nstability level and star-formation rate in light of our empirical results.", "category": "astro-ph_GA" }, { "text": "Survey of Gravitationally-lensed Objects in HSC Imaging (SuGOHI). II.\n Environments and Line-of-Sight Structure of Strong Gravitational Lens\n Galaxies to z ~ 0.8: We investigate the local and line-of-sight overdensities of strong\ngravitational lens galaxies using wide-area multiband imaging from the Hyper\nSuprime-Cam Subaru Strategic Program. We present 41 new definite or probable\nlens candidates discovered in Data Release 2 of the survey. Using a combined\nsample of 87 galaxy-scale lenses out to a lens redshift of $z_{\\mathrm{L}} \\sim\n0.8$, we compare galaxy number counts in lines of sight toward known and\nnewly-discovered lenses in the survey to those of a control sample consisting\nof random lines of sight. We also compare the local overdensity of lens\ngalaxies to a sample of \"twin\" galaxies that have a similar redshift and\nvelocity dispersion to test whether lenses lie in different environments from\nsimilar non-lens galaxies. We find that lens fields contain higher number\ncounts of galaxies compared to the control fields, but this effect arises from\nthe local environment of the lens. Once galaxies in the lens plane are removed,\nthe lens lines of sight are consistent with the control sample. The local\nenvironments of the lenses are overdense compared to the control sample, and\nare slightly overdense compared to those of the twin sample, although the\nsignificance is marginal. There is no significant evidence of the evolution of\nthe local overdensity of lens environments with redshift.", "category": "astro-ph_GA" }, { "text": "A Photodissociation Region study of NGC 4038: We present a model of the photodissociation regions of NGC 4038, which is\npart of the Antennae galaxies. We have considered one-dimensional slabs of\nuniform density all having a maximum $A_V=10\\,{\\rm mag}$, interacting with\nplane-parallel radiation. The density range in our simulations spans four\norders of magnitude ($100\\le n\\le 10^6\\,{\\rm cm}^{-3}$) and the UV field\nstrength spans more than three orders of magnitude ($10\\le\\chi\\le10^{4.5}$\nmultiples of the ${\\rm Draine}$ field), from which we generated a grid of about\n1400 simulations. We compare our results with Herschel SPIRE-FTS, CSO and\nISO-LWS observations of eight CO transition lines ($J=1-0$ to $8-7$) and the\n[CI] 609\\mu m and [OI] 146\\mu m fine structure lines. We find that the\nmolecular and atomic emission lines trace different gas components of NGC 4038,\nthus single emission models are insufficient to reproduce the observed values.\nIn general, low-$J$ CO transition lines correspond to either low density\nregions interacting with low UV field strengths, or high density regions\ninteracting with high UV field strengths. Higher $J$ CO transition lines are\nless dependent on the UV field strength and are fitted by gas with density\n$n\\sim10^{4.5}-10^{5.2}\\,{\\rm cm}^{-3}$. We find that the observed fine\nstructure line ratio of [CI] 609\\mu m/[OI] 146\\mu m is reproduced by clouds\nsubject to weaker UV fields compared to the CO lines. We make estimates of the\n$X_{\\rm CO}$ factor which relates the CO emission with the column density of\nmolecular hydrogen, and find that it is less than the canonical Milky Way\nvalue.", "category": "astro-ph_GA" }, { "text": "The H$\u03b1$ broadband photometric reverberation mapping of four\n Seyfert 1 galaxies: Broadband photometric reverberation mapping (PRM) have been investigated for\nAGNs in recent years, but mostly on accretion disk continuum RM. Due to the\nsmall fraction of broad emission lines in the broadband, PRM for emission lines\nis very challenging. Here we present an ICCF-Cut method for broadband PRM to\nobtain the H$\\alpha$ broad line lag and apply it to four Seyfert 1 galaxies,\nMCG+08-11-011, NGC 2617, 3C 120 and NGC 5548. All of them have high quality\nbroadband lightcurves with daily/sub-daily cadence, which enables us to extract\nH$\\alpha$ lightcurves from the line band by subtracting the contributions from\nthe continuum and host galaxy. Their extracted H$\\alpha$ lightcurves are\ncompared with the lagged continuum band lightcurves, as well as the lagged\nH$\\beta$ lightcurves obtained by spectroscopic RM (SRM) at the same epochs. The\nconsistency of these lightcurves and the comparison with the SRM H$\\beta$ lags\nprovide supports to the H$\\alpha$ lags of these AGNs, in a range from 9 to 19\ndays, obtained by the ICCF-Cut, JAVELIN and $\\chi^2$ methods. The simulations\nto evaluate the reliability of H$\\alpha$ lags and the comparisons between SRM\nH$\\beta$ and PRM H$\\alpha$ lags indicate that the consistency of the ICCF-Cut,\nJAVELIN and $\\chi^2$ results can ensure the reliability of the derived\nH$\\alpha$ lags. These methods may be used to estimate the broad line region\nsizes and black hole masses of a large sample of AGNs in the large multi-epoch\nhigh cadence photometric surveys such as LSST in the future.", "category": "astro-ph_GA" }, { "text": "Cosmological simulations of dwarfs: the need for ISM physics beyond SN\n feedback alone: The dominant feedback mechanism in low mass haloes is usually assumed to take\nthe form of massive stars exploding as supernovae (SNe). We perform very high\nresolution cosmological zoom-in simulations of five dwarf galaxies to z = 4\nwith our mechanical SN feedback model. This delivers the correct amount of\nmomentum corresponding to the stage of the SN remnant evolution resolved, and\nhas been shown to lead to realistic dwarf properties in isolated simulations.\nWe find that in 4 out of our 5 simulated cosmological dwarfs, SN feedback has\ninsufficient impact resulting in excessive stellar masses, extremely compact\nsizes and central super-solar stellar metallicities. The failure of the SN\nfeedback in our dwarfs is physical in nature within our model and is the result\nof the build up of very dense gas in the early universe due to mergers and\ncosmic inflows prior to the first SN occurring. We demonstrate that our results\nare insensitive to resolution (provided that it is high enough), details of the\n(spatially uniform) UV background and reasonable alterations within our star\nformation prescription. We therefore conclude that the ability of SNe to\nregulate dwarf galaxy properties is dependent on other physical processes, such\nas turbulent pressure support, clustering and runaway of SN progenitors and\nother sources of stellar feedback.", "category": "astro-ph_GA" }, { "text": "The evolutionary tracks of young massive star clusters: Stars mostly form in groups consisting of a few dozen to several ten thousand\nmembers. For 30 years, theoretical models provide a basic concept of how such\nstar clusters form and develop: they originate from the gas and dust of\ncollapsing molecular clouds. The conversion from gas to stars being incomplete,\nthe left over gas is expelled, leading to cluster expansion and stars becoming\nunbound. Observationally, a direct confirmation of this process has proved\nelusive, which is attributed to the diversity of the properties of forming\nclusters. Here we take into account that the true cluster masses and sizes are\nmasked, initially by the surface density of the background and later by the\nstill present unbound stars. Based on the recent observational finding that in\na given star-forming region the star formation efficiency depends on the local\ndensity of the gas, we use an analytical approach combined with \\mbox{N-body\nsimulations, to reveal} evolutionary tracks for young massive clusters covering\nthe first 10 Myr. Just like the Hertzsprung-Russell diagram is a measure for\nthe evolution of stars, these tracks provide equivalent information for\nclusters. Like stars, massive clusters form and develop faster than their\nlower-mass counterparts, explaining why so few massive cluster progenitors are\nfound.", "category": "astro-ph_GA" }, { "text": "ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: The Infrared\n Excess of UV-selected z=2-10 galaxies as a function of UV-continuum Slope and\n Stellar Mass: We make use of deep 1.2mm-continuum observations (12.7microJy/beam RMS) of a\n1 arcmin^2 region in the Hubble Ultra Deep Field to probe dust-enshrouded star\nformation from 330 Lyman-break galaxies spanning the redshift range z=2-10 (to\n~2-3 Msol/yr at 1sigma over the entire range). Given the depth and area of\nASPECS, we would expect to tentatively detect 35 galaxies extrapolating the\nMeurer z~0 IRX-beta relation to z>~2 (assuming T_d~35 K). However, only 6\ntentative detections are found at z>~2 in ASPECS, with just three at >3sigma.\nSubdividing z=2-10 galaxies according to stellar mass, UV luminosity, and\nUV-continuum slope and stacking the results, we only find a significant\ndetection in the most massive (>10^9.75 Msol) subsample, with an infrared\nexcess (IRX=L_{IR}/L_{UV}) consistent with previous z~2 results. However, the\ninfrared excess we measure from our large selection of sub-L* (<10^9.75 Msol)\ngalaxies is 0.11(-0.42)(+0.32) and 0.14(-0.14)(+0.15) at z=2-3 and z=4-10,\nrespectively, lying below even an SMC IRX-beta relation (95% confidence). These\nresults demonstrate the relevance of stellar mass for predicting the IR\nluminosity of z>~2 galaxies. We furthermore find that the evolution of the\nIRX-stellar mass relationship depends on the evolution of the dust temperature.\nIf the dust temperature increases monotonically with redshift (as (1+z)^0.32)\nsuch that T_d~44-50 K at z>=4, current results are suggestive of little\nevolution in this relationship to z~6. We use these results to revisit recent\nestimates of the z>~3 SFR density. One less obvious implication is in\ninterpreting the high Halpha EWs seen in z~5 galaxies: our results imply that\nstar-forming galaxies produce Lyman-continuum photons at twice the efficiency\n(per unit UV luminosity) as implied in conventional models. Star-forming\ngalaxies can then reionize the Universe, even if the escape fraction is <10%.", "category": "astro-ph_GA" }, { "text": "Powerful H2 Line Cooling in Stephan's Quintet II. Group-wide Gas and\n Shock Modeling of the Warm H2 and a Comparison with [CII]157.7um Emission and\n Kinematics: We map for the first time the two-dimensional H_2 excitation of warm\nintergalactic gas in Stephan's Quintet on group-wide (50 x 35 kpc^2) scales to\nquantify the temperature, mass and warm-H_2 mass fraction as a function of\nposition using Spitzer. Molecular gas temperatures are seen to rise (to T >\n700K) and the slope of the power--law density-temperature relation flattens\nalong the main ridge of the filament, defining the region of maximum heating.\nWe also performed MHD modeling of the excitation properties of the warm gas, to\nmap the velocity structure and energy deposition rate of slow and fast\nmolecular shocks. Slow magnetic shocks were required to explain the power\nradiated from the lowest--lying rotational states of H_2, and strongly support\nthe idea that energy cascades down to small scales and low velocities from the\nfast collision of NGC 7318b with group-wide gas. The highest levels of heating\nof the warm H_2 is strongly correlated with the large-scale stirring of the\nmedium as measured by [CII] spectroscopy with Herschel. H_2 is also seen\nassociated with a separate bridge which extends towards the Seyfert nucleus in\nNGC 7319, both from Spitzer and CARMA CO observations. This opens up the\npossibility that both galaxy collisions and AGN outflows can turbulently heat\ngas on large-scales in compact groups. The observations provide a laboratory\nfor studying the effects of turbulent energy dissipation on group-wide scales\nthat may provide clues about the heating and cooling of gas at high-z in early\ngalaxy and protogalaxy formation.", "category": "astro-ph_GA" }, { "text": "Probing star formation and feedback in dwarf galaxies. Integral field\n view of the blue compact galaxy Tololo 1937-423: (Abridged) Blue compact galaxies (BCG) are gas-rich, low-mass, small systems\nthat form stars at unusually high rates. This makes them excellent laboratories\nfor investigating the process of star-formation (SF) at galactic scales and the\neffects of massive stellar feedback on the interstellar (and intergalactic)\nmedium.\n We analyzed the BCG Tololo 1937-423 using optical integral field spectroscopy\nwith VIMOS at the Very Large Telescope to probe its morphology, stellar\ncontent, nebular excitation and ionization properties, and the kinematics of\nits warm ionized gas.\n We found that Tololo 1937-423 is currently undergoing an extended starburst,\nwith nine major $H\\alpha$ clumps. The galaxy presents a single continuum peak\nthat is not cospatial with any knot in emission lines, indicating at least two\nrelatively recent episodes of SF. The inhomogeneous dust distribution reaches\nits maximum roughly at the position of the continuum peak. We found shocked\nregions in the galaxy outer regions and at the edges of the SF knots. The\noxygen abundance is similar in all the SF regions, suggesting a chemically\nhomogeneous ionized interstellar medium over spatial scales of several kpc. The\nionized gas kinematics displays an overall regular rotation around a\nnorthwest-southeast axis.\n The morphology of the galaxy and the two different episodes of SF suggest a\nscenario of triggered (induced by supernova shock waves) SF acting in Tololo\n1937-423. The inferred ages for the different SF episodes (~13-80 Myr for the\ncentral post-starburst and 5-7 Myr for the ongoing SF) are consistent with\ntriggered SF, with the most recent SF episode caused by the collective effect\nof stellar winds and supernova explosions from the central post-starburst. The\nvelocity dispersion pattern, with higher velocity dispersions found at the\nedges of the SF regions, and shocked regions in the galaxy, also favor this\nscenario.", "category": "astro-ph_GA" }, { "text": "Identification of High-Redshift Galaxy Overdensities in GOODS-N and\n GOODS-S: We conduct a systematic search for high-redshift galaxy overdensities at $4.9\n< z_{\\,\\mathrm{spec}} < 8.9$ in both the GOODS-N and GOODS-S fields using\nJWST/NIRCam imaging from JADES and JEMS in addition to JWST/NIRCam wide field\nslitless spectroscopy from FRESCO. High-redshift galaxy candidates are\nidentified using HST+JWST photometry spanning $\\lambda = 0.4-5.0\\\n\\mu\\mathrm{m}$. We confirmed the redshifts for roughly a third of these\ngalaxies using JWST/FRESCO spectroscopy over $\\lambda = 3.9-5.0\\ \\mu\\mathrm{m}$\nthrough identification of either $\\mathrm{H} \\alpha$ or\n$\\left[\\mathrm{OIII}\\right]\\lambda5008$ around the best-fit photometric\nredshift. The rest-UV magnitudes and continuum slopes of these galaxies were\ninferred from the photometry: the brightest and reddest objects appear in more\ndense environments and thus are surrounded by more galaxy neighbors than their\nfainter and bluer counterparts, suggesting accelerated galaxy evolution within\noverdense environments. We find $17$ significant ($\\delta_{\\mathrm{gal}} \\geq\n3.04$, $N_{\\mathrm{galaxies}} \\geq 4$) galaxy overdensities across both fields\n($7$ in GOODS-N and $10$ in GOODS-S), including the two highest redshift\nspectroscopically confirmed galaxy overdensities to date at $\\left<\nz_{\\mathrm{\\,spec}} \\right> = 7.955$ and $\\left< z_{\\mathrm{\\,spec}} \\right> =\n8.222$ (representing densities around $\\sim 6$ and $\\sim 12$ times that of a\nrandom volume). We estimate the total halo mass of these large-scale structures\nto be $11.5 \\leq \\mathrm{log}_{10}\\left(M_{\\mathrm{halo}}/M_{\\odot}\\right) \\leq\n13.4$ using an empirical stellar mass to halo mass relation, which are likely\nunderestimates as a result of incompleteness. These protocluster candidates are\nexpected to evolve into massive galaxy clusters with\n$\\mathrm{log}_{10}\\left(M_{\\mathrm{halo}}/M_{\\odot}\\right) \\gtrsim 14$ by $z =\n0$.", "category": "astro-ph_GA" }, { "text": "The pattern speeds of vertical breathing waves: We measure and compare the pattern speeds of vertical breathing, vertical\nbending, and spiral density waves in two isolated N-body+SPH simulations, using\nwindowed Fourier transforms over 1 Gyr time intervals. We show that the pattern\nspeeds of the breathing waves match those of the spirals but are different from\nthose of the bending waves. We also observe matching pattern speeds between the\nbar and breathing waves. Our results not only strengthen the case that,\nthroughout the disc, breathing motions are driven by spirals but indeed that\nthe breathing motions are part and parcel of the spirals.", "category": "astro-ph_GA" }, { "text": "Disk Evolution in W5: Intermediate Mass Stars at 2-5 Myr: We present the results of a survey of young intermediate mass stars (age\n$<$~5 Myr, 1.5 $1000, is one of the radio-loudest quasars in the early universe and\nis the only quasar with observed extended radio jets of kpc-scale at $z \\gtrsim\n6$. Modeling the X-ray spectrum of the quasar with a power law, we find a best\nfit of $\\Gamma = 1.99^{+0.29}_{-0.28}$, leading to an X-ray luminosity of\n$L_{2-10} = 1.26^{+0.45}_{-0.33} \\times 10^{45}\\ {\\rm erg}\\ {\\rm s}^{-1}$ and\nan X-ray to UV brightness ratio of $\\alpha_{\\rm OX} = -1.36 \\pm 0.11$. We\nidentify a diffuse structure 50 kpc (${\\sim}8^{\\prime\\prime}$) to the NW of the\nquasar along the jet axis that corresponds to a $3\\sigma$ enhancement in the\nangular density of emission and can be ruled out as a background fluctuation\nwith a probability of P=0.9985. While with few detected photons the spectral\nfit of the structure is uncertain, we find that it has a luminosity of\n$L_{2-10}\\sim10^{44}\\ {\\rm erg}\\ {\\rm s}^{-1}$. These observations therefore\npotentially represent the most distant quasar jet yet seen in X-rays. We find\nno evidence for excess X-ray emission where the previously-reported radio jets\nare seen (which have an overall linear extent of $0.^{\\prime\\prime}28$), and a\nbright X-ray point source located along the jet axis to the SE is revealed by\noptical and NIR imaging to not be associated with the quasar.", "category": "astro-ph_GA" }, { "text": "Imprints of interaction processes in the globular cluster system of NGC\n 3640: We present a wide-field study of the globular cluster systems (GCS) of the\nelliptical galaxy NGC 3640 and its companion NGC 3641, based on observations\nfrom Gemini Multi-Object Spectrograph/Gemini. NGC 3640 is a shell galaxy which\npresents a complex morphology, which previous studies have indicated as the\nsign of a recent 'dry' merger, although whether its nearest neighbour could\nhave influenced these substructures remains an open question. In this work, we\ntrace the spatial distribution of the globular clusters (GCs) as well as their\ncolour distribution, finding a potential bridge of red GCs that connects NGC\n3640 to its less massive companion, and signs that the blue GCs were spatially\ndisturbed by the event that created the shells.", "category": "astro-ph_GA" }, { "text": "The Carina Project. VIII. The \u03b1-element abundances: We have performed a new abundance analysis of Carina Red Giant (RG) stars\nfrom spectroscopic data collected with UVES (high resolution) and\nFLAMES/GIRAFFE (high and medium resolution) at ESO/VLT. The former sample\nincludes 44 RGs, while the latter consists of 65 (high) and ~800 (medium\nresolution) RGs, covering a significant fraction of the galaxy's RG branch\n(RGB), and red clump stars. To improve the abundance analysis at the faint\nmagnitude limit, the FLAMES/GIRAFFE data were divided into ten surface gravity\nand effective temperature bins. The spectra of the stars belonging to the same\ngravity/temperature bin were stacked. This approach allowed us to increase by\nat least a factor of five the signal-to-noise ratio in the faint limit\n(V>20.5mag). We took advantage of the new photometry index cU,B,I introduced by\nMonelli et al. (2014), as an age and probably a metallicity indicator, to split\nstars along the RGB. These two stellar populations display distinct [Fe/H] and\n[Mg/H] distributions: their mean Fe abundances are -2.15$\\pm$0.06dex\n(sig=0.28), and -1.75$\\pm$0.03dex (sig=0.21), respectively. The two iron\ndistributions differ at the 75% level. This supports preliminary results by\nLemasle et al. (2012) and by Monelli et al. (2014). Moreover, we found that the\nold and intermediate-age stellar populations have mean [Mg/H] abundances of\n-1.91$\\pm$0.05dex (sig=0.22) and -1.35$\\pm$0.03dex (sig=0.22); these differ at\nthe 83% level. Carina's {\\alpha}-element abundances agree, within 1sigma, with\nsimilar abundances for field Halo stars and for cluster (Galactic, Magellanic)\nstars. The same outcome applies to nearby dwarf spheroidals and ultra-faint\ndwarf galaxies, in the iron range covered by Carina stars. Finally, we found\nevidence of a clear correlation between Na and O abundances, thus suggesting\nthat Carina's chemical enrichment history is quite different than in the\nglobular clusters.", "category": "astro-ph_GA" }, { "text": "On the carriers of the 3.4-micrometer absorption and emission bands, and\n their evolution: Based on the results of chemical analysis and simulation of kerogens and\nimmature coals, a large number of chemical structures carrying the 3.4-mum\nfeature were studied by means of computer simulation codes. Further selection\ncriteria were the integrated strength of the absorption lines in the aliphatic\nstretchings wavelength band, weak IR activity in the aromatic stretching band\nand absence of notable activity outside the astronomical UIBs (Unidentified\nInfrared Bands). Most of the structures that were retained can be classed as\nbranched, short and oxygen-bridged CH_{2} chains, and naphtenic chains.\nCombinations of their absorption spectra deliver spectra comparable to those\nobserved in the sky. Absorption spectra were derived from Normal Mode Analysis.\nEmission spectra of the same structures were computed by monitoring their\noverall dipole moment as they vibrate freely in vacuum after excitation. These\nspectra were then combined in suitable proportions, together with those of\naromatic structures, so as to simulate various typical near IR emission spectra\nobserved in the sky.", "category": "astro-ph_GA" }, { "text": "Gentle heating by mixing in cooling flow clusters: We analyze three-dimensional hydrodynamical simulations of the interaction of\njets and the bubbles they inflate with the intra-cluster medium (ICM), and show\nthat the heating of the ICM by mixing hot bubble gas with the ICM operates over\ntens of millions of years, and hence can smooth the sporadic activity of the\njets. The inflation process of hot bubbles by propagating jets forms many\nvortices, and these vortices mix the hot bubble gas with the ICM. The mixing,\nhence the heating of the ICM, starts immediately after the jets are launched,\nbut continues for tens of millions of years. We suggest that the smoothing of\nthe active galactic nucleus (AGN) sporadic activity by the long-lived vortices\naccounts for the recent finding of a gentle energy coupling between AGN heating\nand the ICM.", "category": "astro-ph_GA" }, { "text": "Probing The Ultraviolet Luminosity Function of the Earliest Galaxies\n with the Renaissance Simulations: In this paper, we present the first results from the Renaissance Simulations,\na suite of extremely high-resolution and physics-rich AMR calculations of high\nredshift galaxy formation performed on the Blue Waters supercomputer. These\nsimulations contain hundreds of well-resolved galaxies at $z \\sim 25-8$, and\nmake several novel, testable predictions. Most critically, we show that the\nultraviolet luminosity function of our simulated galaxies is consistent with\nobservations of high-z galaxy populations at the bright end of the luminosity\nfunction (M$_{1600} \\leq -17$), but at lower luminosities is essentially flat\nrather than rising steeply, as has been inferred by Schechter function fits to\nhigh-z observations, and has a clearly-defined lower limit in UV luminosity.\nThis behavior of the luminosity function is due to two factors: (i) the strong\ndependence of the star formation rate on halo virial mass in our simulated\ngalaxy population, with lower-mass halos having systematically lower star\nformation rates and thus lower UV luminosities; and (ii) the fact that halos\nwith virial masses below $\\simeq 2 \\times 10^8$ M$_\\odot$ do not universally\ncontain stars, with the fraction of halos containing stars dropping to zero at\n$\\simeq 7 \\times 10^6$ M$_\\odot$. Finally, we show that the brightest of our\nsimulated galaxies may be visible to current and future ultra-deep space-based\nsurveys, particularly if lensed regions are chosen for observation.", "category": "astro-ph_GA" }, { "text": "An evolutionary continuum from nucleated dwarf galaxies to star clusters: Systematic studies have revealed hundreds of ultra-compact dwarf galaxies\n(UCDs) in the nearby Universe. With half-light radii $r_h$ of approximately\n10-100 parsecs and stellar masses $M_*$ $\\approx$ $10^6-10^8$ solar masses,\nUCDs are among the densest known stellar systems. Although similar in\nappearance to massive globular clusters, the detection of extended stellar\nenvelopes, complex star formation histories, elevated mass-to-light ratio, and\nsupermassive black holes suggest that some UCDs are remnant nuclear star\nclusters of tidally-stripped dwarf galaxies, or even ancient compact galaxies.\nHowever, only a few objects have been found in the transient stage of tidal\nstripping, and this assumed evolutionary path has never been fully traced by\nobservations. Here we show that 106 galaxies in the Virgo cluster have\nmorphologies that are intermediate between normal, nucleated dwarf galaxies and\nsingle-component UCDs, revealing a continuum that fully maps this morphological\ntransition, and fills the `size gap' between star clusters and galaxies. Their\nspatial distribution and redder color are also consistent with stripped\nsatellite galaxies on their first few pericentric passages around massive\ngalaxies. The `ultra-diffuse' tidal features around several of these galaxies\ndirectly show how UCDs are forming through tidal stripping, and that this\nevolutionary path can include an early phase as a nucleated ultra-diffuse\ngalaxy (UDG). These UCDs represent substantial visible fossil remnants of\nancient dwarf galaxies in galaxy clusters, and more low-mass remnants probably\nremain to be found.", "category": "astro-ph_GA" }, { "text": "Post-Starburst Galaxies in SDSS-IV MaNGA: Post-starburst galaxies, identified by their unusually strong Balmer\nabsorption lines and weaker than average emission lines, have traditionally\nbeen selected based on their central stellar populations. Here we identify 360\ngalaxies with post-starburst regions from the MaNGA integral field survey and\nclassify these galaxies into three types: 31 galaxies with central\npost-starburst regions (CPSB), 37 galaxies with off-center ring-like\npost-starburst regions (RPSB) and 292 galaxies with irregular post-starburst\nregions (IPSB). Focussing on the CPSB and RPSB samples, and comparing their\nradial gradients in D$_n$4000, H$\\delta_{\\rm A}$ and W(H$\\alpha$) to control\nsamples, we find that while the CPSBs have suppressed star formation throughout\ntheir bulge and disk, and clear evidence of rapid decline of star formation in\nthe central regions, the RPSBs only show clear evidence of recently rapidly\nsuppressed star formation in their outer regions and an ongoing central\nstarburst. The radial profiles in mass-weighted age and stellar $v/\\sigma$\nindicate that CPSBs and RPSBs are not simply different evolutionary stages of\nthe same event, rather that CPSB galaxies are caused by a significant\ndisruptive event, while RPSB galaxies are caused by disruption of gas fuelling\nto the outer regions. Compared to the control samples, both CPSB and RPSB\ngalaxies show a higher fraction of interactions/mergers, misaligned gas or bars\nthat might be the cause of the gas inflows and subsequent quenching.", "category": "astro-ph_GA" }, { "text": "MIGHTEE-HI: the HI Size-Mass relation over the last billion years: We present the observed HI size-mass relation of $204$ galaxies from the\nMIGHTEE Survey Early Science data. The high sensitivity of MeerKAT allows us to\ndetect galaxies spanning more than 4 orders of magnitude in HI mass, ranging\nfrom dwarf galaxies to massive spirals, and including all morphological types.\nThis is the first time the relation has been explored on a blind homogeneous\ndata set which extends over a previously unexplored redshift range of $0 < z <\n0.084$, i.e. a period of around one billion years in cosmic time. The sample\nfollows the same tight logarithmic relation derived from previous work, between\nthe diameter ($D_{\\rm HI}$) and the mass ($M_{\\rm HI}$) of HI discs. We measure\na slope of $0.501\\pm 0.008$, an intercept of $-3.252^{+0.073}_{-0.074}$, and an\nobserved scatter of $0.057$ dex. For the first time, we quantify the intrinsic\nscatter of $0.054 \\pm 0.003$ dex (${\\sim} 10 \\%$), which provides a constraint\nfor cosmological simulations of galaxy formation and evolution. We derive the\nrelation as a function of galaxy type and find that their intrinsic scatters\nand slopes are consistent within the errors. We also calculate the $D_{\\rm HI}\n- M_{\\rm HI}$ relation for two redshift bins and do not find any evidence for\nevolution with redshift. These results suggest that over a period of one\nbillion years in lookback time, galaxy discs have not undergone significant\nevolution in their gas distribution and mean surface mass density, indicating a\nlack of dependence on both morphological type and redshift.", "category": "astro-ph_GA" }, { "text": "The GALAH survey: Elemental abundances in open clusters using joint\n effective temperature and surface gravity photometric priors: The ability to measure precise and accurate stellar effective temperatures\n($T_{\\rm{eff}}$) and surface gravities ($\\log(g)$) is essential in determining\naccurate and precise abundances of chemical elements in stars. Measuring\n$\\log(g)$ from isochrones fitted to colour-magnitude diagrams of open clusters\nis significantly more accurate and precise compared to spectroscopic $\\log(g)$.\nBy determining the ranges of ages, metallicity, and extinction of isochrones\nthat fit the colour-magnitude diagram, we constructed a joint probability\ndistribution of $T_{\\rm{eff}}$ and $\\log(g)$. The joint photometric probability\nshows the complex correlations between $T_{\\rm{eff}}$ and $\\log(g)$, which\ndepend on the evolutionary stage of the star. We show that by using this\nphotometric prior while fitting spectra, we can acquire more precise\nspectroscopic stellar parameters and abundances of chemical elements. This\nreveals higher-order abundance trends in open clusters like traces of atomic\ndiffusion. We used photometry and astrometry provided by the \\textit{Gaia} DR3\ncatalogue, Padova isochrones, and Galactic Archaeology with HERMES (GALAH) DR4\nspectra. We analysed the spectra of 1979 stars in nine open clusters, using\nMCMC to fit the spectroscopic abundances of 26 elements, $T_{\\rm{eff}}$,\n$\\log(g)$, $v_{\\rm{mic}}$, and $v_{\\rm{broad}}$. We found that using\nphotometric priors improves the accuracy of abundances and $\\log(g)$, which\nenables us to view higher-order trends of abundances caused by atomic diffusion\nin M67 and Ruprecht 147.", "category": "astro-ph_GA" }, { "text": "Galactic Orbital Effects on Pulsar Timing: In the currently accepted paradigm, dark matter is hypothesized as an\nexplanation of the flat rotation curves of galaxies under the assumption of\nvirialized orbits. The use of millisecond pulsar timing as a probe of Galactic\ndark matter content is explored as a means of relaxing this assumption. A\nmethod of inference of the Galactic potential using the frequency derivative\n$\\dot{\\nu}$ is produced, and an estimate for a virialized Galactic rotation\ncurve is given through direct observation of acceleration. The data set used\nincludes 210 pulsars with known $\\dot{\\nu}$ and astrometric properties, a\nsubset of which also have measured $\\ddot{\\nu}$. In principle, this enables the\nexploration of kinematic effects, but in practice, $\\ddot{\\nu}$ values are\nfound to be too imprecise at present to adequately constrain radial velocities\nof pulsars. Additionally, surface magnetic field strengths are inferred from\n$\\dot{\\nu}$ and the magnetic spin-down contribution to $\\ddot{\\nu}$ is\nestimated. For several pulsars the radial velocity is known, and the kinematic\ncontribution to $\\ddot{\\nu}$ is estimated accordingly. The binary orbital\nperiods of PSR J1713+0747 and other binary pulsars are also used to constrain\nGalactic mass density models.", "category": "astro-ph_GA" }, { "text": "Stellar population analysis of MaNGA early-type galaxies: IMF dependence\n and systematic effects: We study systematics associated with estimating simple stellar population\n(SSP) parameters -- age, metallicity [M/H], $\\alpha$-enhancement [$\\alpha$/Fe]\nand IMF shape -- and associated $M_*/L$ gradients, of elliptical slow rotators\n(E-SRs), fast rotators (E-FRs) and S0s from stacked spectra of galaxies in the\nMaNGA survey. These systematics arise from (i) how one normalizes the spectra\nwhen stacking; (ii) having to subtract emission before estimating absorption\nline strengths; (iii) the decision to fit the whole spectrum or just a few\nabsorption lines; (iv) SSP model differences (e.g. isochrones, enrichment,\nIMF). The MILES+Padova SSP models, fit to the H$_\\beta$, $\\langle$Fe$\\rangle$,\nTiO$_{\\rm 2SDSS}$ and [MgFe] Lick indices in the stacks, indicate that out to\nthe half-light radius $R_e$: (a) ages are younger and [$\\alpha$/Fe] values are\nlower in the central regions but the opposite is true of [M/H]; (b) the IMF is\nmore bottom-heavy in the center, but is close to Kroupa beyond about $R_e/2$;\n(c) this makes $M_*/L$ about $2\\times$ larger in the central regions than\nbeyond $R_e/2$. While the models of Conroy et al. (2018) return similar [M/H]\nand [$\\alpha$/Fe] profiles, the age and (hence) $M_*/L$ profiles can differ\nsignificantly even for solar abundances and a Kroupa IMF; different responses\nto non-solar abundances and IMF parametrization further compound these\ndifferences. There are clear (model independent) differences between E-SRs,\nE-FRs and S0s: younger ages and less enhanced [$\\alpha$/Fe] values suggest that\nE-FRs and S0s are not SSPs, but relaxing this assumption is unlikely to change\ntheir inferred $M_*/L$ gradients significantly.", "category": "astro-ph_GA" }, { "text": "Bipolar Outflows out to 10~kpc for Massive Galaxies at Redshift\n $z\\approx 1$: Galactic outflows are believed to play a critical role in the evolution of\ngalaxies by regulating their mass build-up and star formation. Theoretical\nmodels assumes bipolar shapes for the outflows that extends well into the\ncircumgalctic medium (CGM), up to tens of kpc perpendicular to the galaxies.