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Galaxy bias and primordial non-Gaussianity: insights from galaxy
formation simulations with IllustrisTNG: We study the impact that large-scale perturbations of (i) the matter density
and (ii) the primordial gravitational potential with local primordial
non-Gaussianity (PNG) have on galaxy formation using the IllustrisTNG model. We
focus on the linear galaxy bias $b_1$ and the coefficient $b_\phi$ of the
scale-dependent bias induced by PNG, which describe the response of galaxy
number counts to these two types of perturbations, respectively. We perform our
study using separate universe simulations, in which the effect of the
perturbations is mimicked by changes to the cosmological parameters: modified
cosmic matter density for $b_1$ and modified amplitude $\mathcal{A}_s$ of the
primordial scalar power spectrum for $b_\phi$. We find that the widely used
universality relation $b_\phi = 2\delta_c(b_1 - 1)$ is a poor description of
the bias of haloes and galaxies selected by stellar mass $M_*$, which is
instead described better by $b_\phi(M_*) = 2\delta_c(b_1(M_*) - p)$ with $p \in
[0.4, 0.7]$. This is explained by the different impact that matter
overdensities and local PNG have on the median stellar-to-halo-mass relation. A
simple model of this impact allows us to describe the stellar mass dependence
of $b_1$ and $b_\phi$ fairly well. Our results also show a nontrivial relation
between $b_1$ and $b_\phi$ for galaxies selected by color and black hole mass
accretion rate. Our results provide refined priors on $b_\phi$ for local PNG
constraints and forecasts using galaxy clustering. Given that the widely used
universality relation underpredicts $b_\phi(M_*)$, existing analyses may
underestimate the true constraining power on local PNG. | A Generative Model of Galactic Dust Emission Using Variational Inference: Emission from the interstellar medium can be a significant contaminant of
measurements of the intensity and polarization of the cosmic microwave
background (CMB). For planning CMB observations, and for optimizing
foreground-cleaning algorithms, a description of the statistical properties of
such emission can be helpful. Here we examine a machine learning approach to
inferring the statistical properties of dust from either observational data or
physics-based simulations. In particular, we apply a type of neural network
called a Variational Auto Encoder (VAE) to maps of the intensity of emission
from interstellar dust as inferred from Planck sky maps and demonstrate its
ability to a) simulate new samples with similar summary statistics as the
training set, b) provide fits to emission maps withheld from the training set,
and c) produce constrained realizations. We find VAEs are easier to train than
another popular architecture: that of Generative Adversarial Networks (GANs),
and are better-suited for use in Bayesian inference. |
Effects of anisotropy on gravitational infall in galaxy clusters using
an exact general relativistic model: We study the effects and implications of anisotropies at the scale of galaxy
clusters by building an exact general relativistic model of a cluster using the
inhomogeneous and anisotropic Szekeres metric. The model is built from a
modified Navarro-Frenk-White (NFW) density profile. We compare this to a
corresponding spherically symmetric structure in the Lemaitre-Tolman (LT) model
and quantify the impact of introducing varying levels of anisotropy. We examine
two physical measures of gravitational infall -- the growth rate of density and
the velocity of the source dust in the model. We introduce a generalization of
the LT dust velocity profile for the Szekeres metric and demonstrate its
consistency with the growth rate of density. We find that the growth rate of
density in one substructure increases by 0.5%, 1.5%, and 3.75% for 5%, 10%, and
15% levels of introduced anisotropy, which is measured as the fractional
displaced mass relative to the spherically symmetric case. The infall velocity
of the dust is found to increase by 2.5, 10, and 20 km/s (0.5%, 2%, and 4.5%),
respectively, for the same three levels of anisotropy. This response to the
anisotropy in a structure is found to be strongly nonlinear with respect to the
strength of anisotropy. These relative velocities correspond to an equivalent
increase in the total mass of the spherically symmetric structure of 1%, 3.8%,
and 8.4%, indicating that not accounting for the presence of anisotropic mass
distributions in cluster models can strongly bias the determination of physical
properties like the total mass. | Dust Attenuation and H-alpha Star Formation Rates of z~0.5 Galaxies: Using deep narrow-band and broad-band imaging, we identify 401 z~0.40 and 249
z~0.49 H-alpha line-emitting galaxies in the Subaru Deep Field. Compared to
other H-alpha surveys at similar redshifts, our samples are unique since they
probe lower H-alpha luminosities, are augmented with multi-wavelength
(rest-frame 1000AA--1.5 microns) coverage, and a large fraction (20%) of our
samples has already been spectroscopically confirmed. Our spectra allow us to
measure the Balmer decrement for nearly 60 galaxies with H-beta detected above
5-sigma. The Balmer decrements indicate an average extinction of
A(H-alpha)=0.7^{+1.4}_{-0.7} mag. We find that the Balmer decrement
systematically increases with higher H-alpha luminosities and with larger
stellar masses, in agreement with previous studies with sparser samples. We
find that the SFRs estimated from modeling the spectral energy distribution
(SED) is reliable---we derived an "intrinsic" H-alpha luminosity which is then
reddened assuming the color excess from SED modeling. The SED-predicted H-alpha
luminosity agrees with H-alpha narrow-band measurements over 3 dex (rms of 0.25
dex). We then use the SED SFRs to test different statistically-based dust
corrections for H-alpha and find that adopting one magnitude of extinction is
inappropriate: galaxies with lower luminosities are less reddened. We find that
the luminosity-dependent dust correction of Hopkins et al. yields consistent
results over 3 dex (rms of 0.3 dex). Our comparisons are only possible by
assuming that stellar reddening is roughly half of nebular reddening. The
strong correspondence argue that with SED modeling, we can derive reliable
intrinsic SFRs even in the absence of H-alpha measurements at z~0.5. |
Complex Field Inflation: We report first study of complex field inflation. Although understood as a
specific two-field inflation, a complex field inflation is able to make more
robust model predictions on primordial curvature perturbation. Explicitly we
discuss the model realizations of complex chaotic and exponential inflation in
various large-field contexts. Both complex field models contain a single
complex scalar together with only two free parameters. Using numerical handles
aimed to calculate primordial curvature perturbation from multifield inflation,
we show that both models are compatible with current Planck data, and the
individual surviving parameter space can be substantially or fully probed by
future CMB-S4 experiments. | Constraints on Kinematic Model from Recent Cosmic Observations: SN Ia,
BAO and Observational Hubble Data: In this paper, linear first order expansion of deceleration parameter
$q(z)=q_0+q_1(1-a)$ ($M_1$), constant jerk $j=j_0$ ($M_2$) and third order
expansion of luminosity distance ($M_3$) are confronted with cosmic
observations: SCP 307 SN Ia, BAO and observational Hubble data (OHD).
