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Ubiquity of density slope oscillations in the central regions of galaxy
and cluster-sized systems: One usually thinks of a radial density profile as having a monotonically
changing logarithmic slope, such as in NFW or Einasto profiles. However, in two
different classes of commonly used systems, this is often not the case. These
classes exhibit non-monotonic changes in their density profile slopes which we
call oscillations for short. We analyze these two unrelated classes separately.
Class 1 consists of systems that have density oscillations and that are defined
through their distribution function $f(E)$, or differential energy distribution
$N(E)$, such as isothermal spheres, King profiles, or DARKexp, a theoretically
derived model for relaxed collisionless systems. Systems defined through $f(E)$
or $N(E)$ generally have density slope oscillations. Class 1 system
oscillations can be found at small, intermediate, or large radii but we focus
on a limited set of Class 1 systems that have oscillations in the central
regions, usually at $\log(r/r_{-2})\lesssim -2$, where $r_{-2}$ is the largest
radius where $d\log(\rho)/d\log(r)=-2$. We show that the shape of their $N(E)$
can roughly predict the amplitude of oscillations. Class 2 systems which are a
product of dynamical evolution, consist of observed and simulated galaxies and
clusters, and pure dark matter halos. Oscillations in the density profile slope
seem pervasive in the central regions of Class 2 systems. We argue that in
these systems, slope oscillations are an indication that a system is not fully
relaxed. We show that these oscillations can be reproduced by small
modifications to $N(E)$ of DARKexp. These affect a small fraction of systems'
mass and are confined to $\log(r/r_{-2})\lesssim 0$. The size of these
modifications serves as a potential diagnostic for quantifying how far a system
is from being relaxed. | The Halo Mass Function from Excursion Set Theory. I. Gaussian
fluctuations with non-markovian dependence on the smoothing scale: A classic method for computing the mass function of dark matter halos is
provided by excursion set theory, where density perturbations evolve
stochastically with the smoothing scale, and the problem of computing the
probability of halo formation is mapped into the so-called first-passage time
problem in the presence of a barrier. While the full dynamical complexity of
halo formation can only be revealed through N-body simulations, excursion set
theory provides a simple analytic framework for understanding various aspects
of this complex process. In this series of paper we propose improvements of
both technical and conceptual aspects of excursion set theory, and we explore
up to which point the method can reproduce quantitatively the data from N-body
simulations. In paper I of the series we show how to derive excursion set
theory from a path integral formulation. This allows us both to derive
rigorously the absorbing barrier boundary condition, that in the usual
formulation is just postulated, and to deal analytically with the non-markovian
nature of the random walk. Such a non-markovian dynamics inevitably enters when
either the density is smoothed with filters such as the top-hat filter in
coordinate space (which is the only filter associated to a well defined halo
mass) or when one considers non-Gaussian fluctuations. In these cases, beside
``markovian'' terms, we find ``memory'' terms that reflect the non-markovianity
of the evolution with the smoothing scale. We develop a general formalism for
evaluating perturbatively these non-markovian corrections, and in this paper we
perform explicitly the computation of the halo mass function for gaussian
fluctuations, to first order in the non-markovian corrections due to the use of
a tophat filter in coordinate space. |
Evolution in the structural properties of early-type Brightest Cluster
Galaxies at small lookback time and dependence on the environment: At the present time, SDSS early-type BCGs have larger Re than early-type
galaxies of similar L, whether these other objects are in the field, or are
satellites in clusters (Re ~ L for BCGs). At fixed M* and formation time, BCGs
at lower z are larger and have smaller velocity dispersions, i.e. Re increases
and sigma decreases with age. As a result, at z~0.25, corresponding to a
lookback time of order 3 Gyrs, BCGs are smaller than their lower z counterparts
by as much as 70% for the brightest BCGs: Re evolves as (1+z)^{0.85(Mr+21)}.
Qualitatively similar but weaker evolution in the sizes is also seen in the
bulk of the early-type population: at Mr<-22 Re evolves as (1+z)^{0.7(Mr+21)},
while at Mr>-22 the evolution is approximately (1+z)^{-0.7}, independent of Mr.
The sigma-L correlation also evolves: (1+z)^{-0.2(Mr+21)} at Mr < -22 (as for
the BCGs) and (1+z)^{0.2} for fainter galaxies. The Re- and sigma-M*
correlations yield consistent results. These trends are most easily understood
if early-type BCGs grew from many dry minor mergers rather than a few major
mergers. Only in such a scenario can BCGs be the descendents of the superdense
galaxies seen at z~2; major dry mergers, which increase the size in proportion
to the mass, cannot bring these galaxies onto the BCG Re-M* relation at z~0. We
also compared the ages and sizes of our early-type BCGs with satellites. BCGs
are larger than satellites of similar L or M* at the same redshift. Although
both satellites and BCGs trace the same weak age-L or age-M* relation, this can
be understood by noting that BCGs are typically about 1 Gyr older than the
satellites in their group, and they are about 0.5 mags more luminous. Finally,
we find that the mean satellite L is approximately independent of BCG L, in
agreement with recent predictions based on the L-dependence of clustering. | Halo orbits in cosmological disk galaxies: tracers of formation history: We analyze the orbits of stars and dark matter particles in the halo of a
disk galaxy formed in a cosmological hydrodynamical simulation. The halo is
oblate within the inner ~20 kpc and triaxial beyond this radius. About 43% of
orbits are short axis tubes - the rest belong to orbit families that
characterize triaxial potentials (boxes, long-axis tubes and chaotic orbits),
but their shapes are close to axisymmetric. We find no evidence that the
self-consistent distribution function of the nearly oblate inner halo is
comprised primarily of axisymmetric short-axis tube orbits. Orbits of all
families, and both types of particles are highly eccentric with mean
eccentricity >0.6. We find that randomly selected samples of halo stars show no
substructure in "integrals of motion" space. However individual accretion
events can be clearly identified in plots of metallicity versus formation time.
Dynamically young tidal debris is found primarily on a single type of orbit.
However, stars associated with older satellites become chaotically mixed during
the formation process (possibly due to scattering by the central bulge and
disk, and baryonic processes), and appear on all four types of orbits. We find
that the tidal debris in cosmological hydrodynamical simulations experiences
significantly more chaotic evolution than in collisionless simulations, making
it much harder to identify individual progenitors using phase space coordinates
alone. However by combining information on stellar ages and chemical abundances
with the orbital properties of halo stars in the underlying self-consistent
potential, the identification of progenitors is likely to be possible. |
The Dark Matter at the End of the Galaxy: Dark matter density profiles based upon Lambda-CDM cosmology motivate an
ansatz velocity distribution function with fewer high velocity particles than
the Maxwell-Boltzmann distribution or proposed variants. The high velocity tail
of the distribution is determined by the outer slope of the dark matter halo,
the large radius behavior of the Galactic dark matter density. N-body
simulations of Galactic halos reproduce the high velocity behavior of this
ansatz. Predictions for direct detection rates are dramatically affected for
models where the threshold scattering velocity is within 30% of the escape
velocity. | Binary Paths to Type Ia Supernovae Explosions: The Highlights: This Symposium was focused on the hunt for the progenitors of Supernovae of
Type Ia. Is there a main channel for the production of SNeIa? If so, are these
elusive progenitors Single Degenerate or Double Degenerate systems? Although
most participants seemed to favour the Single Degenerate channel, there was no
general agreement on the type of binary system at play. An observational puzzle
that was highlighted was the apparent paucity of Super-Soft Sources in our
Galaxy and also in external galaxies. The Single Degenerate channel (and as it
was pointed out, quite possibly also the Double Degenerate channel) requires
the binary system to pass through a phase of steady nuclear burning. However,
the observed number of Super-Soft sources falls short by a factor of up to 100
in explaining the estimated birth rates of SNeIa. Thus, are these Super-Soft
sources somehow hidden away and radiating at different wavelengths or are we
missing some important pieces of this puzzle that may lead to the elimination
of a certain class of progenitor? Another unanswered question concerns the
dependence of SNeIa luminosities on the age of their host galaxy. Several
hypotheses were put forward, but none was singled out as the most likely
explanation.
It is fair to say that at the end of the Symposium the definitive answer to
the vexed progenitor question remained is well and truly wide open. |
On methods of estimating cosmological bulk flows: We explore similarities and differences between several estimators of the
cosmological bulk flow, $\bf B$, from the observed radial peculiar velocities
of galaxies. A distinction is made between two theoretical definitions of $\bf
B$ as a dipole moment of the velocity field weighted by a radial window
function. One definition involves the three dimensional (3D) peculiar velocity,
while the other is based on its radial component alone. Different methods
attempt at inferring $\bf B$ for either of these definitions which coincide
only for a constant velocity field. We focus on the Wiener Filtering (WF,
Hoffman et al. 2015) and the Constrained Minimum Variance (CMV,Feldman et al.
2010) methodologies. Both methodologies require a prior expressed in terms of
the radial velocity correlation function. Hoffman et al. compute $\bf B$ in
Top-Hat windows from a WF realization of the 3D peculiar velocity field.
Feldman et al. infer $\bf B$ directly from the observed velocities for the
second definition of $\bf B$. The WF methodology could easily be adapted to the
second definition, in which case it will be equivalent to the CMV with the
exception of the imposed constraint. For a prior with vanishing correlations or
very noisy data, CMV reproduces the standard Maximum Likelihood (ML, Kaiser
1988) estimation for $\bf B$ of the entire sample independent of the radial
weighting function. Therefore, this estimator is likely more susceptible to
observational biases that could be present in measurements of distant galaxies.
Finally, two additional estimators are proposed. | Intensity mapping with neutral hydrogen and the Hidden Valley
simulations: This paper introduces the Hidden Valley simulations, a set of
trillion-particle N-body simulations in gigaparsec volumes aimed at intensity
mapping science. We present details of the simulations and their convergence,
then specialize to the study of 21-cm fluctuations between redshifts 2 and 6.
Neutral hydrogen is assigned to halos using three prescriptions, and we
investigate the clustering in real and redshift-space at the 2-point level. In
common with earlier work we find the bias of HI increases from near 2 at z = 2
to 4 at z = 6, becoming more scale dependent at high z. The level of
scale-dependence and decorrelation with the matter field are as predicted by
perturbation theory. Due to the low mass of the hosting halos, the impact of
fingers of god is small on the range relevant for proposed 21-cm instruments.
We show that baryon acoustic oscillations and redshift-space distortions could
be well measured by such instruments. Taking advantage of the large simulation
volume, we assess the impact of fluctuations in the ultraviolet background,
which change HI clustering primarily at large scales. |
Implications for cosmology from Ground-based Cosmic Microwave Background
observations: Cosmic Microwave Background (CMB) anisotropy encodes a lot of information
about our Universe. In this paper we take the ground-based CMB observations
(GCMB), including the South Pole Telescope (SPT), SPTpol and the Atacama
Cosmology Telescope Polarimeter (ACTPol), as a new probe to the CMB anisotropy
independent of two satellite observations, i.e. Wilkinson Microwave Anisotropy
Probe (WMAP) and Planck. The combination of current GCMB data is consistent
with WMAP and Planck. In the spatially flat $\Lambda$CDM model, the Hubble
constant is $H_0=69.72\pm 1.63$ km/s/Mpc at $68\%$ confidence level (CL).
Combining with baryon acoustic oscillation (BAO) and the Pantheon sample of
Type Ia supernovae (SN), we find that $H_0=68.40\pm 0.58$ km/s/Mpc ($68\%$ CL)
in the spatially flat $\Lambda$CDM cosmology which has a tension with local
measurement given by Riess et al. in 2019 at $3.7\sigma$ level, and
$\Omega_k=-0.0013\pm 0.0039$ and $N_{\rm{eff}}=2.90\pm 0.41$ ($68\%$ CL) in the
extended cosmological models. | Varying Constants: Constraints from Seasonal Variations: We analyse the constraints obtained from new atomic clock data on the
possible time variation of the fine structure `constant' and the
electron-proton mass ratio and show how they are strengthened when the seasonal
variation of Sun's gravitational field at the Earth's surface is taken into
account. |
The impact of Self-Interacting Dark Matter on the Intrinsic Alignments
of Galaxies: The formation and evolution of galaxies is known to be sensitive to tidal
processes leading to intrinsic correlations between their shapes and
orientations. Such correlations can be measured to high significance today,
suggesting that cosmological information can be extracted from them. Among the
most pressing questions in particle physics and cosmology is the nature of dark
matter. If dark matter is self-interacting, it can leave an imprint on galaxy
shapes. In this work, we investigate whether self-interactions can produce a
long-lasting imprint on intrinsic galaxy shape correlations. We investigate
this observable at low redshift ($z<0.4$) using a state-of-the-art suite of
cosmological hydro-dynamical simulations where the dark matter model is varied.
We find that dark matter self-interactions induce a mass dependent suppression
in the intrinsic alignment signal by up to 50\% out to ten's of mega-parsecs,
showing that self-interactions can impact structure outside the very core of
clusters. We find evidence that self-interactions have a scale-dependent impact
on the intrinsic alignment signal that is sufficiently different from
signatures introduced by differing baryonic physics prescriptions, suggesting
that it is detectable with up-coming all-sky surveys. | Probing the IGM/Galaxy Connection IV: The LCO/WFCCD Galaxy Survey of 20
Fields Surrounding UV Bright Quasars: We publish the survey for galaxies in 20 fields containing ultraviolet bright
quasars (with z_em 0.1 to 0.5) that can be used to study the association
between galaxies and absorption systems from the low-z intergalactic medium
(IGM). The survey is magnitude limited (R~19.5 mag) and highly complete out to
10' from the quasar in each field. It was designed to detect dwarf galaxies (L
~ 0.1 L*) at an impact parameter rho 1Mpc (z=0.1) from a quasar. The complete
sample (all 20 fields) includes R-band photometry for 84718 sources and
confirmed redshifts for 2800 sources. This includes 1198 galaxies with 0.005 <
z < (z_em - 0.01) at a median redshift of 0.18, which may associated with IGM
absorption lines. All of the imaging was acquired with cameras on the Swope 40"
telescope and the spectra were obtained via slitmask observations using the
WFCCD spectrograph on the Dupont 100" telescope at Las Campanas Observatory
(LCO). This paper describes the data reduction, imaging analysis, photometry,
and spectral analysis of the survey. We tabulate the principal measurements for
all sources in each field and provide the spectroscopic dataset online. |
Constraints on turbulent velocity broadening for a sample of clusters,
groups and elliptical galaxies using XMM-Newton: Using the width of emission lines in XMM-Newton Reflection Grating
Spectrometer spectra, we place direct constraints on the turbulent velocities
of the X-ray emitting medium in the cores of 62 galaxy clusters, groups and
elliptical galaxies. We find five objects where we can place an upper limit on
the line-of-sight broadening of 500 km/s (90 per cent confidence level), using
a single thermal component model. Two other objects are lower than this limit
when two thermal components are used. Half of the objects examined have an
upper limit on the velocity broadening of less than 700 km/s. To look for
objects which have significant turbulent broadening, we use Chandra spectral
maps to compute the expected broadening caused by the spatial extent of the
source. Comparing these with our observed results, we find that Klemola 44 has
extra broadening at the level of 1500 km/s. RX J1347.5-1145 shows weak evidence
for turbulent velocities at 800 km/s. In addition we obtain limits on
turbulence for Zw3146, Abell 496, Abell 1795, Abell 2204 and HCG 62 of less
than 200 km/s. After subtraction of the spatial contribution and including a 50
km/s systematic uncertainty, we find at least 15 sources with less than 20 per
cent of the thermal energy density in turbulence. | CFHTLenS and RCSLenS: Testing Photometric Redshift Distributions Using
Angular Cross-Correlations with Spectroscopic Galaxy Surveys: We determine the accuracy of galaxy redshift distributions as estimated from
photometric redshift probability distributions $p(z)$. Our method utilises
measurements of the angular cross-correlation between photometric galaxies and
an overlapping sample of galaxies with spectroscopic redshifts. We describe the
redshift leakage from a galaxy photometric redshift bin $j$ into a
spectroscopic redshift bin $i$ using the sum of the $p(z)$ for the galaxies
residing in bin $j$. We can then predict the angular cross-correlation between
photometric and spectroscopic galaxies due to intrinsic galaxy clustering when
$i \neq j$ as a function of the measured angular cross-correlation when $i=j$.
We also account for enhanced clustering arising from lensing magnification
using a halo model. The comparison of this prediction with the measured signal
provides a consistency check on the validity of using the summed $p(z)$ to
determine galaxy redshift distributions in cosmological analyses, as advocated
by the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS). We present an
analysis of the photometric redshifts measured by CFHTLenS, which overlaps the
Baryon Oscillation Spectroscopic Survey (BOSS). We also analyse the
Red-sequence Cluster Lensing Survey (RCSLenS), which overlaps both BOSS and the
WiggleZ Dark Energy Survey. We find that the summed $p(z)$ from both surveys
are generally biased with respect to the true underlying distributions. If
unaccounted for, this bias would lead to errors in cosmological parameter
estimation from CFHTLenS by less than $\sim 4\%$. For photometric redshift bins
which spatially overlap in 3-D with our spectroscopic sample, we determine
redshift bias corrections which can be used in future cosmological analyses
that rely on accurate galaxy redshift distributions. |
Significant foreground unrelated non-acoustic anisotropy on the one
degree scale in WMAP 5-year observations: The spectral variation of the cosmic microwave background (CMB) as observed
by WMAP was tested using foreground reduced WMAP5 data, by producing
subtraction maps at the 1$^\circ$ angular resolution between the two
cosmological bands of V and W, for masked sky areas that avoid the Galactic
disk. The resulting $V-W$ map revealed a non-acoustic signal over and above the
WMAP5 pixel noise, with two main properties. Firstly, it possesses quadrupole
power at the $\approx$ 1 $\mu K$ level which may be attributed to foreground
residuals. Second, it fluctuates also at all values of $\ell >$ 2, especially
on the $1^\circ$ scale ($200 \lesssim \ell \lesssim 300$). The behavior is {\it
random and symmetrical} about zero temperature with a r.m.s. amplitude of
$\approx$ 7 $\mu K$, or 10 % of the maximum CMB anisotropy, which would require
a `cosmic conspiracy' among the foreground components if it is a consequence of
their existences. Both anomalies must be properly diagnosed and corrected if
`precision cosmology' is the claim. The second anomaly is, however, more
interesting because it opens the question on whether the CMB anisotropy
genuinely represents primordial density seeds. | Stochastic Gravitational Wave Background generated by Cosmic String
Networks: Velocity-Dependent One-Scale model versus Scale-Invariant Evolution: We compute the power spectrum of the stochastic gravitational wave background
generated by cosmic string networks described by the Velocity-Dependent
One-Scale (VOS) model, for a wide range of macroscopic and microscopic
parameters. The VOS model --- which has been shown to provide an accurate
macroscopic description of the evolution of cosmic string networks --- is used
to demonstrate that cosmic string networks are unable to rapidly attain
scale-invariant evolution after the transition between the radiation and matter
eras. However, in computations of the stochastic gravitational wave background,
it is often assumed that the networks experience scale-invariant evolution
throughout cosmological history. We demonstrate that this assumption leads to
an underestimation of the amplitude and broadness of the peak of the spectrum,
that may consequently lead to inaccurate observational constraints on the
cosmic string tension. |
Substructure of the galaxy clusters in the REXCESS sample: observed
statistics and comparison to numerical simulations: We study the substructure statistics of a representative sample of galaxy
clusters by means of two currently popular substructure characterisation
methods, power ratios and centroid shifts. We use the 31 clusters from the
REXCESS sample, compiled from the southern ROSAT All-Sky cluster survey REFLEX
with a morphologically unbiased selection in X-ray luminosity and redshift, all
of which have been reobserved with XMM-Newton. We investigate the uncertainties
of the substructure parameters and examine the dependence of the results on
projection effects, finding that the uncertainties of the parameters can be
quite substantial. Thus while the quantification of the dynamical state of
individual clusters with these parameters should be treated with extreme
caution, these substructure measures provide powerful statistical tools to
characterise trends of properties in large cluster samples. The centre shift
parameter, w, is found to be more sensitive in general. For the REXCESS sample
neither the occurence of substructure nor the presence of cool cores depends on
cluster mass. There is a significant anti-correlation between the existence of
substantial substructure and cool cores. The simulated clusters show on average
larger substructure parameters than the observed clusters, a trend that is
traced to the fact that cool regions are more pronounced in the simulated
clusters, leading to stronger substructure measures in merging clusters and
clusters with offset cores. Moreover, the frequency of cool regions is higher
in the simulations than in the observations, implying that the description of
the physical processes shaping cluster formation in the simulations requires
further improvement. | Ultra-compact structure in intermediate-luminosity radio quasars:
building a sample of standard cosmological rulers and improving the dark
energy constraints up to $z\sim 3$: In this paper, we present a new compiled milliarcsecond compact radio data
set of 120 intermediate-luminosity quasars in the redshift range $0.46< z
<2.76$. These quasars show negligible dependence on redshifts and intrinsic
luminosity, and thus represents, in the standard model of cosmology, a fixed
comoving-length of standard ruler. We implement a new cosmology-independent
technique to calibrate the linear size of of this standard ruler as $l_m=
11.03\pm0.25$ pc, which is the typical radius at which AGN jets become opaque
at the observed frequency $\nu\sim 2$ GHz. In the framework of flat
$\Lambda$CDM model, we find a high value of the matter density parameter,
$\Omega_m=0.322^{+0.244}_{-0.141}$, and a low value of the Hubble constant,
$H_0=67.6^{+7.8}_{-7.4}\; \rm{kms}^{-1}\rm{Mpc}^{-1}$, which is in excellent
agreement with the CMB anisotropy measurements by \textit{Planck}. We obtain
${\Omega_m}=0.309^{+0.215}_{-0.151}$, $w=-0.970^{+0.500}_{-1.730}$ at 68.3% CL
for the constant $w$ of a dynamical dark-energy model, which demonstrates no
significant deviation from the concordance $\Lambda$CDM model. Consistent
fitting results are also obtained for other cosmological models explaining the
cosmic acceleration, like Ricci dark energy (RDE) or Dvali-Gabadadze-Porrati
(DGP) brane-world scenario. While no significant change in $w$ with redshift is
detected, there is still considerable room for evolution in $w$ and the
transition redshift at which $w$ departing from -1 is located at $z\sim 2.0$.
Our results demonstrate that the method extensively investigated in our work on
observational radio quasar data can be used to effectively derive cosmological
information. Finally, we find the combination of high-redshift quasars and
low-redshift clusters may provide an important source of angular diameter
distances, considering the redshift coverage of these two astrophysical probes. |
Automated galaxy-galaxy strong lens modelling: no lens left behind: The distribution of dark and luminous matter can be mapped around galaxies
that gravitationally lens background objects into arcs or Einstein rings. New
surveys will soon observe hundreds of thousands of galaxy lenses, and current,
labour-intensive analysis methods will not scale up to this challenge. We
instead develop a fully automatic, Bayesian method which we use to fit a sample
of 59 lenses imaged by the Hubble Space Telescope in uniform conditions. We set
out to \textit{leave no lens behind} and focus on ways in which automated fits
fail in a small handful of lenses, describing adjustments to the pipeline that
allows us to infer accurate lens models. Our pipeline ultimately fits {\em all}
59 lenses in our sample, with a high success rate key because catastrophic
outliers would bias large samples with small statistical errors. Machine
Learning techniques might further improve the two most difficult steps:
subtracting foreground lens light and initialising a first, approximate lens
model. After that, increasing model complexity is straightforward. We find a
mean $\sim1\%$ measurement precision on the measurement of the Einstein radius
across the lens sample which {\em does not degrade with redshift} up to at
least $z=0.7$ -- in stark contrast to other techniques used to study galaxy
evolution, like stellar dynamics. Our \texttt{PyAutoLens} software is open
source, and is also installed in the Science Data Centres of the ESA Euclid
mission. | The eROSITA view of the Abell 3391/95 field: Cluster Outskirts and
Filaments: Aims. We aim to characterize the gas properties in the cluster outskirts
($R_{500}<r<R_{200}$) and in the detected inter-cluster filaments ($>R_{200}$)
of the A3391/95 system and to compare them to predictions. Methods. We
performed X-ray image and spectral analyses using the eROSITA PV data to assess
the gas morphology and properties in the outskirts and the filaments in the
directions of the previously detected Northern and Southern Filament of the
A3391/95 system. We took particular care of the foreground. Results. In the
filament-facing outskirts of A3391 and the Northern Clump, we find higher
temperatures than typical cluster outskirts profiles, with a significance of
$1.6-2.8\sigma$, suggesting heating due to their connections with the
filaments. We confirm SB excess in the profiles of the Northern, Eastern, and
Southern Filaments. From spectral analysis, we detect hot gas of ~1 keV for the
Northern and Southern Filaments. The filament metallicities are below 10% solar
metallicity and the $n_e$ range between 2.6 and
$6.3\times10^{-5}~\mathrm{cm^{-3}}$. The characteristic properties of the
Little Southern Clump (~1.5$R_{200}$ from A3395S in the Southern Filament)
suggest that it is a small galaxy group. Excluding the LSC from the analysis of
the Southern Filament decreases the gas density by 30%. This shows the
importance of taking into account any clumps to avoid overestimation of the gas
measurement in the outskirts and filament regions. Conclusions. The $n_e$ of
the filaments are consistent with the WHIM properties as predicted by
cosmological simulations, but the temperatures are higher, close to the upper
WHIM temperature limit. As both filaments are short and located in a denser
environment, stronger gravitational heating may be responsible for this
temperature enhancement. The metallicities are low, but still within the
expected range from the simulations. |
Beating non-linearities: improving the Baryon Acoustic Oscillations with
the linear point: We propose a new way of looking at the Baryon Acoustic Oscillations in the
Large Scale Structure clustering correlation function. We identify a scale s_LP
that has two fundamental features: its position is insensitive to non-linear
gravity, redshift space distortions, and scale-dependent bias at the 0.5%
level; it is geometrical, i.e. independent of the power spectrum of the
primordial density fluctuation parameters. These two properties together make
s_LP, called the "linear point", an excellent cosmological standard ruler. The
linear point is also appealing because it is easily identified irrespectively
of how non-linearities distort the correlation function. Finally, the
correlation function amplitude at s_LP is similarly insensitive to non-linear
corrections to within a few percent. Hence, exploiting the particular Baryon
features in the correlation function, we propose three new estimators for
growth measurements. A preliminary analysis of s_LP in current data is
encouraging. | Extracting Dark-Matter Velocities from Halo Masses: A Reconstruction
Conjecture: Increasing attention has recently focused on non-traditional dark-matter
production mechanisms which result in primordial dark-matter velocity
distributions with highly non-thermal shapes. In this paper, we undertake an
assessment of how the detailed shape of a general dark-matter velocity
distribution impacts structure formation in the non-linear regime. In
particular, we investigate the impact on the halo-mass and subhalo-mass
functions, as well as on astrophysical observables such as satellite and
cluster-number counts. We find that many of the standard expectations no longer
hold in situations in which this velocity distribution takes a highly
non-trivial, even multi-modal shape. For example, we find that the nominal
free-streaming scale alone becomes insufficient to characterize the effect of
free-streaming on structure formation. In addition, we propose a simple
one-line conjecture which can be used to "reconstruct" the primordial
dark-matter velocity distribution directly from the shape of the halo-mass
function. Although our conjecture is completely heuristic, we show that it
successfully reproduces the salient features of the underlying dark-matter
velocity distribution even for non-trivial distributions which are highly
non-thermal and/or multi-modal, such as might occur for non-minimal dark
sectors. Moreover, since our approach relies only on the halo-mass function,
our conjecture provides a method of probing dark-matter properties even for
scenarios in which the dark and visible sectors interact only gravitationally. |
Primordial non-Gaussianity from the covariance of galaxy cluster counts: It has recently been proposed that the large-scale bias of dark matter halos
depends sensitively on primordial non-Gaussianity of the local form. In this
paper we point out that the strong scale dependence of the non-Gaussian halo
bias imprints a distinct signature on the covariance of cluster counts. We find
that using the full covariance of cluster counts results in improvements on
constraints on the non-Gaussian parameter f_NL of three (one) orders of
magnitude relative to cluster counts (counts + clustering variance) constraints
alone. We forecast f_NL constraints for the upcoming Dark Energy Survey in the
presence of uncertainties in the mass-observable relation, halo bias, and
photometric redshifts. We find that the DES can yield constraints on
non-Gaussianity of sigma(f_NL) ~ 1-5 even for relatively conservative
assumptions regarding systematics. Excess of correlations of cluster counts on
scales of hundreds of megaparsecs would represent a smoking gun signature of
primordial non-Gaussianity of the local type. | The three-dimensional geometry and merger history of the massive galaxy
cluster MACS J0358.8-2955: We present results of a combined X-ray/optical analysis of the dynamics of
the massive cluster MACS J0358.8-2955 (z=0.428) based on observations with the
Chandra X-ray Observatory, the Hubble Space Telescope, and the Keck-I telescope
on Mauna Kea. MACS J0358.8-2955 is found to be one of the most X-ray luminous
clusters known at z>0.3, featuring L_X(<r_500) = 4.24*10^45 erg/s, kT = (9.55
+0.58/-0.37) keV, M^{3D}_{gas}(<r_500) = (9.18+/-1.45)*10^13 M_sun, and
M^{3D}_{tot}(<r_500) = (1.12+/-0.18)*10^15 M_sun. The system's high velocity
dispersion of (1440 +130/-110) km/s (890 km/s when the correct relativistic
equation is used), however, is inflated by infall along the line of sight, as
the result of a complex merger of at least three sub-clusters. One collision
proceeds close to head-on, while the second features a significant impact
parameter. The temperature variations in the intra-cluster gas, two tentative
cold fronts, the radial velocities measured for cluster galaxies, and the small
offsets between collisional and non-collisional cluster components all suggest
that both merger events are observed close to core passage and along axes that
are greatly inclined with respect to the plane of the sky. A strong-lensing
analysis of the system anchored upon three triple-image systems (two of which
have spectroscopic redshifts) yields independent constraints on the mass
distribution. For a gas fraction of 8.2%, the resulting strong-lensing mass
profile is in good agreement with our X-ray estimates, and the details of the
mass distribution are fully consistent with our interpretation of the
three-dimensional merger history of this complex system. |
Hubble-induced phase transitions: Walls are not forever: The interplay between non-minimally coupled scalar fields and a
kinetic-dominated era following the end of inflation triggers the spontaneous
symmetry breaking of internal symmetries and the subsequent evolution of the
fields towards large expectation values. We present here a detailed analysis of
the associated dynamics in quintessential inflation scenarios involving a
non-minimally coupled $Z_2$-symmetric spectator field. By analytically
following the evolution of the spectator field fluctuations at early times, we
characterize the formation of classical, homogeneous and spatially-localized
field configurations separated by domain walls. The life expectancy of these
dividing barriers is set by the scale of inflation, the non-minimal coupling
and self-interactions of the spectator field and potentially, but not
necessarily, the duration of the heating stage. For most of the parameter
space, the domain walls are doomed to disappear before big bang
nucleosynthesis. Potential phenomenological consequences of the scenario are
discussed. | The impact of varying inhomogeneous reionization histories on metrics of
Ly$α$ opacity: The epoch of hydrogen reionization is complete by $z=5$, but its progression
at higher redshifts is uncertain. Measurements of Ly$\alpha$ forest opacity
show large scatter at $z<6$, suggestive of spatial fluctuations in neutral
fraction ($x_\mathrm{HI}$), temperature, or ionizing background, either
individually or in combination. However, these effects are degenerate,
necessitating modeling these physics in tandem in order to properly interpret
the observations. We begin this process by developing a framework for modeling
the reionization history and associated temperature fluctuations, with the
intention of incorporating ionizing background fluctuations at a later time. To
do this, we generate several reionization histories using semi-numerical code
AMBER, selecting histories with volume-weighted neutral fractions that adhere
to the observed CMB optical depth and dark pixel fractions. Implementing these
histories in the \texttt{Nyx} cosmological hydrodynamics code, we examine the
evolution of gas within the simulation, and the associated metrics of the
Ly$\alpha$ forest opacity. We find that the pressure smoothing scale within the
IGM is strongly correlated with the adiabatic index of the temperature-density
relation. We find that while models with 20,000 K photoheating at reionization
are better able to reproduce the shape of the observed $z=5$ 1D flux power
spectrum than those with 10,000 K, they fail to match the highest wavenumbers.
