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The bulk flow motion and the Hubble-Lemaître law in the Local
Universe with the ALFALFA survey: The knowledge of the main features of the bulk flow in the Local Universe is
important for a better determination of the relative motions there, an
information that would contribute to a precise calculation of the
Hubble-Lema\^{\i}tre law at very low redshifts. We study how to obtain the
Hubble-Lema\^{\i}tre law in two sky regions using the catalog of HI sources of
the ALFALFA survey, with data $cz_{\odot} < 6000$ km/s. Our methodology aims to
compute $H_0$ in two regions -- located in opposite galactic hemispheres --
mapped by the ALFALFA survey, and look for dependence with distance, direction,
and also test for reference frame changes. We calculate the Hubble constant, in
the Cosmic Microwave Background reference frame, in opposite galactic
hemispheres: $H_0^N = 70.87 \pm 2.38$ and $H_0^S = 66.07 \pm 3.02$, which
allows us to measure the bulk flow velocity $V_{BF} = 401.06 \pm 150.55$ km/s
at the effective distance $31.3 \pm 6.26$ Mpc, a novel result found analysing
the ALFALFA data at low redshift. We confirm the influence of the bulk flow on
the structures of the Local Universe which manifests through a dipolar behavior
of the Hubble constant in opposite hemispheres. | Extragalactic magnetic fields unlikely generated at the electroweak
phase transition: In this letter we show that magnetic fields generated at the electroweak
phase transition are most likely too weak to explain the void magnetic fields
apparently observed today unless they have considerable helicity. We show that,
in the simplest estimates, the helicity naturally produced in conjunction with
the baryon asymmetry is too small to explain observations, which require a
helicity fraction at least of order $10^{-14}-10^{-10}$ depending on the void
fields constraint used. Therefore new mechanisms to generate primordial
helicity are required if magnetic fields generated during the electroweak phase
transition should explain the extragalactic fields. |
Weakly non-Gaussian formula for the Minkowski functionals in general
dimensions: The Minkowski functionals are useful statistics to quantify the morphology of
various random fields. They have been applied to numerous analyses of
geometrical patterns, including various types of cosmic fields, morphological
image processing, etc. In some cases, including cosmological applications,
small deviations from the Gaussianity of the distribution are of fundamental
importance. Analytic formulas for the expectation values of Minkowski
functionals with small non-Gaussianity have been derived in limited cases to
date. We generalize these previous works to derive an analytic expression for
expectation values of Minkowski functionals up to second-order corrections of
non-Gaussianity in a space of general dimensions. The derived formula has
sufficient generality to be applied to any random fields with weak
non-Gaussianity in a statistically homogeneous and isotropic space of any
dimensions. | Statistical Characterization of Temperature Patterns in Anisotropic
Cosmologies: We consider the issue of characterizing the coherent large-scale patterns
from CMB temperature maps in globally anisotropic cosmologies. The methods we
investigate are reasonably general; the particular models we test them on are
the homogeneous but anisotropic relativistic cosmologies described by the
Bianchi classification. Although the temperature variations produced in these
models are not stochastic, they give rise to a "non-Gaussian" distribution of
temperature fluctuations over the sky that is a partial diagnostic of the
model. We explore two methods for quantifying non-Gaussian and/or
non-stationary fluctuation fields in order to see how they respond to the
Bianchi models.We first investigate the behavior of phase correlations between
the spherical harmonic modes of the maps. Then we examine the behavior of the
multipole vectors of the temperature distribution which, though defined in
harmonic space, can indicate the presence of a preferred direction in real
space, i.e. on the 2-sphere. These methods give extremely clear signals of the
presence of anisotropy when applied to the models we discuss, suggesting that
they have some promise as diagnostics of the presence of global asymmetry in
the Universe. |
Exploring Effects on Magnifications due to Line-of-Sight Galaxies in the
Hubble Frontier Fields: Cluster lensing has become an important tool in the search for high redshift
galaxies through its ability to magnify sources. In order to determine the
intrinsic properties of these galaxies, lensing mass models must be constructed
to determine the magnification of the images. These models are traditionally
two-dimensional, focusing on the mass within the cluster and either ignoring or
approximating any contribution from line-of-sight galaxies. In this paper, we
present the first full set of three-dimensional mass models of the six Hubble
Frontier Fields and use them to test for systematic biases in magnifications
due to using the traditional 2D approach. We find that omitting foreground or
background galaxies causes image position offsets between 0.1-0.4", a
non-negligible fraction of the typical 0.3-0.7" residuals of current
state-of-the-art models. We also find that median image magnifications can
shift by up to 6%, though it is dependent on the field. This can be alleviated
in some cases by approximating the mass in the lensing plane, but a 5%
magnification bias still exists in other cases; image position offsets are also
improved, but are still present at 0.10". | The interplay between chemical and mechanical feedback from the first
generation of stars: We study cosmological simulations of early structure formation, including
non-equilibrium molecular chemistry, metal pollution from stellar evolution,
transition from population III (popIII) to population II (popII) star
formation, regulated by a given critical metallicity, and feedback effects. We
investigate the properties of early metal spreading from the different stellar
populations and its interplay with primordial molecular gas. We find that,
independently of the details about popIII modeling, after the onset of star
formation, regions enriched below the critical level are mostly found in
isolated environments, while popII star formation regions are much more
clumped. Typical star forming haloes show average SN driven outflow rates of up
to 10^{-4} Msun/yr in enriched gas, initially leaving the original star
formation regions almost devoid of metals. The polluted material, which is
gravitationally incorporated in over-dense environments on timescales of 10^7
yr, is mostly coming from external, nearby star forming sites ("gravitational
enrichment"). In parallel, the pristine-gas inflow rates are between 10^{-3} -
10^{-1} Msun/yr. However, thermal feedback from SN generates turbulence and
destroys molecules within the pristine gas, and only the polluted material,
incorporated via gravitational enrichment, can continue to cool by atomic metal
fine-structure transitions on time scales short enough to end the initial
popIII regime within less than 10^8 yr. |
Comment on "A Supervoid Imprinting the Cold Spot in the Cosmic Microwave
Background": Recently Finelli et al. [http://arxiv.org/abs/1405.1555] found evidence for a
relatively nearby (z = 0.16) void in a galaxy catalogue in the direction of the
cosmic microwave background (CMB) Cold Spot. Using a perturbative calculation,
they also claimed that such a void would produce a CMB decrement comparable to
that of the observed Cold Spot, mainly via the nonlinear Rees-Sciama effect.
Here I calculate the effect of such a void using a fully general relativistic
model and show that, to the contrary, the linear integrated Sachs-Wolfe effect
dominates and produces a substantially weaker decrement than observed. | A magnified glance into the dark sector: probing cosmological models
with strong lensing in A1689: In this paper we constrain four alternative models to the late cosmic
acceleration in the Universe: Chevallier-Polarski-Linder (CPL), interacting
dark energy (IDE), Ricci holographic dark energy (HDE), and modified polytropic
Cardassian (MPC). Strong lensing (SL) images of background galaxies produced by
the galaxy cluster Abell $1689$ are used to test these models. To perform this
analysis we modify the LENSTOOL lens modeling code. The value added by this
probe is compared with other complementary probes: Type Ia supernovae (SNIa),
baryon acoustic oscillations (BAO), and cosmic microwave background (CMB). We
found that the CPL constraints obtained of the SL data are consistent with
those estimated using the other probes. The IDE constraints are consistent with
the complementary bounds only if large errors in the SL measurements are
considered. The Ricci HDE and MPC constraints are weak but they are similar to
the BAO, SNIa and CMB estimations. We also compute the figure-of-merit as a
tool to quantify the goodness of fit of the data. Our results suggest that the
SL method provides statistically significant constraints on the CPL parameters
but weak for those of the other models. Finally, we show that the use of the SL
measurements in galaxy clusters is a promising and powerful technique to
constrain cosmological models. The advantage of this method is that
cosmological parameters are estimated by modelling the SL features for each
underlying cosmology. These estimations could be further improved by SL
constraints coming from other galaxy clusters. |
Axion as a fuzzy-dark-matter candidate: Proofs in different gauges: Axion as a coherently oscillating massive scalar field is known to behave as
a zero-pressure irrotational fluid with characteristic quantum stress on a
small scale. In relativistic perturbation theory, the case was proved in the
axion-comoving gauge up to fully nonlinear and exact order. Our basic
assumption is that the field is oscillating with Compton frequency and the
Compton wavelength is smaller than the horizon scale. Here, we revisit the
relativistic proof to the linear order in the other gauge conditions. We show
that the same equation for density perturbation known in the non-relativistic
treatment can be derived in two additional gauge conditions: the zero-shear
gauge and the uniform-curvature gauge. The uniform-expansion gauge fails to get
the aimed equation, and the quantum stress term is missing in the synchronous
gauge. For comparison, we present the relativistic density perturbation
equations in the zero-pressure fluid in these gauge conditions. Except for the
comoving and the synchronous gauge, the equations strikingly differ from the
axion case. We clarify that the relativistic analysis based on time averaging
is valid for scales larger than the Compton wavelength. Below the Compton
wavelength, the field is not oscillating, and our oscillatory ansatz does not
apply. We suggest an equation valid in all scales in the comoving gauge. For
comparison, we review the non-relativistic quantum hydrodynamics and present
the Schr\"odinger equation to first-order post-Newtonian expansion in the
cosmological context. | Using the large scale quasar clustering to constrain flat quintessential
universes: We search for the most suitable set of cosmological parameters that describes
the observable universe. The search includes the possibility of quintessential
flat universes, i.e., the analysis is restricted to the determination of the
dimensionless matter density and the quintessential parameters, $\Omega_{\rm
M}$ and $w_{\rm Q}$, respectively. Our study is focused on comparing the
position of features at large scales in the density fluctuation field at
different redshifts by analysing the evolution of the quasar two-point
correlation function. We trace the density field fluctuations at large scales
using a large and homogeneous sample of quasars ($\sim$ 38000 objects with 0.3
$\lesssim$ z $\le$ 2.4 and a median $z=1.45$) drawn from the Sloan Digital Sky
Survey Data Release Six. The analysis relies on the assumption that, in the
linear regime, the length scale of a particular feature should remain fixed at
different times of the universe for the proper cosmological model. Our study
does not assume any particular comoving length scale at which a feature should
be found, but intends to perform a comparison for a wide range of scales
instead. This is done by quantifying the amount of overlap among the quasar
correlation functions at different times using a cross-correlation technique.
The most likely cosmological model is $\Omega_{\rm M}=0.21\pm 0.02$ and $w_{\rm
Q}=-0.93\pm0.04$, in agreement with previous studies. These constraints are the
result of a good overall agreement of the correlation function at different
redshifts over scales $\sim 100-300\mpc$. Under the assumption of a flat
cosmological model, our results indicate that we are living in a low density
universe with a quintessential parameter greater than the one corresponding to
a cosmological constant. |
A catalog of Kazarian galaxies: The entire Kazarian galaxies (KG) catalog is presented which combines
extensive new measurements of their optical parameters with a literature and
database search. The measurements were made using images extracted from the
STScI Digitized Sky Survey (DSS) of Jpg(blue), Fpg(red) and Ipg(NIR) band
photographic sky survey plates obtained by the Palomar and UK Schmidt
telescopes. We provide accurate coordinates, morphological type, spectral and
activity classes, blue apparent diameters, axial ratios, position angles, red,
blue and NIR apparent magnitudes, as well as counts of neighboring objects in a
circle of radius 50 kpc from centers of KG. Special attention was paid to the
individual descriptions of the galaxies in the original Kazarian lists, which
clarified many cases of misidentifications of the objects, particularly among
interacting systems. The total number of individual Kazarian objects in the
database is now 706. We also include the redshifts which are now available for
404 galaxies and the 2MASS infrared magnitudes for 598 KG. The database also
includes extensive notes, which summarize information about the membership of
KG in different systems of galaxies, and about revised activity classes and
redshifts. An atlas of several interesting subclasses of KG is also presented. | Detecting the Highest Redshift (z > 8) QSOs in a Wide, Near Infrared
Slitless Spectroscopic Survey: We investigate the prospects of extending observations of high redshift QSOs
to z>8 by means of a very wide-area near-infrared slitless spectroscopic
survey, e.g. the planned survey with the European Space Agency's Euclid
telescope. For any QSOs at z>8.06 the strong Lyman-alpha line will enter the
wavelength range of the Euclid near-infrared spectrometer and imaging
photometer (NISP). We perform a detailed simulation of Euclid NISP slitless
spectroscopy (with the parameters of the wide survey) in an artificial field
containing QSO spectra at all redshifts up to z=12. The simulation spectra are
analysed with an automated redshift finder, and a detection rate estimated as a
function of H magnitude and redshift. Spectroscopic identification of QSOs
would reach deeper limits for the redshift ranges where either H-alpha
(0.67<z<2.05) or Lyman-alpha (z>8.06) is visible. Furthermore, if
photometrically-selected z>8 spectra can be re-examined and re-fitted to
minimize the effects of spectral contamination, the QSO detection rate in the
Lyman-alpha window will be increased by an estimated 60% and will then be
better here than at any other redshift, with an effective limit H=21.5. With an
extrapolated rate of QSO evolution, we predict the Euclid wide (15000 sq. deg.)
spectroscopic survey will identify 20-35 (19-33 with a small correction for
lineless objects) very luminous QSOs at z>8.06. |
Spectral Variations of the Sky: Constraints on Alternate Universes: The fine tuning of parameters required to reproduce our present day Universe
suggests that our Universe may simply be a region within an eternally inflating
super-region. Many other regions beyond our observable Universe would exist
with each such region governed by a different set of physical parameters.
Collision between these regions, if they occur, should leave signatures of
anisotropy in the cosmic microwave background (CMB) but have not been seen. We
analyze the spectral properties of masked, foreground-cleaned maps between 100
and 545 GHz constructed from the Planck dataset. Four distinct $\sim2-4\arcdeg$
regions associated with CMB cold spots show anomalously strong 143 GHz emission
but no correspondingly strong emission at either 100 or 217 GHz. The signal to
noise of this 143 GHz residual emission is at the $\gtrsim$6$\sigma$ level
which reduces to $3.2-5.4\sigma$ after subtraction of remaining
synchrotron/free-free foregrounds. We assess different mechanisms for this
residual emission and conclude that although there is a 30\% probability that
noise fluctuations may cause foregrounds to fall within 3$\sigma$ of the
excess, there is less than a 0.5\% probability that foregrounds can explain all
the excess. A plausible explanation is that the collision of our Universe with
an alternate Universe whose baryon to photon ratio is a factor of $\sim$4500
larger than ours, could produce enhanced Hydrogen Paschen-series emission at
the epoch of recombination. Future spectral mapping and deeper observations at
100 and 217 GHz are needed to mitigate systematics arising from unknown
Galactic foregrounds and to confirm this unusual hypothesis. | Singularity phenomena in viable f(R) gravity: The curvature singularity in viable f(R) gravity models is examined when the
background density is dense. This singularity could be eliminated by adding the
$R^{2}$ term in the Lagrangian. Some of cosmological consequences, in
particular the source for the scalar mode of gravitational waves, are
discussed. |
Primordial black holes as biased tracers: Primordial black holes (PBHs) are theoretical black holes which may be formed
during the radiation dominant era and, basically, caused by the gravitational
collapse of radiational overdensities. It has been well known that in the
context of the structure formation in our Universe such collapsed objects,
e.g., halos/galaxies, could be considered as bias tracers of underlying matter
fluctuations and the halo/galaxy bias has been studied well. Employing a
peak-background split picture which is known to be a useful tool to discuss the
halo bias, we consider the large scale clustering behavior of the PBH and
propose an almost mass-independent constraint to the scenario that dark matters
(DMs) consist of PBHs. We consider the case where the statistics of the
primordial curvature perturbations is almost Gaussian, but with small
local-type non-Gaussianity. If PBHs account for the DM abundance, such a large
scale clustering of PBHs behaves as nothing but the matter isocurvature
perturbation and constrained strictly by the observations of cosmic microwave
backgrounds (CMB). From this constraint, we show that, in the case a certain
single field causes both CMB temperature perturbations and PBH formations, the
PBH-DM scenario is excluded even with quite small local-type non-Gaussianity,
$|f_\mathrm{NL}|\sim\mathcal{O}(0.01)$, while we give the constraints to
parameters in the case where the source field of PBHs is different from CMB
perturbations. | \textsc{CompaSO}: A new halo finder for competitive assignment to
spherical overdensities: We describe a new method (\textsc{CompaSO}) for identifying groups of
particles in cosmological $N$-body simulations. \textsc{CompaSO} builds upon
existing spherical overdensity (SO) algorithms by taking into consideration the
tidal radius around a smaller halo before competitively assigning halo
membership to the particles. In this way, the \textsc{CompaSO} finder allows
for more effective deblending of haloes in close proximity as well as the
formation of new haloes on the outskirts of larger ones. This halo-finding
algorithm is used in the \textsc{AbacusSummit} suite of $N$-body simulations,
designed to meet the cosmological simulation requirements of the Dark Energy
Spectroscopic Instrument (DESI) survey. \textsc{CompaSO} is developed as a
highly efficient on-the-fly group finder, which is crucial for enabling good
load-balancing between the GPU and CPU and the creation of high-resolution
merger trees. In this paper, we describe the halo-finding procedure and its
particular implementation in \Abacus{Abacus}, accompanying it with a
qualitative analysis of the finder. {We test the robustness of the
\textsc{CompaSO} catalogues before and after applying the cleaning method
described in an accompanying paper and demonstrate its effectiveness by
comparing it with other validation techniques.} We then visualise the haloes
and their density profiles, finding that they are well fit by the NFW
formalism. Finally, we compare other properties such as radius-mass
relationships and two-point correlation functions with that of another widely
used halo finder, \textsc{ROCKSTAR}. |
Matter bispectrum in cubic Galileon cosmologies: In this paper we obtain the bispectrum of dark matter density perturbations
in the frame of covariant cubic Galileon theories. This result is obtained by
means of a semi-analytic approach to second-order perturbations in Galileon
cosmologies, assuming Gaussian initial conditions. In particular, we show that,
even in the presence of large deviations of the linear growth-rate w.r.t. the
{\Lambda}CDM one, at the bispectrum level such deviations are reduced to a few
percent. | Calibrated Ultra Fast Image Simulations for the Dark Energy Survey: Weak lensing by large-scale structure is a powerful technique to probe the
dark components of the universe. To understand the measurement process of weak
lensing and the associated systematic effects, image simulations are becoming
increasingly important. For this purpose we present a first implementation of
the $\textit{Monte Carlo Control Loops}$ ($\textit{MCCL}$; Refregier & Amara
2014), a coherent framework for studying systematic effects in weak lensing. It
allows us to model and calibrate the shear measurement process using image
simulations from the Ultra Fast Image Generator (UFig; Berge et al. 2013). We
apply this framework to a subset of the data taken during the Science
Verification period (SV) of the Dark Energy Survey (DES). We calibrate the UFig
simulations to be statistically consistent with DES images. We then perform
tolerance analyses by perturbing the simulation parameters and study their
impact on the shear measurement at the one-point level. This allows us to
determine the relative importance of different input parameters to the
simulations. For spatially constant systematic errors and six simulation
parameters, the calibration of the simulation reaches the weak lensing
precision needed for the DES SV survey area. Furthermore, we find a sensitivity
of the shear measurement to the intrinsic ellipticity distribution, and an
interplay between the magnitude-size and the pixel value diagnostics in
constraining the noise model. This work is the first application of the
$\textit{MCCL}$ framework to data and shows how it can be used to methodically
study the impact of systematics on the cosmic shear measurement. |
MeerKAT view of the diffuse radio sources in Abell 3667 and their
interactions with the thermal plasma: During their lifetime, galaxy clusters grow through the accretion of matter
from the filaments of the large scale structure and from mergers with other
clusters. These mergers release a large amount of energy into the intracluster
medium (ICM) through merger shocks and turbulence. These phenomena are
associated with the formation of radio sources known as radio relics and radio
halos, respectively. Radio relics and halos are unique proxies to study the
complex properties of these dynamically active regions of clusters and in
general the micro physics of the ICM. Abell 3667 is a spectacular examples of a
merging system hosting a large pair of radio relics. Due to its proximity
(z=0.0553) and large mass, the system enables the study of these sources to a
uniquely high level of detail. We observed Abell 3667 with MeerKAT as part of
the MeerKAT Galaxy Cluster Legacy Survey. We used these data to study the large
scale emission of the cluster, including its polarisation and spectral
properties. We present the most detailed view of the radio relic system in
Abell 3667 to date, with a resolution reaching 3 kpc. The relics are filled
with a network of filaments with different spectral and polarisation properties
that are likely associated with multiple regions of particle acceleration and
local enhancements of the magnetic field. Conversely, the magnetic field in the
space between filaments has strengths close to that expected in unperturbed
regions at the same cluster-centric distance. Comparisons with MHD simulations
supports the idea of filaments as multiple acceleration sites. Our observations
also confirm the presence of an elongated radio halo, developed in the wake of
the bullet-like sub-cluster that merged from the South-East. Finally, we
associate the process of magnetic draping to a thin polarised radio source
surrounding the remnant of the bullet's cool core. | An archival search for type Ia supernova siblings: By searching the Open Supernova Catalog, an extra-galactic transient host
galaxy database, and literature analyses, I present the largest sample of type
Ia supernova (SN Ia) siblings to date. The sample comprises 158 galaxies,
consisting of 327 confirmed SNe Ia - over 10 times larger than existing sibling
SN Ia samples. SN siblings share host galaxies, and thus share global
environmental properties and associated systematic uncertainties. This makes
them valuable for both cosmological and astrophysical analyses; for example,
sibling SNe Ia allow for comparison of environmental properties within the same
galaxy, progenitor comparisons, rates analyses, and multiple calibrations of
the Hubble-Lema\^{\i}tre constant. This large sample will provide a variety of
new avenues of research, and be of great interest to the wider SN Ia community.
To give an example use of this sample, I define a cosmology sub-sample of 44
siblings; and use it to compare light-curve properties between sibling pairs. I
find no evidence for correlations in stretch ($x_1$) and colour ($c$) between
pairs of siblings. Moreover, by comparing to a comparable set of random pairs
of SNe Ia through boot-strapping, I find that siblings are no more similar in
$x_1$ and $c$ than any random pair of SNe Ia. Given that siblings share the
same hosts, differences in $x_1$ and $c$ between siblings cannot be due to
global galaxy properties. This raises important questions regarding
environmental systematics for SN Ia standardisation in cosmology, and motivates
future analyses of sibling SNe Ia. |
An XMM-Newton view of the `bare' nucleus of Fairall 9: We present the spectral results from a 130 ks observation, obtained from the
X-ray Multi-Mirror Mission-Newton (XMM-Newton) observatory, of the type I
Seyfert galaxy Fairall 9. An X-ray hardness-ratio analysis of the light-curves,
reveals a `softer-when-brighter' behaviour which is typical for radio-quiet
type I Seyfert galaxies. Moreover, we analyse the high spectral-resolution data
of the reflection grating spectrometer and we did not find any significant
evidence supporting the presence of warm-absorber in the low X-ray energy part
of the source's spectrum. This means that the central nucleus of Fairall 9 is
`clean' and thus its X-ray spectral properties probe directly the physical
conditions of the central engine. The overall X-ray spectrum in the 0.5-10 keV
energy-range, derived from the EPIC data, can be modelled by a relativistically
blurred disc-reflection model. This spectral model yields for Fairall 9 an
intermediate black-hole best-fit spin parameter of
$\alpha=0.39^{+0.48}_{-0.30}$. | Investigation of X-ray cavities in the cooling flow system Abell 1991: We present results based on the systematic analysis of \textit{Chandra}
archive data on the X-ray bright Abell Richness class-I type cluster Abell 1991
with an objective to investigate properties of the X-ray cavities hosted by
this system. The unsharp masked image as well as 2-d $\beta$ model subtracted
residual image of Abell 1991 reveals a pair of X-ray cavities and a region of
excess emission in the central $\sim$12 kpc region. Both the cavities are of
ellipsoidal shape and exhibit an order of magnitude deficiency in the X-ray
surface brightness compared to that in the undisturbed regions. Spectral
analysis of X-ray photons extracted from the cavities lead to the temperature
values equal to $1.77_{-0.12}^{+0.19}$ keV for N-cavity and
$1.53_{-0.06}^{+0.05}$ keV for S-cavity, while that for the excess X-ray
emission region is found to be equal to $2.06_{-0.07}^{+0.12}$ keV. Radial
temperature profile derived for Abell 1991 reveals a positive temperature
gradient, reaching to a maximum of 2.63 keV at $\sim$ 76 kpc and then declines
in outward direction. 0.5$-$2.0 keV soft band image of the central 15\arcsec
region of Abell 1991 reveals relatively cooler three different knot like
features that are about 10\arcsec off the X-ray peak of the cluster. Total
power of the cavities is found to be equal to $\sim 8.64\times 10^{43}$ \lum,
while the X-ray luminosity within the cooling radius is found to be 6.04
$\times 10^{43}$ \lum, comparison of which imply that the mechanical energy
released by the central AGN outburst is sufficient to balance the radiative
loss. |
Exact general relativistic lensing versus thin lens approximation: the
crucial role of the void: We have used an exact general relativistic model structure within a FRW
cosmological background based on a LTB metric to study the gravitational
lensing of a cosmological structure. The integration of the geodesic equations
turned out to be a delicate task. We realized that the use of the rank 8(7) and
10(11) Runge-Kutta numerical method leads to a numerical effect and is
therefore unreliable. The so-called semi-implicit Rosenbrock method, however,
turned out to be a viable integration method for our problem. The deviation
angle calculated by the integration of the geodesic equations for different
density profiles of the model structure was then compared to those of the
corresponding thin lens approximation. Using the familiar NFW density profile,
it is shown that independent of the truncation details the thin lens
approximation differ substantially from the exact relativistic calculation. The
difference in the deflection angle for different impact parameters may be up to
about 30 percent. However, using the modified NFW density profile with a void
before going over to the FRW background, as required by an exact general
relativistic model, the thin lens approximation coincides almost exactly with
the general relativistic calculation. | Extracting the 21-cm Power Spectrum and the reionization parameters from
mock datasets using Artificial Neural Networks: Detection of the \hi~ 21-cm power spectrum is one of the key science drivers
of several ongoing and upcoming low-frequency radio interferometers. However,
the major challenge in such observations come from bright foregrounds, whose
accurate removal or avoidance is key to the success of these experiments. In
this work, we demonstrate the use of artificial neural networks (ANNs) to
extract the \hi~ 21-cm power spectrum from synthetic datasets and extract the
reionization parameters from the \hi~ 21-cm power spectrum. For the first time,
using a suite of simulations, we present an ANN based framework capable of
extracting the \hi~ signal power spectrum directly from the total observed sky
power spectrum (which contains the 21-cm signal, along with the foregrounds and
effects of the instrument). To achieve this, we have used a combination of two
separate neural networks sequentially. As the first step, \texttt{ANN1}
predicts the 21-cm power spectrum directly from foreground corrupted synthetic
datasets. In the second step, \texttt{ANN2} predicts the reionization
parameters from the predicted \hi~ power spectra from \texttt{ANN1}. Our
ANN-based framework is trained at a redshift of $9.01$, and for \kk-modes in
the range, $\rm{0.17<\kk<0.37~Mpc^{-1}}$. We have tested the network's
performance with mock datasets that include foregrounds and are corrupted with
thermal noise, corresponding to $1080$ hrs of observations of the \textsc{ska-1
low} and \textsc{hera}. Using our ANN framework, we are able to recover the
\hi~ power spectra with an accuracy of $\approx95-99\%$ for the different test
sets. For the predicted astrophysical parameters, we have achieved an accuracy
of $\approx~81-90\%$ and $\approx~50-60\%$ for the test sets corrupted with
thermal noise corresponding to the \textsc{ska-1 low} and \textsc{hera},
respectively. |
ALMA and the First Galaxies: ALMA will become fully operational in a few years and open a new window on
primordial galaxies. The mm and submm domain is privileged, since the peak of
dust emission between 60 and 100 microns is redshifted there for z= 5-10, and
the continuum benefits from a negative K-correction. At least 100 times more
sources than with present instruments could be discovered, so that more normal
galaxies, with lower luminosities than huge starbursts and quasars will be
surveyed. The high spatial resolution will suppress the confusion, which
plagues today single dish bolometer surveys. Several CO lines detected in
broad-band receivers will determine the redshift of objects too obscured to be
seen in the optical. With the present instrumentation, only the most massive
and gas rich objects have been detected in CO at high z, most of them being
ultra-luminous starbursts with an extremely high star formation efficiency.
However, selection biases are omni-present in this domain, and ALMA will
statistically clarify the evolution of star formation efficiency, being fully
complementary to JWST and ELTs. | Ram pressure stripping of tilted galaxies: Ram pressure stripping of galaxies in clusters can yield gas deficient disks.
Previous numerical simulations based on various approaches suggested that,
except for near edge-on disk orientations, the amount of stripping depends very
little on the inclination angle. Following our previous study of face-on
stripping, we extend the set of parameters with the disk tilt angle and explore
in detail the effects of the ram pressure on the interstellar content (ISM) of
tilted galaxies that orbit in various environments of clusters, with compact or
extended distributions of the intra-cluster medium (ICM). We further study how
results of numerical simulations could be estimated analytically. A grid of
numerical simulations with varying parameters is produced using the tree/SPH
code GADGET with a modified method for calculating the ISM-ICM interaction.