\nThey have been directly observed in the local Universe in several individual\ngalaxies, e.g., around the Milky Way and M82. At higher redshifts, cosmological\nsimulations of galaxy formation predict an increase in the frequency and\nefficiency of galactic outflows due to the increasing star formation activity.\nOutflows are responsible for removing potential fuel for star formation from\nthe galaxy, while at the same enriching the CGM and the intergalactic medium.\nThese feedback processes, although incorporated as key elements of cosmological\nsimulations, are still poorly constrained on CGM scales. Here we present an\nultra-deep MUSE image of the mean MgII emission surrounding a sample of\ngalaxies at z~1 that strongly suggests the presence of outflowing gas on\nphysical scales of more than 10kpc. We find a strong dependence of the detected\nsignal on the inclination of the central galaxy, with edge-on galaxies clearly\nshowing enhanced MgII emission along the minor axis, while face-on galaxies\ndisplay much weaker and more isotropic emission. We interpret these findings as\nsupporting the idea that outflows typically have a bipolar cone geometry\nperpendicular to the galactic disk. We demonstrate that the signal is not\ndominated by a few outliers. After dividing the galaxy sample in subsamples by\nmass, the bipolar emission is only detected in galaxies with stellar mass\n$\\mathrm{M_* \\gtrsim 10^{9.5} M_\\odot}$.", "category": "astro-ph_GA" }, { "text": "Metal flows of the circumgalactic medium, and the metal budget in\n galactic halos: We present an analysis of the flow of metals through the circumgalactic\nmedium (CGM) in the Feedback in Realistic Environments (FIRE) simulations of\ngalaxy formation, ranging from isolated dwarfs to $L*$ galaxies. We find that\nnearly all metals produced in high-redshift galaxies are carried out in winds\nthat reach $0.25 R_{\\rm vir}$. When measured at $0.25 R_{\\rm vir}$ the\nmetallicity of outflows is slightly higher than the interstellar medium (ISM)\nmetallicity. Many metals thus reside in the CGM. Cooling and recycling from\nthis reservoir determine the metal budget in the ISM. The outflowing metal flux\ndecreases by a factor of $\\sim2-5$ between $0.25 R_{\\rm vir}$ and $R_{\\rm\nvir}$. Furthermore, outflow metallicity is typically lower at $R_{\\rm vir}$\nowing to dilution of the remaining outflow by metal-poor material swept up from\nthe CGM. The inflow metallicity at $R_{\\rm vir}$ is generally low, but outflow\nand inflow metallicities are similar in the inner halo. At low redshift,\nmassive galaxies no longer generate outflows that reach the CGM, causing a\ndivergence in CGM and ISM metallicity. Dwarf galaxies continue to generate\noutflows, although they preferentially retain metal ejecta. In all but the\nleast massive galaxy considered, a majority of the metals are within the halo\nat $z=0$. We measure the fraction of metals in CGM, ISM and stars, and quantify\nthe thermal state of CGM metals in each halo. The total amount of metals in the\nlow-redshift CGM of two simulated $L*$ galaxies is consistent with estimates\nfrom the COS halos survey, while for the other two it appears to be lower.", "category": "astro-ph_GA" }, { "text": "Increasing the Scientific Return of Stellar Orbits at the Galactic\n Center: We report a factor of $\\sim$3 improvement in Keck Laser Guide Star Adaptive\nOptics (LGSAO) astrometric measurements of stars near the Galaxy's supermassive\nblack hole (SMBH). By carrying out a systematic study of M92, we have produced\na more accurate model for the camera's optical distortion. Updating our\nmeasurements with this model, and accounting for differential atmospheric\nrefraction, we obtain estimates of the SMBH properties that are a factor of\n$\\sim$2 more precise, and most notably, increase the likelihood that the black\nhole is at rest with respect to the nuclear star cluster. These improvements\nhave also allowed us to extend the radius to which stellar orbital parameter\nestimates are possible by a factor of 2.", "category": "astro-ph_GA" }, { "text": "The Presence of Weak Active Galactic Nuclei in High Redshift Star\n Forming Galaxies: We present [OIII 5007A] observations of the star forming galaxy HDF-BMZ1299\n(z=1.598) using Keck Observatory's Adaptive Optics system with the\nnear-infrared integral field spectrograph OSIRIS. Using previous Halpha and\n[NII] measurements of the same source, we are able for the first time to use\nspatially resolved observations to place a high-redshift galaxy's substructure\non a traditional HII diagnostic diagram. We find that HDF-BMZ1299's spatially\nconcentrated nebular ratios in the central ~1.5 kiloparsec (0.\"2) are best\nexplained by the presence of an AGN: log([NII]/Halpha)=-0.22+/-0.05 and 2sigma\nlimit of log([OIII]/Hbeta)>0.26. The dominant energy source of this galaxy is\nstar formation, and integrating a single aperture across the galaxy yields\nnebular ratios that are composite spectra from both AGN and HII regions. The\npresence of an embedded AGN in HDF-BMZ1299 may suggest a potential\ncontamination in a fraction of other high-redshift star forming galaxies, and\nwe suggest that this may be a source of the \"elevated\" nebular ratios\npreviously seen in seeing-limited metallicity studies. HDF-BMZ1299's estimated\nAGN luminosity is L_Halpha = 3.7e41 erg/s and L_[OIII] = 5.8e41 erg/s, making\nit one of the lowest luminosity AGN discovered at this early epoch.", "category": "astro-ph_GA" }, { "text": "CO, H2O, H2O+ line and dust emission in a z = 3.63 strongly lensed\n starburst merger at sub-kiloparsec scales: Using ALMA, we report high angular-resolution observations of the redshift\nz=3.63 galaxy, G09v1.97, one of the most luminous strongly lensed galaxies\ndiscovered by the H-ATLAS survey. We present 0\"2-0\"4 resolution images of the\nrest-frame 188 and 419$\\mu$m dust continuum and the CO(6-5), H2O(211-202) and\nJ=2 H2O+ line emission. We also report the detection of H$_2^{18}$O in this\nsource. The dust continuum and molecular gas emission are resolved into a\nnearly complete ~1\"5 diameter Einstein ring plus a weaker image in the center,\nwhich is caused by a special dual deflector lensing configuration. The observed\nline profiles of the CO, H2O and H2O+ lines are strikingly similar. In the\nsource plane, we reconstruct the dust continuum images and the spectral cubes\nof the line emission at sub-kpc scales. The reconstructed dust emission in the\nsource plane is dominated by a compact disk with an effective radius of 0.7kpc\nplus an overlapping extended disk with a radius twice as large. While the\naverage magnification for the dust continuum is $\\mu$~10-11, the magnification\nof the line emission varies 5 to 22 across different velocity components. The\nemission lines have similar spatial and kinematic distributions. The molecular\ngas and dust content reveal that G09v1.97 is a gas-rich major merger in its\npre-coalescence phase. Both of the merging companions are intrinsically ULIRGs\nwith LIR reaching $\\gtrsim 4\\times10^{12}L_\\odot$, and the total LIR of\nG09v1.97 is $1.4\\times10^{13}L_\\odot$. The approaching southern galaxy shows no\nobvious kinematic structure with a semi-major half-light radius a_s=0.4kpc,\nwhile the receding galaxy resembles an a_s=1.2kpc rotating disk. The two\ngalaxies are separated by a projected distance of 1.3kpc, bridged by weak line\nemission that is co-spatially located with the cold-dust-emission peak,\nsuggesting a large amount of cold ISM in the interacting region. (abridged)", "category": "astro-ph_GA" }, { "text": "Planetary Nebula Candidates Uncovered with the HASH Research Platform: A detailed examination of new high quality radio catalogues (e.g. Cornish) in\ncombination with available mid-infrared (MIR) satellite imagery (e.g. Glimpse)\nhas allowed us to find 70 new planetary nebula (PN) candidates based on\nexisting knowledge of their typical colors and fluxes. To further examine the\nnature of these sources, multiple diagnostic tools have been applied to these\ncandidates based on published data and on available imagery in the HASH (Hong\nKong/ AAO/ Strasbourg H{\\alpha} planetary nebula) research platform. Some\ncandidates have previously-missed optical counterparts allowing for\nspectroscopic follow-up. Indeed, the single object spectroscopically observed\nso far has turned out to be a bona fide PN.", "category": "astro-ph_GA" }, { "text": "New insights on the recoiling/binary black hole candidate J0927+2943 via\n molecular gas observations: The peculiar QSO J0927+2943 shows multiple sets of emission lines in its\noptical spectrum. This signature has been interpreted as the relative motion\nbetween a black hole, either recoiling or bound in a binary system, and its\nhost galaxy, or as a superposition of two galaxies along the line of sight. In\norder to test these scenarios, we have collected 2mm CO(2-1) observations using\nthe IRAM Plateau de Bure Interferometer, and optical images and spectroscopy at\nthe Calar Alto observatory. Together with archival HST images, these data\nprovide unique insights on the nature of this system. The recoiling/binary\nblack hole scenarios are ruled out by the clear detection of a galactic-scale\nmolecular gas reservoir at the same redshift of the QSO broad lines. The\nobservations presented here also disfavour the superposition model, although\nwith less constraints. Thus, the origin of the second, bright set of narrow\nemission lines in J0927+2943 is still unknown.", "category": "astro-ph_GA" }, { "text": "AGN feedback duty cycle in Planck SZ selected clusters using Chandra\n observations: We present a systematic study of X-ray cavities using archival Chandra\nobservations of nearby galaxy clusters selected by their Sunyaev-Zel'dovich\n(SZ) signature in the Planck survey, which provides a nearly unbiased\nmass-selected sample to explore the entire AGN feedback duty cycle. Based on\nX-ray image analysis, we report that 30 of the 164 clusters show X-ray\ncavities, which corresponds to a detection fraction of 18%. After correcting\nfor spatial resolution to match the high-$z$ SPT-SZ sample, the detection\nfraction decreases to 9%, consistent with the high-z sample, hinting that the\nAGN feedback has not evolved across almost 8 Gyrs. Our finding agrees with the\nlack of evolution of cool-core clusters fraction. We calculate the cavity\npower, P_{\\rm cav}, and find that most systems of our sample have enough AGN\nheating to offset the radiative losses of the intracluster medium.", "category": "astro-ph_GA" }, { "text": "Binary Frequencies in Globular Clusters: Binary stars are predicted to have an important role in the evolution of\nglobular clusters, so we obtained binary fractions for 35 globular clusters\nthat were imaged in the F606W and F814W with the ACS on the Hubble Space\nTelescope. When compared to the values of prior efforts (Sollima et al. 2007;\nMilone et al. 2012), we find significant discrepancies, despite each group\ncorrecting for contamination effects and having performed the appropriate\nreliability tests. The most reliable binary fractions are obtained when\nrestricting the binary fraction to q > 0.5. Our analysis indicates that the\nrange of the binary fractions is nearly an order of magnitude for the lowest\ndynamical ages, suggesting that there is a broad distribution in the binary\nfraction at globular cluster formation. Dynamical effects also appears to\ndecrease the core binary fractions by a factor of two over a Hubble time, but\nthis is a weak relationship. We confirm a correlation from previous work that\nthe binary fraction within the core radius decreases with cluster age,\nindicating that younger clusters formed with higher binary fractions. The\nstrong radial gradient in the binary fraction with cluster radius appears to be\na consequence of dynamical interactions. It is often not present in dynamically\nyoung clusters but nearly always present in dynamically old clusters.", "category": "astro-ph_GA" }, { "text": "Origin of reduced dynamical friction by dark matter halos with net\n prograde rotation: We provide an explanation for the reduced dynamical friction on galactic bars\nin spinning dark matter halos. Earlier work based on linear theory predicted an\nincrease in dynamical friction when dark halos have a net forward rotation,\nbecause prograde orbits couple to bars with greater strength than retrograde\norbits. Subsequent numerical studies, however, found the opposite trend:\ndynamical friction weakens with increasing spin of the halo. We revisit this\nproblem and demonstrate that linear theory in fact correctly predicts a reduced\ntorque in forward-rotating halos. We show that shifting the halo mass from\nretrograde to prograde phase space generates a positive gradient in the\ndistribution function near the origin of the z-angular momentum (Lz=0), which\nresults in a resonant transfer of Lz to the bar, making the net dynamical\nfriction weaker. While this effect is subdominant for the major resonances,\nincluding the corotation resonance, it leads to a significant positive torque\non the bar for the series of direct radial resonances, as these resonances are\nstrongest at Lz=0. The overall dynamical friction from spinning halos is shown\nto decrease with the halo's spin, in agreement with the secular behavior of\nN-body simulations. We validate our linear calculation by computing the\nnonlinear torque from individual resonances using the angle-averaged\nHamiltonian.", "category": "astro-ph_GA" }, { "text": "Multi-Element Abundance Measurements from Medium-Resolution Spectra. IV.\n Alpha Element Distributions in Milky Way Dwarf Satellite Galaxies: We derive the star formation histories of eight dwarf spheroidal (dSph) Milky\nWay satellite galaxies from their alpha element abundance patterns. Nearly 3000\nstars from our previously published catalog (Paper II) comprise our data set.\nThe average [alpha/Fe] ratios for all dSphs follow roughly the same path with\nincreasing [Fe/H]. We do not observe the predicted knees in the [alpha/Fe] vs.\n[Fe/H] diagram, corresponding to the metallicity at which Type Ia supernovae\nbegin to explode. Instead, we find that Type Ia supernova ejecta contribute to\nthe abundances of all but the most metal-poor ([Fe/H] < -2.5) stars. We have\nalso developed a chemical evolution model that tracks the star formation rate,\nTypes II and Ia supernova explosions, and supernova feedback. Without metal\nenhancement in the supernova blowout, massive amounts of gas loss define the\nhistory of all dSphs except Fornax, the most luminous in our sample. All six of\nthe best-fit model parameters correlate with dSph luminosity but not with\nvelocity dispersion, half-light radius, or Galactocentric distance.", "category": "astro-ph_GA" }, { "text": "High-quality strong lens candidates in the final Kilo Degree survey\n footprint: We present 97 new high-quality strong lensing candidates found in the final\n$\\sim 350\\,\\rm deg^2$, that completed the full $\\sim 1350\\,\\rm deg^2$ area of\nthe Kilo-Degree Survey (KiDS). Together with our previous findings, the final\nlist of high-quality candidates from KiDS sums up to 268 systems. The new\nsample is assembled using a new Convolutional Neural Network (CNN) classifier\napplied to $r$-band (best seeing) and $g,~r,~i$ color-composited images\nseparately. This optimizes the complementarity of the morphology and color\ninformation on the identification of strong lensing candidates. We apply the\nnew classifiers to a sample of luminous red galaxies (LRGs) and a sample of\nbright galaxies (BGs) and select candidates that received a high probability to\nbe a lens from the CNN ($P_{\\rm CNN}$). In particular, setting $P_{\\rm\nCNN}>0.8$ for the LRGs, the $1$-band CNN predicts 1213 candidates, while the\n$3$-band classifier yields 1299 candidates, with only $\\sim$30\\% overlap. For\nthe BGs, in order to minimize the false positives, we adopt a more conservative\nthreshold, $P_{\\rm CNN} >0.9$, for both CNN classifiers. This results in 3740\nnewly selected objects. The candidates from the two samples are visually\ninspected by 7 co-authors to finally select 97 \"high-quality\" lens candidates\nwhich received mean scores larger than 6 (on a scale from 0 to 10). We finally\ndiscuss the effect of the seeing on the accuracy of CNN classification and\npossible avenues to increase the efficiency of multi-band classifiers, in\npreparation of next-generation surveys from ground and space.", "category": "astro-ph_GA" }, { "text": "Rapid dynamical mass segregation and properties of fractal star clusters: We investigate the evolution of young star clusters using N-body simulations.\nWe confirm that subvirial and fractal-structured clusters will dynamically mass\nsegregate on a short timescale (within 0.5 Myr). We adopt a modified\nminimum-spanning-tree (MST) method to measure the degree of mass segregation,\ndemonstrating that the stars escaping from a cluster's potential are important\nfor the temporal dependence of mass segregation in the cluster. The form of the\ninitial velocity distribution will also affect the degree of mass segregation.\nIf it depends on radius, the outer parts of the cluster would expand without\nundergoing collapse. In velocity space, we find 'inverse mass segregation,'\nwhich indicates that massive stars have higher velocity dispersions than their\nlower-mass counterparts.", "category": "astro-ph_GA" }, { "text": "The Universe is at Most 88% Neutral at z=10.6: Recent observations of GN-z11 with JWST have revealed a Ly$\\alpha$ emission\nline with an equivalent width of 18$\\pm 2$ angstroms. At z=10.6, this galaxy is\nexpected to lie in the heart of reionization. We use a series of inhomogeneous\nreionization simulations to derive the distribution of the Ly$\\alpha$ EW after\ntraveling through the neutral intergalactic medium with varying average neutral\ngas fraction, $x_{HI}$. We use these distribution to place an upper limit of\n$x_{HI} < $ 0.88 at z=10.6 at 95% confidence level. We compare our upper limit\nto different reionization history models, which include the recently identified\nenhancement at the bright end of the luminosity function at z>8. We find that\nmodels in which faint galaxies have higher escape fraction compared to bright\ngalaxies are favored by the new data.", "category": "astro-ph_GA" }, { "text": "Ionization compression impact on dense gas distribution and star\n formation, Probability density functions around H ii regions as seen by\n Herschel: Ionization feedback should impact the probability distribution function (PDF)\nof the column density around the ionized gas. We aim to quantify this effect\nand discuss its potential link to the Core and Initial Mass Function (CMF/IMF).\nWe used in a systematic way Herschel column density maps of several regions\nobserved within the HOBYS key program: M16, the Rosette and Vela C molecular\ncloud, and the RCW 120 H ii region. We fitted the column density PDFs of all\nclouds with two lognormal distributions, since they present a double-peak or\nenlarged shape in the PDF. Our interpretation is that the lowest part of the\ncolumn density distribution describes the turbulent molecular gas while the\nsecond peak corresponds to a compression zone induced by the expansion of the\nionized gas into the turbulent molecular cloud. The condensations at the edge\nof the ionized gas have a steep compressed radial profile, sometimes\nrecognizable in the flattening of the power-law tail. This could lead to an\nunambiguous criterion able to disentangle triggered from pre-existing star\nformation. In the context of the gravo-turbulent scenario for the origin of the\nCMF/IMF, the double peaked/enlarged shape of the PDF may impact the formation\nof objects at both the low-mass and the high-mass end of the CMF/IMF. In\nparticular a broader PDF is required by the gravo-turbulent scenario to fit\nproperly the IMF with a reasonable initial Mach number for the molecular cloud.\nSince other physical processes (e.g. the equation of state and the variations\namong the core properties) have already been suggested to broaden the PDF, the\nrelative importance of the different effects remains an open question.", "category": "astro-ph_GA" }, { "text": "Exploring AGN - starburst coexistence in galaxies at z$\\sim$ 0.8 by the\n [OIII]4959+5007/[OIII]4363 line ratio: We analyze by detailed modelling the spectra observed from the sample\ngalaxies at z$\\sim$0.8 presented by Ly et al (2015), constraining the models by\nthe [OIII]5007+4959/[OIII]4363 line ratios. Composite models accounting for\nshock and photoionization by AGN or starburst are adopted. O/H are about solar\nfor all the objects, except for a few AGN clouds with O/H= 0.3 -0.5 solar.\nStarburst models reproduce most of the data within the observational errors.\nAbout half of the object spectra are well fitted by an accreting AGN. Some\ngalaxies show multiple radiation sources, such as starburst+AGN, or a double\nAGN.", "category": "astro-ph_GA" }, { "text": "A Photometric and Kinematic Analysis of UDG1137+16 (dw1137+16): Probing\n Ultra-Diffuse Galaxy Formation in a Group Environment: The dominant physical formation mechanism(s) for ultra-diffuse galaxies\n(UDGs) is still poorly understood. Here, we combine new, deep imaging from the\nJeanne Rich Telescope with deep integral field spectroscopy from the Keck II\ntelescope to investigate the formation of UDG1137+16 (dw1137+16). Our new\nanalyses confirm both its environmental association with the low density UGC\n6594 group, along with its large size of 3.3 kpc and status as a UDG. The new\nimaging reveals two distinct stellar components for UDG1137+16, indicating that\na central stellar body is surrounded by an outer stellar envelope undergoing\ntidal interaction. Both the components have approximately similar stellar\nmasses. From our integral field spectroscopy we measure a stellar velocity\ndispersion within the half-light radius (15 $\\pm$ 4 $\\mathrm{km\\ s^{-1}}$) and\nfind that UDG1137+16 is similar to some other UDGs in that it is likely dark\nmatter dominated. Incorporating literature measurements, we also examine the\ncurrent state of UDG observational kinematics. Placing these data on the\ncentral stellar velocity dispersion -- stellar mass relation, we suggest there\nis little evidence for UDG1137+16 being created through a strong tidal\ninteraction. Finally, we investigate the constraining power current dynamical\nmass estimates (from stellar and globular cluster velocity dispersions) have on\nthe total halo mass of UDGs. As most are measured within the half-light radius,\nthey are unable to accurately constrain UDG total halo masses.", "category": "astro-ph_GA" }, { "text": "Physical properties of circumnuclear ionising clusters. II. NGC 7469: Circumnuclear star forming regions (CNSFR) are massive clusters found close\nto galactic nuclei. These entities give us an excellent opportunity to study\nstar formation in environments with high metallicity and to relate it with\nactive galactic nuclei. Our principal aim is to derive the physical properties\nand dynamical masses of the CNSFRs in the two rings of the spiral NGC 7469,\ncategorized as a Luminous Infrared Galaxy (ULIRG) and hosting a Seyfert 1\nnucleus. We have used archival data obtained with the MUSE spectrograph\nattached to one of the ESO VLT telescopes and we have applied the techniques\nshown in the first paper of the series. Regions in the studied galaxy show\nlarge sizes which can be explained by the stellar winds produced by WR stars.\nThe inner ring regions seem to be more compact than the outer ones, showing\nhigher electron densities and filling factors. The young stellar population of\nthe clusters has contributions of ionising populations with ages around 5 Ma\nand its masses constitute less than a 1\\% of the total mass of each cluster.\nThe inner ring regions which are close to the active galactic nucleus probably\nare the only ones that have enough mass to survive the action of the AGN. They\nconstitute the $\\sim$ 90 \\% of the total inner ring mass.", "category": "astro-ph_GA" }, { "text": "First images of the molecular gas around a born-again star revealed by\n ALMA: Born-again stars allow probing stellar evolution in human timescales and\nprovide the most promising path for the formation of hydrogen-deficient\npost-asymptotic giant branch objects, but their cold and molecular components\nremain poorly explored. Here we present ALMA observations of V605 Aql that\nunveil for the first time the spatio-kinematic distribution of the molecular\nmaterial associated to a born-again star. Both the continuum and molecular line\nemission exhibit a clumpy ring-like structure with a total extent of\n$\\approx$1$^{\\prime\\prime}$ in diameter. The bulk of the molecular emission is\ninterpreted as being produced in a radially-expanding disk-like structure with\nan expansion velocity v$_{\\rm exp}$$\\sim$90 km s$^{-1}$ and an inclination\n$i$$\\approx$60$^{\\circ}$ with respect to the line-of-sight. The observations\nalso reveal a compact high-velocity component, v$_{\\rm exp}$$\\sim$280 km\ns$^{-1}$, that is aligned perpendicularly to the expanding disk. This component\nis interpreted as a bipolar outflow with a kinematical age $\\tau$$\\lesssim$20\nyr, which could either be material that is currently being ejected from V605\nAql, or it is being dragged from the inner parts of the disk by a stellar wind.\nThe dust mass of the disk is in the range $M_{\\rm\ndust}$$\\sim$0.2-8$\\times$10$^{-3}$ M$_{\\odot}$, depending on the dust\nabsorption coefficient. The mass of the CO is $M_{\\rm\nCO}$$\\approx$1.1$\\times10^{-5}$ $M_{\\odot}$, which is more than three orders of\nmagnitude larger than the mass of the other detected molecules. We estimate a\n$^{12}$C/$^{13}$C ratio of 5.6$\\pm$0.6, which is consistent with the single\nstellar evolution scenario in which the star experienced a very late thermal\npulse instead of a nova-like event as previously suggested.", "category": "astro-ph_GA" }, { "text": "An [$\u03b1$/Fe]-enhanced thick disk in a Milky Way Analogue: The Milky Way disk consists of two prominent components - a thick,\nalpha-rich, low-metallicity component and a thin, metal-rich, low-alpha\ncomponent. External galaxies have been shown to contain thin and thick disk\ncomponents, but whether distinct components in the [$\\alpha$/Fe]-[Z/H] plane\nexist in other Milky Way-like galaxies is not yet known. We present VLT-MUSE\nobservations of UGC 10738, a nearby, edge-on Milky Way-like galaxy. We\ndemonstrate through stellar population synthesis model fitting that UGC 10738\ncontains alpha-rich and alpha-poor stellar populations with similar spatial\ndistributions to the same components in the Milky Way. We discuss how the\nfinding that external galaxies also contain chemically distinct disk components\nmay act as a significant constraint on the formation of the Milky Way's own\nthin and thick disk.", "category": "astro-ph_GA" }, { "text": "Galactic Orbits of Globular Clusters in the Region of the Galactic Bulge: Galactic orbits have been constructed over long time intervals for ten\nglobular clusters located near the Galactic center. A model with an axially\nsymmetric gravitational potential for the Galaxy was initially applied, after\nwhich a non-axially symmetric potential corresponding to the central bar was\nadded. Variations in the trajectories of all these globular clusters in the XY\nplane due to the influence of the bar were detected. These were greatest for\nthe cluster Terzan 4 in the meridional (RZ) plane. The globular clusters Terzan\n1, Terzan 2, Terzan 4, Terzan 9, NGC 6522, and NGC 6558 always remained within\nthe Galactic bulge, no farther than 4 kpc from the Galactic center.", "category": "astro-ph_GA" }, { "text": "Cosmic rays in molecular clouds probed by H$_{2}$ rovibrational lines --\n Perspectives for the James Webb Space Telescope: Cosmic rays (CRs) at sub-TeV energies play a fundamental role in the chemical\nand dynamical evolution of molecular clouds, as they control the ionisation,\ndissociation, and excitation of H$_{2}$. Their characterisation is important\nboth for the interpretation of observations and for the development of\ntheoretical models. The methods used so far for estimating the CR ionisation\nrate ($\\zeta$) in molecular clouds have several limitations due to\nuncertainties in the adopted chemical networks. We refine and extend the method\nproposed by Bialy (2020) to estimate $\\zeta$ by observing rovibrational\ntransitions of H$_{2}$ at near-infrared wavelengths, which are mainly excited\nby secondary CR electrons. Combining models of interstellar CR propagation and\nattenuation with the calculation of the expected secondary electron spectrum\nand updated H$_{2}$ excitation cross sections by electron collisions, we derive\nthe intensity of the four H$_{2}$ rovibrational transitions observable in\ndense, cold gas: (1-0)O(2), (1-0)Q(2), (1-0)S(0), and (1-0)O(4). The proposed\nmethod allows the estimation of $\\zeta$ for a given observed line intensity and\nH$_{2}$ column density. We are also able to deduce the shape of the low-energy\nCR proton spectrum impinging upon the molecular cloud. We present a look-up\nplot and a web-based application that can be used to constrain the low-energy\nspectral slope of the interstellar CR proton spectrum. We comment on the\ncapability of the James Webb Space Telescope to detect these near-infrared\nH$_{2}$ lines, making it possible to derive for the first time spatial\nvariation of $\\zeta$ in dense gas. Besides the implications for the\ninterpretation of the chemical-dynamic evolution of a molecular cloud, it will\nbe possible to test competing models of CR propagation and attenuation in the\ninterstellar medium, as well as compare CR spectra in different Galactic\nregions.", "category": "astro-ph_GA" }, { "text": "A Gaia based photometric and kinematic analysis of the old open cluster\n King 11: This paper presents an investigation of an old age open cluster King 11 using\nGaia's Early Data Release 3 (EDR3) data. Considering the stars with membership\nprobability ($P_{\\mu}$) $> 90\\%$, we identified 676 most probable cluster\nmembers within the cluster's limiting radius. The mean proper motion (PM) for\nKing 11 is determined as: $\\mu_{x}=-3.391\\pm0.006$ and $\\mu_{y}=-0.660\\pm0.004$\nmas yr$^{-1}$. The blue straggler stars (BSS) of King 11 show a centrally\nconcentrated radial distribution. The values of limiting radius, age, and\ndistance are determined as 18.51 arcmin, 3.63$\\pm$0.42 Gyr and $3.33\\pm0.15$\nkpc, respectively. The cluster's apex coordinates ($A=267.84^{\\circ} \\pm\n1.01^{\\circ}$, $D=-27.48^{\\circ} \\pm 1.03^{\\circ}$) are determined using the\napex diagram (AD) method and verified using the ($\\mu_U$,$\\mu_T$) diagram. We\nalso obtained the orbit that the cluster follows in the Galaxy and estimated\nits tentative birthplace in the disk. The resulting spatial velocity of King 11\nis 60.2 $\\pm$ 2.16 km s$^{-1}$. A significant oscillation along the\n$Z$-coordinate up to 0.556$\\pm$0.022~kpc is determined.", "category": "astro-ph_GA" }, { "text": "Star formation in the outskirts of DDO 154: A top-light IMF in a nearly\n dormant disc: We present optical photometry of Hubble Space Telescope (HST) ACS/WFC data of\nthe resolved stellar populations in the outer disc of the dwarf irregular\ngalaxy DDO 154. The photometry reveals that young main sequence stars are\nalmost absent from the outermost HI disc. Instead, most are clustered near the\nmain stellar component of the galaxy. We constrain the stellar initial mass\nfunction (IMF) by comparing the luminosity function of the main sequence stars\nto simulated stellar populations assuming a constant star formation rate over\nthe dynamical timescale. The best-fitting IMF is deficient in high mass stars\ncompared to a canonical Kroupa IMF, with a best-fit slope $\\alpha = -2.45$ and\nupper mass limit $M_U = 16\\ M_{\\odot}$. This top-light IMF is consistent with\npredictions of the Integrated Galaxy-wide IMF theory. Combining the HST images\nwith HI data from The HI Nearby Galaxy Survey Treasury (THINGS) we determine\nthe star formation law (SFL) in the outer disc. The fit has a power law\nexponent $N = 2.92 \\pm0.22$ and zero point $A=4.47 \\pm 0.65 \\times 10^{-7} \\\nM_{\\odot} \\ \\text{yr}^{-1} \\ \\text{kpc}^{-2}$. This is depressed compared to\nthe Kennicutt-Schmidt Star Formation Law, but consistent with weak star\nformation observed in diffuse HI environments. Extrapolating the SFL over the\nouter disc implies that there could be significant star formation occurring\nthat is not detectable in H$\\alpha$. Last, we determine the Toomre stability\nparameter $Q$ of the outer disc of DDO 154 using the THINGS HI rotation curve\nand velocity dispersion map. 72% of the HI in our field has $Q\\leq 4$ and this\nincorporates 96% of the observed MS stars. Hence 28% of the HI in the field is\nlargely dormant.", "category": "astro-ph_GA" }, { "text": "The nuclear properties and extended morphologies of powerful radio\n galaxies: the roles of host galaxy and environment: Powerful radio galaxies exist as either compact or extended sources, with the\nextended sources traditionally classified by their radio morphologies as\nFanaroff--Riley (FR) type I and II sources. FRI/II and compact radio galaxies\nhave also been classified by their optical spectra into two different types:\nhigh excitation (HERG; quasar-mode) and low excitation (LERG; jet-mode). We\npresent a catalogue of visual morphologies for a complete sample of $>$1000\n1.4-GHz-selected extended radio sources from the Sloan Digital Sky Survey. We\nstudy the environment and host galaxy properties of FRI/II and compact sources,\nclassified into HERG/LERG types, in order to separate and distinguish the\nfactors that drive the radio morphological variations from those responsible\nfor the spectral properties. Comparing FRI LERGs with FRII LERGs at fixed\nstellar mass and radio luminosity, we show that FRIs typically reside in richer\nenvironments and are hosted by smaller galaxies with higher mass surface\ndensity; this is consistent with extrinsic effects of jet disruption driving\nthe FR dichotomy. Using matched samples of HERGs and LERGs, we show that HERG\nhost galaxies are more frequently star-forming, with more evidence for\ndisk-like structure than LERGs, in accordance with currently-favoured models of\nfundamentally different fuelling mechanisms. Comparing FRI/II LERGs with\ncompact LERGs, we find the primary difference is that compact objects typically\nharbour less massive black holes. This suggests that lower-mass black holes may\nbe less efficient at launching stable radio jets, or do so for shorter times.