Likelihood is implemented to find the best fit model parameters. All these
models give the same prediction of the evolution of the universe which is
undergoing accelerated expansion currently and experiences a transition from
decelerated expansion to accelerated expansion. But, the transition redshift
depends on the concrete parameterized form of the model assumed. $M_1$ and
$M_2$ give value of transition redshift about $z_t\sim 0.6$. $M_3$ gives a
larger one, say $z_t\sim 1$. The $\chi^2/dof$ implies almost the same goodness
of the models. But, for its badness of evolution of deceleration parameter at
high redshift $z>1$, $M_3$ can not be reliable. $M_1$ and $M_2$ are compatible
with $\Lambda$CDM model at the $2\sigma$ and $1\sigma$ confidence levels
respectively. $M_3$ is not compatible with $\Lambda$CDM model at $2\sigma$
confidence level. From $M_1$ and $M_2$ models, one can conclude that the cosmic
data favor a cosmological model having $j_0<-1$. |
Resolving the Hubble Tension with New Early Dark Energy: New Early Dark Energy (NEDE) is a component of vacuum energy at the electron
volt scale, which decays in a first-order phase transition shortly before
recombination [arXiv:1910.10739]. The NEDE component has the potential to
resolve the tension between recent local measurements of the expansion rate of
the Universe using supernovae (SN) data and the expansion rate inferred from
the early Universe through measurements of the cosmic microwave background
(CMB) when assuming $\Lambda$CDM. We discuss in depth the two-scalar field
model of the NEDE phase transition including the process of bubble percolation,
collision, and coalescence. We also estimate the gravitational wave signal
produced during the collision phase and argue that it can be searched for using
pulsar timing arrays. In a second step, we construct an effective cosmological
model, which describes the phase transition as an instantaneous process, and
derive the covariant equations that match perturbations across the transition
surface. Fitting the cosmological model to CMB, baryonic acoustic oscillations
and SN data, we report $H_0 = 69.6^{+1.0}_{-1.3} \, \textrm{km}\,
\textrm{s}^{-1}\, \textrm{Mpc}^{-1}$ $(68 \%$ C.L.) without the local
measurement of the Hubble parameter, bringing the tension down to $2.5\,
\sigma$. Including the local input, we find $H_0 = 71.4 \pm 1.0 \,
\textrm{km}\, \textrm{s}^{-1}\, \textrm{Mpc}^{-1}$ $(68 \%$ C.L.) and strong
evidence for a non-vanishing NEDE component with a $\simeq 4\, \sigma$
significance. | Baryons do trace dark matter 380,000 years after the big bang: Search
for compensated isocurvature perturbations with WMAP 9-year data: Primordial isocurvature fluctuations between photons and either neutrinos or
non-relativistic species such as baryons or dark matter are known to be
sub-dominant to adiabatic fluctuations. Perturbations in the relative densities
of baryons and dark matter (known as compensated isocurvature perturbations, or
CIPs), however, are surprisingly poorly constrained. CIPs leave no imprint in
the cosmic microwave background (CMB) on observable scales, at least at linear
order in their amplitude and zeroth order in the amplitude of adiabatic
perturbations. It is thus not yet empirically known if baryons trace dark
matter at the surface of last scattering. If CIPs exist, they would spatially
modulate the Silk damping scale and acoustic horizon, causing distinct
fluctuations in the CMB temperature/polarization power spectra across the sky:
this effect is first order in both the CIP and adiabatic mode amplitudes. Here,
temperature data from the Wilkinson Microwave Anisotropy Probe (WMAP) are used
to conduct the first CMB-based observational search for CIPs, using
off-diagonal correlations and the CMB trispectrum. Reconstruction noise from
weak lensing and point sources is shown to be negligible for this data set. No
evidence for CIPs is observed, and a 95%-confidence upper limit of $1.1\times
10^{-2}$ is imposed to the amplitude of a scale-invariant CIP power spectrum.
This limit agrees with CIP sensitivity forecasts for WMAP, and is competitive
with smaller scale constraints from measurements of the baryon fraction in
galaxy clusters. It is shown that the root-mean-squared CIP amplitude on 5-100
degree scales is smaller than 0.07-0.17 (depending on the scale) at the
95%-confidence level. Temperature data from the Planck satellite will provide
an even more sensitive probe for the existence of CIPs, as will the upcoming
ACTPol and SPTPol experiments on smaller angular scales. |
A Measurement of Small Scale Structure in the 2.2 < z < 4.2 Lyman-alpha
Forest: The amplitude of fluctuations in the Ly-a forest on small spatial scales is
sensitive to the temperature of the IGM and its spatial fluctuations. The
temperature of the IGM and its spatial variations contain important information
about hydrogen and helium reionization. We present a new measurement of the
small-scale structure in the Ly-a forest from 40 high resolution, high
signal-to-noise, VLT spectra at z=2.2-4.2. We convolve each Ly-a forest
spectrum with a suitably chosen wavelet filter, which allows us to extract the
amount of small-scale structure in the forest as a function of position across
each spectrum. We compare these measurements with high resolution hydrodynamic
simulations of the Ly-a forest which track more than 2 billion particles. This
comparison suggests that the IGM temperature close to the cosmic mean density
(T_0) peaks near z=3.4, at which point it is greater than 20,000 K at 2-sigma
confidence. The temperature at lower redshift is consistent with the fall-off
expected from adiabatic cooling ($T_0 \propto (1+z)^2$), after the peak
temperature is reached near z=3.4. At z=4.2 our results favor a temperature of
T_0 = 15-20,000 K. However, owing mostly to uncertainties in the mean
transmitted flux at this redshift, a cooler IGM model with T_0 = 10,000 K is
only disfavored at the 2-sigma level here, although such cool IGM models are
strongly discrepant with the z ~ 3-3.4 measurement. We do not detect large
spatial fluctuations in the IGM temperature at any redshift covered by our data
set. The simplest interpretation of our measurements is that HeII reionization
completes sometime near z ~ 3.4, although statistical uncertainties are still
large [Abridged]. | Improved and Quality-assessed Emission and Absorption Line measurements
in Sloan Digital Sky Survey galaxies: We present a new database of absorption and emission-line measurements based
on the entire spectral atlas from the Sloan Digital Sky Survey (SDSS) 7th data
release of galaxies within a redshift of 0.2. Our work makes use of the
publicly available penalized pixel-fitting(pPXF) and gas and absorption line
fitting (gandalf) IDL codes, aiming to improve the existing measurements for
stellar kinematics, the strength of various absorption-line features, and the
flux and width of the emissions from different species of ionised gas. Our fit
to the stellar continuum uses both standard stellar population models and
empirical templates obtained by combining a large number of stellar spectra in
order to fit a subsample of high-quality SDSS spectra for quiescent galaxies.
