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Cosmic slowing down of acceleration for several dark energy
parametrizations: We further investigate slowing down of acceleration of the universe scenario
for five parametrizations of the equation of state of dark energy using four
sets of supernovae data. In a maximal probability analysis we also use the
baryon acoustic oscillation and cosmic microwave background observations. We
found the low redshift transition of the deceleration parameter appears,
independently of the parametrization, using supernovae data alone except for
the Union 2.1 sample. This feature disappears once we combine the supernova
data with high redshift data. We conclude that the rapid variation of the
deceleration parameter is independent of the parametrization. We also found
more evidence for a tension among the supernovae samples, as well as for the
low and high redshift data. | astro-ph_CO |
How large is the contribution of cosmic web to $Ω_Λ$ ? A
preliminary study on a novel inhomogenous model: The distribution of matter in the universe shows a complex pattern, formed by
cluster of galaxies, voids and filaments denoted as cosmic web. Different
approaches have been proposed to model such structure in the framework of the
general relativity. Recently, one of us has proposed a generalization
($\Lambda$FB model) of the Fractal Bubble model, proposed by Wiltshire, which
accounts for such large scale structure. The $\Lambda$FB model is an evolution
of FB model and includes in a consistent way a description of inhomogeneous
matter distribution and a $\Lambda$ term. Here we analyze the $\Lambda$FB model
focusing on the relation between cosmological parameters. The main result is
the consistency of $\Lambda$CDM model values for $\Omega_{\Lambda0}$ ($\approx
0.7$) and $\Omega_{k0}$ ($|\Omega_{k0}|<\approx 0.01$) with a large fraction of
voids. This allows to quantify to which extent the inhomogeneous structure
could account for $\Lambda$ constant consistently with standard values of the
other cosmological parameters. | astro-ph_CO |
The Reionization of Carbon: Observations suggest that CII was more abundant than CIV in the intergalactic
medium towards the end of the hydrogen reionization epoch. This transition
provides a unique opportunity to study the enrichment history of intergalactic
gas and the growth of the ionizing background (UVB) at early times. We study
how carbon absorption evolves from z=10-5 using a cosmological hydrodynamic
simulation that includes a self-consistent multifrequency UVB as well as a
well-constrained model for galactic outflows to disperse metals. Our predicted
UVB is within 2-4 times that of Haardt & Madau (2012), which is fair agreement
given the uncertainties. Nonetheless, we use a calibration in post-processing
to account for Lyman-alpha forest measurements while preserving the predicted
spectral slope and inhomogeneity. The UVB fluctuates spatially in such a way
that it always exceeds the volume average in regions where metals are found.
This implies both that a spatially-uniform UVB is a poor approximation and that
metal absorption is not sensitive to the epoch when HII regions overlap
globally even at column densites of 10^{12} cm^{-2}. We find, consistent with
observations, that the CII mass fraction drops to low redshift while CIV rises
owing the combined effects of a growing UVB and continued addition of carbon in
low-density regions. This is mimicked in absorption statistics, which broadly
agree with observations at z=6-3 while predicting that the absorber column
density distributions rise steeply to the lowest observable columns. Our model
reproduces the large observed scatter in the number of low-ionization absorbers
per sightline, implying that the scatter does not indicate a partially-neutral
Universe at z=6. | astro-ph_CO |
Needlet thresholding methods in component separation: Foreground components in the Cosmic Microwave Background (CMB) are sparse in
a needlet representation, due to their specific morphological features
(anisotropy, non-Gaussianity). This leads to the possibility of applying
needlet thresholding procedures as a component separation tool. In this work,
we develop algorithms based on different needlet-thresholding schemes and use
them as extensions of existing, well-known component separation techniques,
namely ILC and template-fitting. We test soft- and hard-thresholding schemes,
using different procedures to set the optimal threshold level. We find that
thresholding can be useful as a denoising tool for internal templates in
experiments with few frequency channels, in conditions of low signal-to-noise.
We also compare our method with other denoising techniques, showing that
thresholding achieves the best performance in terms of reconstruction accuracy
and data compression while preserving the map resolution. The best results in
our tests are in particular obtained when considering template-fitting in an
LSPE like experiment, especially for B-mode spectra. | astro-ph_CO |
Extended Fast Action Minimisation method: application to SDSS-DR12
Combined Sample: We present the first application of the extended Fast Action Minimization
method (eFAM) to a real dataset, the SDSS-DR12 Combined Sample, to reconstruct
galaxies orbits back-in-time, their two-point correlation function (2PCF) in
real-space, and enhance the baryon acoustic oscillation (BAO) peak. For this
purpose, we introduce a new implementation of eFAM that accounts for selection
effects, survey footprint, and galaxy bias. We use the reconstructed BAO peak
to measure the angular diameter distance, D_A(z)r^{fid}_s/r_s, and the Hubble
parameter, H(z)r_s/r^{fid}_s, normalized to the sound horizon scale for a
fiducial cosmology r^{fid}_s, at the mean redshift of the sample z=0.38,
obtaining D_A(z=0.38)r^{fid}_s/r_s=1090 +/- 29 (Mpc)^{-1}, and
H(z=0.38)r_s}/r^{fid}_s=83 +/- 3 (km s^{-1}Mpc^{-1}), in agreement with
previous measurements on the same dataset. The validation tests, performed
using 400 publicly available SDSS-DR12 mock catalogues, reveal that eFAM
performs well in reconstructing the 2PCF down to separations of 25h^{-1}Mpc$,
i.e. well into the non-linear regime. Besides, eFAM successfully removes the
anisotropies due to redshift-space distortion at all redshifts including that
of the survey, allowing us to decrease the number of free parameters in the
model and fit the full-shape of the back-in-time reconstructed 2PCF well beyond
the BAO peak. Recovering the real-space 2PCF, eFAM improves the precision on
the estimates of the fitting parameters. When compared with the
no-reconstruction case, eFAM reduces the uncertainty of the Alcock-Paczynski
distortion parameters of about 40% and that on the non-linear damping scale of
about 70%. These results show that eFAM can be successfully applied to existing
redshift galaxy catalogues and should be considered as a reconstruction tool
for next-generation surveys alternative to popular methods based on the
Zel'dovich approximation. | astro-ph_CO |
Suppressing hot gas accretion to supermassive black holes by stellar
winds: We argue that one of the basic assumptions of the Bondi accretion process,
that the accreting object has zero pressure, might not hold in many galaxies
because of the pressure exerted by stellar winds of star orbiting the central
super massive black hole (SMBH). Hence, the Bondi accretion cannot be used in
these cases, such as in the galaxy NGC 3115. The winds of these high-velocity
stars are shocked to temperatures above the virial temperature of the galaxy,
leading to the formation of a hot bubble of size ~0.1-10 pc near the center.
This hot bubble can substantially reduce the mass accretion rate by the SMBH.
If the density of the hot bubble is lower than that of the interstellar medium
(ISM), a density-inversion layer is formed. As the gas loses energy by X-ray
radiation, eventually more mass of the cooling shocked stellar winds will be
accreted to the SMBH. This accretion will be of cold clumps. After a period of
millions of years of low AGN activity, therefore, a stronger AGN activity will
occur that will heat and expel gas, much as in cooling flow clusters. Adding to
other problems of the Bondi process, our results render the Bondi accretion
irrelevant for AGN feedback in cooling flow in galaxies and small groups of
galaxies and during galaxy formation. | astro-ph_CO |
Constraining thawing and freezing models with cluster number counts: Measurements of the cluster abundance as a function of mass and redshift
provide an important cosmological test that probe not only the expansion rate
but also the growth of perturbations. In this paper we adopt a scalar field
scenario which admits both thawing and freezing solutions from an appropriate
choice of the model parameters and derived all relevant expressions to
calculate the mass function and the cluster number density. We discuss the
ability of cluster observations to distinguish between these scalar field
behaviors and the standard $\Lambda$CDM scenario by considering the eROSITA and
SPT cluster surveys. | astro-ph_CO |
A new stochastic approach to cumulative weak lensing: We study the weak gravitational lensing effects caused by a stochastic
distribution of dark matter halos. We develop a simple approach to calculate
the magnification probability distribution function which allows us to easily
compute the magnitude bias and dispersion for an arbitrary data sample and a
given universe model. As an application we consider the effects of single-mass
large-scale cosmic inhomogeneities to the SNe magnitude-redshift relation, and
conclude that such structures could bias the PDF enough to affect the
extraction of cosmological parameters from the limited size of present-day SNe
data samples. We also release turboGL, a simple and very fast (<= 1s)
Mathematica code based on the method here presented. | astro-ph_CO |
Observations favor the redshift-evolutionary $L_X$-$L_{UV}$ relation of
quasars from copula: We compare, with data from the quasars, the Hubble parameter measurements,
and the Pantheon+ type Ia supernova, three different relations between X-ray
luminosity ($L_X$) and ultraviolet luminosity ($L_{UV}$) of quasars. These
three relations consist of the standard and two redshift-evolutionary
$L_X$-$L_{UV}$ relations which are constructed respectively by considering a
redshift dependent correction to the luminosities of quasars and using the
statistical tool called copula. By employing the PAge approximation for a
cosmological-model-independent description of the cosmic background evolution
and dividing the quasar data into the low-redshift and high-redshift parts, we
find that the constraints on the PAge parameters from the low-redshift and
high-redshift data, which are obtained with the redshift-evolutionary
relations, are consistent with each other, while they are not when the standard
relation is considered. If the data are used to constrain the coefficients of
the relations and the PAge parameters simultaneously, then the observations
support the redshift-evolutionary relations at more than $3\sigma$. The Akaike
and Bayes information criteria indicate that there is strong evidence against
the standard relation and mild evidence against the redshift-evolutionary
relation constructed by considering a redshift dependent correction to the
luminosities of quasars. This suggests that the redshift-evolutionary
$L_X$-$L_{UV}$ relation of quasars constructed from copula is favored by the
observations. | astro-ph_CO |
Understanding WIMP-baryon interactions with direct detection: A Roadmap: We study prospects of dark-matter direct-detection searches for probing
non-relativistic effective theory for WIMP-baryon scattering. We simulate a
large set of noisy recoil-energy spectra for different scattering scenarios
(beyond the standard momentum-independent contact interaction), for Generation
2 and futuristic experiments. We analyze these simulations and quantify the
probability of successfully identifying the operator governing the scattering,
if a WIMP signal is observed. We find that the success rate depends on a
combination of factors: the WIMP mass, the mediator mass, the type of
interaction, and the experimental energy window. For example, for a 20 GeV
WIMP, Generation 2 is only likely to identify the right operator if the
interaction is Coulomb-like, and is unlikely to do so in any other case. For a
WIMP with a mass of 200 GeV or higher, success is almost guaranteed. We also
find that, regardless of the scattering model and the WIMP parameters, a single
Generation 2 experiment is unlikely to successfully discern the momentum
dependence of the underlying operator on its own, but prospects improve
drastically when experiments with different target materials and energy windows
are analyzed jointly. Furthermore, we examine the quality of parameter
estimation and degeneracies in the multi-dimensional parameter space of the
effective theory. We find in particular that the resulting WIMP mass estimates
can be severely biased if data are analyzed assuming the standard
(momentum-independent) operator while the actual operator has
momentum-dependence. Finally, we evaluate the ultimate reach of direct
detection, finding that the prospects for successful operator selection prior
to reaching the irreducible backgrounds are excellent, if the signal is just
below the current limits, but slim if Generation 2 does not report WIMP
detection. | astro-ph_CO |
Dwarf spheroidals in the M81 Group - Metallicity distribution functions
and population gradients: We study the dwarf spheroidal galaxies in the nearby M81 group in order to
construct their photometric metallicity distributions and to investigate the
potential presence of population gradients. We select all the dwarf spheroidals
with available Hubble Space Telescope / Advanced Camera for Surveys archival
observations, nine in total. We interpolate isochrones so as to assign a
photometric metallicity to each star within a selection box in the
color-magnitude diagram of each dwarf galaxy. We assume that the dwarf
spheroidals contain mainly an old stellar population. In order to search for
metallicity gradients, we examine the spatial distribution of two stellar
populations that we separate according to their metallicities. As a result, we
present the photometric metallicity distribution functions, the cumulative
histograms and smoothed density maps of the metal-poor and metal-rich stars as
well as of the intermediate-age stars. From our photometric data we find that
all the dwarf spheroidals show a wide range in metallicities, with mean values
that are typical for old and metal-poor systems, with the exception of one
dwarf spheroidal, namely IKN. Some of our dwarf spheroidals exhibit
characteristics of transition-type dwarfs. Compared to the Local Group
transition type dwarfs, the M81 group ones appear to have mean metallicity
values slightly more metal-rich at a given luminosity. All the dwarf
spheroidals considered here appear to exhibit either population gradients or
spatial variations in the centroids of their metal-poor and metal-rich
population. In addition, there are luminous AGB stars detected in all of them
with spatial distributions suggesting that they are well mixed with the old
stars. | astro-ph_CO |
Latest data constraint of some parameterized dark energy models: Using various latest cosmological datasets including Type-Ia supernovae,
cosmic microwave background radiation, baryon acoustic oscillations, and
estimations of the Hubble parameter, we test some dark energy models with
parameterized equations of state and try to distinguish or select
observation-preferred models. We obtain the best fitting results of the six
models and calculate their values of the Akaike Information Criteria and Bayes
Information Criterion. And we can distinguish these dark energy models from
each other by using these two information criterions. However, the $\Lambda
$CDM model remains the best fit model. Furthermore, we perform geometric
diagnostics including statefinder and Om diagnostics to understand the
geometric behaviour of the dark energy models. We find that the six DE models
can be distinguished from each other and from $\Lambda$CDM, Chaplygin gas,
quintessence models after the statefinder and Om diagnostics were performed.
Finally, we consider the growth factor of the dark energy models with
comparison to $\Lambda $CDM model. Still, we find the models can be
distinguished from each other and from $\Lambda $CDM model through the growth
factor approximation. | astro-ph_CO |
Deep radio observations of the radio halo of the bullet cluster 1E
0657-55.8: We present deep 1.1-3.1 GHz Australia Telescope Compact Array observations of
the radio halo of the bullet cluster, 1E 0657-55.8. In comparison to existing
images of this radio halo the detection in our images is at higher
significance. The radio halo is as extended as the X-ray emission in the
direction of cluster merger but is significantly less extended than the X-ray
emission in the perpendicular direction. At low significance we detect a faint
second peak in the radio halo close to the X-ray centroid of the smaller
sub-cluster (the bullet) suggesting that, similarly to the X-ray emission, the
radio halo may consist of two components. Finally, we find that the distinctive
shape of the western edge of the radio halo traces out the X-ray detected bow
shock. The radio halo morphology and the lack of strong point-to-point
correlations between radio, X-ray and weak-lensing properties suggests that the
radio halo is still being formed. The colocation of the X-ray shock with a
distinctive radio brightness edge illustrates that the shock is influencing the
structure of the radio halo. These observations support the theory that shocks
and turbulence influence the formation and evolution of radio halo synchrotron
emission. | astro-ph_CO |
Kernel Selection for Gaussian Process in Cosmology: with Approximate
Bayesian Computation Rejection and Nested Sampling: Gaussian Process (GP) has gained much attention in cosmology due to its
ability to reconstruct cosmological data in a model-independent manner. In this
study, we compare two methods for GP kernel selection: Approximate Bayesian
Computation (ABC) Rejection and nested sampling. We analyze three types of
data: cosmic Chronometer data (CC), Type Ia Supernovae (SNIa), and Gamma Ray
Burst (GRB), using five kernel functions. To evaluate the differences between
kernel functions, we assess the strength of evidence using Bayes factors. Our
results show that, for ABC Rejection, the Mat\'ern kernel with $\nu$=5/2 (M52
kernel) outperformes the commonly used Radial Basis Function (RBF) kernel in
approximating all three datasets. Bayes factors indicate that the M52 kernel
typically supports the observed data better than the RBF kernel, but with no
clear advantage over other alternatives. However, nested sampling gives
different results, with the M52 kernel losing its advantage. Nevertheless,
Bayes factors indicate no significant dependence of the data on each kernel. | astro-ph_CO |
Assessing the viability of successful reconstruction of the dynamics of
dark energy using varying fundamental couplings: We assess the viability of successful reconstruction of the evolution of the
dark energy equation of state using varying fundamental couplings, such as the
fine structure constant or the proton-to-electron mass ratio. We show that the
same evolution of the dark energy equation of state parameter with cosmic time
may be associated with arbitrary variations of the fundamental couplings.
