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Growing Massive Black Holes in a Local Group Environment: the Central
Supermassive, Slowly Sinking, and Ejected Populations: We explore the growth of < 10^7 Msun black holes that reside at the centers
of spiral and field dwarf galaxies in a Local Group type of environment. We use
merger trees from a cosmological N-body simulation known as Via Lactea II
(VL-2) as a framework to test two merger-driven semi-analytic recipes for black
hole growth that include dynamical friction, tidal stripping, and gravitational
wave recoil in over 20,000 merger tree realizations. First, we apply a
Fundamental Plane limited (FPL) model to the growth of Sgr A*, which drives the
central black hole to a maximum mass limited by the Black Hole Fundamental
Plane after every merger. Next, we present a new model that allows for
low-level Prolonged Gas Accretion (PGA) during the merger. We find that both
models can generate a Sgr A* mass black hole. We predict a population of
massive black holes in local field dwarf galaxies - if the VL-2 simulation is
representative of the growth of the Local Group, we predict up to 35 massive
black holes (< 10^6 Msun) in Local Group field dwarfs. We also predict that
hundreds of < 10^5 Msun black holes fail to merge, and instead populate the
Milky Way halo, with the most massive of them at roughly the virial radius. In
addition, we find that there may be hundreds of massive black holes ejected
from their hosts into the nearby intergalactic medium due to gravitational wave
recoil. We discuss how the black hole population in the Local Group field
dwarfs may help to constrain the growth mechanism for Sgr A*. | Type Ia Supernova cosmology combining data from the $Euclid$ mission and
the Vera C. Rubin Observatory: The $Euclid$ mission will provide first-of-its-kind coverage in the
near-infrared over deep (three fields, $\sim$10-20 square degrees each) and
wide ($\sim$10000 square degrees) fields. While the survey is not designed to
discover transients, the deep fields will have repeated observations over a
two-week span, followed by a gap of roughly six months. In this analysis, we
explore how useful the deep field observations will be for measuring properties
of Type Ia supernovae (SNe Ia). Using simulations that include $Euclid$'s
planned depth, area and cadence in the deep fields, we calculate that more than
3700 SNe between $0.0<z<1.5$ will have at least five $Euclid$ detections around
peak with signal-to-noise ratio larger than 3. While on their own, $Euclid$
light curves are not good enough to directly constrain distances, when combined
with LSST deep field observations, we find that uncertainties on SN distances
are reduced by 20-30% for $z<0.8$ and by 40-50% for $z>0.8$. Furthermore, we
predict how well additional $Euclid$ mock data can be used to constrain a key
systematic in SN Ia studies - the size of the luminosity 'step' found between
SNe hosted in high mass ($>10^{10} M_{\odot}$) and low mass ($>10^{10}
M_{\odot}$) galaxies. This measurement has unique information in the rest-frame
NIR. We predict that if the step is caused by dust, we will be able to measure
its reduction in the NIR compared to optical at the 4$\sigma$ level. We
highlight that the LSST and $Euclid$ observing strategies used in this work are
still provisional and some level of joint processing is required. Still, these
first results are promising, and assuming $Euclid$ begins observations well
before the Nancy Roman Space Telescope (Roman), we expect this dataset to be
extremely helpful for preparation for Roman itself. |
An alternative approach to the Finger of God in large scale structures: It is generally accepted that linear theory of growth of structure under
gravity produces a squashed structure in the two-point correlation function
(2PCF) along the line of sight (LoS). On the other hand, the observed radial
spread out structure known as Finger of God (FoG) is attributed to non-linear
effects, like virial relaxation or random motions in the inner regions of
galaxy clusters, or non-linear terms in collapse theory. In this paper we argue
that the squashed structure associated with the redshift-space ($s-$) linear
theory 2PCF is obtained only when this function is displayed in real-space
($r-$), or when the mapping from $r-$ to $s-$space is trivialized by one of a
series of approximations: the "wide separation" sometimes mistaken by the
"distant observer", the $\mu(r) \sim \mu(s)$ in the cosine of the position
vector with the LoS, or plainly by approximating $s \sim r$. To display the
$s-$space 2PCF properly in a grid in $s-$space requires one to solve for the
mapping function $\bm s(\bm r)$ and its inverse, which exists in the small
gravitational disturbance case. We find this mapping by using plane of the sky
projections of the $r-$ and $s-$ 2PCFs in the simplest case of the linear
Kaiser spectrum with a conservative power-law $r-$space 2PCF. We show that even
in this simple case, a structure quite similar to the FoG is observed in the
small scale region, while in the large scale the expected squashed structure is
obtained. We show that the observed structure is a function of three
parameters: the dimensionless growth rate for visible matter ($\beta$), the
power-law exponent ($\gamma$) and the cosmological distortion given by the
Alcock-Paczy{\'n}ski parameter ($AP$). We conclude that there appears to be the
way of discerning between cosmological and gravitational redshift distortions
avoiding known degeneracies. | Marginal Bayesian Statistics Using Masked Autoregressive Flows and
Kernel Density Estimators with Examples in Cosmology: Cosmological experiments often employ Bayesian workflows to derive
constraints on cosmological and astrophysical parameters from their data. It
has been shown that these constraints can be combined across different probes
such as Planck and the Dark Energy Survey and that this can be a valuable
exercise to improve our understanding of the universe and quantify tension
between multiple experiments. However, these experiments are typically plagued
by differing systematics, instrumental effects and contaminating signals, which
we collectively refer to as `nuisance' components, that have to be modelled
alongside target signals of interest. This leads to high dimensional parameter
spaces, especially when combining data sets, with > 20 dimensions of which only
around 5 correspond to key physical quantities. We present a means by which to
combine constraints from different data sets in a computationally efficient
manner by generating rapid, reusable and reliable marginal probability density
estimators, giving us access to nuisance-free likelihoods. This is possible
through the unique combination of nested sampling, which gives us access to
Bayesian evidences, and the marginal Bayesian statistics code MARGARINE. Our
method is lossless in the signal parameters, resulting in the same posterior
distributions as would be found from a full nested sampling run over all
nuisance parameters, and typically quicker than evaluating full likelihoods. We
demonstrate our approach by applying it to the combination of posteriors from
the Dark Energy Survey and Planck. |
The mass distribution in Spirals: In the past years a wealth of observations has unraveled the structural
properties of the Dark and Luminous mass distribution in spirals. These have
pointed out to an intriguing scenario not easily explained by present theories
of galaxy formation. The investigation of individual and coadded objects has
shown that the spiral rotation curves follow, from their centers out to their
virial radii, a Universal profile (URC) that arises from the tuned combination
of a stellar disk and of a dark halo. The importance of the latter component
decreases with galaxy mass. Individual objects, on the other hand, have clearly
revealed that the dark halos encompassing the luminous discs have a constant
density core. This resulting observational scenario poses important challenges
to presently favored theoretical $\Lambda$CDM Cosmology. | The 21cm Signature of Early Relic \HII Regions: We calculate the spin temperature and 21 cm brightness of early \HII regions
around the first stars. We use outputs from cosmological
radiation-hydrodynamics simulations of the formation and evolution of early
\HII regions. In the pre-reionization era, \HII regions around massive
primordial stars have diameters of a few kpc. The gas within the \HII regions
is almost fully ionized, but begins recombining after the central stars die
off. The relic \HII regions are then seen as bright {\it emission} sources in
hydrogen 21 cm. We make brightness temperature maps of the \HII regions,
accounting for radiative coupling with Lyman-$\alpha$ photons in a simplified
manner. The spin temperature in the relic \HII region is close to the gas
kinetic temperature, generally several hundred to several thousand degrees. We
show that the relic \HII region can be as bright as $\delta T_{\rm b} \sim 100$
mK in differential temperature against the cosmic microwave background for an
angular resolution of sub-arcseconds. While individual early \HII patches will
not be identified by currently planned radio telescopes, the collective
fluctuations from early \HII regions might imprint signatures in the 21 cm
background. |
Measuring the X-ray Background in the Reionization Era with First
Generation 21 cm Experiments: The X-ray background during the epoch of reionization is currently poorly
constrained. We demonstrate that it is possible to use first generation 21 cm
experiments to calibrate it. Using the semi-numerical simulation, 21cmFAST, we
calculate the dependence of the 21 cm power spectrum on the X-ray background
flux. Comparing the signal to the sensitivity of the Murchison Widefield Array
(MWA) we find that in the redshift interval z=8-14 the 21 cm signal is
detectable based on the upper limit set by the present-day unresolved soft
X-ray background. We show that there is no degeneracy between the X-ray
production efficiency and the Lyman-Alpha production efficiency and that the
degeneracy with the ionization fraction of the intergalactic medium can be
broken. | Electron screening and its effects on Big-Bang nucleosynthesis: We study the effects of electron screening on nuclear reaction rates
occurring during the Big Bang nucleosynthesis epoch. The sensitivity of the
predicted elemental abundances on electron screening is studied in details. It
is shown that electron screening does not produce noticeable results in the
abundances unless the traditional Debye-H\"uckel model for the treatment of
electron screening in stellar environments is enhanced by several orders of
magnitude. The present work rules out electron screening as a relevant
ingredient to Big Bang nucleosynthesis and ruling out exotic possibilities for
the treatment of screening, beyond the mean-field theoretical approach. |
Intermediate inflation from rainbow gravity: It is possible to dualize theories based on deformed dispersion relations and
Einstein gravity so as to map them into theories with trivial dispersion
relations and rainbow gravity. This often leads to "dual inflation" without the
usual breaking of the strong energy condition. We identify the dispersion
relations in the original frame which map into "intermediate" inflationary
models. These turn out to be particularly simple: power-laws modulated by
powers of a logarithm. The fluctuations predicted by these scenarios are near,
but not exactly scale-invariant, with a red running spectral index. These
dispersion relations deserve further study within the context of quantum
gravity and the phenomenon of dimensional reduction in the ultraviolet. | A Test of the Cosmological Principle with Quasars: We study the large-scale anisotropy of the Universe by measuring the dipole
in the angular distribution of a flux-limited, all-sky sample of 1.36 million
quasars observed by the Wide-field Infrared Survey Explorer (WISE). This sample
is derived from the new CatWISE2020 catalog, which contains deep photometric
measurements at 3.4 and 4.6 $\mu$m from the cryogenic, post-cryogenic, and
reactivation phases of the WISE mission. While the direction of the dipole in
the quasar sky is similar to that of the cosmic microwave background (CMB), its
amplitude is over twice as large as expected, rejecting the canonical,
exclusively kinematic interpretation of the CMB dipole with a p-value of
$5\times10^{-7}$ ($4.9\sigma$ for a normal distribution, one-sided), the
highest significance achieved to date in such studies. Our results are in
conflict with the cosmological principle, a foundational assumption of the
concordance $\Lambda$CDM model. |
Forecasts of redshift drift constraints on cosmological parameters: Cosmological observations usually map our present-day past light cone.
However, it is also possible to compare different past light cones. This is the
concept behind the redshift drift, a model-independent probe of fundamental
cosmology. In simple physical terms, this effectively allows us to watch the
Universe expand in real time. While current facilities only allow sensitivities
several orders of magnitude worse than the expected signal, it should be
possible to detect it with forthcoming ones. Here we discuss the potential
impact of measurements by three such facilities: the Extremely Large Telescope
(the subject of most existing redshift drift forecasts), but also the Square
Kilometre Array and intensity mapping experiments. For each of these we assume
the measurement sensitivities estimated respectively in Liske {\it et al.}
(2008), Klockner {\it et al.} (2015) and Yu {\it et al.} (2014). We focus on
the role of these measurements in constraining dark energy scenarios,
highlighting the fact that although on their own they yield comparatively weak
constraints, they do probe regions of parameter space that are typically
different from those probed by other experiments, as well as being
redshift-dependent. Specifically, we quantify how combinations of several
redshift drift measurements at different redshifts, or combinations of redshift
drift measurements with those from other canonical cosmological probes, can
constrain some representative dark energy models. Our conclusion is that a
model-independent mapping of the expansion of the universe from redshift $z=0$
to $z=4$---a challenging but feasible goal for the next generation of
astrophysical facilities---can have a significant impact on fundamental
cosmology. | The formation and evolution of young low-mass stars within halos with
high concentration of dark matter particles: The formation and evolution of low-mass stars within dense halos of dark
matter (DM) leads to evolution scenarios quite different from the classical
stellar evolution. As a result of our detailed numerical work, we describe
these new scenarios for a range of DM densities on the host halo, a range of
scattering cross sections of the DM particles considered, and for stellar
masses from 0.7 to 3 M_{\odot}. For the first time, we also computed the
evolution of young low-mass stars in their Hayashi track in the pre-main
sequence phase and found that, for high DM densities, these stars stop their
gravitational collapse before reaching the main sequence, in agreement with
similar studies on first stars. Such stars remain indefinitely in an
equilibrium state with lower effective temperatures (|\Delta T_eff| > 10^3 K
for a star of one solar mass), the annihilation of captured DM particles in
their core being the only source of energy. In the case of lower DM densities,
these proto-stars continue their collapse and progress through the main
sequence burning hydrogen at a lower rate. A star of 1 M_{\odot} will spend a
time greater than the current age of the universe consuming all the hydrogen in
its core if it evolves in a halo with DM density \rho_{\chi}=10^9 GeV cm^-3. We
also show the strong dependence of the effective temperature and luminosity of
these stars on the characteristics of the DM particles and how this can be used
as an alternative method for DM research. |
Non-Gaussian structure of the lensed CMB power spectra covariance matrix: Gravitational lensing of the Cosmic Microwave Background (CMB) encodes
cosmological information in the observed anisotropies of temperature and
polarization. Accurate extraction of this additional information requires
precise modeling of the covariance matrix of the power spectra of observed CMB
fields. We introduce a new analytical model to describe the non-Gaussian
structure of this covariance matrix and display the importance of second-order
terms that were previously neglected. When compared with direct numerical
simulations our model captures parameter errors to better than a few percent
for cases where the non-Gaussianity causes an order unity degradation in
errors. We also provide a detailed comparison between the information content
of lensed CMB power spectra and ideal reconstruction of the lensing potential.
We illustrate the impact of the non-Gaussian terms in the power spectrum
covariance by providing Fisher errors on the sum of the masses of the
neutrinos, the dark energy equation of state, and the curvature of the
Universe. | Reconstruction of the Primordial Power Spectrum by Direct Inversion: We introduce a new method for reconstructing the primordial power spectrum,
$P(k)$, directly from observations of the Cosmic Microwave Background (CMB). We
employ Singular Value Decomposition (SVD) to invert the radiation perturbation
transfer function. The degeneracy of the multipole $\ell$ to wavenumber $k$
linear mapping is thus reduced. This enables the inversion to be carried out at
each point along a Monte Carlo Markov Chain (MCMC) exploration of the combined
$P(k)$ and cosmological parameter space. We present best--fit $P(k)$ obtained
with this method along with other cosmological parameters. |
Scalar-tensor theories of gravity, neutrino physics, and the $H_0$
tension: We use $Planck$ 2018 data to constrain the simplest models of scalar-tensor
theories characterized by a coupling to the Ricci scalar of the type $F(\sigma)
R$ with $F(\sigma) = N_{pl}^2 + \xi \sigma^2$. We update our results with
previous $Planck$ and BAO data releases obtaining the tightest constraints to
date on the coupling parameters, that is $\xi < 5.5 \times 10^{-4}$ for
$N_{pl}=0$ (induced gravity or equivalently extended Jordan-Brans-Dicke) and
$(N_{pl} \sqrt{8 \pi G})-1 < 1.8 \times 10^{-5}$ for $\xi = -1/6$ (conformal
coupling), both at 95% CL. Because of a modified expansion history after
radiation-matter equality compared to the $\Lambda$CDM model, all these
dynamical models accommodate a higher value for $H_0$ and therefore alleviate
the tension between $Planck$/BAO and distance-ladder measurement from SNe Ia
data from $4.4\sigma$ at best to $2.3\sigma$. We show that all these results
are robust to changes in the neutrino physics. In comparison to the
$\Lambda$CDM model, partial degeneracies between neutrino physics and the
coupling to the Ricci scalar allow for smaller values $N_{\rm eff} \sim 2.8$,
$1\sigma$ lower compared to the standard $N_{\rm eff} = 3.046$, and relax the
upper limit on the neutrino mass up to 40%. | Lopsidedness in WHISP galaxies: II. Morphological lopsidedness: The distribution of stars and gas in many galaxies is asymmetric. This
so-called lopsidedness is expected to significantly affect the dynamics and
evolution of the disc, including the star formation activity. Here, we measure
the degree of lopsidedness for the gas distribution in a selected sample of 70
galaxies from the Westerbork HI Survey of Spiral and Irregular Galaxies. This
complements our earlier work (Paper I) where the kinematic lopsidedness was
derived for the same galaxies. The morphological lopsidedness is measured by
performing a harmonic decomposition of the surface density maps. The amplitude
of lopsidedness A_1, the fractional value of the first Fourier component, is
typically quite high (about 0.1) within the optical disc and has a constant
phase. Thus, lopsidedness is a common feature in galaxies and indicates a
global mode. We measure A_1 out to typically one to four optical radii,
sometimes even further. This is, on average, four times larger than the
distance to which lopsidedness was measured in the past using near-IR as a
tracer for the old stellar component, and will therefore provide a new, more
stringent constraint on the mechanism for the origin of lopsidedness.
Interestingly, the value of A_1 saturates beyond the optical radius.
Furthermore, the plot of A_1 vs. radius shows fluctuations which we argue are
due to local spiral features. We also try to explain the physical origin of
this observed disc lopsidedness. No clear trend is found when the degree of
lopsidedness is compared to a measure of the isolation or interaction
probability of the sample galaxies. However, this does not rule out a tidal
origin if the lopsidedness is long-lived. Additionally, we find that the
early-type galaxies tend to be more morphologically lopsided than late-type
galaxies. Both results together indicate a tidal origin for the lopsidedness. |
Complex Radio Spectral Energy Distributions in Luminous and
Ultraluminous Infrared Galaxies: We use the Expanded Very Large Array to image radio continuum emission from
local luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) in 1 GHz
windows centered at 4.7, 7.2, 29, and 36 GHz. This allows us to probe the
integrated radio spectral energy distribution (SED) of the most energetic
galaxies in the local universe. The 4-8 GHz flux densities agree well with
previous measurements. They yield spectral indices \alpha \approx -0.67 (where
F_\nu \propto \nu^\alpha) with \pm 0.15 (1\sigma) scatter, typical of
nonthermal (synchrotron) emission from star-forming galaxies. The contrast of
our 4-8 GHz data with literature 1.5 and 8.4 GHz flux densities gives further
evidence for curvature of the radio SED of U/LIRGs. The SED appears flatter
near \sim 1 GHz than near \sim 6 GHz, suggesting significant optical depth
effects at the lower frequencies. The high frequency (28-37 GHz) flux densities
are low compared to extrapolations from the 4-8 GHz data. We confirm and extend
to higher frequency a previously observed deficit of high frequency radio
emission for luminous starburst galaxies. | Were progenitors of local L* galaxies Lyman-alpha emitters at high
redshift?: The Lya emission has been observed from galaxies over a redshift span z ~ 0 -
8.6. However, the evolution of high-redshift Lya emitters (LAEs), and the link
between these populations and local galaxies, remain poorly understood. Here,
we investigate the Lya properties of progenitors of a local L* galaxy by
combining cosmological hydrodynamic simulations with three-dimensional
radiative transfer calculations using the new ART^2 code. We find that the main
progenitor (the most massive one) of a Milky Way-like galaxy has a number of
Lya properties close to those of observed LAEs at z ~ 2 - 6, but most of the
fainter ones appear to fall below the detection limits of current surveys. The
Lya photon escape fraction depends sensitively on a number of physical
properties of the galaxy, such as mass, star formation rate, and metallicity,
as well as galaxy morphology and orientation. Moreover, we find that
high-redshift LAEs show blue-shifted Lya line profiles characteristic of gas
inflow, and that the Lya emission by excitation cooling increases with
redshift, and becomes dominant at z > 6. Our results suggest that some observed
LAEs at z ~ 2-6 with luminosity of L_Lya ~ 10^{42-43} ergs/s may be similar to
the main progenitor of the Milky Way at high redshift, and that they may evolve
into present-day L* galaxies. |
Notes on Hidden Mirror World: A few remarks on Dark Matter (DM) models are presented. An example is Mirror
Matter which is the oldest but still viable DM candidate, perhaps not in the
purest form. It can serve as a test-bench for other analogous DM models, since
the properties of macroscopic objects are quite firmly fixed for Mirror Matter.
A pedagogical derivation of virial theorem is given and it is pointed out that
concepts of virial velocity or virial temperature are misleading for some
cases. It is shown that the limits on self-interaction cross-sections derived
from observations of colliding clusters of galaxies are not real limits for
individual particles if they form macroscopic bodies. The effect of the heating
of interstellar medium by Mirror Matter compact stars is very weak but may be
observable. The effect of neutron star heating by accretion of M-baryons may be
negligible. Problems of MACHOs as Mirror Matter stars are touched upon. | All sky CMB map from cosmic strings integrated Sachs-Wolfe effect: By actively distorting the Cosmic Microwave Background (CMB) over our past
light cone, cosmic strings are unavoidable sources of non-Gaussianity.
Developing optimal estimators able to disambiguate a string signal from the
primordial type of non-Gaussianity requires calibration over synthetic full sky
CMB maps, which till now had been numerically unachievable at the resolution of
modern experiments. In this paper, we provide the first high resolution full
sky CMB map of the temperature anisotropies induced by a network of cosmic
strings since the recombination. The map has about 200 million sub-arcminute
pixels in the healpix format which is the standard in use for CMB analyses
(Nside=4096). This premiere required about 800,000 cpu hours; it has been
generated by using a massively parallel ray tracing method piercing through a
thousands of state of art Nambu-Goto cosmic string numerical simulations which
pave the comoving volume between the observer and the last scattering surface.
We explicitly show how this map corrects previous results derived in the flat
sky approximation, while remaining completely compatible at the smallest
scales. |
Constraints on the Alignment of Galaxies in Galaxy Clusters from
$\sim$14,000 Spectroscopic Members: Torques acting on galaxies lead to physical alignments, but the resulting
ellipticity correlations are difficult to predict. As they constitute a major
contaminant for cosmic shear studies, it is important to constrain the
intrinsic alignment signal observationally. We measured the alignments of
satellite galaxies within 90 massive galaxy clusters in the redshift range
0.05<z<0.55 and quantified their impact on the cosmic shear signal. We combined
a sample of 38,104 galaxies with spectroscopic redshifts with high-quality data
from the Canada-France-Hawaii Telescope. We used phase-space information to
select 14,576 cluster members, 14,250 of which have shape measurements and
measured three different types of alignment: the radial alignment of satellite
galaxies toward the brightest cluster galaxies (BCGs), the common orientations
of satellite galaxies and BCGs, and the radial alignments of satellites with
each other. Residual systematic effects are much smaller than the statistical
uncertainties. We detect no galaxy alignment of any kind out to at least 3
r200. The signal is consistent with zero for both blue and red galaxies, bright
and faint ones, and also for subsamples of clusters based on redshift,
dynamical mass, and dynamical state. These conclusions are unchanged if we
expand the sample with bright cluster members from the red sequence. We augment
our constraints with those from the literature to estimate the importance of
the intrinsic alignments of satellites compared to those of central galaxies,
for which the alignments are described by the linear alignment model.
Comparison of the alignment signals to the expected uncertainties of current
surveys such as the Kilo-Degree Survey suggests that the linear alignment model
is an adequate treatment of intrinsic alignments, but it is not clear whether
this will be the case for larger surveys. | Type Ia supernova Hubble diagram with near-infrared and optical
observations: We main goal of this paper is to test whether the NIR peak magnitudes of SNe
Ia could be accurately estimated with only a single observation obtained close
to maximum light, provided the time of B band maximum and the optical stretch
parameter are known. We obtained multi-epoch UBVRI and single-epoch J and H
photometric observations of 16 SNe Ia in the redshift range z=0.037-0.183,
doubling the leverage of the current SN Ia NIR Hubble diagram and the number of
SNe beyond redshift 0.04. This sample was analyzed together with 102 NIR and
458 optical light curves (LCs) of normal SNe Ia from the literature. The
analysis of 45 well-sampled NIR LCs shows that a single template accurately
describes them if its time axis is stretched with the optical stretch
parameter. This allows us to estimate the NIR peak magnitudes even with one
observation obtained within 10 days from B-band maximum. We find that the NIR
Hubble residuals show weak correlation with DM_15 and E(B-V), and for the first
time we report a possible dependence on the J_max-H_max color. The intrinsic
NIR luminosity scatter of SNe Ia is estimated to be around 0.10 mag, which is
smaller than what can be derived for a similarly heterogeneous sample at
optical wavelengths. In conclusion, we find that SNe Ia are at least as good
standard candles in the NIR as in the optical. We showed that it is feasible to
extended the NIR SN Ia Hubble diagram to z=0.2 with very modest sampling of the
NIR LCs, if complemented by well-sampled optical LCs. Our results suggest that
the most efficient way to extend the NIR Hubble diagram to high redshift would
be to obtain a single observation close to the NIR maximum. (abridged) |
The Taiwan ECDFS Near-Infrared Survey: Very Bright End of the Luminosity
Function at z>7: The primary goal of the Taiwan ECDFS Near-Infrared Survey (TENIS) is to find
well screened galaxy candidates at z>7 (z' dropout) in the Extended Chandra
Deep Field-South (ECDFS). To this end, TENIS provides relatively deep J and Ks
data (~25.3 ABmag, 5-sigma) for an area of 0.5*0.5 degree. Leveraged with
existing data at mid-infrared to optical wavelengths, this allows us to screen
for the most luminous high-z objects, which are rare and thus require a survey
over a large field to be found. We introduce new color selection criteria to
select a z>7 sample with minimal contaminations from low-z galaxies and
Galactic cool stars; to reduce confusion in the relatively low angular
resolution IRAC images, we introduce a novel deconvolution method to measure
the IRAC fluxes of individual sources. Illustrating perhaps the effectiveness
at which we screen out interlopers, we find only one z>7 candidate, TENIS-ZD1.
The candidate has a weighted z_phot of 7.8, and its colors and luminosity
indicate a young (45M years old) starburst galaxy with a stellar mass of
3.2*10^10 M_sun. The result matches with the observational luminosity function
analysis and the semi-analytic simulation result based on the Millennium
Simulations, which may over predict the volume density for high-z massive
galaxies. The existence of TENIS-ZD1, if confirmed spectroscopically to be at
z>7, therefore poses a challenge to current theoretical models for how so much
mass can accumulate in a galaxy at such a high redshift. | Potential reconstruction from general power spectrum in single-field
inflation: We suggest a new method to reconstruct, within canonical single-field
inflation, the inflaton potential directly from the primordial power spectrum
which may deviate significantly from near scale-invariance. Our approach relies
on a more generalized slow-roll approximation than the standard one, and can
probe the properties of the inflaton potential reliably. We give a few examples
for reconstructing potential and discuss the validity of our method. |
The Merger Dynamics of the Galaxy Cluster Abell 1775: New Insights from
Chandra and XMM-Newton for a Cluster Simultaneously Hosting a WAT and a NAT
Radio Sources: We present a new study of the merger dynamics of Abell~1775 by analyzing the
high-quality Chandra and XMM-Newton archival data. We confirm/identify an
arc-shaped edge (i.e., the head) at $\sim48$~kpc west of the X-ray peak, a
split cold gas tail that extends eastward to $\sim163$~kpc, and a plume of
spiral-like X-ray excess (within about $81-324$~kpc northeast of the cluster
core) that connects to the end of the tail. The head, across which the
projected gas temperature rises outward from $3.39_{-0.18}^{+0.28}$~keV to
$5.30_{-0.43}^{+0.54}$~keV, is found to be a cold front with a Mach number of
$\mathcal{M}\sim0.79$. Along the surfaces of the cold front and tail, typical
KHI features (noses and wings, etc.) are found and are used to constrain the
upper limit of the magnetic field ($\sim11.2~\mu$G) and the viscosity
suppression factor ($\sim0.01$). Combining optical and radio evidence we
propose a two-body merger (instead of systematic motion in a large-scale gas
environment) scenario and have carried out idealized hydrodynamic simulations
to verify it. We find that the observed X-ray emission and temperature
distributions can be best reproduced with a merger mass ratio of 5 after the
first pericentric passage. The NAT radio galaxy is thus more likely to be a
single galaxy falling into the cluster center at a relative velocity of
2800~$\rm km~s^{-1}$, a speed constrained by its radio morphology. The
infalling subcluster is expected to have a relatively low gas content, because
only a gas-poor subcluster can cause central-only disturbances as observed in
such an off-axis merger. | Non-linear contributions to angular power spectra: Future galaxy clustering surveys will probe small scales where
non-linearities become important. Since the number of modes accessible on
intermediate to small scales is very high, having a precise model at these
scales is important especially in the context of discriminating alternative
cosmological models from the standard one. In the mildly non-linear regime,
such models typically differ from each other, and galaxy clustering data will
become very precise on these scales in the near future. As the observable
quantity is the angular power spectrum in redshift space, it is important to
study the effects of non-linear density and redshift space distortion (RSD) in
the angular power spectrum. We compute non-linear contributions to the angular
power spectrum using a flat-sky approximation that we introduce in this work,
and compare the results of different perturbative approaches with $N$-body
simulations. We find that the TNS perturbative approach is significantly closer
to the $N$-body result than Eulerian or Lagrangian 1-loop approximations,
effective field theory of large scale structure or a halofit-inspired model.
