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Analytic calculation of the non-linear cosmic density-fluctuation power
spectrum in the Born approximation: We derive a non-perturbative, closed, analytic equation for the non-linear
power spectrum of cosmic density fluctuations. This result is based on our
kinetic field theory (KFT) of cosmic structure formation and on evaluating
particle interactions in the Born approximation. At redshift zero, relative
deviations between our analytic result and typical numerical results are ~ 15 %
on average up to wave numbers of k <= 10 h/Mpc. The theory underlying our
analytic equation is fully specified once the statistical properties of the
initial density and momentum fluctuations are set. It has no further adjustable
parameters. Apart from this equation, our main result is that the
characteristic non-linear deformations of the power spectrum at late cosmic
times are determined by the initial momentum correlations and a partial
compensation between diffusion damping and particle interactions. | A direct measure of free electron gas via the Kinematic
Sunyaev-Zel'dovich effect in Fourier-space analysis: We present the measurement of the kinematic Sunyaev-Zel'dovich (kSZ) effect
in Fourier space, rather than in real space. We measure the density-weighted
pairwise kSZ power spectrum, the first use of this promising approach, by
cross-correlating a cleaned Cosmic Microwave Background (CMB) temperature map,
which jointly uses both Planck Release 2 and Wilkinson Microwave Anisotropy
Probe nine-year data, with the two galaxy samples, CMASS and LOWZ, derived fr
om the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 12. With the
current data, we constrain the average optical depth $\tau$ multiplied by the
ratio of the Hubble parameter at redshift $z$ and the present day, $E=H/H_0$;
we find $\tau E = (3.95\pm1.62)\times10^{-5}$ for LOWZ and $\tau E = ( 1.25\pm
1.06)\times10^{-5}$ for CMASS, with the optimal angular radius of an aperture
photometry filter to estimate the CMB temperature distortion associ ated with
each galaxy. By repeating the pairwise kSZ power analysis for various aperture
radii, we measure the optical depth as a function of aperture ra dii. While
this analysis results in the kSZ signals with only evidence for a detection,
${\rm S/N}=2.54$ for LOWZ and $1.24$ for CMASS, the combination of future CMB
and spectroscopic galaxy surveys should enable precision measurements. We
estimate that the combination of CMB-S4 and data from DESI shoul d yield
detections of the kSZ signal with ${\rm S/N}=70-100$, depending on the
resolution of CMB-S4. |
The anamorphic universe: We introduce "anamorphic" cosmology, an approach for explaining the
smoothness and flatness of the universe on large scales and the generation of a
nearly scale-invariant spectrum of adiabatic density perturbations. The
defining feature is a smoothing phase that acts like a contracting universe
based on some Weyl frame-invariant criteria and an expanding universe based on
other frame-invariant criteria. An advantage of the contracting aspects is that
it is possible to avoid the multiverse and measure problems that arise in
inflationary models. Unlike ekpyrotic models, anamorphic models can be
constructed using only a single field and can generate a nearly scale-invariant
spectrum of tensor perturbations. Anamorphic models also differ from pre-big
bang and matter bounce models that do not explain the smoothness. We present
some examples of cosmological models that incorporate an anamorphic smoothing
phase. | Measuring the cosmological density field twice: A novel test of dark
energy using the CMB quadrupole: The scattering of cosmic microwave background (CMB) radiation in galaxy
clusters induces polarization signals according to the quadrupole anisotropy in
the photon distribution at the cluster location. This `remote quadrupole'
derived from the measurements of the induced polarization provides an
opportunity for reconstructing primordial fluctuations on large scales. We
discuss that comparing the local CMB quadrupoles predicted by these
reconstructed primordial fluctuations and the direct measurements done by CMB
satellites may enable us to test the dark energy beyond cosmic variance limits. |
The BAO+BBN take on the Hubble tension: Many attempts to solve the Hubble tension with extended cosmological models
combine an enhanced relic radiation density, acting at the level of background
cosmology, with new physical ingredients affecting the evolution of
cosmological perturbations. Several authors have pointed out the ability of
combined Baryon Acoustic Oscillation (BAO) and Big Bang Nucleosynthesis (BBN)
data to probe the background cosmological history independently of both CMB
maps and supernovae data. Using state-of-the-art assumptions on BBN, we confirm
that combined BAO, deuterium, and helium data are in tension with the SH0ES
measurements under the $\Lambda$CDM assumption at the 3.2$\sigma$ level, while
being in close agreement with the CMB value. We subsequently show that floating
the radiation density parameter $N_\mathrm{eff}$ only reduces the tension down
to the 2.6$\sigma$ level. This conclusion, totally independent of any CMB data,
shows that a high $N_\mathrm{eff}$ accounting for extra relics (either
free-streaming or self-interacting) does not provide an obvious solution to the
crisis, not even at the level of background cosmology. To circumvent this
strong bound, (i) the extra radiation has to be generated after BBN to avoid
helium bounds, and (ii) additional ingredients have to be invoked at the level
of perturbations to reconcile this extra radiation with CMB and LSS data. | First results of the Laser-Interferometric Detector for Axions (LIDA): We present the operating principle and the first observing run of a novel
kind of direct detector for axions and axion-like particles in the galactic
halo. Sensitive to the polarisation rotation of linearly polarised laser light
induced by an axion field, our experiment is the first detector of its kind
collecting scientific data. We discuss our current peak sensitivity of
$1.51\times 10^{-10}$ $\text{GeV}^{-1}$ (95 % confidence level) to the
axion-photon coupling strength in the axion mass range of $1.97$-$2.01$
$\text{neV}$ which is, for instance, motivated by supersymmetric grand-unified
theories. We also report on effects that arise in our high-finesse in-vacuum
cavity at unprecedented optical continuous-wave intensities. Our detector
already belongs to the most sensitive direct searches within its measurement
band, and our results pave the way towards surpassing the current sensitivity
limits in the mass range from $10^{-8}$ $\text{eV}$ down to $10^{-16}$
$\text{eV}$ via quantum-enhanced laser interferometry. |
Toward Accurate Modeling of the Nonlinear Matter Bispectrum: Standard
Perturbation Theory and Transients from Initial Conditions: Accurate modeling of nonlinearities in the galaxy bispectrum, the Fourier
transform of the galaxy three-point correlation function, is essential to fully
exploit it as a cosmological probe. In this paper, we present numerical and
theoretical challenges in modeling the nonlinear bispectrum. First, we test the
robustness of the matter bispectrum measured from N-body simulations using
different initial conditions generators. We run a suite of N-body simulations
using the Zel'dovich approximation and second-order Lagrangian perturbation
theory (2LPT) at different starting redshifts, and find that transients from
initial decaying modes systematically reduce the nonlinearities in the matter
bispectrum. To achieve 1% accuracy in the matter bispectrum for $z\le3$ on
scales $k<1$ $h$/Mpc, 2LPT initial conditions generator with initial redshift
of $z\gtrsim100$ is required. We then compare various analytical formulas and
empirical fitting functions for modeling the nonlinear matter bispectrum, and
discuss the regimes for which each is valid. We find that the next-to-leading
order (one-loop) correction from standard perturbation theory matches with
N-body results on quasi-linear scales for $z\ge1$. We find that the fitting
formula in Gil-Mar\'{\i}n et al. (2012) accurately predicts the matter
bispectrum for $z\le1$ on a wide range of scales, but at higher redshifts, the
fitting formula given in Scoccimarro & Couchman (2001) gives the best agreement
with measurements from N-body simulations. | Is the cosmological dark sector better modeled by a generalized
Chaplygin gas or by a scalar field?: Both scalar fields and (generalized) Chaplygin gases have been widely used
separately to characterize the dark sector of the Universe. Here we investigate
the cosmological background dynamics for a mixture of both these components and
quantify the fractional abundances that are admitted by observational data from
supernovae of type Ia and from the evolution of the Hubble rate. Moreover, we
study how the growth rate of (baryonic) matter perturbations is affected by the
dark-sector perturbations. |
The impact of spin temperature fluctuations on the 21-cm moments: This paper considers the impact of Lyman-alpha coupling and X-ray heating on
the 21-cm brightness-temperature one-point statistics (as predicted by
semi-numerical simulations). The X-ray production efficiency is varied over
four orders of magnitude and the hardness of the X-ray spectrum is varied from
that predicted for high-mass X-ray binaries, to the softer spectrum expected
from the hot inter-stellar medium. We find peaks in the redshift evolution of
both the variance and skewness associated with the efficiency of X-ray
production. The amplitude of the variance is also sensitive to the hardness of
the X-ray SED. We find that the relative timing of the coupling and heating
phases can be inferred from the redshift extent of a plateau that connects a
peak in the variance's evolution associated with Lyman-alpha coupling to the
heating peak. Importantly, we find that late X-ray heating would seriously
hamper our ability to constrain reionization with the variance. Late X-ray
heating also qualitatively alters the evolution of the skewness, providing a
clean way to constrain such models. If foregrounds can be removed, we find that
LOFAR, MWA and PAPER could constrain reionization and late X-ray heating models
with the variance. We find that HERA and SKA (phase 1) will be able to
constrain both reionization and heating by measuring the variance using
foreground-avoidance techniques. If foregrounds can be removed they will also
be able to constrain the nature of Lyman-alpha coupling. | New Statistical Perspective to The Cosmic Void Distribution: In this study, we obtain the size distribution of voids as a 3-parameter
redshift independent log-normal void probability function (VPF) directly from
the Cosmic Void Catalog (CVC). Although many statistical models of void
distributions are based on the counts in randomly placed cells, the log-normal
VPF that we here obtain is independent of the shape of the voids due to the
parameter-free void finder of the CVC. We use three void populations drawn from
the CVC generated by the Halo Occupation Distribution (HOD) Mocks which are
tuned to three mock SDSS samples to investigate the void distribution
statistically and the effects of the environments on the size distribution. As
a result, it is shown that void size distributions obtained from the HOD Mock
samples are satisfied by the 3-parameter log-normal distribution. In addition,
we find that there may be a relation between hierarchical formation, skewness
and kurtosis of the log-normal distribution for each catalog. We also show that
the shape of the 3-parameter distribution from the samples is strikingly
similar to the galaxy log-normal mass distribution obtained from numerical
studies. This similarity of void size and galaxy mass distributions may
possibly indicate evidence of nonlinear mechanisms affecting both voids and
galaxies, such as large scale accretion and tidal effects. Considering in this
study all voids are generated by galaxy mocks and show hierarchical structures
in different levels, it may be possible that the same nonlinear mechanisms of
mass distribution affect the void size distribution. |
On the evolution of the HI column density distribution in cosmological
simulations: We use a set of cosmological simulations combined with radiative transfer
calculations to investigate the distribution of neutral hydrogen in the
post-reionization Universe. We assess the contributions from the metagalactic
ionizing background, collisional ionization and diffuse recombination radiation
to the total ionization rate at redshifts z=0-5. We find that the densities
above which hydrogen self-shielding becomes important are consistent with
analytic calculations and previous work. However, because of diffuse
recombination radiation, whose intensity peaks at the same density, the
transition between highly ionized and self-shielded regions is smoother than
what is usually assumed. We provide fitting functions to the simulated
photoionization rate as a function of density and show that post-processing
simulations with the fitted rates yields results that are in excellent
agreement with the original radiative transfer calculations. The predicted
neutral hydrogen column density distributions agree very well with the
observations. In particular, the simulations reproduce the remarkable lack of
evolution in the column density distribution of Lyman limit and weak damped
Ly\alpha\ systems below z = 3. The evolution of the low column density end is
affected by the increasing importance of collisional ionization with decreasing
redshift. On the other hand, the simulations predict the abundance of strong
damped Ly\alpha\ systems to broadly track the cosmic star formation rate
density. | Chance Estimations for Detecting Gravitational Waves with LIGO/Virgo
Associated with Gamma Ray Bursts: Short Gamma Ray Bursts (SGRB) are believed to originate from the merger of
two compact objects. If this scenario is correct, SGRB will be accompanied by
the emission of strong gravitational waves, detectable by current or planned GW
detectors, such as LIGO and Virgo. No detection of a gravitational wave has
been made up to date. In this paper I will use a set of SGRB with observed
redshifts to fit a model describing the cumulative number of SGRB as a function
of redshift, to determine the rate of such merger events in the nearby
universe. These estimations will be used to make probability statements about
detecting a gravitational wave associated with a short gamma ray burst during
the latest science run of LIGO/Virgo. Chance estimations for the enhanced and
advanced detectors will also be made, and a comparison between the rates
deduced from this work will be compared to the existing literature. |
The morphological dependent Tully-Fisher relation of spiral galaxies: The Tully-Fisher relation of spiral galaxies shows notable dependence on
morphological types, with earlier type spirals having systematically lower
luminosity at fixed maximum rotation velocity $V_{max}$. This decrement of
luminosity is more significant in shorter wavelengths. By modeling the rotation
curve and stellar population of different morphological type spiral galaxies in
combination, we find the $V_{max}$ of spiral galaxies is weakly dependent on
the morphological type, whereas the difference of the stellar population
originating from the bulge disk composition effect mainly account for the
morphological type dependence of the Tully-Fisher relation. | Dark Energy in the Swampland: In this Letter, we study the implications of string Swampland criteria for
dark energy in view of ongoing and future cosmological observations. If string
theory should be the ultimate quantum gravity theory, there is evidence that
exact de Sitter solutions with a positive cosmological constant cannot describe
the fate of the late-time universe. Even though cosmological models with dark
energy given by a scalar field $\pi$ evolving in time are not in direct tension
with string theory, they have to satisfy the Swampland criteria
$|\Delta\pi|<d\sim\mathcal{O}(1)$ and $|V'|/V>c\sim\mathcal{O}(1)$, where $V$
is the scalar field potential. In view of the restrictive implications that the
Swampland criteria have on dark energy, we investigate the accuracy needed for
future observations to tightly constrain standard dark-energy models. We find
that current 3-$\sigma$ constraints with $c \lesssim 1.35$ are still well in
agreement with the string Swampland criteria. However, Stage-4 surveys such as
Euclid, LSST and DESI, tightly constraining the equation of state $w(z)$, will
start putting surviving quintessence models into tensions with the string
Swampland criteria by demanding $c<0.4$. We further investigate whether any
idealised futuristic survey will ever be able to give a decisive answer to the
question whether the cosmological constant would be preferred over a
time-evolving dark-energy model within the Swampland criteria. Hypothetical
surveys with a reduction in the uncertainties by a factor of $\sim20$ compared
to Euclid would be necessary to reveal strong tension between quintessence
models obeying the string Swampland criteria and observations by pushing the
allowed values down to $c<0.1$. In view of such perspectives, there will be
fundamental observational limitations with future surveys. |
How Do Star-Forming Galaxies at Z>3 Assemble Their Masses?: We investigate how star-forming galaxies typically assemble their masses at
high redshift. Using the deep multi-wavelength coverage of the GOODS dataset,
we measure stellar mass of a large sample of star-forming galaxies at z~4 and
5, and make a robust determination of stellar mass function (SMF). We report a
broad correlation between stellar mass and UV luminosity, such that more
UV-luminous galaxies are, on average, more massive. However, the correlation
has a substantial intrinsic scatter evidenced by a non-negligible number of
UV-faint but massive galaxies. Furthermore, the low-mass end of the SMF does
not rise as steeply as the UV luminosity function (alpha_UVLF} -(1.7-1.8),
alpha_SMF -(1.3-1.4)) of the same galaxies. In a smooth formation scenario
where star formation (SF) is sustained at the observed rates for a long time,
these galaxies would have accumulated more mass (by a factor of ~3) than
observed and therefore the SMF would mirror more closely that of the UVLF. The
relatively shallow slope of the SMF is due to the fact that many of the
UV-selected galaxies are not massive enough, and therefore are too faint in
their rest-frame optical bands, to be detected in the current observations. Our
results favor a episodic formation history in which SF in low-mass galaxies
vary significantly over time, a scenario favored by galaxy clustering. Our
findings for the UV-faint galaxies are in contrast with those found for more
UV-luminous galaxies, which exhibit tighter SFR-M_star correlations. The
discrepancy may suggest that galaxies at different luminosities may have
different evolutionary paths. | Helium Reionization Simulations. III. The Helium Lyman-$α$ Forest: In La Plante et al. (2017), we presented a new suite of hydrodynamic
simulations with the aim of accurately capturing the process of helium II
reionization. In this paper, we discuss the observational signatures present in
the He II Ly$\alpha$ forest. We show that the effective optical depth of the
volume $\tau_\mathrm{eff}$ is not sufficient for capturing the ionization state
of helium II, due to the large variance inherent in sightlines. However, the He
II flux PDF can be used to determine the timing of helium II reionization. The
amplitude of the one-dimensional flux power spectrum can also determine the
ionization state of helium II. We show that even given the currently limited
number of observations ($\sim$50 sightlines), measurements of the flux PDF can
yield information about helium II reionization. Further, measurements using the
one-dimensional power spectrum can provide clear indications of the timing of
reionization, as well as the relative bias of sources of ionizing radiation. |
The void-galaxy cross-correlation function with massive neutrinos and
modified gravity: Massive neutrinos and $f(R)$ modified gravity have degenerate observational
signatures that can impact the interpretation of results in galaxy survey
experiments, such as cosmological parameter estimations and gravity model
tests. Because of this, it is important to investigate astrophysical
observables that can break these degeneracies. Cosmic voids are sensitive to
both massive neutrinos and modifications of gravity and provide a promising
ground for disentangling the above mentioned degeneracies. In order to analyse
cosmic voids in the context of non-$\Lambda$CDM cosmologies, we must first
understand how well the current theoretical framework operates in these
settings. We performed a suite of simulations with the RAMSES-based N-body code
ANUBISIS, including massive neutrinos and $f(R)$ modified gravity both
individually and simultaneously. The data from the simulations were compared to
models of the void velocity profile and the void-halo cross-correlation
function (CCF). This was done both with the real space simulation data as model
input and by applying a reconstruction method to the redshift space data. In
addition, we ran Markov chain Monte Carlo (MCMC) fits on the data sets to
assess the capability of the models to reproduce the fiducial simulation values
of $f\sigma_8(z)$ and the Alcock-Paczy\`{n}ski parameter, $\epsilon$. The void
modelling applied performs similarly for all simulated cosmologies, indicating
that more accurate models and higher resolution simulations are needed in order
to directly observe the effects of massive neutrinos and $f(R)$ modified
gravity through studies of the void-galaxy CCF. The MCMC fits show that the
choice of void definition plays an important role in the recovery of the
correct cosmological parameters, but otherwise, there is no clear distinction
between the ability to reproduce $f\sigma_8$ and $\epsilon$ for the various
simulations. | Cosmological constraints on the generalized holographic dark energy: We use the Markov ChainMonte Carlo method to investigate global constraints
on the generalized holographic (GH) dark energy with flat and non-flat universe
from the current observed data: the Union2 dataset of type supernovae Ia
(SNIa), high-redshift Gamma-Ray Bursts (GRBs), the observational Hubble data
(OHD), the cluster X-ray gas mass fraction, the baryon acoustic oscillation
(BAO), and the cosmic microwave background (CMB) data. The most stringent
constraints on the GH model parameter are obtained. In addition, it is found
that the equation of state for this generalized holographic dark energy can
cross over the phantom boundary wde =-1. |
Looking for the first galaxies: Lensing or blank fields?: The identification and study of the first galaxies remains one of the most
exciting topics in observational cosmology. The determination of the best
possible observing strategies is a very important choice in order to build up a
representative sample of spectroscopically confirmed sources at high-z (z>7),
beyond the limits of present-day observations. This paper is intended to
precisely adress the relative efficiency of lensing and blank fields in the
identification and study of galaxies at 6<z<12. The detection efficiency and
field-to-field variance are estimated from direct simulations of both blank and
lensing fields observations. The presence of a strong-lensing cluster along the
line of sight has a dramatic effect on the number of observed sources, with a
positive magnification bias in typical ground-based ``shallow'' surveys
(AB<~25.5). The positive magnification bias increases with the redshift of
sources and decreases with both depth of the survey and the size of the
surveyed area. The maximum efficiency is reached for lensing clusters at
z~0.1-0.3. Observing blank fields in shallow surveys is particularly
inefficient as compared to lensing fields if the UV LF for LBGs is strongly
evolving at z>~7. Also in this case, the number of z>8 sources expected at the
typical depth of JWST (AB~28-29) is much higher in lensing than in blank fields
(e.g. a factor of ~10 for AB<~28). Blank field surveys with a large field of
view are needed to prove the bright end of the LF at z>6-7, whereas lensing
clusters are particularly useful for exploring the mid to faint end of the LF. | Dust-Obscured Galaxies in the Local Universe: We use Wide-field Infrared Survey Explorer (WISE), AKARI, and Galaxy
Evolution Explorer (GALEX) data to select local analogs of high-redshift (z~2)
dust obscured galaxies (DOGs). We identify 47 local DOGs with S_{12\mu
m}/S_{0.22 \mu m}>892 and S_{12\mu m}>20 mJy at 0.05<z<0.08 in the Sloan
Digital Sky Survey data release 7. The infrared luminosities of these DOGs are
in the range 3.4x10^{10} (L_\odot)<L_{IR}<7.0x10^{11} (L_\odot) with a median
L_{IR} of 2.1x10^{11} (L_\odot). We compare the physical properties of local
DOGs with a control sample of galaxies that have lower $S_{12\mu m}/S_{0.22 \mu
m}$ but have similar redshift, IR luminosity, and stellar mass distributions.
Both WISE 12 micron and GALEX near-ultraviolet (NUV) flux densities of DOGs
differ from the control sample of galaxies, but the difference is much larger
in the NUV. Among the 47 DOGs, 36\pm7% have small axis ratios in the optical
(i.e., b/a<0.6), larger than the fraction among the control sample (17\pm3%).
There is no obvious sign of interaction for many local DOGs. No local DOGs have
companions with comparable optical magnitudes closer than ~50 kpc. The large-
and small-scale environments of DOGs are similar to the control sample. Many
physical properties of local DOGs are similar to those of high-z DOGs, even
though the IR luminosities of local objects are an order of magnitude lower
than for the high-z objects: the presence of two classes (active galactic
nuclei- and star formation-dominated) of DOGs, abnormal faintness in the UV
rather than extreme brightness in the mid-infrared, and diverse optical
morphology. These results suggest a common underlying physical origin of local
and high-z DOGs. Both seem to represent the high-end tail of the dust
obscuration distribution resulting from various physical mechanisms rather than
a unique phase of galaxy evolution. |
The measurements of matter density perturbations amplitude from
cosmological data: We compare various physically different measurements of linear matter density
perturbation amplitude, $sigma_8$, which are obtained from the observations of
CMB anisotropy, galaxy cluster mass function, weak gravitation lensing, matter
power spectrum and redshift space distortions. We show that $\sigma_8$
measurement from CMB gravitational lensing signal based on Planck CMB
temperature anisotropy data at high multipoles, $\ell>1000$, contradict to all
other measurements obtained both from remaining Planck CMB anisotropy data and
from other cosmological data, at about $3.7\sigma$ significance level.
Therefore, these data currently should not be combined with other data to
constrain cosmological parameters.
With the exception of Planck CMB temperature anisotropy data at high
multipoles, all other measurements are in good agreement between each other and
give the following measurements of linear density perturbation amplitude:
$\sigma_8=0.792\pm0.006$, mean density of the Universe:
$\Omega_m=0.287\pm0.007$, and Hubble constant: $H_0 = 69.4\pm
0.6$~km~s$^{-1}$~Mpc$^{-1}$. Taking in account the data on baryon acoustic
oscillations and (or) direct measurements of the Hubble constant, one can
obtain different constraints on sum of neutrino mass and number of relativistic
species. | Accidental deep field bias in CMB T and SNe $z$ correlation: Evidence presented by Yershov, Orlov and Raikov apparently showed that the
WMAP/Planck cosmic microwave background (CMB) pixel-temperatures (T) at
supernovae (SNe) locations tend to increase with increasing redshift ($z$).
They suggest this correlation could be caused by the Integrated Sachs-Wolfe
effect and/or by some unrelated foreground emission. Here, we assess this
correlation independently using Planck 2015 SMICA R2.01 data and, following
Yershov et al., a sample of 2783 SNe from the Sternberg Astronomical Institute.
Our analysis supports the prima facie existence of the correlation but
attributes it to a composite selection bias (high CMB T $\times$ high SNe $z$)
caused by the accidental alignment of seven deep survey fields with CMB
hotspots. These seven fields contain 9.2 per cent of the SNe sample (256 SNe).
Spearman's rank-order correlation coefficient indicates the correlation present
in the whole sample ($\rho_s = 0.5$, p-value $= 6.7 \times 10^{-9}$) is
insignificant for a sub-sample of the seven fields together ($\rho_s = 0.2$,
p-value $= 0.2$) and entirely absent for the remainder of the SNe ($\rho_s =
0.1$, p-value $= 0.6$). We demonstrate the temperature and redshift biases of
these seven deep fields, and estimate the likelihood of their falling on CMB
hotspots by chance is at least $\sim$ 6.8 per cent (approximately 1 in 15). We
show that a sample of 7880 SNe from the Open Supernova Catalogue exhibits the
same effect and we conclude that the correlation is an accidental but not
unlikely selection bias. |
Cosmic Shear E/B-mode Estimation with Binned Correlation Function Data: In this work I study the problem of E/B-mode separation with binned cosmic
shear two-point correlation function data. Motivated by previous work on
E/B-mode separation with shear two-point correlation functions and the
practical considerations of data analysis, I consider E/B-mode estimators which
are linear combinations of the binned shear correlation function data points. I
demonstrate that these estimators mix E- and B-modes generally. I then show how
to define estimators which minimize this E/B-mode mixing and give practical
recipes for their construction and use. Using these optimal estimators, I
demonstrate that the vector space composed of the binned shear correlation
function data points can be decomposed into approximately ambiguous, E- and
B-mode subspaces. With simple Fisher information estimates, I show that a
non-trivial amount of information on typical cosmological parameters is
contained in the ambiguous mode subspace computed in this formalism. Next, I
give two examples which apply these practical estimators and recipes to generic
problems in cosmic shear data analysis: data compression and spatially locating
B-mode contamination. In particular, by using wavelet-like estimators with the
shear correlation functions directly, one can pinpoint B-mode contamination to
specific angular scales and extract information on its shape. Finally, I
discuss how these estimators can be used as part of blinded or closed-box
cosmic shear data analyses in order to assess and find B-mode contamination at
high-precision while avoiding observer biases. | HYREC-2: a highly accurate sub-millisecond recombination code: We present the new recombination code HYREC-2, holding the same accuracy as
the state-of-the-art codes HYREC and COSMOREC and, at the same time, surpassing
the computational speed of the code RECFAST commonly used for CMB-anisotropy
data analyses. HYREC-2 is based on an effective 4-level atom model, accounting
exactly for the non-equilibrium of highly excited states of hydrogen, and very
accurately for radiative transfer effects with a correction to the
Lyman-$\alpha$ escape rate. The latter is computed with the original HYREC, and
tabulated, as a function of temperature, along with its derivatives with
respect to the relevant cosmological parameters. This enables the code to keep
the same accuracy as the original HYREC-2 over the full 99.7% confidence region
of cosmological parameters currently allowed by Planck, while running in under
one millisecond on a standard laptop. Our code leads to no noticeable bias in
any cosmological parameters even in the case of an ideal cosmic-variance
limited experiment up to $\ell$ = 5000. Beyond CMB anisotropy calculations,
HYREC-2 will be a useful tool to compute various observables that depend on the
recombination and thermal history, such as the recombination spectrum or the
21-cm signal. |
Linking the spin evolution of massive black holes to galaxy kinematics: We present the results of a semianalytical model that evolves the masses and
spins of massive black holes together with the properties of their host
galaxies along the cosmic history. As a consistency check, our model broadly
reproduces a number of observations, e.g. the cosmic star formation history,
the black hole mass and luminosity function and the galaxy mass function at low
redshift, the black hole to bulge mass relation, and the morphological
distribution at low redshift. For the first time in a semianalytical
investigation, we relax the simplifying assumptions of perfect coherency or
perfect isotropy of the gas fueling the black holes. The dynamics of gas is
instead linked to the morphological properties of the host galaxies, resulting
in different spin distributions for black holes hosted in different galaxy
types. We compare our results with the observed sample of spin measurements
obtained through broad K$\alpha$ iron line fitting. The observational data
disfavor both accretion along a fixed direction and isotropic fueling.