Various examples of models with the same (different) background evolution and
different (the same) time variation of fundamental couplings are studied in the
letter. Although we demonstrate that, for a broad family of models, it is
possible to redefine the scalar field in such a way that its dynamics is that
of a standard quintessence scalar field, in general such redefinition leads to
the breakdown of the linear relation between the scalar field and the variation
of fundamental couplings. This implies that the assumption of a linear coupling
is not sufficient to guarantee a successful reconstruction of the dark energy
dynamics and consequently additional model dependent assumptions about the
scalar field responsible for the dark energy need to be made. | astro-ph_CO |
The Doppler effect on indirect detection of dark matter using dark
matter only simulations: Indirect detection of dark matter is a major avenue for discovery. However,
baryonic backgrounds are diverse enough to mimic many possible signatures of
dark matter. In this work, we study the newly proposed technique of dark matter
velocity spectroscopy\,\cite{speckhard2016}. The non-rotating dark matter halo
and the Solar motion produce a distinct longitudinal dependence of the signal
which is opposite in direction to that produced by baryons. Using collisionless
dark matter only simulations of Milky Way like halos, we show that this new
signature is robust and holds great promise. We develop mock observations by
high energy resolution X-ray spectrometer on a sounding rocket, the Micro-X
experiment, to our test case, the 3.5 keV line. We show that by using six
different pointings, Micro-X can exclude a constant line energy over various
longitudes at $\geq$ 3$\sigma$. The halo triaxiality is an important effect and
it will typically reduce the significance of this signal. We emphasize that
this new {\it smoking gun in motion} signature of dark matter is general, and
is applicable to any dark matter candidate which produces a sharp photon
feature in annihilation or decay. | astro-ph_CO |
Constraints on the End of Reionization from the Density Fields
Surrounding Two Highly Opaque Quasar Sightlines: The observed large-scale scatter in Lyman $\alpha$ opacity of the
intergalactic medium at $z<6$ implies large fluctuations in the neutral
hydrogen fraction that are unexpected long after reionization has ended. A
number of models have emerged to explain these fluctuations that make testable
predictions for the relationship between Ly$\alpha$ opacity and density. We
present selections of $z=5.7$ Ly$\alpha$-emitting galaxies (LAEs) in the fields
surrounding two highly opaque quasar sightlines with long Ly$\alpha$ troughs.
The fields lie towards the $z=6.0$ quasar ULAS J0148+0600, for which we
re-analyze previously published results using improved photometric selection,
and towards the $z=6.15$ quasar SDSS J1250+3130, for which results are
presented here for the first time. In both fields, we report a deficit of LAEs
within 20 $h^{-1}$ Mpc of the quasar. The association of highly opaque
sightlines with galaxy underdensities in these two fields is consistent with
models in which the scatter in Ly$\alpha$ opacity is driven by large-scale
fluctuations in the ionizing UV background, or by an ultra-late reionization
that has not yet concluded at $z=5.7$. | astro-ph_CO |
Enhanced curvature perturbations from spherical domain walls nucleated
during inflation: We investigate spherical domain walls~(DWs) nucleated via quantum tunneling
in multifield inflationary models and curvature perturbations induced by the
inhomogeneous distribution of those DWs. We consider the case that the
Euclidean action $S_{E}$ of DWs changes with time during inflation so that most
of DWs nucleate when $S_{E}$ reaches the minimum value and the radii of DWs are
almost the same. When the Hubble horizon scale exceeds the DW radius after
inflation, DWs begin to annihilate and release their energy into background
radiation. Because of the random nature of the nucleation process, the
statistics of DWs is of the Poisson type and the power spectrum of curvature
perturbations has a characteristic slope ${\cal P}_{\cal R}(k)\propto k^{3}$.
The amplitude of ${\cal P}_{\cal R}(k)$ depends on the tension and abundance of
DWs at the annihilation time while the peak mode depends on the mean separation
of DWs. We also numerically obtain the energy spectra of scalar-induced
gravitational waves from predicted curvature perturbations which are expected
to be observed in multiband gravitational-wave detectors. | astro-ph_CO |
The Quijote simulations: The Quijote simulations are a set of 44,100 full N-body simulations spanning
more than 7,000 cosmological models in the $\{\Omega_{\rm m}, \Omega_{\rm b},
h, n_s, \sigma_8, M_\nu, w \}$ hyperplane. At a single redshift the simulations
contain more than 8.5 trillions of particles over a combined volume of 44,100
$(h^{-1}{\rm Gpc})^3$; each simulation follow the evolution of $256^3$, $512^3$
or $1024^3$ particles in a box of $1~h^{-1}{\rm Gpc}$ length. Billions of dark
matter halos and cosmic voids have been identified in the simulations, whose
runs required more than 35 million core hours. The Quijote simulations have
been designed for two main purposes: 1) to quantify the information content on
cosmological observables, and 2) to provide enough data to train machine
learning algorithms. In this paper we describe the simulations and show a few
of their applications. We also release the Petabyte of data generated,
comprising hundreds of thousands of simulation snapshots at multiple redshifts,
halo and void catalogs, together with millions of summary statistics such as
power spectra, bispectra, correlation functions, marked power spectra, and
estimated probability density functions. | astro-ph_CO |
Scale-dependent CMB power asymmetry from primordial speed of sound and a
generalized $δ$N formalism: We explore a plausible mechanism that the hemispherical power asymmetry in
the CMB is produced by the spatial variation of the primordial sound speed
parameter. We suggest that in a generalized approach of the $\delta N$
formalism the local e-folding number may depend on some other primordial
parameters besides the initial values of inflaton. Here the $\delta N$
formalism is extended by considering the effects of a spatially varying sound
speed parameter caused by a super-Hubble perturbation of a light field. Using
this generalized $\delta N$ formalism, we systematically calculate the
asymmetric primordial spectrum in the model of multi-speed inflation by taking
into account the constraints of primordial non-Gaussianities. We further
discuss specific model constraints, and the corresponding asymmetry amplitudes
are found to be scale-dependent, which can accommodate current observations of
the power asymmetry at different length scales. | astro-ph_CO |
Retrieving the three-dimensional matter power spectrum and galaxy
biasing parameters from lensing tomography: With the availability of galaxy distance indicators in weak lensing surveys,
lensing tomography can be harnessed to constrain the three-dimensional (3D)
matter power spectrum over a range of redshift and physical scale. By combining
galaxy-galaxy lensing and galaxy clustering, this can be extended to probe the
3D galaxy-matter and galaxy-galaxy power spectrum or, alternatively, galaxy
biasing parameters. To achieve this aim, this paper introduces and discusses
minimum variance estimators and a more general Bayesian approach to
statistically invert a set of noisy tomography 2-point correlation functions,
measured within a confined opening angle. Both methods are constructed such
that they probe deviations of the power spectrum from a fiducial power
spectrum, thereby enabling both a direct comparison of theory and data, and in
principle the identification of the physical scale and redshift of deviations.
By devising a new Monte Carlo technique, we quantify the measurement noise in
the correlators for a fiducial survey, and test the performance of the
inversion techniques. We conclude that a shear tomography analysis of near
future weak lensing surveys promises fruitful insights into the effect of
baryons on the nonlinear matter power spectrum at z<~0.3 around k~2 h/Mpc, and
into galaxy biasing (z<~0.5). However, a proper treatment of anticipated
systematics -- not included in the mock analysis but discussed here -- is
likely to reduce the signal-to-noise in the analysis so that a robust
assessment of the 3D matter power spectrum probably asks for a survey area of
at least 1000 sdeg. [Abridged] | astro-ph_CO |
The integrated angular bispectrum: We study the position-dependent power spectrum and the integrated bispectrum
statistic for 2D cosmological fields on the sphere (integrated angular
bispectrum). First, we derive a useful, $m$-independent, formula for the
full-sky integrated angular bispectrum, based on the construction of
azimuthally symmetric patches. We then implement a pipeline for integrated
angular bispectrum estimation, including a mean-field correction to account for
spurious isotropy-breaking effects in realistic conditions (e.g., inhomogenous
noise, sky masking). Finally, we show examples of applications of this
estimator to CMB analysis, both using simulations and actual Planck data. Such
examples include $f_\mathrm{NL}$ estimation, analyses of non-Gaussianity from
secondary anisotropies (ISW-lensing and ISW-tSZ-tSZ bispectra) and studies of
non-Gaussian signatures from foreground contamination. | astro-ph_CO |
A Halo Model of Local IRAS Galaxies Selected at 60 Micron Using
Conditional Luminosity Functions: Using conditional luminosity functions (CLFs) which encode the luminosity
distribution of galaxies as a function of halo mass, we construct a halo model
of IRAS galaxies selected at 60 micron. An abundance matching technique is used
to link galaxy luminosity to the host halo mass. The shape of the mass - light
relation at 60 micron is different from those derived at r-, K- and B-band.
This is because the 60 micron LF can not be fitted by a Schechter function with
a sharp exponential cutoff. We then seek the parameters in the CLFs that best
fit the LF and power spectrum. We find that the predicted galaxy bias as a
function of L60 from the best-fit model agrees well with the clustering
measurements. At the faint end of the LF where quiescent star-forming galaxies
dominate, most IRAS galaxies are central galaxies in halos of M >~ 10^{10}
h^{-1} M_sun but a non-negligible fraction are satellites typically hosted in
more massive halos. The majority of IRAS galaxies with L60 >~ 10^{10} h^{-2}
L_sun are M82 type starbursts which are central galaxies hosted in halos of M
>~ 10^{12.5} h^{-1} M_sun. In comparison, optical galaxies generally reside in
much more massive halos. The rate of change in L60 (an indicator of recent star
formation) as a function of halo mass at M >~ 10^{12.5} h^{-1} M_sun is much
larger that d L_optical / dM or d L_NIR / dM indicating the existence of
physical mechanisms which are very efficient in converting cold gas into stars,
possibly dynamical effects arising from interactions or mergers. We further
calculate the space density of major mergers for halos massive enough to host
ultraluminous infrared galaxies (ULIRGs) using the mean merger rate derived
from the Millennium simulations. Compared to the space density of local ULIRGs,
it implies that either the majority of major mergers at z~0 do not lead to
ULIRGs or the ULIRG phase is relatively short. | astro-ph_CO |
A Full Treatment of Peculiar Velocities on the Reionization Light Cone: Accurate simulations of the 21-cm signal from the Epoch of Reionization
require the generation of maps at specific frequencies given the values of
astrophysical and cosmological parameters. The peculiar velocities of the
hydrogen atoms producing the 21-cm radiation result in a shift in the observed
frequency of the 21-cm radiation and changes the amplitude of the signal
itself. This is not an effect we can remove but instead needs to be accurately
modelled to ensure we infer the correct physical parameters from an
observation. We describe the full calculation of the distortion of the 21-cm
signal, and propose a new code that integrates the 21-cm intensity along the
line of sight for each individual light cone pixel to fully capture the
intensity contributions from multiple redshifts. This algorithm naturally deals
with the typical divergences found in standard approaches, allowing for large
optical depths and 21-cm absorption events at high redshifts. We find the new
method results in up to a 60% decrease in power on the largest scales on the
sky, and an increase of over 80% on the smallest scales on the sky. We find
that the new implementation of the light cone results in a longer tail of
bright temperatures in the brightness temperature distribution, as a result of
the successful circumventing of a previous cap that had to be implemented to
avoid a divergence in the brightness temperature. We conclude that this full
treatment of the evolution of the light cone pixel can be an important effect. | astro-ph_CO |
Magnetic fields in a hot dense neutrino plasma and the Gravitational
Waves: In the present work, we have studied the spectrum of the primordial
gravitational waves due to magnetic instability in the presence of neutrino
asymmetry. The magnetic instability generates a helical magnetic field on a
large scale. The anisotropic stress generated by the magnetic field shown to be
a source of primordial gravitational waves (GWs) at the time of matter-neutrino
decoupling. We expect that the theoretically predicted GWs by this mechanism
may be detected by Square Kilometer Array (SKA) or pulsar time array (PTA)
observations. We also compare our findings with the results obtained by the
earlier work where the effect of magnetic instability was not considered. | astro-ph_CO |
Planck 2015 results. IX. Diffuse component separation: CMB maps: We present foreground-reduced CMB maps derived from the full Planck data set
in both temperature and polarization. Compared to the corresponding Planck 2013
temperature sky maps, the total data volume is larger by a factor of 3.2 for
frequencies between 30 and 70 GHz, and by 1.9 for frequencies between 100 and
857 GHz. In addition, systematic errors in the forms of
temperature-to-polarization leakage, analogue-to-digital conversion
uncertainties, and very long time constant errors have been dramatically
reduced, to the extent that the cosmological polarization signal may now be
robustly recovered on angular scales $\ell\gtrsim40$. On the very largest
scales, instrumental systematic residuals are still non-negligible compared to
the expected cosmological signal, and modes with $\ell < 20$ are accordingly
suppressed in the current polarization maps by high-pass filtering. As in 2013,
four different CMB component separation algorithms are applied to these
observations, providing a measure of stability with respect to algorithmic and
modelling choices. The resulting polarization maps have rms instrumental noise
ranging between 0.21 and 0.27$\,\mu\textrm{K}$ averaged over 55 arcmin pixels,
and between 4.5 and 6.1$\,\mu\textrm{K}$ averaged over 3.4 arcmin pixels. The
cosmological parameters derived from the analysis of temperature power spectra
are in agreement at the $1\sigma$ level with the Planck 2015 likelihood.
Unresolved mismatches between the noise properties of the data and simulations
prevent a satisfactory description of the higher-order statistical properties
of the polarization maps. Thus, the primary applications of these polarization
maps are those that do not require massive simulations for accurate estimation
of uncertainties, for instance estimation of cross-spectra and
cross-correlations, or stacking analyses. | astro-ph_CO |
Circular Polarization of the CMB: A probe of the First stars: While it is revealed that the Cosmic Microwave Background (CMB) is linearly
polarized at 10 % level, it is predicted that there exists no significant
intrinsic source for circular polarization (CP) in the standard cosmology.