\nFinally, we investigate rarer sub-classes: wide-angle tail, head-tail,\nFR-hybrid and double-double sources.", "category": "astro-ph_GA" }, { "text": "Preliminary results of using k-Nearest Neighbours Regression to estimate\n the redshift of radio selected datasets: In the near future, all-sky radio surveys are set to produce catalogues of\ntens of millions of sources with limited multi-wavelength photometry.\nSpectroscopic redshifts will only be possible for a small fraction of these\nnew-found sources. In this paper, we provide the first in-depth investigation\ninto the use of k-Nearest Neighbours Regression for the estimation of redshift\nof these sources. We use the Australia Telescope Large Area Survey radio data,\ncombined with the Spitzer Wide-Area Infrared Extragalactic Survey infra-red,\nthe Dark Energy Survey optical and the Australian Dark Energy Survey\nspectroscopic survey data. We then reduce the depth of photometry to match what\nis expected from upcoming Evolutionary Map of the Universe survey, testing\nagainst both data sets. To examine the generalisation of our methods, we test\none of the sub-fields of Australia Telescope Large Area Survey against the\nother. We achieve an outlier rate of ~10% across all tests, showing that the\nk-Nearest Neighbours regression algorithm is an acceptable method of estimating\nredshift, and would perform better given a sample training set with uniform\nredshift coverage.", "category": "astro-ph_GA" }, { "text": "The WISSH quasars project XI. The mean Spectral Energy Distribution and\n Bolometric Corrections of the most luminous quasars: Hyper-luminous Quasi-Stellar Objects (QSOs) represent the ideal laboratory to\ninvestigate Active Galactic Nuclei (AGN) feedback mechanism since their\nformidable energy release causes powerful winds at all scales and thus the\nmaximum feedback is expected.\n We aim at deriving the mean Spectral Energy Distribution (SED) of a sample of\n85 WISE-SDSS Selected Hyper-luminous (WISSH) quasars. Since the SED provides a\ndirect way to investigate the AGN structure, our goal is to understand if\nquasars at the bright end of the luminosity function have peculiar properties\ncompared to the bulk of the population. We built a mean intrinsic SED after\ncorrecting for the dust extinction, absorption and emission lines and\nintergalactic medium absorption. We also derived bolometric, IR band and\nmonochromatic luminosities together with bolometric corrections at lambda =\n5100 A and 3 micron. We define a new relation for the 3 micron bolometric\ncorrection. We find that the mean SED of hyper-luminous WISSH QSOs is different\nfrom that of less luminous sources, i.e. a relatively lower X-ray emission and\na near and mid IR excess which can be explained assuming a larger dust\ncontribution. WISSH QSOs have stronger emission from both warm and very hot\ndust, the latter being responsible for shifting the typical dip of the AGN SED\nfrom 1.3 to 1.1 micron. We also derived the mean SEDs of two sub-samples\ncreated according to the presence of Broad Absorption Lines and equivalent\nwidth of CIV line. We confirm that BALs are X-ray weak and that they have a\nreddened UV-optical continuum. We also find that BALs tend to have stronger\nemission from the hot dust component. This analysis suggests that\nhyper-luminous QSOs have a peculiar SED compared to less luminous objects. It\nis therefore critical to use SED templates constructed exclusively from very\nbright quasars samples when dealing with particularly luminous sources.", "category": "astro-ph_GA" }, { "text": "Period-Luminosity Relations for Galactic classical Cepheids in the Sloan\n bands: We present the first period-luminosity (PL) and period-Wesenheit (PW)\nrelations in the Sloan-Pans-STARRS gP1rP1iP1 bands for classical fundamental\nmode Cepheids in the Milky Way. We used a relatively modest number of 76 stars\nfor the PL and 84-85 stars for the PW relations calibration. The data for the\nproject were collected with the network of 40-cm telescopes of Las Cumbres\nObservatory, and Gaia Data Release 3 parallaxes were used for the calculations.\nThese gri-band PL and PW relations calibrations will be a useful tool for\ndistance determinations in the era of large sky surveys using the Sloan\nphotometric system, especially with the near-future start of the Large Synoptic\nSurvey of Space and Time (LSST).", "category": "astro-ph_GA" }, { "text": "AGN-driven Cold Gas Outflow of NGC 1068 Characterized by\n Dissociation-Sensitive Molecules: Recent developments in (sub-)millimeter facilities have drastically changed\nthe amount of information obtained from extragalactic spectral scans. In this\npaper, we present a feature extraction technique using principal component\nanalysis (PCA) applied to arcsecond-resolution (1.0-2.0 arcsec = 72-144 pc)\nspectral scan datasets for the nearby type-2 Seyfert galaxy, NGC 1068, using\nBand 3 of the Atacama Large Millimeter/submillimeter Array. We apply PCA to 16\nwell-detected molecular line intensity maps convolved to a common 150 pc\nresolution. In addition, we include the [SIII]/[SII] line ratio and [CI]\n$^3P_1$-$^3P_0$ maps in the literature, both of whose distributions show\nremarkable resemblance with that of a kpc-scale biconical outflow from the\ncentral AGN. We identify two prominent features: (1) central concentration at\nthe circumnuclear disk (CND) and (2) two peaks across the center that coincide\nwith the biconical outflow peaks. The concentrated molecular lines in the CND\nare mostly high-dipole molecules (e.g., H$^{13}$CN, HC$_3$N, and HCN). Line\nemissions from molecules known to be enhanced in irradiated interstellar\nmedium, CN, C$_2$H, and HNC, show similar concentrations and extended\ncomponents along the bicone, suggesting that molecule dissociation is a\ndominant chemical effect of the cold molecular outflow of this galaxy. Although\nfurther investigation should be made, this scenario is consistent with the\nfaintness or absence of the emission lines from CO isotopologues, CH$_3$OH, and\nN$_2$H$^+$, in the outflow, which are easily destroyed by dissociating photons\nand electrons.", "category": "astro-ph_GA" }, { "text": "Extremely inverted peaked spectrum radio sources: We report our ongoing search for extremely inverted spectrum compact radio\ngalaxies, for which the defining feature in the radio spectrum is not the\nspectral peak, but instead the slope of the spectrum (alpha) in the\nhigh-opacity (i.e., lower frequency) part of the radio spectrum. Specifically,\nour focus is on the spectral regime with spectral index, alpha >+2.5. The\nmotivation for our study is, firstly, extragalactic sources with such extreme\nspectral index are extremely rare, because of the unavailability of right\ncombination of sensitivity and resolution over a range of low frequencies. The\nsecond reason is more physically motivated, since alpha = +2.5 is the maximum\nslope theoretically possible for a standard radio source emitting synchrotron\nradiation. Therefore such sources could be the test-bed for some already\nproposed alternative scenarios for synchrotron self-absorption (SSA), like the\nfree-free absorption (FFA) highlighting the importance of jet-ISM interaction\nin the radio galaxy evolution.", "category": "astro-ph_GA" }, { "text": "Discovery of a very Lyman-$\u03b1$-luminous quasar at z=6.62: Distant luminous quasars provide important information on the growth of the\nfirst supermassive black holes, their host galaxies and the epoch of\nreionization. The identification of quasars is usually performed through\ndetection of their Lyman-$\\alpha$ line redshifted to $\\sim$ 0.9 microns at\nz>6.5. Here, we report the discovery of a very Lyman-$\\alpha$ luminous quasar,\nPSO J006.1240+39.2219 at redshift z=6.618, selected based on its red colour and\nmulti-epoch detection of the Lyman-$\\alpha$ emission in a single near-infrared\nband. The Lyman-$\\alpha$-line luminosity of PSO J006.1240+39.2219 is unusually\nhigh and estimated to be 0.8$\\times$10$^{12}$ Solar luminosities (about 3% of\nthe total quasar luminosity). The Lyman-$\\alpha$ emission of PSO\nJ006.1240+39.2219 shows fast variability on timescales of days in the quasar\nrest frame, which has never been detected in any of the known high-redshift\nquasars. The high luminosity of the Lyman-$\\alpha$ line, its narrow width and\nfast variability resemble properties of local Narrow-Line Seyfert 1 galaxies\nwhich suggests that the quasar is likely at the active phase of the black hole\ngrowth accreting close or even beyond the Eddington limit.", "category": "astro-ph_GA" }, { "text": "Lens galaxies in the Illustris simulation: power-law models and the bias\n of the Hubble constant from time-delays: A power-law density model, i.e., $\\rho(r) \\propto r^{-\\gamma'}$ has been\ncommonly employed in strong gravitational lensing studies, including the\nso-called time-delay technique used to infer the Hubble constant $H_0$.\nHowever, since the radial scale at which strong lensing features are formed\ncorresponds to the transition from the dominance of baryonic matter to dark\nmatter, there is no known reason why galaxies should follow a power law in\ndensity. The assumption of a power law artificially breaks the mass-sheet\ndegeneracy, a well-known invariance transformation in gravitational lensing\nwhich affects the product of Hubble constant and time delay and can therefore\ncause a bias in the determination of $H_0$ from the time-delay technique. In\nthis paper, we use the Illustris hydrodynamical simulations to estimate the\namplitude of this bias, and to understand how it is related to observational\nproperties of galaxies. Investigating a large sample of Illustris galaxies that\nhave velocity dispersion $\\sigma_{SIE}$>160 km/s at redshifts below $z=1$, we\nfind that the bias on $H_0$ introduced by the power-law assumption can reach\n20%-50%, with a scatter of $10\\%-30\\%$ (rms). However, we find that by\nselecting galaxies with an inferred power-law model slope close to isothermal,\nit is possible to reduce the bias on $H_0$ to <5%, and the scatter to <10%.\nThis could potentially be used to form less biased statistical samples for\n$H_0$ measurements in the upcoming large survey era.", "category": "astro-ph_GA" }, { "text": "Magnetic field measurement in TMC-1C using 22.3 GHz CCS Zeeman splitting: Measurement of magnetic fields in dense molecular clouds is essential for\nunderstanding the fragmentation process prior to star formation. Radio\ninterferometric observations of CCS 22.3 GHz emission, from the starless core\nTMC-1C, have been carried out with the Karl G. Jansky Very Large Array to\nsearch for Zeeman splitting of the line in order to constrain the magnetic\nfield strength. Toward a region offset from the dust peak, we report a\ndetection of the Zeeman splitting of the CCS 2_1 - 1_0 transition, with an\ninferred magnetic field of ~2 mG. If we interpret the dust peak to be the core\nof TMC-1C, and the region where we have made a detection of the magnetic field\nto be the envelope, then our observed value for the magnetic field is\nconsistent with a subcritical mass-to-flux ratio envelope around a core with\nsupercritical mass-to-flux ratio. The ambipolar diffusion timescale for the\nformation of the core is consistent with the relevant timescale based on\nchemical modeling of the TMC-1C core. This work demonstrates the potential of\ndeep CCS observation to carry out future measurements of magnetic field\nstrengths in dense molecular clouds and, in turn, understand the role of the\nmagnetic field in star formation.", "category": "astro-ph_GA" }, { "text": "Kinematics and Mass Modeling of Messier 33: Halpha observations: As part of a long-term project to revisit the kinematics and dynamics of the\nlarge disc galaxies of the Local Group, we present the first deep, wide-field\n(42' x 56') 3D-spectroscopic survey of the ionized gas disc of Messier 33.\nFabry-Perot interferometry has been used to map its Ha distribution and\nkinematics at unprecedented angular resolution (<3'') and resolving power\n(12600), with the 1.6m telescope at the Observatoire du Mont Megantic. The\nionized gas distribution follows a complex, large-scale spiral structure,\nunsurprisingly coincident with the already-known spiral structures of the\nneutral and molecular gas discs. The kinematical analysis of the velocity field\nshows that the rotation center of the Ha disc is distant from the photometric\ncenter by 170 pc (sky projected distance) and that the kinematical major-axis\nposition angle and disc inclination are in excellent agreement with photometric\nvalues. The Ha rotation curve agrees very well with the HI rotation curves for\n0 < R < 6.5 kpc, but the Ha velocities are 10-20 km/s higher for R > 6.5 kpc.\nThe reason for this discrepancy is not well understood. The velocity dispersion\nprofile is relatively flat around 16 km/s, which is at the low end of velocity\ndispersions of nearby star-forming galactic discs. A strong relation is also\nfound between the Ha velocity dispersion and the Ha intensity. Mass models were\nobtained using the Ha rotation curve but, as expected, the dark matter halo's\nparameters are not very well constrained since the optical rotation curve only\nextends out to 8 kpc.", "category": "astro-ph_GA" }, { "text": "Mid Infrared View of the High Mass Star Formation Region W51A: In this paper we present the results of a mid infrared study of G49.5-0.4, or\nW51A, part of the massive starbirth complex W51. Combining public data from the\n$Spitzer$ IRAC camera, and Gemini mid infrared camera T-ReCS at 7.73, 9.69,\n12.33 and 24.56 \\micron, with spatial resolution of $\\sim$0.5\\arcsec, we have\nidentified the mid infrared counterparts of 8 ultracompact HII regions, showing\nthat two radio sources are deeply embedded in molecular clouds and another is a\ncloud of ionized gas. From the T-ReCS data we have unveiled the central core of\nW51 region, revealing massive young stellar candidates. We modeled the spectral\nenergy distribution of the detected sources suggesting the embedded objects are\nsources with spectral types ranging from B3 to O5, but the majority of the fits\nindicate stellar objects with B1 spectral types. We also present an extinction\nmap of IRS~2, showing that a region with lower extinction corresponds to the\nregion where a proposed jet of gas has impacted the foreground cloud. From this\nmap, we also derived the total extinction towards the enigmatic source IRS~2E,\nwhich amounts to $\\sim$60 magnitudes in the $V$ band. We calculated the color\ntemperature due to thermal emission of the circumstellar dust of the detected\nsources; the temperatures are in the interval of $\\sim$100 -- 150 K, which\ncorresponds to the emission of dust located at 0.1 pc from the central source.\nFinally, we show a possible mid infrared counterpart of a detected source at mm\nwavelengths that was found by \\cite{zap08,zap09} to be a massive young stellar\nobject undergoing a high accretion rate.", "category": "astro-ph_GA" }, { "text": "How the power spectrum of dust continuum images may hide the presence of\n a characteristic filament width: Herschel observations of interstellar clouds support a paradigm for star\nformation in which filaments play a central role. One of the foundations of\nthis paradigm is the finding, based on studies of the radial column density\nprofiles, that nearby filaments share a common inner width of ~0.1 pc. The\nexistence of a characteristic filament width has been questioned, however, as\nit seems inconsistent with the scale-free nature of the power spectrum of cloud\nimages.\n In an effort to clarify the origin of this apparent discrepancy, we examined\nthe power spectra of the Herschel 250 micron images of the Polaris, Aquila, and\nTaurus clouds and performed a number of simple numerical experiments by\ninjecting synthetic filaments in both the Herschel images and synthetic\nbackground images.\n We constructed several populations of synthetic filaments of 0.1 pc width\nwith realistic area filling factors ($A_{\\rm fil}$) and distributions of column\ndensity contrasts ($\\delta_c$). After adding synthetic filaments to the\nHerschel images, we re-computed the image power spectra and compared the\nresults with the original, essentially scale-free power spectra. We used the\n$\\chi^2$ variance of the residuals between the best power-law fit and the\noutput power spectrum as a diagnostic of the presence of a significant\ndeparture from a scale-free power spectrum.\n We found that the $\\chi^2$ variance depends primarily on the combined\nparameter $\\delta_c^2\\, A_{\\rm fil}$. Analysis of the real Herschel data shows\nthat the observed filamentary structure contributes only 1/5 of the power in\nthe power spectra at angular frequencies where an effect of the characteristic\nfilament width is expected.\n We conclude that the scale-free power spectra of Herschel images remain\nconsistent with the existence of a characteristic filament width ~0.1 pc and do\nnot invalidate the conclusions drawn from studies of the filament profiles.", "category": "astro-ph_GA" }, { "text": "An accurate low-redshift measurement of the cosmic neutral hydrogen\n density: Using a spectral stacking technique, we measure the neutral hydrogen (HI)\nproperties of a sample of galaxies at $z < 0.11$ across 35 pointings of the\nWesterbork Synthesis Radio Telescope (WSRT). The radio data contains 1,895\ngalaxies with redshifts and positions known from the Sloan Digital Sky Survey\n(SDSS). We carefully quantified the effects of sample bias, aperture used to\nextract spectra, sidelobes and weighting technique and use our data to provide\na new estimate for the cosmic HI mass density. We find a cosmic HI mass density\nof $\\Omega_{\\rm HI} = (4.02 \\pm 0.26)\\times 10^{-4} h_{70}^{-1}$ at $\\langle\nz\\rangle = 0.066$, consistent with measurements from blind HI surveys and other\nHI stacking experiments at low redshifts. The combination of the small\ninterferometer beam size and the large survey volume makes our result highly\nrobust against systematic effects due to confusion at small scales and cosmic\nvariance at large scales. Splitting into three sub-samples with $\\langle\nz\\rangle$ = 0.038, 0.067 and 0.093 shows no significant evolution of the HI gas\ncontent at low redshift.", "category": "astro-ph_GA" }, { "text": "Stellar Velocity Dispersion in Mergers: The Effects of Dust and Star\n Formation: We investigate the effects of stellar evolution and dust on measurements of\nstellar velocity dispersion in mergers of disk galaxies. $N$-body simulations\nand radiative transfer analysis software are used to obtain mass-weighted and\nflux-weighted measurements of stellar velocity dispersion. We find that the\ndistribution of dust with respect to the distribution of young stars in such\nsystems is more important than the total degree of attenuation. The presence of\ndust typically causes flux-weighted measurements of stellar velocity dispersion\nto be elevated with respect to mass-weighted measurements because dust\npreferentially obscures young stars, which tend to be dynamically cooler than\nolder stellar populations in such systems. In exceptional situations, in which\nyoung stars are not preferentially obscured by dust, flux-weighted velocity\ndispersion measurements tend to be negatively offset with respect to\nmass-weighted measurements because the dynamically cool young stellar\npopulations are more luminous, per unit mass, than older stellar populations.\nOur findings provide a context for comparing observationally-obtained\nmeasurements of velocity dispersion with measurements of velocity dispersion\nobtained from galaxy merger simulations.", "category": "astro-ph_GA" }, { "text": "Linking Compact Dwarf Starburst Galaxies in the RESOLVE Survey to\n Downsized Blue Nuggets: We identify and characterize compact dwarf starburst (CDS) galaxies in the\nRESOLVE survey, a volume-limited census of galaxies in the local universe, to\nprobe whether this population contains any residual ``blue nuggets,'' a class\nof intensely star-forming compact galaxies first identified at high redshift\n$z$. Our 50 low-$z$ CDS galaxies are defined by dwarf masses (stellar mass $M_*\n< 10^{9.5}$ M$_{\\odot}$), compact bulged-disk or spheroid-dominated\nmorphologies (using a quantitative criterion, $\\mu_\\Delta > 8.6$), and specific\nstar formation rates above the defining threshold for high-$z$ blue nuggets\n($\\log$ SSFR [Gyr$^{-1}] > -0.5$). Across redshifts, blue nuggets exhibit three\ndefining properties: compactness relative to contemporaneous galaxies, abundant\ncold gas, and formation via compaction in mergers or colliding streams. Those\nwith halo mass below $M_{\\rm halo} \\sim 10^{11.5}$ M$_{\\odot}$ may in theory\nevade permanent quenching and cyclically refuel until the present day. Selected\nonly for compactness and starburst activity, our CDS galaxies generally have\n$M_{\\rm halo} \\lesssim 10^{11.5}$ M$_{\\odot}$ and gas-to-stellar mass ratio\n$\\gtrsim$1. Moreover, analysis of archival DECaLS photometry and new 3D\nspectroscopic observations for CDS galaxies reveals a high rate of photometric\nand kinematic disturbances suggestive of dwarf mergers. The SSFRs, surface mass\ndensities, and number counts of CDS galaxies are compatible with theoretical\nand observational expectations for redshift evolution in blue nuggets. We argue\nthat CDS galaxies represent a maximally-starbursting subset of traditional\ncompact dwarf classes such as blue compact dwarfs and blue E/S0s. We conclude\nthat CDS galaxies represent a low-$z$ tail of the blue nugget phenomenon formed\nvia a moderated compaction channel that leaves open the possibility of disk\nregrowth and evolution into normal disk galaxies.", "category": "astro-ph_GA" }, { "text": "Bivariate Luminosity Function of Galaxy Pairs: We measure the bivariate luminosity function (BLF) of galaxy pairs and use it\nto probe and characterize the galaxy-galaxy interaction between pair members.\nThe galaxy pair sample is selected from the main galaxy sample of Sloan Digital\nSky Survey and supplied with a significant number of redshifts from the LAMOST\nspectral and GAMA surveys. We find the BLFs depend on the projected distance\n$d_{\\text{p}}$ between pair members. At large separation $d_{\\text{p}} > 150\nh^{-1}\\ \\text{kpc}$, the BLF degenerates into a luminosity function (LF) of\nsingle galaxies, indicating few interactions between pair members. At $100\nh^{-1}\\ \\text{kpc} \\leq d_{\\text{p}} \\leq 150 h^{-1}\\ \\text{kpc}$, the BLF\nstarts to show the correlation between pair members, in the sense that the\nshape of the conditional luminosity function (CLF) of one member galaxy starts\nto depend on the luminosity of the other member galaxy. Specifically, the CLF\nwith a brighter companion has a steeper faint-end slope, which becomes even\nmore significant at $50 h^{-1}\\ \\text{kpc} \\leq d_{\\text{p}} \\leq 100 h^{-1}\\\n\\text{kpc}$. This behavior is consistent with the scenario, \\textit{and also is\nthe observational evidence}, that dynamic friction drives massive major merger\npairs to merge more quickly. At close distance $d_{\\text{p}} \\leq 50 h^{-1}\\\n\\text{kpc}$, besides the merging time-scale effect, the BLF also shows an\noverall brightening of $\\Delta M_r \\geq 0.04$ mag, which reveals the enhanced\nstar formation of the close-pair phase. By combining another statistical\nconclusion that the star formation rate of late-type galaxies in close pairs is\nenhanced at a level of about 40\\%, we further conclude that the average\nstarburst time-scale of close pairs is as long as 0.4 Gyr.", "category": "astro-ph_GA" }, { "text": "How do disks and planetary systems in high-mass open clusters differ\n from those around field stars?: Only star clusters that are sufficiently compact and massive survive largely\nunharmed beyond 10 Myr. However, their compactness means a high stellar density\nwhich can lead to strong gravitational interactions between the stars. As young\nstars are often initially surrounded by protoplanetary disks and later on\npotentially by planetary systems, the question arises to what degree these\nstrong gravitational interactions influence planet formation and the properties\nof planetary systems. Here, we perform simulations of the evolution of compact\nhigh-mass clusters like Trumpler 14 and Westerlund 2 from the embedded to the\ngas-free phase and study the influence of stellar interactions. We concentrate\non the development of the mean disk size in these environments. Our simulations\nshow that in high-mass open clusters $80-90\\%$ of all disks/planetary systems\nshould be smaller than 50 AU just due to the strong stellar interactions in\nthese environments. Already in the initial phases, 3-4 close fly-bys lead to\ntypical disk sizes within the range of 18-27 AU. Afterwards, the disk sizes are\naltered only to a small extent. Our findings agree with the recent observation\nthat the disk sizes in the once dense environment of the Upper Scorpio OB\nassociation, NGC~2362, and h/$\\chi$Persei are at least three times smaller in\nsize than, for example, in Taurus. We conclude that the observed planetary\nsystems in high-mass open clusters should also be on average smaller than those\nfound around field stars; in particular, planets on wide orbits are expected to\nbe extremely rare in such environments.", "category": "astro-ph_GA" }, { "text": "The Mass Distributions of Starless and Protostellar Cores in Gould Belt\n Clouds: Using data from the SCUBA Legacy Catalogue (850 um) and Spitzer Space\nTelescope (3.6 - 70 um), we explore dense cores in the Ophiuchus, Taurus,\nPerseus, Serpens, and Orion molecular clouds. We develop a new method to\ndiscriminate submillimeter cores found by SCUBA as starless or protostellar,\nusing point source photometry from Spitzer wide field surveys. First, we\nidentify infrared sources with red colors associated with embedded young\nstellar objects (YSOs). Second, we compare the positions of these\nYSO-candidates to our submillimeter cores. With these identifications, we\nconstruct new, self-consistent starless and protostellar core mass functions\n(CMFs) for the five clouds. We find best fit slopes to the high-mass end of the\nCMFs of -1.26 +/- 0.20, -1.22 +/- 0.06, -0.95 +/- 0.20, and -1.67 +/- 0.72 for\nOphiuchus, Taurus, Perseus, and Orion, respectively. Broadly, these slopes are\neach consistent with the -1.35 power-law slope of the Salpeter IMF at higher\nmasses, but suggest some differences. We examine a variety of trends between\nthese CMF shapes and their parent cloud properties, potentially finding a\ncorrelation between the high-mass slope and core temperature. We also find a\ntrend between core mass and effective size, but we are very limited by\nsensitivity. We make similar comparisons between core mass and size with visual\nextinction (for A_V >= 3) and find no obvious trends. We also predict the\nnumbers and mass distributions of cores that future surveys with SCUBA-2 may\ndetect in each of these clouds.", "category": "astro-ph_GA" }, { "text": "On the relation of host properties and environment of AGN galaxies\n across the standard optical diagnostic diagram: We study the host properties and environment of active galactic nuclei (AGNs)\ngalaxies, taken from SDSS-DR12, across the $\\text{[O III]}/\\text{H}\\beta$ vs\n$\\text{[N II]}/\\text{H}\\alpha$ diagnostic diagram. We select AGN subsamples\ndefined as parallel and perpendicular to the star-forming locus on the BPT\ndiagram based on the Kauffmann et al. and Schawinski et al. criteria. For\nparallel subsamples we find that AGN host properties exhibit a morphological\nevolution as they become more distant to the star-forming sequence. The local\ndensity environment shows a more evident morphology-density relationship for\nsubsamples mainly formed by Composite and Spiral galaxies than those containing\nLINERs and Seyferts, where the AGN emission is the dominant source. We also\nanalyse the properties of the five closest AGN neighbours observing no\nsignificant differences in the environment, although the AGN host properties of\nevery subsample have noticeable variations. The AGNs belonging to perpendicular\nsubsamples show clear differences on their host properties from left top to\nright bottom on the diagram. However, the analysis of the local density\nenvironment do not reflect strong dependency with the host AGN properties. This\nresult is reinforced by the characteristics of the AGN neighbouring galaxies.