Conversely, when the properties of the accretion flow are anchored to the
kinematics of the host galaxy, we obtain a good match between theoretical
expectations and observations. A mixture of coherent accretion and phases of
activity in which the gas dynamics is similar to that of the stars in bulges
(i.e., with a significant velocity dispersion superimposed to a net rotation)
best describes the data, adding further evidence in support to the coevolution
of massive black holes and their hosts. | Testing Einstein's gravity and dark energy with growth of matter
perturbations: Indications for new Physics?: The growth index of matter fluctuations is computed for ten distinct
accelerating cosmological models and confronted to the latest growth rate data
via a two-step process. First, we implement a joint statistical analysis in
order to place constraints on the free parameters of all models using solely
background data. Second, using the observed growth rate of clustering from
various galaxy surveys we test the performance of the current cosmological
models at the perturbation level while either marginalizing over $\sigma_8$ or
having it as a free parameter. As a result, we find that at a statistical
level, i.e. after considering the best-fit $\chi^2$ or the value of the Akaike
information criterion, most models are in very good agreement with the growth
rate data and are practically indistinguishable from $\Lambda$CDM. However,
when we also consider the internal consistency of the models by comparing the
theoretically predicted values of $(\gamma_0, \gamma_1)$, i.e. the value of the
growth index $\gamma(z)$ and its derivative today, with the best-fit ones, we
find that the predictions of three out of ten dark energy models are in mild
tension with the best-fit ones when $\sigma_8$ is marginalized over. When
$\sigma_8$ is free we find that most models are not only in mild tension, but
also predict low values for $\sigma_8$. This could be attributed to either a
systematic problem with the growth-rate data or the emergence of new physics at
low redshifts, with the latter possibly being related to the well-known issue
of the lack of power at small scales. Finally, by utilizing mock data based on
an LSST-like survey we show that with future surveys and by using the growth
index parameterization, it will be possible to resolve the issue of the low
$\sigma_8$ but also the tension between the fitted and theoretically predicted
values of $(\gamma_0, \gamma_1)$. |
Low-Scale Inflationary Magnetogenesis without Baryon Isocurvature
Problem: Primordial magnetogenesis is an intriguing possibility to explain the origin
of intergalactic magnetic fields (IGMFs). However, the baryon isocurvature
problem has recently been pointed out, ruling out all magnetogenesis models
operating above the electroweak scale. In this letter, we show that lower-scale
inflationary scenarios with a Chern-Simons coupling can evade this problem. We
propose concrete inflationary models whose reheating temperatures are lower
than the electroweak scale and numerically compute the amount of magnetic
fields generated during inflation and reheating. We find that, for lower
reheating temperatures, the magnetic helicity decreases significantly. It is
also possible to generate fully helical magnetic fields by modifying the
inflaton potential. In both cases, the produced magnetic fields can be strong
enough to explain the observed IGMFs, while avoiding the baryon isocurvature
problem. | eLISA: Astrophysics and cosmology in the millihertz regime: This document introduces the exciting and fundamentally new science and
astronomy that the European New Gravitational Wave Observatory (NGO) mission
(derived from the previous LISA proposal) will deliver. The mission (which we
will refer to by its informal name "eLISA") will survey for the first time the
low-frequency gravitational wave band (about 0.1 mHz to 1 Hz), with sufficient
sensitivity to detect interesting individual astrophysical sources out to z =
15. The eLISA mission will discover and study a variety of cosmic events and
systems with high sensitivity: coalescences of massive black holes binaries,
brought together by galaxy mergers; mergers of earlier, less-massive black
holes during the epoch of hierarchical galaxy and black-hole growth;
stellar-mass black holes and compact stars in orbits just skimming the horizons
of massive black holes in galactic nuclei of the present era; extremely compact
white dwarf binaries in our Galaxy, a rich source of information about binary
evolution and about future Type Ia supernovae; and possibly most interesting of
all, the uncertain and unpredicted sources, for example relics of inflation and
of the symmetry-breaking epoch directly after the Big Bang. eLISA's
measurements will allow detailed studies of these signals with high
signal-to-noise ratio, addressing most of the key scientific questions raised
by ESA's Cosmic Vision programme in the areas of astrophysics and cosmology.
They will also provide stringent tests of general relativity in the
strong-field dynamical regime, which cannot be probed in any other way. This
document not only describes the science but also gives an overview on the
mission design and orbits. |
Cosmography by GRBs : Gamma Ray Bursts as possible distance indicators: A new method to constrain the cosmological equation of state is proposed by
using combined samples of gamma-ray bursts (GRBs) and supernovae (SNeIa). The
Chevallier-Polarski-Linder parameterization is adopted for the equation of
state in order to find out a realistic approach to achieve the
deceleration/acceleration transition phase of dark energy models. As results,
we find that GRBs, calibrated by SNeIa, could be, at least, good distance
indicators capable of discriminating cosmological models with respect to
$\Lambda$CDM at high redshift. | Droplet collapse during strongly supercooled transitions: We simulate the decay of isolated, spherically symmetric droplets in a
cosmological phase transition. It has long been posited that such heated
droplets of the metastable state could form, and they have recently been
observed in 3D multi-bubble simulations. In those simulations, the droplets
were associated with a reduction in the wall velocity and a decrease in the
kinetic energy of the fluid, with a consequent suppression in the gravitational
wave power spectrum. In the present work, we track the wall speed and kinetic
energy production in isolated droplets and compare them to those found in
multi-bubble collisions. The late-time wall velocities that we observe match
those of the 3D simulations, though we find that the spherical simulations are
a poor predictor of the kinetic energy production. This implies that
spherically symmetric simulations could be used to refine baryogenesis
predictions due to the formation of droplets, but not to estimate any
accompanying suppression of the gravitational wave signal. |
A designer approach to $f(Q)$ gravity and cosmological implications: We investigate the evolution of linear perturbations in the Symmetric
Teleparallel Gravity, namely $f(Q)$ gravity, for which we design the $f(Q)$
function to match specific expansion histories. We consider different
evolutions of the effective dark energy equation of state, $w_Q(a)$, which
includes $w_Q=-1$, a constant $w_Q \neq -1$ and a fast varying equation of
state. We identify clear patterns in the effective gravitational coupling,
which accordingly modifies the linear growth of large scale structures. We
provide theoretical predictions for the product of the growth rate $\tilde{f}$
and the root mean square of matter fluctuations $\sigma_8$, namely
$\tilde{f}\sigma_8$ and for the sign of the cross-correlation power spectrum of
the galaxy fluctuations and the cosmic microwave background radiation
anisotropies. These properties can be used to distinguish the $f(Q)$ gravity
from the standard cosmological model using accurate cosmological observations. | On the Amplitude and Stokes Parameters of a Stochastic
Gravitational-Wave Background: The direct detection of gravitational waves has provided new opportunities
for studying the universe, but also new challenges, such as the detection and
characterization of stochastic gravitational-wave backgrounds at different
gravitational-wave frequencies. In this paper we examine two different methods
for their description, one based on the amplitude of a gravitational-wave
signal and one on its Stokes parameters. We find that the Stokes parameters are
able to describe anisotropic and correlated backgrounds, whereas the usual
power spectra of the amplitudes cannot -- i.e. the Stokes spectra are sensitive
to properties such as the spatial distribution of the gravitational-wave
sources in a realistic backgrounds. |
Insights on the Formation, Evolution, and Activity of Massive Galaxies
From Ultra-Compact and Disky Galaxies at z=2-3: We present our results on the structure and activity of massive galaxies at
z=1-3 using one of the largest (166 with M_star>=5e10 M_sun) and most diverse
samples of massive galaxies derived from the GOODS-NICMOS survey: (1) Sersic
fits to deep NIC3/F160W images indicate that the rest-frame optical structures
of massive galaxies are very different at z=2-3 compared to z~0. Approximately
40% of massive galaxies are ultra-compact (r_e<=2 kpc), compared to less than
1% at z~0. Furthermore, most (~65%) systems at z=2-3 have a low Sersic index
n<=2, compared to ~13% at z~0. We present evidence that the n<=2 systems at
z=2-3 likely contain prominent disks, unlike most massive z~0 systems. (2)
There is a correlation between structure and star formation rates (SFR). The
majority (~85%) of non-AGN massive galaxies at z=2-3, with SFR high enough to
yield a 5 sigma (30 micro Jy) 24 micron Spitzer detection have low n<=2. Such
n<=2 systems host the highest SFR. (3) The frequency of AGN is ~40% at z=2-3.
Most (~65%) AGN hosts have disky (n<=2) morphologies. Ultra-compact galaxies
appear quiescent in terms of both AGN activity and star formation. (4) Large
stellar surface densities imply massive galaxies at z=2-3 formed via rapid,
highly dissipative events at z>2. The large fraction of n<=2 disky systems
suggests cold mode accretion complements gas-rich major mergers at z>2. In
order for massive galaxies at z=2-3 to evolve into present-day massive E/S0s,
they need to significantly increase (n, r_e). Dry minor and major mergers may
play an important role in this process. | Have Pulsar Timing Arrays detected the Hot Big Bang? Gravitational Waves
from Strong First Order Phase Transitions in the Early Universe: The origins of matter and radiation in the universe lie in a Hot Big Bang. We
present a number of well-motivated cosmologies in which the Big Bang occurs
through a strong first order phase transition -- either at the end of
inflation, after a period of kination ("Kination-Induced Big Bang"), or after a
second period of vacuum-domination in the early universe ("Supercooled Big
Bang"); we also propose a "Dark Big Bang" where only the dark matter in the
Universe is created in a first-order phase transition much after inflation. In
all of these scenarios, the resulting gravitational radiation can explain the
tentative signals reported by the NANOGrav, Parkes and European Pulsar Timing
Array experiments if the reheating temperature of the Hot Big Bang, and
correspondingly the energy scale of the false vacuum, falls in the range $T_*
\sim \rho_{{\rm vac}}^{1/4} $= MeV--100 GeV. All the same models at higher
reheating temperatures will be of interest to upcoming ground- and space-based
interferometer searches for gravitational waves at larger frequency. |
A minimal power-spectrum-based moment expansion for CMB B-mode searches: The characterization and modeling of polarized foregrounds has become a
critical issue in the quest for primordial $B$-modes. A typical method to
proceed is to factorize and parametrize the spectral properties of foregrounds
and their scale dependence (i.e. assuming that foreground spectra are well
described everywhere by their sky average). Since in reality foreground
properties vary across the Galaxy, this assumption leads to inaccuracies in the
model that manifest themselves as biases in the final cosmological parameters
(in this case the tensor-to-scalar ratio $r$). This is particularly relevant
for surveys over large fractions of the sky, such as the Simons Observatory
(SO), where the spectra should be modeled over a distribution of parameter
values. Here we propose a method based on the existing ``moment expansion''
approach to address this issue in a power-spectrum-based analysis that is
directly applicable in ground-based multi-frequency data. Additionally, the
method uses only a small set of parameters with simple physical interpretation,
minimizing the impact of foreground uncertainties on the final $B$-mode
constraints. We validate the method using SO-like simulated observations,
recovering an unbiased estimate of the tensor-to-scalar ratio $r$ with standard
deviation $\sigma(r)\simeq0.003$, compatible with official forecasts. When
applying the method to the public BICEP2/Keck data, we find an upper bound
$r<0.06$ ($95\%\,{\rm C.L.}$), compatible with the result found by BICEP2/Keck
when parametrizing spectral index variations through a scale-independent
frequency decorrelation parameter. We also discuss the formal similarities
between the power spectrum-based moment expansion and methods used in the
analysis of CMB lensing. | Variation in the dust spectral index across M33: Using the Herschel PACS and SPIRE FIR/submm data, we investigate variations
in the dust spectral index $\beta$ in the nearby spiral galaxy M33 at a linear
resolution of 160 pc. We use an iteration method in two different approaches,
single and two-component modified black body models. In both approaches,
$\beta$ is higher in the central disk than in the outer disk similar to the
dust temperature. There is a positive correlation between $\beta$ and Halpha as
well as with the molecular gas traced by CO(2-1). A Monte-Carlo simulation
shows that the physical parameters are better constrained when using the
two-component model. |
Decoding the bispectrum of single-field inflation: Galileon fields arise naturally from the decoupling limit of massive
gravities, and possess special self-interactions which are protected by a
spacetime generalization of Galilean symmetry. We briefly revisit the
inflationary phenomenology of Galileon theories. Working from recent
computations of the fluctuation Lagrangian to cubic order in the most general
model with second-order equations of motion, we show that a distinct shape is
present but with suppressed amplitude. A similar shape has been found in other
higher-derivative models. It may be visible in a theory tuned to suppress the
leading-order shapes, or if the overall bispectrum has large amplitude. Using a
partial-wave expansion of the bispectrum, we suggest a possible origin for the
frequent appearance of this shape. It follows that models with very disparate
microphysics can produce very similar bispectra. We argue that it may be more
profitable to distinguish these models by searching for relations between the
amplitudes of these common shapes. We illustrate this method using the example
of DBI and k-inflation. | The metallicity evolution of low mass galaxies: New constraints at
intermediate redshift: We present abundance measurements from 26 emission-line selected galaxies at
z~0.6-0.7. By reaching stellar masses as low as 10^8 M_{\sun}, these
observations provide the first measurement of the intermediate redshift
mass-metallicity (MZ) relation below 10^9 M_{\sun} For the portion of our
sample above M > 10^9 M_{\sun} (8/26 galaxies), we find good agreement with
previous measurements of the intermediate redshift MZ relation. Compared to the
local relation, we measure an evolution that corresponds to a 0.12 dex decrease
in oxygen abundances at intermediate redshifts. This result confirms the trend
that metallicity evolution becomes more significant towards lower stellar
masses, in keeping with a downsizing scenario where low mass galaxies evolve
onto the local MZ relation at later cosmic times. We show that these galaxies
follow the local fundamental metallicity relation, where objects with higher
specific (mass-normalized) star formation rates (SFRs) have lower
metallicities. Furthermore, we show that the galaxies in our sample lie on an
extrapolation of the SFR-M_{*} relation (the star-forming main sequence).
Leveraging the MZ relation and star-forming main sequence (and combining our
data with higher mass measurements from the literature), we test models that
assume an equilibrium between mass inflow, outflow and star formation. We find
that outflows are required to describe the data. By comparing different outflow
prescriptions, we show that momentum driven winds can describe the MZ relation;
however, this model under-predicts the amount of star formation in low mass
galaxies. This disagreement may indicate that preventive feedback from
gas-heating has been overestimated, or it may signify a more fundamental
deviation from the equilibrium assumption. |
Inflation with moderately sharp features in the speed of sound: GSR and
in-in formalism for power spectrum and bispectrum: We continue the study of mild transient reductions in the speed of sound of
the adiabatic mode during inflation, of their effect on the primordial power
spectrum and bispectrum, and of their detectability in the Cosmic Microwave
Background (CMB). We focus on the regime of \emph{moderately sharp} mild
reductions in the speed of sound during uninterrupted slow-roll inflation, a
theoretically well motivated and self-consistent regime that admits an
effective single-field description. The signatures on the power spectrum and
bispectrum were previously computed using a slow-roll Fourier transform (SRFT)
approximation, and here we compare it with generalized slow-roll (GSR) and
in-in methods, for which we derive new formulas that account for moderately
sharp features. The agreement between them is excellent, and also with the
power spectrum obtained from the numerical solution to the equation of motion.
We show that, in this regime, the SRFT approximation correctly captures with
simplicity the effect of higher derivatives of the speed of sound in the mode
equation, and makes manifest the correlations between power spectrum and
bispectrum features. In a previous paper we reported hints of these
correlations in the Planck data and here we perform several consistency checks
and further analyses of the best fits, such as polarization and local
significance at different angular scales. For the data analysis, we show the
excellent agreement between the CLASS and CAMB Boltzmann codes. Our results
confirm that the theoretical framework is consistent, and they suggest that the
predicted correlations are robust enough to be searched for in CMB and Large
Scale Structure (LSS) surveys. | Galaxy-cluster masses via 21st-century measurements of lensing of 21-cm
fluctuations: We discuss the prospects to measure galaxy-cluster properties via weak
lensing of 21-cm fluctuations from the dark ages and the epoch of reionization
(EOR). We choose as a figure of merit the smallest cluster mass detectable
through such measurements. We construct the minimum-variance quadratic
estimator for the cluster mass based on lensing of 21-cm fluctuations at
multiple redshifts. We discuss the tradeoff between frequency bandwidth,
angular resolution, and number of redshift shells available for a fixed noise
level for the radio detectors. Observations of lensing of the 21-cm background
from the dark ages will be capable of detecting M>~10^12 Msun/h mass halos, but
will require futuristic experiments to overcome the contaminating sources.
Next-generation radio measurements of 21-cm fluctuations from the EOR will,
however, have the sensitivity to detect galaxy clusters with halo masses
M>~10^13 Msun/h, given enough observation time (for the relevant sky patch) and
collecting area to maximize their resolution capabilities. |
Evolution of the Most Massive Galaxies to z ~ 0.6: II. The link between
radio AGN activity and star formation: We analyze the optical spectra of massive (log M*/Msun > 11.4) radio-loud
galaxies at z~0.2 and z~0.6. By comparing stellar population parameters of
these radio-loud samples with radio-quiet control samples, we investigate how
the presence of a radio-emitting jet relates to the recent star formation
history of the host galaxy. We also investigate how the emission-line
properties of the radio galaxies evolve with redshift by stacking their
spectra. Our main results are the following. (1) Both at low and at high
redshift, half as many radio-loud as radio-quiet galaxies have experienced
significant star formation in the past Gyr. (2) The Balmer absorption line
properties of massive galaxies that have experienced recent star formation show
that star formation occurred as a burst in many of these systems. (3) Both the
radio and the emission-line luminosity of radio AGN evolve significantly with
redshift. However, radio galaxies with similar stellar population parameters,
have similar emission-line properties both at high- and at low-redshift. These
results suggest that massive galaxies experience cyclical episodes of gas
accretion, star formation and black hole growth, followed by the production of
a radio jet that shuts down further activity. The behaviour of galaxies with
log M*/Msun > 11.4 is the same at z = 0.6 as it is at z = 0.2, except that
higher redshift galaxies experience more star formation and black hole growth
and produce more luminous radio jets during each accretion cycle. | The uncorrelated long term gamma-ray and X-ray variability of blazars
and its implications on disk-jet coupling: We examine the long term (~10 years) gamma-ray variability of blazars
observed by EGRET and Fermi and find that for six sources the average flux
varied by more than an order of magnitude. For two of these sources (PKS
0208-512 and PKS 0528+134), there were extensive observations (at various
observing periods) by EGRET. Hence these dramatic variations are not due to a
single short time-scale flare, but reflect long term changes in the average
flux. Over the last twenty years, these two sources were also the target of
several X-ray observatories (e.g. ROSAT, ASCA, RXTE, BeppoSAX, Chandra, Suzaku,
XMM-Newton and Swift). While the ratios of the average gamma-ray fluxes between
EGRET and Fermi observations are 22.9 +/- 1.9 and 12.6 +/- 1.5, their estimated
2-10 keV X-ray flux do not show such dramatic variations. The X-ray emission
from such flat spectrum radio quasars (FSRQs) are believed to be due to
synchrotron self Compton, while gamma-rays originate from inverse
Comptonization of external soft photons from an accretion disk and/or broad
line region. We argue that in this scenario, the only explanation for the
uncorrelated variability is that there was an order of magnitude decrease in
the external soft photons, while the jet parameters remained more or less
constant. This result indicates that perhaps the accretion and jet processes
are not tightly coupled in these sources. |
Spectral classification of emission-line galaxies from the Sloan Digital
Sky Survey. II. A supplementary diagnostic for AGNs using the Dn(4000) index: In this paper we present a classification of emission-line galaxies at
intermediate and high redshifts (0.52.5 for near-infrared spectra), using the
Dn(4000) index as a supplementary diagnostic. Our goal is to complement the
diagnostic based only on emission-line ratios from the blue part of the
spectra, which suffer from some limitations for the classification of Seyfert 2
and composite galaxies. We used a sample of 89 379 galaxies with a good
signal-to-noise ratio from the Sloan Digital Sky Survey (data release 7). Using
the classification scheme presented in Paper I, we classified these galaxies
with a diagnostic diagram involving the [Oiii]5007 /Hbeta and [Oii]3726+3729
/Hbeta emission-line ratios. Then we derived a supplementary diagnostic
involving Dn(4000) to improve this classification, in the regions where objects
of different types are mixed. To show the validity of our spectral
classification we established success-rate and contamination charts, then we
compared our results to those obtained with the reference classification that
was scheme obtained also using Halpha, [Nii]6584, and [Sii]6717+6731 emission
lines. We show that our supplementary classification based on the Dn(4000)
index allows to separate unambiguously star-forming galaxies from Seyfert 2 in
the region where they were mixed in Paper I. It also significantly reduces the
region where star-forming galaxies are mixed with composites. | Constraints on the identity of the dark matter from strong gravitational
lenses: The cold dark matter (CDM) cosmological model unambigously predicts that a
large number of haloes should survive as subhaloes when they are accreted into
a larger halo. The CDM model would be ruled out if such substructures were
shown not to exist. By contrast, if the dark matter consists of warm particles
(WDM), then below a threshold mass that depends on the particle mass far fewer
substructures would be present. Finding subhaloes below a certain mass would
then rule out warm particle masses below some value. Strong gravitational
lensing provides a clean method to measure the subhalo mass function through
distortions in the structure of Einstein rings and giant arcs.Using mock
lensing observations constructed from high-resolution N-body simulations, we
show that measurements of approximately 100 strong lens systems with a
detection limit of $10^7 h^{-1} M_{\odot}$ would clearly distinguish CDM from
WDM in the case where this consists of 7 keV sterile neutrinos such as those
that might be responsible for the 3.5 keV X-ray emission line recently detected
in galaxies and clusters. |
Hybrid $P_{\ell}(k)$: general, unified, non-linear matter power spectrum
in redshift space: Constraints on gravity and cosmology will greatly benefit from performing
joint clustering and weak lensing analyses on large-scale structure data sets.
Utilising non-linear information coming from small physical scales can greatly
enhance these constraints. At the heart of these analyses is the matter power
spectrum. Here we employ a simple method, dubbed "Hybrid $P_\ell(k)$", based on
the Gaussian Streaming Model (GSM), to calculate the quasi non-linear redshift
space matter power spectrum multipoles. This employs a fully non-linear and
theoretically general prescription for the matter power spectrum. We test this
approach against comoving Lagrangian acceleration simulation measurements
performed in GR, DGP and $f(R)$ gravity and find that our method performs
comparably or better to the dark matter TNS redshift space power spectrum model
for dark matter. When comparing the redshift space multipoles for halos, we
find that the Gaussian approximation of the GSM with a linear bias and a free
stochastic term, $N$, is competitive to the TNS model. Our approach offers many
avenues for improvement in accuracy as well as further unification under the
halo model. | II. Apples to apples $A^2$: cluster selection functions for
next-generation surveys: We present the cluster selection function for three of the largest
next-generation stage-IV surveys in the optical and infrared:
Euclid-Optimistic, Euclid-Pessimistic and the Large Synoptic Survey Telescope
(LSST). To simulate these surveys, we use the realistic mock catalogues
introduced in the first paper of this series.
We detected galaxy clusters using the Bayesian Cluster Finder (BCF) in the
mock catalogues. We then modeled and calibrated the total cluster stellar mass
observable-theoretical mass ($M^*_{\rm CL}-M_{\rm h}$) relation using a power
law model, including a possible redshift evolution term. We find a moderate
scatter of $\sigma_{M^*_{\rm CL} | M_{\rm h}}$ of 0.124, 0.135 and 0.136 $\rm
dex$ for Euclid-Optimistic, Euclid-Pessimistic and LSST, respectively,
comparable to other work over more limited ranges of redshift. Moreover, the
three datasets are consistent with negligible evolution with redshift, in
agreement with observational and simulation results in the literature.
We find that Euclid-Optimistic will be able to detect clusters with $>80\%$
completeness and purity down to $8\times10^{13} h^{-1} M_{\odot}$ up to $z<1$.
At higher redshifts, the same completeness and purity are obtained with the
larger mass threshold of $2\times10^{14} h^{-1} M_{\odot}$ up to $z=2$. The
Euclid-Pessimistic selection function has a similar shape with $\sim10\%$
higher mass limit. LSST shows $\sim 5\%$ higher mass limit than
Euclid-Optimistic up to $z<0.7$ and increases afterwards, reaching values of
$2\times10^{14} h^{-1} M_{\odot}$ at $z=1.4$. Similar selection functions with
only $80\%$ completeness threshold have been also computed. The complementarity
of these results with selection functions for surveys in other bands is
discussed. |
Late-time Light Curves of Type II Supernovae: Physical Properties of SNe
and Their Environment: We present BVRIJHK band photometry of 6 core-collapse supernovae, SNe 1999bw,
2002hh, 2003gd, 2004et, 2005cs, and 2006bc measured at late epochs (>2 yrs)
based on Hubble Space Telescope (HST), Gemini north, and WIYN telescopes. We
also show the JHK lightcurves of a supernova impostor SN 2008S up to day 575.
Of our 43 HST observations in total, 36 observations are successful in
detecting the light from the SNe alone and measuring magnitudes of all the
targets. HST observations show a resolved scattered light echo around SN 2003gd
at day 1520 and around SN 2002hh at day 1717. Our Gemini and WIYN observations
detected SNe 2002hh and 2004et, as well. Combining our data with previously
published data, we show VRIJHK-band lightcurves and estimate decline magnitude
rates at each band in 4 different phases. Our prior work on these lightcurves
and other data indicate that dust is forming in our targets from day ~300-400,
supporting SN dust formation theory. In this paper we focus on other physical
properties derived from the late time light curves. We estimate 56Ni masses for
our targets (0.5-14 x 10^{-2} Msun) from the bolometric lightcurve of each for
days ~150-300 using SN 1987A as a standard (7.5 x 10^{-2} Msun). The flattening
or sometimes increasing fluxes in the late time light curves of SNe 2002hh,
2003gd, 2004et and 2006bc indicate the presence of light echos. We estimate the
circumstellar hydrogen density of the material causing the light echo and find
that SN 2002hh is surrounded by relatively dense materials (n(H) >400 cm^{-3})
and SNe 2003gd and 2004et have densities more typical of the interstellar
medium (~1 cm^{-3}). The 56Ni mass appears well correlated with progenitor mass
with a slope of 0.31 x 10^{-2}, supporting the previous work by Maeda et al.
(2010), who focus on more massive Type II SNe. The dust mass does not appear to
be correlated with progenitor mass. | Revisiting primordial black holes formation from preheating
instabilities: the case of Starobinsky inflation: The primordial black holes (PBHs) formation in the early universe
inflationary cosmology has received a lot of attention in recent years. One of
the ways PBHs formation can be a possibility is the preheating stage after
inflation and this particular scenario does not require any ad-hoc fine tuning
of the scalar field potential. In this paper, we focus on the growth of
primordial density perturbation and the consequent possibility of PBHs
formation in the preheating stage of the Starobinsky model for inflation. The
typical mechanism for PBH formation during preheating is based on the collapse
of primordial fluctuations that become super-horizon during inflation (type I)
and re-enter the particle horizon in the different phases of cosmic expansion.
In this work, we show that there exists a certain range of modes that remain in
the sub-horizon (not exited) during inflation (type II modes). Those can, in
the later phase of evolution, lead to large density perturbation above the
threshold and can potentially also contribute to the PBH formation. We obtain
in detail the conditions that determine the possible collapse of type I and/or
type II modes. Since the preheating stage is an 'inflaton' (approximately)
matter-dominated phase with the equation of state $w\ll 1$, we follow the
framework of the critical collapse of fluctuations and compute the mass
fraction using the well-known Press-Schechter and the Khlopov-Polnarev
formalisms, and compare the two. Finally, we comment on the implications of our
study for the investigations concerned with primordial accretion and consequent
PBH contribution to the dark matter. |
Cosmic Origins Spectrograph and FUSE Observations of T ~ 10^5 K Gas In A
Nearby Galaxy Filament: We present a detection of a broad Ly-alpha absorber (BLA) with a matching O
VI line in the nearby universe. The BLA is detected at z = 0.01028 in the high
S/N spectrum of Mrk 290 obtained using the Cosmic Origins Spectrograph. The
Ly-alpha absorption has two components, with b(HI) = 55 +/- 1 km/s and b(HI) =
33 +/- 1 km/s, separated in velocity by v ~ 115 km/s. The O VI, detected by
FUSE at z = 0.01027, has a b(OVI) = 29 +/- 3 km/s and is kinematically well
aligned with the broader HI component. The different line widths of the BLA and
OVI suggest a temperature of T = 1.4 x 10^5 K in the absorber. The observed
line strength ratios and line widths favor an ionization scenario in which both
ion-electron collisions and UV photons contribute to the ionization in the gas.
Such a model requires a low-metallicity of -1.7 dex, ionization parameter of
log U ~ -1.4, a large total hydrogen column density of N(H) ~ 4 x 10^19 cm^-2,
and a path length of 400 kpc. The line of sight to Mrk 290 intercepts at the
redshift of the absorber, a megaparsec scale filamentary structure extending
over 20 deg in the sky, with several luminous galaxies distributed within 1.5
Mpc projected distance from the absorber. The collisionally ionized gas in this
absorber is likely tracing a shock-heated gaseous structure, consistent with a
few different scenarios for the origin, including an over-dense region of the
WHIM in the galaxy filament or highly ionized gas in the extended halo of one
of the galaxies in the filament. In general, BLAs with metals provide an
efficient means to study T ~ 10^5 - 10^6 K gas in galaxy halos and in the
intergalactic medium. A substantial fraction of the baryons "missing" from the
present universe is predicted to be in such environments in the form of highly
ionized plasma. | Planck 2013 results. XVIII. Gravitational lensing-infrared background
correlation: The multi-frequency capability of the Planck satellite provides information
both on the integrated history of star formation (via the cosmic infrared
background, or CIB) and on the distribution of dark matter (via the lensing
effect on the cosmic microwave background, or CMB). The conjunction of these
two unique probes allows us to measure directly the connection between dark and
luminous matter in the high redshift (1 < z <3) Universe. We use a three-point
statistic optimized to detect the correlation between these two tracers.
Following a thorough discussion of possible contaminants and a suite of
consistency tests, using lens reconstructions at 100, 143 and 217 GHz and CIB
measurements at 100-857 GHz, we report the first detection of the correlation
between the CIB and CMB lensing. The well matched redshift distribution of
these two signals leads to a detection significance with a peak value of 42
\sigma at 545 GHz and a correlation as high as 80% across these two tracers.
