PhysBERT
Collection
9 items
•
Updated
•
1
text
stringlengths 89
2.49k
| category
stringclasses 19
values |
|---|---|
Implications of Planck2015 for inflationary, ekpyrotic and anamorphic
bouncing cosmologies: The results from Planck2015, when combined with earlier observations from
WMAP, ACT, SPT and other experiments, were the first observations to disfavor
the "classic" inflationary paradigm. To satisfy the observational constraints,
inflationary theorists have been forced to consider plateau-like inflaton
potentials that introduce more parameters and more fine-tuning, problematic
initial conditions, multiverse-unpredictability issues, and a new 'unlikeliness
problem.' Some propose turning instead to a "postmodern" inflationary paradigm
in which the cosmological properties in our observable universe are only
locally valid and set randomly, with completely different properties (and
perhaps even different physical laws) existing in most regions outside our
horizon. By contrast, the new results are consistent with the simplest versions
of ekpyrotic cyclic models in which the universe is smoothed and flattened
during a period of slow contraction followed by a bounce, and another promising
bouncing theory, anamorphic cosmology, has been proposed that can produce
distinctive predictions. | astro-ph_CO |
The spectacular cluster chain Abell 781 as observed with LOFAR, GMRT,
and XMM-Newton: A number of merging galaxy clusters show the presence of large-scale radio
emission associated with the intra-cluster medium (ICM). These synchrotron
sources are generally classified as radio haloes and radio relics. Whilst it is
commonly accepted that mergers play a crucial role in the formation of radio
haloes and relics, not all the merging clusters show the presence of giant
diffuse radio sources and this provides important information concerning
current models. The Abell 781 complex is a spectacular system composed of an
apparent chain of clusters on the sky. Its main component is undergoing a
merger and hosts peripheral emission that is classified as a candidate radio
relic and a disputed radio halo. We used new LOw Frequency ARay (LOFAR)
observations at 143 MHz and archival Giant Metrewave Radio Telescope (GMRT)
observations at 325 and 610 MHz to study radio emission from non-thermal
components in the ICM of Abell 781. Complementary information came from
XMM-Newton data, which allowed us to investigate the connection with the
thermal emission and its complex morphology. The origin of the peripheral
emission is still uncertain. We speculate that it is related to the interaction
between a head tail radio galaxy and shock. However, the current data allow us
only to set an upper limit of $\mathcal{M} < 1.4$ on the Mach number of this
putative shock. Instead, we successfully characterise the surface brightness
and temperature jumps of a shock and two cold fronts in the main cluster
component of Abell 781. Their positions suggest that the merger is involving
three substructures. We do not find any evidence for a radio halo either at the
centre of this system or in the other clusters of the chain. We place an upper
limit to the diffuse radio emission in the main cluster of Abell 781 that is a
factor of 2 below the current radio power-mass relation for giant radio haloes. | astro-ph_CO |
Sound velocity effects on the phase transition gravitational wave
spectrum in the sound shell model: A cosmological first-order phase transition gravitational wave could provide
a novel approach to studying the early Universe. In most cases, the acoustic
gravitational wave from the sound wave mechanism is dominant. Considering
different sound velocities in symmetric and broken phases, we study sound
velocity effects on the acoustic phase transition gravitational wave spectra in
the sound shell model. We demonstrate that different sound velocities could
obviously modify the peak frequency and peak amplitude of the gravitational
wave power spectra. Therefore, taking more realistic sound velocities might
provide more accurate predictions for various gravitational wave experiments. | astro-ph_CO |
Spinning primordial black holes formed during a matter-dominated era: We study the formation of spinning primordial black holes during an early
matter-dominated era. Using non-linear 3+1D general relativistic simulations,
we compute the efficiency of mass and angular momentum transfer in the process
-- which we find to be $\mathcal{O}(10\%)$ and $\mathcal{O}(5\%)$,
respectively. We show that subsequent evolution is important due to the seed
PBH accreting non-rotating matter from the background, which decreases the
dimensionless spin. Unless the matter era is short, we argue that the final
dimensionless spin will be negligible. | astro-ph_CO |
Detectability of Gravitational Waves from High-Redshift Binaries: Recent non-detection of gravitational-wave backgrounds from pulsar timing
arrays casts further uncertainty on the evolution of supermassive black hole
binaries. We study the capabilities of current gravitational-wave observatories
to detect individual binaries and demonstrate that, contrary to conventional
wisdom, some are in principle detectable throughout the Universe. In
particular, a binary with rest-frame mass $\gtrsim10^{10}\,M_\odot$ can be
detected by current timing arrays at arbitrarily high redshifts. The same claim
will apply for less massive binaries with more sensitive future arrays. As a
consequence, future searches for nanohertz gravitational waves could be
expanded to target evolving high-redshift binaries. We calculate the maximum
distance at which binaries can be observed with pulsar timing arrays and other
detectors, properly accounting for redshift and using realistic binary
waveforms. | astro-ph_CO |
Thermal Fluctuations of Dark Matter in Bouncing Cosmology: We investigate the statistical nature of the dark matter particles produced
in bouncing cosmology, especially, the evolution of its thermal fluctuations.
By explicitly deriving and solving the equation of motion of super-horizon
mode, we fully determine the evolution of thermal perturbation of dark matter
in a generic bouncing background. And we also show that the evolution of
super-horizon modes is stable and will not ruin the background evolution of a
generic bouncing universe till the Planck scale. Given no super-horizon thermal
perturbation of dark matter appears in standard inflation scenario such as
WIMP(-less) miracles, such super-horizon thermal perturbation of dark matter
generated during the generic bouncing universe scenario may be significant for
testing and distinguishing these two scenario in near future. | astro-ph_CO |
Precision growth index using the clustering of cosmic structures and
growth data: We use the clustering properties of Luminous Red Galaxies (LRGs) and the
growth rate data provided by the various galaxy surveys in order to constrain
the growth index ($\gamma$) of the linear matter fluctuations. We perform a
standard $\chi^2$-minimization procedure between theoretical expectations and
data, followed by a joint likelihood analysis and we find a value of
$\gamma=0.56\pm 0.05$, perfectly consistent with the expectations of the
$\Lambda$CDM model, and $\Omega_{m0} =0.29\pm 0.01$, in very good agreement
with the latest Planck results. Our analysis provides significantly more
stringent growth index constraints with respect to previous studies, as
indicated by the fact that the corresponding uncertainty is only $\sim 0.09
\gamma$. Finally, allowing $\gamma$ to vary with redshift in two manners
(Taylor expansion around $z=0$, and Taylor expansion around the scale factor),
we find that the combined statistical analysis between our clustering and
literature growth data alleviates the degeneracy and obtain more stringent
constraints with respect to other recent studies. | astro-ph_CO |
The Atlas3D project - XV. Benchmark for early-type galaxies scaling
relations from 260 dynamical models: mass-to-light ratio, dark matter,
Fundamental Plane and Mass Plane: We study the volume-limited and nearly mass selected (stellar mass M>6*10^9
Msun) Atlas3D sample of 260 early-type galaxies. We construct detailed
axisymmetric dynamical models (JAM), which allow for orbital anisotropy,
include a dark matter halo, and reproduce in detail both the galaxy images and
the high-quality integral-field stellar kinematics. We derive accurate total
M/L and dark matter fractions f_DM, within a sphere of radius r=Re. We also
measure the stellar M/L and derive a median dark matter fraction f_DM=13%. We
find that the thin two-dimensional subset spanned by galaxies in the
(M_JAM,sigma_e,R_e) coordinates system, which we call the Mass Plane (MP) has
an observed rms scatter of 19% and an intrinsic one of 11%. The MP satisfies
the scalar virial relation M_JAM sigma_e^2 R_e within our tight errors.
However, the details of how both Re and sigma_e are determined are critical in
defining the precise deviation from the virial exponents. We revisit the
(M/L)-sigma_e relation, which describes most of the deviations between the MP
and the FP. The best-fitting relation is (M/L) sigma_e^0.72 (r-band). It
provides an upper limit to any systematic increase of the IMF mass
normalization with sigma_e. We study of the link between sigma_e and the
galaxies circular velocity V_circ within 1Re (where stars dominate) and find
the relation max(V_circ)~1.76*sigma_e, which has an observed scatter of 7%. The
accurate parameters described in this paper are used in the companion Paper XX
of this series to explore the variation of global galaxy properties, including
the IMF, on the projections of the MP. [Abridged] | astro-ph_CO |
Dark energy, integrated Sachs-Wolfe effect and large-scale magnetic
fields: The impact of large-scale magnetic fields on the interplay between the
ordinary and integrated Sachs-Wolfe effects is investigated in the presence of
a fluctuating dark energy component. The modified initial conditions of the
Einstein-Boltzmann hierarchy allow for the simultaneous inclusion of dark
energy perturbations and of large-scale magnetic fields. The temperature and
polarization angular power spectra are compared with the results obtained in
the magnetized version of the (minimal) concordance model. Purported
compensation effects arising at large scales are specifically investigated. The
fluctuating dark energy component modifies, in a computable manner, the shapes
of the 1- and 2-$\sigma$ contours in the parameter space of the magnetized
background. The allowed spectral indices and magnetic field intensities turn
out to be slightly larger than those determined in the framework of the
magnetized concordance model where the dark energy fluctuations are absent. | astro-ph_CO |
Exacerbating the cosmological constant problem with interacting dark
energy: Future cosmological surveys will probe the expansion history of the universe
and constrain phenomenological models of dark energy. Such models do not
address the fine-tuning problem of the vacuum energy, i.e. the cosmological
constant problem (c.c.p.), but can make it spectacularly worse. We show that
this is the case for 'interacting dark energy' models in which the masses of
the dark matter states depend on the dark energy sector. If realised in nature,
these models have far-reaching implications for proposed solutions to the
c.c.p. that require the number of vacua to exceed the fine-tuning of the vacuum
energy density. We show that current estimates of the number of flux vacua in
string theory, $N_{\rm vac} \sim {\cal O}(10^{272,000})$, is far too small to
realise certain simple models of interacting dark energy \emph{and} solve the
cosmological constant problem anthropically. These models admit distinctive
observational signatures that can be targeted by future gamma-ray
observatories, hence making it possible to observationally rule out the
anthropic solution to the cosmological constant problem in theories with a
finite number of vacua. | astro-ph_CO |
Galaxy Zoo and ALFALFA: Atomic Gas and the Regulation of Star Formation
in Barred Disc Galaxies: We study the observed correlation between atomic gas content and the
likelihood of hosting a large scale bar in a sample of 2090 disc galaxies. Such
a test has never been done before on this scale. We use data on morphologies
from the Galaxy Zoo project and information on the galaxies' HI content from
the ALFALFA blind HI survey. Our main result is that the bar fraction is
significantly lower among gas rich disc galaxies than gas poor ones. This is
not explained by known trends for more massive (stellar) and redder disc
galaxies to host more bars and have lower gas fractions: we still see at fixed
stellar mass a residual correlation between gas content and bar fraction. We
discuss three possible causal explanations: (1) bars in disc galaxies cause
atomic gas to be used up more quickly, (2) increasing the atomic gas content in
a disc galaxy inhibits bar formation, and (3) bar fraction and gas content are
both driven by correlation with environmental effects (e.g. tidal triggering of
bars, combined with strangulation removing gas). All three explanations are
consistent with the observed correlations. In addition our observations suggest
bars may reduce or halt star formation in the outer parts of discs by holding
back the infall of external gas beyond bar co-rotation, reddening the global
colours of barred disc galaxies. This suggests that secular evolution driven by
the exchange of angular momentum between stars in the bar, and gas in the disc,
acts as a feedback mechanism to regulate star formation in intermediate mass
disc galaxies. | astro-ph_CO |
[FeII] as a tracer supernova rate: Supernovae play an integral role in the feedback of processed material into
the ISMof galaxies and are responsible for most of the chemical enrichment of
the universe. The rate of supernovae can also reveal the star formation
histories. Supernova rate is usually measured through the non-thermal radio
continuum luminosity, but in this paper we establish a quantitative
relationship between the [FeII]1.26 luminosity and supernova rate in a sample
of 11 near-by starburst galaxies. SINFONI data cubes are used to perform a
pixel pixel analysis of this correlation. Using Br equivalent width and
luminosity as the only observational inputs into Starburst 99, the supernova
rate is derived at each pixel and a map of supernova rate is created. This is
then compared morphologically and quantitatively to [FeII]1.26 luminosity map.