\nThese findings suggest that mixed AGN/star-forming galaxies present\nenvironmental features more similar to that of non-active galaxies. However, as\nAGNs at the centre of the more evolved galaxies become the dominant source, the\nenvironment tends to provide suitable conditions for the central black hole\nfeeding with an increasing content of gas and likelihood of a higher merger\nrate.", "category": "astro-ph_GA" }, { "text": "Long-term optical spectral monitoring of a changing-look AGN NGC 3516 I:\n Continuum and broad-line flux variability: Here we present the long-term optical spectral monitoring of a changing-look\nactive galactic nuclei (AGN) NGC 3516 that covers 22 years (from 1996 to 2018).\nWe explore a variability in the broad lines and continuum, finding that the\ncontinuum is changing by more than a factor of 2, while the broad lines are\nvarying by more than a factor of 10. The minimum of activity is observed in\n2014, when the broad lines almost disappeared. We confirm that NGC 3516 is a\nchanging-look AGN, and the absorption seen in the UV and X-ray may indicate\nthat there is an obscuring region which is responsible for this.\n The line profiles are also changing. The mean profiles of the broad Halpha\nand Hbeta lines show shoulder-like structure in the wings, and enhanced peak,\nthat may indicate a complex BLR. The rms-profiles of both lines seem to have\nthe same shape and width of around 4200 km/s, indicating practically the same\nkinematics in the Halpha and Hbeta emitting regions.\n Measured time-lags between the continuum and Halpha and Hbeta broad-line\nvariability are ~15 and 17 days, respectively, that in combination with the\nbroad lines width allows us to estimate the NGC 3516 central black hole mass.\nWe find that the black hole mass is 4.73+-1.40 x 10^7M_sun which is in\nagreement with previous estimates.", "category": "astro-ph_GA" }, { "text": "Formation of supermassive stars in the first star clusters: The formation of supermassive stars is believed to be an essential\nintermediate step for the formation of the massive black hole seeds that become\nthe supermassive black holes powering the quasars observed in the early\nUniverse. Numerical simulations have shown that supermassive stars can form in\natomic-cooling halos when protostars reach accretion rates higher than\n$\\sim10^{-2}$ M$_\\odot$ yr$^{-1}$ and fragmentation is suppressed on pc scales.\nIt is however still uncertain if a supermassive star still emerges when\nfragmentation occurs at smaller scales and a cluster of stars is formed\ninstead. In this work we explore the problem of massive object formation due to\nthe interplay of collisions and accretion in star clusters at low metallicity.\nWe model a small embedded cluster of accreting protostars following sub-parsec\nscale fragmentation during the collapse of a primordial gas cloud and follow\nits evolution by performing $N$-body plus hydrodynamical simulations. Our\nresults show that supermassive stars with 10$^3$ and 10$^4$ M$_\\odot$ are\nalways formed due to the interplay of collisions and accretion, and in some\ncases these objects are part of a binary system. The resulting supermassive\nstar is surrounded by tens of smaller stars with typical masses in the range\n$1$-$100$ M$_\\odot$.", "category": "astro-ph_GA" }, { "text": "Galactic Disk Bulk Motions as Revealed by the LSS-GAC DR2: We report a detailed investigation of the bulk motions of the nearby Galactic\nstellar disk, based on three samples selected from the LSS-GAC DR2: a global\nsample containing 0.57 million FGK dwarfs out to $\\sim$ 2 kpc, a local subset\nof the global sample consisting $\\sim$ 5,400 stars within 150 pc, and an\nanti-center sample containing $\\sim$ 4,400 AFGK dwarfs and red clump stars\nwithin windows of a few degree wide centered on the Galactic anti-center. The\nglobal sample is used to construct a three-dimensional map of bulk motions of\nthe Galactic disk from the solar vicinity out to $\\sim$ 2 kpc with a spatial\nresolution of $\\sim$ 250 pc. Typical values of the radial and vertical\ncomponents of bulk motion range from $-$15 km s$^{-1}$ to 15 km s$^{-1}$, while\nthe lag behind the circular speed dominates the azimuthal component by up to\n$\\sim$ 15 km s$^{-1}$. The map reveals spatially coherent, kpc-scale stellar\nflows in the disk, with typical velocities of a few tens km s$^{-1}$. Bending-\nand breathing-mode perturbations are clearly visible, and vary smoothly across\nthe disk plane. Our data also reveal higher-order perturbations, such as breaks\nand ripples, in the profiles of vertical motion versus height. From the local\nsample, we find that stars of different populations exhibit very different\npatterns of bulk motion. Finally, the anti-center sample reveals a number of\npeaks in stellar number density in the line-of-sight velocity versus distance\ndistribution, with the nearer ones apparently related to the known moving\ngroups. The \"velocity bifurcation\" reported by Liu et al. (2012) at\nGalactocentric radii 10--11 kpc is confirmed. However, just beyond this\ndistance, our data also reveal a new triple-peaked structure.", "category": "astro-ph_GA" }, { "text": "Carbon, nitrogen and oxygen abundance gradients in M101 and M31: We present deep spectrophotometry of 18 HII regions in the nearby massive\nspiral galaxies M101 and M31. We have obtained direct determinations of\nelectron temperature in all the nebulae. We detect the CII 4267 line in several\nHII regions, permitting to derive the radial gradient of C/H in both galaxies.\nWe also determine the radial gradients of O/H, N/O, Ne/O, S/O, Cl/O and Ar/O\nratios. As in other spiral galaxies, the C/H gradients are steeper than those\nof O/H producing negative slopes of the C/O gradient. The scatter of the\nabundances of O with respect to the gradient fittings do not support the\npresence of significant chemical inhomogeneities across the discs of the\ngalaxies, especially in the case of M101. We find trends in the S/O, Cl/O and\nAr/O ratios as a function of O/H in M101 that can be reduced using Te\nindicators different from the standard ones for calculating some ionic\nabundances. The distribution of the N/O ratio with respect to O/H is rather\nflat in M31, similarly to previous findings for the MilkyWay. Using the disc\neffective radius, Re, as a normalization parameter for comparing gradients, we\nfind that the latest estimates of Re for the Milky Way provide an excess of\nmetallicity in apparent contradiction with the mass-metallicity relation; a\nvalue about two times larger might solve the problem. Finally, using different\nabundance ratios diagrams we find that the enrichment timescales of C and N\nresult to be fairly similar despite their different nucleosynthetic origin.", "category": "astro-ph_GA" }, { "text": "Size, shade or shape? The contribution of galaxies of different types to\n the star-formation history of the Universe from SDSS-IV MaNGA: By fitting stellar populations to SDSS-IV MaNGA survey observations of ~7000\nsuitably-weighted individual galaxies, we reconstruct the star-formation\nhistory of the Universe, which we find to be in reasonable agreement with\nprevious studies. Dividing the galaxies by their present-day stellar mass, we\ndemonstrate the downsizing phenomenon, whereby the more massive galaxies hosted\nthe most star-formation at earlier times. Further dividing the galaxy sample by\ncolour and morphology, we find that a galaxy's present-day colour tells us more\nabout its historical contribution to the cosmic star formation history than its\ncurrent morphology. We show that downsizing effects are greatest among galaxies\ncurrently in the blue cloud, but that the level of downsizing in galaxies of\ndifferent morphologies depends quite sensitively on the morphological\nclassification used, due largely to the difficulty in classifying the smaller\nlow-mass galaxies from their ground-based images. Nevertheless, we find\nagreement that among galaxies with stellar masses\n$M_{\\star}>6\\times10^{9}\\,M_{\\odot}$, downsizing is most significant in\nspirals. However, there are complicating factors. For example, for more massive\ngalaxies, we find that colour and morphology are predictors of the past star\nformation over a longer timescale than in less massive systems. Presumably this\neffect is reflecting the longer period of evolution required to alter these\nlarger galaxies' physical properties, but shows that conclusions based on any\nsingle property don't tell the full story.", "category": "astro-ph_GA" }, { "text": "Wide field polarimetry around the Perseus cluster at 350 MHz: This paper investigates the fascinating diffuse polarization structures at\n350 MHz that have previously been tentatively attributed to the Perseus cluster\nand, more specifically, tries to find out whether the structures are located at\n(or near) the Perseus cluster, or in the Milky Way. A wide field, eight point\nWesterbork Synthesis Radio Telescope mosaic of the area around the Perseus\ncluster was observed in full polarization. The frequency range was 324 to 378\nMHz and the resolution of the polarization maps was 2'x3'. The maps were\nprocessed using Faraday rotation measure synthesis to counter bandwidth\ndepolarization. The RM-cube covers Faraday depths of -384 to +381 rad m^{-2} in\nsteps of 3 rad m^{-2}. There is emission all over the field at Faraday depths\nbetween -50 and +100 rad m^{-2}. All previously observed structures were\ndetected. However, no compelling evidence was found supporting association of\nthose structures with either the Perseus cluster or large scale structure\nformation gas flows in the Perseus-Pisces super cluster. On the contrary, one\nof the structures is clearly associated with a Galactic depolarization canal at\n1.41 GHz. Another large structure in polarized intensity, as well as Faraday\ndepth at a Faraday depth of +30 rad m^{-2}, coincides with a dark object in\nWHAM H-alpha maps at a kinematic distance of 0.5 \\pm 0.5 kpc. All diffuse\npolarized emission at 350 MHz towards the Perseus cluster is most likely\nlocated within 1 kpc from the Sun. The layers that emit the polarized radiation\nare less than 40 pc/B|| thick.", "category": "astro-ph_GA" }, { "text": "The interacting late-type host galaxy of the radio-loud narrow-line\n Seyfert 1 IRAS 20181-2244: Narrow-line Seyfert 1 galaxies (NLS1s) are a class of active galactic nuclei\n(AGN) which are known to be one of the few sources of $\\gamma$ rays, which\noriginate in a relativistic beamed jet. Becuase of their relatively large\ndistance, a poorly investigated aspect of these jetted NLS1s is their\nenvironment, and in particular their host galaxy. In this work we present the\nresults of a morphological analysis of the host galaxy of the jetted NLS1 IRAS\n20181-2244 observed with the 6.5m Baade Telescope of the Las Campanas\nObservatory. The GALFIT analysis ran on the Ks image, along with additional\nspectroscopic observations performed with the Nordic Optical Telescope, clearly\nrevealed the presence of an interacting system of two galaxies. The data\nsuggest that this NLS1 is hosted by a late-type galaxy, although the result is\nnot conclusive. This analysis, along with other results in the literature,\nmight suggest that two populations of jetted NLS1 exist. Further morphological\nstudies are needed to confirm or disprove this hypothesis.", "category": "astro-ph_GA" }, { "text": "Detection of Broad H$\u03b1$ Emission Lines in the Late-time Spectra of\n a Hydrogen-poor Superluminous Supernova: iPTF13ehe is a hydrogen-poor superluminous supernova (SLSN) at z=0.3434, with\na slow-evolving light curve and spectral features similar to SN2007bi. It rises\nwithin (83-148)days (rest-frame) to reach a peak bolometric luminosity of\n1.3x$10^{44}$erg/s, then decays very slowly at 0.015mag. per day. The measured\nejecta velocity is 13000km/s. The inferred explosion characteristics, such as\nthe ejecta mass (67-220$M_\\odot$), the total radiative and kinetic energy\n($10^{51}$ & 2x$10^{53}$erg respectively), is typical of a slow-evolving H-poor\nSLSN event. However, the late-time spectrum taken at +251days reveals a Balmer\nHalpha emission feature with broad and narrow components, which has never been\ndetected before among other H-poor SLSNe. The broad component has a velocity\nwidth of ~4500km/s and has a ~300km/s blue-ward shift relative to the narrow\ncomponent. We interpret this broad H$\\alpha$ emission with luminosity of\n$\\sim$2$\\times10^{41}$\\,erg\\,s$^{-1}$ as resulting from the interaction between\nthe supernova ejecta and a discrete H-rich shell, located at a distance of\n$\\sim4\\times10^{16}$\\,cm from the explosion site. This ejecta-CSM interaction\ncauses the rest-frame r-band LC to brighten at late times. The fact that the\nlate-time spectra are not completely absorbed by the shock ionized CSM shell\nimplies that its Thomson scattering optical depth is likely <1, thus setting\nupper limits on the CSM mass <30$M_\\odot$ and the volume number density\n<4x$10^8cm^{-3}$. Of the existing models, a Pulsational Pair Instability\nSupernova model can naturally explain the observed 30$M_\\odot$ H-shell, ejected\nfrom a progenitor star with an initial mass of (95-150)$M_\\odot$ about 40 years\nago. We estimate that at least $\\sim$15\\%\\ of all SLSNe-I may have late-time\nBalmer emission lines.", "category": "astro-ph_GA" }, { "text": "The Local Dark Matter Density from SDSS-SEGUE G-dwarfs: We derive the local dark matter density by applying the integrated Jeans\nequation method from Silverwood et al. (2016) to SDSS-SEGUE G-dwarf data\nprocessed and presented by B\\\"udenbender et al. (2015). We use the MultiNest\nBayesian nested sampling software to fit a model for the baryon distribution,\ndark matter and tracer stars, including a model for the 'tilt term' that\ncouples the vertical and radial motions, to the data. The $\\alpha$-young\npopulation from B\\\"udenbender et al. (2015) yields the most reliable result of\n$\\rho_{\\rm DM} = 0.46^{+0.07}_{-0.09}\\, {{\\rm GeV\\, cm}^{-3}} =\n0.012^{+0.001}_{-0.002}\\, {{\\rm M}_\\odot \\, {\\rm pc}^{-3}}$. Our analyses yield\ninconsistent results for the $\\alpha$-young and $\\alpha$-old data, pointing to\nproblems in the tilt term and its modelling, the data itself, the assumption of\na flat rotation curve, or the effects of disequilibria.", "category": "astro-ph_GA" }, { "text": "Variations of Broad Emission Lines from periodicity QSOs under the\n interpretation of supermassive binary black holes with misaligned\n circumbinary broad line regions: Quasars with periodic light curves are considered as candidates of\nsupermassive binary black hole (BBH) systems. One way for further confirmations\nmay be searching for other characteristic signatures, such as those in their\nbroad emission lines (BELs), if any, which require a thorough understanding on\nthe response of BELs to the BBH systems. In Ji et al. (2021), we have\ninvestigated the response of circumbinary broad line region (BLR) to the\ncentral active secondary black hole under the relativistic Doppler boosting\n(BBH-DB) and intrinsic variation (BBH-IntDB) dominant mechanisms for continuum\nvariation by assuming the middle plane of the BLR aligned with the BBH orbital\nplane. In this paper, we explore how the BEL profiles vary when the BLR is\nmisaligned from the BBH orbital plane with different offset angles under both\nthe BBH-DB and BBH-IntDB scenarios. Given a fixed inclination angle of the BBH\norbital plane viewed in edge-on and similar continuum light curves produced by\nthe two scenarios, increasing offset angles make the initial opening angle of\nthe circumbinary BLR enlarged due to orbital precession caused by the BBH\nsystem, especially for clouds in the inner region, which result in Lorentz-like\nBEL profiles for the BBH-DB model but still Gaussian-like profiles for the\nBBH-IntDB model at the vertical BLR case. The amplitude of profile variations\ndecrease with increasing offset angles for the BBH-DB scenario, while keep\nnearly constant for the BBH-IntDB scenario, since the Doppler boosting effect\nis motion direction preferred but the intrinsic variation is radiated\nisotropically. If the circumbinary BLR is composed of a coplanar and a vertical\ncomponents with their number of clouds following the mass ratio of the BBHs,\nthen the bi-BLR features are more significant for the BBH-IntDB model that\nrequire larger mass ratio to generate similar continuum variation than the\nBBH-DB model.", "category": "astro-ph_GA" }, { "text": "The Tucana dwarf spheroidal: a distant backsplash galaxy of M31?: We use the APOSTLE Local Group (LG) cosmological hydro-simulations to examine\nthe properties of \"backsplash\" galaxies, i.e, dwarfs which were within the\nvirial boundaries of the Milky Way (MW) or M31 in the past, but are today\noutside their virial radius ($r_{200}$). More than half of all dwarfs between\n$1-2\\,r_{200}$ of each primary are backsplash. More distant backsplash systems,\ni.e., those reaching distances well beyond $2\\,r_{200}$, are typically close to\napocentre of nearly radial orbits, and, therefore, essentially at rest relative\nto their primary. We use this result to investigate which LG dwarfs beyond\n$\\sim500$ kpc of either primary could be a distant backsplash satellite of MW\nor M31. Tucana dSph, one of the few known quiescent LG field dwarfs, at $d_{\\rm\nM31}\\approx1350$ kpc and $d_{\\rm MW}\\approx880$ kpc, is a promising candidate.\nTucana's radial velocity is consistent with being at rest relative to M31.\nFurther, Tucana is located close to M33's orbital plane around M31, and simple\norbit integrations indicate that Tucana may have been ejected during an early\npericentric passage of M33 $\\sim11$ Gyr ago, a timing which approximately\ncoincides with Tucana's last episode of star formation. We suggest that Tucana\nmay have been an early-infalling satellite of M31 or M33, providing a\ncompelling explanation for its puzzling lack of gas and ongoing star formation\ndespite its isolated nature. In this scenario, M33 should have completed some\norbits around M31, a result that may help to explain the relative dearth of M33\nsatellite-candidates identified so far.", "category": "astro-ph_GA" }, { "text": "LAGER Ly$\u03b1$ Luminosity Function at $z\\sim7$, Implications for\n Reionization: We present a new measurement of the Ly$\\alpha$ luminosity function at\nredshift $z=6.9$, finding moderate evolution from $z=5.7$ that is consistent\nwith a fully or largely ionized $z\\sim7$ intergalactic medium. Our result is\nbased on four fields of the LAGER (Lyman Alpha Galaxies in the Epoch of\nReionization) project. Our survey volume of $6.1\\times10^{6}$ Mpc$^{3}$ is\ndouble that of the next largest $z\\sim 7$ survey. We combine two new LAGER\nfields (WIDE12 and GAMA15A) with two previously reported LAGER fields (COSMOS\nand CDFS). In the new fields, we identify $N=95$ new $z=6.9$ Ly$\\alpha$\nemitters (LAEs); characterize our survey's completeness and reliability; and\ncompute Ly$\\alpha$ luminosity functions. The best-fit Schechter luminosity\nfunction parameters for all four LAGER fields are in good general agreement.\nTwo fields (COSMOS and WIDE12) show evidence for a bright-end excess above the\nSchechter function fit. We find that the Ly$\\alpha$ luminosity density declines\nat the same rate as the UV continuum LF from $z=5.7$ to $z=6.9$. This is\nconsistent with an intergalactic medium that was fully ionized as early as\nredshift $z\\sim 7$, or with a volume-averaged neutral hydrogen fraction of\n$x_{HI} < 0.33$ at $1\\sigma$.", "category": "astro-ph_GA" }, { "text": "Detailed study of the Bootes field using 300-500 MHz uGMRT observations:\n Source Properties and radio--infrared correlations: The dominant source of radio continuum emissions at low frequencies is\nsynchrotron radiation, which originates from star-forming regions in disk\ngalaxies and from powerful jets produced by active galactic nuclei (AGN). We\nstudied the Bootes field using the upgraded Giant Meterwave Radio Telescope\n(uGMRT) at 400 MHz, achieving a central minimum off-source RMS noise of\n35$\\mu$Jy beam$^{-1}$ and a catalogue of 3782 sources in $\\sim6$ sq. degrees of\nthe sky. The resulting catalogue was compared to other radio frequency\ncatalogues, and the corrected normalised differential source counts were\nderived. We use standard multi-wavelength techniques to classify the sources in\nstar-forming galaxies (SFGs), radio-loud (RL) AGN, and radio-quiet (RQ) AGN\nthat confirm a boost in the SFGs and RQ\\,AGN AGN populations at lower flux\nlevels. For the first time, we investigated the properties of the radio--IR\nrelations at 400\\,MHz in this field. The $L_{\\rm 400 MHz}$--$L_{\\rm TIR}$\nrelations for SFGs were found to show a strong correlation with non-linear\nslope values of $1.10\\pm0.01$, and variation of $q_{\\rm TIR}$ with $z$ is given\nas, $q_{\\rm TIR} = (2.19 \\pm 0.07)\\ (1+z)^{-0.15 \\pm 0.08}$. This indicates\nthat the non-linearity of the radio--IR relations can be attributed to the mild\nvariation of $q_{\\rm TIR}$ values with $z$. The derived relationships exhibit\nsimilar behaviour when applied to LOFAR at 150 MHz and also at 1.4 GHz. This\nemphasises the fact that other parameters like magnetic field evolution with\n$z$ or the number densities of cosmic ray electrons can play a vital role in\nthe mild evolution of $q$ values.", "category": "astro-ph_GA" }, { "text": "The Far-IR View of Star and Planet Forming Regions: The far-IR range is a critical wavelength range to characterize the physical\nand chemical processes that transform the interstellar material into stars and\nplanets. Objects in the earliest phases of stellar and planet evolution release\nmost of their energy at these long wavelengths. In this contribution we briefly\nsummarise some of the most relevant scientific advances achieved by the\nHerschel Space Observatory in the field. We also anticipate those that will be\nmade possible by the large increase in sensitivity of SPICA cooled telescope.\nIt is concluded that only through sensitive far-IR observations much beyond\nHerschel capabilities we will be able to constrain the mass, the energy budget\nand the water content of hundreds of protostars and planet-forming disks.", "category": "astro-ph_GA" }, { "text": "X-shaped Radio Galaxies: Optical Properties, Large-scale Environment and\n Relationship to Radio Structure: In order to find clues to the origin of the \"winged\" or \"X-shaped\" radio\ngalaxies (XRGs) we investigate here the parent galaxies of a large sample of\n106 XRGs for optical-radio axes alignment, interstellar medium, black hole\nmass, and large-scale environment. For 41 of the XRGs it was possible to\ndetermine the optical major axis and the primary radio axis and the strong\ntendency for the two axes to be fairly close is confirmed. However, several\ncounter-examples were also found and these could challenge the widely discussed\nbackflow diversion model for the origin of the radio wings. Comparison with a\nwell-defined large sample of normal FR II radio galaxies has revealed that: (i)\nXRGs possess slightly less massive central black holes than the normal radio\ngalaxies (average masses being log$M_{\\rm BH} \\sim$ 8.81 $M_{\\odot}$ and 9.07\n$M_{\\odot}$, respectively); (ii) a much higher fraction of XRGs ($\\sim$ 80%)\nexhibits red mid-IR colors ($W2 - W3 > 1.5$), indicating a population of young\nstars and/or an enhanced dust mass, probably due to relatively recent galaxy\nmerger(s). A comparison of the large-scale environment (i.e., within $\\sim$ 1\nMpc) shows that both XRGs and FRII radio galaxies inhabit similarly poor galaxy\nclustering environments (medium richness being 8.94 and 11.87, respectively).\nOverall, the origin of XRGs seems difficult to reconcile with a single dominant\nphysical mechanism and competing mechanisms seem prevalent.", "category": "astro-ph_GA" }, { "text": "Thermal Instability with Anisotropic Thermal Conduction and Adiabatic\n Cosmic Rays: Implications for Cold Filaments in Galaxy Clusters: Observations of the cores of nearby galaxy clusters show H$\\alpha$ and\nmolecular emission line filaments. We argue that these are the result of {\\em\nlocal} thermal instability in a {\\em globally} stable galaxy cluster core. We\npresent local, high resolution, two-dimensional magnetohydrodynamic simulations\nof thermal instability for conditions appropriate to the intracluster medium\n(ICM); the simulations include thermal conduction along magnetic field lines\nand adiabatic cosmic rays. Thermal conduction suppresses thermal instability\nalong magnetic field lines on scales smaller than the Field length ($\\gtrsim$10\nkpc for the hot, diffuse ICM). We show that the Field length in the cold medium\nmust be resolved both along and perpendicular to the magnetic field in order to\nobtain numerically converged results. Because of negligible conduction\nperpendicular to the magnetic field, thermal instability leads to fine scale\nstructure in the perpendicular direction. Filaments of cold gas along magnetic\nfield lines are thus a natural consequence of thermal instability with\nanisotropic thermal conduction. Nonlinearly, filaments of cold ($\\sim 10^4$ K)\ngas should have lengths (along the magnetic field) comparable to the Field\nlength in the cold medium $\\sim 10^{-4}$ pc! Observations show, however, that\nthe atomic filaments in clusters are far more extended, $\\sim 10$ kpc. Cosmic\nray pressure support (or a small scale turbulent magnetic pressure) may resolve\nthis discrepancy: even a small cosmic ray pressure in the diffuse ICM, $\\sim\n10^{-4}$ of the thermal pressure, can be adiabatically compressed to provide\nsignificant pressure support in cold filaments. This is qualitatively\nconsistent with the large population of cosmic rays invoked to explain the\natomic and molecular line ratios observed in filaments.", "category": "astro-ph_GA" }, { "text": "Confirmation of Enhanced Long Wavelength Dust Emission in OMC 2/3: Previous continuum observations from the MUSTANG camera on the Green Bank\nTelescope (GBT) of the nearby star-forming filament OMC 2/3 found elevated\nemission at 3.3 mm relative to shorter wavelength data. As a consequence, the\ninferred dust emissivity index obtained from modified black body dust spectra\nwas considerably lower than what is typically measured on $\\sim 0.1 \\, {\\rm\npc}$ scales in nearby molecular clouds. Here we present new observations of OMC\n2/3 collected with the MUSTANG-2 camera on the GBT which confirm this elevated\nemission. We also present for the first time sensitive 1 cm observations made\nwith the Ka-band receiver on the GBT which also show higher than expected\nemission. We use these observations--- along with Herschel, JCMT, Mambo, and\nGISMO data--- to assemble spectral energy distributions (SEDs) of a variety of\nstructures in OMC 2/3 spanning the range $160 \\, {\\rm \\mu m}$ to $1 \\, {\\rm\ncm}$. The data at 2 mm and shorter are generally consistent with a modified\nblack body spectrum and a single value of $\\beta \\sim 1.6$. The 3 mm and 1 cm\ndata, however, lie well above such an SED. The spectrum of the long wavelength\nexcess is inconsistent with both free-free emission and standard \"Spinning\nDust\" models for Anomalous Microwave Emission (AME). The 3 mm and 1 cm data\ncould be explained by a flatter dust emissivity at wavelengths shorter than 2\nmm, potentially in concert with AME in some regions.", "category": "astro-ph_GA" }, { "text": "Probing the interplay between jets, winds and multi-phase gas in 11\n radio-quiet PG Quasars: A uGMRT-VLA study: We present polarization-sensitive images from the Karl G. Jansky Very Large\nArray (VLA) at 5 GHz of 11 radio-quiet PG quasars. Based on the radio\nmorphology, spectral index and polarization properties from the VLA study,\ncoupled with the findings of our previous 685 MHz uGMRT data, we find the\npresence of low-power jets on sub-arcsecond and arcsecond scales in 9 sources;\nsome show signatures of bent jets. The origin of radio emission remains unclear\nin the remaining 2 sources. Of the 11 sources, linear polarization is detected\nin four of them with fractional polarization ranging between 2% and 21%. In PG\n1229+204, the inferred B-field direction is parallel to the local kpc-scale jet\ndirection. The inferred B-fields are transverse to the weak southward extension\nin PG 0934+013. For PG 0050+124 and PG 0923+129, the relationship between the\nB-field structure and radio outflow direction remains unclear. Localized or\nsmall-scale jet-medium interactions can be inferred across the sample based on\nthe VLA jet kinetic power arguments and polarization data. These may have the\npotential as a feedback mechanism. We find that the radio properties do not\nshow strong correlations with the star formation, [O III] and CO quantities\npublished in the literature. The lack of evidence of AGN feedback on the global\ngalaxy properties could be due to the relative time scales of AGN activity and\nthose over which any impact might be taking place.", "category": "astro-ph_GA" }, { "text": "Hubble-COS Observations of Galactic High-Velocity Clouds: Four AGN Sight\n Lines through Complex C: We report ultraviolet spectra of Galactic high-velocity clouds (HVCs) in\nComplex C, taken by the Cosmic Origins Spectrograph (COS) on the Hubble Space\nTelescope (HST), together with new 21-cm spectra from the Green Bank Telescope.\nThe wide spectral coverage and higher S/N, compared to previous HST spectra,\nprovide better velocity definition of the HVC absorption, additional ionization\nspecies, and improved abundances in this halo gas. Complex C has a metallicity\nof 0.1-0.3 solar and a wide range of ions, suggesting dynamical and thermal\ninteractions with hot gas in the Galactic halo. Spectra in the COS\nmedium-resolution G130M (1133-1468 A) and G160M (1383-1796 A) gratings detect\nultraviolet absorption lines from 8 elements in low ionization stages (O I, N\nI, C II, S II, Si II, Al II, Fe II, P II) and 3 elements in intermediate and\nhigh-ionization states (Si III, Si IV, C IV, N V). Our four AGN sight lines\ntoward Mrk 817, Mrk 290, Mrk 876, and PG1259+593 have high-velocity H I and O\nVI column densities, log N_HI = 19.39-20.05 and log N_OVI = 13.58-14.10, with\nsubstantial amounts of kinematically associated photoionized gas. The high-ion\nabundance ratios are consistent with cooling interfaces between photoionized\ngas and collisionally ionized gas: N(C IV)/N(O VI) = 0.3-0.5, N(Si IV)/N(O VI)\n= 0.05-0.11, N(N V)/N(O VI) = 0.07-0.13, and N(Si IV)/N(Si III) = 0.2.", "category": "astro-ph_GA" }, { "text": "Modeling Star Formation as a Markov Process in a Supersonic\n Gravoturbulent Medium: Molecular clouds exhibit lognormal probability density functions (PDF) of\nmass densities, which are thought to arise as a consequence of isothermal,\nsupersonic turbulence. Star formation is then widely assumed to occur in\nperturbations in which gravitational collapse is faster than the rate of change\ndue to turbulent motions. Here we use direct numerical simulations to measure\nthis rate as a function of density for a range of turbulent Mach numbers, and\nshow it is faster at high densities than at low densities. Furthermore, we show\nthat both the density PDF and rate of change arise naturally in a simple model\nof turbulence as a continuous Markov process. The one-dimensional Langevin\nequation that describes this evolution depends on only two parameters, yet it\ncaptures the full evolution seen in direct three-dimensional simulations. If it\nis modified to include gravity, the Langevin equation also reproduces the rate\nof material collapsing to high densities seen in turbulent simulations\nincluding self-gravity. When generalized to include both temperature and\ndensity, similar analyses are likely applicable throughout astrophysics.", "category": "astro-ph_GA" }, { "text": "Constraining stellar population parameters from narrow band photometric\n surveys using convolutional neural networks: Upcoming large-area narrow band photometric surveys, such as J-PAS, will\nenable us to observe a large number of galaxies simultaneously and efficiently.