However, during the propagation through a magnetised plasma, the CP of the CMB
could be produced via the Faraday conversion (FC). The FC converts a
pre-existing linear polarization into CP in presence of a magnetic field with
relativistic electrons. In this paper, we focus on the FC due to supernova
remnants of the first stars, also called Pop III stars. We derive an analytic
form for the angular power spectrum of the CP of the CMB generated by the
general FC. We apply this result to the case of the FC triggered by explosions
of the first stars and evaluate the angular power spectrum, CV V . We show that
the amplitude of l(l + 1)C_l^V V /(2pi) > 10^-2 micro Kelvin squared for l >
100, with only one Pop III star per halo, the age of Pop III SN remnants as 104
years and frequency of CMB observation as 1 GHz. We expect the CP of the CMB to
be a very promising probe of the yet unobserved first stars, primarily due to
the expected high signal along with an unique frequency dependence. | astro-ph_CO |
Cosmological dependence of the measurements of luminosity function,
projected clustering and galaxy-galaxy lensing signal: Observables such as the luminosity function of galaxies, \Phi(M), the
projected clustering of galaxies, w_p(r_p), and the galaxy-galaxy lensing
signal, \Delta\Sigma, are often measured from galaxy redshift surveys assuming
a fiducial cosmological model for calculating distances to and between
galaxies. There is a growing number of studies that perform joint analyses of
these measurements and constrain cosmological parameters. We quantify the
amount by which such measurements systematically vary as the fiducial cosmology
used for the measurements is changed, and show that these effects can be
significant at high redshifts (z~0.5). We present a simple way that maps the
measurements made using a particular fiducial cosmological model to any other
cosmological model. Cosmological constraints (or halo occupation distribution
constraints) that use the luminosity function, clustering measurements and
galaxy-galaxy lensing signal but ignore these systematic effects may
underestimate the confidence intervals on the inferred parameters. | astro-ph_CO |
Rapid onset of the 21-cm signal suggests a preferred mass range for dark
matter particle: We are approaching a new era to probe the 21-cm neutral hydrogen signal from
the period of cosmic dawn. This signal offers a unique window to the virgin
Universe, e.g., to study dark matter models with different small-scale
behaviours. The EDGES collaboration has recently published the first results of
the global 21-cm spectrum. We demonstrate that such a signal can be used to
set, unlike most observations concerning dark matter, both lower and upper
limits for the mass of dark matter particles. We study the 21-cm signal
resulting from a simple warm dark matter model with a sharp-$k$ window function
calibrated for high redshifts. We tie the PopIII star formation to Lyman-alpha
and radio background production. Using MCMC to sample the parameter space we
find that to match the EDGES signal, a warm dark matter particle must have a
mass of $7.3^{+1.6}_{-3.3}$ keV at 68\% confidence interval. This translates to
$2.2^{+1.4}_{-1.7} \times 10^{-20}$ eV for fuzzy dark matter and
$63^{+19}_{-35}$ keV for Dodelson-Widrow sterile neutrinos. Cold dark matter is
unable to reproduce the signal due to its slow structure growth. | astro-ph_CO |
Observational constraints on the unified dark matter and dark energy
model based on the quark bag model: In this work we investigate if a small fraction of quarks and gluons, which
escaped hadronization and survived as a uniformly spread perfect fluid, can
play the role of both dark matter and dark energy. This fluid, as developed in
\citep{Brilenkov}, is characterized by two main parameters: $\beta$, related to
the amount of quarks and gluons which act as dark matter; and $\gamma$, acting
as the cosmological constant. We explore the feasibility of this model at
cosmological scales using data from type Ia Supernovae (SNeIa), Long Gamma-Ray
Bursts (LGRB) and direct observational Hubble data. We find that: (i) in
general, $\beta$ cannot be constrained by SNeIa data nor by LGRB or H(z) data;
(ii) $\gamma$ can be constrained quite well by all three data sets,
contributing with $\approx78\%$ to the energy-matter content; (iii) when a
strong prior on (only) baryonic matter is assumed, the two parameters of the
model are constrained successfully. | astro-ph_CO |
A candidate tidal disruption event in the Galaxy cluster Abell 3571: Tidal disruption events are possible sources of temporary nuclear activity in
galactic nuclei and can be considered as good indicators of the existence of
super massive black holes in the centers of galaxies. A new X-ray source has
been serendipitously detected with ROSAT in a PSPC pointed observation of the
galaxy cluster A3571. Given the strong flux decay of the object in subsequent
detections, the tidal disruption scenario is investigated as possible
explanationof the event. We followed up the evolution of the X-ray transient
with ROSAT, XMM-Newton and Chandra for a total period of ~13 years. We also
obtained 7-band optical/NIR photometry with GROND at the ESO/MPI 2.2m
telescope. We report a very large decay of the X-ray flux of ROSAT source
identified with the galaxy LEDA 095953 a member of the cluster Abell 3571. We
measured a maximum 0.3-2.4 keV luminosity Log(L_X)=42.8 erg s^-1. The high
state of the source lasted at least 150 ks, afterwards L_X declined as ~t^-2.
The spectrum of the brightest epoch is consistent with a black body with
temperature kT ~0.12 keV. The total energy released by this event in 10 yr was
estimated to be Delta_E>2x10^50 erg. We interpret this event as a tidal
disruption of a solar type star by the central supermassive black hole (i.e.
~10^7 M_sun) of the galaxy. | astro-ph_CO |
Reionization of the Intergalactic Medium: After recombination the cosmic gas was left in a cold and neutral state.
However, as the first stars and black holes formed within early galactic
systems, their UV and X-ray radiation induced a gradual phase transition of the
intergalactic gas into the warm and ionized state we currently observe. This
process is known as cosmic reionization. Understanding how the energy
deposition connected with galaxy and star formation shaped the properties of
the intergalactic gas is one of the primary goals of present-day cosmology. In
addition, reionization back reacts on galaxy evolution, determining many of the
properties of the high-redshift galaxy population that represent the current
frontier of our discovery of the cosmos. In these two Lectures we provide a
pedagogical overview of cosmic reionization and intergalactic medium and of
some of the open questions in these fields. | astro-ph_CO |
Phase-space structure of protohalos: Vlasov versus Particle-Mesh: The phase-space structure of primordial dark matter halos is revisited using
cosmological simulations with three sine waves and Cold Dark Matter (CDM)
initial conditions. The simulations are performed with the tessellation based
Vlasov solver ColDICE and a Particle-Mesh (PM) $N$-body code. The analyses
include projected density, phase-space diagrams, radial density and
pseudo-phase space density. Particular attention is paid to force and mass
resolution. Because the phase-space sheet complexity, estimated in terms of
total volume and simplices count, increases very quickly, ColDICE can follow
only the early violent relaxation phase of halo formation. During the latter,
agreement between ColDICE and PM simulations having one particle per cell or
more is excellent and halos have a power-law density profile, $\rho(r) \propto
r^{-\alpha}$, $\alpha \in [1.5,1.8]$. This slope, measured prior to any merger,
is slightly larger than in the literature. The phase-space diagrams evidence
complex but coherent patterns with clear signatures of self-similarity in the
sine wave simulations, while the CDM halos are somewhat scribbly. After
additional mass resolution tests, the PM simulations are used to follow the
next stages of evolution. The power-law progressively breaks down with a
convergence of the density profile to the well known "NFW"-like universal
attractor, irrespectively of initial conditions, that is even in the three-sine
wave simulations. This demonstrates again that mergers do not represent a
necessary condition for convergence to the dynamical attractor. Not
surprisingly, the measured pseudo phase-space density is a power-law $Q(r)
\propto r^{-\alpha_Q}$, with $\alpha_{\rm Q}$ close to the prediction of
secondary spherical infall model, $\alpha_{\rm Q} \simeq 1.875$. However this
property is also verified during the early relaxation phase, which is non
trivial. | astro-ph_CO |
Addressing the Hubble tension in Yukawa cosmology?: In Yukawa cosmology, a recent discovery revealed a relationship between
baryonic matter and the dark sector. The relation is described by the parameter
$\alpha$ and the long-range interaction parameter $\lambda$ - an intrinsic
property of the graviton. Applying the uncertainty relation to the graviton
raises a compelling question: Is there a quantum mechanical limit to the
measurement precision of the Hubble constant ($H_0$)? We argue that the
uncertainty relation for the graviton wavelength $\lambda$ can be used to
explain a running of $H_0$ with redshift. We show that the uncertainty in time
has an inverse correlation with the value of the Hubble constant. That means
that the measurement of the Hubble constant is intrinsically linked to length
scales (redshift) and is connected to the uncertainty in time. On cosmological
scales, we found that the uncertainty in time is related to the look-back time
quantity. For measurements with a high redshift value, there is more
uncertainty in time, which leads to a smaller value for the Hubble constant.
Conversely, there is less uncertainty in time for local measurements with a
smaller redshift value, resulting in a higher value for the Hubble constant.
Therefore, due to the uncertainty relation, the Hubble tension is believed to
arise from fundamental limitations inherent in cosmological measurements.
Finally, our findings indicate that the mass of the graviton fluctuates with
specific scales, suggesting a possible mass-varying mechanism for the graviton. | astro-ph_CO |
Probing the evolution of galaxy clusters with the SZ Effect: In galaxy clusters the thermal Sunyaev-Zel'dovich (SZ) effect from the hot
intracluster medium (ICM) provides a direct, self-contained measure of the
pressure integrated over crossing lines of sight, that is intrinsically
independent of redshift and well suited for evolutionary studies. We show in
detail how the size of the effect and its pattern on the sky plane are directly
related to the entropy levels in the ICM, and how they characterize the cluster
cores and outskirts independently. We find that at redshifts z<0.3 the signals
to be expected in the cores considerably exceed those detected at 10'
resolution with the Planck satellite. We propose that at 1' resolutions as
implemented on recent ground instrumentation for mapping features in individual
clusters, the average patterns of the SZ signals can provide a direct and
effective way to find and count cool, low-entropy cores and hot, high-entropy
outskirts out to z~2. Such counts will tell the timing and the mode of the
processes that drive the evolution of the ICM from the distant to the local
cluster population. | astro-ph_CO |
Obtaining non-linear galaxy bias constraints from galaxy-lensing phase
differences: We demonstrate the utility and constraining power of a new statistic for
investigating galaxy bias: the galaxy-lensing phase difference. The statistic
consists in taking the differences of the phases of the harmonic wave-modes
between the weak lensing convergence field and the galaxy count field. We use
dark matter simulations populated with galaxies up to redshift $z=1$ to test
the performance of this estimator. We find that phase differences are sensitive
to the absolute value of the second order bias ($c_2=b_2/b_1$), and demonstrate
why this is the case. For a $\sim$1500 sq. deg. galaxy survey we recover $c_2$
with an error of approximately $0.1$ for a wide range of $c_2$ values; current
constraints from redshift surveys have errors of 0.1-0.6 depending on redshift.
This new statistic is therefore expected to provide constraints for $c_2$ which
are complementary and competitive with constraining power by the conventional
estimators from the power spectrum and bispectrum. For the Dark Energy Survey
(DES), we predict leading measurements of second-order bias. | astro-ph_CO |
The QSO HE0450-2958: Scantily dressed or heavily robed? A normal quasar
as part of an unusual ULIRG: (Abridged) The luminous z=0.286 quasar HE0450-2958 is interacting with a
companion galaxy at 6.5 kpc distance and the whole system is a ULIRG. A so far
undetected host galaxy triggered the hypothesis of a mostly "naked" black hole
(BH) ejected from the companion by three-body interaction. We present new
HST/NICMOS 1.6micron imaging data at 0.1" resolution and VLT/VISIR 11.3micron
images at 0.35" resolution that for the first time resolve the system in the
near- and mid-infrared. We combine these with existing optical HST and CO maps.
(i) At 1.6micron we find an extension N-E of the quasar nucleus that is
likely a part of the host galaxy, though not its main body. If true, this
places HE0450-2958 directly onto the M_BH-M_bulge-relation for nearby galaxies.
(ii) HE0450-2958 is consistent with lying at the high-luminosity end of
Narrow-Line Seyfert 1 Galaxies, and more exotic explanations like a "naked
quasar" are unlikely. (iii) All 11.3micron radiation in the system is emitted
by the quasar nucleus, which is radiating at super-Eddington rate,
L/L_Edd=6.2+3.8-1.8, or 12 M_sun/yr. (iv) The companion galaxy is covered in
optically thick dust and is not a collisional ring galaxy. It emits in the far
infrared at ULIRG strength, powered by Arp220-like star formation (strong
starburst-like). An M82-like SED is ruled out. (v) With its black hole
accretion rate HE0450-2958 produces not enough new stars to maintain its
position on the M_BH-M_bulge-relation, and star formation and black hole
accretion are spatially disjoint; the bulge has to grow by redistribution of
preexisting stars. (vi) Systems similar to HE0450-2958 with spatially disjoint
ULIRG-strength star formation and quasar activity are rare. At z<0.43 we only
find <4% (3/77) candidates for a similar configuration. | astro-ph_CO |
X-ray Point Sources and Radio Galaxies in Clusters of Galaxies: Using Chandra imaging spectroscopy and VLA L-band maps, we have identified
radio galaxies at P(1.4 GHz) >= 3x10^{23} W Hz^{-1} and X-ray point sources
(XPSs) at L(0.3-8 keV) >= 10^{42} ergs s^{-1} in 11 moderate redshift
(0.2<z<0.4) clusters of galaxies. Each cluster is uniquely chosen to have a
total mass similar to predicted progenitors of the present-day Coma Cluster.