We find a strong linear and morphological correlation between supernova rate
and [FeII]1.26 on a pixel-pixel basis: log SNrate yr-1 pc-2 = (1.01 \pm 0.2)
\ast log[FeII]1.26 ergs-1 pc-2 - 41.17 \pm 0.9 The Starburst 99 derived
supernova rates are also in good agreement with the radio derived supernova
rates, which further demonstrates the strength of [FeII] as a tracer of
supernova rate. With the strong correlation found in this sample of galaxies,
we now qualitatively use [FeII]1.26 to derive supernova rate on either a
pixel-pixel or integrated galactic basis. | astro-ph_CO |
Haro15: Is it actually a low metallicity galaxy?: We present a detailed study of the physical properties of the nebular
material in multiple knots of the blue compact dwarf galaxy Haro 15. Using long
slit and echelle spectroscopy, obtained at Las Campanas Observatory, we study
the physical conditions (electron density and temperature), ionic and total
chemical abundances of several atoms, reddening and ionization structure. The
latter was derived by comparing the oxygen and sulphur ionic ratios to their
corresponding observed emission line ratios (the eta and eta' plots) in
different regions of the galaxy. Applying direct and empirical methods for
abundance determination, we perform a comparative analysis between these
regions. | astro-ph_CO |
Constraints on primordial black holes and curvature perturbations from
the global 21cm signal: The recent observations of the global 21cm signal by EDGES and gravitational
waves by LIGO/VIGO have revived interest in PBHs. Different from previous
works, we investigate the influence of PBHs on the evolution of the IGM for the
mass range $6\times 10^{13} {\rm g} \lesssim M_{\rm PBH}\lesssim 3\times
10^{14} \rm g$. Since the lifetime of these PBHs is smaller than the present
age of the Universe, they have evaporated by the present day. Due to Hawking
radiation, the heating effects of PBHs on the IGM can suppress the absorption
amplitude of the global 21cm signal. In this work, by requiring that the
differential brightness temperature of the global 21cm signals in the redshift
range of $10\lesssim z \lesssim 30$, e.g., $\delta T_{b} \lesssim -100~\rm mK$,
we obtain upper limits on the initial mass fraction of PBHs. We find that the
strongest upper limit is $\beta_{\rm PBH} \sim 2\times 10^{-30}$. Since the
formation of PBHs is related to primordial curvature perturbations, by using
the constraints on the initial mass fraction of PBHs we obtain the upper limits
on the power spectrum of primordial curvature perturbations for the scale range
$8.0\times 10^{15}\lesssim k \lesssim 1.8\times 10^{16}~\rm Mpc^{-1}$,
corresponding to the mass range considered here. We find that the strongest
upper limit is $\mathcal P_{\mathcal R}(k) \sim 0.0046$. By comparing with
previous works, we find that for the mass range (or the scale range)
investigated in this work the global 21cm signals or the 21cm power spectrum
should give the strongest upper limits on the initial mass fraction of PBHs and
on the power spectrum of primordial curvature perturbations. | astro-ph_CO |
Constraining the Black Hole Mass Spectrum with LISA Observations II:
Direct comparison of detailed models: A number of scenarios have been proposed for the origin of the supermassive
black holes (SMBHs) that are found in the centres of most galaxies. Many such
scenarios predict a high-redshift population of massive black holes (MBHs),
with masses in the range 100 to 100000 times that of the Sun. When the Laser
Interferometer Space Antenna (LISA) is finally operational, it is likely that
it will detect on the order of 100 of these MBH binaries as they merge. The
differences between proposed population models produce appreciable effects in
the portion of the population which is detectable by LISA, so it is likely that
the LISA observations will allow us to place constraints on them. However,
gravitational wave detectors such as LISA will not be able to detect all such
mergers nor assign precise black hole parameters to the merger, due to weak
gravitational wave signal strengths. This paper explores LISA's ability to
distinguish between several MBH population models. In this way, we go beyond
predicting a LISA observed population and consider the extent to which LISA
observations could inform astrophysical modellers. The errors in LISA parameter
estimation are applied with a direct method which generates random sample
parameters for each source in a population realisation. We consider how the
distinguishability varies depending on the choice of source parameters (1 or 2
parameters chosen from masses, redshift or spins) used to characterise the
model distributions, with confidence levels determined by 1 and 2-dimensional
tests based on the Kolmogorov-Smirnov test. | astro-ph_CO |
Detecting Baryon Acoustic Oscillations in Dark Matter from Kinematic
Weak Lensing Surveys: We investigate the feasibility of extracting Baryon Acoustic Oscillations
(BAO) from cosmic shear tomography. We particularly focus on the BAO scale
precision that can be achieved by future spectroscopy-based, kinematic weak
lensing (KWL) surveys \citep[e.g.,][]{Huff13} in comparison to the traditional
photometry-based weak lensing surveys. We simulate cosmic shear tomography data
of such surveys with a few simple assumptions to focus on the BAO information,
extract the spacial power spectrum, and constrain the recovered BAO feature.
Due to the small shape noise and the shape of the lensing kernel, we find that
a Dark Energy Task Force Stage IV version of such KWL survey can detect the BAO
feature in dark matter by $3$-$\sigma$ and measure the BAO scale at the
precision level of 4\% while it will be difficult to detect the feature in
photometry-based weak lensing surveys. With a more optimistic assumption, a
KWL-Stage IV could achieve a $\sim 2\%$ BAO scale measurement with
$4.9$-$\sigma$ confidence. A built-in spectroscopic galaxy survey within such
KWL survey will allow cross-correlation between galaxies and cosmic shear,
which will tighten the constraint beyond the lower limit we present in this
paper and therefore possibly allow a detection of the BAO scale bias between
galaxies and dark matter. | astro-ph_CO |
Revisiting Primordial Black Holes Constraints from Ionization History: Much attention has been drawn to the recent discoveries by the Advanced Laser
Interferometer Gravitational-Wave Observatory (LIGO) of merging intermediate
mass black holes. Of particular interest is the possibility that the merger
events detected could be evidence of dark matter in the form of primordial
black holes (PBHs). It has been argued that the presence of many black holes
would effect the thermal and ionization history of the universe via their
accretion of matter which would have strong signatures in the Cosmic Microwave
Background's (CMB) power spectra evident in the damping of anisotropies and
change in low-$l$ polarization power. In general the accretion is quite
sensitive to the specific physics involved and the conditions of the early
universe. In this work, we take a minimal approach and find constraints on PBHs
not including the model dependent effects of nonlinear structure of formation
or transition between different accretion models which would work to increase
the effect. In addition, we include the relative velocity between dark matter
and baryonic matter including the effects of supersonic streaming at high
redshift which work to significantly reduce the constraining power. We also
examine the constraints on more astrophysically-motivated extended black hole
mass functions and discuss how mergers might effect this distribution. We find
constraints on PBHs in the range $ \approx 30 M_\odot$, finding that they could
not compose more than $10\%$ of the total dark matter content. | astro-ph_CO |
Energy-conservation constraints on cosmic string loop production and
distribution functions: A network of cosmic strings would lead to gravitational waves which may be
detected by pulsar timing or future interferometers. The details of the
gravitational wave signal depend on the distribution of cosmic string loops,
which are produced by intercommutations from the scaling network of long
strings. We analyze the limits imposed by energy conservation, i.e., by the
fact that the total amount of string flowing into loops cannot exceed the
amount leaving the long strings. We show that some recent suggestions for the
cosmic string loop production rate and distribution are ruled out by these
limits. As a result, gravitational waves based on such suggestions, in
particular "model 3" used in LIGO data analysis, are not to be expected. | astro-ph_CO |
Observations of flat-spectrum radio sources at 850 microns from the
James Clerk Maxwell Telescope II. April 2000 to June 2005: Calibrated data for 143 flat-spectrum extragalactic radio sources are
presented at a wavelength of 850 microns covering a five-year period from April
2000. The data, obtained at the James Clerk Maxwell Telescope using the SCUBA
camera in pointing mode, were analysed using an automated pipeline process
based on the Observatory Reduction and Acquisition Control - Data Reduction
(ORAC-DR) system. This paper describes the techniques used to analyse and
calibrate the data, and presents the database of results along with a
representative sample of the better-sampled lightcurves. A re-analysis of
previously published data from 1997 to 2000 is also presented. The combined
catalogue, comprising 10493 flux density measurements, provides a unique and
valuable resource for studies of extragalactic radio sources. | astro-ph_CO |
The accretion of dark matter subhaloes within the cosmic web: primordial
anisotropic distribution and its universality: The distribution of galaxies displays anisotropy on different scales and it
is often referred as galaxy alignment. To understand the origin of galaxy
alignments on small scales, one must investigate how galaxies were accreted in
the early universe and quantify their primordial anisotropic at the time of
accretion. In this paper we use N-body simulations to investigate the accretion
of dark matter subhaloes, focusing on their alignment with the host halo shape
and the orientation of mass distribution on large scale, defined using the
hessian matrix of the density field. The large/small (e1/e3) eigenvalues of the
hessian matrix define the fast/slow collapse direction of dark matter on large
scale. We find that: 1) the halo major axis is well aligned with the e3 (slow
collapse) direction, and it is stronger for massive haloes; 2) subhaloes are
predominately accreted along the major axis of the host halo, and the alignment
increases with the host halo mass. Most importantly, this alignment is
universal; 3) accretion of subhaloes with respect to the e3 direction is not
universal. In massive haloes, subhaloes are accreted along the e3 (even
stronger than the alignment with the halo major axis), but in low-mass haloes
subhaloes are accreted perpendicular to the e3. The transit mass is lower at
high redshift. The last result well explains the puzzled correlation (both in
recent observations and simulations) that massive galaxies/haloes have their
spin perpendicular to the filament, and the spin of low-mass galaxies/haloes is
slightly aligned with the filament, under the assumption that the orbital
angular momentum of subhaloes is converted to halo spin. | astro-ph_CO |
Non-parametric Lagrangian biasing from the insights of neural nets: We present a Lagrangian model of galaxy clustering bias in which we train a
neural net using the local properties of the smoothed initial density field to
predict the late-time mass-weighted halo field. By fitting the mass-weighted
halo field in the AbacusSummit simulations at z=0.5, we find that including
three coarsely spaced smoothing scales gives the best recovery of the halo
power spectrum. Adding more smoothing scales may lead to 2-5% underestimation
of the large-scale power and can cause the neural net to overfit. We find that
the fitted halo-to-mass ratio can be well described by two directions in the
original high-dimension feature space. Projecting the original features into
these two principal components and re-training the neural net either reproduces
the original training result, or outperforms it with a better match of the halo
power spectrum. The elements of the principal components are unlikely to be
assigned physical meanings, partly owing to the features being highly
correlated between different smoothing scales. Our work illustrates a potential
need to include multiple smoothing scales when studying galaxy bias, and this
can be done easily with machine-learning methods that can take in high
dimensional input feature space. | astro-ph_CO |
On the Sunyaev-Zel'dovich effect from dark matter annihilation or decay
in galaxy clusters: We revisit the prospects for detecting the Sunyaev Zel'dovich (SZ) effect
induced by dark matter (DM) annihilation or decay. We show that with standard
(or even extreme) assumptions for DM properties, the optical depth associated
with relativistic electrons injected from DM annihilation or decay is much
smaller than that associated with thermal electrons, when averaged over the
angular resolution of current and future experiments. For example, we find:
$\tau_{\rm DM} \sim 10^{-9}-10^{-5}$ (depending on the assumptions) for $\mchi
= 1$ GeV and a density profile $\rho\propto r^{-1}$ for a template cluster
located at 50 Mpc and observed within an angular resolution of $10"$, compared
to $\tau_{\rm th}\sim 10^{-3}-10^{-2}$. This, together with a full spectral
analysis, enables us to demonstrate that, for a template cluster with generic
properties, the SZ effect due to DM annihilation or decay is far below the
sensitivity of the Planck satellite. This is at variance with previous claims
regarding heavier annihilating DM particles. Should DM be made of lighter
particles, the current constraints from 511 keV observations on the
annihilation cross section or decay rate still prevent a detectable SZ effect.
Finally, we show that spatial diffusion sets a core of a few kpc in the
electron distribution, even for very cuspy DM profiles, such that improving the
angular resolution of the instrument, e.g. with ALMA, does not necessarily
improve the detection potential. We provide useful analytical formulae
parameterized in terms of the DM mass, decay rate or annihilation cross section
and DM halo features, that allow quick estimates of the SZ effect induced by
any given candidate and any DM halo profile. | astro-ph_CO |
Multi-scale initial conditions for cosmological simulations: We discuss a new algorithm to generate multi-scale initial conditions with
multiple levels of refinements for cosmological "zoom-in" simulations. The
method uses an adaptive convolution of Gaussian white noise with a real space
transfer function kernel together with an adaptive multi-grid Poisson solver to
generate displacements and velocities following first (1LPT) or second order
Lagrangian perturbation theory (2LPT). The new algorithm achieves RMS relative
errors of order 10^(-4) for displacements and velocities in the refinement
region and thus improves in terms of errors by about two orders of magnitude
over previous approaches. In addition, errors are localized at coarse-fine
boundaries and do not suffer from Fourier-space induced interference ringing.
An optional hybrid multi-grid and Fast Fourier Transform (FFT) based scheme is
introduced which has identical Fourier space behaviour as traditional
approaches. Using a suite of re-simulations of a galaxy cluster halo our real
space based approach is found to reproduce correlation functions, density
profiles, key halo properties and subhalo abundances with per cent level
accuracy. Finally, we generalize our approach for two-component baryon and
dark-matter simulations and demonstrate that the power spectrum evolution is in
excellent agreement with linear perturbation theory. For initial baryon density
fields, it is suggested to use the local Lagrangian approximation in order to
generate a density field for mesh based codes that is consistent with
Lagrangian perturbation theory instead of the current practice of using the
Eulerian linearly scaled densities. | astro-ph_CO |
Primordial non-Gaussianity and Bispectrum Measurements in the Cosmic
Microwave Background and Large-Scale Structure: The most direct probe of non-Gaussian initial conditions has come from
bispectrum measurements of temperature fluctuations in the Cosmic Microwave
Background and of the matter and galaxy distribution at large scales. Such
bispectrum estimators are expected to continue to provide the best constraints
on the non-Gaussian parameters in future observations. We review and compare
the theoretical and observational problems, current results and future
prospects for the detection of a non-vanishing primordial component in the
bispectrum of the Cosmic Microwave Background and large-scale structure, and
the relation to specific predictions from different inflationary models. | astro-ph_CO |
Galaxy-galaxy weak gravitational lensing in $f(R)$ gravity: We present an analysis of galaxy-galaxy weak gravitational lensing (GGL) in
chameleon $f(R)$ gravity - a leading candidate of non-standard gravity models.