However, none of these prescriptions is accurate enough to model the angular
power spectrum well into the non-linear regime. In addition, for narrow
redshift bins, $\Delta z \lesssim 0.01$, the angular power spectrum acquires
non-linear contributions on all scales, right down to $\ell=2$, and is hence
not a reliable tool at this time. To overcome this problem, we need to model
non-linear RSD terms, for example as TNS does, but for a matter power spectrum
that remains reasonably accurate well into the deeply non-linear regime, such
as halofit. |
A Study on the Chemical Properties of Blue Compact Dwarf Galaxies: In this paper, we report our studies on the gaseous and chemical properties
of a relatively large sample (53 members) of blue compact dwarf galaxies
(BCDs). The results of correlations among the oxygen abundance, stellar mass,
gas mass, baryonic mass, and gas fraction are present both for E- and I-type
BCDs, which are classified according to Loose & Thuan (1985) and show
elliptical and irregular outer haloes, respectively. These correlations of
I-type BCDs show similar slopes to those of E-type ones. However, in general,
E-type BCDs are more gas-poor and metal-rich than I-type ones at a given
baryonic mass. Based on these results, we suggest that E-type BCDs, at least a
part of them, and I-type ones might be likely at different evolutionary phases
and/or having different progenitors. Our investigation of the correlation
between oxygen abundance and gas fraction shows that BCDs appear to have not
evolved as isolated systems, but to have experienced some gas flows and/or
mergers. | The moment of truth for WIMP Dark Matter: We know that dark matter constitutes 85% of all the matter in the Universe,
but we do not know of what it is made. Amongst the many Dark Matter candidates
proposed, WIMPs (weakly interacting massive particles) occupy a special place,
as they arise naturally from well motivated extensions of the standard model of
particle physics. With the advent of the Large Hadron Collider at CERN, and a
new generation of astroparticle experiments, the moment of truth has come for
WIMPs: either we will discover them in the next five to ten years, or we will
witness the inevitable decline of WIMP paradigm. |
Yakov Zeldovich and the Cosmic Web Paradigm: I discuss the formation of the modern cosmological paradigm. In more detail I
describe the early study of dark matter and cosmic web and the role of Yakov
Zeldovich in the formation of the present concepts on these subjects. | General Analytical Conditions for Inflaton Fragmentation: Quick and Easy
Tests for its Occurrence: Understanding the physics of inflaton condensate fragmentation in the early
Universe is crucial as the existence of fragments in the form of
non-topological solitons (oscillons or Q-balls) may potentially modify the
evolution of the post-inflation Universe. Furthermore, such fragments may
evolve into primordial black holes and form dark matter, or emit gravitational
waves. Due to the non-perturbative and non-linear nature of the dynamics, most
of the studies rely on numerical lattice simulations. Numerical simulations of
condensate fragmentation are, however, challenging and, without knowing where
to look in the parameter space, they are likely to be time-consuming as well.
In this paper, we provide generic analytical conditions for the perturbations
of an inflaton condensate to undergo growth to non-linearity in the cases of
both symmetric and asymmetric inflaton potentials. We apply the conditions to
various inflation models and demonstrate that our results are in good agreement
with explicit numerical simulations. Our analytical conditions are easy to use
and may be utilised in order to quickly identify models that may undergo
fragmentation and determine the conditions under which they do so, which can
guide subsequent in-depth numerical analyses. |
Multiwavelength Analysis of A1240, the Double Radio Relic Merging Galaxy
Cluster Embedded in a ~80 Mpc-long Cosmic Filament: We present a multiwavelength study of the double radio relic cluster A1240 at
z=0.195. Our Subaru-based weak lensing analysis detects three mass clumps
forming a ~4 Mpc filamentary structure elongated in the north-south
orientation. The northern ($M_{200}=2.61_{-0.60}^{+0.51}\times10^{14}
M_{\odot}$) and middle ($M_{200}=1.09_{-0.43}^{+0.34}\times10^{14} M_{\odot}$)
mass clumps separated by ~1.3 Mpc are associated with A1240 and co-located with
the X-ray peaks and cluster galaxy overdensities revealed by Chandra and
MMT/Hectospec observations, respectively. The southern mass clump
($M_{200}=1.78_{-0.55}^{+0.44}\times10^{14} M_{\odot}$), ~1.5 Mpc to the south
of the middle clump, coincides with the galaxy overdensity in A1237, the A1240
companion cluster at z=0.194. Considering the positions, orientations, and
polarization fractions of the double radio relics measured by the LOFAR study,
we suggest that A1240 is a post-merger binary system in the returning phase
with the time-since-collision ~1.7 Gyr. With the SDSS DR16 data analysis, we
also find that A1240 is embedded in the much larger-scale (~80 Mpc) filamentary
structure whose orientation is in remarkable agreement with the hypothesized
merger axis of A1240. | On the use of galaxies as clocks and the universal expansion: We set out to rederive the 8 Hubble parameter values obtained from estimated
relative galaxy ages by Simon et al. [Physical Review D, 71, 123001 (2005)]. We
find that to obtain the level of precision claimed in $H(z)$, unrealistically
small galaxy age uncertainties have to be assumed. Also, some parameter values
will be correlated. In our analysis we find that the uncertainties in the
Hubble parameter values are significantly larger when 8 independent $H(z)$ are
obtained using Monte Carlo sampling. Smaller uncertainties can be obtained
using Gaussian processes, but at the cost of strongly correlated results. We do
not obtain any useful constraints on the Hubble parameter from the galaxy data
employed. |
Searching for planar signatures in WMAP: We search for planar deviations of statistical isotropy in the Wilkinson
Microwave Anisotropy Probe (WMAP) data by applying a recently introduced
angular-planar statistics both to full-sky and to masked temperature maps,
including in our analysis the effect of the residual foreground contamination
and systematics in the foreground removing process as sources of error. We
confirm earlier findings that full-sky maps exhibit anomalies at the planar
($l$) and angular ($\ell$) scales $(l,\ell)=(2,5),(4,7),$ and $(6,8)$, which
seem to be due to unremoved foregrounds since this features are present in the
full-sky map but not in the masked maps. On the other hand, our test detects
slightly anomalous results at the scales $(l,\ell)=(10,8)$ and $(2,9)$ in the
masked maps but not in the full-sky one, indicating that the foreground
cleaning procedure (used to generate the full-sky map) could not only be
creating false anomalies but also hiding existing ones. We also find a
significant trace of an anomaly in the full-sky map at the scale
$(l,\ell)=(10,5)$, which is still present when we consider galactic cuts of
18.3% and 28.4%. As regards the quadrupole ($\ell=2$), we find a coherent
over-modulation over the whole celestial sphere, for all full-sky and cut-sky
maps. Overall, our results seem to indicate that current CMB maps derived from
WMAP data do not show significant signs of anisotropies, as measured by our
angular-planar estimator. However, we have detected a curious coherence of
planar modulations at angular scales of the order of the galaxy's plane, which
may be an indication of residual contaminations in the full- and cut-sky maps. | Sources of the Radio Background Considered: We investigate different scenarios for the origin of the extragalactic radio
background. The surface brightness of the background, as reported by the ARCADE
2 collaboration, is several times higher than that which would result from
currently observed radio sources. We consider contributions to the background
from diffuse synchrotron emission from clusters and the intergalactic medium,
previously unrecognized flux from low surface brightness regions of radio
sources, and faint point sources below the flux limit of existing surveys. By
examining radio source counts available in the literature, we conclude that
most of the radio background is produced by radio point sources that dominate
at sub microJy fluxes. We show that a truly diffuse background produced by
electrons far from galaxes is ruled out because such energetic electrons would
overproduce the obserevd X-ray/gamma-ray background through inverse Compton
scattering of the other photon fields. Unrecognized flux from low surface
brightness regions of extended radio sources, or moderate flux sources missed
entirely by radio source count surveys, cannot explain the bulk of the observed
background, but may contribute as much as 10 per cent. We consider both radio
supernovae and radio quiet quasars as candidate sources for the background, and
show that both fail to produce it at the observed level because of insufficient
number of objects and total flux, although radio quiet quasars contribute at
the level of at least a few percent. We conclude that if the radio background
is at the level reported, a majority of the total surface brightness would have
to be produced by ordinary starforming galaxies above redshift 1 characterized
by an evolving radio far-infrared correlation, which changes toward the radio
loud with redshift. |
Turbulent Motions and Shocks Waves in Galaxy Clusters simulated with AMR: We have implemented an Adaptive Mesh Refinement criterion explicitly designed
to increase spatial resolution around discontinuities in the velocity field in
ENZO cosmological simulations. With this technique, shocks and turbulent eddies
developed during the hierarchical assembly of galaxy clusters are followed with
unprecedented spatial resolution, even at large distances from the clusters
center. By measuring the spectral properties of the gas velocity field, its
time evolution and the properties of shocks for a reference galaxy cluster, we
investigate the connection between accretion processes and the onset of chaotic
motions in the simulated Inter Galactic Medium over a wide range of scales | Model independent calibrations of gamma ray bursts using machine
learning: We alleviate the circularity problem, whereby gamma-ray bursts are not
perfect distance indicators, by means of a new model-independent technique
based on B\'ezier polynomials. To do so, we use the well consolidate
\textit{Amati} and \textit{Combo} correlations. We consider improved calibrated
catalogs of mock data from differential Hubble rate points. To get our mock
data, we use those machine learning scenarios that well adapt to gamma ray
bursts, discussing in detail how we handle small amounts of data from our
machine learning techniques. In particular, we explore only three machine
learning treatments, i.e. \emph{linear regression}, \emph{neural network} and
\emph{random forest}, emphasizing quantitative statistical motivations behind
these choices. Our calibration strategy consists in taking Hubble's data,
creating the mock compilation using machine learning and calibrating the
aforementioned correlations through B\'ezier polynomials with a standard
chi-square analysis first and then by means of a hierarchical Bayesian
regression procedure. The corresponding catalogs, built up from the two
correlations, have been used to constrain dark energy scenarios. We thus employ
Markov Chain Monte Carlo numerical analyses based on the most recent Pantheon
supernova data, baryonic acoustic oscillations and our gamma ray burst data. We
test the standard $\Lambda$CDM model and the Chevallier-Polarski-Linder
parametrization. We discuss the recent $H_0$ tension in view of our results.
Moreover, we highlight a further severe tension over $\Omega_m$ and we conclude
that a slight evolving dark energy model is possible. |
Cosmic void exclusion models and their impact on the distance scale
measurements from large scale structure: Baryonic Acoustic Oscillations (BAOs) studies based on the clustering of
voids and matter tracers provide important constraints on cosmological
parameters related to the expansion of the Universe. However, modelling the
void exclusion effect is an important challenge for fully exploiting the
potential of this kind of analyses. We thus develop two numerical methods to
describe the clustering of cosmic voids. Neither model requires additional
cosmological information beyond that assumed within the galaxy de-wiggled
model. The models consist in power spectra whose performance we assess in
comparison to a parabolic model on Patchy cubic and light-cone mocks. Moreover,
we test their robustness against systematic effects and the reconstruction
technique. The void model power spectra and the parabolic model with a fixed
parameter provide strongly correlated values for the Alcock-Paczynski
($\alpha$) parameter, for boxes and light-cones likewise. The resulting
$\alpha$ values -- for all three models -- are unbiased and their uncertainties
are correctly estimated. However, the numerical models show less variation with
the fitting range compared to the parabolic one. The Bayesian evidence suggests
that the numerical techniques are often favoured compared to the parabolic
model. Moreover, the void model power spectra computed on boxes can describe
the void clustering from light-cones as well as from boxes. The same void model
power spectra can be used for the study of pre- and post-reconstructed
data-sets. Lastly, the two numerical techniques are resilient against the
studied systematic effects. Consequently, using either of the two new void
models, one can more robustly measure cosmological parameters. | Cosmological Parameter Forecasts for a CMB-HD Survey: We present forecasts on cosmological parameters for a CMB-HD survey. For a
$\Lambda$CDM + $N_{eff}$ + $\sum m_\nu$ model, we find $\sigma(n_s) = 0.0013$
and $\sigma(N_{eff}) = 0.014$ using CMB and CMB lensing multipoles in the range
of $\ell \in [30, 20000]$, after adding anticipated residual foregrounds,
delensing the acoustic peaks, and adding DESI BAO data. This is about a factor
of two improvement in ability to probe inflation via $n_s$ compared to
precursor CMB surveys. The $N_{eff}$ constraint can rule out light thermal
particles back to the end of inflation with 95% CL; for example, it can rule
out the QCD axion in a model-independent way assuming the Universe's reheating
temperature was high enough that the axion thermalized. We find that delensing
the acoustic peaks and adding DESI BAO tightens parameter constraints. We also
find that baryonic effects can bias parameters if not marginalized over, and
that uncertainties in baryonic effects can increase parameter error bars;
however, the latter can be mitigated by including information about baryonic
effects from kinetic and thermal Sunyaev-Zel'dovich measurements by CMB-HD. The
CMB-HD likelihood and Fisher estimation codes used here are publicly available;
the likelihood is integrated with Cobaya to facilitate parameter forecasting. |
Curvature from strong gravitational lensing: a spatially closed Universe
or systematics?: Model-independent constraints on the spatial curvature are not only closely
related to important problems such as the evolution of the Universe and
properties of dark energy, but also provide a test of the validity of the
fundamental Copernican principle. In this paper, with the distance sum rule in
the Friedmann-Lema\^{i}tre-Robertson-Walker metric, we achieve
model-independent measurements of the spatial curvature from the latest type Ia
supernovae and strong gravitational lensing (SGL) observations. We find that a
spatially closed Universe is preferred. Moreover, by considering different
kinds of velocity dispersion and subsample, we study possible factors which
might affect model-independent estimations for the spatial curvature from SGL
observations. It is suggested that the combination of observational data from
different surveys might cause a systematic bias and the tension between the
spatially flat Universe and SGL observations is alleviated when the subsample
only from the Sloan Lens ACS Survey is used or a more complex treatment for the
density profile of lenses is considered. | The dark atoms of dark matter: The nonbaryonic dark matter of the Universe is assumed to consist of new
stable particles. A specific case is possible, when new stable particles bear
ordinary electric charge and bind in heavy "atoms" by ordinary Coulomb
interaction. Such possibility is severely restricted by the constraints on
anomalous isotopes of light elements that form positively charged heavy species
with ordinary electrons. The trouble is avoided, if stable particles $X^{--}$
with charge -2 are in excess over their antiparticles (with charge +2) and
there are no stable particles with charges +1 and -1. Then primordial helium,
formed in Big Bang Nucleosynthesis, captures all $X^{--}$ in neutral "atoms" of
O-helium (OHe), thus creating a specific Warmer than Cold nuclear-interacting
composite dark matter. Slowed down in the terrestrial matter, OHe is elusive
for direct methods of underground dark. However OHe-nucleus interaction leads
to their binding and in OHe-Na system the energy of such level can be in the
interval of energy 2-4 keV. It explains the results of DAMA/NaI and DAMA/LIBRA
experiments. The puzzles of direct dark matter searches appear in this solution
as a reflection of nontrivial nuclear physics of OHe. (abridged) |
The interaction between feedback from active galactic nuclei and
supernovae: Energetic feedback from supernovae (SNe) and from active galactic nuclei
(AGN) are both important processes that are thought to control how much gas is
able to condense into galaxies and form stars. We show that although both AGN
and SNe suppress star formation, they mutually weaken one another's effect by
up to an order of magnitude in haloes in the mass range for which both feedback
processes are efficient (10^11.25 M_sun < m_200 < 10^12.5 M_sun). These results
demonstrate the importance of the simultaneous, non-independent inclusion of
these two processes in models of galaxy formation to estimate the total
feedback strength. These results are of particular relevance to semi-analytic
models, which implicitly assume the effects of the two feedback processes to be
independent, and also to hydrodynamical simulations that model only one of the
feedback processes. | Statistical mechanics of collisionless orbits. I. Origin of central
cusps in dark-matter halos: We present an equilibrium statistical mechanical theory of collisionless
self-gravitational systems with isotropic velocity distributions. Compared to
existing standard theories, we introduce two changes: (1) the number of
possible microstates is computed in energy (orbit) space rather than phase
space and (2) low occupation numbers are treated more appropriately than using
Stirling's approximation. Combined, the two modifications predict that the
relaxed parts of collisionless self-gravitating systems, such as dark-matter
halos, have a differential energy distribution N(E) ~ [exp(phi_0 - E) - 1],
dubbed "DARKexp". Such systems have central power-law density cusps rho(r) ~
r^-1, which suggests a statistical mechanical origin of cusps in simulated
dark-matter halos. |
Using the Bright Ultra-Hard XMM-Newton Survey to define an IR selection
of luminous AGN based on WISE colours: We present a highly complete and reliable mid-infrared (MIR) colour selection
of luminous AGN candidates using the 3.4, 4.6, and 12 um bands of the WISE
survey. The MIR colour wedge was defined using the wide-angle Bright Ultra-Hard
XMM-Newton Survey (BUXS), one of the largest complete flux-limited samples of
bright (f(4.5-10 keV)>6x10^{-14} erg cm^-2 s^-1) "ultra-hard" (4.5-10 keV)
X-ray selected AGN to date. BUXS includes 258 objects detected over a total sky
area of 44.43 deg^2 of which 251 are spectroscopically identified and
classified, with 145 being type-1 AGN and 106 type-2 AGN. Our technique is
designed to select objects with red MIR power-law spectral energy distributions
(SED) in the three shortest bands of WISE and properly accounts for the errors
in the photometry and deviations of the MIR SEDs from a pure power-law. The
completeness of the MIR selection is a strong function of luminosity. At L(2-10
keV)>10^{44} erg s^-1, where the AGN is expected to dominate the MIR emission,
97.1_{-4.8}^{+2.2}% and 76.5_{-18.4}^{+13.3}% of the BUXS type-1 and type-2 AGN
meet the selection. Our technique shows one of the highest reliability and
efficiency of detection of the X-ray selected luminous AGN population with WISE
amongst those in the literature. In the area covered by the BUXS survey our
selection identifies 2755 AGN candidates detected with SNR>5 in the three
shorter wavelength bands of WISE with 38.5% having a detection at 2-10 keV
X-ray energies. We also analyzed the possibility of including the 22um WISE
band to select AGN candidates, but neither the completeness nor the reliability
of the selection improves. This is likely due to both the significantly
shallower depth at 22um compared with the first three bands of WISE and
star-formation contributing to the 22um emission at the WISE 22um sensitivity. | Near-IR Atlas of S0-Sa galaxies (NIRS0S): An atlas of Ks-band images of 206 early-type galaxies is presented, including
160 S0-S0/a galaxies, 12 ellipticals, and 33 Sa galaxies. A majority of the
Atlas galaxies belong to a magnitude-limited (mB<12.5 mag) sample of 185 NIRS0S
(Near-IR S0 galaxy Survey) galaxies. To assure that mis-classified S0s are not
omitted, 25 ellipticals from RC3 classified as S0s in the Carnegie Atlas were
included in the sample. The images are 2-3 mag deeper than 2MASS images. Both
visual and photometric classifications are made. Special attention is paid to
the classification of lenses, coded in a systematic manner. A new lens-type,
called a 'barlens', is introduced. Also, boxy/peanut/x-shaped structures are
identified in many barred galaxies, even-though the galaxies are not seen in
edge-on view, indicating that vertical thickening is not enough to explain
them. Multiple lenses appear in 25% of the Atlas galaxies, which is a challenge
to the hierarchical evolutionary picture of galaxies. Such models need to
explain how the lenses were formed and survived in multiple merger events that
galaxies may have suffered during their lifetimes. Following the early
suggestion by van den Bergh, candidates of S0c galaxies are shown, which
galaxies are expected to be former Sc-type spirals stripped out of gas. |
Inflation in the Mixed Higgs-$R^2$ Model: We analyze a two-field inflationary model consisting of the Ricci scalar
squared ($R^2$) term and the standard Higgs field non-minimally coupled to
gravity in addition to the Einstein $R$ term. Detailed analysis of the power
spectrum of this model with mass hierarchy is presented, and we find that one
can describe this model as an effective single-field model in the slow-roll
regime with a modified sound speed. The scalar spectral index predicted by this
model coincides with those given by the $R^2$ inflation and the Higgs inflation
implying that there is a close relation between this model and the $R^2$
inflation already in the original (Jordan) frame. For a typical value of the
self-coupling of the standard Higgs field at the high energy scale of
inflation, the role of the Higgs field in parameter space involved is to modify
the scalaron mass, so that the original mass parameter in the $R^2$ inflation
can deviate from its standard value when non-minimal coupling between the Ricci
scalar and the Higgs field is large enough. | Galaxy-Wide Shocks in Late-Merger Stage Luminous Infrared Galaxies: We present an integral field spectroscopic study of two nearby Luminous
Infrared Galaxies (LIRGs) that exhibit evidence of widespread shock excitation
induced by ongoing merger activity, IC 1623 and NGC 3256. We show the
importance of carefully separating excitation due to shocks vs. excitation by
HII regions and the usefulness of IFU data in interpreting the complex
processes in LIRGs. Our analysis focuses primarily on the emission line gas
which is extensive in both systems and is a result of the abundant ongoing star
formation as well as widespread LINER-like excitation from shocks. We use
emission-line ratio maps, line kinematics, line-ratio diagnostics and new
models as methods for distinguishing and analyzing shocked gas in these
systems. We discuss how our results inform the merger sequence associated with
local U/LIRGs and the impact that widespread shock excitation has on the
interpretation of emission-line spectra and derived quantities of both local
and high-redshift galaxies. |
Type 1 AGN at low z. II. The relative strength of narrow lines and the
nature of intermediate type AGN: We explore the relative strength of the narrow emission lines in an SDSS
based sample of broad H-alpha selected AGN, defined in paper I. We find a
decrease in the narrow to broad H-alpha luminosity (L_bHa) ratio with
increasing L_bHa, such that both L([OIII] lambda5007) and L(narrow H-alpha)
scale as L_bHa^0.7 for 10^40 < L_bHa < 10^45 ergs s^-1. Following our earlier
result that L_bHa \propto L_bol, this trend indicates that the relative narrow
line luminosity decreases with increasing L_bol. We derive L_bol / 10^43 ergs
s^-1 = 4000 (L([OIII]) / 10^43 ergs s^-1)^1.39. This implies that the
bolometric correction factor, L_bol / L([OIII]), decreases from 3,000 at L_bol
= 10^46.1 ergs s^-1 to 300 at L_bol = 10^42.5 ergs s^-1. At low luminosity, the
narrow component dominates the observed H-alpha profile, and most type 1 AGN
appear as intermediate type AGN. Partial obscuration or extinction cannot
explain the dominance of intermediate type AGN at low luminosity, and the most
likely mechanism is a decrease in the narrow line region covering factor with
increasing L_bol. Deviations from the above trend occur in objects with L /
L_Edd <~ 10^-2.6, probably due to the transition to LINERs with suppressed
[OIII] emission, and in objects with M_BH > 10^8.5 M_Sun, probably due to the
dominance of radio loud AGN, and associated enhanced [OIII] emission. | The Cosmic Timeline Implied by the JWST High-redshift Galaxies: The so-called `impossibly early galaxy' problem, first identified via the
Hubble Space Telescope's observation of galaxies at redshifts z > 10, appears
to have been exacerbated by the more recent James Webb Space Telescope (JWST)
discovery of galaxy candidates at even higher redshifts (z ~ 17) which,
however, are yet to be confirmed spectroscopically. These candidates would have
emerged only ~ 230 million years after the big bang in the context of LCDM,
requiring a more rapid star formation in the earliest galaxies than appears to
be permitted by simulations adopting the concordance model parameters. This
time-compression problem would therefore be inconsistent with the age-redshift
relation predicted by LCDM. Instead, the sequence of star formation and galaxy
assembly would confirm the timeline predicted by the R_h=ct universe, a
theoretically advanced version of LCDM that incorporates the `zero active mass'
condition from general relativity. This model has accounted for many
cosmological data better than LCDM, and eliminates all of its inconsistencies,
including the horizon and initial entropy problems. The latest JWST discoveries
at z > 14, if confirmed, would add further support to the idea that the R_h=ct
universe is favored by the observations over the current standard model. |
Color Distributions, Number and Mass Densities of Massive Galaxies at
1.5 < z < 3: Comparing Observations with Merger Simulations: We present a comparison between the observed color distribution, number and
mass density of massive galaxies at 1.5 < z < 3 and a model by Hopkins et al.
that relates the quasar and galaxy population on the basis of gas-rich mergers.