Within a projected radius of 1 Mpc we detect 20 radio galaxies and 8 XPSs
confirmed to be cluster members above these limits. 75% of these are detected
within 500 kpc of the cluster center. This result is inconsistent with a random
selection from bright, red sequence ellipticals at the > 99.999% level. All but
one of the XPSs are hosted by luminous ellipticals which otherwise show no
other evidence for AGN activity. These objects are unlikely to be highly
obscured AGN since there is no evidence for large amounts of X-ray or optical
absorption. The most viable model for these sources are low luminosity BL Lac
Objects. The expected numbers of lower luminosity FR 1 radio galaxies and BL
Lacs in our sample converge to suggest that very deep radio and X-ray images of
rich clusters will detect AGN in a large fraction of bright elliptical galaxies
in the inner 500 kpc. Because both the radio galaxies and the XPSs possess
relativistic jets, they can inject heat into the ICM. Using the most recent
scalings of P_jet ~ L_radio^{0.5} from Birzan et al. (2008), radio sources
weaker than our luminosity limit probably contribute the majority of the heat
to the ICM. If a majority of ICM heating is due to large numbers of low power
radio sources, triggered into activity by the increasing ICM density as they
move inward, this may be the feedback mechanism necessary to stabilize cooling
in cluster cores. | astro-ph_CO |
The impact of baryons on the matter power spectrum from the Horizon-AGN
cosmological hydrodynamical simulation: Accurate cosmology from upcoming weak lensing surveys relies on knowledge of
the total matter power spectrum at percent level at scales $k < 10$ $h$/Mpc,
for which modelling the impact of baryonic physics is crucial. We compare
measurements of the total matter power spectrum from the Horizon cosmological
hydrodynamical simulations: a dark matter-only run, one with full baryonic
physics, and another lacking Active Galactic Nuclei (AGN) feedback. Baryons
cause a suppression of power at $k\simeq 10$ $h/$Mpc of $<15\%$ at $z=0$, and
an enhancement of a factor of a few at smaller scales due to the more efficient
cooling and star formation. The results are sensitive to the presence of the
highest mass haloes in the simulation and the distribution of dark matter is
also impacted up to a few percent. The redshift evolution of the effect is
non-monotonic throughout $z=0-5$ due to an interplay between AGN feedback and
gas pressure, and the growth of structure. We investigate the effectiveness of
an analytic `baryonic correction model' in describing our results. We require a
different redshift evolution and propose an alternative fitting function with
$4$ free parameters that reproduces our results within $5\%$. Compared to other
simulations, we find the impact of baryonic processes on the total matter power
spectrum to be smaller at $z=0$. Correspondingly, our results suggest that AGN
feedback is not strong enough in the simulation. Total matter power spectra
from the Horizon simulations are made publicly available at
https://www.horizon-simulation.org/catalogues.html | astro-ph_CO |
A simple model linking galaxy and dark matter evolution: We construct a simple phenomenological model for the evolving galaxy
population by incorporating pre-defined baryonic prescriptions into a dark
matter hierarchical merger tree. Specifically the model is based on the simple
gas-regulator model introduced by Lilly et al. 2013 coupled with the empirical
quenching rules of Peng et al. 2010/12. The simplest model already does quite
well in reproducing, without re-adjusting the input parameters, many
observables including the Main Sequence sSFR-mass relation, the faint end slope
of the galaxy mass function and the shape of the star-forming and passive mass
functions. Compared with observations and/or the recent phenomenological model
of Behroozi et al. 2013 based on epoch-dependent abundance-matching, our model
also qualitatively reproduces the evolution of the Main Sequence sSFR(z) and
SFRD(z) star formation rate density relations, the $M_s - M_h$ stellar-to-halo
mass relation and also the $SFR - M_h$ relation. Quantitatively the evolution
of sSFR(z) and SFRD(z) is not steep enough, the $M_s - M_h$ relation is not
quite peaked enough and, surprisingly, the ratio of quenched to star-forming
galaxies around M* is not quite high enough. We show that these deficiencies
can simultaneously be solved by ad hoc allowing galaxies to re-ingest some of
the gas previously expelled in winds, provided that this is done in a
mass-dependent and epoch-dependent way. These allow the model galaxies to
reduce an inherent tendency to saturate their star-formation efficiency. This
emphasizes how efficient galaxies around M* are in converting baryons into
stars and highlights the fact that quenching occurs just at the point when
galaxies are rapidly approaching the maximum possible efficiency of converting
baryons into stars. | astro-ph_CO |
Lensing constraints on ultradense dark matter halos: Cosmological observations precisely measure primordial variations in the
density of the Universe at megaparsec and larger scales, but much smaller
scales remain poorly constrained. However, sufficiently large initial
perturbations at small scales can lead to an abundance of ultradense dark
matter minihalos that form during the radiation epoch and survive into the
late-time Universe. Because of their early formation, these objects can be
compact enough to produce detectable microlensing signatures. We investigate
whether the EROS, OGLE, and HSC surveys can probe these halos by fully
accounting for finite source size and extended lens effects. We find that
current data may already constrain the amplitudes of primordial curvature
perturbations in a new region of parameter space, but this conclusion is
strongly sensitive to yet undetermined details about the internal structures of
these ultradense halos. Under optimistic assumptions, current and future HSC
data would constrain a power spectrum that features an enhancement at scales $k
\sim 10^7/{\rm Mpc}$, and an amplitude as low as $\mathcal{P}_\zeta\simeq
10^{-4}$ may be accessible. This is a particularly interesting regime because
it connects to primordial black hole formation in a portion of the
LIGO/Virgo/Kagra mass range and the production of scalar-induced gravitational
waves in the nanohertz frequency range reachable by pulsar timing arrays. These
prospects motivate further study of the ultradense halo formation scenario to
clarify their internal structures. | astro-ph_CO |
An updated Gamma Ray Bursts Hubble diagram: Gamma ray bursts (GRBs) have recently attracted much attention as a possible
way to extend the Hubble diagram to very high redshift. To this aim, the
luminosity (or isotropic emitted energy) of a GRB at redshift z must be
evaluated from a correlation with a distance independent quantity so that one
can then solve for the luminosity distance D_L(z) and hence the distance
modulus mu(z). Averaging over five different two parameters correlations and
using a fiducial cosmological model to calibrate them, Schaefer (2007) has
compiled a sample of 69 GRBs with measured mu(z) which has since then been
widely used to constrain cosmological parameters. We update here that sample by
many aspects. First, we add a recently found correlation for the X - ray
afterglow and use a Bayesian inspired fitting method to calibrate the different
GRBs correlations known insofar assuming a fiducial LCDM model in agreement
with the recent WMAP5 data. Averaging over six correlations, we end with a new
GRBs Hubble diagram comprising 83 objects. We also extensively explore the
impact of varying the fiducial cosmological model considering how the estimated
mu(z) change as a function of the $(\Omega_M, w_0, w_a)$ parameters of the
Chevallier - Polarski - Linder phenomenological dark energy equation of state.
In order to avoid the need of assuming an {\it a priori} cosmological model, we
present a new calibration procedure based on a model independent local
regression estimate of mu(z) using the Union SNeIa sample to calibrate the GRBs
correlations. This finally gives us a GRBs Hubble diagram made out of 69 GRBs
whose estimated distance modulus mu(z) is almost independent on the underlying
cosmological model. | astro-ph_CO |
Explaining Excess Dipole in NVSS Data Using Superhorizon Perturbation: Many observations in recent times have shown evidence against the standard
assumption of isotropy in the Big Bang model. Introducing a superhorizon scalar
metric perturbation has been able to explain some of these anomalies. In this
work, we probe the net velocity arising due to the perturbation. We find that
this extra component does not contribute to the CMB dipole amplitude while it
does contribute to the dipole in large scale structures. Thus, within this
model's framework, our velocity with respect to the large scale structure is
not the same as that extracted from the CMB dipole, assuming it to be of purely
kinematic origin. Taking this extra velocity component into account, we study
the superhorizon mode's implications for the excess dipole observed in the NRAO
VLA Sky Survey (NVSS). We find that the mode can consistently explain both the
CMB and NVSS observations. We also find that the model leads to small
contributions to the local bulk flow and the dipole in Hubble parameter, which
are consistent with observations. The model leads to several predictions which
can be tested in future surveys. In particular, it implies that the observed
dipole in large scale structure should be redshift dependent and should show an
increase in amplitude with redshift. We also find that the Hubble parameter
should show a dipole anisotropy whose amplitude must increase with redshift in
the CMB frame. Similar anisotropic behaviour is expected for the observed
redshift as a function of the luminosity distance. | astro-ph_CO |
Direct detection of galaxy stellar halos : NGC 3957 as a test case: We present a direct detection of the stellar halo of the edge-on S0 galaxy
NGC 3957, using ultra-deep VLT/VIMOS V and R images. This is achieved with a
sky subtraction strategy based on infrared techniques. These observations allow
us to reach unprecedented high signal-to-noise ratios up to 15 kpc away from
the galaxy center, rendering photon-noise negligible. The 1 sigma detection
limits are R = 30.6 mag/arcsec^2 and V = 31.4 mag/arcsec^2. We conduct a
thorough analysis of the possible sources of systematic errors that could
affect the data: flat-fielding, differences in CCD responses, scaling of the
sky background, the extended halo itself, and PSF wings. We conclude that the
V-R colour of the NGC 3957 halo, calculated between 5 and 8 kpc above the disc
plane where the systematic errors are modest, is consistent with an old and
preferentially metal-poor normal stellar population, like that revealed in
nearby galaxy halos from studies of their resolved stellar content. We do not
find support for the extremely red colours found in earlier studies of diffuse
halo emission, which we suggest might have been due to residual systematic
errors. | astro-ph_CO |
Mass of the universe in a black hole: If spacetime torsion couples to the intrinsic spin of matter according to the
Einstein-Cartan-Sciama-Kibble theory of gravity, then the resulting
gravitational repulsion at supranuclear densities prevents the formation of
singularities in black holes. Consequently, the interior of every black hole
becomes a new universe that expands from a nonsingular bounce. We consider
gravitational collapse of fermionic spin-fluid matter with the stiff equation
of state in a stellar black hole. Such a collapse increases the mass of the
matter, which occurs through the Parker-Zel'dovich-Starobinskii quantum
particle production in strong, anisotropic gravitational fields. The subsequent
pair annihilation changes the stiff matter into an ultrarelativistic fluid. We
show that the universe in a black hole of mass $M_\textrm{BH}$ at the bounce
has a mass $M_\textrm{b}\sim M^2_\textrm{BH}
m^{1/2}_\textrm{n}/m^{3/2}_\textrm{Pl}$, where $m_\textrm{n}$ is the mass of a
neutron and $m_\textrm{Pl}$ is the reduced Planck mass. For a typical stellar
black hole, $M_\textrm{b}$ is about $10^{32}$ solar masses, which is $10^6$
larger than the mass of our Universe. As the relativistic black-hole universe
expands, its mass decreases until the universe becomes dominated by
nonrelativistic heavy particles. | astro-ph_CO |
C-GOALS: Chandra observations of a complete sample of luminous infrared
galaxies from the IRAS Revised Bright Galaxy Survey: We present X-ray data for a complete sample of 44 luminous infrared galaxies
(LIRGs), obtained with the Chandra X-ray Observatory. These are the X-ray
observations of the high luminosity portion of the Great Observatory All-sky
LIRG Survey (GOALS), which includes the most luminous infrared selected
galaxies, log (Lir/Lsun) > 11.73, in the local universe, z < 0.088. X-rays were
detected from 43 out of 44 objects, and their arcsec-resolution images,
spectra, and radial brightness distributions are presented. With a selection by
hard X-ray colour and the 6.4 keV iron line, AGN are found in 37% of the
objects, with higher luminosity sources more likely to contain an AGN. These
AGN also tend to be found in late-stage mergers. The AGN fraction would
increase to 48% if objects with mid-IR [Ne V] detection are included. Double
AGN are clearly detected only in NGC 6240 among 24 double/triple systems. Other
AGN are found either in single nucleus objects or in one of the double nuclei
at similar rates. Objects without conventional X-ray signatures of AGN appear
to be hard X-ray quiet, relative to the X-ray to far-IR correlation for
starburst galaxies, as discussed elsewhere. Most objects also show extended
soft X-ray emission, which is likely related to an outflow from the nuclear
region, with a metal abundance pattern suggesting enrichment by core collapse
supernovae, as expected for a starburst. | astro-ph_CO |
Improving the Estimation of Star formation Rates and Stellar Population
Ages of High-redshift Galaxies from Broadband Photometry: We explore methods to improve the estimates of star formation rates and mean
stellar population ages from broadband photometry of high redshift star-forming
galaxies. We use synthetic spectral templates with a variety of simple
parametric star formation histories to fit broadband spectral energy
distributions. These parametric models are used to infer ages, star formation
rates and stellar masses for a mock data set drawn from a hierarchical
semi-analytic model of galaxy evolution. Traditional parametric models
generally assume an exponentially declining rate of star-formation after an
initial instantaneous rise. Our results show that star formation histories with
a much more gradual rise in the star formation rate are likely to be better
templates, and are likely to give better overall estimates of the age
distribution and star formation rate distribution of Lyman break galaxies. For
B- and V-dropouts, we find the best simple parametric model to be one where the
star formation rate increases linearly with time. The exponentially-declining
model overpredicts the age by 100 % and 120 % for B- and V-dropouts, on
average, while for a linearly-increasing model, the age is overpredicted by 9 %
and 16 %, respectively. Similarly, the exponential model underpredicts
star-formation rates by 56 % and 60 %, while the linearly-increasing model
underpredicts by 15 % 22 %, respectively. For U-dropouts, the models where the
star-formation rate has a peak (near z ~ 3) provide the best match for age --
overprediction is reduced from 110 % to 26 % -- and star-formation rate --
underprediction is reduced from 58 % to 22 %. We classify different types of
star-formation histories in the semi-analytic models and show how the biases
behave for the different classes. We also provide two-band calibration formulae
for stellar mass and star formation rate estimations. | astro-ph_CO |
MOND effects in the inner solar system: I pinpoint a previously unrecognized MOND effect that may act in the inner
solar system, and is due to the galactic acceleration, g_g=eta*a0: a byproduct
of the MOND external-field effect. Predictions of the effect are not generic to
the MOND paradigm, but depend on the particular MOND formulation at hand.
However, the modified-Poisson formulation, on which I concentrate, uniquely
predicts a subtle anomaly that may be detected in planetary and spacecraft
motions (and perhaps in other precision systems, such as binary pulsars),
despite their very high accelerations, and even if the MOND interpolating
function is arbitrarily close to unity at high accelerations. Near the sun,
this anomaly appears as a quadrupole field, with the acceleration at position u
from the sun being g_i(u)=-q_{ij}u^j, with q_{ij} diagonal, axisymmetric, and
traceless: -2q_{xx}=-2q_{yy}=q_{zz}=q(eta)*(a0/R_M), where
R_M=(MG/a0)^{1/2}=8*10^3 au is the MOND radius of the sun. The anomaly is
described and analyzed as the Newtonian field of the fictitious cloud of
``phantom matter'' that hovers around the sun. I find, for the relevant range
of eta values, and for a range of interpolating functions, mu(x), values of
10^{-2}<-q< 0.3, which turn out to be sensitive to the form of mu(x) around the
MOND-to-Newtonian transition. This range verges on the present bounds from
solar system measurements. There might thus exist favorable prospects for
either measuring the effect, or constraining the theory and the relevant
parameters. | astro-ph_CO |
The Habitable Epoch of the Early Universe: In the redshift range 100<(1+z)<137, the cosmic microwave background (CMB)
had a temperature of 273-373K (0-100 degrees Celsius), allowing early rocky
planets (if any existed) to have liquid water chemistry on their surface and be
habitable, irrespective of their distance from a star. In the standard LCDM
cosmology, the first star-forming halos within our Hubble volume started
collapsing at these redshifts, allowing the chemistry of life to possibly begin
when the Universe was merely 10-17 million years old. The possibility of life
starting when the average matter density was a million times bigger than it is
today argues against the anthropic explanation for the low value of the
cosmological constant. | astro-ph_CO |
Turbocharging constraints on dark matter substructure through a
synthesis of strong lensing flux ratios and extended lensed arcs: Strong gravitational lensing provides a purely gravitational means to infer
properties of dark matter halos and thereby constrain the particle nature of
dark matter. Strong lenses sometimes appear as four lensed images of a
background quasar accompanied by spatially-resolved emission from the quasar
host galaxy encircling the main deflector (lensed arcs). We present methodology
to simultaneously reconstruct lensed arcs and relative image magnifications
(flux ratios) in the presence of full populations of dark matter subhalos and
line-of-sight halos. To this end, we develop a new approach for multi-plane ray
tracing that accelerates lens mass and source light reconstruction by factors
of $\sim 100-1000$. Using simulated data with a cold dark matter (CDM) ground
truth, we show that simultaneous reconstruction of lensed arcs and flux ratios
isolates small-scale perturbations to flux ratios by dark matter substructure
from uncertainties associated with the main deflector mass profile on larger
angular scales. Relative to analyses that use only image positions and flux
ratios to constrain the lens model, incorporating arcs strengthens likelihood
ratios penalizing warm dark matter (WDM) with a characteristic suppression
scale $m_{\rm{hm}} / M_{\odot}$ in the range $\left[10^7 - 10^{7.5}\right]$,
$\left[10^{7.5} - 10^{8}\right]$, $\left[10^8 - 10^{8.5}\right]$,
$\left[10^{8.5} - 10^{9}\right]$ by factors of $1.3$, $2.5$, $5.6$, and $13.1$,
respectively, and the $95\%$ exclusion limit improves by 0.5 dex in $\log_{10}
m_{\rm{hm}}$. The enhanced sensitivity to low-mass halos enabled by these
methods pushes the observational frontier of substructure lensing to the
threshold of galaxy formation, enabling stringent tests of any theory that
alters the properties of dark matter halos. | astro-ph_CO |
FAST-PT II: an algorithm to calculate convolution integrals of general
tensor quantities in cosmological perturbation theory: Cosmological perturbation theory is a powerful tool to predict the statistics
of large-scale structure in the weakly non-linear regime, but even at 1-loop
order it results in computationally expensive mode-coupling integrals. Here we
present a fast algorithm for computing 1-loop power spectra of quantities that
depend on the observer's orientation, thereby generalizing the FAST-PT
framework (McEwen et al., 2016) that was originally developed for scalars such
as the matter density. This algorithm works for an arbitrary input power
spectrum and substantially reduces the time required for numerical evaluation.