For the analysis we have created mock galaxy catalogues based on dark matter
haloes from two sets of numerical simulations, using a halo occupation
distribution (HOD) prescription which allows a redshift dependence of galaxy
number density. To make a fairer comparison between the $f(R)$ and $\Lambda$CDM
models, their HOD parameters are tuned so that the galaxy two-point correlation
functions in real space (and therefore the projected two-point correlation
functions) match. While the $f(R)$ model predicts an enhancement of the
convergence power spectrum by up to $\sim30\%$ compared to the standard
$\Lambda$CDM model with the same parameters, the maximum enhancement of GGL is
only half as large and less than 5\% on separations above $\sim1$-$2h^{-1}$Mpc,
because the latter is a cross correlation of shear (or matter, which is more
strongly affected by modified gravity) and galaxy (which is weakly affected
given the good match between galaxy auto correlations in the two models)
fields. We also study the possibility of reconstructing the matter power
spectrum by combination of GGL and galaxy clustering in $f(R)$ gravity. We find
that the galaxy-matter cross correlation coefficient remains at unity down to
$\sim2$-$3h^{-1}$Mpc at relevant redshifts even in $f(R)$ gravity, indicating
joint analysis of GGL and galaxy clustering can be a powerful probe of matter
density fluctuations in chameleon gravity. The scale dependence of the model
differences in their predictions of GGL can potentially allow to break the
degeneracy between $f(R)$ gravity and other cosmological parameters such as
$\Omega_m$ and $\sigma_8$. | astro-ph_CO |
Evolution of gaseous disk viscosity driven by supernova explosion in
star-forming galaxies at high redshift: Motivated by Genzel et al.'s observations of high-redshift star-forming
galaxies, containing clumpy and turbulent rings or disks, we build a set of
equations describing the dynamical evolution of gaseous disks with inclusion of
star formation and its feedback. Transport of angular momentum is due to
"turbulent" viscosity induced by supernova explosions in the star formation
region. Analytical solutions of the equations are found for the initial cases
of a gaseous ring and the integrated form for a gaseous disk, respectively. For
a ring with enough low viscosity, it evolves in a slow processes of gaseous
diffusion and star formation near the initial radius. For a high viscosity, the
ring rapidly diffuses in the early phase. The diffusion drives the ring into a
region with a low viscosity and start the second phase undergoing pile-up of
gas at a radius following the decreased viscosity torque. The third is a
sharply deceasing phase because of star formation consumption of gas and
efficient transportation of gas inward forming a stellar disk. We apply the
model to two $z\sim 2$ galaxies BX 482 and BzK 6004, and find that they are
undergoing a decline in their star formation activity. | astro-ph_CO |
Extensions to models of the galaxy-halo connection: We explore two widely used empirical models for the galaxy-halo connection,
subhalo abundance matching (SHAM) and the halo occupation distribution (HOD)
and compare their predictions with the hydrodynamical simulation IllustrisTNG
(TNG) for a range of statistics that quantify the galaxy distribution at
$n_{\rm gal}\approx1.3\times10^{-3}\,[{\rm Mpc}/h]^{-3}$. We observe that in
their most straightforward implementations, both models fail to reproduce the
two-point clustering measured in TNG. We find that SHAM models constructed
using the relaxation velocity, $V_{\rm relax}$, and the peak velocity, $V_{\rm
peak}$, perform best, and match the clustering reasonably well, although
neither model captures adequately the one-halo clustering. Splitting the total
sample into sub-populations, we discover that SHAM overpredicts the clustering
of high-mass, blue, star-forming, and late-forming galaxies and uderpredicts
that of low-mass, red, quiescent, and early-forming galaxies. We also study
various baryonic effects, finding that subhalos in the dark-mater-only
simulation have consistently higher values of their SHAM-proxy properties than
their full-physics counterparts. We then consider a two-dimensional
implementation of the HOD model augmented with a secondary parameter
(environment, velocity anisotropy, $\sigma^2R_{\rm halfmass}$, and total
potential) and tuned so as to match the two-point clustering of the
IllustrisTNG galaxies on large scales. We analyze these galaxy populations
adopting alternative statistical tools such as galaxy-galaxy lensing,
void-galaxy cross-correlations and cumulants of the smoothed density field,
finding that the hydrodynamical galaxy distribution disfavors $\sigma^2 R_{\rm
halfmass}$ and the total potential as secondary parameters, while the
environment and velocity anisotropy samples are consistent with full-physics
across all statistical probes examined. | astro-ph_CO |
GRB Probes of the Early Universe with EXIST: With the Swift detection of GRB090423 at z = 8.2, it was confirmed that GRBs
are now detectable at (significantly) larger redshifts than AGN, and so can
indeed be used as probes of the Early Universe. The proposed Energetic X-ray
Imaging Survey Telescope (EXIST) mission has been designed to detect and
promptly measure redshifts and both soft X-ray (0.1 - 10 keV) and simultaneous
nUV-nIR (0.3 - 2.3microns) imaging and spectra for GRBs out to redshifts z ~18,
which encompasses (or even exceeds) current estimates for Pop III stars that
are expected to be massive and possibly GRB sources. Scaling from Swift for the
~10X greater sensitivity of EXIST, more than 100 GRBs at z >=8 may be detected
and would provide direct constraints on the formation and evolution of the
first stars and galaxies. For GRBs at redshifts z >= 8, with Lyman breaks at
greater than 1.12microns, spectra at resolution R = 30 or R = 3000 for
afterglows with AB magnitudes brighter than 24 or 20 (respectively) within
~3000sec of trigger will directly probe the Epoch of Reionization, formation of
galaxies, and cosmic star formation rate. The proposed EXIST mission can probe
these questions, and many others, given its unparalleled combination of
sensitivity and spatial-spectral-temporal coverage and resolution. Here we
provide an overview of the key science objectives for GRBs as probes of the
early Universe and of extreme physics, and the mission plan and technical
readiness to bring this to EXIST. | astro-ph_CO |
Imprint of Scalar Dark Energy on Cosmic Microwave Background
Polarization: We study the imprint of a coupling of scalar dark energy to photon on the
cosmic microwave background (CMB) polarization. The time-evolving field value
as well as the perturbation of the scalar generically induce $B$-mode
polarization. Future CMB data will find either a cosmic parity violation in
temperature-polarization correlation due to the field value, or
perturbation-induced $B$-mode polarization that is almost indistinguishable
from that generated by gravitational lensing or primordial gravitational waves. | astro-ph_CO |
The Herschel Virgo Cluster Survey: I. Luminosity functions: We describe the Herschel Virgo Cluster Survey (HeViCS) and the first data
obtained as part of the Science Demonstration Phase (SDP). The data cover a
central 4x4 sq deg region of the cluster. We use SPIRE and PACS photometry data
to produce 100, 160, 250, 350 and 500 micron luminosity functions (LFs) for
optically bright galaxies that are selected at 500 micron and detected in all
bands. We compare these LFs with those previously derived using IRAS, BLAST and
Herschel-ATLAS data. The Virgo Cluster LFs do not have the large numbers of
faint galaxies or examples of very luminous galaxies seen previously in surveys
covering less dense environments. | astro-ph_CO |
Simulations of primary beam effects on the cosmic bispectrum phase
observed with the Hydrogen Epoch of Reionization Array: The 21~cm transition from neutral Hydrogen promises to be the best
observational probe of the Epoch of Reionisation. The main difficulty in
measuring the 21 cm signal is the presence of bright foregrounds that require
very accurate interferometric calibration. Closure quantities may circumvent
the calibration requirements but may be, however, affected by direction
dependent effects, particularly antenna primary beam responses. This work
investigates the impact of antenna primary beams affected by mutual coupling on
the closure phase and its power spectrum. Our simulations show that primary
beams affected by mutual coupling lead to a leakage of foreground power into
the EoR window, which can be up to $\sim4$ orders magnitude higher than the
case where no mutual coupling is considered. This leakage is, however,
essentially confined at $k < 0.3$~$h$~Mpc$^{-1}$ for triads that include 29~m
baselines. The leakage magnitude is more pronounced when bright foregrounds
appear in the antenna sidelobes, as expected. Finally, we find that triads that
include mutual coupling beams different from each other have power spectra
similar to triads that include the same type of mutual coupling beam,
indicating that beam-to-beam variation within triads (or visibility pairs) is
not the major source of foreground leakage in the EoR window. | astro-ph_CO |
The Clowes-Campusano Large Quasar Group Survey: I. GALEX selected sample
of LBGs at z$\sim$1: The nature of galaxy structures on large scales is a key observational
prediction for current models of galaxy formation. The SDSS and 2dF galaxy
surveys have revealed a number of structures on 40-150 h^-1 Mpc scales at low
redshifts, and some even larger ones. To constrain galaxy number densities,
luminosities, and stellar populations in large structures at higher redshift,
we have investigated two sheet-like structures of galaxies at z=0.8 and 1.3
spanning 150 h^-1 comoving Mpc embedded in large quasar groups extending over
at least 200 h^-1 Mpc. We present first results of an analysis of these
sheet--like structures using two contiguous 1deg GALEX fields (FUV and NUV)
cross-correlated with optical data from the Sloan Digital Sky Survey (SDSS). We
derive a sample of 462 Lyman Break Galaxy (LBG) candidates coincident with the
sheets. Using the GALEX and SDSS data, we show that the overall average
spectral energy distribution of a LBG galaxy at z~1 is flat (in f_lambda) in
the rest frame wavelength range from 1500A, to 4000A, implying evolved
populations of stars in the LBGs. From the luminosity functions we get
indications for overdensities in the two LQGs compared to their foreground
regions. Similar conclusions come from the calculation of the 2-point
correlation function, showing a 2sigma overdensity for the LBGs in the z~0.8
LQG on scales of 1.6 to 4.8 Mpc, indicating similar correlation scales for our
LBG sample as their z~3 counterparts. | astro-ph_CO |
The (relative) size does not matter in inflation: We show that a tiny correction to the inflaton potential can make critical
changes in the inflationary observables for some types of inflation models. | astro-ph_CO |
Constraining Dark-Matter Ensembles with Supernova Data: The constraints on non-minimal dark sectors involving ensembles of unstable
dark-matter species are well established and quite stringent in cases in which
these species decay to visible-sector particles. However, in cases in which
these ensembles decay exclusively to other, lighter dark-sector states, the
corresponding constraints are less well established. In this paper, we
investigate how information about the expansion rate of the universe at low
redshifts gleaned from observations of Type Ia supernovae can be used to
constrain ensembles of unstable particles which decay primarily into dark
radiation. | astro-ph_CO |
The chemical evolution of IC10: Dwarf irregular galaxies are relatively simple unevolved objects where it is
easy to test models of galactic chemical evolution. We attempt to determine the
star formation and gas accretion history of IC10, a local dwarf irregular for
which abundance, gas, and mass determinations are available. We apply detailed
chemical evolution models to predict the evolution of several chemical elements
(He, O, N, S) and compared our predictions with the observational data. We
consider additional constraints such as the present-time gas fraction, the star
formation rate (SFR), and the total estimated mass of IC10. We assume a dark
matter halo for this galaxy and study the development of a galactic wind. We
consider different star formation regimes: bursting and continuous. We explore
different wind situations: i) normal wind, where all the gas is lost at the
same rate and ii) metal-enhanced wind, where metals produced by supernovae are
preferentially lost. We study a case without wind. We vary the star formation
efficiency (SFE), the wind efficiency, and the time scale of the gas infall,
which are the most important parameters in our models. We find that only models
with metal-enhanced galactic winds can reproduce the properties of IC10. The
star formation must have proceeded in bursts rather than continuously and the
bursts must have been less numerous than ~10 over the whole galactic lifetime.
Finally, IC10 must have formed by a slow process of gas accretion with a
timescale of the order of 8 Gyr. | astro-ph_CO |
The formation of CDM haloes I: Collapse thresholds and the ellipsoidal
collapse model: In the excursion set approach to structure formation initially spherical
regions of the linear density field collapse to form haloes of mass $M$ at
redshift $z_{\rm id}$ if their linearly extrapolated density contrast, averaged
on that scale, exceeds some critical threshold, $\delta_{\rm c}(z_{\rm id})$.
The value of $\delta_{\rm c}(z_{\rm id})$ is often calculated from the
spherical or ellipsoidal collapse model, which provide well-defined predictions
given auxiliary properties of the tidal field at a given location. We use two
cosmological simulations of structure growth in a $\Lambda$ cold dark matter
scenario to quantify $\delta_{\rm c}(z_{\rm id})$, its dependence on the
surrounding tidal field, as well as on the shapes of the Lagrangian regions
that collapse to form haloes at $z_{\rm id}$. Our results indicate that the
ellipsoidal collapse model provides an accurate description of the mean
dependence of $\delta_{\rm c}(z_{\rm id})$ on both the strength of the tidal
field and on halo mass. However, for a given $z_{\rm id}$, $\delta_{\rm
c}(z_{\rm id})$ depends strongly on the halo's characteristic formation
redshift: the earlier a halo forms, the higher its initial density contrast.
Surprisingly, the majority of haloes forming $today$ fall below the ellipsoidal
collapse barrier, contradicting the model predictions. We trace the origin of
this effect to the non-spherical shapes of Lagrangian haloes, which arise
naturally due to the asymmetry of the linear tidal field. We show that a
modified collapse model, that accounts for the triaxial shape of protohaloes,
provides a more accurate description of the measured minimum overdensities of
recently collapsed objects. | astro-ph_CO |
Circular Polarization of the Astrophysical Gravitational Wave Background: The circular polarization of gravitational waves is a powerful observable to
test parity violation in gravity and to distinguish between the primordial or
the astrophysical origin of the stochastic background. This property comes from
the expected unpolarized nature of the homogeneous and isotropic astrophysical
background, contrary to some specific cosmological sources that can produce a
polarized background. However, in this work we show that there is a
non-negligible amount of circular polarization also in the astrophysical
background, generated by Poisson fluctuations in the number of unresolved
sources, which can be detected by the third-generation interferometers with
signal-to-noise ratio larger than one. We also explain in which cases the
gravitational wave maps can be cleaned from this extra source of noise,
exploiting the frequency and the angular dependence, in order to search for
signals from the early Universe. Future studies about the detection of
polarized cosmological backgrounds with ground- and space-based interferometers
should account for the presence of such a foreground contribution. | astro-ph_CO |
Going beyond the Kaiser redshift-space distortion formula: a full
general relativistic account of the effects and their detectability in galaxy
clustering: Kaiser redshift-space distortion formula describes well the clustering of
galaxies in redshift surveys on small scales, but there are numerous additional
terms that arise on large scales. Some of these terms can be described using
Newtonian dynamics and have been discussed in the literature, while the others
require proper general relativistic description that was only recently
developed. Accounting for these terms in galaxy clustering is the first step
toward tests of general relativity on horizon scales. The effects can be
classified as two terms that represent the velocity and the gravitational
potential contributions. Their amplitude is determined by effects such as the
volume and luminosity distance fluctuation effects and the time evolution of
galaxy number density and Hubble parameter. We compare the Newtonian
approximation often used in the redshift-space distortion literature to the
fully general relativistic equation, and show that Newtonian approximation
accounts for most of the terms contributing to velocity effect. We perform a
Fisher matrix analysis of detectability of these terms and show that in a
single tracer survey they are completely undetectable. To detect these terms
one must resort to the recently developed methods to reduce sampling variance
and shot noise. We show that in an all-sky galaxy redshift survey at low
redshift the velocity term can be measured at a few sigma if one can utilize
halos of mass M>10^12 Msun (this can increase to 10-sigma or more in some more
optimistic scenarios), while the gravitational potential term itself can only
be marginally detected. We also demonstrate that the general relativistic
effect is not degenerate with the primordial non-Gaussian signature in galaxy
bias, and the ability to detect primordial non-Gaussianity is little
compromised. | astro-ph_CO |
Mass-radius relation of Newtonian self-gravitating Bose-Einstein
condensates with short-range interactions: II. Numerical results: We develop the suggestion that dark matter could be a Bose-Einstein
condensate. We determine the mass-radius relation of a Newtonian
self-gravitating Bose-Einstein condensate with short-range interactions
described by the Gross-Pitaevskii-Poisson system. We numerically solve the
equation of hydrostatic equilibrium describing the balance between the
gravitational attraction and the pressure due to quantum effects (Heisenberg's
uncertainty principle) and short-range interactions (scattering). We connect
the non-interacting limit to the Thomas-Fermi limit. We also consider the case
of attractive self-interaction. We compare the exact mass-radius relation
obtained numerically with the approximate analytical relation obtained with a
Gaussian ansatz. An overall good agreement is found. | astro-ph_CO |
Extended Light in E/S0 Galaxies and Implications for Disk Rebirth: The recent discovery of extended ultraviolet (XUV) disks around a large
fraction of late-type galaxies provides evidence for unexpectedly large-scale
disk building at recent epochs. Combining GALEX UV observations with deep
optical and Spitzer IR imaging, we search for XUV disks in a sample of nearby
low-to-intermediate mass E/S0 galaxies to explore evidence for disk rebuilding
after mergers. Preliminary visual classification yields ten XUV-disk candidates
from the full sample of 30, intriguingly similar to the ~30% frequency for
late-type galaxies. These XUV candidates occur at a wide range of masses and on
both the red and blue sequences in color vs. stellar mass, indicating a
possible association with processes like gas accretion and/or galaxy
interactions that would affect the galaxy population broadly. We go on to apply
the quantitative Type 1 and Type 2 XUV-disk definitions to a nine-galaxy
subsample analyzed in detail. For this subsample, six of the nine are Type 1
XUVs, i.e., galaxies with UV structure beyond the expected star formation
threshold. The other three come close to satisfying the Type 2 definition, but
that definition proves problematic to apply to this sample: the NUV-derived
star formation threshold radii for our E/S0s often lie inside the 80% Ks-band
light (K80) radii, violating an implicit assumption of the Type 2 definition,
or lie outside but not as far as the definition requires. Nonetheless, the
three otherwise Type 2-like galaxies ("modified Type 2 XUVs") have higher star
formation rates and bluer FUV - NUV colors than the Type 1 XUVs in the sample.