Furthermore, our fit to the nebular spectrum includes an exhaustive list of
both recombination and forbidden lines. Foreground Galactic extinction is
implicitly treated in our models, whereas reddening in the SDSS galaxies is
included in the form of a simple dust screen component affecting the entire
spectrum that is accompanied by a second reddening component affecting only the
ionised gas emission. In order to check for systematic departures, we provide a
quality assessment for our fit to the SDSS spectra in our sample. This quality
assessment also allows the identification of objects with either problematic
data or peculiar features. For example, based on the quality assessment,
approximately 1% of the SDSS spectra classified as "galaxies" by the SDSS
pipeline do in fact require additional broad lines to be matched, even though
they do not show a strong continuum from an active nucleus, as do the SDSS
objects classified as "quasars". Finally, we provide new spectral templates for
galaxies of different Hubble types, obtained by combining the results of our
spectral fit for a subsample of 452 morphologically selected objects. |
Confirmation of NIKA2 investigation of the Sunyaev-Zel'dovich effect by
using synthetic clusters of galaxies: The NIKA2 Sunyaev-Zel'dovich Large Program (SZLP) is focused on mapping the
thermal SZ signal of a representative sample of selected Planck and ACT
clusters spanning the redshift range 0.5<$z$<0.9. Hydrodynamical N-body
simulations prove to be a powerful tool to endorse NIKA2 capabilities for
estimating the impact of IntraCluster Medium (ICM) disturbances when recovering
the pressure radial profiles. For this goal we employ a subsample of objects,
carefully extracted from the catalog "Marenostrum MUltidark SImulations of
galaxy Clusters" (MUSIC), spanning equivalent redshift and mass ranges as the
LPSZ. The joint analysis of real observations of the tSZ with NIKA2 and Planck
enables to validate the NIKA2 pipeline and to estimate the ICM pressure
profiles. Moreover, the possibility to identify "a priori" the dynamical state
of the selected synthetic clusters allows us to verify the impact on the
recovered ICM profile shapes and their scatters. Morphological analysis of maps
of the Compton parameter seems to be a way to observationally segregate the
sample based on the dynamical state in relaxed and disturbed synthetic
clusters. | The 6dF Galaxy Survey: Final Redshift Release (DR3) and Southern
Large-Scale Structures: We report the final redshift release of the 6dF Galaxy Survey, a combined
redshift and peculiar velocity survey over the southern sky (|b|>10 deg). Its
136,304 spectra have yielded 110,256 new extragalactic redshifts and a new
catalogue of 125,071 galaxies making near-complete samples with (K, H, J, r_F,
b_J) <= (12.65, 12.95, 13.75, 15.60, 16.75). The median redshift of the survey
is 0.053. Survey data, including images, spectra, photometry and redshifts, are
available through an online database. We describe changes to the information in
the database since earlier interim data releases. Future releases will include
velocity dispersions, distances and peculiar velocities for the brightest
early-type galaxies, comprising about 10% of the sample. Here we provide
redshift maps of the southern local universe with z<=0.1, showing nearby
large-scale structures in hitherto unseen detail. A number of regions known
previously to have a paucity of galaxies are confirmed as significantly
underdense regions. The URL of the 6dFGS database is
http://www-wfau.roe.ac.uk/6dFGS |
Heating and enriching the intracluster medium: We present numerical simulations of galaxy clusters with stochastic heating
from active galactic nuclei (AGN) that are able to reproduce the observed
entropy and temperature profiles of non-cool-core (NCC) clusters. Our study
uses N-body hydrodynamical simulations to investigate how star formation, metal
production, black hole accretion and the associated feedback from supernovae
and AGN heat and enrich diffuse gas in galaxy clusters. We assess how different
implementations of these processes affect the thermal and chemical properties
of the intracluster medium (ICM), using high-quality X-ray observations of
local clusters to constrain our models. For the purposes of this study we have
resimulated a sample of 25 massive galaxy clusters extracted from the
Millennium Simulation. Sub-grid physics is handled using a semi-analytic model
of galaxy formation, thus guaranteeing that the source of feedback in our
simulations is a population of galaxies with realistic properties. We find that
supernova feedback has no effect on the entropy and metallicity structure of
the ICM, regardless of the method used to inject energy and metals into the
diffuse gas. By including AGN feedback, we are able to explain the observed
entropy and metallicity profiles of clusters, as well as the X-ray
luminosity-temperature scaling relation for NCC systems. A stochastic model of
AGN energy injection motivated by anisotropic jet heating - presented for the
first time here - is crucial for this success. With the addition of
metal-dependent radiative cooling, our model is also able to produce CC
clusters, without overcooling of gas in dense, central regions. | The VLBA Galactic Plane Survey -- VGaPS: This paper presents accurate absolute positions from a 24 GHz Very Long
Baseline Array (VLBA) search for compact extragalactic sources in an area where
the density of known calibrators with precise coordinates is low. The goals
were to identify additional sources suitable for use as phase calibrators for
galactic sources, determine their precise positions, and produce radio images.
In order to achieve these goals, we developed a new software package, PIMA, for
determining group delays from wide-band data with much lower detection limit.
With the use of PIMA we have detected 327 sources out of 487 targets observed
in three 24 hour VLBA experiments. Among the 327 detected objects, 176 are
within 10 degrees of the Galactic plane. This VGaPS catalogue of source
positions, plots of correlated flux density versus projected baseline length,
contour plots, as well as weighted CLEAN images and calibrated visibility data
in FITS format, are available on the Web at http://astrogeo.org/vgaps.
Approximately one half of objects from the 24 GHz catalogue were observed at
dual band 8.6 GHz and 2.3 GHz experiments. Position differences at 24 GHz
versus 8.6/2.3 GHz for all but two objects on average are strictly within
reported uncertainties. We found that for two objects with complex structure
positions at different frequencies correspond to different components of a
source. |
Non-linear mode coupling and the growth of perturbations in LCDM: Cosmic structures at small non-linear scales $k>L\sim 0.2 h $ Mpc$^{-1}$ have
an impact on the longer (quasi-)linear wavelengths with $k<L$ via non-linear
UV-IR mode coupling. We evaluate this effect for a $\Lambda$CDM universe
applying the effective fluid method of Baumann, Nicolis, Senatore and
Zaldarriaga. For $k<L$ the $\Lambda$CDM growth function for the density
contrast is found to receive a scale dependent correction and an effective
anisotropic stress sources a shift between the two gravitational potentials,
setting $\phi$ - $\psi \neq 0$. Since such a situation is generically
considered as a signature of modified gravity and/or dark energy, these effects
should be taken into account before any conclusions on the dark sector are
drawn from the interpretation of future observations. | Testing the dark energy with gravitational lensing statistics: We study the redshift distribution of two samples of early-type gravitational
lenses, extracted from a larger collection of 122 systems, to constrain the
cosmological constant in the LCDM model and the parameters of a set of
alternative dark energy models (XCDM, Dvali-Gabadadze-Porrati and Ricci dark
energy models), under a spatially flat universe. The likelihood is maximized
for $\Omega_\Lambda= 0.70 \pm 0.09$ when considering the sample excluding the
SLACS systems (known to be biased towards large image-separation lenses) and
no-evolution, and $\Omega_\Lambda= 0.81\pm 0.05$ when limiting to gravitational
lenses with image separation larger than 2" and no-evolution. In both cases,
results accounting for galaxy evolution are consistent within 1$\sigma$. The
present test supports the accelerated expansion, by excluding the
null-hypothesis (i.e., $\Omega_\Lambda = 0 $) at more than 4$\sigma$,
regardless of the chosen sample and assumptions on the galaxy evolution. A
comparison between competitive world models is performed by means of the
Bayesian information criterion. This shows that the simplest cosmological
constant model - that has only one free parameter - is still preferred by the
available data on the redshift distribution of gravitational lenses. We perform
an analysis of the possible systematic effects, finding that the systematic
errors due to sample incompleteness, galaxy evolution and model uncertainties
approximately equal the statistical errors, with present-day data. We find that
the largest sources of systemic errors are the dynamical normalization and the
high-velocity cut-off factor, followed by the faint-end slope of the velocity
dispersion function. |
Minimal Basis for Exact Time Dependent Kernels in Cosmological
Perturbation Theory and Application to $Λ$CDM and $w_0w_a$CDM: We derive a minimal basis of kernels furnishing the perturbative expansion of
the density contrast and velocity divergence in powers of the initial density
field that is applicable to cosmological models with arbitrary expansion
history, thereby relaxing the commonly adopted Einstein-de-Sitter (EdS)
approximation. For this class of cosmological models, the non-linear kernels
are at every order given by a sum of terms, each of which factorizes into a
time-dependent growth factor and a wavenumber-dependent basis function. We show
how to reduce the set of basis functions to a minimal amount, and give explicit
expressions up to order $n=5$. We find that for this minimal basis choice, each
basis function individually displays the expected scaling behaviour due to
momentum conservation, being non-trivial at $n\geq 4$. This is a highly
desirable property for numerical evaluation of loop corrections. In addition,
it allows us to match the density field to an effective field theory (EFT)
description for cosmologies with an arbitrary expansion history, which we
explicitly derive at order four. We evaluate the differences to the EdS
approximation for $\Lambda$CDM and $w_0w_a$CDM, paying special attention to the
irreducible cosmology dependence that cannot be absorbed into EFT terms for the
one-loop bispectrum. Finally, we provide algebraic recursion relations for a
special generalization of the EdS approximation that retains its simplicity and
is relevant for mixed hot and cold dark matter models. | Two-Dimensional Magnetohydrodynamic Simulations of Barred Galaxies: Barred galaxies are known to possess magnetic fields that may affect the
properties of bar substructures such as dust lanes and nuclear rings. We use
two-dimensional high-resolution magnetohydrodynamic (MHD) simulations to
investigate the effects of magnetic fields on the formation and evolution of
such substructures as well as on the mass inflow rates to the galaxy center.