We apply the algorithm to four examples: intrinsic alignments of galaxies in
the tidal torque model; the Ostriker-Vishniac effect; the secondary CMB
polarization due to baryon flows; and the 1-loop matter power spectrum in
redshift space. Code implementing this algorithm and these applications is
publicly available at https://github.com/JoeMcEwen/FAST-PT . | astro-ph_CO |
Cosmological neutrino entropy changes due to flavor statistical mixing: Entropy changes due to delocalization and decoherence effects should modify
the predictions for the cosmological neutrino background (C$\nu$B) temperature
when one treats neutrino flavors in the framework of composite quantum systems.
Assuming that the final stage of neutrino interactions with the $\gamma
e^{-}e^{+}$ radiation plasma before decoupling works as a measurement scheme
that projects neutrinos into flavor quantum states, the resulting
free-streaming neutrinos can be described as a statistical ensemble of
flavor-mixed neutrinos. Even not corresponding to an electronic-flavor pure
state, after decoupling the statistical ensemble is described by a density
matrix that evolves in time with the full Hamiltonian accounting for flavor
mixing, momentum delocalization and, in case of an open quantum system
approach, decoherence effects. Since the statistical weights, $w$, shall follow
the electron elastic scattering cross section rapport given by $0.16\,w_{e} =
w_{\mu} = w_{\tau}$, the von-Neumann entropy will deserve some special
attention. Depending on the quantum measurement scheme used for quantifying the
entropy, mixing associated to dissipative effects can lead to an increasing of
the flavor associated von-Neumann entropy for free-streaming neutrinos. The
production of von-Neumann entropy mitigates the constraints on the predictions
for energy densities and temperatures of a cosmologically evolving isentropic
fluid, in this case, the cosmological neutrino background. The effects of
entropy changes on the cosmological neutrino temperature are quantified, and
the {\em constraint} involving the number of neutrino species, $N_{\nu} \approx
3$, in the phenomenological confront with Big Bang nucleosynthesis parameters
is consistently relieved. | astro-ph_CO |
GRB Probes of the High-z Universe with EXIST: The Energetic X-ray Imaging Survey Telescope (EXIST) mission concept is
optimized for study of high-z GRBs as probes of the early Universe. With a High
Energy Telescope (HET) incorporating a 4.5m^2 5-600keV (CZT; 0.6mm pixels)
detector plane for coded aperture imaging a 90deg x 70deg (>10% coding
fraction) field of view with 2' resolution and <20" (90% conf.) positions for
>5 sigma sources, EXIST will perform rapid (<200sec) slews onto GRBs. Prompt
images and spectra are obtained with a co-aligned soft X-ray telescope (SXI;
0.1 - 10keV) and with a 1.1m optical-IR telescope (IRT) simultaneously in 4
bands (0.3 - 0.52micron, 0.52 - 0.9micron, 0.9 - 1.38micron, and 1.38 -
2.3micron). An initial image (100s) will yield prompt identification within the
HET error circle from a <2" prompt SXI position; or from VIS vs. IR dropouts or
variability. An autonomous spacecraft re-point (<30") will then put the GRB on
a 0.3" x 4" slit for either R = 3000 (for AB <21) or R =30 (for AB ~21-25)
prompt spectra over the 0.3 - 0.9 micron and 0.9 - 2.3 micron bands. This will
provide onboard redshifts within ~500-2000sec for most GRBs, reaching z ~20
(for Lyman-alpha breaks) if such GRBs exist, and spectra for studies of the
host galaxy and local re-ionization patchiness as well as intervening cosmic
structure. With ~600 GRBs/yr expected, including ~7-10% expected at z >7, EXIST
will open a new era in studies of the early Universe as well as carry out a
rich program of AGN and transient-source science. An overview of the GRB
science objectives and a brief discussion of the overall mission design and
operations is given, and example high-z GRB IRT spectra are shown. EXIST is
being proposed to the Astro2010 Decadal Survey as a 5 year Medium Class mission
that could be launched as early as 2017. | astro-ph_CO |
HSC Year 1 cosmology results with the minimal bias method:
HSC$\times$BOSS galaxy-galaxy weak lensing and BOSS galaxy clustering: We present cosmological parameter constraints from a blinded joint analysis
of galaxy-galaxy weak lensing, $\Delta\!\Sigma(R)$, and projected correlation
function, $w_\mathrm{p}(R)$, measured from the first-year HSC (HSC-Y1) data and
SDSS spectroscopic galaxies over $0.15<z<0.7$. We use luminosity-limited
samples as lens samples for $\Delta\!\Sigma$ and as large-scale structure
tracers for $w_\mathrm{p}$ in three redshift bins, and use the HSC-Y1 galaxy
catalog to define a secure sample of source galaxies at $z_\mathrm{ph}>0.75$
for the $\Delta\!\Sigma$ measurements, selected based on their photometric
redshifts. For theoretical template, we use the "minimal bias" model for the
cosmological clustering observables for the flat $\Lambda$CDM cosmological
model. We compare the model predictions with the measurements in each redshift
bin on large scales, $R>12$ and $8~h^{-1}\mathrm{Mpc}$ for $\Delta\!\Sigma(R)$
and $w_\mathrm{p}(R)$, respectively, where the perturbation theory-inspired
model is valid. When we employ weak priors on cosmological parameters, without
CMB information, we find $S_8=0.936^{+0.092}_{-0.086}$,
$\sigma_8=0.85^{+0.16}_{-0.11}$, and $\Omega_\mathrm{m}=0.283^{+0.12}_{-0.035}$
for the flat $\Lambda$CDM model. Although the central value of $S_8$ appears to
be larger than those inferred from other cosmological experiments, we find that
the difference is consistent with expected differences due to sample variance,
and our results are consistent with the other results to within the statistical
uncertainties. (abriged) | astro-ph_CO |
Phenomenology of fermion production during axion inflation: We study the production of fermions through a derivative coupling with a
pseudoscalar inflaton and the effects of the produced fermions on the scalar
primordial perturbations. We present analytic results for the modification of
the scalar power spectrum due to the produced fermions, and we estimate the
amplitude of the non-Gaussianities in the equilateral regime. Remarkably, we
find a regime where the effect of the fermions gives the dominant contribution
to the scalar spectrum while the amplitude of the bispectrum is small and in
agreement with observation. We also note the existence of a regime in which the
backreaction of the fermions on the evolution of the zero-mode of the inflaton
can lead to inflation even if the potential of the inflaton is steep and does
not satisfy the slow-roll conditions. | astro-ph_CO |
Snowmass2021 CMB-HD White Paper: CMB-HD is a proposed millimeter-wave survey over half the sky that would be
ultra-deep (0.5 uK-arcmin) and have unprecedented resolution (15 arcseconds at
150 GHz). Such a survey would answer many outstanding questions about the
fundamental physics of the Universe. Major advances would be 1.) the use of
gravitational lensing of the primordial microwave background to map the
distribution of matter on small scales (k~10 h Mpc^(-1)), which probes dark
matter particle properties. It will also allow 2.) measurements of the thermal
and kinetic Sunyaev-Zel'dovich effects on small scales to map the gas density
and velocity, another probe of cosmic structure. In addition, CMB-HD would
allow us to cross critical thresholds: 3.) ruling out or detecting any new,
light (< 0.1 eV) particles that were in thermal equilibrium with known
particles in the early Universe, 4.) testing a wide class of multi-field models
that could explain an epoch of inflation in the early Universe, and 5.) ruling
out or detecting inflationary magnetic fields. CMB-HD would also provide
world-leading constraints on 6.) axion-like particles, 7.) cosmic
birefringence, 8.) the sum of the neutrino masses, and 9.) the dark energy
equation of state. The CMB-HD survey would be delivered in 7.5 years of
observing 20,000 square degrees of sky, using two new 30-meter-class off-axis
crossed Dragone telescopes to be located at Cerro Toco in the Atacama Desert.
Each telescope would field 800,000 detectors (200,000 pixels), for a total of
1.6 million detectors. | astro-ph_CO |
Primordial magnetic fields in the $f^{2}FF$ model in large field
inflation under de Sitter and power law expansion: We use the $f^{2}FF$ model to study the generation of primordial magnetic
fields (PMF) in the context of large field inflation (LFI), described by the
potential, $V \sim M \phi^{p}$. We compute the magnetic and electric spectra
for all possible values of the model parameters under de Sitter and power law
expansion. We show that scale invariant PMF are not obtained in LFI to first
order in the slow roll approximation, if we impose the constraint
$V(\phi=0)\sim 0$. Alternatively, if these constraints are relaxed, the scale
invariant PMF can be generated. The associated electric field energy can fall
below the energy density of inflation, $\rho_{\rm{Inf}}$ for the ranges of
comoving wavenumbers, $ k > 8 \times 10^{-7} \rm{Mpc^{-1}}$ and $ k > 4 \times
10^{-6} \rm{Mpc^{-1}}$ in de Sitter and power law (PL) expansion. Further, it
can drop below $\rho_{\rm{Inf}}$ on the ranges, e-foldings $N > 51$, $p<1.66$,
$p >2.03$, $l_0 > 3 \times 10^5 {M_{\rm{Pl}}}^{-1} (H_i < 3.3 \times 10^{-6}
M_{\rm{Pl}})$, and $M > 2.8 \times 10^{-3} M_{\rm{Pl}}$. All of the above
ranges fit with the observational constraints. | astro-ph_CO |
Revealing modified gravity signal in matter and halo hierarchical
clustering: We use a set of N-body simulations employing a modified gravity (MG) model
with Vainshtein screening to study matter and halo hierarchical clustering. As
test-case scenarios we consider two normal branch Dvali-Gabadadze-Porrati
(nDGP) gravity models with mild and strong growth rate enhancement. We study
higher-order correlation functions $\xi_n(R)$ up to $n=9$ and associated
hierarchical amplitudes $S_n(R)\equiv\xi_n(R)/\sigma(R)^{2n-2}$. We find that
the matter PDFs are strongly affected by the fifth-force on scales up to
$50h^{-1}$Mpc, and the deviations from GR are maximised at $z=0$. For reduced
cumulants $S_n$, we find that at small scales $R\leq10h^{-1}$Mpc the MG is
characterised by lower values, with the deviation growing from $7\%$ in the
reduced skewness up to even $40\%$ in $S_5$. To study the halo clustering we
use a simple abundance matching and divide haloes into thee fixed number
density samples. The halo two-point functions are weakly affected, with a
relative boost of the order of a few percent appearing only at the smallest
pair separations ($r\leq 5h^{-1}$Mpc). In contrast, we find a strong MG signal
in $S_n(R)$'s, which are enhanced compared to GR. The strong model exhibits a
$>3\sigma$ level signal at various scales for all halo samples and in all
cumulants. In this context, we find that the reduced kurtosis to be an
especially promising cosmological probe of MG. Even the mild nDGP model leaves
a $3\sigma$ imprint at small scales $R\leq3h^{-1}$Mpc, while the stronger model
deviates from a GR-signature at nearly all scales with a significance of
$>5\sigma$. Since the signal is persistent in all halo samples and over a range
of scales, we advocate that the reduced kurtosis estimated from galaxy
catalogues can potentially constitute a strong MG-model discriminatory as well
as GR self-consistency test. | astro-ph_CO |
New insight on galaxy structure from GALPHAT I. Motivation, methodology,
and benchmarks for Sersic models: We introduce a new galaxy image decomposition tool, GALPHAT (GALaxy
PHotometric ATtributes), to provide full posterior probability distributions
and reliable confidence intervals for all model parameters. GALPHAT is designed
to yield a high speed and accurate likelihood computation, using grid
interpolation and Fourier rotation. We benchmark this approach using an
ensemble of simulated Sersic model galaxies over a wide range of observational
conditions: the signal-to-noise ratio S/N, the ratio of galaxy size to the PSF
and the image size, and errors in the assumed PSF; and a range of structural
parameters: the half-light radius $r_e$ and the Sersic index $n$. We
characterise the strength of parameter covariance in Sersic model, which
increases with S/N and $n$, and the results strongly motivate the need for the
full posterior probability distribution in galaxy morphology analyses and later
inferences.
The test results for simulated galaxies successfully demonstrate that, with a
careful choice of Markov chain Monte Carlo algorithms and fast model image
generation, GALPHAT is a powerful analysis tool for reliably inferring
morphological parameters from a large ensemble of galaxies over a wide range of
different observational conditions. (abridged) | astro-ph_CO |
Probing Physics Beyond the Standard Model: Limits from BBN and the CMB
Independently and Combined: We present new Big Bang Nucleosynthesis (BBN) limits on the cosmic expansion
rate or relativistic energy density, quantified via the number $N_\nu$ of
equivalent neutrino species. We use the latest light element observations,
neutron mean lifetime, and update our evaluation for the nuclear rates $d+d
\rightarrow He3 + n$ and $d+d \rightarrow H3 + p$. Combining this result with
the independent constraints from the cosmic microwave background (CMB) yields
tight limits on new physics that perturbs $N_\nu$ and $\eta$ prior to cosmic
nucleosynthesis: a joint BBN+CMB analysis gives $N_\nu = 2.898 \pm 0.141$,
resulting in $N_\nu < 3.180$ at $2\sigma$. We apply these limits to a wide
variety of new physics scenarios including right-handed neutrinos, dark
radiation, and a stochastic gravitational wave background. We also search for
limits on potential {\em changes} in $N_\nu$ and/or the baryon-to-photon ratio
$\eta$ between the two epochs. The present data place strong constraints on the
allowed changes in $N_\nu$ between BBN and CMB decoupling; for example, we find
$-0.708 < N_\nu^{\rm CMB}-N_\nu^{\rm BBN} < 0.328$ in the case where $\eta$ and
the primordial helium mass fraction $Y_p$ are unchanged between the two epochs;
we also give limits on the allowed variations in $\eta$ or in $(\eta,N_\nu)$
jointly. Looking to the future, we forecast the tightened precision for $N_\nu$
arising from both CMB Stage 4 measurements as well as improvements in
astronomical \he4 measurements. We find that CMB-S4 combined with present BBN
and light element observation precision can give $\sigma(N_\nu) \simeq 0.03$.
Such future precision would reveal the expected effect of neutrino heating
($N_{\rm eff}-3=0.044$) of the CMB during BBN, and would be near the level to
reveal any particle species ever in thermal equilibrium with the standard
model. | astro-ph_CO |
Discovering a new well: Decaying dark matter with profile likelihoods: A large number of studies, all using Bayesian parameter inference from Markov
Chain Monte Carlo methods, have constrained the presence of a decaying dark
matter component. All such studies find a strong preference for either very
long-lived or very short-lived dark matter. However, in this letter, we
demonstrate that this preference is due to parameter volume effects that drive
the model towards the standard $\Lambda$CDM model, which is known to provide a
good fit to most observational data.
Using profile likelihoods, which are free from volume effects, we instead
find that the best-fitting parameters are associated with an intermediate
regime where around $3 \%$ of cold dark matter decays just prior to
recombination. With two additional parameters, the model yields an overall
preference over the $\Lambda$CDM model of $\Delta \chi^2 \approx -2.8$ with
\textit{Planck} and BAO and $\Delta \chi^2 \approx -7.8$ with the SH0ES $H_0$
measurement, while only slightly alleviating the $H_0$ tension. Ultimately, our
results reveal that decaying dark matter is more viable than previously
assumed, and illustrate the dangers of relying exclusively on Bayesian
parameter inference when analysing extensions to the $\Lambda$CDM model. | astro-ph_CO |
relensing: Reconstructing the mass profile of galaxy clusters from
gravitational lensing: In this work we present relensing, a package written in python whose goal is
to model galaxy clusters from gravitational lensing. With relensing we extend
the amount of software available, which provides the scientific community with
a wide range of models that help to compare and therefore validate the physical
results that rely on them. We implement a free-form approach which computes the
gravitational deflection potential on an adaptive irregular grid, from which
one can characterize the cluster and its properties as a gravitational lens.