\nHowever, it will be challenging to analyse the spatially-resolved stellar\npopulations of galaxies from such big data to investigate galaxy formation and\nevolutionary history. We have applied a convolutional neural network (CNN)\ntechnique, which is known to be computationally inexpensive once it is trained,\nto retrieve the metallicity and age from J-PAS-like narrow band images. The CNN\nwas trained using mock J-PAS data created from the CALIFA IFU survey and the\nage and metallicity at each data point, which are derived using full spectral\nfitting to the CALIFA spectra. We demonstrate that our CNN model can\nconsistently recover age and metallicity from each J-PAS-like spectral energy\ndistribution. The radial gradients of the age and metallicity for galaxies are\nalso recovered accurately, irrespective of their morphology. However, it is\ndemonstrated that the diversity of the dataset used to train the neural\nnetworks has a dramatic effect on the recovery of galactic stellar population\nparameters. Hence, future applications of CNNs to constrain stellar populations\nwill rely on the availability of quality spectroscopic data from samples\ncovering a wide range of population parameters.", "category": "astro-ph_GA" }, { "text": "Collisional excitation of HC3N by para- and ortho-H2: New calculations for rotational excitation of cyanoacetylene by collisions\nwith hydrogen molecules are performed to include the lowest 38 rotational\nlevels of HC3N and kinetic temperatures to 300 K. Calculations are based on the\ninteraction potential of Wernli et al. A&A, 464, 1147 (2007) whose accuracy is\nchecked against spectroscopic measurements of the HC3N-H2 complex. The quantum\ncoupled-channel approach is employed and complemented by quasi-classical\ntrajectory calculations. Rate coefficients for ortho-H2 are provided for the\nfirst time. Hyperfine resolved rate coefficients are also deduced. Collisional\npropensity rules are discussed and comparisons between quantum and classical\nrate coefficients are presented. This collisional data should prove useful in\ninterpreting HC3N observations in the cold and warm ISM, as well as in\nprotoplanetary disks.", "category": "astro-ph_GA" }, { "text": "GC-IRS13E - A puzzling association of three early-type stars: We present a detailed analysis of high resolution near-infrared imaging and\nspectroscopy of the potential star cluster IRS13E very close to the massive\nblack hole in the Galactic Center. We detect 19 objects in IRS13E from Ks-band\nimages, 15 of which are also detected reliably in H-band. We derive consistent\nproper motions for these objects from the two bands. Most objects share a\nsimilar westward proper motion. We characterize the objects using spectroscopy\n(1.45 to 2.45 micrometer) and (narrow-band) imaging from H- (1.66 mircrometer)\nto L'-band (3.80 micrometer). Nine of the objects detected in both Ks- and\nH-band are very red, and we find that they are all consistent with being warm\ndust clumps. The dust emission may be caused by the colliding winds of the two\nWolf-Rayet stars in the cluster. Three of the six detected stars do not share\nthe motion or spectral properties of the three bright stars. This leaves only\nthe three bright, early-type stars as potential cluster members. It is unlikely\nthat these stars are a chance configuration. Assuming the presence of an IMBH,\na mass of about 14000 solar masses follows from the velocities and positions of\nthese three stars. However, our acceleration limits make such an IMBH nearly as\nunlikely as a chance occurrence of such a star association. Furthermore, there\nis no variable X-ray source in IRS13E despite the high density of dust and gas.\nTherefore, we conclude that is unlikely that IRS13E hosts a black hole massive\nenough to bind the three stars.", "category": "astro-ph_GA" }, { "text": "The Presence of Thermally Unstable X-ray Filaments and the Production of\n Cold Gas in the NGC 5044 Group: We present the results of a deep Chandra observation of the X-ray bright,\nmoderate cooling flow group NGC 5044 along with the observed correlations\nbetween the ionized, atomic, and molecular gas in this system. The Chandra\nobservation shows that the central AGN has undergone two outbursts in the past\n100 Myrs, based on the presence of two pairs of nearly bipolar X-ray cavities.\nThe molecular gas and dust within the central 2kpc is aligned with the\norientation of the inner pair of bipolar X-ray cavities, suggesting that the\nmost recent AGN outburst had a dynamical impact on the molecular gas. NGC 5044\nalso hosts many X-ray filaments within the central 8kpc, but there are no\nobvious connections between the X-ray and H$\\alpha$ filaments and the more\nextended X-ray cavities that were inflated during the prior AGN outburst. Using\nthe linewidth of the blended Fe-L line complex as a diagnostic for multiphase\ngas, we find that the majority of the multiphase, thermally unstable gas in NGC\n5044 is confined within the X-ray filaments. While the cooling time and entropy\nof the gas within the X-ray filaments are very similar, not all filaments show\nevidence of gas cooling or an association with Ha emission. We suggest that the\nvarious observed properties of the X-ray filaments are suggestive of an\nevolutionary sequence where thermally unstable gas begins to cool, becomes\nmultiphased, develops Ha emitting plasma, and finally produces cold gas.", "category": "astro-ph_GA" }, { "text": "What does the first highly-redshifted 21-cm detection tell us about\n early galaxies?: The Experiment to Detect the Global Epoch of Reionization Signature (EDGES)\nrecently reported a strong 21-cm absorption signal relative to the cosmic\nmicrowave background at $z \\sim 18$. While its anomalous amplitude may indicate\nnew physics, in this work we focus on the timing of the signal, as it alone\nprovides an important constraint on galaxy formation models. Whereas rest-frame\nultraviolet luminosity functions (UVLFs) over a broad range of redshifts are\nwell fit by simple models in which galaxy star formation histories track the\nassembly of dark matter halos, we find that these same models, with reasonable\nassumptions about X-ray production in star-forming galaxies, cannot generate a\nnarrow absorption trough at $z \\sim 18$. If verified, the EDGES signal\ntherefore requires the fundamental inputs of galaxy formation models to evolve\nrapidly at $z \\gtrsim 10$. Unless extremely faint sources residing in halos\nbelow the atomic cooling threshold are responsible for the EDGES signal, star\nformation in $\\sim 10^8$-$10^{10} \\ M_{\\odot}$ halos must be more efficient\nthan expected, implying that the faint-end of the UVLF at $M_{\\mathrm{UV}}\n\\lesssim -12$ must steepen at the highest redshifts. This steepening provides a\nconcrete test for future galaxy surveys with the James Webb Space Telescope and\nongoing efforts in lensed fields, and is required regardless of whether the\namplitude of the EDGES signal is due to new cooling channels or a strong radio\nbackground in the early Universe. However, the radio background solution\nrequires that galaxies at $z > 15$ emit 1-2 GHz photons with an efficiency\n$\\sim 10^3$ times greater than local star-forming galaxies, posing a challenge\nfor models of low-frequency photon production in the early Universe.", "category": "astro-ph_GA" }, { "text": "The Effect of Noise on the Dust Temperature - Spectral Index Correlation: We investigate how uncertainties in flux measurements affect the results from\nmodified blackbody SED fits. We show that an inverse correlation between the\ndust temperature T and spectral index (beta) naturally arises from least\nsquares fits due to the uncertainties, even for sources with a single T and\nbeta. Fitting SEDs to noisy fluxes solely in the Rayleigh-Jeans regime produces\nunreliable T and beta estimates. Thus, for long wavelength observations (lambda\n>~ 200 micron), or for warm sources (T >~ 60 K), it becomes difficult to\ndistinguish sources with different temperatures. We assess the role of noise in\nrecent observational results that indicate an inverse and continuously varying\nT - beta relation. Though an inverse and continuous T - beta correlation may be\na physical property of dust in the ISM, we find that the observed inverse\ncorrelation may be primarily due to noise.", "category": "astro-ph_GA" }, { "text": "Exploring the interstellar medium of NGC 891 at millimeter wavelengths\n using the NIKA2 camera: In the framework of the IMEGIN Large Program, we used the NIKA2 camera on the\nIRAM 30-m telescope to observe the edge-on galaxy NGC 891 at 1.15 mm and 2 mm\nand at a FWHM of 11.1\" and 17.6\", respectively. Multiwavelength data enriched\nwith the new NIKA2 observations fitted by the HerBIE SED code (coupled with the\nTHEMIS dust model) were used to constrain the physical properties of the ISM.\nEmission originating from the diffuse dust disk is detected at all wavelengths\nfrom mid-IR to mm, while mid-IR observations reveal warm dust emission from\ncompact HII regions. Indications of mm excess emission have also been found in\nthe outer parts of the galactic disk. Furthermore, our SED fitting analysis\nconstrained the mass fraction of the small (< 15 Angstrom) dust grains. We\nfound that small grains constitute 9.5% of the total dust mass in the galactic\nplane, but this fraction increases up to ~ 20% at large distances (|z| > 3 kpc)\nfrom the galactic plane.", "category": "astro-ph_GA" }, { "text": "Quenching in Cosmic Sheets: Tracing the Impact of Large Scale Structure\n Collapse on the Evolution of Dwarf Galaxies: Dwarf galaxies are thought to quench primarily due to environmental processes\nmost typically occurring in galaxy groups and clusters or around single,\nmassive galaxies. However, at earlier epochs, ($5 < z < 2$), the collapse of\nlarge scale structure (forming Zel'dovich sheets and subsequently filaments of\nthe cosmic web) can produce volume-filling accretion shocks which elevate large\nswaths of the intergalactic medium (IGM) in these structures to a hot ($T>10^6$\nK) phase. We study the impact of such an event on the evolution of central\ndwarf galaxies ($5.5 < \\log M_* < 8.5$) in the field using a spatially large,\nhigh resolution cosmological zoom simulation which covers the cosmic web\nenvironment between two protoclusters. We find that the shock-heated sheet acts\nas an environmental quencher much like clusters and filaments at lower\nredshift, creating a population of quenched, central dwarf galaxies. Even\nmassive dwarfs which do not quench are affected by the shock, with reductions\nto their sSFR and gas accretion. This process can potentially explain the\npresence of isolated quenched dwarf galaxies, and represents an avenue of\npre-processing, via which quenched satellites of bound systems quench before\ninfall.", "category": "astro-ph_GA" }, { "text": "ALMA observations of molecular tori around massive black holes: We report ALMA observations of CO(3-2) emission in a sample of 7\nSeyfert/LINER galaxies at the unprecedented spatial resolution of 0.1'' = 4-9\npc. Our aim is to explore the close environment of AGN, and the dynamical\nstructures leading to its fueling. The selected galaxies host low-luminosity\nAGN, and have a wide range of activity types, and barred or ringed\nmorphologies. The observed maps reveal the existence of circum-nuclear disk\nstructures, defined by their morphology and decoupled kinematics. We call these\nstructures \"molecular tori\", even though they appear often as disks, without\nholes in the center. They have varied orientations, unaligned with their host\ngalaxy. The radius of the tori ranges from 6 to 27 pc, and their mass from 0.7\n10$^7$ to 3.9 10$^7$ Msun. At larger scale, the gas is always piled up in a few\n100~pc scale resonant rings, that play the role of a reservoir to fuel the\nnucleus. In some cases, a trailing spiral is observed inside the ring,\nproviding evidence for feeding processes. Most frequently, the torus and the\nAGN are slightly off-centered, with respect to the bar-resonant ring position,\nimplying that the black hole is wandering by a few 10~pc amplitude around the\ncenter of mass of the galaxy. Our spatial resolution allows us to measure gas\nvelocities inside the sphere of influence of the central black holes. By\nfitting the observations with different simulated cubes, varying the torus\ninclination and the black hole mass, it is possible to estimate the mass of the\ncentral black hole, which is in general difficult for such late-type galaxies,\nwith only a pseudo-bulge.", "category": "astro-ph_GA" }, { "text": "Investigating the Baryon Cycle in Interacting Dwarfs with the Very Large\n Array and Pan-STARRS: We present resolved HI synthesis maps from the Very Large Array (VLA) of\nthree interacting dwarf systems: the NGC 3664 dwarf pair, the NGC 3264 dwarf\npair, and the UGC 4638 dwarf triplet. All three dwarf systems are captured at\nvarious stages of interaction and span a range of environments. We detect clear\nhallmarks of tidal interactions through the presence of HI bridges, and diffuse\nHI extensions that surround the dwarfs. We overlay the HI data on Pan-STARRS\nr-band images and find further evidence of tidal interactions through\ncoincident distorted HI and tidal stellar features in NGC 3264 and UGC 4638,\nand an unwound spiral arm pointing towards its smaller companion in NGC 3264.\nIn UGC 4638, both the gas and diffuse stars are extended to similar radii east\nof the primary, which could indicate that the smaller dwarf in the system has\nalready completed one pass through the primary. We additionally find that our\nthree systems, and those from the Local Volume TiNy Titans survey, are not HI\ndeficient and thus the interaction has not resulted in a loss of gas from the\nsystems. A comparison with non-interacting dwarf galaxies shows that the\ninteractions have a significant impact on the kinematics of the systems. Our\nnew resolved HI kinematics, combined with detailed stellar and HI morphologies,\nprovide crucial constraints for future dynamical modelling of hierarchical\nmergers and the baryon cycle at the low-mass scale.", "category": "astro-ph_GA" }, { "text": "Comparisons of Different Fitting Methods for the Physical Parameters of\n A Star Cluster Sample of M33 with Spectroscopy and Photometry: Star clusters are good tracers for formation and evolution of galaxies. We\ncompared different fitting methods by using spectra (or by combining\nphotometry) to determine the physical parameters. We choose a sample of 17 star\nclusters in M33, which previously lacked spectroscopic observations. The\nlow-resolution spectra were taken with the Xinglong 2.16-m reflector of NAOC.\nThe photometry used in the fitting includes $\\rm u_{SC}$ and $\\rm v_{SAGE}$\nbands from the SAGE survey, as well as the published $UBVRI$ and $ugriz$\nphotometry. We firstly derived ages and metallicities with the {\\sc ULySS}\n(Vazdekis et al. and {\\sc pegase-hr}) SSP model and the Bruzual \\& Charlot\n(2003) (BC03) stellar population synthesis models for the full-spectrum\nfitting. The fitting results of both the BC03 and {\\sc ULySS} models seem\nconsistent with those of previous works as well. Then we add the SAGE $\\rm\nu_{SC}$ and $\\rm v_{SAGE}$ photometry in the spectroscopic fitting with the\nBC03 models. It seems the results become much better, especially for the Padova\n2000+Chabrier IMF set. Finally we add more photometry data, $UBVRI$ and\n$ugriz$, in the fitting and we found that the results do not improve\nsignificantly. Therefore, we conclude that the photometry is useful for\nimproving the fitting results, especially for the blue bands ($\\lambda <4000$\n{\\AA}), e.g., $\\rm u_{SC}$ and $\\rm v_{SAGE}$ band. At last, we discuss the\n\"UV-excess\" for the star clusters and we find five star clusters have\nUV-excess, based on the $GALEX$ FUV, NUV photometry.", "category": "astro-ph_GA" }, { "text": "The impact of baryonic discs on the shapes and profiles of\n self-interacting dark matter halos: We employ isolated N-body simulations to study the response of\nself-interacting dark matter (SIDM) halos in the presence of the baryonic\npotentials. Dark matter self-interactions lead to kinematic thermalization in\nthe inner halo, resulting in a tight correlation between the dark matter and\nbaryon distributions. A deep baryonic potential shortens the phase of SIDM core\nexpansion and triggers core contraction. This effect can be further enhanced by\na large self-scattering cross section. We find the final SIDM density profile\nis sensitive to the baryonic concentration and the strength of dark matter\nself-interactions. Assuming a spherical initial halo, we also study evolution\nof the SIDM halo shape together with the density profile. The halo shape at\nlater epochs deviates from spherical symmetry due to the influence of the\nnon-spherical disc potential, and its significance depends on the baryonic\ncontribution to the total gravitational potential, relative to the dark matter\none. In addition, we construct a multi-component model for the Milky Way,\nincluding an SIDM halo, a stellar disc and a bulge, and show it is consistent\nwith observations from stellar kinematics and streams.", "category": "astro-ph_GA" }, { "text": "BAL effect in quasars due to source orientation: We investigated a scenario where the presence of a broad absorption line\n(BAL) feature in quasars (QSOs) is contingent upon the line of sight being\nsituated within an outflow cone emanating from the source. We examined the\nmechanism of dust-driven winds based on the failed radiatively accelerated\ndusty outflow (FRADO) model proposed by Czerny & Hryniewicz, letting it be\nresponsible for the formation of massive outflow. We calculated the probability\nof observing the BAL effect from the geometry of outflow which is a function of\nglobal parameters of black hole mass (M$_{BH}$), Eddington ratio\n($\\alpha_{Edd}$), and metallicity (Z). We then compared the results with\nprevalence of BAL QSOs in a sample of observational data from SDSS. The\nconsistency of our model with the data supports the interpretation of the BAL\nphenomenon as a result of source orientation, rather than a transitory stage in\nAGN evolution", "category": "astro-ph_GA" }, { "text": "An Isolated Compact Galaxy Triplet: We report the discovery of an isolated compact galaxy triplet SDSS\nJ084843.45+164417.3, which is first detected by the LAMOST spectral survey and\nthen confirmed by the spectroscopic observation of the BFOSC of the 2.16 meter\ntelescope. It is found that this triplet is an isolated and extremely compact\nsystem, which has an aligned configuration and very small radial velocity\ndispersion. The member galaxies have similar colors and show marginal star\nformation activities. These results enhance the opinion that the compact\ntriplets are well-evolved systems rather than the hierarchically forming\nstructures. This occasional discovery reveals the limitations of the fiber\nspectral redshift surveys in studying such compact system, and declares the\nnecessity of additional observations to complete the current redshift sample.", "category": "astro-ph_GA" }, { "text": "High Galactic latitude runaway stars as tracers of the spiral arms: A direct observation of the spiral structure of the Galaxy is hindered by our\nposition in the middle of the Galactic plane. We propose a method based on the\nanalysis of the birthplaces of high Galactic latitude runaway stars to map the\nspiral arms and determine their dynamics. As a proof of concept, the method is\napplied to a local sample of early-type stars and a sample of runaways stars to\nobtain estimates of the pattern speed and the spiral arm's phase angle. We also\nestimate the performance of this method once the data gathered by Gaia, in\nparticular for runaway stars observed on the other side of the Galaxy, is\navailable.", "category": "astro-ph_GA" }, { "text": "The Effects of Inhomogeneities within Colliding Flows on the Formation\n and Evolution of Molecular Clouds: Observational evidence from local star-forming regions mandates that star\nformation occurs shortly after, or even during, molecular cloud formation.\nModels of the formation of molecular clouds in large-scale converging flows\nhave identified the physical mechanisms driving the necessary rapid\nfragmentation. They also point to global gravitational collapse driving\nsupersonic turbulence in molecular clouds. Previous cloud formation models have\nfocused on turbulence generation, gravitational collapse, magnetic fields, and\nfeedback. Here, we explore the effect of structure in the flow on the resulting\nclouds and the ensuing gravitational collapse. We compare two extreme cases,\none with a collision between two smooth streams, and one with streams\ncontaining small clumps. We find that structured converging flows lead to a\ndelay of local gravitational collapse (\"star formation\"). Thus, more gas has\ntime to accumulate, eventually leading to a strong global collapse, and thus to\na high star formation rate. Uniform converging flows fragment hydrodynamically\nearly on, leading to the rapid onset of local gravitational collapse and an\noverall low sink formation rate.", "category": "astro-ph_GA" }, { "text": "Characteristics of remnant radio galaxies detected in the deep radio\n continuum observations from the SKA pathfinders: The cessation of AGN activity in radio galaxies leads to a remnant phase\nduring which jets are no longer sustained, but lobes can be detected for a\nperiod of time before they fade away due to radiative and dynamical energy\nlosses. The time-scale of the remnant phase and AGN duty cycle are vital to\nunderstanding the evolution of radio galaxies. In this paper, we report new\nband-3 observations with the upgraded Giant Meterwave Radio Telescope (uGMRT)\nfor five remnant radio galaxies. Our uGMRT observations reveal emission of\nlow-surface-brightness in all five remnants with 400 MHz surface brightness in\nthe range of 36$-$201 mJy arcmin$^{-2}$. With band-3 uGMRT observations, we\ndiscover wing-shaped radio morphology in one of our sample sources. Using radio\nobservations at 150 MHz, 325 MHz, 400 MHz, and 1.5 GHz, we model the radio\nspectral energy distributions (SEDs) of our sample sources with the continuous\ninjection-off model (CI$_{\\rm OFF}$), that assumes an active phase with\ncontinuous injection followed by a remnant phase. We obtain total source ages\n($t_{\\rm s}$) in the range of 20.3 Myr to 41.4 Myr with $t_{\\rm OFF}$/$t_{\\rm\ns}$ distributed in the range of 0.16 to 0.63, which in turn suggests them to\nbelong to different evolutionary phases. We note that, in comparison to the\nremnants reported in the literature, our sample sources tend to show lower\nspectral ages that can be explained by the combined effects of more dominant\ninverse Compton losses for our sources present at the relatively higher\nredshifts and possible rapid expansion of lobes in their less dense\nenvironments.", "category": "astro-ph_GA" }, { "text": "Clocking the Evolution of Post-Starburst Galaxies: Methods and First\n Results: Detailed modeling of the recent star formation histories (SFHs) of\npost-starburst (or \"E+A\") galaxies is impeded by the degeneracy between the\ntime elapsed since the starburst ended (post-burst age), the fraction of\nstellar mass produced in the burst (burst strength), and the burst duration. To\nresolve this issue, we combine GALEX ultraviolet photometry, SDSS photometry\nand spectra, and new stellar population synthesis models to fit the SFHs of 532\npost-starburst galaxies. In addition to an old stellar population and a recent\nstarburst, 48% of the galaxies are best fit with a second recent burst. Lower\nstellar mass galaxies (log M$_\\star$/M$_\\odot<10.5$) are more likely to\nexperience two recent bursts, and the fraction of their young stellar mass is\nmore strongly anti-correlated with their total stellar mass. Applying our\nmethodology to other, younger post-starburst samples, we identify likely\nprogenitors to our sample and examine the evolutionary trends of molecular gas\nand dust content with post-burst age. We discover a significant (4$\\sigma$)\ndecline, with a 117-230 Myr characteristic depletion time, in the molecular gas\nto stellar mass fraction with the post-burst age. The implied rapid gas\ndepletion rate of 2-150 M$_\\odot$yr$^{-1}$ cannot be due to current star\nformation, given the upper limits on the current SFRs in these post-starbursts.\nNor are stellar winds or SNe feedback likely to explain this decline. Instead,\nthe decline points to the expulsion or destruction of molecular gas in\noutflows, a possible smoking gun for AGN feedback.", "category": "astro-ph_GA" }, { "text": "The Host Galaxies of Hybrid Morphology Radio Sources: Based on their differing radio morphologies, powerful radio galaxies can be\nseparated into the Fanaroff-Riley I (FR-I) and II (FR-II) classes. Hybrid\nmorphology radio sources (HyMoRS) contain morphologies consistent with each\ntype of jet on either side: a powerful, highly relativistic FR-II-like jet\nterminating in a hotspot on one side and an FRI-like plume on the other. HyMoRS\npresent a unique opportunity to study the conditions which give rise to the\ndichotomy. Using host galaxy properties, we conduct the first multiwavelength\ninvestigation into whether orientation can explain HyMoRS morphology. Through\noptical spectroscopy and mid-infrared photometry, we analyze the emission\ncharacteristics, and evaluate the broad characteristics of five HyMoRS host\ngalaxies at intermediate redshifts (0.4 < z < 1.5). The HyMoRS host galaxies in\nour sample have properties consistent with typical host galaxies of FR-II\nsources, suggesting that the observed hybrid morphologies may be caused by a\ndense, cluster-like environment bending FR-II jets combined with a favorable\norientation which can make one side appear similar to an FR-I jet. Our results\nthus support the hypothesis that HyMoRS are mainly caused by environment and\norientation.", "category": "astro-ph_GA" }, { "text": "Numerical Models for the Diffuse Ionized Gas in Galaxies. II.\n Three-dimensional radiative transfer in inhomogeneous interstellar structures\n as a tool for analyzing the diffuse ionized gas: Aims: We systematically explore a plausible subset of the parameter space\ninvolving effective temperatures and metallicities of the ionizing stellar\nsources, the effects of the hardening of their radiation by surrounding leaky\nHII regions with different escape fractions, as well as different scenarios for\nthe clumpiness of the DIG, and compute the resulting line strength ratios for a\nnumber of diagnostic optical emission lines.\n Methods: For the ionizing fluxes we compute a grid of stellar spectral energy\ndistributions (SEDs) from detailed, fully non-LTE model atmospheres that\ninclude the effects of stellar winds and line blocking and blanketing. To\ncalculate the ionization and temperature structure in the HII regions and the\ndiffuse ionized gas we use spherically symmetric photoionization models as well\nas state-of-the-art three-dimensional (3D) non-LTE radiative transfer\nsimulations, considering hydrogen, helium, and the most abundant metals.\n Results: We provide quantitative predictions of how the line ratios from HII\nregions and the DIG vary as a function of metallicity, stellar effective\ntemperature, and escape fraction from the HII region. The range of predicted\nline ratios reinforces the hypothesis that the DIG is ionized by (filtered)\nradiation from hot stars; however, comparison of observed and predicted line\nratios indicates that the DIG is typically ionized with a softer SED than\npredicted by the chosen stellar population synthesis model. Even small changes\nin simulation parameters like the clumping factor can lead to considerable\nvariation in the ionized volume. Both for a more homogeneous gas and a very\ninhomogeneous gas containing both dense clumps and channels with low gas\ndensity, the ionized region in the dilute gas above the galactic plane can\ncease to be radiation-bounded, allowing the ionizing radiation to leak into the\nintergalactic medium.", "category": "astro-ph_GA" }, { "text": "Herschel observations of Extra-Ordinary Sources: H2S as a Probe of Dense\n Gas and Possibly Hidden Luminosity Toward the Orion KL Hot Core: We present Herschel/HIFI observations of the light hydride H$_{2}$S obtained\nfrom the full spectral scan of the Orion Kleinmann-Low nebula (Orion KL) taken\nas part of the HEXOS GT key program. In total, we observe 52, 24, and 8\nunblended or slightly blended features from H$_{2}$$^{32}$S, H$_{2}$$^{34}$S,\nand H$_{2}$$^{33}$S, respectively. We only analyze emission from the so called\nhot core, but emission from the plateau, extended ridge, and/or compact ridge\nare also detected. Rotation diagrams for ortho and para H$_{2}$S follow\nstraight lines given the uncertainties and yield T$_{\\rm rot}$=141$\\pm$12 K.\nThis indicates H$_{2}$S is in LTE and is well characterized by a single kinetic\ntemperature or an intense far-IR radiation field is redistributing the\npopulation to produce the observed trend. We argue the latter scenario is more\nprobable and find that the most highly excited states (E$_{\\rm up}$>1000 K) are\nlikely populated primarily by radiation pumping. We derive an H$_{2}$$^{32}$S\ncolumn density, N$_{\\rm tot}$(H$_{2}$$^{32}$S)=9.5$\\pm$1.9$\\times$10$^{17}$\ncm$^{-2}$, gas kinetic temperature, T$_{\\rm kin}$=120$\\pm^{13}_{10}$ K, and\nconstrain the H$_{2}$ volume density, n$_{H2}$>9$\\times$10$^{7}$ cm$^{-3}$, for\nthe H$_{2}$S emitting gas. These results point to an H$_{2}$S origin in\nmarkedly dense, heavily embedded gas, possibly in close proximity to a hidden\nself-luminous source (or sources), which are conceivably responsible for Orion\nKL's high luminosity. We also derive an H$_{2}$S ortho/para ratio of\n1.7$\\pm$0.8 and set an upper limit for HDS/H2S of <4.9$\\times$10$^{-3}$.", "category": "astro-ph_GA" }, { "text": "On Synthetic Absorption Line Profiles of Thermally Driven Winds from\n Active Galactic Nuclei: The warm absorbers observed in more than half of all nearby active galactic\nnuclei (AGN) are tracers of ionized outflows located at parsec scale distances\nfrom the central engine. If the smallest inferred ionization parameters\ncorrespond to plasma at a few $10^4$~K, then the gas undergoes a transition\nfrom being bound to unbound provided it is further heated to $\\sim 10^6$~K at\nlarger radii. Dannen et al. recently discovered that under these circumstances,\nthermally driven wind solutions are unsteady and even show very dense clumps\ndue to thermal instability. To explore the observational consequences of these\nnew wind solutions, we compute line profiles based on the one-dimensional\nsimulations of Dannen et al. We show how the line profiles from even a simple\nsteady state wind solution depend on the ionization energy (IE) of absorbing\nions, which is a reflection of the wind ionization stratification. To organize\nthe diversity of the line shapes, we group them into four categories: weak\nGaussians, saturated boxy profiles with and without an extended blue wing, and\nbroad weak profiles. The lines with profiles in the last two categories are\nproduced by ions with the highest IE that probe the fastest regions. Their\nmaximum blueshifts agree with the highest flow velocities in thermally unstable\nmodels, both steady state and clumpy versions. In contrast, the maximum\nblueshifts of the most high IE lines in thermally stable models can be less\nthan half of the actual solution velocities. Clumpy solutions can additionally\nimprint distinguishable absorption troughs at widely separated velocities.", "category": "astro-ph_GA" }, { "text": "Cosmicflows 4: The Calibration of Optical and Infrared Tully-Fisher\n Relations: This study is a part of the Cosmicflows-4 project with the aim of measuring\nthe distances of more than ~10,000 spiral galaxies in the local universe up to\n~15,000 km/s. New HI linewidth information has come primarily from the Arecibo\nLegacy Fast ALFA Survey. Photometry of our sample galaxies has been carried out\nin optical (SDSS u, g, r, i, z) and infrared (WISE W1 and W2) bands.\nInclinations have been determined using an online graphical interface\naccessible to a collaboration of citizen scientists. Galaxy distances are\nmeasured based on the correlation between the rotation rate of spirals and\ntheir absolute luminosity, known as the Tully-Fisher Relation (TFR). In this\nstudy, we present the calibration of the TFR using a subsample of ~600 spirals\nlocated in 20 galaxy clusters. Correlations among such observables as color,\nsurface brightness, and relative HI content are explored in an attempt to\nreduce the scatter about the TFR with the goal of obtaining more accurate\ndistances. A preliminary determination of the Hubble constant from the\ndistances and velocities of the calibrator clusters is\nH0=76.0+-1.1(stat.)+-2.3(sys.) km/s/Mpc.", "category": "astro-ph_GA" }, { "text": "CHORUS. III. Photometric and Spectroscopic Properties of Ly$\u03b1$\n Blobs at $z=4.9-7.0$: We report the Subaru Hyper Suprime-Cam (HSC) discovery of two Ly$\\alpha$\nblobs (LABs), dubbed z70-1 and z49-1 at $z=6.965$ and $z=4.888$ respectively,\nthat are Ly$\\alpha$ emitters with a bright ($\\log L_{\\rm Ly\\alpha}/{\\rm [erg\\\ns^{-1}]}>43.4$) and spatially-extended Ly$\\alpha$ emission, and present the\nphotometric and spectroscopic properties of a total of seven LABs; the two new\nLABs and five previously-known LABs at $z=5.7-6.6$. The z70-1 LAB shows the\nextended Ly$\\alpha$ emission with a scale length of $1.4\\pm 0.2$ kpc, about\nthree times larger than the UV continuum emission, making z70-1 the most\ndistant LAB identified to date. All of the 7 LABs, except z49-1, exhibit no AGN\nsignatures such as X-ray emission, {\\sc Nv}$\\lambda$1240 emission, or\nLy$\\alpha$ line broadening, while z49-1 has a strong {\\sc Civ}$\\lambda$1548\nemission line indicating an AGN on the basis of the UV-line ratio diagnostics.