These SPH calculations extend the set of existing results obtained from
different codes using various numerical techniques. The simulations confirm the
general trend of less stripping at orientations close to edge-on. The
dependence on the disk tilt angle is more pronounced for compact ICM
distributions, however it almost vanishes for strong ram pressure pulses.
Although various hydrodynamical effects are present in the ISM-ICM interaction,
the main quantitative stripping results appear to be roughly consistent with a
simple scenario of momentum transfer from the encountered ICM. This behavior
can also be found in previous simulations. To reproduce the numerical results
we propose a fitting formula depending on the disk tilt angle and on the column
density of the encountered ICM. Such a dependence is superior to that on the
peak ram pressure used in previous simple estimates. |
Constraints on parameters of models with extra dimension from primordial
nucleosynthesis: 5D models with one 3D brane and one infinite extra dimension are studied.
Matter is confined to the brane, gravity extends to the bulk. Models with
positive and negative tension of the brane are studied. Cosmological solutions
on the brane are obtained by solving the generalized Friedmann equation. As the
input in cosmological solutions we use the present-time observational
cosmological parameters. We find constraints on dimensionless combinations of
scales of 5D models which follow from the requirement that the models reproduce
the data on production of ${}^4 He$ in primordial nucleosynthesis. | Probing the interaction between dark energy and dark matter with future
fast radio burst observations: Interacting dark energy (IDE) scenario assumes that there exists a direct
interaction between dark energy and cold dark matter, but this interaction is
hard to be tightly constrained by the current data. Fast radio bursts (FRBs)
will be seen in large numbers by future radio telescopes, and thus they have
potential to become a promising low-redshift cosmological probe. In this work,
we investigate the capability of future FRBs of constraining the dimensionless
coupling parameter $\beta$ in four phenomenological IDE models. If we fix the
FRB properties, about $10^5$ FRB data can give constraints on $\beta$ tighter
than the current cosmic microwave background data in the IDE models with the
interaction proportional to the energy density of dark energy. In all the IDE
models, about $10^6$ FRB data can achieve the absolute errors of $\beta$ to
less than $0.10$, providing a way to precisely measure $\beta$ by only one
cosmological probe. Jointly constraining the FRB properties and cosmological
parameters would increase the constraint errors of $\beta$ by a factor of about
0.5-2. |
Dust-obscured star formation and the contribution of galaxies escaping
UV/optical color selections at z~2: A substantial fraction of the stellar mass growth across cosmic time occurred
within dust-enshrouded environments. Yet, the exact amount of star-forming
activity that took place in high-redshift dusty galaxies currently missed by
optical surveys has been barely explored. Using the Spitzer observations of
COSMOS we determined the fraction of luminous star-forming galaxies at 1.5<z<3
escaping the traditional color selection techniques because of dust extinction,
as well as their contribution to the cosmic star formation density at high
redshift. We find that the BzK criterion offers an almost complete (~90%)
identification of the 24mic sources at 1.4<z<2.5, while the BM/BX criterion
miss 50% of the MIPS population. Similarly the criterion based on the presence
of a stellar bump in massive sources (so-called "IRAC peakers") miss up to 40%
of the IR luminosity density and only 25% of the IR energy density at z~2 is
produced by Optically-Faint IR-bright galaxies selected based on their extreme
mid-IR to optical flux ratios. We conclude that color selections of distant
star-forming galaxies must be used with lots of care given the substantial bias
they can suffer. In particular, the effect of dust extinction strongly impacts
the completeness of identifications at the bright end of the bolometric
luminosity function, which implies large and uncertain extrapolations to
account for the contribution of dusty galaxies missed by these selections. In
the context of forthcoming facilities that will operate at long wavelengths
(e.g., $JWST$, ALMA, SAFARI, EVLA, SKA), this emphasizes the importance of
minimizing the extinction biases when probing the activity of star formation in
the early Universe. | Addressing Decadal Survey Science through Community Access to Highly
Multiplexed Spectroscopy with BigBOSS on the KPNO Mayall Telescope: This document summarizes the results of a community-based discussion of the
potential science impact of the Mayall+BigBOSS highly multiplexed multi-object
spectroscopic capability. The KPNO Mayall 4m telescope equipped with the DOE-
and internationally-funded BigBOSS spectrograph offers one of the most
cost-efficient ways of accomplishing many of the pressing scientific goals
identified for this decade by the "New Worlds, New Horizons" report. The
BigBOSS Key Project will place unprecedented constraints on cosmological
parameters related to the expansion history of the universe. With the addition
of an open (publicly funded) community access component, the scientific impact
of BigBOSS can be extended to many important astrophysical questions related to
the origin and evolution of galaxies, stars, and the IGM. Massive spectroscopy
is the critical missing ingredient in numerous ongoing and planned ground- and
space-based surveys, and BigBOSS is unique in its ability to provide this to
the US community. BigBOSS data from community-led projects will play a vital
role in the education and training of students and in maintaining US leadership
in these fields of astrophysics. We urge the NSF-AST division to support
community science with the BigBOSS multi-object spectrograph through the period
of the BigBOSS survey in order to ensure public access to the extraordinary
spectroscopic capability. |
Cosmological Implications of Light Sterile Neutrinos produced after the
QCD Phase Transition: We study the production of sterile neutrinos in the early universe from $\pi
\rightarrow l \nu_s$ shortly after the QCD phase transition in the absence of a
lepton asymmetry while including finite temperature corrections to the $\pi$
mass and decay constant $f_{\pi}$. Sterile neutrinos with masses $\lesssim 1
MeV$ produced via this mechanism freeze-out at $T_f \simeq 10 MeV$ with a
distribution function that is highly non-thermal and features a sharp
enhancement at low momentum thereby making this species \emph{cold} even for
very light masses. Dark matter abundance constraints from the CMB and phase
space density constraints from the most dark matter dominated dwarf spheroidal
galaxies provide upper and lower bounds respectively on combinations of mass
and mixing angles. For $\pi \rightarrow \mu \nu_s$, the bounds lead to a narrow
region of compatibility with the latest results from the $3.55 \mathrm{KeV}$
line. The non-thermal distribution function leads to free-streaming lengths
(today) in the range of $\sim \mbox{few kpc}$ consistent with the observation
of cores in dwarf galaxies. For sterile neutrinos with mass $\lesssim 1 eV$
that are produced by this reaction, the most recent accelerator and
astrophysical bounds on $U_{ls}$ combined with the non-thermal distribution
function suggests a substantial contribution from these sterile neutrinos to
$N_{eff}$. | Interacting Quintessence and Growth of Structure: In standard cosmologies, dark energy interacts only gravitationally with dark
matter. An extension to this picture is interacting quintessence (IQ) model,
where scalar field coupled directly to cold dark matter. The percentage
deviation is studied in IQ model wrt $\Lambda$CDM for varied values of
interacting parameter W. We investigated the effect of interaction on matter,
Kaiser and galaxy power spectrums. Deviation in power spectrum increases with
interaction on both large and small scales. On small scale, variation is
comparatively smaller than on large scale. On large scale, it is due to dark
energy perturbation while it is background evolution that causes a difference
on small scale. These variations decrease with increase in redshift. Herein
thawing class of model with linear potential is studied. |
A parametrisation of modified gravity on nonlinear cosmological scales: Viable modifications of gravity on cosmological scales predominantly rely on
screening mechanisms to recover Einstein's Theory of General Relativity in the
Solar System, where it has been well tested. A parametrisation of the effects
of such modifications in the spherical collapse model is presented here for the
use of modelling the modified nonlinear cosmological structure. The formalism
allows an embedding of the different screening mechanisms operating in
scalar-tensor theories through large values of the gravitational potential or
its first or second derivatives as well as of linear suppression effects or
more general transitions between modified and Einstein gravity limits. Each
screening or suppression mechanism is parametrised by a time, mass, and
environment dependent screening scale, an effective modified gravitational
coupling in the fully unscreened limit that can be matched to linear theory,
the exponent of a power-law radial profile of the screened coupling, determined
by derivatives, symmetries, and potentials in the scalar field equation, and an
interpolation rate between the screened and unscreened limits. Along with
generalised perturbative methods, the parametrisation may be used to formulate
a nonlinear extension to the linear parametrised post-Friedmannian framework to
enable generalised tests of gravity with the wealth of observations from the
nonlinear cosmological regime. | Dust extinction from Balmer decrements of star-forming galaxies at
0.75<z<1.5 with HST/WFC3 spectroscopy from the WISP survey: Spectroscopic observations of Halpha and Hbeta emission lines of 128
star-forming galaxies in the redshift range 0.75<z<1.5 are presented. These
data were taken with slitless spectroscopy using the G102 and G141 grisms of
the Wide-Field-Camera 3 (WFC3) on board the Hubble Space Telescope as part of
the WFC3 Infrared Spectroscopic Parallel (WISP) survey. Interstellar dust
extinction is measured from stacked spectra that cover the Balmer decrement
(Halpha/Hbeta). We present dust extinction as a function of Halpha luminosity
(down to 3 x 10^{41} erg/s), galaxy stellar mass (reaching 4 x 10^{8} Msun),
and rest-frame Halpha equivalent width. The faintest galaxies are two times
fainter in Halpha luminosity than galaxies previously studied at z~1.5. An
evolution is observed where galaxies of the same Halpha luminosity have lower
extinction at higher redshifts, whereas no evolution is found within our error
bars with stellar mass. The lower Halpha luminosity galaxies in our sample are
found to be consistent with no dust extinction. We find an anti-correlation of
the [OIII]5007/Halpha flux ratio as a function of luminosity where galaxies
with L_{Halpha}<5 x 10^{41} erg/s are brighter in [OIII]5007 than Halpha. This
trend is evident even after extinction correction, suggesting that the
increased [OIII]5007/Halpha ratio in low luminosity galaxies is likely due to
lower metallicity and/or higher ionization parameters. |
Constancy of the Cluster Gas Mass Fraction in the R_h=ct Universe: The ratio of baryonic to dark matter densities is assumed to have remained
constant throughout the formation of structure. With this, simulations show
that the fraction f_gas(z) of baryonic mass to total mass in galaxy clusters
should be nearly constant with redshift z. However, the measurement of these
quantities depends on the angular distance to the source, which evolves with z
according to the assumed background cosmology. An accurate determination of
f_gas(z) for a large sample of hot (kT_e > 5 keV), dynamically relaxed clusters
could therefore be used as a probe of the cosmological expansion up to z < 2.
The fraction f_gas(z) would remain constant only when the "correct" cosmology
is used to fit the data. In this paper, we compare the predicted gas mass
fractions for both LCDM and the R_h=ct Universe and test them against the 3
largest cluster samples. We show that R_h=ct is consistent with a constant
f_gas in the redshift range z < 2, as was previously shown for the reference
LCDM model (with parameter values H_0=70 km/s/Mpc, Omega_m=0.3 and w_de=-1).
Unlike LCDM, however, the R_h=ct Universe has no free parameters to optimize in
fitting the data. Model selection tools, such as the Akaike Information
Criterion (AIC) and the Bayes Information Criterion (BIC), therefore tend to
favour R_h=ct over LCDM. For example, the BIC favours R_h=ct with a likelihood
of ~95% versus ~5% for LCDM. | The cluster population of the irregular galaxy NGC 4449 as seen by the
Hubble Advanced Camera for Surveys: We present a study of the star cluster population in the starburst irregular
galaxy NGC 4449 based on B, V, I, and Ha images taken with the Advanced Camera
for Surveys on the Hubble Space Telescope. We derive the cluster properties
such as size, ellipticity, and total magnitudes. Cluster ages and masses are
derived fitting the observed spectral energy distributions with different
population synthesis models. Our analysis is strongly affected by the
age-metallicity degeneracy; however, if we assume a metallicity of ~1/4 solar,
as derived from spectroscopy of HII regions, we find that the clusters have
ages distributed quite continuously over a Hubble time, and they have masses
from ~10^3 M_sun up to ~2 x 10^6 M_sun, assuming a Salpeters' IMF down to 0.1
M_sun. Young clusters are preferentially located in regions of young star
formation, while old clusters are distributed over the whole NGC 4449 field of
view, like the old stars (although we notice that some old clusters follow
linear structures, possibly a reflection of past satellite accretion). The high
SF activity in NGC 4449 is confirmed by its specific frequency of young massive
clusters, higher than the average value found in nearby spirals and in the LMC
(but lower than in other starburst dwarfs such as NGC 1705 and NGC 1569), and
by the flat slope of the cluster luminosity function (dN(L_V)\propto L_V^{-1.5}
dL for clusters younger than 1 Gyr). We use the upper envelope of the cluster
log(mass) versus log(age) distribution to quantify cluster disruption, and do
not find evidence for the high (90%) long-term infant mortality found by some
studies. For the red clusters, we find correlations between size, ellipticity,
luminosity and mass: brighter and more massive clusters tend to be more
compact, and brighter clusters tend to be also more elliptical. |
Constraining neutrino mass with weak lensing Minkowski Functionals: The presence of massive neutrinos affects structure formation, leaving
imprints on large-scale structure observables such as the weak lensing field.
The common lensing analyses with two-point statistics are insensitive to the
large amount of non-Gaussian information in the density field. We investigate
non-Gaussian tools, in particular the Minkowski Functionals
(MFs)---morphological descriptors including area, perimeter, and genus---in an
attempt to recover the higher-order information. We use convergence maps from
the Cosmological Massive Neutrino Simulations (\texttt{MassiveNus}) and assume
galaxy noise, density, and redshift distribution for an LSST-like survey. We
show that MFs are sensitive to the neutrino mass sum, and the sensitivity is
redshift dependent and is non-Gaussian. We find that redshift tomography
significantly improves the constraints on neutrino mass for MFs, compared to
the improvements for the power spectrum. We attribute this to the stronger
redshift dependence of neutrino effects on small scales. We then build an
emulator to model the power spectrum and MFs, and study the constraints on
$[M_{\nu}$, $\Omega_{m}$, $A_{s}]$ from the power spectrum, MFs, and their
combination. We show that MFs significantly outperform the power spectrum in
constraining neutrino mass, by more than a factor of four. However, a thorough
study of the impact from systematics such as baryon physics and galaxy shape
and redshift biases will be important to realize the full potential of MFs. | The Imperatives of Cosmic Biology: The transformation of organic molecules into the simplest self-replicating
living system,a microorganism, is accomplished from a unique event or rare
events that occurred early in the Universe. The subsequent dispersal on cosmic
scales and evolution of life is guaranteed, being determined by well-understood
processes of physics and biology. Entire galaxies and clusters of galaxies can
be considered as connected biospheres, with lateral gene transfers, as
initially theorized by Joseph (2000), providing for genetic mixing and
Darwinian evolution on a cosmic scale. Big bang cosmology modified by modern
fluid mechanics suggests the beginning and wide intergalactic dispersal of life
occurred immediately after the end of the plasma epoch when the gas of
protogalaxies in clusters fragmented into clumps of planets. Stars are born
from binary mergers of such planets within such clumps. When stars devour their
surrounding planets to excess they explode, distributing necessary fertilizing
chemicals created only in stars with panspermial templates created only in
adjacent planets, moons and comets, to be gravitationally collected by the
planets and further converted to living organisms. Recent infrared images of
nearby star forming regions suggest that life formation on planets like Earth
is possible, but not inevitable. |
Paschen-alpha Emission in the Gravitationally Lensed Galaxy SMM
J163554.2+661225: We report the detection of the Paschen-alpha emission line in the z=2.515
galaxy SMM J163554.2+661225 using Spitzer spectroscopy. SMM J163554.2+661225 is
a sub-millimeter-selected infrared (IR)-luminous galaxy maintaining a high
star-formation rate (SFR), with no evidence of an AGN from optical or infrared
spectroscopy, nor X-ray emission. This galaxy is lensed gravitationally by the
cluster Abell 2218, making it accessible to Spitzer spectroscopy. Correcting
for nebular extinction derived from the H-alpha and Pa-alpha lines, the
dust-corrected luminosity is L(Pa-alpha) = (2.57+/-0.43) x 10^43 erg s^-1,
which corresponds to an ionization rate, Q = (1.6+/-0.3) x 10^55 photons s^-1.
The instantaneous SFR is 171+/-28 solar masses per year, assuming a
Salpeter-like initial mass function. The total IR luminosity derived using 70,
450, and 850 micron data is L(IR) = (5-10) x 10^11 solar luminosities,
corrected for gravitational lensing. This corresponds to a SFR=90-180 solar
masses per year, where the upper range is consistent with that derived from the
Paschen-alpha luminosity. While the L(8 micron) / L(Pa-alpha) ratio is
consistent with the extrapolated relation observed in local galaxies and
star-forming regions, the rest-frame 24 micron luminosity is significantly
lower with respect to local galaxies of comparable Paschen-alpha luminosity.
Thus, SMM J163554.2+661225 arguably lacks a warmer dust component (T ~ 70 K),
which is associated with deeply embedded star formation, and which contrasts
with local galaxies with comparable SFRs. Rather, the starburst is consistent
with star-forming local galaxies with intrinsic luminosities, L(IR) ~ 10^10
solar luminosities, but "scaled-up" by a factor of 10-100. | Behavior of $F(R)$ gravity around a crossing of the phantom divide: We study a model of $F(R)$ gravity in which a crossing of the phantom divide
can be realized. In particular, we demonstrate the behavior of $F(R)$ gravity
around a crossing of the phantom divide by taking into account the presence of
cold dark matter. |
Starburst and old stellar populations in two z=3.8 radio galaxies 4C
41.17 and TN J2007-1316: The new evolutionary code Pegase.3 is used for the spectral synthesis of
continuous optical-Spitzer-Herschel-submm spectral energy distributions (SEDs)
of two z=3.8 radio galaxies 4C 41.17 and TN J2007-1316. Both galaxies are
selected from the Herschel Radio Galaxy Evolution Project for their faint AGN
contribution and because they show evidence of a large stellar contribution to
their bolometric luminosity. Pegase.3 coherently models the reprocessing of the
stellar luminosity to dust emission, allowing to build UV to IR-submm libraries
by types. These templates allow to predict SEDs at redshifts z in the
observer's frame by using z=0 templates corrected for cosmology and evolution.
Our best fits are a sum of two distinct evolving stellar populations: i) a very
massive starburst observed ~30 Myrs after formation from optical and far-IR
peaks ii) a significantly older (~1Gyr old) massive early-type population
revealed from mid-IR Spitzer data. The AGN emission fits a roughly thermal
model. These results confirm that many of the stellar populations in high-z
radio galaxies were already formed by massive (a few thousands of billion solar
masses) starbursts at z=4, confirming the previous K-z diagram interpretation.
Gas-rich mergers and/or jet-cloud interactions are favored for triggering the
intense star formation, possibly in relation with massive super black holes of
these radio galaxies. These multiple stellar populations may be a generic
feature of the luminous infrared radio galaxy population as a whole and
strongly constrain mass accumulation and galaxy formation models. | Correlation between Line Width and Line Flux of Double-Peaked Broad
Halpha of 3C390.3: In this manuscript, we carefully check the correlation between the line width
and the line flux of the double-peaked broad H$\alpha$ of the well-known mapped
AGN 3C390.3, in order to show some further distinctions between double-peaked
emitters and normal broad line AGN. Based on the Virialization assumption and
the empirical relation about $R_{BLR}$, one strong negative correlation of line
parameters of the double-peaked broad lines should be expected for 3C390.3,
such as the negative correlation confirmed for the mapped broad line object
NGC5548. But, based on the public spectra around 1995 from the AGNWATCH project
for 3C390.3, one reliable positive correlation is found. In the context of the
proposed theoretical accretion disk model for double-peaked emitters, the
unexpected positive correlation can be naturally explained, due to different
time delays for inner parts and outer parts of disk-like BLR of 3C390.3.
Moreover, the Virialization assumption is checked and found to be still
available for 3C390.3. However, time-varying size of the BLR of 3C390.3 can not
be expected by the empirical relation $R_{BLR}\propto L^{\sim0.5}$, the
continuum emission strengthening leads to the size of BLR decreasing (not
increasing) in different moments for 3C390.3. Then, we compared our results of
3C390.3 with the previous results reported in the literature for the other
double-peaked emitters, and found that before to clearly correct effects from
disk physical parameters varying for long-term observed line spectra and
effects from the probable 'external' ionizing source with so far unclear
structures, it is hard to give one conclusion that the positive correlation can
be found for all double-peaked emitters. However, once one positive correlation
of broad line parameters was found, the accretion disk origination of the broad
line should be firstly considered. |
Statistical anisotropy as a consequence of inflation: Cosmological inflation remains to be a unique mechanism of generation of
plausible initial conditions in the early universe. In particular, it generates
the primordial quasiclassical perturbations with power spectrum determined by
the fundamental principles of quantum field theory. In this work, we pay
attention to the fact that the quasiclassical perturbations permanently
generated at early stages of inflation break homogeneity and isotropy of the
cosmological background. The evolution of the small-scale quantum vacuum modes
on this inhomogeneous background results in statistical anisotropy of the
primordial power spectrum, which can manifest itself in the observable
large-scale structure and cosmic microwave background. The effect is predicted
to have almost scale-invariant form dominated by a quadrupole and may serve as
a non-trivial test of the inflationary scenario. Theoretical expectation of the
magnitude of this statistical anisotropy depends on the assumptions about the
physics in the trans-Planckian region of wavenumbers. | Discovery of Multi-Phase Cold Accretion in a Massive Galaxy at z=0.7: We present detailed photo+collisional ionization models and kinematic models
of the multi-phase absorbing gas, detected within the HST/COS, HST/STIS, and
Keck/HIRES spectra of the background quasar TON 153, at 104 kpc along the
projected minor axis of a star-forming spiral galaxy (z=0.6610). Complementary
g'r'i'Ks photometry and stellar population models indicate that the host galaxy
is dominated by a 4 Gyr stellar population with slightly greater than solar
metallicity and has an estimated log(M*)=11 and a log(Mvir)=13. Photoionization
models of the low ionization absorption, (MgI, SiII, MgII and CIII) which trace
the bulk of the hydrogen, constrain the multi-component gas to be cold
(logT=3.8-5.2) and metal poor (-1.68<[X/H]<-1.64). A lagging halo model
reproduces the low ionization absorption kinematics, suggesting gas coupled to
the disk angular momentum, consistent with cold accretion mode material in
simulations. The CIV and OVI absorption is best modeled in a separate
collisionally ionized metal-poor (-2.50<[X/H]<-1.93) warm phase with logT=5.3.
Although their kinematics are consistent with a wind model, given the 2-2.5dex
difference between the galaxy stellar metallicity and the absorption
metallicity indicates the gas cannot arise from galactic winds. We discuss and
conclude that although the quasar sight-line passes along the galaxy minor axis
at projected distance of 0.3 virial radii, well inside its virial shock radius,
the combination of the relative kinematics, temperatures, and relative
metallicities indicated that the multi-phase absorbing gas arises from cold
accretion around this massive galaxy. Our results appear to contradict recent
interpretations that absorption probing the projected minor axis of a galaxy is
sampling winds. |
The evolution of neutral gas in damped Lyman $α$ systems from the
XQ-100 survey: We present a sample of 38 intervening Damped Lyman $\alpha$ (DLA) systems
identified towards 100 $z>3.5$ quasars, observed during the XQ-100 survey. The
XQ-100 DLA sample is combined with major DLA surveys in the literature. The
final combined sample consists of 742 DLAs over a redshift range approximately
$1.6 < z_{\rm abs} < 5.0$. We develop a novel technique for computing
$\Omega_{\rm HI}^{\rm DLA}$ as a continuous function of redshift, and we
thoroughly assess and quantify the sources of error therein, including fitting
errors and incomplete sampling of the high column density end of the column
density distribution function. There is a statistically significant redshift
evolution in $\Omega_{\rm HI}^{\rm DLA}$ ($\geq 3 \sigma$) from $z \sim 2$ to
$z \sim$ 5. In order to make a complete assessment of the redshift evolution of
$\Omega_{\rm HI}$, we combine our high redshift DLA sample with absorption
surveys at intermediate redshift and 21cm emission line surveys of the local
universe. Although $\Omega_{\rm HI}^{\rm DLA}$, and hence its redshift
evolution, remains uncertain in the intermediate redshift regime ($0.1 < z_{\rm
abs} < 1.6$), we find that the combination of high redshift data with 21cm
surveys of the local universe all yield a statistically significant evolution
in $\Omega_{\rm HI}$ from $z \sim 0$ to $z \sim 5$ ($\geq 3 \sigma$). Despite
its statistical significance, the magnitude of the evolution is small: a linear
regression fit between $\Omega_{\rm HI}$ and $z$ yields a typical slope of
$\sim$0.17$\times 10^{-3}$, corresponding to a factor of $\sim$ 4 decrease in
$\Omega_{\rm HI}$ between $z=5$ and $z=0$. | Characterising the optical properties of galaxy clusters with GMPhoRCC: We introduce the Gaussian Mixture full Photometric Red sequence Cluster
Characteriser (GMPhoRCC), an algorithm for determining the redshift and
richness of a galaxy cluster candidate. By using data from a multi-band sky
survey with photometric redshifts, a red sequence colour magnitude relation
(CMR) is isolated and modelled and used to characterise the optical properties
of the candidate. GMPhoRCC provides significant advantages over existing
methods including, treatment of multi-modal distributions, variable width full
CMR red sequence, richness extrapolation and quality control in order to
algorithmically identify catastrophic failures. We present redshift comparisons
for clusters from the GMBCG, NORAS, REFLEX and XCS catalogues, where the
GMPhoRCC estimates are in excellent agreement with spectra, showing accurate,
unbiased results with low scatter ($\sigma_{\delta z / (1+z)} \sim 0.014$). We
conclude with the evaluation of GMPhoRCC performance using empirical Sloan
Digital Sky Survey (SDSS) like mock galaxy clusters. GMPhoRCC is shown to
produce highly pure characterisations with very low probabilities ($<1\%$) of
spurious, clean characterisations. In addition GMPhoRCC is shown to demonstrate
high rates of completeness with respect to recovering redshift, richness and
correctly identifying the BCG. |
Synergistic tests of inflation: We investigate the possibility of utilising 21cm intensity mapping, optical
galaxy, and Cosmic Microwave Background (CMB) surveys to constrain the power
spectrum of primordial fluctuations predicted by single-field slow-roll
inflation models. Implementing a Fisher forecast analysis, we derive
constraints on the spectral tilt parameter $n_{\rm s}$ and its first and second
runnings $(\alpha_{\rm s},\beta_{\rm s})$. We show that 21cm intensity mapping
surveys with instruments like the Square Kilometre Array, CHIME, and HIRAX, can
be powerful probes of the primordial features. We combine our forecasts with
the ones derived for a COrE-like CMB survey, as well as for a Stage IV optical
galaxy survey similar to Euclid. The synergies between different surveys can be
exploited to rule out a large fraction of the available inflationary models. | The cosmological analysis of X-ray cluster surveys V. The potential of
cluster counts in the $1<z<2$ range: Cosmological studies have now entered Stage IV according to the Dark Energy
Task Force prescription, thanks to new missions (Euclid, Rubin Observatory,
SRG/eROSITA) that are expected to provide the required ultimate accuracy in the
dark energy (DE) equation of state (EoS). However, none of these projects have
the power to systematically unveil the galaxy cluster population at $z>1$.