The gaseous medium is assumed to be infinitesimally-thin, isothermal,
non-self-gravitating, and threaded by initially uniform, azimuthal magnetic
fields. We find that there exists an outermost x1-orbit relative to which
gaseous responses to an imposed stellar bar potential are completely different
between inside and outside. Inside this orbit, gas is shocked into dust lanes
and infalls to form a nuclear ring. Magnetic fields are compressed in dust
lanes, reducing their peak density. Magnetic stress removes further angular
momentum of the gas at the shocks, temporarily causing the dust lanes to bend
into an 'L' shape and eventually leading to a smaller and more centrally
distributed ring than in unmagnetized models. The mass inflow rates in
magnetized models correspondingly become larger, by more than two orders of
magnitude when the initial fields have an equipartition value with thermal
energy, than in the unmagnetized counterparts. Outside the outermost x1-orbit,
on the other hand, an MHD dynamo due to the combined action of the bar
potential and background shear operates near the corotation and bar-end
regions, efficiently amplifying magnetic fields. The amplified fields shape
into trailing magnetic arms with strong fields and low density. The base of the
magnetic arms has a thin layer in which magnetic fields with opposite polarity
reconnect via a tearing-mode instability. This produces numerous magnetic
islands with large density which propagate along the arms to turn the outer
disk into a highly chaotic state. |
Toward a concordance teleparallel Cosmology II: Linear perturbation: Late time cosmic acceleration may be achieved by modifying gravity on large
scales. This should also have consequences on the evolution of perturbations.
We thus extend our study of exponential infrared $f(T)$ teleparallel gravity to
examine the viability of the theory at the linear perturbation level,
evaluating the full CMB and matter power spectra. As the theory does not
introduce extra free parameters, it fits within the minimal six parameter space
of standard $\Lambda$CDM. Using Planck 2018 CMB (TT+TE+EE+lensing) alone, best
fits predict those parameters to be almost identical to $\Lambda$CDM, with
slightly smaller $\chi^2_{min}$. The resulting $H_0=72.24\pm 0.64$ km/s/Mpc,
which "practically" alleviates the tension with local measurements, due to late
time phantom behaviour. Inclusion of BAO data however reduces $H_0$, reflecting
furthermore systematic deviations from data that are also present in supernova
distances and the growth rate of structure (increasing the apparent tension in
the latter case). As the theory, unlike other viable $f(T)$ models, does not
reduce to $\Lambda$CDM through extra free parameters, those conclusions are
generic; applying to any modified gravity or dynamical dark energy with phantom
behaviour. With best fit parameters, the present scenario produces a CMB
spectrum almost identical to $\Lambda$CDM, with slight deviation at
low-multipole $\ell < 30$, where cosmic variance is large. The matter power
spectrum is also quite close to $\Lambda$CDM; with percent level scale free
modifications affecting modes significantly smaller than the horizon, arising
primarily from modified background evolution. More significant deviations
appear on larger scales, and may in principle distinguish modified gravity
scenarios of the type studied here from dynamical dark energy. | The First Generation of Virgo Cluster Dwarf Elliptical Galaxies?: In the light of the question whether most early-type dwarf (dE) galaxies in
clusters formed through infall and transformation of late-type progenitors, we
search for an imprint of such an infall history in the oldest, most centrally
concentrated dE subclass of the Virgo cluster: the nucleated dEs that show no
signatures of disks or central residual star formation. We select dEs in a
(projected) region around the central elliptical galaxies, and subdivide them
by their line-of-sight velocity into fast-moving and slow-moving ones. These
subsamples turn out to have significantly different shapes: while the fast dEs
are relatively flat objects, the slow dEs are nearly round. Likewise, when
subdividing the central dEs by their projected axial ratio into flat and round
ones, their distributions of line-of-sight velocities differ significantly: the
flat dEs have a broad, possibly two-peaked distribution, whereas the round dEs
show a narrow single peak. We conclude that the round dEs probably are on
circularized orbits, while the flat dEs are still on more eccentric or radial
orbits typical for an infalling population. In this picture, the round dEs
would have resided in the cluster already for a long time, or would even be a
cluster-born species, explaining their nearly circular orbits. They would thus
be the first generation of Virgo cluster dEs. Their shape could be caused by
dynamical heating through repeated tidal interactions. Further investigations
through stellar population measurements and studies of simulated galaxy
clusters would be desirable to obtain definite conclusions on their origin. |
A 5% measurement of the Hubble constant from Type II supernovae: The most stringent local measurement of the Hubble-Lema\^itre constant from
Cepheid-calibrated Type Ia supernovae (SNe~Ia) differs from the value inferred
via the cosmic microwave background radiation ({\it Planck}$+\Lambda$CDM) by
$\sim 5\sigma$. This so-called "Hubble tension" has been confirmed by other
independent methods, and thus does not appear to be a possible consequence of
systematic errors. Here, we continue upon our prior work of using Type II
supernovae to provide another, largely-independent method to measure the
Hubble-Lema\^itre constant. From 13 SNe~II with geometric, Cepheid, or tip of
the red giant branch (TRGB) host-galaxy distance measurements, we derive H$_0=
75.4^{+3.8}_{-3.7}$\,km\,s$^{-1}$\,Mpc$^{-1}$ (statistical errors only),
consistent with the local measurement but in disagreement by $\sim 2.0\sigma$
with the {\it Planck}$+\Lambda$CDM value. Using only Cepheids ($N=7$), we find
H$_0 = 77.6^{+5.2}_{-4.8}$\,km\,s$^{-1}$\,Mpc$^{-1}$, while using only TRGB
($N=5$), we derive H$_0 = 73.1^{+5.7}_{-5.3}$\,km\,s$^{-1}$\,Mpc$^{-1}$. Via 13
variants of our dataset, we derive a systematic uncertainty estimate of
1.5\,km\,s$^{-1}$\,Mpc$^{-1}$. The median value derived from these variants
differs by just 0.3\,km\,s$^{-1}$\,Mpc$^{-1}$ from that produced by our
fiducial model. Because we only replace SNe~Ia with SNe~II -- and we do not
find statistically significant difference between the Cepheid and TRGB H$_0$
measurements -- our work reveals no indication that SNe~Ia or Cepheids could be
the sources of the "H$_0$ tension." We caution, however, that our conclusions
rest upon a modest calibrator sample; as this sample grows in the future, our
results should be verified. | The Cosmic Linear Anisotropy Solving System (CLASS) IV: Efficient
implementation of non-cold relics: We present a new flexible, fast and accurate way to implement massive
neutrinos, warm dark matter and any other non-cold dark matter relics in
Boltzmann codes. For whatever analytical or numerical form of the phase-space
distribution function, the optimal sampling in momentum space compatible with a
given level of accuracy is automatically found by comparing quadrature methods.