In order to test the hypothesis that quiescent red galaxies are formed after a
gas-rich merger involving quasar activity, we confront photometry of massive (M
> 4x10^10 Msun) galaxies extracted from the FIRES, GOODS-South, and MUSYC
surveys, together spanning an area of 496 arcmin^2, with synthetic photometry
from hydrodynamical merger simulations. As in the Hopkins et al. (2006b) model,
we use the observed quasar luminosity function to estimate the merger rate. We
find that the synthetic U-V and V-J colors of galaxies that had a quasar phase
in their past match the colors of observed galaxies that are best characterized
by a quiescent stellar population. At z ~ 2.6, the observed number and mass
density of quiescent red galaxies with M > 4x10^10 Msun is consistent with the
model in which every quiescent massive galaxy underwent a quasar phase in the
past. At z ~ 1.9, 2.8 times less quiescent galaxies are observed than predicted
by the model as descendants of higher redshift quasars. The merger model also
predicts a large number of galaxies undergoing merger-driven star formation. We
find that the predicted number and mass density accounts for 30-50% of the
observed massive star-forming galaxies. However, their colors do not match
those of observed star-forming galaxies. In particular, the colors of dusty red
galaxies are not reproduced by the simulations. Several possible origins of
this discrepancy are discussed. The observational constraints on the validity
of the model are currently limited by cosmic variance and uncertainties in
stellar population synthesis and radiative transfer. | Account of the baryonic feedback effect in gamma-ray measurements of
intergalactic magnetic fields: Intergalactic magnetic fields in the voids of the large-scale structure can
be probed via measurements of secondary gamma-ray emission from gamma-ray
interactions with extragalactic background light. Lower bounds on the magnetic
field in the voids were derived from the non-detection of this emission. It is
not clear a priori what kind of magnetic field is responsible for the
suppression of the secondary gamma-ray flux: a cosmological magnetic field that
might be filling the voids or the field spread by galactic winds driven by star
formation and active galactic nuclei. We used IllustrisTNG cosmological
simulations to study the effect of magnetized galactic wind bubbles on the
secondary gamma-ray flux. We show that within the IllustrisTNG model of
baryonic feedback, the galactic wind bubbles typically provide
energy-independent secondary flux suppression at the level of about 10%. The
observed flux suppression effect has to be due to the cosmological magnetic
field in the voids. This might not be the case for a special case when the
primary gamma-ray source has a hard intrinsic gamma-ray spectrum that peaks in
the energy range above 50 TeV. In this case, the observational data may be
strongly affected by the magnetized bubble that is blown by the source host
galaxy. |
Going deep with Minkowski functionals of convergence maps: Stage IV lensing surveys promise to make available an unprecedented amount of
excellent data which will represent a huge leap in terms of both quantity and
quality. This will open the way to the use of novel tools, which go beyond the
standard second order statistics probing the high order properties of the
convergence field. We discuss the use of Minkowski Functionals (MFs) as
complementary probes to increase the lensing Figure of Merit (FoM), for a
survey made out of a wide total area $A_{\rm{tot}}$ imaged at a limiting
magnitude $\rm{mag_{W}}$ containing a subset of area $A_{\rm{deep}}$ where
observations are pushed to a deeper limiting magnitude $\rm{mag_{D}}$. We
present an updated procedure to match the theoretically predicted MFs to the
measured ones, taking into account the impact of map reconstruction from noisy
shear data. We validate this renewed method against simulated data sets with
different source redshift distributions and total number density, setting these
quantities in accordance with the depth of the survey. We can then rely on a
Fisher matrix analysis to forecast the improvement in the FoM due to the joint
use of shear tomography and MFs under different assumptions on
$(A_{\rm{tot}},\,A_{\rm{deep}},\,\rm{mag_{D}})$, and the prior on the MFs
nuisance parameters. It turns out that MFs can provide a valuable help in
increasing the FoM of the lensing survey, provided the nuisance parameters are
known with a non negligible precision. What is actually more interesting is the
possibility to compensate for the loss of FoM due to a cut in the multipole
range probed by shear tomography, which makes the results more robust against
uncertainties in the modeling of nonlinearities. This makes MFs a promising
tool to both increase the FoM and make the constraints on the cosmological
parameters less affected by theoretical systematic effects. | The cosmological bulk flow: consistency with $Λ$CDM and $z\approx
0$ constraints on $σ_8$ and $γ$: We derive estimates for the cosmological bulk flow from the SFI++
Tully-Fisher (TF) catalog. For a sphere of radius $40 \hmpc$ centered on the
MW, we derive a bulk flow of $333 \pm 38\kms $ towards Galactic $
(l,b)=(276^\circ,14^\circ)$ within a $3^\circ$ $1\sigma$ error. Within a $
100\hmpc$ we get $ 257\pm 44\kms$ towards $(l,b)=(279^\circ, 10^\circ)$ within
a $6^\circ$ error. These directions are at a $40^\circ$ with the Supergalactic
plane, close to the apex of the motion of the Local Group of galaxies after the
Virgocentric infall correction. Our findings are consistent with the
$\Lambda$CDM model with the latest WMAP best fit cosmological parameters. But
the bulk flow allows independent constraints. For WMAP inferred Hubble
parameter $h=0.71$ and baryonic mean density parameter $\Omega_b=0.0449$, the
constraint from the bulk flow on the matter density $\Omega_m$, the
normalization of the density fluctuations, $\sigma_8$, and the growth index,
$\gamma$, can be expressed as
$\sigma_8\Omega_m^{\gamma-0.55}(\Omega_m/0.266)^{0.28}=0.86\pm 0.11$ (for
$\Omega_m\approx 0.266$). Fixing $\sigma_8=0.8$ and $\Omega_m=0.266$ as favored
by WMAP, we get $\gamma=0.495\pm 0.096$. The constraint derived here rules out
popular DGP models at more than the 99% confidence level. Our results are based
on a method termed \ace\ (All Space Constrained Estimate) which reconstructs
the bulk flow from an all space three dimensional peculiar velocity field
constrained to match the TF measurements. At large distances \ace\ generates a
robust bulk flow from the SFI++ that is insensitive to the assumed prior. For
comparison, a standard straightforward maximum likelihood estimate leads to
very similar results. |
Parameter likelihood of intrinsic ellipticity correlations: Subject of this paper are the statistical properties of ellipticity
alignments between galaxies evoked by their coupled angular momenta. Starting
from physical angular momentum models, we bridge the gap towards ellipticity
correlations, ellipticity spectra and derived quantities such as aperture
moments, comparing the intrinsic signals with those generated by gravitational
lensing, with the projected galaxy sample of EUCLID in mind. We investigate the
dependence of intrinsic ellipticity correlations on cosmological parameters and
show that intrinsic ellipticity correlations give rise to non-Gaussian
likelihoods as a result of nonlinear functional dependencies. Comparing
intrinsic ellipticity spectra to weak lensing spectra we quantify the magnitude
of their contaminating effect on the estimation of cosmological parameters and
find that biases on dark energy parameters are very small in an
angular-momentum based model in contrast to the linear alignment model commonly
used. Finally, we quantify whether intrinsic ellipticities can be measured in
the presence of the much stronger weak lensing induced ellipticity
correlations, if prior knowledge on a cosmological model is assumed. | The Variance and Covariance of Counts-in-Cells Probabilities: Counts-in-cells (CIC) measurements contain a wealth of cosmological
information yet are seldom used to constrain theories. Although we can predict
the shape of the distribution for a given cosmology, to fit a model to the
observed CIC probabilities requires the covariance matrix -- both the variance
of counts in one probability bin and the covariance between counts in different
bins. To date, there have been no general expressions for these variances. Here
we show that correlations of particular levels, or "slices," of the density
field determine the variance and covariance of CIC probabilities. We derive
explicit formulae that accurately predict the variance and covariance among
subvolumes of a simulated galaxy catalog, opening the door to the use of CIC
measurements for cosmological parameter estimation. |
A kinematic study of planetary nebulae in the dwarf irregular galaxy
IC10: We present positions, kinematics, and the planetary nebula luminosity
function (PNLF) for 35 planetary nebulae (PNe) in the nearest starburst galaxy
IC10 extending out to 3kpc from the galaxy's centre. We take advantage of the
deep imaging and spectroscopic capabilities provided by the spectrograph FOCAS
on the 8.2m Subaru telescope. The PN velocities were measured through the
slitless-spectroscopy technique, which allows us to explore the kinematics of
IC10 with high precision. Using these velocities, we conclude that there is a
kinematic connection between the HI envelope located around IC10 and the
galaxy's PN population. By assuming that the PNe in the central regions and in
the outskirts have similar ages, our results put strong observational
constraints on the past tidal interactions in the Local Group. This is so
because by dating the PN central stars, we, therefore, infer the epoch of a
major episode of star formation likely linked to the first encounter of the HI
extended envelope with the galaxy. Our deep [OIII] images also allow us to use
the PNLF to estimate a distance modulus of 24.1+/-0.25, which is in agreement
with recent results in the literature based on other techniques. | Are Radio AGN Powered by Accretion or Black Hole Spin?: We compare accretion and black hole spin as potential energy sources for
outbursts from AGN in brightest cluster galaxies (BCGs). Based on our adopted
spin model, we find that the distribution of AGN power estimated from X-ray
cavities is consistent with a broad range of both spin parameter and accretion
rate. Sufficient quantities of molecular gas are available in most BCGs to
power their AGN by accretion alone. However, we find no correlation between AGN
power and molecular gas mass over the range of jet power considered here. For a
given AGN power, the BCG's gas mass and accretion efficiency, defined as the
fraction of the available cold molecular gas that is required to power the AGN,
both vary by more than two orders of magnitude. Most of the molecular gas in
BCGs is apparently consumed by star formation or is driven out of the nucleus
by the AGN before it reaches the nuclear black hole. Bondi accretion from hot
atmospheres is generally unable to fuel powerful AGN, unless their black holes
are more massive than their bulge luminosities imply. We identify several
powerful AGN that reside in relatively gas-poor galaxies, indicating an
unusually efficient mode of accretion, or that their AGN are powered by another
mechanism. If these systems are powered primarily by black hole spin, rather
than by accretion, spin must also be tapped efficiently in some systems, i.e.,
$P_{\rm jet} > \dot Mc^2$, or their black hole masses must be substantially
larger than the values implied by their bulge luminosities. We constrain the
(model dependent) accretion rate at the transition from radiatively inefficient
to radiatively efficient accretion flows to be a few percent of the Eddington
rate, a value that is consistent with other estimates. |
Observational evidence for cosmological coupling of black holes and its
implications for an astrophysical source of dark energy: Observations have found black holes spanning ten orders of magnitude in mass
across most of cosmic history. The Kerr black hole solution is however
provisional as its behavior at infinity is incompatible with an expanding
universe. Black hole models with realistic behavior at infinity predict that
the gravitating mass of a black hole can increase with the expansion of the
universe independently of accretion or mergers, in a manner that depends on the
black hole's interior solution. We test this prediction by considering the
growth of supermassive black holes in elliptical galaxies over
$0<z\lesssim2.5$. We find evidence for cosmologically coupled mass growth among
these black holes, with zero cosmological coupling excluded at 99.98%
confidence. The redshift dependence of the mass growth implies that, at
$z\lesssim7$, black holes contribute an effectively constant cosmological
energy density to Friedmann's equations. The continuity equation then requires
that black holes contribute cosmologically as vacuum energy. We further show
that black hole production from the cosmic star formation history gives the
value of $\Omega_{\Lambda}$ measured by Planck while being consistent with
constraints from massive compact halo objects. We thus propose that stellar
remnant black holes are the astrophysical origin of dark energy, explaining the
onset of accelerating expansion at $z \sim 0.7$. | Measuring Black Hole Spin in OJ287: We model the binary black hole system OJ287 as a spinning primary and a
non-spinning secondary. It is assumed that the primary has an accretion disk
which is impacted by the secondary at specific times. These times are
identified as major outbursts in the light curve of OJ287. This identification
allows an exact solution of the orbit, with very tight error limits. Nine
outbursts from both the historical photographic records as well as from recent
photometric measurements have been used as fixed points of the solution: 1913,
1947, 1957, 1973, 1983, 1984, 1995, 2005 and 2007 outbursts. This allows the
determination of eight parameters of the orbit. Most interesting of these are
the primary mass of $1.84\cdot 10^{10} M_\odot$, the secondary mass $1.46\cdot
10^{8} M_\odot$, major axis precession rate $39^\circ.1$ per period, and the
eccentricity of the orbit 0.70. The dimensionless spin parameter is
$0.28\:\pm\:0.01$ (1 sigma). The last parameter will be more tightly
constrained in 2015 when the next outburst is due. The outburst should begin on
15 December 2015 if the spin value is in the middle of this range, on 3 January
2016 if the spin is 0.25, and on 26 November 2015 if the spin is 0.31. We have
also tested the possibility that the quadrupole term in the Post Newtonian
equations of motion does not exactly follow Einstein's theory: a parameter $q$
is introduced as one of the 8 parameters. Its value is within 30% (1 sigma) of
the Einstein's value $q = 1$. This supports the $no-hair theorem$ of black
holes within the achievable precision. We have also measured the loss of
orbital energy due to gravitational waves. The loss rate is found to agree with
Einstein's value with the accuracy of 2% (1 sigma). |
Observational Constraints on Constant Roll Inflation: Constant-roll inflation was recently introduced by Motohashi, Starobinsky and
Yokoyama as a phenomenological way to parametrize deviations from the slow-roll
scenarios. In this paper, we investigate the dynamics of both the background
and the perturbations in this model, without making any slow-roll assumptions.
The perturbation spectra are computed with an efficient and accurate novel
method that allowed us to quickly scan the parameter space of constant-roll
inflation. We derive the constraints on the model parameters from the cosmic
microwave background anisotropy measurements provided by the joint analysis of
the Planck Collaboration and the BICEP2/Keck Array data. | The impact of baryonic physics and massive neutrinos on weak lensing
peak statistics: We study the impact of baryonic processes and massive neutrinos on weak
lensing peak statistics that can be used to constrain cosmological parameters.
We use the BAHAMAS suite of cosmological simulations, which self-consistently
include baryonic processes and the effect of massive neutrino free-streaming on
the evolution of structure formation. We construct synthetic weak lensing
catalogues by ray-tracing through light-cones, and use the aperture mass
statistic for the analysis. The peaks detected on the maps reflect the
cumulative signal from massive bound objects and general large-scale structure.
We present the first study of weak lensing peaks in simulations that include
both baryonic physics and massive neutrinos (summed neutrino mass $M_{\nu} =$
0.06, 0.12, 0.24, and 0.48 eV assuming normal hierarchy), so that the
uncertainty due to physics beyond the gravity of dark matter can be factored
into constraints on cosmological models. Assuming a fiducial model of baryonic
physics, we also investigate the correlation between peaks and massive haloes,
over a range of summed neutrino mass values. As higher neutrino mass tends to
suppress the formation of massive structures in the Universe, the halo mass
function and lensing peak counts are therefore modified as a function of
$M_{\nu}$. Over most of the S/N range, the impact of fiducial baryonic physics
is greater (less) than neutrinos for 0.06 and 0.12 (0.24 and 0.48) eV models.
Both baryonic physics and massive neutrinos should be accounted for when
deriving cosmological parameters from weak lensing observations. |
The Formation of the massive galaxies in the SSA22 z=3.1 protocluster: The properties of K-band selected galaxies (K_AB<24) in the z = 3.09 SSA22
protocluster field are studied. 430 galaxies at 2.6 < z_phot < 3.6 are selected
as potential protocluster members in a 112 arcmin^2 area based on their
photometric redshifts. We find that \approx 20% of the massive galaxies with
stellar masses >10^11 M_sun at z_phot \sim 3.1 have colors consistent with
those of quiescent galaxies with ages > 0.5 Gyr. This fraction increases to
\approx 50% after correcting for unrelated foreground/background objects. We
also find that 30% of the massive galaxies are heavily reddened dusty
star-forming galaxies. Few such quiescent galaxies at similar redshifts are
seen in typical survey fields. An excess surface density of 24\mu m sources at
z_phot \sim 3.1 is also observed, implying the presence of dusty star-formation
activity in the protocluster. Cross-correlation with the X-ray data indicates
that the fraction of K-band selected protocluster galaxies hosting active
galactic nuclei (AGN) is also high compared with the field. The sky
distribution of the quiescent galaxies, the 24\mu m sources, and the X-ray AGNs
show clustering around a density peak of z=3.1 Ly\alpha emitters (LAEs). A
significant fraction of the massive galaxies have already become quiescent,
while the dusty star-formation is still active in the SSA22 protocluster. These
findings indicate that we are witnessing the formation epoch of massive
early-type galaxies at the center of predecessors to present-day rich galaxy
clusters. | The properties of (sub)millimetre-selected galaxies as revealed by
CANDELS HST WFC3/IR imaging in GOODS-South: We have exploited the HST CANDELS WFC3/IR imaging to study the properties of
(sub-)mm galaxies in GOODS-South. After using the deep radio and Spitzer
imaging to identify galaxy counterparts for the (sub-)mm sources, we have used
the new CANDELS data in two ways. First, we have derived improved photometric
redshifts and stellar masses, confirming that the (sub-)mm galaxies are massive
(<M*>=2.2x10^11 M_solar) galaxies at z=1-3. Second, we have exploited the depth
and resolution of the WFC3/IR imaging to determine the sizes and morphologies
of the galaxies at rest-frame optical wavelengths, fitting two-dimensional
axi-symmetric Sersic models. Crucially, the WFC3/IR H-band imaging enables
modelling of the mass-dominant galaxy, rather than the blue high-surface
brightness features which often dominate optical (rest-frame UV) images of
(sub-)mm galaxies, and can confuse visual morphological classification. As a
result of this analysis we find that >95% of the rest-frame optical light in
almost all of the (sub-)mm galaxies is well-described by either a single
exponential disk, or a multiple-component system in which the dominant
constituent is disk-like. We demonstrate that this conclusion is consistent
with the results of high-quality ground-based K-band imaging, and explain why.
The massive disk galaxies which host luminous (sub-)mm emission are reasonably
extended (r_e=4 kpc), consistent with the sizes of other massive star-forming
disks at z~2. In many cases we find evidence of blue clumps within the sources,
with the mass-dominant disk becoming more significant at longer wavelengths.
Finally, only a minority of the sources show evidence for a major galaxy-galaxy
interaction. Taken together, these results support the view that most (sub-)mm
galaxies at z~2 are simply the most extreme examples of normal star-forming
galaxies at that era. |
Estimating the Turn-Around Radii of Six Isolated Galaxy Groups in the
Local Universe: The estimates of the turn-around radii of six isolated galaxy groups in the
nearby universe are presented. From the Tenth Data Release of the Sloan Digital
Sky Survey, we first select those isolated galaxy groups at redshifts $z\le
0.05$ in the mass range of [0.3-1]$\times10^{14}\,h^{-1}M_{\odot}$ whose
nearest neighbor groups are located at distances larger than fiften times their
virial radii. Then, we search for a gravitationally interacting web-like
structure around each isolated group, which appears as an inclined streak
pattern in the anisotropic spatial distribution of the neighbor field galaxies
. Out of 59 isolated groups, only seven are found to possess such web-like
structures in their neighbor zones, but one of them turns out to be NGC 5353/4,
whose turn-around radius was already measured in the previous work and thus
excluded from our analysis. Applying the Turn-around Radius Estimator algorithm
devised by Lee et al. to the identified web-like structures of the remaining
six target groups, we determine their turn-around radii and show that three out
of the six targets have larger turn-around radii than the spherical bound limit
predicted by the Planck cosmology. We discuss possible sources of the apparent
violations of the three groups, including the underestimated spherical
bound-limit due to the approximation of the turn-around mass by the virial
mass. | A synthetic view of AGN evolution and supermassive black holes growth: I will describe the constraints available from a study of AGN evolution
synthesis models on the growth of the supermassive black holes (SMBH)
population in the two main 'modes' observed (kinetic- and
radiatively-dominated, respectively). I will show how SMBH mass function
evolves anti-hierarchically, i.e. the most massive holes grew earlier and
faster than less massive ones, and I will also derive tight constraints on the
average radiative efficiency of AGN. An outlook on the redshift evolution of
the AGN kinetic luminosity function will also be discussed, thus providing a
robust physical framework for phenomenological models of AGN feedback within
structure formation. Finally, I will present new constraints on the evolution
of the black hole-galaxy scaling relation at 1<z<2 derived by exploiting the
full multi-wavelength coverage of the COSMOS survey on a complete sample of 90
type 1 AGN. |
The active CGCG 077-102 NED02 galaxy within the Abell 2063 galaxy
cluster: Within the framework of investigating the link between central super massive
black holes in the core of galaxies and the galaxies themselves, we detected a
variable X-ray source in the center of CGCG 077-102 NED02, member of the CGCG
077-102 galaxy pair within the Abell 2063 galaxy cluster. Our goal was then to
combine X-ray and optical data to demonstrate that this object harbors an
active super massive black hole in its core, and to relate this to the
dynamical status of the galaxy pair within the Abell 2063 cluster. We used
Chandra and XMM-Newton archival data to derive the X-ray spectral shape and
variability. We also obtained optical spectroscopy to detect the expected
emission lines that are typically found in Active Galactic Nuclei. And we
finally used public ZTF imaging data to investigate the optical variability.
There is no evidence of multiple X-ray sources or extended component within
CGCG 077-102 NED02. Single X-ray spectral models fit well the source.
Non-random significant X-ray flux inter-observation X-ray variabilities were
detected, between ~4days for short term variations and up to ~700days for long
term variations. Optical spectroscopy points toward a passive galaxy for CGCG
077-102 NED01 and a Seyfert for CGCG 077-102 NED02. We did not detect
short-term variability in the optical ZTF light curves. However, we found a
significant long-term stochastic variability in the g-band that can be well
described by the damped random walk model. Finally, the CGCG 077-102 galaxy
pair is deeply embedded within the Abell 2063 potential, and has underwent the
cluster influence for a long time. Our observations point toward a moderatly
massive black hole in the center of CGCG 077-102 NED02, of ~10^6 Msol. CGCG
077-102 NED02 is not heavily obscured, perhaps due to surrounding intra cluster
medium ram pressure stripping. | Renormalization group computation of likelihood functions for
cosmological data sets: I show how a renormalization group (RG) method can be used to incrementally
integrate the information in cosmological large-scale structure data sets
(including CMB, galaxy redshift surveys, etc.). I show numerical tests for
Gaussian fields, where the method allows arbitrarily close to exact computation
of the likelihood function in order $\sim N$ time, even for problems with no
symmetry, compared to $N^3$ for brute force linear algebra (where $N$ is the
number of data points -- to be fair, methods already exist to solve the
Gaussian problem in at worst $N \log N$ time, and this method will not
necessarily be faster in practice). The method requires no sampling or other
Monte Carlo (random) element. Non-linearity/non-Gaussianity can be accounted
for to the extent that terms generated by integrating out small scale modes can
be projected onto a sufficient basis, e.g., at least in the sufficiently
perturbative regime. The formulas to evaluate are straightforward and require
no understanding of quantum field theory, but this paper may also serve as a
pedagogical introduction to Wilsonian RG for astronomers. |
Shocks in the Early Universe: We point out a surprising consequence of the usually assumed initial
conditions for cosmological perturbations. Namely, a spectrum of Gaussian,
linear, adiabatic, scalar, growing mode perturbations not only creates acoustic
oscillations of the kind observed on very large scales today, it also leads to
the production of shocks in the radiation fluid of the very early universe.
Shocks cause departures from local thermal equilibrium as well as creating
vorticity and gravitational waves. For a scale-invariant spectrum and standard
model physics, shocks form for temperatures $1$ GeV$<T<10^{7}$ GeV. For more
general power spectra, such as have been invoked to form primordial black
holes, shock formation and the consequent gravitational wave emission provides
a signal detectable by current and planned gravitational wave experiments,
allowing them to strongly constrain conditions present in the primordial
universe as early as $10^{-30}$ seconds after the big bang. | Full analytical approximation to the stochastic gravitational wave
background generated by cosmic string networks: We derive a full analytical approximation to the stochastic gravitational
wave background generated by the loops that are produced throughout the
cosmological evolution of cosmic string networks. We show that this
approximation not only predicts the amplitude of the radiation-era plateau
exactly, but also provides a good fit to the high-frequency cut-off and to the
low-frequency peak generated by the loops that decay during the matter era,
irrespective of cosmic string tension and of the length of loops created. We
then find that it provides a good quantitative description of the full
stochastic gravitational wave background across the relevant frequency range. |
A Semi-Parametric Approach to Fitting Gas Pressure Profiles of Galaxy
Clusters: This study focuses on modelling galaxy cluster gas profiles via a
semi-parametric nodal approach. While traditional methods like the generalised
Navarro-Frenk-White (gNFW) often encounter parameter degeneracy, our flexible
node-based method precisely defines a cluster gas pressure profile. Using
Planck space telescope data from the Coma region, our model, focused on the
pressure-radius relationship, showcases enhanced flexibility over the gNFW.
Bayesian analyses indicated an optimal five-node structure for the Coma cluster
pressure profile. | An unidentified line in X-ray spectra of the Andromeda galaxy and
Perseus galaxy cluster: We report a weak line at 3.52+/-0.02 keV in X-ray spectra of M31 galaxy and
the Perseus galaxy cluster observed by MOS and PN cameras of XMM-Newton
telescope. This line is not known as an atomic line in the spectra of galaxies
or clusters. It becomes stronger towards the centers of the objects; is
stronger for Perseus than for M31; is absent in the spectrum of a deep "blank
sky'' dataset. Although for each object it is hard to exclude that the feature
is due to an instrumental effect or an atomic line, it is consistent with the
behavior of a dark matter decay line. Future (non-)detections of this line in
multiple objects may help to reveal its nature. |
Systematic Study of Gravitational Waves from Galaxy Merger: A systematic study of gravitational waves from galaxy mergers, through N-body
simulations, was performed. In particular, we investigated the relative
importance of galaxy components (disk, bulge and halo) and effects of initial
relative velocity, relative angular momentum and mass ratio of the galaxies. We
found that the features of light curve of gravitational waves, such as peak
width and luminosity, are reliably simulated with particle numbers larger than
~10^4. Dominant contribution to gravitational wave emission came from the halo
component, while peak luminosity amounted to 10^31 erg/sec for the collision of
two halos with mass 3.8 x10^12Msun/h. We also found that the initial relative
velocity in the direction of the initial separation did not significantly
affect gravitational wave emission, while the initial relative angular momentum
broadened the peak width and suppressed the luminosity. Mass dependence of the
peak luminosity was also investigated, and we obtained evidence that the
luminosity is proportional to the cubic mass when the scaling relation is
satisfied. This behavior was considered by a simple analysis. | Search for cold gas in strong MgII absorbers at 0.5<z<1.5: nature and
evolution of 21-cm absorbers: We report 4 new detections of 21-cm absorption from a systematic search of
21-cm absorption in a sample of 17 strong (Wr(MgII 2796)>1A) intervening MgII
absorbers at 0.5<z<1.5. We also present 20-cm milliarcsecond scale maps of 40
quasars having 42 intervening strong MgII absorbers for which we have searched
for 21-cm absorption. Combining 21-cm absorption measurements for 50 strong
MgII systems from our surveys with the measurements from literature, we obtain
a sample of 85 strong MgII absorbers at 0.5<z<1 and 1.1<z<1.5. We present
detailed analysis of this sample, taking into account the effect of the varying
21-cm optical depth sensitivity and covering factor associated with the
different quasar sight lines. We find that the 21-cm detection rate is higher
towards the quasars with flat or inverted spectral index at cm wavelengths.
About 70% of 21-cm detections are towards the quasars with linear size, LS<100
pc. The 21-cm absorption lines having velocity widths, DeltaV>100 km/s are
mainly seen towards the quasars with extended radio morphology at arcsecond
scales. However, we do not find any correlation between the integrated 21-cm
optical depth or DeltaV with the LS measured from the milliarcsecond scale
images. All this can be understood if the absorbing gas is patchy with a
typical correlation length of ~30-100 pc. We show that within the measurement
uncertainty, the 21-cm detection rate in strong MgII systems is constant over
0.5<z<1.5, i.e., over ~30% of the total age of universe. We show that the
detection rate can be underestimated by up to a factor 2 if 21-cm optical
depths are not corrected for the partial coverage estimated using
milliarcsecond scale maps. Since stellar feedback processes are expected to
diminish the filling factor of cold neutral medium over 0.5<z<1, this lack of
evolution in the 21-cm detection rate in strong MgII absorbers is intriguing.
[abridged] |
The Carnegie Supernova Project-I: Correlation Between Type Ia Supernovae
and Their Host Galaxies from Optical to Near-Infrared Bands: We present optical and near-infrared ($ugriYJH$) photometry of host galaxies
of Type Ia supernovae (SN~Ia) observed by the \textit{Carnegie Supernova
Project-I}. We determine host galaxy stellar masses and, for the first time,
study their correlation with SN~Ia standardized luminosity across optical and
near-infrared ($uBgVriYJH$) bands. In the individual bands, we find that SNe~Ia
are more luminous in more massive hosts with luminosity offsets ranging between
$-0.07 \pm0.03$ mag to $-0.15\pm0.04$ mag after light-curve standardization.
The slope of the SN~Ia Hubble residual-host mass relation is negative across
all $uBgVriYJH$ bands with values ranging between $-0.036\pm 0.025$ mag/dex to
$-0.097\pm 0.027$ mag/dex -- implying that SNe~Ia in more massive galaxies are
brighter than expected. The near-constant observed correlations across optical
and near-infrared bands indicate that dust may not play a significant role in
the observed luminosity offset--host mass correlation. We measure projected
separations between SNe~Ia and their host centers, and find that SNe~Ia that
explode beyond a projected 10 kpc have a $\rm 30\% \ to \ 50\%$ reduction of
the dispersion in Hubble residuals across all bands -- making them a more
uniform subset of SNe~Ia. Dust in host galaxies, peculiar velocities of nearby
SN~Ia, or a combination of both may drive this result as the color excesses of
SNe~Ia beyond 10 kpc are found to be generally lower than those interior, but
there is also a diminishing trend of the dispersion as we exclude nearby
events. We do not find that SN~Ia average luminosity varies significantly when
they are grouped in various host morphological types. Host galaxy data from
this work will be useful, in conjunction with future high-redshift samples, in
constraining cosmological parameters. | Let Effective Field Theory of Inflation flow: stochastic generation of
models with red/blue tensor tilt: We extend the method of Flow Equations to the Effective Field Theory
framework of inflation, in order to investigate the observable predictions of a
very broad class of inflationary models. Focusing our attention on the
gravitational-wave sector, we derive a general expression for the consistency
relation for effective models and provide a numerical implementation which
allows to study how the generated models populate the $(r,nt)$ plane. We
analyse $5 \times 10^{4}$ realizations of inflationary scenarios that respect
the Null-Energy Condition ($\epsilon > 0$) and $5 \times 10^{4}$ realizations
that violate it ($\epsilon > 0$). In both cases, 90% of the viable models are
below the most recent upper bound on the tensor-to-scalar ratio from Planck and
BICEP2/Keck Array BK15 data: $r_{0.002} < 0.056$ at 95 % CL. We find that
general EFT inflationary models with $\epsilon > 0$ are typically characterized
by $n_{t} < 0$, whereas the vast majority of NEC-violating models presents a
blue-tilted spectrum ($n_{t} > 0$). Since a blue tensor spectral index implies
more power on small scales, this result is of considerable interest in view of
a possible direct detection of the primordial gravitational-wave background. |
3D Weak Gravitational Lensing of the CMB and Galaxies: In this paper we present a power spectrum formalism that combines the full
three-dimensional information from the galaxy ellipticity field, with
information from the cosmic microwave background (CMB). We include in this
approach galaxy cosmic shear and galaxy intrinsic alignments, CMB deflection,
CMB temperature and CMB polarisation data; including the inter-datum power
spectra between all quantities. We apply this to forecasting cosmological
parameter errors for CMB and imaging surveys for Euclid-like, Planck, ACTPoL,
and CoRE-like experiments. We show that the additional covariance between the
CMB and ellipticity measurements can improve dark energy equation of state
measurements by 15%, and the combination of cosmic shear and the CMB, from
Euclid-like and CoRE-like experiments, could in principle measure the sum of
neutrino masses with an error of 0.003 eV. | Single-epoch VLBI imaging study of bright active galactic nuclei at 2
and 8 GHz: We investigate statistical and individual astrophysical properties of active
galactic nuclei (AGNs), such as parsec-scale flux density, core dominance,
angular and linear sizes, maximum observed brightness temperatures of VLBI core
components, spectral index distributions for core and jet components, and
evolution of brightness temperature along the jets. Furthermore, we
statistically compare core flux densities and brightness temperature as well as
jet spectral indices of gamma-ray bright and weak sources. We used 19 very long
baseline interferometry (VLBI) observing sessions carried out simultaneously at
2.3 and 8.6 GHz with the participation of 10 Very Long Baseline Array (VLBA)
stations and up to 10 additional geodetic telescopes. The observations span the
period 1998-2003. We present here single-epoch results from high-resolution
radio observations of 370 AGNs. Our VLBI images at 2.3 and 8.6 GHz as well as
Gaussian models are presented and analyzed. At least one-fourth of the cores
are completely unresolved on the longest baselines of the global VLBI
observations. The VLBI core components are partially opaque with the median
value of spectral index of alpha_core=0.3, while the jet features are usually
optically thin alpha_jet=-0.7. The spectral index typically decreases along the
jet ridge line owing to the spectral aging, with a median value of -0.05
mas^-1. Brightness temperatures are found to be affected by Doppler boosting
and reaching up to \sim10^13 K with a median of \sim2.5x10^11 K at both
frequencies. The brightness temperature gradients along the jets typically
follow a power law T_b\simr^-2.2 at both frequencies. 147 sources (40%)
positionally associated with gamma-ray detections from the Fermi LAT Second
Source Catalog have higher core flux densities and brightness temperatures, and
are characterized by the less steep radio spectrum of the optically thin jet
emission. |
Do AGN suppress star formation in early-type galaxies?: The observation that AGN host galaxies preferentially inhabit the "green
valley" between the blue cloud and the red sequence has significant
consequences for our understanding of the co-evolution of galaxies and black
holes via accretion events. I discuss the interpretation of green valley AGN
host galaxy colours with particular focus on early-type galaxies. | Probing Population III Stars in Galaxy IOK-1 at z = 6.96 through He II
Emission: The He II \lambda 1640 emission line has been suggested as a direct probe of
Population III (Pop III) stars at high-redshift, since it can arise from highly
energetic ionizing photons associated with hot, metal free stars. We use the
HST WFC3/F130N IR narrowband filter to probe He II \lambda 1640 emission in
galaxy IOK-1 at z=6.96. The sensitivity of this measurement is >5x deeper than
for previous measurements. From this deep narrowband imaging, combined with
broadband observations in the F125W and F160W filters, we find the He II flux
to be 1.2+/- 1.0x 10^-18 ergs/s/cm^2, corresponding to a 1\sigma upper limit on
the Pop III star formation rate (SFR) of ~ 0.5 M_sun/yr for the case of a
Salpeter IMF with 50-500M_sun and mass loss. Given that the broadband
measurements can be fit with a UV continuum spectral flux density of ~ 4.85x
10^-10x \lambda ^-2.46 ergs/s/cm^2/A, which corresponds to an overall SFR of
~16+/-2.6 M_sun/yr, massive Pop III stars represent < 6% of the total star
formation. This measurement places the strongest limit yet on metal-free star
formation at high redshift, although the exact conversion from He II luminosity
to Pop III SFR is highly uncertain due to the unknown IMF, stellar evolution,
and photoionization effects. Although we have not detected He II \lambda 1640
at more than the 1.2\sigma level, our work suggests that a > 3\sigma level
detection is possible with JWST. |
A Merger Shock in Abell 2034: We present a $250\,$ks Chandra observation of the cluster merger A2034 with
the aim of understanding the nature of a sharp edge previously characterized as
a cold front. The new data reveal that the edge is coherent over a larger
opening angle and is significantly more bow-shock-shaped than previously
thought. Within $\sim 27\,$degrees about the axis of symmetry of the edge the
density, temperature and pressure drop abruptly by factors of
$1.83^{+0.09}_{-0.08}$, $1.85^{+0.41}_{-0.41}$ and $3.4^{+0.8}_{-0.7}$,
respectively. This is inconsistent with the pressure equilibrium expected of a
cold front and we conclude that the edge is a shock front. We measure a Mach
number $M = 1.59^{+0.06}_{-0.07}$ and corresponding shock velocity $v_{\rm
shock}\simeq 2057\,$km/s. Using spectra collected at the MMT with the Hectospec
multi-object spectrograph we identify 328 spectroscopically confirmed cluster
members. Significantly, we find a local peak in the projected galaxy density
associated with a bright cluster galaxy which is located just ahead of the nose
of the shock. The data are consistent with a merger viewed within $\sim
23\,$degrees of the plane of the sky. The merging subclusters are now moving
apart along a north-south axis approximately $0.3\,$Gyr after a small impact
parameter core passage. The gas core of the secondary subcluster, which was
driving the shock, appears to have been disrupted by the merger. Without a
driving 'piston' we speculate that the shock is dying. Finally, we propose that
the diffuse radio emission near the shock is due to the revival of pre-existing
radio plasma which has been overrun by the shock. | Cosmology of F(R) nonlinear massive gravity: The theory of nonlinear massive gravity can be extended into the F(R) form as
developed in Phys.Rev.D90, 064051 (2014). Being free of the Boulware-Deser
ghost, such a construction has the additional advantage of exhibiting no linear
instabilities around a cosmological background. We investigate various
cosmological evolutions of a universe governed by this generalized massive
gravitational theory. Specifically, under the Starobinsky ansantz, this model
provides a unified description of the cosmological history, from early-time
inflation to late-time self-acceleration. Moreover, under viable F(R) forms,
the scenario leads to a very interesting dark-energy phenomenology, including
the realization of the quintom scenario without any pathology. Finally, we
provide a detailed analysis of the cosmological perturbations at linear order,
as well as the Hamiltonian constraint analysis, in order to examine the
physical degrees of freedom. |
Dynamically Induced Planck Scale and Inflation: Theories where the Planck scale is dynamically generated from dimensionless
interactions provide predictive inflationary potentials and super-Planckian
field variations. We first study the minimal single-field realisation in the
low-energy effective field theory limit, finding the predictions $n_s \approx
0.96$ for the spectral index and $r \approx 0.13$ for the tensor-to-scalar
ratio, which can be reduced down to $\approx 0.04$ in presence of large
couplings. Next we consider agravity as a dimensionless quantum gravity theory
finding a multi-field inflation that converges towards an attractor trajectory
that predicts $n_s\approx 0.96$ and $0.003<r<0.13$, interpolating between the
quadratic and Starobinsky inflation. These theories relate the smallness of the
weak scale to the smallness of inflationary perturbations: both arise naturally
because of small couplings, implying a reheating temperature of $10^{7-9}$ GeV.