Our full set of multi-frequency measurements (both CIB auto- and CIB-lensing
cross-spectra) are consistent with a simple halo-based model, with a
characteristic mass scale for the halos hosting CIB sources of
log_{10}(M/M_sun) = 10.5 \pm 0.6. Leveraging the frequency dependence of our
signal, we isolate the high redshift contribution to the CIB, and constrain the
star formation rate (SFR) density at z>1. We measure directly the SFR density
with around 2 sigma significance for three redshift bins between z=1 and 7,
thus opening a new window into the study of the formation of stars at early
times. |
New Probes of Large Scale Structure: This is the second paper in a series where we propose a method of indirectly
measuring large scale structure using information from small scale
perturbations. The idea is to build a quadratic estimator from small scale
modes that provides a map of structure on large scales. We demonstrated in the
first paper that the quadratic estimator works well on a dark-matter-only
N-body simulation at a snapshot of $z=0$. Here we generalize the theory to the
case of a light cone halo catalog with a non-cubic region taken into
consideration. We successfully apply the generalized version of the quadratic
estimator to the light cone halo catalog based on an N-body simulation of
volume $\sim15.03\,(h^{-1}\,\rm Gpc)^3$. The most distant point in the light
cone is at a redshift of $1.42$, indicating the applicability of our method to
next generation of galaxy surveys. | Emergent Cosmology Revisited: We explore the possibility of emergent cosmology using the effective
potential formalism. We discover new models of emergent cosmology which satisfy
the constraints posed by the cosmic microwave background (CMB). We demonstrate
that, within the framework of modified gravity, the emergent scenario can arise
in a universe which is spatially open/closed. By contrast, in general
relativity (GR) emergent cosmology arises from a spatially closed past-eternal
Einstein Static Universe (ESU). In GR the ESU is unstable, which creates fine
tuning problems for emergent cosmology. However, modified gravity models
including Braneworld models, Loop Quantum Cosmology (LQC) and Asymptotically
Free Gravity result in a stable ESU. Consequently, in these models emergent
cosmology arises from a larger class of initial conditions including those in
which the universe eternally oscillates about the ESU fixed point. We
demonstrate that such an oscillating universe is necessarily accompanied by
graviton production. For a large region in parameter space graviton production
is enhanced through a parametric resonance, casting serious doubts as to
whether this emergent scenario can be past-eternal. |
Superclusters from velocity divergence fields: Superclusters are a convenient way to partition and characterize the large
scale structure of the Universe. In this Letter we explore the advantages of
defining superclusters as watershed basins in the divergence velocity field. We
apply this definition on diverse datasets generated from linear theory and
N-body simulations, with different grid sizes, smoothing scales and types of
tracers. From this framework emerges a linear scaling relation between the
average supercluster size and the autocorrelation length in the divergence
field, a result that holds for one order of magnitude from 10 Mpc/h up to 100
Mpc/h. These results suggest that the divergence-based definition provides a
robust context to quantitatively compare results across different observational
or computational frameworks. Through its connection with linear theory, it can
also facilitate the exploration of how supercluster properties depend on
cosmological parameters, paving the way to use superclusters as cosmological
probes. | 2D mapping of young stars in the inner 180 pc of NGC 1068: correlation
with molecular gas ring and stellar kinematics: We report the first two-dimensional mapping of the stellar population and
non-stellar continua within the inner 180 pc (radius) of NGC 1068 at a spatial
resolution of 8 pc, using integral field spectroscopy in the near-infrared. We
have applied the technique of spectral synthesis to data obtained with the
instrument NIFS and the adaptive optics module ALTAIR at the Gemini North
Telescope. Two episodes of recent star formation are found to dominate the
stellar population contribution: the first occurred 300 Myr ago, extending over
most of the nuclear region; the second occurred just 30 Myr ago, in a ring-like
structure at ~100 pc from the nucleus, where it is coincident with an expanding
ring of H2 emission. Inside the ring, where a decrease in the stellar velocity
dispersion is observed, the stellar population is dominated by the 300 Myr age
component. In the inner 35 pc, the oldest age component (age > 2Gyr) dominates
the mass, while the flux is dominated by black-body components with
temperatures in the range 700 < T < 800 K which we attribute to the dusty
torus. We also find some contribution from black-body and power-law components
beyond the nucleus which we attribute to dust emission and scattered light. |
Color and Stellar Population Gradients in Passively Evolving Galaxies at
z~2 from HST/WFC3 Deep Imaging in the Hubble Ultra Deep Field: We report the detection of color gradients in six massive (stellar mass >
10^{10} M_{sun}) and passively evolving (specific SFR < 10^{-11}/yr) galaxies
at redshift 1.3<z<2.5 identified in the HUDF using HST ACS and WFC3/IR images.
After matching different PSFs, we obtain color maps and multi-band
optical/near-IR photometry (BVizYJH) in concentric annuli, from the smallest
resolved radial (~1.7 kpc) up to several times the H-band effective radius. We
find that the inner regions of these galaxies have redder rest-frame
UV--optical colors than the outer parts. The slopes of the color gradients
mildly depend on the overall dust obscuration and rest-frame (U-V) color, with
more obscured or redder galaxies having steeper color gradients. The z~2 color
gradients are also steeper than those of local early-types. The gradient of a
single parameter (age, extinction or metallicity) cannot fully explain the
observed color gradients. Fitting spatially resolved HST seven-band photometry
to stellar population synthesis models, we find that, regardless of assumptions
for metallicity gradient, the redder inner regions of the galaxies have
slightly higher dust obscuration than the bluer outer regions, although the
magnitude depends on the assumed extinction law. The derived age gradient
depends on the assumptions for metallicity gradient. We discuss the
implications of a number of assumptions for metallicity gradient on the
formation and evolution of these galaxies. We find that the evolution of the
mass--size relationship from z~2 to z~0 cannot be driven by in--situ extended
star formation, implying that accretion or merger is mostly responsible for the
evolution. The lack of a correlation between color gradient and stellar mass
argues against the metallicity gradient predicted by the monolithic collapse,
which would require significant major mergers to evolve into the one observed
at z~0. (Abridged) | Frequency-Dependent Constraints on Cosmic Birefringence from the LFI and
HFI Planck Data Release 4: We present new constraints on the frequency dependence of the cosmic
birefringence angle from the Planck data release 4 polarization maps. An axion
field coupled to electromagnetism predicts a nearly frequency-independent
birefringence angle, $\beta_\nu = \beta$, while Faraday rotation from local
magnetic fields and Lorentz violating theories predict a cosmic birefringence
angle that is proportional to the frequency, $\nu$, to the power of some
integer $n$, $\beta_\nu \propto \nu^n$. In this work, we first sample
$\beta_\nu$ individually for each polarized HFI frequency band in addition to
the 70 GHz channel from the LFI. We also constrain a power-law formula for the
birefringence angle, $\beta_\nu=\beta_0(\nu/\nu_0)^n$, with $\nu_0 = 150$ GHz.
For a nearly full-sky measurement, $f_{\text{sky}}=0.93$, we find $\beta_0 =
0.26^{\circ}\pm0.11^\circ$ $(68\% \text{ C.L.})$ and $n=-0.45^{+0.61}_{-0.82}$
when we ignore the intrinsic $EB$ correlations of the polarized foreground
emission, and $\beta_0 = 0.33^\circ \pm 0.12^\circ$ and
$n=-0.37^{+0.49}_{-0.64}$ when we use a filamentary dust model for the
foreground $EB$. Next, we use all the polarized Planck maps, including the 30
and 44 GHz frequency bands. These bands have a negligible foreground
contribution from polarized dust emission. We, therefore, treat them
separately. Without any modeling of the intrinsic $EB$ of the foreground, we
generally find that the inclusion of the 30 and 44 GHz frequency bands raises
the measured values of $\beta_\nu$ and tightens $n$. At nearly full-sky, we
measure $\beta_0=0.29^{\circ+0.10^\circ}_{\phantom{\circ}-0.11^\circ}$ and
$n=-0.35^{+0.48}_{-0.47}$. Assuming no frequency dependence, we measure
$\beta=0.33^\circ \pm 0.10^\circ$. If our measurements have effectively
mitigated the $EB$ of the foreground, our constraints are consistent with a
mostly frequency-independent signal of cosmic birefringence. |
Constructing high-fidelity halo merger trees in AbacusSummit: Tracking the formation and evolution of dark matter haloes is a critical
aspect of any analysis of cosmological $N$-body simulations. In particular, the
mass assembly of a halo and its progenitors, encapsulated in the form of its
merger tree, serves as a fundamental input for constructing semi-analytic
models of galaxy formation and, more generally, for building mock catalogues
that emulate galaxy surveys. We present an algorithm for constructing halo
merger trees from AbacusSummit, the largest suite of cosmological $N$-body
simulations performed to date consisting of nearly 60 trillion particles, and
which has been designed to meet the Cosmological Simulation Requirements of the
Dark Energy Spectroscopic Instrument (DESI) survey. Our method tracks the cores
of haloes to determine associations between objects across multiple timeslices,
yielding lists of halo progenitors and descendants for the several tens of
billions of haloes identified across the entire suite. We present an
application of these merger trees as a means to enhance the fidelity of
AbacusSummit halo catalogues by flagging and "merging" haloes deemed to exhibit
non-monotonic past merger histories. We show that this cleaning technique
identifies portions of the halo population that have been deblended due to
choices made by the halo finder, but which could have feasibly been part of
larger aggregate systems. We demonstrate that by cleaning halo catalogues in
this post-processing step, we remove potentially unphysical features in the
default halo catalogues, leaving behind a more robust halo population that can
be used to create highly-accurate mock galaxy realisations from AbacusSummit. | Exploring the distance-redshift relation with gravitational wave
standard sirens and tomographic weak lensing: Gravitational waves from inspiraling compact objects provide us with
information of the distance scale since we can infer the absolute luminosity of
the source from analysis of the wave form, which is known as standard sirens.
The first detection of the gravitational wave signal of the binary black hole
merger event by Advanced LIGO has opened up the possibility of utilizing
standard sirens as cosmological probe. In order to extract information of the
distance-redshift relation, we cross-correlate weak lensing, which is an
unbiased tracer of matter distribution in the Universe, with the projected
number density of gravitational wave sources. For weak lensing, we employ
tomography technique to efficiently obtain information of large-scale
structures at wide ranges of redshifts. Making use of the cross-correlations
along with the auto-correlations, we present forecast of constraints on four
cosmological parameters, i.e., Hubble parameter, matter density, the equation
of state parameter of dark energy, and the amplitude of matter fluctuation. To
fully explore the ability of cross-correlations, which require large
overlapping sky coverage, we consider the specific case with the upcoming
surveys by \textit{Euclid} for weak lensing and Einstein Telescope for standard
sirens. We show that cosmological parameters can be tightly constrained solely
by these auto- and cross-correlations of standard sirens and weak lensing. For
example, the $1\text{-}\sigma$ error of Hubble parameter is expected to be
$\sigma (H_0) = 0.33 \, \mathrm{km} \, \mathrm{s}^{-1} \, \mathrm{Mpc}^{-1}$.
Thus, the proposed statistics will be a promising probe into the distance
scale. |
Numerically evaluating the bispectrum in curved field-space - with
PyTransport 2.0: We extend the transport framework for numerically evaluating the power
spectrum and bispectrum in multi-field inflation to the case of a curved
field-space metric. This method naturally accounts for all sub- and
super-horizon tree level effects, including those induced by the curvature of
the field-space. We present an open source implementation of our equations in
an extension of the publicly available PyTransport code. Finally we illustrate
how our technique is applied to examples of inflationary models with a
non-trivial field-space metric. | HI in very metal-poor galaxies: the SBS 0335-052 system: We present Giant Metrewave Radio Telescope (GMRT), HI 21cm observations of
SBS 0335-052E and SBS 0335-052W, a close pair of dwarf galaxies, which are
further unusual in being the most metal-poor star-forming galaxies known. We
present images at several angular resolutions, ranging from ~40 to 4 arcsec.
These images show that SBS 0335-052 is a strongly interacting system, with a
faint diffuse HI bridge seen at low resolution, and elongated tails seen at the
higher resolutions. The overall morphology suggests that the pair represents a
major merger of extremely gas-rich galaxies. The low-resolution velocity field
is dominated by the velocity difference between the two galaxies and the
velocity gradient along the tidal features. However, for SBS 0335-052W at
least, at high angular resolution, one sees a central velocity field that could
be associated with the spin of the original undisturbed disc. The highest
angular resolution HI images show that the ionized superbubble, identified by
Thuan, Izotov & Lipovetsky (1997), in the Hubble Space Telescope (HST) images
of SBS 0335-052E, is extended along one of the diffuse tidal features, and that
there is a high-density HI clump at the other end of the superbubble. The star
formation in SBS 0335-052E occurs mainly in a group of superstar clusters
(SSCs) with a clear age gradient; the age decreases as one approaches the dense
HI clump. We suggest that this propagating star formation is driven by the
superbubble expanding into a medium with a tidally-produced density gradient.
The high pressures associated with the compressed material would also naturally
explain why current star formation is mainly concentrated in superstar
clusters. |
AKARI observation of the fluctuation of the near-infrared background: We report a search for fluctuations of the sky brightness toward the north
ecliptic pole (NEP) with the Japanese infrared astronomical satellite AKARI,at
2.4, 3.2, and 4.1 \mum. We obtained circular maps with 100 diameter field of
view which clearly show a spatial structure on scale of a few hundred arcsec. A
power spectrum analysis shows that there is a significant excess fluctuation at
angular scales larger than 10000 that can't be explained by zodiacal light,
diffuse Galactic light, shot noise of faint galaxies or clustering of low
redshift galaxies. These results are consistent with observations at 3.6 and
4.5 \mum by NASA's Spitzer Space Telescope. The fluctuating component observed
at large angular scales has a blue stellar spectrum which is similar to that of
the spectrum of the excess isotropic emission observed with IRTS. A significant
spatial correlation between wavelength bands was found, and the slopes of the
linear correlations is consistent with the spectrum of the excess fluctuation.
These findings indicate that the detected fluctuation could be attributed to
the first stars of the universe, i.e. pop. III stars. The observed fluctuation
provides an important constraints on the era of the first stars. | Systematic Continuum Errors in the Lyman-Alpha Forest and The Measured
Temperature-Density Relation: Continuum fitting uncertainties are a major source of error in estimates of
the temperature-density relation (usually parametrized as a power-law, $T
\propto \Delta^{\gamma - 1} $) of the inter-galactic medium (IGM) through the
flux probability distribution function (PDF) of the Lyman-$\alpha$ forest.
Using a simple order-of-magnitude calculation, we show that few percent-level
systematic errors in the placement of the quasar continuum due to e.g. a
uniform low-absorption Gunn-Peterson component, could lead to errors in
$\gamma$ of order unity. This is quantified further using a simple
semi-analytic model of the Lya forest flux PDF. We find that
under-(over-)estimates in the continuum level can lead to a lower (higher)
measured value of $\gamma$. Within current observational uncertainties,
continuum biases double the error in $\gamma$ from $\sigma_{\gamma} \approx
0.1$ to $\sigma_{\gamma} \approx 0.2$ within our model. We argue that steps
need to be taken to directly estimate the level of continuum bias in order to
make recent claims of an inverted \tdr\ more robust. |
Bayesian approach to constraining the properties of ionized bubbles
during reionization: A possible way to study the reionization of cosmic hydrogen is by observing
the large ionized regions (bubbles) around bright individual sources, e.g.,
quasars, using the redshifted 21 cm signal. It has already been shown that
matched filter-based methods are not only able to detect the weak 21 cm signal
from these bubbles but also aid in constraining their properties. In this work,
we extend the previous studies to develop a rigorous Bayesian framework to
explore the possibility of constraining the parameters that characterize the
bubbles. To check the accuracy with which we can recover the bubble parameters,
we apply our method on mock observations appropriate for the upcoming SKA1-low.
For a region of size $\gtrsim 50$ cMpc around a typical quasar at redshift 7,
we find that $\approx 20$ h of integration with SKA1-low will be able to
constrain the size and location of the bubbles, as well as the difference in
the neutral hydrogen fraction inside and outside the bubble, with $\lesssim
10\%$ precision. The recovery of the parameters are more precise and the SNR of
the detected signal is higher when the bubble sizes are larger and their shapes
are close to spherical. Our method can be useful in identifying regions in the
observed field which contain large ionized regions and hence are interesting
for following up with deeper integration times. | Phase-transition sound of inflation at gravitational waves detectors: It is well-known that the first-order phase transition (PT) will yield a
stochastic gravitational waves (GWs) background with a logo-like spectrum.
However, we show that when such a PT happened during the primordial inflation,
the GWs spectrum brought by the PT will be reddened, which thus records the
unique voiceprint of inflation. We assess the abilities of the GW detectors to
detect the corresponding signal. |
Detecting the relativistic bispectrum in 21cm intensity maps: We investigate the detectability of leading-order relativistic effects in the
bispectrum of future 21cm intensity mapping surveys. The relativistic signal
arises from Doppler and other line-of-sight effects in redshift space. In the
power spectrum of a single tracer, these effects are suppressed by a factor
$\cH^2/k^2$. By contrast, in the bispectrum the relativistic signal couples to
short-scale modes, leading to an imaginary contribution that scales as $\cH/k$,
thus increasing the possibility of detection. Previous work has shown that this
relativistic signal is detectable in a Stage IV H$\alpha$ galaxy survey. {We
show that the signal is also detectable by next-generation 21cm intensity maps,
but typically with a lower signal-to-noise, due to foreground and telescope
beam effects. | Pressure of the hot gas in simulations of galaxy clusters: We analyze the radial pressure profiles, the ICM clumping factor and the
Sunyaev-Zel'dovich (SZ) scaling relations of a sample of simulated galaxy
clusters and groups identified in a set of hydrodynamical simulations based on
an updated version of the TreePM-SPH GADGET-3 code. Three different sets of
simulations are performed: the first assumes non-radiative physics, the others
include, among other processes, AGN and/or stellar feedback. Our results are
analyzed as a function of redshift, ICM physics, cluster mass and cluster
cool-coreness or dynamical state. In general, the mean pressure profiles
obtained for our sample of groups and clusters show a good agreement with X-ray
and SZ observations. Simulated cool-core (CC) and non-cool-core (NCC) clusters
also show a good match with real data. We obtain in all cases a small (if any)
redshift evolution of the pressure profiles of massive clusters, at least back
to z=1. We find that the clumpiness of gas density and pressure increases with
the distance from the cluster center and with the dynamical activity. The
inclusion of AGN feedback in our simulations generates values for the gas
clumping ($\sqrt C_{\rho}\sim 1.2$ at $R_{200}$) in good agreement with recent
observational estimates. The simulated $Y_{SZ}-M$ scaling relations are in good
accordance with several observed samples, especially for massive clusters. As
for the scatter of these relations, we obtain a clear dependence on the cluster
dynamical state, whereas this distinction is not so evident when looking at the
subsamples of CC and NCC clusters. |
Cosmology with the EFTofLSS and BOSS: dark energy constraints and a note
on priors: We analyse the BOSS DR12 galaxy power spectrum data jointly with BAO data for
three models of dark energy. We use recent measurements using a windowless
estimator, and an independent and fast pipeline based on EFTofLSS implemented
via the FAST-PT algorithm to compute the redshift-space loop corrections. We
accelerate our analysis by using the BACCO linear emulator instead of a
Boltzmann solver. We perform two sets of analyses: one with $3\sigma$ Planck
priors on $A_s$ and $n_s$, and another that is CMB-free, without such priors.
Firstly, we study $\Lambda$CDM, reproducing previous results obtained with the
same estimator. We find a low value of $A_s$ in the CMB-free case, in agreement
with many previous full-shape analyses of the BOSS data. We then study $w$CDM,
finding a lower value of the amplitude in the CMB-free run, coupled with a
preference for phantom dark energy with $w=-1.17^{+0.12}_{-0.11}$, again in
broad agreement with previous results. Finally, we investigate the dark
scattering model, which we label $wA$CDM. In the CMB-free analysis, we find a
large degeneracy between the interaction strength $A$ and the amplitude $A_s$,
hampering measurements of those parameters. On the contrary, in our run with a
CMB prior, we are able to constrain the dark energy parameters to be
$w=-0.972^{+0.036}_{-0.029}$ and $A = 3.9^{+3.2}_{-3.7}$, which show a
1$\sigma$ hint of interacting dark energy. This is the first measurement of
this parameter and demonstrates the ability of this model to alleviate the
$\sigma_8$ tension. Our analysis can be used as a guide for any model with
scale-independent growth. Finally, we study the dependence of the results on
the priors of the nuisance parameters and find these priors to be informative,
with their broadening creating shifts in the contours. We argue for an in depth
study of this issue, which can affect current and forthcoming analyses of LSS
data. | Log-dependent slope of scalar induced gravitational waves in the
infrared regions: We analytically calculate the scalar induced gravitational waves (SIGWs) and
find a log-dependent slope of SIGW in the infrared regions $(f<f_c)$, namely
$n_{\mathrm{GW}}(f)=3-2/\ln(f_c/f)$, and $n_{\mathrm{GW}}(f)=2-2/\ln(f_c/f)$
near the peak if the power spectrum of scalar curvature perturbation is quite
narrow, where $f_c$ is roughly the frequency at the peak of SIGW. Such a
log-dependent slope can be taken as a new template for distinguishing SIGW from
other sources. |
Separate Universe Simulations with IllustrisTNG: baryonic effects on
power spectrum responses and higher-order statistics: We measure power spectrum response functions in the presence of baryonic
physical processes using separate universe simulations with the IllustrisTNG
galaxy formation model. The response functions describe how the small-scale
power spectrum reacts to long-wavelength perturbations and they can be
efficiently measured with the separate universe technique by absorbing the
effects of the long modes into a modified cosmology. Specifically, we focus on
the total first-order matter power spectrum response to an isotropic density
fluctuation $R_1(k,z)$, which is fully determined by the logarithmic derivative
of the nonlinear matter power spectrum ${\rm dln}P_m(k,z)/{\rm dln}k$ and the
growth-only response function $G_1(k,z)$. We find that $G_1(k,z)$ is not
affected by the baryonic physical processes in the simulations at redshifts $z
< 3$ and on all scales probed ($k \lesssim 15h/{\rm Mpc}$, i.e. length scales
$\gtrsim 0.4 {\rm Mpc}/h$). In practice, this implies that the power spectrum
fully specifies the baryonic dependence of its response function. Assuming an
idealized lensing survey setup, we evaluate numerically the baryonic impact on
the squeezed-lensing bispectrum and the lensing super-sample power spectrum
covariance, which are given in terms of responses. Our results show that these
higher-order lensing statistics can display varying levels of sensitivity to
baryonic effects compared to the power spectrum, with the squeezed-bispectrum
being the least sensitive. We also show that ignoring baryonic effects on
lensing covariances slightly overestimates the error budget (and is therefore
conservative from the point of view of parameter error bars) and likely has
negligible impact on parameter biases in inference analyses. | Teleparallel Dark Energy with Purely Non-minimal Coupling to Gravity: We propose the simplest model of teleparallel dark energy with purely a
non-minimal coupling to gravity but no self-potential, a single model
possessing various interesting features: simplicity, self-potential-free, the
guaranteed late-time cosmic acceleration driven by the non-minimal coupling to
gravity, tracker behavior of the dark energy equation of state at earlier
times, a crossing of the phantom divide at a late time, and the existence of a
finite-time future singularity. We find the analytic solutions of the
dark-energy scalar field respectively in the radiation, matter, and dark energy
dominated eras, thereby revealing the above features. We further illustrate
possible cosmic evolution patterns and present the observational constraint of
this model obtained by numerical analysis and data fitting. |
Measuring the distance-redshift relation with the cross-correlation of
gravitational wave standard sirens and galaxies: Gravitational waves from inspiraling compact binaries are known to be an
excellent absolute distance indicator, yet it is unclear whether
electromagnetic counterparts of these events are securely identified for
measuring their redshifts, especially in the case of black hole-black hole
mergers such as the one recently observed with the Advanced LIGO. We propose to
use the cross-correlation between spatial distributions of gravitational wave
sources and galaxies with known redshifts as an alternative means of
constraining the distance-redshift relation from gravitational waves. In our
analysis, we explicitly include the modulation of the distribution of
gravitational wave sources due to weak gravitational lensing. We show that the
cross-correlation analysis in next-generation observations will be able to
tightly constrain the relation between the absolute distance and the redshift,
and therefore constrain the Hubble constant as well as dark energy parameters. | Limits on Polarized Dust Spectral Index Variations for CMB Foreground
Analysis: Using Planck polarization data, we search for and constrain spatial
variations of the polarized dust foreground for cosmic microwave background
(CMB) observations, specifically in its spectral index, $\beta_d$. Failure to
account for such variations will cause errors in the foreground cleaning that
propagate into errors on cosmological parameter recovery from the cleaned CMB
map. It is unclear how robust prior studies of the Planck data which
constrained $\beta_d$ variations are due to challenges with noise modeling,
residual systematics, and priors. To clarify constraints on $\beta_d$ and its
variation, we employ two pixel space analyses of the polarized dust foreground
at $>3.7^{\circ}$ scales on $\approx 60\%$ of the sky at high Galactic
latitudes. A template fitting method, which measures $\beta_d$ over three
regions of $\approx 20\%$ of the sky, does not find significant deviations from
an uniform $\beta_d = 1.55$, consistent with prior Planck determinations. An
additional analysis in these regions, based on multifrequency fits to a dust
and CMB model per pixel, puts limits on $\sigma_{\beta_d}$, the Gaussian
spatial variation in $\beta_d$. At the highest latitudes, the data support
$\sigma_{\beta_d}$ up to $0.45$, $0.30$ at mid-latitudes, and $0.15$ at
low-latitudes. We also demonstrate that care must be taken when interpreting
the current Planck constraints, $\beta_d$ maps, and noise simulations. Due to
residual systematics and low dust signal to noise at high latitudes, forecasts
for ongoing and future missions should include the possibility of large values
of $\sigma_{\beta_d}$ as estimated in this paper, based on current polarization
data. |
A weak lensing view on primordial non-Gaussianities: We investigate the signature of primordial non-Gaussianities in the weak
lensing bispectrum, in particular the signals generated by local, orthogonal
and equilateral non-Gaussianities. The questions we address include the
signal-to-noise ratio generated in the Euclid weak lensing survey (we find the
1sigma-errors for fNL are 200, 575 and 1628 for local, orthogonal and
equilateral non-Gaussianities, respectively), misestimations of fNL if one
chooses the wrong non-Gaussianity model (misestimations by up to a factor of
+/-3 in fNL are possible, depending on the choice of the model), the
probability of noticing such a mistake (improbably large values for the
chi^2-functional occur from fNL 200 on), degeneracies of the primordial
bispectrum with other cosmological parameters (only the matter density Omega_m
plays a significant role), and the subtraction of the much larger,
structure-formation generated bispectrum. If a prior on a standard
wCDM-parameter set is available from Euclid and Planck, the structure formation
bispectrum can be predicted accurately enough for subtraction, and any residual
structure formation bispectrum would influence the estimation of fNL to a minor
degree. Configuration-space integrations which appear in the evaluation of
chi^2-functionals and related quantities can be carried out very efficiently
with Monte-Carlo techniques, which reduce the complexity by a factor of O(10^4)
while delivering sub-percent accuracies. Weak lensing probes smaller scales
than the CMB and hence provide an additional constraint on non-Gaussianities,
even though they are not as sensitive to primordial non-Gaussianities as the
CMB. | Particle re-acceleration and diffuse radio sources in the galaxy cluster
Abell 1550: We study diffuse radio emission in the galaxy cluster A1550, with the aim of
constraining particle re-acceleration in the intra-cluster medium. We exploit
observations at four different frequencies: 54, 144, 400 and 1400 MHz. To
complement our analysis, we make use of archival Chandra X-ray data. At all
frequencies we detect an ultra-steep spectrum radio halo ($S_\nu \propto
\nu^{-1.6}$) with an extent of 1.2 Mpc at 54 MHz. Its morphology follows the
distribution of the thermal intra-cluster medium inferred from the Chandra
observation. West of the centrally located head-tail radio galaxy, we detect a
radio relic with projected extent of 500 kpc. From the relic, a 600 kpc long
bridge departs and connect it to the halo. Between the relic and the radio
galaxy, we observe what is most likely a radio phoenix, given its curved
spectrum. The phoenix is connected to the tail of the radio galaxy through two
arms, which show a nearly constant spectral index for 300 kpc. The halo could
be produced by turbulence induced by a major merger, with its axis lying in the
NE-SW direction. This is supported by the position of the relic, whose origin
could be attributed to a shock propagating along the merger axis. It is
possible that the same shock has also produced the phoenix through adiabatic
compression, while the bridge could be generated by electrons which were
pre-accelerated by the shock, and then re-accelerated by turbulence. Finally,
we detect hints of gentle re-energisation in the two arms which depart from the
tail of the radio galaxy. |
Cosmic Gamma-Ray Background from Star-Forming Galaxies: The origin of the extragalactic gamma-ray background is a pressing
cosmological mystery. The Fermi Gamma-Ray Space Telescope has recently measured
the intensity and spectrum of this background; both are substantially different
from previous measurements. We present a novel calculation of the gamma-ray
background from normal star-forming galaxies. Contrary to long-standing
expectations, we find that numerous but individually faint normal galaxies may
comprise the bulk of the Fermi signal, rather than rare but intrinsically
bright active galaxies. This result has wide-ranging implications, including:
the possibility to probe the cosmic star formation history with gamma rays; the
ability to infer the cosmological evolution of cosmic rays and galactic
magnetic fields; and an increased likelihood of identifying subdominant
components from rare sources (e.g., dark matter clumps) through their large
anisotropy. | Cospatial 21 cm and metal-line absorbers in the epoch of reionization --
I : Incidence and observability: Overdense, metal-rich regions, shielded from stellar radiation might remain
neutral throughout reionization and produce metal as well as 21 cm absorption
lines. Simultaneous absorption from metals and 21 cm can complement each other
as probes of underlying gas properties. We use Aurora, a suite of high
resolution radiation-hydrodynamical simulations of galaxy formation, to
investigate the occurrence of such "aligned" absorbers. We calculate absorption
spectra for 21 cm, OI, CII, SiII and FeII. We find velocity windows with
absorption from at least one metal and 21 cm, and classify the aligned
absorbers into two categories: 'aligned and cospatial absorbers' and 'aligned
but not cospatial absorbers'. While 'aligned and cospatial absorbers' originate
from overdense structures and can be used to trace gas properties, 'aligned but
not cospatial absorbers' are due to peculiar velocity effects. The incidence of
absorbers is redshift dependent, as it is dictated by the interplay between
reionization and metal enrichment, and shows a peak at $z \approx 8$ for the
aligned and cospatial absorbers. While aligned but not cospatial absorbers
disappear towards the end of reionization because of the lack of an ambient 21
cm forest, aligned and cospatial absorbers are associated with overdense
pockets of neutral gas which can be found at lower redshift. We produce mock
observations for a set of sightlines for the next generation of telescopes like
the ELT and SKA1-LOW, finding that given a sufficiently bright background
quasar, these telescopes will be able to detect both types of absorbers
throughout reionization. |
A List of Groups of Dwarf Galaxies in the Local Supercluster: We report a list of groups consisting of dwarf galaxies only. The sample
contains 126 objects, mainly combined in pairs. The most populated group
contains six dwarf galaxies. The majority of systems considered reside in the
low-density regions and evolve unaffected by massive galaxies. The
characteristic sizes and velocity dispersions of groups are 30 kpc and 11 km/s,
respectively. They resemble the associations of dwarf galaxies, but are more
compact. On the whole, groups and associations form a continuous sequence.