There therefore remains the need for an ATHENA-like mission to run independent
cosmological investigations and scrutinise the consistency between the results
from the $0<z<1$ and $1<z<2$ epochs. We study the constraints on the DE EoS and
on primordial non-Gaussanities for typical X-ray cluster surveys executed by
ATHENA. We consider two survey designs: 50 deg$^2$ at 80ks (survey A) and 200
deg$^2$ at 20ks (survey B). We analytically derive cluster counts in a space of
observable properties, and predict the cosmological potential of the
corresponding samples with a Fisher analysis. The achieved depth allows us to
unveil the halo mass function down to the group scale out to $z=2$. We predict
the detection of thousands of clusters down to a few 10$^{13} h^{-1}
M_{\odot}$, in particular 940 and 1400 clusters for surveys A and B,
respectively, at $z>1$. Such samples will allow a detailed modelling of the
evolution of cluster physics along with a standalone cosmological analysis. Our
results suggest that survey B has the optimal design as it provides greater
statistics. Remarkably, high-$z$ clusters, despite representing 15% or less of
the full samples, allow a significant reduction of the uncertainty on the
cosmological parameters: $\Delta w_a$ is reduced by a factor of 2.3 and $\Delta
f_{NL}^{loc}$ by a factor of 3. Inventorying the high-$z$ X-ray cluster
population can play a crucial role in ensuring overall cosmological
consistency. This will be the major aim of future new-generation ATHENA-like
missions. |
Thinking outside the halo: Tracing the large-scale distribution of
diffuse cosmic metals with semi-analytic models: With the installation of the Cosmic Origins Spectrograph on the Hubble Space
Telescope, measurements of the metal content of the low redshift intergalactic
medium (IGM) are now available. Using a new grid-based model for diffuse gas
coupled to the SAGE semi-analytic model of galaxy formation, we examine the
impact of supernova feedback on the pollution of the IGM. We consider different
assumptions for the reheating and ejection of gas by supernovae and their
dependence on galaxy circular velocity and gas surface density. Where metals
are present, we find the most likely metallicity to be $-1.5 <
$log$_{10}$(Z/Z$_{\odot}$)$< -1.0$ at $z = 0$, consistent with both
observations and more sophisticated hydrodynamic simulations. Our model
predicts that the regions of the IGM with the highest metallicities will be
near galaxies with M$_{\star} \sim 10^{10.5}h^{-1}$M$_{\odot}$ and in
environments of densities $\sim 10 \times$ the mean. We also find that 90% of
IGM metals at $z = 0$ are ejected by galaxies with stellar masses less than
$10^{10.33}h^{-1}$M$_{\odot}$. | Advances in Constraining Intrinsic Alignment Models with Hydrodynamic
Simulations: We use galaxies from the IllustrisTNG, MassiveBlack-II and Illustris
hydrodynamic simulations to investigate the behaviour of large scale galaxy
intrinsic alignments. Our analysis spans four redshift slices over the
approximate range of contemporary lensing surveys $z=0-1$. We construct
comparable weighted samples from the three simulations, which we then analyse
using an alignment model that includes both linear and quadratic alignment
contributions. Our data vector includes galaxy-galaxy, galaxy-shape and
shape-shape projected correlations, with the joint covariance matrix estimated
analytically. In all of the simulations, we report non-zero IAs at the level of
several $\sigma$. For a fixed lower mass threshold, we find a relatively strong
redshift dependence in all three simulations, with the linear IA amplitude
increasing by a factor of $\sim 2$ between redshifts $z=0$ and $z=1$. We report
no significant evidence for non-zero values of the tidal torquing amplitude,
$A_2$, in TNG, above statistical uncertainties, although MassiveBlack-II
favours a moderately negative $A_2\sim-2$. Examining the properties of the TATT
model as a function of colour, luminosity and galaxy type (satellite or
central), our findings are consistent with the most recent measurements on real
data. We also outline a novel method for constraining the TATT model parameters
directly from the pixelised tidal field, alongside a proof of concept exercise
using TNG. This technique is shown to be promising, although the comparison
with previous results obtained via other methods is non-trivial. |
General CMB and Primordial Bispectrum Estimation I: Mode Expansion,
Map-Making and Measures of f_NL: We present a detailed implementation of two bispectrum estimation methods
which can be applied to general non-separable primordial and CMB bispectra. The
method exploits bispectrum mode decompositions on the domain of allowed
wavenumber or multipole values. Concrete mode examples constructed from
symmetrised tetrahedral polynomials are given, demonstrating rapid convergence
for known bispectra. We use these modes to generate simulated CMB maps of high
resolution (l > 2000) given an arbitrary primordial power spectrum and
bispectrum or an arbitrary late-time CMB angular power spectrum and bispectrum.
By extracting coefficients for the same separable basis functions from an
observational map, we are able to present an efficient and general f_NL
estimator for a given theoretical model. The estimator has two versions
comparing theoretical and observed coefficients at either primordial or late
times, thus encompassing a wider range of models, including secondary
anisotropies, lensing and cosmic strings. We provide examples and validation of
both f_NL estimation methods by direct comparison with simulations in a
WMAP-realistic context. In addition, we show how the full bispectrum can be
extracted from observational maps using these mode expansions, irrespective of
the theoretical model under study. We also propose a universal definition of
the bispectrum parameter F_NL for more consistent comparison between
theoretical models. We obtain WMAP5 estimates of f_NL for the equilateral model
from both our primordial and late-time estimators which are consistent with
each other, as well as with results already published in the literature. These
general bispectrum estimation methods should prove useful for the analysis of
nonGaussianity in the Planck satellite data, as well as in other contexts. | The Formation of the Local Group Planes of Galaxies: The confinement of most satellite galaxies in the Local Group to thin planes
presents a challenge to the theory of hierarchical galaxy clustering. The
PAndAS collaboration has identified a particularly thin configuration with
kinematic coherence among companions of M31 and there have been long standing
claims that the dwarf companions to the Milky Way lie in a plane roughly
orthogonal to the disk of our galaxy. This discussion investigates the possible
origins of four Local Group planes: the plane similar, but not identical to
that identified by PAndAS, an adjacent slightly tilted plane, and two planes
near the Milky Way: one with nearer galaxies and the other with more distant
ones. Plausible orbits are found by using a combination of Numerical Action
methods and a backward in time integration procedure. For M31, M33, IC10, and
LeoI, solutions are found that are consistent with measurements of their proper
motions. For galaxies in planes, there must be commonalities in their proper
motions, and this constraint greatly limits the number of physically plausible
solutions. Key to the formation of the planar structures has been the
evacuation of the Local Void and consequent build-up of the Local Sheet, a wall
of this void. Most of the M31 companion galaxies were born in early-forming
filamentary or sheet-like substrata that chased M31 out of the void. M31 is a
moving target because of its attraction toward the Milky Way, and the result
has been alignments stretched toward our galaxy. In the case of the
configuration around the Milky Way, it appears that our galaxy was in a
three-way competition for companions with M31 and Centaurus A. Only those
within a modest band fell our way. The Milky Ways' attraction toward the Virgo
Cluster resulted in alignments along the Milky Way-Virgo Cluster line. |
An Estimator for Lensing Potential from Galaxy Number Counts: We derive an estimator for the lensing potential from galaxy number counts
which contains a linear and a quadratic term. We show that this estimator has a
much larger signal-to-noise ratio than the corresponding estimator from
intensity mapping. This is due to the additional lensing term in the number
count angular power spectrum which is present already at linear order. We
estimate the signal-to-noise ratio for future photometric surveys. Particularly
at high redshifts, $z\gtrsim 1.5$, the signal to noise ratio can become of
order 30. Therefore, the number counts in photometric surveys would be an
excellent means to measure tomographic lensing spectra. | Phase-Space Delaunay Tessellation Field Estimator: The reconstruction of density and velocity fields is of central importance to
the interpretation of $N$-body simulations. We propose a phase-space extension
of the Delaunay tessellation field estimator (DTFE) that tracks the dark matter
fluid in phase-space. The new reconstruction scheme removes several artifacts
from the conventional DTFE in multi-stream regions, while preserving the
adaptive resolution in high-density regions and yielding continuous fields. The
estimator also removes tessellation artifacts of a previously proposed
phase-space reconstruction scheme. |
PINION: Physics-informed neural network for accelerating radiative
transfer simulations for cosmic reionization: With the advent of the Square Kilometre Array Observatory (SKAO), scientists
will be able to directly observe the Epoch of Reionization by mapping the
distribution of neutral hydrogen at different redshifts. While physically
motivated results can be simulated with radiative transfer codes, these
simulations are computationally expensive and can not readily produce the
required scale and resolution simultaneously. Here we introduce the
Physics-Informed neural Network for reIONization (PINION), which can accurately
and swiftly predict the complete 4-D hydrogen fraction evolution from the
smoothed gas and mass density fields from pre-computed N-body simulation. We
trained PINION on the C$^2$-Ray simulation outputs and a physics constraint on
the reionization chemistry equation is enforced. With only five redshift
snapshots and a propagation mask as a simplistic approximation of the ionizing
photon mean free path, PINION can accurately predict the entire reionization
history between $z=6$ and $12$. We evaluate the accuracy of our predictions by
analysing the dimensionless power spectra and morphology statistics estimations
against C$^2$-Ray results. We show that while the network's predictions are in
good agreement with simulation to redshift $z>7$, the network's accuracy
suffers for $z<7$ primarily due to the oversimplified propagation mask. We
motivate how PINION performance can be drastically improved and potentially
generalized to large-scale simulations. | The most luminous quasars do not live in the most massive dark matter
haloes at any redshift: Quasars represent the brightest Active Galactic Nuclei (AGN) in the Universe
and are thought to indicate the location of prodigiously growing Black Holes
(BHs), with luminosities as high as 10^48 erg/sec. It is often expected though
that such an extremely energetic process will take place in the most massive
bound structures in the dark matter (DM) distribution. We show that in contrast
to this expectation, in a galaxy formation model which includes AGN feedback,
quasars are predicted to live in average DM halo environments with typical
masses of a few times 10^12 Msun. This fundamental prediction arises from the
fact that quasar activity (i.e., BH accretion with luminosity greater than
10^46 erg/sec) is inhibited in DM haloes where AGN feedback operates. The
galaxy hosts of quasars in our simulations are identified with over massive (in
gas and stars) spheroidal galaxies, in which BH accretion is triggered via a
galaxy merger or secular processes. We further show that the z=0 descendants of
high redshift (z~6) QSOs span a wide range of morphologies, galaxy and halo
masses. The z~6 BHs typically grow only by a modest factor by the present day.
Remarkably, high redshift QSOs never inhabit the largest DM haloes at that time
and their descendants are very seldom found in the most massive haloes at z=0.
We also show that observationally it is very likely to find an enhancement in
the abundance of galaxies around quasars at z~5. However, these enhancements
are considerably weaker compared to the overdensities expected at the extreme
peaks of the DM distribution. Thus, it is very unlikely that a quasar detected
in the $z\gtrsim5$ Universe pinpoints the location of the progenitors of
superclusters in the local Universe. |
The Shift of the Baryon Acoustic Oscillation Scale: A Simple Physical
Picture: A shift of the baryon acoustic oscillation (BAO) scale to smaller values than
predicted by linear theory was observed in simulations. In this paper, we try
to provide an intuitive physical understanding of why this shift occurs,
explaining in more pedagogical detail earlier perturbation theory calculations.
We find that the shift is mainly due to the following physical effect. A
measurement of the BAO scale is more sensitive to regions with long wavelength
overdensities than underdensities, because (due to non-linear growth and bias)
these overdense regions contain larger fluctuations and more tracers and hence
contribute more to the total correlation function. In overdense regions the BAO
scale shrinks because such regions locally behave as positively curved closed
universes, and hence a smaller scale than predicted by linear theory is
measured in the total correlation function. Other effects which also contribute
to the shift are briefly discussed. We provide approximate analytic expressions
for the non-linear shift including a brief discussion of biased tracers and
explain why reconstruction should entirely reverse the shift. Our expressions
and findings are in agreement with simulation results, and confirm that
non-linear shifts should not be problematic for next-generation BAO
measurements. | SALT2 Versus SALT3: Updated Model Surfaces and Their Impacts on Type Ia
Supernova Cosmology: For the past decade, SALT2 has been the most common model used to fit Type Ia
supernova (SN Ia) light curves for dark energy analyses. Recently, the SALT3
model was released, which upgraded a number of model features but has not yet
been used for measurements of dark energy. Here, we evaluate the impact of
switching from SALT2 to SALT3 for a SN cosmology analysis. We train SALT2 and
SALT3 on an identical training sample of 1083 well-calibrated Type Ia
supernovae, ensuring that any differences found come from the underlying model
framework. We publicly release the results of this training (the SALT
"surfaces"). We then run a cosmology analysis on the public Dark Energy Survey
3-Year Supernova data sample (DES-SN3YR), and on realistic simulations of those
data. We provide the first estimate of the SN+CMB systematic uncertainty
arising from the choice of SALT model framework (i.e. SALT2 versus SALT3),
$\Delta w = +0.001 \pm 0.005$ -- a negligible effect at the current level of
dark energy analyses. We also find that the updated surfaces are less sensitive
to photometric calibration uncertainties than previous SALT2 surfaces, with the
average spectral energy density dispersion reduced by a factor of two over
optical wavelengths. This offers an opportunity to reduce the contribution of
calibration errors to SN cosmology uncertainty budgets. |
Designing and testing inflationary models with Bayesian networks: Even simple inflationary scenarios have many free parameters. Beyond the
variables appearing in the inflationary action, these include dynamical initial
conditions, the number of fields, and couplings to other sectors. These
quantities are often ignored but cosmological observables can depend on the
unknown parameters. We use Bayesian networks to account for a large set of
inflationary parameters, deriving generative models for the primordial spectra
that are conditioned on a hierarchical set of prior probabilities describing
the initial conditions, reheating physics, and other free parameters. We use
$N_f$--quadratic inflation as an illustrative example, finding that the number
of $e$-folds $N_*$ between horizon exit for the pivot scale and the end of
inflation is typically the most important parameter, even when the number of
fields, their masses and initial conditions are unknown, along with possible
conditional dependencies between these parameters. | Viable inflationary magnetogenesis with helical coupling: We consider helical coupling to electromagnetism and present a simple
scenario of evolution of the coupling function leading to a viable inflationary
magnetogenesis without the problem of back-reaction. In this scenario, helical
magnetic fields of strength of order up to $10^{- 7}\,\text{G}$, when
extrapolated to the current epoch, can be generated in a narrow spectral band
centered at any reasonable wavenumber by adjusting the model parameters. We
discuss implications of this model for baryogenesis, which impose additional
constraints on the strength and correlation length of magnetic field. |
Optimal void finders in weak lensing maps: Cosmic voids are a key component of the large-scale structure that contain a
plethora of cosmological information. Typically, voids are identified from the
underlying galaxy distribution, which is a biased tracer of the total matter
field. Previous works have shown that 2D voids identified in weak lensing maps
-- weak lensing voids -- correspond better to true underdense regions along the
line of sight. In this work, we study how the properties of weak lensing voids
depend on the choice of void finder, by adapting several popular void finders.
We present and discuss the differences between identifying voids directly in
the convergence maps, and in the distribution of weak lensing peaks. Particular
effort has been made to test how these results are affected by galaxy shape
noise, which is a dominant source of noise in weak lensing observations. By
studying the signal-to-noise ratios (SNR) for the tangential shear profile of
each void finder, we find that voids identified directly in the convergence
maps have the highest SNR but are also the ones most affected by galaxy shape
noise. Troughs are least affected by noise, but also have the lowest SNR. The
tunnel algorithm, which identifies voids in the distribution of weak lensing
peaks, represents a good compromise between finding a large tangential shear
SNR and mitigating the effect of galaxy shape noise. | Mass, shape and thermal properties of A1689 by a multi-wavelength X-ray,
lensing and Sunyaev-Zel'dovich analysis: Knowledge of mass and concentration of galaxy clusters is crucial to
understand their formation and evolution. Unbiased estimates require the
understanding of the shape and orientation of the halo as well as its
equilibrium status. We propose a novel method to determine the intrinsic
properties of galaxy clusters from a multi-wavelength data set spanning from
X-ray spectroscopic and photometric data to gravitational lensing to the
Sunyaev-Zel'dovich effect (SZe). The method relies on two quite non informative
geometrical assumptions: the distributions of total matter or gas are
approximately ellipsoidal and co-aligned; they have different, constant axial
ratios but share the same degree of triaxiality. Weak and strong lensing probe
the features of the total mass distribution in the plane of the sky. X-ray data
measure size and orientation of the gas in the plane of the sky. Comparison
with the SZ amplitude fixes the elongation of the gas along the line of sight.
These constraints are deprojected thanks to Bayesian inference. The mass
distribution is described as a Navarro-Frenk-White halo with arbitrary
orientation, gas density and temperature are modelled with parametric profiles.
We applied the method to Abell 1689. Independently of the priors, the cluster
is massive, M_{200}=(1.3+-0.2)*10^{15}M_sun, and over-concentrated,
c_{200}=8+-1, but still consistent with theoretical predictions. The total
matter is triaxial (minor to major axis ratio ~0.5+-0.1 exploiting priors from
N-body simulations) with the major axis nearly orientated along the line of
sight. The gas is rounder (minor to major axis ratio ~0.6+-0.1) and deviates
from hydrostatic equilibrium. The contribution of non-thermal pressure is
~20-50 per cent in inner regions, <~ 300 kpc, and ~25+-5 per cent at ~1.5 Mpc. |
Constraining Dark Energy Perturbations: the Role of Early Dark Energy: Dark Energy not only has background effects through its equation of state
$w_{DE}$, but also it can cluster through its sound speed $c^2_{sDE}$, subject
to certain conditions. As is well-known, for dynamical dark energy models, dark
energy perturbations get sourced into matter perturbations through metric
perturbations which is always accompanied by the term $(1+w_{DE})$. Hence, for
dynamical dark energy models with $w_{DE}$ close $-1$, their perturbations get
almost decoupled from metric leaving nearly null imprints on matter power
spectra. Furthermore, Quintessence models with its sound speed equal to speed
of light, washes out almost any inhomogeneities occurred within sub-Hubble
scales, hence making detectability of dark energy perturbations far more
difficult than already is. In this article we look for these imprints by going
beyond Quintessence considering an Early Dark Energy parametrization that not
only have a non-negligible energy density at early times, but also it can
achieve $w_{DE}$ far from $-1$, making dark energy perturbations detectable in
sub-horizon scales. With the help of current datasets, we are able to constrain
sound speed of dark energy to a low value ($c^2_{sDE} \sim 0.14$), along with a
much higher range allowed for early dark energy density, with strong
constraints on it ($\Omega_e \sim 0.02$). We discuss effects of different
datasets on this parametrization along with possible explanation for deviation
on certain parameter(s) comparing between $c^2_{sDE}=1$ case and the case where
it is kept open. | Galaxy Phase-Space Density Data Preclude that Bose-Einstein Condensate
be the Total Dark Matter: Light scalars (as the axion) with mass m ~ 10^{-22} eV forming a
Bose-Einstein condensate (BEC) exhibit a Jeans length in the kpc scale and were
therefore proposed as dark matter (DM) candidates. Our treatment here is
generic, independent of the particle physics model and applies to all DM BEC,
in or out of equilibrium. Two observed quantities crucially constrain DM in an
inescapable way: the average DM density rho_{DM} and the phase-space density Q.
The observed values of rho_{DM} and Q in galaxies today constrain both the
possibility to form a BEC and the DM mass m. These two constraints robustly
exclude axion DM that decouples just after the QCD phase transition. Moreover,
the value m ~ 10^{-22} eV can only be obtained with a number of
ultrarelativistic degrees of freedom at decoupling in the trillions which is
impossible for decoupling in the radiation dominated era. In addition, we find
for the axion vacuum misalignment scenario that axions are produced strongly
out of thermal equilibrium and that the axion mass in such scenario turns to be
17 orders of magnitude too large to reproduce the observed galactic structures.
Moreover, we also consider inhomogenous gravitationally bounded BEC's supported
by the bosonic quantum pressure independently of any particular particle
physics scenario. For a typical size R ~ kpc and compact object masses M ~ 10^7
Msun they remarkably lead to the same particle mass m ~ 10^{-22} eV as the BEC
free-streaming length. However, the phase-space density for the gravitationally
bounded BEC's turns to be more than sixty orders of magnitude smaller than the
galaxy observed values. We conclude that the BEC's and the axion cannot be the
DM particle. However, an axion in the mili-eV scale may be a relevant source of
dark energy through the zero point cosmological quantum fluctuations. |
The Impact of Cross-Covariances Between the CMB and Reconstructed
Lensing Power: Weak gravitational lensing of the Cosmic Microwave Background (CMB) changes
CMB statistics in a nontrivial way, allowing for reconstruction of the lensing
potential and the use of these reconstructed maps in determining cosmological
parameters that affect the formation of intervening large-scale structures.
Although in principle there are correlations between the primary CMB and the
reconstructed lensing potential due to the lensing procedure itself, in
practice CMB analyses treat these as negligible when combining these band
powers in likelihoods. In this paper we quantify explicitly the impact on
parameter constraints due to these cross-covariances between the lensed CMB and
reconstructed lensing power, and we compare to the effect of including all
lensing-induced non-Gaussian covariances, which have previously shown to impact
parameter constraints on the order of 10%. We perform our analysis for a range
of experimental setups, scanning over instrumental noise levels of 0.5 to 10.0
$\mu$K-arcmin in temperature assuming fully polarized detectors, and using a
fixed beam size of 1.4 arcmin. When the correlations between the lensed CMB and
lensing power are neglected, we find that forecasted constraints shift by at
most 3% of the error bar for a 6-parameter $\Lambda$CDM model, and for the
noise levels considered in this paper. For some of the $\Lambda$CDM extensions
considered here, however, these correlations have a nontrivial impact, in some
cases more than 10% of the error bar, even for current experimental noise
levels. | High redshift radio galaxies and divergence from the CMB dipole: Previous studies have found our velocity in the rest frame of radio galaxies
at high redshift to be substantially larger than that inferred from the CMB
temperature dipole anisotropy. We construct a full sky catalogue NVSUMSS, by
merging the NVSS and SUMSS catalogues and removing local sources by various
means including cross-correlating with the 2MRS catalogue. We take into account
both aberration and Doppler boost to deduce our velocity from the hemispherical
number count asymmetry, as well as via a 3-dimensional linear estimator. Both
the magnitude and direction depend on cuts made to the catalogue, e.g. on the
lowest source flux, however these effects are small. With the hemispheric
number count asymmetry method we obtain a velocity of 1729 $\pm$ 187 km/s i.e.
about 4 times larger than that obtained from the CMB dipole, but close in
direction, towards RA=149 $\pm$ 2 degree, DEC = -17 $\pm$ 12 degree. With the
3-dimensional estimator, the derived velocity is 1355 $\pm$ 174 km/s towards
RA=141 $\pm$ 11 degree, DEC=-9 $\pm$ 10 degree. We assess the statistical
significance of these results by constructing catalogues of random
distributions and show that they are at best significant at the $2.81 \sigma$
(99.95% confidence) level. |
4098 galaxy clusters to z~0.6 in the Sloan Digital Sky Survey equatorial
Stripe 82: We present a catalogue of 4098 photometrically selected galaxy clusters with
a median redshift <z> = 0.32 in the 270 square degree 'Stripe 82' region of the
Sloan Digital Sky Survey (SDSS), covering the celestial equator in the Southern
Galactic Cap (-50 < RA < 59 deg, |Dec| < 1.25 deg). Owing to the multi-epoch
SDSS coverage of this region, the ugriz photometry is ~2 magnitudes deeper than
single scans within the main SDSS footprint. We exploit this to detect clusters
of galaxies using an algorithm that searches for statistically significant
overdensities of galaxies in a Voronoi tessellation of the projected sky. 32%
of the clusters have at least one member with a spectroscopic redshift from
existing public data (SDSS Data Release 7, 2SLAQ & WiggleZ), and the remainder
have a robust photometric redshift (accurate to ~5-9% at the median redshift of
the sample). The weighted average of the member galaxies' redshifts provides a
reasonably accurate estimate of the cluster redshift. The cluster catalogue is
publicly available for exploitation by the community to pursue a range of
science objectives. In addition to the cluster catalogue, we provide a linked
catalogue of 18,295 V<21 mag quasar sight-lines with impact parameters within
<3 Mpc of the cluster cores selected from the catalogue of Veron et al. (2010).
The background quasars cover 0.25 < z < 2, where MgII absorption-line systems
associated with the clusters are detectable in optical spectra. | Cosmic Ray-Dominated AGN Jets and the Formation of X-ray Cavities in
Galaxy Clusters: It is widely accepted that feedback from active galactic nuclei (AGN) plays a
key role in the evolution of gas in groups and clusters of galaxies.
Unequivocal evidence comes from quasi-spherical X-ray cavities observed near
cluster centers having sizes ranging from a few to tens of kpc, some containing
radio emission. Cavities apparently evolve from the interaction of AGN jets
with the intracluster medium (ICM). However, in numerical simulations it has
been difficult to create such fat cavities from narrow jets. Ultra-hot thermal
jets dominated by kinetic energy typically penetrate deep into the ICM, forming
radially elongated cavities at large radii unlike those observed. Here, we
study very light jets dominated energetically by relativistic cosmic rays (CRs)
with axisymmetric hydrodynamic simulations, investigating the jet evolution
both when they are active and when they are later turned off. We find that,
when the thermal gas density in a CR-dominated jet is sufficiently low, the jet
has a correspondingly low inertia, and thus decelerates quickly in the ICM.
Furthermore, CR pressure causes the jet to expand laterally, encounter and
displace more decelerating ICM gas, naturally producing fat cavities near
cluster centers similar to those observed. Our calculations of cavity formation
imply that AGN jets responsible for creating fat X-ray cavities (radio bubbles)
are very light, and dominated by CRs. This scenario is consistent with radio
observations of Fanaroff-Riley I jets that appear to decelerate rapidly,
produce strong synchrotron emission and expand typically at distances of a few
kpc from the central AGN. |
An Upper Limit on the Initial Temperature of the Radiation-Dominated
Universe: Gravitational waves (GWs) are produced by colliding particles through the
gravitational analogue of electromagnetic bremsstrahlung. We calculate the
contribution of free-free emission in the radiation-dominated Universe to the
stochastic GW background. We find that the energy density of the resulting GW
radiation is heavily dependent on the number of elementary particles,
$N_{\mathrm{tot}}$, and the maximum initial temperature, $T_{\mathrm{max}}$. We
rule out $N_{\mathrm{tot}}\gtrsim N_{\mathrm{SM}}$ for $T_{\mathrm{max}}\sim
T_{\mathrm{Planck}}\approx10^{19}$ GeV and
$N_{\mathrm{tot}}\gtrsim10^{13}\times N_{\mathrm{SM}}$ for
$T_{\mathrm{max}}\sim10^{16}$ GeV, where $N_{\mathrm{SM}}$ is the number of
particles in the Standard Model. In the case of inflation, existing
cosmological data constrain $T_{\mathrm{max}}\lesssim10^{16}$ GeV. However,
alternative models to inflation such as bouncing cosmologies allow for
$T_{\mathrm{max}}$ near $T_{\mathrm{Planck}}$. At the energy scales we are
considering, the extra number of particles arise naturally in models of extra
dimensions. | Variable Accretion Rates and Fluffy First Stars: We combine the output of hydrodynamical simulations of Population III star
cluster formation with stellar evolution models, and calculate the evolution of
protostars experiencing variable mass accretion rates due to interactions
within a massive disk. We find that the primordial protostars are extended
'fluffy' objects for the bulk of their pre-main-sequence lifetimes. Accretion
luminosity feedback from such objects is high, but as shown in previous work,
has a minimal effect on the star cluster. The extended radii of the protostars,
combined with the observation of close encounters in the simulations, suggests
that mergers will occur in such systems. Furthermore, mass transfer between
close protostellar binaries with extended radii could lead to massive tight
binaries, which are a possible progenitor of gamma ray bursts. |
Hybrid modeling of redshift space distortions: The observed power spectrum in redshift space appears distorted due to the
peculiar motion of galaxies, known as redshift-space distortions (RSD). While
all the effects in RSD are accounted for by the simple mapping formula from
real to redshift spaces, accurately modeling redshift-space power spectrum is
rather difficult due to the non-perturbative properties of the mapping. Still,
however, a perturbative treatment may be applied to the power spectrum at
large-scales, and on top of a careful modeling of the Finger-of-God effect
caused by the small-scale random motion, the redshift-space power spectrum can
be expressed as a series of expansion which contains the higher-order
correlations of density and velocity fields. In our previous work [JCAP 8
(Aug., 2016) 050], we provide a perturbation-theory inspired model for power
spectrum in which the higher-order correlations are evaluated directly from the
cosmological $N$-body simulations. Adopting a simple Gaussian ansatz for
Finger-of-God effect, the model is shown to quantitatively describe the
simulation results. Here, we further push this approach, and present an
accurate power spectrum template which can be used to estimate the growth of
structure as a key to probe gravity on cosmological scales. Based on the
simulations, we first calibrate the uncertainties and systematics in the
pertrubation theory calculation in a fiducial cosmological model. Then, using
the scaling relations, the calibrated power spectrum template is applied to a
different cosmological model. We demonstrate that with our new template, the
best-fitted growth functions are shown to reproduce the fiducial values in a
good accuracy of 1 \% at $k<0.18 \hompc$ for cosmologies with different Hubble
parameters. | The relative impact of baryons and cluster shape on weak lensing mass
estimates of galaxy clusters: Weak gravitational lensing depends on the integrated mass along the line of
sight. Baryons contribute to the mass distribution of galaxy clusters and the
resulting mass estimates from lensing analysis. We use the cosmo-OWLS suite of
hydrodynamic simulations to investigate the impact of baryonic processes on the
bias and scatter of weak lensing mass estimates of clusters. These estimates
are obtained by fitting NFW profiles to mock data using MCMC techniques. In
particular, we examine the difference in estimates between dark matter-only
runs and those including various prescriptions for baryonic physics. We find no
significant difference in the mass bias when baryonic physics is included,
though the overall mass estimates are suppressed when feedback from AGN is
included. For lowest-mass systems for which a reliable mass can be obtained
($M_{200} \approx 2 \times 10^{14}$ $M_{\odot}$), we find a bias of $\approx
-10$ per cent. The magnitude of the bias tends to decrease for higher mass
clusters, consistent with no bias for the most massive clusters which have
masses comparable to those found in the CLASH and HFF samples. For the lowest
mass clusters, the mass bias is particularly sensitive to the fit radii and the
limits placed on the concentration prior, rendering reliable mass estimates
difficult. The scatter in mass estimates between the dark matter-only and the
various baryonic runs is less than between different projections of individual
clusters, highlighting the importance of triaxiality. |
The evolution of the star forming sequence in hierarchical galaxy
formation models: It has been argued that the specific star formation rates of star forming
galaxies inferred from observational data decline more rapidly below z = 2 than
is predicted by hierarchical galaxy formation models. We present a detailed
analysis of this problem by comparing predictions from the GALFORM
semi-analytic model with an extensive compilation of data on the average star
formation rates of star-forming galaxies. We also use this data to infer the
form of the stellar mass assembly histories of star forming galaxies. Our
analysis reveals that the currently available data favour a scenario where the
stellar mass assembly histories of star forming galaxies rise at early times
and then fall towards the present day. In contrast, our model predicts stellar
mass assembly histories that are almost flat below z = 2 for star forming
galaxies, such that the predicted star formation rates can be offset with
respect to the observational data by factors of up to 2-3. This disagreement
can be explained by the level of coevolution between stellar and halo mass
assembly that exists in contemporary galaxy formation models. In turn, this
arises because the standard implementations of star formation and supernova
feedback used in the models result in the efficiencies of these process
remaining approximately constant over the lifetime of a given star forming
galaxy. We demonstrate how a modification to the timescale for gas ejected by
feedback to be reincorporated into galaxy haloes can help to reconcile the
model predictions with the data. | Galaxy Cluster Radio Relics in Adaptive Mesh Refinement Cosmological
Simulations: Relic Properties and Scaling Relationships: Cosmological shocks are a critical part of large-scale structure formation,
and are responsible for heating the intracluster medium in galaxy clusters. In
addition, they are also capable of accelerating non-thermal electrons and
protons. In this work, we focus on the acceleration of electrons at shock
fronts, which is thought to be responsible for radio relics - extended radio
features in the vicinity of merging galaxy clusters. By combining high
resolution AMR/N-body cosmological simulations with an accurate shock finding
algorithm and a model for electron acceleration, we calculate the expected
synchrotron emission resulting from cosmological structure formation. We
produce synthetic radio maps of a large sample of galaxy clusters and present
luminosity functions and scaling relationships. With upcoming long wavelength
radio telescopes, we expect to see an abundance of radio emission associated
with merger shocks in the intracluster medium. By producing observationally
motivated statistics, we provide predictions that can be compared with
observations to further improve our understanding of magnetic fields and
electron shock acceleration. |
Mitigating the optical depth degeneracy using the kinematic
Sunyaev-Zel'dovich effect with CMB-S4: The epoch of reionization is one of the major phase transitions in the
history of the universe, and is a focus of ongoing and upcoming cosmic
microwave background (CMB) experiments with improved sensitivity to small-scale
fluctuations. Reionization also represents a significant contaminant to
CMB-derived cosmological parameter constraints, due to the degeneracy between
the Thomson-scattering optical depth, $\tau$, and the amplitude of scalar
perturbations, $A_s$. This degeneracy subsequently hinders the ability of
large-scale structure data to constrain the sum of the neutrino masses, a major
target for cosmology in the 2020s. In this work, we explore the kinematic
Sunyaev-Zel'dovich (kSZ) effect as a probe of reionization, and show that it
can be used to mitigate the optical depth degeneracy with high-sensitivity,
high-resolution data from the upcoming CMB-S4 experiment. We discuss the
dependence of the kSZ power spectrum on physical reionization model parameters,
as well as on empirical reionization parameters, namely $\tau$ and the duration
of reionization, $\Delta z$. We show that by combining the kSZ two-point
function and the reconstructed kSZ four-point function, degeneracies between
$\tau$ and $\Delta z$ can be strongly broken, yielding tight constraints on
both parameters. We forecast $\sigma(\tau) = 0.003$ and $\sigma(\Delta z) =
0.25$ for a combination of CMB-S4 and Planck data, including detailed treatment
of foregrounds and atmospheric noise. The constraint on $\tau$ is nearly
identical to the cosmic-variance limit that can be achieved from large-angle
CMB polarization data. The kSZ effect thus promises to yield not only detailed
information about the reionization epoch, but also to enable high-precision
cosmological constraints on the neutrino mass. | Early-Type Galaxy Archeology: Ages, Abundance Ratios, and Effective
Temperatures from Full-Spectrum Fitting: The stellar populations of galaxies hold vital clues to their formation
histories. In this paper we present results based on modeling stacked spectra
of early-type galaxies drawn from the Sloan Digital Sky Survey (SDSS) as a
function of velocity dispersion, sigma, from 90 km/s to 300 km/s. The spectra
are of extremely high quality, with typical S/N of 1000/A, and a wavelength
coverage of 4000A-8800A. Our population synthesis model includes variation in
16 elements from C to Ba, the shift in effective temperature, Delta(Teff), of
the stars with respect to a solar metallicity isochrone, amongst other
parameters. In our approach we fit the full optical spectra rather than a
select number of spectral indices and are able to, for the first time, measure
the abundances of the elements V, Cr, Mn, Co, and Ni from the integrated light
of distant galaxies. Our main results are as follows: 1) light-weighted stellar
ages range from 6-12 Gyr from low to high sigma; 2) [Fe/H] varies by less than
0.1 dex across the entire sample; 3) Mg closely tracks O, and both increase
from ~0.0 at low sigma to ~0.25 at high sigma; Si and Ti show a shallower rise
with sigma, and Ca tracks Fe rather than O; 4) the iron peak elements V, Cr,
Mn, and Ni track Fe, while Co tracks O, suggesting that Co forms primarily in
massive stars; 5) C and N track O over the full sample and [C/Fe] and [N/Fe]
exceed 0.2 at high sigma; and 6) the variation in Delta(Teff) with total
metallicity follows theoretical predictions based on stellar evolution theory.