We propose that Type 1 XUVs may reflect early or inefficient stages of star
formation, while modified Type 2 XUVs perhaps reflect inside-out disk regrowth. | astro-ph_CO |
The ATLAS Survey of the CDFS and ELAIS-S1 Fields: The first phase of the ATLAS (Australia Telescope Large Area Survey) project
surveyed a total 7 square degrees down to 30 micro Jy rms at 1.4 GHz and is the
largest sensitive radio survey ever attempted. We report on the scientific
achievements of ATLAS to date and plans to extend the project as a path finder
for the proposed EMU (Evolutionary map of the Universe) project which has been
designed to use ASKAP (Australian Square Kilometre Array Pathfinder). | astro-ph_CO |
Constraints on parity violation from ACTpol and forecasts for
forthcoming CMB experiments: We use the ACTpol published cosmic microwave background (CMB) polarization
data to constrain cosmological birefringence, a tracer of parity violation
beyond the standard model of particle physics. To this purpose, we employ all
the polarized ACTpol spectra, including the cross-correlations between
temperature anisotropy and B mode polarization (TB) and between E mode and B
mode (EB), which are most sensitive to the effect. We build specific, so-called
D-estimators for birefringence and assess their performances and error budgets
by using realistic Monte Carlo simulations based on the experimental
characteristics provided by the ACTpol collaboration. We determine the optimal
multipole range for our analysis to be $250 < \ell < 3025$ over which we find a
null result for the uniform birefringence angle $\alpha = 0.29^\circ \pm
0.28^\circ$ (stat.) $\pm 0.5^\circ$ (syst.), the latter uncertainty being the
estimate published by the ACTpol team on their global systematic error budget.
We show that this result holds consistently when other multipole ranges are
considered. Finally, we forecast the capability of several forthcoming ground
based, balloon and space borne CMB experiments to constrain the birefringence
angle, showing, e.g., that the proposed post-Planck COrE satellite mission
could in principle constrain $\alpha$ at a level of 10 arcsec, provided that
all systematics are under control. Under the same circumstances, we find the
COrE constraints to be at least 2 or 3 times better than what could ideally be
achieved by the other experiments considered. | astro-ph_CO |
Cosmological evidence for leptonic asymmetry after Planck: Recently, the Planck satellite found a larger and most precise value of the
matter energy density, that impacts on the present values of other cosmological
parameters such as the Hubble constant, the present cluster abundances and the
age of the Universe. The existing tension between Planck determination of these
parameters in the frame of the base LambdaCDM model and their direct
measurements generated lively discussions and several interpretations. In this
paper we quantify this tension by exploring several extensions of the base
LambdaCDM model that include the leptonic asymmetry. We set bounds on the
radiation content of the Universe and neutrino properties by using the latest
cosmological measurements, imposing also self-consistent BBN constraints on the
primordial helium abundance. For all cosmological asymmetric models we find the
preference of cosmological data for smaller values of active and sterile
neutrino masses. This increases the tension between cosmological and short
baseline neutrino oscillation data that favor a sterile neutrino with the mass
of around 1 eV. For the case of degenerate massive neutrinos, we find that the
discrepancies with direct determinations of the Hubble constant, the present
cluster abundances and the age of the Universe are alleviated at ~ 1.3 sigma
for all leptonic asymmetric models. We also find ~2 sigma statistical evidence
of the preference of cosmological data for the normal neutrino hierarchy. This
is more evident for the case of cosmological models involving leptonic
asymmetry and three massive neutrino species. We conclude that the current
cosmological data favor the leptonic asymmetric extension of the base LambdaCDM
model and normal neutrino mass hierarchy over the models with additional
sterile neutrino species and/or inverted neutrino mass hierarchy. | astro-ph_CO |
Intergalactic stellar populations in intermediate redshift clusters: A substantial fraction of the total stellar mass in rich clusters of galaxies
resides in a diffuse intergalactic component usually referred to as the
Intra-Cluster Light (ICL). Theoretical models indicate that these intergalactic
stars originate mostly from the tidal interaction of the cluster galaxies
during the assembly history of the cluster, and that a significant fraction of
these stars could have formed in-situ from the late infall of cold metal-poor
gas clouds onto the cluster. The models make predictions about the age
distribution of the ICL stars, which may provide additional observational
constraints. However, these models also over-predict the fraction of stellar
mass in the ICL by a substantial margin. Here we present population synthesis
models for the ICL of a dumb-bell dominated intermediate redshift (z=0.29)
X-ray cluster for which we have deep MOS data obtained with the FORS2
instrument. In a previous paper we have proposed that the dumbell galaxy act as
a grinding machine tearing to pieces the galaxies that pass nearby thus
enriching the intergalactic medium. In this paper we analyze the spectra at
different locations within the ICL and find that it is dominated by old metal
rich stars, at odds with what has been found in nearby clusters where the stars
that dominate the ICL are old and metal poor. While we see a weak evidence of a
young, metal poor, component, if real, these young stars would amount to less
than 1% of the total ICL mass, much less than the up to 30% predicted by the
models. We propose that the very metal rich (i.e. 2.5 times solar) stars in the
ICL of our cluster, which comprise approximately 40% of the total mass,
originate mostly from the central dumb-bell galaxy, while the remaining solar
and metal poor stars come from spiral, post-starburst (E+A), and metal poor
dwarf galaxies. About 16% of the ICL stars are old and metal poor. | astro-ph_CO |
The evolution of the star forming sequence in hierarchical galaxy
formation models: It has been argued that the specific star formation rates of star forming
galaxies inferred from observational data decline more rapidly below z = 2 than
is predicted by hierarchical galaxy formation models. We present a detailed
analysis of this problem by comparing predictions from the GALFORM
semi-analytic model with an extensive compilation of data on the average star
formation rates of star-forming galaxies. We also use this data to infer the
form of the stellar mass assembly histories of star forming galaxies. Our
analysis reveals that the currently available data favour a scenario where the
stellar mass assembly histories of star forming galaxies rise at early times
and then fall towards the present day. In contrast, our model predicts stellar
mass assembly histories that are almost flat below z = 2 for star forming
galaxies, such that the predicted star formation rates can be offset with
respect to the observational data by factors of up to 2-3. This disagreement
can be explained by the level of coevolution between stellar and halo mass
assembly that exists in contemporary galaxy formation models. In turn, this
arises because the standard implementations of star formation and supernova
feedback used in the models result in the efficiencies of these process
remaining approximately constant over the lifetime of a given star forming
galaxy. We demonstrate how a modification to the timescale for gas ejected by
feedback to be reincorporated into galaxy haloes can help to reconcile the
model predictions with the data. | astro-ph_CO |
Probing primordial features with the primary CMB: CMB photons travel from the last scattering surface, when the primary CMB has
been generated, along the surface of the light cone to us. During their travel,
they are affected by many secondary effects such as the integrated Sachs-Wolfe
effect and CMB lensing. These CMB secondary effects modify the CMB primary
power spectrum adding degeneracies and decreasing the sensibility to primordial
parameters. The possibility to reconstruct the primary CMB anisotropies will
allow us to have a more direct observable to test the physics of the early
universe. We propose to study the imprint of features in the primordial power
spectrum with the primary CMB after the subtraction of the reconstructed ISW
signal from the observed CMB temperature angular power spectrum. We consider
the application to features models able to fit two of the large scales
anomalies observed in the CMB temperature angular power spectrum: the deficit
of power at $\ell \sim 2$ and at $\ell \sim 22$. This method allows to improve
significantly the constraints on the features parameters up to $16\%$ for
models predicting a suppression of power of the quadrupole and up to $27\%$ for
models with features at $\ell \sim 22$, assuming instrumental sensitivity
similar to the $Planck$ satellite (depending on the goodness of the ISW
reconstruction). Furthermore, it gives the opportunity to understand if these
anomalies are attributed to early- or late-time physics. | astro-ph_CO |
Halo/Galaxy Bispectrum with Primordial non-Gaussianity from integrated
Perturbation Theory (iPT): We derive a formula for the halo/galaxy bispectrum on the basis of the
integrated Perturbation Theory (iPT). In addition to the gravity-induced
non-Gaussianity, we consider the non-Gaussianity of the primordial curvature
perturbations, and investigate in detail the effect of such primordial
non-Gaussianity on the large-scale halo/galaxy bispectrum. In iPT, the effects
of primordial non-Gaussianity are wholly encapsulated in the linear
(primordial) polyspectra, and we systematically calculate the contributions to
the large-scale behaviors arising from the three types of primordial bispectrum
(local-, equilateral-, and orthogonal-types), and primordial trispectrum of the
local-type non-Gaussianity. We find that the equilateral- and orthogonal-type
non-Gaussianities show distinct scale-dependent behaviors which can dominate
the gravity-induced non-Gaussianity at very large scales. For the local-type
non-Gaussianity, higher-order loop corrections are found to give a
significantly large contribution to the halo/galaxy bispectrum of the squeezed
shape, and eventually dominate over the other contributions on large scales. A
diagrammatic approach based on the iPT helps us to systematically investigate
an impact of such higher-order contributions to the large-scale halo/galaxy
bispectrum. | astro-ph_CO |
Power Spectra beyond the Slow Roll Approximation in Theories with
Non-Canonical Kinetic Terms: We derive analytical expressions for the power spectra at the end of
inflation in theories with two inflaton fields and non-canonical kinetic terms.
We find that going beyond the slow-roll approximation is necessary and that the
nature of the non-canonical terms have an important impact on the final power
spectra at the end of inflation. We study five models numerically and find
excellent agreement with our analytical results. Our results emphasise the fact
that going beyond the slow-roll approximation is important in times of
high-precision data coming from cosmological observations. | astro-ph_CO |
Herschel-ATLAS/GAMA: a census of dust in optically selected galaxies
from stacking at submillimetre wavelengths: We use the Herschel-ATLAS survey to conduct the first large-scale statistical
study of the submm properties of optically selected galaxies. Using ~80,000
r-band selected galaxies from 126 deg^2 of the GAMA survey, we stack into submm
imaging at 250, 350 and 500{\mu}m to gain unprecedented statistics on the dust
emission from galaxies at z < 0.35. We find that low redshift galaxies account
for 5% of the cosmic 250{\mu}m background (4% at 350{\mu}m; 3% at 500{\mu}m),
of which approximately 60% comes from 'blue' and 20% from 'red' galaxies
(rest-frame g - r). We compare the dust properties of different galaxy
populations by dividing the sample into bins of optical luminosity, stellar
mass, colour and redshift. In blue galaxies we find that dust temperature and
luminosity correlate strongly with stellar mass at a fixed redshift, but red
galaxies do not follow these correlations and overall have lower luminosities
and temperatures. We make reasonable assumptions to account for the
contaminating flux from lensing by red sequence galaxies and conclude that
galaxies with different optical colours have fundamentally different dust
emission properties. Results indicate that while blue galaxies are more
luminous than red galaxies due to higher temperatures, the dust masses of the
two samples are relatively similar. Dust mass is shown to correlate with
stellar mass, although the dust/stellar mass ratio is much higher for low
stellar mass galaxies, consistent with the lowest mass galaxies having the
highest specific star formation rates. We stack the 250{\mu}m/NUV luminosity
ratio, finding results consistent with greater obscuration of star formation at
lower stellar mass and higher redshift. Submm luminosities and dust masses of
all galaxies are shown to evolve strongly with redshift, indicating a fall in
the amount of obscured star formation in ordinary galaxies over the last four
billion years. | astro-ph_CO |
Constraints on the Redshift Evolution of the L_X-SFR Relation from the
Cosmic X-Ray Backgrounds: Observations of local star forming galaxies have revealed a correlation
between the rate at which galaxies form stars and their X-Ray luminosity. We
combine this correlation with the most recent observational constraints on the
integrated star formation rate density, and find that star forming galaxies
account for 5-20% of the total soft and hard X-ray backgrounds, where the
precise number depends on the energy band and the assumed average X-ray
spectral energy distribution of the galaxies below ~20 keV. If we combine the
L_X-SFR relation with recently derived star formation rate function, then we
find that star forming galaxies whose X-ray flux falls well (more than a factor
of 10) below the detection thresholds of the Chandra Deep Fields, can fully
account for the unresolved soft X-ray background, which corresponds to ~6% of
its total. Motivated by this result, we put limits on the allowed redshift
evolution of the parameter c_X \equiv L_X/SFR, and/or its evolution towards
lower and higher star formation rates. If we parametrize the redshift evolution
of c_X ~ (1+z)^b, then we find that b \leq 1.3 (95% CL). On the other hand, the
observed X-ray luminosity functions (XLFs) of star forming galaxies indicate
that c_X may be increasing towards higher redshifts and/or higher star
formation rates at levels that are consistent with the X-ray background, but
possibly at odds with the locally observed L_X-SFR relation. | astro-ph_CO |
Gamma rays from ultracompact primordial dark matter minihalos: Ultracompact minihalos have recently been proposed as a new class of dark
matter structure. These minihalos would be produced by phase transitions in the
early Universe or features in the inflaton potential, and constitute
non-baryonic massive compact halo objects (MACHOs) today. We examine the
prospect of detecting ultracompact minihalos in gamma-rays if dark matter
consists of self-annihilating particles. We compute present-day fluxes from
minihalos produced in the electron-positron annihilation epoch, and the QCD and
electroweak phase transitions in the early Universe. Even at a distance of 100
pc, minihalos produced during the electron-positron annihilation epoch should
be eminently detectable today, either by the Fermi satellite, current Air
Cherenkov telescopes, or even in archival EGRET data. Within ~1 pc, minihalos
formed in the QCD phase transition would have similar predicted fluxes to the
dwarf spheroidal galaxies targeted by current indirect dark matter searches, so
might also be detectable by present or upcoming experiments. | astro-ph_CO |
Reconstruction of high-resolution SZ maps from heterogeneous datasets
using needlets: The aim of this work is to propose a joint exploitation of heterogeneous
datasets from high-resolution/few-channel experiments and
low-resolution/many-channel experiments by using a multiscale needlet Internal
Linear Combination (ILC), in order to optimize the thermal Sunyaev-Zeldovich
(SZ) effect reconstruction at high resolution. We highlight that needlet ILC is
a powerful and tunable component separation method which can easily deal with
multiple experiments with various specifications. Such a multiscale analysis
renders possible the joint exploitation of high-resolution and low-resolution
data, by performing for each needlet scale a combination of some specific
channels, either from one dataset or both datasets, selected for their
relevance to the angular scale considered, thus allowing to simultaneously
extract high resolution SZ signal from compact clusters and remove Galactic
foreground contamination at large scales. | astro-ph_CO |
Star Formation in Nearby Isolated Galaxies: We use the FUV fluxes measured with the GALEX to study the star formation
properties of galaxies collected in the "Local Orphan Galaxies" catalog (LOG).