\nWe carefully model the point-spread functions of the HSC images, and conduct\ntwo-component exponential profile fitting to the extended Ly$\\alpha$ emission\nof the LABs. The Ly$\\alpha$ scale lengths of the core (star-forming region) and\nthe halo components are $r_{\\rm c}=0.6-1.2$ kpc and $r_{\\rm h}=2.0-13.8$ kpc,\nrespectively. The average $r_{\\rm h}$ of the LABs falls on the extrapolation of\nthe $r_{\\rm h}$-Ly$\\alpha$ luminosity relation of the Ly$\\alpha$ halos around\nVLT/MUSE star-forming galaxies at the similar redshifts, suggesting that\ntypical LABs at $z\\gtrsim5$ are not special objects, but star-forming galaxies\nat the bright end.", "category": "astro-ph_GA" }, { "text": "The Subaru high-z quasar survey: discovery of faint z~6 quasars: We present the discovery of one or two extremely faint z~6 quasars in 6.5\ndeg^2 utilizing a unique capability of the wide-field imaging of the\nSubaru/Suprime-Cam. The quasar selection was made in (i'-z_B) and (z_B-z_R)\ncolors, where z_B and z_R are bandpasses with central wavelengths of 8842A and\n9841A, respectively. The color selection can effectively isolate quasars at z~6\nfrom M/L/T dwarfs without the J-band photometry down to z_R<24.0, which is 3.5\nmag. deeper than SDSS. We have selected 17 promising quasar candidates. The\nfollow-up spectroscopy for seven targets identified one apparent quasar at\nz=6.156 with M_1450=-23.10. We also identified one possible quasar at z=6.041\nwith a faint continuum of M_1450=-22.58 and a narrow Lyman-alpha emission with\nHWHM=427 km/s, which cannot be distinguished from Lyman-alpha emitters. We\nderive the quasar luminosity function at z~6 by combining our faint quasar\nsample with the bright quasar samples by SDSS and CFHQS. Including our data\npoints invokes a higher number density in the faintest bin of the quasar\nluminosity function than the previous estimate employed. This suggests a\nsteeper faint-end slope than lower-z, though it is yet uncertain based on a\nsmall number of spectroscopically identified faint quasars and several quasar\ncandidates are still remain to be diagnosed. The steepening of the quasar\nluminosity function at the faint-end does increase the expected emission rate\nof the ionizing photon, however, it only changes by a factor of ~2-6. This was\nfound to be still insufficient for the required photon budget of reionization\nat z~6.", "category": "astro-ph_GA" }, { "text": "ALMACAL VI: Molecular gas mass density across cosmic time via a blind\n search for intervening molecular absorbers: We are just starting to understand the physical processes driving the\ndramatic change in cosmic star-formation rate between $z\\sim 2$ and the present\nday. A quantity directly linked to star formation is the molecular gas density,\nwhich should be measured through independent methods to explore variations due\nto cosmic variance and systematic uncertainties. We use intervening CO\nabsorption lines in the spectra of mm-bright background sources to provide a\ncensus of the molecular gas mass density of the Universe. The data used in this\nwork are taken from ALMACAL, a wide and deep survey utilizing the ALMA\ncalibrator archive. While we report multiple Galactic absorption lines and one\nintrinsic absorber, no extragalactic intervening molecular absorbers are\ndetected. However, thanks to the large redshift path surveyed ($\\Delta z=182$),\nwe provide constraints on the molecular column density distribution function\nbeyond $z\\sim 0$. In addition, we probe column densities of N(H$_2$) >\n10$^{16}$ atoms~cm$^{-2}$, five orders of magnitude lower than in previous\nstudies. We use the cosmological hydrodynamical simulation IllustrisTNG to show\nthat our upper limits of $\\rho ({\\rm H}_2)\\lesssim 10^{8.3} \\text{M}_{\\odot}\n\\text{Mpc}^{-3}$ at $0 < z \\leq 1.7$ already provide new constraints on current\ntheoretical predictions of the cold molecular phase of the gas. These results\nare in agreement with recent CO emission-line surveys and are complementary to\nthose studies. The combined constraints indicate that the present decrease of\nthe cosmic star-formation rate history is consistent with an increasing\ndepletion of molecular gas in galaxies compared to $z\\sim 2$.", "category": "astro-ph_GA" }, { "text": "HI-to-H$_2$ Transitions in Dust-Free Interstellar Gas: We present numerical computations and analysis of atomic to molecular\n(HI-to-H$_2$) transitions in cool ($\\sim$100 K) low-metallicity dust-free\n(primordial) gas, in which molecule formation occurs via cosmic-ray driven\nnegative ion chemistry, and removal is by a combination of far-UV\nphotodissociation and cosmic-ray ionization and dissociation. For any gas\ntemperature, the behavior depends on the ratio of the Lyman-Werner (LW) band\nFUV intensity to gas density, $I_{\\rm LW}/n$, and the ratio of the cosmic-ray\nionization rate to the gas density, $\\zeta/n$. We present sets of HI-to-H$_2$\nabundance profiles for a wide range of $\\zeta/n$ and $I_{\\rm LW}/n$, for\ndust-free gas. We determine the conditions for which H$_2$ absorption line\nself-shielding in optically thick clouds enables a transition from atomic to\nmolecular form for ionization-driven chemistry. We also examine the effects of\ncosmic-ray energy losses on the atomic and molecular density profiles and\ntransition points. For a unit Galactic interstellar FUV field intensity\n($I_{\\rm LW}=1$) with LW flux $2.07\\times 10^7$ photons cm$^{-2}$ s$^{-1}$, and\na uniform cosmic-ray ionization rate $\\zeta=10^{-16}$ s$^{-1}$, an HI-to-H$_2$\ntransition occurs at a total hydrogen gas column density of $4\\times 10^{21}$\ncm$^{-2}$, within $3\\times 10^7$ yr, for a gas volume density of $n=10^6$\ncm$^{-3}$ at 100 K. For these parameters, the dust-free limit obtains for a\ndust-to-gas ratio Z$^\\prime_d \\lesssim 10^{-5}$, which may be reached for\noverall metallicities $Z^\\prime\\lesssim 0.01$ relative to Galactic solar\nvalues.", "category": "astro-ph_GA" }, { "text": "Neutral Hydrogen Observations of Low Surface Brightness Galaxies around\n M101 and NGC 5485: We present atomic hydrogen (HI) observations using the Robert C. Byrd Green\nBank Telescope along the lines-of-sight to 27 low surface brightness (LSB)\ndwarf galaxy candidates discovered in optical searches around M101. We detect\nHI reservoirs in 5 targets and place stringent upper limits on the remaining\n22, implying that they are gas poor. The distances to our HI detections range\nfrom 7 Mpc --150 Mpc, demonstrating the utility of wide-bandpass HI\nobservations as a follow-up tool. The systemic velocities of 3 detections are\nconsistent with that of the NGC~5485 group behind M101, and we suggest that our\n15 non-detections with lower distance limits from the optical are associated\nwith and have been stripped by that group. We find that the gas richnesses of\nconfirmed M101 satellites are broadly consistent with those of the Milky Way\nsatellites, as well as with those of satellites around other hosts of\ncomparable mass, when survey completeness is taken into account. This suggests\nthat satellite quenching and gas stripping proceeds similarly around halos of\nsimilar mass, in line with theoretical expectations.", "category": "astro-ph_GA" }, { "text": "Evolution of virial clouds-I: from surface of last scattering up to the\n formation of population-III stars: The analysis of WMAP and Planck CMB data has shown the presence of\ntemperature asymmetries towards the halos of several galaxies, which is\nprobably due to the rotation of clouds present in these halos about the\nrotational axis of the galaxies. It had been proposed that these are hydrogen\nclouds that {\\it should} be in equilibrium with the CMB. However, standard\ntheory did not allow equilibrium of such clouds at the very low CMB\ntemperature, but it was recently shown that the equilibrium {\\it could} be\nstable. This still does not prove that the cloud concentration and that the\nobserved temperature asymmetry is due to clouds in equilibrium with the CMB. To\ninvestigate the matter further, it would be necessary to trace the evolution of\nsuch clouds, which we call \"virial clouds\", from their formation epoch to the\npresent, so as to confront the model with the observational data. The task is\nto be done in two steps: (1) from the cloud formation before the formation of\nfirst generation of stars; (2) from that time to the present. In this paper we\ndeal with the first step leaving the second one to a subsequent analysis.", "category": "astro-ph_GA" }, { "text": "Genetically modified halos: towards controlled experiments in\n $\u039b$CDM galaxy formation: We propose a method to generate `genetically-modified' (GM) initial\nconditions for high-resolution simulations of galaxy formation in a\ncosmological context. Building on the Hoffman-Ribak algorithm, we start from a\nreference simulation with fully random initial conditions, then make controlled\nchanges to specific properties of a single halo (such as its mass and merger\nhistory). The algorithm demonstrably makes minimal changes to other properties\nof the halo and its environment, allowing us to isolate the impact of a given\nmodification. As a significant improvement over previous work, we are able to\ncalculate the abundance of the resulting objects relative to the reference\nsimulation. Our approach can be applied to a wide range of cosmic structures\nand epochs; here we study two problems as a proof-of-concept. First, we\ninvestigate the change in density profile and concentration as the collapse\ntime of three individual halos are varied at fixed final mass, showing good\nagreement with previous statistical studies using large simulation suites.\nSecond, we modify the $z=0$ mass of halos to show that our theoretical\nabundance calculations correctly recover the halo mass function. The results\ndemonstrate that the technique is robust, opening the way to controlled\nexperiments in galaxy formation using hydrodynamic zoom simulations.", "category": "astro-ph_GA" }, { "text": "Measuring the dust attenuation law of galaxies using photometric data: Fitting model spectral energy distributions (SED) to galaxy photometric data\nis a widely used method to recover galaxy parameters from galaxy surveys.\nHowever, the parameter space used to describe galaxies is wide and\ninterdependent, and distinctions between real and spurious correlations that\nare found between these parameters can be difficult to discern. In this work,\nwe use the SED fitting code BAGPIPES to investigate degeneracies between galaxy\nparameters and the effect of the choice of different sets of photometric bands.\nIn particular, we focus on optical to infrared wavelength coverage, and on two\nparameters describing the galaxies' dust attenuation law: $A_V$ and $\\delta$,\nwhich characterize dust column density and the slope of a flexible dust\nattenuation law, respectively. We demonstrate that 1) a degeneracy between the\nresidual (the difference between truth and recovered value) $A_V$ and star\nformation rate exists, but this is lifted when WISE bands are included; 2)\nBAGPIPES is able to accurately recover the input $A_V$ and $\\delta$\ndistributions and relations (differences in slope of less than 1.7$\\sigma$ for\na flat relation, less than 1.2$\\sigma$ for an observationally-motivated\nrelation from Salim et al. 2018) and is not introducing spurious correlations\nbetween these parameters. Our findings suggest that the information needed to\nconstrain $A_V$ and $\\delta$ well enough individually exists in the data,\nespecially when IR is added. This indicates that recent works finding a\ncorrelation between $A_V$ and $\\delta$ are not being misled by fitting\ndegeneracies from their SED fitting code.", "category": "astro-ph_GA" }, { "text": "The OTELO survey: Nature and mass-metallicity relation for H$\u03b1$\n emitters at $z\\sim\\,0.4$: A sample of low-mass H$\\alpha$ emission line sources (ELS) at $z\\,\\sim\\,0.4$\nwas studied in the context of the mass-metallicty relation (MZR) and its\npossible evolution. We drew our sample from the OSIRIS Tunable Emission Line\nObject (OTELO) survey, which exploits the red tunable filter of OSIRIS at the\nGran Telescopio Canarias to perform a blind narrow-band spectral scan in a\nselected field of the Extended Groth Strip. We were able to directly measure\nemission line fluxes and equivalent widths from the analysis of OTELO\npseudo-spectra. This study aims to explore the MZR in the very low-mass regime.\nOur sample reaches stellar masses ($M_*$) as low as $10^{6.8}\\,M_\\odot$, where\n63\\% of the sample have $M_*\\,<10^9\\,M_\\odot$. We also explore the relation of\nthe star formation rate (SFR) and specific SFR (sSFR) with $M_*$ and gas-phase\noxygen abundances, as well as the $M_*$-size relation and the morphological\nclassification. The $M_*$ were estimated using synthetic rest-frame colours.\nUsing an $\\chi^2$ minimization method, we separated the contribution of\n\\Nii$\\lambda$6583 to the H$\\alpha$ emission lines. Using the N2 index, we\nseparated active galactic nuclei from star-forming galaxies (SFGs) and\nestimated the gas metallicity. We studied the morphology of the sampled\ngalaxies qualitatively (visually) and quantitatively (automatically) using\nhigh-resolution data from the \\textit{Hubble Space Telescope}-ACS. The physical\nsize of the galaxies was derived from the morphological analysis using\n\\texttt{GALAPAGOS2/GALFIT}, where we fit a single-S\\'ersic 2D model to each\nsource.", "category": "astro-ph_GA" }, { "text": "Detecting Low-Mass Perturbers in Cluster Lenses using Curved Arc Bases: Strong gravitationally lensed arcs produced by galaxy clusters have been\nobservationally detected for several decades now. These strong lensing\nconstraints provided high-fidelity mass models for cluster lenses that include\nsubstructure down to $10^{9-10}\\,\\mathrm{M}_\\odot$. Optimizing lens models,\nwhere the cluster mass distribution is modeled by a smooth component and\nsubhalos associated with the locations of individual cluster galaxies, has\nenabled deriving the subhalo mass function, providing important constraints on\nthe nature and granularity of dark matter. In this work, we explore and present\na novel method to detect and measure individual perturbers (subhalos,\nline-of-sight halos, and wandering supermassive black holes) by exploiting\ntheir proximity to highly distorted lensed arcs in galaxy clusters, and by\nmodeling the local lensing distortions with curved arc bases. This method\noffers the possibility of detecting individual low-mass perturber subhalos in\nclusters and halos along the line-of-sight down to a mass resolution of\n$10^8\\,\\mathrm{M}_\\odot$. We quantify our sensitivity to low-mass perturbers\n($M\\sim 10^{7-9}\\,\\mathrm{M}_\\odot$) in clusters ($M\\sim\n10^{14-15}\\mathrm{M}_\\odot$), by creating realistic mock data. Using three\nlensed images of a background galaxy in the cluster SMACS J0723, taken by the\n$\\textit{James Webb Space Telescope}$, we study the retrieval of the properties\nof potential perturbers with masses $M=10^{7-9}\\,\\mathrm{M}_\\odot$. From the\nderived posterior probability distributions for the perturber, we constrain its\nconcentration, redshift, and ellipticity. By allowing us to probe lower-mass\nsubstructures, the use of curved arc bases can lead to powerful constraints on\nthe nature of dark matter as discrimination between dark matter models appears\non smaller scales.", "category": "astro-ph_GA" }, { "text": "The formation and physical origin of highly ionized cooling gas: We present a simple model that explains the origin of warm diffuse gas seen\nprimarily as highly ionized absorption line systems in the spectra of\nbackground sources. We predict the observed column densities of several highly\nionized transitions such as OVI, OVIII, NeVIII, NV, and MgX; and present a\nunified comparison of the model predictions with absorption lines seen in the\nMilky Way disk, Milky Way halo,starburst galaxies, the circumgalactic medium\nand the intergalactic medium at low and high redshifts. We show that diffuse\ngas seen in such diverse environments can be simultaneously explained by a\nsimple model of radiatively cooling gas. We show that most of such absorption\nline systems are consistent with being collisionally ionized, and estimate the\nmaximum likelihood temperature of the gas in each observation. This model\nsatisfactorily explains why OVI is regularly observed around star-forming low-z\nL* galaxies, and why NV is rarely seen around the same galaxies. We further\npresent some consequences of this model in quantifying the dynamics of the\ncooling gas around galaxies and predict the shock velocities associated with\nsuch flows. A unique strength of this model is that while it has only one free\n(but physically well-constrained) parameter, it nevertheless successfully\nreproduces the available data on O VI absorbers in the interstellar,\ncircumgalactic, intra-group, and intergalactic media, as well as the available\ndata on other absorption-line from highly ionized species.", "category": "astro-ph_GA" }, { "text": "The X-SHOOTER Lyman-$\u03b1$ survey at z=2 (XLS-z2) I: What makes a\n galaxy a Lyman-$\u03b1$ emitter?: We present the first results from the X-SHOOTER Lyman-$\\alpha$ survey at\n$z=2$ (XLS-$z2$). XLS-$z2$ is a deep spectroscopic survey of 35 Lyman-$\\alpha$\nemitters (LAEs) utilising $\\approx90$ hours of exposure time with VLT/X-SHOOTER\nand covers rest-frame Ly$\\alpha$ to H$\\alpha$ emission with R$\\approx4000$. We\npresent the sample selection, the observations and the data reduction. Systemic\nredshifts are measured from rest-frame optical lines for 33/35 sources. In the\nstacked spectrum, our LAEs are characterised by an interstellar medium with\nlittle dust, a low metallicity and a high ionisation state. The ionising\nsources are young hot stars that power strong emission-lines in the optical and\nhigh ionisation lines in the UV. The LAEs exhibit clumpy UV morphologies and\nhave outflowing kinematics with blue-shifted SiII absorption, a broad [OIII]\ncomponent and a red-skewed Ly$\\alpha$ line. Typically 30 % of the Ly$\\alpha$\nphotons escape, of which one quarter on the blue side of the systemic velocity.\nA fraction of Ly$\\alpha$ photons escapes directly at the systemic suggesting\nclear channels enabling a $\\approx10$ % escape of ionising photons, consistent\nwith an inference based on MgII. A combination of a low effective HI column\ndensity, a low dust content and young star-burst determine whether a star\nforming galaxy is observed as a LAE. The first is possibly related to outflows\nand/or a fortunate viewing angle, while we find that the latter two in LAEs are\ntypical for their stellar mass of 10$^9$ M$_{\\odot}$.", "category": "astro-ph_GA" }, { "text": "Early Science with the Large Millimeter Telescope: discovery of the\n 12CO(1-0) emission line in the ring galaxy, VIIZw466: We report an early science discovery of the CO(1-0) emission line in the\ncollisional ring galaxy, VII Zw466, using the Redshift Search Receiver\ninstrument on the Large Millimeter Telescope Alfonso Serrano.The apparent\nmolecular-to-atomic gas ratio either places the ISM of VII Zw466 in the\nHI-dominated regime or implies a large quantity of CO-dark molecular gas, given\nits high star formation rate. The molecular gas densities and star formation\nrate densities of VII Zw466 are consistent with the standard Kennicutt-Schmidt\nstar formation law even though we find this galaxy to be H2-deficient. The\nchoice of CO-to-H2 conversion factors cannot explain the apparent H2 deficiency\nin its entirety. Hence, we find that the collisional ring galaxy, VII Zw466, is\neither largely deficient in both H2 and HI or contains a large mass of CO-dark\ngas. A low molecular gas fraction could be due to the enhancement of feedback\nprocesses from previous episodes of star formation as a result of the\nstar-forming ISM being confined to the ring. We conclude that collisional ring\ngalaxy formation is an extreme form of galaxy interaction that triggers a\nstrong galactic-wide burst of star formation that may provide immediate\nnegative feedback towards subsequent episodes of star formation---resulting in\na short-lived star formation history or, at least, the appearance of a\nmolecular gas deficit.", "category": "astro-ph_GA" }, { "text": "Host Galaxy Properties and Black Hole Mass of Swift J164449.3+573451\n from Multi-Wavelength Long-Term Monitoring and HST Data: We study the host galaxy properties of the tidal disruption object, Swift\nJ164449.3+573451 using long-term optical to near-infrared (NIR) data. First, we\ndecompose the galaxy surface brightness distribution and analyze the morphology\nof the host galaxy using high resolution \\emph{HST} WFC3 images. We conclude\nthat the host galaxy is a bulge-dominant galaxy that is well described by a\nsingle S\\'{e}rsic model with S\\'{e}rsic index $n=3.43\\pm0.05$. Adding a disk\ncomponent, the bulge to total host galaxy flux ratio (B/T) is $0.83\\pm0.03$,\nwhich still indicates a bulge-dominant galaxy. Second, we estimate multi-band\nfluxes of the host galaxy through long-term light curves. Our long-term NIR\nlight curves reveal the pure host galaxy fluxes $\\sim500$ days after the burst.\nWe fit spectral energy distribution (SED) models to the multi-band fluxes from\nthe optical to NIR of the host galaxy and determine its properties. The stellar\nmass, the star formation rate, and the age of stellar population are\n$\\log(M_{\\star}/M_{\\odot}) = 9.14^{+0.13}_{-0.10}$, $0.03^{+0.28}_{-0.03}\\,\nM_{\\odot}$/yr, and $0.63^{+0.95}_{-0.43}$ Gyr. Finally, we estimate the mass of\nthe central super massive black hole which is responsible for the tidal\ndisruption event. The black hole mass is estimated to be $10^{6.7\\pm0.4}\\,\nM_{\\odot}$ from $M_{\\mathrm{BH}}$ - $M_{\\star,\\mathrm{bul}}$ and\n$M_{\\mathrm{BH}}$ - $L_{\\mathrm{bul}}$ relations for the $K$ band, although a\nsmaller value of $\\sim10^5\\, M_{\\odot}$ cannot be excluded convincingly if the\nhost galaxy harbors a pseudobulge.", "category": "astro-ph_GA" }, { "text": "Interactions of the Infrared bubble N4 with the surroundings: The physical mechanisms that induce the transformation of a certain mass of\ngas in new stars are far from being well understood. Infrared bubbles\nassociated with HII regions have been considered to be good samples of\ninvestigating triggered star formation. In this paper we report on the\ninvestigation of the dust properties of the infrared bubble N4 around the HII\nregion G11.898+0.747, analyzing its interaction with its surroundings and star\nformation histories therein, with the aim of determining the possibility of\nstar formation triggered by the expansion of the bubble. Using Herschel PACS\nand SPIRE images with a wide wavelength coverage, we reveal the dust properties\nover the entire bubble. Meanwhile, we are able to identify six dust clumps\nsurrounding the bubble, with a mean size of 0.50 pc, temperature of about 22 K,\nmean column density of 1.7 $\\times10^{22}$ cm$^{-2}$, mean volume density of\nabout 4.4 $\\times10^{4}$ cm$^{-3}$, and a mean mass of 320 $M_{\\odot}$. In\naddition, from PAH emission seen at 8 $\\mu$m, free-free emission detected at 20\ncm and a probability density function in special regions, we could identify\nclear signatures of the influence of the HII region on the surroundings. There\nare hints of star formation, though further investigation is required to\ndemonstrate that N4 is the triggering source.", "category": "astro-ph_GA" }, { "text": "The Dust Properties of Bubble HII Regions as seen by Herschel: Because of their relatively simple morphology, \"bubble\" HII regions have been\ninstrumental to our understanding of star formation triggered by HII regions.\nWith the far-infrared (FIR) spectral coverage of the Herschel satellite, we can\naccess the wavelengths where these regions emit the majority of their energy\nthrough their dust emission. At Herschel wavelengths 70 micron to 500 micron,\nthe emission associated with HII regions is dominated by the cool dust in their\nphotodissociation regions (PDRs). We find average dust temperatures of 26K\nalong the PDRs, with little variation between the HII regions in the sample,\nwhile local filaments and infrared dark clouds average 19K and 15K\nrespectively. Higher temperatures lead to higher values of the Jeans mass,\nwhich may affect future star formation. The mass of the material in the PDR,\ncollected through the expansion of the HII region, is between ~300 and ~10,000\nSolar masses for the HII regions studied here. These masses are in rough\nagreement with the expected masses swept up during the expansion of the \\hii\\\nregions. Approximately 20% of the total FIR emission is from the direction of\nthe bubble central regions. This suggests that we are detecting emission from\nthe \"near-side\" and \"far-side\" PDRs along the line of sight and that bubbles\nare three-dimensional structures. We find only weak support for a relationship\nbetween dust temperature and beta, of a form similar to that caused by noise\nand calibration uncertainties alone.", "category": "astro-ph_GA" }, { "text": "The Mechanical Alignment of Dust (MAD) I: On the spin-up process of\n fractal grains by a gas-dust drift: Context: Aligned dust grains are commonly exploited to probe the magnetic\nfield orientation. However, the exact physical processes that result in a\ncoherent large-scale grain alignment are far from being constrained. Aims: In\nthis work, we aim to investigate the impact of a gas-dust drift leading to a\nmechanical alignment of dust (MAD) and to dust polarization. Methods: We\nexplore fractal dust aggregates to statistically analyze the average alignment\nbehavior of distinct grain ensembles. The spin-up efficiencies for individual\naggregates are determined utilizing MC simulations. These efficiencies are\nanalyzed to identify stable points for the grain alignment in direction of the\ngas-dust drift and along the magnetic field lines. Finally, the net dust\npolarization is calculated per grain ensemble. Results: The mechanical spin-up\nwithin the CNM is sufficient to drive grains to a stable alignment. A likely\nmechanical grain alignment is parallel to the drift direction. All grains can\nalign at subsonic conditions. Here, we predict a polarization efficiency in the\norder of unity for the MAD. A supersonic drift may result in a rapid rotation\nwhere dust grains may become rotationally disrupted and the polarization\nbecomes drastically reduced. In the presence of a magnetic field, the drift\nrequired for the alignment of elongated grains is roughly one order of\nmagnitude higher compared to the pure MAD. Here, the dust polarization\nefficiency is 0.6-0.9 indicating that a drift can provide the prerequisites to\nprobe the magnetic field. The alignment is inefficient when the direction of\nthe drift and the field lines are perpendicular. Conclusions: We find that MAD\nhas to be taken into consideration as an alternative driving mechanism where\nthe standard RAT alignment theory fails to account for the full spectrum of\navailable dust polarization observations.", "category": "astro-ph_GA" }, { "text": "Neutral carbon and CO in 76 (U)LIRGs and starburst galaxy centers A\n method to determine molecular gas properties in luminous galaxies: We present fluxes in both neutral carbon [CI] lines at the centers of 76\ngalaxies with FIR luminosities between 10^{9} and 10^{12} L(o) obtained with\nHerschel-SPIRE and with ground-based facilities, along with the J=7-6, J=4-3,\nJ=2-1 12CO and J=2-1 13CO line fluxes. We investigate whether these lines can\nbe used to characterize the molecular ISM of the parent galaxies in simple ways\nand how the molecular gas properties define the model results. In most\nstarburst galaxies, the [CI]/13CO flux ratio is much higher than in Galactic\nstar-forming regions, and it is correlated to the total FIR luminosity. The\n[CI](1-0)/CO(4-3), the [CI](2-1) (2-1)/CO(7-6), and the [CI] (2-1)/(1-0) flux\nratios are also correlated, and trace the excitation of the molecular gas. In\nthe most luminous infrared galaxies (LIRGs), the ISM is fully dominated by\ndense and moderately warm gas clouds that appear to have low [C]/[CO] and\n[13CO]/[12CO] abundances. In less luminous galaxies, emission from gas clouds\nat lower densities becomes progressively more important, and a multiple-phase\nanalysis is required to determine consistent physical characteristics. Neither\nthe CO nor the [CI] velocity-integrated line fluxes are good predictors of H2\ncolumn densities in individual galaxies, and X(CI) conversion factors are not\nsuperior to X(CO) factors. The methods and diagnostic diagrams outlined in this\npaper also provide a new and relatively straightforward means of deriving the\nphysical characteristics of molecular gas in high-redshift galaxies up to z=5,\nwhich are otherwise hard to determine.", "category": "astro-ph_GA" }, { "text": "H2CO ortho-to-para ratio in the protoplanetary disk HD 163296: Ortho-to-para (o/p) ratios of species like water, ammonia and formaldehyde\n(H2CO) are believed to encode information about the formation history of the\nmolecule. Measurements of o/p ratios in protoplanetary disks could thus be used\nto constrain their physical and chemical histories. We present the first\nmeasurement of the H2CO o/p ratio in a protoplanetary disk, using three ortho\nand two para lines observed with the Sub-millimeter Array (SMA) combined with\none highly resolved measurement of a single H2CO line with ALMA toward the disk\naround Herbig Ae star HD 163296. We find a disk-averaged H2CO o/p ratio of\n1.8-2.8 (depending on the assumed disk structure), corresponding to a spin\ntemperature of 11-22 K. We also derive a rotational temperature of 24 K from\nthe flux ratio of the three ortho lines. The observed spatial distribution, as\nseen by ALMA, as well as the rotational temperature and the o/p ratio, at the\nlarge scales the SMA is most sensitive to, are consistent with a\nlow-temperature formation pathway, most likely grain surface chemistry, of H2CO\nin this disk.", "category": "astro-ph_GA" }, { "text": "The Star Formation Reference Survey. II. Activity demographics and\n host-galaxy properties for Infrared-selected galaxies: We present activity demographics and host-galaxy properties of\ninfrared-selected galaxies in the local Universe, using the representative Star\nFormation Reference Survey (SFRS). Our classification scheme is based on a\ncombination of optical emission-line diagrams (BPT) and IR-color diagnostics.\nUsing the weights assigned to the SFRS galaxies based on its parent sample, a\nfar-infrared-selected sample comprises 71\\% H\\,\\textsc{ii} galaxies, 13\\%\nSeyferts, 3\\% Transition Objects (TOs), and 13\\% Low-Ionization Nuclear\nEmission-Line Regions (LINERs). For the SFRS H\\,\\textsc{ii} galaxies we derive\nnuclear star-formation rates and gas-phase metallicities. We measure\nhost-galaxy metallicities for all galaxies with available long-slit\nspectroscopy and abundance gradients for a subset of 12 face-on galaxies. The\nmajority of H\\,\\textsc{ii} galaxies show a narrow range of metallicities, close\nto solar, and flat metallicity profiles. Based on their host-galaxy and nuclear\nproperties, the dominant ionizing source in the far-infrared selected TOs is\nstar-forming activity. LINERs are found mostly in massive hosts (median of\n$10^{10.5}$ M$_{\\odot} $), median $L(60\\mu m) = 10^{9}$ L$_{\\odot}$, median\ndust temperatures of $ F60/F100 = 0.36 $, and median $L_{\\textrm{H}\\alpha}$\nsurface density of $ 10^{40.2} $ erg s$ ^{-1} $kpc$ ^{-2} $, indicating older\nstellar populations as their main ionizing source rather than AGN activity.", "category": "astro-ph_GA" }, { "text": "Galaxy evolution within the Kilo-Degree Survey: The ESO Public Kilo-Degree Survey (KiDS) is an optical wide-field imaging\nsurvey carried out with the VLT Survey Telescope and the OmegaCAM camera. KiDS\nwill scan 1500 square degrees in four optical filters (u, g, r, i). Designed to\nbe a weak lensing survey, it is ideal for galaxy evolution studies, thanks to\nthe high spatial resolution of VST, the good seeing and the photometric depth.