Our derived [Mg/Fe] and [O/Fe] abundance ratios are 0.05-0.1 dex lower than
most previous determinations. Under the conventional interpretation that the
variation in these ratios is due to star formation timescale variations, our
results suggest longer star formation timescales for massive early-type
galaxies than previous studies. (ABRIDGED) |
Cosmology Intertwined IV: The Age of the Universe and its Curvature: A precise measurement of the curvature of the Universe is of primeval
importance for cosmology since it could not only confirm the paradigm of
primordial inflation but also help in discriminating between different early
Universe scenarios. The recent observations, while broadly consistent with a
spatially flat standard $\Lambda$ Cold Dark Matter ($\Lambda$CDM) model, are
showing tensions that still allow (and, in some cases, even suggest) a few
percent deviations from a flat universe. In particular, the Planck Cosmic
Microwave Background power spectra, assuming the nominal likelihood, prefer a
closed universe at more than 99\% confidence level. While new physics could be
in action, this anomaly may be the result of an unresolved systematic error or
just a statistical fluctuation. However, since a positive curvature allows a
larger age of the Universe, an accurate determination of the age of the oldest
objects provides a smoking gun in confirming or falsifying the current flat
$\Lambda$CDM model. | The Atacama Cosmology Telescope: Two-Season ACTPol Spectra and
Parameters: We present the temperature and polarization angular power spectra measured by
the Atacama Cosmology Telescope Polarimeter (ACTPol). We analyze night-time
data collected during 2013-14 using two detector arrays at 149 GHz, from 548
deg$^2$ of sky on the celestial equator. We use these spectra, and the spectra
measured with the MBAC camera on ACT from 2008-10, in combination with Planck
and WMAP data to estimate cosmological parameters from the temperature,
polarization, and temperature-polarization cross-correlations. We find the new
ACTPol data to be consistent with the LCDM model. The ACTPol
temperature-polarization cross-spectrum now provides stronger constraints on
multiple parameters than the ACTPol temperature spectrum, including the baryon
density, the acoustic peak angular scale, and the derived Hubble constant.
Adding the new data to planck temperature data tightens the limits on damping
tail parameters, for example reducing the joint uncertainty on the number of
neutrino species and the primordial helium fraction by 20%. |
The smearing scale in Laguerre reconstructions of the correlation
function: To a good approximation, on large cosmological scales the evolved two-point
correlation function of biased tracers is related to the initial one by a
convolution. For Gaussian initial conditions, the smearing kernel is Gaussian,
so if the initial correlation function is parametrized using simple polynomials
then the evolved correlation function is a sum of generalized Laguerre
functions of half-integer order. This motivates an analytic Laguerre
reconstruction algorithm which previous work has shown is fast and accurate.
This reconstruction requires as input the width of the smearing kernel. We show
that the method can be extended to estimate the width of the smearing kernel
from the same dataset. This estimate, and associated uncertainties, can then be
used to marginalize over the distribution of reconstructed shapes, and hence
provide error estimates on the value of the distance scale which are not tied
to a particular cosmological model. We also show that if, instead, we
parametrize the evolved correlation function using simple polynomials, then the
initial one is a sum of Hermite polynomials, again enabling fast and accurate
deconvolution. If one is willing to use constraints on the smearing scale from
other datasets, then marginalizing over its value is simpler for Hermite
reconstruction, potentially providing further speed-up in cosmological
analyses. | Relativistic distortions in galaxy density-ellipticity correlations:
gravitational redshift and peculiar velocity effects: We study relativistic effects, arising from the light propagation in an
inhomogeneous universe. We particularly investigate the effects imprinted in a
cross-correlation function between galaxy positions and intrinsic galaxy shapes
(GI correlation). Considering the Doppler and gravitational redshift effects as
major relativistic effects, we present an analytical model of the GI
correlation function, from which we find that the relativistic effects induce
non-vanishing odd multipole anisotropies. Focusing particularly on the dipole
anisotropy, we show that the Doppler effect dominates at large scales, while
the gravitational redshift effect originated from the halo potential dominates
at the scales below $10$-$30\, {\rm Mpc}/h$, with the amplitude of the dipole
GI correlation being positive over all the scales. Also, we newly derive the
covariance matrix for the modelled GI dipole. Taking into account the full
covariance, we estimate the signal-to-noise ratio and show that the GI dipole
induced by the relativistic effects is detectable in future large-volume galaxy
surveys. We discuss how the measurement of dipole GI correlation could be
helpful to detect relativistic effects in combination with the conventional
galaxy-galaxy cross correlation. |
aeons: approximating the end of nested sampling: This paper presents analytic results on the anatomy of nested sampling, from
which a technique is developed to estimate the run-time of the algorithm that
works for any nested sampling implementation. We test these methods on both toy
models and true cosmological nested sampling runs. The method gives an
order-of-magnitude prediction of the end point at all times, forecasting the
true endpoint within standard error around the halfway point. | First results of the EDELWEISS-II WIMP search using Ge cryogenic
detectors with interleaved electrodes: The EDELWEISS-II collaboration has performed a direct search for WIMP dark
matter with an array of ten 400 g heat-and-ionization cryogenic detectors
equipped with interleaved electrodes for the rejection of near-surface events.
Six months of continuous operation at the Laboratoire Souterrain de Modane have
been achieved. The observation of one nuclear recoil candidate above 20 keV in
an effective exposure of 144 kgd is interpreted in terms of limits on the
cross-section of spin-independent interactions of WIMPs and nucleons. A
cross-section of 1.0x10^-7 pb is excluded at 90%CL for a WIMP mass of 80
GeV/c2. This result demonstrates for the first time the very high background
rejection capabilities of these simple and robust detectors in an actual WIMP
search experiment. |
HSC Year 1 cosmology results with the minimal bias method:
HSC$\times$BOSS galaxy-galaxy weak lensing and BOSS galaxy clustering: We present cosmological parameter constraints from a blinded joint analysis
of galaxy-galaxy weak lensing, $\Delta\!\Sigma(R)$, and projected correlation
function, $w_\mathrm{p}(R)$, measured from the first-year HSC (HSC-Y1) data and
SDSS spectroscopic galaxies over $0.15<z<0.7$. We use luminosity-limited
samples as lens samples for $\Delta\!\Sigma$ and as large-scale structure
tracers for $w_\mathrm{p}$ in three redshift bins, and use the HSC-Y1 galaxy
catalog to define a secure sample of source galaxies at $z_\mathrm{ph}>0.75$
for the $\Delta\!\Sigma$ measurements, selected based on their photometric
redshifts. For theoretical template, we use the "minimal bias" model for the
cosmological clustering observables for the flat $\Lambda$CDM cosmological
model. We compare the model predictions with the measurements in each redshift
bin on large scales, $R>12$ and $8~h^{-1}\mathrm{Mpc}$ for $\Delta\!\Sigma(R)$
and $w_\mathrm{p}(R)$, respectively, where the perturbation theory-inspired
model is valid. When we employ weak priors on cosmological parameters, without
CMB information, we find $S_8=0.936^{+0.092}_{-0.086}$,
$\sigma_8=0.85^{+0.16}_{-0.11}$, and $\Omega_\mathrm{m}=0.283^{+0.12}_{-0.035}$
for the flat $\Lambda$CDM model. Although the central value of $S_8$ appears to
be larger than those inferred from other cosmological experiments, we find that
the difference is consistent with expected differences due to sample variance,
and our results are consistent with the other results to within the statistical
uncertainties. (abriged) | An estimation of local bulk flow with the maximum-likelihood method: A maximum-likelihood method, tested as an unbiased estimator from numerical
simulations, is used to estimate cosmic bulk flow from peculiar velocity
surveys. The likelihood function is applied to four observational catalogues
(ENEAR, SFI++, A1SN and SC) constructed from galaxy peculiar velocity surveys
and Type-Ia supernovae data at low redshift ($z \leq 0.03$). We find that the
Spiral Field {\it I}-band catalogue constrains the bulk flow to be $V=290 \pm
30 {\,{\rm km}\,{\rm s}^{-1}}$ towards $l=281^{\circ} \pm 7^{\circ}$,
$b=8^{\circ +6^{\circ}}_{-5^{\circ}}$ on effective scales of $ 58 {\,{h^{-1}
{\rm Mpc}}}$, which is the tightest constraints achievable at the present time.
By comparing the amplitudes of our estimated bulk flows with theoretical
prediction, we find excellent agreement between the two. In addition,
directions of estimated bulk flows are also consistent with measurements in
other studies. |
The Swift/UVOT catalogue of NGC4321 star forming sources: A case against
density wave theory: We study the star forming regions in the spiral galaxy NGC4321, taking
advantage of the spatial resolution (2.5 arcsec FWHM) of the Swift/UVOT camera
and the availability of three UV passbands in the region 1600-3000 A, in
combination with optical and IR imaging from SDSS, KPNO/Ha and Spitzer/IRAC, to
obtain a catalogue of 787 star forming regions out to three disc scale lengths.
We determine the properties of the young stellar component and its relationship
with the spiral arms. The Ha luminosities of the sources have a strong
decreasing radial trend, suggesting more massive star forming regions in the
central part of the galaxy. When segregated with respect to NUV-optical colour,
blue sources have a significant excess of flux in the IR at 8 micron, revealing
the contribution from PAHs, although the overall reddening of these sources
stays below E(B-V)=0.2 mag. The distribution of distances to the spiral arms is
compared for subsamples selected according to Ha luminosity, NUV-optical
colour, or ages derived from a population synthesis model. An offset is
expected between these subsamples as a function of radius if the pattern speed
of the spiral arm were constant - as predicted by classic density wave theory.
No significant offsets are found, favouring instead a mechanism where the
pattern speed has a radial dependence. | Photo-z Quality Cuts and their Effect on the Measured Galaxy Clustering: Photometric galaxy surveys are an essential tool to further our understanding
of the large-scale structure of the universe, its matter and energy content and
its evolution. These surveys necessitate the determination of the galaxy
redshifts using photometric techniques (photo-z). Oftentimes, it is
advantageous to remove from the galaxy sample those for which one suspects that
the photo-z estimation might be unreliable. In this paper, we show that
applying these photo-z quality cuts blindly can grossly bias the measured
galaxy correlations within and across photometric redshift bins. We then extend
the work of Ho et al. (2012) and Ross et al. (2011) to develop a simple and
effective method to correct for this using the data themselves. Finally, we
apply the method to the Mega-Z catalog, containing about a million luminous red
galaxies in the redshift range 0.45 < z < 0.65. After splitting the sample into
four \Delta z = 0.05 photo-z bins using the BPZ algorithm, we see how our
corrections bring the measured galaxy auto- and cross-correlations into
agreement with expectations. We then look for the BAO feature in the four bins,
with and without applying the photo-z quality cuts, and find a broad agreement
between the BAO scales extracted in both cases. Intriguingly, we observe a
correlation between galaxy density and photo-z quality even before any photo-z
quality cuts are applied. This may be due to uncorrected observational effects
that result in correlated gradients across the sky of the galaxy density and
the galaxy photo-z precision. Our correction procedure could also help to
mitigate some of these systematic effects. |
Galaxy dispersion measured by Fast Radio Bursts as a probe of baryonic
feedback models: Fast Radio Bursts (FRBs) are a sensitive probe of the electron distribution
in both the large-scale structure and their host galaxies through the
dispersion measure (DM) of the radio pulse. Baryonic feedback models are
crucial for modelling small scales for ongoing cosmological surveys that are
expected to change the electron distribution in galaxies in a way that can be
probed by FRB observations. In this paper, we explore the impact of baryonic
feedback on FRB hosts using numerical simulations and make a detailed study of
the host galaxy dispersion as a function of redshift, galaxy type, feedback
model and how these properties vary in independent simulation codes. We find
that the host galaxy dispersion varies dramatically between different
implementations of baryonic feedback, allowing FRBs with host identification to
be a valuable probe of feedback physics and thus provide necessary priors for
upcoming analysis of the statistical properties of the large-scale structure.
We further find that any dependency on the exact location of events within
the halo is small. While there exists an evolution of the dispersion measure
with redshift and halo mass, it is largely driven by varying star formation
rates of the halo. Spectral information from FRB hosts can therefore be used to
put priors on the host galaxy dispersion measure, and FRBs can be used to
distinguish between competing models of baryonic feedback in future studies. | Galaxy flows within 8,000 km/s from Numerical Action methods: The trajectories since z=4 of systems of galaxies (`halos') with cz < 8,000
km/s are found through Numerical Action reconstructions. A set of 9,719 halos
from a 2MASS group catalog and Cosmicflows-3 catalogs are given attention.
Present distances are adjusted to minimize departures from observed redshifts.
For those with the most precisely determined distances, compromises are made
between distance and redshift agreement. $H_0$ is varied from 69 to 77 km
s$^{-1}$ Mpc$^{-1}$ with $\Omega_m$ set by the baryon acoustic oscillation
constraint from the Planck Satellite. A best fitting amplitude of the
mass-to-light relation is found. A uniform density associated with the
interhalo medium accounts for the matter not in halos. The solution paths
provide the histories of the formation of the nearby large structures and
depict how the voids emptied. Assuming no local over/underdensity, the best
model has $H_0=73$ km s$^{-1}$ Mpc$^{-1}$ with nearly the same density arising
from interhalo matter (IHM) as from halos. We examine local over/underdensities
by varying the IHM density and find a valley of best fit models along $H_0 =
73.0 (1 + 0.165\delta)$ km s$^{-1}$ Mpc$^{-1}$. Friedmann models with distinct
densities internal and external to the study region give a similar
relationship. The fraction of matter in the IHM seen in n-body simulations
roughly matches that in our $H_0=72$ scenario. Videos have been created to
visualize the complexities of formation of large-scale structures. Standard
n-body calculations starting from the first time-steps as tests of the NAM
solutions, and continue until cosmic scale factor $a=2$ provide glimpses into
the future. |
Discovery of a possibly old galaxy at $z=6.027$, multiply imaged by the
massive cluster Abell 383: We report the discovery of a unique $z=6.027$ galaxy, multiply imaged by the
cluster Abell 383 and detected in new Hubble Space Telescope ACS and WFC3
imaging, as well as in Warm Spitzer observations. This galaxy was selected as a
pair of i-dropouts; its suspected high redshift was confirmed by the
measurement of a strong Lyman-alpha line in both images using Keck/DEIMOS.
Combining Hubble and Spitzer photometry after correcting for contamination by
line emission (estimated to be a small effect), we identify a strong Balmer
break of 1.5 magnitudes. Taking into account the magnification factor of
11.4+/-1.9 (2.65+/-0.17 mag) for the brightest image, the unlensed AB magnitude
for the source is 27.2+/-0.05 in the H band, corresponding to a 0.4 L* galaxy,
and 25.7+/-0.08 at 3.6 um. The UV slope is consistent with beta~2.0, and from
the rest-frame UV continuum we measure a current star formation rate of
2.4+/-1.1 Msol/yr. The unlensed half-light radius is measured to be 300 pc,
from which we deduce a star-forming surface density of ~10 Msol/yr/kpc2. The
Lyman-alpha emission is found to be extended over ~3" along the slit,
corresponding to ~5 kpc in the source plane. This can be explained by the
presence of a much larger envelope of neutral hydrogen around the star-forming
region. Finally, fitting the spectral energy distribution using 7 photometric
data points with simple SED models, we derive the following properties: very
little reddening, an inferred stellar mass of M*=6e9 Msol, and an inferred age
of ~800 Myrs (corresponding to a redshift of formation of ~18). The
star-formation rate of this object was likely much stronger in the past than at
the time of observation, suggesting that we may be missing a fraction of
galaxies at z~6 which have already faded in rest-frame UV wavelengths. | Multicolor Photometry of the Galaxy Cluster A98: Substructures and Star
Formation Properties: An optical photometric observation with the
Beijing-Arizona-Taiwan-Connecticut (BATC) multicolor system is carried out for
A98 (z=0.104), a galaxy cluster with two large enhancements in X-ray surface
brightness. The spectral energy distributions (SEDs) covering 15 intermediate
bands are obtained for all sources detected down to V ~ 20 mag in a field of
$58' \times 58'$. After the star-galaxy separation by the color-color diagrams,
a photometric redshift technique is applied to the galaxy sample for further
membership determination. The color-magnitude relation is taken as a further
restriction of the early-type cluster galaxies. As a result, a list of 198
faint member galaxies is achieved. Based on newly generated sample of member
galaxies, the dynamical substructures, A98N, A98S, and A98W, are investigated
in detail. A separate galaxy group, A98X, is also found to the south of main
concentration of A98, which is gravitationally unbound to A98. For 74
spectroscopically confirmed member galaxies, the environmental effect on the
star formation histories is found. The bright galaxies in the core region are
found to have shorter time scales of star formation, longer mean stellar ages,
and higher metallicities of interstellar medium, which can be interpreted in
the context of hierarchical cosmological scenario. |
A review of elliptical and disc galaxy structure, and modern scaling
laws: A century ago, in 1911 and 1913, Plummer and then Reynolds introduced their
models to describe the radial distribution of stars in `nebulae'. This article
reviews the progress since then, providing both an historical perspective and a
contemporary review of the stellar structure of bulges, discs and elliptical
galaxies. The quantification of galaxy nuclei, such as central mass deficits
and excess nuclear light, plus the structure of dark matter halos and cD galaxy
envelopes, are discussed. Issues pertaining to spiral galaxies including dust,
bulge-to-disc ratios, bulgeless galaxies, bars and the identification of
pseudobulges are also reviewed. An array of modern scaling relations involving
sizes, luminosities, surface brightnesses and stellar concentrations are
presented, many of which are shown to be curved. These 'redshift zero'
relations not only quantify the behavior and nature of galaxies in the Universe
today, but are the modern benchmark for evolutionary studies of galaxies,
whether based on observations, N-body-simulations or semi-analytical modelling.
For example, it is shown that some of the recently discovered compact
elliptical galaxies at 1.5 < z < 2.5 may be the bulges of modern disc galaxies. | Kahler moduli double inflation: We show that double inflation is naturally realized in K\"ahler moduli
inflation, which is caused by moduli associated with string compactification.
We find that there is a small coupling between the two inflatons which leads to
amplification of perturbations through parametric resonance in the intermediate
stage of double inflation. This results in the appearance of a peak in the
power spectrum of the primordial curvature perturbation. We numerically
calculate the power spectrum and show that the power spectrum can have a peak
on observationally interesing scales. We also compute the TT-spectrum of CMB
based on the power spectrum with a peak and see that it better fits WMAP
7-years data. |
Orbital anisotropy in cosmological haloes revisited: The velocity anisotropy of particles inside dark matter (DM) haloes is an
important physical quantity, which is required for the accurate modelling of
mass profiles of galaxies and clusters of galaxies. It is typically measured
using the ratio of the radial-to-tangential velocity dispersions at a given
distance from the halo centre. However, this measure is insufficient to
describe the dynamics of realistic haloes, which are typically quite elongated.
Studying the velocity distribution in massive DM haloes in cosmological
simulations, we find that in the inner parts of the haloes the local velocity
ellipsoids are strongly aligned with the major axis of the halo, the alignment
being stronger for more relaxed haloes. In the outer regions of the haloes, the
alignment becomes gradually weaker and the orientation is more random. These
two distinct regions of different degree of the alignment coincide with two
characteristic regimes of the DM density profile: shallower and steeper than
\rho r^{-2}. This alignment of the local velocity ellipsoids requires
reinterpretation of features found in measurements based on the spherically
averaged ratio of the radial-to-tangential velocity dispersions. In particular,
we show that the velocity distribution in the central halo regions is highly
anisotropic. For cluster-size haloes with mass 10^{14}-10^{15} h^-1 Msun, the
velocity anisotropy along the major axis is nearly independent of radius and is
equal to \beta=1-\sigma^2_{perp}/\sigma^2_{radial}=0.4, which is significantly
larger than the previously estimated spherically averaged velocity anisotropy.
The alignment of density and velocity anisotropies, and the radial trends may
also have some implications for the mass modelling based on kinematical data of
such objects as galaxy clusters or dwarf spheroidals, where the orbital
anisotropy is a key element in an unbiased mass inference. | The effect of local universe constraints on halo abundance and
clustering: Cosmological $N$-body simulations of the dark matter component of the
universe typically use initial conditions with a fixed power spectrum and
random phases of the density field, leading to structure consistent with the
local distribution of galaxies only in a statistical sense. It is, however,
possible to infer the initial phases which lead to the configuration of
galaxies and clusters that we see around us. We analyse the CSiBORG suite of
101 simulations, formed by constraining the density field within 155 Mpc$/h$
with dark matter particle mass $4.38\times10^9 M_\odot$, to quantify the degree
to which constraints imposed on 2.65 Mpc$/h$ scales reduce variance in the halo
mass function and halo-halo cross-correlation function on a range of scales.
This is achieved by contrasting CSiBORG with a subset of the unconstrained
Quijote simulations and expectations for the $\Lambda$CDM average. Using the
FOF, PHEW and HOP halofinders, we show that the CSiBORG suite beats cosmic
variance at large mass scales ($\gtrsim 10^{14}M_{\odot}/h$), which are most
strongly constrained by the initial conditions, and exhibits a significant
halo-halo cross-correlation out to $\sim30$ Mpc$/h$. Moreover, the effect of
the constraints percolates down to lower mass objects and to scales below those
on which they are imposed. Finally, we develop an algorithm to "twin" halos
between realisations and show that approximately 50% of halos with mass greater
than $10^{15}M_{\odot}/h$ can be identified in all realisations of the CSiBORG
suite. We make the CSiBORG halo catalogues publicly available for future
applications requiring knowledge of the local halo field. |
Cosmology with Strong Lensing Systems: In this paper, we assemble a catalog of 118 strong gravitational lensing
systems from SLACS, BELLS, LSD and SL2S surveys and use them to constrain the
cosmic equation of state. In particular we consider two cases of dark energy
phenomenology: $XCDM$ model where dark energy is modeled by a fluid with
constant $w$ equation of state parameter and in Chevalier - Polarski - Linder
(CPL) parametrization where $w$ is allowed to evolve with redshift: $w(z) = w_0
+ w_1 \frac{z}{1+z}$. We assume spherically symmetric mass distribution in
lensing galaxies, but relax the rigid assumption of SIS model in favor to more
general power-law index $\gamma$, also allowing it to evolve with redshifts
$\gamma(z)$. Our results for the $XCDM$ cosmology show the agreement with
values (concerning both $w$ and $\gamma$ parameters) obtained by other authors.
We go further and constrain the CPL parameters jointly with $\gamma(z)$. The
resulting confidence regions for the parameters are much better than those
obtained with a similar method in the past. They are also showing a trend of
being complementary to the supernova Ia data. Our analysis demonstrates that
strong gravitational lensing systems can be used to probe cosmological
parameters like the cosmic equation of state for dark energy. Moreover, they
have a potential to judge whether the cosmic equation of state evolved with
time or not. | On the formation of Lyman $α$ emission from resonantly scattered
continuum photons of GRB's afterglow: We study the formation and evolution of the spectral imprint of resonantly
scattered Lyman $\alpha$ photons in the context of GRB's continuum optical
afterglow. Based on an analytic model and a complete treatment of all the
scatterings using Monte Carlo simulations, we found that the flux of the
Ly$\alpha$ emission is mainly contributed by photons which are scattered only
once. The flux is of order $10^{-4}$ to $10^{-9}$ relative to the undecayed
maximum flux of the transmitted continuum, making the feature negligible but
potentially observable. If not obscured by host galaxy's DLA or intergalactic
neutral hydrogen, the feature may appear sometime from one hour to several
years when the directly transmitted light has faded away.This scattered
emission feature can be distinguished from Ly$\alpha$ photons of other origins
by its luminosity evolution, and by its gradual narrowing of profile with time.