Among 517 LOG galaxies having radial velocities V(LG) < 3500 km/s and Galactic
latitudes |b|> 15 degr, 428 objects have been detected in FUV. We briefly
discuss some scaling relations between the specific star formation rate (SSFR)
and stellar mass, HI-mass, morphology, and surface brightness of galaxies
situated in extremely low density regions of the Local Supercluster. Our sample
is populated with predominantly late-type, gas-rich objects with the median
morphological type of Sdm. Only 5% of LOG galaxies are classified as early
types: E, S0, S0/a, however, they systematically differ from normal E and S0
galaxies by lower luminosity and presence of gas and dust. We find that almost
all galaxies in our sample have their SSFR below 0.4 [Gyr^{-1}]. This limit is
also true even for a sample of 260 active star-burst Markarian galaxies
situated in the same volume. The existence of such a quasi-Eddington limit for
galaxies seems to be a key factor which characterizes the transformation of gas
into stars at the current epoch. | astro-ph_CO |
Supervoids in the WISE-2MASS catalogue imprinting Cold Spots in the
Cosmic Microwave Background: The Cold Spot (CS) is a clear feature in the Cosmic Microwave Background
(CMB); it could be of primordial origin, or caused by a intervening structure
along the line of sight. We identified a large projected underdensity in the
recently constructed WISE-2MASS all-sky infrared galaxy catalogue aligned with
the Cold Spot direction at $(l,b)\approx(209^\circ,-57^\circ)$. It has an
angular size of tens of degrees, and shows a $\sim20\%$ galaxy underdensity in
the center. Moreover, we find another large underdensity in the projected
WISE-2MASS galaxy map at $(l,b)\approx(101^\circ,46^\circ)$ (hereafter Draco
Supervoid), also aligned with a CMB decrement, although less significant than
that of the CS direction. Motivated by these findings, we develop spherically
symmetric Lemaitre-Tolman-Bondi (LTB) compensated void models to explain the
observed CMB decrements with these two underdensities, or "supervoids". Within
our perturbative treatment of the LTB voids, we find that the Integrated
Sachs-Wolfe and Riess-Sciama effects due to the Draco Supervoid can account for
the CMB decrement observed in the same direction. On the contrary, the
extremely deep CMB decrement in the CS direction is more difficult to explain
by the presence of the CS supervoid only. Nevertheless, the probability of a
random alignment between the CS and the corresponding supervoid is disfavored,
and thus its contribution as a secondary anisotropy cannot be neglected. We
comment on how the approximations used in this paper, in particular the
assumption of spherical symmetry, could change quantitatively our conclusions
and might provide a better explanation for the CMB CS. | astro-ph_CO |
Warm Dark Matter as a solution to the small scale crisis: new
constraints from high redshift Lyman-alpha forest data: We present updated constraints on the free-streaming of warm dark matter
(WDM) particles derived from an analysis of the Lya flux power spectrum
measured from high-resolution spectra of 25 z > 4 quasars obtained with the
Keck High Resolution Echelle Spectrometer (HIRES) and the Magellan Inamori
Kyocera Echelle (MIKE) spectrograph. We utilize a new suite of high-resolution
hydrodynamical simulations that explore WDM masses of 1, 2 and 4 keV (assuming
the WDM consists of thermal relics), along with different physically motivated
thermal histories. We carefully address different sources of systematic error
that may affect our final results and perform an analysis of the Lya flux power
with conservative error estimates. By using a method that samples the
multi-dimensional astrophysical and cosmological parameter space, we obtain a
lower limit mwdm > 3.3 keV (2sigma) for warm dark matter particles in the form
of early decoupled thermal relics. Adding the Sloan Digital Sky Survey (SDSS)
Lya flux power spectrum does not improve this limit. Thermal relics of masses 1
keV, 2 keV and 2.5 keV are disfavoured by the data at about the 9sigma, 4sigma
and 3sigma C.L., respectively. Our analysis disfavours WDM models where there
is a suppression in the linear matter power spectrum at (non-linear) scales
corresponding to k=10h/Mpc which deviates more than 10% from a LCDM model.
Given this limit, the corresponding "free-streaming mass" below which the mass
function may be suppressed is 2x10^8 Msun/h. There is thus very little room for
a contribution of the free-streaming of WDM to the solution of what has been
termed the small scale crisis of cold dark matter. | astro-ph_CO |
The strongest gravitational lenses: I. The statistical impact of cluster
mergers: For more than a decade now, it has been controversial whether or not the high
rate of giant gravitational arcs and the largest observed Einstein radii are
consistent with the standard cosmological model. Recent studies indicate that
mergers provide an efficient mechanism to substantially increase the
strong-lensing efficiency of individual clusters. Based on purely semi-analytic
methods, we investigated the statistical impact of cluster mergers on the
distribution of the largest Einstein radii and the optical depth for giant
gravitational arcs of selected cluster samples. Analysing representative
all-sky realizations of clusters at redshifts z < 1 and assuming a constant
source redshift of z_s = 2.0, we find that mergers increase the number of
Einstein radii above 10 arcsec (20 arcsec) by ~ 35 % (~ 55 %). Exploiting the
tight correlation between Einstein radii and lensing cross sections, we infer
that the optical depth for giant gravitational arcs with a length-to-width
ratio > 7.5 of those clusters with Einstein radii above 10 arcsec (20 arcsec)
increases by ~ 45 % (85 %). Our findings suggest that cluster mergers
significantly influence in particular the statistical lensing properties of the
strongest gravitational lenses. We conclude that semi-analytic studies must
inevitably take these events into account before questioning the standard
cosmological model on the basis of the largest observed Einstein radii and the
statistics of giant gravitational arcs. | astro-ph_CO |
Very High Energy Active Galactic Nuclei Synchrotron self-Compton
Modeling Tour: The current very high energy (VHE; E>100GeV) experiments have tremendously
increased the number of detected extragalactic sources. We present a
synchrotron self-Compton modeling tour of the active galactic nuclei currently
established as VHE emitters so far, and investigate possible correlations among
the intrinsic and derived parameters. | astro-ph_CO |
Modeling the Alignment Profile of Satellite Galaxies in Clusters: Analyzing the halo and galaxy catalogs from the Millennium simulations at
redshifts $z=0,\ 0.5,\ 1$, we determine the alignment profiles of cluster
galaxies by measuring the average alignments between the major axes of the
pseudo inertia tensors from all satellites within cluster's virial radius and
from only those satellites within some smaller radius as a function of the
top-hat scale difference. The alignment profiles quantify how well the
satellite galaxies retain the memory of the external tidal fields after merging
into their host clusters and how fast they lose the initial alignment tendency
as the cluster's relaxation proceeds. It is found that the alignment profile
drops faster at higher redshifts and on smaller mass scales. This result is
consistent with the picture that the faster merging of the satellites and
earlier onset of the nonlinear effect inside clusters tend to break the
preferential alignments of the satellites with the external tidal fields.
Modeling the alignment profile of cluster galaxies as a power-law of the
density correlation coefficient that is independent of the power spectrum
normalization ($\sigma_{8}$) and demonstrating that the density correlation
coefficient varies sensitively with the density parameter ($\Omega_{m}$) and
neutrino mass fraction ($f_{\nu}$), we suggest that the alignment profile of
cluster galaxies might be useful for breaking the $\Omega_{m}$-$\sigma_{8}$ and
$f_{\nu}$-$\sigma_{8}$ degeneracies. | astro-ph_CO |
Searching for Anisotropic Cosmic Birefringence with Polarization Data
from SPTpol: We present a search for anisotropic cosmic birefringence in 500 deg$^2$ of
southern sky observed at 150 GHz with the SPTpol camera on the South Pole
Telescope. We reconstruct a map of cosmic polarization rotation anisotropies
using higher-order correlations between the observed cosmic microwave
background (CMB) $E$ and $B$ fields. We then measure the angular power spectrum
of this map, which is found to be consistent with zero. The non-detection is
translated into an upper limit on the amplitude of the scale-invariant cosmic
rotation power spectrum, $L(L+1)C_L^{\alpha\alpha}/2\pi < 0.10 \times 10^{-4}$
rad$^2$ (0.033 deg$^2$, 95% C.L.). This upper limit can be used to place
constraints on the strength of primordial magnetic fields, $B_{1 \rm Mpc} < 17
{\rm nG} $ (95% C.L.), and on the coupling constant of the Chern-Simons
electromagnetic term $g_{a\gamma} < 4.0 \times 10^{-2}/H_I $ (95% C.L.), where
$H_I$ is the inflationary Hubble scale. For the first time, we also
cross-correlate the CMB temperature fluctuations with the reconstructed
rotation angle map, a signal expected to be non-vanishing in certain
theoretical scenarios, and find no detectable signal. We perform a suite of
systematics and consistency checks and find no evidence for contamination. | astro-ph_CO |
Large Field Polynomial Inflation: Parameter Space, Predictions and
(Double) Eternal Nature: Simple monomial inflationary scenarios have been ruled out by recent
observations. In this work we revisit the next simplest scenario, a
single--field model where the scalar potential is a polynomial of degree four
which features a concave ``almost'' saddle point. We focus on trans--Planckian
field values. We reparametrize the potential, which greatly simplifies the
procedure for finding acceptbale model parameters. This allows for the first
comprehensive scan of parameter space consistent with recent Planck and
BICEP/Keck 2018 measurements. Even for trans--Planckian field values the
tensor--to--scalar ratio $r$ can be as small as $\mathcal{O}(10^{-8})$, but the
model can also saturate the current upper bound. In contrast to the
small--field version of this model, radiative stability does not lead to strong
constraints on the parameters of the inflaton potential. For very large field
values the potential can be approximated by the quartic term; as well known,
this allows eternal inflation even for field energy well below the reduced
Planck mass $M_{\rm Pl}$, with Hubble parameter $H \sim 10^{-2} M_{\rm Pl}$.
More interestingly, we find a region of parameter space that even supports {\em
two phases of eternal inflation}. The second epoch only occurs if the slope at
the would--be saddle point is very small, and has $H \sim 10^{-5} M_{\rm Pl}$;
it can only be realized if $r \sim 10^{-2}$, within the sensitivity range of
next--generation CMB observations. | astro-ph_CO |
Supernova 2011fe from an Exploding Carbon-Oxygen White Dwarf Star: Type Ia supernovae (SNe Ia) have been used empirically as standardized
candles to reveal the accelerating universe even though fundamental details,
such as the nature of the progenitor system and how the star explodes, remained
a mystery. There is consensus that a white dwarf star explodes after accreting
matter in a binary system, but the secondary could be anything from a main
sequence star to a red giant, or even another white dwarf. The uncertainty
stems from the fact that no recent SN Ia has been discovered close enough to
detect the stars before explosion. Here we report early observations of SN
2011fe (PTF11kly) in M101 at a distance of 6.4 Mpc, the closest SN Ia in the
past 25 years. We find that the exploding star was likely a carbon-oxygen white
dwarf, and from the lack of an early shock we conclude that the companion was
most likely a main sequence star. Early spectroscopy shows high-velocity oxygen
that varies on a time scale of hours and extensive mixing of newly synthesized
intermediate mass elements in the outermost layers of the supernova. A
companion paper uses pre-explosion images to rule out luminous red giants and
most helium stars as companions. | astro-ph_CO |
Results of optical monitoring of 5 SDSS double QSOs with the Nordic
Optical Telescope: We present optical R-band light curves of five SDSS double QSOs (SDSS
J0903+5028, SDSS J1001+5027, SDSS J1206+4332, SDSS J1353+1138, SDSS J1335+0118)
obtained from monitoring at the Nordic Optical Telescope (NOT) between
September 2005 and September 2007. We also present analytical and pixelated
modeling of the observed systems. For SDSS J1206+4332, we measured the time
delay to be 116 days, which, for a Singular Isothermal Ellipsoid model,
corresponds to a Hubble constant of 73 km/s/Mpc. Simultaneous pixeleted
modeling of five other systems for which a time delay has now been previously
measured at the NOT leads to H_0 = 61.5 km/s/Mpc. Finally, by comparing
lightcurves of the two images of each system, suitably shifted by the predicted
or observed time-delays, we found no evidence for microlensing variability over
the course of the monitoring period. | astro-ph_CO |
Mining the Herschel-ATLAS: submillimeter-selected blazars in equatorial
fields: The Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) provides an
unprecedented opportunity to search for blazars at sub-mm wavelengths. We
cross-matched the FIRST radio source catalogue with the 11655 sources brighter
than 35 mJy at 500{\mu}m in the \sim 135 square degrees of the sky covered by
the H-ATLAS equatorial fields at 9 h and 15 h, plus half of the field at 12 h.