Alike the associations, our groups possess high mass-to-luminosity ratios, what
is indicative of a large amount of dark matter present in these systems. | Einstein-Cartan gravity with scalar-fermion interactions: In this paper, we have considered the g-essence and its particular cases,
k-essence and f-essence, within the framework of the Einstein-Cartan theory. We
have shown that a single fermionic field can give rise to the accelerated
expansion within the Einstein-Cartan theory. The exact analytical solution of
the Einstein-Cartan-Dirac equations is found. This solution describes the
accelerated expansion of the Universe with the equation of state parameter
$w=-1$ as in the case of $\Lambda$CDM model. |
Affleck-Dine baryogenesis with modulated reheating: Modulated reheating scenario is one of the most attractive models that
predict possible detections of not only the primordial non-Gaussianity but also
the tensor fluctuation through future CMB observations such as the Planck
satellite, the PolarBeaR and the LiteBIRD satellite experiments. We study the
baryonic-isocurvature fluctuations in the Affleck-Dine baryogenesis with the
modulated reheating scenario. We show that the Affleck-Dine baryogenesis can be
consistent with the modulated reheating scenario with respect to the current
observational constraint on the baryonic-isocurvature fluctuations. | Did the Universe Reheat After Recombination?: A key assumption of the standard cosmological model is that the temperature
of the cosmic microwave background (CMB) radiation scales with cosmological
redshift $z$ as $T_{\rm CMB}(z) \propto (1+z)$ at all times after recombination
at $z_\star \simeq 1090$. However, this assumption has only been precisely
tested at $z \lesssim 3$. Here, we consider cosmological models with
post-recombination reheating (PRR), in which the CMB monopole temperature
abruptly increases due to energy injection after last scattering. Such a
scenario can potentially resolve tensions between inferences of the current
cosmic expansion rate (the Hubble constant, $H_0$). We consider an explicit
model in which a metastable sub-component of dark matter (DM) decays to
Standard Model photons, whose spectral energy distribution is assumed to be
close to that of the CMB blackbody. A fit to Planck CMB anisotropy, COBE/FIRAS
CMB monopole, and SH0ES distance-ladder measurements yields $H_0 = 71.2 \pm
1.1$ km/s/Mpc, matter fluctuation amplitude $S_8 = 0.774 \pm 0.018$, and CMB
temperature increase $\delta T_{\rm CMB} = 0.109^{+0.033}_{-0.044}$ K, which is
sourced by DM decay at $z \gtrsim 10$. However, matter density constraints from
baryon acoustic oscillation and supernovae data highly constrain this scenario,
with a joint fit to all datasets yielding $H_0 = 68.69 \pm 0.35$ km/s/Mpc, $S_8
= 0.8035 \pm 0.0081$, and $\delta T_{\rm CMB} < 0.0342$ K (95% CL upper limit).
These bounds can be weakened if additional dark relativistic species are
present in the early universe, yielding higher $H_0$. We conclude that current
data disfavor models with significant PRR solely through its impact on
background and linear-theory observables, completely independent of CMB
spectral distortion constraints. However, a small amount of such energy
injection could play a role in restoring cosmological concordance. |
Measuring Cosmological Parameters with Type Ia Supernovae in redMaGiC
galaxies: Current and future cosmological analyses with Type Ia Supernovae (SNe Ia)
face three critical challenges: i) measuring redshifts from the supernova or
its host galaxy; ii) classifying SNe without spectra; and iii) accounting for
correlations between the properties of SNe Ia and their host galaxies. We
present here a novel approach that addresses each challenge. In the context of
the Dark Energy Survey (DES), we analyze a SNIa sample with host galaxies in
the redMaGiC galaxy catalog, a selection of Luminous Red Galaxies. Photo-$z$
estimates for these galaxies are expected to be accurate to $\sigma_{\Delta
z/(1+z)}\sim0.02$. The DES-5YR photometrically classified SNIa sample contains
approximately 1600 SNe and 125 of these SNe are in redMaGiC galaxies. We
demonstrate that redMaGiC galaxies almost exclusively host SNe Ia, reducing
concerns with classification uncertainties. With this subsample, we find
similar Hubble scatter (to within $\sim0.01$ mag) using photometric redshifts
in place of spectroscopic redshifts. With detailed simulations, we show the
bias due to using photo-$z$s from redMaGiC host galaxies on the measurement of
the dark energy equation-of-state $w$ is up to $\Delta w \sim 0.01-0.02$. With
real data, we measure a difference in $w$ when using redMaGiC photometric
redshifts versus spectroscopic redshifts of $\Delta w = 0.005$. Finally, we
discuss how SNe in redMaGiC galaxies appear to be a more standardizable
population due to a weaker relation between color and luminosity ($\beta$)
compared to the DES-3YR population by $\sim5\sigma$; this finding is consistent
with predictions that redMaGiC galaxies exhibit lower reddening ratios
($\textrm{R}_\textrm{V}$) than the general population of SN host galaxies.
These results establish the feasibility of performing redMaGiC SN cosmology
with photometric survey data in the absence of spectroscopic data. | The Next Generation Virgo Cluster Survey. IV. NGC 4216: A Bombarded
Spiral in the Virgo Cluster: We present an investigation into the origins of a series of interlaced narrow
filamentary stellar structures, loops and plumes in the vicinity of the Virgo
Cluster, edge-on spiral galaxy, NGC 4216 that were previously identified by the
Blackbird Telescope. Using the deeper, higher-resolution and precisely
calibrated optical CFHT/MegaCam images obtained as part of the Next Generation
Virgo Cluster Survey (NGVS), we confirm the previously identified features and
identify a few additional structures. The NGVS data allowed us to make a
physical study of these low-surface brightness features and investigate their
origin. The likely progenitors of the structures were identified as either
already catalogued VCC dwarfs or newly discovered satellites caught in the act
of being destroyed. They have the same g-i color index and likely contain
similar stellar populations. The alignment of three dwarfs along an apparently
single stream is intriguing, and we cannot totally exclude that these are
second-generation dwarf galaxies being born inside the filament from the debris
of an original dwarf. The observed complex structures, including in particular
a stream apparently emanating from a satellite of a satellite, point to a high
rate of ongoing dwarf destruction/accretion in the region of the Virgo Cluster
where NGC 4216 is located. We discuss the age of the interactions and whether
they occurred in a group that is just falling into the cluster and shows signs
of so-called "pre-processing" before it gets affected by the cluster
environment, or in a group which already ventured towards the central regions
of Virgo Cluster. |
Luminosity Distribution of Gamma-Ray Burst Host Galaxies at redshift z=1
in Cosmological Smoothed Particle Hydrodynamic Simulations: Implications for
the Metallicity Dependence of GRBs: We study the relationship between the metallicity of gamma-ray burst (GRB)
progenitors and the probability distribution function (PDF) of GRB host
galaxies as a function of luminosity using cosmological hydrodynamic
simulations of galaxy formation. We impose a maximum limit to the gas
metallicity in which GRBs can occur, and examine how the predicted luminosity
PDF of GRB host galaxies changes in the simulation. We perform the
Kolmogorov-Smirnov test, and show that the result from our simulation agrees
with the observed luminosity PDF of core-collapse supernovae (SNe) host
galaxies when we assume that the core-collapse SNe trace star formation. When
we assume that GRBs occur only in a low-metallicity environment with $Z\lesssim
0.1 \Zsun$, GRBs occur in lower luminosity galaxies, and the simulated
luminosity PDF becomes quantitatively consistent with the observed luminosity
PDF. The observational bias against the host galaxies of optically dark GRBs
owing to dust extinction may be another reason for the lower luminosities of
GRB host galaxies, but the observed luminosity PDF of GRB host galaxies cannot
be reproduced solely by the dust bias in our simulation. | Statistical and dynamical decoupling of the IGM from Dark Matter: The mean mass densities of cosmic dark matter is larger than that of baryonic
matter by a factor of about 5 in the $\Lambda$CDM universe. Therefore, the
gravity on large scales should be dominant by the distribution of dark matter
in the universe. However, a series of observations incontrovertibly show that
the velocity and density fields of baryonic matter are decoupling from
underlying dark matter field. This paper shows our attemps to unveil the
physics behind this puzzle. In linear approximation, the dynamics of the baryon
fluid is completely governed by the gravity of the dark matter. Consequently,
the mass density field of baryon matter $\rho_b({\bf r},t)$ will be
proportional to that of dark matter $\rho_{\rm dm}({\bf r},t)$, even though
they are different from each other initially. In weak and moderate nonlinear
regime, the dynamics of the baryon fluid can be sketched by Burgers equation. A
basic feature of the Burgers dynamics is to yield shocks. When the Reynolds
number is large, the Burgers fluid will be in the state of Burgers turbulence,
which consists of shocks and complex structures. On the other hand, the
collisionless dark matter may not show such shock, but a multivalued velocity
field. Therefore, the weak and moderate nonlinear evolution leads to the
IGM-dark matter deviation. Yet, the velocity field of Burgers fluid is still
irrotational, as gravity is curl-free. In fully nonlinear regime, the vorticity
of velocity field developed, and the cosmic baryonic fluid will no longer be
potential, as the dynamics of vorticity is independent of gravity and can be
self maintained by the nonlinearity of hydrodynamics. In this case, the cosmic
baryon fluid is in the state of fully developed turbulence, which is
statistically and dynamically decoupling from dark matter. This scenario
provides a mechanism of cohenent explanation of observations. |
Towards a proof of the equivalence between FRW background expansion and
statistical isotropy: We will expose in this paper our advances towards a proof of the equivalence
between FRW background expansion, during some period of time that contains
primordial inflation, and the statistical isotropy of the primordial curvature
perturbation $\zeta$ at the end of this period of time. Our motivation rests on
the growing interest in the existence of a preferred direction in the Universe
hinted by the continuous presence of anomalies in the CMB data. | Search for TeV $γ$ -rays from H1426+428 during 2004-07 with the
TACTIC telescope: The BL Lac object H1426+428 ($z\equiv 0.129$) is an established source of TeV
$\gamma$-rays and detections of these photons from this object also have
important implications for estimating the Extragalactic Background Light (EBL)
in addition to the understanding of the particle acceleration and $\gamma$-ray
production mechanisms in the AGN jets. We have observed this source for about
244h in 2004, 2006 and 2007 with the TACTIC $\gamma$-ray telescope located at
Mt. Abu, India. Detailed analysis of these data do not indicate the presence of
any statistically significant TeV $\gamma$-ray signal from the source
direction. Accordingly, we have placed an upper limit of
$\leq1.18\times10^{-12}$ $photons$ $cm^{-2}$ $s^{-1}$ on the integrated
$\gamma$-ray flux at 3$\sigma$ significance level. |
A new model for the infrared emission of IRAS F10214+4724: We present a new model for the infrared emission of the high redshift
hyperluminous infrared galaxy IRAS F10214+4724 which takes into account recent
photometric data from Spitzer and Herschel that sample the peak of its spectral
energy distribution. We first demonstrate that the combination of the AGN
tapered disc and starburst models of Efstathiou and coworkers, while able to
give an excellent fit to the average spectrum of type 2 AGN measured by
Spitzer, fails to match the spectral energy distribution of IRAS F10214+4724.
This is mainly due to the fact that the nuSnu distribution of the galaxy falls
very steeply with increasing frequency (a characteristic of heavy absorption by
dust) but shows a silicate feature in emission. We propose a model that assumes
two components of emission: clouds that are associated with the narrow-line
region and a highly obscured starburst. The emission from the clouds must
suffer significantly stronger gravitational lensing compared to the emission
from the torus to explain the observed spectral energy distribution. | Herschel-ATLAS/GAMA: SDSS cross-correlation induced by weak lensing: We report a highly significant ($>10\sigma$) spatial correlation between
galaxies with $S_{350\mu\rm m}\ge 30\,$mJy detected in the equatorial fields of
the \textsl{Herschel} Astrophysical Terahertz Large Area Survey (H-ATLAS) with
estimated redshifts $\gtrsim 1.5$, and SDSS or GAMA galaxies at $0.2\le z\le
0.6$. The significance of the cross-correlation is much higher than those
reported so far for samples with non-overlapping redshift distributions
selected in other wavebands. Extensive, realistic simulations of clustered
sub-mm galaxies amplified by foreground structures confirm that the
cross-correlation is explained by weak gravitational lensing ($\mu<2$). The
simulations also show that the measured amplitude and range of angular scales
of the signal are larger than can be accounted for by galaxy-galaxy weak
lensing. However, for scales $\lesssim 2\,$arcmin, the signal can be reproduced
if SDSS/GAMA galaxies act as signposts of galaxy groups/clusters with halo
masses in the range $10^{13.2}$--$10^{14.5} M_{\odot}$. The signal detected on
larger scales appears to reflect the clustering of such halos. |
Non-Gaussianity from Isocurvature Perturbations : Analysis of
Trispectrum: Non-Gaussianity may exist in the CDM isocurvature perturbation. We provide
general expressions for the bispectrum and trispectrum of both adiabatic and
isocurvature pertubations. We apply our result to the QCD axion case, and found
a consistency relation between the coefficients of the bispectrum and
trispectrum : tau_{NL}^(iso)~10^3 [f_{NL}^(iso)]^{4/3}, if the axion is
dominantly produced by quantum fluctuation. Thus future observations of the
trispectrum, as well as the bispectrum, will be important for understanding the
origin of the CDM and baryon asymmetry. | Organised Randoms: Learning and correcting for systematic galaxy
clustering patterns in KiDS using self-organising maps: We present a new method for the mitigation of observational systematic
effects in angular galaxy clustering via corrective random galaxy catalogues.
Real and synthetic galaxy data, from the Kilo Degree Survey's (KiDS)
4$^{\rm{th}}$ Data Release (KiDS-$1000$) and the Full-sky Lognormal
Astro-fields Simulation Kit (FLASK) package respectively, are used to train
self-organising maps (SOMs) to learn the multivariate relationships between
observed galaxy number density and up to six systematic-tracer variables,
including seeing, Galactic dust extinction, and Galactic stellar density. We
then create `organised' randoms, i.e. random galaxy catalogues with spatially
variable number densities, mimicking the learnt systematic density modes in the
data. Using realistically biased mock data, we show that these organised
randoms consistently subtract spurious density modes from the two-point angular
correlation function $w(\vartheta)$, correcting biases of up to $12\sigma$ in
the mean clustering amplitude to as low as $0.1\sigma$, over a high
signal-to-noise angular range of 7-100 arcmin. Their performance is also
validated for angular clustering cross-correlations in a bright, flux-limited
subset of KiDS-$1000$, comparing against an analogous sample constructed from
highly-complete spectroscopic redshift data. Each organised random catalogue
object is a `clone' carrying the properties of a real galaxy, and is
distributed throughout the survey footprint according to the parent galaxy's
position in systematics-space. Thus, sub-sample randoms are readily derived
from a single master random catalogue via the same selection as applied to the
real galaxies. Our method is expected to improve in performance with increased
survey area, galaxy number density, and systematic contamination, making
organised randoms extremely promising for current and future clustering
analyses of faint samples. |
Observable Deviations from Homogeneity in an Inhomogeneous Universe: How does inhomogeneity affect our interpretation of cosmological
observations? It has long been wondered to what extent the observable
properties of an inhomogeneous universe differ from those of a corresponding
Friedman-Lemaitre-Robertson-Walker (FLRW) model, and how the inhomogeneities
affect that correspondence. Here, we use numerical relativity to study the
behavior of light beams traversing an inhomogeneous universe and construct the
resulting Hubble diagrams. The universe that emerges exhibits an average FLRW
behavior, but inhomogeneous structures contribute to deviations in observables
across the observer's sky. We also investigate the relationship between angular
diameter distance and the angular extent of a source, finding deviations that
grow with source redshift. These departures from FLRW are important
path-dependent effects with implications for using real observables in an
inhomogeneous universe such as our own. | On the inconsistency between the estimates of cosmic star formation rate
and stellar mass density of high redshift galaxies: There are mainly two different approaches to measure the cosmic star
formation history: direct star formation rate density (SFRD) and stellar mass
density rhostar as functions of redshift. Compilations of current observations
seem to show a disparity in the two quantities, in the sense that the integral
of SFRD is higher than the observed rhostar (after considering gas recycling).
Using cosmological smoothed particle hydrodynamics simulations based on the
concordance Lambda cold dark matter model, we show that the two quantities
become more consistent with each other when we consider the observed galaxy
mass limit. The comparison between simulations and (dust corrected) observed
cosmic SFRD shows a good agreement, while the observed rhostar is significantly
lower than the simulation results. This can be reconciled if the current
high-$z$ galaxy surveys are missing faint low-mass galaxies due to their flux
limit. Our simulated GSMFs have steep low-mass end slopes of alpha < -2 at z>3,
and when these numerous low-mass galaxies are included, the total rhostar
matches with the integral of SFRD. |
Comments on the mass sheet degeneracy in cosmography analyses: We make a number of comments regarding modeling degeneracies in strong
lensing measurements of the Hubble parameter $H_0$. The first point concerns
the impact of weak lensing associated with different segments of the line of
sight. We show that external convergence terms associated with the lens-source
and observer-lens segments need to be included in cosmographic modeling, in
addition to the usual observer-source term, to avoid systematic bias in the
inferred value of $H_0$. Specifically, we show how an incomplete account of
some line of sight terms biases stellar kinematics as well as ray tracing
simulation methods to alleviate the mass sheet degeneracy. The second point
concerns the use of imaging data for multiple strongly-lensed sources in a
given system. We show that the mass sheet degeneracy is not fully resolved by
the availability of multiple sources: some degeneracy remains because of
differential external convergence between the different sources. Similarly,
differential external convergence also complicates the use of multiple sources
in addressing the approximate mass sheet degeneracy associated with a local
("internal") core component in lens galaxies. This internal-external degeneracy
is amplified by the non-monotonicity of the angular diameter distance as a
function of redshift. For a rough assessment of the weak lensing effects, we
provide estimates of external convergence using the nonlinear matter power
spectrum, paying attention to non-equal time correlators. | Constraining dark matter-dark energy interaction with gas mass fraction
in galaxy clusters: The recent observational evidence for the current cosmic acceleration have
stimulated renewed interest in alternative cosmologies, such as scenarios with
interaction in the dark sector (dark matter and dark energy). In general, such
models contain an unknown negative-pressure dark component coupled with the
pressureless dark matter and/or with the baryons that results in an evolution
for the Universe rather different from the one predicted by the standard
$\Lambda$CDM model. In this work we test the observational viability of such
scenarios by using the most recent galaxy cluster gas mass fraction versus
redshift data (42 X-ray luminous, dynamically relaxed galaxy clusters spanning
the redshift range 0.063 < z < 1.063) (Allen et al. 2008) to place bounds on
the parameter $\epsilon$ that characterizes the dark matter/dark energy
coupling. The resulting are consistent with, and typically as constraining as,
those derived from other cosmological data. Although a time-independent
cosmological constant ($\Lambda$CDM model) is a good fit to these galaxy
cluster data, an interacting dark energy component cannot yet be ruled out. |
The Luminosity Function of Lyman alpha Emitters at Redshift z=7.7: Lyman alpha (Lya) emission lines should be attenuated in a neutral
intergalactic medium (IGM). Therefore the visibility of Lya emitters at high
redshifts can serve as a valuable probe of reionization at about the 50% level.
We present an imaging search for z=7.7 Lya emitting galaxies using an
ultra-narrowband filter (filter width= 9A) on the NEWFIRM imager at the Kitt
Peak National Observatory. We found four candidate Lya emitters in a survey
volume of 1.4 x 10^4 Mpc^3, with a line flux brighter than 6x10^-18 erg/cm^2/s
(5 sigma in 2" aperture). We also performed a detailed Monte-Carlo simulation
incorporating the instrumental effects to estimate the expected number of Lya
emitters in our survey, and found that we should expect to detect one Lya
emitter, assuming a non-evolving Lya luminosity function (LF) between z=6.5 and
z=7.7. Even if one of the present candidates is spectroscopically confirmed as
a z~8 Lya emitter, it would indicate that there is no significant evolution of
the Lya LF from z=3.1 to z~8. While firm conclusions would need both
spectroscopic confirmations and larger surveys to boost the number counts of
galaxies, we successfully demonstrate the feasibility of sensitive
near-infrared (1.06 um) narrow-band searches using custom filters designed to
avoid the OH emission lines that make up most of the sky background. | Parity-violating CMB correlators with non-decaying statistical
anisotropy: We examine the cosmological correlators induced by the simultaneous breaking
of parity and of statistical isotropy, e.g., in presence of the coupling ${\cal
L} = f(\phi) ( - \frac{1}{4} F^2 + \frac{\gamma}{4} F \tilde{F} )$ between the
inflaton $\phi$ and a vector field with vacuum expectation value ${\bf A}$. For
a suitably chosen function $f$, the energy in the vector field $\rho_{\rm A}$
does not decay during inflation. This results in nearly scale-invariant
signatures of broken statistical isotropy and parity. Specifically, we find
that the scalar-scalar correlator of primordial curvature perturbations
includes a quadrupolar anisotropy, $P_\zeta ( {\bf k}) = P(k)[ 1 + g_* (
\hat{\bf k} \cdot \hat{\bf A})^2]$, and a (angle-averaged) scalar bispectrum
that is a linear combination of the first $3$ Legendre polynomials,
$B_\zeta(k_1, k_2, k_3) = \sum_L c_L P_L (\hat{\bf k}_1 \cdot \hat{\bf k}_2)
P(k_1) P(k_2) + 2~{\rm perms} $, with $c_0 : c_1 : c_2 = 2 : -3 : 1$ ($c_1 \neq
0$ is a consequence of parity violation, corresponding to the constant $\gamma
\neq 0$). The latter is one of the main results of this paper, which provides
for the first time a clear example of an inflationary model where a
non-negligible $c_1$ contribution to the bispectrum is generated. The
scalar-tensor and tensor-tensor correlators induce characteristic signatures in
the Cosmic Microwave Background temperature anisotropies (T) and polarization
(E/B modes); namely, non-diagonal contributions to $\langle a_{\ell_1 m_1}
a_{\ell_2 m_2}^* \rangle$, with $|\ell_1 - \ell_2| = 1$ in TT, TE, EE and BB,
and $|\ell_1 - \ell_2| = 2$ in TB and EB. The latest CMB bounds on the scalar
observables ($g_*$, $c_0$, $c_1$ and $c_2$), translate into the upper limit
$\rho_{\rm A} / \rho_\phi \lesssim 10^{-9}$ at $\gamma=0$. We find that the
upper limit on the vector energy density becomes much more stringent as
$\gamma$ grows. |
Galaxy cluster Sunyaev-Zel'dovich effect scaling-relation and type Ia
supernova observations as a test for the cosmic distance duality relation: In this paper, we propose a new test to the cosmic distance duality relation
(CDDR), $D_L=D_A(1+z)^2$, where $D_L$ and $D_A$ are the luminosity and angular
diameter distances, respectively. The data used correspond to 61 Type Ia
Supernova luminosity distances and $Y_{SZE}-Y_X$ measurements of 61 galaxy
clusters obtained by the {\it Planck} mission and the deep XMM-Newton X-ray
data, where $Y_{SZE}$ is the integrated comptonization parameter obtained via
Sunyaev-Zel'dovich effect observations and $Y_X$ is the X-ray counterpart. More
precisely, we use the $Y_{SZE}D_{A}^{2}/C_{XSZE}Y_X$ scaling-relation and a
deformed CDDR, such as $D_L/D_A(1+z)^2=\eta(z)$, to verify if $\eta(z)$ is
compatible with the unity. Two $\eta(z)$ functions are used, namely,
$\eta(z)=1+\eta_0 z$ and $\eta(z)=1+\eta_0 z /(1+z)$. { We obtain that the CDDR
validity ($\eta_0=0$) is verified within $\approx 1.5\sigma$ c.l. for both
$\eta(z)$ functions.}. | Complete super-sample lensing covariance in the response approach: We derive the complete super-sample covariance (SSC) of the matter and weak
lensing convergence power spectra using the power spectrum response formalism
to accurately describe the coupling of super- to sub-survey modes. The SSC term
is completely characterized by the survey window function, the nonlinear matter
power spectrum and the full first-order nonlinear power spectrum response
function, which describes the response to super-survey density and tidal field
perturbations. Generalized separate universe simulations can efficiently
measure these responses in the nonlinear regime of structure formation, which
is necessary for lensing applications. We derive the lensing SSC formulae for
two cases: one under the Limber and flat-sky approximations, and a more general
one that goes beyond the Limber approximation in the super-survey mode and is
valid for curved sky applications. Quantitatively, we find that for sky
fractions $f_{\rm sky} \approx 0.3$ and a single source redshift at $z_S=1$,
the use of the flat-sky and Limber approximation underestimates the total SSC
contribution by $\approx 10\%$. The contribution from super-survey tidal fields
to the lensing SSC, which has not been included in cosmological analyses so
far, is shown to represent about $5\%$ of the total lensing covariance on
multipoles $\ell_1,\ell_2 \gtrsim 300$. The SSC is the dominant off-diagonal
contribution to the total lensing covariance, making it appropriate to include
these tidal terms and beyond flat-sky/Limber corrections in cosmic shear
analyses. |
Long-Lived Time-Dependent Remnants During Cosmological Symmetry
Breaking: From Inflation to the Electroweak Scale: Through a detailed numerical investigation in three spatial dimensions, we
demonstrate that long-lived time-dependent field configurations emerge
dynamically during symmetry breaking in an expanding de Sitter spacetime. We
investigate two situations: a single scalar field with a double-well potential
and the bosonic sector of an SU(2) non-Abelian Higgs model. For the single
scalar, we show that large-amplitude oscillon configurations emerge
spontaneously and persist to contribute about 1.2% of the energy density of the
universe. We also show that for a range of parameters, oscillon lifetimes are
enhanced by the expansion and that this effect is a result of parametric
resonance. For the SU(2) case, we see about 4% of the final energy density in
oscillons. | The Large-Scale Observational Signatures of Low-Mass Galaxies During
Reionization: Observations of the epoch of reionization give us clues about the nature and
evolution of the sources of ionizing photons, or early stars and galaxies. We
present a new suite of structure formation and radiative transfer simulations
from the PRACE4LOFAR project designed to investigate whether the mechanism of
radiative feedback, or the suppression of star formation in ionized regions
from UV radiation, can be inferred from these observations. Our source halo
mass extends down to $10^8 M_\odot$, with sources in the mass range $10^8$ to
$10^9 M_\odot$ expected to be particularly susceptible to feedback from
ionizing radiation, and we vary the aggressiveness and nature of this
suppression. Not only do we have four distinct source models, we also include
two box sizes (67 Mpc and 349 Mpc), each with two grid resolutions. This suite
of simulations allows us to investigate the robustness of our results. All of
our simulations are broadly consistent with the observed electron-scattering
optical depth of the cosmic microwave background and the neutral fraction and
photoionization rate of hydrogen at $z\sim6$. In particular, we investigate the
redshifted 21-cm emission in anticipation of upcoming radio interferometer
observations. We find that the overall shape of the 21-cm signal and various
statistics are robust to the exact nature of source suppression, the box size,
and the resolution. There are some promising model discriminators in the
non-Gaussianity and small-scale power spectrum of the 21-cm signal. |
Rolling in the Modulated Reheating Scenario: In the modulated reheating scenario, the field that drives inflation has a
spatially varying decay rate, and the resulting inhomogeneous reheating process
generates adiabatic perturbations. We examine the statistical properties of the
density perturbations generated in this scenario. Unlike earlier analyses, we
include the dynamics of the field that determines the inflaton decay rate. We
show that the dynamics of this modulus field can significantly alter the
amplitude of the power spectrum and the bispectrum, even if the modulus field
has a simple potential and its effective mass is smaller than the Hubble rate.
In some cases, the evolution of the modulus amplifies the non-Gaussianity of
the perturbations to levels that are excluded by recent observations of the
cosmic microwave background. Therefore, a proper treatment of the modulus
dynamics is required to accurately calculate the statistical properties of the
perturbations generated by modulated reheating. | On the space of non-Gaussian fields with single-clock bispectra: We develop a mathematical construction of non-Gaussian fields whose bispectra
satisfy the single-clock inflation consistency relation. At the same order that
our basis for bispectra recovers the two simplest single clock templates, we
also find a third orthogonal template which has the single clock squeezed
limit, peaks in folded configurations, and has very small coupling in the
equilateral limit. We explore the map between templates and operators in a very
general Lagrangian for single-clock fluctuations and find no significant
overlap between the new template and models in the literature. We comment on
the physical implications of this conclusion. Our findings add support for the
idea that both theory and data driven considerations will be best served if
next generation non-Gaussianity constraints are made in a basis that uses the
degree of coupling between long and short wavelength modes as an organizing
principle. |
Neutrino mass in cosmology: status and prospects: I give an overview of the effects of neutrino masses in cosmology, focussing
on the role they play in the evolution of cosmological perturbations. I discuss
how recent observations of the cosmic microwave background anisotropies and the
large-scale matter distribution can probe neutrino masses with greater
precision than current laboratory experiments. I describe several new
techniques that will be used to probe cosmology in the future, as well as
recent advances in the computation of the nonlinear matter power spectrum and
related observables. | Cosmology with Galaxy Cluster Properties using Machine Learning: [Abridged] Galaxy clusters are the most massive gravitationally-bound systems
in the universe and are widely considered to be an effective cosmological
probe. We propose the first Machine Learning method using galaxy cluster
properties to derive unbiased constraints on a set of cosmological parameters,
including Omega_m, sigma_8, Omega_b, and h_0. We train the machine learning
model with mock catalogs including "measured" quantities from Magneticum
multi-cosmology hydrodynamical simulations, like gas mass, gas bolometric
luminosity, gas temperature, stellar mass, cluster radius, total mass, velocity
dispersion, and redshift, and correctly predict all parameters with
uncertainties of the order of ~14% for Omega_m, ~8% for sigma_8, ~6% for
Omega_b, and ~3% for h_0. This first test is exceptionally promising, as it
shows that machine learning can efficiently map the correlations in the
multi-dimensional space of the observed quantities to the cosmological
parameter space and narrow down the probability that a given sample belongs to
a given cosmological parameter combination. In the future, these ML tools can
be applied to cluster samples with multi-wavelength observations from surveys
like LSST, CSST, Euclid, Roman in optical and near-infrared bands, and eROSITA
in X-rays, to constrain both the cosmology and the effect of the baryonic
feedback. |
An optimal FFT-based anisotropic power spectrum estimator: Measurements of line-of-sight dependent clustering via the galaxy power
spectrum's multipole moments constitute a powerful tool for testing theoretical
models in large-scale structure. Recent work shows that this measurement,
including a moving line-of-sight, can be accelerated using Fast Fourier
Transforms (FFTs) by decomposing the Legendre polynomials into products of
Cartesian vectors. Here, we present a faster, optimal means of using FFTs for
this measurement. We avoid redundancy present in the Cartesian decomposition by
using a spherical harmonic decomposition of the Legendre polynomials.