The typical time scale for spectral variance is that of the light crossing time
of a hydrogen clump close to the GRB. |
Moderate Galaxy-Galaxy Lensing: We study moderate gravitational lensing where a background galaxy is
magnified substantially, but not multiply imaged, by an intervening galaxy. We
focus on the case where both the lens and source are elliptical galaxies. The
signatures of moderate lensing include isophotal distortions and systematic
shifts in the fundamental plane and Kormendy relation, which can potentially be
used to statistically determine the galaxy mass profiles. These effects are
illustrated using Monte Carlo simulations of galaxy pairs where the foreground
galaxy is modelled as a singular isothermal sphere model and observational
parameters appropriate for the Large Synoptic Survey Telescope (LSST). The
range in radius probed by moderate lensing will be larger than that by strong
lensing, and is in the interesting regime where the density slope may be
changing. | Brightest Cluster Galaxies and Core Gas Density in REXCESS Clusters: We investigate the relationship between brightest cluster galaxies (BCGs) and
their host clusters using a sample of nearby galaxy clusters from the
Representative XMM Cluster Structure Survey (REXCESS). The sample was imaged
with the Southern Observatory for Astrophysical Research (SOAR) in R band to
investigate the mass of the old stellar population. Using a metric radius of
12h^-1 kpc, we found that the BCG luminosity depends weakly on overall cluster
mass as L_BCG \propto M_cl^0.18+-0.07, consistent with previous work. We found
that 90% of the BCGs are located within 0.035 r_500 of the peak of the X-ray
emission, including all of the cool core (CC) clusters. We also found an
unexpected correlation between the BCG metric luminosity and the core gas
density for non-cool core (non-CC) clusters, following a power law of n_e
\propto L_BCG^2.7+-0.4 (where n_e is measured at 0.008 r_500). The correlation
is not easily explained by star formation (which is weak in non-CC clusters) or
overall cluster mass (which is not correlated with core gas density). The trend
persists even when the BCG is not located near the peak of the X-ray emission,
so proximity is not necessary. We suggest that, for non-CC clusters, this
correlation implies that the same process that sets the central entropy of the
cluster gas also determines the central stellar density of the BCG, and that
this underlying physical process is likely to be mergers. |
Probing the end of reionization with the near-zones of z > 6 QSOs: QSO near-zones are an important probe of the the ionization state of the IGM
at z ~ 6-7, at the end of reionization. We present here high-resolution
cosmological 3D radiative transfer simulations of QSO environments for a wide
range of host halo masses, 10$^{10-12.5}$ M_sun. Our simulated near-zones
reproduce both the overall decrease of observed near-zone sizes at 6 < z < 7
and their scatter. The observable near-zone properties in our simulations
depend only very weakly on the mass of the host halo. The size of the H II
region expanding into the IGM is generally limited by (super-)Lyman Limit
systems loosely associated with (low-mass) dark matter haloes. This leads to a
strong dependence of near-zone size on direction and drives the large observed
scatter. In the simulation centred on our most massive host halo, many
sightlines show strong red damping wings even for initial volume averaged
neutral hydrogen fractions as low as ~ 10$^{-3}$. For QSO lifetimes long enough
to allow growth of the central supermassive black hole while optically bright,
we can reproduce the observed near-zone of ULAS J1120+0641 only with an IGM
that is initially neutral. Our results suggest that larger samples of z > 7
QSOs will provide important constraints on the evolution of the neutral
hydrogen fraction and thus on how late reionization ends. | Late time transitions in the quintessence field and the $H_0$ tension: We consider a quintessence field which transitions from a matter-like to a
cosmological constant behavior between recombination and the present time. We
aim at easing the tension in the measurement of the present Hubble rate, and we
assess the $\Lambda$CDM model properly enlarged to include our quintessence
field against cosmological observations. The model does not address the scope
we proposed. This result allows us to exclude a class of quintessential models
as a solution to the tension in the Hubble constant measurements. |
The Growth of the Stellar Seeds of Supermassive Black Holes: The collapse of baryons into extremely massive stars with masses exceeding
10^4 M_Sun in a small fraction of protogalaxies at z > 10 is a promising
candidate for the origin of supermassive black holes, some of which grow to a
billion solar masses by z ~ 7. We determine the maximum masses such stars can
attain by accreting primordial gas. We find that at relatively low accretion
rates the strong ionizing radiation of these stars limits their masses to M_* ~
10^3 M_Sun (dM_acc/dt / 10^-3 M_Sun yr^-1)^8/7, where dM_acc/dt is the rate at
which the star gains mass. However, at the higher central infall rates usually
found in numerical simulations of protogalactic collapse (>~ 0.1 M_Sun yr^-1),
the lifetime of the star instead limits its final mass to >~ 10^6 M_Sun.
Furthermore, for the spherical accretion rates at which the star can grow, its
ionizing radiation is confined deep within the protogalaxy, so the evolution of
the star is decoupled from that of its host galaxy. Lyman alpha emission from
the surrounding H II region is trapped in these heavy accretion flows and
likely reprocessed into strong Balmer series emission, which may be observable
by the James Webb Space Telescope. This, along with strong He II 1640 Angstrom
and continuum emission, are likely to be the key observational signatures of
the progenitors of supermassive black holes at high redshift. | The galaxy bias at second order in general relativity with Non-Gaussian
initial conditions: We present a systematic study of galaxy bias in the presence of primordial
non-Gaussianity in General Relativity (GR) at second order in perturbation
theory. The non-linearity of the Poisson equation in GR and primordial
non-Gaussianity are consistently included. We show that the inclusion of
non-local primordial non-Gaussianity in addition to local non-Gaussianity is
important to show the absence of the modulation of small scale clustering by
the long-wavelength mode in the single field slow-roll inflation. We study the
bispectrum of the relativistic galaxy density in several gauges and identify
the effect of primordial non-Gaussianity and GR corrections. |
Constraints on Primordial Magnetic Fields from Inflation: We present generic bounds on magnetic fields produced from cosmic inflation.
By investigating field bounds on the vector potential, we constrain both the
quantum mechanical production of magnetic fields and their classical growth in
a model independent way. For classical growth, we show that only if the
reheating temperature is as low as T_{reh} <~ 10^2 MeV can magnetic fields of
10^{-15} G be produced on Mpc scales in the present universe. For purely
quantum mechanical scenarios, even stronger constraints are derived. Our bounds
on classical and quantum mechanical scenarios apply to generic theories of
inflationary magnetogenesis with a two-derivative time kinetic term for the
vector potential. In both cases, the magnetic field strength is limited by the
gravitational back-reaction of the electric fields that are produced
simultaneously. As an example of quantum mechanical scenarios, we construct
vector field theories whose time diffeomorphisms are spontaneously broken, and
explore magnetic field generation in theories with a variable speed of light.
Transitions of quantum vector field fluctuations into classical fluctuations
are also analyzed in the examples. | Metal distribution in sloshing galaxy clusters: the case of A496: We report results from a detailed study of the sloshing gas in the core of
A496. We detect the low temperature/entropy spiral feature found in several
cores, we also find that conduction between the gas in the spiral and the
ambient medium must be suppressed by more than one order of magnitude with
respect to Spitzer conductivity. Intriguingly, while the gas in the spiral
features a higher metal abundance than the surrounding medium, it follows the
entropy vs metal abundance relation defined by gas lying outside the spiral.
The most plausible explanation for this behavior is that the low entropy metal
rich plasma uplifted through the cluster atmosphere by sloshing, suffers little
heating or mixing with the ambient medium. While sloshing appears to be capable
of uplifting significant amounts of gas, the limited heat exchange and mixing
between gas in and outside the spiral implies that this mechanism is not at all
effective in: 1) permanently redistributing metals within the core region and
2) heating up the coolest and densest gas, thereby providing little or no
contribution to staving of catastrophic cooling in cool cores. |
zCOSMOS - 10k-bright spectroscopic sample. The bimodality in the Galaxy
Stellar Mass Function: exploring its evolution with redshift: We present the Galaxy Stellar Mass Function (MF) up to z~1 from the
zCOSMOS-bright 10k spectroscopic sample. We investigate the total MF and the
contribution of ETGs and LTGs, defined by different criteria (SED, morphology
or star formation). We unveil a galaxy bimodality in the global MF, better
represented by 2 Schechter functions dominated by ETGs and LTGs, respectively.
For the global population we confirm that low-mass galaxies number density
increases later and faster than for massive galaxies. We find that the MF
evolution at intermediate-low values of Mstar (logM<10.6) is mostly explained
by the growth in stellar mass driven by smoothly decreasing star formation
activities. The low residual evolution is consistent with ~0.16 merger per
galaxy per Gyr (of which fewer than 0.1 are major). We find that ETGs increase
in number density with cosmic time faster for decreasing Mstar, with a median
"building redshift" increasing with mass, in contrast with hierarchical models.
For LTGs we find that the number density of blue or spiral galaxies remains
almost constant from z~1. Instead, the most extreme population of active star
forming galaxies is rapidly decreasing in number density. We suggest a
transformation from blue active spirals of intermediate mass into blue
quiescent and successively (1-2 Gyr after) into red passive types. The complete
morphological transformation into red spheroidals, required longer time-scales
or follows after 1-2 Gyr. A continuous replacement of blue galaxies is expected
by low-mass active spirals growing in stellar mass. We estimate that on average
~25% of blue galaxies is transforming into red per Gyr for logM<11. We conclude
that the build-up of galaxies and ETGs follows the same downsizing trend with
mass as the formation of their stars, converse to the trend predicted by
current SAMs. We expect a negligible evolution of the global Galaxy Baryonic
MF. | The Full-Sky Angular Bispectrum in Redshift Space: We compute the redshift-dependent angular bispectrum of galaxy number counts
at tree-level, including nonlinear clustering bias and estimating numerically
for the first time the effect of redshift space distortions (RSD). We show that
for narrow redshift bins the amplitude of nonlinear RSD is comparable with the
matter density perturbations. While our numerical results only include terms
relevant on sub-horizon scales, the formalism can readily be extended to the
full tree-level bispectrum. Our approach does not rely on the flat-sky
approximation and it can be easily generalized to different sources by
including the appropriate bias expansion. We test the accuracy of Limber
approximation for different z-bins. We highlight the subtle but relevant
differences in the angular bispectrum of galaxy number counts with respect to
CMB, due to the different scale dependence of perturbations. Our formalism can
also be directly applied to the angular HI intensity mapping bispectrum. |
Strong gravitational lensing and microlensing of supernovae: Strong gravitational lensing and microlensing of supernovae (SNe) are
emerging as a new probe of cosmology and astrophysics in recent years. We
provide an overview of this nascent research field, starting with a summary of
the first discoveries of strongly lensed SNe. We describe the use of the time
delays between multiple SN images as a way to measure cosmological distances
and thus constrain cosmological parameters, particularly the Hubble constant,
whose value is currently under heated debates. New methods for measuring the
time delays in lensed SNe have been developed, and the sample of lensed SNe
from the upcoming Rubin Observatory Legacy Survey of Space and Time (LSST) is
expected to provide competitive cosmological constraints. Lensed SNe are also
powerful astrophysical probes. We review the usage of lensed SNe to constrain
SN progenitors, acquire high-z SN spectra through lensing magnifications, infer
SN sizes via microlensing, and measure properties of dust in galaxies. The
current challenge in the field is the rarity and difficulty in finding lensed
SNe. We describe various methods and ongoing efforts to find these spectacular
explosions, forecast the properties of the expected sample of lensed SNe from
upcoming surveys particularly the LSST, and summarize the observational
follow-up requirements to enable the various scientific studies. We anticipate
the upcoming years to be exciting with a boom in lensed SN discoveries. | Predicted multiply-imaged X-ray AGNs in the XXL survey: We estimate the incidence of multiply-imaged AGNs among the optical
counterparts of X-ray selected point-like sources in the XXL field. We also
derive the expected statistical properties of this sample, such as the redshift
distribution of the lensed sources and of the deflectors that lead to the
formation of multiple images, modelling the deflectors using both spherical
(SIS) and ellipsoidal (SIE) singular isothermal mass distributions. We further
assume that the XXL survey sample has the same overall properties as the
smaller XMM-COSMOS sample restricted to the same flux limits and taking into
account the detection probability of the XXL survey. Among the X-ray sources
with a flux in the [0.5-2] keV band larger than 3.0x10$^{-15}$ erg cm$^{-2}$
s$^{-1}$ and with optical counterparts brighter than an r-band magnitude of 25,
we expect ~20 multiply-imaged sources. Out of these, ~16 should be detected if
the search is made among the seeing-limited images of the X-ray AGN optical
counterparts and only one of them should be composed of more than two lensed
images. Finally, we study the impact of the cosmological model on the expected
fraction of lensed sources. |
The migration of nearby spirals from the blue to red sequence: AGN
feedback or environmental effects?: We combine ultraviolet to near-infrared photometry with HI 21cm line
observations for a complete volume-limited sample of nearby galaxies in
different environments (from isolated galaxies to Virgo cluster members), to
study the migration of spirals from the blue to the red sequence. Although our
analysis confirms that, in the transition region between the two sequences, a
high fraction of spirals host active galactic nuclei (AGN), it clearly shows
that late-types with quenched star formation are mainly HI deficient galaxies
preferentially found in the Virgo cluster. This not only suggests that
environmental effects could play a significant role in driving the migration of
local galaxies from the blue sequence, but it also implies that a physical link
between AGN feedback and quenching may not be assumed from a correlation
between nuclear activity and colour. | Accretion History of Subhalo Population now and then: In the standard model of structure formation galaxies reside in virialized
dark matter haloes which extend much beyond the observational radius of the
central system. The dark matter halo formation process is hierarchical, small
systems collapse at high redshift and then merge together forming larger ones.
In this work we study the mass assembly history of host haloes at different
observation redshifts and the mass function of accreted satellites (haloes that
merge directly on the main halo progenitor). We show that the satellite mass
function is universal, both independent on the host halo mass and observation
redshift. The satellite mass function also turn out to be universal once only
satellites before or after the host halo formation redshift (time at which the
main halo progenitor assembles half of its final mass) are considered. We show
that the normalizations of these distributions are directly related to the main
halo progenitor mass distributions before and after its formation, while their
slope and the exponential high mass cut-off remain unchanged. |
Scalar Bispectrum Beyond Slow-Roll in the Unified EFT of Inflation: We present a complete formulation of the scalar bispectrum in the unified
effective field theory (EFT) of inflation, which includes the Horndeski and
beyond-Horndeski Gleyzes-Langlois-Piazza-Vernizzi classes, in terms of a set of
simple one-dimensional integrals. These generalized slow-roll expressions
remain valid even when slow-roll is transiently violated and encompass all
configurations of the bispectrum. We show analytically that our expressions
explicitly preserve the squeezed-limit consistency relation beyond slow-roll.
As an example application of our results, we compute the scalar bispectrum in a
model in which potential-driven G-inflation at early times transitions to
chaotic inflation at late times, showing that our expressions accurately track
the bispectrum when slow-roll is violated and conventional slow-roll
approximations fail. | Detecting shocked intergalactic gas with X-ray and radio observations: Detecting the thermal and non-thermal emission from the shocked cosmic gas
surrounding large-scale structures represents a challenge for observations, as
well as a unique window into the physics of the warm-hot intergalactic medium.
In this work, we present synthetic radio and X-ray surveys of large
cosmological simulations in order to assess the chances of jointly detecting
the cosmic web in both frequency ranges. We then propose best observing
strategies tailored for existing (LOFAR, MWA and XMM) or future instruments
(SKA-LOW and SKA-MID, ATHENA and eROSITA). We find that the most promising
targets are the extreme peripheries of galaxy clusters in an early merging
stage, where the merger causes the fast compression of warm-hot gas onto the
virial region. By taking advantage of a detection in the radio band, future
deep X-ray observations will probe this gas in emission, and help us to study
plasma conditions in the dynamic warm-hot intergalactic medium with
unprecedented detail. |
Golden gravitational lensing systems from the Sloan Lens ACS Survey. I.
SDSS J1538+5817: one lens for two sources: We present a lensing and photometric study of the exceptional system SDSS
J1538+5817, identified by the SLACS survey. The lens is a luminous elliptical
at redshift z=0.143. Using HST public images in two different filters, the
presence of two background sources lensed into an Einstein ring and a double
system is ascertained. Our new spectroscopic observations, performed at the
NOT, reveal that the two sources are located at the same redshift z=0.531. We
investigate the total mass distribution of the lens between 1 and 4 kpc from
the galaxy center by means of parametric and non-parametric lensing codes that
describe the multiple images as point-like objects. Several disparate lensing
models agree on: (1) reproducing accurately the observed image positions; (2)
predicting a nearly axisymmetric total mass distribution, centered and oriented
as the light distribution; (3) measuring a value of 8.11 x 10^{10} M_{Sun} for
the total mass projected within the Einstein radius of 2.5 kpc; (4) estimating
a total mass density profile slightly steeper than an isothermal one. A fit of
the SDSS multicolor photometry with CSP models provides a value of 20 x 10^{10}
M_{Sun} for the total stellar mass of the galaxy and of 0.9 for the fraction of
projected luminous over total mass enclosed inside the Einstein radius. By
combining lensing and photometric mass measurements, we differentiate the lens
mass content in terms of luminous and dark matter components. This
two-component modeling, which is viable only in extraordinary systems like SDSS
J1538+5817, leads to a description of the global properties of the galaxy dark
matter halo. Extending these results to a larger number of lenses would improve
considerably our understanding of galaxy formation and evolution processes in
the LCDM scenario. | Detecting Adiabatic Contraction in Rotation Curves: We examine the structure of adiabatically contracted Einasto profiles, using
the prescriptions of Blumenthal et al. (1986) and Gnedin et al. (2004), and its
impact on rotation curves. Adiabatically contracted halos display a central
power index of ~0.7+/-0.1 for nearly all values of the Einasto shape parameter,
alpha, and are well fit inside ~>1 kpc by double power laws. However, attempts
to fit exponential disc and uncontracted halos to adiabatically contracted
rotation curves yield disc masses and central power indices that are too large.
We also determine whether or not the rotation curve of NGC 6503 displays
evidence of adiabatic contraction using previously published bar formation
constraints, and find that NGC 6503 most likely has a minimally contracted
halo. However, this conclusion depends on the correct choice of circular
velocity curve. |
Stable analytic bounce in non-local Einstein-Gauss-Bonnet cosmology: We consider the most general quadratic in curvature stringy motivated
non-local action for the modified Einstein's gravity. We present exact analytic
cosmological solutions including the bouncing ones and develop the relevant
techniques for the further study of this type of models. We also elaborate on
the perturbation formalism and argue that the found bouncing solution is stable
during the bounce phase. | The splashback radius as a physical halo boundary and the growth of halo
mass: The boundaries of cold dark matter halos are commonly defined to enclose a
density contrast $\Delta$ relative to a reference (mean or critical) density.
We argue that a more physical boundary of halos is the radius at which accreted
matter reaches its first orbital apocenter after turnaround. This splashback
radius, $R_{sp}$, manifests itself as a sharp density drop in the halo
outskirts, at a location that depends upon the mass accretion rate. We present
calibrations of $R_{sp}$ and the enclosed mass, $M_{sp}$, as a function of the
accretion rate and alternatively peak height. We find that $R_{sp}$ varies
between $\approx0.8-1R_{200m}$ for rapidly accreting halos and
$\approx1.5R_{200m}$ for slowly accreting halos. The extent of a halo and its
associated environmental effects can thus extend well beyond the conventionally
defined "virial" radius. We show that $M_{sp}$ and $R_{sp}$ evolve relatively
strongly compared to other commonly used definitions. In particular, $M_{sp}$
evolves significantly even for the smallest dwarf-sized halos at $z=0$. We also
contrast $M_{sp}$ with the mass enclosed within four scale radii of the halo
density profile, $M_{<4rs}$, which characterizes the inner halo. During the
early stages of halo assembly, $M_{sp}$ and $M_{<4rs}$ evolve similarly, but in
the late stages $M_{<4rs}$ stops increasing while $M_{sp}$ continues to grow
significantly. This illustrates that halos at low $z$ can have "quiet"
interiors while continuing to accrete mass in their outskirts. We discuss
potential observational estimates of the splashback radius and show that it may
already have been detected in galaxy clusters. |
Modelling redshift-space distortion in the post-reionization ${\rm HI}$
21-cm power spectrum: The post-reionization ${\rm HI}$ 21-cm signal is an excellent candidate for
precision cosmology, this however requires accurate modelling of the expected
signal. Sarkar et al. (2016) have simulated the real space ${\rm HI}$ 21-cm
signal, and have modelled the ${\rm HI}$ power spectrum as $P_{{\rm HI}}(k)=b^2
P(k)$ where $P(k)$ is the dark matter power spectrum and $b(k)$ is a (possibly
complex) scale dependent bias for which fitting formulas have been provided.
This paper extends these simulations to incorporate redshift space distortion
and predict the expected redshift space ${\rm HI}$ 21-cm power spectrum
$P^s_{{\rm HI}}(k_{\perp},k_{\parallel})$ using two different prescriptions for
the ${\rm HI}$ distributions and peculiar velocities. We model $P^s_{{\rm
HI}}(k_{\perp},k_{\parallel})$ assuming that it is the product of $P_{{\rm
HI}}(k)=b^2 P(k)$ with a Kaiser enhancement term and a Finger of God (FoG)
damping which has $\sigma_p$ the pair velocity dispersion as a free parameter.
Considering several possibilities for the bias and the damping profile, we find
that the models with a scale dependent bias and a Lorentzian damping profile
best fit the simulated $P^s_{{\rm HI}}(k_{\perp},k_{\parallel})$ over the
entire range $1 \le z \le 6$. The best fit value of $\sigma_p$ falls
approximately as $(1+z)^{-m}$ with $m=2$ and $1.2$ respectively for the two
different prescriptions. The model predictions are consistent with the
simulations for $k < 0.3 \, {\rm Mpc}^{-1}$ over the entire $z$ range for the
monopole $P^s_0(k)$, and at $z \le 3$ for the quadrupole $P^s_2(k)$. At $z \ge
4$ the models underpredict $P^s_2(k)$ at large $k$, and the fit is restricted
to $k < 0.15 \, {\rm Mpc}^{-1}$. | Reconstructing the growth index $γ$ with Gaussian Processes: Alternative cosmological models have been proposed to alleviate the tensions
reported in the concordance cosmological model, or to explain the current
accelerated phase of the universe. One way to distinguish between General
Relativity and modified gravity models is using current astronomical data to
measure the growth index $\gamma$, a parameter related to the growth of matter
perturbations, which behaves differently in different metric theories. We
propose a model independent methodology for determining $\gamma$, where our
analyses combine diverse cosmological data sets, namely $\{ f(z_i) \}$, $\{
[f\sigma_8](z_i) \}$, and $\{ H(z_i) \}$, and use Gaussian Processes, a
non-parametric approach suitable to reconstruct functions. This methodology is
a new consistency test for $\gamma$ constant. Our results show that, for the
redshift interval $0 < z < 1$, $\gamma$ is consistent with the constant value
$\gamma = 0.55$, expected in General Relativity theory, within $2 \sigma$
confidence level (CL). Moreover, we find $\gamma(z=0)$ = $0.311 \pm 0.229$ and
$\gamma(z=0) = 0.336 \pm 0.107$ for the reconstructions using the $\{ f(z_i)
\}$ and $\{ [f\sigma_8](z_i) \}$ data sets, respectively, values that also
agree at a 2$\sigma$ CL with $\gamma = 0.55$. Our main results are a third way
in light of the current discussion in literature that point out to some
possible evidence for the growth index evolution. |
The impact of the locally measured Hubble parameter on the mass of
Sterile neutrino: We present a precise analysis to test hypothetical models involving sterile
neutrinos beyond the standard flat-$\Lambda$CDM cosmology with the CMB
observations from the $Planck$ mission and BAO measurements. This analysis
shows that adding the locally measured Hubble parameter $H_{0}$ = $73.00\pm1.75
$ km $\textrm s^{-1}$ Mp$\textrm c^{-1} $ to the data removes the need for the
informative physical $m_{sterile}^{thermal}$ prior in CMB constraints of $
m_{\nu,sterile}^{eff}$. Under the constraints from the data containing the
locally measured $H_{0}$ we obtain an upper limit $ m_{\nu,sterile}^{eff} <
0.306 $ eV scale mass for the massive sterile neutrino, and an upper limit
$\Sigma m_{\nu} < 0.214$ eV scale mass for the three degenerate massive
neutrino (95 per cent confidence level). We also obtain the value $\sigma_{8} $
= $0.81^{+0.05}_{-0.06} $ (95 per cent confidence level), which is in
compatibility with the constraints from $Planck$ 2015 CMB data at the 1$\sigma$
level. We find that introducing parameter $ m_{\nu,sterile}^{eff}$ to the model
of cosmology reduces the $\sigma_{8} $ value and moves it closer to the
obtained value for this parameter from the KiDS-450 analysis. Our results show
that the locally measured Hubble parameter can increase constraints on
$\sigma_{8} $ values. | Cosmic acceleration and the challenge of modifying gravity: I briefly discuss the challenges presented by attempting to modify general
relativity to obtain an explanation for the observed accelerated expansion of
the universe. Foremost among these are the questions of theoretical consistency
- the avoidance of ghosts in particular - and the constraints imposed by
precision local tests of gravity within the solar system. For those models that
clear these highly constraining hurdles, modern observational cosmology offers
its own suite of tests, improving with upcoming datasets, that offer the
possibility of ruling out modified gravity approaches or providing an
intriguing hint of new infrared physics. In the second half of the talk, I
discuss a recent approach to extracting cosmology from higher-dimensional
induced gravity models. |
Large-scale variation in reionization history caused by Baryon-dark
matter streaming velocity: At cosmic recombination, there was supersonic relative motion between baryons
and dark matter, which originated from the baryonic acoustic oscillations in
the early universe. This motion has been considered to have a negligible impact
on the late stage of cosmic reionization because the relative velocity quickly
decreases. However, recent studies have suggested that the recombination in gas
clouds smaller than the local Jeans mass ($\lesssim$ $10^8~M_\odot$) can affect
the reionization history by boosting the number of ultraviolet photons required
for ionizing the intergalactic medium. Motivated by this, we performed a series
of radiation-hydrodynamic simulations to investigate whether the streaming
motion can generate variation in the local reionization history by smoothing
out clumpy small-scale structures and lowering the ionizing photon budget. We
found that the streaming velocity can add a variation of $\Delta z_e$ $\sim$
$0.05$ $-$ $0.5$ in the end-of-reionization redshift, depending on the level of
X-ray preheating and the time evolution of ionizing sources. The variation
tends to be larger when the ionizing efficiency of galaxies decreases toward
later times. Given the long spatial fluctuation scales of the streaming motion
($\gtrsim 100$ Mpc), it can help to explain the Ly$\alpha$ opacity variation
observed from quasars and leave large-scale imprints on the ionization field of
the intergalactic medium during the reionization. The pre-reionization heating
by X-ray sources is another critical factor that can suppress small-scale gas
clumping and can diminish the variation in $z_e$ introduced by the streaming
motion. | Search for annual and diurnal rate modulations in the LUX experiment: Various dark matter models predict annual and diurnal modulations of dark
matter interaction rates in Earth-based experiments as a result of the Earth's
motion in the halo. Observation of such features can provide generic evidence
for detection of dark matter interactions. This paper reports a search for both
annual and diurnal rate modulations in the LUX dark matter experiment using
over 20 calendar months of data acquired between 2013 and 2016. This search
focuses on electron recoil events at low energies, where leptophilic dark
matter interactions are expected to occur and where the DAMA experiment has
observed a strong rate modulation for over two decades. By using the innermost
volume of the LUX detector and developing robust cuts and corrections, we
obtained a stable event rate of 2.3$\pm$0.2~cpd/keV$_{\text{ee}}$/tonne, which
is among the lowest in all dark matter experiments. No statistically
significant annual modulation was observed in energy windows up to
26~keV$_{\text{ee}}$. Between 2 and 6~keV$_{\text{ee}}$, this analysis
demonstrates the most sensitive annual modulation search up to date, with
9.2$\sigma$ tension with the DAMA/LIBRA result. We also report no observation
of diurnal modulations above 0.2~cpd/keV$_{\text{ee}}$/tonne amplitude between
2 and 6~keV$_{\text{ee}}$. |
Oscillations in the dark energy EoS: new MCMC lessons: We study the possibility of detecting oscillating patterns in the equation of
state (EoS) of the dark energy using different cosmological datasets. We follow
a phenomenological approach and study three different oscillating models for
the EoS, one of them periodic and the other two damped (proposed here for the
first time). All the models are characterised by the amplitude value, the
centre and the frequency of oscillations. In contrast to previous works in the
literature, we do not fix the value of the frequency to a fiducial value
related to the time extension of chosen datasets, but consider a discrete set
of values, so to avoid arbitrariness and try and detect any possible time
period in the EoS. We test the models using a recent collection of SNeIa,
direct Hubble data and Gamma Ray Bursts data. Main results are: I. even if
constraints on the amplitude are not too strong, we detect a trend of it versus
the frequency, i.e. decreasing (and even negatives) amplitudes for higher
frequencies; II. the centre of oscillation (which corresponds to the present
value of the EoS parameter) is very well constrained, phantom behaviour is
excluded at $1\sigma$ level and trend which is in agreement with the one for
the amplitude appears; III. the frequency is hard to constrain, showing similar
statistical validity for all the values of the discrete set chosen, but the
best fit of all the scenarios considered is associated with a period which is
in the redshift range depicted by our cosmological data. The "best" oscillating
models are compared with $\Lambda$CDM using dimensionally consistent a Bayesian
approach based information criterion and the conclusion reached is the non
existence of significant evidence against dark energy oscillations. | A new double radio relic in PSZ1 G096.89+24.17 and a radio relic
mass-luminosity relation: Radio relics are diffuse synchrotron sources in galaxy clusters that are
believed to trace large-scale shock waves. We have discovered a new double
radio relic system in PSZ1 G096.89+24.17 (z=0.3) and have carried out a
full-polarization radio observation using the Westerbork Synthesis Radio
Telescope (WSRT) at 1.4 GHz. The observation revealed the presence of two
relics located on the two diametrically opposite sides of the cluster and hints
of a central radio halo. The linear sizes of the relics are $\sim 0.9$ and
$\sim 1.4$ Mpc.