A measurement of $r$ by Keck/Bicep3 would give us information on quantum
gravity in the dimensionless scenario. | Oscillations and stability of polytropic filaments: We study the oscillations and stability of self-gravitating cylindrically
symmetric fluid systems and collisionless systems. This is done by studying
small perturbations to the equilibrium system and finding the normal modes,
using methods similar to those used in astroseismology. We find that there is a
single sequence of purely radial modes that become unstable if the adiabatic
exponent is less than 1. Nonradial modes can be divided into p modes, which are
stable and pressure-driven, and g modes, which are are gravity driven. The g
modes become unstable if the adiabatic exponent is greater than the polytrope
index. These modes are analogous to the modes of a spherical star, but their
behavior is somewhat different because a cylindrical geometry has less symmetry
than a spherical geometry. This implies that perturbations are classified by a
radial quantum number, an azimuthal quantum number, and wavelength in the z
direction, which can become arbitrarily large. We find that decreasing this
wavelength increases the frequency of stable modes and increases the growth
rate of unstable modes. We use use variational arguments to demonstrate that
filaments of collisionless matter with ergodic distribution functions are
stable to purely radial perturbations, and that filaments with ergodic
power-law distribution functions are stable to all perturbations. |
X-ray Absorption of High Redshift Quasars: Soft X-ray photoelectric absorption of high-z quasars has been known for two
decades, but has no unambiguous astro-physical context. We construct the
largest sample to date of 58 high redshift quasars (z > 0.45) selected from the
XMM-Newton archive based on a high photon count criterion (> 1800). We measure
the optical depth tau at 0.5 keV, and find that 43% of the quasars show
significant absorption. We aim to find which physical parameters of the quasars
drive their observed absorption, e.g., redshift, radio luminosity, radio
loudness, or the X-ray luminosity. We compare the absorption behavior with
redshift with the pattern expected if the diffuse intergalactic medium (IGM) is
responsible for the observed absorption, and with a comparison sample of gamma
ray burst (GRB) X-ray afterglows. Although the z > 2 quasar opacity is
consistent with diffuse IGM absorption, many intermediate z (0.45 < z < 2)
quasars are not sufficiently absorbed for this scenario, and are appreciably
less absorbed than GRBs. Only 10/37 quasars at z < 2 are absorbed, and only
5/30 radio quiet quasars are absorbed. We find a weak correlation between tau
and z, and even a weaker correlation between tau and radio luminosity, which
leads to the conclusion that although a diffuse IGM origin for the quasar
absorption is unlikely, optical depth does seem to increase with redshift,
roughly as (1+z)^{2.2+-0.6}, tending at high-z to tau ~ 0.4, similar to the
high-z GRB values. This result can be explained by an ionized and clumpy IGM at
z < 2, and a cold, diffuse IGM at higher redshift. If, conversely, ascribed to
local absorption at the quasar, and owing to the steep L_x ~ (1+z)^{7.1+-0.5}
correlation in the present sample, the host column density scales as N_H ~
L_x^{0.7+-0.1}. | Revisiting the abundance gradient in the maser host galaxy NGC 4258: New spectroscopic observations of 36 HII regions in NGC 4258 obtained with
the Gemini telescope are combined with existing data from the literature to
measure the radial oxygen abundance gradient in this galaxy. The [OIII]4363
auroral line was detected in four of the outermost targets (17 to 22 kpc from
the galaxy center), allowing a determination of the electron temperature Te of
the ionized gas. From the use of different calibrations of the R23 abundance
indicator an oxygen abundance gradient of approximately -0.012 +/- 0.002
dex/kpc is derived. Such a shallow gradient, combined with the difference in
the distance moduli measured from the Cepheid Period-Luminosity relation by
Macri et al. between two distinct fields in NGC 4258, would yield an
unrealistically strong effect of metallicity on the Cepheid distances. This
strengthens the suggestion that systematic biases might affect the Cepheid
distance of the outer field. Evidence for a similar effect in the differential
study of M33 by Scowcroft et al. is presented. A revision of the transformation
between strong-line and Te-based abundances in Cepheid-host galaxies is
discussed. In the Te abundance scale, the oxygen abundance of the inner field
of NGC 4258 is found to be comparable with the LMC value. |
Formation history, structure and dynamics of discs and spheroids in
simulated Milky Way mass galaxies: We study the stellar discs and spheroids in eight simulations of galaxy
formation within Milky Way-mass haloes in a Lambda Cold Dark Matter cosmology.
A first paper in this series concentrated on disc properties. Here, we extend
this analysis to study how the formation history, structure and dynamics of
discs and spheroids relate to the assembly history and structure of their
haloes. We find that discs are generally young, with stars spanning a wide
range in stellar age: the youngest stars define thin discs and have
near-circular orbits, while the oldest stars form thicker discs which rotate ~2
times slower than the thin components, and have 2-3 times larger velocity
dispersions. Unlike the discs, spheroids form early and on short time-scales,
and are dominated by velocity dispersion. We find great variety in their
structure. The inner regions are bar- or bulge-like, while the extended outer
haloes are rich in complex non-equilibrium structures such as stellar streams,
shells and clumps. Our discs have very high in-situ fractions, i.e. most of
their stars formed in the disc itself. Nevertheless, there is a non-negligible
contribution (~15 percent) from satellites that are accreted on nearly coplanar
orbits. The inner regions of spheroids also have relatively high in-situ
fractions, but 65-85 percent of their outer stellar population is accreted. We
analyse the circular velocities, rotation velocities and velocity dispersions
of our discs and spheroids, both for gas and stars, showing that the dynamical
structure is complex as a result of the non-trivial interplay between cooling
and SN heating. | MOIRCS Deep Survey. X. Evolution of Quiescent Galaxies as a Function of
Stellar Mass at 0.5<z<2.5: We study the evolution of quiescent galaxies at 0.5<z<2.5 as a function of
stellar mass, using very deep NIR imaging data taken with the Multi-Object
Infrared Camera and Spectrograph on the Subaru Telescope in the GOODS-North
region. The deep NIR data allow us to construct a stellar mass-limited sample
of quiescent galaxies down to ~10^{10} Msun even at z~2 for the first time. We
selected quiescent galaxies with age/tau>6 by performing SED fitting of the
multi broad-band photometry from the U to Spitzer 5.8um bands with the
population synthesis model of Bruzual & Charlot (2003) where exponentially
decaying star formation histories are assumed. The number density of quiescent
galaxies increases by a factor of ~3 from 1.0<z<1.5 to 0.5<z<1.0, and by a
factor of ~10 from 1.5<z<2.5 to 0.5<z<1.0, while that of star-forming galaxies
with age/tau<4 increases only by factors of ~2 and ~3 in the same redshift
ranges. At 0.5<z<2.5, the low-mass slope of the stellar mass function of
quiescent galaxies is alpha ~ 0 -- 0.6, which is significantly flatter than
those of star-forming galaxies (alpha ~ -1.3 -- -1.5). As a result, the
fraction of quiescent galaxies in the overall galaxy population increases with
stellar mass in the redshift range. The fraction of quiescent galaxies at
10^{11}-10^{11.5} Msun increases from ~20-30% at z~2 to ~40-60% at z~0.75,
while that at 10^{10}-10^{10.5} Msun increases from <~ 5% to ~15% in the same
redshift range. These results could suggest that the quenching of star
formation had been more effective in more massive galaxies at 1<~z<~2. Such a
mass-dependent quenching could explain the rapid increase of the number density
of ~M* galaxies relative to lower-mass galaxies at z >~ 1-1.5. |
Redshift-space distortions with split densities: Accurate modelling of redshift-space distortions (RSD) is challenging in the
non-linear regime for two-point statistics e.g. the two-point correlation
function (2PCF). We take a different perspective to split the galaxy density
field according to the local density, and cross-correlate those densities with
the entire galaxy field. Using mock galaxies, we demonstrate that combining a
series of cross-correlation functions (CCFs) offers improvements over the 2PCF
as follows: 1. The distribution of peculiar velocities in each split density is
nearly Gaussian. This allows the Gaussian streaming model for RSD to perform
accurately within the statistical errors of a ($1.5\,h^{-1}$Gpc)$^3$ volume for
almost all scales and all split densities. 2. The PDF of the density field at
small scales is non-Gaussian, but the CCFs of split densities capture the
non-Gaussianity, leading to improved cosmological constraints over the 2PCF. We
can obtain unbiased constraints on the growth parameter $f\sigma_{12}$ at the
per-cent level, and Alcock-Paczynski (AP) parameters at the sub-per-cent level
with the minimal scale of $15\,h^{-1}{\rm Mpc}$. This is a $\sim$30 per cent
and $\sim$6 times improvement over the 2PCF, respectively. The diverse and
steep slopes of the CCFs at small scales are likely to be responsible for the
improved constraints of AP parameters. 3. Baryon acoustic oscillations (BAO)
are contained in all CCFs of split densities. Including BAO scales helps to
break the degeneracy between the line-of-sight and transverse AP parameters,
allowing independent constraints on them. We discuss and compare models for RSD
around spherical densities. | Tracking the origin of black holes with the stochastic gravitational
wave background popcorn signal: Unresolved sources of gravitational waves (GWs) produced by the merger of a
binary of black holes at cosmological distances combine into a stochastic
background. Such a background is in the continuous or popcorn regime, depending
on whether the GW rate is high enough so that two or more events overlap in the
same frequency band. These two regimes respectively correspond to large and
small values of the so-called {\it duty cycle}. We study the detection regime
of the background in models of Primordial Black Holes (PBHs) and compare it to
the one produced by black holes of stellar origin. Focusing on ground-based
detectors, we show that the duty cycle of the PBH-origin background is larger
than that of astrophysical black holes because of differences in their mass
function and the merger rate. Our study opens up the possibility to learn about
the primordial or astrophysical nature of black hole populations by examining
the statistical properties of the stochastic background. |
Probing the large-scale structure of the universe through
gravitational-wave observations: The improvements in the sensitivity of the gravitational wave (GW) network
enable the detection of several large redshift GW sources by third-generation
GW detectors. These advancements provide an independent method to probe the
large-scale structure of the universe by using the clustering of the binary
black holes. The black hole catalogs are complementary to the galaxy catalogs
because of large redshifts of GW events, which may imply that binary black
holes (BBHs) are a better choice than galaxies to probe the large-scale
structure of the universe and cosmic evolution over a large redshift range. To
probe the large-scale structure, we used the sky position of the binary black
holes observed by third-generation GW detectors to calculate the angular
correlation function (ACF) and the bias factor of the population of binary
black holes. This method is also statistically significant as 5000 BBHs are
simulated. Moreover, for the third-generation GW detectors, we found that the
bias factor can be recovered to within 33$\%$ with an observational time of ten
years. This method only depends on the GW source-location posteriors; hence, it
can be an independent method to reveal the formation mechanisms and origin of
the BBH mergers compared to the electromagnetic method. | The role of black holes in galaxy formation and evolution: Virtually all massive galaxies, including our own, host central black holes
ranging in mass from millions to billions of solar masses. The growth of these
black holes releases vast amounts of energy that powers quasars and other
weaker active galactic nuclei. A tiny fraction of this energy, if absorbed by
the host galaxy, could halt star formation by heating and ejecting ambient gas.
A central question in galaxy evolution is the degree to which this process has
caused the decline of star formation in large elliptical galaxies, which
typically have little cold gas and few young stars, unlike spiral galaxies. |
A dichotomy in radio jet orientations in elliptical galaxies: We have investigated the correlations between optical and radio isophotal
position angles for 14302 SDSS galaxies with r magnitudes brighter than 18. All
the galaxies are identified with extended FIRST radio sources. For passive
early-type galaxies, which we distinguish from the others by using the colour,
concentration and their principal components, we find a strong statistical
alignment of the radio axes with the optical minor axes. Since the radio
emission is driven by accretion on to a nuclear black hole we argue that the
observed correlation gives new insight into the structure of elliptical
galaxies, for example, whether or not the nuclear kinematics are decoupled from
the rest of the galaxy. Our results imply that a significant fraction of the
galaxies are oblate spheroids, perhaps rotationally supported, with their radio
emission aligned with the stellar minor axis. Remarkably, the strength of the
correlation of the radio major axis with the optical minor axis depends on
radio loudness. Those objects with a low ratio of FIRST radio flux density to
total stellar light show a strong minor axis correlation while the stronger
radio sources do not. This split may reflect different formation histories and
we suggest this may be a new manifestation of the better known dichotomy
between slow rotating and fast rotating ellipticals. | Resurrecting Quadratic Inflation with a non-minimal coupling to gravity: We study Quadratic Inflation with the inflaton field $\phi$ coupled
non-minimally to the curvature scalar $R$, so that the potential during
inflation is of the form $V\propto m^2\phi^2+\xi R\phi^2$. We show that with a
suitable choice of the non-minimal coupling strength,
$\xi=\mathcal{O}(10^{-3})$, one can resurrect the success of the scenario when
compared against the Planck and BICEP2/Keck Array data, and that in the region
of the parameter space which is still allowed the model predicts values of the
tensor-to-scalar ratio in the range $0.01\leq r < 0.12$, making it possible to
either confirm the scenario or rule it out already by the current or
near-future experiments, such as BICEP3 or LiteBIRD. However, we show that in
this case the near-future observations are unlikely to be able to distinguish
between the metric and Palatini formulations of gravity. |
Higher order statistics of curvature perturbations in IFF model and its
Planck constraints: We compute the power spectrum P_\zeta, and non-linear parameters f_nl and
\tau_nl of the curvature perturbation induced during inflation by the
electromagnetic fields in the kinetic coupling model (IFF model). By using the
observational result of P_\zeta, f_nl and \tau_nl reported by the Planck
collaboration, we study the constraint on the model comprehensively.
Interestingly, if the single slow-rolling inflaton is responsible for the
observed P_\zeta, the constraint from \tau_nl is most stringent. We also find a
general relationship between f_nl and \tau_nl generated in this model. Even if
f_nl \sim O(1), a detectable \tau_nl can be produced. | A SAURON study of dwarf elliptical galaxies in the Virgo Cluster:
kinematics and stellar populations: Dwarf elliptical galaxies (dEs) are the most common galaxy type in nearby
galaxy clusters; even so, many of their basic properties have yet to be
quantified. Here we present the results of our study of 4 Virgo dwarf
ellipticals obtained with the SAURON integral field unit on the William
Herschel Telescope (La Palma, Spain). While traditional long-slit observations
are likely to miss more complicated kinematic features, with SAURON we are able
to study both kinematics and stellar populations in two dimensions, obtaining a
much more detailed view of the mass distribution and star formation histories.
What is visible even in such a small sample is that dEs are not a uniform
group, not only morphologically, but also as far as their kinematic and stellar
population properties are concerned. We find the presence of substructures,
varying degrees of flattening and of rotation, as well as differences in age
and metallicity gradients. We confirm that two of our galaxies are
significantly flattened, yet non-rotating objects, which makes them likely
triaxial systems. The comparison between the dwarf and the giant groups shows
that dEs could be a low-mass extension of Es in the sense that they do seem to
follow the same trends with mass. However, dEs as progenitors of Es seem less
likely as we have seen that dEs have much lower abundance ratios. |
The Highest Redshift Quasar at $z=7.085$: A Radio Quiet Source: We present 1-2 GHz Very Large Array A-configuration continuum observations on
the highest redshift quasar known to date, the $z=7.085$ quasar ULAS
J112001.48+064124.3. The results show no radio continuum emission at the
optical position of the quasar or its vicinity at a level of $\geq 3\sigma$ or
$23.1 \mu$Jy beam$^{-1}$. This $3\sigma$ limit corresponds to a rest frame 1.4
GHz luminosity density limit of $L_{\nu,1.4\,GHz} < 1.76 \times 10^{24}$ W
Hz$^{-1}$ for a spectral index of $\alpha=0$, and $L_{\nu,1.4\,GHz} < 1.42
\times 10^{25}$ W Hz$^{-1}$ for a spectral index of $\alpha=-1$. The rest-frame
1.4 GHz luminosity limits are $L_{rad} < 6.43 \times 10^6 L_{\odot}$ and
$L_{\rm rad} < 5.20 \times 10^7 L_{\odot}$ for $\alpha=0$ and $\alpha=-1$,
respectively. The derived limits for the ratio of the rest frame 1.4 GHz
luminosity density to the $B$-band optical luminosity density are
$R\rlap{}_{1.4}^{*} < 0.53$ and $< 4.30$ for the above noted spectral indices,
respectively. Given our upper limits on the radio continuum emission and the
radio-to-optical luminosity ratio, we conclude that this quasar is radio-quiet
and located at the low end of the radio quiet distribution of high redshift ($z
\gtrsim 6$) quasars. | Deep 1.1 mm-wavelength imaging of the GOODS-S field by AzTEC/ASTE - I.
Source catalogue and number counts: [Abridged] We present the first results from a 1.1 mm confusion-limited map
of the GOODS-S field taken with AzTEC on the ASTE telescope. We imaged a 270
sq. arcmin field to a 1\sigma depth of 0.48 - 0.73 mJy/beam, making this one of
the deepest blank-field surveys at mm-wavelengths ever achieved. Although our
GOODS-S map is extremely confused, we demonstrate that our source
identification and number counts analyses are robust, and the techniques
discussed in this paper are relevant for other deeply confused surveys. We find
a total of 41 dusty starburst galaxies with S/N >= 3.5 within this uniformly
covered region, where only two are expected to be false detections. We derive
the 1.1mm number counts from this field using both a "P(d)" analysis and a
semi-Bayesian technique, and find that both methods give consistent results.
Our data are well-fit by a Schechter function model with (S', N(3mJy), \alpha)
= (1.30+0.19 mJy, 160+27 (mJy/deg^2)^(-1), -2.0). Given the depth of this
survey, we put the first tight constraints on the 1.1 mm number counts at
S(1.1mm) = 0.5 mJy, and we find evidence that the faint-end of the number
counts at S(850\mu m) < 2.0 mJy from various SCUBA surveys towards lensing
clusters are biased high. In contrast to the 870 \mu m survey of this field
with the LABOCA camera, we find no apparent under-density of sources compared
to previous surveys at 1.1 mm. Additionally, we find a significant number of
SMGs not identified in the LABOCA catalogue. We find that in contrast to
observations at wavelengths < 500 \mu m, MIPS 24 \mu m sources do not resolve
the total energy density in the cosmic infrared background at 1.1 mm,
demonstrating that a population of z > 3 dust-obscured galaxies that are
unaccounted for at these shorter wavelengths potentially contribute to a large
fraction (~2/3) of the infrared background at 1.1 mm. |
Dark matter halo's and self similarity: This papers explores the self similar solutions of the Vlasov-Poisson system
and their relation to the gravitational collapse of dynamically cold systems.
Analytic solutions are derived for power law potential in one dimension, and
extensions of these solutions in three dimensions are proposed. Next the self
similarity of the collapse of cold dynamical systems is investigated
numerically. The fold system in phase space is consistent with analytic self
similar solutions, the solutions present all the proper self-similar scalings.