Consequently, our method is substantially faster: a given multipole of order
$\ell$ requires only $2\ell+1$ FFTs rather than the $(\ell+1)(\ell+2)/2$ FFTs
of the Cartesian approach. For the hexadecapole ($\ell = 4$), this translates
to $40\%$ fewer FFTs, with increased savings for higher $\ell$. The reduction
in wall-clock time enables the calculation of finely-binned wedges in
$P(k,\mu)$, obtained by computing multipoles up to a large $\ell_{\rm max}$ and
combining them. This transformation has a number of advantages. We demonstrate
that by using non-uniform bins in $\mu$, we can isolate plane-of-sky (angular)
systematics to a narrow bin at $\mu \simeq 0$ while eliminating the
contamination from all other bins. We also show that the covariance matrix of
clustering wedges binned uniformly in $\mu$ becomes ill-conditioned when
combining multipoles up to large values of $\ell_{\rm max}$, but that the
problem can be avoided with non-uniform binning. As an example, we present
results using $\ell_{\rm max}=16$, for which our procedure requires a factor of
3.4 fewer FFTs than the Cartesian method, while removing the first $\mu$ bin
leads only to a 7% increase in statistical error on $f \sigma_8$, as compared
to a 54% increase with $\ell_{\rm max}=4$. | X-rays from a radio-loud compact BAL Quasar 1045+352 and the nature of
outflows in radio-loud BAL Quasars: We present new results on X-ray properties of radio loud broad absorption
line (BAL) quasars and focus on broad-band spectral properties of a high
ionization BAL (HiBAL) compact steep spectrum (CSS) radio-loud quasar 1045+352.
This HiBAL quasar has a very complex radio morphology indicating either strong
interactions between a radio jet and the surrounding interstellar medium or a
possible re-start of the jet activity. We detected 1045+352 quasar in a short 5
ksec Chandra ACIS-S observation. We applied theoretical models to explain
spectral energy distribution (SED) of 1045+352 and argue that non-thermal,
inverse-Compton emission from the innermost parts of the radio jet can account
for a large fraction of the observed X-ray emission. In our analysis we also
consider a scenario in which the observed X-ray emission from radio-loud BAL
quasars can be a sum of inverse-Compton jet X-ray emission and optically thin
corona X-ray emission. We compiled a sample of radio-loud BAL quasars that were
observed in X-rays to date and report no correlation between their X-ray and
radio luminosity. However, the radio-loud BAL quasars show a large range of
X-ray luminosities and absorption columns. This is consistent with the results
obtained earlier for radio-quiet BAL quasars and may indicate an orientation
effect in BAL quasars or more complex dependence between X-ray emission, radio
emission and an orientation based on the radio morphology. |
Imprints of non-standard Dark Energy and Dark Matter Models on the 21cm
Intensity Map Power Spectrum: We study the imprint of non-standard dark energy (DE) and dark matter (DM)
models on the 21cm intensity map power spectra from high-redshift neutral
hydrogen (HI) gas. To this purpose we use halo catalogs from N-body simulations
of dynamical DE models and DM scenarios which are statistically
indistinguishable from the standard Cold Dark Matter model with Cosmological
Constant (LCDM) using currently available cosmological observations. We limit
our analysis to halo catalogs at redshift z = 1 and 2.3 which are common to all
simulations. For each catalog we model the HI distribution by using a simple
prescription to associate the HI gas mass to N-body halos. We find that the DE
models leave a distinct signature on the HI spectra across a wide range of
scales, which correlates with differences in the halo mass function and the
onset of the non-linear regime of clustering. In the case of the non-standard
DM model significant differences of the HI spectra with respect to the LCDM
model only arise from the suppressed abundance of low mass halos. These
cosmological model dependent features also appear in the 21cm spectra. In
particular, we find that future SKA measurements can distinguish the imprints
of DE and DM models at high statistical significance. | The Effective Fluid approach for Modified Gravity and its applications: In this review we briefly summarize the so-called effective fluid approach,
which is a compact framework that can be used to describe a plethora of
different modified gravity models as general relativity (GR) and a dark energy
(DE) fluid. This approach, which is complementary to the cosmological effective
field theory, has several benefits as it allows for the easier inclusion of
most modified gravity models into the state-of-the-art Boltzmann codes, that
are typically hard-coded for GR and DE. Furthermore, it can also provide
theoretical insights into their behavior, since in linear perturbation theory
it is easy to derive physically motivated quantities such as the DE anisotropic
stress or the DE sound speed. We also present some explicit applications of the
effective fluid approach with $f(R)$, Horndeski and Scalar-Vector-Tensor
models, namely how this approach can be used to easily solve the perturbation
equations and incorporate the aforementioned modified gravity models into
Boltzmann codes so as to obtain cosmological constraints using Monte Carlo
analyses. |
Sub-structure and merger detection in resolved NIKA Sunyaev-Zel'dovich
images of distant clusters: Sub-structures in the hot gas of galaxy clusters are related to their
formation history and to the astrophysical processes at play in the
intracluster medium (ICM). The thermal Sunyaev-Zel'dovich (tSZ) effect is
directly sensitive to the line-of-sight integrated ICM pressure, and is thus
particularly adapted to study ICM sub-structures. We apply
structure-enhancement filtering algorithms to high resolution tSZ observations
of distant clusters, in order to search for pressure discontinuities,
compressions, as well as secondary peaks in the ICM. The same filters are
applied to synthetic tSZ images extracted from RHAPSODY-G hydrodynamic
simulations, in order to better interpret the extracted features. We also study
the noise propagation trough the filters and quantify the impact of systematic
effects, point source residuals being identified as the dominant potential
contaminant. In 3 of our 6 NIKA clusters we identify features at high S/N that
show clear evidence for merger events. In MACSJ0717 (z=0.55), three strong
pressure gradients are observed on the E, SE and W sectors, and two main peaks
in the pressure distribution are identified. We observe a lack of tSZ compact
structure in the cool-core cluster PSZ1G045.85 (z=0.61), and a tSZ gradient
ridge dominates in the SE. In the highest z cluster, CLJ1227 (z=0.89), we
detect a ~45" (360 kpc) long ridge pressure gradient associated with a
secondary pressure peak in the W region. Our results show that current tSZ
facilities have now reached the angular resolution and sensitivity to allow an
exploration of the details of pressure sub-structures in clusters, even at high
z. This opens the possibility to quantify the impact of the dynamical state on
the relation between the tSZ signal and the mass of clusters, which is
important when using tSZ clusters to test cosmological models. This work also
marks the first NIKA cluster sample data release. | Strong gravitational lensing's 'external shear' is not shear: The distribution of mass in galaxy-scale strong gravitational lenses is often
modelled as an elliptical power law plus 'external shear', which notionally
accounts for neighbouring galaxies and cosmic shear. We show that it does not.
Except in a handful of rare systems, the best-fit values of external shear do
not correlate with independent measurements of shear: from weak lensing in 45
Hubble Space Telescope images, or in 50 mock images of lenses with complex
distributions of mass. Instead, the best-fit shear is aligned with the major or
minor axis of 88% of lens galaxies; and the amplitude of the external shear
increases if that galaxy is disky. We conclude that 'external shear' attached
to a power law model is not physically meaningful, but a fudge to compensate
for lack of model complexity. Since it biases other model parameters that are
interpreted as physically meaningful in several science analyses (e.g.
measuring galaxy evolution, dark matter physics or cosmological parameters), we
recommend that future studies of galaxy-scale strong lensing should employ more
flexible mass models. |
Radio and spectroscopic properties of miniature radio galaxies:
revealing the bulk of the radio-loud AGN population: We explore radio and spectroscopic properties of a sample of 14 miniature
radio galaxies, i.e. early-type core galaxies hosting radio-loud AGN of
extremely low radio power, 10^(27-29) erg s^(-1) Hz^(-1) at 1.4 GHz. Miniature
radio galaxies smoothly extend the relationships found for the more powerful
FRI radio galaxies between emission line, optical and radio nuclear
luminosities to lower levels. However, they have a deficit of a factor of ~100
in extended radio emission with respect to that of the classical example of
3CR/FRI. This is not due to their low luminosity, since we found radio galaxies
of higher radio core power, similar to those of 3CR/FRI, showing the same
behavior, i.e. lacking significant extended radio emission. Such sources form
the bulk of the population of radio-loud AGN in the Sloan Digital Sky Survey.
At a given level of nuclear emission, one can find radio sources with an
extremely wide range, a factor of >~100, of radio power. We argue that the
prevalence of sources with luminous extended radio structures in flux limited
samples is due to a selection bias, since the inclusion of such objects is
highly favored. The most studied catalogues of radio galaxies are thus composed
by the minority of radio-loud AGN that meet the physical conditions required to
form extended radio sources, while the bulk of the population is virtually
unexplored. | Modified Gravity-GADGET: A new code for cosmological hydrodynamical
simulations of modified gravity models: We present a new massively parallel code for N-body and cosmological
hydrodynamical simulations of modified gravity models. The code employs a
multigrid-accelerated Newton-Gauss-Seidel relaxation solver on an adaptive mesh
to efficiently solve for perturbations in the scalar degree of freedom of the
modified gravity model. As this new algorithm is implemented as a module for
the P-Gadget3 code, it can at the same time follow the baryonic physics
included in P-Gadget3, such as hydrodynamics, radiative cooling and star
formation. We demonstrate that the code works reliably by applying it to simple
test problems that can be solved analytically, as well as by comparing
cosmological simulations to results from the literature. Using the new code, we
perform the first non-radiative and radiative cosmological hydrodynamical
simulations of an f(R)-gravity model. We also discuss the impact of AGN
feedback on the matter power spectrum, as well as degeneracies between the
influence of baryonic processes and modifications of gravity. |
CosmoLike - Cosmological Likelihood Analyses for Photometric Galaxy
Surveys: We explore strategies to extract cosmological constraints from a joint
analysis of cosmic shear, galaxy-galaxy lensing, galaxy clustering, cluster
number counts and cluster weak lensing. We utilize the CosmoLike software to
simulate results from an LSST like data set, specifically, we 1) compare
individual and joint analyses of the different probes, 2) vary the selection
criteria for lens and source galaxies, 3) investigate the impact of blending,
4) investigate the impact of the assumed cosmological model in multi-probe
covariances, 6) quantify information content as a function of scales, and 7)
explore the impact of intrinsic galaxy alignment in a multi-probe context. Our
analyses account for all cross correlations within and across probes and
include the higher-order (non-Gaussian) terms in the multi-probe covariance
matrix. We simultaneously model cosmological parameters and a variety of
systematics, e.g. uncertainties arising from shear and photo-z calibration,
cluster mass-observable relation, galaxy intrinsic alignment, and galaxy bias
(up to 54 parameters altogether). We highlight two results: First, increasing
the number density of source galaxies by ~30%, which corresponds to solving
blending for LSST, only gains little information. Second, including small
scales in clustering and galaxy-galaxy lensing, by utilizing HODs, can
substantially boost cosmological constraining power. The CosmoLike modules used
to compute the results in this paper will be made publicly available at
https://github.com/elikrause/CosmoLike_Forecasts. | Primordial black holes in scalar field inflation coupled to the
Gauss-Bonnet term with fractional power-law potentials: In this study, we investigate the formation of primordial black holes (PBHs)
in a scalar field inflationary model coupled to the Gauss-Bonnet (GB) term with
fractional power-law potentials. The coupling function enhances the curvature
perturbations, then results in the generation of PBHs and detectable secondary
gravitational waves (GWs). % We identify three separate sets of parameters for
the potential functions of the form $\phi^{1/3}$, $\phi^{2/5}$, and
$\phi^{2/3}$. By adjusting the model parameters, we decelerate the inflaton
during the ultra slow-roll (USR) phase and enhance curvature perturbations. %
Our calculations predict the formation of PBHs with masses of ${\cal
O}(10)M_{\odot}$, which are compatible with LIGO-Virgo observational data.
Additionally, we find PBHs with masses around ${\cal O}(10^{-6})M_{\odot}$ and
${\cal O}(10^{-5})M_{\odot}$, which can explain ultrashort-timescale
microlensing events in OGLE data. % Furthermore, our proposed mechanism could
lead to the formation of PBHs in mass scales around ${\cal
O}(10^{-14})M_{\odot}$ and ${\cal O}(10^{-13})M_{\odot}$, contributing to
approximately 99\% of the dark matter in the universe. % We also study the
production of secondary GWs in our model. In all cases of the model, the
density parameter of secondary GWs $\Omega_{\rm GW_0}$ exhibits peaks that
intersect the sensitivity curves of GWs detectors, providing a means to verify
our findings using data of these detectors. % Our numerical results demonstrate
a power-law behavior for the spectra of $\Omega_{\rm GW_0}$ with respect to
frequency, given by $\Omega_{\rm GW_0} (f) \sim (f/f_c)^{n}$. Additionally, in
the infrared regime where $f\ll f_{c}$, the power index takes a log-dependent
form, specifically $n=3-2/\ln(f_c/f)$. |
Constraining the formation of inner bars. Photometry, kinematics and
stellar populations in NGC 357: Double-barred galaxies are common in the local Universe, with approximately
one third of barred spirals hosting an smaller, inner bar. Nested bars have
been proposed as a mechanism for transporting gas to the very central regions
of the galaxy, trigger star formation and contribute to the growth of the
bulge. To test this idea, we perform for the first time a detailed analysis of
the photometry, kinematics and stellar populations of a double-barred galaxy:
NGC 357. We find that this galaxy is either hosting a pseudobulge or a
classical bulge together with an inner disc. We compare the relative mean
luminosity-weighted age, metallicity and alpha-enhancement between the
(pseudo)bulge, inner bar and outer bar, finding that the three structures are
nearly coeval and old. Moreover, the bulge and inner bar present the same
metallicity and overabundance, whereas the outer bar tends to be less
metal-rich and more alpha-enhanced. These results point out that, rather than
the classical secular scenario in which gas and star formation play a major
role, the redistribution of the existing stars is driving the formation of the
inner structures. | Moderate-Luminosity Growing Black Holes From 1.25 < z < 2.7: Varied
Accretion In Disk-Dominated Hosts: We compute black hole masses and bolometric luminosities for 57 active
galactic nuclei (AGN) in the redshift range 1.25 < z < 2.67, selected from the
GOODS-South deep multi-wavelength survey field via their X-ray emission. We
determine host galaxy morphological parameters by separating the galaxies from
their central point sources in deep HST images, and host stellar masses and
colors by multi-wavelength SED fitting. 90% of GOODS AGN at these redshifts
have detected rest-frame optical nuclear point sources; bolometric luminosities
range from 2e43 - 2e46 erg/s. The black holes are growing at a range of
accretion rates, with at least 50% of the sample having L/L_Edd < 0.1. 70% of
host galaxies have stellar masses M* > 1e10 M_sun, with a range of colors
suggesting a complex star formation history. We find no evolution of AGN
bolometric luminosity within the sample, and no correlation between AGN
bolometric luminosity and host stellar mass, color or morphology. Fully half
the sample of host galaxies is disk-dominated, with another 25% having strong
disk components. Fewer than 15% of the systems appear to be at some stage of a
major merger. These moderate-luminosity AGN hosts are therefore inconsistent
with a dynamical history dominated by mergers strong enough to destroy disks,
indicating minor mergers or secular processes dominate the co-evolution of
galaxies and their central black holes at z ~ 2. |
Observing the End of Cold Flow Accretion using Halo Absorption Systems: We use cosmological SPH simulations to study the cool, accreted gas in two
Milky Way-size galaxies through cosmic time to z=0. We find that gas from
mergers and cold flow accretion results in significant amounts of cool gas in
galaxy halos. This cool circum-galactic component drops precipitously once the
galaxies cross the critical mass to form stable shocks, Mvir = Msh ~ 10^12
Msun. Before reaching Msh, the galaxies experience cold mode accretion (T<10^5
K) and show moderately high covering fractions in accreted gas: f_c ~ 30-50%
for R<50 co-moving kpc and N_HI>10^16 cm^-2. These values are considerably
lower than observed covering fractions, suggesting that outflowing gas (not
included here) is important in simulating galaxies with realistic gaseous
halos. Within ~500 Myr of crossing the Msh threshold, each galaxy transitions
to hot mode gas accretion, and f_c drops to ~5%. The sharp transition in
covering fraction is primarily a function of halo mass, not redshift. This
signature should be detectable in absorption system studies that target
galaxies of varying host mass, and may provide a direct observational tracer of
the transition from cold flow accretion to hot mode accretion in galaxies. | Primordial Black Hole Constraints with Large Extra Dimensions: We study how the constraints on the primordial black hole density arising
from the extragalactic photon background are modified in the scenario that
there exist extra large spatial dimensions. We find that though the overall
magnitude of the constraints is not substantially different, the mass ranges to
which they apply are, and for some choices of mass it is possible for the black
holes to constitute the entirety of the dark matter. |
From diffuse extragalactic and galactic gamma rays to limits on extra
dimensions: We derive the maximum fraction of energy emitted in the form of massive
(Kaluza- Klein) gravitons by core collapse supernovae, and the corresponding
minimal extra-dimensional Planck mass M* in the ADD gravity framework at TeV
scales. Our constraints arise: a) from the extragalactic gamma ray background
observed by Fermi-LAT after astrophysical sources have been removed, and b) via
the residual galactic emission left after astrophysical and potentially dark
matter emission have been removed. We focus on a number of extra dimensions 3
and 4, since M* is then in the TeV range, where astrophysical and collider
constraints compete. Lower limits on M* are derived in case a) of 8.0 TeV and
1.1 TeV, and in case b) of 16 TeV and 1.9 TeV, for a number of extra dimensions
n=3 and n=4 respectively. These limits are especially robust and insensitive to
the various uncertainties involved. | Likelihood Non-Gaussianity in Large-Scale Structure Analyses: Standard present day large-scale structure (LSS) analyses make a major
assumption in their Bayesian parameter inference --- that the likelihood has a
Gaussian form. For summary statistics currently used in LSS, this assumption,
even if the underlying density field is Gaussian, cannot be correct in detail.
We investigate the impact of this assumption on two recent LSS analyses: the
Beutler et al. (2017) power spectrum multipole ($P_\ell$) analysis and the
Sinha et al. (2017) group multiplicity function ($\zeta$) analysis. Using
non-parametric divergence estimators on mock catalogs originally constructed
for covariance matrix estimation, we identify significant non-Gaussianity in
both the $P_\ell$ and $\zeta$ likelihoods. We then use Gaussian mixture density
estimation and Independent Component Analysis on the same mocks to construct
likelihood estimates that approximate the true likelihood better than the
Gaussian $pseudo$-likelihood. Using these likelihood estimates, we accurately
estimate the true posterior probability distribution of the Beutler et al.
(2017) and Sinha et al. (2017) parameters. Likelihood non-Gaussianity shifts
the $f\sigma_8$ constraint by $-0.44\sigma$, but otherwise, does not
significantly impact the overall parameter constraints of Beutler et al.
(2017). For the $\zeta$ analysis, using the pseudo-likelihood significantly
underestimates the uncertainties and biases the constraints of Sinha et al.
(2017) halo occupation parameters. For $\log M_1$ and $\alpha$, the posteriors
are shifted by $+0.43\sigma$ and $-0.51\sigma$ and broadened by $42\%$ and
$66\%$, respectively. The divergence and likelihood estimation methods we
present provide a straightforward framework for quantifying the impact of
likelihood non-Gaussianity and deriving more accurate parameter constraints. |
On the extended structure of the Phoenix dwarf galaxy: We present the star formation history (SFH) and its variations with
galactocentric distance for the Local Group dwarf galaxy of Phoenix.
Color-magnitude diagram was obtained from WFPC2@HST reaching the oldest main
sequence turnoffs. The IAC-star and IAC-pop codes and the MinnIAC suite have
been used to obtain the star formation rate as a function of time, metallicity,
and radius. We find that Phoenix has had ongoing but gradually decreasing star
formation over nearly a Hubble time. The highest level of star formation
occurred from the formation of the galaxy till 10.5 Gyr ago, when 50% of the
total star formation had already taken place. From that moment, star formation
continues at a significant level until 6 Gyr ago, and at a very low level till
the present time. The chemical enrichment law shows a trend of slowly
increasing metallicity as a function of time till 8--6 Gyr ago, when Z starts
to increase steeply to the current value.
Young stars are found in the inner region of the galaxy only, but
intermediate-age and old stars can be found at all galactocentric distances.
This study shows that star formation started at all galactocentric distances in
Phoenix at an early epoch. Our results are compatible with a scenario in which
the star formation region envelope slowly shrinks as time goes on, possibly as
a natural result of pressure support reduction as gas supply diminishes. As a
consequence, star formation stopped first in outer regions and the scale-length
of the stellar mass density distribution decreased with time. No traces of a
true, old halo are apparent in Phoenix either in its stellar age distribution
or in the stellar mass density distribution, at least out to 0.5 kpc (about 2.5
scale-lengths) from the center. | The radio properties of a complete, X-ray selected sample of nearby,
massive elliptical galaxies: We investigate the radio properties of a complete sample of nearby, massive,
X-ray bright elliptical and S0 galaxies. Our sample contains 18 galaxies with
ROSAT All-Sky Survey X-ray fluxes Fx_(0.1-2.4 keV) > 3 x 10^(-12) erg/s/cm^2,
within a distance of 100 Mpc. For these galaxies, we have complete (18/18) VLA
radio and Chandra X-ray coverage. Nuclear radio emission is detected from 17/18
of the galaxies. Ten of the galaxies exhibit extended radio emission; of these
ten, all but one also exhibit clear evidence of interaction of the radio source
with the surrounding, X-ray emitting gas. Among the seven galaxies with
unresolved radio sources, one has clear, and one has small, cavity-like
features in the Chandra X-ray images; a third has a disturbed X-ray morphology.
Using a radio luminosity limit equivalent to L_(1.4 Ghz) > 10^(23) W/Hz to
calculate the radio-loud fraction, we find that this misses the majority of the
radio detected galaxies in the sample. We determine integrated radio-to-X-ray
flux ratios for the galaxies, GRx, which are shown to span a large range
(factor of 100). We calculate the mass-weighted cooling times within 1 kpc, and
find hints for an anticorrelation with the radio luminosity. We also calculate
limits on k/f, where k is the ratio of the total particle energy to that of
relativistic electrons radiating in the range 10 MHz-10 GHz and f is the volume
filling factor of the plasma in the cavity. The k/f distribution is also broad,
reflecting previous results for larger galaxy clusters. Lowering the X-ray flux
limit, at the expense of less complete VLA and Chandra coverage, increases the
size of our sample to 42 galaxies. Nuclear radio activity is detected in at
least 34/42 of this extended sample. |
Fractal analysis of the galaxy distribution in the redshift range 0.45 <
z < 5.0: Evidence is presented that the galaxy distribution can be described as a
fractal system in the redshift range of the FDF galaxy survey. The fractal
dimension $D$ was derived using the FDF galaxy volume number densities in the
spatially homogeneous standard cosmological model with $\Omega_{m_0}=0.3$,
$\Omega_{\Lambda_0}=0.7$ and $H_0=70 \; \mbox{km} \; {\mbox{s}}^{-1} \;
{\mbox{Mpc}}^{-1}$. The ratio between the differential and integral number
densities $\gamma$ and $\gamma^\ast$ obtained from the red and blue FDF
galaxies provides a direct method to estimate $D$, implying that $\gamma$ and
$\gamma^\ast$ vary as power-laws with the cosmological distances. The
luminosity distance $d_{\scriptscriptstyle L}$, galaxy area distance
$d_{\scriptscriptstyle G}$ and redshift distance $d_z$ were plotted against
their respective number densities to calculate $D$ by linear fitting. It was
found that the FDF galaxy distribution is characterized by two single fractal
dimensions at successive distance ranges. Two straight lines were fitted to the
data, whose slopes change at $z \approx 1.3$ or $z \approx 1.9$ depending on
the chosen cosmological distance. The average fractal dimension calculated
using $\gamma^\ast$ changes from $\langle D \rangle=1.4^{\scriptscriptstyle
+0.7}_{\scriptscriptstyle -0.6}$ to $\langle D \rangle=0.5^{\scriptscriptstyle
+1.2}_{\scriptscriptstyle -0.4}$ for all galaxies, and $D$ decreases as $z$
increases. Small values of $D$ at high $z$ mean that in the past galaxies were
distributed much more sparsely and the large-scale galaxy structure was then
possibly dominated by voids. Results of Iribarrem et al. (2014,
arXiv:1401.6572) indicating similar fractal features with $\langle D \rangle
=0.6 \pm 0.1$ in the far-infrared sources of the Herschel/PACS evolutionary
probe (PEP) at $1.5 \lesssim z \lesssim 3.2$ are also mentioned. | Avoiding bias in measurements of fundamental constants from high
resolution quasar spectra: Recent advances in spectroscopic instrumentation and calibration methods
dramatically improve the quality of quasar spectra. Supercomputer calculations
show that, at high spectral resolution, procedures used in some previous
analyses of spacetime variations of fundamental constants are likely to
generate spurious measurements, biased systematically towards a null result.
Developments in analysis methods are also summarised and a prescription given
for the analysis of new and forthcoming data. |
Adaptive friends-of-friends algorithm for identifying gravitationally
bound cosmological structures: The Universe at the present epoch is found to be a network of matter
over-dense and under-dense regions. To date, this picture of the Universe is
best revealed through cosmological large-volume simulations and large-scale
galaxy redshift surveys, in which, the most important step is the appropriate
identification of structures. So far, these structures are identified using
various group finding codes, mostly based on the friends-of-friends (FoF) or
spherical over-density (SO) algorithms. Although, the main purpose is to
identify gravitationally bound structures, surprisingly, the mass information
has hardly been used effectively by these codes. Moreover, the methods used so
far either constrain the over-density or use the real unstructured geometry
only. Even though these are key factors in the accurate determination of
structures-mass information, hardly any attempt has been made as yet to
consider these important parameters together while formulating the grouping
algorithms. In this paper, we present our proposed algorithm which takes care
of all the above-mentioned relevant features and ensures the bound structures
by means of physical quantities, mainly mass and the total energy information.
We introduced a novel concept of physically relevant arm-length for each
element depending on their individual gravity leading to a distinct linking
length for each unique pair of elements. This proposed algorithm is thus
fundamentally new that, not only able to catch the gravitationally bound, real
unstructured geometry, it does identify it roughly within a predefined
physically motivated density threshold. Such a thing could not be
simultaneously achieved before by any of the usual FoF or SO-based methods. We
also demonstrate the unique ability of the code in the appropriate
identification of structures, both from large volume cosmological simulations
as well as from galaxy redshift surveys. | A new approach to the assessment of stochastic errors of radio source
position catalogues: Assessing the external stochastic errors of radio source position catalogues
derived from VLBI observations is important for tasks such as estimating the
quality of the catalogues and their weighting during combination. One of the
widely used methods to estimate these errors is the three-cornered-hat
technique, which can be extended to the N-cornered-hat technique. A critical
point of this method is how to properly account for the correlations between
the compared catalogues. We present a new approach to solving this problem that
is suitable for simultaneous investigations of several catalogues. To compute
the correlation between two catalogues $A$ and $B$, the differences between
these catalogues and a third arbitrary catalogue $C$ are computed. Then the
correlation between these differences is considered as an estimate of the
correlation between catalogues $A$ and $B$. The average value of these
estimates over all catalogues $C$ is taken as a final estimate of the target
correlation. In this way, an exhaustive search of all possible combinations
allows one to compute the paired correlations between all catalogues. As an
additional refinement of the method, we introduce the concept of weighted
correlation coefficient. This technique was applied to nine recently published
radio source position catalogues. We found large systematic differences between
catalogues, that significantly impact determination of their stochastic errors.
Finally, we estimated the stochastic errors of the nine catalogues. |
Schwarzschild Lecture 2014: HectoMAPping The Universe: During the last three decades progress in mapping the universe from an age of
400,000 years to the present has been stunning. Instrument/telescope
combinations have naturally determined the sampling of various redshift ranges.
Here we outline the impact of the Hectospec on the MMT on exploration of the
universe in the redshift range 0.2 < z < 0.8. We focus on dense redshift
surveys, SHELS and HectoMAP. SHELS is a complete magnitude limited survey
covering 8 square degrees. The HectoMAP survey combines a red-selected dense
redshift survey and a weak lensing map covering 50 square degrees. Combining
the dense redshift survey with a Subaru HyperSuprimeCam (HSC) weak lensing map
will provide a powerful probe of the way galaxies trace the distribution of
dark matter on a wide range of physical scales. | The minimally extended Varying Speed of Light (meVSL): Even though there have been the various varying speed of light (VSL)
cosmology models, they remain out of the mainstream because of their possible
violation of physics laws built into fundamental physics. In order to be the
VSL as a viable theory, it should inherit the success of special relativity
including Maxwell equations and thermodynamics at least. Thus, we adopt that
the speed of light, $\tilde c$ varies for the cosmic time not for the local
time, i.e., $\tilde c[z]$ where $z$ is the cosmological redshift. When one
describes the background FLRW universe, one can define the constant-time
hypersurface by using physical quantities such as temperature, density, and
$\tilde c$. It is because they evolve in time, and the homogeneity of the
Universe demands that they must equal at the equal cosmic time. The variation
of $\tilde c$ accompanies the joint variations of all related physical
constants in order to satisfy the Lorentz invariance, thermodynamics, and
Bianchi identity. We call this VSL model as a "minimally extended VSL (meVSL)".
We derive cosmological observables of meVSL and obtain the constraints on the
variation of $\tilde c$ by using the current observations. Interestingly, $z$
and all geometrical distances except the luminosity distance of meVSL are the
same as those of general relativity. However, the Hubble parameter of meVSL is
rescaled as $H = (1+z)^{-b/4} H^{(\rm GR)}$ which might be used as a solution
for the tension of the Hubble parameter measurements. In this manuscript, we
provide the main effects of meVSL on various cosmological observations
including BBN, CMB, SZE, BAO, SNe, GWs, H, SL, and $\Delta \alpha$. |
Locating the "missing" baryons with extragalactic dispersion measure
estimates: Recently, Thornton and coworkers (2013) confirmed a class of millisecond
radio bursts likely of extragalactic origin that is well-suited for estimating
dispersion measures (DMs). We calculate the probability distribution of DM(z)
in different models for how the cosmic baryons are distributed (both
analytically and with cosmological simulations). We show that the distribution
of DM is quite sensitive to whether the "missing" baryons lie around the virial
radius of 10^11-10^13 Msun halos or further out, which is not easily
constrained with other observational techniques. The intrinsic contribution to
DM from each source could complicate studies of the extragalactic contribution.