The simulated autocorrelation function and optical depth distributions are
systematically low and narrow, respectively, compared to the observed values,
but are in better agreement when the reionization history is longer in
duration, more symmetric in its distribution of reionization redshifts, or if
there are remaining neutral regions at $z<6$. The systematically low variance
likely requires the addition of a fluctuating UVB. |
A giant ring-like structure at 0.78<z<0.86 displayed by GRBs: According to the cosmological principle, Universal large-scale structure is
homogeneous and isotropic. The observable Universe, however, shows complex
structures even on very large scales. The recent discoveries of structures
significantly exceeding the transition scale of 370 Mpc pose a challenge to the
cosmological principle.
We report here the discovery of the largest regular formation in the
observable Universe; a ring with a diameter of 1720 Mpc, displayed by 9 gamma
ray bursts (GRBs), exceeding by a factor of five the transition scale to the
homogeneous and isotropic distribution. The ring has a major diameter of $43^o$
and a minor diameter of $30^o$ at a distance of 2770 Mpc in the 0.78<z<0.86
redshift range, with a probability of $2\times 10^{-6}$ of being the result of
a random fluctuation in the GRB count rate.
Evidence suggests that this feature is the projection of a shell onto the
plane of the sky. Voids and string-like formations are common outcomes of
large-scale structure. However, these structures have maximum sizes of 150 Mpc,
which are an order of magnitude smaller than the observed GRB ring diameter.
Evidence in support of the shell interpretation requires that temporal
information of the transient GRBs be included in the analysis.
This ring-shaped feature is large enough to contradict the cosmological
principle. The physical mechanism responsible for causing it is unknown. | Oscillating cosmic evolution and constraints on big bang nucleosynthesis
in the extended Starobinsky model: We investigate the cosmic evolutions in the extended Starobinsky model (eSM)
obtained by adding one $R^{ab}R_{ab}$ term to the Starobinsky model. We discuss
the possibility of various cosmic evolutions with a special focus on the
radiation-dominated era (RDE). Using simple assumptions, a second-order
non-linear differential equation describing the various cosmic evolutions in
the eSM is introduced. By solving this non-linear equation numerically, we show
that the various cosmic evolutions, such as the standard cosmic evolution ($a
\propto t^{1/2}$) and a unique oscillating cosmic evolution, are feasible due
to the effects of higher-order terms introduced beyond Einstein's gravity.
Furthermore, we consider big bang nucleosynthesis (BBN), which is the most
important observational result in the RDE, to constrain the free parameters of
the eSM. The primordial abundances of the light elements, such as $^{4}$He, D,
$^{3}$He, $^{7}$Li, and $^{6}$Li by the cosmic evolutions are compared with the
most recent observational data. It turns out that most non-standard cosmic
evolutions can not easily satisfy these BBN constraints, but a free parameter
of the viable models with the oscillating cosmic evolution is shown to have an
upper limit by the constraints. In particular, we find that the free parameter
is most sensitive to deuterium and $^4$He abundances, which are being precisely
measured among other elements. Therefore, more accurate measurements in the
near future may enable us to distinguish the eSM from the standard model as
well as other models. |
The Spitzer Survey of the Small Magellanic Cloud (S3MC): Insights into
the Life-Cycle of Polycyclic Aromatic Hydrocarbons: We present the results of modeling dust SEDs across the SMC with the aim of
mapping the distribution of PAHs in a low-metallicity environment. Using
Spitzer Survey of the SMC (S3MC) photometry from 3.6-160 um over the main
star-forming regions of the Wing and Bar along with spectral mapping from 5-38
um from the Spitzer Spectroscopic Survey of the SMC (S4MC) in selected regions,
we model the dust SED and emission spectrum to determine the fraction of dust
in PAHs across the SMC. We use the regions of overlapping photometry and
spectroscopy to test the reliability of the PAH fraction as determined from SED
fits alone. The PAH fraction in the SMC is low compared to the Milky Way and
variable--with relatively high fractions (q_PAH~1-2%) in molecular clouds and
low fractions in the diffuse ISM (<q_PAH>=0.6%). We use the map of PAH fraction
across the SMC to test a number of ideas regarding the production, destruction
and processing of PAHs in the ISM. We find weak or no correlation between the
PAH fraction and the distribution of carbon AGB stars, the location of
supergiant H I shells and young SN remnants, or the turbulent Mach number. We
find that the PAH fraction is correlated with CO intensity, peaks in the dust
surface density and the molecular gas surface density as determined from 160 um
emission. The PAH fraction is high in regions of active star-formation, as
predicted by its correlation with molecular gas, but is suppressed in H II
regions. Because the PAH fraction in the diffuse ISM is generally very low--in
accordance with previous work on modeling the SED of the SMC--and the PAH
fraction is relatively high in molecular regions, we suggest that PAHs are
destroyed in the diffuse ISM of the SMC and/or PAHs are forming in molecular
clouds. We discuss the implications of these observations for our understanding
of the PAH life cycle, particularly in low-metallicity galaxies. | A Future Percent-Level Measurement of the Hubble Expansion at Redshift
0.8 With Advanced LIGO: Simultaneous measurements of distance and redshift can be used to constrain
the expansion history of the universe and associated cosmological parameters.
Merging binary black hole (BBH) systems are standard sirens---their
gravitational waveform provides direct information about the luminosity
distance to the source. Because gravity is scale-free, there is a perfect
degeneracy between the source masses and redshift; some non-gravitational
information is necessary to break the degeneracy and determine the redshift of
the source. Here we suggest that the pair instability supernova (PISN) process,
thought to be the source of the observed upper-limit on the black hole (BH)
mass in merging BBH systems at $\sim 45 \, M_\odot$, imprints a mass scale in
the population of BBH mergers and permits a measurement of the
redshift-luminosity-distance relation with these sources. We simulate five
years of BBH detections in the Advanced LIGO and Virgo detectors with realistic
assumptions about the BBH merger rate, a mass distribution incorporating a
smooth PISN cutoff, and measurement uncertainty. We show that after one year of
operation at design sensitivity (circa 2021) the BBH population can constrain
$H(z)$ to $6.1\%$ at a pivot redshift $z \simeq 0.8$. After five years (circa
2025) the constraint improves to $2.9\%$. This measurement relies only on
general relativity and the presence of a cutoff mass scale that is
approximately fixed or calibrated across cosmic time; it is independent of any
distance ladder or cosmological model. Observations by future
``third-generation'' gravitational wave detectors, which can see BBH mergers
throughout the universe, would permit sub-percent cosmographical measurements
to $z \gtrsim 4$ within one month of observation. |
The AARTFAAC Cosmic Explorer: observations of the 21-cm power spectrum
in the EDGES absorption trough: The 21-cm absorption feature reported by the EDGES collaboration is several
times stronger than that predicted by traditional astrophysical models. If
genuine, a deeper absorption may lead to stronger fluctuations on the 21-cm
signal on degree scales (up to 1~Kelvin in rms), allowing these fluctuations to
be detectable in nearly 50~times shorter integration times compared to previous
predictions. We commenced the "AARTFAAC Cosmic Explorer" (ACE) program, that
employs the AARTFAAC wide-field imager, to measure or set limits on the power
spectrum of the 21-cm fluctuations in the redshift range $z = 17.9-18.6$
($\Delta\nu = 72.36-75.09$~MHz) corresponding to the deep part of the EDGES
absorption feature. Here, we present first results from two LST bins:
23.5-23.75h and 23.5-23.75h, each with 2~h of data, recorded in `semi
drift-scan' mode. We demonstrate the application of the new ACE data-processing
pipeline (adapted from the LOFAR-EoR pipeline) on the AARTFAAC data. We observe
that noise estimates from the channel and time-differenced Stokes~$V$
visibilities agree with each other. After 2~h of integration and subtraction of
bright foregrounds, we obtain $2\sigma$ upper limits on the 21-cm power
spectrum of $\Delta_{21}^2 < (8139~\textrm{mK})^2$ and $\Delta_{21}^2 <
(8549~\textrm{mK})^2$ at $k = 0.144~h\,\textrm{cMpc}^{-1}$ for the two LST
bins. Incoherently averaging the noise bias-corrected power spectra for the two
LST bins yields an upper limit of $\Delta_{21}^2 < (7388~\textrm{mK})^2$ at $k
= 0.144~h\,\textrm{cMpc}^{-1}$. These are the deepest upper limits thus far at
these redshifts. | Constraints on variations in inflaton decay rate from modulated
preheating: Modulated (p)reheating is thought to be an alternative mechanism for
producing super-horizon curvature perturbations in CMB. But large
non-gaussianity and iso-curvature perturbations produced by this mechanism rule
out its acceptability as the sole process responsible for generating CMB
perturbations. We explore the situation where CMB perturbations are mostly
generated by usual quantum fluctuations of inflaton during inflation, but a
modulated coupling constant between inflaton and a secondary scalar affects the
preheating process and produces some extra curvature perturbations. If the
modulating scalar field is considered to be a dark matter candidate, coupling
constant between the fields has to be unnaturally fine tuned in order to keep
the local-form non-gaussianity and the amplitude of iso-curvature perturbations
within observational limit; otherwise parameters of the models have to be
tightly constrained. Those constraints imply that the curvature perturbations
generated by modulated preheating should be less than 15% of the total observed
CMB perturbations. On the other hand if the modulating scalar field is not a
dark matter candidate, parameters of the models could not be constrained, but
the constraints on the maximum amount of the curvature perturbations coming
from modulated preheating remain valid. |
Polarizing primordial gravitational waves by parity violation: We study primordial gravitational waves (PGWs) in the Horava-Lifshitz (HL)
theory of quantum gravity, in which high-order spatial derivative operators,
including the ones violating parity, generically appear in order for the theory
to be power-counting renormalizable and ultraviolet (UV) complete. Because of
both parity violation and non-adiabatic evolution of the modes due to a
modified dispersion relationship, a large polarization of PGWs becomes
possible, and it could be well within the range of detection of the BB, TB and
EB power spectra of the forthcoming cosmic microwave background (CMB)
observations. | Momentum dependence of the bispectrum in two-field inflation: We examine the momentum dependence of the bispectrum of two-field
inflationary models within the long-wavelength formalism. We determine the
sources of scale dependence in the expression for the parameter of
non-Gaussianity fNL and study two types of variation of the momentum triangle:
changing its size and changing its shape. We introduce two spectral indices
that quantify the possible types of momentum dependence of the local type fNL
and illustrate our results with examples. |
Merger Hydrodynamics of the Luminous Cluster RXJ1347.5-1145: We present an analysis of the complex gas hydrodynamics in the X-ray luminous
galaxy cluster RXJ1347.5-1145 caught in the act of merging with a subcluster to
its southeast using a combined $186$ ks Chandra exposure, $2.5$ times greater
than previous analyses. The primary cluster hosts a sloshing cold front spiral
traced by four surface brightness edges $5.^{\prime \prime}85^{+0.04}_{-0.03}$
west, $7.^{\prime \prime}10^{+0.07}_{-0.03}$ southeast, $11.^{\prime
\prime}5^{+1.3}_{-1.2}$ east, and $16.^{\prime \prime}7^{+0.3}_{-0.5}$
northeast from the primary central dominant galaxy, suggesting the merger is in
the plane of the sky. We measure temperature and density ratios across these
edges, confirming they are sloshing cold fronts. We observe the eastern edge of
the subcluster infall shock, confirming the observed subcluster is traveling
from the southwest to the northeast in a clockwise orbit. We measure a shock
density contrast of $1.38^{+0.16}_{-0.15}$ and infer a Mach number
$1.25\pm0.08$ and a shock velocity of $2810^{+210}_{-240}$ km s$^{-1}$.
Temperature and entropy maps show cool, low entropy gas trailing the subcluster
in a southwestern tail, consistent with core shredding. Simulations suggest a
perturber in the plane of the sky on a clockwise orbit would produce a sloshing
spiral winding counterclockwise, opposite to that observed. The most compelling
solution to this discrepancy is that the observed southeastern subcluster is on
its first passage, shock heating gas during its clockwise infall, while the
main cluster's clockwise cold front spiral formed from earlier encounters with
a second perturber orbiting counterclockwise. | Testing time evolution of the mass distribution of the black hole
mergers: The detection of gravitational-wave events revealed that there are numerous
populations of black hole (BH) binaries that can merge within the age of the
Universe. Although several formation channels of such binaries are known,
considerable theoretical uncertainties associated with each channel defeat the
robust prediction of how much each channel contributes to the total merger rate
density. Given that the time evolution of the merger rate density in some
channels is (exactly or nearly) independent of BH masses, clarifying this
feature from observational data will shed some light on the nature of BH
binaries. On the basis of this motivation, we formulate a methodology to
perform a statistical test of whether the mass distribution of BH mergers
evolves over time by hypothesis testing. Our statistical test requires neither
a priori specification of the mass distribution, which is largely uncertain,
nor that of the time dependence of merger rate. We then apply it to mock data
for some concrete shapes of the merger rate density and show that the proposed
method rejects/(does not reject) the null hypothesis correctly for a large
sample size. After this verification, the method is applied to a catalog of the
gravitational-wave events obtained during the LIGO-Virgo's third observing run.
We find that the selection bias degrades the effectiveness of our method for
the O3 catalog owing to the reduction in the number of and the maximum
redshifts of the merger events that we can explore. Within the range where the
method can be applied, there is no indication of the time evolution of the mass
distribution of merger rate density. This limitation will be eased in future
observations containing more events, and our hypothesis testing will help
determine whether the merger rate density evolves over time independently of BH
masses. |
Magnetic fields in nearby galaxies: Observations of synchrotron radiation and the Faraday rotation of its
polarized component allow us to investigate the magnetic properties of the
diffuse interstellar medium in nearby galaxies, on scales down to roughly one
hundred parsecs. All disc galaxies seem to have a mean, or regular, magnetic
field component that is ordered on length scales comparable to the size of the
galaxy as well as a random magnetic field of comparable or greater strength. I
present an overview of what is currently known observationally about galactic
magnetic fields, focusing on the common features among galaxies that have been
studied rather than the distinctive or unusual properties of individual
galaxies. Of particular interest are the azimuthal patterns formed by regular
magnetic fields and their pitch angles as these quantities can be directly
related to the predictions of the mean field dynamo theory, the most promising
theoretical explanation for the apparent ubiquitous presence of regular
magnetic fields in disc galaxies. | Towards a Bias-Free Selection Function in Shear Measurement: Sample selection is a necessary preparation for weak lensing measurement. It
is well-known that selection itself may introduce bias in the measured shear
signal. Using image simulation and the Fourier_Quad shear measurement pipeline,
we quantify the selection bias in various commonly used selection function
(signal-to-noise-ratio, magnitude, etc.). We proposed a new selection function
defined in the power spectrum of the galaxy image. This new selection function
has low selection bias, and it is particularly convenient for shear measurement
pipelines based on Fourier transformation. |
2MASS Photometric Redshift catalog: a comprehensive three-dimensional
census of the whole sky: Key cosmological applications require the three-dimensional galaxy
distribution on the entire celestial sphere. These include measuring the
gravitational pull on the Local Group, estimating the large-scale bulk flow and
testing the Copernican principle. However, the largest all-sky redshift surveys
-- the 2MRS and IRAS PSCz -- have median redshifts of only z=0.03 and sample
the very local Universe. There exist all-sky galaxy catalogs reaching much
deeper -- SuperCOSMOS in the optical, 2MASS in the near-IR and WISE in the
mid-IR -- but these lack complete redshift information. At present, the only
rapid way towards larger 3D catalogs covering the whole sky is through
photometric redshift techniques. In this paper we present the 2MASS Photometric
Redshift catalog (2MPZ) containing 1 million galaxies, constructed by
cross-matching 2MASS XSC, WISE and SuperCOSMOS all-sky samples and employing
the artificial neural network approach (the ANNz algorithm), trained on such
redshift surveys as SDSS, 6dFGS and 2dFGRS. The derived photometric redshifts
have errors nearly independent of distance, with an all-sky accuracy of
sigma_z=0.015 and a very small percentage of outliers. In this way, we obtain
redshift estimates with a typical precision of 12% for all the 2MASS XSC
galaxies that lack spectroscopy. In addition, we have made an early effort
towards probing the entire 3D sky beyond 2MASS, by pairing up WISE with
SuperCOSMOS and training the ANNz on GAMA redshift data reaching currently to
z_med~0.2. This has yielded photo-z accuracies comparable to those in the 2MPZ.
These all-sky photo-z catalogs, with a median z~0.1 for the 2MPZ, and
significantly deeper for future WISE-based samples, will be the largest and
most complete of their kind for the foreseeable future. | Counting Dark Sub-halos with Star Stream Gaps: The Cold Dark Matter paradigm predicts vast numbers of dark matter sub-halos
to be orbiting in galactic halos. The sub-halos are detectable through the gaps
they create gaps in stellar streams. The gap-rate is an integral over the
density of sub-halos, their mass function, velocity distribution and the
dynamical age of the stream. The rate of visible gap creation is a function of
the width of the stream. The available data for four streams: the NW stream of
M31, the Pal~5 stream, the Orphan Stream and the Eastern Banded Structure, are
compared to the LCDM predicted relation. We find a remarkably good agreement,
although there remains much to be done to improve the quality of the result.
The narrower streams require that there is a total population of order 10^5
sub-halos above 10^5 M_sun to create the gaps. |
Measurement of Hubble constant: Non-Gaussian Errors in HST key project
data: Assuming the Central Limit Theorem, experimental uncertainties in any data
set are expected to follow the Gaussian distribution with zero mean. We propose
an elegant method based on Kolmogorov-Smirnov statistic to test the above; and
apply it on the measurement of Hubble constant which determines the expansion
rate of the Universe. The measurements were made using Hubble Space Telescope.
Our analysis shows that the uncertainties in the above measurement are
non-Gaussian. | Weak lensing observations of potentially X-ray underluminous galaxy
clusters: Optically selected clusters of galaxies display a relation between their
optical mass estimates and their X-ray luminosities Lx that has a large
scatter. A substantial fraction of optically selected clusters have Lx
estimates or upper limits significantly below the values expected from the
Lx-mass relation established for X-ray selected clusters, i.e., these clusters
are X-ray underluminous for their mass. We attempt to confirm or falsify the
X-ray underluminous nature of two clusters, Abell 315 and Abell 1456, by using
weak gravitational lensing as a third and independent measure of the clusters'
masses. We obtained optical wide-field imaging data and selected background
galaxies using their colors and measured the shear exerted by the tidal field
of the foreground galaxy clusters. We then fitted parametrized models to our
shear catalogs. After accounting for projections of large-scale structure and
halo triaxiality, we find that A 315 is significantly X-ray underluminous for
its mass, while no significant lensing signal was detected for A 1456. We
re-evaluate earlier kinematic and X-ray analyses of these two clusters and
discuss the nature of the X-ray underluminous cluster A 315 and why A 1456 was
probably erroneously identified as being X-ray underluminous. |
Challenges for the statistical gravitational-wave method to measure the
Hubble constant: Gravitational waves (GW) can be employed as standard sirens that will soon
measure the Hubble constant with sufficient precision to weigh in on the $\sim
5\sigma$ Hubble tension. Most GW sources will have no identified
electromagnetic counterpart, leading to uncertainty in the redshift of the
source, and in turn a degeneracy between host galaxy distance, redshift, and
$H_0$. In the case where no electromagnetic counterparts are identified, it has
been proposed that a statistical canvassing of candidate GW hosts, found in a
large galaxy survey for example, can be used to accurately constrain the Hubble
constant. We study and simulate this "galaxy voting" method to compute $H_0$.
We find that the Hubble constant posterior is in general biased relative to the
true value even when making optimistic assumptions about the statistical
properties of the sample. Using the MICECAT light-cone catalog, we find that
the bias in the $H_0$ posteriors depends on the realization of the underlying
galaxy sample and the precision of the GW source distance measurement. | Axions in Cold Dark Matter and Inflation Models: The subjects of this thesis are the invisible axion and the more general
family of axion-like particles.
The invisible axion is a hypothetical elementary particle and a cold dark
matter candidate. I present an improved computation of the constraints on the
parameter space of the cold dark matter axion in the standard cosmology, that
includes the contributions from anharmonicities in the axion potential and from
the decay of axionic strings. In this scenario, I update the value of the mass
of the cold dark matter axion, finding the value $(67\pm17){\rm \mu eV}$,
approximately one order of magnitude larger than previous computations.
The effect of nonstandard cosmological scenarios on the parameter space of
axion cold dark matter is studied for the first time. In particular, I consider
the cases of low-temperature reheating and kination cosmologies, and I show
that the mass of the cold dark matter axion can differ from the value in the
standard cosmological scenario by orders of magnitude.
Finally, I consider the family of axion-like particles, assuming that these
particles serve as the inflaton in the context of warm inflation. I find that
the axion energy scale $f$, which in the standard inflation scenario is of the
order of the Planck mass, can be lowered to the much safer Grand Unification
Theory scale $f \sim 10^{16}{\rm GeV}$. I also constrain the parameter space
and the amount of gravitational waves from this model, using results from the
Wilkinson Microwave Anisotropy Probe 7-year data. |
Rapid onset of the 21-cm signal suggests a preferred mass range for dark
matter particle: We are approaching a new era to probe the 21-cm neutral hydrogen signal from
the period of cosmic dawn. This signal offers a unique window to the virgin
Universe, e.g., to study dark matter models with different small-scale
behaviours. The EDGES collaboration has recently published the first results of
the global 21-cm spectrum. We demonstrate that such a signal can be used to
set, unlike most observations concerning dark matter, both lower and upper
limits for the mass of dark matter particles. We study the 21-cm signal
resulting from a simple warm dark matter model with a sharp-$k$ window function
calibrated for high redshifts. We tie the PopIII star formation to Lyman-alpha
and radio background production. Using MCMC to sample the parameter space we
find that to match the EDGES signal, a warm dark matter particle must have a
mass of $7.3^{+1.6}_{-3.3}$ keV at 68\% confidence interval. This translates to
$2.2^{+1.4}_{-1.7} \times 10^{-20}$ eV for fuzzy dark matter and
$63^{+19}_{-35}$ keV for Dodelson-Widrow sterile neutrinos. Cold dark matter is
unable to reproduce the signal due to its slow structure growth. | Dark matter and halo bispectrum in redshift space: theory and
applications: We present a phenomenological modification of the standard perturbation
theory prediction for the bispectrum in redshift space that allows us to extend
the model to mildly non-linear scales over a wide range of redshifts,
$z\leq1.5$. We find that we can describe the bispectrum of dark matter
particles with $\sim5%$ accuracy for $k_i\lesssim0.10\,h/{\rm Mpc}$ at $z=0$,
for $k_i\lesssim0.15\,h/{\rm Mpc}$ at $z=0.5$, for $k_i\lesssim0.17\,h/{\rm
Mpc}$ at $z=1.0$ and for $k_i\lesssim0.20\,h/{\rm Mpc}$ at $z=1.5$. We also
test that the fitting formula is able to describe with similar accuracy the
bispectrum of cosmologies with different $\Omega_m$, in the range $0.2\lesssim
\Omega_m \lesssim 0.4$, and consequently with different values of the
logarithmic grow rate $f$ at $z=0$, $0.4\lesssim f(z=0) \lesssim 0.6$. We apply
this new formula to recover the bias parameters, $f$ and $\sigma_8$, by
combining the redshift space power spectrum monopole and quadrupole with the
bispectrum monopole for both dark matter particles and haloes. We find that the
combination of these three statistics can break the degeneracy between $b_1$,
$f$ and $\sigma_8$. For dark matter particles the new model can be used to
recover $f$ and $\sigma_8$ with $\sim1%$ accuracy. For dark matter haloes we
find that $f$ and $\sigma_8$ present larger systematic shifts, $\sim10%$. The
systematic offsets arise because of limitations in the modelling of the
interplay between bias and redshift space distortions, and represent a
limitation as the statistical errors of forthcoming surveys reach this level.
Conveniently, we find that these residual systematics are mitigated for
combinations of parameters. The improvement on the modelling of the bispectrum
presented in this paper will be useful for extracting information from current
and future galaxy surveys. [abridged] |
Cosmological dinosaurs: The hypothesis of existence of primordial black holes with large masses (\geq
10^6 M\odot), formed at the earliest stages of the Universe evolution, is
considered in the paper. The possibility does not contradict some theories, see
e.g. Barkana & Loeb (2001), and may match new observational data. In
particular, this scenario of evolution could describe some peculiarities in
distant galaxies and quasars. Calculations of evolution of central body mass in
protogalaxies for different initial conditions are presented. It is shown that
the sufficient rate of BH mass growth is not achieved in the standard scheme
without complex additional assumptions. Moreover, the appearance of a
primordial black hole in the epoch of primordial nucleosynthesis could
significantly change the chemical composition around it. This can lead to
different exotic stars with low mass and nonstandart metals enrichment. The
proposed scheme is not considered as universal. On the other hand, if only tiny
part of existed objects have the considered nature, it gives a unique
possibility to study extremal stages of matter and fields evolution in our
Universe. | A MeerKAT view on galaxy clusters: Almost two decades of observations of radio emission in galaxy clusters have
proven the existence of relativistic particles and magnetic fields that
generate extended synchrotron emission in the form of radio halos. In the
current scenario, radio halos are generated through re--acceleration of
relativistic electrons by turbulence generated by cluster mergers. Although
this theoretical framework has received increasingly supporting observational
evidence over the last ten years, observations of statistically complete
samples are needed in order to fundamentally test model predictions. In this
paper we briefly review our 7--element Karoo Radio Telescope observations of a
sample of nearby clusters aimed to test the predictions of the turbulent
re--acceleration model in small systems ($M_{500} > 4 \times 10^{14}$
M$_{\odot}$). We conclude by presenting two galaxy cluster surveys to be
carried out with MeerKAT in order to provide crucial test of models of radio
halo formation in nearby ($z < 0.1$) and high redshift ($z > 0.4$) systems
respectively. |
Joint Minkowski Functionals and Bispectrum Constraints on
Non-Gaussianity in the CMB: Two of the most commonly used tools to constrain the primordial
non-Gaussianity are the bispectrum and the Minkowski functionals of CMB
temperature anisotropies. These two measures of non-Gaussianity in principle
provide distinct (though correlated) information, but in the past constraints
from them have only been loosely compared, and not statistically combined. In
this work we evaluate, for the first time, the covariance matrix between the
local non-Gaussianity coefficient fnl estimated through the bispectrum and
Minkowski functionals. We find that the estimators are positively correlated,
with corerlation coefficient r ~ 0.3. Using the WMAP7 data to combine the two
measures and accounting for the point-source systematics, we find the combined
constraint fnl=37+/-28, which has a ~20% smaller error than either of the
individual constraints. | Exploring the Correlations between Globular Cluster Populations and
Supermassive Black Holes in Giant Galaxies: This paper presents an analysis of the correlation between the number of
globular clusters (N_GC) in giant galaxies and the mass of the galaxies'
central supermassive black hole (M_SMBH). I construct a sample of 20
elliptical, spiral, and S0 galaxies with known SMBH masses and with
accurately-measured globular cluster system properties derived from wide-field
imaging studies. The coefficients of the best-fitting N_GC-M_SMBH relation for
the early-type galaxies are consistent with those from previous work but in
some cases have smaller relative errors. I examine the correlation between N_GC
and M_SMBH for various subsamples and find that elliptical galaxies show the
strongest correlation while S0 and pseudobulge galaxies exhibit increased
scatter. I also compare the quality of the fit of the numbers of metal-poor
globular clusters versus SMBH mass and the corresponding fit for metal-rich
globular clusters. I supplement the 20-galaxy sample with ten additional
galaxies with reliable N_GC determinations but without measured M_SMBH. I use
this larger sample to investigate correlations between N_GC and host galaxy
properties like total galaxy luminosity and stellar mass and bulge luminosity
and mass. I find that the tightest correlation is between N_GC and total galaxy
stellar mass. This lends support to the notion that N_GC and M_SMBH are not
directly linked but are correlated because both quantities depend on the host
galaxy potential. Finally, I use the N_GC-M_SMBH relation derived from the
20-galaxy sample to calculate predicted M_SMBH values for the ten galaxies with
accurate N_GC measurements but without measured SMBH masses. |
Microlensing in globular clusters: the first confirmed lens: Microlensing observations toward globular clusters could be very useful to
probe their low mass star and brown dwarf content. Using the large set of
microlensing events detected so far toward the Galactic centre we investigated
whether for some of the observed events the lenses are located in the Galactic
globular clusters. Indeed, we found that in four cases some events might be due
to lenses located in the globular clusters themselves. Moreover, we discuss a
microlensing event found in M22. Using the adaptive optics system NACO at ESO
VLT it was possible to identify the lens, which turned out to be a low mass
star of about 0.18 solar masses in the globular cluster M22 itself. | Astronomical bounds on a cosmological model allowing a general
interaction in the dark sector: Non-gravitational interaction between two barotropic dark fluids, namely the
pressureless dust and the dark energy in a spatially flat
Friedmann-Lema\^{i}tre-Robertson-Walker model has been discussed. It is shown
that for the interactions which are linear in terms the energy densities of the
dark components and their first order derivatives, the net energy density is
governed by a second order differential equation with constant coefficients.