The perturbation integration is made even faster by switching to an approximate
viscous fluid description inside the Hubble radius, which differs from previous
approximations discussed in the literature. When adding one massive neutrino to
the minimal cosmological model, CLASS becomes just 1.5 times slower, instead of
about 5 times in other codes (for fixed accuracy requirements). We illustrate
the flexibility of our approach by considering a few examples of standard or
non-standard neutrinos, as well as warm dark matter models. |
Pairwise velocities in the "Running FLRW" cosmological model: We present an analysis of the pairwise velocity statistics from a suite of
cosmological N-body simulations describing the "Running
Friedmann-Lema\^itre-Robertson-Walker" (R-FLRW) cosmological model. This model
is based on quantum field theory in a curved space-time and extends
{\Lambda}CDM with a time-evolving vacuum energy density. To enforce local
conservation of matter a time-evolving gravitational coupling is also included.
Our results constitute the first study of velocities in the R-FLRW cosmology,
and we also compare with other dark energy simulations suites, repeating the
same analysis. We find a strong degeneracy between the pairwise velocity and
{\sigma}_8 at z=0 for almost all scenarios considered, which remains even when
we look back to epochs as early as z=2. We also investigate various Coupled
Dark Energy models, some of which show minimal degeneracy, and reveal
interesting deviations from {\Lambda}CDM which could be readily exploited by
future cosmological observations to test and further constrain our
understanding of dark energy. | Radio structures of the nuclei of nearby Seyfert galaxies and the nature
of the missing diffuse emission: We present archival high spatial resolution VLA and VLBA data of the nuclei
of seven of the nearest and brightest Seyfert galaxies in the Southern
Hemisphere. At VLA resolution (~0.1 arcsec), the nucleus of the Seyfert
galaxies is unresolved, with the exception of MCG-5-23-16 and NGC 7469 showing
a core-jet structure. Three Seyfert nuclei are surrounded by diffuse radio
emission related to star-forming regions. VLBA observations with parsec-scale
resolution pointed out that in MRK 1239 the nucleus is clearly resolved into
two components separated by ~30 pc, while the nucleus of NGC 3783 is
unresolved. Further comparison between VLA and VLBA data of these two sources
shows that the flux density at parsec scales is only 20% of that measured by
the VLA. This suggests that the radio emission is not concentrated in a single
central component, as in elliptical radio galaxies, and an additional
low-surface brightness component must be present. A comparison of Seyfert
nuclei with different radio spectra points out that the ``presence'' of
undetected flux on milli-arcsecond scale is common in steep-spectrum objects,
while in flat-spectrum objects essentially all the radio emission is recovered.
In the steep-spectrum objects, the nature of this ``missing'' flux is likely
due to non-thermal AGN-related radiation, perhaps from a jet that gets
disrupted in Seyfert galaxies because of the denser environment of their spiral
hosts. |
The Dilaton and Modified Gravity: We consider the dilaton in the strong string coupling limit and elaborate on
the original idea of Damour and Polyakov whereby the dilaton coupling to matter
has a minimum with a vanishing value at finite field-value. Combining this type
of coupling with an exponential potential, the effective potential of the
dilaton becomes matter density dependent. We study the background cosmology,
showing that the dilaton can play the role of dark energy. We also analyse the
constraints imposed by the absence of violation of the equivalence principle.
Imposing these constraints and assuming that the dilaton plays the role of dark
energy, we consider the consequences of the dilaton on large scale structures
and in particular the behaviour of the slip functions and the growth index at
low redshift. | Inadequacy of internal covariance estimation for super-sample covariance: We give an analytical interpretation of how subsample-based internal
covariance estimators lead to biased estimates of the covariance, due to
underestimating the super-sample covariance (SSC). This includes the jackknife
and bootstrap methods as estimators for the full survey area, and subsampling
as an estimator of the covariance of subsamples. The limitations of the
jackknife covariance have been previously presented in the literature because
it is effectively a rescaling of the covariance of the subsample area. However
we point out that subsampling is also biased, but for a different reason: the
subsamples are not independent, and the corresponding lack of power results in
SSC underprediction. We develop the formalism in the case of cluster counts
that allows the bias of each covariance estimator to be exactly predicted. We
find significant effects for a small-scale area or when a low number of
subsamples is used, with auto-redshift biases ranging from 0.4% to 15% for
subsampling and from 5% to 75% for jackknife covariance estimates. The
cross-redshift covariance is even more affected; biases range from 8% to 25%
for subsampling and from 50% to 90% for jackknife. Owing to the redshift
evolution of the probe, the covariances cannot be debiased by a simple
rescaling factor, and an exact debiasing has the same requirements as the full
SSC prediction. These results thus disfavour the use of internal covariance
estimators on data itself or a single simulation, leaving analytical prediction
and simulations suites as possible SSC predictors. |
Vortices and Angular Momentum in Bose-Einstein-Condensed Cold Dark
Matter Halos: If cold dark matter elementary particles form a Bose-Einstein condensate,
their superfluidity may distinguish them from other forms of cold dark matter,
including creation of quantum vortices. We demonstrate here that such vortices
are favoured in strongly-coupled condensates, while this is not the case for
axions, which are generally presumed to form a Bose-Einstein condensate but are
effectively non-interacting. | Domain walls and gravitational waves in the Standard Model: We study domain walls which can be created in the Standard Model under the
assumption that it is valid up to very high energy scales. We focus on domain
walls interpolating between the physical electroweak vacuum and the global
minimum appearing at very high field strengths. The creation of the network
which ends up in the electroweak vacuum percolating through the Universe is not
as difficult to obtain as one may expect, although it requires certain tuning
of initial conditions. Our numerical simulations confirm that such domain walls
would swiftly decay and thus cannot dominate the Universe. We discuss the
possibility of detection of gravitational waves produced in this scenario. We
have found that for the standard cosmology the energy density of these
gravitational waves is too small to be observed in present and planned
detectors. |
BICEP2 in Corpuscular Description of Inflation: A corpuscular quantum description of inflation shows that there is no
fundamental problem with trans-Planckian excursions of the inflaton field up to
about 100 Planck masses, with the upper bound coming from the corpuscular
quantum effects. In this description the r-parameter measures the ratio of
occupation numbers of gravitons versus inflatons, which, according to BICEP2,
was roughly a half at the time of 60 e-foldings prior to the end of inflation.