An additional point is the appearance of an $x^{-(1/2)}$ law at the center of
the system for initial conditions with power law index larger than $-(1/2)$. It
is found that the first appearance of the $x^{-(1/2)}$ law corresponds to the
formation of a singularity very close to the center. Finally the general
properties of self similar multi dimensional solutions near equilibrium are
investigated. Smooth and continuous self similar solutions have power law
behavior at equilibrium. However cold initial conditions result in
discontinuous phase space solutions, and the smoothed phase space density
looses its auto similar properties. This problem is easily solved by observing
that the probability distribution of the phase space density $P$ is identical
except for scaling parameters to the probability distribution of the smoothed
phase space density $P_S$. As a consequence $P_S$ inherit the self similar
properties of $P$. This particular property is at the origin of the universal
power law observed in numerical simulation for ${\rho}/{\sigma^3}$. The self
similar properties of $P_S$ implies that other quantities should have also an
universal power law behavior with predictable exponents. This hypothesis is
tested using a numerical model of the phase space density of cold dark matter
halo's, an excellent agreement is obtained. | Starburst Galaxies: Outflows of Metals and Energy into the IGM: What is the contribution of mass, metals and energy from starburst galaxies
to the Intergalactic Medium? Starburst galaxies drive galactic-scale outflows
or "superwinds" that may be responsible for removing metals from galaxies and
polluting the Intergalactic Medium (IGM). In the last decade tremendous
progress was made in mapping cool entrained gas in superwinds through
UV/optical imaging and absorption line spectroscopy. These studies demonstrated
that superwinds are ubiquitous in galaxies forming stars at high surface
densities and that the most powerful starbursts can drive outflows near escape
velocity. Theoretical models of galaxy evolution have begun to incorporate
superwinds, using various ad-hoc prescriptions based on our knowledge of the
cool gas. However, these efforts are fundamentally impeded by our lack of
information about the hot phase of these outflows. The hot X-ray emitting phase
of a superwind contains the majority of its energy and newly-synthesized
metals, and given its high specific energy and inefficient cooling it is also
the component most likely escape from the galaxy's gravitational potential
well. Knowledge of the chemical composition and velocity of the hot gas are
crucial to assess the energy and chemical feedback from a starburst. A high
priority for the next decade is to enable direct measurements to be made of the
rates at which starburst galaxies of all masses eject gas, metals, and energy
into the IGM. This will require a high sensitivity X-ray imaging spectrometer
capable of measuring velocities in faint diffuse X-ray emission with a velocity
accuracy of ~ 100 km/s. Such spectral resolution automatically allows detailed
line-based plasma diagnostics, and thus composition, energetics and flow rates
can be derived. |
Constraining dark energy using observational growth rate data: Observational growth rate data had been derived from observations of redshift
distortions in galaxy redshift surveys. Here we use the growth rate data to
place constraints on the dark energy model parameters. By performing a joint
analysis with the Type Ia supernova, baryon acoustic oscillation and cosmic
microwave background data, it is found that the growth rate data are useful for
improving the constraints. The joint constraints show that the $\Lambda$CDM
model is still in good agreement with current observations, although a
time-variant dark energy still cannot be ruled out. It is argued that the
growth rate data are helpful for understanding the dark energy. With more
accurate data available in the future, we will have a powerful tool for
constraining the cosmological and dark energy parameters. | Simple parametrisation for coupled dark energy: We propose a phenomenological generalisation of the standard model with only
one extra degree of freedom that parametrises the evolution of a scalar field
responsible for the cosmic acceleration. The model also foresees an additional
parameter in the form of a coupling between dark energy and dark matter. This
model captures a large diversity of dark energy evolutions at low redshift and
could usefully complement common CPL parametrisations widely used. In this
context, we have been constraining the parametrisation with data from Planck
and KiDS, bringing different results between the early and late universe
observations. |
Simulation-based marginal likelihood for cluster strong lensing
cosmology: Comparisons between observed and predicted strong lensing properties of
galaxy clusters have been routinely used to claim either tension or consistency
with $\Lambda$CDM cosmology. However, standard approaches to such cosmological
tests are unable to quantify the preference for one cosmology over another. We
advocate approximating the relevant Bayes factor using a marginal likelihood
that is based on the following summary statistic: the posterior probability
distribution function for the parameters of the scaling relation between
Einstein radii and cluster mass, $\alpha$ and $\beta$. We demonstrate, for the
first time, a method of estimating the marginal likelihood using the X-ray
selected $z>0.5$ MACS clusters as a case in point and employing both N-body and
hydrodynamic simulations of clusters. We investigate the uncertainty in this
estimate and consequential ability to compare competing cosmologies, that
arises from incomplete descriptions of baryonic processes, discrepancies in
cluster selection criteria, redshift distribution, and dynamical state. The
relation between triaxial cluster masses at various overdensities provide a
promising alternative to the strong lensing test. | Excess entropy and energy feedback from within cluster cores up to
r$_{200}$: We estimate the "non-gravitational" entropy-injection profiles, $\Delta K$,
and the resultant energy feedback profiles, $\Delta E$, of the intracluster
medium for 17 clusters using their Planck SZ and ROSAT X-Ray observations,
spanning a large radial range from $0.2r_{500}$ up to $r_{200}$. The feedback
profiles are estimated by comparing the observed entropy, at fixed gas mass
shells, with theoretical entropy profiles predicted from non-radiative
hydrodynamic simulations. We include non-thermal pressure and gas clumping in
our analysis. The inclusion of non-thermal pressure and clumping results in
changing the estimates for $r_{500}$ and $r_{200}$ by 10\%-20\%. When
clumpiness is not considered it leads to an under-estimation of $\Delta
K\approx300$ keV cm$^2$ at $r_{500}$ and $\Delta K\approx1100$ keV cm$^2$ at
$r_{200}$. On the other hand, neglecting non-thermal pressure results in an
over-estimation of $\Delta K\approx 100$ keV cm$^2$ at $r_{500}$ and
under-estimation of $\Delta K\approx450$ keV cm$^2$ at $r_{200}$. For the
estimated feedback energy, we find that ignoring clumping leads to an
under-estimation of energy per particle $\Delta E\approx1$ keV at $r_{500}$ and
$\Delta E\approx1.5$ keV at $r_{200}$. Similarly, neglect of the non-thermal
pressure results in an over-estimation of $\Delta E\approx0.5$ keV at $r_{500}$
and under-estimation of $\Delta E\approx0.25$ keV at $r_{200}$. We find entropy
floor of $\Delta K\approx300$ keV cm$^2$ is ruled out at $\approx3\sigma$
throughout the entire radial range and $\Delta E\approx1$ keV at more than
3$\sigma$ beyond $r_{500}$, strongly constraining ICM pre-heating scenarios. We
also demonstrate robustness of results w.r.t sample selection, X-Ray analysis
procedures, entropy modeling etc. |
Including relativistic and primordial Non-Gaussianity contributions in
cosmological simulations by modifying the initial condition: We present a method to implement relativistic corrections to the evolution of
dark matter structures in Newtonian simulations of a LCDM universe via the
initial conditions. We take the nonlinear correspondence between the Lagrangian
(Newtonian) evolution of dark matter inhomogeneities and the
synchronous-comoving (relativistic) matter density description, and use it to
promote the relativistic constraint as the initial condition for numerical
simulations of structure formation. In this case, the incorporation of
Primordial non-Gaussianity (PNG) contributions as initial conditions is
straightforward. We implement the relativistic,fNL and gNLcontributions as
initial conditions for the L-PICOLA code, and compute the power spectrum and
bispectrum of the evolved matter field. We focus specifically on the case of
largest values of non-Gaussianity allowed at 1-sigma by Planck
observations(fNL=-4.2 and gNL=-7000). As a checkup, we show consistency with
the one-loop perturbative prescription and with a fully relativistic simulation
(GRAMSES) on the adequate scales. Our results confirm that both relativistic
and PNG features are most prominent at very large scales and for squeezed
triangulations. We discuss future prospects to probe these two contributions in
the bispectrum of the matter density distribution | High resolution calibration of the cosmic strings velocity dependent
one-scale model: The canonical velocity-dependent one-scale (VOS) model for cosmic string
evolution must be calibrated using high resolution numerical simulations, We
exploit our state of the art graphics processing unit accelerated
implementation of the evolution of local Abelian-Higgs string networks to
provide a detailed and statistically robust calibration of the VOS model. We
rely on the largest set of high resolution simulations carried out to date,
with a wide range of cosmological expansion rates, and explore the impact of
key numerical parameters, including the dynamic range (comparing box sizes from
$1024^3$ to $4096^3$), the lattice spacing, and the choice of numerical
estimators for the string velocity. We explore the sensitivity of the VOS model
parameters to these numerical parameters, with a particular emphasis on the
observationally crucial loop chopping efficiency, and also identify key
differences between the equation of state and conjugate momentum estimators for
the string velocities, showing that the latter one is more reliable for fast
expansion rates (while in Minkowski space the opposite has been previously
shown). Finally, we briefly illustrate how our results impact observational
constraints on cosmic strings. |
Ghost Dark Matter: We revisit ghost dark matter, the possibility that ghost condensation may
serve as an alternative to dark matter. In particular, we investigate the
Friedmann-Robertson-Walker (FRW) background evolution and the large-scale
structure (LSS) in the $\Lambda$GDM universe, i.e. a late-time universe
dominated by a cosmological constant and ghost dark matter. The FRW background
of the $\Lambda$GDM universe is indistinguishable from that of the standard
$\Lambda$CDM universe if $M\gtrsim 1 {\rm eV}$, where $M$ is the scale of
spontaneous Lorentz breaking. From the LSS we find a stronger bound: $M\gtrsim
10 {\rm eV}$. For smaller $M$, ghost dark matter would have non-negligible
sound speed after the matter-radiation equality, and thus the matter power
spectrum would significantly differ from observation. These bounds are
compatible with the phenomenological upper bound $M\lesssim 100 {\rm GeV}$
known in the literature. | Quasars as probes of cosmological reionization: Quasars are the most luminous non-transient sources in the epoch of
cosmological reionization (i.e., which ended a billion years after the Big
Bang, corresponding to a redshift of z ~ 5), and are powerful probes of the
inter-galactic medium at that time. This review covers current efforts to
identify high-redshift quasars and how they have been used to constrain the
reionization history. This includes a full description of the various processes
by which neutral hydrogen atoms can absorb/scatter ultraviolet photons, and
which lead to the Gunn-Peterson effect, dark gap and dark pixel analyses,
quasar near zones and damping wing absorption. Finally, the future prospects
for using quasars as probes of reionization are described. |
Extragalactic relativistic jets: Extragalactic relativistic jets are engines able to carry out to large
distances a huge amount of power, not only in the form of radiation, but
especially in the form of kinetic energy of matter and fields. As such, they
can be thought as one of the most efficient engines of Nature, perhaps even
more efficient than accretion. We are starting to disclose these features
through a detailed study of their properties, made possible by the analysis of
the energy band where they emit most of their electromagnetic output, namely
the gamma-ray band. That is why the observations by the Fermi satellite and by
the ground based Cherenkov telescopes are crucial to understand extragalactic
jets. At the start, we believe they are magnetically dominated. And yet, on the
scale where they emit most of their luminosity, their power is already in the
form of kinetic energy of particles. The spectral properties of bright sources
show a trend, controlled mainly by the bolometric apparent luminosity. With
improved sensitivity, and the detection of weaker sources, we can explore the
idea that the spectral trends are a result of the same physical quantities
controlling the emission of non-jetted sources: the black hole mass and the
accretion rate. This is based on recent results on sources showing a thermal
component in their spectrum, besides a non-thermal continuum. That the jet
power should be linked to accretion is intriguing. Most of the apparent
diversity of extragalactic radio sources can then be understood on the basis of
the viewing angle, controlling the relativistic Doppler boosting of the
emission, the black hole mass and the accretion rate. | Large Late-time Asphericities in Three Type IIP Supernovae: Type II-plateau supernovae (SNe IIP) are the results of the explosions of red
supergiants and are the most common subclass of core-collapse supernovae. Past
observations have shown that the outer layers of the ejecta of SNe IIP are
largely spherical, but the degree of asphericity increases toward the core. We
present evidence for high degrees of asphericity in the inner cores of three
recent SNe IIP (SNe 2006my, 2006ov, and 2007aa), as revealed by late-time
optical spectropolarimetry. The three objects were all selected to have very
low interstellar polarization (ISP), which minimizes the uncertainties in ISP
removal and allows us to use the continuum polarization as a tracer of
asphericity. The three objects have intrinsic continuum polarizations in the
range of 0.83-1.56% in observations taken after the end of the photometric
plateau, with the polarization dropping to almost zero at the wavelengths of
strong emission lines. Our observations of SN 2007aa at earlier times, taken on
the photometric plateau, show contrastingly smaller continuum polarizations
(~0.1%). The late-time H-alpha and [O I] line profiles of SN 2006ov provide
further evidence for asphericities in the inner ejecta. Such high core
polarizations in very ordinary core-collapse supernovae provide further
evidence that essentially all core-collapse supernova explosions are highly
aspherical, even if the outer parts of the ejecta show only small deviations
from spherical symmetry. |
Damped Lyα Absorption Systems in Semi-Analytic Models with
Multiphase Gas: We investigate the properties of damped Ly{\alpha} absorption systems (DLAs)
in semi-analytic models of galaxy formation, including partitioning of cold gas
in galactic discs into atomic, molecular, and ionized phases with a molecular
gas-based star formation recipe. We investigate two approaches for partitioning
gas into these constituents: a pressure-based and a metallicity-based recipe.
We identify DLAs by passing lines of sight through our simulations to compute
HI column densities. We find that models with "standard" gas radial profiles -
where the average specific angular momentum of the gas disc is equal to that of
the host dark matter halo - fail to reproduce the observed column density
distribution of DLAs. These models also fail to reproduce the distribution of
velocity widths {\Delta}v, overproducing low {\Delta}v relative to high
{\Delta}v systems. Models with "extended" radial gas profiles - corresponding
to gas discs with higher specific angular momentum - are able to reproduce
quite well the column density distribution of absorbers over the column density
range 19 < log NHI < 22.5 in the redshift range 2 < z < 3.5. The model with
pressure-based gas partitioning also reproduces the observed line density of
DLAs, HI gas density, and {\Delta}v distribution at z < 3 remarkably well.
However all of the models investigated here underproduce DLAs and the HI gas
density at z > 3. If this is the case, the flatness in the number of DLAs and
HI gas density over the redshift interval 0 < z < 5 may be due to a cosmic
coincidence where the majority of DLAs at z > 3 arise from intergalactic gas in
filaments while those at z < 3 arise predominantly in galactic discs. We
further investigate the dependence of DLA metallicity on redshift and
{\Delta}v, and find reasonably good agreement with the observations,
particularly when including the effects of metallicity gradients (abbrv.). | Snowmass2021 Cosmic Frontier White Paper: High Density Galaxy Clustering
in the Regime of Cosmic Acceleration: Joint studies of imaging and spectroscopic samples, informed by theory and
simulations, offer the potential for comprehensive tests of the cosmological
model over redshifts z<1.5. Spectroscopic galaxy samples at these redshifts can
be increased beyond the planned Dark Energy Spectroscopic Instrument (DESI)
program by at least an order of magnitude, thus offering significantly more
constraining power for these joint studies. Spectroscopic observations of these
galaxies in the latter half of the 2020's and beyond would leverage the theory
and simulation effort in this regime. In turn, these high density observations
will allow enhanced tests of dark energy, physics beyond the standard model,
and neutrino masses that will greatly exceed what is currently possible. Here,
we present a coordinated program of simulations, theoretical modeling, and
future spectroscopy that would enable precise cosmological studies in the
accelerating epoch where the effects of dark energy are most apparent. |
Cosmology and the massive photon frequency shift in the Standard-Model
Extension: The total red shift $z$ might be recast as a combination of the expansion red
shift and a static shift due to the energy-momentum tensor non-conservation of
a photon propagating through Electro-Magnetic (EM) fields. If massive, the
photon may be described by the de Broglie-Proca (dBP) theory which satisfies
the Lorentz(-Poincar\'e) Symmetry (LoSy) but not gauge-invariance. The latter
is regained in the Standard-Model Extension (SME), associated with LoSy
Violation (LSV) that naturally dresses photons of a mass. The non-conservation
stems from the vacuum expectation value of the vector and tensor LSV fields.
The final colour (red or blue) and size of the static shift depend on the
orientations and strength of the LSV and EM multiple fields encountered along
the path of the photon. Turning to cosmology, for a zero $\Omega_{\Lambda}$
energy density, the discrepancy between luminosity and red shift distances of
SNeIa disappears thanks to the recasting of $z$. Massive photons induce an
effective dark energy acting `optically' but not dynamically. | A holistic view on ram pressure stripping in the Virgo cluster - The
first complete model-based time sequence: Based on a comparison of dynamical models with observations of the
interstellar gas in 6 Virgo cluster spiral galaxies a first complete ram
pressure stripping time sequence has been established. The observational
characteristics of the different stages of ram pressure stripping are
presented. The dynamical models yield the 3D velocity vectors of the galaxies,
peak ram pressures, and times to peak ram pressure. In the case of a smooth,
static, and spherical intracluster medium, peak ram pressure occurs during the
galaxy's closest approach to the cluster center, i.e. when the galaxy's
velocity vector is perpendicular to its distance vector from the cluster center
(M 87). Assuming this condition the galaxy's present line-of-sight distance and
its 3D position during peak ram pressure can be calculated. The linear orbital
segments derived in this way together with the intracluster medium density
distribution derived from X-ray observations give estimates of the ram pressure
that are on average a factor of 2 higher than derived from the dynamical
simulations for NGC 4501, NGC 4330, and NGC 4569. Resolving this discrepancy
would require either a 2 times higher intracluster medium density than derived
from X-ray observations, or a 2 times higher stripping efficiency than assumed
by the dynamical models. Compared to NGC 4501, NGC 4330, and NGC 4569, NGC 4388
requires a still 2 times higher local intracluster medium density or a
direction which is moderately different from that derived from the dynamical
model. A possible scenario for the dynamical evolution of NGC 4438 and M 86
within the Virgo cluster is presented. |
AMIGA project: Quantification of the isolation of 950 CIG galaxies: The role of the environment on galaxy evolution is still not fully
understood. In order to quantify and set limits on the role of nurture one must
identify and study a sample of isolated galaxies. The AMIGA project "Analysis
of the Interstellar Medium of Isolated GAlaxies" is doing a multi-wavelength
study of a large sample of isolated galaxies in order to examine their
interstellar medium and star formation activity. We processed data for 950
galaxies from the Catalogue of Isolated Galaxies (CIG, Karachentseva 1973) and
evaluated their isolation using an automated star-galaxy classification
procedure (down to M_B ~17.5) on large digitised POSS-I fields surrounding each
isolated galaxy (within a projected radius of at least 0.5 Mpc). We defined,
compared and discussed various criteria to quantify the degree of isolation for
these galaxies: e.g. Karachentseva's revised criterion, local surface density
computations, estimation of the external tidal force affecting each isolated
galaxy. We found galaxies violating Karachentseva's original criterion, and we
defined various subsamples of galaxies according to their degree of isolation.
Additionally, we sought for the redshifts of the primary and companion galaxies
to access the radial dimension. We also applied our pipeline to triplets,
compact groups and clusters and interpret the isolated galaxy population in
light of these control samples. | Living on the Fermi Edge: On Baryon Transport and Fermi Condensation: The transfer function of the baryon power spectrum from redshift $z\approx
1100$ to today has recently been, for the first time, determined from data by
Pardo and Spergel. We observe a remarkable coincidence between this function
and the transport function of a cold ideal Fermi gas at different redshifts.
Guided by this, we unveil an infinite set of critical temperatures of the
relativistic ideal Fermi gas which depend on a very finely quantized
long-distance cutoff. The sound horizon scale of Baryon Acoustic Oscillations
(BAO) seems to set such a cutoff, which dials a critical temperature that is
subsequently reached during redshift. At the critical point the Fermi gas
becomes scale invariant and may condense to subsequently undergo gravitational
collapse, seeding small scale structure. We mention some profound implications
including the apparent quantization of Fermi momentum conjugate to the cutoff
and the corresponding "gapping" of temperature. |
Fifth force constraints from galaxy warps: Intra-galaxy signals contain a wealth of information on fundamental physics,
both the dark sector and the nature of gravity. While so far largely
unexplored, such probes are set to rise dramatically in importance as upcoming
surveys provide data of unprecedented quantity and quality on galaxy structure
and dynamics. In this paper, we use warping of stellar disks to test the
chameleon- or symmetron-screened fifth forces which generically arise when new
fields couple to matter. We take r-band images of mostly late-type galaxies
from the Nasa Sloan Atlas and develop an automated algorithm to quantify the
degree of U-shaped warping they exhibit. We then forward-model the warp signal
as a function of fifth-force strength $\Delta G/G_N$ and range $\lambda_C$, and
the gravitational environments and internal properties of the galaxies,
including full propagation of the non-Gaussian uncertainties. Convolving this
fifth-force likelihood function with a Gaussian describing astrophysical and
observational noise and then constraining $\Delta G/G_N$ and $\lambda_C$ by
Markov Chain Monte Carlo, we find the overall likelihood to be significant
increased ($\Delta\log(\mathcal{L}) \simeq 20$) by adding a screened fifth
force with $\lambda_C \simeq 2$ Mpc, $\Delta G/G_N \simeq 0.01$. The variation
of $\Delta\log(\mathcal{L})$ with $\lambda_C$ is quantitatively as expected
from the correlation of the magnitude of the fifth-force field with the force's
range, and a similar model without screening achieves no increase in likelihood
over the General Relativistic case $\Delta G=0$. Although these results are in
good agreement with a previous analysis of the same model using offsets between
galaxies' stellar and gas mass centroids (Desmond et al. 2018), we caution that
the effects of confounding baryonic and dark matter physics must be thoroughly
investigated for the results of the inference to be unambiguous. | The History and Environment of a Faded Quasar: Hubble Space Telescope
observations of Hanny's Voorwerp and IC 2497: We present Hubble Space Telescope imaging and spectroscopy for the extended
high-ionization cloud known as Hanny's Voorwerp, near the spiral galaxy IC
2497. WFC3 images show complex dust absorption near the nucleus of IC 2497.
STIS spectra show a type 2 Seyfert AGN of rather low luminosity. The ionization
parameter log U = -3.5 is in accord with its weak X-ray emission. We find no
high-ionization gas near the nucleus, adding to evidence that the AGN is
currently at low radiative output (perhaps now dominated by kinetic energy).
The nucleus is accompanied by an expanding ring of ionized gas 500 pc in
projected diameter on the side opposite Hanny's Voorwerp, with Doppler offset
300 km/s from the nucleus (kinematic age < 7 x10^5 years). [O III] and H-alpha
+ [N II] images show fine structure in Hanny's Voorwerp, with limb-brightened
sections and small areas where H-alpha is strong. We identify these as regions
ionized by recent star formation, in contrast to the AGN ionization of the
entire cloud. These candidate "normal" H II regions contain blue continuum
objects, whose colors are consistent with young stellar populations; they
appear only in a 2-kpc region toward IC 2497 in projection. The
ionization-sensitive ratio [O III]/H-alpha shows no discernible pattern near
the prominent "hole" in the ionized gas. The independence of ionization and
surface brightness suggests that substantial spatial structure remains
unresolved, to such an extent that the surface brightness sample the number of
denser filaments rather than the characteristic density in emission regions.
These results fit with our picture of an ionization echo from an AGN whose
ionizing luminosity has dropped by a factor > 100 (and possibly much more)
within the last 1-2 x 10^5 years; we suggest a sequence of events and discuss
implications of such rapid fluctuations for AGN demographics. (Abridged) |
Mass and Environment as Drivers of Galaxy Evolution II: The quenching of
satellite galaxies as the origin of environmental effects: We extend the phenomenological study of the evolving galaxy population of
Peng et al (2010) to the central/satellite dichotomy in Yang et al. SDSS
groups. We find that satellite galaxies are responsible for all the
environmental effects in our earlier work. The fraction of centrals that are
red does not depend on their environment but only on their stellar masses,
whereas that of the satellites depends on both. We define a relative satellite
quenching efficiency, which is the fraction of blue centrals that are quenched
upon becoming the satellite of another galaxy. This is shown to be independent
of stellar mass, but to depend strongly on local overdensity. The red fraction
of satellites correlate much better with the local overdensity, a measure of
location within the group, than with the richness of the group, i.e. dark
matter halo mass. This, and the fact that satellite quenching depends on local
density and not on either the stellar mass of the galaxy or the halo mass gives
clues as to the nature of the satellite-quenching process. We furthermore show
that the action of mass-quenching on satellite galaxies is also independent of
the DM mass of the parent halo. We then apply the Peng et al (2010) approach to
predict the mass functions of central and satellite galaxies, split into
passive and active galaxies, and show that these match very well the observed
mass functions from SDSS, further strengthening the validity of this
phenomenological approach. We highlight the fact that the observed M* is the
same for the star-forming centrals and satellites and the observed M* for the
star-forming satellites is independent of halo mass above 10^12M\odot, which
emphasizes the universality of the mass-quenching process that we identified in
Peng et al (2010). Post-quenching merging modifies the mass function of the
central galaxies but can increase the mass of typical centrals by only about
25%. | Gas circulation and galaxy evolution: Galaxies must form and evolve via the acquisition of gas from the
intergalactic environment, however the way this gas accretion takes place is
still poorly understood. Star-forming galaxies are surrounded by multiphase
halos that appear to be mostly produced by internal processes, e.g., galactic
fountains. However, a small fraction of the halo gas shows features that point
to an external origin. Estimates of the halo-gas accretion rate in the local
Universe consistently give values much lower than what would be required to
sustain star formation at the observed rate. Thus, most of the gas accretion
must be "hidden" and not seen directly. I discuss possible mechanisms that can
cause the intergalactic gas to cool and join the star-forming galactic disks. A
possibility is that gas accretion is driven by the galactic-fountain process
via turbulent mixing of the fountain gas with the coronal low-metallicity gas. |
HI as a Probe of the Large Scale Structure in the Post-Reionization
Universe: We model the distribution of neutral Hydrogen (HI hereafter) in the
post-reionization universe. This model uses gravity only N-Body simulations and
an ansatz to assign HI to dark matter haloes that is consistent with
observational constraints and theoretical models. We resolve the smallest
haloes that are likely to host HI in the simulations, care is also taken to
ensure that any errors due to the finite size of the simulation box are small.
We then compute the smoothed one point probability distribution function and
the power spectrum of fluctuations in HI. This is compared with other
predictions that have been made using different techniques. We highlight the
significantly high bias for the HI distribution at small scales. This aspect
has not been discussed before. We then discuss the prospects for detection with
the MWA, GMRT and the hypothetical MWA5000. The MWA5000 can detect visibility
correlations at large angular scales at all redshifts in the post-reionization
era. The GMRT can detect visibility correlations at lower redshifts,
specifically there is a strong case for a survey at z=1.3. We also discuss
prospects for direct detection of rare peaks in the HI distribution using the
GMRT. We show that direct detection should be possible with an integration time
that is comparable to, or even less than, the time required for a statistical
detection. Specifically, it is possible to make a statistical detection of the
HI distribution by measuring the visibility correlation, and, direct detection
of rare peaks in the HI distribution at z = 1.3 with the GMRT in less than 1000
hours of observations. | Canonical and Non-canonical Inflation in the light of the recent
BICEP/Keck results: We discuss implications of the latest BICEP/Keck data release for
inflationary models, with particular emphasis on scalar fields with
non-canonical Lagrangians of the type ${\cal L} = X^\alpha - V(\phi)$. The
observational upper bound on the tensor-to-scalar ratio, $r \leq 0.036$,
implies that the whole family of monomial power law potentials $V(\phi) \sim
\phi^p$ are now ruled out in the canonical framework at $95\%$ confidence,
which includes the simplest classic inflationary potentials such as
$\frac{1}{2}m^2 \phi^2$ and $\lambda \phi^4$. Instead, current observations
strongly favour asymptotically flat plateau potentials. However, working in the
non-canonical framework, we demonstrate that monomial potentials, as well as
the Higgs potential with its Standard Model self-coupling, can easily be
accommodated by current CMB data. We find striking similarities between the
$\lbrace n_{_S}, r\rbrace$ flow lines of monomial potentials in the
non-canonical framework and the T-model $\alpha$-attractors in the canonical
framework. Significantly, $V(\phi)$ can originate from Planck scale initial
values $V(\phi) \simeq m_p^4$ in non-canonical models while in plateau-like
canonical inflation the initial value of the potential is strongly suppressed
$V_{\rm plat}(\phi) \leq 10^{-10} m_p^4$. This has bearing on the issue of
initial conditions for inflation and allows for the equipartition of the
kinetic and potential terms in non-canonical models. |
Is the metallicity of their hosts a good measure of the metallicity of
Type Ia supernovae?: The efficient use of Type Ia supernovae (SNIa) for cosmological studies
requires knowledge of any parameter that can affect their luminosity in either
systematic or statistical ways. Observational samples of SNIa commonly use the
metallicity of the host galaxy, Z_host, as an estimator of the supernova
progenitor metallicity, Z_Ia, that is one of the primary factors affecting SNIa
magnitude. Here, we present a theoretical study of the relationship between
Z_Ia and Z_host. We follow the chemical evolution of homogeneous galaxy models
together with the evolution of the supernova rates in order to evaluate the
metallicity distribution function, MDF(Delta Z), i.e. the probability that the
logarithm of the metallicity of a SNIa exploding now differs in less than Delta
Z from that of its host. We analyse several model galaxies aimed to represent
from active to passive galaxies, including dwarf galaxies prone to experience
supernova driven outflows. We analyse the sensitivity of the MDF to uncertain
ingredients: IMF, star-formation law, stellar lifetime, stellar yields, and
SNIa delay-time distribution. There is a remarkable degree of agreement between
the mean Z_Ia in a galaxy and its Z_host when they both are measured as the CNO
abundance, especially if the DTD peaks at small time delays, while the average
Fe abundance of host and SNIa may differ up to 0.4-0.6 dex in passive galaxies.
The dispersion of Z_Ia in active galaxy models is quite small, meaning that
Z_host is a quite good estimator of the supernova metallicity. Passive galaxies
present a larger dispersion, which is more pronounced in low mass galaxies. We
discuss the use of different metallicity indicators: Fe vs. O, and gas-phase
metallicity vs. stellar metallicity. The results of the application of our
formalism to a galactic catalogue (VESPA) are roughly consistent with our
theoretical estimates. (abridged) | Recovering lost 21 cm radial modes via cosmic tidal reconstruction: 21 cm intensity mapping has emerged as a promising technique to map the
large-scale structure of the Universe, at redshifts $z$ from 1 to 10.
Unfortunately, many of the key cross-correlations with the cosmic microwave
background and photo-$z$ galaxies have been thought to be impossible due to the
foreground contamination for radial modes with small wave numbers. In this
paper, we apply tidal reconstruction to the simulated 21 cm fields and recover
the lost large-scale radial modes successfully. We estimate the detectability
of the cross-correlation signals and find they can be detected at high
significance with current 21 cm experiments. The tidal field reconstruction
method opens up a new set of possibilities to probe the Universe and is
extremely valuable not only for 21 cm surveys but also for cosmic microwave
background and photometric-redshift observations. |
Coarse-Grained Cosmological Perturbation Theory: Semi-analytical methods, based on Eulerian perturbation theory, are a
promising tool to follow the time evolution of cosmological perturbations at
small redshifts and at mildly nonlinear scales. All these schemes are based on
two approximations: the existence of a smoothing scale and the single-stream
approximation, where velocity dispersion of the dark matter fluid, as well as
higher moments of the particle distributions, are neglected. Despite being
widely recognized, these two assumptions are, in principle, incompatible, since
any finite smoothing scale gives rise to velocity dispersion and higher moments
at larger scales. We describe a new approach to perturbation theory, where the
Vlasov and fluid equations are derived in presence of a finite coarse-graining
scale: this allows a clear separation between long and short distance modes and
leads to a hybrid approach where the former are treated perturbatively and the
effect of the latter is encoded in external source terms for velocity, velocity
dispersion, and all the higher order moments, which can be computed from N-body
simulations. We apply the coarse-grained perturbation theory to the computation
of the power spectrum and the cross-spectrum between density and velocity
dispersion, and compare the results with N-body simulations, finding good
agreement. | Effect of inhomogeneities on high precision measurements of cosmological
distances: We study effects of inhomogeneities on distance measures in an exact
relativistic Swiss-cheese model of the universe, focusing on the distance
modulus. The model has LCDM background dynamics, and the `holes' are
non-symmetric structures described by the Szekeres metric. The Szekeres exact
solution of Einstein's equations, which is inhomogeneous and anisotropic,
allows us to capture potentially relevant effects on light propagation due to
nontrivial evolution of structures in an exact framework. Light beams
traversing a single Szekeres structure in different ways can experience either
magnification or demagnification, depending on the particular path, and we
explore a small additional effect due time evolution of the structures. We
study the probability distributions of $\Delta\mu=\mu_{LCDM}-\mu_{SC}$ for
sources at different redshifts in various Swiss-cheese constructions, where the
light beams travel through a large number of randomly oriented holes with
random impact parameters. We find for $\Delta\mu$ the dispersions $0.004\le
\sigma_{\Delta\mu} \le 0.008$ mag for sources with redshifts $1.0\le z \le
1.5$, which are smaller than the intrinsic dispersion of, for example,
magnitudes of type Ia supernovae. The shapes of the distributions we obtain for
our Swiss-cheese constructions are peculiar in the sense that they are not
consistently skewed toward the demagnification side, as they are in analyses of
lensing in cosmological simulations, reflecting a limitation of these
constructions. This could be the result of requiring the continuity of
Einstein's equations throughout the overall spacetime patchwork, which imposes
the condition that compensating overdense shells must accompany the underdense
void regions in the holes. The possibility to explore other uses of these
constructions that could circumvent this limitation and lead to different
statistics remains open. (Abridged) |
Average luminosity distance in inhomogeneous universes: The paper studies the correction to the distance modulus induced by
inhomogeneities and averaged over all directions from a given observer. The
inhomogeneities are modeled as mass-compensated voids in random or regular
lattices within Swiss-cheese universes. Void radii below 300 Mpc are
considered, which are supported by current redshift surveys and limited by the
recently observed imprint such voids leave on CMB. The averaging over all
directions, performed by numerical ray tracing, is non-perturbative and
includes the supernovas inside the voids. Voids aligning along a certain
direction produce a cumulative gravitational lensing correction that increases
with their number. Such corrections are destroyed by the averaging over all
directions, even in non-randomized simple cubic void lattices. At low
redshifts, the average correction is not zero but decays with the peculiar
velocities and redshift. Its upper bound is provided by the maximal average
correction which assumes no random cancelations between different voids. It is
described well by a linear perturbation formula and, for the voids considered,
is 20% of the correction corresponding to the maximal peculiar velocity. The
average correction calculated in random and simple cubic void lattices is
severely damped below the predicted maximal one after a single void diameter.