\nThe surface photometry have provided with structural parameters (e.g. size and\nS\\'ersic index), aperture and total magnitudes have been used to derive\nphotometric redshifts from Machine learning methods and stellar\nmasses/luminositites from stellar population synthesis. Our project aimed at\ninvestigating the evolution of the colour and structural properties of galaxies\nwith mass and environment up to redshift $z \\sim 0.5$ and more, to put\nconstraints on galaxy evolution processes, as galaxy mergers.", "category": "astro-ph_GA" }, { "text": "A flux-ratio anomaly in the CO spectral line emission from\n gravitationally-lensed quasar MG J0414+0534: We present an analysis of archival observations with the Atacama Large\n(sub-)Millimetre Array (ALMA) of the gravitationally lensed quasar MG\nJ0414+0534, which show four compact images of the quasar and an Einstein ring\nfrom the dust associated with the quasar host galaxy. We confirm that the\nflux-ratio anomalies observed in the mid-infrared and radio persists into the\nsub-mm for the continuum images of the quasar. We report the detection of CO\n(11-10) spectral line emission, which traces a region of compact gas around the\nquasar nucleus. This line emission also shows evidence of a flux-ratio anomaly\nbetween the merging lensed images that is consistent with those observed at\nother wavelengths, suggesting high-excitation CO can also provide a useful\nprobe of substructures that is unaffected by microlensing or dust extinction.\nHowever, we do not detect the candidate dusty dwarf galaxy that was previously\nreported with this dataset, which we conclude is due to a noise artefact. Thus,\nthe cause of the flux-ratio anomaly between the merging lensed images is still\nunknown. The composite compact and diffuse emission in this system suggest\nlensed quasar-starbursts will make excellent targets for detecting dark\nsub-haloes and testing models for dark matter.", "category": "astro-ph_GA" }, { "text": "HH 80/81: Structure and Kinematics of the Fastest Protostellar Outflow: Hubble Space Telescope images obtained in 2018 are combined with archival HST\ndata taken in 1995 to detect changes and measure proper motions in the HH 80/81\nshock complex which is powered by the fastest known jet driven by a forming\nstar, the massive object IRAS 18162-2048. Some persistent features close to the\nradio jet axis have proper motions grater than 1,000 km/s away from IRAS\n18162-2048. About 3 to 5 parsecs downstream from the IRAS source and beyond HH\n80/81, H-alpha emission traces the rim of a parsec-scale bubble blown by the\njet. Lower speed motions are seen in [Sii] away from the jet axis; these\nfeatures have a large component of motion at right-angles to the jet. We\nidentify new HH objects and H2 shocks in the counterflow opposite HH 80/81. The\nnortheastern counterflow to HH 80/81 exhibits an extended but faint complex of\n2.12 um H2 shocks. The inner portion of the outflow is traced by dim 1.64 um\n[Feii] emission. The full extent of this outflow is at least 1,500\" (about 10\npc in projection at a distance of 1.4 kpc). We speculate about the conditions\nresponsible for the production of the ultra-fast jet and the absence of\nprominent large-scale molecular outflow lobes.", "category": "astro-ph_GA" }, { "text": "Rapid Chemical Enrichment by Intermittent Star Formation in GN-z11: We interpret the peculiar super-solar nitrogen abundance recently reported by\nthe James Webb Space Telescope observations for GN-z11 ($z=10.6$) using our\nstate-of-the-art chemical evolution models. The observed CNO ratios can be\nsuccessfully reproduced -- independently of the adopted initial mass function,\nnucleosynthesis yields, and presence of supermassive ($>$1000$M_\\odot$) stars\n-- if the galaxy has undergone an intermittent star formation history with a\nquiescent phase lasting $\\sim$100 Myr, separating two strong starbursts.\nImmediately after the second burst, Wolf--Rayet stars (up to $120M_\\odot$)\nbecome the dominant enrichment source, also temporarily ($<$1 Myr) enhancing\nparticular elements (N, F, Na, and Al) and isotopes ($^{13}$C and $^{18}$O).\nAlternative explanations involving (i) single burst models, also including very\nmassive stars and/or pair-instability supernovae, or (ii) pre-enrichment\nscenarios fail to match the data. Feedback-regulated, intermittent star\nformation might be common in early systems. Elemental abundances can be used to\ntest this hypothesis and to get new insights on nuclear and stellar\nastrophysics.", "category": "astro-ph_GA" }, { "text": "An All-Sky Sample of Intermediate-Mass Star-Forming Regions: We present an all-sky sample of 984 candidate intermediate-mass Galactic\nstar-forming regions color-selected from the Infrared Astronomical Satellite\n(IRAS) Point Source Catalog and morphologically classify each object using\nmid-infrared Wide-field Infrared Survey Explorer (WISE) images. Of the 984\ncandidates, 616 are probable star-forming regions (62.6%), 128 are filamentary\nstructures (13.0%), 39 are point-like objects of unknown nature (4.0%), and 201\nare galaxies (20.4%). We conduct a study of four of these regions, IRAS\n00259+5625, IRAS 00420+5530, IRAS 01080+5717, and IRAS 05380+2020, at Galactic\nlatitudes |b| > 5 degrees using optical spectroscopy from the Wyoming Infrared\nObservatory along with near-infrared photometry from the Two-Micron All Sky\nSurvey to investigate their stellar content. New optical spectra,\ncolor-magnitude diagrams, and color-color diagrams reveal their extinctions,\nspectrophotometric distances, and the presence of small stellar clusters\ncontaining 20-78 solar masses of stars. These low-mass diffuse star clusters\ncontain 65-250 stars for a typical initial mass function, including one or more\nmid-B stars as their most massive constituents. Using infrared spectral energy\ndistributions we identify young stellar objects near each region and assign\nprobable masses and evolutionary stages to the protostars. The total infrared\nluminosity lies in the range 190 to 960 solar luminosities, consistent with the\nsum of the luminosities of the individually identified young stellar objects.", "category": "astro-ph_GA" }, { "text": "The Spitzer Local Volume Legacy (LVL) Global Optical Photometry: We present the global optical photometry of 246 galaxies in the Local Volume\nLegacy (LVL) survey. The full volume-limited sample consists of 258 nearby (D <\n11 Mpc) galaxies whose absolute B-band magnitude span a range of -9.6 < M_B <\n-20.7 mag. A composite optical (UBVR) data set is constructed from observed\nUBVR and SDSS ugriz imaging, where the ugriz magnitudes are transformed into\nUBVR. We present photometry within three galaxy apertures defined at UV,\noptical, and IR wavelengths. Flux comparisons between these apertures reveal\nthat the traditional optical R25 galaxy apertures do not fully encompass\nextended sources. Using the larger IR apertures we find color-color\nrelationships where later-type spiral and irregular galaxies tend to be bluer\nthan earlier-type galaxies. These data provide the missing optical emission\nfrom which future LVL studies can construct the full panchromatic\n(UV-optical-IR) spectral energy distributions.", "category": "astro-ph_GA" }, { "text": "A VLT/FLAMES study of the peculiar intermediate-age Large Magellanic\n Cloud star cluster NGC 1846 - I. Kinematics: In this paper we present high resolution VLT/FLAMES observations of red giant\nstars in the massive intermediate-age Large Magellanic Cloud star cluster NGC\n1846, which, on the basis of its extended main-sequence turn-off (EMSTO),\npossesses an internal age spread of ~300 Myr. We describe in detail our target\nselection and data reduction procedures, and construct a sample of 21 stars\npossessing radial velocities indicating their membership of NGC 1846 at high\nconfidence. We consider high-resolution spectra of the planetary nebula Mo-17,\nand conclude that this object is also a member of the cluster. Our measured\nradial velocities allow us to conduct a detailed investigation of the internal\nkinematics of NGC 1846, the first time this has been done for an EMSTO system.\nThe key result of this work is that the cluster exhibits a significant degree\nof systemic rotation, of a magnitude comparable to the mean velocity\ndispersion. Using an extensive suite of Monte Carlo models we demonstrate that,\ndespite our relatively small sample size and the substantial fraction of\nunresolved binary stars in the cluster, the rotation signal we detect is very\nlikely to be genuine. Our observations are in qualitative agreement with the\npredictions of simulations modeling the formation of multiple populations of\nstars in globular clusters, where a dynamically cold, rapidly rotating second\ngeneration is a common feature. NGC 1846 is less than one relaxation time old,\nso any dynamical signatures encoded during its formation ought to remain\npresent.", "category": "astro-ph_GA" }, { "text": "Identification of Ambient Molecular Clouds Associated with Galactic\n Supernova Remnant IC443: The Galactic supernova remnant (SNR) IC443 is one of the most studied\ncore-collapse SNRs for its interaction with molecular clouds. However, the\nambient molecular clouds with which IC443 is interacting have not been\nthoroughly studied and remain poorly understood. Using Five College Radio\nAstronomy Observatory 14m telescope, we obtained fully sampled maps of ~\n1{\\deg} \\times 1{\\deg} region toward IC443 in the 12CO J=1-0 and HCO+ J=1-0\nlines. In addition to the previously known molecular clouds in the velocity\nrange v_lsr = -6 to -1 km/s (-3 km/s clouds), our observations reveal two new\nambient molecular cloud components: small (~ 1') bright clouds in v_lsr = -8 to\n-3 km/s (SCs), and diffuse clouds in v_lsr = +3 to +10 km/s (+5 km/s clouds).\nOur data also reveal the detailed kinematics of the shocked molecular gas in\nIC443, however the focus of this paper is the physical relationship between the\nshocked clumps and the ambient cloud components. We find strong evidence that\nthe SCs are associated with the shocked clumps. This is supported by the\npositional coincidence of the SCs with shocked clumps and other tracers of\nshocks. Furthermore, the kinematic features of some shocked clumps suggest that\nthese are the ablated material from the SCs upon the impact of the SNR shock.\nThe SCs are interpreted as dense cores of parental molecular clouds that\nsurvived the destruction by the pre-supernova evolution of the progenitor star\nor its nearby stars. We propose that the expanding SNR shock is now impacting\nsome of the remaining cores and the gas is being ablated and accelerated\nproducing the shocked molecular gas. The morphology of the +5 km/s clouds\nsuggests an association with IC443. On the other hand, the -3 km/s clouds show\nno evidence for interaction.", "category": "astro-ph_GA" }, { "text": "Analysis of the interstellar matter at the periphery of the supershell\n surrounding the CYG OB1 association in 2.12 micron molecular hydrogen line: We present observations of the vdB 130 cluster vicinity in a narrow-band\nfilter centered at a $2.12\\,\\mu$m molecular hydrogen line performed at the\nCaucasus Mountain Observatory of the Lomonosov Moscow State University. The\nobservations reveal an H$_2$ emission shell around vdB 130, coincident with a\nbright infrared shell, visible in all \\textit{Spitzer} bands. Also, numerous\nH$_{2}$ emission features are detected around infrared Blobs E and W and in the\nvicinity of a protocluster located to the east of the shell, in a tail of a\ncometary molecular cloud. H$_2$ emission in the vicinity of the vdB~130 cluster\nis mostly generated in well-developed \\HII\\ regions and is of fluorescent\nnature. In the protocluster area, isolated spots are observed, where H$_2$\nemission is collisionally excited and is probably related to shocks in\nprotostellar outflows. Obtained results are discussed in the context of\npossible sequential star formation in the vicinity of the vdB 130 cluster,\ntriggered by the interaction of the expanding supershell surrounding the Cyg\nOB1 association with the molecular cloud and an associated molecular filament.", "category": "astro-ph_GA" }, { "text": "Magnetic Field of Molecular Gas Measured with the Velocity Gradient\n Technique I. Orion A: Magnetic fields play an important role in the evolution of molecular clouds\nand star formation. Using the Velocity Gradient Technique (VGT) model, we\nmeasured the magnetic field in Orion A using the 12CO, 13CO, and C18O (1-0)\nemission lines at a scale of 0.07 pc. The measured B-field shows an east-west\norientation that is perpendicular to the integral shaped filament of Orion A at\nlarge scale. The VGT magnetic fields obtained from 13CO and C18O are in\nagreement with the B-field that is measured from the Planck 353 GHz dust\npolarization at a scale of 0.55 pc. Removal of density effects by using a\nVelocity Decomposition Algorithm can significantly improve the accuracy of the\nVGT in tracing magnetic fields with the 12CO (1-0) line. The magnetic field\nstrength of seven sub-clouds, OMC-1, OMC-2, OMC-3, OMC-4, OMC-5, L 1641-N, and\nNGC 1999 has also been estimated with the Davis-Chandrasekhar-Fermi (DCF) and\nMM2 technique, and these are found to be in agreement with previous results\nobtained from dust polarization at far-infrared and sub-millimeter wavelengths.\nAt smaller scales, the VGT proves a good method to measure magnetic fields.", "category": "astro-ph_GA" }, { "text": "Gas morphology and energetics at the surface of PDRs: new insights with\n Herschel observations of NGC 7023: We investigate the physics and chemistry of the gas and dust in dense\nphoton-dominated regions (PDRs), along with their dependence on the\nilluminating UV field. Using Herschel-HIFI observations, we study the gas\nenergetics in NGC 7023 in relation to the morphology of this nebula. NGC 7023\nis the prototype of a PDR illuminated by a B2V star and is one of the key\ntargets of Herschel. Our approach consists in determining the energetics of the\nregion by combining the information carried by the mid-IR spectrum (extinction\nby classical grains, emission from very small dust particles) with that of the\nmain gas coolant lines. In this letter, we discuss more specifically the\nintensity and line profile of the 158 micron (1901 GHz) [CII] line measured by\nHIFI and provide information on the emitting gas. We show that both the [CII]\nemission and the mid-IR emission from polycyclic aromatic hydrocarbons (PAHs)\narise from the regions located in the transition zone between atomic and\nmolecular gas. Using the Meudon PDR code and a simple transfer model, we find\ngood agreement between the calculated and observed [CII] intensities. HIFI\nobservations of NGC 7023 provide the opportunity to constrain the energetics at\nthe surface of PDRs. Future work will include analysis of the main coolant line\n[OI] and use of a new PDR model that includes PAH-related species.", "category": "astro-ph_GA" }, { "text": "UVIT view of dwarf irregular galaxy IC 2574 : Is the star formation\n triggered due to expanding H$~$I shells?: Star forming dwarf galaxies in the local volume are diverse and are ideal\ntest beds to understand details of star formation in a variety of environments.\nHere, we present a deep FUV imaging study of a nearby dwarf irregular galaxy IC\n2574 using the Ultraviolet Imaging Telescope (UVIT). We identified 419 FUV\nbright regions with radii between 15 - 285 pc in the galaxy and found that\n28.6\\% of them to be located in H~I shells, 12.6\\% inside holes and 60.1\\% to\nbe away from the holes. The H~I column density is found to be more than\n$10^{21} cm^{-2}$ for 82.3\\% of the identified regions. 30 out of the 48 H~I\nholes show triggered star formation in their shells while 16 holes do not show\nany related FUV emission. Cross-matching with H$\\alpha$ emission, we found that\n23 holes have both FUV and H$\\alpha$ emission in their shells signifying very\nrecent trigger. Therefore, star formation in the galaxy has been partly\ntriggered due to the expanding H~I holes whereas in majority of the sites it is\ndriven by other mechanisms. Irrespective of the location, larger star forming\ncomplexes were found to have multiple sub-structures. We report two resolved\ncomponents for the remnant cluster of the super giant shell and estimated their\nmasses. The star formation rate of IC 2574 is found to be 0.57 $M_{\\odot}$/yr,\nwhich is slightly higher compared to the average value of other nearby dwarf\nirregular galaxies.", "category": "astro-ph_GA" }, { "text": "The star formation history in the solar neighborhood as told by massive\n white dwarfs: White dwarfs are the remnants of low and intermediate mass stars. Because of\nelectron degeneracy, their evolution is just a simple gravothermal process of\ncooling. Recently, thanks to Gaia data, it has been possible to construct the\nluminosity function of massive (0.9 < M/Msun < 1.1) white dwarfs in the solar\nneighborhood (d < 100 pc). Since the lifetime of their progenitors is very\nshort, the birth times of both, parents and daughters, are very close and allow\nto reconstruct the (effective) star formation rate. This rate started growing\nfrom zero during the early Galaxy and reached a maximum 6-7 Gyr ago. It\ndeclined and ~5 Gyr ago started to climb once more reaching a maximum 2 - 3 Gyr\nin the past and decreased since then. There are some traces of a recent star\nformation burst, but the method used here is not appropriate for recently born\nwhite dwarfs.", "category": "astro-ph_GA" }, { "text": "Still at Odds with Conventional Galaxy Evolution: The Star Formation\n History of Ultra-Diffuse Galaxy Dragonfly 44: We study the star formation history (SFH) of the ultra-diffuse galaxy (UDG)\nDragonfly 44 (DF44) based on the simultaneous fit to near-ultraviolet to\nnear-infrared photometry and high signal-to-noise optical spectroscopy. In\nfitting the observations we adopt an advanced physical model with a flexible\nSFH, and we discuss the results in the context of the degeneracies between\nstellar population parameters. Through reconstructing the mass-assembly history\nwith a prior for extended star formation (akin to methods in the literature) we\nfind that DF44 formed 90 per cent of its stellar mass by $z\\sim 0.9$ ($\\sim\n7.2$ Gyr ago). In comparison, using a prior that prefers concentrated star\nformation (as informed by previous studies of DF44's stellar populations)\nsuggests that DF44 formed as early as $z\\sim 8$ ($\\sim 12.9$ Gyr ago).\nRegardless of whether DF44 is old or very old, the SFHs imply early star\nformation and rapid quenching. This result, together with DF44's large size and\nevidence that it is on its first infall into the Coma cluster, challenges UDG\nformation scenarios from simulations that treat all UDGs as contiguous with the\ncanonical dwarf population. While our results cannot confirm any particular\nformation scenario, we can conclude from this that DF44 experienced a rare\nquenching event.", "category": "astro-ph_GA" }, { "text": "DNC/HNC and N2D+/N2H+ ratios in high-mass star forming cores: Chemical models predict that the deuterated fraction (the column density\nratio between a molecule containing D and its counterpart containing H) of\nN2H+, Dfrac(N2H+), is high in massive pre-protostellar cores and rapidly drops\nof an order of magnitude after the protostar birth, while that of HNC,\nDfrac(HNC), remains constant for much longer. We tested these predictions by\nderiving Dfrac(HNC) in 22 high-mass star forming cores divided in three\ndifferent evolutionary stages, from high-mass starless core candidates (HMSCs,\n8) to high-mass protostellar objects (HMPOs, 7) to Ultracompact HII regions\n(UCHIIs, 7). For all of them, Dfrac (N2H+) was already determined through\nIRAM-30m Telescope observations, which confirmed the theoretical rapid decrease\nof Dfrac(N2H+) after protostar birth (Fontani et al. 2011). Therefore our\ncomparative study is not affected by biases introduced by the source selection.\nWe have found average Dfrac(HNC) of 0.012, 0.009 and 0.008 in HMSCs, HMPOs and\nUCHIIs, respectively, with no statistically significant differences among the\nthree evolutionary groups. These findings confirm the predictions of the\nchemical models, and indicate that large values of Dfrac(N2H+) are more\nsuitable than large values of Dfrac(HNC) to identify cores on the verge of\nforming high-mass stars, likewise what found in the low-mass regime.", "category": "astro-ph_GA" }, { "text": "The Einasto model for dark matter haloes: Context: The Einasto model has become one of the most popular models for\ndescribing the density profile of dark matter haloes. There have been\nrelatively few comprehensive studies on the dynamical structure of the Einasto\nmodel, mainly because only a limited number of properties can be calculated\nanalytically. Aims: We want to systematically investigate the photometric and\ndynamical structure of the family of Einasto models over the entire model\nparameter space. Methods: We used the SpheCow code to explore the properties of\nthe Einasto model. We systematically investigated how the most important\nproperties change as a function of the Einasto index $n$. We considered both\nisotropic models and radially anisotropic models with an Osipkov-Merritt\norbital structure. Results: We find that all Einasto models with $n<\\tfrac12$\nhave a formal isotropic or Osipkov-Merritt distribution function that is\nnegative in parts of phase space, and hence cannot be supported by such orbital\nstructures. On the other hand, all models with larger values of $n$ can be\nsupported by an isotropic orbital structure, or by an Osipkov-Merritt\nanisotropy, as long as the anisotropy radius is larger than a critical value.\nThis critical anisotropy radius is a decreasing function of $n$, indicating\nthat less centrally concentrated models allow for a larger degree of radial\nanisotropy. Conclusions: Studies of the structure and dynamics of models for\ngalaxies and dark matter haloes should not be restricted to completely\nanalytical models. Numerical codes such as SpheCow can help open up the range\nof models that are systematically investigated. This applies to the Einasto\nmodel discussed here, but also to other proposed models for dark matter haloes,\nincluding different extensions to the Einasto model.", "category": "astro-ph_GA" }, { "text": "Warm Molecular Gas in the Central Parsecs of the Buried Nucleus of NGC\n 4418 Traced with the Fundamental CO Ro-vibrational Absorptions: We investigated the inner buried nucleus of a nearby luminous infrared galaxy\nNGC 4418 using high-resolution spectroscopy of fundamental carbon monoxide (CO)\nro-vibrational absorptions around $4.67 \\mu$m for the first time. This method\nallowed us to examine the physical and kinematical properties in the hot inner\nregion of this nucleus. We detected a series of both very deep (partly\nsaturated) $^{12}$CO and moderately deep (optically thin) $^{13}$CO absorption\nlines and inferred a large column density ($N_\\mathrm{H2}=(5\\pm3)\\times10^{23}$\ncm$^{-2}$ in front of the $5 \\mu$m photosphere) of warm\n($T_\\mathrm{ex}\\simeq170$ K) molecular gas by assuming an isothermal\nplane-parallel slab illuminated by a compact background MIR-emitting source. We\nmodeled that the warm CO absorber almost covers the central heating source and\nthat it is an inner layer around the $5 \\mu$m photosphere (at $r=$several pc)\nof a compact shroud of gas and dust ($d\\sim100$ pc). The width of the\nabsorption lines ($110$ km s$^{-1}$) and their small deviation from the\nsystemic velocity ($<10$ km s$^{-1}$) are consistent with a warm and turbulent\nlayer with little bulk motion in the radial direction.", "category": "astro-ph_GA" }, { "text": "Dynamical masses of brightest cluster galaxies II: constraints on the\n stellar IMF: We use stellar and dynamical mass profiles, combined with a stellar\npopulation analysis, of 32 brightest cluster galaxies (BCGs) at redshifts of\n0.05 $\\leq z \\leq$ 0.30, to place constraints on their stellar Initial Mass\nFunction (IMF). We measure the spatially-resolved stellar population properties\nof the BCGs, and use it to derive their stellar mass-to-light ratios\n($\\Upsilon_{\\star \\rm POP}$). We find young stellar populations ($<$200 Myr) in\nthe centres of 22 per cent of the sample, and constant $\\Upsilon_{\\star \\rm\nPOP}$ within 15 kpc for 60 per cent of the sample. We further use the stellar\nmass-to-light ratio from the dynamical mass profiles of the BCGs\n($\\Upsilon_{\\star \\rm DYN}$), modelled using a Multi-Gaussian Expansion (MGE)\nand Jeans Anisotropic Method (JAM), with the dark matter contribution\nexplicitly constrained from weak gravitational lensing measurements. We\ndirectly compare the stellar mass-to-light ratios derived from the two\nindependent methods, $\\Upsilon_{\\star \\rm POP}$ (assuming some IMF) to\n$\\Upsilon_{\\star \\rm DYN}$ for the subsample of BCGs with no young stellar\npopulations and constant $\\Upsilon_{\\star \\rm POP}$. We find that for the\nmajority of these BCGs, a Salpeter (or even more bottom-heavy) IMF is needed to\nreconcile the stellar population and dynamical modelling results although for a\nsmall number of BCGs, a Kroupa (or even lighter) IMF is preferred. For those\nBCGs better fit with a Salpeter IMF, we find that the mass-excess factor\nagainst velocity dispersion falls on an extrapolation (towards higher masses)\nof known literature correlations. We conclude that there is substantial scatter\nin the IMF amongst the highest-mass galaxies.", "category": "astro-ph_GA" }, { "text": "A population of dust-enshrouded objects orbiting the Galactic black hole: The central 0.1 parsecs of the Milky Way host a supermassive black hole\nidentified with the position of the radio and infrared source Sagittarius A*, a\ncluster of young, massive stars (the S stars) and various gaseous features.\nRecently, two unusual objects have been found to be closely orbiting\nSagittarius A*: the so-called G sources, G1 and G2. These objects are\nunresolved (having a size of the order of 100 astronomical units, except at\nperiapse, where the tidal interaction with the black hole stretches them along\nthe orbit) and they show both thermal dust emission and line emission from\nionized gas. G1 and G2 have generated attention because they appear to be\ntidally interacting with the supermassive Galactic black hole, possibly\nenhancing its accretion activity. No broad consensus has yet been reached\nconcerning their nature: the G objects show the characteristics of gas and dust\nclouds but display the dynamical properties of stellar-mass objects. Here we\nreport observations of four additional G objects, all lying within 0.04 parsecs\nof the black hole and forming a class that is probably unique to this\nenvironment. The widely varying orbits derived for the six G objects\ndemonstrate that they were commonly but separately formed.", "category": "astro-ph_GA" }, { "text": "ISM properties of a Massive Dusty Star-Forming Galaxy discovered at z ~\n 7: We report the discovery and constrain the physical conditions of the\ninterstellar medium of the highest-redshift millimeter-selected dusty\nstar-forming galaxy (DSFG) to date, SPT-S J031132-5823.4 (hereafter\nSPT0311-58), at $z=6.900 +/- 0.002$. SPT0311-58 was discovered via its 1.4mm\nthermal dust continuum emission in the South Pole Telescope (SPT)-SZ survey.\nThe spectroscopic redshift was determined through an ALMA 3mm frequency scan\nthat detected CO(6-5), CO(7-6) and [CI](2-1), and subsequently confirmed by\ndetections of CO(3-2) with ATCA and [CII] with APEX. We constrain the\nproperties of the ISM in SPT0311-58 with a radiative transfer analysis of the\ndust continuum photometry and the CO and [CI] line emission. This allows us to\ndetermine the gas content without ad hoc assumptions about gas mass scaling\nfactors. SPT0311-58 is extremely massive, with an intrinsic gas mass of $M_{\\rm\ngas} = 3.3 \\pm 1.9 \\times10^{11}\\,M_{\\odot}$. Its large mass and intense star\nformation is very rare for a source well into the Epoch of Reionization.", "category": "astro-ph_GA" }, { "text": "Orbital tori for non-axisymmetric galaxies: Our Galaxy's bar makes the Galaxy's potential distinctly non-axisymmetric.\nAll orbits are affected by non-axisymmetry, and significant numbers are\nqualitatively changed by being trapped at a resonance with the bar. Orbital\ntori are used to compute these effects. Thick-disc orbits are no less likely to\nbe trapped by corotation or a Lindblad resonance than thin-disc orbits.\nPerturbation theory is used to create non-axisymmetric orbital tori from\nstandard axisymmetric tori, and both trapped and untrapped orbits are recovered\nto surprising accuracy. Code is added to the TorusModeller library that makes\nit as easy to manipulate non-axisymmetric tori as axisymmetric ones. The\naugmented TorusModeller is used to compute the velocity structure of the solar\nneighbourhood for bars of different pattern speeds and a simple action-based\ndistribution function. The technique developed here can be applied to any\nnon-axisymmetric potential that is stationary in a rotating from - hence also\nto classical spiral structure.", "category": "astro-ph_GA" }, { "text": "Discovery of the Magellanic Stellar Stream Out to 100 Kiloparsecs: The Magellanic Stream (MS) - an enormous ribbon of gas spanning $140^\\circ$\nof the southern sky trailing the Magellanic Clouds - has been exquisitely\nmapped in the five decades since its discovery. However, despite concerted\nefforts, no stellar counterpart to the MS has been conclusively identified.\nThis stellar stream would reveal the distance and 6D kinematics of the MS,\nconstraining its formation and the past orbital history of the Clouds. We have\nbeen conducting a spectroscopic survey of the most distant and luminous red\ngiant stars in the Galactic outskirts. From this dataset, we have discovered a\nprominent population of 13 stars matching the extreme angular momentum of the\nClouds, spanning up to $100^\\circ$ along the MS at distances of $60-120$ kpc.\nFurthermore, these kinemetically-selected stars lie along a\n[$\\alpha$/Fe]-deficient track in chemical space from $-2.5 < \\mathrm{[Fe/H]} <\n-0.5$, consistent with their formation in the Clouds themselves. We identify\nthese stars as high-confidence members of the Magellanic Stellar Stream. Half\nof these stars are metal-rich and closely follow the gaseous MS, whereas the\nother half are more scattered and metal-poor. We argue that the metal-rich\nstream is the recently-formed tidal counterpart to the MS, and speculate that\nthe metal-poor population was thrown out of the SMC outskirts during an earlier\ninteraction between the Clouds. The Magellanic Stellar Stream provides a strong\nset of constraints - distances, 6D kinematics, and birth locations - that will\nguide future simulations towards unveiling the detailed history of the Clouds.", "category": "astro-ph_GA" }, { "text": "History-independent tracers: Forgetful molecular probes of the physical\n conditions of the dense interstellar medium: Molecular line emission is a powerful probe of the physical conditions of\nastrophysical objects but can be complex to model, and it is often unclear\nwhich transitions would be the best targets for observers who wish to constrain\na given parameter. We therefore produce a list of molecular species for which\nthe gas history can be ignored, removing a major modelling complexity. We then\ndetermine the best of these species to observe when attempting to constrain\nvarious physical parameters. To achieve this, we use a large set of chemical\nmodels with different chemical histories to determine which species have\nabundances at 1 MYr that are insensitive to the initial conditions. We then use\nradiative transfer modelling to produce the intensity of every transition of\nthese molecules. We finally compute the mutual information between the physical\nparameters and all transitions and transition ratios in order to rank their\nusefulness in determining the value of a given parameter.