We carried out an analysis of all known double radio relics by using radio,
X-ray and Sunyaev-Zeldovich (SZ) data. We find that the radio luminosity of
double relics is a steep function of the cluster mass, with $L_R \propto
M^{2.83\pm0.39}$. If we include single radio relics, this relation is
maintained. This dependence has implications for the origin of magnetic fields
at the relic's locations. |
A Unified Description of Screened Modified Gravity: We consider modified gravity models driven by a scalar field whose effects
are screened in high density regions due to the presence of non-linearities in
its interaction potential and/or its coupling to matter. Our approach covers
chameleon, f(R) gravity, dilaton and symmetron models and allows a unified
description of all these theories. We find that the dynamics of modified
gravity are entirely captured by the time variation of the scalar field mass
and its coupling to matter evaluated at the cosmological minimum of its
effective potential, where the scalar field sits since an epoch prior to Big
Bang Nucleosynthesis. This new parameterisation of modified gravity allows one
to reconstruct the potential and coupling to matter and therefore to analyse
the full dynamics of the models, from the scale dependent growth of structures
at the linear level to non-linear effects requiring N-body simulations. This
procedure is illustrated with explicit examples of reconstruction for
chameleon, dilaton, f(R) and symmetron models. | Planck 2015 results. III. LFI systematic uncertainties: We present the current accounting of systematic effect uncertainties for the
Low Frequency Instrument (LFI) that are relevant to the 2015 release of the
Planck cosmological results, showing the robustness and consistency of our data
set, especially for polarization analysis. We use two complementary approaches:
(i) simulations based on measured data and physical models of the known
systematic effects; and (ii) analysis of difference maps containing the same
sky signal ("null-maps"). The LFI temperature data are limited by instrumental
noise. At large angular scales the systematic effects are below the cosmic
microwave background (CMB) temperature power spectrum by several orders of
magnitude. In polarization the systematic uncertainties are dominated by
calibration uncertainties and compete with the CMB $E$-modes in the multipole
range 10--20. Based on our model of all known systematic effects, we show that
these effects introduce a slight bias of around $0.2\,\sigma$ on the
reionization optical depth derived from the 70\,GHz $EE$ spectrum using the 30
and 353\,GHz channels as foreground templates. At 30\,GHz the systematic
effects are smaller than the Galactic foreground at all scales in temperature
and polarization, which allows us to consider this channel as a reliable
template of synchrotron emission. We assess the residual uncertainties due to
LFI effects on CMB maps and power spectra after component separation and show
that these effects are smaller than the CMB amplitude at all scales. We also
assess the impact on non-Gaussianity studies and find it to be negligible. Some
residuals still appear in null maps from particular sky survey pairs,
particularly at 30 GHz, suggesting possible straylight contamination due to an
imperfect knowledge of the beam far sidelobes. |
Dark neutrino interactions make gravitational waves blue: New interactions of neutrinos can stop them from free streaming in the early
Universe even after the weak decoupling epoch. This results in the enhancement
of the primordial gravitational wave amplitude on small scales compared to the
standard $\Lambda$CDM prediction. In this paper we calculate the effect of dark
matter neutrino interactions in CMB tensor $B$-modes spectrum. We show that the
effect of new neutrino interactions generates a scale or $\ell$ dependent
imprint in the CMB $B$-modes power spectrum at $\ell \gtrsim 100$. In the event
that primordial $B$-modes are detected by future experiments, a departure from
scale invariance, with a blue spectrum, may not necessarily mean failure of
simple inflationary models but instead may be a sign of non-standard
interactions of relativistic particles. New interactions of neutrinos also
induce a phase shift in the CMB B-mode power spectrum which cannot be mimicked
by simple modifications of the primordial tensor power spectrum. There is rich
information hidden in the CMB $B$-modes spectrum beyond just the tensor to
scalar ratio. | Star formation properties in the Local Volume galaxies via $Hα$ and
FUV fluxes: A distance-limited sample of 869 objects from the Updated Nearby Galaxy
Catalog is used to characterize the star formation status of the Local Volume
population. We present a compiled list of 1217 star formation rate (SFR)
estimates for 802 galaxies within 11 Mpc from us, derived from the H-alpha
imaging surveys and GALEX far-ultraviolet survey. We briefly discuss some basic
scaling relations between SFR and luminosity, morphology, HI-mass, surface
brightness, as well as environment of the galaxies. About 3/4 of our sample
consist of dwarf galaxies, for which we offer a more refined classification. We
note that the specific star formation rate of nearly all luminous and dwarf
galaxies does not exceed the maximum value: $\log(SFR/L_K) = -9.4$ [yr$^{-1}$].
The bulk of spiral and blue dwarf galaxies have enough time to generate their
stellar mass during the cosmological time, $T_0$, with the observed SFRs. They
dispose of a sufficient amount of gas to support their present SFRs over the
next $T_0$ term. We note that only a minor part of BCD, Im, and Ir galaxies
(about 1/20) proceeds in a mode of vigorous star-burst activity. In general,
the star formation history of spiral and blue dwarf galaxies is mainly driven
by their internal processes. The present SFRs of E, S0 and dSph galaxies are
typically (1/30 - 1/300) of their former activity. |
A roadmap to cosmological parameter analysis with third-order shear
statistics III: Efficient estimation of third-order shear correlation
functions and an application to the KiDS-1000 data: Third-order lensing statistics contain a wealth of cosmological information
that is not captured by second-order statistics. However, the computational
effort for estimating such statistics on forthcoming stage IV surveys is
prohibitively expensive. We derive and validate an efficient estimation
procedure for the three-point correlation function (3PCF) of polar fields such
as weak lensing shear. We then use our approach to measure the shear 3PCF and
the third-order aperture mass statistics on the KiDS-1000 survey. We construct
an efficient estimator for third-order shear statistics which builds on the
multipole decomposition of the 3PCF. We then validate our estimator on mock
ellipticity catalogs obtained from $N$-body simulations. Finally, we apply our
estimator to the KiDS-1000 data and present a measurement of the third-order
aperture statistics in a tomographic setup. Our estimator provides a speedup of
a factor of $\sim$ 100-1000 compared to the state-of-the-art estimation
procedures. It is also able to provide accurate measurements for squeezed and
folded triangle configurations without additional computational effort. We
report a significant detection of the tomographic third-order aperture mass
statistics in the KiDS-1000 data $(\mathrm{S/N}=6.69)$. Our estimator will make
it computationally feasible to measure third-order shear statistics in
forthcoming stage IV surveys. Furthermore, it can be used to construct
empirical covariance matrices for such statistics. | Strong New Constraints on the Extragalactic Background Light in the
Near- to Mid-IR: Direct measurements of the extragalactic background light (EBL) in the
near-IR to mid-IR waveband are extremely difficult due to an overwhelming
foreground from the zodiacal light that outshines the faint cosmological
diffuse radiation field by more than an order of magnitude. Indirect
constraints on the EBL are provided by gamma-ray observations of AGN. Using the
combination of the Fermi Gamma-Ray Space Telescope together with the current
generation of ground-based air Cherenkov telescopes (H.E.S.S., MAGIC, and
VERITAS) provides unprecedented sensitivity and spectral coverage for
constraining the EBL in the near- to mid-IR. In this paper we present new
limits on the EBL based on the analysis of the broad-band spectra of a select
set of gamma-ray blazars covering 200 MeV to several TeV. The EBL intensity at
15 microns is constrained to be 1.36 +/- 0.58 nW m^-2 sr^-1. We find that the
fast evolution and baseline EBL models of Stecker et al. (2006), as well as the
model of Kneiske et al. (2004), predict significantly higher EBL intensities in
the mid-IR (15 microns) than is allowed by the constraints derived here. In
addition, the model of Franceschini et al. (2008) and the fiducial model of
Dominguez et al. (2011) predict near- to mid-IR ratios smaller than that
predicted by our analysis. Namely, their intensities in the near-IR are too low
while their intensities in the mid-IR are marginally too high. All of the
aforementioned models are inconsistent with our analysis at the >3 sigma level. |
The Sunyaev-Zel'dovich Effect at Five Arc-seconds: RXJ1347.5-1145 Imaged
by ALMA: We present the first image of the thermal Sunyaev-Zel'dovich effect (SZE)
obtained by the Atacama Large Millimeter/submillimeter Array (ALMA). Combining
7-m and 12-m arrays in Band 3, we create an SZE map toward a galaxy cluster
RXJ1347.5-1145 with 5 arc-second resolution (corresponding to the physical size
of 20 kpc/h), the highest angular and physical spatial resolutions achieved to
date for imaging the SZE, while retaining extended signals out to 40
arc-seconds. The 1-sigma statistical sensitivity of the image is 0.017 mJy/beam
or 0.12 mK_CMB at the 5 arc-second full width at half maximum. The SZE image
shows a good agreement with an electron pressure map reconstructed
independently from the X-ray data and offers a new probe of the small-scale
structure of the intracluster medium. Our results demonstrate that ALMA is a
powerful instrument for imaging the SZE in compact galaxy clusters with
unprecedented angular resolution and sensitivity. As the first report on the
detection of the SZE by ALMA, we present detailed analysis procedures including
corrections for the missing flux, to provide guiding methods for analyzing and
interpreting future SZE images by ALMA. | SRoll2: an improved mapmaking approach to reduce large-scale systematic
effects in the Planck High Frequency Instrument legacy maps: This paper describes an improved mapmaking approach with respect to the one
used for the Planck High Frequency Instrument 2018 Legacy release. The
algorithm SRoll2 better corrects the known instrumental effects that still
affected mostly the polarized large-angular-scale data by distorting the
signal, and/or leaving residuals observable in null tests. The main systematic
effect is the nonlinear response of the onboard analog-to-digital convertors
that was cleaned in the Planck HFI Legacy release as an empirical time-varying
linear detector chain response which is the first-order effect. The SRoll2
method fits the model parameters for higher-order effects and corrects the full
distortion of the signal. The model parameters are fitted using the
redundancies in the data by iteratively comparing the data and a model. The
polarization efficiency uncertainties and associated errors have also been
corrected based on the redundancies in the data and their residual levels
characterized with simulations. This paper demonstrates the effectiveness of
the method using end-to-end simulations, and provides a measure of the
systematic effect residuals that now fall well below the detector noise level.
Finally, this paper describes and characterizes the resulting SRoll2 frequency
maps using the associated simulations that are} released to the community at
http://sroll20.ias.u-psud.fr. |
Confronting semi-analytic galaxy models with galaxy-matter correlations
observed by CFHTLenS: Testing predictions of semi-analytic models of galaxy evolution against
observations help to understand the complex processes that shape galaxies. We
compare predictions from the Garching and Durham models implemented on the
Millennium Run with observations of galaxy-galaxy lensing (GGL) and
galaxy-galaxy-galaxy lensing (G3L) for various galaxy samples with stellar
masses in the range 0.5 < (M_* / 10^10 M_Sun) < 32 and photometric redshift
range 0.2 < z < 0.6 in the Canada-France-Hawaii Telescope Lensing Survey
(CFHTLenS). We find that the predicted GGL and G3L signals are in qualitative
agreement with CFHTLenS data. Quantitatively, the models succeed in reproducing
the observed signals in the highest stellar mass bin (16 < ( M_* / 10^10 M_Sun)
< 32) but show different degrees of tension for the other stellar mass samples.
The Durham models are strongly excluded at the 95% confidence level by the
observations as they largely over-predict the amplitudes of the GGL and G3L
signals, probably because they predict too many satellite galaxies in massive
halos. | Separation of CMB $μ$ spectral distortions from foregrounds with
poorly defined spectral shapes: This paper proposes a new approach to separate the $\mu$ spectral distortions
of the cosmic microwave background from foregrounds with poorly defined
spectral shapes. The idea is based on finding the optimal response to the
observed signal. This response is weakly sensitive to foregrounds with
parameters that are within some certain limits of their possible variations
and, at the same time, very sensitive to the amplitude of $\mu$ distortion. The
algorithm described in this paper is stable, easy to implement, and
simultaneously minimizes the response to foregrounds and photon noise. |
Galactic Outflows and Photoionization Heating in the Reionization Epoch: We carry out a new suite of cosmological radiation hydrodynamic simulations
and explore the relative impacts on reionization-epoch star formation of
galactic outflows and photoionization heating. By itself, an extragalactic
ultraviolet background (EUVB) suppresses the luminosity function by less than
50% at z=6, overproducing the observed galaxy abundance by a factor of 3-5.
Galactic outflows restore agreement with observations without preventing
Population II star formation from reionizing the Universe by z=6. The resulting
EUVB suppresses star formation in halos with virial temperatures below 10^5K
but has a weaker impact in more massive halos. Nonetheless, the low-mass halos
contribute up to 50% of all ionizing photons owing to the EUVB's inhomogeneity.
Overall, star formation rate scales as halo mass M_h to the 1.3-1.4 in halos
with $M_h=10^{8.2--10.2}\msun$. This is a steeper dependence than is often
assumed in reionization models, boosting the expected power spectrum of 21
centimeter fluctuations on large scales. The luminosity function rises steeply
to at least M_1600=-13, indicating that reionization was driven by faint
galaxies (M_1600 >= -15) that have not yet been observed. Our models cannot
simultaneously explain observations of galaxies, the cosmic microwave
background, and the intergalactic medium. Increased dynamic range will
alleviate the existing discrepancies, but observations may still require
additional physics such as a variable ionizing escape fraction (abridged). | New water masers in Seyfert and FIR bright galaxies. IV. Interferometric
follow-ups: Very luminous extragalactic water masers, the megamasers, are associated with
active galactic nuclei (AGN) in galaxies characterized by accretion disks,
radio jets, and nuclear outflows. Weaker masers, the kilomasers, seem to be
mostly related to star formation activity, although the possibility exists that
some of these sources may belong to the weak tail of the AGN maser
distribution. It is of particular importance to accurately locate the water
maser emission to reveal its origin and shed light onto extragalactic star
forming activity or to elucidate the highly obscured central regions of
galaxies. We performed interferometric observations of three galaxies, NGC3556,
Arp299, and NGC4151, where water emission was found. Statistical tools have
been used to study the relation between OH and water maser emission in
galaxies. The maser in NGC3556 is associated with a compact radio continuum
source that is most likely a supernova remnant or radio supernova. In Arp299,
the luminous water maser has been decomposed in three main emitting regions
associated with the nuclear regions of the two main galaxies of the system,
NGC3690 and IC694, and the region of overlap. In NGC4151, only one of the two
previously observed maser components has been tentatively detected. This
feature, if real, is associated with the galaxy's central region. The only
galaxy, so far, where luminous maser emission from two maser species, OH and
H2O has been confidently detected is Arp299. Weaker masers from these two
species do instead coexist in a number of objects. A larger number of objects
searched for both maser species are, however, necessary to better assess these
last two results. |
Dynamics and cosmological constraints on Brans-Dicke cosmology: We investigate observational constraints on the Brans-Dicke cosmological
model using observational data coming from distant supernovae type Ia, the
Hubble function $H(z)$ measurements, information coming from the
Alcock-Paczy{\'n}ski test, and baryon acoustic oscillations. Our analysis is
based on the modified Friedmann function resulting form dynamical
investigations of Brans-Dicke cosmology in the vicinity of a de Sitter state.
The qualitative theory of dynamical systems enables us to obtain three
different behaviors in the vicinity of this state. We find for a linear
approach to the de Sitter state
$\omega_{\textrm{BD}}=-0.8606^{+0.8281}_{-0.1341}$, for an oscillatory approach
to the de Sitter state $\omega_{\textrm{BD}}=-1.1103^{+0.1872}_{-0.1729}$, and
for the transient de Sitter state represented by a saddle-type critical point
$\omega_{\textrm{BD}}=-2.3837^{+0.4588}_{-4.5459}$. We obtain the mass of the
Brans-Dicke scalar field at the present epoch as $m_{\phi}\sim H_{0}$. The
Bayesian methods of model comparison are used to discriminate between obtained
models. We show that observational data point toward vales of the
$\omega_{\textrm{BD}}$ parameter close to the value suggested by the low-energy
limit of the bosonic string theory. | Constraints from microlensing experiments on clustered primordial black
holes: It has recently been proposed that massive primordial black holes (PBH) could
constitute all of the dark matter, providing a novel scenario of structure
formation, with early reionization and a rapid growth of the massive black
holes at the center of galaxies and dark matter halos. The scenario arises from
broad peaks in the primordial power spectrum that give both a spatially
clustered and an extended mass distribution of PBH. The constraints from the
observed microlensing events on the extended mass function have already been
addressed. Here we study the impact of spatial clustering on the microlensing
constraints. We find that the bounds can be relaxed significantly for
relatively broad mass distributions if the number of primordial black holes
within each cluster is typically above one hundred. On the other hand, even if
they arise from individual black holes within the cluster, the bounds from CMB
anisotropies are less stringent due to the enhanced black hole velocity in such
dense clusters. This way, the window between a few and ten solar masses has
opened up for PBH to comprise the totality of the dark matter. |
Primordial Non-Gaussianity in the Forest: 3D Bispectrum of Ly-alpha Flux
Spectra Along Multiple Lines of Sight: We investigate the possibility of constraining primordial non-Gaussianity
using the 3D bispectrum of Ly-alpha forest. The strength of the quadratic
non-Gaussian correction to an otherwise Gaussian primordial gravitational field
is assumed to be dictated by a single parameter fnl. We present the first
prediction for bounds on fnl using Ly-alpha flux spectra along multiple lines
of sight. The 3D Ly-$\alpha$ transmitted flux field is modeled as a biased
tracer of the underlying matter distribution sampled along 1D skewers
corresponding to quasars sight lines. The precision to which fnl can be
constrained depends on the survey volume, pixel noise and aliasing noise
(arising from discrete sampling of the density field). We consider various
combinations of these factors to predict bounds on fnl. We find that in an
idealized situation of full sky survey and negligible Poisson noise one may
constrain fnl ~ 23 in the equilateral limit. Assuming a Ly-alpha survey
covering large parts of the sky (k_{min} = 8 * 10^{-4} Mpc^{-1}) and with a
quasar density of \bar n = 5 * 10^{-3} Mpc^{-2} it is possible to constrain fnl
~ 100 for equilateral configurations. The possibility of measuring fnl at a
precision comparable to LSS studies maybe useful for joint constraining of
inflationary scenarios using different data sets. | X-rays from the explosion site: Fifteen years of light curves of SN
1993J: We present a comprehensive analysis of the X-ray light curves of SN 1993J in
a nearby galaxy M81. This is the only supernova other than SN 1987A, which is
so extensively followed in the X-ray bands.
Here we report on SN 1993J observations with the {\it Chandra} in the year
2005 and 2008, and Swift observations in 2005, 2006 and 2008. We combined these
observations with all available archival data of SN 1993J, which includes
ROSAT, ASCA, {\it Chandra}, and XMM-{\it Newton} observations from 1993 April
to 2006 August. In this paper we report the X-ray light curves of SN 1993J,
extending up to fifteen years, in the soft (0.3--2.4 keV), hard (2--8 keV) and
combined (0.3--8 keV) bands. The hard and soft-band fluxes decline at different
rates initially, but after about 5 years they both undergo a $t^{-1}$ decline.
The soft X-rays, which are initially low, start dominating after a few hundred
days. We interpret that most of the emission below 8 keV is coming from the
reverse shock which is radiative initially for around first 1000-2000 days and
then turn into adiabatic shock. Our hydrodynamic simulation also confirms the
reverse shock origin of the observed light curves. We also compare the
H$\alpha$ line luminosity of SN 1993J with its X-ray light curve and note that
the H$\alpha$ line luminosity has a fairly high fraction of the X-ray emission,
indicating presence of clumps in the emitting plasma. |
Supersymmetric chameleons and ultra-local models: Super-chameleon models where all types of matter belong to three secluded
sectors, i.e. the dark, supersymmetry breaking and matter sectors, are shown to
be dynamically equivalent to ultra-local models of modified gravity. In the
dark sector, comprising both dark matter and dark energy, the interaction range
between the dark energy field and dark matter is constrained to be extremely
short, i.e. shorter than the inverse gravitino mass set by supersymmetry
breaking. This realises an extreme version of chameleon screening of the dark
energy interaction. On the other hand, the baryonic matter sector decouples
from the dark energy in a Damour-Polyakov way. These two mechanisms preclude
the existence of any modification of gravity locally in the Solar System due to
the presence of the super-chameleon field. On larger scales, the
super-chameleon can have effects on the growth of structure and the number of
dark matter halos. It can also affect the dynamics of galaxies where the fifth
force interaction that it induces can have the same order of magnitude as
Newton's interaction. | Astro 2020 Science White Paper: Fundamental Cosmology in the Dark Ages
with 21-cm Line Fluctuations: The Dark Ages are the period between the last scattering of the cosmic
microwave background and the appearance of the first luminous sources, spanning
approximately 1100 < z < 30. The only known way to measure fluctuations in this
era is through the 21-cm line of neutral hydrogen. Such observations have
enormous potential for cosmology, because they span a large volume while the
fluctuations remain linear even on small scales. Observations of 21-cm
fluctuations during this era can therefore constrain fundamental aspects of our
Universe, including inflation and any exotic physics of dark matter. While the
observational challenges to these low-frequency 21-cm observations are
enormous, especially from the terrestrial environment, they represent an
important goal for cosmology. |
Rindler force at large distances: Given some assumptions it is possible to derive the most general post-general
relativistic theory of gravity for the distant field of a point mass. The force
law derived from this theory contains a Rindler term in addition to well-known
contributions, a Schwarzschild mass and a cosmological constant. The same force
law recently was confronted with solar system precision data. The Rindler
force, if present in Nature, has intriguing consequences for gravity at large
distances. In particular, the Rindler force is capable of explaining about 10%
of the Pioneer anomaly and simultaneously ameliorates the shape of galactic
rotation curves. | New constraints on axion-gauge field dynamics during inflation from
$Planck$ and BICEP/Keck data sets: We present new constraints on spectator axion-${\rm U}(1)$ gauge field
interactions during inflation using the latest $Planck$ (PR4) and BICEP/Keck
2018 data releases. This model can source tensor perturbations from amplified
gauge field fluctuations, driven by an axion rolling for a few e-folds during
inflation. The gravitational waves sourced in this way have a strongly
scale-dependent (and chiral) spectrum, with potentially visible contributions
to large/intermediate scale $B$-modes of the CMB. We first derive theoretical
bounds on the model imposing validity of the perturbative regime and negligible
backreaction of the gauge field on the background dynamics. Then, we determine
bounds from current CMB observations, adopting a frequentist profile likelihood
approach. We study the behaviour of constraints for typical choices of the
model's parameters, analyzing the impact of different dataset combinations. We
find that observational bounds are competitive with theoretical ones and
together they exclude a significant portion of the model's parameter space. We
argue that the parameter space still remains large and interesting for future
CMB experiments targeting large/intermediate scales $B$-modes. |
Cross correlation surveys with the Square Kilometre Array: By the time that the first phase of the Square Kilometre Array is deployed it
will be able to perform state of the art Large Scale Structure (LSS) as well as
Weak Gravitational Lensing (WGL) measurements of the distribution of matter in
the Universe. In this chapter we concentrate on the synergies that result from
cross-correlating these different SKA data products as well as external
correlation with the weak lensing measurements available from CMB missions. We
show that the Dark Energy figures of merit obtained individually from WGL/LSS
measurements and their independent combination is significantly increased when
their full cross-correlations are taken into account. This is due to the
increased knowledge of galaxy bias as a function of redshift as well as the
extra information from the different cosmological dependences of the
cross-correlations. We show that the cross-correlation between a spectroscopic
LSS sample and a weak lensing sample with photometric redshifts can calibrate
these same photometric redshifts, and their scatter, to high accuracy by
modelling them as nuisance parameters and fitting them simultaneously
cosmology. Finally we show that Modified Gravity parameters are greatly
constrained by this cross-correlations because weak lensing and redshift space
distortions (from the LSS survey) break strong degeneracies in common
parameterisations of modified gravity. | Inverse volume corrections to emergent tachyonic inflation in loop
quantum cosmology: The emergent model in the context of loop quantum cosmology with a tachyon
scalar field is studied. We find that there is a center equilibrium point in
the semiclassical region and a saddle point in the classical region. If the
potential of the tachyon field satisfies some conditions, the universe can stay
at the center equilibrium point past-eternally and then oscillate infinitely
around this point with the tachyon climbing up its potential. Once the
potential reaches a critical value, these two equilibrium points coincide with
each other and the oscillation phase is broken by an emergent inflation. In
order to obtain a successful emergent tachyon inflation, a constraint on
$\dot{\phi}^2$ of tachyon is required. |
Investigating Cluster Astrophysics and Cosmology with Cross-Correlation
of the Thermal Sunyaev-Zel'dovich Effect and Weak Lensing: Recent detections of the cross-correlation of the thermal Sunyaev-Zel'dovich
(tSZ) effect and weak gravitational lensing (WL) enable unique studies of
cluster astrophysics and cosmology. In this work, we present constraints on the
amplitude of the non-thermal pressure fraction in galaxy clusters, $\alpha_0$,
and the amplitude of the matter power spectrum, $\sigma_8$, using measurements
of the tSZ power spectrum from Planck, and the tSZ-WL cross-correlation from
Planck and the Red Cluster Sequence Lensing Survey. We fit the data to a
semi-analytic model with the covariance matrix using $N$-body simulations. We
find that the tSZ power spectrum alone prefers $\sigma_8 \sim 0.85$ and a large
fraction of non-thermal pressure ($\alpha_0 \sim 0.2$-$0.3$). The tSZ-WL
cross-correlation on the other hand prefers a significantly lower $\sigma_8
\sim 0.6$, and low $\alpha_0 \sim 0.05$. We show that this tension can be
mitigated by allowing for a steep slope in the stellar-mass-halo-mass relation,
which would cause a reduction of the gas in low-mass halos. In such a model,
the combined data prefer $\sigma_8 \sim 0.7$ and $\alpha_0 \sim 0.2$,
consistent with predictions from hydrodynamical simulations. | Broaden the search for dark matter: Bold strategies are needed to identify most of the elusive particles that
should make up most of the Universe's mass |
Cosmological signatures of brane inflation: Cosmology motivated by string theory has been studied extensively in the
recent literature. String theory is promising because it has interesting
features such as unifying gravity, electromagnetic, weak and strong nuclear
forces. However, even the energy scale of the experiments at the Large Hadron
Collider (~TeV) is too low to detect any strong evidence for string theory. The
energy scale of inflation can be above ~10^9 TeV. Therefore, it is expected to
find some signature of string theory in cosmology.
String theory predicts ten space-time dimensions. In the brane world
scenario, our four dimensional Universe is confined onto the higher dimensional
object called the Brane in the ten dimensional space time. The
Dirac-Born-Infeld (DBI) inflation is based on this idea. DBI inflation predicts
a characteristic statistical feature in the Cosmic Microwave Background (CMB)
temperature anisotropies. In this thesis, we study the predictions of the DBI
inflation models on the CMB temperature anisotropies. | Finding universal relations in subhalo properties with artificial
intelligence: We use a generic formalism designed to search for relations in
high-dimensional spaces to determine if the total mass of a subhalo can be
predicted from other internal properties such as velocity dispersion, radius,
or star-formation rate. We train neural networks using data from the Cosmology
and Astrophysics with MachinE Learning Simulations (CAMELS) project and show
that the model can predict the total mass of a subhalo with high accuracy: more
than 99% of the subhalos have a predicted mass within 0.2 dex of their true
value. The networks exhibit surprising extrapolation properties, being able to
accurately predict the total mass of any type of subhalo containing any kind of
galaxy at any redshift from simulations with different cosmologies,
astrophysics models, subgrid physics, volumes, and resolutions, indicating that
the network may have found a universal relation. We then use different methods
to find equations that approximate the relation found by the networks and
derive new analytic expressions that predict the total mass of a subhalo from
its radius, velocity dispersion, and maximum circular velocity. We show that in
some regimes, the analytic expressions are more accurate than the neural
networks. We interpret the relation found by the neural network and
approximated by the analytic equation as being connected to the virial theorem. |
Searching for HI imprints in cosmic web filaments with 21-cm intensity
mapping: We investigate the possible presence of neutral hydrogen (HI) in
intergalactic filaments at very low redshift ($z\sim 0.08$), by stacking a set
of 274,712 2dFGRS galaxy pairs over 21-cm maps obtained with dedicated
observations conducted with the Parkes radio telescope, over a total sky area
of approximately 1,300 square degrees covering two patches in the northern and
in the southern Galactic hemispheres. The stacking is performed by combining
local maps in which each pair is brought to a common reference frame; the
resulting signal from the edge galaxies is then removed to extract the filament
residual emission. We repeat the analysis on maps cleaned removing either 10 or
20 foreground modes in a principal component analysis. Our study does not
reveal any clear HI excess in the considered filaments in either case; we
determine upper limits on the total filament HI brightness temperature at
$T_{\rm b} \lesssim 10.3 \,\mu\text{K}$ for the 10-mode and at $T_{\rm b}
\lesssim 4.8 \,\mu\text{K}$ for the 20-mode removed maps at the 95% confidence
level. These estimates translate into upper limits for the local filament HI
density parameter, $\Omega_{\rm HI}^{\rm (f)} \lesssim 7.0\times10^{-5}$ and
$\Omega_{\rm HI}^{\rm (f)} \lesssim 3.2\times10^{-5}$ respectively, and for the
HI column density, $N_{\rm HI} \lesssim 4.6\times10^{15}\,\text{cm}^{-2}$ and
$N_{\rm HI} \lesssim 2.1\times10^{15}\,\text{cm}^{-2}$ respectively. These
column density constraints are consistent with previous detections of HI in the
warm-hot intergalactic medium obtained observing broad Ly $\alpha$ absorption
systems. The present work shows for the first time how such constraints can be
achieved using the stacking of galaxy pairs on 21-cm maps. | Analyzing derived metallicities and ionization parameters from
model-based determinations in ionized gaseous nebulae: We analyze the reliability of oxygen abundances and ionization parameters
obtained from different diagnostic diagrams. For this, we compiled from the
literature observational emission line intensities and oxygen abundance of 446
star-forming regions whose O/H abundance was determined by direct estimation of
electron temperature. The abundances compiled were compared with the values
calculated in this work using different diagnostic diagrams in combination with
results from a grid of photoionization models. We found that the
[\ion{O}{iii}]/[\ion{O}{ii}] vs. [\ion{N}{ii}]/[\ion{O}{ii}],
[\ion{O}{iii}]/H$\beta$ vs. [\ion{N}{ii}]/[\ion{O}{ii}], and
([\ion{O}{iii}]/H$\beta$)/([\ion{N}{ii}]/H$\alpha$) vs.