Here, we use two alternative penalty functions to constrain strong lensing. We
apply relensing to two toy models, in order to explore under which conditions
one can get a better performance in the reconstruction. We find that by
applying a smoothing to the deflection potential, we are able to increase the
capability of this approach to recover the shape and size of the mass profile
of galaxy clusters, as well as its magnification map. This translates into a
better estimation of the critical and caustic curves. The power that the
smoothing provides is also tested on the simulated clusters Ares and Hera, for
which we get an rms on the lens plane of ~0.17 arcsec and ~0.16 arcsec,
respectively. Our results represent an improvement with respect to
reconstructions that were carried out with methods of the same nature as
relensing. At the same time, the smoothing also increases the stability of our
implementation, and decreases the computation time. In its current state,
relensing is available upon request. | astro-ph_CO |
Lensed Type Ia Supernovae as Probes of Cluster Mass Models: Using three magnified Type Ia supernovae (SNe Ia) detected behind CLASH
clusters, we perform a first pilot study to see whether standardizable candles
can be used to calibrate cluster mass maps created from strong lensing
observations. Such calibrations will be crucial when next generation HST
cluster surveys (e.g. FRONTIER) provide magnification maps that will, in turn,
form the basis for the exploration of the high redshift Universe. We classify
SNe using combined photometric and spectroscopic observations, finding two of
the three to be clearly of type SN Ia and the third probable. The SNe exhibit
significant amplification, up to a factor of 1.7 at $\sim5\sigma$ significance
(SN-L2). We conducted this as a blind study to avoid fine tuning of parameters,
finding a mean amplification difference between SNe and the cluster lensing
models of $0.09 \pm 0.09^{stat} \pm 0.05^{sys}$ mag. This impressive agreement
suggests no tension between cluster mass models and high redshift standardized
SNe Ia. However, the measured statistical dispersion of $\sigma_{\mu}=0.21$ mag
appeared large compared to the dispersion expected based on statistical
uncertainties ($0.14$). Further work with the supernova and cluster lensing
models, post unblinding, reduced the measured dispersion to
$\sigma_{\mu}=0.12$. An explicit choice should thus be made as to whether SNe
are used unblinded to improve the model, or blinded to test the model. As the
lensed SN samples grow larger, this technique will allow improved constraints
on assumptions regarding e.g. the structure of the dark matter halo. | astro-ph_CO |
An ALMA survey of Sub-millimetre Galaxies in the Extended Chandra Deep
Field South: Detection of [C II] at z=4.4: We present ALMA 870-um (345GHz) observations of two sub-millimetre galaxies
(SMGs) drawn from an ALMA study of the 126 sub-millimeter sources from the
LABOCA Extended Chandra Deep Field South Survey (LESS). The ALMA data identify
the counterparts to these previously unidentified sub-millimeter sources and
serendipitously detect bright emission lines in their spectra which we show are
most likely to be [C II]157.74um emission yielding redshifts of z=4.42 and
z=4.44. This blind detection rate within the 7.5-GHz bandpass of ALMA is
consistent with the previously derived photometric redshift distribution of
SMGs and suggests a modest, but not dominant (<25%), tail of 870-um selected
SMGs at z>4. We find that the ratio of L_CII/L_FIR in these SMGs is much higher
than seen for similarly far-infrared-luminous galaxies at z~0, which is
attributed to the more extended gas reservoirs in these high-redshift ULIRGs.
Indeed, in one system we show that the [C II] emission shows hints of extended
emission on >3kpc scales. Finally, we use the volume probed by our ALMA survey
to show that the bright end of the [C II] luminosity function evolves strongly
between z=0 and z~4.4, reflecting the increased ISM cooling in galaxies as a
result of their higher star-formation rates. These observations demonstrate
that even with short integrations, ALMA is able to detect the dominant fine
structure cooling lines from high-redshift ULIRGs, measure their energetics and
trace their evolution with redshift. | astro-ph_CO |
A Very Large ($θ_{E}\gtrsim40$") Strong Gravitational Lens Selected
with the Sunyaev-Zel'dovich Effect: PLCK G287.0+32.9 ($z$ = 0.38): Since galaxy clusters sit at the high-end of the mass function, the number of
galaxy clusters both massive and concentrated enough to yield particularly
large Einstein radii poses useful constraints on cosmological and structure
formation models. To date, less than a handful of clusters are known to have
Einstein radii exceeding $\sim40$" (for a source at $z_{s}\simeq2$, nominally).
Here, we report an addition to that list of the Sunyaev-Zel'dovich (SZ)
selected cluster, PLCK G287.0+32.9 ($z=0.38$), the second-highest SZ-mass
($M_{500}$) cluster from the Planck catalog. We present the first strong
lensing analysis of the cluster, identifying 20 sets of multiply-imaged
galaxies and candidates in new \emph{Hubble Space Telescope} data, including a
long, $l\sim22$" giant arc, as well as a quadruply-imaged, apparently bright
(magnified to J$_{F110W}=$25.3 AB), likely high-redshift dropout galaxy at
$z_{phot}=6.90$ [6.13--8.43] (95\% C.I.). Our analysis reveals a very large
critical area (1.55 arcmin$^{2}$, $z_{s}\simeq2$), corresponding to an
effective Einstein radius of $\theta_{E}\sim42$". The model suggests the
critical area will expand to 2.58 arcmin$^{2}$ ($\theta_{E}\sim54$") for
sources at $z_{s}\sim10$. Our work adds to recent efforts to model very massive
clusters towards the launch of the James Webb Space Telescope, in order to
identify the most useful cosmic lenses for studying the early Universe.
Spectroscopic redshifts for the multiply-imaged galaxies and additional HST
data will be necessary for refining the lens model and verifying the nature of
the $z\sim7$ dropout. | astro-ph_CO |
Cosmic Filaments from Cosmic Strings: Cosmic strings are generically predicted in many extensions of the Standard
Model of particle physics. We propose a new avenue for detecting cosmic strings
through their effect on the filamentary structure in the cosmic web. Using
cosmological simulations of the density wake from a cosmic string, we examine a
variety of filament structure probes. We show that the largest effect of the
cosmic string is an overdensity in the filament distribution around the string
wake. The signal from the overdensity is stronger at higher redshift, and more
robust with a wider field. We analyze the spatial distribution of filaments
from a publicly available catalog of filaments built from SDSS galaxies. With
existing data, we find no evidence for the presence of a cosmic string wake
with string tension parameter $G\mu$ above $5\times 10^{-6}$. However, we
project WFIRST will be able to detect a signal from such a wake at the $99\%$
confidence level at redshift $z=2$, with significantly higher confidence and
the possibility of probing lower tensions ($G\mu \sim 10^{-6}$), at $z=10$. The
sensitivity of this method is not competitive with constraints derived from the
CMB. However, it provides an independent discovery channel at low redshift,
which could be a smoking-gun in scenarios where the CMB bound can be weakened. | astro-ph_CO |
LoCuSS: The Mass Density Profile of Massive Galaxy Clusters at z=0.2: We present a stacked weak-lensing analysis of an approximately mass-selected
sample of 50 galaxy clusters at 0.15<z<0.3, based on observations with
Suprime-Cam on the Subaru Telescope. We develop a new method for selecting
lensed background galaxies from which we estimate that our sample of red
background galaxies suffers just 1% contamination. We detect the stacked
tangential shear signal from the full sample of 50 clusters, based on this red
sample of background galaxies, at a total signal-to-noise ratio of S/N=32.7.
The Navarro-Frenk-White model is an excellent fit to the data, yielding sub-10%
statistical precision on mass and concentration:
Mvir=7.19^{+0.53}_{-0.50}\times10^{14}h^{-1}Msol, cvir=5.41^{+0.49}_{-0.45}
(c_{200}=4.22^{+0.40}_{-0.36}). Tests of a range of possible systematic errors,
including shear calibration and stacking-related issues, indicate that they are
sub-dominant to the statistical errors. The concentration parameter obtained
from stacking our approximately mass-selected cluster sample is broadly in line
with theoretical predictions. Moreover, the uncertainty on our measurement is
comparable with the differences between the different predictions in the
literature. Overall our results highlight the potential for stacked
weak-lensing methods to probe the mean mass density profile of cluster-scale
dark matter halos with upcoming surveys, including Hyper-Suprime-Cam, Dark
Energy Survey, and KIDS. | astro-ph_CO |
$Λ_{\rm s}$CDM cosmology from a type-II minimally modified gravity: We have successfully integrated $\Lambda_{\rm s}$CDM, a promising model for
alleviating cosmological tensions, into a theoretical framework by endowing it
with a specific Lagrangian from the VCDM model, a type-II minimally modified
gravity. In this theory, we demonstrate that an auxiliary scalar field with a
linear potential induces an effective cosmological constant, enabling the
realization of an abrupt mirror AdS-dS transition in the late universe through
a piecewise linear potential. To eliminate the sudden singularity in this setup
and ensure stable transitions, we smooth out this potential. Realized within
the VCDM theory, the $\Lambda_{\rm s}$CDM model facilitates two types of rapid
smooth mirror AdS-dS transitions: (i) the agitated transition, associated with
a smooth jump in the potential, where $\Lambda_{\rm s}$, and consequently $H$,
exhibits a bump around the transition's midpoint; and (ii) the quiescent
transition, associated with a smooth change in the slope of the potential,
where $\Lambda_{\rm s}$ transitions gracefully. These transitions are likely to
leave distinct imprints on the background and perturbation dynamics,
potentially allowing the observational data to distinguish between them. This
novel theoretical framework propels $\Lambda_{\rm s}$CDM into a fully
predictive model capable of exploring the evolution of the Universe including
the late-time AdS-dS transition epoch, and extends the applicability of the
model. We believe further research is crucial in establishing $\Lambda_{\rm
s}$CDM as a leading candidate or guide for a new concordance cosmological
model. | astro-ph_CO |
Mg II Absorption Characteristics of a Volume-Limited Sample of Galaxies
at z ~ 0.1: We present an initial survey of Mg II absorption characteristics in the halos
of a carefully constructed, volume-limited subsample of galaxies embedded in
the spectroscopic part of the Sloan Digital Sky Survey. We observed quasars
near sightlines to 20 low-redshift (z ~ 0.1), luminous M_r <= -20.5 galaxies in
SDSS DR4 and DR6 with the LRIS-B spectrograph on the Keck I telescope. The
primary systematic criteria for the targeted galaxies are a redshift z >~ 0.1
and the presence of an appropriate bright background quasar within a projected
75 kpc/h of its center, although we preferentially sample galaxies with lower
impact parameters and slightly more star formation within this range. Of the
observed systems, six exhibit strong [EW(2796) >= 0.3 Ang.] Mg II absorption at
the galaxy's redshift, six systems have upper limits which preclude strong Mg
II absorption, while the remaining observations rule out very strong [EW(2796)
>= 1-2 Ang] absorption. The absorbers fall at higher impact parameters than
many non-absorber sightlines, indicating a covering fraction f_c <~ 0.4 for >=
0.3-Angstrom absorbers at z ~ 0.1, even at impact parameters <= 35 kpc/h (f_c ~
0.25). The data are consistent with a possible dependence of covering fraction
and/or absorption halo size on the environment or star-forming properties of
the central galaxy. | astro-ph_CO |
Convergence properties of fine structure constant measurements using
quasar absorption systems: Searches for spacetime variations of fundamental constants have entered an
era of unprecedented precision. New, high quality quasar spectra require
increasingly refined analytic methods. In this article, a continuation in a
series to establish robust and unbiased methodologies, we explore how
convergence criteria in non-linear least squares optimisation impact on quasar
absorption system measurements of the fine structure constant alpha. Given
previous claims for high-precision constraints, we critically examine the
veracity of a so-called ``blinding'' approach, in which alpha is fixed at the
terrestrial value during the model building process, releasing it as a free
parameter only after the ``final'' absorption system kinematic structure has
been obtained. We show that this approach results in an extended flat canyon in
chi squared-alpha space, such that convergence is unlikely to be reached, even
after as many as 1000 iterations. The fix is straightforward: alpha must be
treated as a free parameter from the earliest possible stages of absorption
system model building. The implication of the results presented here is that
all previous measurements that have used initially-fixed alpha should be
reworked. | astro-ph_CO |
Rastall gravity extension of the standard $Λ$CDM model:
theoretical features and observational constraints: We present a detailed investigation of the Rastall gravity extension of the
standard $\Lambda$CDM model. We review the model for two simultaneous
modifications of different nature in the Friedmann equation due to the Rastall
gravity: the new contributions of the material (actual) sources (considered as
effective source) and the altered evolution of the material sources. We discuss
the role/behavior of these modifications with regard to some low redshift
tensions, including the so-called $H_0$ tension, prevailing within the standard
$\Lambda$CDM. We constrain the model at the level of linear perturbations, and
obtain the first constraints through a robust and accurate analysis using the
latest full Planck CMB data, with and without including BAO data. We find that
the Rastall parameter $\epsilon$ (null for general relativity) is consistent
with zero at 68\% CL (with a tendency towards positive values, $-0.0001 <
\epsilon < 0.0007$ (CMB+BAO) at 68\% CL), which in turn implies no significant
statistical evidence for deviation from general relativity, and also a
precision of $\mathcal{O}(10^{-4})$ for the coefficient $-1/2$ of the term
$g_{\mu\nu}R$ in the Einstein field equations of general relativity
(guaranteeing the local energy-momentum conservation). We explore the
consequences led by the Rastall gravity on the cosmological parameters in the
light of the observational analyses. It turns out that the effective source
dynamically screens the usual vacuum energy at high redshifts, but this
mechanism barely works due to the opposition by the altered evolution of CDM.
Consequently, two simultaneous modifications of different nature in the
Friedmann equation act against each other, and do not help to considerably
relax the so-called low redshift tensions. Our results may offer a guide for
the research community that studies the Rastall gravity in various aspects of
gravitation and cosmology. | astro-ph_CO |
Improving Dark Energy Constraints with High Redshift Type Ia Supernovae
from CANDELS and CLASH: Aims. We investigate the degree of improvement in dark energy constraints
that can be achieved by extending Type Ia Supernova (SN Ia) samples to
redshifts z > 1.5 with the Hubble Space Telescope (HST), particularly in the
ongoing CANDELS and CLASH multi-cycle treasury programs.
Methods. Using the popular CPL parametrization of the dark energy, w = w0
+wa(1-a), we generate mock SN Ia samples that can be projected out to higher
redshifts. The synthetic datasets thus generated are fitted to the CPL model,
and we evaluate the improvement that a high-z sample can add in terms of
ameliorating the statistical and systematic uncertainties on cosmological
parameters.
Results. In an optimistic but still very achievable scenario, we find that
extending the HST sample beyond CANDELS+CLASH to reach a total of 28 SN Ia at z
> 1.0 could improve the uncertainty in the wa parameter by up to 21%. The
corresponding improvement in the figure of merit (FoM) would be as high as 28%.
Finally, we consider the use of high-redshift SN Ia samples to detect
non-cosmological evolution in SN Ia luminosities with redshift, finding that
such tests could be undertaken by future spacebased infrared surveys using the
James Webb Space Telescope (JWST). | astro-ph_CO |
Tomography-based observational measurements of the halo mass function
via the submillimeter magnification bias: Aims. The main goal of this paper is to derive observational constraints on
the halo mass fuction (HMF) by performing a tomographic analysis of the
magnification bias signal on a sample of background submillimeter galaxies. The
results can then be compared with those from a non-tomographic study. Methods.