This difficulty is avoided by stacking based on the impact parameter to
foreground galaxies. We show that a stacking analysis using a sample of ~100 DM
measurements from arcminute-localized, z >~ 0.5 sources would place interesting
constraints at 0.2-2 halo virial radii on the baryonic mass profile surrounding
different galaxy types. Conveniently for intergalactic studies, sightlines that
intersect intervening galactic disks should be easily identified owing to
scattering. A detectable level of scattering may also result from turbulence in
the circumgalactic medium. | The impact of relativistic effects on cosmological parameter estimation: Future surveys will access large volumes of space and hence very long
wavelength fluctuations of the matter density and gravitational field. It has
been argued that the set of secondary effects that affect the galaxy
distribution, relativistic in nature, will bring new, complementary
cosmological constraints. We study this claim in detail by focusing on a subset
of wide-area future surveys: Stage-4 cosmic microwave background experiments
and photometric redshift surveys. In particular, we look at the magnification
lensing contribution to galaxy clustering and general relativistic corrections
to all observables. We quantify the amount of information encoded in these
effects in terms of the tightening of the final cosmological constraints as
well as the potential bias in inferred parameters associated with neglecting
them. We do so for a wide range of cosmological parameters, covering neutrino
masses, standard dark-energy parametrizations and scalar-tensor gravity
theories. Our results show that, while the effect of lensing magnification to
number counts does not contain a significant amount of information when galaxy
clustering is combined with cosmic shear measurements, this contribution does
play a significant role in biasing estimates on a host of parameter families if
unaccounted for. Since the amplitude of the magnification term is controlled by
the slope of the source number counts with apparent magnitude, $s(z)$, we also
estimate the accuracy to which this quantity must be known to avoid systematic
parameter biases, finding that future surveys will need to determine $s(z)$ to
the $\sim$5-10\% level. On the contrary, large-scale general-relativistic
corrections are irrelevant both in terms of information content and parameter
bias for most cosmological parameters, but significant for the level of
primordial non-Gaussianity. |
Tomographic Alcock-Paczynski Test with Redshift-Space Correlation
Function: Evidence for the Dark Energy Equation of State Parameter w>-1: The apparent shape of galaxy clustering depends on the adopted cosmology used
to convert observed redshift to comoving distance, the $r(z)$ relation, as it
changes the line elements along and across the line of sight differently. The
Alcock-Paczy\'nski (AP) test exploits this property to constrain the expansion
history of the universe. We present an extensive review of past studies on the
AP test. We adopt an extended AP test method introduced by Park et al. (2019),
which uses the full shape of redshift-space two-point correlation function (CF)
as the standard shape, and apply it to the SDSS DR7, BOSS, and eBOSS LRG
samples covering the redshift range up to $z=0.8$.We calibrate the test against
the nonlinear cosmology-dependent systematic evolution of the CF shape using
the Multiverse simulations. We focus on examining whether or not the flat
$\Lambda$CDM `concordance' model is consistent with observation. We constrain
the flat $w$CDM model to have $w=-0.892_{-0.050}^{+0.045}$ and
$\Omega_m=0.282_{-0.023}^{+0.024}$ from our AP test alone, which is
significantly tighter than the constraints from the BAO or SNe I$a$ methods by
a factor of 3 - 6. When the AP test result is combined with the recent BAO and
SNe I$a$ results, we obtain $w=-0.903_{-0.023}^{+0.023}$ and
$\Omega_m=0.285_{-0.009}^{+0.014}$. This puts a strong tension with the flat
$\Lambda$CDM model with $w=-1$ at $4.2\sigma$ level. Consistency with $w=-1$ is
obtained only when the Planck CMB observation is combined. It remains to see if
this tension between observations of galaxy distribution at low redshifts and
CMB anisotropy at the decoupling epoch becomes greater in the future studies
and leads us to a new paradigm of cosmology. | The importance of magnification effects in galaxy-galaxy lensing: Magnification changes the observed number counts of galaxies on the sky. This
biases the observed tangential shear profiles around galaxies, the so-called
galaxy-galaxy lensing (GGL) signal, and the related excess mass profile.
Correspondingly, inference of physical quantities, such as the mean mass
profile of halos around galaxies, are affected by magnification effects. We use
simulated shear and galaxy data of the Millennium Simulation to quantify the
effect on shear and mass estimates from magnified lens and source number
counts. The former are due to the large-scale matter distribution in the
foreground of the lenses, the latter are caused by magnification of the source
population by the matter associated with the lenses. The GGL signal is
calculated from the simulations by an efficient fast-Fourier transform that can
also be applied to real data. The numerical treatment is complemented by a
leading-order analytical description of the magnification effects, which is
shown to fit the numerical shear data well. We find the magnification effect is
strongest for steep galaxy luminosity functions and high redshifts. For a lens
redshift of $z_\mathrm{d}=0.83$, a limiting magnitude of $22\,\mathrm{mag}$ in
the $r$-band and a source redshift of $z_\mathrm{s}=0.99$, we find that a
magnification correction changes the shear profile up to $45\%$ and the mass is
biased by up to $55 \%$. For medium-redshift galaxies the relative change in
shear and mass is typically a few percent. As expected, the sign of the bias
depends on the local slope of the lens luminosity function $\alpha_\mathrm{d}$,
where the mass is biased low for $\alpha_\mathrm{d}<1$ and biased high for
$\alpha_\mathrm{d}>1$. Whereas the magnification effect of sources is rarely
than more $1\%$, the statistical power of future weak lensing surveys warrants
correction for this effect. |
AGN dust tori: the X-ray-infrared connection: We have combined the CLASXS Chandra survey in Lockman with the Spitzer SWIRE
survey data to study the X-ray-infrared connection for AGN. The sample consists
of 401 X-ray-sources, of which 306 are detected by Spitzer, and a further 257
AGN candidates detected through their dust torus, but not by Chandra. For X-ray
sources the X-ray hardness ratio has been modelled in terms of a power-law with
absorption N(H). The optical and infrared data have been modelled in terms of
our well-established optical galaxy and QSO templates, and infrared templates
based on radiative transfer models.
Our estimate of the N(H) distribution is consistent with other studies, but
we do find a higher proportion of low absorption objects at z < 0.5 than at z >
0.5. While we find only one X-ray AGN with N(H) > 10^{24} cm^{-2}, we argue
that 10 objects with torus luminosity apparently exceeding the bolometric X-ray
to 3 \mu m luminosity are strong candidates for being heavily absorbed in
X-rays. We also estimate that at least half of the infrared-detected AGN dust
tori which are undetected in X-rays are likely to be Compton thick. Our
estimate of the total number of Compton-thick objects corresponds to > 20%$ of
the combined SWIRE-CLASXS sample (and with an upper limit of 39 %).
The range of dust covering factors is 1-100 %, with a mean of 40 %, ie a Type
2 fraction of 40 %. Measured by the ratio of dust torus luminosity to X-ray or
(for Type 1 objects) optical luminosity, the covering factor appears to
decrease towards intermediate AGN luminosity, in contradiction to estimates
based on ratios of narrow-line and broad-line spectra, but may increase again
at low AGN luminosity. | $Λ$CDM: Much more than we expected, but now less than what we want: The $\rm\Lambda$CDM cosmological model is remarkable: with just 6 parameters
it describes the evolution of the Universe from a very early time when all
structures were quantum fluctuations on subatomic scales to the present, and it
is consistent with a wealth of high-precision data, both laboratory
measurements and astronomical observations. However, the foundation of
$\rm\Lambda$CDM involves physics beyond the standard model of particle physics:
particle dark matter, dark energy and cosmic inflation. Until this `new
physics' is clarified, $\rm\Lambda$CDM is at best incomplete and at worst a
phenomenological construct that accommodates the data. I discuss the path
forward, which involves both discovery and disruption, some grand challenges
and finally the limits of scientific cosmology. |
Time-varying neutrino mass from a supercooled phase transition: current
cosmological constraints and impact on the $Ω_m$-$σ_8$ plane: In this paper we investigate a time-varying neutrino mass model, motivated by
the mild tension between cosmic microwave background (CMB) measurements of the
matter fluctuations and those obtained from low-redshift data. We modify the
minimal case of the model proposed by Dvali and Funcke (2016) that predicts
late neutrino mass generation in a post-recombination cosmic phase transition,
by assuming that neutrino asymmetries allow for the presence of relic neutrinos
in the late-time Universe. We show that, if the transition is supercooled,
current cosmological data (including CMB temperature, polarization and lensing,
baryon acoustic oscillations, and Type Ia supernovae) prefer the scale factor
$a_s$ of the phase transition to be very large, peaking at $a_s\sim 1$, and
therefore supporting a cosmological scenario in which neutrinos are almost
massless until very recent times. We find that in this scenario the
cosmological bound on the total sum of the neutrino masses today is
significantly weakened compared to the standard case of constant-mass
neutrinos, with $\sum m_\nu<4.8$~eV at 95\% confidence, and in agreement with
the model predictions. The main reason for this weaker bound is a large
correlation arising between the dark energy and neutrino components in the
presence of false vacuum energy that converts into the non-zero neutrino masses
after the transition. This result provides new targets for the coming KATRIN
and PTOLEMY experiments. We also show that the time-varying neutrino mass model
considered here does not provide a clear explanation to the existing
cosmological $\Omega_m$-$\sigma_8$ discrepancies. | CMB Isotropy Anomalies and the Local Kinetic Sunyaev-Zel'dovich Effect: Several anomalies have been identified which may imply a breakdown of the
statistical isotropy of the cosmic microwave background (CMB). In particular,
an anomalous alignment of the quadrupole and octopole and a hemispherical power
asymmetry have increased in significance as the data have improved. There have
been several attempts to explain these observations which explore isotropy
breaking mechanisms within the early universe, but little attention has been
given to the possibility that these anomalies have their origin within the
local universe. We explore such a mechanism by considering the kinetic
Sunyaev-Zel'dovich effect due to a gaseous halo associated with the Milky Way.
Considering several physical models of an anisotropic free electron optical
depth contributed by such a halo, we find that the associated screening maps of
the primordial anisotropies have the necessary orientations to affect the
anomaly statistics very significantly, but only if the column density of free
electrons in the halo is at least an order of magnitude higher than indicated
by current observations. |
Discovery of an Excess of Halpha Emitters around 4C 23.56 at z=2.48: We report the discovery of a significant excess of candidate Halpha emitters
(HAEs) in the field of the radio galaxy 4C 23.56 at z=2.483. Using the MOIRCS
near-infrared imager on the Subaru Telescope we found 11 candidate
emission-line galaxies to a flux limit of ~7.5 10^-17 erg s-1 cm-2, which is
about 5 times excess from the expected field counts with ~3-sigma significance.
Three of these are spectroscopically confirmed as redshifted Halpha at z=2.49.
The distribution of candidate emitters on the sky is tightly confined to a
1.2-Mpc-radius area at z=2.49, locating 4C 23.56 at the western edge of the
distribution. Analysis of the deep Spitzer MIPS 24 mu m imaging shows that
there is also an excess of faint MIPS sources. All but two of the 11 HAEs are
also found in the MIPS data. The inferred star-formation rate (SFR) of the HAEs
based on the extinction-corrected Halpha luminosity (median SFR >~100 M_solar
yr-1) is similar to those of HAEs in random fields at z~2. On the other hand,
the MIPS-based SFR for the HAEs is on average 3.6 times larger, suggesting the
existence of the star-formation significanly obscured by dust. The comparison
of the Halpha-based star-formation activities of the HAEs in the 4C 23.56 field
to those in another proto-cluster around PKS 1138-262 at z=2.16 reveals that
the latter tend to have fainter Halpha emission despite similar K-band
magnitudes. This suggests that star-formation may be suppressed in the PKS
1138-262 protocluster relative to the 4C 23.56 protocluster. This difference
among the HAEs in the two proto-clusters at z > 2 may imply that some massive
cluster galaxies are just forming at these epochs with some variation among
clusters. | The X-ray brightest clusters of galaxies from the Massive Cluster Survey: We present a statistically complete sample of very X-ray luminous galaxy
clusters detected in the MAssive Cluster Survey (MACS). This second MACS
release comprises all 34 MACS clusters with nominal X-ray fluxes in excess of
2x10^(-12) erg/s/cm^2 (0.1-2.4 keV) in the ROSAT Bright Source Catalogue; two
thirds of them are new discoveries. Extending over the redshift range from 0.3
to 0.5, this subset complements the complete sample of the 12 most distant MACS
clusters (z>0.5) published in 2007 and further exemplifies the efficacy of
X-ray selection for the compilation of samples of intrinsically massive galaxy
clusters. Extensive follow-up observations with Chandra/ACIS led to three
additional MACS cluster candidates being eliminated as (predominantly) X-ray
point sources. For another four clusters --- which, however, remain in our
sample of 34 --- the point-source contamination was found to be about 50%. The
median X-ray luminosity of 1.3x10^45 erg/s (0.1-2.4 keV, Chandra, within r_500)
of the clusters in this subsample demonstrates the power of the MACS survey
strategy to find the most extreme and rarest clusters out to significant
redshift. A comparison of the optical and X-ray data for all clusters in this
release finds a wide range of morphologies with no obvious bias in favour of
either relaxed or merging systems. |
A z=1.82 Analog of Local Ultra-massive Elliptical Galaxies: We present observations of a very massive galaxy at z=1.82 which show that
its morphology, size, velocity dispersion and stellar population properties
that are fully consistent with those expected for passively evolving
progenitors of today's giant ellipticals. These findings are based on a deep
optical rest-frame spectrum obtained with the Multi-Object InfraRed Camera and
Spectrograph (MOIRCS) on the Subaru telescope of a high-z passive galaxy
candidate (pBzK) from the COSMOS field, for which we accurately measure its
redshift of z=1.8230 and obtain an upper limit on its velocity dispersion
sigma_star<326 km/s. By detailed stellar population modeling of both the galaxy
broad-band SED and the rest-frame optical spectrum we derive a
star-formation-weighted age and formation redshift of t_sf~1-2 Gyr and
z_form~2.5-4, and a stellar mass of M_star~(3-4)x10^{11} M_sun. This is in
agreement with a virial mass limit of M_vir<7x10^{11}M_sun, derived from the
measured sigma_star value and stellar half-light radius, as well as with the
dynamical mass limit based on the Jeans equations. In contrast with previously
reported super-dense passive galaxies at z~2, the present galaxy at z=1.82
appears to have both size and velocity dispersion similar to early-type
galaxies in the local Universe with similar stellar mass. This suggests that
z~2 massive and passive galaxies may exhibit a wide range of properties, then
possibly following quite different evolutionary histories from z~2 to z=0. | The void halo mass function: a promising probe of neutrino mass: Cosmic voids, the underdense regions in the universe, are particularly
sensitive to diffuse density components such as cosmic neutrinos. This
sensitivity is enhanced by the match between void sizes and the free-streaming
scale of massive neutrinos. Using the massive neutrino simulations
\texttt{MassiveNuS}, we investigate the effect of neutrino mass on dark matter
halos as a function of environment. We find that the halo mass function depends
strongly on neutrino mass and that this dependence is more pronounced in voids
than in high-density environments. An observational program that measured the
characteristic mass of the most massive halos in voids should be able to place
novel constraints on the sum of the masses of neutrinos $\sum m_\nu$. The
neutrino mass effect in the simulations is quite strong: In a 512$^3$ $h^{-3}$
Mpc$^3$ survey, the mean mass of the 1000 most massive halos in the void
interiors is $(4.82 \pm 0.11) \times 10^{12} h^{-1}M_{\odot}$ for $\sum m_\nu =
0.6$ eV and $(8.21 \pm 0.13) \times 10^{12} h^{-1}M_{\odot}$ for $\sum m_\nu =
0.1$ eV. Subaru (SuMIRe), Euclid and WFIRST will have both spectroscopic and
weak lensing surveys. Covering volumes at least 50 times larger than our
simulations, they should be sensitive probes of neutrino mass through void
substructure. |
Perspectives on Intracluster Enrichment and the Stellar Initial Mass
Function in Elliptical Galaxies: Stars formed in galaxy cluster potential wells must be responsible for the
high level of enrichment measured in the intracluster medium (ICM); however,
there is increasing tension between this truism and the parsimonious assumption
that the stars in the generally old population studied optically in cluster
galaxies emerged from the same formation sites at the same epochs. We construct
a phenomenological cluster enrichment model to demonstrate that ICM elemental
abundances are underestimated by a factor >2 for standard assumptions about the
stellar population -- a discrepancy we term the "cluster elemental abundance
paradox". Recent evidence of an elliptical galaxy IMF skewed to low masses
deepens the paradox. We quantify the adjustments to the star formation
efficiency and initial mass function (IMF), and SNIa production efficiency,
required to resolve this while being consistent with the observed ICM abundance
pattern. The necessary enhancement in metal enrichment may, in principle,
originate in the observed stellar population if a larger fraction of stars in
the supernova-progenitor mass range form from an initial mass function (IMF)
that is either bottom-light or top-heavy, with the latter in some conflict with
observed ICM abundance ratios. Other alternatives that imply more modest
revisions to the IMF, mass return and remnant fractions, and primordial
fraction, posit an increase in the fraction of 3-8 solar mass stars that
explode as SNIa or assume that there are more stars than conventionally thought
-- although the latter implies a high star formation efficiency. We discuss the
feasibility of these various solutions and the implications for the diversity
of star formation in the universe, the process of elliptical galaxy formation,
and the origin of this "hidden" source of ICM metal enrichment. | Zonal Modes of Cosmic Microwave Background Temperature Maps: All-sky maps of the cosmic microwave background temperature fluctuations are
usually represented by a spherical harmonic decomposition involving modes
labelled by their degree l and order m (where -l < m < +l). The zonal modes
(i.e those with m = 0) are of particular interest because they vary only with
galactic latitude; any anomalous behaviour in them might therefore be an
indication of erroneous foreground substraction. We perform a simple
statistical analysis of the modes with low l for sky maps derived via different
cleaning procedures from the Wilkinson Microwave Anisotropy Probe (WMAP) and
show that the zonal modes provide a useful diagnostic of possible systematics. |
Developing a unified pipeline for large-scale structure data analysis
with angular power spectra -- II. A case study for magnification bias and
radio continuum surveys: Following on our purpose of developing a unified pipeline for large-scale
structure data analysis with angular (i.e. harmonic-space) power spectra, we
now include the weak lensing effect of magnification bias on galaxy clustering
in a publicly available, modular parameter estimation code. We thus forecast
constraints on the parameters of the concordance cosmological model, dark
energy, and modified gravity theories from galaxy clustering tomographic
angular power spectra. We find that a correct modelling of magnification is
crucial in order not to bias the estimation of cosmological parameters,
especially in the case of deep galaxy surveys. Our case study adopts
specifications of the Evolutionary Map of the Universe (EMU), which is a
full-sky, deep radio-continuum survey, and is expected to probe the Universe up
to redshift $z\sim6$. We assume the Limber approximation, and include
magnification bias on top of density fluctuations and redshift-space
distortions. By restricting our analysis to the regime where the Limber
approximation holds true, we significantly minimise the computational time
needed, compared to that of the exact calculation. We also show that there is a
trend for more biased parameter estimates from neglecting magnification when
the redshift bins are very wide. We conclude that this result implies a strong
dependence on the lensing contribution, which is an integrated effect and
becomes dominant when wide redshift bins are considered. Finally, we note that
instead of being considered a contaminant, magnification bias encodes important
cosmological information, and its inclusion leads to an alleviation of the
degeneracy between the galaxy bias and the amplitude normalisation of the
matter fluctuations. | Bispectrum as Baryon Acoustic Oscillation Interferometer: The galaxy bispectrum, measuring excess clustering of galaxy triplets, offers
a probe of dark energy via baryon acoustic oscillations (BAOs). However up to
now it has been severely underused due to the combinatorically explosive number
of triangles. Here we exploit interference in the bispectrum to identify
triangles that amplify BAOs. This approach reduces the computational cost of
estimating covariance matrices, offers an improvement in BAO constraints
equivalent to lengthening BOSS by 30%, and simplifies adding bispectrum BAO
information to future large-scale redshift survey analyses. |
DEMNUni: The clustering of large-scale structures in the presence of
massive neutrinos: (abridged) We analyse the clustering features of Large Scale Structures (LSS)
in the presence of massive neutrinos, employing a set of large-volume,
high-resolution cosmological N-body simulations, where neutrinos are treated as
a separate collisionless fluid. The volume of 8$\cGpc$, combined with a
resolution of about $8\times 10^{10}\Ms$ for the cold dark matter (CDM)
component, represents a significant improvement over previous N-body
simulations in massive neutrino cosmologies. We show that most of the nonlinear
evolution is generated exclusively by the CDM component. We find that
accounting only for the nonlinear evolution of the CDM power spectrum allows to
recover the total matter power spectrum with the same accuracy as the massless
case. Indeed, we show that, the most recent version of the \halofit\ formula
calibrated on $\Lambda$CDM simulations can be applied directly to the linear
CDM power spectrum without requiring additional fitting parameters in the
massive case. As a second step, we study the abundance and clustering
properties of CDM halos, confirming that, in massive neutrino cosmologies, the
proper definition of the halo bias should be made with respect to the {\em
cold} rather than the {\em total} matter distribution, as recently shown in the
literature. Here we extend these results to the redshift space, finding that,
when accounting for massive neutrinos, an improper definition of the linear
bias can lead to a systematic error of about 1-$2 \%$ in the determination of
the linear growth rate from anisotropic clustering. This result is quite
important if we consider that future spectroscopic galaxy surveys, as \eg\
Euclid, are expected to measure the linear growth-rate with statistical errors
less than about $3 \%$ at $z\lesssim1$. | The Impact of Realistic Foreground and Instrument Models on 21cm Epoch
of Reionization Experiments: Predictions for the ability of 21-cm interferometric experiments to
discriminate Epoch of Reionization (EoR) signal models are typically limited by
the simplicity of data models, whereby foreground signals and characteristics
of the instrument are often simplified or neglected.To move towards more
realistic scenarios, we explore the effects of applying more realistic
foreground and instrument models to the 21cm signal, and the ability to
estimate astrophysical parameters with these additional complexities. We use a
highly-optimized version of \textsc{21cmFAST}, integrated into \textsc{21cmMC},
to generate lightcones of the brightness temperature fluctuation for Bayesian
parameter estimation. We include a statistical point-source foreground model
and an instrument model based on the Murchison Widefield Array (MWA) scaled in
observation time to have an effective sensitivity similar to the future Square
Kilometre Array (SKA). We also extend the current likelihood prescription to
account for the presence of beam convolution and foregrounds, the 2-Dimensional
Power Spectrum (PS), and the correlation of PS modes. We use frequency bands
between 150 and 180 MHz to constrain the ionizing efficiency ($\zeta$), the
minimum virial temperature of halos ($T_{\mathrm{vir}}$), the soft X-ray
emissivity per unit Star Formation Rate (SFR) ($L_X/SFR$ ), and the X-ray
energy threshold ($E_0$). We find that the inclusion of realistic foregrounds
and instrumental components biases the parameter constraints due to unaccounted
for cross-power between the EoR signal, foregrounds and thermal noise. This
causes estimates of $\zeta$ to be biased by up to $5\sigma$ but the estimates
of $T_{vir}$, L$_X$/SFR and E$_0$ remain unaffected and are all within
$1\sigma$. |
Gravitational wave cosmology with extreme mass-ratio inspirals: The Laser Interferometer Space Antenna (LISA) will open the mHz frequency
window of the gravitational wave (GW) landscape. Among all the new GW sources
expected to emit in this frequency band, extreme mass-ratio inspirals (EMRIs)
constitute a unique laboratory for astrophysics and fundamental physics. Here
we show that EMRIs can also be used to extract relevant cosmological
information, complementary to both electromagnetic (EM) and other GW
observations. By using the loudest EMRIs (SNR$>$100) detected by LISA as dark
standard sirens, statistically matching their sky localisation region with mock
galaxy catalogs, we find that constraints on $H_0$ can reach $\sim$1.1%
($\sim$3.6%) accuracy, at the 90% credible level, in our best (worst) case
scenario. By considering a dynamical dark energy (DE) cosmological model, with
$\Lambda$CDM parameters fixed by other observations, we further show that in
our best (worst) case scenario $\sim$5.9% ($\sim$12.3%) relative uncertainties
at the 90% credible level can be obtained on $w_0$, the DE equation of state
parameter. Besides being relevant in their own right, EMRI measurements will be
affected by different systematics compared to both EM and ground-based GW
observations. Cross validation with complementary cosmological measurements
will therefore be of paramount importance, especially if convincing evidence of
physics beyond $\Lambda$CDM emerges from future observations. | Implications and Applications of Kinematic Galaxy Scaling Relations: Galaxy scaling relations, which describe a connection between ostensibly
unrelated physical characteristics of galaxies, testify to an underlying order
in galaxy formation that requires understanding. I review the development of a
scaling relation that 1) unites the well-known Fundamental Plane (FP) relation
of giant elliptical galaxies and Tully-Fisher (TF) relation of disk galaxies,
2) fits low mass spheroidal galaxies, including the ultra-faint satellites of
our Galaxy, 3) explains the apparent shift of lenticular (S0) galaxies relative
to both FP or TF, 3) describes all stellar dynamical systems, including systems
with no dark matter (stellar clusters), 4) associates explicitly the numerical
coefficients that account for the apparent "tilt" of the FP away from the
direct expectation drawn from the virial theorem with systematic variations in
the total mass-to-light ratio of galaxies within the half-light radius, 5)
connects with independent results that demonstrate the robustness of mass
estimators when applied at the half-light radius, and 6) results in smaller
scatter for disk galaxies than the TF relation. The relation develops naturally
from the virial theorem, but implies the existence of additional galaxy
formation physics that must now be a focus of galaxy formation studies. More
pragmatically, the relation provides a lynchpin that can be used to measure
distances and galaxy masses. I review two applications: 1) the
cross-calibration of distance measurement methods, and 2) the determination of
mass-to-light ratios of simple stellar populations as a function of age, and
implications of the latter for the stellar initial mass function. |
Turbulence and Vorticity in Galaxy Clusters Generated by Structure
Formation: Turbulence is a key ingredient for the evolution of the intracluster medium,
whose properties can be predicted with high resolution numerical simulations.
We present initial results on the generation of solenoidal and compressive
turbulence in the intracluster medium during the formation of a small-size
cluster using highly resolved, non-radiative cosmological simulations, with a
refined monitoring in time. In this first of a series of papers, we closely
look at one simulated cluster whose formation was distinguished by a merger
around $z \sim 0.3$. We separate laminar gas motions, turbulence and shocks
with dedicated filtering strategies and distinguish the solenoidal and
compressive components of the gas flows using Hodge-Helmholtz decomposition.
Solenoidal turbulence dominates the dissipation of turbulent motions ($\sim
95\%$) in the central cluster volume at all epochs. The dissipation via
compressive modes is found to be more important ($\sim 30 \%$ of the total)
only at large radii ($\geq 0.5 ~r_{\rm vir}$) and close to merger events. We
show that enstrophy (vorticity squared) is good proxy of solenoidal turbulence.