Taking a generalized interaction, which includes a number of already known
interactions as special cases, the dynamics of the universe is described for
three types of the dark energy equation of state, namely that of interacting
quintessence, interacting vacuum energy density and interacting phantom. The
models have been constrained using the standard cosmological probes, Supernovae
type Ia data from joint light curve analysis and the observational Hubble
parameter data. Two geometric tests, the cosmographic studies and the $Om$
diagnostic have been invoked so as to ascertain the behaviour of the present
model vis-a-vis the $\Lambda$-cold dark matter model. We further discussed the
interacting scenarios taking into account the thermodynamic considerations. |
The effect of bars on the M-sigma relation: offset, scatter and
residuals correlations: We analyse a set of collisionless disc galaxy simulations to study the
consequences of bar formation and evolution on the M-sigma relation of
supermassive black holes. The redistribution of angular momentum driven by bars
leads to a mass increase within the central region, raising the velocity
dispersion of the bulge, sigma, on average by ~12% and as much as ~20%. If a
disc galaxy with a SMBH satisfying the M-sigma relation forms a bar, and the
SMBH does not grow in the process, then the increase in sigma moves the galaxy
off the M-sigma relation. We explore various effects that can affect this
result including contamination from the disc and anisotropy. The displacement
from the M-sigma relation for individual model barred galaxies correlates with
both M(B)/M(B+D) and beta_phi(B+D) measured within the effective radius of the
bulge. Overall, this process leads to an M-sigma for barred galaxies offset
from that of unbarred galaxies, as well as an increase in its scatter. We
assemble samples of unbarred and barred galaxies with classical bulges and find
tentative hints of an offset between the two consistent with the predicted.
Including all barred galaxies, rather than just those with a classical bulge,
leads to a significantly larger offset. | The effect of the recoil energy window on the results of direct dark
matter experiments: The effect of the chosen analysis energy window on the results of a dark
matter experiment is exemplified by the curious intersection of the exclusion
plots of the XENON10 and the CDMS experiments. After proving that the narrow
energy window XENON10 chose to analyze is indeed the cause of such
intersection, a method to determine the high-energy extreme of the recoil
energy window an experiment should use is obtained. |
A brief Review of the Scalar Field Dark Matter model: In the last time the cold dark matter (CDM) model has suggested more and more
that it is not able to describe all the properties of nearby galaxies that can
be observed in great detail as well as that it has some problems in the
mechanism by which matter is more rapidly gathered into large-scale structure
such as galaxies and clusters of galaxies. In this work we revisit an
alternative model, the scalar field dark matter (SFDM) model, which proposes
that the galactic haloes form by condensation of a scalar field (SF) very early
in the Universe, i.e., in this model the haloes of galaxies are astronomical
Bose-Einstein Condensate drops of SF. On the other hand, large-scale structures
like clusters or superclusters of galaxies form similar to the $\Lambda$CDM
model, by hierarchy, thus all the predictions of the $\Lambda$CDM model at
cosmological scales are reproduced by SFDM. This model predicts that all galaxy
haloes must be very similar and exist for higher redshifts than in the
$\Lambda$CDM model. In the first part of this review we revisit the
cosmological evolution of SFDM model with a scalar potential
$m^2\Phi^2/2+\lambda\Phi^4/4$ with two different frameworks: the field and
fluid approach. The scalar fluctuations have an oscillating growing mode and
therefore, this kind of dark matter could lead to the early formation of
gravitational structures in the Universe. In the last part, we study the core
central density profiles of BEC dark matter haloes and fit high-resolution
rotation curves of low surface brightness galaxies. The mean value of the
logarithmic inner density slopes is $\alpha = - $0.27 $\pm$ 0.18 and we show
that the recent observation of the constant dark matter central surface density
can be reproduced. We conclude that in light of the difficulties that the
$\Lambda$CDM model is currently facing the SFDM model can be a worthy
alternative to keep exploring further. | The Physical Properties of the Cosmic Acceleration: The observed late-time acceleration of the cosmic expansion constitutes a
fundamental problem in modern theoretical physics and cosmology. In an attempt
to weight the validity of a large number of dark energy models, I use the
recent measurements of the expansion rate of the Universe, the clustering of
galaxies the CMB fluctuations as well as the large scale structure formation,
to put tight constraints on the different models. |
A closer look at CMB constraints on WIMP dark matter: We use Cosmic Microwave Background data from the WMAP, SPT, BICEP, and QUaD
experiments to obtain constraints on the dark matter particle mass $m_\chi$,
and show that the combined data requires $m_\chi > 7.6$ GeV at the 95%
confidence level for the $\chi \chi \rightarrow b \bar b$ channel assuming
$s-$wave annihilation and a thermal cross section $<\sigma_{\rm a} v> = 3
\times 10^{-26}$ cm$^3/$s. We examine whether the bound on $m_\chi$ is
sensitive to $\sigma_8$ measurements made by galaxy cluster observations. The
large uncertainty in $\sigma_8$ and the degeneracy with $\Omega_{\rm m}$ allow
only small improvements in the dark matter mass bound. Increasing the number of
effective neutrino-like degrees of freedom to $N_{\rm eff} = 3.85$ improves the
mass bound to $m_\chi > 8.6$ GeV at 95% confidence, for the $\chi \chi
\rightarrow b \bar b$ channel. We also study models in which dark matter halos
at $z<60$ reionize the Universe. We compute the Ostriker-Vishniac power
resulting from partial reionization at intermediate redshifts $10<z<60$, but
find the effect to be small. We discuss the importance of the large angle
polarization as a complementary probe of dark matter annihilation. By
performing Monte Carlo simulations, we show that future experiments that
measure the $EE$ power spectrum from $20 < l < 50$ can exclude $m_\chi \sim$ 10
GeV at the 2 (3) $\sigma$ level provided the error bars are smaller than 4 (3)
$\times$ cosmic variance. We show that the Planck experiment will significantly
improve our knowledge of dark matter properties. | Simulated Effects of 1/f Noise on an SKA Intensity Mapping Survey: It has been proposed recently that the SKA1-MID could be used to conduct an
HI intensity mapping survey that could rival upcoming Stage IV dark energy
surveys. However, measuring the weak HI signal is expected to be very
challenging due to contaminations such as residual Galactic emission, RFI, and
instrumental 1/f noise. Modelling the effects of these contaminants on the
cosmological HI signal requires numerical end-to-end simulations. Here we
present how 1/f noise within the receiver can double the effective uncertainty
of an SKA-like survey to HI on large angular scales (l < 50). |
The Extended Chandra Deep Field-South Survey: Optical spectroscopy of
faint X-ray sources with the VLT and Keck: We present the results of a program to acquire high-quality optical spectra
of X-ray sources detected in the E-CDF-S and its central area. New
spectroscopic redshifts are measured for 283 counterparts to Chandra sources
with deep exposures (t~2-9 hr per pointing) using multi-slit facilities on both
the VLT and Keck thus bringing the total number of spectroscopically-identified
X-ray sources to over 500 in this survey field. We provide a comprehensive
catalog of X-ray sources detected in the E-CDF-S including the optical and
near-infrared counterparts, and redshifts (both spectroscopic and photometric)
that incorporate published spectroscopic catalogs thus resulting in a final
sample with a high fraction (80%) of X-ray sources having secure
identifications. We demonstrate the remarkable coverage of the Lx-z plane now
accessible from our data while emphasizing the detection of AGNs that
contribute to the faint end of the luminosity function at 1.5<z<3. Our redshift
catalog includes 17 type 2 QSOs that significantly increases such samples (2x).
With our deepest VIMOS observation, we identify "elusive" optically-faint
galaxies (R~25) at z~2-3 based upon the detection of interstellar absorption
lines; we highlight one such case, an absorption-line galaxy at z=3.208 having
no obvious signs of an AGN in its optical spectrum. In addition, we determine
distances to eight galaxy groups with extended X-ray emission. Finally, we
measure the physical extent of known large-scale structures (z~0.7) evident in
the CDF-S. While a thick sheet (radial size of 67.7 Mpc) at z~0.67 extends over
the full field, the z~0.73 structure is thin (18.8 Mpc) and filamentary as
traced by both AGNs and galaxy groups. In the appendix, we provide
spectroscopic redshifts for 49 counterparts to fainter X-ray sources detected
only in the 1 and 2 Ms catalogs, and 48 VLA radio sources not detected in
X-rays. | On the equation-of-motion versus in-in approach in cosmological
perturbation theory: In this paper, we study several issues in the linear equation-of-motion (EoM)
and in-in approaches of computing the two-point correlation functions in
multi-field inflation. We prove the equivalence between this EoM approach and
the first-principle in-in formalism. We check this equivalence using several
explicit examples, including cases with scale-invariant corrections and
scale-dependent features. Motivated by the explicit proof, we show that the
usual procedures in these approaches can be extended and applied to some
interesting model categories beyond what has been studied in the literature so
far. These include the density perturbations with strong couplings and
correlated multi-field initial states. |
First constraints on Helium $^{+}{\rm He}^3$ evolution in $z=3-4$ using
the 8.67GHz hyperfine transition: We present the first constraints on the cross-correlation power spectrum of
HeII ($^{+}{\rm He}^3$) signal strength using the redshifted 8.67GHz hyperfine
transition between $z=2.9$ and $z=4.1$ and with interferometric data obtained
from the public archive of the Australia Telescope Compact Array. 210 hours of
observations of the primary calibrator source B1934-638 were extracted from
data obtained with the telescope from 2014--2021, and coherently combined in a
power spectrum pipeline to measure the HeII power across a range of spatial
scales, and at three redshifts that span the period of Helium reionization. Our
best limit places the brightness temperature fluctuation to be less than
557$\mu$K on spatial scales of 30 arcmin at $z=2.91$, and less than 755$\mu$K
on scales of 30 arcmin at $z=4.14$ (2-sigma noise-limited). We measure a
temperature of 489$\mu$K at $z=2.91$. ATCA's few antennas and persistent
remaining RFI in the data prevent deeper integrations improving the results.
This work is a proof of principle to demonstrate how this type of experiment
can be undertaken to reach the 0.01--1$\mu$K level expected for the Helium
signal at $z \sim 4$. | Soft X-ray and ultra-violet metal-line emission from the gas around
galaxies: (Abridged) A large fraction of the gas in galactic haloes has temperatures
between 10^4.5 and 10^7 K. At these temperatures, cooling is dominated by
metal-line emission if the metallicity Z>~0.1 Zsun. We explore the
detectability of several lines using large cosmological, hydrodynamical
simulations. We stack surface brightness maps centred on galaxies to calculate
the expected mean surface brightness profiles for different halo masses.
Assuming a detection limit of 10^-1 photon s^-1 cm^-2 sr^-1, proposed X-ray
telescopes can detect O VIII emission from z=0.125 out to 80% of the virial
radius (Rvir) of groups and clusters and out to 0.4Rvir for haloes with masses
Mhalo=10^12-13 Msun. Emission lines from C VI, N VII, O VII, and Ne X can be
detected out to smaller radii, 0.1-0.5Rvir. With a detection limit of 10^-20
erg s^-1 cm^-2 arcsec^-2, future UV telescopes can detect C III emission out to
0.2-0.6Rvir at z=0.25. C IV, O VI, Si III, and Si IV can be seen out to
0.1-0.2Rvir for Mhalo>10^12 Msun. Optical HI H-alpha emission is comparable in
strength to C III emission. At z=3 it may be possible to observe C III out to
0.2-0.3Rvir and other rest-frame UV lines out to ~0.1Rvir for Mhalo>10^11 Msun
with upcoming optical instruments. Metal-line emission is typically biased
towards high density and metallicity and towards the temperature at which the
emissivity curve of the corresponding metal line peaks. The bias is similar for
the different soft X-ray lines considered, whereas it varies strongly between
different UV lines. Active galactic nucleus (AGN) feedback can change the inner
surface brightness profiles significantly, but it generally does not change the
radius out to which the emission can be observed. Metal-line emission is a
promising probe of the warm and hot, enriched gas around galaxies and provides
a unique window into the interactions between galaxies and their gaseous
haloes. |
On the Constraints on Superconducting Cosmic Strings from 21-cm
Cosmology: Constraints on the potential properties of superconducting cosmic strings
provide an indirect probe of physics beyond the standard model at energies
inaccessible to terrestrial particle colliders. In this study, we perform the
first joint Bayesian analysis to extract constraints on superconducting cosmic
strings from current 21-cm signal measurements while accounting rigorously for
the uncertainties in foregrounds and high redshift astrophysics. We include the
latest publicly available 21-cm power spectrum upper limits from HERA, 21-cm
global signal data from SARAS 3, and the synergistic probe of the unresolved
X-ray background in our final analysis. This paper thus constitutes the first
attempt to use 21-cm power spectrum data to probe cosmic strings. In contrast
to previous works, we find no strong constraints can be placed on
superconducting cosmic strings from current 21-cm measurements. This is because
of uncertainties in the X-ray emission efficiency of the first galaxies, with
X-ray emissivities greater than $3 \times 10^{40}$erg s$^{-1}$ M$_{\odot}^{-1}$
yr able to mask the presence of cosmic strings in the 21-cm signal. We conclude
by discussing the prospects for future constraints from definitive 21-cm signal
measurements and argue that the recently proposed soft photon heating should be
cause for optimism due to its potential to break degeneracies that would have
otherwise made the signatures of cosmic strings difficult to distinguish from
those of astrophysical origin. | Graduated dark energy: Observational hints of a spontaneous sign switch
in the cosmological constant: We study the cosmological constant ($\Lambda$) in the standard $\Lambda$CDM
model by introducing the \textit{graduated dark energy} (gDE) characterised by
a minimal dynamical deviation from the null inertial mass density of the
$\Lambda$ in the form $\rho_{\rm inert}\propto \rho^{\lambda}<0$ with
$\lambda<1$ being a ratio of two odd integers, for which its energy density
$\rho$ dynamically takes negative values in the finite past. For large negative
values of $\lambda$, it creates a phenomenological model described by a smooth
function that approximately describes the $\Lambda$ spontaneously switching
sign in the late universe to become positive today. We confront the model with
the latest combined observational data sets of PLK+BAO+SN+$H$. It is striking
that the data predict bimodal posterior probability distributions for the
parameters of the model along with large negative $\lambda$ values; the new
maximum significantly excludes the $\Lambda$, and the old maximum contains the
$\Lambda$. The improvement in the goodness of fit for the $\Lambda$ reaches
highly significant levels, $\Delta\chi_{\rm min}^2=6.4$ for the new maxima,
while it remains at insignificant levels, $\Delta\chi_{\rm min}^2\lesssim0.02$,
for the old maxima. We show that, in contrast to the old maxima, which do not
distinguish from the $\Lambda$, the new maxima agree with the model-independent
$H_0$ measurements, high-precision Ly-$\alpha$ data, and model-independent
$Omh^2$ diagnostic estimates. Our results provide strong hints of a spontaneous
sign switch in the cosmological constant and lead us to conjecture that the
universe has transitioned from AdS vacua to dS vacua, at a redshift $z\approx
2.32$ and triggered the late-time acceleration, and suggests looking for such
mechanisms in string theory constructions. |
Search for bosonic superweakly interacting massive dark matter particles
with the XMASS-I detector: Bosonic superweakly interacting massive particles (super-WIMPs) are a
candidate for warm dark matter. With the absorption of such a boson by a xenon
atom these dark matter candidates would deposit an energy equivalent to their
rest mass in the detector. This is the first direct detection experiment
exploring the vector super-WIMPs in the mass range between 40 and 120 keV.
Using 165.9 days of data no significant excess above background was observed in
the fiducial mass of 41 kg. The present limit for the vector super-WIMPs
excludes the possibility that such particles constitute all of dark matter. The
absence of a signal also provides the most stringent direct constraint on the
coupling constant of pseudoscalar super-WIMPs to electrons. The unprecedented
sensitivity was achieved exploiting the low background at a level $10^{-4}$
kg$^{-1}$keV$_{ee}^{-1}$day$^{-1}$ in the detector. | An overview of the completed Canada-France-Hawaii Telescope Lensing
Survey (CFHTLenS): The Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) represents the most
powerful weak lensing survey carried out to date. The CFHTLenS
(Canada-France-Hawaii Telescope Lensing Survey) team was formed in 2008 to
analyse the data from the CFHTLS focussing on a rigorous treatment of
systematic effects in shape measurements and photometric redshifts. Here we
review the technical challenges that we faced in analysing these data and their
solutions which set the current standard for weak lensing analyses. We also
present some science highlights that were made possible by this effort
including cosmic shear tomography, tests for modified gravity models, and the
mapping of dark matter structures over unprecedentedly large scales. An outlook
is given on current and future surveys that are analysed with the tools
prepared for CFHTLenS. CFHTLenS represents the first and only weak lensing data
set that has been made publicly available so far. We encourage other surveys to
follow this example. |
Dark energy-dark matter interactions as a solution to the $S_8$ tension: In this work we consider a scenario where the dark energy is a dynamical
fluid whose energy density can be transferred to the dark matter via a coupling
function proportional to the energy density of the dark energy. In particular,
we investigate this model's ability to address the $S_8$ tension and find that
against data from Planck, BAO and Pantheon the model 1) can significantly
reduce the significance of the tension, 2) does so without exacerbating nor
introducing any other tension (such as the $H_0$ tension) and 3) without
worsening the fit to the considered data sets with respect to the $\Lambda$CDM
model. We also test the model against data from weak lensing surveys such as
KiDS and DES, and find that the model's ability to address the $S_8$ tension
further improves, without a significant impact on any other parameter nor
statistical measure. | Physical properties of blazar jets from VLBI observations: (abridged) Relativistic jets, formed in the vicinity of central supermassive
black holes in AGN, show ample evidence connecting them to physical conditions
in the accretion disc and broad-line region. The jets are responsible for a
large fraction of non-thermal continuum emission (particularly during powerful
flares), which makes understanding their physics an important aspect of studies
of blazars characterised by profound flaring activity arising from extremely
compact regions. Imaging and polarimetry of radio emission on milliarcsecond
scales provided by very long baseline interferometry (VLBI) offers a range of
possibilities for studying ultra-compact regions in relativistic jets and
relating them to main manifestations of the blazar activity in AGN.
Simultaneous monitoring of optical/high energy variability and evolution of
parsec-scale radio structures yields arguably the most detailed picture of the
relation between acceleration and propagation of relativistic flows and
non-thermal continuum generation in blazars. These effects are reviewed and
discussed in the context of deriving accurate and self-consistent models for
central regions of blazars. |
Applying scale-free mass estimators to the Local Group in Constrained
Local Universe Simulations: We use the recently proposed scale-free mass estimators to determine the
masses of the Milky Way (MW) and Andromeda (M31) galaxy in a dark matter only
Constrained Local UniversE Simulation (CLUES). While these mass estimators work
rather well for isolated spherical host systems, we examine here their
applicability to a simulated binary system with a unique satellite population
similar to the observed satellites of MW and M31. We confirm that the
scale-free estimators work also very well in our simulated Local Group galaxies
with the right number of satellites which follow the observed radial
distribution. In the isotropic case and under the assumption that the
satellites are tracking the total gravitating mass, the power-law index of the
radial satellite distribution $N(<r)\propto r^{3-\gamma}$ is directly related
to the host's mass profile $M(<r)\propto r^{1-\alpha}$ as $\alpha=\gamma-2$.
The use of this relation for any given $\gamma$ leads to highly accurate mass
estimations which is a crucial point for observer, since they do not know a
priori the mass profile of the MW and M31 haloes. We discuss possible bias in
the mass estimators and conclude that the scale-free mass estimators can be
satisfactorily applied to the real MW and M31 system. | The Synthetic Emission Line COSMOS catalog: H$α$ and [OII] galaxy
luminosity functions and counts at $0.3<z<2.5$: Star-forming galaxies with strong nebular and collisional emission lines are
privileged target galaxies in forthcoming cosmological large galaxy redshift
surveys. We use the COSMOS2015 photometric catalog to model galaxy spectral
energy distributions and emission-line fluxes. We adopt an empirical but
physically-motivated model that uses information from the best-fitting spectral
energy distribution of stellar continuum to each galaxy. The emission-line flux
model is calibrated and validated against direct flux measurements in subsets
of galaxies that have 3D-HST or zCOSMOS-Bright spectra. We take a particular
care in modelling dust attenuation such that our model can explain both
H$\alpha$ and [OII] observed fluxes at different redshifts. We find that a
simple solution to this is to introduce a redshift evolution in the dust
attenuation fraction parameter, $f=E_{\rm star}(B-V)/E_{\rm gas}(B-V)$, as
$f(z)=0.44+0.2z$. From this catalog, we derive the H$\alpha$ and [OII]
luminosity functions up to redshifts of about 2.5 after carefully accounting
for emission line flux and redshift errors. This allows us to make predictions
for H$\alpha$ and [OII] galaxy number counts in next-generation cosmological
redshift surveys. Our modeled emission lines and spectra in the COSMOS2015
catalog shall be useful to study the target selection for planned
next-generation galaxy redshift surveys and we make them publicly available as
`EL-COSMOS' on the ASPIC database. |
Photo-z outlier self-calibration in weak lensing surveys: Calibrating photometric redshift errors in weak lensing surveys with external
data is extremely challenging. We show that both Gaussian and outlier photo-z
parameters can be self-calibrated from the data alone. This comes at no cost
for the neutrino masses, curvature and dark energy equation of state $w_0$, but
with a 65% degradation when both $w_0$ and $w_a$ are varied. We perform a
realistic forecast for the Vera Rubin Observatory (VRO) Legacy Survey of Space
and Time (LSST) 3x2 analysis, combining cosmic shear, projected galaxy
clustering and galaxy - galaxy lensing. We confirm the importance of
marginalizing over photo-z outliers. We examine a subset of internal
cross-correlations, dubbed "null correlations", which are usually ignored in
3x2 analyses. Despite contributing only $\sim$ 10% of the total
signal-to-noise, these null correlations improve the constraints on photo-z
parameters by up to an order of magnitude. Using the same galaxy sample as
sources and lenses dramatically improves the photo-z uncertainties too.
Together, these methods add robustness to any claim of detected new Physics,
and reduce the statistical errors on cosmology by 15% and 10% respectively.
Finally, including CMB lensing from an experiment like Simons Observatory or
CMB-S4 improves the cosmological and photo-z posterior constraints by about
10%, and further improves the robustness to systematics. To give intuition on
the Fisher forecasts, we examine in detail several toy models that explain the
origin of the photo-z self-calibration. Our Fisher code LaSSI (Large-Scale
Structure Information), which includes the effect of Gaussian and outlier
photo-z, shear multiplicative bias, linear galaxy bias, and extensions to
$\Lambda$CDM, is publicly available at https://github.com/EmmanuelSchaan/LaSSI . | Tension with the flat ΛCDM model from a high redshift Hubble
Diagram of supernovae, quasars and gamma-ray bursts: In the current framework, the standard parametrization of our Universe is the
so-called Lambda Cold Dark Matter ({\Lambda}CDM) model. Recently, Risaliti &
Lusso (2019) have shown a ~4{\sigma} tension with the {\Lambda}CDM model
through a model-independent parametrization of a Hubble Diagram of supernovae
Ia (SNe Ia) from the JLA survey and quasars. Model-independent approaches and
independent samples over a wide redshift range are key to testing this tension
and any possible systematics. Here we present an analysis of a combined Hubble
Diagram of SNe Ia, quasars, and gamma-ray bursts (GRBs) to check the agreement
of the quasar and GRB cosmological parameters at high redshifts (z>2) and to
test the concordance flat {\Lambda}CDM model with improved statistical
accuracy. We build a Hubble diagram with SNe Ia from the Pantheon sample
(Scolnic et al. 2018), quasars from the Risaliti & Lusso (2019) sample, and
GRBs from the Demianski et al. (2017a) sample, where quasars are standardised
through the observed non-linear relation between their ultraviolet and X-ray
emission and GRBs through the correlation between the spectral peak energy and
the isotropic-equivalent radiated energy (the so-called "Amati relation"). We
fit the data with cosmographic models consisting of a fourth-order logarithmic
polynomial and a fifth-order linear polynomial, and compare the results with
the expectations from a flat {\Lambda}CDM model. We confirm the tension between
the best fit cosmographic parameters and the {\Lambda}CDM model at ~4{\sigma}
with SNe Ia and quasars, at ~2{\sigma} with SNe Ia and GRBs, and at >4{\sigma}
with the whole SNe Ia+quasars+GRB data set. The completely independent
high-redshift Hubble diagrams of quasars and GRBs are fully consistent with
each other, strongly suggesting that the deviation from the standard model is
not due to unknown systematic effects but to new physics. |
The Atacama Cosmology Telescope: Two-Season ACTPol Lensing Power
Spectrum: We report a measurement of the power spectrum of cosmic microwave background
(CMB) lensing from two seasons of Atacama Cosmology Telescope Polarimeter
(ACTPol) CMB data. The CMB lensing power spectrum is extracted from both
temperature and polarization data using quadratic estimators. We obtain results
that are consistent with the expectation from the best-fit Planck LCDM model
over a range of multipoles L=80-2100, with an amplitude of lensing A_lens =
1.06 +/- 0.15 (stat.) +/- 0.06 (sys.) relative to Planck. Our measurement of
the CMB lensing power spectrum gives sigma_8 Omega_m^0.25 = 0.643 +/- 0.054;
including baryon acoustic oscillation scale data, we constrain the amplitude of
density fluctuations to be sigma_8 = 0.831 +/- 0.053. We also update
constraints on the neutrino mass sum. We verify our lensing measurement with a
number of null tests and systematic checks, finding no evidence of significant
systematic errors. This measurement relies on a small fraction of the ACTPol
data already taken; more precise lensing results can therefore be expected from
the full ACTPol dataset. | Star Formation Timescales and the Schmidt Law: We offer a simple parameterization of the rate of star formation in galaxies.