That is traced to cancellations between the corrections from the fronts and
backs of different voids. All that implies that voids cannot imitate the effect
of dark energy unless they have radii and peculiar velocities much larger than
the currently observed. The results obtained allow one to readily predict the
redshift above which the direction-averaged fluctuation in the Hubble diagram
falls below a required precision and suggest a method to extract the background
Hubble constant from low redshift data without the need to correct for peculiar
velocities. | Recovering galaxy stellar population properties from broad-band spectral
energy distribution fitting II. The case with unknown redshift: (Abridged) In a recent work we explored the dependence of galaxy stellar
population properties derived from broad-band spectral energy distribution
fitting on the fitting parameters, e.g. SFHs, age grid, metallicity, IMF, dust
reddening, reddening law, filter setup and wavelength coverage. In this paper
we consider also redshift as a free parameter in the fit and study whether one
can obtain reasonable estimates of photometric redshifts and stellar population
properties at once. We use mock star-forming as well as passive galaxies placed
at various redshifts (0.5 to 3) as test particles. Mock star-forming galaxies
are extracted from a semi-analytical galaxy formation model. We show that for
high-z star-forming galaxies photometric redshifts, stellar masses and
reddening can be determined simultaneously when using a broad wavelength
coverage and a wide template setup in the fit. Masses are similarly well
recovered (median ~ 0.2 dex) as at fixed redshift. For old galaxies with little
recent star formation masses are better recovered than in the fixed redshift
case, such that the median recovered stellar mass improves by up to 0.3 dex
whereas the uncertainty in the redshift accuracy increases by only ~ 0.05.
However, a failure in redshift recovery also means a failure in mass recovery.
As at fixed redshift mismatches in SFH and degeneracies between age, dust and
now also redshift cause underestimated ages, overestimated reddening and
underestimated masses. Stellar masses are best determined at low redshift
without reddening in the fit (median underestimation ~ 0.1 dex for similarly
well recovered redshifts). Not surprisingly, the recovery of properties is
substantially better for passive galaxies. In all cases, the recovery of
physical parameters is crucially dependent on the wavelength coverage adopted
in the fitting. Scaling relations for the transformation of stellar masses are
provided. |
Mechanisms of Baryon Loss for Dark Satellites in Cosmological SPH
Simulations: We present a study of satellites in orbit around a high-resolution, smoothed
particle hydrodynamics (SPH) galaxy simulated in a cosmological context. The
simulated galaxy is approximately the same mass as the Milky Way. The
cumulative number of luminous satellites at z = 0 is similar to the observed
system of satellites orbiting the Milky Way although an analysis of the
satellite mass function reveals an order of magnitude more dark satellites than
luminous. Some of the dark subhalos are more massive than some of the luminous
subhalos at z = 0. What separates luminous and dark subhalos is not their mass
at z = 0, but the maximum mass the subhalos ever achieve. We study the effect
of four mass loss mechanisms on the subhalos: ultraviolet (UV) ionising
radiation, ram pressure stripping, tidal stripping, and stellar feedback, and
compare the impact of each of these four mechanisms on the satellites. In the
lowest mass subhalos, UV is responsible for the majority of the baryonic mass
loss. Ram pressure stripping removes whatever mass remains from the low mass
satellites. More massive subhalos have deeper potential wells and retain more
mass during reionisation. However, as satellites pass near the centre of the
main halo, tidal forces cause significant mass loss from satellites of all
masses. Satellites that are tidally stripped from the outside can account for
the luminous satellites that are lower mass than some of the dark satellites.
Stellar feedback has the greatest impact on medium mass satellites that had
formed stars, but lost all their gas by z = 0. Our results demonstrate that the
missing satellite problem is not an intractable issue with the cold dark matter
cosmology, but is rather a manifestation of baryonic processes. | A New Unified Dark Fluid Model and Its Cosmic Constraint: In this paper, we propose a new unified dark fluid (UDF) model with equation
of state (EoS) $w(a)=-\alpha/(\beta a^{-n}+1)$, which includes the generalized
Chaplygin gas model (gGg) as its special case, where $\alpha$, $\beta$ and $n$
are three positive numbers. It is clear that this model reduces to the gCg
model with EoS $w(a)=-B_s/(B_s+(1-B_s)a^{-3(1+\alpha)})$, when $\alpha=1$,
$\beta=(1-B_s)/B_s$ and $n=3(1+\alpha)$. By combination the cold dark matter
and the cosmological constant, one can coin a EoS of unified dark fluid in the
form of $w(a)=-1/(1+(1-\Omega_{\Lambda})a^{-3}/\Omega_{\Lambda})$. With this
observations, our proposed EoS provides a possible deviation from $\Lambda$CDM
model when the model parameters $\alpha$ and $n$ deviate from 1 and 3
respectively. By using the currently available cosmic observations from type Ia
supernovae (SN Ia) Union2.1, baryon acoustic oscillation (BAO) and cosmic
microwave background radiation (CMB), we test the viability of this model and
detect the possible devotion from the $\Lambda$CDM model. The results show that
the new UDF model fits the cosmic observation as well as that of the
$\Lambda$CDM model and no deviation is found from the $\Lambda$CDM model in
$3\sigma$ confidence level. However, our new UDF model can give a non-zero
sound speed, as a contrast, which is zero for the $\Lambda$CDM model. We expect
the large structure formation information can distinct the new UDF model from
the $\Lambda$CDM model. |
Insight into primordial magnetic fields from 21-cm line observation with
EDGES experiment: The recent observation of the 21-cm global absorption signal by EDGES
suggests that the intergalactic medium (IGM) gas has been cooler than the
cosmic microwave background during $15 \lesssim z \lesssim 20$. This result can
provide a strong constraint on heating sources for the IGM gas at these
redshifts. In this paper we study the constraint on the primordial magnetic
fields (PMFs) by the EDGES result. The PMFs can heat the IGM gas through their
energy dissipation due to the magnetohydrodynamic effects. By numerically
solving the thermal evolution of the IGM gas with the PMFs, we find that the
EDGES result gives a stringent limit on the PMFs as $B_{1\mathrm{Mpc}} \lesssim
10^{-10}$ G. | New tests of dark sector interactions from the full-shape galaxy power
spectrum: We explore the role of redshift-space galaxy clustering data in constraining
non-gravitational interactions between dark energy (DE) and dark matter (DM),
for which state-of-the-art limits have so far been obtained from late-time
background measurements. We use the joint likelihood for pre-reconstruction
full-shape (FS) galaxy power spectrum and post-reconstruction Baryon Acoustic
Oscillation (BAO) measurements from the BOSS DR12 sample, alongside Cosmic
Microwave Background (CMB) data from \textit{Planck}: from this dataset
combination we infer $H_0=68.02^{+0.49}_{-0.60}\,{\rm km}/{\rm s}/{\rm Mpc}$
and the 2$\sigma$ lower limit $\xi>-0.12$, among the strongest limits ever
reported on the DM-DE coupling strength $\xi$ for the particular model
considered. Contrary to what has been observed for the $\Lambda$CDM model and
simple extensions thereof, we find that the CMB+FS combination returns tighter
constraints compared to the CMB+BAO one, suggesting that there is valuable
additional information contained in the broadband of the power spectrum. We
test this finding by running additional CMB-free analyses and removing sound
horizon information, and discuss the important role of the equality scale in
setting constraints on DM-DE interactions. Our results reinforce the critical
role played by redshift-space galaxy clustering measurements in the epoch of
precision cosmology, particularly in relation to tests of non-minimal dark
sector extensions of the $\Lambda$CDM model. |
The galaxy stellar mass function and its evolution with time show no
dependence on global environment: We present the analysis of the galaxy stellar mass function in different
environments at intermediate redshift (0.3<z<0.8) for two mass-limited galaxy
samples. We use the IMACS Cluster Building Survey (ICBS), at masses M_ast
>10^(10.5) M_sun, to study cluster, group, and field galaxies at z=0.3-0.45,
and the ESO Distant Cluster Survey (EDisCS), at masses M_ast > 10^(10.2) M_sun,
to investigate cluster and group galaxies at z=0.4-0.8. Therefore, in our
analysis we include galaxies that are slightly less massive than the Milky Way.
Having excluded the brightest cluster galaxies, we show thatthe shape of the
mass distribution does not seem to depend on global environment. Our two main
results are: (1) Galaxies in the virialized regions of clusters, in groups, and
in the field follow a similar mass distribution. (2) Comparing both ICBS and
EDisCS mass functions to mass functions in the local Universe, we find
evolution from z~0.4-0.6 to z~0.07. The population of low-mass galaxies has
proportionally grown with time with respect to that of massive galaxies. This
evolution is independent of environment -- the same for clusters and the field.
Furthermore, considering only clusters, we find that no differences can be
detected neither within the virialized regions, nor when we compare galaxies
within and outside the virial radius. Subdividing galaxies in terms of color,
in clusters, groups, and field red and blue galaxies are regulated by different
mass functions, but comparing separately the blue and red mass functions in
different environments, no differences are detected in their shape. | Quasar -- CIV forest cross-correlation with SDSS DR12: We present a new determination of the large-scale clustering of the CIV
forest (i.e., the absorption due to all CIV absorbers) using its
cross-correlation with quasars in the Sloan Digital Sky Survey (SDSS) Data
Release 12 (DR12). We fit a linear bias model to the measured
cross-correlation. We find that the transmission bias of the CIV forest,
$b_{Fc}$, at a mean redshift of $z=2.3$, obeys the relation $(1+\beta_c)b_{F c}
= -0.024 \pm 0.003$. Here, $\beta_{c}$ is the linear redshift space distortion
parameter of the CIV absorption, which can only be poorly determined at
$\beta_c=1.1\pm 0.6$ from our data. This transmission bias is related to the
bias of CIV absorbers and their host halos through the effective mean optical
depth of the CIV forest, $\bar\tau_c$. Estimating a value $\bar \tau_c(z)
\simeq 0.01$ from previous studies of the CIV equivalent width distribution,
our measurement implies a CIV absorber bias near unity, with a large error due
to uncertainties in both $\beta_c$ and $\bar\tau_c$. This makes it compatible
with the higher DLA bias $b_{\rm DLA}\simeq 2$ measured previously from the
cross-correlation of DLAs and the Lyman-$\alpha$ forest. We discuss the
implications of the CIV absorber bias for the mass distribution of their host
halos. More accurate determinations of $\bar \tau_c(z)$ and $\beta_c$ are
necessary to obtain a more robust measurement of this CIV absorber bias. |
Uncertainty-aware and Data-efficient Cosmological Emulation using
Gaussian Processes and PCA: Bayesian parameter inference is one of the key elements for model selection
in cosmological research. However, the available inference tools require a
large number of calls to simulation codes which can lead to high and sometimes
even infeasible computational costs. In this work we propose a new way of
emulating simulation codes for Bayesian parameter inference. In particular,
this novel approach emphasizes the uncertainty-awareness of the emulator, which
allows to state the emulation accuracy and ensures reliable performance. With a
focus on data efficiency, we implement an active learning algorithm based on a
combination of Gaussian Processes and Principal Component Analysis. We find
that for an MCMC analysis of Planck and BAO data on the $\Lambda$CDM model (6
model and 21 nuisance parameters) we can reduce the number of simulation calls
by a factor of $\sim$500 and save about $96\%$ of the computational costs. | The Rise and Fall of Type Ia Supernova Light Curves in the SDSS-II
Supernova Survey: We analyze the rise and fall times of type Ia supernova (SN Ia) light curves
discovered by the SDSS-II Supernova Survey. From a set of 391 light curves
k-corrected to the rest frame B and V bands, we find a smaller dispersion in
the rising portion of the light curve compared to the decline. This is in
qualitative agreement with computer models which predict that variations in
radioactive nickel yield have less impact on the rise than on the spread of the
decline rates. The differences we find in the rise and fall properties suggest
that a single 'stretch' correction to the light curve phase does not properly
model the range of SN Ia light curve shapes. We select a subset of 105 light
curves well-observed in both rise and fall portions of the light curves and
develop a '2-stretch' fit algorithm which estimates the rise and fall times
independently. We find the average time from explosion to B-band peak
brightness is 17.38 +/- 0.17 days. Our average rise time is shorter than the
19.5 days found in previous studies; this reflects both the different light
curve template used and the application of the 2-stretch algorithm. We find
that slow declining events tend to have fast rise times, but that the
distribution of rise minus fall time is broad and single-peaked. This
distribution is in contrast to the bimodality in this parameter that was first
suggested by Strovink (2007) from an analysis of a small set of local SNe Ia.
We divide the SDSS-II sample in half based on the rise minus fall value, tr-tf
<= 2 days and tr-tf>2 days, to search for differences in their host galaxy
properties and Hubble residuals; we find no difference in host galaxy
properties or Hubble residuals in our sample. |
The Impact of Suzaku Measurements on Astroparticle Physics: Results from the Suzaku X-ray broad-band observations of clusters of galaxies
are summarized. Aiming at understanding the physics of gas heating/particle
acceleration and the cluster dynamical evolution, we search for non-thermal
hard X-ray emission from merging clusters, particularly A2163 and the Bullet
Cluster, based on the Suzaku and XMM-Newton/Chandra joint analyses. The
observed hard X-ray emission is well represented by single- or
multi-temperature thermal models, including super-hot (kT~20 keV) gas. However,
no significant non-thermal hard X-ray emission has been detected. Together with
the presently available literature, the hard X-ray properties have been studied
for about 10 clusters with Suzaku. The present status on Suzaku measurements of
non-thermal X-ray emission and the cluster magnetic field are summarized and
compared with those from the RXTE, BeppoSAX, and Swift satellites. The future
prospects are briefly mentioned. | Searching for Stringy Topologies in the Cosmic Microwave Background: We consider a universe with a non-classical stringy topology that has fixed
points. We concentrate on the simplest example, an orbifold point, and study
its observable imprints on the cosmic microwave background (CMB). We show that
an orbifold preserves the Gaussian nature of the temperature fluctuations, yet
modifies the angular correlation function. A direct signature of an orbifold is
a single circle in the CMB that is invariant under rotation by 180 degrees.
Searching the 7-year ILC map of WMAP, we find one candidate circle with high
statistical significance. However, a closer look reveals that the temperature
profile does not fit an orbifold. We place a lower bound on the distance to an
orbifold point at ~85% of the distance to the surface of last scattering. |
Galaxy pairs in the Sloan Digital Sky Survey - IV: Interactions trigger
AGN: Galaxy-galaxy interactions are predicted to cause gas inflows leading to
enhanced nuclear star formation. In this paper we test the further prediction
that the gas inflows lead to enhanced accretion onto the central supermassive
black hole, triggering activity in the nucleus. Based on a sample of 11,060
SDSS galaxies with a close companion (rp < 80 kpc, Delta V < 200 km/s), we
classify AGN based either on emission line ratios or on spectral classification
as a quasar. The AGN fraction in the close pairs sample is compared to a
control sample of 110,600 mass- and redshift-matched control galaxies with no
nearby companion. We find a clear increase in the AGN fraction in close pairs
of galaxies with projected separations < 40 kpc by up to a factor of 2.5
relative to the control sample (although the enhancement depends on the chosen
S/N cut of the sample). The increase in AGN fraction is strongest in equal mass
galaxy pairings, and weakest in the lower mass component of an unequal mass
pairing. The increased AGN fraction at small separations is accompanied by an
enhancement in the number of `composite' galaxies whose spectra are the result
of photoionization by both AGN and stars. Our results indicate that AGN
activity occurs (at least in some cases) well before final coalescence and
concurrently with ongoing star formation. Finally, we find a marked increase at
small projected separations of the fraction of pairs in which BOTH galaxies
harbour AGN. We demonstrate that the fraction of double AGN exceeds the
expected random fraction, indicating that some pairs undergo correlated nuclear
activity. Taken together with complimentary studies, we favour an
interpretation where interactions trigger AGN, but are not the only cause of
nuclear activity. | Non-minimal dark sector physics and cosmological tensions: We explore whether non-standard dark sector physics might be required to
solve the existing cosmological tensions. The properties we consider in
combination are an interaction between the dark matter and dark energy
components, and a dark energy equation of state $w$ different from that of the
canonical cosmological constant $w=-1$. In principle, these two parameters are
independent. In practice, to avoid early-time, superhorizon instabilities,
their allowed parameter spaces are correlated. We analyze three classes of
extended interacting dark energy models in light of the 2019 Planck CMB results
and Cepheid-calibrated local distance ladder $H_0$ measurements of Riess et al.
(R19), as well as recent BAO and SNeIa distance data. We find that in
quintessence coupled dark energy models, where $w > -1$, the evidence for a
non-zero coupling between the two dark sectors can surpass the $5\sigma$
significance. On the other hand, in phantom coupled dark energy models, there
is no such preference for a non-zero dark sector coupling. All the models we
consider significantly raise the value of the Hubble constant easing the $H_0$
tension. The addition of low-redshift BAO and SNeIa measurements leaves some
residual tension with R19 but at a level that could be justified by a
statistical fluctuation. Bayesian evidence considerations mildly disfavour both
the coupled quintessence and phantom models, while mildly favouring a coupled
vacuum scenario, even when late-time datasets are considered. We conclude that
non-minimal dark energy cosmologies, such as coupled quintessence, phantom, or
vacuum models, are still an interesting route towards softening existing
cosmological tensions, even when low-redshift datasets and Bayesian evidence
considerations are taken into account. (abstract severely abridged) |
Gauge-preheating and the end of axion inflation: We study the onset of the reheating epoch at the end of axion-driven
inflation where the axion is coupled to an Abelian, $U(1)$, gauge field via a
Chern-Simons interaction term. We focus primarily on $m^2\phi^2$ inflation and
explore the possibility that preheating can occur for a range of coupling
values consistent with recent observations and bounds on the overproduction of
primordial black holes. We find that for a wide range of parameters preheating
is efficient. In certain cases the inflaton is seen to transfer all its energy
to the gauge fields within a few oscillations. In most cases, we find that the
gauge fields on sub-horizon scales end preheating in an unpolarized state due
to the existence of strong rescattering between the inflaton and gauge-field
modes. We also present a preliminary study of an axion monodromy model coupled
to $U(1)$ gauge fields, seeing a similarly efficient preheating behavior as
well as indications that the coupling strength has an effect on the creation of
oscillons. | Boltzmann or Bogoliubov? Approaches Compared in Gravitational Particle
Production: Gravitational particle production is a minimal contribution to reheating the
Universe after the end of inflation. To study this production channel, two
different approaches have commonly been considered, one of which is based on
the Boltzmann equation, and the other is based on the Bogoliubov
transformation. Each of these has pros and cons in practice. The collision term
in the Boltzmann equation can be computed based on quantum field theory in the
Minkowski spacetime, and thus many techniques have been developed so far. On
the other hand, the Bogoliubov approach may deal with the particle production
beyond the perturbation theory and is able to take into account the effect of
the curved spacetime, whereas in many cases one should rely on numerical
methods, such as lattice computation. We show by explicit numerical and
analytical computations of the purely gravitational production of a scalar that
these two approaches give consistent results for particle production with large
momenta during reheating, whereas the Boltzmann approach is not capable of
computing particle production out of vacuum during inflation. We also provide
analytic approximations of the spectrum of produced scalar with/without mass
for the low momentum regime obtained from the Bogoliubov approach. |
On the separation between baryonic and dark matter: evidence for phantom
dark matter?: The recent years have seen combined measurements of X-ray and (weak) lensing
contours for colliding galaxy clusters such as, for instance, the famous
"Bullet" cluster. These observations have revealed offsets in the peaks of the
baryonic and (dominant) gravitational matter component of order ~(100-200) kpc.
Such discrepancies are difficult to explain using modified theories for gravity
other than dark matter. Or are they not? Here we use the concept of "phantom
dark matter" that is based upon a Newtonian interpretation of the MONDian
gravitational potential. We show that this idea is in fact capable of producing
substantial offsets in idealistic density configurations, involving a uniform
external field. However, when analysed in a MONDian cosmological framework we
deduce that the size (and probablity) of the effect is too small to explain the
observed offsets found in the most recent observations, at least in the
simplest incarnation of phantom dark matter as discussed here. The lensing
centers in merging galaxy clusters are likely very close to the centers of true
mass even in a MONDian cosmology. This gives the support to the idea that
neutrino-like non-collisional matter might be responsible for the observed
offsets of lensing and X-ray peaks. | Analysis of the Amplitude of the Sunyaev-Zel'dovich Effect out to
Redshift z=0.8: The interaction of the cosmic microwave background (CMB) with the hot gas in
clusters of galaxies, the so-called Sunyaev--Zel'dovich (SZ) effect, is a very
useful tool that allows us to determine the physical conditions in such
clusters and fundamental parameters of the cosmological models. In this work,
we determine the dependence of the the SZ surface brightness amplitude with
redshift and mass of the clusters. We have used PLANCK+IRAS data in the
microwave-far infrared and a catalog with >10^5 clusters of galaxies extracted
from the SDSS by Wen et al. (2012). We estimate and subtract the dust emission
from those clusters. From the residual flux, we extract its SZ flux densities.
The absolute value of the SZ amplitude indicates that the gas mass is around
10% of the total mass for cluster masses of M~10^{14} M_sun. This amplitude is
compatible with no evolution with redshift and proportional to M^{2.70+/-0.37}
(using X-ray derived masses) or M^{2.51+/-0.38} (using weak-lensing derived
masses), with some tension regarding the expectations of the self-similar
dependence (amplitude proportional to M^{5/3}).
Other secondary products of our analysis include that clusters have a dust
emission with emissivity index beta~2 and temperature T~25 K; we confirm that
the CMB temperature agrees with a dependence of T_0(1+z) with clusters of much
lower mass than those explored previously; and we find that the cluster masses
derived by Wen et al. (2012) from a richness-mass relationship are biased by a
factor of (1+z)^{-1.8} with respect to the X-ray and weak-lensing measurements. |
Exploring the deviation of cosmological constant by a generalized
pressure dark energy model: We bring forward a generalized pressure dark energy (GPDE) model to explore
the evolution of the universe. This model has covered three common pressure
parameterization types and can be reconstructed as quintessence and phantom
scalar fields, respectively. We adopt the cosmic chronometer (CC) datasets to
constrain the parameters. The results show that the inferred late-universe
parameters of the GPDE model are (within $1\sigma$): The present value of
Hubble constant $H_{0}=(72.30^{+1.26}_{-1.37})$km s$^{-1}$ Mpc$^{-1}$; Matter
density parameter $\Omega_{\text{m0}}=0.302^{+0.046}_{-0.047}$, and the
universe bias towards quintessence. While when we combine CC data and the $H_0$
data from Planck, the constraint implies that our model matches the
$\Lambda$CDM model nicely. Then we perform dynamic analysis on the GPDE model
and find that there is an attractor or a saddle point in the system
corresponding to the different values of parameters. Finally, we discuss the
ultimate fate of the universe under the phantom scenario in the GPDE model. It
is demonstrated that three cases of pseudo rip, little rip, and big rip are all
possible. | Global properties of the growth index: mathematical aspects and physical
relevance: We analyze the global behaviour of the growth index of cosmic inhomogeneities
in an isotropic homogeneous universe filled by cold non-relativistic matter and
dark energy (DE) with an arbitrary equation of state. Using a dynamical system
approach, we find the critical points of the system. That unique trajectory for
which the growth index $\gamma$ is finite from the asymptotic past to the
asymptotic future is identified as the so-called heteroclinic orbit connecting
the critical points $(\Omega_m=0,~\gamma_{\infty})$ in the future and
$(\Omega_m=1,~\gamma_{-\infty})$ in the past. The first is an attractor while
the second is a saddle point, confirming our earlier results. Further, in the
case when a fraction of matter (or DE tracking matter) $\varepsilon \Omega^{\rm
tot}_m$ remains unclustered, we find that the limit of the growth index in the
past $\gamma_{-\infty}^{\varepsilon}$ does not depend on the equation of state
of DE, in sharp contrast with the case $\varepsilon=0$ (for which
$\gamma_{-\infty}$ is obtained). We show indeed that there is a mathematical
discontinuity: one cannot obtain $\gamma_{-\infty}$ by taking
$\lim_{\varepsilon \to 0} \gamma^{\varepsilon}_{-\infty}$ (i.e. the limits
$\varepsilon\to 0$ and $\Omega^{\rm tot}_m\to 1$ do not commute). We recover in
our analysis that the value $\gamma_{-\infty}^{\varepsilon}$ corresponds to
tracking DE in the asymptotic past with constant
$\gamma=\gamma_{-\infty}^{\varepsilon}$ found earlier. |
Could quasar lensing time delays hint to a core component in halos,
instead of H0 tension?: The time delay measured between the images of gravitationally lensed quasars
probes a combination of the angular diameter distance to the source-lens system
and the mass density profile of the lens. Observational campaigns to measure
such systems have reported a determination of the Hubble parameter H0 that
shows significant tension with independent determination based on the cosmic
microwave background (CMB) and large scale structure (LSS). We show that lens
mass models that exhibit a cored component, coexisting with a cusp, probe a
degenerate direction in the lens model parameter space, being an approximate
mass sheet transformation. This family of lens models has not been considered
by the cosmographic analyses. Once added to the model, the cosmographic error
budget should become dependent on stellar kinematics uncertainties. We propose
that a core component coexisting with a cusp could bring the lensing
measurements of H0 to accord with the CMB/LSS value. | Variation of fundamental constants and white dwarfs: Theories that attempt to unify the four fundamental interactions and
alternative theories of gravity predict time and/or spatial variation of the
fundamental constants of nature. Different versions of these theories predict
different behaviours for these variations. In consequence, experimental and
observational bounds are an important tool to check the validity of such
proposals. In this paper, we review constraints on the possible variation of
the fundamental constants from astronomical observations and geophysical
experiments designed to test the constancy of the fundamental constants of
nature over different timescales. We also focus on the limits that can be
obtained from white dwarfs, which can constrain the variation of the constants
with the gravitational potential. |
Shot noise in the astrophysical gravitational-wave background: We calculate the noise induced in the anisotropies of the astrophysical
gravitational-wave background by finite sampling of both the galaxy
distribution and the compact binary coalescence event rate. This shot noise
leads to a scale-invariant bias term in the angular power spectrum $C_\ell$,
for which we derive a simple analytical expression. We find that this bias
dominates over the true cosmological power spectrum in any reasonable observing
scenario, and that only with very long observing times and removal of a large
number of foreground sources can the true power spectrum be recovered. | Radio Halos in future surveys in the radio continuum: Giant radio halos (RH) are Mpc-scale synchrotron sources detected in a
significant fraction of massive and merging galaxy clusters.Their statistical
properties can be used to discriminate among various models for their origin.
Theoretical predictions are important as new radio telescopes are about to
begin to survey the sky at low and high frequencies with unprecedented
sensitivity. We carry out Monte Carlo simulations to model the formation and
evolution of RH in a cosmological framework by assuming that RH are either
generated in turbulent merging clusters, or are purely hadronic sources
generated in more relaxed clusters, "off-state" halos. The models predict that
the luminosity function of RH at high radio luminosities is dominated by the
contribution of RH generated in turbulent clusters. The generation of these RH
becomes less efficient in less massive systems causing a flattening of the
luminosity function at lower luminosities. This flattening is compensated by
the contribution of "off-state" RH that dominate at lower luminosities. By
restricting to clusters at z<0.6, we show that the planned EMU+WODAN surveys at
1.4 GHz have the potential to detect up to ~200 RH, increasing their number by
one order of magnitude. A fraction of these sources will be "off-state" RH that
should be found at flux level < 10 mJy, presently accessible only to deep
pointed observations. We also explore the synergy between the Tier 1 LOFAR
survey at 150 MHz and the EMU+WODAN surveys at 1.4 GHz. We predict a larger
number of RH in the LOFAR survey due to the high LOFAR sensitivity, but also
due to the existence of RH with very steep spectrum that glow up preferentially
at lower frequencies. These RH are only predicted in the framework of turbulent
re-acceleration models and should not have counterparts in the EMU+WODAN
surveys, thus the combination of the two surveys will test theoretical models. |
The Soft, Fluctuating UVB at $z\sim6$ as Traced by C IV, SiIV, and CII: The sources that drove cosmological reionization left clues regarding their
identity in the slope and inhomogeneity of the ultraviolet ionizing background
(UVB): Bright quasars (QSOs) generate a hard UVB with predominantly large-scale
fluctuations while Population II stars generate a softer one with smaller-scale
fluctuations. Metal absorbers probe the UVB's slope because different ions are
sensitive to different energies. Likewise, they probe spatial fluctuations
because they originate in regions where a galaxy-driven UVB is harder and more
intense. We take a first step towards studying the reionization-epoch UVB's
slope and inhomogeneity by comparing observations of 12 metal absorbers at
$z\sim6$ versus predictions from a cosmological hydrodynamic simulation using
three different UVBs: a soft, spatially-inhomogeneous "galaxies+QSOs" UVB; a
homogeneous "galaxies+QSOs" UVB (Haardt & Madau 2012); and a QSOs-only model.
All UVBs reproduce the observed column density distributions of CII, SiIV, and
CIV reasonably well although high-column, high-ionization absorbers are
underproduced, reflecting numerical limitations. With upper limits treated as
detections, only a soft, fluctuating UVB reproduces both the observed SiIV/CIV
and CII/CIV distributions. The QSOs-only UVB overpredicts both CIV/CII and
CIV/SiIV, indicating that it is too hard. The Haardt & Madau (2012) UVB
underpredicts CIV/SiIV, suggesting that it lacks amplifications near galaxies.