We found that 379 of the H-ATLAS sources have a FIRST counterpart within 10
arcsec, including 8 catalogued blazars (plus one known blazar that was found at
the edge of one the H-ATLAS maps). To search for additional blazar candidates
we have devised new diagnostic diagrams and found that known blazars occupy a
region of the log(S500{\mu}m/S350{\mu}m) vs. log(S500{\mu}m/S1.4GHz) plane
separated from that of the other sub-mm sources with radio counterparts. Using
this diagnostic we have selected 12 further candidates that turn out to be
scattered in the (r-z) vs. (u-r) plane or in the WISE colour-colour diagram
proposed by Massaro et al. (2012), where known blazars are concentrated in well
defined strips. This suggests that the majority of them either are not blazars
or have spectral energy distributions contaminated by their host galaxies. A
significant fraction of true blazars are found to be hosted by star-forming
galaxies. This finding, supported by an analysis of blazars detected in Planck
545 and 857 GHz bands, is at odds with the notion that blazar hosts are passive
ellipticals and indicates that the sub-mm selection is providing a novel
prospect on blazar properties. Based on an inspection of the available
photometric data, including the WISE all-sky survey, the unpublished VIKING
survey and new radio observations, we tentatively estimate that there are 11
blazars with synchrotron flux density S500{\mu}m > 35mJy over the considered
area. This result already allows us to constrain blazar evolution models. | astro-ph_CO |
Gödel-type universes and chronology protection in Horava-Lifshitz
gravity: In the attempts toward a quantum gravity theory, general relativity faces a
serious difficulty since it is non-renormalizable theory. Ho\v{r}ava-Lifshitz
gravity offers a framework to circumvent this difficulty, by sacrificing the
local Lorentz invariance at ultra-high energy scales in exchange of
power-counting renormalizability. The Lorentz symmetry is expected to be
recovered at low and medium energy scales. If gravitation is to be described by
a Ho\v{r}ava-Lifshitz gravity theory there are a number of issues that ought to
be reexamined in its context, including the question as to whether this gravity
incorporates a chronology protection, or particularly if it allows G\"odel-type
solutions with violation of causality. We show that Ho\v{r}ava-Lifshitz gravity
only allows hyperbolic G\"odel-type space-times whose essential parameters $m$
and $\omega$ are in the chronology respecting intervals, excluding therefore
any noncausal G\"odel-type space-times in the hyperbolic class. There emerges
from our results that the famous noncausal G\"odel model is not allowed in
Ho\v{r}ava-Lifshitz gravity. The question as to whether this quantum gravity
theory permits hyperbolic G\"odel-type solutions in the chronology preserving
interval of the essential parameters is also examined. We show that
Ho\v{r}ava-Lifshitz gravity not only excludes the noncausal G\"odel universe,
but also rules out any hyperbolic G\"odel-type solutions for physically
well-motivated perfect-fluid matter content. | astro-ph_CO |
The HBI in a quasi-global model of the intracluster medium: In this paper we investigate how convective instabilities influence heat
conduction in the intracluster medium (ICM) of cool-core galaxy clusters. The
ICM is a high-beta, weakly collisional plasma in which the transport of
momentum and heat is aligned with the magnetic field. The anisotropy of heat
conduction, in particular, gives rise to instabilities that can access energy
stored in a temperature gradient of either sign. We focus on the heat-flux
buoyancy-driven instability (HBI), which feeds on the outwardly increasing
temperature profile of cluster cool cores. Our aim is to elucidate how the
global structure of a cluster impacts on the growth and morphology of the
linear HBI modes when in the presence of Braginskii viscosity, and ultimately
on the ability of the HBI to thermally insulate cores. We employ an idealised
quasi-global model, the plane-parallel atmosphere, which captures the essential
physics -- e.g. the global radial profile of the cluster -- while letting the
problem remain analytically tractable. Our main result is that the dominant HBI
modes are localised to the the innermost (~<20%) regions of cool cores. It is
then probable that, in the nonlinear regime, appreciable field-line insulation
will be similarly localised. Thus, while radio-mode feedback appears necessary
in the central few tens of kpc, heat conduction may be capable of offsetting
radiative losses throughout most of a cool core over a significant fraction of
the Hubble time. Finally, our linear solutions provide a convenient numerical
test for the nonlinear codes that tackle the saturation of such convective
instabilities in the presence of anisotropic transport. | astro-ph_CO |
The Case for Standard Irradiated Accretion Disks in Active Galactic
Nuclei: We analyze the broadband photometric light curves of Seyfert 1 galaxies from
the Sergeev et al. (2005) sample and find that a) perturbations propagating
across the continuum emitting region are a general phenomenon securely detected
in most cases, b) it is possible to obtain reliable time-delays between
continuum emission in different wavebands, which are not biased by the
contribution of broad emission lines to the signal, and that c) such lags are
consistent with the predictions of standard irradiated accretion disk models,
given the optical luminosity of the sources. These findings provide new and
independent support for standard accretion disks being responsible for the bulk
of the (rest) optical emission in low-luminosity active galactic nuclei (AGN).
We interpret our lag measurements in individual objects within the framework of
this model and estimate the typical mass accretion rate to be <~0.1Msol/yr,
with little dependence on the black hole mass. Assuming bolometric corrections
typical of type-I sources, we find tentative evidence for the radiative
efficiency of accretion flows being a rising function of the black hole mass.
With upcoming surveys that will regularly monitor the sky, we may be able to
better quantify possible departures from standard self-similar models, and
identify other modes of accretion in AGN. | astro-ph_CO |
Are there cool-core clusters at high-redshift? Chandra results and
prospects with WFXT: In this contribution we trace the evolution of cool-core clusters out to
z~1.3 using high-resolution Chandra data of three representative cluster
samples spanning different redshift ranges. Our analysis is based on the
measurement of the surface brightness (SB) concentration, c_SB, which strongly
anti-correlates with the central cooling time and allows us to characterize the
cool-core strength in low S/N data. We confirm a negative evolution in the
fraction of cool-core clusters with redshift, in particular for very strong
cool-cores. Still, we find evidence for a large population of well formed
cool-cores at z ~ 1. This analysis is potentially very effective in
constraining the nature and the evolution of the cool-cores, once large samples
of high-z clusters will be available. In this respect, we explore the potential
of the proposed mission Wide Field X-ray Telescope (WFXT) to address this
science case. We conclude that WFXT provides the best trade-off of angular
resolution, sensitivity and covered solid angle in order to discover and fully
characterize the cool-core cluster population up to z=1.5. | astro-ph_CO |
Research Update on Extreme-Mass-Ratio Inspirals: The inspirals of stellar-mass mass compact objects into massive black holes
in the centres of galaxies are one of the most important sources of
gravitational radiation for space-based detectors like LISA or eLISA. These
extreme-mass-ratio inspirals (EMRIs) will enable an ambitious research program
with implications for astrophysics, cosmology, and fundamental physics. This
article is a summary of the talks delivered at the plenary session on EMRIs at
the 10th International LISA Symposium. It contains research updates on the
following topics: astrophysics of EMRIs; EMRI science potential; and EMRI
modeling. | astro-ph_CO |
Cosmological consequences of a scalar field with oscillating equation of
state: A possible solution to the fine-tuning and coincidence problems: We propose a new dark energy model for solving the cosmological fine-tuning
and coincidence problems. A default assumption is that the fine-tuning problem
disappears if we do not interpret dark energy as vacuum energy. The key idea to
solving the coincidence problem is that the Universe may have several
acceleration phases across the whole cosmic history. The specific example we
study is a quintessence model with approximately repeated double exponential
potential, which only introduces one Planck scale parameter and three
dimensionless parameters of order unity. The cosmological background evolution
equations can be recast into a four-dimensional dynamical system and its main
properties are discussed in details. Preliminary calculations show that our
model is able to explain the observed cosmic late-time acceleration. | astro-ph_CO |
Bogoliubov Excited States and the Lyth Bound: We show that Bogoliubov excited scalar and tensor modes do not alleviate
Planckian evolution during inflation if one assumes that $r$ and the Bogoliubov
coefficients are approximately scale invariant. We constrain the excitation
parameter for the scalar fluctuations, $\beta$, and tensor perturbations,
$\tilde{\beta}$, by requiring that there be at least three decades of scale
invariance in the scalar and tensor power spectrum. For the scalar fluctuations
this is motivated by the observed nearly scale invariant scalar power spectrum.
For the tensor fluctuations this assumption may be shown to be valid or invalid
by future experiments. | astro-ph_CO |
Formation of disk galaxies in preheated media: a preventative feedback
model: We introduce a semi-analytic galaxy formation model implementing a
self-consistent treatment for the hot halo gas configuration and the assembly
of central disks. Using the model, we explore a preventative feedback model, in
which the circum-halo medium is assumed to be preheated up to a certain entropy
level by early starbursts or other processes, and compare it with an ejective
feedback model, in which baryons are first accreted into dark matter halos and
subsequently ejected out by feedback. The model demonstrates that when the
medium is preheated to an entropy comparable to the halo virial entropy the
baryon accretion can be largely reduced and delayed. In addition, the preheated
medium can establish an extended low density gaseous halo when it accretes into
the dark matter halos, and result in a specific angular momentum of the cooling
gas large enough to form central disks as extended as those observed. Combined
with simulated halo assembly histories, the preventative feedback model can
reproduce remarkably well a number of observational scaling relations. These
include the cold baryon (stellar plus cold gas) mass fraction-halo mass
relations, star formation histories, disk size-stellar mass relation and its
evolution, and the number density of low-mass galaxies as a function of
redshift. In contrast, the conventional ejective feedback model fails to
reproduce these observational trends. Using the model, we demonstrate that the
properties of disk galaxies are closely tied to the thermal state of hot halo
gas and even possibly the circum-halo medium, which suggests that observational
data for the disk properties and circum-galactic hot/warm medium may jointly
provide interesting constraints for galaxy formation models. | astro-ph_CO |
Kinematic consistency relations of large-scale structures: We describe how the kinematic consistency relations satisfied by density
correlations of the large-scale structures of the Universe can be derived
within the usual Newtonian framework. These relations express a kinematic
effect and show how the $(\ell+n)$-density correlation factors in terms of the
$n$-point correlation and $\ell$ linear power spectrum factors, in the limit
where the $\ell$ soft wave numbers become linear and much smaller than the $n$
other wave numbers. We describe how these relations extend to multifluid cases.
In the standard cosmology, these consistency relations derive from the
equivalence principle. A detection of their violation would indicate
non-Gaussian initial conditions, non-negligible decaying modes, or a
modification of gravity that does not converge to General Relativity on large
scales. | astro-ph_CO |
Perturbative Resonance in WIMP paradigm and its Cosmological
Implications on Cosmic Reheating and Primordial Gravitational Wave Detection: We investigate the co-evolution of dark matter (DM) density perturbation and
metric perturbation in the WIMP paradigm. Instead of adopting the conventional
assumption that DM starts out in thermal equilibrium, we propose a simple phase
of DM production for the WIMP paradigm and extend our analysis to this phase.
Being free from the envelop of thermal equilibrium, an amplified perturbative
resonance between DM density perturbation and scalar modes of metric
perturbation takes place during the DM production phase, and consequently
results in a suppression of the tensor-to-scalar ratio of metric perturbation.
By specifying the cosmic background with a typical realization of cosmic
reheating, we establish a relation between DM particle mass $m_\chi$ and the
tensor-to-scalar ratio $r$ in the WIMP paradigm, which also contains two
reheating parameters, the reheating temperature $T_{R_f}$ and the dissipative
constant $\Gamma_0$. Notably, for a sizeable parameter region of WIMP candidate
and cosmic reheating, this relation predicts a smaller value of $r$ in
comparing with the conventional expectation obtained by assuming DM starts out
in thermal equilibrium. Once the suppression of $r$ is measured in future
observations of primordial gravitational wave in CMB, this relation can be used
to constrain $m_\chi$, $T_{R_f}$ and $\Gamma_0$ in principle. | astro-ph_CO |
Preparing old and recent radio source tables for the VO age: Current
status: Independent of established data centers, and partly for my own research, I
have been collecting the tabular data from nearly 1500 articles concerned with
radio sources. Optical character recognition (OCR) was used to recover tables
from nearly 600 of these. Tables from only 44 percent of these articles are
available in the CDS or CATS catalog collections. This fraction is 62 percent
for articles with over 100 sources. Surprisingly, these fractions are not
better for articles published electronically since 2001, perhaps partly due to
the fact that often tabular data are published in formats not useful for direct
machine reading. The databases Simbad and NED recognize only about 60 percent
of the bibliographic references corresponding to the existing electronic radio
source lists, and the number of objects associated with these references is
much smaller still. Both, object databases like NED and Simbad, as well as
catalog browsers (VizieR, CATS) need to be consulted to obtain the most
complete information on radio sources. More human resources at the data centers
and better collaboration between authors, referees, editors, publishers, and
data centers are required to improve the flow of tabular data from journals to
public databases. Current efforts within the Virtual Observatory (VO) project,
to provide retrieval and analysis tools for different types of published and
archival data stored at various sites, should be balanced by an equal effort to
recover and include large amounts of published data not currently available in
this way. If human resources can be found, the data sets collected by the
author will be made available for the preparation of metadata necessary for
their ingression into catalog browsers. | astro-ph_CO |
Detecting Baryon Acoustic Oscillations in Dark Matter from Kinematic
Weak Lensing Surveys: We investigate the feasibility of extracting Baryon Acoustic Oscillations
(BAO) from cosmic shear tomography. We particularly focus on the BAO scale
precision that can be achieved by future spectroscopy-based, kinematic weak
lensing (KWL) surveys \citep[e.g.,][]{Huff13} in comparison to the traditional
photometry-based weak lensing surveys. We simulate cosmic shear tomography data
of such surveys with a few simple assumptions to focus on the BAO information,
extract the spacial power spectrum, and constrain the recovered BAO feature.
Due to the small shape noise and the shape of the lensing kernel, we find that
a Dark Energy Task Force Stage IV version of such KWL survey can detect the BAO
feature in dark matter by $3$-$\sigma$ and measure the BAO scale at the
precision level of 4\% while it will be difficult to detect the feature in
photometry-based weak lensing surveys. With a more optimistic assumption, a
KWL-Stage IV could achieve a $\sim 2\%$ BAO scale measurement with
$4.9$-$\sigma$ confidence. A built-in spectroscopic galaxy survey within such
KWL survey will allow cross-correlation between galaxies and cosmic shear,
which will tighten the constraint beyond the lower limit we present in this
paper and therefore possibly allow a detection of the BAO scale bias between
galaxies and dark matter. | astro-ph_CO |
Galaxy and Mass Assembly (GAMA): Dust obscuration in galaxies and their
recent star formation histories: We present self-consistent star formation rates derived through pan-spectral
analysis of galaxies drawn from the Galaxy and Mass Assembly (GAMA) survey. We
determine the most appropriate form of dust obscuration correction via
application of a range of extinction laws drawn from the literature as applied
to Halpha, [O{II}] and UV luminosities. These corrections are applied to a
sample of 31,508 galaxies from the GAMA survey at z < 0.35. We consider several
different obscuration curves, including those of Milky Way, Calzetti (2001) and
Fischera and Dopita (2005) curves and their effects on the observed
luminosities. At the core of this technique is the observed Balmer decrement,
and we provide a prescription to apply optimal obscuration corrections using
the Balmer decrement. We carry out an analysis of the star formation history
(SFH) using stellar population synthesis tools to investigate the evolutionary
history of our sample of galaxies as well as to understand the effects of
variation in the Initial Mass Function (IMF) and the effects this has on the
evolutionary history of galaxies. We find that the Fischera and Dopita (2005)
obscuration curve with an R_{v} value of 4.5 gives the best agreement between
the different SFR indicators. The 2200A feature needed to be removed from this
curve to obtain complete consistency between all SFR indicators suggesting that
this feature may not be common in the average integrated attenuation of galaxy
emission. We also find that the UV dust obscuration is strongly dependent on
the SFR. | astro-ph_CO |
Far-Infrared Properties of Spitzer-selected Luminous Starbursts: We present SHARC-2 350 micron data on 20 luminous z ~ 2 starbursts with
S(1.2mm) > 2 mJy from the Spitzer-selected samples of Lonsdale et al. and
Fiolet et al. All the sources were detected, with S(350um) > 25 mJy for 18 of
them. With the data, we determine precise dust temperatures and luminosities
for these galaxies using both single-temperature fits and models with power-law
mass--temperature distributions. We derive appropriate formulae to use when
optical depths are non-negligible. Our models provide an excellent fit to the
6um--2mm measurements of local starbursts. We find characteristic
single-component temperatures T1 ~ 35.5+-2.2 K and integrated infrared (IR)
luminosities around 10^(12.9+-0.1) Lsun for the SWIRE-selected sources.