In this new approach, we make explicit and decouple the timescales associated
(a) with disruptive effects the star formation event itself, from (b) the
timescales associated with the cloud assembly and collapse mechanisms leading
up to star formation. The star formation law in near-by galaxies, as measured
on sub-kiloparsec scales, has recently been shown by Bigiel et al. to be
distinctly non-linear in its dependence on total gas density. Our
parameterization of the spatially resolved Schmidt-Sanduleak relation naturally
accommodates that dependence. The parameterized form of the relation is rho_* ~
epsilon x rho_g/(tau_s + rho_g ^{-n}), where rho_g is the gas density, epsilon
is the efficiency of converting gas into stars, and rho_g^{-n} captures the
physics of cloud collapse. Accordingly at high gas densities quiescent star
formation is predicted to progress as rho_* ~ rho_g, while at low gas densities
rho_* ~ rho_g^{1+n}, as is now generally observed. A variable efficiency in
locally converting gas into stars as well as the unknown plane thickness
variations from galaxy to galaxy, and radially within a given galaxy, can
readily account for the empirical scatter in the observed (surface density
rather than volume density) relations, and also plausibly account for the noted
upturn in the relation at very high apparent projected column densities. |
Vainshtein mechanism after GW170817: The almost simultaneous detection of gravitational waves and a short
gamma-ray burst from a neutron star merger has put a tight constraint on the
difference between the speed of gravity and light. In the four-dimensional
scalar-tensor theory with second order equations of motion, the Horndeski
theory, this translates into a significant reduction of the viable parameter
space of the theory. Recently, extensions of Horndeski theory, which are free
from Ostrogradsky ghosts despite the presence of higher order derivatives in
the equations of motion, have been identified and classified exploiting the
degeneracy criterium. In these new theories, the fifth force mediated by the
scalar field must be suppressed in order to evade the stringent Solar System
constraints. We study the Vainshtein mechanism in the most general degenerate
higher order scalar-tensor theory in which light and gravity propagate at the
same speed. We find that the Vainshtein mechanism generally works outside a
matter source but it is broken inside matter, similarly to beyond Horndeski
theories. This leaves interesting possibilities to test these theories that are
compatible with gravitational wave observations using astrophysical objects. | Another coincidence problem for $Λ$CDM?: Over the last nine years of cosmic microwave background observations, the
Wilkinson Microwave Anisotropy Probe ($WMAP$) results were consistent with a
$\Lambda$CDM cosmological model in which the age of the Universe is one Hubble
time, and the time-averaged value of the deceleration parameter is consistent
with zero. This curious observation has been put forward as a new coincidence
problem for the $\Lambda$CDM concordance cosmology, which is in fact a
`greater' coincidence than the near equality of the density parameters of
matter and the cosmological constant. At the moment of writing these conference
proceedings, the Planck Collaboration has released its first cosmological data,
which revealed a small shift in the $\Lambda$CDM cosmological parameters when
compared to $WMAP$. We show that under the assumption of a spatially flat
$\Lambda$CDM cosmology, Planck's results remove this coincidence problem for
$\Lambda$CDM at greater than 99\% confidence level. |
Total to central luminosity ratios of quiescent galaxies in MODS as an
indicator of size evolution: Using the very deep Subaru images of the GOODS-N region, from the MOIRCS Deep
Survey and images from the HST/ACS, we have measured the Luminosity Ratio (LR)
of the outer to the central regions of massive (M>10^{10.5}M_{Sun}) galaxies at
fixed radii in a single rest-frame for z<3.5 as a new approach to the problem
of size evolution. We didn't observe any evolution in the median LR. Had a
significant size growth occurred, the outer to central luminosity ratios would
have demonstrated a corresponding increase with a decrease in redshift. | Non-parametric spatial curvature inference using late-universe
cosmological probes: Inferring high-fidelity constraints on the spatial curvature parameter,
$\Omega_{\rm K}$, under as few assumptions as possible, is of fundamental
importance in cosmology. We propose a method to non-parametrically infer
$\Omega_{\rm K}$ from late-Universe probes alone. Using Gaussian Processes (GP)
to reconstruct the expansion history, we combine Cosmic Chronometers (CC) and
Type Ia Supernovae (SNe~Ia) data to infer constraints on curvature,
marginalized over the expansion history, calibration of the CC and SNe~Ia data,
and the GP hyper-parameters. The obtained constraints on $\Omega_{\rm K}$ are
free from parametric model assumptions for the expansion history, and are
insensitive to the overall calibration of both the CC and SNe~Ia data (being
sensitive only to relative distances and expansion rates). Applying this method
to \textit{Pantheon} SNe~Ia and the latest compilation of CCs, we find
$\Omega_{\rm K} = -0.03 \pm 0.26$, consistent with spatial flatness at the
$\mathcal{O}(10^{-1})$ level, and independent of any early-Universe probes.
Applying our methodology to future Baryon Acoustic Oscillations and SNe~Ia data
from upcoming Stage IV surveys, we forecast the ability to constrain
$\Omega_{\rm K}$ at the $\mathcal{O}(10^{-2})$ level. |
Gravitational lensing in the Supernova Legacy Survey (SNLS): The observed brightness of Type Ia supernovae is affected by gravitational
lensing caused by the mass distribution along the line of sight, which
introduces an additional dispersion into the Hubble diagram. We look for
evidence of lensing in the SuperNova Legacy Survey 3-year data set. We
investigate the correlation between the residuals from the Hubble diagram and
the gravitational magnification based on a modeling of the mass distribution of
foreground galaxies. A deep photometric catalog, photometric redshifts, and
well established mass luminosity relations are used. We find evidence of a
lensing signal with a 2.3 sigma significance. The current result is limited by
the number of SNe, their redshift distribution, and the other sources of
scatter in the Hubble diagram. Separating the galaxy population into a red and
a blue sample has a positive impact on the significance of the signal
detection. On the other hand, increasing the depth of the galaxy catalog, the
precision of photometric redshifts or reducing the scatter in the mass
luminosity relations have little effect. We show that for the full SuperNova
Legacy Survey sample (~400 spectroscopically confirmed Type Ia SNe and ~200
photometrically identified Type Ia SNe), there is an 80% probability of
detecting the lensing signal with a 3 sigma significance. | Redshift inference from the combination of galaxy colors and clustering
in a hierarchical Bayesian model $-$ Application to realistic $N$-body
simulations: Photometric galaxy surveys constitute a powerful cosmological probe but rely
on the accurate characterization of their redshift distributions using only
broadband imaging, and can be very sensitive to incomplete or biased priors
used for redshift calibration. S\'anchez & Bernstein (2019) presented a
hierarchical Bayesian model which estimates those from the robust combination
of prior information, photometry of single galaxies and the information
contained in the galaxy clustering against a well-characterized tracer
population. In this work, we extend the method so that it can be applied to
real data, developing some necessary new extensions to it, especially in the
treatment of galaxy clustering information, and we test it on realistic
simulations. After marginalizing over the mapping between the clustering
estimator and the actual density distribution of the sample galaxies, and using
prior information from a small patch of the survey, we find the incorporation
of clustering information with photo-$z$'s to tighten the redshift posteriors,
and to overcome biases in the prior that mimic those happening in spectroscopic
samples. The method presented here uses all the information at hand to reduce
prior biases and incompleteness. Even in cases where we artificially bias the
spectroscopic sample to induce a shift in mean redshift of $\Delta \bar z
\approx 0.05,$ the final biases in the posterior are $\Delta \bar z
\lesssim0.003.$ This robustness to flaws in the redshift prior or training
samples would constitute a milestone for the control of redshift systematic
uncertainties in future weak lensing analyses. |
Detection of diffuse radio emission in the galaxy clusters A800, A910,
A1550, and CL1446+26: Radio halos are elusive sources located at the center of merging galaxy
clusters. To date, only about 40 radio halos are known, thus the discovery of
new halos provide important insights on this class of sources. To improve the
statistics of radio halos, we investigated the radio continuum emission in a
sample of galaxy clusters. We analyzed archival Very Large Array observations
at 1.4 GHz, with a resolution of about 1 arcmin. These observations
complemented by X-ray, optical, and higher resolution radio data allowed to
detect a new radio halo in the central region of A800 and A1550. We discovered
a radio relic in the periphery of A910, and finally we revealed both a halo and
a relic in CL1446+26.Clusters hosting these new halos show an offset between
the radio and the X-ray peak. By analyzing this offset statistically we found
that radio halos can be quite asymmetric with respect to the X-ray gas
distribution, with an average radio - X-ray displacement of about 180 kpc. When
the offsets are normalized by the halo size, there is a tendency for smaller
halos to show larger displacements. | Statistical isotropy violation in WMAP CMB maps resulting from
non-circular beams: Statistical isotropy (SI) of Cosmic Microwave Background (CMB) fluctuations
is a key observational test to validate the cosmological principle underlying
the standard model of cosmology. While a detection of SI violation would have
immense cosmological ramification, it is important to recognise their possible
origin in systematic effects of observations. WMAP seven year (WMAP-7) release
claimed significant deviation from SI in the bipolar spherical harmonic
(BipoSH) coefficients $A_{ll}^{20}$ and $A_{l-2l}^{20}$. Here we present the
first explicit reproduction of the measurements reported in WMAP-7, confirming
that beam systematics alone can completely account for the measured SI
violation. The possibility of such a systematic origin was alluded to in WMAP-7
paper itself and other authors but not as explicitly so as to account for it
accurately. We simulate CMB maps using the actual WMAP non-circular beams and
scanning strategy. Our estimated BipoSH spectra from these maps match the
WMAP-7 results very well. It is also evident that only a very careful and
adequately detailed modelling, as carried out here, can conclusively establish
that the entire signal arises from non-circular beam effect. This is important
since cosmic SI violation signals are expected to be subtle and dismissing a
large SI violation signal as observational artefact based on simplistic
plausibility arguments run the serious risk of "throwing the baby out with the
bathwater". |
Perturbation Theory for BAO reconstructed fields: one-loop results in
real-space matter density field: We compute the power spectrum at one-loop order in standard perturbation
theory for the matter density field to which a standard Lagrangian Baryonic
acoustic oscillation (BAO) reconstruction technique is applied. The BAO
reconstruction method corrects the bulk motion associated with the
gravitational evolution using the inverse Zel'dovich approximation (ZA) for the
smoothed density field. We find that the overall amplitude of one-loop
contributions in the matter power spectrum substantially decrease after
reconstruction. The reconstructed power spectrum thereby approaches the initial
linear spectrum when the smoothed density field is close enough to linear,
i.e., the smoothing scale $R_s$ larger than around 10$h^{-1}$Mpc. On smaller
$R_s$,however, the deviation from the linear spectrum becomes significant on
large scales ($k\lt R_s^{-1}$) due to the nonlinearity in the smoothed density
field, and the reconstruction is inaccurate. Compared with N-body simulations,
we show that the reconstructed power spectrum at one loop order agrees with
simulations better than the unreconstructed power spectrum. We also calculate
the tree-level bispectrum in standard perturbation theory to investigate
non-Gaussianity in the reconstructed matter density field. We show that the
amplitude of the bispectrum significantly decreases for small $k$ after
reconstruction and that the tree-level bispectrum agrees well with N-body
results in the weakly nonlinear regime. | Constraining H0 Via Extragalactic Parallax: We examine the prospects for measurement of the Hubble parameter $H_0$ via
observation of the secular parallax of other galaxies due to our own motion
relative to the cosmic microwave background rest frame. Peculiar velocities
make distance measurements to individual galaxies highly uncertain, but a
survey sampling many galaxies can still yield a precise $H_0$ measurement. We
use both a Fisher information formalism and simulations to forecast errors in
$H_0$ from such surveys, marginalizing over the unknown peculiar velocities.
The optimum survey observes $\sim 10^2$ galaxies within a redshift
$z_\mathrm{max}=0.06$. The required errors on proper motion are comparable to
those that can be achieved by Gaia and future astrometric instruments. A
measurement of $H_0$ via parallax has the potential to shed light on the
tension between different measurements of $H_0$. |
Hidden Negative Energies in Strongly Accelerated Universes: We point out that theories of cosmological acceleration which have equation
of state, w, such that 1+w is small but positive may still secretly violate the
null energy condition. This violation implies the existence of observers for
whom the background has infinitely negative energy densities, despite the fact
that the perturbations are free of ghosts and gradient instabilities. | The axis ratio distribution of X-ray clusters observed by XMM-Newton: We derive the axis ratio distribution of X-ray clusters using the XMM-Newton
catalogue (Snowden et al. 2008). By fitting the contour lines of the X-ray
image by ellipses, we confirm the X-ray distribution is well approximated by
the elliptic distribution with a constant axis ratio and direction. We
construct a simple model describing the axis ratio of the X-ray gas assuming
the hydrostatic equilibrium embedded in the triaxial dark matter halo model
proposed by Jing & Suto (2002) and the hydrostatic equilibrium. We find that
the observed probability density function of the axis ratio is consistent with
this model prediction. |
Ultra-light dark matter in disk galaxies: Analytic arguments and numerical simulations show that bosonic ultra-light
dark matter (ULDM) would form cored density distributions (`solitons') at the
center of galaxies. ULDM solitons offer a promising way to exclude or detect
ULDM by looking for a distinctive feature in the central region of galactic
rotation curves. Baryonic contributions to the gravitational potential pose an
obstacle to such analyses, being (i) dynamically important in the inner galaxy
and (ii) highly non-spherical in rotation-supported galaxies, resulting in
non-spherical solitons. We present an algorithm for finding the ground state
soliton solution in the presence of stationary non-spherical background
baryonic mass distribution. We quantify the impact of baryons on the predicted
ULDM soliton in the Milky Way and in low surface-brightness galaxies from the
SPARC database. | Prospects for constraining interacting dark energy models from
gravitational wave and gamma ray burst joint observation: With the measurement of the electromagnetic (EM) counterpart, a gravitational
wave (GW) event could be treated as a standard siren. As a novel cosmological
probe, GW standard sirens will bring significant implications for cosmology. In
this paper, by considering the coincident detections of GW and associated
$\gamma$ ray burst (GRB), we find that only about 400 GW bright standard sirens
from binary neutron star mergers could be detected in a 10-year observation of
the Einstein Telescope and the THESEUS satellite mission. Based on this mock
sample, we investigate the implications of GW standard sirens on the
interaction between dark energy and dark matter. In our analysis, four viable
interacting dark energy (IDE) models, with interaction forms $Q=3\beta H
\rho_{\mathrm{de}}$ and $Q=3 \beta H \rho_{\mathrm{c}}$, are considered.
Compared with the traditional EM observational data such as CMB, BAO, and SN
Ia, the combination of both GW and EM observations could effectively break the
degeneracies between different cosmological parameters and provide more
stringent cosmological fits. We find that the GW data could play a more
important role for determining the interaction in the models with $Q=3 \beta H
\rho_{\mathrm{c}}$, compared with the models with $Q=3\beta H
\rho_{\mathrm{de}}$. We also show that constraining IDE models with mock GW
data based on different fiducial $H_0$ values yield different results,
indicating that accurate determination of $H_0$ is significant for exploring
the interaction between dark energy and dark matter. |
Collisions of cosmic strings with chiral currents: We present an analytic study of cosmic superconducting chiral string
collisions in Minkowski space, applying the kinematic constraints that arise
from the relevant generalization of the Nambu-Goto action. In particular, we
revisit the solution for chiral superconducting cosmic strings and demonstrate
that Y junction production for such strings is possible. We consider the
collision of chiral current-carrying straight strings and obtain the region in
angle-velocity space that allows the production of string junctions. This study
contributes to the understanding of the complex evolution of chiral
superconducting string networks. | Maximum redshift of gravitational wave merger events: Future generation of gravitational wave detectors will have the sensitivity
to detect gravitational wave events at redshifts far beyond any detectable
electromagnetic sources. We show that if the observed event rate is greater
than one event per year at redshifts z > 40, then the probability distribution
of primordial density fluctuations must be significantly non-Gaussian or the
events originate from primordial black holes. The nature of the excess events
can be determined from the redshift distribution of the merger rate. |
Higher-Order Spectra of Weak Lensing Convergence Maps in Parameterized
Theories of Modified Gravity: We compute the low-$\ell$ limit of the family of higher-order spectra for
projected (2D) weak lensing convergence maps. In this limit, these spectra are
computed to an arbitrary order using {\em tree-level} perturbative
calculations. We use the flat-sky approximation and Eulerian perturbative
results based on a generating function approach. We test these results for the
lower-order members of this family, i.e. the skew- and kurt-spectra against
state-of-the-art simulated all-sky weak lensing convergence maps and find our
results to be in very good agreement. We also show how these spectra can be
computed in the presence of a realistic sky-mask and Gaussian noise. We
generalize these results to three-dimensions (3D) and compute the {\em
equal-time} higher-order spectra. These results will be valuable in analyzing
higher-order statistics from future all-sky weak lensing surveys such as the
{\em Euclid} survey at low-$\ell$ modes. As illustrative examples, we compute
these statistics in the context of the {\em Horndeski} and {\em Beyond
Horndeski} theories of modified gravity. They will be especially useful in
constraining theories such as the Gleyzes-Langlois-Piazza-Vernizzi (GLPV)
theories and Degenerate Higher-Order Scalar-Tensor (DHOST) theories as well as
the commonly used normal-branch of Dvali-Gabadadze-Porrati (nDGP) model,
clustering quintessence models, and scenarios with massive neutrinos. | Studying reionization with the next generation of Ly-alpha emitter
surveys: We study the prospects for constraining the ionized fraction of the
intergalactic medium (IGM) at $z>6$ with the next generation of large
Ly$\alpha$ emitter surveys. We make predictions for the upcoming Subaru Hyper
Suprime-Cam (HSC) Ly$\alpha$ survey and a hypothetical spectroscopic survey
performed with the James Webb Space Telescope (JWST). Considering various
scenarios where the observed evolution of the Ly$\alpha$ luminosity function of
Ly$\alpha$ emitters at $z>6$ is explained partly by an increasingly neutral IGM
and partly by intrinsic galaxy evolution, we show how clustering measurements
will be able to distinguish between these scenarios. We find that the HSC
survey should be able to detect the additional clustering induced by a neutral
IGM if the global IGM neutral fraction is greater than $\sim$20 per cent at
$z=6.5$. If measurements of the Ly$\alpha$ equivalent widths (EWs) are also
available, neutral fractions as small as 10 per cent may be detectable by
looking for correlation between the EW and the local number density of objects.
In this case, if it should turn out that the IGM is significantly neutral at
$z=6.5$ and the intrinsic EW distribution is relatively narrow, the observed
EWs can also be used to construct a map of the locations and approximate sizes
of the largest ionized regions. For the JWST survey, the results appear a bit
less optimistic. Since such surveys probe a large range of redshifts, the
effects of the IGM will be mixed up with any intrinsic galaxy evolution that is
present, making it difficult to disentangle the effects. However, we show that
a survey with the JWST will have a possibility of observing a large group of
galaxies at $z\sim7$, which would be a strong indication of a partially neutral
IGM. |
Complex gas kinematics in compact, rapidly assembling star-forming
galaxies: Deep, high resolution spectroscopic observations have been obtained for six
compact, strongly star-forming galaxies at redshift z~0.1-0.3, most of them
also known as Green Peas. Remarkably, these galaxies show complex emission-line
profiles in the spectral region including H\alpha, [NII]$\lambda\lambda 6548,
6584$ and [SII]$\lambda\lambda 6717, 6731$, consisting of the superposition of
different kinematical components on a spatial extent of few kpc: a very broad
line emission underlying more than one narrower component. For at least two of
the observed galaxies some of these multiple components are resolved spatially
in their 2D-spectra, whereas for another one a faint detached H\alpha\ blob
lacking stellar continuum is detected at the same recessional velocity ~7 kpc
away from the galaxy. The individual narrower H\alpha\ components show high
intrinsic velocity dispersion (\sigma ~30-80 km s$^{-1}$), suggesting together
with unsharped masking HST images that star formation proceeds in an ensemble
of several compact and turbulent clumps, with relative velocities of up to ~500
km s$^{-1}$. The broad underlying H\alpha\ components indicate in all cases
large expansion velocities (full width zero intensity FWZI $\ge$ 1000 km
s$^{-1}$) and very high luminosities (up to ~10$^{42}$ erg s$^{-1}$), probably
showing the imprint of energetic outflows from SNe. These intriguing results
underline the importance of Green Peas for studying the assembly of low-mass
galaxies near and far. | Modeling Intrinsic Galaxy Alignment in the MICE Simulation: The intrinsic alignment (IA) of galaxies is potentially a major limitation in
deriving cosmological constraints from weak lensing surveys. In order to
investigate this effect we assign intrinsic shapes and orientations to galaxies
in the light-cone output of the MICE simulation, spanning $\sim5000\,{\rm
deg}^2$ and reaching redshift $z=1.4$. This assignment is based on a
'semi-analytic' IA model that uses photometric properties of galaxies as well
as the spin and shape of their host halos. Advancing on previous work, we
include more realistic distributions of galaxy shapes and a luminosity
dependent galaxy-halo alignment. The IA model parameters are calibrated against
COSMOS and BOSS LOWZ observations. The null detection of IA in observations of
blue galaxies is accounted for by setting random orientations for these
objects. We compare the two-point alignment statistics measured in the
simulation against predictions from the analytical IA models NLA and TATT over
a wide range of scales, redshifts and luminosities for red and blue galaxies
separately. We find that both models fit the measurements well at scales above
$8\,h^{-1}{\rm Mpc}$, while TATT outperforms NLA at smaller scales. The IA
parameters derived from our fits are in broad agreement with various
observational constraints from red galaxies. Lastly, we build a realistic
source sample, mimicking DES Year 3 observations and use it to predict the IA
contamination to the observed shear statistics. We find this prediction to be
within the measurement uncertainty, which might be a consequence of the random
alignment of blue galaxies in the simulation. |
A Hubble Diagram for Quasars: We present a new method to test the cosmological model, based on the
non-linear relation between ultraviolet and X-ray luminosity of quasars. We
built a data set of ~1,138 quasars by merging several literature samples with
X-ray measurements at 2 keV and SDSS photometry, which was used to estimate the
extinction-corrected 2500 Angstrom flux. We obtained three main results: (1) we
checked the relation between X-ray and UV luminosities in small redshift bins
up to z~6, confirming that it holds at all redshifts with the same slope; (2)
we built a Hubble diagram for quasars up to z~6, which is well matched to that
of supernovae in the common z=0-1.4 interval, and extends the test of the
cosmological model up to z~6; (3) we showed that this relation is a powerful
tool to estimate cosmological parameters. Assuming a LambdaCDM model, we obtain
Omega_M=0.22+0.08-0.10 and Omega_Lambda=0.92+0.18-0.30 (Omega_M=0.28+-0.04 and
Omega_\Lambda=0.73+-0.08 from a joint quasar-SNe fit). However, much more
precise measurements will be achieved in the future. A few thousands SDSS
quasars already have serendipitous X-ray observations with Chandra or
XMM-Newton, and at least 100,000 quasars with UV and X-ray data will be
available from the eROSITA all-sky survey in a few years. Euclid, LSST, and
Athena surveys will further increase the sample size to at least several
hundred thousands. Our simulations show that these samples will provide tight
constraints on the cosmological parameters, and will allow to test possible
deviations from the standard model with higher precisions than available today. | Nonlinear Effects in the Amplitude of Cosmological Density Fluctuations: The amplitude of cosmological density fluctuations, sigma_8, has been studied
and estimated by analysing many cosmological observations. The values of the
estimates vary considerably between the various probes. However, different
estimators probe the value of sigma_8 in different cosmological scales and do
not take into account the nonlinear evolution of the parameter at late times.
We show that estimates of the amplitude of cosmological density fluctuations
derived from cosmic flows are systematically higher than those inferred at
early epochs from the CMB because of nonlinear evolution at later times. We
discuss the past and future evolution of linear and nonlinear perturbations,
derive corrections to the value of sigma_8 and compare amplitudes after
accounting for these differences. |
Galactic Disk Formation and the Angular Momentum Problem: Galactic disk formation requires knowledge about the initial conditions under
which disk galaxies form, the boundary conditions that affect their secular
evolution and the micro-physical processes that drive the multi-phase
interstellar medium and regulate their star formation history. Most of these
ingredients are still poorly understood. Recent high-resolution observations of
young high-redshift disk galaxies provide insight into early phases of galactic
disk formation and evolution. Combined with low-redshift disk data these
observations should eventually allow us to reconstruct the origin and evolution
of late-type galaxies. I summarize some of the major problems that need to be
addressed for a more consistent picture of galactic disk formation and
evolution. | A SINFONI Integral Field Spectroscopy Survey for Galaxy Counterparts to
Damped Lyman-alpha Systems - I. New Detections and Limits for Intervening and
Associated Absorbers: Detailed studies of Damped and sub-Damped Lyman-alpha systems (DLA), the
galaxies probed by the absorption they produce in the spectra of background
quasars, rely on identifying the galaxy responsible for the absorber with more
traditional methods. Integral field spectroscopy provides an efficient way of
detecting faint galaxies near bright quasars, further providing immediate
redshift confirmation. Here, we report the detection of H-alpha emission from a
DLA and a sub-DLA galaxy among a sample of 6 intervening quasar absorbers
targeted. We derive F(H-alpha)=7.7+/-2.7*10^-17 erg/s/cm^2 (SFR=1.8+/-0.6
M_sun/yr) at impact parameter b=25 kpc towards quasar Q0302-223 for the DLA at
z_abs=1.009 and F(H-alpha)=17.1+/-6.0*10^-17 erg/s/cm^2 (SFR=2.9+/-1.0
M_sun/yr) at b=39 kpc towards Q1009-0026 for the sub-DLA at z_abs=0.887. These
results are in line with low star formation rates previously reported in the
literature for quasar absorbers. We use the NII 6585/H-alpha ratio to derive
the HII emission metallicities and compare them with the neutral gas H I
absorption metallicities derived from high-resolution spectra. In one case, the
absorption metallicity is actually found to be higher than the emission line
metallicity. For the remaining objects, we achieve 3-sigma limiting fluxes of
the order F(H-alpha)~10^-17 erg/s/cm^2 (corresponding to SFR~ 0.1 M_sun/yr at
z~1 and ~1 M_sun/yr at z~2), i.e. among the lowest that have been possible with
ground-based observations. We also present two other galaxies associated with C
IV systems and serendipitously discovered in our data. |
Symphony: Cosmological Zoom-in Simulation Suites over Four Decades of
Host Halo Mass: We present Symphony, a compilation of $262$ cosmological,
cold-dark-matter-only zoom-in simulations spanning four decades of host halo
mass, from $10^{11}$$-$$10^{15}~M_{\mathrm{\odot}}$. This compilation includes
three existing simulation suites at the cluster and Milky Way$-$mass scales,
and two new suites: $39$ Large Magellanic Cloud-mass
($10^{11}~M_{\mathrm{\odot}}$) and $49$ strong-lens-analog
($10^{13}~M_{\mathrm{\odot}}$) group-mass hosts. Across the entire host halo
mass range, the highest-resolution regions in these simulations are resolved
with a dark matter particle mass of $\approx 3\times 10^{-7}$ times the host
virial mass and a Plummer-equivalent gravitational softening length of $\approx
9\times 10^{-4}$ times the host virial radius, on average. We measure
correlations between subhalo abundance and host concentration, formation time,
and maximum subhalo mass, all of which peak at the Milky Way host halo mass
scale. Subhalo abundances are $\approx 50\%$ higher in clusters than in
lower-mass hosts at fixed sub-to-host halo mass ratios. Subhalo radial
distributions are approximately self-similar as a function of host mass and are
less concentrated than hosts' underlying dark matter distributions. We compare
our results to the semianalytic model $\mathrm{\texttt{Galacticus}}$, which
predicts subhalo mass functions with a higher normalization at the low-mass end
and radial distributions that are slightly more concentrated than Symphony. We
use $\mathrm{\texttt{UniverseMachine}}$ to model halo and subhalo star
formation histories in Symphony, and we demonstrate that these predictions
resolve the formation histories of the halos that host nearly all currently
observable satellite galaxies in the universe. To promote open use of Symphony,
data products are publicly available at
http://web.stanford.edu/group/gfc/symphony. | Photon Trapping Enables Super-Eddington Growth of Black-Hole Seeds in
Galaxies at High Redshift: We identify a physical mechanism that would have resulted in rapid, obscured
growth of seed super-massive black-holes in galaxies at z>6. Specifically, we
find that the density at the centre of typical high redshift galaxies was at a
level where the Bondi accretion rate implies a diffusion speed of photons that
was slower than the gravitational infall velocity, resulting in photons being
trapped within the accretion flow and advected into the black-hole. We show
that there is a range of black-hole masses (M_bh ~ 10^3-10^5 solar masses)
where the accretion flow traps radiation, corresponding to black-holes that
were massive enough to generate a photon trapping accretion flow, but small
enough that their Bondi radii did not exceed the isothermal scale height of
self-gravitating gas. Under these conditions we find that the accretion reaches
levels far in excess of the Eddington rate. A prediction of this scenario is
that X-ray number counts of active galactic nuclei at z>6 would exhibit a
cutoff at the low luminosities corresponding to black-hole masses below ~10^5
solar masses. At low redshifts we find photon trapping to be unimportant
because it could only occur in rare low spin halos, and would require
black-hole masses in excess of expectations from the observed black-hole - halo
mass relation. The super-Eddington growth of ~10^5 solar mass seed black-holes
at high redshift may have provided a natural acceleration towards the growth of
super-massive black-holes at z~6-7, less than a billion years after the Big
Bang. |
COSEBIs: Extracting the full E-/B-mode information from cosmic shear
correlation functions: Cosmic shear is considered one of the most powerful methods for studying the
properties of Dark Energy in the Universe. As a standard method, the two-point
correlation functions $xi_\pm(theta)$ of the cosmic shear field are used as
statistical measures for the shear field. In order to separate the observed
shear into E- and B-modes, the latter being most likely produced by remaining
systematics in the data set and/or intrinsic alignment effects, several
statistics have been defined before. Here we aim at a complete E-/B-mode
decomposition of the cosmic shear information contained in the $xi_\pm$ on a
finite angular interval. We construct two sets of such E-/B-mode measures,
namely Complete Orthogonal Sets of E-/B-mode Integrals (COSEBIs), characterized
by weight functions between the $xi_\pm$ and the COSEBIs which are polynomials
in $theta$ or polynomials in $ln(theta)$, respectively. Considering the
likelihood in cosmological parameter space, constructed from the COSEBIs, we
study their information contents. We show that the information grows with the
number of COSEBI modes taken into account, and that an asymptotic limit is
reached which defines the maximum available information in the E-mode component
of the $xi_\pm$. We show that this limit is reached the earlier (i.e., for a
smaller number of modes considered) the narrower the angular range is over
which $xi_\pm$ are measured, and it is reached much earlier for logarithmic
weight functions. For example, for $xi_\pm$ on the interval $1'\le \theta\le
400'$, the asymptotic limit for the parameter pair $(Omega_m, sigma_8)$ is
reached for $\sim 25$ modes in the linear case, but already for 5 modes in the
logarithmic case. The COSEBIs form a natural discrete set of quantities, which
we suggest as method of choice in future cosmic shear likelihood analyses. | Estimating cosmic velocity fields from density fields and tidal tensors: In this work we investigate the nonlinear and nonlocal relation between
cosmological density and peculiar velocity fields. Our goal is to provide an
algorithm for the recon- struction of the nonlinear velocity field from the
fully nonlinear density. We find that including the gravitational tidal field
tensor using second order Lagrangian perturba- tion theory (2LPT) based upon an
estimate of the linear component of the nonlinear density field significantly
improves the estimate of the cosmic flow in comparison to linear theory not
only in the low density, but also and more dramatically in the high density
regions. In particular we test two estimates of the linear component: the log-
normal model and the iterative Lagrangian linearisation. The present approach
relies on a rigorous higher order Lagrangian perturbation theory analysis which
incorpo- rates a nonlocal relation. It does not require additional fitting from
simulations being in this sense parameter free, it is independent of
statistical-geometrical optimisation and it is straightforward and efficient to
compute. The method is demonstrated to yield an unbiased estimator of the
velocity field on scales ~> 5 Mpc/h with closely Gaussian distributed errors.