Hence current observations prefer a soft, fluctuating UVB as expected from a
predominantly Population II background although they cannot rule out a harder
one. Future observations probing a factor of two deeper in metal column density
will distinguish between the soft, fluctuating and QSOs-only UVBs. | The thick disk in the galaxy NGC 4244 from S4G imaging: If thick disks are ubiquitous and a natural product of disk galaxy formation
and/or evolution processes, all undisturbed galaxies which have evolved during
a significant fraction of a Hubble time should have a thick disk. The late-type
spiral galaxy NGC 4244 has been reported as the only nearby edge-on galaxy
without a confirmed thick disk. Using data from the Spitzer Survey of Stellar
Structure in Galaxies (S4G) we have identified signs of two disk components in
this galaxy. The asymmetries between the light profiles on both sides of the
mid-plane of NGC 4244 can be explained by a combination of the galaxy not being
perfectly edge-on and a certain degree of opacity of the thin disk. We argue
that the subtlety of the thick disk is a consequence of either a limited
secular evolution in NGC 4244, a small fraction of stellar material in the
fragments which built the galaxy, or a high amount of gaseous accretion after
the formation of the galaxy. |
Non-Gaussian isocurvature perturbations in dark radiation: We study non-Gaussian properties of the isocurvature perturbations in the
dark radiation, which consists of the active neutrinos and extra light species,
if exist. We first derive expressions for the bispectra of primordial
perturbations which are mixtures of curvature and dark radiation isocurvature
perturbations. We also discuss CMB bispectra produced in our model and forecast
CMB constraints on the nonlinearity parameters based on the Fisher matrix
analysis. Some concrete particle physics motivated models are presented in
which large isocurvature perturbations in extra light species and/or the
neutrino density isocurvature perturbations as well as their non-Gaussianities
may be generated. Thus detections of non-Gaussianity in the dark radiation
isocurvature perturbation will give us an opportunity to identify the origin of
extra light species and lepton asymmetry. | Multifield consequences for D-brane inflation: We analyse the multifield behaviour in D-brane inflation when contributions
from the bulk are taken into account. For this purpose, we study a large number
of realisations of the potential; we find the nature of the inflationary
trajectory to be very consistent despite the complex construction. Inflation is
always canonical and occurs in the vicinity of an inflection point. Extending
the transport method to non-slow-roll and to calculate the running, we obtain
distributions for observables. The spectral index is typically blue and the
running positive, putting the model under moderate pressure from WMAP7
constraints. The local f_NL and tensor-to-scalar ratio are typically
unobservably small, though we find approximately 0.5% of realisations to give
observably large local f_NL. Approximating the potential as sum-separable, we
are able to give fully analytic explanations for the trends in observed
behaviour. Finally we find the model suffers from the persistence of
isocurvature perturbations, which can be expected to cause further evolution of
adiabatic perturbations after inflation. We argue this is a typical problem for
models of multifield inflation involving inflection points and renders models
of this type technically unpredictive without a description of reheating. |
Cosmological Constraints on the DGP braneworld model with Gamma-ray
bursts: We investigate observational constraints on the Dvali, Gabadadze and Porrati
(DGP) model with Gamma-ray bursts (GRBs) at high redshift obtained directly
from the Union2 Type Ia supernovae data (SNe Ia) set. With the
cosmology-independent GRBs, the Union2 set, as well as the cosmic microwave
background (CMB) observations from the WMAP7 result, the baryon acoustic
oscillation, the baryon mass fraction in clusters and the observed $H(z)$ data,
we obtain that the best-fit values of the DGP model are ${\Omega_{M0},
\Omega_{rc}} =\{0.235_{-0.014}^{+0.015},0.138_{-0.048}^{+0.051}\}$, which favor
a flat universe; and the transition redshift of the DGP model is
$z_T=0.67_{-0.04}^{+0.03}$. These results lead to more stringent constraints
than the previous results for the DGP model. | Mass Variance from Archival X-ray Properties of Dark Energy Survey
Year-1 Galaxy Clusters: Using archival X-ray observations and a log-normal population model, we
estimate constraints on the intrinsic scatter in halo mass at fixed optical
richness for a galaxy cluster sample identified in Dark Energy Survey Year-One
(DES-Y1) data with the redMaPPer algorithm. We examine the scaling behavior of
X-ray temperatures, $T_X$, with optical richness, $\lambda_{RM}$, for clusters
in the redshift range $0.2<z<0.7$. X-ray temperatures are obtained from Chandra
and XMM observations for 58 and 110 redMaPPer systems, respectively. Despite
non-uniform sky coverage, the $T_X$ measurements are $> 50\%$ complete for
clusters with $\lambda_{RM} > 130$. Regression analysis on the two samples
produces consistent posterior scaling parameters, from which we derive a
combined constraint on the residual scatter, $\sigma_{\ln Tx | \lambda} = 0.275
\pm 0.019$. Joined with constraints for $T_X$ scaling with halo mass from the
Weighing the Giants program and richness--temperature covariance estimates from
the LoCuSS sample, we derive the richness-conditioned scatter in mass,
$\sigma_{\ln M | \lambda} = 0.30 \pm 0.04\, _{({\rm stat})} \pm 0.09\, _{({\rm
sys})}$, at an optical richness of approximately 70. Uncertainties in external
parameters, particularly the slope and variance of the $T_X$--mass relation and
the covariance of $T_X$ and $\lambda_{RM}$ at fixed mass, dominate the
systematic error. The $95\%$ confidence region from joint sample analysis is
relatively broad, $\sigma_{\ln M | \lambda} \in [0.14, \, 0.55]$, or a factor
ten in variance. |
The Cosmological Impact of Intrinsic Alignment Model Choice for Cosmic
Shear: We consider the effect of galaxy intrinsic alignments (IAs) on dark energy
constraints from weak gravitational lensing. We summarise the latest version of
the linear alignment model of IAs, following the brief note of Hirata & Seljak
(2010) and further interpretation in Laszlo et al. (2011). We show the
cosmological bias on the dark energy equation of state parameters w0 and wa
that would occur if IAs were ignored. We find that w0 and wa are both
catastrophically biased, by an absolute value of just greater than unity under
the Fisher matrix approximation. This contrasts with a bias several times
larger for the earlier IA implementation. Therefore there is no doubt that IAs
must be taken into account for future Stage III experiments and beyond. We use
a flexible grid of IA and galaxy bias parameters as used in previous work, and
investigate what would happen if the universe used the latest IA model, but we
assumed the earlier version. We find that despite the large difference between
the two IA models, the grid flexibility is sufficient to remove cosmological
bias and recover the correct dark energy equation of state. In an appendix, we
compare observed shear power spectra to those from a popular previous
implementation and explain the differences. | Cosmic anisotropies from quasars: from polarization to structural-axis
alignments: The comparison of the orientations of the optical-polarization vectors of
quasars that are separated by billions of light-years has led to the discovery
that they are aligned instead of pointing in random directions as expected.
This discovery has been confirmed and the significance of the correlations
enhanced. We devoted this doctoral thesis to an in-depth analysis of these
striking observations that imply Gpc-scale correlations. We developed a new and
independent statistical method which is dedicated to the study and the
characterization of the distribution of the orientations of vectorial
quantities that are perpendicular to the lines of sight of a set of sources
spread on the celestial sphere. This allowed us to confirm independently the
large-scale polarization-vector alignments and to refine the limits of the
alignment regions through an unbiased characterization of the signal. We also
provided a detailed analysis of a large sample of polarization measurements
made at radio wavelengths in which similar polarization-vector alignments are
found. The regions of alignments of the quasar-radio-polarization vectors are
found to be close to these of optical alignments. This might suggest that
quasar axes themselves could be aligned. Based on new observations, we further
analyzed the optical-polarization vectors of quasars that belong to two large
groups. Taking into account the link between the optical-polarization vectors
and the morphologies of the quasars, we found that the spin axes of the quasars
align with the axis of the large-quasar group to which they belong. We
reinforced our findings using radio-polarization data and a large sample of
large-quasar groups. We additionally found that the preferred orientations of
the quasar spin axes depend on the richness of their host groups. |
An optical/NIR survey of globular clusters in early-type galaxies II.
Ages of GC systems and the relation to galaxy morphology: Context: Some photometric studies of extragalactic globular cluster (GC)
systems using the optical and near-infrared colour combination have suggested
the presence of a large fraction of intermediate-age (2-8 Gyrs) GCs. Aims: We
investigate the age distributions of GC systems in 14 E/S0 galaxies. Methods:
We carry out a differential comparison of the (g-z) vs. (g-K) two-colour
diagrams for GC systems in the different galaxies in order to see whether there
are indications of age differences. We also compare the different GC systems
with a few simple stellar population models. Results: No significant difference
is detected in the mean ages of GCs among elliptical galaxies. S0 galaxies on
the other hand, show evidence for younger GCs. Surprisingly, this appears to be
driven by the more metal-poor clusters. The age distribution of GCs in NGC4365
seems to be similar to that of other large ellipticals (e.g. NGC4486, NGC4649).
Padova SSPs with recently released isochrones for old ages (14 Gyrs) show less
of an offset with respect to the photometry than previously published models.
Conclusions: We suggest that E type galaxies assembled most of their GCs in a
shorter and earlier period than S0 type galaxies. The latter galaxy type, seems
to have a more extended period of GC formation/assembly. | Alleviating the tension at low multipole through Axion Monodromy: There exists some tension on large scales between the Planck data and the
LCDM concordance model of the Universe, which has been amplified by the
recently claimed discovery of non-zero tensor to scalar ratio $r$. At the same
time, the current best-fit value of $r$ suggests large field inflation delta
phi>M_p, which requires a UV complete description of inflation. A very
promising working example that predicts large tensor modes and can be UV
completed is axion monodromy inflation. This realization of inflation naturally
produces oscillating features, as consequence of a broken shift symmetry. We
analyse a combination of Planck, ACT, SPT, WMAP low l polarization and BICEP2
data, and show a long wavelength feature from a periodic potential can
alleviate the tension at low multipoles with an improvement delta chi^2 ~2.5-4
per degree of freedom, depending on the level of foreground subtraction. As
with an introduction of running, one expects that any scale dependence should
lead to a worsened fit at high multipoles. We show that the logarithmic nature
of the axion feature in combination with a tilt n_s~1 allows the fit to be
identical to a no feature model at the 2 percent level on scales 100 =< l
=<3500, and quite remarkable actually slightly improves the fit at scales l
>2000. We also consider possible unremoved dust foregrounds and show that
including these hardly changes the best-fit parameters. Our analysis suggests
an axion decay constant of f/M_p ~O(.01). We discuss how Planck measurements of
the TE and EE spectra can further constrain axion monodromy inflation with such
a large feature. A measurement of the large scale structure power spectrum is
even more promising, as the effect is much bigger since the tensor modes do not
affect the large scales. At the same time, a feature could also lead to a lower
sigma8, lifting the tension between CMB and SZ constraints on sigma8. |
A new method for classifying galaxy SEDs from multi-wavelength
photometry: We present a new method to classify the broad band optical-NIR spectral
energy distributions (SEDs) of galaxies using three shape parameters
(super-colours) based on a Principal Component Analysis of model SEDs. As well
as providing a compact representation of the wide variety of SED shapes, the
method allows for easy visualisation of information loss and biases caused by
the incomplete sampling of the rest-frame SED as a function of redshift. We
apply the method to galaxies in the UKIDSS Ultra Deep Survey with 0.9<z<1.2,
and confirm our classifications by stacking rest-frame optical spectra for a
fraction of objects in each class. As well as cleanly separating a tight
red-sequence from star-forming galaxies, three unusual populations are
identifiable by their unique colours: very dusty star-forming galaxies with
high metallicity and old mean stellar age; post-starburst galaxies which have
formed greater than around 10% of their mass in a recent unsustained starburst
event; and metal-poor quiescent dwarf galaxies. We find that quiescent galaxies
account for 45% of galaxies with log(M*/Msol)>11, declining steadily to 13% at
log(M*/Msol)=10. The properties and mass-function of the post-starburst
galaxies are consistent with a scenario in which gas-rich mergers contribute to
the growth of the low and intermediate mass range of the red sequence. | Multi-Wavelength Study of a Complete IRAC 3.6micron-Selected Galaxy
Sample: a Fair Census of Red and Blue Populations at Redshifts 0.4-1: We present a multi-wavelength study of a 3.6 $\mu$m-selected galaxy sample in
the Extended Groth strip. The sample is complete for galaxies with stellar mass
$>10^{9.5}$ \Msun and redshift $0.4<z<1.2$. In this redshift range, the IRAC
3.6 $\mu$m band measures the rest-frame near-infrared band, permitting nearly
unbiased selection with respect to both quiescent and star-forming galaxies.
The numerous spectroscopic redshifts available in the EGS are used to train an
Artificial Neural Network to estimate photometric redshifts. The distribution
of photometric redshift errors is Gaussian with standard deviation
${\sim}0.025(1+z)$, and the fraction of redshift failures (${>}3\sigma$ errors)
is about 3.5%. A new method of validation based on pair statistics confirms the
estimate of standard deviation even for galaxies lacking spectroscopic
redshifts. Basic galaxy properties measured include rest-frame $U-B$ colors,
$B$- and $K$-band absolute magnitudes, and stellar masses. We divide the sample
into quiescent and star-forming galaxies according to their rest-frame $U-B$
colors and 24 to 3.6 \micron\ flux density ratios and derive rest $K$-band
luminosity functions and stellar mass functions for quiescent, star forming,
and all galaxies. The results show that massive, quiescent galaxies were in
place by $z\approx1$, but lower mass galaxies generally ceased their star
formation at later epochs. |
Fast and easy super-sample covariance of large scale structure
observables: We present a numerically cheap approximation to super-sample covariance (SSC)
of large scale structure cosmological probes, first in the case of angular
power spectra. It necessitates no new elements besides those used for the
prediction of the considered probes, thus relieving analysis pipelines from
having to develop a full SSC modeling, and reducing the computational load. The
approximation is asymptotically exact for fine redshift bins $\Delta z
\rightarrow 0$. We furthermore show how it can be implemented at the level of a
Gaussian likelihood or a Fisher matrix forecast, as a fast correction to the
Gaussian case without needing to build large covariance matrices. Numerical
application to a Euclid-like survey show that, compared to a full SSC
computation, the approximation recovers nicely the signal-to-noise ratio as
well as Fisher forecasts on cosmological parameters of the $w$CDM cosmological
model. Moreover it allows for a fast prediction of which parameters are going
to be the most affected by SSC and at which level. In the case of photometric
galaxy clustering with Euclid-like specifications, we find that $\sigma_8$,
$n_s$ and the dark energy equation of state $w$ are particularly heavily
affected. We finally show how to generalize the approximation for probes other
than angular spectra (correlation functions, number counts and bispectra), and
at the likelihood level, allowing for the latter to be non-Gaussian if needs
be. We release publicly a Python module allowing to implement the SSC
approximation, as well as a notebook reproducing the plots of the article, at
https://github.com/fabienlacasa/PySSC | Investigating the Hubble Constant Tension -- Two Numbers in the Standard
Cosmological Model: The current Hubble constant tension is usually presented by comparing
constraints on $H_0$ only. However, the post-recombination background cosmic
evolution is determined by two parameters in the standard $\Lambda$CDM model,
the Hubble constant ($H_0$) and today's matter energy fraction
($\Omega_{\rm{m}}$). If we therefore compare all constraints individually in
the $H_0$-$\Omega_{\rm{m}}$ plane, (1) various constraints can be treated as
independently as possible, (2) single-sided constraints are easier to consider,
(3) compatibility among different constraints can be viewed in a more robust
way, (4) the model dependence of each constraint is clear, and (5) whether or
not a nonstandard model is able to reconcile all constraints in tension can be
seen more effectively. We perform a systematic comparison of different
constraints in the $H_0$-$\Omega_{\rm{m}}$ space based on a flat $\Lambda$CDM
model, treating them as separately as possible. Constraints along different
degeneracy directions consistently overlap in one region of the space, with the
local measurement from Cepheid variable-calibrated supernovae being the most
outlying, followed by the time-delay strong-lensing result. Considering the
possibility that some nonstandard physics may reconcile the constraints, we
provide a general discussion on nonstandard models with modifications at high,
mid, or low redshifts, and the effect of local environmental factors. Due to
the different responses of individual constraints to a modified model, it is
not easy for nonstandard models to reconcile all constraints if none of them
have unaccounted-for systematic effects. |
MultiModeCode: An efficient numerical solver for multifield inflation: We present MultiModeCode, a Fortran 95/2000 package for the numerical
exploration of multifield inflation models. This program facilitates efficient
Monte Carlo sampling of prior probabilities for inflationary model parameters
and initial conditions and is the first publicly available code that can
efficiently generate large sample-sets for inflation models with $\mathcal
O(100)$ fields. The code numerically solves the equations of motion for the
background and first-order perturbations of multi-field inflation models with
canonical kinetic terms and arbitrary potentials, providing the adiabatic,
isocurvature, and tensor power spectra at the end of inflation. For models with
sum-separable potentials MultiModeCode also computes the slow-roll prediction
via the $\delta N$ formalism for easy model exploration and validation. We pay
particular attention to the isocurvature perturbations as the system approaches
the adiabatic limit, showing how to avoid numerical instabilities that affect
some other approaches to this problem. We demonstrate the use of MultiModeCode
by exploring a few toy models. Finally, we give a concise review of multifield
perturbation theory and a user's manual for the program. | Turbulent formation of protogalaxies at the plasma to gas transition: The standard model of gravitational structure formation is based on the Jeans
1902 acoustic theory, neglecting crucial effects of viscosity, turbulence and
diffusion. A Jeans length scale L_J emerges that exceeds the scale of causal
connection ct during the plasma epoch. Photon-viscous forces initially dominate
all others including gravity. The first structures formed were at density
minima by fragmentation when the viscous-gravitional scale L_SV matched ct at
30,000 years to produce protosupercluster voids and protosuperclusters. Weak
turbulence produced at expanding void boundaries guides the morphology of
smaller fragments down to protogalaxy size just before transition to gas at
300,000 years. The observed 10^20 meter size of protogalaxies reflects the
plasma Kolmogorov scale with Nomura linear and spiral morphology. On transition
to gas the kinematic viscosity decreases so the protogalaxies fragment into
Jeans scale clouds, each with a trillion earth-mass planets. The planets form
stars near the cores of the protogalaxies. High resolution images of planetary
nebula and supernova remnants reveal thousands of frozen hydrogen-helium dark
matter planets. Galaxy mergers show frictional trails of young globular
clusters formed in place, proving that dark matter halos of galaxies consist of
dark matter planets in metastable clumps. |
Constraining the halo-ISM connection through multi-transition carbon
monoxide line-intensity mapping: Line-intensity mapping (LIM) surveys will characterise the cosmological
large-scale structure of emissivity in a range of atomic and molecular spectral
lines, but existing literature rarely considers whether these surveys can
recover excitation properties of the tracer gas species, such as the carbon
monoxide (CO) molecule. Combining basic empirical and physical assumptions with
the off-the-shelf Radex radiative transfer code or a Gaussian process emulator
of Radex outputs, we devise a basic dark matter halo model for CO emission by
tying bulk CO properties to halo properties, exposing physical variables
governing CO excitation as free parameters. The CO Mapping Array Project
(COMAP) is working towards a multi-band survey programme to observe both
CO(1-0) and CO(2-1) at $z\sim7$. We show that this programme, as well as a
further 'Triple Deluxe' extension to higher frequencies covering CO(3-2), is
fundamentally capable of successfully recovering the connection between halo
mass and CO abundances, and constraining the molecular gas kinetic temperature
and density within the star-forming interstellar medium in ways that
single-transition CO LIM cannot. Given a fiducial thermal pressure of
$\sim10^4$ K cm$^{-3}$ for molecular gas in halos of $\sim10^{10}\,M_\odot$,
simulated multi-band COMAP surveys successfully recover the thermal pressure
within 68% interval half-widths of 0.5--0.6 dex. Construction of
multi-frequency LIM instrumentation to access multiple CO transitions is
crucial in harnessing this capability, as part of a cosmic statistical probe of
gas metallicity, dust chemistry, and other physical parameters in star-forming
regions of the first galaxies and proto-galaxies out of reionisation. | The impact of braiding covariance and in-survey covariance on
next-generation galaxy surveys: As galaxy surveys become more precise and push to smaller scales, the need
for accurate covariances beyond the classical Gaussian formula becomes more
acute. Here, I investigate the analytical implementation and impact of
non-Gaussian covariance terms that I previously derived for galaxy clustering.
Braiding covariance is such a class of terms and it gets contribution both from
in-survey and super-survey modes. I present an approximation for braiding
covariance which speeds up the numerical computation. I show that including
braiding covariance is a necessary condition for including other non-Gaussian
terms: the in-survey 2-, 3- and 4-halo covariance, which yield covariance
matrices with negative eigenvalues if considered on their own. I then quantify
the impact on parameter constraints, with forecasts for a Euclid-like survey.
Compared to the Gaussian case, braiding and in-survey covariances significantly
increase the error bars on cosmological parameters, in particular by 50% for w.
The Halo Occupation Distribution (HOD) error bars are also affected between 12%
and 39%. Accounting for super-sample covariance (SSC) also increases parameter
errors, by 90% for w and between 7% and 64% for HOD. In total, non-Gaussianity
increases the error bar on w by 120% (between 15% and 80% for other
cosmological parameters), and the error bars on HOD parameters between 17% and
85%. Accounting for the 1-halo trispectrum term on top of SSC is not sufficient
for capturing the full non-Gaussian impact: braiding and the rest of in-survey
covariance have to be accounted for. Finally, I discuss why the inclusion of
non-Gaussianity generally eases up parameter degeneracies, making cosmological
constraints more robust to astrophysical uncertainties. The data and a Python
notebook reproducing the results and plots of the article are available at
\url{https://github.com/fabienlacasa/BraidingArticle}. [Abridged] |
Microlensing events from galactic globular clusters: We present an analysis of the large set of microlensing events detected so
far toward the Galactic center with the purpose of investigating whether some
of the dark lenses are located in Galactic globular clusters. We find that in
four cases some events might indeed be due to lenses located in the globular
clusters themselves. We also give a rough estimate for the average lens mass of
the events being highly aligned with Galactic globular cluster centers and find
that, under reasonable assumptions, the deflectors could most probably be
either brown dwarfs, M-stars or stellar remnants. | Constraining the growth rate of structure with phase correlations: We show that correlations between the phases of the galaxy density field in
redshift space provide additional information about the growth rate of
large-scale structure that is complementary to the power spectrum multipoles.
In particular, we consider the multipoles of the line correlation function
(LCF), which correlates phases between three collinear points, and use the
Fisher forecasting method to show that the LCF multipoles can break the
degeneracy between the measurement of the growth rate of structure $f$ and the
amplitude of perturbations $\sigma_8$ that is present in the power spectrum
multipoles at large scales. This leads to an improvement in the measurement of
$f$ and $\sigma_8$ by up to 220 per cent for $k_{\rm max} = 0.15 \,
h\mathrm{Mpc}^{-1}$ and up to 50 per cent for $k_{\rm max} = 0.30 \,
h\mathrm{Mpc}^{-1}$ at redshift $z=0.25$, with respect to power spectrum
measurements alone for the upcoming generation of galaxy surveys like DESI and
Euclid. The average improvements in the constraints on $f$ and $\sigma_8$ for
$k_{\rm max} = 0.15 \, h\mathrm{Mpc}^{-1}$ are $\sim 90$ per cent for the DESI
BGS sample with mean redshift $\overline{z}=0.25$, $\sim 40$ per cent for the
DESI ELG sample with $\overline{z}=1.25$, and $\sim 40$ per cent for the Euclid
H$\alpha$ galaxies with $\overline{z}=1.3$. For $k_{\rm max} = 0.30 \,
h\mathrm{Mpc}^{-1}$, the average improvements are $\sim 40$ per cent for the
DESI BGS sample and $\sim 20$ per cent for both the DESI ELG and Euclid
H$\alpha$ galaxies. |
Alignment of Radio Galaxy Axes using FIRST Catalogue: We study the alignment of radio galaxies axes using the FIRST catalogue. we
impose several cuts in order to select the candidates which are most likely to
be free of systematic bias. In our study we primarily focus on testing for
alignment among sources within a certain angular separation from one another
since for most sources redshift information is not available. We find a very
significant effect for angular distances less than 1 degrees. The distance
scale of alignment is found to be roughly 28 Mpc, in agreement with earlier
estimates, assuming that these sources are dominantly at redshift of 0.8.
However we are not able to entirely rule out the possibility of systematic bias
in data. We also perform a full three dimensional analysis using a smaller data
sample for which redshift information is available. In this case we only find a
very weak signal at much larger distances. | Threshing in Action - The tidal disruption of a dwarf galaxy by the
Hydra I Cluster: We report on the discovery of strong tidal features around a dwarf spheroidal
galaxy in the Hydra I galaxy cluster, indicating its ongoing tidal disruption.
This very low surface brightness object, HCC-087, was originally classified as
an early-type dwarf in the Hydra Cluster Catalogue (HCC), but our re-analysis
of the ESO-VLT/FORS images of the HCC unearthed a clear indication of an
S-shaped morphology and a large spatial extent. Its shape, luminosity
(M_V=-11.6 mag), and physical size (at a half-light radius of 3.1 kpc and a
full length of ~5.9 kpc) are comparable to the recently discovered NGC 4449B
and the Sagittarius dwarf spheroidal, all of which are undergoing clear tidal
disruption. Aided by N-body simulations we argue that HCC-087 is currently at
its first apocenter, at 150 kpc, around the cluster center and that it is being
tidally disrupted by the galaxy cluster's potential itself. An interaction with
the near-by (50 kpc) S0 cluster galaxy HCC-005, at M* ~ 3 x 10^10 M_sun is
rather unlikely, as this constellation requires a significant amount of
dynamical friction and thus low relative velocities. The S-shaped morphology
and large spatial extent of the satellite would, however, also appear if
HCC-087 would orbit the cluster center. These features appear to be
characteristic properties of satellites that are seen in the process of being
tidally disrupted, independent of the environment of the destruction. An
important finding of our simulations is an orientation of the tidal tails
perpendicular to the orbit. |
SDSS DR7 superclusters. Morphology: We study the morphology of a set of superclusters drawn from the SDSS DR7. We
calculate the luminosity density field to determine superclusters from a flux-
limited sample of galaxies from SDSS DR7, and select superclusters with 300 and
more galaxies for our study. The morphology of superclusters is described with
the fourth Minkowski functional V3, the morphological signature (the curve in
the shapefinder's K1-K2 plane) and the shape parameter (the ratio of the
shapefinders K1/K2). We investigate the supercluster sample using
multidimensional normal mixture modelling, and use Abell clusters to identify
our superclusters with known superclusters and to study the large-scale
distribution of superclusters. The superclusters in our sample form three
chains of superclusters; one of them is the Sloan Great Wall. Most
superclusters have filament-like overall shapes. Superclusters can be divided
into two sets; more elongated superclusters are more luminous, richer, have
larger diameters, and a more complex fine structure than less elongated
superclusters. The fine structure of superclusters can be divided into four
main morphological types: spiders, multispiders, filaments, and multibranching
filaments. We present the 2D and 3D distribution of galaxies and rich groups,
the fourth Minkowski functional, and the morphological signature for all
superclusters. Widely different morphologies of superclusters show that their
evolution has been dissimilar. A study of a larger sample of superclusters from
observations and simulations is needed to understand the morphological variety
of superclusters and the possible connection between the morphology of
superclusters and their large-scale environment. | Effects of baryons on the gravitational redshift profile of ΛCDM
halos: Gravitational redshifts and other relativistic effects are beginning to be
studied in the context of galaxy clustering. Distortions consistent with those
expected in General Relativity have been measured in galaxy cluster redshift
profiles by Wojtak et al. and others and in the the cross-correlation function
of galaxy populations by Alam et al. On scales below ~20 Mpc/$h$ simulations
have shown that gravitational redshift dominates over other effects. However,
this signal is related to the shape and depth of gravitational potentials, and
therefore the matter density in galaxies and galaxy clusters that is
responsible for them. We investigate the effects of baryonic physics on the
gravitational redshift profiles of massive (group and cluster-sized) halos. We
compare the profiles of different components in halos taken from the
MassiveBlack-II cosmological hydrodynamic simulation and a dark matter-only
version of the same simulation. We find that inclusion of baryons, cooling,
star formation and feedback significantly alters the relevant inner density
profiles. These baryonic effects lead to overall increases in both
gravitational redshifts and the transverse relativistic Doppler effects by up
to ~50% for group size halos. We show how modified Navarro Frenk White halo
profiles can be used to parametrize these differences, and provide relevant
halo profile fits. |
How accurately can we measure the baryon acoustic oscillation feature?: Baryon acoustic oscillations (BAO) represent one of the cleanest probes of
dark energy, allowing for tests of the cosmological model through the
measurement of distance and expansion rate from a 3D galaxy distribution. The
signal appears at large scales in the correlation function where linear theory
applies, allowing for the construction of accurate models. However, due to the
lower number of modes available at these scales, sample variance has a
significant impact on the signal, and may sharpen or widen the underlying peak.