[\ion{S}{ii}]/[\ion{S}{iii}] diagnostic diagrams give O/H values close to the
$T_{\rm e}$-method, with differences of about 0.04 dex and dispersion of about
0.3 dex. Similar results were obtained by detailed models but with a dispersion
of 0.08 dex. The origin of the dispersion found in the use of diagnostic
diagrams is probably due to differences between the real N/O-O/H relation of
the sample and the one assumed in the models. This is confirmed by the use of
detailed models that do not have a fixed N/O-O/H relation. We found no
correlation between ionization parameter and the metallicity for the objects of
our sample. We conclude that the combination of two line ratio predicted by
photoionization models, one sensitive to the metallicity and another sensitive
to the ionization parameter, which takes into account the physical conditions
of star-forming regions, gives O/H estimates close to the values derived using
direct detections of electron temperatures. |
The UDF05 Follow-up of the Hubble Ultra Deep Field. III. The Luminosity
Function at z~6: In this paper, we present a derivation of the rest-frame 1400A luminosity
function (LF) at redshift six from a new application of the maximum likelihood
method by exploring the five deepest HST/ACS fields, i.e., the HUDF, two UDF05
fields, and two GOODS fields. We work on the latest improved data products,
which makes our results more robust than those of previous studies. We use
un-binned data and thereby make optimal use of the information contained in the
dataset. We focus on the analysis to a magnitude limit where the completeness
is larger than 50% to avoid possibly large errors in the faint end slope that
are difficult to quantify. We also take into account scattering in and out of
the dropout sample due to photometric errors by defining for each object a
probability that it belongs to the dropout sample. We find the best fit
Schechter parameters to the z~6 LF are: alpha = 1.87 +/- 0.14, M* = -20.25 +/-
0.23, and phi*=1.77^{+0.62}_{-0.49} * 10^{-3} Mpc^{-3}. Such a steep slope
suggests that galaxies, especially the faint ones, are possibly the main
sources of ionizing photons in the universe at redshift six. We also combine
results from all studies at z~6 to reach an agreement in 95% confidence level
that -20.45<M*<-20.05 and -1.90<alpha<-1.55. The luminosity density has been
found not to evolve significantly between z~6 and z~5, but considerable
evolution is detected from z~6 to z~3. | Planck 2015 results. XVII. Constraints on primordial non-Gaussianity: The Planck full mission cosmic microwave background(CMB) temperature and
E-mode polarization maps are analysed to obtain constraints on primordial
non-Gaussianity(NG). Using three classes of optimal bispectrum estimators -
separable template-fitting (KSW), binned, and modal - we obtain consistent
values for the local, equilateral, and orthogonal bispectrum amplitudes,
quoting as our final result from temperature alone fNL^local=2.5+\-5.7,
fNL^equil=-16+\-70 and fNL^ortho=-34+\-33(68%CL). Combining temperature and
polarization data we obtain fNL^local=0.8+\-5.0, fNL^equil=-4+\-43 and
fNL^ortho=-26+\-21 (68%CL). The results are based on cross-validation of these
estimators on simulations, are stable across component separation techniques,
pass an extensive suite of tests, and are consistent with Minkowski functionals
based measurements. The effect of time-domain de-glitching systematics on the
bispectrum is negligible. In spite of these test outcomes we conservatively
label the results including polarization data as preliminary, owing to a known
mismatch of the noise model in simulations and the data. Beyond fNL estimates,
we present model-independent reconstructions of the CMB bispectrum and derive
constraints on early universe scenarios that generate NG, including general
single-field and axion inflation, initial state modifications, parity-violating
tensor bispectra, and directionally dependent vector models. We also present a
wide survey of scale-dependent oscillatory bispectra, and we look for
isocurvature NG. Our constraint on the local primordial trispectrum amplitude
is gNL^local=(-9.0+\-7.7)x10^4 (68%CL), and we perform an analysis of
additional trispectrum shapes. The global picture is one of consistency with
the premises of the LambdaCDM cosmology, namely that the structure we observe
today was sourced by adiabatic, passive, Gaussian, and primordial seed
perturbations.[abridged] |
Observational constraints on anisotropies for bouncing alternatives to
inflation: We calculate how primordial anisotropies in the background space-time affect
the evolution of cosmological perturbations for bouncing alternatives to
inflation, like ekpyrosis and the matter bounce scenario. We find that the
leading order effect of anisotropies in the contracting phase of the universe
is to induce anisotropies in the cosmic microwave background with a very
concrete form: a scale-invariant quadrupolar angular distribution. Sub-leading
effects are the generation of higher-order moments in the angular distribution,
as well as cross-correlations between scalar and tensor modes. We also find
that observational constraints from the cosmic microwave background on the
quadrupole moment provide strong bounds on allowed anisotropies for bouncing
alternatives to inflation that are significantly more constraining than the
bounds previously obtained using scaling arguments based on the conjectured
Belinski-Khalatnikov-Lifshitz instability. | Recovering 21cm Monopole Signals Without Smoothness: We expect the monopole signal at the lowest frequencies below $100\,$MHz to
be composed to two components: the deep Rayleigh-Jeans tail of the cosmic
microwave background and two distinct features: the dark ages trough at $\sim
17\,$MHz and the cosmic dawn trough at $\sim 75\,$Mhz. These are hidden under
orders of magnitude brighter foregrounds whose emission is approximately a
power-law with a spectral index $\approx -2.5$. It is usually assumed that
monopole signals of interest are separable from foregrounds on the basis of
spectral smoothness. We argue that this is a difficult approach and likely
impossible for the Dark Ages trough. Instead, we suggest that the fluctuations
in the foreground emission around the sky should be used to build a model
distribution of possible shapes of foregrounds, which can be used to constrain
presence of a monopole signal. We implement this idea using normalizing flows
and show that this technique allows for efficient unsupervised detection of the
amplitude, width and center of the Dark Ages trough as well as Rayleigh-Jeans
tail of the cosmic microwave background for a sufficiently sensitive
experiment. We discuss the limitations of the inherent assumptions in this
method and the impact on the design of future low-frequency experiments. |
A new weak lensing shear analysis method using ellipticity defined by
0th order moments: We developed a new method that uses ellipticity defined by 0th order moments
(0th-ellipticity) for weak gravitational lensing shear analysis. Although there
is a strong correlation between the ellipticity calculated using this approach
and the usual ellipticity defined by the 2nd order moment, the ellipticity
calculated here has a higher signal-to-noise ratio because it is weighted to
the central region of the image. These results were confirmed using data for
Abell 1689 from the Subaru telescope. For shear analysis, we adopted the
ellipticity of re-smeared artificial image (ERA) method for point spread
function (PSF) correction, and we tested the precision of this 0th-ellipticity
with simple simulation, then we obtained the same level of precision with the
results of ellipticity defined by quadrupole moments. Thus, we can expect that
weak lensing analysis using 0 shear will be improved in proportion to the
statistical error. | A suspected Dark Lens revealed with the e-EVN: The e-VLBI technique offers a unique opportunity for users to probe the
milliarcsecond (mas) scale structure of unidentified radio sources, and
organise quick follow-up observations in case of detection. Here we report on
e-EVN results for a peculiar radio source that has been suggested to act as a
gravitational lens. However the lensing galaxy has not been identified in the
optical or the IR bands so far. Our goal was to look for an active galactic
nucleus (AGN) in this suspected dark lens system. The results indicate strong
AGN activity, and rule out the possibility that the radio source itself is
gravitationally lensed. |
The effect of metal enrichment and galactic winds on galaxy formation in
cosmological zoom simulations: We investigate the differential effects of metal cooling and galactic stellar
winds on the cosmological formation of individual galaxies with three sets of
cosmological, hydrodynamical zoom simulations of 45 halos in the mass range
10^11<M_halo<10^13M_sun. Models including both galactic winds and metal cooling
(i) suppress early star formation at z>1 and predict reasonable star formation
histories, (ii) produce galaxies with high cold gas fractions (30-60 per cent)
at high redshift, (iii) significantly reduce the galaxy formation efficiencies
for halos (M_halo<10^12M_sun) at all redshifts in agreement with observational
and abundance matching constraints, (iv) result in high-redshift galaxies with
reduced circular velocities matching the observed Tully-Fisher relation at z~2,
and (v) significantly increase the sizes of low-mass galaxies
(M_stellar<3x10^10M_sun) at high redshift resulting in a weak size evolution -
a trend in agreement with observations. However, the low redshift (z<0.5) star
formation rates of massive galaxies are higher than observed (up to ten times).
No tested model predicts the observed size evolution for low-mass and high-mass
galaxies simultaneously. Due to the delayed onset of star formation in the wind
models, the metal enrichment of gas and stars is delayed and agrees well with
observational constraints. Metal cooling and stellar winds are both found to
increase the ratio of in situ formed to accreted stars - the relative
importance of dissipative vs. dissipationless assembly. For halo masses below
~10^12M_sun, this is mainly caused by less stellar accretion and compares well
to predictions from semi-analytical models but still differs from abundance
matching models. For higher masses, the fraction of in situ stars is
over-predicted due to the unrealistically high star formation rates at low
redshifts. | The Carnegie-Chicago Hubble Program. IV. The Distances to NGC 4424, NGC
4526, and NGC 4536 via the Tip of the Red Giant Branch: The Carnegie-Chicago Hubble Program (CCHP) is undertaking a re-calibration of
the extragalactic distance scale, using Type Ia supernovae that are tied to Tip
of the Red Giant Branch (TRGB) distances to local galaxies. We present here
deep Hubble Space Telescope (HST) ACS/WFC imaging of the resolved stellar
populations in the metal-poor halos of the SN Ia host galaxies NGC 4424, NGC
4526, and NGC 4536. These three Virgo constellation galaxies are prime targets
for calibrating the extragalactic distance scale given their relative proximity
in the local Universe and their low line-of-sight reddenings. Anchoring the
TRGB zero-point to the geometric distance to the Large Magellanic Cloud via
detached eclipsing binaries, we measure extinction-corrected distance moduli of
31.00 +/- 0.03 (stat) +/- 0.06 (sys) mag, 30.98 +/- 0.03 (stat) +/- 0.06 (sys)
mag, and 30.99 +/- 0.03 (stat) +/- 0.06 (sys) mag for NGC 4424, NGC 4526, and
NGC 4536, respectively, or 15.8 +/- 0.2 (stat) +/- 0.4 (sys) Mpc, 15.7 +/- 0.2
(stat) +/- 0.4 (sys) Mpc, and 15.8 +/- 0.2 (stat) +/- 0.4 (sys) Mpc. For these
three galaxies, the distances are the first based on the TRGB, and for NGC 4424
and NGC 4526, they are the highest precision distances published to date, each
measured to 3%. Finally, we report good agreement between our TRGB distances
and the available Cepheid distances for NGC 4424 and NGC 4536, demonstrating
consistency between the distance scales currently derived from stars of
Population I and II. |
Viscosity in cosmic fluids: The effective theory of large-scale structure formation based on $\Lambda$CDM
paradigm predicts finite dissipative effects in the resulting fluid equations.
In this work, we study how viscous effect that could arise if one includes
self-interaction among the dark-matter particles combines with the effective
theory. It is shown that these two possible sources of dissipation can operate
together in a cosmic fluid and the interplay between them can play an important
role in determining dynamics of the cosmic fluid. In particular, we demonstrate
that the viscosity coefficient due to self-interaction is added inversely with
the viscosity calculated using effective theory of $\Lambda$CDM model. Thus the
larger viscosity has less significant contribution in the effective viscosity.
Using the known bounds on $\,\sigma/m$ for self-interacting dark-matter, where
$\,\sigma\,$ and $m$ are the cross-section and mass of the dark-matter
particles respectively, we discuss role of the effective viscosity in various
cosmological scenarios. | On Measuring the CMB Temperature at Redshift 0.89: We report on a measurement of the temperature of the cosmic microwave
background radiation field, T_CMB, at z = 0.88582 by imaging HC3N (3-2) and
(5-4) absorption in the foreground galaxy of the gravitationally lens magnified
radio source PKS 1830-211 using the Very Long Baseline Array and the phased
Very Large Array. Low-resolution imaging of the data yields a value of Trot =
5.6+2.5-0.9 K, for the rotational temperature, Trot, which is consistent with
the temperature of the cosmic microwave background at the absorber's redshift
of 2.73(1+z) K. However, our high-resolution imaging reveals that the
absorption peak position of the foreground gas is offset from the continuum
peak position of the synchrotron radiation from PKS 1830-211 SW, which
indicates that the absorbing cloud is covering only part of the emission from
PKS 1830-211, rather than the entire core-jet region. This changes the
line-to-continuum ratios, and we find Trot between 1.1 and 2.5 K, which is
lower than the expected value. This shows that previous, Trot, measurements
could be biased due to unresolved structure. |
Uneven flows: On cosmic bulk flows, local observers, and gravity: Using N-body simulations we study the impact of various systematic effects on
the bulk flow (BF) and the Cosmic Mach Number (CMN). We consider two types of
systematics: those related to survey properties and those induced by observer's
location in the Universe. In the former category we model sparse sampling,
velocity errors, and survey incompleteness. In the latter, we consider Local
Group (LG) analogue observers, placed in a specific location within the Cosmic
Web, satisfying various observational criteria. We differentiate such LG
observers from Copernican ones, who are at random locations. We report strong
systematic effects on the measured BF and CMN induced by sparse sampling,
velocity errors and radial incompleteness. For BF most of these effects exceed
10\% for scales $R\leq100h^{-1}$Mpc. For CMN some of these systematics can be
catastrophically large ($>50\%$) also on bigger scales. Moreover, we find that
the position of the observer in the Cosmic Web significantly affects the
locally measured BF (CMN), with effects as large as $\sim20\%$ ($30\%)$ at
$R\leq50h^{-1}$Mpc for a LG-like observer as compared to a random one. This
effect is comparable to the sample variance. To highlight the importance of
these systematics, we additionally study a model of modified gravity (MG) with
$\sim15\%$ enhanced growth rate. We found that the systematic effects can mimic
the modified gravity signal. The worst-case scenario is realized for a case of
a LG-like observer, when the effects induced by local structures are degenerate
with the enhanced growth rate fostered by MG. Our results indicate that
dedicated constrained simulations and realistic mock galaxy catalogs will be
absolutely necessary to fully benefit from the statistical power of the
forthcoming peculiar velocity data from surveys such as TAIPAN, WALLABY, Cosmic
Flows-4 and SKA. | Primordial black hole isocurvature modes from non-Gaussianity: Primordial black holes (PBHs) are black holes that might have formed in high
density regions in the early universe. The presence of local-type
non-Gaussianity can lead to large-scale fluctuations in the PBH formation rate.
If PBHs make up a non-negligible fraction of dark matter, these fluctuations
can appear as isocurvature modes, and be used to constrain the amplitude of
non-Gaussianity. Assuming that the parameters of non-Gaussianity are constant
over all scales, we build upon the results of previous work by extending the
calculation to include peaks theory and making use of the compaction $C$ for
the formation criteria, accounting for non-linearities between $C$ and the
curvature perturbation $\zeta$. For quadratic models of non-Gaussianity, our
updated calculation gives constraints that are largely unaltered compared to
those previously found, while for cubic models the constraints worsen
significantly. In case all of the DM is made up of PBHs, the parameters of
non-Gaussianity are $-2.9\cdot10^{-4}<f<3.8\cdot10^{-4}$ and
$-1.5\cdot10^{-3}<g<1.9\cdot10^{-3}$ for quadratic and cubic models
respectively. |
The environmental dependence of neutral hydrogen in the GIMIC
simulations: We use the Galaxies-Intergalactic Medium Interaction Calculation (GIMIC)
cosmological hydrodynamic simulation at z=0 to study the distribution and
environmental dependence of neutral hydrogen (HI) gas in the outskirts of
simulated galaxies. This gas can currently be probed directly in, for example,
Ly$\alpha$ absorption via the observation of background quasars. Radio
facilities, such as the Square Kilometre Array, will provide a complementary
probe of the diffuse HI in emission and will constrain the physics underpinning
the complex interplay between accretion and feedback mechanisms which affect
the intergalactic medium. We extract a sample of 488 galaxies from a
re-simulation of the average cosmic density GIMIC region. We estimate the
neutral hydrogen content of these galaxies and the surrounding intergalactic
medium within which they reside. We investigate the average HI radial profiles
by stacking the individual profiles according to both mass and environment. We
find high HI column densities at large impact parameters in group environments
and markedly lower HI densities for non-group galaxies. We suggest that these
results likely arise from the combined effects of ram pressure stripping and
tidal interactions present in group environments. | Topology beyond the horizon: how far can it be probed?: The standard cosmological model does not determine the spatial topology of
the universe. This article revisits the signature of a non-trivial topology on
the properties of the cosmic microwave background anisotropies. We show that
the correlation function of the coefficients of the expansion of the
temperature and polarization anisotropies in spherical harmonics, encodes a
topological signature that can be used to distinguish a multi-connected space
from an infinite space on sizes larger than the last scattering surface. The
effect of the instrumental noise and of a galactic cut are estimated. We thus
establish boundaries for the size of the biggest torus dintinguisable with
temperature and polarization CMB data. We also describe the imprint of the
spatial topology on the 3-point function and on non-Gaussianity. |
Primordial Gravitational Waves in the Cosmic Bubble Chamber: We explore the effect of relic gravitational waves on the primordial phase
change from the quark-gluon plasma into the low density hadron gas that
occurred approximately $10^{-5}$s after the beginning. We show that the
gravitational wave, through doing work on the fluid, modulates the local
volumes, causing a pressure modulation which either suppresses or boosts the
bubble cavitation rate. The boosted rate is significant, implying that the
phase transition could have occurred earlier than if this interaction is not
considered. | Planck 2013 results. XXV. Searches for cosmic strings and other
topological defects: Planck data have been used to provide stringent new constraints on cosmic
strings and other defects. We describe forecasts of the CMB power spectrum
induced by cosmic strings, calculating these from network models and
simulations using line-of-sight Boltzmann solvers. We have studied Nambu-Goto
cosmic strings, as well as field theory strings for which radiative effects are
important, thus spanning the range of theoretical uncertainty in strings
models. We have added the angular power spectrum from strings to that for a
simple adiabatic model, with the extra fraction defined as $f_{10}$ at
multipole $\ell=10$. This parameter has been added to the standard six
parameter fit using COSMOMC with flat priors. For the Nambu-Goto string model,
we have obtained a constraint on the string tension of $G\mu/c^2 < 1.5 x
10^{-7}$ and $f_{10} < 0.015$ at 95% confidence that can be improved to
$G\mu/c^2 < 1.3 x 10^{-7}$ and $f_{10} < 0.010$ on inclusion of high-$\ell$ CMB
data. For the abelian-Higgs field theory model we find, $G\mu_{AH}/c^2 < 3.2 x
10^{-7}$ and $f_{10} < 0.028$. The marginalized likelihoods for $f_{10}$ and in
the $f_{10}$--$\Omega_b h^2$ plane are also presented. We have also obtained
constraints on $f_{10}$ for models with semi-local strings and global textures
for which $G\mu/c^2 < 1.1 x 10^{-6}$. We have made complementarity searches for
the specific non-Gaussian signatures of cosmic strings, calibrating with
all-sky Planck resolution CMB maps generated from networks of
post-recombination strings. We have obtained upper limits on the string tension
at 95% confidence of $G\mu/c^2 < 8.8 x 10^{-7}$ using modal bispectrum
estimation and $G\mu/c^2 < 7.8 x 10^{-7}$ for real space searches with
Minkowski functionals. These are conservative upper bounds because only
post-recombination string contributions have been included in the non-Gaussian
analysis. |
A search for CII-158$μ$m line emission in HCM\,6A, a Lyman-$α$
emitter at $z=6.56$: We report a Plateau de Bure interferometer search for CII-158$\mu$m emission
from HCM6A, a lensed Lyman-$\alpha$ emitter (LAE) at $z = 6.56$. Our
non-detections of CII-158$\mu$m line emission and 1.2mm radio continuum
emission yield $3\sigma$ limits of L$_{\rm CII} < 6.4 \times 10^7 \times
(\Delta V/100 km s^{-1})^{1/2}$ L$_\odot$ on the CII-158$\mu$m line luminosity
and S$_{\rm 1.2mm} < 0.68$ mJy on the 1.2mm flux density. The local conversion
factor between L$_{\rm CII}$ and star formation rate (SFR) yields an SFR $<
4.7$ M$_\odot$ yr$^{-1}$, $\approx 2$ times lower than that inferred from the
ultraviolet (UV) continuum, suggesting that the local factor may not be
applicable in high-$z$ LAEs. The non-detection of 1.2mm continuum emission
yields a total SFR $< 28$ M$_\odot$/yr; any obscured star formation is thus
within a factor of two of the visible star formation. Our best-fit model to the
rest-frame UV/optical spectral energy distribution of HCM6A yields a stellar
mass of $1.3 \times 10^9$ M$_\odot$ and an SFR of ~10 M$_\odot$/yr, with
negligible dust obscuration. We fortuitously detect CO J=3-2 emission from a
$z=0.375$ galaxy in the foreground cluster Abell370, obtaining a CO line
luminosity of L$^\prime ({\rm CO}) > (8.95 \pm 0.79) \times 10^8$ K km s$^{-1}$
pc$^2$, and a molecular gas mass of M$({\rm H_2}) > (4.12 \pm 0.36) \times
10^9$ M$_\odot$, for a CO-to-H$_2$ conversion factor of 4.6 M$_\odot$ (K km
s$^{-1}$ pc$^2$)$^{-1}$. | Accretion onto Black Holes from Large Scales Regulated by Radiative
Feedback. III. Enhanced Luminosity of Intermediate Mass Black Holes Moving at
Supersonic Speeds: In this third paper of a series, we study the growth and luminosity of black
holes (BHs) in motion with respect to their surrounding medium. We run a large
set of two-dimensional (2D) axis-symmetric simulations to explore a large
parameter space of initial conditions and formulate an analytical model for the
accretion. Contrary to the case without radiation feedback, the accretion rate
increases with increasing BH velocity $\vbh$ reaching a maximum value at
$\vbh=2c_{\rm s,in}\sim 50$ km/s, where $c_{\rm s,in}$ is the sound speed
inside the "cometary-shaped" \hii region around the BH, before decreasing as
$\vbh^{-3}$ when the I-front becomes {\it R}-type (rarefied) and the accretion
rate approaches the classical Bondi-Hoyle-Lyttleton solution. The increase of
the accretion rate with $\vbh$ is produced by the formation of a {\it D}-type
(dense) ionization front (I-front) preceded by a standing bow-shock that
reduces the downstream gas velocity to transonic values. There is a range of
densities and velocities where the dense shell is unstable producing periodic
accretion rate peaks which can significantly increase the detectability of
intermediate mass BHs. We find that the mean accretion rate for a moving BH is
larger than that of a stationary BH of the same mass if the medium temperature
is $T_\infty<10^4$ K. This result could be important for the growth of seed BHs
in the multi-phase medium of the first galaxies and for building and early
X-ray background that may affect the formation of the first galaxies and the
reionization process. |
Interacting vacuum energy in the dark sector: We analyse three cosmological scenarios with interaction in the dark sector,
which are particular cases of a general expression for the energy flux from
vacuum to matter. In the first case the interaction leads to a transition from
an unstable de Sitter phase to a radiation dominated universe, avoiding in this
way the initial singularity. In the second case the interaction gives rise to a
slow-roll power-law inflation. Finally, the third scenario is a concordance
model for the late-time universe, with the vacuum term decaying into cold dark
matter. We identify the physics behind these forms of interaction and show that
they can be described as particular types of the modified Chaplygin gas. | Formation and evolution of dwarf early-type galaxies in the Virgo
cluster II. Kinematic Scaling Relations: We place our sample of 18 Virgo dwarf early-type galaxies (dEs) on the V-K -
velocity dispersion, Faber-Jackson, and Fundamental Plane (FP) scaling
relations for massive early-type galaxies (Es). We use a generalized velocity
dispersion, which includes rotation, to be able to compare the location of both
rotationally and pressure supported dEs with those of early and late-type
galaxies. We find that dEs seem to bend the Faber-Jackson relation of Es to
lower velocity dispersions, being the link between Es and dwarf spheroidal
galaxies (dSphs). Regarding the FP relation, we find that dEs are significantly
offset with respect to massive hot stellar systems, and re-casting the FP into
the so-called kappa-space suggests that this offset is related to dEs having a
total mass-to-light ratio higher than Es but still significantly lower than
dSph galaxies. Given a stellar mass-to-light ratio based on the measured line
indices of dEs, the FP offset allows us to infer that the dark matter fraction
within the half light radii of dEs is on average >~ 42% (uncertainties of 17%
in the K band and 20% in the V band), fully consistent with an independent
estimate in an earlier paper in this series. We also find that dEs in the
size-luminosity relation in the near-infrared, like in the optical, are offset
from early-type galaxies, but seem to be consistent with late-type galaxies. We
thus conclude that the scaling relations show that dEs are different from Es,
and that they further strengthen our previous findings that dEs are closer to
and likely formed from late-type galaxies. |
Anisotropies in Cosmological 21 cm Background by Oscillons/I-balls of
Ultra-light Axion-like Particle: Ultra-light axion-like particle (ULAP) with mass $m \sim 10^{-22}
~\mathrm{eV}$ has recently been attracting attention as a possible solution to
the small-scale crisis. ULAP forms quasi-stable objects called
oscillons/I-balls, which can survive up to a redshift $z \sim 10$ and affect
the structure formation on a scale $\sim \mathcal{O}(0.1)~\mathrm{Mpc}$ by
amplifying the density fluctuations. We study the effect of oscillons on 21~cm
anisotropies caused by neutral hydrogen in minihalos. It is found that this
effect can be observed in a wide mass range by future observations such as
Square Kilometer Array~(SKA) if the fraction of ULAP to the total dark matter
density is $\mathcal{O}(0.01 \text{--} 0.1)$. | Calcium H & K Induced by Galaxy Halos: We present a measurement of the mean density profile of Ca II gas around
galaxies out to ~ 200 kpc, traced by Fraunhofer's H & K absorption lines. The
measurement is based on cross-correlating the positions of about one million
foreground galaxies at z ~ 0.1 and the flux decrements induced in the spectra
of about 10^5 background quasars from the Sloan Digital Sky Survey. This
technique allows us to trace the total amount of Ca II absorption induced by
the circumgalactic medium, including absorbers too weak to be detected in
individual spectra. We can statistically measure Ca II rest equivalent widths
down to several mA, corresponding to column densities of about 5x10^10 cm^{-2}.
We find that the Ca II column density distribution follows N ~ rp^{-1.4} and
the mean Ca II mass in the halo within 200 kpc is ~ 5x10^3 Msolar, averaged
over the foreground galaxy sample with median mass ~ 10^10.3 Msolar. This is
about an order-of-magnitude larger than the Ca II mass in the interstellar
medium of the Milky Way, suggesting more than 90% of Ca II in the Universe is
in the circum- and inter-galactic environments. Our measurements indicate that
the amount of Ca II in halos is larger for galaxies with higher stellar mass
and higher star formation rate. For edge-on galaxies we find Ca II to be more
concentrated along the minor axis, i.e. in the polar direction. This suggests
that bipolar outflows induced by star formation must have played a significant
role in producing Ca II in galaxy halos. |
CMB Lensing Beyond the Power Spectrum: Cosmological Constraints from the
One-Point PDF and Peak Counts: Unprecedentedly precise cosmic microwave background (CMB) data are expected
from ongoing and near-future CMB Stage-III and IV surveys, which will yield
reconstructed CMB lensing maps with effective resolution approaching several
arcminutes. The small-scale CMB lensing fluctuations receive non-negligible
contributions from nonlinear structure in the late-time density field. These
fluctuations are not fully characterized by traditional two-point statistics,
such as the power spectrum. Here, we use $N$-body ray-tracing simulations of
CMB lensing maps to examine two higher-order statistics: the lensing
convergence one-point probability distribution function (PDF) and peak counts.