Moreover, the statistics of the divergence of the peculiar velocity field is
extremely well recovered showing a good agreement with the true one from N-body
simulations. The typical errors of about 10 km/s (1 sigma confidence intervals)
are reduced by more than 80% with respect to linear theory in the scale range
between 5 and 10 Mpc/h in high density regions ({\delta} > 2). We also find
that iterative Lagrangian linearisation is significantly superior in the low
density regime with respect to the lognormal model. |
The Atacama Cosmology Telescope: A Measurement of the Thermal
Sunyaev-Zel'dovich Effect Using the Skewness of the CMB Temperature
Distribution: We present a detection of the unnormalized skewness <T^3> induced by the
thermal Sunyaev-Zel'dovich (tSZ) effect in filtered Atacama Cosmology Telescope
(ACT) 148 GHz cosmic microwave background temperature maps. Contamination due
to infrared and radio sources is minimized by template subtraction of resolved
sources and by constructing a mask using outlying values in the 218 GHz
(tSZ-null) ACT maps. We measure <T^3>= -31 +- 6 \mu K^3 (measurement error
only) or +- 14 \mu K^3 (including cosmic variance error) in the filtered ACT
data, a 5-sigma detection. We show that the skewness is a sensitive probe of
sigma_8, and use analytic calculations and tSZ simulations to obtain
cosmological constraints from this measurement. From this signal alone we infer
a value of sigma_8= 0.79 +0.03 -0.03 (68 % C.L.) +0.06 -0.06 (95 % C.L.). Our
results demonstrate that measurements of non-Gaussianity can be a useful method
for characterizing the tSZ effect and extracting the underlying cosmological
information. | Imprints of dark energy on cosmic structure formation: II)
Non-Universality of the halo mass function: The universality of the halo mass function is investigated in the context of
dark energy cosmologies. This widely used approximation assumes that the mass
function can be expressed as a function of the matter density omega_m and the
rms linear density fluctuation sigma only, with no explicit dependence on the
properties of dark energy or redshift. In order to test this hypothesis we run
a series of 15 high-resolution N-body simulations for different cosmological
models. These consists of three LCDM cosmologies best fitting WMAP-1, 3 and 5
years data, and three toy-models characterized by a Ratra-Peebles quintessence
potential with different slopes and amounts of dark energy density. These toy
models have very different evolutionary histories at the background and linear
level, but share the same sigma8 value. For each of these models we measure the
mass function from catalogues of halos identified in the simulations using the
Friend-of-Friend (FoF) algorithm. We find redshift dependent deviations from a
universal behaviour, well above numerical uncertainties and of non-stochastic
origin, which are correlated with the linear growth factor of the investigated
cosmologies. Using the spherical collapse as guidance, we show that such
deviations are caused by the cosmology dependence of the non-linear collapse
and virialization process. For practical applications, we provide a fitting
formula of the mass function accurate to 5 percents over the all range of
investigated cosmologies. We also derive an empirical relation between the FoF
linking parameter and the virial overdensity which can account for most of the
deviations from an exact universal behavior. Overall these results suggest that
the halo mass function contains unique cosmological information since it
carries a fossil record of the past cosmic evolution. |
Berkeley Supernova Ia Program II: Initial Analysis of Spectra Obtained
Near Maximum Brightness: In this second paper in a series we present measurements of spectral features
of 432 low-redshift (z < 0.1) optical spectra of 261 Type Ia supernovae (SNe
Ia) within 20 d of maximum brightness. The data were obtained from 1989 through
the end of 2008 as part of the Berkeley SN Ia Program (BSNIP) and are presented
in BSNIP I (Silverman et al. 2012). We describe in detail our method of
automated, robust spectral feature definition and measurement which expands
upon similar previous studies. Using this procedure, we attempt to measure
expansion velocities, pseudo-equivalent widths (pEW), spectral feature depths,
and fluxes at the centre and endpoints of each of nine major spectral feature
complexes. We investigate how velocity and pEW evolve with time and how they
correlate with each other. Various spectral classification schemes are employed
and quantitative spectral differences among the subclasses are investigated.
Several ratios of pEW values are calculated and studied. The so-called Si II
ratio, often used as a luminosity indicator (Nugent et al. 1995), is found to
be well correlated with the so-called "SiFe" ratio and anticorrelated with the
analogous "SSi ratio," confirming the results of previous studies. Furthermore,
SNe Ia that show strong evidence for interaction with circumstellar material or
an aspherical explosion are found to have the largest near-maximum expansion
velocities and pEWs, possibly linking extreme values of spectral observables
with specific progenitor or explosion scenarios. [Abridged] | Molecular Gas in NUclei of GAlaxies (NUGA): XII. The head-on collision
in NGC1961: We present high-resolution CO(1-0) and CO(2-1) maps of the LINER 2 galaxy
NGC1961. This galaxy is unusual among late-type (Sc) disk galaxies in having a
very large radial extent and inferred dynamical mass. We propose a head-on
collision scenario to explain the perturbed morphology of this galaxy- both the
off-centered rings and the inflated radius. This scenario is supported by the
detection of a steep velocity gradient in the CO(1-0) map at the position of a
southwest peak in radio continuum and near-infrared emission. This peak would
represent the remnant of the disrupting companion. We use numerical models to
demonstrate the plausibility of the scenario. While ram pressure stripping
could in principle be important for shocking the atomic gas and produce the
striking head-tail morphology, the non detection of this small galaxy group in
X-ray emission suggests that any hot intragroup medium has too low a density.
The collision with the companion of mass ratio 1:4 produces a lopsided wave,
which accounts for the sharp boundary observed in the atomic gas on the
southern side. We argue that NGC1961 has a strongly warped disk, which gives
the false impression of a nearly face-on system; the main disk is actually more
edge-on, and this error in the true inclination has led to the surprisingly
high dynamical mass for a morphologically late-type galaxy. In addition, the
outward propagating ring artificially enlarges the disk. The collision
de-stabilizes the inner disk and can provide gas inflow to the active nucleus. |
The anatomy of the NGC 5044 group -- II. Stellar populations and
star-formation histories: The distribution of galaxy properties in groups and clusters holds important
information on galaxy evolution and growth of structure in the Universe. While
clusters have received appreciable attention in this regard, the role of groups
as fundamental to formation of the present day galaxy population has remained
relatively unaddressed. Here we present stellar ages, metallicities and
alpha-element abundances derived using Lick indices for 67 spectroscopically
confirmed members of the NGC 5044 galaxy group with the aim of shedding light
on galaxy evolution in the context of the group environment.
We find that galaxies in the NGC 5044 group show evidence for a strong
relationship between stellar mass and metallicity, consistent with their
counterparts in both higher and lower mass groups and clusters. Galaxies show
no clear trend of age or alpha-element abundance with mass, but these data form
a tight sequence when fit simultaneously in age, metallicity and stellar mass.
In the context of the group environment, our data support the tidal disruption
of low-mass galaxies at small group-centric radii, as evident from an apparent
lack of galaxies below ~10^9 M_sun within ~100 kpc of the brightest group
galaxy. Using a joint analysis of absorption- and emission-line metallicities,
we are able to show that the star-forming galaxy population in the NGC 5044
group appears to require gas removal to explain the ~1.5 dex offset between
absorption- and emission-line metallicities observed in some cases. A
comparison with other stellar population properties suggests that this gas
removal is dominated by galaxy interactions with the hot intragroup medium. | Blind detections of CO J = 1--0 in 11 H-ATLAS galaxies at z = 2.1--3.5
with the GBT/Zpectrometer: We report measurements of the carbon monoxide ground state rotational
transition (12C16O J = 1--0) with the Zpectrometer ultra-wideband spectrometer
on the 100-m diameter Green Bank Telescope. The sample comprises 11 galaxies
with redshifts between z = 2.1 and 3.5 from a total sample of 24 targets
identified by Herschel-ATLAS photometric colors from the SPIRE instrument. Nine
of the CO measurements are new redshift determinations, substantially adding to
the number of detections of galaxies with rest-frame peak submillimeter
emission near 100um. The CO detections confirm the existence of massive gas
reservoirs within these luminous dusty star-forming galaxies (DSFGs). The CO
redshift distribution of the 350um-selected galaxies is strikingly similar to
the optical redshifts of 850um-selected submillimeter galaxies (SMGs) in 2.1 <
z < 3.5. Spectroscopic redshifts break a temperature-redshift degeneracy;
optically thin dust models fit to the far-infrared photometry indicate
characteristic dust temperatures near 34 K for most of the galaxies we detect
in CO. Detections of two warmer galaxies and statistically significant
nondetections hint at warmer or molecule-poor DSFGs with redshifts difficult
determine from from Herschel-SPIRE photometric colors alone. Many of the
galaxies identified by H-ATLAS photometry are expected to be amplified by
foreground gravitational lenses. Analysis of CO linewidths and luminosities
provides a method for finding approximate gravitational lens magnifications mu
from spectroscopic data alone, yielding mu ~ 3--20. Corrected for
magnification, most galaxy luminosities are consistent with an ultra-luminous
infrared galaxy (ULIRG) classification, but three are candidate hyper-LIRGs
with luminosities greater than 10^13 L_sun. |
Induced Gravitational Waves with Kination Era for Recent Pulsar Timing
Array Signals: The evidence of the stochastic gravitational-wave background around the
nano-hertz frequency range was recently found by worldwide pulsar timing array
(PTA) collaborations. One of the cosmological explanations is the gravitational
waves induced by enhanced curvature perturbations, but the issue of primordial
black hole (PBH) overproduction in this scenario was pointed out in the
literature. Motivated by this issue and the $\Omega_\text{GW} \sim f^2$ scaling
suggested by the data, we study the gravitational waves induced in a
cosmological epoch dominated by a stiff fluid ($w=1$) and find that they can
safely explain the PTA data well without PBH overproduction. | Emulation of reionization simulations for Bayesian inference of
astrophysics parameters using neural networks: Next generation radio experiments such as LOFAR, HERA and SKA are expected to
probe the Epoch of Reionization and claim a first direct detection of the
cosmic 21cm signal within the next decade. Data volumes will be enormous and
can thus potentially revolutionize our understanding of the early Universe and
galaxy formation. However, numerical modelling of the Epoch of Reionization can
be prohibitively expensive for Bayesian parameter inference and how to
optimally extract information from incoming data is currently unclear.
Emulation techniques for fast model evaluations have recently been proposed as
a way to bypass costly simulations. We consider the use of artificial neural
networks as a blind emulation technique. We study the impact of training
duration and training set size on the quality of the network prediction and the
resulting best fit values of a parameter search. A direct comparison is drawn
between our emulation technique and an equivalent analysis using 21CMMC. We
find good predictive capabilities of our network using training sets of as low
as 100 model evaluations, which is within the capabilities of fully numerical
radiative transfer codes. |
HerMES: SPIRE Science Demonstration Phase Maps: We describe the production and verification of sky maps of the five SPIRE
fields observed as part of the Herschel Multi-tiered Extragalactic Survey
(HerMES) during the Science Demonstration Phase (SDP) of the Herschel mission.
We have implemented an iterative map-making algorithm (SHIM; The SPIRE-HerMES
Iterative Mapper) to produce high fidelity maps that preserve extended diffuse
emission on the sky while exploiting the repeated observations of the same
region of the sky with many detectors in multiple scan directions to minimize
residual instrument noise. We specify here the SHIM algorithm and outline the
various tests that were performed to determine and characterize the quality of
the maps and verify that the astrometry, point source flux and power on all
relevant angular scales meets the needs of the HerMES science goals. These
include multiple jackknife tests, determination of the map transfer function
and detailed examination of the power spectra of both sky and jackknife maps.
The map transfer function is approximately unity on scales from one arcminute
to one degree. Final maps (v1.0), including multiple jackknives, as well as the
SHIM pipeline, have been used by the HerMES team for the production of SDP
papers. | A 14 $h^{-3}$ Gpc$^3$ study of cosmic homogeneity using BOSS DR12 quasar
sample: The BOSS quasar sample is used to study cosmic homogeneity with a 3D survey
in the redshift range $2.2<z<2.8$. We measure the count-in-sphere, $N(<\! r)$,
i.e. the average number of objects around a given object, and its logarithmic
derivative, the fractal correlation dimension, $D_2(r)$. For a homogeneous
distribution $N(<\! r) \propto r^3$ and $D_2(r)=3$. Due to the uncertainty on
tracer density evolution, 3D surveys can only probe homogeneity up to a
redshift dependence, i.e. they probe so-called "spatial isotropy". Our data
demonstrate spatial isotropy of the quasar distribution in the redshift range
$2.2<z<2.8$ in a model-independent way, independent of any FLRW fiducial
cosmology, resulting in $3-\langle D_2 \rangle < 1.7 \times 10^{-3}$ (2
$\sigma$) over the range $250<r<1200 \, h^{-1}$Mpc for the quasar distribution.
If we assume that quasars do not have a bias much less than unity, this implies
spatial isotropy of the matter distribution on large scales. Then, combining
with the Copernican principle, we finally get homogeneity of the matter
distribution on large scales. Alternatively, using a flat $\Lambda$CDM fiducial
cosmology with CMB-derived parameters, and measuring the quasar bias relative
to this $\Lambda$CDM model, our data provide a consistency check of the model,
in terms of how homogeneous the Universe is on different scales. $D_2(r)$ is
found to be compatible with our $\Lambda$CDM model on the whole $10<r<1200 \,
h^{-1}$Mpc range. For the matter distribution we obtain $3-\langle D_2 \rangle
< 5 \times 10^{-5}$ (2 $\sigma$) over the range $250<r<1200 \, h^{-1}$Mpc,
consistent with homogeneity on large scales. |
Cosmological perturbation theory using generalized Einstein de Sitter
cosmologies: The separable analytical solution in standard perturbation theory for an
Einstein de Sitter (EdS) universe can be generalized to the wider class of such
cosmologies (``generalized EdS'', or gEdS) in which a fraction of the
pressure-less fluid does not cluster. We derive the corresponding kernels in
both Eulerian perturbation theory (EPT) and Lagrangian perturbation theory,
generalizing the canonical EdS expressions to a one-parameter family where the
parameter can be taken to be the exponent $\alpha$ of the growing mode linear
amplification $D(a) \propto a^{\alpha}$. For the power spectrum (PS) at one
loop in EPT, the contribution additional to standard EdS is given, for each of
the `13' and `22' terms, as a function of two infra-red safe integrals. In the
second part of the paper we show that the calculation of cosmology-dependent
corrections in perturbation theory in standard (e.g. LCDM-like) models can be
simplified, and their magnitude and parameter dependence better understood, by
relating them to our analytic results for gEdS models. At second order the time
dependent kernels are equivalent to the analytic kernels of the gEdS model with
$\alpha$ replaced by a single redshift dependent effective growth rate
$\alpha_2(z)$. At third order the time evolution can be conveniently
parametrized in terms of two additional such effective growth rates. For the PS
calculated at one loop order, the correction to the PS relative to the EdS
limit can be expressed in terms of just $\alpha_2(z)$, one additional effective
growth rate function and the four infra-red safe integrals of the gEdS limit.
This is much simplified compared to expressions in the literature that use six
or eight red-shift dependent functions and are not explicitly infra-red safe.
Using the analytic gEdS expression for the PS with $\alpha=\alpha_2(z)$ gives a
good approximation (to $\sim 25 \%$) for the exact result. | The Alignment of Galaxy Clusters: Conclusive Evidence for a Cosmic Axis: This paper has been withdrawn. I belatedly found that the alignment I saw in
galaxy cluster axes was bogus. It turns out that it is due to a well-known
effect called the "Fingers of God" that stretches out the redshifts of galaxies
in a cluster due to their motion within the cluster. This would not cause an
overall bias if the SDSS survey were complete, but there is no coverage toward
right ascensions near 90 degrees or 270 deg. Thus the apparent alignment
appears along 0 -- 180 deg. |
Scaling solutions as Early Dark Energy resolutions to the Hubble tension: A wide class of scalar field models including Quintessence and K-essence have
the attractive property of tracker regimes, where the energy density stored in
the field evolves so as to mimic that of the dominant background component for
a period of time. During this evolution, for a brief period of time there is an
increase in the energy density of the field as it spirals in towards it's
attractor solution. We show that when the peak of this energy density occurs
around the epoch of equality, we can address a key requirement of early dark
energy (EDE), postulated as a solution to the Hubble tension. In particular we
demonstrate how this can occur in a wide class of Quintessence, axion and
K-essence models, before showing that the Quintessence models suffer in that
they generally lead to sound speeds incompatible with the requirements of EDE,
whereas the K-essence and axion models can do a better job of fitting the data. | Outlying HII Regions in HI-Selected Galaxies: We present results from the first systematic search for outlying HII regions,
as part of a sample of 96 emission-line point sources (referred to as ELdots -
emission-line dots) derived from the NOAO Survey for Ionization in Neutral Gas
Galaxies (SINGG). Our automated ELdot-finder searches SINGG narrow-band and
continuum images for high equivalent width point sources outside the optical
radius of the target galaxy (> 2 X r25 in the R-band). Follow-up longslit
spectroscopy and deep GALEX images (exposure time > 1000 s) distinguish
outlying HII regions from background galaxies whose strong emission lines
([OIII], Hbeta or [OII]) have been redshifted into the SINGG bandpass. We find
that these deep GALEX images can serve as a substitute for spectroscopic
follow-up because outlying HII regions separate cleanly from background
galaxies in color-color space. We identify seven SINGG systems with outlying
massive star formation that span a large range in Halpha luminosities
corresponding to a few O stars in the most nearby cases, and unresolved dwarf
satellite companion galaxies in the most distant cases. Six of these seven
systems feature galaxies with nearby companions or interacting galaxies.
Furthermore, our results indicate that some outlying HII regions are linked to
the extended-UV disks discovered by GALEX, representing emission from the most
massive O stars among a more abundant population of lower mass (or older) star
clusters. The overall frequency of outlying HII regions in this sample of
gas-rich galaxies is 8 - 11% when we correct for background emission-line
galaxy contamination (~75% of ELdots). |
The metallicity bimodality of globular cluster systems: a test of galaxy
assembly and of the evolution of the galaxy mass-metallicity relation: (Abridged) We build a theoretical model to study the origin of the globular
cluster metallicity bimodality in the hierarchical galaxy assembly scenario,
based on the observed galaxy mass-[O/H] relation and the galaxy stellar mass
function up to z ~4, and on theoretical merger rates. We derive a new galaxy
[Fe/H]-M(star) relation as a function of z, and by assuming that GCs share the
metallicity of their parent galaxy when they form, we populate the merger tree
with GCs. We perform a series of Monte-Carlo simulations of the galaxy
assembly, and study the properties of the final GC population as a function of
galaxy mass, assembly and star formation history, and under different
assumptions for the evolution of the galaxy mass-[Fe/H] relation. The main
results are: 1) The hierarchical clustering scenario naturally predicts a
metallicity bimodality in the galaxy GC population: the metal-rich GCs are
formed in the galaxy main progenitor around z~2, and the metal-poor GCs are
accreted from satellites and formed at z~3-4. 2) The model reproduces the
observed relations for the metallicity of the metal-rich and metal-poor GCs as
a function of galaxy mass. The positions of the metal-poor and metal-rich peaks
depend exclusively on the evolution of the galaxy mass-[Fe/H] relation and the
[O/Fe], both of which can be constrained by this method. We find that the
galaxy [O/Fe] evolves linearly with z from a value of ~0.5 at z~4 to a value of
~0.1 at z=0. 3) Given a galaxy mass, the relative strength of the metal-rich
and metal-poor peaks depends exclusively on the galaxy assembly and star
formation history: galaxies in denser environments and/or early types galaxies
show a larger fraction of metal-poor GCs, while galaxies with a sparse merger
history and/or late type galaxies are dominated by metal-rich GCs. 4) The GC
metallicity bimodality disappears for galaxy masses below M(star)~1e9, and for
z>2. | Irruption of massive particle species during inflation: All species of (non-conformally-coupled) particles are produced during
inflation so long as their mass $M$ is not too much larger than $H$, the
expansion rate during inflation. It has been shown that if a particle species
that is normally massive ($M\gg H$) couples to the inflaton field in such a way
that its mass vanishes, or at least becomes small ($M < H$), for a particular
value of the inflaton field, then not only are such particles produced, but an
irruption of that particle species can occur during inflation. In this paper we
analyze creation of a massive particle species during inflation in a variety of
settings, paying particular attention to models which realize such an irruptive
production mechanism. |
Dark energy, non-minimal couplings and the origin of cosmic magnetic
fields: In this work we consider the most general electromagnetic theory in curved
space-time leading to linear second order differential equations, including
non-minimal couplings to the space-time curvature. We assume the presence of a
temporal electromagnetic background whose energy density plays the role of dark
energy, as has been recently suggested. Imposing the consistency of the theory
in the weak-field limit, we show that it reduces to standard electromagnetism
in the presence of an effective electromagnetic current which is generated by
the momentum density of the matter/energy distribution, even for neutral
sources. This implies that in the presence of dark energy, the motion of
large-scale structures generates magnetic fields. Estimates of the present
amplitude of the generated seed fields for typical spiral galaxies could reach
$10^{-9}$ G without any amplification. In the case of compact rotating objects,
the theory predicts their magnetic moments to be related to their angular
momenta in the way suggested by the so called Schuster-Blackett conjecture. | Inhomogeneous Metal Distribution in the Intra-Cluster Medium: The hot gas that fills the space between galaxies in clusters is rich in
metals. In their large potential wells, galaxy clusters accumulate metals over
the whole cluster history and hence they retain important information on
cluster formation and evolution. We use a sample of 5 cool core clusters to
study the distribution of metals in the ICM. We investigate whether the X-ray
observations yield good estimates for the metal mass and whether the heavy
elements abundances are consistent with a certain relative fraction of SN Ia to
SNCC. We derive detailed metallicity maps of the clusters from XMM - Newton
observations and we use them as a measure for the metal mass in the ICM. We
determine radial profiles for several elements and using population synthesis
and chemical enrichment models, we study the agreement between the measured
abundances and the theoretical yields. We show that even in relaxed clusters
the distribution of metals show a lot of inhomogeneities. Using metal maps
usually gives a metal mass 10-30% higher than the metal mass computed using a
single extraction region, hence it is expected that most previous metal mass
determination have underestimated metal mass. The abundance ratio of
{\alpha}-elements to Fe, even in the central parts of clusters, are consistent
with an enrichment due to the combination of SN Ia and SNCC. |
Astro2010 Decadal Survey Whitepaper: Coordinated Science in the
Gravitational and Electromagnetic Skies: It is widely expected that the coming decade will witness the first direct
detection of gravitational waves (GWs). The ground-based LIGO and Virgo GW
observatories are being upgraded to advanced sensitivity, and are expected to
observe a significant binary merger rate. The launch of The Laser
Interferometer Space Antenna (LISA) would extend the GW window to low
frequencies, opening new vistas on dynamical processes involving massive (M >~
10^5 M_Sun) black holes. GW events are likely to be accompanied by
electromagnetic (EM) counterparts and, since information carried
electromagnetically is complementary to that carried gravitationally, a great
deal can be learned about an event and its environment if it becomes possible
to measure both forms of radiation in concert. Measurements of this kind will
mark the dawn of trans-spectral astrophysics, bridging two distinct spectral
bands of information. The aim of this whitepaper is to articulate future
directions in both theory and observation that are likely to impact broad
astrophysical inquiries of general interest. What will EM observations reflect
on the nature and diversity of GW sources? Can GW sources be exploited as
complementary probes of cosmology? What cross-facility coordination will expand
the science returns of gravitational and electromagnetic observations? | Identifying clustering at high redshift through actively star-forming
galaxies: Identifying galaxy clustering at high redshift (i.e. z > 1) is essential to
our understanding of the current cosmological model. However, at increasing
redshift, clusters evolve considerably in star-formation activity and so are
less likely to be identified using the widely-used red sequence method. Here we
assess the viability of instead identifying high redshift clustering using
actively star-forming galaxies (SMGs associated with over-densities of
BzKs/LBGs). We perform both a 2- and 3-D clustering analysis to determine
whether or not true (3D) clustering can be identified where only 2D data are
available. As expected, we find that 2D clustering signals are weak at best and
inferred results are method dependant. In our 3D analysis, we identify 12 SMGs
associated with an over-density of galaxies coincident both spatially and in
redshift - just 8% of SMGs with known redshifts in our sample. Where an SMG in
our target fields lacks a known redshift, their sightline is no more likely to
display clustering than blank sky fields; prior redshift information for the
SMG is required to identify a true clustering signal. We find that the strength
of clustering in the volume around typical SMGs, while identifiable, is not
exceptional. However, we identify a small number of highly clustered regions,
all associated with an SMG. The most notable of these, surrounding
LESSJ033336.8-274401, potentially contains an SMG, a QSO and 36 star-forming
galaxies (a > 20sig over-density) all at z~1.8. This region is highly likely to
represent an actively star-forming cluster and illustrates the success of using
star-forming galaxies to select sites of early clustering. Given the increasing
number of deep fields with large volumes of spectroscopy, or high quality and
reliable photometric redshifts, this opens a new avenue for cluster
identification in the young Universe. |
Locating the Youngest HII Regions in M82 with 7 mm Continuum Maps: We present 7mm Very Large Array continuum images of the starburst galaxy M82.
On arcsecond scales, two-thirds of the 7mm continuum consists of free-free
emission from HII regions. In the subarcsecond resolution map, we identify 14
compact sources, including 9 bright HII regions with N_Lyc > 10^51 sec^-1. Four
of the HII regions have rising spectra, implying emission measures > 10^8 cm^-6
pc. Except for one compact source with peculiar features, all other compact
radio sources are found in dust lanes and do not have optical or near-infrared
continuum counterparts. Four regions of extended, high brightness (EM > 10^7
cm-6 pc) radio emission are found in our high resolution map, including some as
large as ~2", or 30 pc, representing either associations of small HII regions,
or sheetlike structures of denser gas. The good correlation between 7 mm
emission and Spitzer IRAC 8 micron continuum-removed PAH feature suggests that
PAH emission may track the recently formed OB stars. We find an excellent
correlation between molecular gas and star formation, particularly dense gas
traced by HCN, down to the ~ 45 pc scale in M82. We also find star formation
efficiencies (SFEs) of 1-10% on the same scale, based on CO maps. The highest
SFE are found in regions with the highest dense gas fractions. | Spectral Optical Monitoring of the Narrow Line Seyfert 1 galaxy Ark 564: We present the results of a long-term (1999--2010) spectral optical
monitoring campaign of the active galactic nucleus (AGN) Ark 564, which shows a
strong Fe II line emission in the optical. This AGN is a narrow line Seyfert 1
(NLS1) galaxies, a group of AGNs with specific spectral characteristics. We
analyze the light curves of the permitted Ha, Hb, optical Fe II line fluxes,
and the continuum flux in order to search for a time lag between them.
Additionally, in order to estimate the contribution of iron lines from
different multiplets, we fit the Hb and Fe II lines with a sum of Gaussian
components. We found that during the monitoring period the spectral variation
(F_max/F_min) of Ark 564 was between 1.5 for Ha to 1.8 for the Fe II lines. The
correlation between the Fe II and Hb flux variations is of higher significance
than that of Ha and Hb (whose correlation is almost absent). The permitted-line
profiles are Lorentzian-like, and did not change shape during the monitoring
period. We investigated, in detail, the optical Fe II emission and found
different degrees of correlation between the Fe II emission arising from
different spectral multiplets and the continuum flux. The relatively weak and
different degrees of correlations between permitted lines and continuum fluxes
indicate a rather complex source of ionization of the broad line emission
region. |
The Relationship Between Intergalactic HI/OVI and Nearby (z<0.017)
Galaxies: We analyze intergalactic HI and OVI absorbers with v<5000 km/s in HST and
FUSE spectra of 76 AGNs. The baryons traced by HI/OVI absorption are clearly
associated with the extended surroundings of galaxies; for impact parameters
<400 kpc they are ~5 times more numerous as those inside the galaxies. This
large reservoir of matter likely plays a major role in galaxy evolution. We
tabulate the fraction of absorbers having a galaxy of a given luminosity within
a given impact parameter (rho) and velocity difference (Dv), as well as the
fraction of galaxies with an absorber closer than a given rho and Dv. We
identify possible "void absorbers" (rho>3 Mpc to the nearest L* galaxy),
although at v<2500 km/s all absorbers are within 1.5 Mpc of an L>0.1 L* galaxy.