Therefore, equivalent mock realizations of a galaxy survey present different
errors in the position of the peak when uncertainties are estimated from the
posterior probability distribution corresponding to the individual mocks. Hence
the posterior width, often quoted as the error in BAO survey measurements, is
subject to sample noise. A different definition of the error is provided by the
asymptotic variance of the maximum likelihood estimator, which involves the
average over multiple realizations, and is not subject to sample noise. In this
work we re-analyse the main galaxy survey data available for BAO measurements
and quantify the impact of the noise component on the error quoted for BAO
measurements. We quantify the difference between three definitions of the
error: the confidence region computed from a single posterior, the average of
the variances of many realizations, and the Fisher matrix prediction assuming a
Gaussian likelihood. | Dark aspects of massive spinor electrodynamics: We investigate the cosmology of massive spinor electrodynamics when torsion
is non-vanishing. A non-minimal interaction is introduced between the torsion
and the vector field and the coupling constant between them plays an important
role in subsequential cosmology. It is shown that the mass of the vector field
and torsion conspire to generate dark energy and pressureless dark matter, and
for generic values of the coupling constant, the theory effectively provides an
interacting model between them with an additional energy density of the form
$\sim 1/a^6$. The evolution equations mimic $\Lambda$CDM behavior up to $1/a^3$
term and the additional term represents a deviation from $\Lambda$CDM. We show
that the deviation is compatible with the observational data, if it is very
small. We find that the non-minimal interaction is responsible for generating
an effective cosmological constant which is directly proportional to the mass
squared of the vector field and the mass of the photon within its current
observational limit could be the source of the dark energy. |
Dark Dimension and Decaying Dark Matter Gravitons: We explore the cosmology of the Dark Dimension scenario taking into account
perturbations in the linear regime. In the context of the Dark Dimension
scenario, a natural candidate for dark matter in our universe is the
excitations of a tower of massive spin-2 KK gravitons. These dark gravitons are
produced in the early universe and decay to lighter KK gravitons during the
course of cosmological evolution. The decay causes the average dark matter mass
to decrease as the universe evolves. In addition, the kinetic energy liberated
in each decay leads to a kick velocity for the dark matter particles leading to
a suppression of structure formation. Using current CMB (Planck), BAO and
cosmic shear (KiDS-1000) data, we put a bound on the dark matter kick velocity
today $v_\mathrm{today} \leq 2.2 \times 10^{-4} c$ at 95\% CL. This leads to
rather specific regions of parameter space for the dark dimension scenario. The
combination of the experimental bounds from cosmology, astrophysics and
table-top experiments lead to the range $l_5\sim 1- 10 \, \mu m$ for the size
of the Dark Dimension. The Dark Dimension scenario is found to be remarkably
consistent with current observations and provides signatures that are within
reach of near-future experiments. | The fitting problem in a lattice Universe: We present a regular cubic lattice solution to Einstein field equations that
is exact at second order in a small parameter. We show that this solution is
kinematically equivalent to the Friedmann-Lema\^itre-Robertson-Walker (FLRW)
solution with the same averaged energy density. This allows us to discuss the
fitting problem in that framework: are observables along the past lightcone of
observers equivalent to those in the analogue FLRW model obtained by smoothing
spatially the distribution of matter? We find a criterion on the compacity of
the objects that must be satisfied in order for the answer to this question to
be positive and given by perturbative arguments. If this criterion is not met,
the answer to this question must be addressed fully non perturbatively along
the past lightcone, even though the spacetime geometry can be described
perturbatively. |
The Pal 5 Star Stream Gaps: Pal 5 is a low mass, low velocity dispersion, globular cluster with
spectacular tidal tails. We use the SDSS DR8 data to extend the density
measurements of the trailing star stream to 23 degrees distance from the
cluster, at which point the stream runs off the edge of the available sky
coverage. The size and the number of gaps in the stream are measured using a
filter which approximates the structure of the gaps found in stream
simulations. We find 5 gaps that are at least 99% confidence detections with
about a dozen gaps at 90% confidence. The statistical significance of a gap is
estimated using bootstrap re-sampling of the control regions on either side of
the stream. The density minimum closest to the cluster is likely the result of
the epicyclic orbits of the tidal outflow and has been discounted. To create
the number of 99% confidence gaps per unit length at the mean age of the stream
requires a halo population of nearly a thousand dark matter sub-halos with peak
circular velocities above 1 km/s within 30kpc of the galactic center. These
numbers are a factor of about 3 below cold stream simulation at this sub-halo
mass or velocity, but given the uncertainties in both measurement and more
realistic warm stream modeling, are in substantial agreement with the LCDM
prediction | Testing the Distance-Duality Relation in the $R_h=ct$ Universe: In this paper, we test the cosmic distance duality (CDD) relation using the
luminosity distances from joint light-curve analysis (JLA) type Ia supernovae
(SNe Ia) sample and angular diameter distance sample from galaxy clusters. The
$R_h=ct$ and $\Lambda$CDM models are considered. In order to compare the two
models, we constrain the CCD relation and the SNe Ia light-curve parameters
simultaneously. Considering the effects of Hubble constant, we find that
$\eta\equiv D_A(1+z)^2/D_L=1$ is valid at the 2$\sigma$ confidence level in
both models with $H_0 = 67.8\pm0.9$ km/s/Mpc. However, the CDD relation is
valid at 3$\sigma$ confidence level with $H_0 = 73.45\pm1.66$ km/s/Mpc. Using
the Akaike Information Criterion (AIC) and the Bayesian Information Criterion
(BIC), we find that the $\Lambda$CDM model is very strongly preferred over the
$R_h=ct$ model with these data sets for the CDD relation test. |
Stochastic gravitational-wave background as a tool to investigate
multi-channel astrophysical and primordial black-hole mergers: The formation of merging binary black holes can occur through multiple
astrophysical channels such as, e.g., isolated binary evolution and dynamical
formation or, alternatively, have a primordial origin. Increasingly large
gravitational-wave catalogs of binary black-hole mergers have allowed for the
first model selection studies between different theoretical predictions to
constrain some of their model uncertainties and branching ratios. In this work,
we show how one could add an additional and independent constraint to model
selection by using the stochastic gravitational-wave background. In contrast to
model selection analyses that have discriminating power only up to the
gravitational-wave detector horizons (currently at redshifts $z\lesssim 1$ for
LIGO-Virgo), the stochastic gravitational-wave background accounts for the
redshift integration of all gravitational-wave signals in the Universe. As a
working example, we consider the branching ratio results from a model selection
study that includes potential contribution from astrophysical and primordial
channels. We renormalize the relative contribution of each channel to the
detected event rate to compute the total stochastic gravitational-wave
background energy density. The predicted amplitude lies below the current
observational upper limits of GWTC-2 by LIGO-Virgo, indicating that the results
of the model selection analysis are not ruled out by current background limits.
Furthermore, given the set of population models and inferred branching ratios,
we find that, even though the predicted background will not be detectable by
current generation gravitational-wave detectors, it will be accessible by
third-generation detectors such as the Einstein Telescope and space-based
detectors such as LISA. | MC$^2$: Dynamical Analysis of the Merging Galaxy Cluster MACS
J1149.5+2223: We present an analysis of the merging cluster MACS J1149.5+2223 using
archival imaging from Subaru/Suprime-Cam and multi-object spectroscopy from
Keck/DEIMOS and Gemini/GMOS. We employ two and three dimensional substructure
tests and determine that MACS J1149.5+2223 is composed of two separate mergers
between three subclusters occurring $\sim$1 Gyr apart. The primary merger gives
rise to elongated X-ray morphology and a radio relic in the southeast. The
brightest cluster galaxy is a member of the northern subcluster of the primary
merger. This subcluster is very massive
(16.7$^{+\text{1.25}}_{-\text{1.60}}\times\text{10}^{\text{14}}$ M$_{\odot}$).
The southern subcluster is also very massive
(10.8$^{+\text{3.37}}_{-\text{3.54}}\times\text{10}^{\text{14}}$ M$_{\odot}$),
yet it lacks an associated X-ray surface brightness peak, and it has been
unidentified previously despite the detailed study of this \emph{Frontier
Field} cluster. A secondary merger is occurring in the north along the line of
sight with a third, less massive, subcluster
(1.20$^{+\text{0.19}}_{-\text{0.34}}\times\text{10}^{\text{14}}$ M$_{\odot}$).
We perform a Monte Carlo dynamical analysis on the main merger and estimate a
collision speed at pericenter of 2770$^{+\text{610}}_{-\text{310}}$ km
s$^{-\text{1}}$. We show the merger to be returning from apocenter with core
passage occurring 1.16$^{+\text{0.50}}_{-\text{0.25}}$ Gyr before the observed
state. We identify the line of sight merging subcluster in a strong lensing
analysis in the literature and show that it is likely bound to MACS J1149
despite having reached an extreme collision velocity of $\sim$4000 km
s$^{-\text{1}}$. |
Searching for dark matter in X-rays: how not to check the dark matter
origin of a spectral feature: In a recent preprint entitled "Searching for dark matter in X-rays: how to
check the dark matter origin of a spectral feature" [arXiv:1001.0644v1], the
authors have claimed that some archival X-ray data could be used to rule out
dark matter in the form of 5-keV sterile neutrinos at the level of 20 sigma.
Unfortunately, the limit was derived incorrectly. We point out the shortcomings
of this analysis and show that the tentative detection of a spectral feature
consistent with a 5-keV sterile neutrino is not in contradiction with existing
limits. Future observations of dwarf spheroidal galaxies will test this
hypothesis. | Gravitational wave observations of galactic intermediate-mass black hole
binaries with DECIGO Path Finder: DECIGO Path Finder (DPF) is a space-borne gravitational wave (GW) detector
with sensitivity in the frequency band 0.1--100Hz. As a first step mission to
DECIGO, it is aiming for launching in 2016--2017. Although its main objective
is to demonstrate technology for GW observation in space, DPF still has a
chance of detecting GW signals and performing astrophysical observations. With
an observable range up to 50 kpc, its main targets are GW signals from galactic
intermediate mass black hole (IMBH) binaries. By using inspiral-merger-ringdown
phenomenological waveforms, we perform both pattern-averaged analysis and Monte
Carlo simulations including the effect of detector motion to find that the
masses and (effective) spins of the IMBHs could be determined with errors of a
few percent, should the signals be detected. Since GW signals from IMBH
binaries with masses above $10^4 M_\odot$ cannot be detected by ground-based
detectors, these objects can be unique sources for DPF. If the inspiral signal
of a $10^3M_\odot$ IMBH binary is detected with DPF, it can give alert to the
ringdown signal for the ground-based detectors $10^2$--$10^3$s before
coalescence. We also estimate the possible bound on the graviton Compton
wavelength from a possible IMBH binary in $\omega$ Centauri. We obtain a
slightly weaker constraint than the solar system experiment and an about 2
orders of magnitude stronger constraint than the one from binary pulsar tests.
Unfortunately, the detection rate of IMBH binaries is rather small. |
Consistency Relations for Large Field Inflation: Consistency relations for chaotic inflation with a monomial potential and
natural inflation and hilltop inflation are given which involve the scalar
spectral index $n_s$, the tensor-to-scalar ratio $r$ and the running of the
spectral index $\alpha$. The measurement of $\alpha$ with $O(10^{-3})$ and the
improvement in the measurement of $n_s$ could discriminate monomial model from
natural/hilltop inflation models. A consistency region for general large field
models is also presented. | X-ray selected AGN Hosts are Similar to Inactive Galaxies out to z=3:
Results from CANDELS/CDF-S: We use multi-band spatially resolved photometry from the Cosmic Assembly
Near-IR Deep Legacy Survey (CANDELS) in the 4 MSec Chandra Deep Field-South
(CDF-S) to explore the nuclear and extended colors, color gradients and stellar
populations of X-ray selected AGN host galaxies out to z=3. Based on a study of
their central light, we develop X-ray based criteria to exclude objects with
strong AGN contamination. We use stellar masses from the FIREWORKS database to
understand and account for stellar mass selection effects, and carefully study,
for the first time, the resolved host galaxy properties of AGNs at z~2 in their
rest-frame optical light without substantial nuclear contamination. AGN hosts
span a sizable range of stellar masses, colors and color gradients at these
redshifts. Their colors, color gradients and stellar population properties are
very similar to inactive galaxies of the same stellar mass. At z~1, we find a
slightly narrower range in host colors compared to inactive galaxies, as well
as hints of more recent star-formation. These differences are weaker or
non-existent among AGN hosts at z~2. We discuss the importance of AGN driven
feedback in the quenching of galaxies at z>~1 and speculate on possible
evolution in the relationship between black hole accretion and the host galaxy
towards high redshifts. |
Neutrino energy transport in weak decoupling and big bang
nucleosynthesis: We calculate the evolution of the early universe through the epochs of weak
decoupling, weak freeze-out and big bang nucleosynthesis (BBN) by
simultaneously coupling a full strong, electromagnetic, and weak nuclear
reaction network with a multi-energy group Boltzmann neutrino energy transport
scheme. The modular structure of our code provides the ability to dissect the
relative contributions of each process responsible for evolving the dynamics of
the early universe in the absence of neutrino flavor oscillations. Such an
approach allows a detailed accounting of the evolution of the $\nu_e$,
$\bar\nu_e$, $\nu_\mu$, $\bar\nu_\mu$, $\nu_\tau$, $\bar\nu_\tau$ energy
distribution functions alongside and self-consistently with the nuclear
reactions and entropy/heat generation and flow between the neutrino and
photon/electron/positron/baryon plasma components. This calculation reveals
nonlinear feedback in the time evolution of neutrino distribution functions and
plasma thermodynamic conditions (e.g., electron-positron pair densities), with
implications for: the phasing between scale factor and plasma temperature; the
neutron-to-proton ratio; light-element abundance histories; and the
cosmological parameter \neff. We find that our approach of following the time
development of neutrino spectral distortions and concomitant entropy production
and extraction from the plasma results in changes in the computed value of the
BBN deuterium yield. For example, for particular implementations of quantum
corrections in plasma thermodynamics, our calculations show a $0.4\%$ increase
in deuterium. These changes are potentially significant in the context of
anticipated improvements in observational and nuclear physics uncertainties. | EMPRESS. VIII. A New Determination of Primordial He Abundance with
Extremely Metal-Poor Galaxies: A Suggestion of the Lepton Asymmetry and
Implications for the Hubble Tension: The primordial He abundance $Y_\mathrm{P}$ is a powerful probe of cosmology.
Currently, $Y_\mathrm{P}$ is best determined by observations of metal-poor
galaxies, while there are only a few known local extremely metal-poor ($<0.1
Z_\odot$) galaxies (EMPGs) having reliable He/H measurements with
HeI$\lambda$10830 near-infrared (NIR) emission. Here we present deep Subaru NIR
spectroscopy for 10 EMPGs. Combining the existing optical data, He/H values of
5 out of the 10 EMPGs are reliably derived by the Markov chain Monte Carlo
algorithm. Adding the existing 3 EMPGs and 51 moderately metal-poor ($0.1-0.4
Z_\odot$) galaxies with reliable He/H estimates, we obtain
$Y_\mathrm{P}=0.2370^{+0.0034}_{-0.0033}$ by linear regression in the
$\mathrm{(He/H)}-\mathrm{(O/H)}$ plane, where we increase the number of EMPGs
from 3 to 8 anchoring He/H of the most metal-poor gas in galaxies. Although our
$Y_\mathrm{P}$ measurement and previous measurements are consistent, our result
is slightly ($\sim 1\sigma$) smaller due to our EMPGs. With our $Y_\mathrm{P}$
and the existing primordial deuterium $D_\mathrm{P}$ measurement, we constrain
the effective number of neutrino species $N_\mathrm{eff}$ and the
baryon-to-photon ratio $\eta$ showing $\gtrsim 1-2\sigma$ tensions with the
Standard Model and Planck Collaboration et al. (2020). Motivated by the
tensions, we allow the degeneracy parameter of electron-neutrino $\xi_e$ to
vary as well as $N_\mathrm{eff}$ and $\eta$. We obtain $\xi_e =
0.05^{+0.03}_{-0.02}$, $N_\mathrm{eff}=3.11^{+0.34}_{-0.31}$, and
$\eta\times10^{10}=6.08^{+0.06}_{-0.06}$ from the $Y_\mathrm{P}$ and
$D_\mathrm{P}$ measurements with a prior of $\eta$ taken from Planck
Collaboration et al. (2020). Our constraints suggest a lepton asymmetry and
allow for a high value of $N_\mathrm{eff}$ within the $1\sigma$ level, which
could mitigate the Hubble tension. |
ORIGAMI: Delineating Cosmic Structures with Phase-Space Folds: Structures like galaxies and filaments of galaxies in the Universe come about
from the origami-like folding of an initially flat three-dimensional manifold
in 6D phase space. The ORIGAMI method identifies these structures in a
cosmological simulation, delineating the structures according to their outer
folds. Structure identification is a crucial step in comparing cosmological
simulations to observed maps of the Universe. The ORIGAMI definition is
objective, dynamical and geometric: filament, wall and void particles are
classified according to the number of orthogonal axes along which dark-matter
streams have crossed. Here, we briefly review these ideas, and speculate on how
ORIGAMI might be useful to find cosmic voids. | Discovery of strongly blue shifted mid-infrared [NeIII] and [NeV]
emission in ULIRGs: We report the discovery of blue shifted (delta(V) > 200 km/s) mid-infrared
[NeIII] and/or [NeV] emission in 25 out of 82 ULIRGs (30% of our sample). The
incidence of blue shifted [NeV] emission is even higher (59%) among the sources
with a [NeV] detection -- the tell-tale signature of an active galactic nucleus
(AGN). Sixteen ULIRGs in our sample, eleven of which are optically classified
as AGN, have [NeIII] blue shifts above 200 km/s. A comparison of the line
profiles of their 12.81um [NeII], 15.56um [NeIII] and 14.32um [NeV] lines
reveals the ionization of the blue shifted gas to increase with blue shift,
implying decelerating outflows in a stratified medium, photo-ionized by the
AGN. The strong correlation of the line width of the [NeIII] line with the
radio luminosity indicates that interaction of expanding radio jets with the
dense ISM surrounding the AGN may explain the observed neon line kinematics for
the strongest radio sources in this sample. |
Role of intracluster supernovae in radio mini-halos in galaxy clusters: A possibility of generating a population of cosmic-ray particles accelerated
in supernovae typeIa (SNIa) remnants in the intracluster medium (ICM) is
discussed. The presently constrained host-less SNIa rates in the clusters are
found to be sufficient to fill a few hundred kpc region with cosmic-ray
electrons within their typical synchrotron life-time of 100 Myr. The SNIa have
already been considered potential sources of excess Fe abundance in cool-core
clusters, distributed heating and turbulence in ICM. A good fraction of total
radio power from mini-halos can be sourced from the SNIa energy deposited in
the ICM with required energy conversion efficiency <1 per cent. The radio power
estimated from low Mach number shock acceleration in SNIa remnants is
consistent with the observations within the uncertainties in the estimates.
Some observational properties of the radio mini-halos are broadly consistent
with the SNIa scenario. It is also speculated that radio powers and possibly
detections of mini-halos are linked to star formation and merger histories of
the clusters. | Tidal Stripping of Globular Clusters in the Virgo Cluster: With the aim of finding evidence of tidal stripping of globular clusters
(GCs) we analysed a sample of 13 elliptical galaxies taken from the ACS Virgo
Cluster Survey (VCS). These galaxies belong to the main concentration of the
Virgo cluster (VC) and present absolute magnitudes $-18.5<M_z<-22.5$. We used
the public GC catalog of Jord\'an et al. (2008) and separated the GC population
into metal poor (blue) and metal rich (red) according to their integrated
colors. The galaxy properties were taken from \citet{Peng:2008}. We found that:
1) The specific frequencies ($S_N$) of total and blue GC populations increase
as a function of the projected galaxy distances $r_p$ to M87. A similar result
is observed when 3-dimensional distances $r_{3D}$ are used. The same behaviours
are found if the analysis are made using the number of GCs per $10^9\Msun$
($T$). The correlations with the clustocentric distance of the host galaxy are
interpreted as evidence of GCs stripping due to tidal forces. 2) No correlation
is found between the slope of GC density profiles of host galaxies and the
galaxy distance to M87 (Virgo central galaxy). 3) We also computed the local
density of GCs ($\rho_{out}$) located further than $6.2 \kpc$ from the galaxy
center for nine galaxies of our sample. We find that the GC population around
most of these galaxies is mainly composed of blue GCs.
Our results suggest that the number and the fraction of blue and red GCs
observed in elliptical galaxies located near the centers of massive clusters,
could be significantly different from the underlying GC population. These
differences could be explained by tidal stripping effects that occur as
galaxies approach the centers of clusters. |
Cosmology with bulk viscosity and the gravitino problem: The gravitino problem is revisited in the framework of cosmological models in
which the primordial cosmic matter is described by a relativistic imperfect
fluid. Dissipative effects (or bulk viscosity effects) arise owing to the
different cooling rates of the fluid components. We show that the effects of
the bulk viscosity allow to avoid the late abundance of gravitinos. In
particular, we found that for a particular choice of the parameters
characterizing the cosmological model, the gravitino abundance turns out to be
independent on the reheating temperature. | A Pair of O VI and Broad Ly-alpha Absorbers Probing Warm Gas in a Galaxy
Group Environment at z ~ 0.4: We report on the detection of two O VI absorbers separated in velocity by 710
km/s at z ~ 0.4 towards the background quasar SBS0957+599. Both absorbers are
multiphase systems tracing substantial reservoirs of warm baryons. The low and
intermediate ionization metals in the first absorber is consistent with an
origin in photoionized gas. The O VI has a velocity structure different from
other metal species. The Ly-alpha shows the presence of a broad feature. The
line widths for O VI and the broad Ly-alpha suggest T = 7.1 x 10^5 K. This warm
medium is probing a baryonic column which is an order of magnitude more than
the total hydrogen in the cooler photoionized gas. The second absorber is
detected only in H I and O VI. Here the temperature of 4.6 x 10^4 K supports O
VI originating in a low-density photoionized gas. A broad component is seen in
the Ly-alpha, offset from the O VI. The temperature in the broad Ly-alpha is T
< 2.1 x 10^5 K. The absorbers reside in a galaxy overdensity region with 7
spectroscopically identified galaxies within ~ 10 Mpc and delta_v ~ 1000 km/s
of the first absorber, and 2 galaxies inside a similar separation from the
second absorber. The distribution of galaxies relative to the absorbers suggest
that the line of sight could be intercepting a large-scale filament connecting
galaxy groups, or the extended halo of a sub-L* galaxy. Though kinematically
proximate, the two absorbers reaffirm the diversity in the physical conditions
of low redshift O VI systems and the galactic environments they inhabit. |
Gravitational Flexion by Elliptical Dark Matter Haloes: We present equations for the gravitational lensing flexion expected for an
elliptical lens mass distribution. These can be reduced to one-dimensional
finite integrals, thus saving significant computing time over a full
two-dimensional calculation. We estimate constraints on galaxy halo
ellipticities for a range of potential future surveys, finding that the
constraints from the two different types of flexion are comparable and are up
to two orders of magnitude tighter than those from shear. Flexion therefore
appears to be a very promising potential tool for constraining the shapes of
galaxy haloes from future surveys. | CMB constraints on ultra-light primordial black holes with extended mass
distributions: We examine the effects ultra-light primordial black holes (PBHs) have on the
anisotropies of the cosmic microwave background (CMB). PBHs in the mass range
of $10^{15}$ to $10^{17}$ g emit Hawking radiation in the early Universe,
modifying the standard recombination history. This leads to a damping of
small-scale temperature and polarisation anisotropies and enhances large-scale
polarisation fluctuations. As some models of inflation predict PBHs with a
range of masses, we investigate the impacts of extended mass distributions on
PBH abundance constraints. We model PBH energy injection using a ground-up
approach incorporating species-dependent deposition efficiencies. By allowing
the $\Lambda$CDM parameters to vary simultaneously with the PBH fraction and
mass, we show that exclusion bounds on the PBH fraction of DM $f_\text{PBH}$
are relaxed by up to an order of magnitude, compared to the case of fixed
$\Lambda$CDM parameters. We also give 95% exclusion regions for $f_\text{PBH}$
for a variety of mass distributions. In particular, for a uniform mass
distribution between $10^{15}$ and $10^{17}$ g, we find $f_\text{PBH} < 1.6
\times 10^{-5}$ when allowing $\Lambda$CDM parameters to vary. |
Late-time acceleration in a brane with curvature effects: In this paper we investigate if the phantom-like regime in the LDGP model can
be enlarged by the inclusion of a Gauss-Bonnet (GB) term into the bulk.
However, we show that the opposite occurs: the GB effect seems instead to
induce a breakdown of the phantom-like behaviour at an even smaller redshift. | Probing large scale coherence between Spitzer IR and Chandra X-ray
source-subtracted cosmic backgrounds: We present new measurements of the large scale clustering component of the
cross-power spectra of the source-subtracted Spitzer-IRAC Cosmic Infrared
Background (CIB) and Chandra-ACIS Cosmic X-ray Background (CXB) surface
brightness fluctuations. Our investigation uses data from the Chandra Deep
Field South (CDFS), Hubble Deep Field North (HDFN), EGS/AEGIS field and
UDS/SXDF surveys, comprising 1160 Spitzer hours and $\sim$ 12 Ms of Chandra
data collected over a total area of 0.3 deg$^2$. We report the first
($>$5$\sigma$) detection of a cross-power signal on large angular scales >20
arcsec between [0.5-2] keV and the 3.6 and 4.5$\mu$m bands, at $\sim$5$\sigma$
and 6.3$\sigma$ significance, respectively. The correlation with harder X-ray
bands is marginally significant. Comparing the new observations with existing
models for the contribution of the known unmasked source population at $z<$7,
we find an excess of about an order of magnitude at 5$\sigma$ confidence. We
discuss possible interpretations for the origin of this excess in terms of the
contribution from accreting early black holes, including both direct collapse
black holes and primordial black holes, as well as from scattering in the
interstellar medium and intra-halo light. |
Non-Gaussianity in two-field inflation beyond the slow-roll
approximation: We use the long-wavelength formalism to investigate the level of bispectral
non-Gaussianity produced in two-field inflation models with standard kinetic
terms. Even though the Planck satellite has so far not detected any primordial
non-Gaussianity, it has tightened the constraints significantly, and it is
important to better understand what regions of inflation model space have been
ruled out, as well as prepare for the next generation of experiments that might
reach the important milestone of Delta f_NL(local) = 1. We derive an
alternative formulation of the previously derived integral expression for f_NL,
which makes it easier to physically interpret the result and see which types of
potentials can produce large non-Gaussianity. We apply this to the case of a
sum potential and show that it is very difficult to satisfy simultaneously the
conditions for a large f_NL and the observational constraints on the spectral
index n_s. In the case of the sum of two monomial potentials and a constant we
explicitly show in which small region of parameter space this is possible, and
we show how to construct such a model. Finally, the new general expression for
f_NL also allows us to prove that for the sum potential the explicit
expressions derived within the slow-roll approximation remain valid even when
the slow-roll approximation is broken during the turn of the field trajectory
(as long as only the epsilon slow-roll parameter remains small). | Painting baryons onto N-body simulations of galaxy clusters with
image-to-image deep learning: Galaxy cluster mass functions are a function of cosmology, but mass is not a
direct observable, and systematic errors abound in all its observable proxies.
Mass-free inference can bypass this challenge, but it requires large suites of
simulations spanning a range of cosmologies and models for directly observable
quantities. In this work, we devise a U-net - an image-to-image machine
learning algorithm - to ``paint'' the IllustrisTNG model of baryons onto
dark-matter-only simulations of galaxy clusters. Using 761 galaxy clusters with
$M_{200c} \gtrsim 10^{14}M_\odot$ from the TNG-300 simulation at $z<1$, we
train the algorithm to read in maps of projected dark matter mass and output
maps of projected gas density, temperature, and X-ray flux. The models train in
under an hour on two GPUs, and then predict baryonic images for $\sim2700$ dark
matter maps drawn from the TNG-300 dark-matter-only (DMO) simulation in under
two minutes. Despite being trained on individual images, the model reproduces
the true scaling relation and scatter for the $M_{DM}-L_X$, as well as the
distribution functions of the cluster X-ray luminosity and gas mass. For just
one decade in cluster mass, the model reproduces three orders of magnitude in
$L_X$. The model is biased slightly high when using dark matter maps from the
DMO simulation. The model performs well on inputs from TNG-300-2, whose mass
resolution is 8 times coarser; further degrading the resolution biases the
predicted luminosity function high. We conclude that U-net-based baryon
painting is a promising technique to build large simulated cluster catalogs
which can be used to improve cluster cosmology by combining existing
full-physics and large $N$-body simulations. |
The Gravitational Universe: The last century has seen enormous progress in our understanding of the
Universe. We know the life cycles of stars, the structure of galaxies, the
remnants of the big bang, and have a general understanding of how the Universe
evolved. We have come remarkably far using electromagnetic radiation as our
tool for observing the Universe. However, gravity is the engine behind many of
the processes in the Universe, and much of its action is dark. Opening a
gravitational window on the Universe will let us go further than any
alternative. Gravity has its own messenger: Gravitational waves, ripples in the
fabric of spacetime. They travel essentially undisturbed and let us peer deep
into the formation of the first seed black holes, exploring redshifts as large
as z ~ 20, prior to the epoch of cosmic re-ionisation. Exquisite and
unprecedented measurements of black hole masses and spins will make it possible
to trace the history of black holes across all stages of galaxy evolution, and
at the same time constrain any deviation from the Kerr metric of General
Relativity. eLISA will be the first ever mission to study the entire Universe
with gravitational waves. eLISA is an all-sky monitor and will offer a wide
view of a dynamic cosmos using gravitational waves as new and unique messengers
to unveil The Gravitational Universe. It provides the closest ever view of the
early processes at TeV energies, has guaranteed sources in the form of
verification binaries in the Milky Way, and can probe the entire Universe, from
its smallest scales around singularities and black holes, all the way to
cosmological dimensions. | Dark matter seeding and the kinematics and rotation of neutron stars: Self-annihilation of dark matter accreted from the galactic halo in the inner
regions of neutron stars may affect their kinematical properties, namely
velocity kicks and rotation patterns. We find that if a stable long-lived
single or multiple strangelet off-center seed forms, there is an associated
change in momentum and torque that may affect the kinematical observables of
the star. |
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