\n We find 48 species that are insensitive to the chemical history of the gas,\n23 of which have collisional data available. We produce a ranked list of all\nthe transitions and ratios of these species using their mutual information with\nvarious gas properties. We show mutual information is an adequate measure of\nhow well a transition can constrain a physical parameter by recovering known\nprobes and demonstrating that random forest regression models become more\naccurate predictors when high-scoring features are included. Therefore, this\nlist can be used to select target transitions for observations in order to\nmaximize knowledge about those physical parameters.", "category": "astro-ph_GA" }, { "text": "The black hole and host galaxy growth in an isolated $z\\sim 6$ QSO\n observed with ALMA: The outstanding mass growth of supermassive black holes (SMBHs) at the\nReionisation Epoch and how it is related to the concurrent growth of their host\ngalaxies, poses challenges to theoretical models aimed at explaining how these\nsystems formed in short timescales (<1 Gyr). To trace the average evolutionary\npaths of quasi-stellar objects (QSOs) and their host galaxies in the BH\nmass-host mass ($M_{\\rm dyn}$) plane, we compare the star formation rate (SFR),\nderived from the accurate estimate of the dust temperature and the dust mass\n($T_{\\rm dust}, M_{\\rm dust}$), with the BH accretion rate. To this aim, we\nanalysed a deep, $900$ pc resolution ALMA observation of the sub-mm continuum,\n[CII] and H$_2$O of the $z\\sim 6$ QSO J2310+1855, enabling a detailed study of\ndust properties and cold gas kinematics. We performed an accurate SED analysis\nobtaining a dust temperature of $T_{\\rm dust} = 71$ K and a dust mass of\n$M_{\\rm dust}= 4.4 \\times 10^8\\ \\rm M_{\\odot}$. The implied AGN-corrected SFR\nis $1240 \\ \\rm M_{\\odot}yr^{-1}$, a factor of 2 smaller than previously\nreported for this QSO. We derived the best estimate of the dynamical mass\n$M_{\\rm dyn} = 5.2\\times 10^{10}\\ \\rm M_{\\odot}$ within $r = 1.7$ kpc, based on\na dynamical model of the system. We found that ${\\rm SFR}/M_{\\rm dyn}>\\dot\nM_{\\rm BH}/M_{\\rm BH}$, suggesting that AGN feedback might be efficiently\nacting to slow down the SMBH accretion, while the stellar mass assembly is\nstill vigorously taking place in the host galaxy. In addition, we were also\nable to detect high-velocity emission on the red and blue sides of the [CII]\nemission line, that traces a gaseous outflow, and for the first time, we mapped\na spatially-resolved water vapour disk through the H$_2$O v=0\n$3_{(2,2)}-3_{(1,3)}$ emission line detected at $\\nu_{\\rm obs} = 274.074$ GHz,\nwhose kinematic properties and size are broadly consistent with those of the\n[CII] disk.", "category": "astro-ph_GA" }, { "text": "MMT Spectroscopy of Lyman-alpha at z$\\simeq$7: Evidence for Accelerated\n Reionization Around Massive Galaxies: Reionization-era galaxies tend to exhibit weak Ly$\\alpha$ emission, likely\nreflecting attenuation from an increasingly neutral IGM. Recent observations\nhave begun to reveal exceptions to this picture, with strong Ly$\\alpha$\nemission now known in four of the most massive z=7$-$9 galaxies in the CANDELS\nfields, all of which also exhibit intense [OIII]$+$H$\\beta$ emission (EW$>$800\n$\\mathrm{\\mathring{A}}$). To better understand why Ly$\\alpha$ is anonymously\nstrong in a subset of massive z$\\simeq$7$-$9 galaxies, we have initiated an\nMMT/Binospec survey targeting a larger sample (N=22) of similarly luminous\n($\\simeq$1$-$6 L$^{\\ast}_{\\mathrm{UV}}$) z$\\simeq$7 galaxies selected over very\nwide-area fields ($\\sim$3 deg$^2$). We confidently ($>$7$\\sigma$) detect\nLy$\\alpha$ in 78% (7/9) of galaxies with strong [OIII]$+$H$\\beta$ emission\n(EW$>$800 $\\mathrm{\\mathring{A}}$) as opposed to only 8% (1/12) of galaxies\nwith more moderate (EW=200$-$800 $\\mathrm{\\mathring{A}}$) [OIII]$+$H$\\beta$. We\nargue that the higher Ly$\\alpha$ EWs of the strong [OIII]$+$H$\\beta$ population\nlikely reflect enhanced ionizing photon production efficiency owing to their\nlarge sSFRs ($\\gtrsim$30 Gyr$^{-1}$). We also find evidence that Ly$\\alpha$\ntransmission from massive galaxies declines less rapidly over $65.0 {\\mu}m. In this work we analyse the\nimpact of choosing different combinations of NIRCam and MIRI broad-band filters\n(F070W to F770W), as well as having ancillary data at {\\lambda}<0.6 {\\mu}m, on\nthe derived photometric redshifts (zphot) of a total of 5921 real and simulated\ngalaxies, with known input redshifts z=0-10. We found that observations at\n{\\lambda}<0.6 {\\mu}m are necessary to control the contamination of high-z\nsamples by low-z interlopers. Adding MIRI (F560W and F770W) photometry to the\nNIRCam data mitigates the absence of ancillary observations at {\\lambda}<0.6\n{\\mu}m and improves the redshift estimation. At z=7-10, accurate zphot can be\nobtained with the NIRCam broad bands alone when S/N>=10, but the zphot quality\nsignificantly degrades at S/N<=5. Adding MIRI photometry with one magnitude\nbrighter depth than the NIRCam depth allows for a redshift recovery of 83-99%,\ndepending on SED type, and its effect is particularly noteworthy for galaxies\nwith nebular emission. The vast majority of NIRCam galaxies with [F150W]=29 AB\nmag at z=7-10 will be detected with MIRI at [F560W, F770W]<28 mag if these\nsources are at least mildly evolved or have spectra with emission lines\nboosting the mid-infrared fluxes.", "category": "astro-ph_GA" }, { "text": "High redshift JWST predictions from IllustrisTNG: III. Infrared\n luminosity functions, obscured star formation and dust temperature of\n high-redshift galaxies: We post-process galaxies in the IllustrisTNG simulations with SKIRT radiative\ntransfer calculations to make predictions for the rest-frame near-infrared\n(NIR) and far-infrared (FIR) properties of galaxies at $z\\geq 4$. The\nrest-frame $K$- and $z$-band galaxy luminosity functions from TNG are overall\nconsistent with observations, despite a $\\sim 0.5\\,\\mathrm{dex}$\nunderprediction at $z=4$ for $M_{\\rm K}\\lesssim -25$ and $M_{\\rm z}\\lesssim\n-24$. Predictions for the JWST MIRI observed galaxy luminosity functions and\nnumber counts are given. Based on theoretical estimations, we show that the\nnext-generation survey conducted by JWST can detect 500 (30) galaxies in F1000W\nin a survey area of $500\\,{\\rm arcmin}^{2}$ at $z=6$ ($z=8$). As opposed to the\nconsistency in the UV, optical and NIR, we find that TNG, combined with our\ndust modelling choices, significantly underpredicts the abundance of most\ndust-obscured and thus most luminous FIR galaxies. As a result, the obscured\ncosmic star formation rate density (SFRD) and the SFRD contributed by\noptical/NIR dark objects are underpredicted. The discrepancies discovered here\ncould provide new constraints on the sub-grid feedback models, or the dust\ncontents, of simulations. Meanwhile, although the TNG predicted dust\ntemperature and its relations with IR luminosity and redshift are qualitatively\nconsistent with observations, the peak dust temperature of $z\\geq 6$ galaxies\nare overestimated by about $20\\,{\\rm K}$. This could be related to the limited\nmass resolution of our simulations to fully resolve the porosity of the\ninterstellar medium (or specifically its dust content) at these redshifts.", "category": "astro-ph_GA" }, { "text": "Formation of the first galaxies in the aftermath of the first supernovae: We perform high-resolution cosmological hydrodynamic simulations to study the\nformation of the first galaxies that reach the masses of\n$10^{8-9}~h^{-1}~M_\\odot$ at $z=9$. The resolution of the simulations is high\nenough to resolve minihaloes and allow us to successfully pursue the formation\nof multiple Population (Pop) III stars, their supernova (SN) explosions,\nresultant metal-enrichment of the inter-galactic medium (IGM) in the course of\nthe build-up of the system. Metals are ejected into the IGM by multiple Pop III\nSNe, but some of the metal-enriched gas falls back onto the halo after $\\gtrsim\n100~\\rm Myr$. The star formation history of the first galaxy depends\nsensitively on the initial mass function (IMF) of Pop III stars. The dominant\nstellar population transits from Pop III to Pop II at $z\\sim 12-15$ in the case\nof power-law Pop III IMF, ${\\rm d}n/{\\rm d}M \\propto M^{-2.35}$ with the mass\nrange $10-500~M_\\odot$. At $z\\lesssim 12$, stars are stably formed in the first\ngalaxies with a star formation rate of $\\sim 10^{-3}$-$10^{-1}~M_\\odot/{\\rm\nyr}$. In contrast, for the case with a flat IMF, gas-deprived first galaxies\nform due to frequent Pop III pair-instability SNe, resulting in the suppression\nof subsequent Pop II star formation. In addition, we calculate UV continuum,\nLy$\\alpha$- and H$\\alpha$-line fluxes from the first galaxies. We show that the\nJames Webb Space Telescope will be able to detect both UV continuum, Ly$\\alpha$\nand H$\\alpha$ line emission from first galaxies with halo mass $\\gtrsim\n10^{9}~M_\\odot$ at $z \\gtrsim 10$.", "category": "astro-ph_GA" }, { "text": "Application of Convolutional Neural Networks to Predict Magnetic Fields\n Directions in Turbulent Clouds: We adopt the deep learning method CASI-3D (Convolutional Approach to\nStructure Identification-3D) to infer the orientation of magnetic fields in\nsub-/trans- Alfvenic turbulent clouds from molecular line emission. We carry\nout magnetohydrodynamic simulations with different magnetic field strengths and\nuse these to generate synthetic observations. We apply the 3D radiation\ntransfer code RADMC-3d to model 12CO and 13CO (J = 1-0) line emission from the\nsimulated clouds and then train a CASI-3D model on these line emission data\ncubes to predict magnetic field morphology at the pixel level. The trained\nCASI-3D model is able to infer magnetic field directions with low error (<\n10deg for sub-Alfvenic samples and <30deg for trans-Alfvenic samples). We\nfurthermore test the performance of CASI-3D on a real sub-/trans- Alfvenic\nregion in Taurus. The CASI-3D prediction is consistent with the magnetic field\ndirection inferred from Planck dust polarization measurements. We use our\ndeveloped methods to produce a new magnetic field map of Taurus that has a\nthree-times higher angular resolution than the Planck map.", "category": "astro-ph_GA" }, { "text": "The Extremely Luminous Quasar Survey in the Pan-STARRS 1 Footprint\n (PS-ELQS): We present the results of the Extremely Luminous Quasar Survey in the $3\\pi$\nsurvey of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS;\nPS1). This effort applies the successful quasar selection strategy of the\nExtremely Luminous Survey in the Sloan Digital Sky Survey footprint\n($\\sim12,000\\,\\rm{deg}^2$) to a much larger area\n($\\sim\\rm{21486}\\,\\rm{deg}^2$). This spectroscopic survey targets the most\nluminous quasars ($M_{1450}\\le-26.5$; $m_{i}\\le18.5$) at intermediate redshifts\n($z\\ge2.8$). Candidates are selected based on a near-infrared JKW2 color cut\nusing WISE AllWISE and 2MASS photometry to mainly reject stellar contaminants.\nPhotometric redshifts ($z_{\\rm{reg}}$) and star-quasar classifications for each\ncandidate are calculated from near-infrared and optical photometry using the\nsupervised machine learning technique random forests. We select 806 quasar\ncandidates at $z_{\\rm{reg}}\\ge2.8$ from a parent sample of 74318 sources. After\nexclusion of known sources and rejection of candidates with unreliable\nphotometry, we have taken optical identification spectra for 290 of our 334\ngood PS-ELQS candidates. We report the discovery of 190 new $z\\ge2.8$ quasars\nand an additional 28 quasars at lower redshifts. A total of 44 good PS-ELQS\ncandidates remain unobserved. Including all known quasars at $z\\ge2.8$, our\nquasar selection method has a selection efficiency of at least $77\\%$. At lower\ndeclinations $-30\\le\\rm{Decl.}\\le0$ we approximately triple the known\npopulation of extremely luminous quasars. We provide the PS-ELQS quasar catalog\nwith a total of 592 luminous quasars ($m_{i}\\le18.5$, $z\\ge2.8$). This unique\nsample will not only be able to provide constraints on the volume density and\nquasar clustering of extremely luminous quasars, but also offers valuable\ntargets for studies of the intergalactic medium.", "category": "astro-ph_GA" }, { "text": "A gas cloud on its way towards the super-massive black hole in the\n Galactic Centre: Measurements of stellar orbits provide compelling evidence that the compact\nradio source Sagittarius A* at the Galactic Centre is a black hole four million\ntimes the mass of the Sun. With the exception of modest X-ray and infrared\nflares, Sgr A* is surprisingly faint, suggesting that the accretion rate and\nradiation efficiency near the event horizon are currently very low. Here we\nreport the presence of a dense gas cloud approximately three times the mass of\nEarth that is falling into the accretion zone of Sgr A*. Our observations\ntightly constrain the cloud's orbit to be highly eccentric, with an innermost\nradius of approach of only ~3,100 times the event horizon that will be reached\nin 2013. Over the past three years the cloud has begun to disrupt, probably\nmainly through tidal shearing arising from the black hole's gravitational\nforce. The cloud's dynamic evolution and radiation in the next few years will\nprobe the properties of the accretion flow and the feeding processes of the\nsuper-massive black hole. The kilo-electronvolt X-ray emission of Sgr A* may\nbrighten significantly when the cloud reaches pericentre. There may also be a\ngiant radiation flare several years from now if the cloud breaks up and its\nfragments feed gas into the central accretion zone.", "category": "astro-ph_GA" }, { "text": "Spectropolarimetry of the changing-look active galactic nucleus Mrk 1018: We have obtained new spectropolarimetric observations at visible wavelengths\nof the changing-look active galactic nucleus (AGN) Mrk 1018. The AGN direct\nspectrum shows an extremely weak continuum with faint broad H$\\beta$ and\nH$\\alpha$ emission lines. Both lines can be fit with a single very broad\nemission line component of full width at half maximum FWHM $\\simeq$ 7200 km\ns$^{-1}$, with no evidence of the additional 3000 km s$^{-1}$-wide component\nthat was previously detected. While this is in agreement with line formation in\na Keplerian disk, the line profile variability suggests that the broad emission\nline region is likely more complex. The continuum polarization of Mrk 1018 is\nlow; it is not higher in the current faint state compared to the past bright\nstate, confirming that dust obscuration is not the mechanism at the origin of\nthe change of look. The polarization profile of the H$\\alpha$ line is\nasymmetric with no rotation of the polarization angle, which possibly reveals\nline formation in a polar outflow. Alternatively, the polarization profile may\nbe the consequence of a time delay between the direct and the polarized light.\nInterestingly, the polarization signatures predicted for broad lines emitted\naround supermassive binary black holes are not observed.", "category": "astro-ph_GA" }, { "text": "Implications of the SPEAR FUV Maps on Our Understanding of the ISM: The distribution of a low-density transition temperature (10^4.5 - 10^5.5 K)\ngas in the interstellar medium conveys the character and evolution of diffuse\nmatter in the Galaxy. This difficult to observe component of the ISM emits\nmainly in the far-ultraviolet (FUV) (912-1800 {\\AA}) band. We describe spectral\nmaps of FUV emission lines from the highly ionized species CIV and OVI likely\nto be the dominant cooling mechanisms of transition temperature gas in the ISM.\nThe maps were obtained using an orbital spectrometer, SPEAR, that was launched\nin 2003 and has observed the FUV sky with a spectral resolution of \\sim 550 and\nan angular resolution of 10'. We compare distribution of flux in these maps\nwith three basic models of the distribution of transition temperature gas. We\nfind that the median distribution of CIV and OVI emission is consistent with\nthe spatial distribution and line ratios expected from a McKee-Ostriker (MO)\ntype model of evaporative interfaces. However, the intensities are a factor of\nthree higher than would be expected at the MO preferred parameters. Some high\nintensity regions are clearly associated with supernova remnants and\nsuperbubble structures. Others may indicate regions where gas is cooling\nthrough the transition temperature.", "category": "astro-ph_GA" }, { "text": "Galactic Wind in the Nearby Starburst Galaxy NGC 253 Observed with the\n Kyoto3DII Fabry-Perot Mode: We have observed the central region of the nearby starburst galaxy NGC 253\nwith the Kyoto Tridimensional Spectrograph II (Kyoto3DII) Fabry-Perot mode in\norder to investigate the properties of its galactic wind. Since this galaxy has\na large inclination, it is easy to observe its galactic wind. We produced the\nHa, [N II]6583, and [S II]6716,6731 images, as well as those line ratio maps.\nThe [N II]/Ha ratio in the galactic wind region is larger than those in H II\nregions in the galactic disk. The [N II]/Ha ratio in the southeastern filament,\na part of the galactic wind, is the largest and reaches about 1.5. These large\n[N II]/Ha ratios are explained by shock ionization/excitation. Using the [S\nII]/Ha ratio map, we spatially separate the galactic wind region from the\nstarburst region. The kinetic energy of the galactic wind can be sufficiently\nsupplied by supernovae in a starburst region in the galactic center. The shape\nof the galactic wind and the line ratio maps are non-axisymmetric about the\ngalactic minor axis, which is also seen in M82. In the [N II]6583/[S\nII]6716,6731 map, the positions with large ratios coincide with the positions\nof star clusters found in the Hubble Space Telescope (HST) observation. This\nmeans that intense star formation causes strong nitrogen enrichment in these\nregions. Our unique data of the line ratio maps including [S II] lines have\ndemonstrated their effectiveness for clearly distinguishing between shocked gas\nregions and starburst regions, determining the extent of galactic wind and its\nmass and kinetic energy, and discovering regions with enhanced nitrogen\nabundance.", "category": "astro-ph_GA" }, { "text": "The AGORA High-Resolution Galaxy Simulations Comparison Project: We introduce the AGORA project, a comprehensive numerical study of\nwell-resolved galaxies within the LCDM cosmology. Cosmological hydrodynamic\nsimulations with force resolutions of ~100 proper pc or better will be run with\na variety of code platforms to follow the hierarchical growth, star formation\nhistory, morphological transformation, and the cycle of baryons in and out of 8\ngalaxies with halo masses M_vir ~= 1e10, 1e11, 1e12, and 1e13 Msun at z=0 and\ntwo different (\"violent\" and \"quiescent\") assembly histories. The numerical\ntechniques and implementations used in this project include the smoothed\nparticle hydrodynamics codes GADGET and GASOLINE, and the adaptive mesh\nrefinement codes ART, ENZO, and RAMSES. The codes will share common initial\nconditions and common astrophysics packages including UV background,\nmetal-dependent radiative cooling, metal and energy yields of supernovae, and\nstellar initial mass function. These are described in detail in the present\npaper. Subgrid star formation and feedback prescriptions will be tuned to\nprovide a realistic interstellar and circumgalactic medium using a\nnon-cosmological disk galaxy simulation. Cosmological runs will be\nsystematically compared with each other using a common analysis toolkit, and\nvalidated against observations to verify that the solutions are robust - i.e.,\nthat the astrophysical assumptions are responsible for any success, rather than\nartifacts of particular implementations. The goals of the AGORA project are,\nbroadly speaking, to raise the realism and predictive power of galaxy\nsimulations and the understanding of the feedback processes that regulate\ngalaxy \"metabolism.\" The proof-of-concept dark matter-only test of the\nformation of a galactic halo with a z=0 mass of M_vir ~= 1.7e11 Msun by 9\ndifferent versions of the participating codes is also presented to validate the\ninfrastructure of the project.", "category": "astro-ph_GA" }, { "text": "Strong suppression of star formation and spiral arm formation in disk\n galaxies with counter-rotating gas disks: Galaxy-wide star formation can be quenched by a number of physical processes\nsuch as environmental effects (e.g., ram pressure stripping) and supernova\nfeedback. Using numerical simulations, we here demonstrate that star formation\ncan be severely suppressed in disk galaxies with their gas disks\ncounter-rotating with respect to their stellar disks. This new mechanism of\nstar formation suppression (or quenching) does not depend so strongly on model\nparameters of disk galaxies, such as bulge-to-disk- ratios and gas mass\nfractions. Such severe suppression of star formation is due largely to the\nsuppression of the gas density enhancing mechanism i.e spiral arm formation in\ndisk galaxies with counter-rotating gas. Our simulations also show that\nmolecular hydrogen and dust can be rather slowly consumed by star formation in\ndisk galaxies with counter-rotating gas disks (i.e., long gas depletion\ntimescale). Based on these results, we suggest that spiral and S0 galaxies with\ncounter-rotation can have rather low star formation rate for their gas\ndensities. Also we suggest that a minor fraction of S0 galaxies have no\nprominent spiral arms, because they have a higher fraction of counter-rotating\ngas. We predict that poststarburst E+A disk galaxies with cold gas could have\ncounter-rotating gas.", "category": "astro-ph_GA" }, { "text": "Comparisons of Different Fitting Methods for the Physical Parameters of\n A Star Cluster Sample of M33 with Spectroscopy and Photometry: Star clusters are good tracers for formation and evolution of galaxies. We\ncompared different fitting methods by using spectra (or by combining\nphotometry) to determine the physical parameters. We choose a sample of 17 star\nclusters in M33, which previously lacked spectroscopic observations. The\nlow-resolution spectra were taken with the Xinglong 2.16-m reflector of NAOC.\nThe photometry used in the fitting includes $\\rm u_{SC}$ and $\\rm v_{SAGE}$\nbands from the SAGE survey, as well as the published $UBVRI$ and $ugriz$\nphotometry. We firstly derived ages and metallicities with the {\\sc ULySS}\n(Vazdekis et al. and {\\sc pegase-hr}) SSP model and the Bruzual \\& Charlot\n(2003) (BC03) stellar population synthesis models for the full-spectrum\nfitting. The fitting results of both the BC03 and {\\sc ULySS} models seem\nconsistent with those of previous works as well. Then we add the SAGE $\\rm\nu_{SC}$ and $\\rm v_{SAGE}$ photometry in the spectroscopic fitting with the\nBC03 models. It seems the results become much better, especially for the Padova\n2000+Chabrier IMF set. Finally we add more photometry data, $UBVRI$ and\n$ugriz$, in the fitting and we found that the results do not improve\nsignificantly. Therefore, we conclude that the photometry is useful for\nimproving the fitting results, especially for the blue bands ($\\lambda <4000$\n{\\AA}), e.g., $\\rm u_{SC}$ and $\\rm v_{SAGE}$ band. At last, we discuss the\n\"UV-excess\" for the star clusters and we find five star clusters have\nUV-excess, based on the $GALEX$ FUV, NUV photometry.", "category": "astro-ph_GA" }, { "text": "Testing Galaxy Formation Simulations with Damped Lyman-$\u03b1$\n Abundance and Metallicity Evolution: We examine the properties of damped Lyman-$\\alpha$ absorbers (DLAs) emerging\nfrom a single set of cosmological initial conditions in two state-of-the-art\ncosmological hydrodynamic simulations: {\\sc Simba} and {\\sc Technicolor Dawn}.\nThe former includes star formation and black hole feedback treatments that\nyield a good match with low-redshift galaxy properties, while the latter uses\nmulti-frequency radiative transfer to model an inhomogeneous ultraviolet\nbackground (UVB) self-consistently and is calibrated to match the Thomson\nscattering optical depth, UVB amplitude, and Ly-$\\alpha$ forest mean\ntransmission at $z>5$. Both simulations are in reasonable agreement with the\nmeasured stellar mass and star formation rate functions at $z\\geq 3$, and both\nreproduce the observed neutral hydrogen cosmological mass density, $\\Omega_{\\rm\nHI}(z)$. However, the DLA abundance and metallicity distribution are sensitive\nto the galactic outflows' feedback and the UVB amplitude. Adopting a strong UVB\nand/or slow outflows under-produces the observed DLA abundance, but yields\nbroad agreement with the observed DLA metallicity distribution. By contrast,\nfaster outflows eject metals to larger distances, yielding more metal-rich DLAs\nwhose observational selection may be more sensitive to dust bias. The DLA\nmetallicity distribution in models adopting an ${\\rm H}_2$-regulated star\nformation recipe includes a tail extending to $[M/H] \\ll -3$, lower than any\nDLA observed to date, owing to curtailed star formation in low-metallicity\ngalaxies. Our results show that DLA observations play an imporant role in\nconstraining key physical ingredients in galaxy formation models, complementing\ntraditional ensemble statistics such as the stellar mass and star formation\nrate functions.", "category": "astro-ph_GA" }, { "text": "Image Stacking Analysis of SDSS Galaxies with AKARI Far-Infrared\n Surveyor Maps at 65\u03bcm, 90\u03bcm, and 140\u03bcm: We perform image stacking analysis of Sloan Digital Sky Survey (SDSS)\nphotometric galaxies over the AKARI Far-Infrared Surveyor (FIS) maps at\n65{\\mu}m, 90{\\mu}m, and 140{\\mu}m. The resulting image profiles are decomposed\ninto the central galaxy component (single term) and the nearby galaxy component\n(clustering term), as a function of the r-band magnitude, m_r of the central\ngalaxy. We find that the mean far-infrared (FIR) flux of a galaxy with\nmagnitude m_r is well fitted with f^s_{90{\\mu}m}=13*10^{0.306(18-m_r)}[mJy].\nThe FIR amplitude of the clustering term is consistent with that expected from\nthe angular-correlation function of the SDSS galaxies, but galaxy morphology\ndependence needs to be taken into account for a more quantitative conclusion.\nWe also fit the spectral energy distribution of stacked galaxies at 65{\\mu}m,\n90{\\mu}m, and 140{\\mu}m, and derive a mean dust temperature of ~30K. This is\nconsistent with the typical dust temperature of galaxies that are FIR luminous\nand individually detected.", "category": "astro-ph_GA" }, { "text": "Lyman continuum leakage in faint star-forming galaxies at redshift\n z=3-3.5 probed by gamma-ray bursts: We present the observations of Lyman continuum (LyC) emission in the\nafterglow spectra of GRB 191004B at $z=3.5055$, together with those of the\nother two previously known LyC-emitting long gamma-ray bursts (LGRB) (GRB\n050908 at $z=3.3467$, and GRB 060607A at $z=3.0749$), to determine their LyC\nescape fraction and compare their properties. From the afterglow spectrum of\nGRB 191004B we determine a neutral hydrogen column density at the LGRB redshift\nof $\\log(N_{\\rm HI}/cm^{-2})= 17.2 \\pm 0.15$, and negligible extinction\n($A_{\\rm V}=0.03 \\pm 0.02$ mag). The only metal absorption lines detected are\nCIV and SiIV. In contrast to GRB 050908 and GRB 060607A, the host galaxy of GRB\n191004B displays significant Ly$\\alpha$ emission. From its Ly$\\alpha$ emission\nand the non-detection of Balmer emission lines we constrain its star-formation\nrate (SFR) to $1 \\leq$ SFR $\\leq 4.7$ M$_{\\odot}\\ yr^{-1}$. We fit the\nLy$\\alpha$ emission with a shell model and find parameters values consistent\nwith the observed ones. The absolute LyC escape fractions we find for GRB\n191004B, GRB 050908 and GRB 060607A are of $0.35^{+0.10}_{-0.11}$,\n$0.08^{+0.05}_{-0.04}$ and $0.20^{+0.05}_{-0.05}$, respectively. We compare the\nLyC escape fraction of LGRBs to the values of other LyC emitters found from the\nliterature, showing that LGRB afterglows can be powerful tools to study LyC\nescape for faint high-redshift star-forming galaxies. Indeed we could push LyC\nleakage studies to much higher absolute magnitudes. The host galaxies of the\nthree LGRB presented here have all $M_{\\rm 1600} > -19.5$ mag, with the GRB\n060607A host at $M_{\\rm 1600} > -16$ mag. LGRB hosts may therefore be\nparticularly suitable for exploring the ionizing escape fraction in galaxies\nthat are too faint or distant for conventional techniques. Furthermore the time\ninvestment is very small compared to galaxy studies. [Abridged]", "category": "astro-ph_GA" }, { "text": "PACS photometry of the Herschel Reference Survey -\n Far-infrared/sub-millimeter colours as tracers of dust properties in nearby\n galaxies: We present Herschel/PACS 100 and 160 micron integrated photometry for the 323\ngalaxies in the Herschel Reference Survey (HRS), a K-band-, volume-limited\nsample of galaxies in the local Universe. Once combined with the Herschel/SPIRE\nobservations already available, these data make the HRS the largest\nrepresentative sample of nearby galaxies with homogeneous coverage across the\n100-500 micron wavelength range. In this paper, we take advantage of this\nunique dataset to investigate the properties and shape of the\nfar-infrared/sub-millimeter spectral energy distribution in nearby galaxies. We\nshow that, in the stellar mass range covered by the HRS (83$ the standard optical diagnostic diagrams (N2-BPT or S2-VO87)\nbecome unable to distinguish many AGN from other sources of photoionisation.\nTherefore, we also use high ionisation lines, such as HeII$\\lambda$4686,\nHeII$\\lambda$1640, NeIV$\\lambda$2422, NeV$\\lambda$3420, and NV$\\lambda$1240,\nalso in combination with other UV transitions, to trace the presence of AGN.\nOut of a parent sample of 209 galaxies, we identify 42 type-2 AGN (although 10\nof them are tentative), giving a fraction of galaxies in JADES hosting type-2\nAGN of about $20\\pm3$\\%, which does not evolve significantly in the redshift\nrange between 2 and 10. The selected type-2 AGN have estimated bolometric\nluminosities of $10^{41.3-44.9}$ erg s$^{-1}$ and host-galaxy stellar masses of\n$10^{7.2-9.3}$ M$_{\\odot}$. The star formation rates of the selected AGN host\ngalaxies are consistent with those of the star-forming main sequence. The AGN\nhost galaxies at z=4-6 contribute $\\sim$8-30 \\% to the UV luminosity function,\nslightly increasing with UV luminosity.", "category": "astro-ph_GA" }, { "text": "An Active Galactic Nucleus Recognition Model based on Deep Neural\n Network: To understand the cosmic accretion history of supermassive black holes,\nseparating the radiation from active galactic nuclei (AGNs) and star-forming\ngalaxies (SFGs) is critical. However, a reliable solution on photometrically\nrecognising AGNs still remains unsolved. In this work, we present a novel AGN\nrecognition method based on Deep Neural Network (Neural Net; NN). The main\ngoals of this work are (i) to test if the AGN recognition problem in the North\nEcliptic Pole Wide (NEPW) field could be solved by NN; (ii) to shows that NN\nexhibits an improvement in the performance compared with the traditional,\nstandard spectral energy distribution (SED) fitting method in our testing\nsamples; and (iii) to publicly release a reliable AGN/SFG catalogue to the\nastronomical community using the best available NEPW data, and propose a better\nmethod that helps future researchers plan an advanced NEPW database. Finally,\naccording to our experimental result, the NN recognition accuracy is around\n80.29% - 85.15%, with AGN completeness around 85.42% - 88.53% and SFG\ncompleteness around 81.17% - 85.09%.", "category": "astro-ph_GA" }, { "text": "Evidence for a Rotational Component in the Circumgalactic Medium of\n Nearby Galaxies: We present results of a study comparing the relative velocity of $\\rm\nLy\\alpha$ absorbers to the rotation velocity of nearby galaxy disks in the\nlocal universe ($z \\leq 0.03$). We have obtained rotation curves via long-slit\nspectroscopy of eight galaxies with the Southern African Large Telescope, and\ncombine this dataset with an additional 16 galaxies with data from the\nliterature. Each galaxy appears within $3R_{\\rm vir}$ of a QSO sightline with\narchival Cosmic Origin Spectrograph (COS) spectra. We study the velocity\norientation of absorbers with respect to nearby galaxy's rotation, and compare\nwith results from both the Steidel et al. (2002) monolithic halo model and a\nnew cylindrical Navarro-Frenk-White galaxy halo model to interpret these data\nin the context of probing 3D galaxy halos via 1D QSO absorption-line\nspectroscopy. Relative to these models we find that up to $59\\pm5\\%$ of $\\rm\nLy\\alpha$ absorbers have velocities consistent with co-rotation. We find the\n$\\rm Ly\\alpha$ co-rotation fraction to decrease with galaxy luminosity ($L^*$)\nand impact parameter in a model-independent fashion. We report that both\nanti-rotating absorbers and those found near luminous galaxies ($L \\gtrsim 0.5\nL^*$) mostly have low Doppler $b$-parameters ($b \\lesssim 50$ km $\\rm s^{-1}$).\nAbsorbers consistent with co-rotation show a wide range of Doppler\n$b$-parameters. Finally, we find a strong anticorrelation between co-rotation\nfraction and galaxy inclination, which is at odds with recent metal-line\nkinematic studies and suggests the kinematic and geometric distribution of the\ncircumgalactic medium is complex and multiphase.", "category": "astro-ph_GA" } ]