The absorber properties depend on rho, but the relations are not simple
correlations. For four absorbers with rho=50-350 kpc from an edge-on galaxy
with known orientation of its rotation, we find no clear relation between
absorber velocities and the rotation curve of the underlying galaxy. For
rho<350 kpc the covering factor of Ly-alpha (OVI) around L>0.1 L* galaxies is
100% for field galaxies and 65% for group galaxies; 50% of galaxy groups have
associated Ly-alpha. All OVI absorbers occur within 550 kpc of an L>0.25 L*
galaxy. The properties of three of 14 OVI absorbers are consistent with
photoionization, for five the evidence points to collisional ionization; the
others are ambiguous. The fraction of broad Ly-alpha lines increases from z=3
to z=0 and with decreasing impact parameter, consistent with the idea that gas
inside ~500 kpc from galaxies is heating up, although alternative explanations
can not be clearly excluded. | Intrinsic alignment from multiple shear estimates: A first application
to data and forecasts for Stage IV: Without mitigation, the intrinsic alignment (IA) of galaxies poses a
significant threat to achieving unbiased cosmological parameter constraints
from precision weak lensing surveys. Here, we apply for the first time to data
a method to extract the scale dependence of the IA contribution to
galaxy-galaxy lensing, which takes advantage of the difference in alignment
signal as measured by shear estimators with different sensitivities to galactic
radii. Using data from Year 1 of the Dark Energy Survey, with shear estimators
METACALIBRATION and IM3SHAPE, we investigate and address method systematics
including non-trivial selection functions, differences in weighting between
estimators, and multiplicative bias. We obtain a null detection of IA, which
appears qualitatively consistent with existing work. We then forecast the
application of this method to Rubin Observatory Legacy Survey of Space and Time
(LSST) data and place requirements on a pair of shear estimators for detecting
IA and constraining its 1-halo scale dependence. We find that for LSST Year 1,
shear estimators should have at least a $40\%$ difference in IA amplitude, and
the Pearson correlation coefficient of their shape noise should be at least
$\rho=0.50$, to ensure a $1\sigma$ detection of IA and a constraint on its
1-halo scale dependence with a signal-to-noise ratio greater than $1$. For Year
10, a $1\sigma$ detection and constraint become possible for $20\%$ differences
in alignment amplitude and $\rho=0.50$. |
Non-parametric reconstruction of interaction in the cosmic dark sector: The possibility of a non-gravitational interaction between the dark matter
and the dark energy has been reconstructed using some recent datasets. The
crucial aspect is that the interaction is not parametrized at the outset, but
rather reconstructed directly from the data in a non-parametric way. The Cosmic
Chronometer Hubble data, the Pantheon Supernova compilation of CANDELS and
CLASH Multy-Cycle Treasury programs obtained by the HST, and the Baryon
Acoustic Oscillation Hubble data have been considered in this work. The widely
accepted Gaussian Process is used for the reconstruction. The results clearly
indicate that a no interaction scenario is quite a possibility. Also, the
interaction, if any, is not really significant at the present epoch. The
direction of the flow of energy is clearly from the dark energy to the dark
matter which is consistent with the thermodynamic requirement. | Shapes and Probabilities of Galaxy Clusters II: Comparisons with
observations: We identify low redshift clusters and groups in the Sloan Digital Sky Survey
(SDSS) and estimate their kinetic and correlation potential energies. We
compare the distribution of these energies to the predictions by Yang and
Saslaw (2012) and in the process estimate a measure of an average 3-dimensional
velocity and spatial anisotropy of a sample of clusters. We find that the
inferred velocity anisotropy is correlated with the inferred spatial
anisotropy. We also find that the general shape of the energy distribution
agrees with theory over a wide range of scales from small groups to
superclusters once the uncertainties and fluctuations in the estimated energies
are included. |
CARMA Survey Toward Infrared-bright Nearby Galaxies (STING): Molecular
Gas Star Formation Law in NGC4254: This study explores the effects of different assumptions and systematics on
the determination of the local, spatially resolved star formation law. Using
four star formation rate (SFR) tracers (H\alpha with azimuthally averaged
extinction correction, mid-infrared 24 micron, combined H\alpha and
mid-infrared 24 micron, and combined far-ultraviolet and mid-infrared 24
micron), several fitting procedures, and different sampling strategies we probe
the relation between SFR and molecular gas at various spatial resolutions and
surface densities within the central 6.5 kpc in the disk of NGC4254. We find
that in the high surface brightness regions of NGC4254 the form of the
molecular gas star formation law is robustly determined and approximately
linear and independent of the assumed fraction of diffuse emission and the SFR
tracer employed. When the low surface brightness regions are included, the
slope of the star formation law depends primarily on the assumed fraction of
diffuse emission. In such case, results range from linear when the fraction of
diffuse emission in the SFR tracer is ~30% or less (or when diffuse emission is
removed in both the star formation and the molecular gas tracer), to
super-linear when the diffuse fraction is ~50% and above. We find that the
tightness of the correlation between gas and star formation varies with the
choice of star formation tracer. The 24 micron SFR tracer by itself shows the
tightest correlation with the molecular gas surface density, whereas the
H\alpha corrected for extinction using an azimuthally-averaged correction shows
the highest dispersion. We find that for R<0.5R_25 the local star formation
efficiency is constant and similar to that observed in other large spirals,
with a molecular gas depletion time ~2 Gyr. | HIFI spectroscopy of low-level water transitions in M82: We present observations of the rotational ortho-water ground transition, the
two lowest para-water transitions, and the ground transition of ionised
ortho-water in the archetypal starburst galaxy M82, performed with the HIFI
instrument on the Herschel Space Observatory. These observations are the first
detections of the para-H2O(111-000) (1113\,GHz) and ortho-H2O+(111-000)
(1115\,GHz) lines in an extragalactic source. All three water lines show
different spectral line profiles, underlining the need for high spectral
resolution in interpreting line formation processes. Using the line shape of
the para-H2O(111-000) and ortho-H2O+(111-000) absorption profile in conjunction
with high spatial resolution CO observations, we show that the (ionised) water
absorption arises from a ~2000 pc^2 region within the HIFI beam located about
~50 pc east of the dynamical centre of the galaxy. This region does not
coincide with any of the known line emission peaks that have been identified in
other molecular tracers, with the exception of HCO. Our data suggest that water
and ionised water within this region have high (up to 75%) area-covering
factors of the underlying continuum. This indicates that water is not
associated with small, dense cores within the ISM of M82 but arises from a more
widespread diffuse gas component. |
The effects of He I 10830 on helium abundance determinations: Observations of helium and hydrogen emission lines from metal-poor
extragalactic H II regions provide an independent method for determining the
primordial helium abundance, Y_p. Traditionally, the emission lines employed
are in the visible wavelength range, and the number of suitable lines is
limited. Furthermore, when using these lines, large systematic uncertainties in
helium abundance determinations arise due to the degeneracy of physical
parameters, such as temperature and density. Recently, Izotov, Thuan, & Guseva
(2014) have pioneered adding the He 10830 infrared emission line in helium
abundance determinations. The strong electron density dependence of He 10830
makes it ideal for better constraining density, potentially breaking the
degeneracy with temperature. We revisit our analysis of the dataset published
by Izotov, Thuan, & Stasinska (2007) and incorporate the newly available
observations of He 10830 by scaling them using the observed-to-theoretical
Paschen-gamma ratio. The solutions are better constrained, in particular for
electron density, temperature, and the neutral hydrogen fraction, improving the
model fit to data, with the result that more spectra now pass screening for
quality and reliability, in addition to a standard 95% confidence level cut.
Furthermore, the addition of He 10830 decreases the uncertainty on the helium
abundance for all galaxies, with reductions in the uncertainty ranging from
10-80%. Overall, we find a reduction in the uncertainty on Y_p by over 50%.
From a regression to zero metallicity, we determine Y_p = 0.2449 +/- 0.0040,
consistent with the BBN result, Y_p = 0.2470 +/- 0.0002, based on the Planck
determination of the baryon density. The dramatic improvement in the
uncertainty from incorporating He 10830 strongly supports the case for
simultaneous (thus not requiring scaling) observations of visible and infrared
helium emission line spectra. | The effective Lagrangian of dark energy from observations: Using observational data on the expansion rate of the universe (H(z)) we
constrain the effective Lagrangian of the current accelerated expansion. Our
results show that the effective potential is consistent with being flat i.e., a
cosmological constant; it is also consistent with the field moving along an
almost flat potential like a pseudo-Goldstone boson. We show that the potential
of dark energy does not deviate from a constant at more than 6% over the
redshift range 0 < z < 1. The data can be described by just a constant term in
the Lagrangian and do not require any extra parameters; therefore there is no
evidence for augmenting the number of parameters of the LCDM paradigm. We also
find that the data justify the effective theory approach to describe
accelerated expansion and that the allowed parameters range satisfy the
expected hierarchy. Future data, both from cosmic chronometers and baryonic
acoustic oscillations, that can measure H(z) at the % level, could greatly
improve constraints on the flatness of the potential or shed some light on
possible mechanisms driving the accelerated expansion. Besides the above
result, it is shown that the effective Lagrangian of accelerated expansion can
be constrained from cosmological observations in a model-independent way and
that direct measurements of the expansion rate H(z) are most useful to do so. |
Magnetic Fields in Cooling Flow Clusters: A Critical View: Shortly after the first results of Chandra and XMM-Newton appeared, many
researchers in the field abandoned the term "cooling flow clusters" in favor of
the name "cool core clusters". This change, I argue, has been causing damage by
promoting the view that there is no substantial cooling in these clusters. In
this contribution I discuss the following points, with emphasize on the last
one that deals with magnetic fields in cooling flow clusters. (1) Both
AGN-feedback and hot-gas cooling to form stars occur during galaxy formation as
well as in cooling flow clusters. Ignoring cooling of the intra-cluster medium,
as implied by the term "cool core", does not encourage comparative study of AGN
feedback in cooling flow clusters with that of galaxy formation. (2) The line
of thought that there is no cooling might lead to wrong questions and research
directions. (3) A key question in both cooling flow clusters and during galaxy
formation is the mode of accretion by the super massive black hole (SMBH). When
cooling is neglected only accretion from the hot phase remains. Accretion from
the hot phase, such as the Bondi accretion, suffers from some severe problems.
(4) When it is accepted that moderate quantities of gas are cooling, it becomes
clear that global heat conduction must be substantially suppressed. This does
not favor a globally ordered magnetic field. As well, it makes global heat
conduction unattractive. | Massive neutrino self-interactions with a light mediator in cosmology: Nonstandard self-interactions can alter the evolution of cosmological
neutrinos, mainly by damping free streaming, which should leave traces in
cosmological observables. Although overall effects are opposite to those
produced by neutrino mass and a larger $N_{\rm eff}$, they cannot be totally
canceled by these last. We harness cosmological data that includes Cosmic
Microwave Background from Plank 2018, BAO measurements, local $H_0$,
Ly-$\alpha$ and SNIa, to constrain massive neutrino self-interactions with a
very light scalar mediator. We find that the effective coupling constant, at
the 95\% C.L., should be $g_{\rm eff}< 1.94 \times 10^{-7}$ for only Planck
2018 data and $1.97\times10^{-7}$ when Planck + BAO are considered. This bound
relaxes to $2.27\times 10^{-7}$ ($2.3\times 10^{-7}$) for $H_0$
($H_0$+SNe+Ly-$\alpha$) data. Using the Planck + BAO dataset, the $H_0$ tension
lowers from 4.3$\sigma$ (for $\Lambda$CDM) to 3.2$\sigma$. The Akaike
Information Criterion penalizes the self-interacting model due to its larger
parameter space for Plank or Planck + BAO data, but favors the interacting
model when we use local $H_0$ measurements. A somewhat larger value for $H_0$
is preferred when we include the whole data pool, which comes accompanied with
a larger value of $N_{\rm eff}$ and a more constricted bound on $\Sigma m_\nu$. |
The XFaster Power Spectrum and Likelihood Estimator for the Analysis of
Cosmic Microwave Background Maps: We present the XFaster analysis package. XFaster is a fast, iterative angular
power spectrum estimator based on a diagonal approximation to the quadratic
Fisher matrix estimator. XFaster uses Monte Carlo simulations to compute noise
biases and filter transfer functions and is thus a hybrid of both Monte Carlo
and quadratic estimator methods. In contrast to conventional pseudo-$C_\ell$
based methods, the algorithm described here requires a minimal number of
simulations, and does not require them to be precisely representative of the
data to estimate accurate covariance matrices for the bandpowers. The formalism
works with polarization-sensitive observations and also data sets with
identical, partially overlapping, or independent survey regions. The method was
first implemented for the analysis of BOOMERanG data, and also used as part of
the Planck analysis. Here, we describe the full, publicly available analysis
package, written in Python, as developed for the analysis of data from the 2015
flight of the SPIDER instrument. The package includes extensions for
self-consistently estimating null spectra and for estimating fits for Galactic
foreground contributions. We show results from the extensive validation of
XFaster using simulations, and its application to the SPIDER data set. | ICM Signatures from Multiple Outbursts in the Galaxy Group NGC 5813: A
Window to AGN Feedback: We present results from Chandra observations of NGC 5813, the dominant
central galaxy in a nearby galaxy group. We focus on three main results. 1) The
diffuse gas shows clear signatures from three distinct outbursts of the central
AGN, with three pairs of roughly collinear cavities. The inner two cavity pairs
are associated with unambiguous elliptical shock fronts, with Mach numbers
M~1.7 and M~1.5 for the inner and outer shocks, respectively. 2) The mean power
of the two most recent outbursts differs by a factor of six, indicating that
the mean jet power varies over long (~10^7 yr) time scales. 3) The heating from
the shocks alone is sufficient to balance radiative cooling of the gas within
at least the central 10 kpc, allowing feedback to operate isotropically at
small radii. |
Foreground-immune CMB lensing with shear-only reconstruction: CMB lensing from current and upcoming wide-field CMB experiments such as
AdvACT, SPT-3G and Simons Observatory relies heavily on temperature (vs.
polarization). In this regime, foreground contamination to the temperature map
produces significant lensing biases, which cannot be fully controlled by
multi-frequency component separation, masking or bias hardening. In this
letter, we split the standard CMB lensing quadratic estimator into a new set of
optimal "multipole" estimators. On large scales, these multipole estimators
reduce to the known magnification and shear estimators, and a new shear B-mode
estimator. We leverage the different symmetries of the lensed CMB and
extragalactic foregrounds to argue that the shear-only estimator should be
approximately immune to extragalactic foregrounds. We build a new method to
compute separately and without noise the primary, secondary and trispectrum
biases to CMB lensing from foreground simulations. Using this method, we
demonstrate that the shear estimator is indeed insensitive to extragalactic
foregrounds, even when applied to a single-frequency temperature map
contaminated with CIB, tSZ, kSZ and radio point sources. This dramatic
reduction in foreground biases allows us to include higher temperature
multipoles than with the standard quadratic estimator, thus increasing the
total lensing signal-to-noise beyond the quadratic estimator. In addition,
magnification-only and shear B-mode estimators provide useful diagnostics for
potential residuals. Our Python code LensQuEst to forecast the signal-to-noise
of the various estimators, generate mock maps, lense them, and apply the
various lensing estimators to them is publicly available at
https://github.com/EmmanuelSchaan/LensQuEst . | Topology and Geometry of Gaussian random fields I: on Betti Numbers,
Euler characteristic and Minkowski functionals: This study presents a numerical analysis of the topology of a set of
cosmologically interesting three-dimensional Gaussian random fields in terms of
their Betti numbers $\beta_0$, $\beta_1$ and $\beta_2$. We show that Betti
numbers entail a considerably richer characterization of the topology of the
primordial density field. Of particular interest is that Betti numbers specify
which topological features - islands, cavities or tunnels - define its spatial
structure.
A principal characteristic of Gaussian fields is that the three Betti numbers
dominate the topology at different density ranges. At extreme density levels,
the topology is dominated by a single class of features. At low levels this is
a \emph{Swiss-cheeselike} topology, dominated by isolated cavities, at high
levels a predominantly \emph{Meatball-like} topology of isolated objects. At
moderate density levels, two Betti number define a more \emph{Sponge-like}
topology. At mean density, the topology even needs three Betti numbers,
quantifying a field consisting of several disconnected complexes, not of one
connected and percolating overdensity.
A {\it second} important aspect of Betti number statistics is that they are
sensitive to the power spectrum. It reveals a monotonic trend in which at a
moderate density range a lower spectral index corresponds to a considerably
higher (relative) population of cavities and islands.
We also assess the level of complementary information that Betti numbers
represent, in addition to conventional measures such as Minkowski functionals.
To this end, we include an extensive description of the Gaussian Kinematic
Formula (GKF), which represents a major theoretical underpinning for this
discussion. |
Weak-lensing by the large scale structure in a spatially anisotropic
universe: theory and predictions: This article details the computation of the two-point correlators of the
convergence, $E$- and $B$-modes of the cosmic shear induced by the weak-lensing
by large scale structure assuming that the background spacetime is spatially
homogeneous and anisotropic. After detailing the perturbation equations and the
general theory of weak-lensing in an anisotropic universe, it develops a weak
shear approximation scheme in which one can compute analytically the evolution
of the Jacobi matrix. It allows one to compute the angular power spectrum of
the $E$- and $B$-modes. In the linear regime, the existence of $B$-modes is a
direct tracer of a late time anisotropy and their angular power spectrum scales
as the square of the shear. It is then demonstrated that there must also exist
off-diagonal correlations between the $E$-modes, $B$-modes and convergence that
are linear in the geometrical shear and allow one to reconstruct the
eigendirections of expansion. These spectra can be measured in future large
scale surveys, such as Euclid and SKA, and offer a new tool to test the
isotropy of the expansion of the universe at low redshift. | Did BICEP2 see vector modes? First B-mode constraints on cosmic defects: Scaling networks of cosmic defects, such as strings and textures, actively
generate scalar, vector and tensor metric perturbations throughout the history
of the universe. In particular, {\em vector} modes sourced by defects are an
efficient source of the CMB B-mode polarization. We use the recently released
BICEP2 and POLARBEAR B-mode polarization spectra to constrain properties of a
wide range of different types of cosmic strings networks. We find that in order
for strings to provide a satisfactory fit on their own, the effective
inter-string distance needs to be extremely large -- spectra that fit the data
best are more representative of global strings and textures. When a local
string contribution is considered together with the inflationary B-mode
spectrum, the fit is improved. We discuss implications of these results for
theories that predict cosmic defects. |
21-cm Lensing and the Cold Spot in the Cosmic Microwave Background: An extremely large void and a cosmic texture are two possible explanations
for the cold spot seen in the cosmic microwave background. We investigate how
well these two hypotheses can be tested with weak lensing of 21-cm fluctuations
from the epoch of reionization (EoR) measured with the Square Kilometer Array
(SKA). While the void explanation for the cold spot can be tested with SKA,
given enough observation time, the texture scenario requires significantly
prolonged observations, at the highest frequencies that correspond to the EoR,
over the field of view containing the cold spot. | The ATLAS3D project - II. Morphologies, kinemetric features and
alignment between photometric and kinematic axes of early-type galaxies: [Abridged] We use the ATLAS3D sample of 260 early-type galaxies (ETGs) to
study the apparent kinematic misalignment angle, Psi, defined as the angle
between the photometric and kinematic major axis. We find that 71% of nearby
ETGs are strictly aligned systems (Psi > 5 deg), an additional 14% have 5 < Psi
< 10 deg and 90% of galaxies have Psi < 15 deg. Taking into account measurement
uncertainties, 90% of galaxies can be considered aligned to better than 5 deg,
suggesting that only a small fraction of early-type galaxies (~10%) are not
consistent with axisymmetry within the projected half-light radius. We identify
morphological features such as bars and rings (30%), dust structures (16%),
blue nuclear colours (6%) and evidence of interactions (8%). We use kinemetry
to analyse the mean velocity maps and separate galaxies in two broad types of
regular and non-regular rotators. We find 82% of regular rotators and 17%
non-regular rotators, with 2 galaxies that we were not able to classify due to
data quality. The non-regular rotators are typically found in dense regions and
are massive. The majority of galaxies do not have any specific kinemetric
features, but we highlight here the frequency of the kinematically distinct
cores (7%) and the aligned double peaks in the velocity dispersion maps (4%).
Most of the galaxies that are misaligned have complex kinematics and are
non-regular rotators. While the trends are weak, there is a tendency that large
values of Psi are found in galaxies at intermediate environmental densities and
among the most massive galaxies in the sample. We suggest that the most common
formation mechanism for ETGs preserves the axisymmetry of the disk progenitors.
Less commonly, the formation process results in a triaxial galaxy with much
lower net angular momentum. |
The Aemulus Project VI: Emulation of beyond-standard galaxy clustering
statistics to improve cosmological constraints: There is untapped cosmological information in galaxy redshift surveys in the
non-linear regime. In this work, we use the AEMULUS suite of cosmological
$N$-body simulations to construct Gaussian process emulators of galaxy
clustering statistics at small scales ($0.1-50 \: h^{-1}\,\mathrm{Mpc}$) in
order to constrain cosmological and galaxy bias parameters. In addition to
standard statistics -- the projected correlation function
$w_\mathrm{p}(r_\mathrm{p})$, the redshift-space monopole of the correlation
function $\xi_0(s)$, and the quadrupole $\xi_2(s)$ -- we emulate statistics
that include information about the local environment, namely the underdensity
probability function $P_\mathrm{U}(s)$ and the density-marked correlation
function $M(s)$. This extends the model of AEMULUS III for redshift-space
distortions by including new statistics sensitive to galaxy assembly bias. In
recovery tests, we find that the beyond-standard statistics significantly
increase the constraining power on cosmological parameters of interest:
including $P_\mathrm{U}(s)$ and $M(s)$ improves the precision of our
constraints on $\Omega_m$ by 27%, $\sigma_8$ by 19%, and the growth of
structure parameter, $f \sigma_8$, by 12% compared to standard statistics. We
additionally find that scales below $\sim6 \: h^{-1}\,\mathrm{Mpc}$ contain as
much information as larger scales. The density-sensitive statistics also
contribute to constraining halo occupation distribution parameters and a
flexible environment-dependent assembly bias model, which is important for
extracting the small-scale cosmological information as well as understanding
the galaxy-halo connection. This analysis demonstrates the potential of
emulating beyond-standard clustering statistics at small scales to constrain
the growth of structure as a test of cosmic acceleration. | Chiral primordial blue tensor spectra from the axion-gauge couplings: We suggest the new feature of primordial gravitational waves sourced by the
axion-gauge couplings, whose forms are motivated by the dimensional reduction
of the form field in the string theory.
In our inflationary model, as an inflaton we adopt two types of axion, dubbed
the model-independent axion and the model-dependent axion, which couple with
two gauge groups with different sign combination each other.
Due to these forms both polarization modes of gauge fields are amplified and
enhance both helicies of tensor modes during inflation.
We point out the possibility that a primordial blue-tilted tensor power
spectra with small chirality are provided by the combination of these
axion-gauge couplings, intriguingly both amplitudes and chirality are
potentially testable by future space-based gravitational wave interferometers
such as DECIGO and BBO project. |
Mirror dark matter cosmology - predictions for $N_{eff} [CMB]$ and
$N_{eff} [BBN]$: Mirror dark matter interacting with ordinary matter via photon-mirror photon
kinetic mixing can explain the DAMA, CoGeNT and CRESSTII direct detection
experiments. This explanation requires kinetic mixing of strength $\epsilon
\sim 10^{-9}$. Such kinetic mixing will have important implications for early
Universe cosmology. We calculate the additional relativistic energy density at
recombination, $\delta N_{eff} [CMB]$. We also calculate the effects for big
bang nucleosynthesis, $\delta N_{eff} [BBN]$. Current hints that both $\delta
N_{eff} [CMB]$ and $\delta N_{eff} [BBN]$ are non-zero and positive can be
accommodated within this framework if $\epsilon \approx few \times 10^{-9}$. In
the near future, measurements from the Planck mission will either confirm these
hints or constrain $\epsilon \stackrel{<}{\sim} 10^{-9}$. | GalWeight: A New and Effective Weighting Technique for Determining
Galaxy Cluster and Group Membership: We introduce GalWeight, a new technique for assigning galaxy cluster
membership. This technique is specifically designed to simultaneously maximize
the number of bona fide cluster members while minimizing the number of
contaminating interlopers. The GalWeight technique can be applied to both
massive galaxy clusters and poor galaxy groups. Moreover, it is effective in
identifying members in both the virial and infall regions with high efficiency.
We apply the GalWeight technique to MDPL2 \& Bolshoi N-body simulations, and
find that it is $> 98\%$ accurate in correctly assigning cluster membership. We
show that GalWeight compares very favorably against four well-known existing
cluster membership techniques (shifting gapper, den Hartog, caustic, SIM). We
also apply the GalWeight technique to a sample of twelve Abell clusters
(including the Coma cluster) using observations from the Sloan Digital Sky
Survey. We end by discussing GalWeight's potential for other astrophysical
applications. |
Tracing the redshift evolution of Hubble parameter with
gravitational-wave standard sirens: Proposed space-based gravitational-wave detectors such as BBO and DECIGO can
detect ~10^6 neutron-star binaries and determine luminosity distance to the
binaries with a high precision. Combining the luminosity distance and
electromagnetically-derived redshift, one would be able to probe cosmological
expansion out to high redshift. In this paper, we show that the Hubble
parameter as a function of redshift can be directly measured with monopole and
dipole components of the luminosity distance on the sky. As a result, the
measurement accuracies of the Hubble parameter in each redshift bin up to z=1
are 3-14 %, 1.5-8 %, and 0.8-4% for the observation time 1 yr, 3 yr, and 10 yr,
respectively. | Extreme host galaxy growth in powerful early-epoch radio galaxies: During the first half of the universe's age, a heyday of star-formation must
have occurred because many massive galaxies are in place after that epoch in
cosmic history. Our observations with the revolutionary Herschel Space
Observatory reveal vigorous optically obscured star-formation in the
ultra-massive hosts of many powerful high-redshift 3C quasars and radio
galaxies. This symbiotic occurrence of star-formation and black hole driven
activity is in marked contrast to recent results dealing with Herschel
observations of X-ray selected active galaxies. Three archetypal radio
galaxies, at redshifts 1.132,1.575, and 2.474 are presented here, with inferred
star-formation rates of hundreds of solar masses per year. A series of
spectacular coeval AGN/starburst events may have formed these ultra-massive
galaxies and their massive central black holes during their relatively short
lifetimes. |
A Multi-Wavelength Analysis of NGC 4178: A Bulgeless Galaxy with an AGN: We present {\it Gemini} longslit optical spectroscopy and VLA radio
observations of the nuclear region of NGC 4178, a late-type bulgeless disk
galaxy recently confirmed to host an AGN through infrared and X-ray
observations. Our observations reveal that the dynamical center of the galaxy
is coincident with the location of the {\it Chandra} X-ray point source
discovered in a previous work, providing further support for the presence of an
AGN. While the X-ray and IR observations provide robust evidence for an AGN,
the optical spectrum shows no evidence for the AGN, underscoring the need for
the penetrative power of mid-IR and X-ray observations in finding buried or
weak AGNs in this class of galaxy. Finally, the upper limit to the radio flux,
together with our previous X-ray and IR results, is consistent with the
scenario in which NGC 4178 harbors a deeply buried AGN accreting at a high
rate. | Exotic Image Formation in Strong Gravitational Lensing by Clusters of
Galaxies -- III: Statistics with HUDF: We study the image formation near point singularities (swallowtail and
umbilics) in the simulated strongly lensed images of Hubble Ultra Deep Field
(HUDF) by the Hubble Frontier Fields (HFF) clusters. In this work, we only
consider nearly half of the brightest (a total of 5271) sources in the HUDF
region. For every HFF cluster, we constructed 11 realizations of strongly
lensed HUDF with an arbitrary translation of the cluster centre within the
central region of HUDF and an arbitrary rotation. In each of these
realizations, we visually identify the characteristic/exotic image formation
corresponding to the different point singularities. We find that our current
results are consistent with our earlier results based on different approaches.
We also study time delay in these exotic image formations and compare it with
typical five-image geometries. We find that the typical time delay in exotic
image formations is an order of magnitude smaller than the typical time delay
in a generic five-image geometry. |
Intermediate inflation in Gauss-Bonnet braneworld: In this article we study an intermediate inflationary universe models using
the Gauss-Bonnet brane. General conditions required for these models to be
realizable are derived and discussed. We use recent astronomical observations
to constraint the parameters appearing in the model. | Faraday Rotation Measure due to the Intergalactic Magnetic Field II: the
Cosmological Contribution: We investigate the Faraday rotation measure (RM) due to the intergalactic
magnetic field (IGMF) through the cosmic web up to cosmological distances,
using a model IGMF based on turbulence dynamo in the large-scale structure of
the universe. By stacking the IGMF and gas density data up to redshift $z=5$
and taking account of the redshift distribution of polarized background radio
sources against which the RM is measured, we simulate the sky map of the RM.
The contribution from galaxy clusters is subtracted from the map, based on
several different criteria of X-ray brightness and temperature. Our findings
are as follows. The distribution of RM for radio sources of different redshifts
shows that the root-mean-square (rms) value increases with redshift and
saturates for $z \ga 1$. The saturated value is RM$_{\rm rms} \approx$ several
${\rm rad m^{-2}}$. The probability distribution function of $|{\rm RM}|$
follows the lognormal distribution. The power spectrum has a broad plateau over
the angular scale of $\sim 1 - 0.1^\circ$ with a peak around $\sim 0.15^\circ$.