We measure the cross-correlation function between a sample of foreground GAMA
galaxies with spectroscopic redshifts in the range $0.1 < z < 0.8$ (and divided
up into four bins) and a sample of background submillimeter galaxies from
H-ATLAS with photometric redshifts in the range $1.2 < z < 4.0$. We model the
weak lensing signal within the halo model formalism and carry out a Markov
chain Monte Carlo algorithm to obtain the posterior distribution of all HMF
parameters, which we assume to follow the Sheth and Tormen (ST) three-parameter
and two-parameter fits. Results. While the observational constraints on the HMF
from the non-tomographic analysis are not stringent, there is a remarkable
improvement in terms of uncertainty reduction when tomography is adopted.
Moreover, with respect to the traditional ST triple of values from numerical
simulations, the results from the three-parameter fit predict a higher number
density of halos at masses below $10^{12}M_{\odot}/h$ at 95% credibility. The
two-parameter fit yields even more restricting results, with a larger number
density of halos below $10^{13}M_{\odot}/h$ and a lower one above
$10^{14}M_{\odot}/h$, this time at more than 3$\sigma$ credibility. Our results
are therefore in disagreement with the standard N-body values for the ST fit at
2$\sigma$ and 3$\sigma$, respectively. | astro-ph_CO |
Constraints on active and sterile neutrinos in an interacting dark
energy cosmology: We investigate the impacts of dark energy on constraining massive
(active/sterile) neutrinos in interacting dark energy (IDE) models by using the
current observations. We employ two typical IDE models, the interacting $w$
cold dark matter (I$w$CDM) model and the interacting holographic dark energy
(IHDE) model, to make an analysis. To avoid large-scale instability, we use the
parameterized post-Friedmann approach to calculate the cosmological
perturbations in the IDE models. The cosmological observational data used in
this work include the Planck cosmic microwave background (CMB) anisotropies
data, the baryon acoustic oscillation data, the type Ia supernovae data, the
direct measurement of the Hubble constant, the weak lensing data, the
redshift-space distortion data, and the CMB lensing data. We find that the dark
energy properties could influence the constraint limits of active neutrino mass
and sterile neutrino parameters in the IDE models. We also find that the dark
energy properties could influence the constraints on the coupling strength
parameter $\beta$, and a positive coupling constant, $\beta>0$, can be detected
at the $2.5\sigma$ statistical significance for the IHDE+$\nu_s$ model by using
the all-data combination. In addition, we also discuss the "Hubble tension"
issue in these scenarios. We find that the $H_0$ tension can be effectively
relieved by considering massive sterile neutrinos, and in particular in the
IHDE+$\nu_s$ model the $H_0$ tension can be reduced to be at the $1.28\sigma$
level. | astro-ph_CO |
The impact of sloshing on the intra-group medium and old radio lobe of
NGC 5044: We present temperature and abundance maps of the central 125 kpc of the NGC
5044 galaxy group, based an a deep XMM-Newton observation. The abundance map
reveals an asymmetrical abundance structure, with the centroid of the highest
abundance gas offset ~22 kpc northwest of the galaxy centre, and moderate
abundances extending almost twice as far to the southeast than in any other
direction. The abundance distribution is closely correlated with two
previously-identified cold fronts and an arc--shaped region of surface
brightness excess, and it appears that sloshing, induced by a previous tidal
encounter, has produced both the abundance and surface brightness features.
Sloshing dominates the uplift of heavy elements from the group core on large
scales, and we estimate that the southeast extension (the tail of the sloshing
spiral) contains at least 1.2x10^5 solar masses more iron than would be
expected of gas at its radius. Placing limits on the age of the encounter we
find that if, as previously suggested, the disturbed spiral galaxy NGC 5054 was
the perturber, it must have been moving supersonically when it transited the
group core. We also examine the spectral properties of emission from the old,
detached radio lobe southeast of NGC 5044, and find that they are consistent
with a purely thermal origin, ruling out this structure as a significant source
of spectrally hard inverse-Compton emission. | astro-ph_CO |
Precision cosmology with a combination of wide and deep
Sunyaev-Zeldovich cluster surveys: We show the advantages of a wedding cake design for Sunyaev-Zel'dovich
cluster surveys. We show that by dividing up a cluster survey into a wide and a
deep survey, one can essentially recover the cosmological information that
would be diluted in a single survey of the same duration due to the
uncertainties in our understanding of cluster physics. The parameter degeneracy
directions of the deep and wide surveys are slightly different, and combining
them breaks these degeneracies effectively. A variable depth survey with a few
thousand clusters is as effective at constraining cosmological parameters as a
single depth survey with a much larger cluster sample. | astro-ph_CO |
Multipole vectors of completely random microwave skies for $l \leq 50$: The statistical cosmological principle states that observables on the
celestial sphere are sampled from a rotationally invariant distribution.
Previously certain large scale anomalies which violate this principle have been
found, for example an alignment of the lowest multipoles with the cosmic dipole
direction. In this work we continue the search for possible anomalies using
multipole vectors which represent a convenient tool for this purpose. In order
to study the statistical behavior of multipole vectors, we revisit several
construction methods. We investigate all four full-sky foreground-cleaned maps
from the Planck 2015 release with respect to four meaningful physical
directions using computationally cheap statistics that have a simple geometric
interpretation. We find that the full-sky SEVEM map deviates from all the other
cleaned maps, as it shows a strong correlation with the Galactic Pole and
Galactic Center. The other three maps COMMANDER, NILC and SMICA show a
consistent behavior. On the largest angular scales, $l \leq 5$, as well as on
intermediate scales, $l = 20, 21, 22, 23, 24$, all of them are unusually
correlated with the cosmic dipole direction. These scales coincide with the
scales on which the angular power spectrum deviates from the Planck 2015
best-fit {\Lambda}CDM model. In the range $2 \leq l \leq 50$ as a whole there
is no unusual behavior visible globally. We do not find abnormal intramultipole
correlation, i.e. correlation of multipole vectors inside a given multipole
without reference to any outer direction. | astro-ph_CO |
Active and Sterile Neutrino Emission and SN1987A Pulsar Velocity: Recently estimates have been made of the velocities of pulsars produced by
the emission of sterile neutrinos during the first 10 seconds and by active
neutrinos during the second 10 seconds after a supernova event reaches thermal
equilibrium. Neutrinos produced with electrons in the lowest Landau level are
emitted in the direction of the magnetic field, and the resulting pulsar
velocity depends mainly on the temperature. Using measurements of the neutrino
energies emitted from SN1987A, the temperature can be estimated, and from this
we estimate the velocity of the resulting pulsar from both active and large
mixing-angle sterile neutrinos. | astro-ph_CO |
Ionized nitrogen at high redshift: We present secure [NII[ detections in two mm-bright, strongly lensed objects
at high redshift, APM08279+5255 (z=3.911) and MM18423+5938 (z=3.930), using the
IRAM Plateau de Bure Interferometer. Due to its ionization energy [NII] is a
good tracer of the ionized gas phase in the interstellar medium. The measured
fluxes are S([NII])=(4.8+/-0.8) Jy km/s and (7.4+/-0.5) Jy km/s respectively,
yielding line luminosities of L([NII]) =(1.8+/-0.3) x 10^9 \mu^{-1} Lsun for
APM08279+5255 and L([NII]) =(2.8+/-0.2) x 10^9 \mu^{-1} Lsun for MM18423+5938.
Our high-resolution map of the [NII] and 1 mm continuum emission in
MM18423+5938 clearly resolves an Einstein ring in this source, and reveals a
velocity gradient in the dynamics of the ionized gas. A comparison of these
maps with high-resolution EVLA CO observations enables us to perform the first
spatially-resolved study of the dust continuum-to-molecular gas surface
brightness (Sigma_{FIR} Sigma_{CO}^N, which can be interpreted as the star
formation law) in a high-redshift object. We find a steep relation
(N=1.4+/-0.2), consistent with a starbursting environment. We measure a
[NII]/FIR luminosity ratio in APM0828+5255 and MM18423+5938 of 9.0 x 10^{-6}
and 5.8 x 10^{-6}, respectively. This is in agreement with the decrease of the
[NII]/FIR ratio at high FIR luminosities observed in local galaxies. | astro-ph_CO |
Making Galaxies in a Cosmological Context: The Need for Early Stellar
Feedback: We introduce the Making Galaxies in a Cosmological Context (MaGICC) program
of smoothed particle hydrodynamics (SPH) simulations. We describe a parameter
study of galaxy formation simulations of an L* galaxy that uses early stellar
feedback combined with supernova feedback to match the stellar mass--halo mass
relationship. While supernova feedback alone can reduce star formation enough
to match the stellar mass--halo mass relationship, the galaxy forms too many
stars before z=2 to match the evolution seen using abundance matching. Our
early stellar feedback is purely thermal and thus operates like a UV ionization
source as well as providing some additional pressure from the radiation of
massive, young stars. The early feedback heats gas to >10^6 K before cooling to
10^4 K. The pressure from this hot gas creates a more extended disk and
prevents more star formation prior to z=1 than supernovae feedback alone. The
resulting disk galaxy has a flat rotation curve, an exponential surface
brightness profile, and matches a wide range of disk scaling relationships. The
disk forms from the inside-out with an increasing exponential scale length as
the galaxy evolves. Overall, early stellar feedback helps to simulate galaxies
that match observational results at low and high redshifts. | astro-ph_CO |
SkyMapper Southern Survey: Data Release 4: We present the fourth data release (DR4) of the SkyMapper Southern Survey
(SMSS), the last major step in our hemispheric survey with six optical filters:
u, v, g, r, i, z. SMSS DR4 covers 26,000 sq.deg from over 400,000 images
acquired by the 1.3m SkyMapper telescope between 2014-03 and 2021-09. The
6-band sky coverage extends from the South Celestial Pole to Dec = +16deg, with
some images reaching Dec ~ +28deg. In contrast to previous DRs, we include all
good-quality images from the facility taken during that time span, not only
those explicitly taken for the public Survey. From the image dataset, we
produce a catalogue of nearly 13 billion detections made from ~700 million
unique astrophysical objects. The typical 10sigma depths for each field range
between 18.5 and 20.5 mag, depending on the filter, but certain sky regions
include longer exposures that reach as deep as 22 mag in some filters. As with
previous SMSS catalogues, we have cross-matched with a host of other imaging
and spectroscopic datasets to facilitate additional science outcomes. SMSS DR4
is now available to the worldwide astronomical community. | astro-ph_CO |
Asymptotic Giant Branch Stars in the Sculptor Dwarf Spheroidal Galaxy: JHK_S photometry is presented for a 35 arcmin square field centred on the
Sculptor dwarf spheroidal galaxy. With the aid of published kinematic data
definite galaxy members are identified and the width in J-K of the
colour-magnitude diagram is shown to be consistent with an old population of
stars with a large range in metal abundance. We identify two Asymptotic Giant
Branch variables, both carbon Miras, with periods of 189 and 554 days,
respectively, and discuss their ages, metallicities and mass loss as well as
their positions in the Mira period-luminosity diagram. There is evidence for a
general period-age relation for Local Group Miras. The mass-loss rate for the
554-day variable, MAG29, appears to be consistent with that found for Miras of
comparable period in other Local Group galaxies. | astro-ph_CO |
Optical Spectra of SNR Candidates in NGC 300: We present moderate-resolution (<5A) long-slit optical spectra of 51 nebular
objects in the nearby Sculptor Group galaxy NGC 300 obtained with the 2.3 meter
Advanced Technology Telescope at Siding Spring Observatory, Australia. Adopting
the criterion of [SII]/Ha>=0.4 to confirm supernova remnants (SNRs) from
optical spectra, we find that of 28 objects previously proposed as SNRs from
optical observations, 22 meet this criterion with six showing [SII]/Ha of less
than 0.4. Of 27 objects suggested as SNRs from radio data, four are associated
with the 28 previously proposed SNRs. Of these four, three (included in the 22
above) meet the criterion. In all, 22 of the 51 nebular objects meet the
[SII]/Ha criterion as SNRs while the nature of the remaining 29 objects remains
undetermined by these observations. | astro-ph_CO |
N-body simulation of the Stephan's Quintet: The evolution of compact groups of galaxies may represent one of the few
places in the nearby universe in which massive galaxies are being forged
through a complex set of processes involving tidal interaction, ram-pressure
stripping, and perhaps finally "dry-mergers" of galaxies stripped of their cool
gas. Using collisionless N-body simulations, we propose a possible scenario for
the formation of one of the best studied compact groups: Stephan's Quintet. We
define a serial approach which allows us to consider the history of the group
as sequence of galaxy-galaxy interactions seen as relatively separate events in
time, but chained together in such a way as to provide a plausible scenario
that ends in the current configuration of the galaxies. By covering a large set
of parameters, we claim that it is very unlikely that both major tidal tails of
the group have been created by the interaction between the main galaxy and a
single intruder. We propose instead a scenario based on two satellites orbiting
the main disk, plus the recent involvement of an additional interloper, coming
from the background at high speed. This purely N-body study of the quintet will
provide a parameter-space exploration of the basic dynamics of the group that
can be used as a basis for a more sophisticated N-body/hydrodynamic study of
the group that is necessary to explain the giant shock structure and other
purely gaseous phenomena observed in both the cold, warm and hot gas in the
group. | astro-ph_CO |
Radiation and energy release in a background field of axion-like dark
matter: We find that a fuzzy dark matter background and the mG scale magnetic field
in the galactic center can give rise to a radiation with a very large energy
release. The frequency of the radiation field is the same as the frequency of
the oscillating axion-like background field. We show that there is an energy
transfer between the fuzzy dark matter sector and the electromagnetic sector
because of the presence of the generated radiation field and the galactic
magnetic field. The energy release rate of radiation is found to be very slow
in comparison with the energy of fuzzy dark matter but could be significant
comparing with the energy of galactic magnetic field in the source region.
Using this example, we show that the fuzzy dark matter together with a large
scale magnetic field is possible to give rise to fruitful physics. | astro-ph_CO |
Fast shimming algorithm based on Bayesian optimization for magnetic
resonance based dark matter search: The sensitivity and accessible mass range of magnetic resonance searches for
axionlike dark matter depends on the homogeneity of applied magnetic fields.