We stress that in non-Wilsonian UV self-completion of gravity any
trans-Planckian mode coupled to inflaton is a black hole. Unlike the Wilsonian
case, their integration-out gives an exponentially-suppressed effect and is
unable to prevent trans-Planckian excursions of the inflaton field. | A new perspective on Dark Energy modeling via Genetic Algorithms: We use Genetic Algorithms to extract information from several cosmological
probes, such as the type Ia supernovae (SnIa), the Baryon Acoustic Oscillations
(BAO) and the growth rate of matter perturbations. This is done by implementing
a model independent and bias-free reconstruction of the various scales and
distances that characterize the data, like the luminosity $d_L(z)$ and the
angular diameter distance $d_A(z)$ in the SnIa and BAO data, respectively, or
the dependence with redshift of the matter density $\om_m(a)$ in the growth
rate data, $f\sigma_8(z)$. These quantities can then be used to reconstruct the
expansion history of the Universe, and the resulting Dark Energy (DE) equation
of state $w(z)$ in the context of FRW models, or the mass radial function
$\om_M(r)$ in LTB models. In this way, the reconstruction is completely
independent of our prior bias. Furthermore, we use this method to test the
Etherington relation, ie the well-known relation between the luminosity and the
angular diameter distance, $\eta \equiv \frac{d_L(z)}{(1+z)^2 d_A(z)}$, which
is equal to 1 in metric theories of gravity. We find that the present data seem
to suggest a 3-$\sigma$ deviation from one at redshifts $z\sim 0.5$. Finally,
we present a novel way, within the Genetic Algorithm paradigm, to analytically
estimate the errors on the reconstructed quantities by calculating a Path
Integral over all possible functions that may contribute to the likelihood. We
show that this can be done regardless of the data being correlated or
uncorrelated with each other and we also explicitly demonstrate that our
approach is in good agreement with other error estimation techniques like the
Fisher Matrix approach and the Bootstrap Monte Carlo. |
The mass accretion rate of galaxy clusters: a measurable quantity: We explore the possibility of measuring the mass accretion rate (MAR) of
galaxy clusters from their mass profiles beyond the virial radius $R_{200}$. We
derive the accretion rate from the mass of a spherical shell whose inner radius
is $2R_{200}$, whose thickness changes with redshift, and whose infall velocity
is assumed to be equal to the mean infall velocity of the spherical shells of
dark matter halos extracted from $N$-body simulations. This approximation is
rather crude in hierarchical clustering scenarios where both smooth accretion
and aggregation of smaller dark matter halos contribute to the mass accretion
of clusters.Nevertheless, in the redshift range $z=[0,2]$, our prescription
returns an average MAR within $20-40 \%$ of the average rate derived from the
merger trees of dark matter halos extracted from $N$-body simulations. The MAR
of galaxy clusters has been the topic of numerous detailed numerical and
theoretical investigations, but so far it has remained inaccessible to
measurements in the real universe. Since the measurement of the mass profile of
clusters beyond their virial radius can be performed with the caustic technique
applied to dense redshift surveys of the cluster outer regions, our result
suggests that measuring the mean MAR of a sample of galaxy clusters is actually
feasible. We thus provide a new potential observational test of the
cosmological and structure formation models. | Non-Gaussian Likelihoods for Type Ia Supernovae Cosmology: Implications
for Dark Energy and $H_0$: The latest improvements in the scale and calibration of Type Ia supernovae
catalogues allow us to constrain the specific nature and evolution of dark
energy through its effect on the expansion history of the universe. We present
the results of Bayesian cosmological model comparison on the SNe~Ia catalogue
Pantheon+, where Flat $\Lambda$CDM is preferred by the data over all other
models and we find moderate evidence ($\Delta \log \mathcal{Z} \sim 2.5$) to
reject a number of the alternate dark energy models. The effect of peculiar
velocity corrections on model comparison is analysed, where we show that
removing the peculiar velocity corrections results in a varying fit on
non-$\Lambda$CDM parameters. As well as comparing cosmological models, the
Bayesian methodology is extended to comparing the scatter model of the data,
testing for non-gaussianity in the Pantheon+ Hubble residuals. We find that
adding a scale parameter to the Pantheon+ covariances, or alternately using a
multivariate Student's t-distribution fits the data better than the fiducial
analysis, producing a cosmology independent evidence increase of $\Delta \log
\mathcal{Z} = 2.29 $ and $2.46$ respectively. This improved treatment of the
scatter decreases the uncertainty in the constraint on the Hubble constant,
finding $H_0 = 73.67 \pm 0.99 $ km s$^{-1}$ Mpc$^{-1}$, in $ 5.7 \sigma$
tension with Planck. We also explore $M_B$ transition models as a potential
solution for the Hubble tension, finding no evidence to support these models
among the SNe data. |
On the Orbits of Infalling Satellite Halos: The orbital properties of infalling satellite halos set the initial
conditions which control the subsequent evolution of subhalos and the galaxies
that they host, with implications for mass stripping, star formation quenching,
and merging. Using a high-resolution, cosmological N-body simulation, I examine
the orbital parameters of satellite halos as they merge with larger host halos,
focusing primarily on orbital circularity and pericenter. I explore in detail
how these orbital parameters depend on mass and redshift. Satellite orbits
become more radial and plunge deeper into their host halo at higher host halo
mass, but they do not significantly depend on satellite halo mass.