The second-order structure function has a flat profile in the angular
separation of $\ga 0.2^\circ$. Our results could provide useful insights for
surveys to explore the IGMF with the Square Kilometer Array (SKA) and upcoming
SKA pathfinders. |
Observational constraints on an interacting dark energy model: We use observations of cosmic microwave background anisotropies, supernova
luminosities and the baryon acoustic oscillation signal in the galaxy
distribution to constrain the cosmological parameters in a simple interacting
dark energy model with a time-varying equation of state. Using a Monte Carlo
Markov Chain technique we determine the posterior likelihoods. Constraints from
the individual data sets are weak, but the combination of the three data sets
confines the interaction constant $\Gamma$ to be less than 23% of the expansion
rate of the Universe $H_0$; at 95% CL $-0.23 < \Gamma/H_0 < +0.15$. The CMB
acoustic peaks can be well fitted even if the interaction rate is much larger,
but this requires a larger or smaller (depending on the sign of interaction)
matter density today than in the non-interacting model. Due to this degeneracy
between the matter density and the interaction rate, the only observable effect
on the CMB is a larger or smaller integrated Sachs-Wolfe (ISW) effect. While SN
or BAO data alone do not set any direct constraints on the interaction, they
exclude the models with very large matter density, and hence indirectly
constrain the interaction rate when jointly analysed with the CMB data. To
enable the analysis described in this paper, we present in a companion paper
[arXiv:0907.4981] a new systematic analysis of the early radiation era solution
to find the adiabatic initial conditions for the Boltzmann integration. | The Faint End of the Quasar Luminosity Function at z~4: We have conducted a spectroscopic survey to find faint quasars (-26.0 <
M_{1450} < -22.0) at redshifts z=3.8-5.2 in order to measure the faint end of
the quasar luminosity function at these early times. Using available optical
imaging data from portions of the NOAO Deep Wide-Field Survey and the Deep Lens
Survey, we have color-selected quasar candidates in a total area of 3.76 deg^2.
Thirty candidates have R <= 23 mags. We conducted spectroscopic followup for 28
of our candidates and found 23 QSOs, 21 of which are reported here for the
first time, in the 3.74 < z <5.06 redshift range. We estimate our survey
completeness through detailed Monte Carlo simulations and derive the first
measurement of the density of quasars in this magnitude and redshift interval.
We find that the binned luminosity function is somewhat affected by the
K-correction used to compute the rest-frame absolute magnitude at 1450A.
Considering only our R <= 23 sample, the best-fit single power-law (Phi \propto
L^beta) gives a faint-end slope beta = -1.6+/-0.2. If we consider our larger,
but highly incomplete sample going one magnitude fainter, we measure a steeper
faint-end slope -2 < beta < -2.5. In all cases, we consistently find faint-end
slopes that are steeper than expected based on measurements at z ~ 3. We
combine our sample with bright quasars from the Sloan Digital Sky Survey to
derive parameters for a double-power-law luminosity function. Our best fit
finds a bright-end slope, alpha = -2.4+/-0.2, and faint-end slope, beta =
-2.3+/-0.2, without a well-constrained break luminosity. This is effectively a
single power-law, with beta = -2.7+/-0.1. We use these results to place limits
on the amount of ultraviolet radiation produced by quasars and find that
quasars are able to ionize the intergalactic medium at these redshifts. |
The Great Observatories Origins Deep Survey - VLT/ISAAC Near-Infrared
Imaging of the GOODS-South Field: We present the final public data release of the VLT/ISAAC near-infrared
imaging survey in the GOODS-South field. The survey covers an area of 172.5,
159.6 and 173.1 arcmin^2 in the J, H, and Ks bands, respectively. For point
sources total limiting magnitudes of J=25.0, H=24.5, and Ks=24.4 (5 sigma, AB)
are reached within 75% of the survey area. Thus these observations are
significantly deeper than the previous EIS Deep Public Survey which covers the
same region. The image quality is characterized by a point spread function
ranging between 0.34 arcsec and 0.65 arcsec FWHM. The images are registered
with an accuracy of ~0.06 arcsec RMS over the whole field. The overall
photometric accuracy, including all systematic effects, adds up to 0.05 mag.
The data are publicly available from the ESO science archive facility. We
define a catalog of Ks-selected sources which contains JHKs photometry for 7079
objects. We briefly discuss the resulting color distributions in the context of
available redshift data. Furthermore, we estimate the completeness fraction and
relative contamination due to spurious detections for source catalogs extracted
from the survey data. With respect to previous deep near-infrared surveys, the
surface density of faint galaxies has been established with unprecedented
accuracy by virtue of the unique combination of depth and area of this survey.
We derived galaxy number counts over eight magnitudes in flux up to J=25.25,
H=25.0, Ks=25.25 (in the AB system). Very similar faint-end logarithmic slopes
between 0.24 and 0.27 per mag were measured in the three bands. We found no
evidence for a significant change in the slope of the logarithmic galaxy number
counts at the faint end. | Caught in the cosmic web: Environmental effect on halo concentrations,
shape, and spin: Using a set of high-resolution simulations we study the statistical
correlation of dark matter halo properties with the large-scale environment. We
consider halo populations split into four Cosmic Web (CW) elements: voids,
walls, filaments, and nodes. For the first time we present a study of CW
effects for halos covering six decades in mass: $10^{8}-10^{14}{h^{-1}{\rm
M}_{\odot}}$. We find that the fraction of halos living in various web
components is a strong function of mass, with the majority of
$M>10^{12}{h^{-1}{\rm M}_{\odot}}$ halos living in filaments and nodes. Low
mass halos are more equitably distributed in filaments, walls, and voids. For
halo density profiles and formation times we find a universal mass threshold of
$M_{th}\sim6\times10^{10}{h^{-1}{\rm M}_{\odot}}$ below which these properties
vary with environment. Here, filament halos have the steepest
concentration-mass relation, walls are close to the overall mean, and void
halos have the flattest relation. This amounts to $c_{200}$ for filament and
void halos that are respectively $14\%$ higher and $7\%$ lower than the mean at
$M=2\times10^8{h^{-1}{\rm M}_{\odot}}$, with low-mass node halos being most
likely splashed-back. We find double power-law fits that very well describe
$c(M)$ for the four environments in the whole probed mass range. A
complementary picture is found for the average formation times, with the
mass-formation time relations following trends shown for the concentrations:
the nodes halos being the oldest and void halo the youngest. The CW
environmental effect is much weaker when studying the halo spin and shapes. The
trends with halo mass is reversed: the small halos with $M<10^{10}{h^{-1}{\rm
M}_{\odot}}$ seem to be unaffected by the CW environment. Some weak trends are
visible for more massive void and walls halos, which, on average, are
characterized by lower spin and higher triaxiality parameters. |
Indications of a late-time interaction in the dark sector: We show that a general late-time interaction between cold dark matter and
vacuum energy is favoured by current cosmological datasets. We characterize the
strength of the coupling by a dimensionless parameter $q_V$ that is free to
take different values in four redshift bins from the primordial epoch up to
today. This interacting scenario is in agreement with measurements of cosmic
microwave background temperature anisotropies from the Planck satellite,
supernovae Ia from Union 2.1 and redshift space distortions from a number of
surveys, as well as with combinations of these different datasets. We show that
a non-zero interaction is very likely at late times. We then focus on the case
$q_V\not=0$ in a single low-redshift bin, obtaining a nested one parameter
extension of the standard $\Lambda$CDM model. We study the Bayesian evidence,
with respect to $\Lambda$CDM, of this late-time interaction model, finding
moderate evidence for an interaction starting at $z=0.9$, dependent upon the
prior range chosen for the interaction strength parameter $q_V$. For this case
the null interaction ($q_V=0$, i.e.$\Lambda$CDM) is excluded at 99% c.l.. | Lognormal Distribution of Cosmic Voids in Simulations and Mocks: Following up on previous studies, we here complete a full analysis of the
void size distributions of the Cosmic Void Catalog (CVC) based on three
different simulation and mock catalogs; dark matter, haloes and galaxies. Based
on this analysis, we attempt to answer two questions: Is a 3-parameter
log-normal distribution a good candidate to satisfy the void size distributions
obtained from different types of environments? Is there a direct relation
between the shape parameters of the void size distribution and the
environmental effects? In an attempt to answer these questions, we here find
that all void size distributions of these data samples satisfy the 3-parameter
log-normal distribution whether the environment is dominated by dark matter,
haloes or galaxies. In addition, the shape parameters of the 3-parameter
log-normal void size distribution seem highly affected by environment,
particularly existing substructures. Therefore, we show two quantitative
relations given by linear equations between the skewness and the maximum tree
depth, and variance of the void size distribution and the maximum tree depth
directly from the simulated data. In addition to this, we find that the
percentage of the voids with nonzero central density in the data sets has a
critical importance. If the number of voids with nonzero central densities
reaches greater and or equal to 3.84 percentage in a simulation/mock sample,
then a second population is observed in the void size distributions. This
second population emerges as a second peak in the log-normal void size
distribution at larger radius. |
Hierarchical Inference With Bayesian Neural Networks: An Application to
Strong Gravitational Lensing: In the past few years, approximate Bayesian Neural Networks (BNNs) have
demonstrated the ability to produce statistically consistent posteriors on a
wide range of inference problems at unprecedented speed and scale. However, any
disconnect between training sets and the distribution of real-world objects can
introduce bias when BNNs are applied to data. This is a common challenge in
astrophysics and cosmology, where the unknown distribution of objects in our
Universe is often the science goal. In this work, we incorporate BNNs with
flexible posterior parameterizations into a hierarchical inference framework
that allows for the reconstruction of population hyperparameters and removes
the bias introduced by the training distribution. We focus on the challenge of
producing posterior PDFs for strong gravitational lens mass model parameters
given Hubble Space Telescope (HST) quality single-filter, lens-subtracted,
synthetic imaging data. We show that the posterior PDFs are sufficiently
accurate (i.e., statistically consistent with the truth) across a wide variety
of power-law elliptical lens mass distributions. We then apply our approach to
test data sets whose lens parameters are drawn from distributions that are
drastically different from the training set. We show that our hierarchical
inference framework mitigates the bias introduced by an unrepresentative
training set's interim prior. Simultaneously, given a sufficiently broad
training set, we can precisely reconstruct the population hyperparameters
governing our test distributions. Our full pipeline, from training to
hierarchical inference on thousands of lenses, can be run in a day. The
framework presented here will allow us to efficiently exploit the full
constraining power of future ground- and space-based surveys. | Some spectral properties of the quasar ultraviolet bump: In the present work the part of the quasar UV-optical bump within the
wavelength range 1210-1450\AA\ was studied with the help of composite spectra
compiled from the samples of SDSS DR7 spectra with the similar spectral index
\alpha_{\lambda} within 1270-1480 \AA. This division allowed to see weak
emission lines, which were not detected in previous studies of the quasar
composite spectra, but were known from individual optical or composite UV
spectra from the Hubble Space Telescope. Although the physical explanation of
the difference in spectral indices between quasars and their dependence on
quasar parameters is still not clear, it is obvious that this difference has to
be taken into account when generating composite spectra, e.g. for redshift
measurements. It was also shown that the equivalent width of the emission lines
does not depend on the spectral index. |
Daughters mimic sterile neutrinos (almost!) perfectly: Since only recently, cosmological observations are sensitive to hot dark
matter (HDM) admixtures with sub-eV mass, $m_\text{hdm}^\text{eff}$ < eV, that
are not fully-thermalised, $N_\text{eff}$ < 1. We argue that their almost
automatic interpretation as a sterile neutrino species is neither from
theoretical nor practical parsimony principles preferred over HDM formed by
decay products (daughters) of an out-of-equilibrium particle decay. While
daughters mimic sterile neutrinos in $N_\text{eff}$ and
$m_\text{hdm}^\text{eff}$, there are opportunities to assess this possibility
in likelihood analyses. Connecting cosmological parameters and moments of
momentum distribution functions, we show that --also in the case of
mass-degenerate daughters with indistinguishable main physical effects-- the
mimicry breaks down when the next moment, the skewness, is considered.
Predicted differences of order one in the root-mean-squares of absolute momenta
are too small for current sensitivities. | Neutrino Masses, Dark Energy and the Gravitational Lensing of
Pregalactic HI: We study the constraints which the next generation of radio telescopes could
place on the mass and number of neutrino species by studying the gravitational
lensing of high redshift 21 cm emission in combination with wide-angle surveys
of galaxy lensing. We use simple characterizations of reionization history and
of proposed telescope designs to forecast the constraints and detectability
threshold for neutrinos. It is found that the degeneracy between neutrino
parameters and dark energy parameters is significantly reduced by incorporating
21 cm lensing. The combination of galaxy and 21 cm lensing could constrain the
sum of the neutrino masses to within ~ 0.04 eV and the number of species to
within ~ 0.1. This is an improvement of a factor of 2.6 in mass and 1.3 in
number over a galaxy lensing survey alone. This includes marginalizing over an
11 parameter cosmological model with a two parameter model for the dark energy
equation of state. If the dark energy equation of state is held fixed at w =
p/\rho=-1 the constraints improve to ~0.03 eV and 0.04. These forecasted errors
depend critically on the fraction of sky that can be surveyed in redshifted 21
cm emission (25% is assumed here) and the redshift of reionization ($z=7$ is
assumed here). It is also found that neutrinos with masses too small to be
detected in the data could none the less cause a significant bias in the
measured dark energy equation of state. |
XMM-Newton, Swift and ROSAT observations of LBQS 0102-2713: We have analyzed the first XMM-Newton, Swift and archival ROSAT PSPC
observations of the quasar LBQS 0102-2713.The object was selected from the
ROSAT archive as being notable due to the steep soft X-ray photon index and due
to the UV brightness based on HST and optical spectroscopic observations. The
first XMM-Newton observations carried out in December 2009 and the first Swift
observations from 2010 have confirmed the steepness of the soft X-ray photon
index, which ranges between 3.35 and 4.41 for the different XMM-Newton and
ROSAT detectors, the UV brightness of the source and the absence of significant
absorption by neutral hydrogen. The new data allow a combined spectral fitting
to the Swift UVOT and the XMM-Newton/ROSAT data which results in a huge
luminosity of (6.2+-0.2)x10^47 erg s^(-1) and alpha_ox values ranging between
(-1.87+-0.11) and (-2.11+-0.12). The nature of the soft X-ray emission can be
explained as local Comptonized emission of the UV disc photons in the
pseudo-Newtonian potential. The black hole mass is estimated from the Mg II
line and translates into an Eddington ratio of L/L_edd = 18(+33)(-12). For the
dimensionless electron temperature of the plasma cloud theta = kT_e/ (m_e c^2)
we derive an upper limit of about 10 keV. | The X-ray emission of local luminous infrared galaxies: We study the X-ray emission of a representative sample of 27 local luminous
infrared galaxies (LIRGs). The median IR luminosity of our sample is log
L_IR/L_sun = 11.2, thus the low-luminosity end of the LIRG class is well
represented. We used new XMM-Newton data as well as Chandra and XMM-Newton
archive data. The soft X-ray (0.5-2 keV) emission of most of the galaxies
(>80%), including LIRGs hosting a Seyfert 2 nucleus, is dominated by
star-formation related processes. These LIRGs follow the star-formation rate
(SFR) versus soft X-ray luminosity correlation observed in local starbursts. We
find that ~15% of the non-Seyfert LIRGs (3 out of 20) have an excess hard X-ray
emission relative to that expected from star-formation that might indicate the
presence of an obscured AGN. The rest of the non-Seyfert LIRGs follow the SFR
versus hard X-ray (2-10 keV) luminosity correlation of local starbursts. The
non-detection of the 6.4 keV Fe K alpha emission line in the non-Seyfert LIRGs
allows us to put an upper limit to the bolometric luminosity of an obscured
AGN, L_bol <1043 erg s-1 . That is, in these galaxies, if they hosted a low
luminosity AGN, its contribution to total luminosity would be less than 10%.
Finally we estimate that the AGN contribution to the total luminosity for our
sample of local LIRGs is between 7% and 10%. |
Cosmological implications of gravitational collapse in F(R) theories: We will make a comparison between the dynamics of spherical gravitational
collapse for a perturbed FLRW universe to first order in the context of general
relativity, with the corresponding results obtained for the gravitational
collapse under theories of modified gravity f(R). This work is aimed at
obtaining an analytical model of explanation a source of large scale structures
in the universe presenting an approximation of model spherical gravitational
collapse under theories of modified gravity f(R). | Detection of intercluster gas in superclusters using the thermal
Sunyaev-Zel'dovich effect: Using a thermal Sunyaev-Zel'dovich (tSZ) signal, we search for hot gas in
superclusters identified using the Sloan Digital Sky Survey Data Release 7
(SDSS/DR7) galaxies. We stack a Comptonization y map produced by the Planck
Collaboration around the superclusters and detect the tSZ signal at a
significance of 6.4 sigma. We further search for an intercluster component of
gas in the superclusters. For this, we remove the intracluster gas in the
superclusters by masking all galaxy groups/clusters detected by the Planck tSZ,
ROSAT X-ray, and SDSS optical surveys down to a total mass of 10^13 Msun. We
report the first detection of intercluster gas in superclusters with y = (3.5
+- 1.4) * 10^(-8) at a significance of 2.5 sigma. Assuming a simple isothermal
and flat density distribution of intercluster gas over superclusters, the
estimated baryon density is (Omega_gas / Omega_b) * (T_e/(8*10^6 K)) = 0.067 +-
0.006 +- 0.025. This quantity is inversely proportional to the temperature,
therefore taking values from simulations and observations, we find that the gas
density in superclusters may account for 17 - 52 % of missing baryons at low
redshifts. A better understanding of the physical state of gas in the
superclusters is required to accurately estimate the contribution of our
measurements to missing baryons. |
Not a Copernican observer: biased peculiar velocity statistics in the
local Universe: We assess the effect of the local large scale structure on the estimation of
two-point statistics of the observed radial peculiar velocities of galaxies. A
large N-body simulation is used to examine these statistics from the
perspective of random observers as well as "Local Group (LG)-like" observers
conditioned to reside in an environment resembling the observed universe within
20 Mpc. The local environment systematically distorts the shape and amplitude
of velocity statistics with respect to ensemble-averaged measurements made by a
Copernican (random) observer. The Virgo cluster has the most significant
impact, introducing large systematic deviations in all the statistics. For a
simple "top-hat" selection function, an idealized survey extending to $\sim
160h^{-1}\,{\rm Mpc}$ or deeper is needed to completely mitigate the effects of
the local environment. Using shallower catalogues leads to systematic
deviations of the order of $50$ to $200\%$ depending on the scale considered.
For a flat redshift distribution similar to the one of the CosmicFlows-3
survey, the deviations are even more prominent in both the shape and amplitude
at all separations considered $({\stackrel{<}{{}_\sim}} 100h^{-1}\,{\rm Mpc})$.
Conclusions based on statistics calculated without taking into account the
impact of the local environment should be revisited. | The kinetic Sunyaev-Zel'dovich signal from inhomogeneous reionization: a
parameter space study: [ABRIDGED] Inhomogeneous reionization acts as a source of arcminute-scale
anisotropies in the cosmic microwave background (CMB), the most important of
which is the kinetic Sunyaev-Zel'dovich (kSZ) effect. Observational efforts
with the Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT)
are poised to detect this signal for the first time. Indeed, recent SPT
measurements place a bound on the dimensionless kSZ power spectrum around a
multipole of l=3000 of P_tot < 2.8 (6) micro K^2 at 95% C.L., by ignoring
(allowing) correlations between the thermal Sunyaev-Zel'dovich (tSZ) effect and
the cosmic infrared background (CIB). To interpret these and upcoming
observations, we compute the kSZ signal from a suite of ~ 100 reionization
models using the publicly available code 21cmFAST. Our physically motivated
reionization models are parameterized by the ionizing efficiency of
high-redshift galaxies, the minimum virial temperature of halos capable of
hosting stars, and the ionizing photon mean free path. We predict the
contribution of patchy reionization to be P_patchy = 1.5-3.5 micro K^2.
Therefore, even when conservatively adopting a low estimate of the
post-reionization signal, P_OV ~ 2 micro K^2, none of our models are consistent
with the aggressive 2sigma SPT bound that does not include correlations. This
implies that either: (i) the early stages of reionization occurred in a much
more homogeneous manner than suggested by the stellar-driven scenarios we
explore, such as would be the case if, e.g., very high energy X-rays or exotic
particles contributed significantly; and/or (ii) that there is a significant
correlation between the CIB and the tSZ. On the other hand, the conservative
SPT bound is compatible with all of our models, and is on the boarder of
constraining reionization. |
An upper limit to the central density of dark matter haloes from
consistency with the presence of massive central black holes: We study the growth rates of massive black holes in the centres of galaxies
from accretion of dark matter from their surrounding haloes. By considering
only the accretion due to dark matter particles on orbits unbound to the
central black hole, we obtain a firm lower limit to the resulting accretion
rate. We find that a runaway accretion regime occurs on a timescale which
depends on the three characteristic parameters of the problem: the initial mass
of the black hole, and the volume density and velocity dispersion of the dark
matter particles in its vicinity. An analytical treatment of the accretion rate
yields results implying that for the largest black hole masses inferred from
QSO studies ($>10^{9} M_{\odot}$), the runaway regime would be reached on time
scales which are shorter than the lifetimes of the haloes in question for
central dark matter densities in excess of $250 M_{\odot}$pc$^{-3}$. Since
reaching runaway accretion would strongly distort the host dark matter halo,
the inferences of QSO black holes in this mass range lead to an upper limit on
the central dark matter densities of their host haloes of $\rho_{0} < 250
M_{\odot} $pc$^{-3}$. This limit scales inversely with the assumed central
black hole mass. However, thinking of dark matter profiles as universal across
galactic populations, as cosmological studies imply, we obtain a firm upper
limit for the central density of dark matter in such structures. | Large scale density perturbations from a uniform distribution by wave
transport: It has long been known that a uniform distribution of matter cannot produce a
Poisson distribution of density fluctuations on very large scales $1/k > ct$ by
the motion of discrete particles over timescale $t$. The constraint is part of
what is sometimes referred to as the Zel'dovich bound. We investigate in this
paper the transport of energy by the propagation of waves emanating {\it
incoherently} from a regular and infinite lattice of oscillators, each having
the same finite amount of energy reserve initially. The model we employ does
not involve the expansion of the Universe -- the scales of interest are all
deeply sub-horizon -- but the size of regions over which perturbations are
evaluated far exceed $ct$, where $t$ is the time elapsed since the start of
emission (it is assumed that $t$ greatly exceeds the duration of emission). We
find that to lowest order, when only wave fields $\propto 1/r$ are included,
there is exact compensation between the energy loss of the oscillators and the
energy emitted into space, which means $P(0)=0$ for the power spectrum of
density fluctuations on the largest scales. This is consistent with the
Zel'dovich bound. To the next order when near fields $\propto r^{-2}$ are
included, however, $P(0)$ settles at late times to a positive value that
depends only on time, as $t^{-2}$ (the same applies to an energy non-conserving
term). Even though this effect looks like superluminal energy transport, there
is no violation of causality because the two-point function vanishes completely
for $r>t$ if the emission of each oscillator is truncated beyond some duration.
The result calls to question any need of enlisting cosmic inflation to seed
large scale density perturbations. When applied to fast radio bursts --
uniformly distributed transients (to lowest order) that repeat at other
locations -- the result supports Hoyle's hypothesis of constant energy
injection. |
The rates of Type Ia Supernovae. II. Diversity of events at low and high
redshift: This paper investigates on the possible systematic difference of Supernovae
Ia (SN Ia) properties related to the age and masses of the progenitors that
could introduce a systematic bias between low and high redshift SN Ia's. The
relation between the main features of the distribution of the delay times (DTD)
and the masses of the progenitors is illustrated for the single (SD) and double
degenerate (DD) models. Mixed models, which assume contributions from both the
SD and DD channels, are also presented and tested versus the observed
correlations between the SN Ia rates and the parent galaxy properties. It is
shown that these correlations can be accounted for with both single channel and
mixed models, and that the rate in S0 and E galaxies may effectively provide
clues on the contribution of SD progenitors to late epoch explosions. A wide
range of masses for the CO WD at the start of accretion is expected in almost
all galaxy types; only in galaxies of the earliest types the properties of the
progenitors are expected to be more uniform. For mixed models, late type
galaxies should host SD and DD explosions in comparable fractions, while in
early type galaxies DD explosions should largely prevail. Events hosted by star
forming galaxies span a wide range of delay times; \textit{prompt} events could
dominate only in the presence of a strong star-burst. It is concluded that
nearby SN Ia samples should well include the young, massive and hot progenitors
that necessarily dominate at high redshift. | Hierarchical Clustering in $Λ$CDM Cosmologies via Persistence
Energy: In this research, we investigate the structural evolution of the cosmic web,
employing advanced methodologies from Topological Data Analysis. Our approach
involves leveraging LITE, an innovative method from recent literature that
embeds persistence diagrams into elements of vector spaces. Utilizing this
methodology, we analyze three quintessential cosmic structures: clusters,
filaments, and voids. A central discovery is the correlation between
\textit{Persistence Energy} and redshift values, linking persistent homology
with cosmic evolution and providing insights into the dynamics of cosmic
structures. |
The Second INTEGRAL AGN Catalogue: The INTEGRAL mission provides a large data set for studying the hard X-ray
properties of AGN and allows testing of the unified scheme for AGN. We present
analysis of INTEGRAL IBIS/ISGRI, JEM-X, and OMC data for 199 AGN supposedly
detected by INTEGRAL above 20 keV. The data analysed here allow a significant
spectral extraction on 148 objects and an optical variability study of 57 AGN.
The slopes of the hard X-ray spectra of Seyfert 1 and Seyfert~2 galaxies are
found to be consistent within the uncertainties, whereas higher cut-off
energies and lower luminosities are measured for the more absorbed / type 2
AGN. The intermediate Seyfert 1.5 objects exhibit hard X-ray spectra consistent
with those of Seyfert 1. When applying a Compton reflection model, the
underlying continua appear the same in Seyfert 1 and 2 with photon index 2, and
the reflection strength is about R = 1, when assuming different inclination
angles. A significant correlation is found between the hard X-ray and optical
luminosity and the mass of the central black hole in the sense that the more
luminous objects appear to be more massive. There is also a general trend
toward the absorbed sources and type 2 AGN having lower Eddington ratios. The
black holemass appears to form a fundamental plane together with the optical
and X-ray luminosity of the form Lv being proportional to Lx^0.6 M^0.2, similar
to that found between radio luminosity Lr, Lx, and M. The unified model for
Seyfert galaxies seems to hold, showing in hard X-rays that the central engine
is the same in Seyfert 1 and 2, but seen under different inclination angles and
absorption. (Abridged) | Characterizing the Pressure Smoothing Scale of the Intergalactic Medium: The thermal state of the intergalactic medium (IGM) at z < 6 constrains the
nature and timing of cosmic reionization events, but its inference from the
Ly-alpha forest is degenerate with the 3-D structure of the IGM on ~100 kpc
scales, where, analogous to the classical Jeans argument, the pressure of the
T~$10^4$ K gas supports it against gravity. We simulate the IGM using smoothed
particle hydrodynamics, and find that, at z < 6, the gas density power spectrum
does not exhibit the expected Jeans filtering cutoff, because dense gas in
collapsed halos dominates the small-scale power masking pressure smoothing
effects. We introduce a new statistic, the real-space Ly-alpha flux,
$F_\mathrm{real}$, which naturally suppresses dense gas, and is thus robust
against the poorly understood physics of galaxy formation, revealing pressure
smoothing in the diffuse IGM. The $F_\mathrm{real}$ power spectrum is
accurately described by a simple fitting function with cutoff at $\lambda_F$,
allowing us to rigorously quantify the filtering scale for the first time: we
find $\lambda_F$ = 79 kpc (comoving) at z=3 for our fiducial thermal model.