Optimizing homogeneity through shimming requires exploring a large parameter
space which can be prohibitively time consuming. We have automated the process
of tuning the shim-coil currents by employing an algorithm based on Bayesian
optimization. This method is especially suited for applications where the
duration of a single optimization step prohibits exploring the parameter space
extensively or when there is no prior information on the optimal operation
point. Using the Cosmic Axion Spin Precession Experiment (CASPEr)-gradient
low-field apparatus, we show that for our setup this method converges after
approximately 30 iterations to a sub-10 parts-per-million field homogeneity
which is desirable for our dark matter search. | astro-ph_CO |
Moving mesh cosmology: tracing cosmological gas accretion: We investigate the nature of gas accretion onto haloes and galaxies at z=2
using cosmological hydrodynamic simulations run with the moving mesh code
AREPO. Implementing a Monte Carlo tracer particle scheme to determine the
origin and thermodynamic history of accreting gas, we make quantitative
comparisons to an otherwise identical simulation run with the smoothed particle
hydrodynamics (SPH) code GADGET-3. Contrasting these two numerical approaches,
we find significant physical differences in the thermodynamic history of
accreted gas in haloes above 10^10.5 solar masses. In agreement with previous
work, GADGET simulations show a cold fraction near unity for galaxies forming
in massive haloes, implying that only a small percentage of accreted gas heats
to an appreciable fraction of the virial temperature during accretion. The same
galaxies in AREPO show a much lower cold fraction, <20% in haloes above 10^11
solar masses. This results from a hot gas accretion rate which, at this same
halo mass, is an order of magnitude larger than with GADGET, while the cold
accretion rate is also lower. These discrepancies increase for more massive
systems, and we explain both as due to numerical inaccuracies in the standard
formulation of SPH. We also observe that the relatively sharp transition from
cold to hot mode dominated accretion, at a halo mass of ~10^11, is a
consequence of comparing past gas temperatures to a constant threshold value
independent of virial temperature. Examining the spatial distribution of
accreting gas, we find that gas filaments in GADGET tend to remain collimated
and flow coherently to small radii, or artificially fragment and form a large
number of purely numerical "blobs". Similar gas streams in AREPO show increased
heating and disruption at 0.25-0.5 virial radii and contribute to the hot gas
accretion rate in a manner distinct from classical cooling flows. | astro-ph_CO |
On the Correlations between Galaxy Properties and Supermassive Black
Hole Mass: We use a large sample of upper limits and accurate estimates of supermassive
black holes masses coupled with libraries of host galaxy velocity dispersions,
rotational velocities and photometric parameters extracted from Sloan Digital
Sky Survey i-band images to establish correlations between the SMBH and host
galaxy parameters. We test whether the mass of the black hole, MBH, is
fundamentally driven by either local or global galaxy properties. We explore
correlations between MBH and stellar velocity dispersion sigma, bulge
luminosity, bulge mass Sersic index, bulge mean effective surface brightness,
luminosity of the galaxy, galaxy stellar mass, maximum circular velocity Vc,
galaxy dynamical and effective masses. We verify the tightness of the MBH-sigma
relation and find that correlations with other galaxy parameters do not yield
tighter trends. We do not find differences in the MBH-sigma relation of barred
and unbarred galaxies. The MBH-sigma relation of pseudo-bulges is also coarser
and has a different slope than that involving classical bulges. The MBH-bulge
mass is not as tight as the MBH-sigma relation, despite the bulge mass proving
to be a better proxy of MBH than bulge luminosity. We find a rather poor
correlation between MBH and Sersic index suggesting that MBH is not related to
the bulge light concentration. The correlations between MBH and galaxy
luminosity or mass are not a marked improvement over the MBH sigma relation. If
Vc is a proxy for the dark matter halo mass, the large scatter of the MBH-Vc
relation then suggests that MBH is more coupled to the baryonic rather than the
dark matter. We have tested the need for a third parameter in the MBH scaling
relations, through various linear correlations with bulge and galaxy
parameters, only to confirm that the fundamental plane of the SMBH is mainly
driven by sigma, with a small tilt due to the effective radius. (Abridged) | astro-ph_CO |
$f(R)$ gravity modifications: from the action to the data: It is a very well established matter nowadays that many modified gravity
models can offer a sound alternative to General Relativity for the description
of the accelerated expansion of the universe. But it is also equally well known
that no clear and sharp discrimination between any alternative theory and the
classical one has been found so far. In this work, we attempt at formulating a
different approach starting from the general class of $f(R)$ theories as test
probes: we try to reformulate $f(R)$ Lagrangian terms as explicit functions of
the redshift, i.e., as $f(z)$. In this context, the $f(R)$ setting to the
consensus cosmological model, the $\Lambda$CDM model, can be written as a
polynomial including just a constant and a third-order term. Starting from this
result, we propose various different polynomial parameterizations $f(z)$,
including new terms which would allow for deviations from $\Lambda$CDM, and we
thoroughly compare them with observational data. While on the one hand we have
found no statistically preference for our proposals (even if some of them are
as good as $\Lambda$CDM by using Bayesian Evidence comparison), we think that
our novel approach could provide a different perspective for the development of
new and observationally reliable alternative models of gravity. | astro-ph_CO |
Gravitational Waves Notes, Issue #3 : "Stellar cusps in galactic nuclei
- How stars distribute around a massive black hole": GW Notes was born from the need for a journal where the distinct communities
involved in gravitation wave research might gather. While these three
communities - Astrophysics, General Relativity and Data Analysis - have made
significant collaborative progress over recent years, we believe that it is
indispensable to future advancement that they draw closer, and that they speak
a common idiom. For this GW Notes issue we have approached Miguel Preto
(Heidelberg University) to expand a recent work on how stars distribute around
massive black holes for our highlight article. | astro-ph_CO |
Solar-system tests of the inflation model with a Weyl term: Recently, there has been an interest in inflation and modified gravity with a
Weyl term added to the general-relativistic action (N. Derulle, M. Sasaki, Y.
Sendouda and A. Youssef, JCAP, 3, 040 (2011)). In this paper we study empirical
constraint on this modified gravity from solar-system experiments/observations.
We first derive linearized equation of motion in the weak field limit and solve
it for isolated system in the slow motion limit. We then use it to derive the
light propagation equations, and obtain the relativistic Shapiro time delay and
the light deflection in one-body central problem. Applying these results to the
solar-system measurements, we obtain constraints on the Weyl term parameter
{\gamma}_W; the most stringent constraint, which comes from the Cassini
relativistic time delay experiment, is for {\gamma}_W to be less than 0.0015
AU^2, or |{\gamma}_W|^(1/2) less than 0.039 AU (19 s). Analysis of precision
laboratory gravity experiments put further limit on the Weyl term parameter
{\gamma}_W to below the laboratory scale. | astro-ph_CO |
Understanding the neutrino mass constraints achievable by combining CMB
lensing and spectroscopic galaxy surveys: We perform a thorough examination of the neutrino mass ($M_\nu$) constraints
achievable by combining future spectroscopic galaxy surveys with cosmic
microwave background (CMB) experiments, focusing on the contribution of CMB
lensing and galaxy-CMB lensing. CMB lensing can help by breaking the
$M_\nu$-curvature degeneracy when combined with baryon acoustic oscillation
(BAO)-only measurements, but we demonstrate this combination wastes a great
deal of constraining power, as the broadband shape of the power spectrum
contributes significantly to constraints. We also expand on previous work to
demonstrate how cosmology-independent constraints on $M_\nu$ can be extracted
by combining measurements of the scale-dependence in the power spectrum caused
by neutrino free-streaming with the full power of future CMB surveys. These
free-streaming constraints are independent of the optical depth to the CMB
($\tau$) and competitive with constraints from BAOs for extended cosmologies,
even when both are combined with CMB lensing and galaxy-CMB lensing. | astro-ph_CO |
Probing cluster formation under extreme conditions: massive star
clusters in blue compact galaxies: The numerous and massive young star clusters in blue compact galaxies (BCGs)
are used to investigate the properties of their hosts. We test whether BCGs
follow claimed relations between cluster populations and their hosts, such as
the the fraction of the total luminosity contributed by the clusters as
function of the mean star formation rate density; the $V$ band luminosity of
the brightest youngest cluster as related to the mean host star formation rate;
and the cluster formation efficiency (i.e., the fraction of star formation
happening in star clusters) versus the density of the SFR. We find that BCGs
follow the trends, supporting a scenario where cluster formation and
environmental properties of the host are correlated. They occupy, in all the
diagrams, the regions of higher SFRs, as expected by the extreme nature of the
starbursts operating in these systems. We find that the star clusters
contribute almost to the 20 % of the UV luminosity of the hosts. We suggest
that the BCG starburst environment has most likely favoured the compression and
collapse of the giant molecular clouds, enhancing the local star formation
efficiency, so that massive clusters have been formed. The estimated cluster
formation efficiency supports this scenario. BCGs have a cluster formation
efficiency comparable to luminous IR galaxies and spiral starburst nuclei (the
averaged value is about 35 %) which is much higher than the 8 - 10 % reported
for quiescent spirals and dwarf star-forming galaxies. | astro-ph_CO |
Constraining dark sector perturbations II: ISW and CMB lensing
tomography: Any Dark Energy (DE) or Modified Gravity (MG) model that deviates from a
cosmological constant requires a consistent treatment of its perturbations,
which can be described in terms of an effective entropy perturbation and an
anisotropic stress. We have considered a recently proposed generic
parameterisation of DE/MG perturbations and compared it to data from the Planck
satellite and six galaxy catalogues, including temperature-galaxy (Tg), CMB
lensing-galaxy and galaxy-galaxy (gg) correlations. Combining these observables
of structure formation with tests of the background expansion allows us to
investigate the properties of DE/MG both at the background and the perturbative
level. Our constraints on DE/MG are mostly in agreement with the cosmological
constant paradigm, while we also find that the constraint on the equation of
state w (assumed to be constant) depends on the model assumed for the
perturbation evolution. We obtain $w=-0.92^{+0.20}_{-0.16}$ (95% CL; CMB+gg+Tg)
in the entropy perturbation scenario; in the anisotropic stress case the result
is $w=-0.86^{+0.17}_{-0.16}$. Including the lensing correlations shifts the
results towards higher values of w. If we include a prior on the expansion
history from recent Baryon Acoustic Oscillations (BAO) measurements, we find
that the constraints tighten closely around $w=-1$, making it impossible to
measure any DE/MG perturbation evolution parameters. If, however, upcoming
observations from surveys like DES, Euclid or LSST show indications for a
deviation from a cosmological constant, our formalism will be a useful tool
towards model selection in the dark sector. | astro-ph_CO |
First results from the IllustrisTNG simulations: radio haloes and
magnetic fields: We introduce the IllustrisTNG project, a new suite of cosmological
magnetohydrodynamical simulations performed with the moving-mesh code AREPO
employing an updated Illustris galaxy formation model. Here we focus on the
general properties of magnetic fields and the diffuse radio emission in galaxy
clusters. Magnetic fields are prevalent in galaxies, and their build-up is
closely linked to structure formation. We find that structure formation
amplifies the initial seed fields ($10^{-14}$ comoving Gauss) to the values
observed in low-redshift galaxies ($1-10\,\mu{\rm G}$). The magnetic field
topology is closely connected to galaxy morphology such that irregular fields
are hosted by early-type galaxies, while large-scale, ordered fields are
present in disc galaxies. Using two simple models for the energy distribution
of relativistic electrons we predict the diffuse radio emission of $280$
clusters with a baryonic mass resolution of $1.1\times 10^{7}\,{\rm
M_{\odot}}$, and generate mock observations for VLA, LOFAR, ASKAP and SKA. Our
simulated clusters show extended radio emission, whose detectability correlates
with their virial mass. We reproduce the observed scaling relations between
total radio power and X-ray emission, $M_{500}$, and the Sunyaev-Zel'dovich
$Y_{\rm 500}$ parameter. The radio emission surface brightness profiles of our
most massive clusters are in reasonable agreement with VLA measurements of Coma
and Perseus. Finally, we discuss the fraction of detected extended radio haloes
as a function of virial mass and source count functions for different
instruments. Overall our results agree encouragingly well with observations,
but a refined analysis requires a more sophisticated treatment of relativistic
particles in large-scale galaxy formation simulations. | astro-ph_CO |
Submillimetre Cosmology at High Angular Resolution: Over the last decade observations at submillimetre (submm) and millimetre
(mm) wavelengths, with their unique ability to trace molecular gas and dust,
have attained a central role in our exploration of galaxies at all redshifts.
Due to the limited sensitivities and angular resolutions of current submm/mm
telescopes, however, only the most luminous objects have been uncovered at high
redshifts, with interferometric follow-up observations succeeding in resolving
the dust and gas reservoirs in only a handful of cases. The coming years will
witness a drastic improvement in the current situation, thanks to the arrival
of a new suite of powerful submm observatories (single-dish and
interferometers) with an order of magnitude improvement in sensitivity and
resolution. In this overview I outline a few of what I expect to be the major
advances in the field of galaxy formation and evolution that these new
ground-breaking facilities will facilitate. | astro-ph_CO |
An interacting model for the cosmological dark sector: We discuss a new interacting model for the cosmological dark sector in which
the attenuated dilution of cold dark matter scales as $a^{-3}f(a)$, where f(a)
is an arbitrary function of the cosmic scale factor $a$. From thermodynamic
arguments, we show that f(a) is proportional to entropy source of the particle
creation process. In order to investigate the cosmological consequences of this
kind of interacting models, we expand f(a) in a power series and viable
cosmological solutions are obtained. Finally, we use current observational data
to place constraints on the interacting function f(a). | astro-ph_CO |
Influence of early dark matter halos on the primordial black holes
merger rate: Primordial black hole (PBH) binaries forming in the early Universe may
contribute to the merger events observed by the LIGO-Virgo-KAGRA
collaborations. Moreover, the inferred merger rate constraints the fraction of
PBH with masses $m \sim 10 \, M_{\odot}$ in the dark matter (DM) to $f_{PBH}
\lesssim 10^{-3}$. This constraint assumes that after the formation of PBH
binaries, they do not get destroyed or their parameters are not perturbed until
the merger. However, PBHs themselves contribute to the formation of early DM
structures in which the interactions between PBHs take place actively. This
leads to the fact that the binaries can be perturbed in such a way that their
lifetime becomes longer than the Hubble time $t_H$. In this work, we consider
the effect of the initial spatial Poisson distribution of PBHs on the structure
formation at the high redshifts $z \gtrsim 10$. Next, we explore the evolution
of such halos due to the interaction of PBHs with each other and with DM
particles. We show that the early halos evolve on timescales much shorter than
the age of the Universe. Furthermore, for fractions of PBHs $f_{PBH} < 1$, the
internal dynamics of a halo is significantly accelerated due to the dynamical
friction of PBHs against DM particles. As a result, a significant fraction of
binaries will be perturbed in such structures, and the gravitational waves
constraints on PBHs with masses $m \sim 10 \, M_{\odot}$ can be weakened to
$f_{PBH} \sim 0.1$. | astro-ph_CO |
Constraints on the velocity of gravitational waves from NANOGrav 15-year
data set: General relativity predicts that gravitational waves propagate at the speed
of light. Although ground-based gravitational-wave detectors have successfully
constrained the velocity of gravitational waves in the high-frequency range,
extending this constraint to the lower frequency range remains a challenge. In
this work, we utilize the deviations in the overlap reduction function for a
gravitational-wave background within pulsar timing arrays to investigate the
velocity of gravitational waves in the nanohertz frequency band. By analyzing
the NANOGrav 15-year data set, we obtain a well-constrained lower bound for the
velocity of gravitational waves that $v \gtrsim 0.87\,c$, where $c$ is the
speed of light. | astro-ph_CO |
Planck Early Results XXVI: Detection with Planck and confirmation by
XMM-Newton of PLCK G266.6-27.3, an exceptionally X-ray luminous and massive
galaxy cluster at z~1: We present first results on PLCK G266.6-27.3, a galaxy cluster candidate
detected at a signal-to-noise ratio of 5 in the Planck All Sky survey. An
XMM-Newton validation observation has allowed us to confirm that the candidate
is a bona fide galaxy cluster. With these X-ray data we measure an accurate
redshift, z = 0.94 +/- 0.02, and estimate the cluster mass to be M_500 = (7.8
+/- 0.8)e+14 solar masses. PLCK G266.6-27.3 is an exceptional system: its
luminosity of L_X(0.5-2.0 keV)=(1.4 +/- 0.05)e+45 erg/s, equals that of the two
most luminous known clusters in the z > 0.5 universe, and it is one of the most
massive clusters at z~1. Moreover, unlike the majority of high-redshift
clusters, PLCK G266.6-27.3 appears to be highly relaxed. This observation
confirms Planck's capability of detecting high-redshift, high-mass clusters,
and opens the way to the systematic study of population evolution in the
exponential tail of the mass function. | astro-ph_CO |
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