All terms ruling the evolution of enstrophy (i.e. baroclinic, compressive,
stretching and advective terms) are found to be significant, but in amounts
that vary with time and location. Two important trends for the growth of
enstrophy in our simulation are identified: first, enstrophy is continuously
accreted into the cluster from the outside, and most of that accreted enstrophy
is generated near the outer accretion shocks by baroclinic and compressive
processes. Second, in the cluster interior vortex stretching is dominant,
although the other terms also contribute substantially. | An accurate physical model for halo concentrations: The relation between halo mass, M, and concentration, c, is a critical
component in our understanding of the structure of dark matter halos. While
numerous models for this relation have been proposed, almost none of them
attempt to derive the evolution of the relation analytically. We build on
previous efforts to model the c-M relation as a function of physical parameters
such as the peak height, $\nu$, and the effective power spectrum slope, $n_{\rm
eff}$, which capture the dependence of $c$ on halo mass, redshift, and
cosmology. We present three major improvements over previous models. First, we
derive an analytical expression for the c-M relation that is valid under the
assumption of pseudo-evolution, i.e., assuming that the density profiles of
halos are static in physical coordinates while the definition of their boundary
evolves. We find that this ansatz is highly successful in describing the
evolution of the low-mass end of the c-M relation. Second, we employ a new
physical variable, the effective exponent of linear growth, $\alpha_{\rm eff}$,
to parameterize deviations from an Einstein-de Sitter expansion history. Third,
we combine an updated definition of $n_{\rm eff}$ with the additional
dependence on $\alpha_{\rm eff}$ and propose a phenomenological extension of
our analytical framework to include all halo masses. This semianalytical model
matches simulated concentrations in both scale-free models and LambdaCDM to 5%
accuracy with very few exceptions and differs significantly from all previously
proposed models. We present a publicly available code to compute the
predictions of our model in the python toolkit Colossus, including updated
parameters for the model of Diemer and Kravtsov. |
COMAP Early Science: I. Overview: The CO Mapping Array Project (COMAP) aims to use line intensity mapping of
carbon monoxide (CO) to trace the distribution and global properties of
galaxies over cosmic time, back to the Epoch of Reionization (EoR). To validate
the technologies and techniques needed for this goal, a Pathfinder instrument
has been constructed and fielded. Sensitive to CO(1-0) emission from
$z=2.4$-$3.4$ and a fainter contribution from CO(2-1) at $z=6$-8, the
Pathfinder is surveying $12$ deg$^2$ in a 5-year observing campaign to detect
the CO signal from $z\sim3$. Using data from the first 13 months of observing,
we estimate $P_\mathrm{CO}(k) = -2.7 \pm 1.7 \times 10^4\mu\mathrm{K}^2
\mathrm{Mpc}^3$ on scales $k=0.051-0.62 \mathrm{Mpc}^{-1}$ - the first direct
3D constraint on the clustering component of the CO(1-0) power spectrum. Based
on these observations alone, we obtain a constraint on the amplitude of the
clustering component (the squared mean CO line temperature-bias product) of
$\langle Tb\rangle^2<49$ $\mu$K$^2$ - nearly an order-of-magnitude improvement
on the previous best measurement. These constraints allow us to rule out two
models from the literature. We forecast a detection of the power spectrum after
5 years with signal-to-noise ratio (S/N) 9-17. Cross-correlation with an
overlapping galaxy survey will yield a detection of the CO-galaxy power
spectrum with S/N of 19. We are also conducting a 30 GHz survey of the Galactic
plane and present a preliminary map. Looking to the future of COMAP, we examine
the prospects for future phases of the experiment to detect and characterize
the CO signal from the EoR. | Dark Energy Survey Year 3 results: Cosmology with peaks using an
emulator approach: We constrain the matter density $\Omega_{\mathrm{m}}$ and the amplitude of
density fluctuations $\sigma_8$ within the $\Lambda$CDM cosmological model with
shear peak statistics and angular convergence power spectra using mass maps
constructed from the first three years of data of the Dark Energy Survey (DES
Y3). We use tomographic shear peak statistics, including cross-peaks: peak
counts calculated on maps created by taking a harmonic space product of the
convergence of two tomographic redshift bins. Our analysis follows a
forward-modelling scheme to create a likelihood of these statistics using
N-body simulations, using a Gaussian process emulator. We include the following
lensing systematics: multiplicative shear bias, photometric redshift
uncertainty, and galaxy intrinsic alignment. Stringent scale cuts are applied
to avoid biases from unmodelled baryonic physics. We find that the additional
non-Gaussian information leads to a tightening of the constraints on the
structure growth parameter yielding
$S_8~\equiv~\sigma_8\sqrt{\Omega_{\mathrm{m}}/0.3}~=~0.797_{-0.013}^{+0.015}$
(68% confidence limits), with a precision of 1.8%, an improvement of ~38%
compared to the angular power spectra only case. The results obtained with the
angular power spectra and peak counts are found to be in agreement with each
other and no significant difference in $S_8$ is recorded. We find a mild
tension of $1.5 \thinspace \sigma$ between our study and the results from
Planck 2018, with our analysis yielding a lower $S_8$. Furthermore, we observe
that the combination of angular power spectra and tomographic peak counts
breaks the degeneracy between galaxy intrinsic alignment $A_{\mathrm{IA}}$ and
$S_8$, improving cosmological constraints. We run a suite of tests concluding
that our results are robust and consistent with the results from other studies
using DES Y3 data. |
CMB and BAO constraints for an induced gravity dark energy model with a
quartic potential: We study the predictions for structure formation in an induced gravity dark
energy model with a quartic potential. By developing a dedicated
Einstein-Boltzmann code, we study self-consistently the dynamics of homogeneous
cosmology and of linear perturbations without using any parametrization. By
evolving linear perturbations with initial conditions in the radiation era, we
accurately recover the quasi-static analytic approximation in the matter
dominated era. We use Planck 2013 data and a compilation of baryonic acoustic
oscillation (BAO) data to constrain the coupling $\gamma$ to the Ricci
curvature and the other cosmological parameters. By connecting the
gravitational constant in the Einstein equation to the one measured in a
Cavendish-like experiment, we find $\gamma < 0.0012$ at 95% CL with Planck 2013
and BAO data. This is the tightest cosmological constraint on $\gamma$ and on
the corresponding derived post-Newtonian parameters. Because of a degeneracy
between $\gamma$ and the Hubble constant $H_0$, we show how larger values for
$\gamma$ are allowed, but not preferred at a significant statistical level,
when local measurements of $H_0$ are combined in the analysis with Planck 2013
data. | The luminosities of backsplash galaxies in constrained simulations of
the Local Group: We study the differences and similarities in the luminosities of bound,
infalling and the so-called backsplash (Gill et al. 2005) galaxies of the Milky
Way and M31 using a hydrodynamical simulation performed within the Constrained
Local UniversE Simulation (CLUES) project. The simulation models the formation
of the Local Group within a self-consistent cosmological framework. We find
that even though backsplash galaxies passed through the virial radius of their
host halo and hence may have lost a (significant) fraction of their mass, their
stellar populations are hardly affected. This leaves us with comparable
luminosity functions for infalling and backsplash galaxies and hence little
hope to decipher their past (and different) formation and evolutionary
histories by luminosity measurements alone. Nevertheless, due to the tidal
stripping of dark matter we find that the mass-to-light ratios have changed
when comparing the various populations against each other: they are highest for
the infalling galaxies and lowest for the bound satellites with the backsplash
galaxies in-between. |
The Herschel Space Observatory view of dust in M81: We use Herschel Space Observatory data to place observational constraints on
the peak and Rayleigh-Jeans slope of dust emission observed at 70-500 microns
in the nearby spiral galaxy M81. We find that the ratios of wave bands between
160 and 500 microns are primarily dependent on radius but that the ratio of 70
to 160 micron emission shows no clear dependence on surface brightness or
radius. These results along with analyses of the spectral energy distributions
imply that the 160-500 micron emission traces 15-30 K dust heated by evolved
stars in the bulge and disc whereas the 70 micron emission includes dust heated
by the active galactic nucleus and young stars in star forming regions. | Constraining the substructure of dark matter haloes with galaxy-galaxy
lensing: With galaxy groups constructed from the Sloan Digital Sky Survey (SDSS), we
analyze the expected galaxy-galaxy lensing signals around satellite galaxies
residing in different host haloes and located at different halo-centric
distances. We use Markov Chain Monte Carlo (MCMC) method to explore the
potential constraints on the mass and density profile of subhaloes associated
with satellite galaxies from SDSS-like surveys and surveys similar to the Large
Synoptic Survey Telescope (LSST). Our results show that for SDSS-like surveys,
we can only set a loose constraint on the mean mass of subhaloes. With
LSST-like surveys, however, both the mean mass and the density profile of
subhaloes can be well constrained. |
Galaxy Properties from the Ultra-violet to the Far-Infrared: Lambda-CDM
models confront observations: We combine a semi-analytic model of galaxy formation with simple analytic
recipes describing the absorption and re-emission of starlight by dust in the
interstellar medium of galaxies. We use the resulting models to predict galaxy
counts and luminosity functions from the far-ultraviolet to the sub-mm, from
redshift five to the present, and compare with an extensive compilation of
observations. We find that in order to reproduce the rest-UV and optical
luminosity functions at high redshift, we must assume an evolving normalization
in the dust-to-metal ratio, implying that galaxies of a given bolometric
luminosity (or metal column density) must be less extinguished than their local
counterparts. In our best-fit model, we find remarkably good agreement with
observations from rest-frame 1500 Angstroms to 250 microns. At longer
wavelengths, most dramatically in the sub-mm, our models underpredict the
number of bright galaxies by a large factor. The models reproduce the observed
total IR luminosity function fairly well. We show the results of varying
several ingredients of the models, including various aspects of the dust
attenuation recipe, the dust emission templates, and the cosmology. We use our
models to predict the integrated Extragalactic Background Light (EBL), and
compare with an observationally-motivated EBL model and with other available
observational constraints. | Numerical Challenges in Modeling Gravothermal Collapse in
Self-Interacting Dark Matter Halos: When dark matter has a large cross section for self scattering, halos can
undergo a process known as gravothermal core collapse, where the inner core
rapidly increases in density and temperature. To date, several methods have
been used to implement Self-Interacting Dark Matter~(SIDM) in N-body codes, but
there has been no systematic study of these different methods or their accuracy
in the core-collapse phase. In this paper, we compare three different numerical
implementations of SIDM, including the standard methods from the GIZMO and
Arepo codes, by simulating idealized dwarf halos undergoing significant dark
matter self interactions ($\sigma/m = 50$~cm$^2$/g). When simulating these
halos, we also vary the mass resolution, time-stepping criteria, and
gravitational force-softening scheme. The various SIDM methods lead to distinct
differences in a halo's evolution during the core-collapse phase, as each
results in slightly different scattering rates and spurious energy
gains/losses. The use of adaptive force softening for gravity can lead to
numerical heating that artificially accelerates core collapse, while an
insufficiently small simulation time step can cause core evolution to stall or
completely reverse. Additionally, particle numbers must be large enough to
ensure that the simulated halos are not sensitive to noise in the initial
conditions. Even for the highest-resolution simulations tested in this study
($10^6$ particles per halo), we find that variations of order $10\%$ in
collapse time are still present. The results of this work underscore the
sensitivity of SIDM modeling on the choice of numerical implementation and
motivate a careful study of how these results generalize to halos in a
cosmological context. |
Dark Energy Survey Year 3 Results: Galaxy clustering and systematics
treatment for lens galaxy samples: In this work we present the galaxy clustering measurements of the two DES
lens galaxy samples: a magnitude-limited sample optimized for the measurement
of cosmological parameters, MagLim, and a sample of luminous red galaxies
selected with the redMaGiC algorithm. MagLim / redMaGiC sample contains over 10
million / 2.5 million galaxies and is divided into six / five photometric
redshift bins spanning the range $z\in[0.20,1.05]$ / $z\in[0.15,0.90]$. Both
samples cover 4143 deg$^2$ over which we perform our analysis blind, measuring
the angular correlation function with a S/N $\sim 63$ for both samples. In a
companion paper (DES Collaboration et al. 2021)), these measurements of galaxy
clustering are combined with the correlation functions of cosmic shear and
galaxy-galaxy lensing of each sample to place cosmological constraints with a
3$\times$2pt analysis. We conduct a thorough study of the mitigation of
systematic effects caused by the spatially varying survey properties and we
correct the measurements to remove artificial clustering signals. We employ
several decontamination methods with different configurations to ensure the
robustness of our corrections and to determine the systematic uncertainty that
needs to be considered for the final cosmology analyses. We validate our
fiducial methodology using log-normal mocks, showing that our decontamination
procedure induces biases no greater than $0.5\sigma$ in the $(\Omega_m, b)$
plane, where $b$ is galaxy bias. We demonstrate that failure to remove the
artificial clustering would introduce strong biases up to $\sim 7 \sigma$ in
$\Omega_m$ and of more than $4 \sigma$ in galaxy bias. | Maps of the Southern Millimeter-wave Sky from Combined 2500 deg$^2$
SPT-SZ and Planck Temperature Data: We present three maps of the millimeter-wave sky created by combining data
from the South Pole Telescope (SPT) and the Planck satellite. We use data from
the SPT-SZ survey, a survey of 2540 deg$^2$ of the the sky with arcminute
resolution in three bands centered at 95, 150, and 220 GHz, and the
full-mission Planck temperature data in the 100, 143, and 217 GHz bands. A
linear combination of the SPT-SZ and Planck data is computed in spherical
harmonic space, with weights derived from the noise of both instruments. This
weighting scheme results in Planck data providing most of the
large-angular-scale information in the combined maps, with the smaller-scale
information coming from SPT-SZ data. A number of tests have been done on the
maps. We find their angular power spectra to agree very well with theoretically
predicted spectra and previously published results. |
Zipf's law for cosmic structures: how large are the greatest structures
in the universe?: The statistical characterization of the distribution of visible matter in the
universe is a central problem in modern cosmology. In this respect, a crucial
question still lacking a definitive answer concerns how large are the greatest
structures in the universe. This point is closely related to whether or not
such a distribution can be approximated as being homogeneous on large enough
scales. Here we assess this problem by considering the size distribution of
superclusters of galaxies and by leveraging on the properties of
Zipf-Mandelbrot law, providing a novel approach which complements standard
analysis based on the correlation functions. We find that galaxy superclusters
are well described by a pure Zipf's law with no deviations and this implies
that all the catalogs currently available are not sufficiently large to spot a
truncation in the power-law behavior. This finding provides evidence that
structures larger than the greatest superclusters already observed are expected
to be found when deeper redshift surveys will be completed. As a consequence
the scale beyond which galaxy distribution crossovers toward homogeneity, if
any, should increase accordingly | Probing gravitational non-minimal coupling with dark energy surveys: We investigate observational constraints on a specific one-parameter
extension to the minimal quintessence model, where the quintessence field
acquires a quadratic coupling to the scalar curvature through a coupling
constant $\xi$. The value of $\xi$ is highly suppressed in typical tracker
models if the late-time cosmic acceleration is driven at some field values near
the Planck scale. We test $\xi$ in a second class of models in which the field
value today becomes a free model parameter. We use the combined data from
type-Ia supernovae, cosmic microwave background, baryon acoustic oscillations
and matter power spectrum, to weak lensing measurements and find a best-fit
value $\xi > 0.289$ where $\xi = 0$ is excluded outside the 95 per cent
confidence region. The effective gravitational constant $G_{\rm eff}$ subject
to the hint of a non-zero $\xi$ is constrained to $-0.003 < 1- G_{\rm eff}/G <
0.033$ at the same confidence level on cosmological scales, and can be narrowed
down to $1- G_{\rm eff}/G < 2.2 \times 10^{-5}$ when combining with Solar
System tests. |
T-ReX: a graph-based filament detection method: Numerical simulations and observations show that galaxies are not uniformly
distributed in the universe but, rather, they are spread across a filamentary
structure. In this large-scale pattern, highly dense regions are linked
together by bridges and walls, all of them surrounded by vast, nearly-empty
areas. While nodes of the network are widely studied in the literature,
simulations indicate that half of the mass budget comes from a more diffuse
part of the network, which is made up of filaments. In the context of recent
and upcoming large galaxy surveys, it becomes essential that we identify and
classify features of the Cosmic Web in an automatic way in order to study their
physical properties and the impact of the cosmic environment on galaxies and
their evolution.
In this work, we propose a new approach for the automatic retrieval of the
underlying filamentary structure from a 2D or 3D galaxy distribution using
graph theory and the assumption that paths that link galaxies together with the
minimum total length highlight the underlying distribution. To obtain a
smoothed version of this topological prior, we embedded it in a Gaussian
mixtures framework. In addition to a geometrical description of the pattern, a
bootstrap-like estimate of these regularised minimum spanning trees allowed us
to obtain a map characterising the frequency at which an area of the domain is
crossed. Using the distribution of halos derived from numerical simulations, we
show that the proposed method is able to recover the filamentary pattern in a
2D or 3D distribution of points with noise and outliers robustness with a few
comprehensible parameters. | Abundance gradient slopes versus mass in spheroids: predictions by
monolithic models: We investigate whether it is possible to explain the wide range of observed
gradients in early type galaxies in the framework of monolithic models. To do
so, we extend the set of hydrodynamical simulations by Pipino et al. (2008a) by
including low-mass ellipticals and spiral (true) bulges. These models satisfy
the mass-metallicity and the mass-[alpha/Fe] relations. The typical metallicity
gradients predicted by our models have a slope of -0.3 dex per decade variation
in radius, consistent with the mean values of several observational samples.
However, we also find a few quite massive galaxies in which this slope is -0.5
dex per decade, in agreement with some recent data. In particular, we find a
mild dependence from the mass tracers when we transform the stellar abundance
gradients into radial variations of the Mg_2 line-strength index, but not in
the Mg_b. We conclude that, rather than a mass- slope relation, is more
appropriate to speak of an increase in the scatter of the gradient slope with
the galactic mass. We can explain such a behaviour with different efficiencies
of star formation in the framework of the revised monolithic formation
scenario, hence the scatter in the observed gradients should not be used as an
evidence of the need of mergers. Indeed, model galaxies that exhibit the
steepest gradient slopes are preferentially those with the highest star
formation efficiency at that given mass. |
Isotropic vs. Anisotropic components of BAO data: a tool for model
selection: We conduct a selective analysis of the isotropic ($D_V$) and anisotropic
($AP$) components of the most recent Baryon Acoustic Oscillations (BAO) data.
We find that these components provide significantly different constraints and
could provide strong diagnostics for model selection, also in view of more
precise data to arrive. For instance, in the $\Lambda$CDM model, we find a mild
tension of $\sim 2 \sigma$ for the $\Omega_m$ estimates obtained using $D_V$
and $AP$ separately. Considering both $\Omega_k$ and $w$ as free parameters, we
find that the concordance model is in tension with the best-fit values provided
by the BAO data alone at 2.2$\sigma$. We complemented the BAO data with the
Supernova Ia (SNIa) and Observational \textit{Hubble} datasets to perform a
joint analysis on the $\Lambda$CDM model and its standard extensions. By
assuming $\Lambda$CDM scenario, we find that these data provide $H_0 = 69.4 \pm
1.7$ \text{km/s Mpc$^{-1} $} as the best-fit value for the present expansion
rate. In the $k\Lambda$CDM scenario we find that the evidence for acceleration
using the BAO data alone is more than $\sim 5.8\sigma$, which increases to $8.4
\sigma$ in our joint analysis. | Dispersion Distance and the Matter Distribution of the Universe in
Dispersion Space: We propose that "standard pings", brief broadband radio impulses, can be used
to study the three-dimensional clustering of matter in the Universe even in the
absence of redshift information. The dispersion of radio waves as they travel
through the intervening plasma can, like redshift, be used as a cosmological
distance measure. Because of inhomogeneities in the electron density along the
line of sight, dispersion is an imperfect proxy for radial distance and we show
that this leads to calculable dispersion-space distortions in the apparent
clustering of sources. Fast radio bursts (FRBs) are a new class of radio
transients that are the prototypical standard ping and, due to their high
observed dispersion, have been interpreted as originating at cosmological
distances. The rate of fast radio bursts has been estimated to be several
thousand over the whole sky per day and, if cosmological, the sources of these
events should trace the large-scale structure of the Universe. We calculate the
dispersion-space power spectra for a simple model where electrons and FRBs are
biased tracers of the large-scale structure of the Universe and we show that
the clustering signal could be measured using as few as 10 000 events. Such a
survey is in line with what may be achieved with upcoming wide-field radio
telescopes. |
Bulk flows in the local Universe and the importance of relativistic
effects: Bulk flow velocities are typically estimated in the idealised picture where
observers are moving within a perfectly homogeneous and isotropic space-time.
This picture is consistent within standard perturbation theory up to
relativistic effects that lead to correction terms of order $v z$, where $z$ is
the redshift of observation, and $v$ is the amplitude of the bulk flow. The
dominant relativistic contributions at scales $z \lesssim 1$ are caused by
gravitational redshift and time evolution of the velocity field. We include
these effects within a broadly applicable weak-field approximation, and provide
a cosmographic formula for estimating bulk flows at a high precision. Based on
this formula, we judge that recent bulk flow estimates are biased toward larger
values by $\sim 10\%$. This theoretical bias surpasses the measurement biases
of the same estimates, and it will become still more important to account for
the relativistic effects as the scales at which bulk flows are estimated to
increase. | The clustering of galaxies in the completed SDSS-III Baryon Oscillation
Spectroscopic Survey: tomographic BAO analysis of DR12 combined sample in
Fourier space: We perform a tomographic baryon acoustic oscillations (BAO) analysis using
the monopole, quadrupole and hexadecapole of the redshift-space galaxy power
spectrum measured from the pre-reconstructed combined galaxy sample of the
completed Sloan Digital Sky Survey (SDSS-III) Baryon Oscillation Spectroscopic
Survey (BOSS) Data Release (DR)12 covering the redshift range of $0.20<z<0.75$.
By allowing for overlap between neighbouring redshift slices, we successfully
obtained the isotropic and anisotropic BAO distance measurements within nine
redshift slices to a precision of $1.5\%-3.4\%$ for $D_V/r_d$, $1.8\% -4.2\%$
for $D_A/r_d$ and $3.7\% - 7.5\%$ for $H \ r_d$, depending on effective
redshifts. We provide our BAO measurement of $D_A/r_d$ and $H \ r_d$ with the
full covariance matrix, which can be used for cosmological implications. Our
measurements are consistent with those presented in \citet{Acacia}, in which
the BAO distances are measured at three effective redshifts. We constrain dark
energy parameters using our measurements, and find an improvement of the
Figure-of-Merit of dark energy in general due to the temporal BAO information
resolved. This paper is part of a set that analyses the final galaxy clustering
dataset from BOSS. |
Reconstruction of Reionization History through Dispersion Measure of
Fast Radio Bursts: In this paper, we study the evolution of the ionization fraction $x_e(z)$
during the epoch of reionization by using the dispersion measurements (DMs) of
fast radio bursts (FRBs). Different from the previous studies, here we turn to
consider the large-scale clustering information of observed DMs of FRB catalog,
which only needs the rough redshift distribution, instead of the exact redshift
information of each FRB. Firstly, we consider the instantaneous
``\texttt{tanh}'' model for $x_e(z)$ and find that including the
auto-correlation information of the mock catalog, about $10^4$ FRBs with the
intrinsic DM scatter of 100 $\rm pc/cm^3$ spanning 20\% of all sky, could
significantly improve the constraint on the width $\Delta_z$ of the model, when
comparing with that from the CMB data alone. The evolution shape of the
ionization fraction will be tightly narrowed, namely the duration of the epoch
of reionization has been shrunk, $z_{\rm dur}<2.24$ (95\% C.L.). Furthermore,
we also use another redshift-asymmetric reionization model and obtain that the
FRB mock catalog could measure the ionization fraction at $z=6$ precisely with
the $1\sigma$ error $\Delta x_e(z=6)=0.012$, which means that the large-scale
clustering information of observed DMs of FRB catalog is very sensitive to the
ionization fraction of the end of reionization epoch. We conclude that the
observation of high-redshift FRBs could be a complementary probe to study the
reionization history in the future. | Galaxy Three-Point Correlation Functions and Halo/Subhalo Models: We present the measurements of the luminosity-dependent redshift-space
three-point correlation functions (3PCFs) for the Sloan Digital Sky Survey
(SDSS) DR7 Main galaxy sample. We compare the 3PCF measurements to the
predictions from three different halo and subhalo models. One is the halo
occupation distribution (HOD) model and the other two are extensions of the
subhalo abundance matching (SHAM) model by allowing the central and satellite
galaxies to have different occupation distributions in the host halos and
subhalos. Parameters in all the models are chosen to best describe the
projected and redshift-space two-point correlation functions (2PCFs) of the
same set of galaxies. All three model predictions agree well with the 3PCF
measurements for the most luminous galaxy sample, while the HOD model better
performs in matching the 3PCFs of fainter samples (with luminosity threshold
below $L^*$), which is similar in trend to the case of fitting the 2PCFs. The
decomposition of the model 3PCFs into contributions from different types of
galaxy triplets shows that on small scales the dependence of the 3PCFs on
triangle shape is driven by nonlinear redshift-space distortion (and not by the
intrinsic halo shape) while on large scales it reflects the filamentary
structure. The decomposition also reveals more detailed differences in the
three models, which are related to the radial distribution, the mean occupation
function, and the velocity distribution of satellite galaxies inside halos. The
results suggest that galaxy 3PCFs can further help constrain the above
galaxy-halo relation and test theoretical models. |
Using strong gravitational lensing to probe the post reionization \HI
power spectrum: Probing statistical distribution of the neutral hydrogen (\HI) using the
redshifted 21-cm hyperfine-transition spectral line holds the key to understand
the formation and evolution of the matter density in the universe. The
two-point statistics of the \HI distribution can be estimated by measuring the
power spectrum of the redshifted 21-cm signal using visibility correlation. A
major challenge in this regard is that the expected signal is weak compared to
the foreground contribution from the Galactic synchrotron emission and
extragalactic point sources in the observing frequencies. In this work, we
investigate the possibility of detecting the power spectrum of the redshifted
21-cm signal by using strong gravitational lensing of the galaxy clusters. This
method has the advantage that it only enhances the \HI signal and not the
diffuse galactic foreground. Based on four simple models of the cluster
potentials we show that the strong lenses at relatively lower redshifts with
more than one dark matter halo significantly enhances the 21-cm signal from the
post reionization era. We discuss the merits and demerits of the method and the
future studies required for further investigations. | Cosmological surveys with the Australian Square Kilometre Array
Pathfinder: This is a design study into the capabilities of the Australian Square
Kilometre Array Pathfinder in performing a full-sky low redshift neutral
hydrogen survey, termed WALLABY, and the potential cosmological constraints one
can attain from measurement of the galaxy power spectrum. We find that the full
sky survey will likely attain 0.6 million redshifts which, when combined with
expected Planck CMB data, will constrain the Dark Energy equation of state to
20%, representing a coming of age for radio observations in creating
cosmological constraints. |
On the Likelihood of Observing Extragalactic Civilizations: Predictions
from the Self-Indication Assumption: Ambitious civilizations that expand for resources at an intergalactic scale
could be observable from a cosmological distance, but how likely is one to be
visible to us? The question comes down to estimating the appearance rate of
such things in the cosmos --- a radically uncertain quantity. Despite this
prior uncertainty, anthropic considerations give rise to Bayesian updates, and
thus predictions. The Self-Sampling Assumption (SSA), a school of anthropic
probability, has previously been used for this purpose. Here, we derive
predictions from the alternative school, the Self-Indication Assumption (SIA),
and point out its features. SIA favors a higher appearance rate of
expansionistic life, but our existence at the present cosmic time means that
such life cannot be too common (else our galaxy would long ago have been
overrun). This combination squeezes our vast prior uncertainty into a few
orders of magnitude. Details of the background cosmology fall out, and we are
left with some stark conclusions. E.g. if the limits to technology allow a
civilization to expand at speed $v$, the probability of at least one expanding
cosmological civilization being visible on our past light cone is
$1-\frac{v^3}{c^3}$. We also show how the SIA estimate can be updated from the
results of a hypothetical full-sky survey that detects "$n$" expanding
civilizations (for $n \geq 0$), and calculate the implied final extent of life
in the universe. | Effect of Inhomogeneity on Primordial Black Hole Formation in the Matter
Dominated Era: We investigate the effect of inhomogeneity on primordial black hole formation
in the matter dominated era. In the gravitational collapse of an inhomogeneous
density distribution, a black hole forms if apparent horizon prevents
information of the central region of the configuration from leaking. Since
information cannot propagate faster than the speed of light, we identify the
threshold of the black hole formation by considering the finite speed for
propagation of information. We show that the production probability
$\beta_{inhom}(\sigma)$ of primordial black holes, where $\sigma$ is density
fluctuation at horizon entry, is significantly enhanced from that derived in
previous work in which the speed of propagation was effectively regarded as
infinite. For $\sigma \ll 1$, we obtain $\beta_{inhom}\simeq 3.70
\sigma^{3/2}$, which is larger by about an order of magnitude than the
probability derived in earlier work by assuming instantaneous propagation of
information. |
Broadband Fizeau Interferometers for Astrophysics: Measurements of the 2.7 K cosmic microwave background (CMB) radiation now
provide the most stringent constraints on cosmological models. The power
spectra of the temperature anisotropies and the $E$-mode polarization of the
CMB are explained well by the inflationary paradigm. The next generation of CMB
experiments aim at providing the most direct evidence for inflation through the
detection of $B$-modes in the CMB polarization, presumed to have been caused by
gravitational waves generated during the inflationary epoch around $10^{-34}$s.
The $B$-mode polarization signals are very small ($\leq$10$^{-8}$K) compared
with the temperature anisotropies ($\sim 10^{-4}$K). Systematic effects in CMB
telescopes can cause leakage from temperature anisotropy into polarization.
Bolometric interferometry (BI) is a novel approach to measuring this small
signal with lower leakage. If BI can be made to work over wide bandwidth
($\sim20-30\%$) it can provide similar sensitivity to imagers. Subdividing the
frequency passband of a Fizeau interferometer would mitigate the problem of
`fringe smearing.' Furthermore, the approach should allow simultaneous
measurements in image space and visibility space. For subdividing the frequency
passsband (`sub-band splitting' henceforth), we write an expression for the
output from every baseline at every detector in the focal plane as a sum of
visibilities in different frequency sub-bands. For operating the interferometer
simultaneously as an imager, we write the output as two integrals over the sky
and the focal plane, with all the phase differences accounted for.}{The
sub-band splitting method described here is general and can be applied to
broad-band Fizeau interferometers across the electromagnetic spectrum.
Applications to CMB measurements and to long-baseline optical interferometry
are promising. | A Unique Approach to Classify Inflationary Potentials: Inflationary cosmology has made significant strides in understanding the
physics driving the rapid expansion of the early universe. However, many
inflation models with diverse potential shapes present analysis, comparison,
and classification challenges. In this paper, we propose a novel approach to
tackle this issue. We introduce a general potential formula encompassing all
inflationary potentials, whether single-field or multi-field, into a single
mathematical framework. This formula establishes a unified framework for
systematically classifying inflation models based on their potential functions.
We showcase the efficacy of the general potential formula by successfully
reproducing well-known inflation models, such as the Starobinsky potential and
the Valley Hybrid Inflation model. Moreover, we derive general inflationary
parameters, including the slow-roll parameters and power spectra, using the
proposed formula. Our approach provides a versatile tool for classifying and
studying various inflationary scenarios, simplifying the analysis and
comparison of different models in the field of inflationary cosmology. |
Disentangling non-Gaussianity, bias and GR effects in the galaxy
distribution: Local non-Gaussianity, parametrized by $f_{\rm NL}$, introduces a
scale-dependent bias that is strongest at large scales, precisely where General
Relativistic (GR) effects also become significant. With future data, it should
be possible to constrain $f_{\rm NL} = {\cal O}(1)$ with high redshift surveys.