We show that these statistics contain significant information not captured by
the two-point function, and provide specific forecasts for the ongoing
Stage-III Advanced Atacama Cosmology Telescope (AdvACT) experiment. Considering
only the temperature-based reconstruction estimator, we forecast 9$\sigma$
(PDF) and 6$\sigma$ (peaks) detections of these statistics with AdvACT. Our
simulation pipeline fully accounts for the non-Gaussianity of the lensing
reconstruction noise, which is significant and cannot be neglected. Combining
the power spectrum, PDF, and peak counts for AdvACT will tighten cosmological
constraints in the $\Omega_m$-$\sigma_8$ plane by $\approx 30\%$, compared to
using the power spectrum alone. | Primordial Black Holes from First-Order Cosmological Phase Transitions: We discuss the possibility of forming primordial black holes during a
first-order phase transition in the early Universe. As is well known, such a
phase transition proceeds through the formation of true-vacuum bubbles in a
Universe that is still in a false vacuum. When there is a particle species
whose mass increases significantly during the phase transition, transmission of
the corresponding particles through the advancing bubble walls is suppressed.
Consequently, an overdensity can build up in front of the walls and become
sufficiently large to trigger primordial black hole formation. We track this
process quantitatively by solving a Boltzmann equation, and we determine the
resulting black hole density and mass distribution as a function of model
parameters. |
The abundance of voids and the excursion set formalism: We present measurements of the number density of voids in the dark matter
distribution from a series of N-body simulations of a \Lambda CDM cosmology. We
define voids as spherical regions of \rho_v = 0.2\rho_m around density minima
in order to relate our results to the predicted abundances using the excursion
set formalism. Using a linear underdensity of \delta_v = -2.7, from a spherical
evolution model, we find that a volume conserving model, which does not
conserve number density in the mapping from the linear to nonlinear regime,
matches the measured abundance to within 16% for a range of void radii 1<
r(Mpc/h)<15. This model fixes the volume fraction of the universe which is in
voids and assumes that voids of a similar size merge as they expand by a factor
of 1.7 to achieve a nonlinear density of \rho_v = 0.2\rho_m today. We find that
the model of Sheth & van de Weygaert (2004) for the number density of voids
greatly overpredicts the abundances over the same range of scales. We find that
the volume conserving model works well at matching the number density of voids
measured from the simulations at higher redshifts, z=0.5 and 1, as well as
correctly predicting the abundances to within 25% in a simulation of a matter
dominated \Omega_m = 1 universe. We examine the abundance of voids in the halo
distribution and find fewer small, r<10 Mpc/h, voids and many more large, r>10
Mpc/h, voids compared to the dark matter. These results indicate that voids
identified in the halo or galaxy distribution are related to the underlying
void distribution in the dark matter in a complicated way which merits further
study if voids are to be used as a precision probe of cosmology. | Modified Gravity and Dark Energy models Beyond $w(z)$CDM Testable by
LSST: One of the main science goals of the Large Synoptic Survey Telescope (LSST)
is to uncover the nature of cosmic acceleration. In the base analysis, possible
deviations from the Lambda-Cold-Dark-Matter ($\Lambda$CDM) background evolution
will be probed by fitting a $w(z)$CDM model, which allows for a
redshift-dependent dark energy equation of state with $w(z)$, within general
relativity (GR). A rich array of other phenomena can arise due to deviations
from the standard $\Lambda$CDM+GR model though, including modifications to the
growth rate of structure and lensing, and novel screening effects on non-linear
scales. Concrete physical models are needed to provide consistent predictions
for these (potentially small) effects, to give us the best chance of detecting
them and separating them from astrophysical systematics. A complex plethora of
possible models has been constructed over the past few decades, with none
emerging as a particular favorite. This document prioritizes a subset of these
models along with rationales for further study and inclusion into the LSST Dark
Energy Science Collaboration (DESC) data analysis pipelines, based on their
observational viability, theoretical plausibility, and level of theoretical
development. We provide references and theoretical expressions to aid the
integration of these models into DESC software and simulations, and give
justifications for why other models were not prioritized. While DESC efforts
are free to pursue other models, we provide here guidelines on which theories
appear to have higher priority for collaboration efforts due to their perceived
promise and greater instructional value. |
Brane-like singularities with no brane: We use a method of linearization to study the emergence of the future
cosmological singularity characterized by finite value of the cosmological
radius. We uncover such singularities that keep Hubble parameter finite while
making all higher derivatives of the scale factor (starting out from the $\ddot
a$) diverge as the cosmological singularity is approached. Since such
singularities has been obtained before in the brane world model we name them
the "brane-like" singularities. These singularities can occur during the
expanding phase in usual Friedmann universe filled with both a self-acting,
minimally coupled scalar field and a homogeneous tachyon field. We discover a
new type of finite-time, future singularity which is different from type I-IV
cosmological singularities in that it has the scale factor, pressure and
density finite and nonzero. The generalization of $w$-singularity is obtained
as well. | The Threshold for Primordial Black Hole Formation: a Simple Analytic
Prescription: Primordial black holes could have been formed in the early universe from non
linear cosmological perturbations re-entering the cosmological horizon when the
Universe was still radiation dominated. Starting from the shape of the power
spectrum on superhorizon scales, we provide a simple prescription, based on the
results of numerical simulations, to compute the threshold $\delta_c$ for
primordial black hole formation. Our procedure takes into account both the non
linearities between the Gaussian curvature perturbation and the density
contrast and, for the first time in the literature, the non linear effects
arising at horizon crossing, which increase the value of the threshold by about
a factor two with respect to the one computed on superhorizon scales. |
Statistically-Anisotropic Tensor Bispectrum from Inflation: We develop a possibility of generating tensor non-Gaussianity in a kind of
anisotropic inflation, where a $U(1)$ gauge field is kinetically coupled to a
spectator scalar field. Owing to this coupling, the coherent mode of the
electric field appears and softly breaks the isotropy of the Universe. We
compute the bispectrum of linearly-polarized tensor perturbations sourced by
the gauge field and find that it is strongly red-tilted and has distinctive
statistical anisotropies including higher-order multipole moments.
Interestingly, the tensor bispectra with the specific combinations of linear
polarization modes are dominant, and their amplitudes depend on the different
sets of multipole moments. This new type of statistically-anisotropic tensor
non-Gaussianity can be potentially testable with the upcoming cosmic microwave
background B-mode polarization experiments. | Unmasking the Masked Universe: the 2M++ catalogue through Bayesian eyes: This work describes a full Bayesian analysis of the Nearby Universe as traced
by galaxies of the 2M++ survey. The analysis is run in two sequential steps.
The first step self-consistently derives the luminosity dependent galaxy
biases, the power-spectrum of matter fluctuations and matter density fields
within a Gaussian statistic approximation. The second step makes a detailed
analysis of the three dimensional Large Scale Structures, assuming a fixed bias
model and a fixed cosmology. This second step allows for the reconstruction of
both the final density field and the initial conditions at z=1000 assuming a
fixed bias model. From these, we derive fields that self-consistently
extrapolate the observed large scale structures. We give two examples of these
extrapolation and their utility for the detection of structures: the visibility
of the Sloan Great Wall, and the detection and characterization of the Local
Void using DIVA, a Lagrangian based technique to classify structures. |
Probing modified gravity in cosmic filaments: Multiple modifications of general relativity (GR) have been proposed in the
literature in order to understand the nature of the accelerated expansion of
the Universe. However, thus far all the predictions of GR have been confirmed
with constantly increasing accuracy. In this work, we study the imprints of a
particular class of models -- "screened" modified gravity theories -- on cosmic
filaments. We have utilized the $N$-body code ISIS/RAMSES to simulate the
symmetron model and the Hu-Sawicky $f(R)$ model, and we post-process the output
with DisPerSE to identify the filaments of the cosmic web. We investigated how
the global properties of the filaments -- such as their lengths, masses, and
thicknesses -- as well as their radial density and speed profiles change under
different gravity theories. We find that filaments are, on average, shorter and
denser in modified gravity models compared to in $\Lambda$CDM. We also find
that the speed profiles of the filaments are enhanced, consistent with
theoretical expectations. Overall, our results suggest that cosmic filaments
can be an effective complementary probe of screened modified gravity theories
on Mpc scales. | Dark energy in thermal equilibrium with the cosmological horizon?: According to a generalization of black hole thermodynamics to a cosmological
framework, it is possible to define a temperature for the cosmological horizon.
The hypothesis of thermal equilibrium between the dark energy and the horizon
has been considered by many authors. We find the restrictions imposed by this
hypothesis on the energy transfer rate ($Q_i$) between the cosmological fluids,
assuming that the temperature of the horizon have the form $T=b/2\pi R$, where
$R$ is the radius of the horizon. We more specifically consider two types of
dark energy: holographic dark energy (HDE) and dark energy with a constant EoS
parameter ($w$DE). In each case, we show that for a given radius $R$, there is
an unique term $Q_{de}$ that is consistent with thermal equilibrium. We also
consider the situation where, in addition to dark energy, other fluids (cold
matter, radiation) are in thermal equilibrium with the horizon. We find that
the interaction terms required for this will generally violate energy
conservation ($\sum_i Q_i=0$). |
The LBT Bootes Field Survey: I. The Rest-frame UV and Luminosity
Functions and Clustering of Bright Lyman Break Galaxies at z~3: We present a deep LBT/LBC U-band imaging survey (9 deg2) covering the NOAO
Bootes field. A total of 14,485 Lyman Break Galaxies (LBGs) at z~3 are
selected, which are used to measure the rest-frame UV luminosity function (LF).
The large sample size and survey area reduce the LF uncertainties due to
Poisson statistics and cosmic variance by >3 compared to previous studies. At
the bright end, the LF shows excess power compared to the best-fit Schechter
function, which can be attributed to the contribution of $z\sim3$ quasars. We
compute the rest-frame near-infrared LF and stellar mass function (SMF) of z~3
LBGs based on the R-band and IRAC [4.5 micro m]-band flux relation. We
investigate the evolution of the UV LFs and SMFs between z~7 and z~3, which
supports a rising star formation history in the LBGs. We study the spatial
correlation function of two bright LBG samples and estimate their average host
halo mass. We find a tight relation between the host halo mass and the galaxy
star formation rate (SFR),which follows the trend predicted by the baryonic
accretion rate onto the halo, suggesting that the star formation in LBGs is
fueled by baryonic accretion through the cosmic web. By comparing the SFRs with
the total baryonic accretion rates, we find that cosmic star formation
efficiency is about 5%-20% and it does not evolve significantly with redshift,
halo mass, or galaxy luminosity. | Bayesian analysis of spatially distorted cosmic signals from Poissonian
data: Reconstructing the matter density field from galaxy counts is a problem
frequently addressed in current literature. Two main sources of error are shot
noise from galaxy counts and insufficient knowledge of the correct galaxy
position caused by peculiar velocities and redshift measurement uncertainty.
Here we address the reconstruction problem of a Poissonian sampled log-normal
density field with velocity distortions in a Bayesian way via a maximum a
posteriory method. We test our algorithm on a 1D toy case and find significant
improvement compared to simple data inversion. In particular, we address the
following problems: photometric redshifts, mapping of extended sources in coded
mask systems, real space reconstruction from redshift space galaxy distribution
and combined analysis of data with different point spread functions. |
Constraints On Dark Matter From Reionization: This conference proceedings paper provides a short summary of the constraints
presented in Menci et al. 2016, 2017 on the mass of thermal WDM candidates, and
of the results presented in Romanello et al. 2021 on how Reionization scenarios
are affected by early galaxy formation in WDM cosmologies. The abundance of
galaxies in the epoch of reionization ($z>$6) is dependent on fundamental
cosmological parameters, most importantly on the properties of dark matter,
such that it can be used as a powerful cosmological probe. Here we show how the
number density of primordial galaxies allows to constrain the mass of thermal
WDM candidates, and we discuss the constraints that will be made possible by
future JWST observations. We then investigate how the Reionization process is
affected by early galaxy formation in different cosmological scenarios. We use
a semi-analytic model with suppressed initial power spectra to obtain the UV
Luminosity Function in thermal Warm Dark Matter and sterile neutrino
cosmologies. For each cosmology, we find an upper limit to fixed $f_{esc}$,
which guarantees the completion of the process at $z<6.7$. | Broadband X-ray properties of absorbed AGN: In this paper we report on the broadband X-ray properties of a complete
sample of 33 absorbed Seyfert galaxies hard X-ray selected with integral. The
high quality broadband spectra obtained with both xmm, and integral-IBIS data
are well reproduced with an absorbed primary emission with a high energy cutoff
and its scattered fraction below 2-3 keV, plus the Compton reflection features.
A high energy cut-off is found in 30% of the sample, with an average value
below 150 keV. The diagnostic plot NH vs Fobs(2-10 keV)/F(20-100 keV) allowed
the isolation of the Compton thick objects, and may represent a useful tool for
future hard X-ray observations of newly discovered AGN. We are unable to
associate the reflection components with the absorbing gas as a torus, a more
complex scenario being necessary. In the Compton thin sources, a fraction (but
not all) of the Fe K line needs to be produced in a gas possibly associated
with the optical Broad Line Region, responsible also for the absorption. We
still need a Compton thick medium (not intercepting the line of sight) likely
associated to a torus, which contributes to the Fe line intensity and produces
the observed reflection continuum above 10 keV. The so-called Iwasawa-Taniguchi
effect can not be confirmed with our data. Finally, the comparison with a
sample of unobscured AGN shows that, type 1 and type 2 (once corrected for
absorption) Seyfert are characterized by the same nuclear/accretion properties
(luminosity, bolometric luminosity, Eddington ratio), supporting the "unified"
view. |
Deep observations of CO line emission from star-forming galaxies in a
cluster candidate at z=1.5: We report results from a deep Jansky Very Large Array (JVLA) search for CO
1-0 line emission from galaxies in a candidate galaxy cluster at z~1.55 in the
COSMOS field. We target 4 galaxies with optical spectroscopic redshifts in the
range z=1.47-1.59. Two of these 4 galaxies, ID51613 and ID51813, are nominally
detected in CO line emission at the 3-4 sigma level. We find CO luminosities of
2.4x10^10 K km/s pc^2 and 1.3x10^10 K km/s pc^2, respectively. Taking advantage
from the clustering and 2-GHz bandwidth of the JVLA, we perform a search for
emission lines in the proximity of optical sources within the field of view of
our observations. We limit our search to galaxies with K<23.5 (AB) and
z_phot=1.2-1.8. We find 2 bright optical galaxies to be associated with
significant emission line peaks (>4 sigma) in the data cube, which we identify
with the CO line emission. To test the reliability of the line peaks found, we
performed a parallel search for line peaks using a Bayesian inference method.
Monte Carlo simulations show that such associations are statistically
significant, with probabilities of chance association of 3.5% and 10.7% for ID
51207 and ID 51380, respectively. Modeling of their optical/IR SEDs indicates
that the CO detected galaxies and candidates have stellar masses and SFRs in
the range (0.3-1.1)x10^11 M_sun and 60-160 M_sun/yr, with SFEs comparable to
that found in other star-forming galaxies at similar redshifts. By comparing
the space density of CO emitters derived from our observations with the space
density derived from previous CO detections at z~1.5, and with semi-analytic
predictions for the CO luminosity function, we suggest that the latter tend to
underestimate the number of CO galaxies detected at high-redshift. Finally, we
argue about the benefits of future blind CO searches in clustered fields with
upcoming submm/radio facilities. | Coordinate independent approach to the calculation of the effects of
local structure on the luminosity distance: Local structure can have important effects on luminosity distance
observations, which could for example affect the local estimation of the Hubble
constant based on low red-shift type Ia supernovae. Using a spherically
symmetric exact solution of the Eistein's equations and a more accurate
expansion of the solution of the geodesic equations, we improve the low
red-shift expansion of the monopole of the luminosity distance in terms of the
curvature function. Based on this we derive the coordinate independent low
red-shift expansion of the monopole of the luminosity distance in terms of the
monopole of the density contrast. The advantage of this approach is that it
relates the luminosity distance directly to density observations, without any
dependency on the radial coordinate choice. We compute the effects of different
inhomogeneities on the luminosity distance, and find that the formulae in terms
of the density contrast are in good agreement with numerical calculations, in
the non linear regime are more accurate than the results obtained using linear
perturbation theory, and are also more accurate than the formulae in terms of
the curvature function. |
Black Hole Demography: From scaling relations to models: In this contributed paper I review our current knowledge of the local Black
Hole (BH) scaling relations, and their impact on the determination of the local
BH mass function. I particularly emphasize the remaining systematic
uncertainties impinging upon a secure determination of the BH mass function and
how progress can be made. I then review and discuss the evidence for a
different time evolution for separate BH-galaxy scaling relations, and how
these independent empirical evidences can be reconciled with the overall
evolution of the structural properties of the host galaxies. I conclude
discussing BH demography in the context of semi-empirical continuity accretion
models, as well as more complex evolutionary models, emphasizing the general
constraints we can set on them. | Signatures of the neutrino thermal history in the spectrum of primordial
gravitational waves: In this paper we study the effect of the anisotropic stress generated by
neutrinos on the propagation of primordial cosmological gravitational waves.
The presence of anisotropic stress, like the one generated by free-streaming
neutrinos, partially absorbs the gravitational waves (GWs) propagating across
the Universe. We find that in the standard case of three neutrino families, 22%
of the intensity of the wave is absorbed, in fair agreement with previous
studies. We have also calculated the maximum possible amount of damping,
corresponding to the case of a flat Universe completely dominated by
ultrarelativistic collisionless particles. In this case 43% of the intensity of
the wave is absorbed. Finally, we have taken into account the effect of
collisions, using a simple form for the collision term parameterized by the
mean time between interactions, that allows to go smoothly from the case of a
tigthly-coupled fluid to that of a collisionless gas. The dependence of the
absorption on the neutrino energy density and on the effectiveness of the
interactions opens the interesting possibility of observing spectral features
related to particular events in the thermal history of the Universe, like
neutrino decoupling and electron-positron annihilation, both occurring at T~1
MeV. GWs entering the horizon at that time will have today a frequency $\nu\sim
10^{-9} \Hz$, a region that is going to be probed by Pulsar Timing Arrays. |
PBHs and secondary GWs from ultra slow roll and punctuated inflation: [Abridged] The primordial scalar power spectrum is well constrained on large
scales, primarily by the observations of the anisotropies in the cosmic
microwave background (CMB). Over the last few years, it has been recognized
that a sharp rise in power on small scales will lead to enhanced formation of
primordial black holes (PBHs) and also generate secondary gravitational waves
(GWs) of higher and, possibly, detectable amplitudes. It is well understood
that scalar power spectra with COBE normalized amplitude on the CMB scales and
enhanced amplitudes on smaller scales can be generated due to deviations from
slow roll in single, canonical scalar field models of inflation. In fact, an
epoch of so-called ultra slow roll inflation can lead to the desired
amplification. We find that scenarios that lead to ultra slow roll can be
broadly classified into two types, one wherein there is a brief departure from
inflation (a scenario referred to as punctuated inflation) and another wherein
such a departure does not arise. We consider a set of single field inflationary
models involving the canonical scalar field that lead to ultra slow roll and
punctuated inflation and examine the formation of PBHs as well as the
generation of secondary GWs in these models. Apart from considering specific
models, we reconstruct potentials from certain functional choices of the first
slow roll parameter leading to ultra slow roll and punctuated inflation and
investigate their observational signatures. In addition to the secondary tensor
power spectrum, we calculate the secondary tensor bispectrum in the equilateral
limit in these scenarios. Moreover, we calculate the inflationary scalar
bispectrum that arises in all the cases and discuss the imprints of the scalar
non-Gaussianities on the extent of PBHs formed and the amplitude of the
secondary GWs. | Constraints on intrinsic alignment contamination of weak lensing surveys
using the MegaZ-LRG sample: Correlations between the intrinsic shapes of galaxies and the large-scale
galaxy density field provide an important tool to investigate galaxy intrinsic
alignments, which constitute a major astrophysical systematic in cosmological
weak lensing (cosmic shear) surveys, but also yield insight into the formation
and evolution of galaxies. We measure galaxy position-shape correlations in the
MegaZ-LRG sample for more than 800,000 luminous red galaxies, making the first
such measurement with a photometric redshift sample. In combination with a
re-analysis of several spectroscopic SDSS samples, we constrain an intrinsic
alignment model for early-type galaxies over long baselines in redshift (z ~
0.7) and luminosity (4mag). We develop and test the formalism to incorporate
photometric redshift scatter in the modelling. For r_p > 6 Mpc/h, the fits to
galaxy position-shape correlation functions are consistent with the scaling
with r_p and redshift of a revised, nonlinear version of the linear alignment
model for all samples. An extra redshift dependence proportional to (1+z)^n is
constrained to n=-0.3+/-0.8 (1sigma). To obtain consistent amplitudes for all
data, an additional dependence on galaxy luminosity proportional to L^b with
b=1.1+0.3-0.2 is required. The normalisation of the intrinsic alignment power
spectrum is found to be (0.077 +/- 0.008)/rho_{cr} for galaxies at redshift 0.3
and r band magnitude of -22 (k- and evolution-corrected to z=0). Assuming zero
intrinsic alignments for blue galaxies, we assess the bias on cosmological
parameters for a tomographic CFHTLS-like lensing survey. Both the resulting
mean bias and its uncertainty are smaller than the 1sigma statistical errors
when using the constraints from all samples combined. The addition of MegaZ-LRG
data reduces the uncertainty in intrinsic alignment bias on cosmological
parameters by factors of three to seven. (abridged) |
IR-derived covering factors for a large sample of quasars from
WISE-UKIDSS-SDSS: We investigate the range of covering factors (determined from the ratio of IR
to UV/optical luminosity) seen in luminous type 1 quasars using a combination
of data from the WISE, UKIDSS and SDSS surveys. Accretion disk (UV/optical) and
obscuring dust (IR) luminosities are measured via the use of a simple three
component SED model. We use these estimates to investigate the distribution of
covering factors and its relationship to both accretion luminosity and IR SED
shape. The distribution of covering factors (f_C) is observed to be log-normal,
with a bias-corrected mean of <log10 f_C>=-0.41 and standard deviation of 0.2.
The fraction of IR luminosity emitted in the near-IR (1--5 micron) is found to
be high (~40 per cent), and strongly dependant on covering factor. | CosmoHammer: Cosmological parameter estimation with the MCMC Hammer: We study the benefits and limits of parallelised Markov chain Monte Carlo
(MCMC) sampling in cosmology. MCMC methods are widely used for the estimation
of cosmological parameters from a given set of observations and are typically
based on the Metropolis-Hastings algorithm. Some of the required calculations
can however be computationally intensive, meaning that a single long chain can
take several hours or days to calculate. In practice, this can be limiting,
since the MCMC process needs to be performed many times to test the impact of
possible systematics and to understand the robustness of the measurements being
made. To achieve greater speed through parallelisation, MCMC algorithms need to
have short auto-correlation times and minimal overheads caused by tuning and
burn-in. The resulting scalability is hence influenced by two factors, the MCMC
overheads and the parallelisation costs. In order to efficiently distribute the
MCMC sampling over thousands of cores on modern cloud computing infrastructure,
we developed a Python framework called CosmoHammer which embeds emcee, an
implementation by Foreman-Mackey et al. (2012) of the affine invariant ensemble
sampler by Goodman and Weare (2010). We test the performance of CosmoHammer for
cosmological parameter estimation from cosmic microwave background data. While
Metropolis-Hastings is dominated by overheads, CosmoHammer is able to
accelerate the sampling process from a wall time of 30 hours on a dual core
notebook to 16 minutes by scaling out to 2048 cores. Such short wall times for
complex data sets opens possibilities for extensive model testing and control
of systematics. |
A Photometric Redshift of z ~ 9.4 for GRB 090429B: Gamma-ray bursts (GRBs) serve as powerful probes of the early Universe, with
their luminous afterglows revealing the locations and physical properties of
star forming galaxies at the highest redshifts, and potentially locating first
generation (Population III) stars. Since GRB afterglows have intrinsically very
simple spectra, they allow robust redshifts from low signal to noise
spectroscopy, or photometry. Here we present a photometric redshift of z~9.4
for the Swift-detected GRB 090429B based on deep observations with
Gemini-North, the Very Large Telescope, and the GRB Optical and Near-infrared
Detector. Assuming a Small Magellanic Cloud dust law (which has been found in a
majority of GRB sight-lines), the 90% likelihood range for the redshift is 9.06
< z < 9.52, although there is a low-probability tail to somewhat lower
redshifts. Adopting Milky Way or Large Magellanic Cloud dust laws leads to very
similar conclusions, while a Maiolino law does allow somewhat lower redshift
solutions, but in all cases the most likely redshift is found to be z>7. The
non-detection of the host galaxy to deep limits (Y_AB >~ 28 mag, which would
correspond roughly to 0.001 L* at z=1) in our late time optical and infrared
observations with the Hubble Space Telescope strongly supports the extreme
redshift origin of GRB 090429B, since we would expect to have detected any
low-z galaxy, even if it were highly dusty. Finally, the energetics of GRB
090429B are comparable to those of other GRBs, and suggest that its progenitor
is not greatly different to those of lower redshift bursts. | Canonical high power blazars: The jets of powerful blazars propagate within regions relatively dense of
radiation produced externally to the jet. This radiation is a key ingredient to
understand the origin of the high energy emission of blazars, from the X-ray to
the gamma-ray energy band. These external radiation fields control the amount
of the inverse Compton radiation with respect to the synchrotron flux.
Therefore the predicted spectral energy distribution (SED) will depend on where
the jet dissipates part of its energy to produce the observed radiation. We
investigate in detail how the SED changes as a function of the location of the
jet dissipation region, by assuming rather "standard" (i.e. "canonical")
prescriptions for the accretion disk and its X-ray corona, the profile of the
jet magnetic field and the external radiation. The magnetic energy density of a
"canonical" jet almost never dominates the radiative cooling of the emitting
electrons, and consequently the inverse Compton flux almost always dominates
the bolometric output. This is more so for large black hole masses. Dissipation
taking place beyond the broad line region is particularly interesting, since it
accounts in a simple way for the largest inverse Compton to synchrotron flux
ratios accompanied by an extremely hard X-ray spectrum. Furthermore it makes
the high power blazars at high redshift useful tools to study the optical to UV
cosmic backgrounds. |
Cosmological constraints on R2-AB model: Nowadays, efforts are being devoted to the study of alternative cosmological
scenarios, in which, modifications of General Relativity (GR) theory have been
proposed to explain the late cosmic acceleration, without assuming the
existence of the dark energy (DE) component. We investigate the $R^2$-corrected
Appleby-Battye model, or $R^2$-AB model, which consists of an $f(R)$ model with
only one extra free parameter $b$, besides the cosmological parameters of the
flat-$\Lambda$CDM model: $H_0$ and $\Omega_{m,0}$. Regarding this model, it was
already shown that a positive value for $b$ is required for the model to be
consistent with Solar System tests, moreover, the condition for the existence
of a de~Sitter state requires $b \ge 1.6$. To impose observational constraints
on the $R^2$-AB model, we consider in our analyses two data sets: cosmic
chronometer $H(z)$ data for the background level, and $[f\sigma_8](z)$ data,
for the perturbative level. The first one provides $b = 1.6^{+3.1}_{-0.0}$ and
the cosmological parameters $\{H_0 ,\Omega_{m,0}\}$ in agreement to Planck
values, while the second one, indicates $b = 1.76^{+2.91}_{-0.15}$ and the
parameters $\{\Omega_{m,0},\sigma_{8,0} \}$ also in agreement to Planck values;
in the last case the data was marginalized over the parameter $H_0$.
Additionally, we perform illustrative analyses that compare this $f(R)$ model
with the flat-$\Lambda$CDM model, considering several values of the parameter
$b$, for diverse cosmological functions like the Hubble function $H(z)$, the
equation of state $w_{eff}(z)$, the parametrized growth rate of cosmic
structures $[f \sigma_8](z)$, and $\sigma_8(z)$. | Massive black hole factories: Supermassive and quasi-star formation in
primordial halos: Supermassive stars and quasi-stars (massive stars with a central black hole)
are both considered as potential progenitors for the formation of supermassive
black holes. They are expected to form from rapidly accreting protostars in
massive primordial halos. We explore how long rapidly accreting protostars
remain on the Hayashi track, implying large protostellar radii and weak
accretion luminosity feedback. We assess the potential role of energy
production in the nuclear core, and determine what regulates the evolution of
such protostars into quasi-stars or supermassive stars. We follow the
contraction of characteristic mass scales in rapidly accreting protostars, and
infer the timescales for them to reach nuclear densities. We compare the
characteristic timescales for nuclear burning with those for which the extended
protostellar envelope can be maintained. We find that the extended envelope can
be maintained up to protostellar masses of 3.6x10^8 \dot{m}^3 solar, where
\dot{m} denotes the accretion rate in solar masses per year. We expect the
nuclear core to exhaust its hydrogen content in 7x10^6 yrs. If accretion rates
\dot{m}>>0.14 can still be maintained at this point, a black hole may form
within the accreting envelope, leading to a quasi-star. Alternatively, the
accreting object will gravitationally contract to become a main-sequence
supermassive star. Due to the limited gas reservoir in dark matter halos with
10^7 solar masses, the accretion rate onto the central object may drop at late
times, implying the formation of supermassive stars as the typical outcome of
direct collapse. However, if high accretion rates are maintained, a quasi-star
with an interior black hole may form. |
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