Additionally, satellite orbits become more radial and plunge deeper into their
host halos at higher redshift. I also examine satellite velocities, finding
that most satellites infall with less specific angular momentum than the host
halo virial value, but that satellites are `hotter' than the host virial
velocity. I discuss the implications of these results to the processes of
galaxy formation and evolution, and I provide fitting formulas to the mass and
redshift dependence of satellite orbital circularity and pericenter. | A massive disk galaxy at z>3 along the sightline of QSO 1508+5714: We have obtained deep images in the BVRIJHKs bands of the field centered on
QSO 1508+5714 (z_{em} =4.28) with the Suprime camera, FOCAS and MOIRCS cameras
on Subaru telescope. We report here the detection of a B-dropout galaxy, which
is $3\secpoint 5$ north-west of the QSO sightline. A photometric redshift
analysis is presented to complement the color selection. Given the photometric
properties of this object ($M = -22.2$, making $ L\approx 3 L^{\ast}$, if
placed at its photometric redshift $z\sim 3.5$), as well as the
S$\acute{e}$rsic index ($ n \sim 1$) derived from a 2-D imaging decomposition
of the HST WFPC2 image taken in the $I_{F814}$ filter, the identified system is
consistent with a massive disk galaxy at z>3. If confirmed, it would be one of
the most distant massive disk galaxies known so far. |
High Mass X-ray Binaries and the Cosmic 21-cm Signal: Impact of Host
Galaxy Absorption: By heating the intergalactic medium (IGM) before reionization, X-rays are
expected to play a prominent role in the early Universe. The cosmic 21-cm
signal from this "Epoch of Heating" (EoH) could serve as a clean probe of
high-energy processes inside the first galaxies. Here we improve on prior
estimates of this signal by using high-resolution hydrodynamic simulations to
calculate the X-ray absorption due to the interstellar medium (ISM) of the host
galaxy. X-rays absorbed inside the host galaxy are unable to escape into the
IGM and contribute to the EoH. We find that the X-ray opacity through these
galaxies can be approximated by a metal-free ISM with a typical column density
of log[N / cm^-2] = 21.4 +0.40-0.65. We compute the resulting 21-cm signal by
combining these ISM opacities with public spectra of high-mass X-ray binaries
(thought to be important X-ray sources in the early Universe). Our results
support "standard scenarios" in which the X-ray heating of the IGM is
inhomogeneous, and occurs before the bulk of reionization. The large-scale (k ~
0.1/Mpc) 21-cm power reaches a peak of ~100 mK^2 at z = 10 - 15, with the
redshift depending on the cosmic star formation history. This is in contrast to
some recent work, motivated by the much larger X-ray absorption towards local
HMXBs inside the Milky Way. Our main results can be reproduced by approximating
the X-ray emission from HMXBs with a power-law spectrum with energy index alpha
= 1, truncated at energies below 0.5 keV. | Projection effects in the strong lensing study of subhaloes: The defining characteristic of the cold dark matter (CDM) hypothesis is the
presence of a very large number of low-mass haloes, too small to have made a
visible galaxy. Other hypotheses for the nature of the dark matter, such as
warm dark matter (WDM), predict a much smaller number of such low-mass haloes.
Strong lensing systems offer the possibility of detecting small-mass haloes
through the distortions they induce in the lensed image. Here we show that the
main contribution to the image distortions comes from haloes along the line of
sight rather than subhaloes in the lens as has normally been assumed so far.
These interlopers enhance the differences between the predictions of CDM and
WDM models. We derive the total perturber mass function, including both
subhaloes and interlopers, and show that measurements of approximately 20
strong lens systems with a detection limit of $M_{\rm low}=10^7 h^{-1}
M_{\odot}$ would distinguish (at 3 sigma) between CDM and a WDM model
consisting of 7 keV sterile neutrinos such as those required to explain the
recently detected 3.5 keV X-ray emission line from the centres of galaxies and
clusters. |
Wide-field VLBI imaging of M31 - first results: One of our closest neighbours, the Andromeda Galaxy (M31) has been the
subject of numerous large area studies across the entire spectrum, but so far
full-disk radio surveys have been conducted only at low resolution. The new
wide-field capabilities of the DiFX software correlator present the possibility
of imaging the entire primary beam of a VLBI array, thus enabling a high
resolution wide-field study of the entire galaxy. Using the VLBA and EVN, pilot
observations of M31 have been carried out with the aim of using these new
wide-field techniques to characterise the population of compact components at
VLBI resolution both within and behind one of our nearest neighbours. This
contribution describes the observations carried out, the preliminary processing
and first results. | Constraints on Multi-Field Inflation from the BOSS Galaxy Survey: We use redshift-space galaxy clustering data from the BOSS survey to
constrain local primordial non-Gaussianity (LPNG). This is of particular
importance due to the consistency relations, which imply that a detection of
LPNG would rule out all single-field inflationary models. Our constraints are
based on the consistently analyzed redshift-space galaxy power spectra and
bispectra, extracted from the public BOSS data with optimal window-free
estimators. We use a complete perturbation theory model including all one-loop
power spectrum corrections generated by LPNG. Our constraint on the amplitude
of the local non-Gaussian shape is $f_{\rm NL}^{\rm local}=-33\pm 28$ at
68\%\,CL, yielding no evidence for primordial non-Gaussianity. The addition of
the bispectrum tightens the $f_{\rm NL}^{\rm local}$ constraints from BOSS by
$20\%$, and allows breaking of degeneracies with non-Gaussian galaxy bias.
These results set the stage for the analysis of future surveys, whose larger
volumes will yield significantly tighter constraints on LPNG. |
Probing the thermal state of the intergalactic medium at $z>5$ with the
transmission spikes in high-resolution Ly$α$ forest spectra: We compare a sample of five high-resolution, high S/N Ly$\alpha$ forest
spectra of bright $6<z \lesssim 6.5$ QSOs aimed at spectrally resolving the
last remaining transmission spikes at $z>5$ with those obtained from mock
absorption spectra from the Sherwood and Sherwood-Relics suites of
hydrodynamical simulations of the intergalactic medium (IGM). We use a profile
fitting procedure for the inverted transmitted flux, $1-F$, similar to the
widely used Voigt profile fitting of the transmitted flux $F$ at lower
redshifts, to characterise the transmission spikes that probe predominately
underdense regions of the IGM. We are able to reproduce the width and height
distributions of the transmission spikes, both with optically thin simulations
of the post-reionization Universe using a homogeneous UV background and full
radiative transfer simulations of a late reionization model. We find that the
width of the fitted components of the simulated transmission spikes is very
sensitive to the instantaneous temperature of the reionized IGM. The internal
structures of the spikes are more prominant in low temeperature models of the
IGM. The width distribution of the observed transmission spikes, which require
high spectral resolution ($\leq $ 8 km/s) to be resolved, is reproduced for
optically thin simulations with a temperature at mean density of $T_0= (11000
\pm 1600,10500\pm 2100,12000 \pm 2200)$ K at $z= (5.4,5.6,5.8)$. This is weakly
dependent on the slope of the temperature-density relation, which is favoured
to be moderately steeper than isothermal. In the inhomogeneous, late
reionization, full radiative transfer simulations where islands of neutral
hydrogen persist to $z\sim5.3$, the width distribution of the observed
transmission spikes is consistent with the range of $T_0$ caused by spatial
fluctuations in the temperature-density relation. | Cluster mass estimation through Fair Galaxies: We analyse a catalogue of simulated clusters within the theoretical framework
of the Spherical Collapse Model (SCM), and demonstrate that the relation
between the infall velocity of member galaxies and the cluster matter
overdensity can be used to estimate the mass profile of clusters, even though
we do not know the full dynamics of all the member galaxies. In fact, we are
able to identify a limited subset of member galaxies, the 'fair galaxies',
which are suitable for this purpose. The fair galaxies are identified within a
particular region of the galaxy distribution in the redshift (line-of-sight
velocity versus sky-plane distance from the cluster centre). This 'fair region'
is unambiguously defined through statistical and geometrical assumptions based
on the SCM. These results are used to develop a new technique for estimating
the mass profiles of observed clusters and subsequently their masses. We tested
our technique on a sample of simulated clusters; the mass profiles estimates
are proved to be efficient from 1 up to 7 virialization radii, within a typical
uncertainty factor of 1.5, for more than 90 per cent of the clusters
considered. Moreover, as an example, we used our technique to estimate the mass
profiles and the masses of some observed clusters of the Cluster Infall Regions
in the Sloan Digital Sky Survey catalogue. The technique is shown to be
reliable also when it is applied to sparse populated clusters. These
characteristics make our technique suitable to be used in clusters of large
observational catalogues. |
AI-assisted super-resolution cosmological simulations II: Halo
substructures, velocities and higher order statistics: In this work, we expand and test the capabilities of our recently developed
super-resolution (SR) model to generate high-resolution (HR) realizations of
the full phase-space matter distribution, including both displacement and
velocity, from computationally cheap low-resolution (LR) cosmological N-body
simulations. The SR model enhances the simulation resolution by generating 512
times more tracer particles, extending into the deeply non-linear regime where
complex structure formation processes take place. We validate the SR model by
deploying the model in 10 test simulations of box size 100 Mpc/h, and examine
the matter power spectra, bispectra and 2D power spectra in redshift space. We
find the generated SR field matches the true HR result at percent level down to
scales of k ~ 10 h/Mpc. We also identify and inspect dark matter halos and
their substructures. Our SR model generate visually authentic small-scale
structures, that cannot be resolved by the LR input, and are in good
statistical agreement with the real HR results. The SR model performs
satisfactorily on the halo occupation distribution, halo correlations in both
real and redshift space, and the pairwise velocity distribution, matching the
HR results with comparable scatter, thus demonstrating its potential in making
mock halo catalogs. The SR technique can be a powerful and promising tool for
modelling small-scale galaxy formation physics in large cosmological volumes. | The Outer Limits of the M31 System: Kinematics of the Dwarf Galaxy
Satellites And XXVIII and And XXIX: We present Keck/DEIMOS spectroscopy of resolved stars in the M31 satellites
And XXVIII & And XXIX. We show that these are likely self-bound galaxies based
on 18 and 24 members in And XXVIII & And XXIX, respectively. And XXVIII has a
systemic velocity of -331.1 +/- 1.8 km/s and velocity dispersion of 4.9+/-1.6
km/s, implying a mass-to-light ratio (within r_1/2) of ~ 44 +/- 41. And XXIX
has a systemic velocity of -194.4 +/- 1.5 km/s and velocity dispersion of
5.7+/-1.2 km/s, implying a mass-to-light ratio (within r_1/2) of ~ 124 +/- 72.