Molecular gas masses are estimated at 4 x 10^(10) Msun, assuming
kappa(850um)=0.15 m^2/kg and a submillimeter-selected galaxy (SMG)-like
gas-to-dust mass ratio. The best-fit models imply >~2 kpc emission scales. We
also note a tight correlation between rest-frame 1.4 GHz radio and IR
luminosities confirming star formation as the predominant power source. The
far-IR properties of our sample are indistinguishable from the purely
submillimeter-selected populations from current surveys. We therefore conclude
that our original selection criteria, based on mid-IR colors and 24 um flux
densities, provides an effective means for the study of SMGs at z ~ 1.5--2.5. | astro-ph_CO |
Cosmological constraints from large-scale structure growth rate
measurements: We compile a list of $14$ independent measurements of large-scale structure
growth rate between redshifts $0.067 \leq z \leq 0.8$ and use this to place
constraints on model parameters of constant and time-evolving
general-relativistic dark energy cosmologies. With the assumption that gravity
is well-modeled by general relativity, we discover that growth-rate data
provide restrictive cosmological parameter constraints. In combination with
type Ia supernova apparent magnitude versus redshift data and Hubble parameter
measurements, the growth rate data are consistent with the standard
spatially-flat $\Lambda$CDM model, as well as with mildly evolving dark energy
density cosmological models. | astro-ph_CO |
On the Contribution of Active Galactic Nuclei to the High-Redshift
Metagalactic Ionizing Background: Motivated by the claimed detection of a large population of faint active
galactic nuclei (AGN) at high redshift, recent studies have proposed models in
which AGN contribute significantly to the z > 4 H I ionizing background. In
some models, AGN are even the chief sources of reionization. If correct, these
models would make necessary a complete revision to the standard view that
galaxies dominated the high-redshift ionizing background. It has been suggested
that AGN-dominated models can better account for two recent observations that
appear to be in conflict with the standard view: (1) large opacity variations
in the z ~ 5.5 H I Lyman-alpha forest, and (2) slow evolution in the mean
opacity of the He II Lyman-alpha forest. Large spatial fluctuations in the
ionizing background from the brightness and rarity of AGN may account for the
former, while the earlier onset of He II reionization in these models may
account for the latter. Here we show that models in which AGN emissions source
>~ 50 % of the ionizing background generally provide a better fit to the
observed H I Lyman-alpha forest opacity variations compared to standard
galaxy-dominated models. However, we argue that these AGN-dominated models are
in tension with constraints on the thermal history of the intergalactic medium
(IGM). Under standard assumptions about the spectra of AGN, we show that the
earlier onset of He II reionization heats up the IGM well above recent
temperature measurements. We further argue that the slower evolution of the
mean opacity of the He II Lyman-alpha forest relative to simulations may
reflect deficiencies in current simulations rather than favor AGN-dominated
models as has been suggested. | astro-ph_CO |
Baryonic effects for weak lensing. Part II. Combination with X-ray data
and extended cosmologies: An accurate modelling of baryonic feedback effects is required to exploit the
full potential of future weak-lensing surveys such as Euclid or LSST. In this
second paper in a series of two, we combine Euclid-like mock data of the cosmic
shear power spectrum with an eROSITA X-ray mock of the cluster gas fraction to
run a combined likelihood analysis including both cosmological and baryonic
parameters. Following the first paper of this series, the baryonic effects
(based on the baryonic correction model of Schneider et al. 2019) are included
in both the tomographic power spectrum and the covariance matrix. However, this
time we assume the more realistic case of a $\Lambda$CDM cosmology with massive
neutrinos, and we consider several extensions of the currently favoured
cosmological model. For the standard $\Lambda$CDM case, we show that including
X-ray data reduces the uncertainties on the sum of the neutrino mass by
$\sim30$ percent, while there is only a mild improvement on other parameters
such as $\Omega_m$ and $\sigma_8$. As extensions of $\Lambda$CDM, we consider
the cases of a dynamical dark energy model (wCDM), a $f(R)$ gravity model
(fRCDM), and a mixed dark matter model ($\Lambda$MDM) with both a cold and a
warm/hot dark matter component. We find that combining weak lensing with X-ray
data only leads to a mild improvement of the constraints on the additional
parameters of wCDM, while the improvement is more substantial for both fRCDM
and $\Lambda$MDM. Ignoring baryonic effects in the analysis pipeline leads to
significant false-detections of either phantom dark energy or a light
subdominant dark matter component. Overall we conclude that for all cosmologies
considered, a general parametrisation of baryonic effects is both necessary and
sufficient to obtain tight constraints on cosmological parameters. | astro-ph_CO |
Quasi-evaporating black holes and cold dark matter: Vilkovisky has claimed to have solved the black hole backreaction problem and
finds that black holes lose only ten percent of their mass to Hawking radiation
before evaporation ceases. We examine the implications of this scenario for
cold dark matter, assuming that primordial black holes are created during the
reheating period after inflation. The mass spectrum is expected to be dominated
by 10-gram black holes. Nucleosynthesis constraints and the requirement that
the earth presently exist do not come close to ruling out such black holes as
dark matter candidates. They also evade the demand that the photon density
produced by evaporating primordial black holes does not exceed the present
cosmic radiation background by a factor of about one thousand. | astro-ph_CO |
Doubling Strong Lensing as a Cosmological Probe: Strong gravitational lensing provides a geometric probe of cosmology in a
unique manner through distance ratios involving the source and lens. This is
well known for the time delay distance derived from measured delays between
lightcurves of the images of variable sources such as quasars. Recently, double
source plane lens systems involving two constant sources lensed by the same
foreground lens have been proposed as another probe, involving a different
ratio of distances measured from the image positions and fairly insensitive to
the lens modeling. Here we demonstrate that these two different sets of strong
lensing distance ratios have strong complementarity in cosmological leverage.
Unlike other probes, the double source distance ratio is actually more
sensitive to the dark energy equation of state parameters $w_0$ and $w_a$ than
to the matter density $\Omega_m$, for low redshift lenses. Adding double source
distance ratio measurements can improve the dark energy figure of merit by 40%
for a sample of fewer than 100 low redshift systems, or even better for the
optimal redshift distribution we derive. | astro-ph_CO |
Correlation of AGN Jet Power with the Entropy Profile in Cooling Flow
Clusters: We find that the power of jets that inflate bubble pairs in cooling flow
clusters of galaxies correlates with the size of the inner region where the
entropy profile is flat, as well as with the gas mass in that region and the
entropy floor (the entropy value at the center of the cluster). These
correlations strengthen the cold feedback mechanism that is thought to operate
in cooling flow clusters and during galaxy formation. In the cold feedback
mechanism the central super-massive black hole (SMBH) is fed with cold clumps
that originate in an extended region of the cooling flow volume, in particular
from the inner region that has a flat entropy profile. Such a process ensures a
tight feedback between radiative cooling and heating by the SMBH (the AGN). The
derived expressions should be used instead of the Bondi accretion rate when
studying AGN feedback. We find that the mass of molecular gas also correlates
with the entropy profile parameters, despite that the jet power does not
correlate with the molecular gas mass. This further suggests that the entropy
profile is a fundamental parameter determining cooling and feedback in cooling
flow clusters. | astro-ph_CO |
Hubble parameter reconstruction from a principal component analysis:
minimizing the bias: A model-independent reconstruction of the cosmic expansion rate is essential
to a robust analysis of cosmological observations. Our goal is to demonstrate
that current data are able to provide reasonable constraints on the behavior of
the Hubble parameter with redshift, independently of any cosmological model or
underlying gravity theory. Using type Ia supernova data, we show that it is
possible to analytically calculate the Fisher matrix components in a Hubble
parameter analysis without assumptions about the energy content of the
Universe. We used a principal component analysis to reconstruct the Hubble
parameter as a linear combination of the Fisher matrix eigenvectors (principal
components). To suppress the bias introduced by the high redshift behavior of
the components, we considered the value of the Hubble parameter at high
redshift as a free parameter. We first tested our procedure using a mock sample
of type Ia supernova observations, we then applied it to the real data compiled
by the Sloan Digital Sky Survey (SDSS) group. In the mock sample analysis, we
demonstrate that it is possible to drastically suppress the bias introduced by
the high redshift behavior of the principal components. Applying our procedure
to the real data, we show that it allows us to determine the behavior of the
Hubble parameter with reasonable uncertainty, without introducing any ad-hoc
parameterizations. Beyond that, our reconstruction agrees with completely
independent measurements of the Hubble parameter obtained from red-envelope
galaxies. | astro-ph_CO |
A new catalogue of polar-ring galaxies selected from the SDSS: (Abridged) Galaxies with polar rings (PRGs) are a unique class of
extragalactic objects allowing to investigate a wide range of problems, linked
with the formation and evolution of galaxies, and to study the properties of
their dark haloes. The progress in the study of PRGs is constrained by a small
number of known objects of this type. Up to date, we can only attribute about
two dozens of kinematically-confirmed galaxies to this class, mostly from
Whitmore et al. (1990) catalogue. We present a new catalogue of PRGs based on
the results of the original Galaxy Zoo project. Based on the preliminary
classification of the Galaxy Zoo, we viewed more than 40000 images of the Sloan
Digital Sky Survey (SDSS) and selected 275 galaxies, included in our catalogue.
Our Sloan-based Polar Ring Catalog (SPRC) contains 70 galaxies that we
classified as "the best candidates", among which we expect to have a very high
proportion of true PRGs, and 115 good PRG candidates. 53 galaxies are
classified as PRG related objects.We identified 37 galaxies that have their
presumed polar rings seen almost face-on. The SPRC objects are on the average
fainter and located further away than the galaxies from the catalog by Whitmore
et al., although our catalogue does include dozens of new nearby candidate
PRGs. The new catalogue significantly increases the number of genuine PRG
candidates, and may serve as a good basis both for the further detailed study
of individual galaxies, and for the statistical analysis of PRGs as a separate
class of objects. We performed spectroscopic observations of six galaxies from
the SPRC at the 6-m telescope. The existence of polar rings was confirmed in
five galaxies, and one object appeared to be a projection of a pair of
galaxies. Adding the literature data, we can already classify 10 galaxies from
our catalogue to the kinematically-confirmed PRGs. | astro-ph_CO |
Cosmic Radio Background from Primordial Black Holes at Cosmic Dawn: The presence of an extra radio background besides the cosmic microwave
background has important implications for the observation of the 21-cm signal
during the cosmic Dark Ages, Cosmic Dawn, and epoch of Reionization. The strong
absorption trough found in the 21-cm global spectrum measured by the EDGES
experiment, which has a much greater depth than the standard model prediction,
has drawn great interest to this scenario, but more generally it is still of
great interest to consider such a cosmic radio background (CRB) in the early
Universe. To be effective in affecting the 21-cm signal at early time, such a
radio background must be produced by sources which can emit strong radio
signals but modest amount of X-rays, so that the gas is not heated up too
early. We investigate the scenario that such a radio background is produced by
the primordial black holes (PBHs). For PBH with a single mass, we find that if
the PBHs' abundance $\log(f_{\rm PBH})$ (ratio of total PBH mass density to
total matter density) and mass satisfy the relation $\log(f_{\rm PBH}) \sim
-1.8\log(M_\bullet/{\rm M}_{\odot})-3.5$ for $1\,{\rm M}_\odot \lesssim
M_\bullet \lesssim 300 {\rm M}_\odot$, and have jet emission, they can generate
a CRB required for reproducing the 21-cm absorption signal seen by the EDGES.
The accretion rate can be boosted if the PBHs are surrounded by dark matter
halos, which permits lower $f_{\rm PBH}$ value to satisfy the EDGES
observation. In the latter scenario, since the accretion rate can evolve
rapidly during the Cosmic Dawn, the frequency (redshift) and depth of the
absorption trough can determine the mass and abundance of the PBHs
simultaneously. For absorption trough redshift $\sim$ 17 and depth $\sim -500$
mK, it corresponds to $M_\bullet \sim 1.05\,{\rm M}_{\odot}$ and $f_{\rm
PBH}\sim 1.5\times10^{-4}$. | astro-ph_CO |
HST Morphologies of z ~ 2 Dust-Obscured Galaxies II: Bump Sources: We present Hubble Space Telescope (HST) imaging of 22 ultra-luminous infrared
galaxies (ULIRGs) at z~2 with extremely red R-[24] colors (called dust-obscured
galaxies, or DOGs) which have a local maximum in their spectral energy
distribution (SED) at rest-frame 1.6um associated with stellar emission. These
sources, which we call "bump DOGs", have star-formation rates of 400-4000
Msun/yr and have redshifts derived from mid-IR spectra which show strong
polycyclic aromatic hydrocarbon emission --- a sign of vigorous on-going
star-formation. Using a uniform morphological analysis, we look for
quantifiable differences between bump DOGs, power-law DOGs (Spitzer-selected
ULIRGs with mid-IR SEDs dominated by a power-law and spectral features that are
more typical of obscured active galactic nuclei than starbursts),
sub-millimeter selected galaxies (SMGs), and other less-reddened ULIRGs from
the Spitzer extragalactic First Look Survey (XFLS). Bump DOGs are larger than
power-law DOGs (median Petrosian radius of 8.4 +/- 2.7 kpc vs. 5.5 +/- 2.3 kpc)
and exhibit more diffuse and irregular morphologies (median M_20 of -1.08 +/-
0.05 vs. -1.48 +/- 0.05). These trends are qualitatively consistent with
expectations from simulations of major mergers in which merging systems during
the peak star-formation rate period evolve from M_20 = -1.0 to M_20 = -1.7.
Less obscured ULIRGs (i.e., non-DOGs) tend to have more regular, centrally
peaked, single-object morphologies rather than diffuse and irregular
morphologies. This distinction in morphologies may imply that less obscured
ULIRGs sample the merger near the end of the peak star-formation rate period.