This statistic has the added advantage that it directly relates to observations
of correlated Ly-alpha forest absorption in close quasar pairs, recently
proposed as a method to measure the filtering scale. Our results enable one to
quantify the filtering scale in simulations, and ask meaningful questions about
its dependence on reionization and thermal history. Accordingly, the standard
description of the IGM in terms of the amplitude $T_0$ and slope $\gamma$ of
the temperature-density relation $T = T_0\Delta^{\gamma-1}$ should be augmented
with a third filtering scale parameter $\lambda_F$. |
The Weak Lensing Masses of Filaments between Luminous Red Galaxies: In the standard model of non-linear structure formation, a cosmic web of
dark-matter dominated filaments connects dark matter halos. In this paper, we
stack the weak lensing signal of an ensemble of filaments between groups and
clusters of galaxies. Specifically, we detect the weak lensing signal, using
CFHTLenS galaxy ellipticities, from stacked filaments between SDSS-III/BOSS
luminous red galaxies (LRGs). As a control, we compare the physical LRG pairs
with projected LRG pairs that are more widely separated in redshift space. We
detect the excess filament mass density in the projected pairs at the $5\sigma$
level, finding a mass of $(1.6 \pm 0.3) \times 10^{13} M_{\odot}$ for a stacked
filament region 7.1 $h^{-1}$ Mpc long and 2.5 $h^{-1}$ Mpc wide. This filament
signal is compared with a model based on the three-point
galaxy-galaxy-convergence correlation function, as developed in Clampitt, Jain
& Takada (2014), yielding reasonable agreement. | The Odd-Parity Galaxy Bispectrum: The galaxy bispectrum contains a wealth of information about the early
universe, gravity, as well as astrophysics such as galaxy bias. In this paper,
we study the parity-odd part of the galaxy bispectrum which is hitherto
unexplored. In the standard cosmological model, the odd-parity bispectrum is
generated by galaxy velocities through redshift-space distortions. While small
in the case of General Relativity coupled with smooth dark energy, the signal
could be larger in modified gravity scenarios. Thus, apart from being a very
useful consistency test of measurements of galaxy clustering, the odd
bispectrum offers a novel avenue for searching for new physics. |
The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey:
Large-scale Structure Catalogs for Cosmological Analysis: We present large-scale structure catalogs from the completed extended Baryon
Oscillation Spectroscopic Survey (eBOSS). Derived from Sloan Digital Sky Survey
(SDSS) -IV Data Release 16 (DR16), these catalogs provide the data samples,
corrected for observational systematics, and random positions sampling the
survey selection function. Combined, they allow large-scale clustering
measurements suitable for testing cosmological models. We describe the methods
used to create these catalogs for the eBOSS DR16 Luminous Red Galaxy (LRG) and
Quasar samples. The quasar catalog contains 343,708 redshifts with $0.8 < z <
2.2$ over 4,808\,deg$^2$. We combine 174,816 eBOSS LRG redshifts over
4,242\,deg$^2$ in the redshift interval $0.6 < z < 1.0$ with SDSS-III BOSS LRGs
in the same redshift range to produce a combined sample of 377,458 galaxy
redshifts distributed over 9,493\,deg$^2$. Improved algorithms for estimating
redshifts allow that 98 per cent of LRG observations result in a successful
redshift, with less than one per cent catastrophic failures ($\Delta z > 1000$
${\rm km~s}^{-1}$). For quasars, these rates are 95 and 2 per cent (with
$\Delta z > 3000$ ${\rm km~s}^{-1}$). We apply corrections for trends between
the number densities of our samples and the properties of the imaging and
spectroscopic data. For example, the quasar catalog obtains a $\chi^2$/DoF$=
776/10$ for a null test against imaging depth before corrections and a
$\chi^2$/DoF$=6/8$ after. The catalogs, combined with careful consideration of
the details of their construction found here-in, allow companion papers to
present cosmological results with negligible impact from observational
systematic uncertainties. | Investigating Emission Line Galaxy Surveys with the Sloan Digital Sky
Survey Telescope: The Baryon Acoustic Oscillation (BAO) feature in the power spectrum of
galaxies provides a standard ruler to probe the accelerated expansion of the
Universe. The current surveys covering a comoving volume sufficient to unveil
the BAO scale are limited to redshift $z \lesssim 0.7$. In this paper, we study
several galaxy selection schemes aiming at building an emission-line-galaxy
(ELG) sample in the redshift range $0.6<z<1.7$, that would be suitable for
future BAO studies using the Baryonic Oscillation Spectroscopic Survey (BOSS)
spectrograph on the Sloan Digital Sky Survey (SDSS) telescope. We explore two
different colour selections using both the SDSS and the Canada France Hawai
Telescope Legacy Survey (CFHT-LS) photometry in the u, g, r, and i bands and
evaluate their performance selecting luminous ELG. From about 2,000 ELG, we
identified a selection scheme that has a 75 percent redshift measurement
efficiency. This result confirms the feasibility of massive ELG surveys using
the BOSS spectrograph on the SDSS telescope for a BAO detection at redshift
$z\sim1$, in particular the proposed eBOSS experiment, which plans to use the
SDSS telescope to combine the use of the BAO ruler with redshift space
distortions using emission line galaxies and quasars in the redshift
$0.6<z<2.2$. |
The Complex Structure of the Multi-Phase Galactic Wind in a Starburst
Merger: Neutral outflows have been detected in many ultraluminous infrared galaxies
(ULIRGs) via the Na I D $\lambda\lambda 5890, 5896$ absorption-line doublet.
For the first time, we have mapped and analyzed the 2-D kinematics of a cool
neutral outflow in a ULIRG, F10565+2448, using the integral field unit (IFU) on
Gemini North to observe the Na I D feature. At the same time we have mapped the
ionized outflow with the [NII] and H$\alpha$ emission lines. We find a systemic
rotation curve that is consistent with the rotation of the molecular disk
determined from previous CO observations. The absorption lines show evidence of
a nuclear outflow with a radial extent of at least 3 kpc, consistent with
previous observations. The strength of the Na I D lines have a strong,
spatially resolved correlation with reddening, suggesting that dust is present
in the outflow. Surprisingly, the outflow velocities of the neutral gas show a
strong asymmetry in the form of a major-axis gradient that is opposite in sign
to disk rotation. This is inconsistent with entrained material rotating along
with the galaxy or with a tilted minor-axis outflow. We hypothesize that this
unusual behavior is due to an asymmetry in the distribution of the ambient gas.
We also see evidence of asymmetric ionized outflow in the emission-line
velocity map, which appear to be decoupled from the neutral outflow. Our
results strengthen the hypothesis that ULIRG outflows differ in morphology from
those in more quiescent disk galaxies. | Maximal spin and energy conversion efficiency in a symbiotic system of
black hole, disk and jet: We study a combined model of black hole - accretion disk - magnetosphere -
jet symbiosis, applicable for supermassive black holes. We quantify the mass
and spin evolution and we analyze how the limiting value of the spin parameter
and the conversion efficiency of accreted mass into radiation depend on the
interplay of electromagnetic radiation reaction, magnetosphere characteristics
and truncation radius of radiation. The dominant effect comes from the closed
magnetic field line region, which reduces the spin limit to values ~0.89
(instead ~0.99 in its absence). Therefore observations on black hole spins
could favour or disfavour the existence of the closed magnetic field line
region (or its coupling to the disk). We also find that the suppression of
radiation from the innermost part of the accretion disk, inferred from
observations, and a collimated jet both increase the spin limit and the energy
conversion efficiency. |
Weighing the Neutrinos with the Galaxy Shape-Shape Correlations: The galaxies form and evolve in the early epochs through the anisotropic
merging process along the primary narrow filaments, in the direction of which
their shapes become elongated and intrinsically aligned. The nonlinear
evolution of the cosmic web broadens the primary filaments, by entangling them
with multiple secondary filaments, which has an effect of reducing the
anisotropy of the merging process and in consequence weakens the galaxy
shape-shape correlations in the later epochs. Assuming that the degree of the
nonlinearity and complexity of the cosmic web depends on the nature of dark
matter, we propose a hypothesis that the galaxy shape-shape correlation
function, $\eta(r)$, may be a powerful complimentary probe of the total
neutrino mass, $M_{\nu}$. Testing this hypothesis against a high resolution
N-body simulation, we show that the $M_{\nu}$-dependence of $\eta(r)$ at $z=0$
is sensitive enough to distinguish between $M_{\nu}=0.0$ eV and $M_{\nu}=0.1$
eV. We also show that the differences in $\eta(r)$ at $r\le 5\,h^{-1}$Mpc
between the models with massless and massive neutrinos cannot be explained by
their differences in the small-scale density powers, $\sigma_{8}$, which
implies that the galaxy shape-shape correlation function has a potential to
break the notorious cosmic degeneracy between $M_{\nu}$ and $\sigma_{8}$. | Probing the cosmic web: inter-cluster filament detection using
gravitational lensing: The problem of detecting dark matter filaments in the cosmic web is
considered. Weak lensing is an ideal probe of dark matter, and therefore forms
the basis of particularly promising detection methods. We consider and develop
a number of weak lensing techniques that could be used to detect filaments in
individual or stacked cluster fields, and apply them to synthetic lensing data
sets in the fields of clusters from the Millennium Simulation. These techniques
are multipole moments of the shear and convergence, mass reconstruction, and
parameterized fits to filament mass profiles using a Markov Chain Monte Carlo
approach. In particular, two new filament detection techniques are explored
(multipole shear filters and Markov Chain Monte Carlo mass profile fits), and
we outline the quality of data required to be able to identify and quantify
filament profiles. We also consider the effects of large scale structure on
filament detection. We conclude that using these techniques, there will be
realistic prospects of detecting filaments in data from future space-based
missions. The methods presented in this paper will be of great use in the
identification of dark matter filaments in future surveys. |
Cluster magnetic fields through the study of polarized radio halos in
the SKA era: Galaxy clusters are unique laboratories to investigate turbulent fluid
motions and large scale magnetic fields. Synchrotron radio halos at the center
of merging galaxy clusters provide the most spectacular and direct evidence of
the presence of relativistic particles and magnetic fields associated with the
intracluster medium. The study of polarized emission from radio halos is
extremely important to constrain the properties of intracluster magnetic fields
and the physics of the acceleration and transport of the relativistic
particles. However, detecting this polarized signal is a very hard task with
the current radio facilities.We use cosmological magneto-hydrodynamical
simulations to predict the expected polarized surface brightness of radio halos
at 1.4 GHz. We compare these expectations with the sensitivity and the
resolution reachable with the SKA1. This allows us to evaluate the potential
for studying intracluster magnetic fields in the surveys planned for SKA1. | Observational constraints on key-parameters of cosmic reionisation
history: We discuss constraints on cosmic reionisation and their implications on a
cosmic SFR density $\rho_\mathrm{SFR}$ model; we study the influence of
key-parameters such as the clumping factor of ionised hydrogen in the
intergalactic medium (IGM) $C_{H_{II}}$ and the fraction of ionising photons
escaping star-forming galaxies to reionise the IGM $f_\mathrm{esc}$. Our
analysis uses SFR history data coming from luminosity functions, assuming that
star-forming galaxies were sufficient to lead the reionisation process at high
redshift. We add two other sets of constraints: measurements of the IGM ionised
fraction and the most recent result from Planck Satellite about the integrated
Thomson optical depth of the Cosmic Microwave Background (CMB)
$\tau_\mathrm{Planck}$. We also consider various possibilities for the
evolution of these two parameters with redshift, and confront them with
observational data cited above. We conclude that, if the model of a constant
clumping factor is chosen, the fiducial value of $3$ often used in papers is
consistent with observations; even if a redshift-dependent model is considered,
the resulting optical depth is strongly correlated to $C_{H_{II}}$ mean value
at $z>7$, an additional argument in favour of the use of a constant clumping
factor. Besides, the escape fraction is related to too many astrophysical
parameters to allow us to use a complete and fully satisfactory model. A
constant value with redshift seems again to be the most likely expression:
considering it as a fit parameter, we get from the maximum likelihood (ML)
model $f_\mathrm{esc}=0.24\pm0.08$; with a redshift-dependent model, we find an
almost constant evolution, slightly increasing with $z$, around
$f_\mathrm{esc}=0.23$. Last, our analysis shows that a reionisation beginning
as early as $z\geq14$ and persisting until $z\sim6$ is a likely storyline. |
Cosmological Constraints from Galaxy Clusters and Groups in the eROSITA
Final Equatorial Depth Survey: We present the first cosmological study of a sample of $eROSITA$ clusters,
which were identified in the $eROSITA$ Final Equatorial Depth Survey (eFEDS).
In a joint selection on X-ray and optical observables, the sample contains
$455$ clusters within a redshift range of $0.1<z<1.2$, of which $177$ systems
are covered by the public data from the Hyper Suprime-Cam (HSC) survey that
enables uniform weak-lensing cluster mass constraints. With minimal
assumptions, at each cluster redshift $z$ we empirically model (1) the scaling
relations between the cluster halo mass and the observables, which include the
X-ray count rate, the optical richness, and the weak-lensing mass, and (2) the
X-ray selection in terms of the completeness function $\mathtt{C}$. Using the
richness distribution of the clusters, we directly measure the X-ray
completeness and adopt those measurements as informative priors for the
parameters of $\mathtt{C}$. In a blinded analysis, we obtain the cosmological
constraints $\Omega_{\mathrm{m}} = 0.245^{+0.048}_{-0.058}$, $\sigma_{8} =
0.833^{+0.075}_{-0.063}$ and $S_{8} \equiv
\sigma_{8}\left(\Omega_{\mathrm{m}}/0.3\right)^{0.3}= 0.791^{+0.028}_{-0.031}$
in a flat $\Lambda$CDM cosmology. Extending to a flat $w$CDM cosmology leads to
the constraint on the equation of state parameter of the dark energy of $w =
-1.25\pm 0.47$. The eFEDS constraints are in good agreement with the results
from the $Planck$ mission, the galaxy-galaxy lensing and clustering analysis of
the Dark Energy Survey, and the cluster abundance analysis of the SPT-SZ survey
at a level of $\lesssim1\sigma$. With the empirical modelling, this work
presents the first fully self-consistent cosmological constraints based on a
synergy between wide-field X-ray and weak lensing surveys. | Inference of gravitational lensing and patchy reionization with future
CMB data: We develop an optimal Bayesian solution for jointly inferring secondary
signals in the Cosmic Microwave Background (CMB) originating from gravitational
lensing and from patchy screening during the epoch of reionization. This method
is able to extract full information content from the data, improving upon
previously considered quadratic estimators for lensing and screening. We
forecast constraints using the Marginal Unbiased Score Expansion (MUSE) method,
and show that they are largely dominated by CMB polarization, and depend on the
exact details of reionization. For models consistent with current data which
produce the largest screening signals, a detection (3\,$\sigma$) of the
cross-correlation between lensing and screening is possible with SPT-3G, and a
detection of the auto-correlation is possible with CMB-S4. Models with the
lowest screening signals evade the sensitivity of SPT-3G, but are still
possible to detect with CMB-S4 via their lensing cross-correlation. |
A First Detection of the Connected 4-Point Correlation Function of
Galaxies Using the BOSS CMASS Sample: We present an $8.1\sigma$ detection of the non-Gaussian 4-Point Correlation
Function (4PCF) using a sample of $N_{\rm g} \approx 8\times 10^5$ galaxies
from the BOSS CMASS dataset. Our measurement uses the $\mathcal{O}(N_{\rm
g}^2)$ NPCF estimator of Philcox et al. (2021), including a new modification to
subtract the disconnected 4PCF contribution (arising from the product of two
2PCFs) at the estimator level. This approach is unlike previous work and
ensures that our signal is a robust detection of gravitationally-induced
non-Gaussianity. The estimator is validated with a suite of lognormal
simulations, and the analytic form of the disconnected contribution is
discussed. Due to the high dimensionality of the 4PCF, data compression is
required; we use a signal-to-noise-based scheme calibrated from theoretical
covariance matrices to restrict to $\sim$ $100$ basis vectors. The compression
has minimal impact on the detection significance and facilitates traditional
$\chi^2$-like analyses using a suite of mock catalogs. The significance is
stable with respect to different treatments of noise in the sample covariance
(arising from the limited number of mocks), but decreases to $4.7\sigma$ when a
minimum galaxy separation of $14 h^{-1}\mathrm{Mpc}$ is enforced on the 4PCF
tetrahedra (such that the statistic can be modelled more easily). The
detectability of the 4PCF in the quasi-linear regime implies that it will
become a useful tool in constraining cosmological and galaxy formation
parameters from upcoming spectroscopic surveys. | Increasing Fisher Information by Moving-Mesh Reconstruction: Reconstruction techniques are commonly used in cosmology to reduce
complicated nonlinear behaviours to a more tractable linearized system. We
study a new reconstruction technique that uses the Moving-Mesh algorithm to
estimate the displacement field from nonlinear matter distribution. We show the
performance of this new technique by quantifying its ability to reconstruct
linear modes. We study the cumulative Fisher information $I(<k_n)$ about the
initial matter power spectrum in the matter power spectra in 130 $N$-body
simulations before and after reconstruction, and find that the nonlinear
plateau of $I(<k_n)$ is increased by a factor of $\sim 50$ after
reconstruction, from $I \simeq 2.5 \times 10^{-5} /({\rm Mpc}/h)^3$ to $I
\simeq 1.3 \times 10^{-3}/({\rm Mpc}/h)^3$ at large $k$. This result includes
the decorrelation between initial and final fields, which has been neglected in
some previous studies. We expect this technique to be beneficial to problems
such as baryonic acoustic oscillations, redshift space distortions and cosmic
neutrinos that rely on accurately disentangling nonlinear evolution from
underlying linear effects. |
Spectropolarimetric Evidence for Radiatively Inefficient Accretion in an
Optically Dull Active Galaxy: We present Subaru/FOCAS spectropolarimetry of two active galaxies in the
Cosmic Evolution Survey. These objects were selected to be optically dull, with
the bright X-ray emission of an AGN but missing optical emission lines in our
previous spectroscopy. Our new observations show that one target has very weak
emission lines consistent with an optically dull AGN, while the other object
has strong emission lines typical of a host-diluted Type 2 Seyfert galaxy. In
neither source do we observe polarized emission lines, with 3-sigma upper
limits of P_BLR < 2%. This means that the missing broad emission lines (and
weaker narrow emission lines) are not due to simple anisotropic obscuration,
e.g., by the canonical AGN torus. The weak-lined optically dull AGN exhibits a
blue polarized continuum with P = 0.78 +/- 0.07% at 4400 A < lambda_rest < 7200
A (P = 1.37 +/- 0.16% at 4400 A < lambda_rest < 5050 A). The wavelength
dependence of this polarized flux is similar to that of an unobscured AGN
continuum and represents the intrinsic AGN emission, either as synchrotron
emission or the outer part of an accretion disk reflected by a clumpy dust
scatterer. Because this intrinsic AGN emission lacks emission lines, this
source is likely to have a radiatively inefficient accretion flow. | Primordial black hole dark matter in the presence of p-wave WIMP
annihilation: We study the allowed primordial black hole (PBH) dark matter abundance in the
mixed dark matter scenarios consisting of PBHs and self-annihilating weakly
interacting massive particles (WIMPs) with a velocity dependent annihilation
cross section. We first briefly illustrate how the WIMP dark matter halo
profile changes for the velocity suppressed p-wave annihilation scenarios,
compared with the familiar s-wave annihilation scenarios, and then discuss the
PBH mass dependent upper bound on the allowed PBH dark matter abundance. The
WIMPs can accrete onto a PBH to form an ultracompact minihalo with a spiky
density profile. Such a spike is moderated in the central region of a halo
because the WIMPs are annihilated away and this moderation is less effective
for a smaller annihilation cross section. The WIMP core density becomes larger
while the core radius becomes smaller for a velocity suppressed p-wave
annihilation cross section than those for the s-wave annihilation scenarios.
The annihilation cross section is dependent on the velocity which varies across
the halo, and, in addition to the change of the WIMP density profile, another
interesting feature is the PBH mass dependent bound on PBH dark matter
abundance. This is in stark contrast to the s-wave annihilation scenarios where
the PBH abundance bound is independent of the PBH mass. The allowed PBH dark
matter fraction (with respect to the total dark matter abundance) is of order
$f_{PBH}\lesssim {\cal
O}(10^{-7})(M_{\odot}/M_{PBH})^{(-6+2\gamma_{sp})/(3\gamma_{sp}+3)}$ for the
thermal relic p-wave dark matter with the mass $100$ GeV where $\gamma_{sp}$ is
the slope index of the spike profile, to be compared with $f_{PBH}\lesssim
{\cal O}(10^{-9})$ for the corresponding thermal relic s-wave dark matter
scenarios. |
A Moderate Cooling Flow Phase at Galaxy Formation: I study the possibility that a cooling flow (CF) exists at the main phase of
super massive black hole (SMBH) growth during galaxy formation. To ensure that
jets launched by the SMBH efficiently expel gas from the galaxy, as is required
by recent results, the gas should be in the hot phase, rather than in cold
clouds. The short radiative cooling time of the hot gas leads to the formation
of a CF, but heating by the active galactic nucleus (AGN) prevents catastrophic
cooling. Cold blobs that start as instabilities in the hot phase feed the SMBH
from an extended region, form an accretion disk, and lead to the formation of
jets. These jets can expel large quantities of gas out of the galaxy. This
cycle, that is termed cold feedback mechanism in CFs in clusters of galaxies,
might explain the correlation of SMBH to bulge masses. Stars are formed, but at
a lower rate than what is expected when heating is not included. Such a CF is
termed a moderate CF. | Pitch angle variations in spiral galaxies: We present a detailed photometric study and measurements of spiral arm pitch
angles for a sample of 50 non-barred or weakly barred grand-design spiral
galaxies selected from Sloan Digital Sky Survey. In order to find pitch angles,
we used a new method based on the window Fourier analysis of their images. This
method allows us not only to infer the average pitch angle, but to obtain its
value as a function of galactocentric radius as well. Our main results are as
follows:
(1) Spiral arms of most galaxies cannot be described by a single value of the
pitch angle. About 2/3 of galaxies demonstrate pitch angle variations exceeding
20%. In most galaxies in the sample their pitch angle decreases by increasing
the distance from the centre.
(2) Pitch angle variations correlate with the properties of galaxies - with
the shape of the surface brightness distribution (envelope-type or truncated
disc), and with the sign of stellar disc colour gradient.
(3) More luminous and bright bulges produce more tightly wound spiral arms,
that is in agreement with current models for spiral arms formation. |
On Primordial Black Holes and secondary gravitational waves generated
from inflation with solo/multi-bumpy potential: It is well known that a primordial black hole (PBH) can be generated in the
inflation process of the early universe, especially when the inflation field
has a number of non-trivial features that could break the slow-roll condition.
In this study, we investigate a toy model of inflation with bumpy potential,
which has one or several bumps. We determined that the potential with
multi-bump can generate power spectra with multi-peaks in small-scale region,
which can in turn predict the generation of primordial black holes in various
mass ranges. We also consider the two possibilities of PBH formation by
spherical and elliptical collapses. Finally, we discuss the scalar-induced
gravitational waves(SIGWs)generated by linear scalar perturbations at second
order. | Ultraviolet Spectroscopy of Supernovae: The First Two Years of Swift
Observations: We present the entire sample of ultraviolet (UV) spectra of supernovae (SNe)
obtained with the Ultraviolet/Optical Telescope (UVOT) on board the Swift
satellite during the first 2 years of observations (2005/2006). A total of 29
UV-grism and 22 V-grism spectra of 9 supernovae (SNe) have been collected, of
which 6 are thermonuclear (type Ia) and 3 core collapse (type Ibc/II) SNe. All
the spectra have been obtained during the photospheric phase. After a
comparison of the spectra of our sample with those in the literature (SNe
1992A, 1990N and 1999em), we confirm some degree of diversity in the UV
emission of Type Ia SNe and a greater homogeneity in the Type II Plateau SN
sample. Signatures of interaction between the ejecta and the circumstellar
environment have been found in the UV spectrum of SN 2006jc, the only SN Type
Ib/c for which UVOT grism data are available. Currently, Swift UVOT is the best
suited instrument for early SN studies in the UV due to its fast response and
flexible scheduling capabilities. However, in order to increase the quality of
the data and significantly improve our understanding of the UV properties of
SNe and to fully maximize the scientific potential of UVOT grism observations,
a larger investment in observing time and longer exposures are needed. |
Accurate classification of 17 AGNs detected with Swift/BAT: Through an optical campaign performed at 5 telescopes located in the northern
and the southern hemispheres, plus archival data from two on line sky surveys,
we have obtained optical spectroscopy for 17 counterparts of suspected or
poorly studied hard X-ray emitting active galactic nuclei (AGNs) detected with
Swift/BAT in order to determine or better classify their nature. We find that 7
sources of our sample are Type 1 AGNs, 9 are Type 2 AGNs, and 1 object is an
X-ray bright optically normal galaxy; the redshifts of these objects lie in a
range between 0.012 and 0.286. For all these sources, X-ray data analysis was
also performed to estimate their absorption column and to search for possible
Compton thick candidates. Among our type 2 objects, we did not find any clear
Compton thick AGN, but at least 6 out of 9 of them are highly absorbed (N_H >
10^23 cm^-2), while one does not require intrinsic absorption; i.e., it appears
to be a naked Seyfert 2 galaxy. | Cosmological Simulations with Self-Interacting Dark Matter II: Halo
Shapes vs. Observations: If dark matter has a large self-interaction scattering cross section, then
interactions among dark-matter particles will drive galaxy and cluster halos to
become spherical in their centers. Work in the past has used this effect to
rule out velocity-independent, elastic cross sections larger than sigma/m ~
0.02 cm^2/g based on comparisons to the shapes of galaxy cluster lensing
potentials and X-ray isophotes. In this paper, we use cosmological simulations
to show that these constraints were off by more than an order of magnitude
because (a) they did not properly account for the fact that the observed
ellipticity gets contributions from the triaxial mass distribution outside the
core set by scatterings, (b) the scatter in axis ratios is large and (c) the
core region retains more of its triaxial nature than estimated before.
Including these effects properly shows that the same observations now allow
dark matter self-interaction cross sections at least as large as sigma/m = 0.1
cm^2/g. We show that constraints on self-interacting dark matter from
strong-lensing clusters are likely to improve significantly in the near future,
but possibly more via central densities and core sizes than halo shapes. |
Lyman alpha Luminosity Functions at Redshift z = 4.5: We present a spectroscopically confirmed sample of Lyman alpha emitting
galaxies (LAEs) at z ~ 4.5 in the Extended Chandra Deep Field South (ECDFS),
which we combine with a sample of z ~ 4.5 LAEs from the Large Area Lyman Alpha
(LALA) survey to build a unified Lya luminosity function (LF). We
spectroscopically observed 64 candidate LAEs in the ECDFS, confirming 46
objects as z~4.5 LAEs. We did not detect significant flux from neither C_iv
1549\AA\ nor the He_ii 1640\AA\ emission in individual LAE spectra, even with a
coadded spectrum. With the coadded line ratio of He_ii to Lya constraining the
Population III star formation rate (SFR) to be <0.3% of the total SFR, and
<1.25% of the observed SFR (both at the 2-$\sigma$ level). Only one LAE was
detected in both the X-ray and radio, while the other objects remained
undetected, even when stacked. The Lya LF in our two deepest narrowband filters
in the ECDFS differ at >2$\sigma$ significance, and the product $L^*\Phi^*$
differs by a factor of >3. Similar LF differences have been used to infer
evolution in the neutral gas fraction in the intergalactic medium at z>6, yet
here the difference is likely due to cosmic variance, given that the two
samples are from adjoining line-of-sight volumes. Combining our new sample of
LAEs with those from previous LALA narrowband surveys at z = 4.5, we obtain one
of the best measured Lya LFs to date of L* = 42.83 $\pm$ 0.06 and $\Phi^*$ =
-3.48 $\pm$ 0.09. We compare our new LF to others from the literature to study
the evolution of the Lya luminosity density at 0 < z < 7. We find tentative
evidence for evolution in the product $L^* \Phi^*$, which approximately tracks
the cosmic SFR density, but since field-to-field and survey-to-survey
variations are in some cases as large as the possible evolution, some caution
is needed in interpreting this trend. | The formation of the extremely primitive star SDSS J102915+172927 relies
on dust: The relative importance of metals and dust grains in the formation of the
first low-mass stars has been a subject of debate. The recently discovered
Galactic halo star SDSS J102915+172927 (Caffau et al. 2011) has a mass less
than 0.8 Msun and a metallicity of Z = 4.5 10^{-5} Zsun. We investigate the
origin and properties of this star by reconstructing the physical conditions in
its birth cloud. We show that the observed elemental abundance trend of SDSS
J102915+172927 can be well fitted by the yields of core-collapse supernovae
with metal-free progenitors of 20 Msun and 35 Msun. Using these selected
supernova explosion models, we compute the corresponding dust yields and the
resulting dust depletion factor taking into account the partial destruction by
the supernova reverse shock. We then follow the collapse and fragmentation of a
star forming cloud enriched by the products of these SN explosions at the
observed metallicity of SDSS J102915+172927. We find that [0.05 - 0.1] Msun
mass fragments, which then lead to the formation of low-mass stars, can occur
provided that the mass fraction of dust grains in the birth cloud exceeds 0.01
of the total mass of metals and dust. This, in turn, requires that at least 0.4
Msun of dust condense in the first supernovae, allowing for moderate
destruction by the reverse shock. If dust formation in the first supernovae is
less efficient or strong dust destruction does occur, the thermal evolution of
the SDSS J102915+172927 birth cloud is dominated by molecular cooling, and only
> 8 Msun fragments can form. We conclude that the observed properties of SDSS
J102915+172927 support the suggestion that dust must have condensed in the
ejecta of the first supernovae and played a fundamental role in the formation
of the first low-mass stars. |
A new analysis of quasar polarisation alignments: We propose a new method to analyse the alignment of optical polarisation
vectors from quasars. This method leads to a definition of intrinsic preferred
axes and to a determination of the probability $p^{\sigma}$ that the
distribution of polarisation directions is random. This probability is found to
be as low as 0.003% for one of the regions of redshift. | First cosmological constraints combining Planck with the recent
gravitational-wave standard siren measurement of the Hubble constant: The recent observations of gravitational-wave and electromagnetic emission
produced by the merger of the binary neutron-star system GW170817 have opened
the possibility of using standard sirens to constrain the value of the Hubble
constant. While the reported bound of $H_0=70_{-8}^{+12}$ at $68 \%$ C.L. is
significantly weaker than those recently derived by observations of Cepheid
variables, it does not require any form of cosmic distance ladder and can be
considered as complementary and, in principle, more conservative. Here we
combine, for the first time, the new measurement with the Planck Cosmic
Microwave Background observations in a $12$ parameters extended $\Lambda$CDM
scenario, where the Hubble constant is weakly constrained from CMB data alone
and bound to a low value $H_0=55^{+7}_{-20}$ km/s/Mpc at $68 \%$ C.L. We point
out that the non-Gaussian shape of the GW170817 bound makes lower values of the
Hubble constant in worst agreement with observations than what expected from a
Gaussian form. The inclusion of the new GW170817 Hubble constant measurement
therefore significantly reduces the allowed parameter space, improving the
cosmological bounds on several parameters as the neutrino mass, curvature and
the dark energy equation of state. |
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