GR corrections to the power spectrum and ambiguities in the gauge used to
define bias introduce effects similar to $f_{\rm NL}= {\cal O}(1)$, so it is
essential to disentangle these effects. For the first time in studies of
primordial non-Gaussianity, we include the consistent GR calculation of galaxy
power spectra, highlighting the importance of a proper definition of bias. We
present observable power spectra with and without GR corrections, showing that
an incorrect definition of bias can mimic non-Gaussianity. However, these
effects can be distinguished by their different redshift and scale dependence,
so as to extract the true primordial non-Gaussianity. | A Joint Chandra and XMM-Newton View of Abell 3158: Massive Off-Centre
Cool Gas Clump As A Robust Diagnostic of Merger Stage: By analysing the Chandra and XMM-Newton archived data of the nearby galaxy
cluster Abell 3158, which was reported to possess a relatively regular, relaxed
morphology in the X-ray band in previous works, we identify a bow edge-shaped
discontinuity in the X-ray surface brightness distribution at about
$120h_{71}^{-1}$ kpc west of the X-ray peak. This feature is found to be
associated with a massive, off-centre cool gas clump, and actually forms the
west boundary of the cool clump. We find that the cool gas clump is moving at a
subsonic velocity of ~700 km/s toward west on the sky plane. We exclude the
possibility that this cool clump was formed by local inhomogeneous radiative
cooling in the intra-cluster medium, due to the effectiveness of the thermal
conduction on the time-scale of $\sim 0.3$ Gyr. Since no evidence for central
AGN activity has been found in Abell 3158, and this cool clump bears many
similarities to the off-centre cool gas clumps detected in other merging
clusters in terms of their mass, size, location, and thermal properties (e.g.
lower temperature and higher abundance as compared with the environment), we
speculate that the cool clump in Abell 3158 was caused by a merger event, and
is the remnant of the original central cool-core of the main cluster or the
infalling sub-cluster. This idea is supported not only by the study of
line-of-sight velocity distribution of the cluster member galaxies, but also by
the study of gas entropy-temperature correlation. This example shows that the
appearance of such massive, off-centre cool gas clumps can be used to diagnose
the dynamical state of a cluster, especially when prominent shocks and cold
fronts are absent. |
The mass and angular momentum distribution of simulated massive
early-type galaxies to large radii: We study the dark and luminous mass distributions, circular velocity curves
(CVC), line-of-sight kinematics, and angular momenta for a sample of 42
cosmological zoom simulations of massive galaxies. Using a temporal smoothing
technique, we are able to reach large radii. We find that: (i)The dark matter
halo density profiles outside a few kpc follow simple power-law models, with
flat dark matter CVCs for lower-mass systems, and rising CVCs for high-mass
haloes. The projected stellar density distributions at large radii can be
fitted by Sersic functions with n>10, larger than for typical ETGs. (ii)The
massive systems have nearly flat total CVCs at large radii, while the less
massive systems have mildly decreasing CVCs. The slope of the CVC at large
radii correlates with v_circ itself. (iii)The dark matter fractions within Re
are in the range 15-30% and increase to 40-65% at 5Re. Larger and more massive
galaxies have higher dark matter fractions. (iv)The short axes of simulated
galaxies and their host dark matter haloes are well aligned and their
short-to-long axis ratios are correlated. (v)The stellar vrms(R) profiles are
slowly declining, in agreement with planetary nebulae observations in the outer
haloes of most ETGs. (vi)The line-of-sight velocity fields v show that rotation
properties at small and large radii are correlated. Most radial profiles for
the cumulative specific angular momentum parameter lambda(R) are nearly flat or
slightly rising, with values in [0.06,0.75] from 2Re to 5Re. (vii)Stellar mass,
ellipticity at 5Re, and lambda(5Re) are correlated: the more massive systems
have less angular momentum and are rounder, as for observed ETGs. (viii)More
massive galaxies with a large fraction of accreted stars have radially
anisotropic velocity distributions outside Re. Tangential anisotropy is seen
only for galaxies with high fraction of in-situ stars. (Full abstract in PDF) | Y-junction intercommutations of current carrying strings: Under certain conditions the collision and intercommutation of two cosmic
strings can result in the formation of a third string, with the three strings
then remaining connected at Y-junctions. The kinematics and dynamics of
collisions of this type have been the subject of analytical and numerical
analyses in the special case in which the strings are Nambu-Goto. Cosmic
strings, however, may well carry currents, in which case their dynamics is not
given by the Nambu-Goto action. Our aim is to extend the kinematic analysis to
more general kinds of string model. We focus in particular on the collision of
strings described by conservative elastic string models, characteristic of
current carrying strings, and which are expected to form in a cosmological
context. As opposed to Nambu-Goto strings collisions, we show that in this case
the collision cannot lead to the formation of a third elastic string: if
dynamically such a string forms then the joining string must be described by a
more general equation of state. This process will be studied numerically in a
forthcoming publication. |
The Atacama Cosmology Telescope: Constraints on Cosmic Birefringence: We present new constraints on anisotropic birefringence of the cosmic
microwave background polarization using two seasons of data from the Atacama
Cosmology Telescope covering $456$ square degrees of sky. The birefringence
power spectrum, measured using a curved-sky quadratic estimator, is consistent
with zero. Our results provide the tightest current constraint on birefringence
over a range of angular scales between $5$ arcminutes and $9$ degrees. We
improve previous upper limits on the amplitude of a scale-invariant
birefringence power spectrum by a factor of between $2$ and $3$. Assuming a
nearly-massless axion field during inflation, our result is equivalent to a
$2\,\sigma$ upper limit on the Chern-Simons coupling constant between axions
and photons of $g_{\alpha\gamma}<4.0\times 10^{-2}/H_I$ where $H_I$ is the
inflationary Hubble scale. | Constraining early and interacting dark energy with gravitational wave
standard sirens: the potential of the eLISA mission: We perform a forecast analysis of the capability of the eLISA space-based
interferometer to constrain models of early and interacting dark energy using
gravitational wave standard sirens. We employ simulated catalogues of standard
sirens given by merging massive black hole binaries visible by eLISA, with an
electromagnetic counterpart detectable by future telescopes. We consider
three-arms mission designs with arm length of 1, 2 and 5 million km, 5 years of
mission duration and the best-level low frequency noise as recently tested by
the LISA Pathfinder. Standard sirens with eLISA give access to an intermediate
range of redshift $1\lesssim z \lesssim 8$, and can therefore provide
competitive constraints on models where the onset of the deviation from
$\Lambda$CDM (i.e. the epoch when early dark energy starts to be
non-negligible, or when the interaction with dark matter begins) occurs
relatively late, at $z\lesssim 6$. If instead early or interacting dark energy
is relevant already in the pre-recombination era, current cosmological probes
(especially the cosmic microwave background) are more efficient than eLISA in
constraining these models, except possibly in the interacting dark energy model
if the energy exchange is proportional to the energy density of dark energy. |
Ly$α$NNA: A Deep Learning Field-level Inference Machine for the
Lyman-$α$ Forest: The inference of astrophysical and cosmological properties from the
Lyman-$\alpha$ forest conventionally relies on summary statistics of the
transmission field that carry useful but limited information. We present a deep
learning framework for inference from the Lyman-$\alpha$ forest at field-level.
This framework consists of a 1D residual convolutional neural network (ResNet)
that extracts spectral features and performs regression on thermal parameters
of the IGM that characterize the power-law temperature-density relation. We
train this supervised machinery using a large set of mock absorption spectra
from Nyx hydrodynamic simulations at $z=2.2$ with a range of thermal parameter
combinations (labels). We employ Bayesian optimization to find an optimal set
of hyperparameters for our network, and then employ a committee of ten neural
networks for increased statistical robustness of the network inference. In
addition to the parameter point predictions, our machine also provides a
self-consistent estimate of their covariance matrix with which we construct a
pipeline for inferring the posterior distribution of the parameters. We compare
the results of our framework with the traditional summary (PDF and power
spectrum of transmission) based approach in terms of the area of the 68%
credibility regions as our figure of merit (FoM). In our study of the
information content of perfect (noise- and systematics-free) Ly$\alpha$ forest
spectral data-sets, we find a significant tightening of the posterior
constraints -- factors of 5.65 and 1.71 in FoM over power spectrum only and
jointly with PDF, respectively -- that is the consequence of recovering the
relevant parts of information that are not carried by the classical summary
statistics. | Sampling Artifact in Volume Weighted Velocity Measurement.--- II.
Detection in simulations and comparison with theoretical modelling: Measuring the volume weighted velocity power spectrum suffers from a severe
systematic error, due to imperfect sampling of the velocity field from
inhomogeneous distribution of dark matter particles/halos in simulations or
galaxies with velocity measurement. This "sampling artifact" depends on both
the mean particle number density $\bar{n}_P$ and the intrinsic large scale
structure (LSS) fluctuation in the particle distribution. (1) We report robust
detection of this sampling artifact in N-body simulations. It causes $\sim 12$%
underestimation of the velocity power spectrum at $k=0.1$h/Mpc for samples with
$\bar{n}_P=6\times10^{-3}$ (Mpc/h)$^{-3}$. This systematic underestimation
increases with decreasing $\bar{n}_P$ and increasing $k$. Its dependence on the
intrinsic LSS fluctuations is also robustly detected. (2) All these findings
are expected by our theoretical modelling in paper I \cite{Zhang14}. In
particular, the leading order theoretical approximation agrees quantitatively
well with simulation result for $\bar{n}_P\gtrsim6\times
10^{-4}$(Mpc/h)$^{-3}$. Furthermore, we provide an ansatz to take high order
terms into account. It improves the model accuracy to $\lesssim1$% at
$k\lesssim0.1$h/Mpc over 3 orders of magnitude in $\bar{n}_P$ and over typical
LSS clustering from $z=0$ to $z=2$. (3) The sampling artifact is determined by
the deflection ${\bf D}$ field, which is straightforwardly available in both
simulations and data of galaxy velocity. Hence the sampling artifact in the
velocity power spectrum measurement can be self-calibrated within our
framework. By applying such self-calibration in simulations, it becomes
promising to determine the {\it real} large scale velocity bias of
$10^{13}M_\odot$ halos with $\sim 1$% accuracy, and that of lower mass halos by
better accuracy. ...[abridged] |
A study on the Clustering Properties of Radio-Selected sources in the
Lockman Hole Region at 325 MHz: Studying the spatial distribution of extragalactic source populations is
vital in understanding the matter distribution in the Universe. It also enables
understanding the cosmological evolution of dark matter density fields and the
relationship between dark matter and luminous matter. Clustering studies are
also required for EoR foreground studies since it affects the relevant angular
scales. This paper investigates the angular and spatial clustering properties
and the bias parameter of radio-selected sources in the Lockman Hole field at
325 MHz. The data probes sources with fluxes $\gtrsim$0.3 mJy within a radius
of 1.8$^\circ$ around the phase center of a $6^\circ \times 6^\circ$ mosaic.
Based on their radio luminosity, the sources are classified into Active
Galactic Nuclei (AGNs) and Star-Forming Galaxies (SFGs). Clustering and bias
parameters are determined for the combined populations and the classified
sources. The spatial correlation length and the bias of AGNs are greater than
SFGs -- indicating that more massive haloes host the former. This study is the
first reported estimate of the clustering property of sources at 325 MHz,
intermediate between the preexisting studies at high and low-frequency bands.
It also probes a well-studied deep field at an unexplored frequency with
moderate depth and area. Clustering studies require such observations along
different lines of sight, with various fields and data sets across frequencies
to avoid cosmic variance and systematics. Thus, an extragalactic deep field has
been studied in this work to contribute to this knowledge. | Upper Bound on the First Star Formation History: Our understanding of the nature of the extragalactic background light (EBL)
has improved with the recent development of gamma-ray observation techniques.
An open subject in the context of the EBL is the reionization epoch, which is
an important probe of the formation history of first stars, the so-called
Population III (Pop III) stars. Although the mechanisms for the formation of
Pop III stars are rather well understood on theoretical grounds, their
formation history is still veiled in mystery because of their faintness. To
shed light into this matter, we study jointly the gamma-ray opacity of distant
objects and the reionization constraints from studies of intergalactic gas. By
combining these studies, we obtain a sensitive upper bound on the Pop III star
formation rate density as $\dot\rho_{*}(z)<0.01[(1+z)/{(1+7.0)}]^{3.4}({f_{\rm
esc}}/{0.2})^{-1}({C}/{3.0})\ {\rm M}_{\odot} {\rm yr}^{-1}\ {\rm Mpc}^{-3}$ at
$z\ge7$, where $f_{\rm esc}$ and $C$ are the escape fraction of ionizing
photons from galaxies and the clumping factor of the intergalactic hydrogen
gas. This limit is a $\sim10$ times tighter constraint compared with previous
studies that take into account gamma-ray opacity constraints only. Even if we
do not include the current gamma-ray constraints, the results do not change.
This is because the detected gamma-ray sources are still at $z\le4.35$ where
the reionization has already finished. |
Confirmation of the spectral excess in DAMIC at SNOLAB with skipper CCDs: We present results from a 3.1 kg-day target exposure of two charge-coupled
devices (CCDs), each with 24 megapixels and skipper readout, deployed in the
DAMIC (DArk Matter In CCDs) setup at SNOLAB. With a reduction in pixel readout
noise of a factor of 10 relative to the previous detector, we investigate the
excess population of low-energy bulk events previously observed above expected
backgrounds. We address the dominant systematic uncertainty of the previous
analysis through a depth fiducialization designed to reject surface backgrounds
on the CCDs. The measured bulk ionization spectrum confirms with higher
significance the presence of an excess population of low-energy events in the
CCD target with characteristic rate of ${\sim}7$ events per kg-day and
electron-equivalent energies of ${\sim}80~$eV, whose origin remains unknown. | Implications of the Cosmic Birefringence Measurement for the Axion Dark
Matter Search: We show that a recent constraint on the cosmic birefringence effect due to
dark energy can be related to the constraints on the coupling of axion dark
matter to photon, by relying on a simple model of two-axion alignment mechanism
with periodic potentials. Owing to the alignment of the potentials, one linear
combination of two fields provides a nearly flat direction and acts as dark
energy, whereas the other combination provides a steep direction and acts as
dark matter. This scenario solves the known conceptual issues of one-field
model for dark energy and predicts the connection between seemingly disparate
constraints on the dark sectors of our universe. |
Primordial power spectrum: a complete analysis with the WMAP nine-year
data: We have improved further the error sensitive Richardson-Lucy deconvolution
algorithm making it applicable directly on the un-binned measured angular power
spectrum of Cosmic Microwave Background observations to reconstruct the form of
the primordial power spectrum. This improvement makes the application of the
method significantly more straight forward by removing some intermediate stages
of analysis allowing a reconstruction of the primordial spectrum with higher
efficiency and precision and with lower computational expenses. Applying the
modified algorithm we fit the WMAP 9 year data using the optimized
reconstructed form of the primordial spectrum with more than 300 improvement in
\chi^2 with respect to the best fit power-law. This is clearly beyond the reach
of other alternative approaches and reflects the efficiency of the proposed
method in the reconstruction process and allow us to look for any possible
feature in the primordial spectrum projected in the CMB data. Though the
proposed method allow us to look at various possibilities for the form of the
primordial spectrum, all having good fit to the data, proper error-analysis is
needed to test for consistency of theoretical models since, along with possible
physical artefacts, most of the features in the reconstructed spectrum might be
arising from fitting noises in the CMB data. Reconstructed error-band for the
form of the primordial spectrum using many realizations of the data, all
bootstrapped and based on WMAP 9 year data, shows proper consistency of
power-law form of the primordial spectrum with the WMAP 9 data at all wave
numbers. Including WMAP polarization data in to the analysis have not improved
much our results due to its low quality but we expect Planck data will allow us
to make a full analysis on CMB observations on both temperature and
polarization separately and in combination. | Prospects for Constraining interacting dark energy cosmology with
gravitational-wave bright sirens detected by future SKA-era pulsar timing
arrays: Pulsar timing arrays (PTAs) have the potential to detect Nanohertz
gravitational waves (GWs) that are usually generated by the individual
inspiraling supermassive black hole binaries (SMBHBs) in the galactic centers.
The GW signals as cosmological standard sirens can provide the absolute cosmic
distances, thereby can be used to constrain the cosmological parameters. In
this paper, we analyze the ability of future SKA-era PTAs to detect the
existing SMBHBs candidates assuming the root mean square of timing noise
$\sigma_t=20\ {\rm ns}$, and use the simulated PTA data to constrain the
interacting dark energy (IDE) models with energy transfer rate $Q = \beta
H\rho_c$. We find that, the future SKA-era PTAs will play an important role in
constraining the IDE cosmology. Using only the mock PTA data consisting of 100
pulsars, we obtain $\sigma(H_0)=0.239\ {\rm km} \ {\rm s}^{-1} {\rm Mpc}^{-1}$
and $\sigma(\Omega_m)=0.0103$ in the I$\Lambda$CDM model, which are much better
than the results from the Planck TT, TE, EE+lowE. However, the PTA data cannot
provide a tight constraint on the coupling parameter $\beta$ compared with
Planck, but the data combination of Planck+PTA can provide a rather tight
constraint, i.e., $\sigma(\beta)=0.00232$, since the PTA data could break the
parameter degeneracies inherent in CMB. In the I$w$CDM model, we obtain
$\sigma(\beta)=0.00137$ and $\sigma(w)=0.0492$ from the Planck+PTA data
combination. In addition, we also find that with the increase of the number of
pulsars in PTA, the constraint results from the Planck+PTA will be further
improved to some extent. We show that the observations of Nanohertz GWs with
future SKA-era PTAs will provide a powerful tool for exploring the nature of
dark energy and measuring the coupling between dark energy and dark matter. |
Forecast for weighing neutrinos in cosmology with SKA: We investigate what role the SKA neutral hydrogen (HI) intensity mapping (IM)
sky survey observation will play in weighing neutrinos in cosmology. We use the
simulated data of the baryon acoustic oscillation (BAO) measurements from the
HI IM survey based on SKA1 and SKA2 to do the analysis. For the current
observations, we use the Planck 2015 cosmic microwave background (CMB)
anisotropies observation, the optical BAO measurements, the type Ia supernovae
(SN) observation (Pantheon compilation), and the latest $H_0$ measurement. We
consider three mass ordering cases for massive neutrinos, i.e., the normal
hierarchy (NH), inverted hierarchy (IH), and degenerate hierarchy (DH) cases.
It is found that the SKA observation can significantly improve the constraints
on $\Omega_{\rm m}$ and $H_0$. Compared to the current observation, the SKA1
data can improve the constraints on $\Omega_{\rm m}$ by about 33%, and on $H_0$
by about 36%; the SKA2 data can improve the constraints on $\Omega_{\rm m}$ by
about 58%, and on $H_0$ by about 66%. It is also found that the SKA observation
can only slightly improve the constraints on $\sum m_\nu$. Compared to the
current observation, the SKA1 data can improve the constraints on $\sum m_\nu$
by about 4%, 3%, and 10%, for the NH, IH, and DH cases, respectively; the SKA2
data can improve the constraints on $\sum m_\nu$ by about 7%, 7%, and 16%, for
the NH, IH, and DH cases, respectively. | Perturbation theory of LSS in the $Λ$CDM Universe: exact time
evolution and the two-loop power spectrum: We derive exact analytic solutions for density and velocity fields to all
orders in Eulerian standard perturbation theory for $\Lambda$CDM cosmology. In
particular, we show that density and velocity field kernels can be written in a
separable form in time and momenta at each perturbative order. The kernel
solutions are built from an analytic basis of momentum operators and their
time-dependent coefficients, which solve a set of recursive differential
equations. We also provide an exact closed perturbative solution for such
coefficients, expanding around the (quasi-)EdS approximation. We find that the
perturbative solution rapidly converges towards the numerically obtained
solutions and its leading order result suffices for any practical requirements.
To illustrate our findings, we compute the exact two-loop dark matter density
and velocity power spectra in $\Lambda$CDM cosmology. We show that the
difference between the exact $\Lambda$CDM and the (quasi-)EdS approximated
result can reach the level of several percent (at redshift zero, for
wavenumbers $k<1h/$Mpc). This deviation can be partially mitigated by
exploiting the degeneracy with the EFT counterterms. As an additional benefit
of our algorithm for the solutions of time-dependent coefficients, the
computational complexity of power spectra loops in $\Lambda$CDM is comparable
to the EdS case. In performing the two-loop computation, we devise an explicit
method to implement the so-called IR cancellations, as well as the
cancellations arising as a consequence of mass and momentum conservation. |
The significance of anisotropic signals hiding in the type Ia supernovae: We use two different methods, i.e., dipole-fitting (DF) and hemisphere
comparison (HC), to search for the anisotropic signals hiding in the Union2.1
data set. We find that the directions of maximum matter density derived using
these two methods are about $114^{\circ}$ away from each other. We construct
four Union2.1-like mock samples to test the statistical significance of these
two methods. It is shown that DF method is statistically significant, while HC
method is strongly biased by the distribution of data points in the sky. Then
we assume that the anisotropy of distance modulus is mainly induced by the
anisotropy of matter density, which is modeled to be the dipole form
$\Omega_M=\Omega_{M0}(1-\cos\theta)$. We fit our model to Union2.1, and find
that the direction of maximum matter density is well consistent with the
direction derived using DF method, but it is very different from the direction
previously claimed. Monte Carlo simulations show that our method is
statistically more significant than HC method, although it is not as
significant as DF method. The statistical significance can be further improved
if the data points are homogeneously distributed in the sky. Due to the low
quality of present supernovae data, however, it is still premature to claim
that the Universe has any preferred direction. | Recovering 3D structural properties of galaxies from SDSS-like
photometry: Because of the 3D nature of galaxies, an algorithm for constructing spatial
density distribution models of galaxies on the basis of galaxy images has many
advantages over surface density distribution approximations. We present a
method for deriving spatial structure and overall parameters of galaxies from
images and estimate its accuracy and derived parameter degeneracies on a sample
of idealised model galaxies. The test galaxies consist of a disc-like component
and a spheroidal component with varying proportions and properties. Both
components are assumed to be axially symmetric and coplanar. We simulate these
test galaxies as if observed in the SDSS project through ugriz filters, thus
gaining a set of realistically imperfect images of galaxies with known
intrinsic properties. These artificial SDSS galaxies were thereafter remodelled
by approximating the surface brightness distribution with a 2D projection of a
bulge+disc spatial distribution model and the restored parameters were compared
to the initial ones. Down to the r-band limiting magnitude 18, errors of the
restored integral luminosities and colour indices remain within 0.05 mag and
errors of the luminosities of individual components within 0.2 mag. Accuracy of
the restored bulge-to-disc ratios (B/D) is within 40% in most cases, and
becomes worse for galaxies with low B/D, but the general balance between bulges
and discs is not shifted systematically. Assuming that the intrinsic disc axial
ratio is < 0.3, the inclination angles can be estimated with errors < 5deg for
most of the galaxies with B/D < 2 and with errors < 15deg up to B/D = 6. Errors
of the recovered sizes of the galactic components are below 10% in most cases.
In general, models of disc components are more accurate than models of
spheroidal components for geometrical reasons. |
Southern Cosmology Survey II: Massive Optically-Selected Clusters from
70 square degrees of the SZE Common Survey Area: We present a catalog of 105 rich and massive ($M>3\times10^{14}M_{\sun}$)
optically-selected clusters of galaxies extracted from 70 square-degrees of
public archival griz imaging from the Blanco 4-m telescope acquired over 45
nights between 2005 and 2007. We use the clusters' optically-derived properties
to estimate photometric redshifts, optical luminosities, richness, and masses.
We complement the optical measurements with archival XMM-Newton and ROSAT X-ray
data which provide additional luminosity and mass constraints on a modest
fraction of the cluster sample. Two of our clusters show clear evidence for
central lensing arcs; one of these has a spectacular large-diameter,
nearly-complete Einstein Ring surrounding the brightest cluster galaxy. A
strong motivation for this study is to identify the massive clusters that are
expected to display prominent signals from the Sunyaev-Zeldovich Effect (SZE)
and therefore be detected in the wide-area mm-band surveys being conducted by
both the Atacama Cosmology Telescope and the South Pole Telescope. The optical
sample presented here will be useful for verifying new SZE cluster candidates
from these surveys, for testing the cluster selection function, and for
stacking analyzes of the SZE data. | Large slow-roll corrections to the bispectrum of noncanonical inflation: Nongaussian statistics are a powerful discriminant between inflationary
models, particularly those with noncanonical kinetic terms. Focusing on
theories where the Lagrangian is an arbitrary Lorentz-invariant function of a
scalar field and its first derivatives, we review and extend the calculation of
the observable three-point function. We compute the "next-order" slow-roll
corrections to the bispectrum in closed form, and obtain quantitative estimates
of their magnitude in DBI and power-law k-inflation. In the DBI case our
results enable us to estimate corrections from the shape of the potential and
the warp factor: these can be of order several tens of percent. We track the
possible sources of large logarithms which can spoil ordinary perturbation
theory, and use them to obtain a general formula for the scale dependence of
the bispectrum. Our result satisfies the next-order version of Maldacena's
consistency condition and an equivalent consistency condition for the scale
dependence. We identify a new bispectrum shape available at next-order, which
is similar to a shape encountered in Galileon models. If fNL is sufficiently
large this shape may be independently detectable. |
Angular momentum transfer and the size - mass relation in early - type
galaxies: Early - type galaxies (ETGs) define a narrow strip in the size - mass plane
because of the observed correlation between the effective radius $R_{eff}$ and
the total stellar mass $M_{\star}$. When expressed in logarithmic units, a
linear relation, $\log{R_{eff}} \propto \gamma \log{M_{\star}}$, is indeed
observationally found, but the slope $\gamma$ deviates from the canonical
$\gamma = 1/2$ value which can be naively predicted for a spherically symmetric
isotropic system. We propose here that a transfer of angular momentum to the
stellar component induces an anisotropy in the velocity space thus leading to a
modified distribution function (DF). Assuming an Osipkov - Merritt like
anisotropic DF, we derive an analytic relation between the slope $\gamma$ of
the size - mass relation and the slope $\alpha$ of the angular momentum term in
the DF. With this simple model, we are then able to recover the observed
$\gamma$ value provided $\alpha$ is suitably set. It turns out that an
anisotropy profile which is tangential inside $\sim 0.6 r_a$ and radial
outside, with $r_a$ the anisotropy radius, is able to reproduce the observed
size - mass relation observed for massive ($M_{\star} \ge 2 \times 10^{10} \
h^{-1} {\rm M}_{\odot}$) elliptical galaxies. | Thermal instability in the collisionally cooled gas: We have presented the non-equilibrium (time-dependent) cooling rate and
ionization state calculations for a gas behind shock waves with $v \sim 50-150$
km s$^{-1}$ ($T_s \sim 0.5 - 6\times 10^5$ K). Such shock waves do not lead to
the radiative precursor formation, i.e. the thermal evolution of a gas behind
the shock waves are controlled by collisions only. We have found that the
cooling rate in a gas behind the shock waves with $v \sim 50-120$ km s$^{-1}$
($T_s \sim 0.5 - 3\times 10^5$ K) differs considerably from the cooling rate
for a gas cooled from $T = 10^8$ K. It is well-known that a gas cooled from $T
= 10^8$ K is thermally unstable for isobaric and isochoric perturbations at $T
\simgt 2\times 10^4$ K. We have studied the thermal instability in a
collisionally controlled gas for shock waves with $v \sim 50-150$ km s$^{-1}$.
We have found that the temperature range, where the postshock gas is thermally
unstable, is significantly modified and depends on both gas metallicity and
ionic composition of a gas before shock wave. For $Z \simgt 0.1Z_\odot$ the
temperature range, where the thermal instability criterion for isochoric
perturbations is not fulfilled, widens in comparison with that for a gas cooled
from $T = 10^8$ K, while that for isobaric perturbations remains almost without
a change. For $Z\sim Z_\odot$ a gas behind shock waves with $v \simlt 65$ km
s$^{-1}$ ($T_s \simlt 10^5$ K) is thermally stable to isochoric perturbations
during full its evolution. We have shown that the transition from isobaric to
isochoric cooling for a gas with $Z \simgt 0.1Z_\odot$ behind shock waves with
$T_s = 0.5 - 3\times 10^5$ K proceeds at lower column density layer behind a
shock wave than that for a gas cooled from $T = 10^8$ K. (abridged) |
Cosmology with the MaunaKea Spectroscopic Explorer: This document summarizes the science cases related to cosmology studies with
the MaunaKea Spectroscopic Explorer (MSE), a highly-multiplexed (4332 fibers),
wide FOV (1.5 sq deg), large aperture (11.25 m in diameter), optical/NIR (360nm
to 1300nm) facility. The MSE High-z Cosmology Survey is designed to probe a
large volume of the Universe with a galaxy density sufficient to measure the
extremely-large-scale density fluctuations required to explore primordial
non-Gaussianity and therefore inflation. We expect a measurement of the local
parameter $f_{NL}$ to a precision $\sigma(f_{NL}) = 1.8$. Combining the MSE
High-z Cosmology Survey data with data from a next generation CMB stage 4
experiment and existing DESI data will provide the first $5\sigma$ confirmation
of the neutrino mass hierarchy from astronomical observations. In addition, the
Baryonic Acoustic Oscillations (BAO) observed within the sample will provide
measurements of the distance-redshift relationship in six different redshift
bins between $z=1.6$ and 4.0, each with an accuracy of $\sim0.6\%$. The
simultaneous measurements of Redshift Space Distortions (RSD) constrain the
amplitude of the fluctuations, at a level ranging from $1.9\%$ to $3.6\%$. The
proposed survey covers 10,000 ${\rm deg}^2$, measuring redshifts for three
classes of target objects: Emission Line Galaxies (ELGs) with $1.6<z<2.4$,
Lyman Break Galaxies (LBGs) with $2.4<z<4.0$, and quasars $2.1<z<3.5$. The ELGs
and LBGs will be used as direct tracers of the underlying density field, while
the Lyman-$\alpha$ forests in the quasar spectra will be utilized to probe
structure. Exposures of duration 1,800sec will guarantee a redshift
determination efficiency of $90\%$ for ELGS and at least $50\%$ for LBGs. The
survey will represent 100 nights per year for a 5-year MSE program. Finally,
three ideas for additional projects of cosmological interest are proposed. | Morphology of Galaxy Clusters: A Cosmological Model-Independent Test of
the Cosmic Distance-Duality Relation: Aiming at comparing different morphological models of galaxy clusters, we use
two new methods to make a cosmological model-independent test of the
distance-duality (DD) relation. The luminosity distances come from Union2
compilation of Supernovae Type Ia. The angular diameter distances are given by
two cluster models (De Filippis et al. and Bonamente et al.). The advantage of
our methods is that it can reduce statistical errors. Concerning the
morphological hypotheses for cluster models, it is mainly focused on the
comparison between elliptical $\beta$-model and spherical $\beta$-model. The
spherical $\beta$-model is divided into two groups in terms of different
reduction methods of angular diameter distances, i.e. conservative spherical
$\beta$-model and corrected spherical $\beta$-model. Our results show that the
DD relation is consistent with the elliptical $\beta$-model at $1\sigma$
confidence level (CL) for both methods, whereas for almost all spherical
$\beta$-model parameterizations, the DD relation can only be accommodated at
$3\sigma$ CL, particularly for the conservative spherical $\beta$-model. In
order to minimize systematic uncertainties, we also apply the test to the
overlap sample, i.e. the same set of clusters modeled by both De Filippis et
al. and Bonamente et al.. It is found that the DD relation is compatible with
the elliptically modeled overlap sample at $1\sigma$ CL, however for most of
the parameterizations, the DD relation can not be accommodated even at
$3\sigma$ CL for any of the two spherical $\beta$-models. Therefore it is
reasonable that the marked triaxial ellipsoidal model is a better geometrical
hypothesis describing the structure of the galaxy cluster compared with the
spherical $\beta$-model if the DD relation is valid in cosmological
observations. |
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