Alternatively, it may indicate that the intense star-formation in these
less-obscured ULIRGs is not the result of a recent major merger. | astro-ph_CO |
Cosmological Evolution With Interaction Between Dark Energy And Dark
Matter: In this review we consider in detail different theoretical topics associated
with interaction in the dark sector. We study linear and nonlinear interactions
which depend on the dark matter and dark energy densities. We consider a number
of different models (including the holographic dark energy and dark energy in a
fractal universe) with interacting dark energy (DE) and dark matter (DM), have
done a thorough analysis of these models. The main task of this review was not
only to give an idea about the modern set of different models of dark energy,
but to show how much can be diverse dynamics of the universe in these models.
We find that the dynamics of a Universe that contains interaction in the dark
sector can differ significantly from the Standard Cosmological Model (SCM). | astro-ph_CO |
A Density Independent Formulation of Smoothed Particle Hydrodynamics: The standard formulation of the smoothed particle hydrodynamics (SPH) assumes
that the local density distribution is differentiable. This assumption is used
to derive the spatial derivatives of other quantities. However, this assumption
breaks down at the contact discontinuity. At the contact discontinuity, the
density of the low-density side is overestimated while that of the high-density
side is underestimated. As a result, the pressure of the low (high) density
side is over (under) estimated. Thus, unphysical repulsive force appears at the
contact discontinuity, resulting in the effective surface tension. This tension
suppresses fluid instabilities. In this paper, we present a new formulation of
SPH, which does not require the differentiability of density. Instead of the
mass density, we adopt the internal energy density (pressure), and its
arbitrary function, which are smoothed quantities at the contact discontinuity,
as the volume element used for the kernel integration. We call this new
formulation density independent SPH (DISPH). It handles the contact
discontinuity without numerical problems. The results of standard tests such as
the shock tube, Kelvin-Helmholtz and Rayleigh-Taylor instabilities, point like
explosion, and blob tests are all very favorable to DISPH. We conclude that
DISPH solved most of known difficulties of the standard SPH, without
introducing additional numerical diffusion or breaking the exact force symmetry
or energy conservation. Our new SPH includes the formulation proposed by
Ritchie & Thomas (2001) as a special case. Our formulation can be extended to
handle a non-ideal gas easily. | astro-ph_CO |
Neutrino clustering around spherical dark matter halos: Cold dark matter halos form within a smoothly distributed background of relic
neutrinos -- at least some of which are massive and non-relativistic at late
times. We calculate the accumulation of massive neutrinos around spherically
collapsing cold dark matter halos in a cosmological background. We identify the
physical extent of the "neutrino halo" in the spherical collapse model, which
is large in comparison with the virial radius of the dark matter, and
conditions under which neutrinos reaching the cold dark matter halo will remain
bound to the halo at late times. We calculate the total neutrino mass and bound
neutrino mass associated with isolated spherical halos for several neutrino
mass hierarchies and provide fitting formulae for these quantities in terms of
the cold dark matter halo mass and the masses of the individual neutrino
species. | astro-ph_CO |
zCOSMOS 20k: Satellite galaxies are the main drivers of environmental
effects in the galaxy population at least to z~0.7: We explore the role of environment in the evolution of galaxies over
0.1<z<0.7 using the final zCOSMOS-bright data set. Using the red fraction of
galaxies as a proxy for the quenched population, we find that the fraction of
red galaxies increases with the environmental overdensity and with the stellar
mass, consistent with previous works. As at lower redshift, the red fraction
appears to be separable in mass and environment, suggesting the action of two
processes: mass and environmental quenching. The parameters describing these
appear to be essentially the same at z~0.7 as locally. We explore the relation
between red fraction, mass and environment also for the central and satellite
galaxies separately, paying close attention to the effects of impurities in the
central-satellite classification and using carefully constructed samples
matched in stellar mass. There is little evidence for a dependence of the red
fraction of centrals on overdensity. Satellites are consistently redder at all
overdensities, and the satellite quenching efficiency increases with
overdensity at 0.1<z<0.4. This is less marked at higher redshift, but both are
nevertheless consistent with the equivalent local measurements. At a given
stellar mass, the fraction of galaxies that are satellites also increases with
the overdensity. At a given overdensity and mass, the obtained relation between
the environmental quenching and the satellite fraction agrees well with the
satellite quenching efficiency, demonstrating that the environmental quenching
in the overall population is consistent with being entirely produced through
the satellite quenching process at least up to z=0.7. However, despite the
unprecedented size of our high redshift samples, the associated statistical
uncertainties are still significant and our statements should be understood as
approximations to physical reality, rather than physically exact formulae. | astro-ph_CO |
Observability of lensing of gravitational waves from massive black hole
binaries with LISA: The gravitational waves emitted by massive black hole binaries in the LISA
band can be lensed. Wave-optics effects in the lensed signal are crucial when
the Schwarzschild radius of the lens is smaller than the wavelength of the
radiation. These frequency-dependent effects can enable us to infer the lens
parameters, possibly with a single detection alone. In this work, we assess the
observability of wave-optics effects with LISA by performing an
information-matrix analysis using analytical solutions for both point-mass and
singular isothermal sphere lenses. We use gravitational-waveform models that
include the merger, ringdown, higher harmonics, and aligned spins to study how
waveform models and source parameters affect the measurement errors in the lens
parameters. We find that previous work underestimated the observability of
wave-optics effects and that LISA can detect lensed signals with higher impact
parameters and lower lens masses. | astro-ph_CO |
Why a Windy Torus?: Mass ejection in the form of winds or jets appears to be as fundamental to
quasar activity as accretion, and can be directly observed in many objects with
broadened and blue-shifted UV absorption features. A convincing argument for
radiation pressure driving this ionized outflow can be made within the dust
sublimation radius. Beyond, radiation pressure is even more important, as high
energy photons from the central engine can now push on dust grains. This
physics underlies the dusty-wind model for the putative obscuring torus.
Specifically, the dusty wind in our model is first launched from the outer
accretion disk as a magneto-centrifugal wind and then accelerated and shaped by
radiation pressure from the central continuum. Such a wind can plausibly
account for both the necessary obscuring medium to explain the ratio of
broad-to-narrow-line objects and the mid-infrared emission commonly seen in
quasar spectral energy distributions. A convincing demonstration that
large-scale, organized magnetic fields are present in radio-quiet active
galactic nuclei is now required to bolster the case for this paradigm. | astro-ph_CO |
Generalised DBI-Quintessence: We investigate the phase space of a quintessence theory governed by a
generalised version of the DBI action, using a combination of numeric and
analytic methods. The additional degrees of freedom lead to a vastly richer
phase space structure, where the field covers the full equation of state
parameter space; $-1 \le \omega \le 1$. We find many non-trivial solution
curves to the equations of motion which indicate that DBI quintessence is an
interesting candidate for a viable k-essence model. | astro-ph_CO |
ALMA follows streaming of dense gas down to 40 pc from the supermassive
black hole in NGC1097: We present a kinematic analysis of the dense molecular gas in the central 200
parsecs of the nearby galaxy NGC1097, based on Cycle 0 observations with the
Atacama Large Millimeter/sub-millimeter Array (ALMA). We use the HCN(4-3) line
to trace the densest interstellar molecular gas, and quantify its kinematics,
and estimate an inflow rate for the molecular gas. We find a striking
similarity between the ALMA kinematic data and the analytic spiral inflow model
that we have previously constructed based on ionized gas velocity fields on
larger scales. We are able to follow dense gas streaming down to 40 pc distance
from the supermassive black hole in this Seyfert 1 galaxy. In order to fulfill
marginal stability, we deduce that the dense gas is confined to a very thin
disc, and we derive a dense gas inflow rate of 0.09 Msun/yr at 40 pc radius.
Combined with previous values from the Ha and CO gas, we calculate a combined
molecular and ionized gas inflow rate of 0.2 Msun/yr at 40 pc distance from the
central supermassive black hole of NGC1097. | astro-ph_CO |
Planck 2018 constraints on anisotropic birefringence and its
cross-correlation with CMB anisotropy: Parity-violating extensions of standard electromagnetism produce cosmic
birefringence, the in vacuo rotation of the linear polarisation direction of a
photon during propagation. We employ {\it Planck} 2018 CMB polarised data to
constrain anisotropic birefringence, modeled by its angular power spectrum
$C_{\ell}^{\alpha \alpha}$, and the cross-correlation with CMB temperature
maps, $C_{\ell}^{\alpha T}$, at scales larger than $\sim$15 degrees. We present
joint limits on the scale invariant quantity, $A^{\alpha \alpha} \equiv \ell
(\ell +1) \, C_{\ell}^{\alpha \alpha} / 2 \pi$, and on the analogous amplitude
for the cross-correlation, $A^{\alpha T} \equiv \ell (\ell +1) \,
C_{\ell}^{\alpha T} / 2 \pi$. We find no evidence of birefringence within the
error budget and obtain $A^{\alpha \alpha} < 0.104 \, \mbox{[deg$^2$]}$ and
$A^{\alpha T}=1.50^{+2.41}_{-4.10} \, \mbox{[$\mu$K$\cdot$deg] both at } 95 \%
\mbox{ C.L.}$. The latter bound appears competitive in constraining a few early
dark energy models recently proposed to alleviate the $H_{0}$ tension. Slicing
the joint likelihood at $A^{\alpha T}=0$, the bound on $A^{\alpha \alpha}$
becomes tighter at $A^{\alpha \alpha} < 0.085 \, \mbox{[deg$^2$]}$ at 95$\%
\mbox{ C.L.}$. In addition we recast the constraints on $A^{\alpha \alpha}$ as
a bound on the amplitude of primordial magnetic fields responsible for Faraday
rotation, finding $B_{1 {\tiny \mbox{Mpc}}} < 26.9$ nG and $B_{1 {\tiny
\mbox{Mpc}}} < 24.3$ nG at 95$\%$ C.L. for the marginalised and sliced case
respectively. | astro-ph_CO |
Biased Tracers and Time Evolution: We study the effect of time evolution on galaxy bias. We argue that at any
order in perturbations, the galaxy density contrast can be expressed in terms
of a finite set of locally measurable operators made of spatial and temporal
derivatives of the Newtonian potential. This is checked in an explicit third
order calculation. There is a systematic way to derive a basis for these
operators. This basis spans a larger space than the expansion in gravitational
and velocity potentials usually employed, although new operators only appear at
fourth order. The basis is argued to be closed under renormalization. Most of
the arguments also apply to the structure of the counter-terms in the effective
theory of large-scale structure. | astro-ph_CO |
Aemulus $ν$: Precise Predictions for Matter and Biased Tracer Power
Spectra in the Presence of Neutrinos: We present the Aemulus $\nu$ simulations: a suite of 150 $(1.05 h^{-1}\rm
Gpc)^3$ $N$-body simulations with a mass resolution of $3.51\times 10^{10}
\frac{\Omega_{cb}}{0.3} ~ h^{-1} M_{\odot}$ in a $w\nu$CDM cosmological
parameter space. The simulations have been explicitly designed to span a broad
range in $\sigma_8$ to facilitate investigations of tension between large scale
structure and cosmic microwave background cosmological probes. Neutrinos are
treated as a second particle species to ensure accuracy to $0.5\, \rm eV$, the
maximum neutrino mass that we have simulated. By employing Zel'dovich control
variates, we increase the effective volume of our simulations by factors of
$10-10^5$ depending on the statistic in question. As a first application of
these simulations, we build new hybrid effective field theory and matter power
spectrum surrogate models, demonstrating that they achieve $\le 1\%$ accuracy
for $k\le 1\, h\,\rm Mpc^{-1}$ and $0\le z \le 3$, and $\le 2\%$ accuracy for
$k\le 4\, h\,\rm Mpc^{-1}$ for the matter power spectrum. We publicly release
the trained surrogate models, and estimates of the surrogate model errors in
the hope that they will be broadly applicable to a range of cosmological
analyses for many years to come. | astro-ph_CO |
Detection of spatial correlations of fundamental plane residuals, and
cosmological implications: The fundamental plane (FP) is a widely used tool to investigate the
properties of early-type galaxies, and the tight relation between its
parameters has spawned several cosmological applications, including its use as
a distance indicator for peculiar velocity surveys and as a means to suppress
intrinsic noise in cosmic size magnification measurements. Systematic trends
with the large-scale structure across the FP could cause serious biases for
these cosmological probes, but may also yield new insights into the early-type
population. Here we report the first detection of spatial correlations among
offsets in galaxy size from an FP that explicitly accounts for redshift trends,
using a sample of about $95,000$ elliptical galaxies from the Sloan Digital Sky
Survey. We show that these offsets correlate with the density field out to at
least $10h^{-1}$Mpc at $4\sigma$ significance in a way that cannot be explained
by systematic errors in galaxy size estimates. We propose a physical
explanation for the correlations by dividing the sample into central,
satellite, and field galaxies, identifying trends for each galaxy type
separately. Central (satellite) galaxies lie on average above (below) the FP,
which we argue could be due to a higher (lower) than average mass-to-light
ratio. We fit a simple model to the correlations of FP residuals and use it to
predict the impact on peculiar velocity power spectra, finding a contamination
larger than $10\,\%$ for $k>0.04\,h/$Mpc. Moreover, cosmic magnification
measurements based on an FP could be severely contaminated over a wide range of
scales by the intrinsic FP correlations. | astro-ph_CO |
Cosmology of Single Species Hidden Dark Matter: Cosmology and astrophysics provide various ways to study the properties of
dark matter even if they have negligible non-gravitational interactions with
the Standard Model particles and remain hidden. We study a type of hidden dark
matter model in which the dark matter is completely decoupled from the Standard
Model sector except gravitationally, and consists of a single species with a
conserved comoving particle number. This category of hidden dark matter
includes models that act as warm dark matter but is more general. In
particular, in addition to having an independent temperature from the Standard
Model sector, it includes cases in which dark matter is in its own thermal
equilibrium or is free-streaming, obeys fermionic or bosonic statistics, and
processes a chemical potential that controls the particle occupation number.
While the usual parameterization using the free-streaming scale or the particle
mass no longer applies, we show that all cases can be well approximated by a
set of functions parameterized by only one parameter as long as the chemical
potential is nonpositive: the characteristic scale factor at the time of the
relativistic-to-nonrelativistic transition. We study the constraints from Big
Bang Nucleosynthesis, the cosmic microwave background, the Lyman-$\alpha$
forest, and the smallest halo mass. We show that the most significant
phenomenological impact is the suppression of the small-scale matter power
spectrum -- a typical feature when the dark matter has a velocity dispersion or
pressure at early times. So far, small dark matter halos provide the strongest
constraint, limiting the transition scale factor to be no larger than
$\sim1.4\times10^{-4}$ times the scale factor at matter-radiation equality. | astro-ph_CO |
End of preview. Expand
in Dataset Viewer.
README.md exists but content is empty.
- Downloads last month
- 29
Size of downloaded dataset files:
22.3 MB
Size of the auto-converted Parquet files:
11.6 MB
Number of rows:
19,000