The internal kinematics and implied masses of And XXVIII & And XXIX are similar
to dwarf spheroidals (dSphs) of comparable luminosities, implying that these
objects are dark matter-dominated dwarf galaxies. Despite the large projected
distances from their host (380 and 188 kpc), the kinematics of these dSph
suggest that they are bound M31 satellites. |
Galaxy properties in different environments at z > 1.5 in the
GOODS-NICMOS Survey: We present a study of the relationship between galaxy colour, stellar mass,
and local galaxy density in a deep near-infrared imaging survey up to a
redshift of z~3 using the GOODS NICMOS Survey (GNS). The GNS is a very deep,
near-infrared Hubble Space Telescope survey imaging a total of 45 arcmin^2 in
the GOODS fields, reaching a stellar mass completeness limit of M* = 10^9.5
M_sun at z=3. Using this data we measure galaxy local densities based on galaxy
counts within a fixed aperture, as well as the distance to the 3rd, 5th and 7th
nearest neighbour. We find a strong correlation between colour and stellar mass
at all redshifts up to z~3. We do not find a strong correlation between colour
and local density, however, the highest overdensities might be populated by a
higher fraction of blue galaxies than average or underdense areas, indicating a
possible reversal of the colour-density relation at high redshift. Our data
suggests that the possible higher blue fraction at extreme overdensities might
be due to a lack of massive red galaxies at the highest local densities. | Science-driven 3D data compression: Photometric redshift surveys map the distribution of matter in the Universe
through the positions and shapes of galaxies with poorly resolved measurements
of their radial coordinates. While a tomographic analysis can be used to
recover some of the large-scale radial modes present in the data, this approach
suffers from a number of practical shortcomings, and the criteria to decide on
a particular binning scheme are commonly blind to the ultimate science goals.
We present a method designed to separate and compress the data into a small
number of uncorrelated radial modes, circumventing some of the problems of
standard tomographic analyses. The method is based on the Karhunen-Lo\`{e}ve
transform (KL), and is connected to other 3D data compression bases advocated
in the literature, such as the Fourier-Bessel decomposition. We apply this
method to both weak lensing and galaxy clustering. In the case of galaxy
clustering, we show that the resulting optimal basis is closely associated with
the Fourier-Bessel basis, and that for certain observables, such as the effects
of magnification bias or primordial non-Gaussianity, the bulk of the signal can
be compressed into a small number of modes. In the case of weak lensing we show
that the method is able to compress the vast majority of the signal-to-noise
into a single mode, and that optimal cosmological constraints can be obtained
considering only three uncorrelated KL eigenmodes, considerably simplifying the
analysis with respect to a traditional tomographic approach. |
An environmental Butcher-Oemler effect in intermediate redshift X-ray
clusters: We present uniform CFHT Megacam g and r photometry for 34 X-ray selected
galaxy clusters drawn from the X-ray Multi-Mirror (XMM) Large Scale Structure
(LSS) survey and the Canadian Cluster Comparison Project (CCCP). The clusters
possess well determined X-ray temperatures spanning the range 1<kT(keV)<12. In
addition, the clusters occupy a relatively narrow redshift interval
(0.15<z<0.41) in order to minimize any redshift dependent photometric effects.
We investigate the colour bimodality of the cluster galaxy populations and
compute blue fractions using criteria derived from Butcher and Oemler (1984).
We identify a trend to observe increasing blue fraction versus redshift in
common with numerous previous studies of cluster galaxy populations. However,
in addition we identify an environmental dependence of cluster blue fraction in
that cool (low mass) clusters display higher blue fractions than hotter (higher
mass) clusters. Finally, we tentatively identify a small excess population of
extremely blue galaxies in the coolest X-ray clusters (essentially massive
groups) and note that these may be the signature of actively star bursting
galaxies driven by galaxy-galaxy interactions in the group environment. | BUDHIES I: characterizing the environments in and around two clusters at
z~0.2: We present the optical spectroscopy for the Blind Ultra Deep HI Environmental
Survey (BUDHIES). With the Westerbork Synthesis Radio Telescope, BUDHIES has
detected HI in over 150 galaxies in and around two Abell clusters at z~0.2.
With the aim of characterizing the environments of the HI-detected galaxies, we
obtained multi-fiber spectroscopy with the William Herschel Telescope. In this
paper, we describe the spectroscopic observations, report redshifts and EW[OII]
measurements for ~600 galaxies, and perform an environmental analysis. In
particular, we present cluster velocity dispersion measurements for 5 clusters
and groups in the BUDHIES volume, as well as a detailed substructure analysis. |
Alignments of galaxies within cosmic filaments from SDSS DR7: Using a sample of galaxy groups selected from the Sloan Digital Sky Survey
Data Release 7 (SDSS DR7), we examine the alignment between the orientation of
galaxies and their surrounding large scale structure in the context of the
cosmic web. The latter is quantified using the large-scale tidal field,
reconstructed from the data using galaxy groups above a certain mass threshold.
We find that the major axes of galaxies in filaments tend to be preferentially
aligned with the directions of the filaments, while galaxies in sheets have
their major axes preferentially aligned parallel to the plane of the sheets.
The strength of this alignment signal is strongest for red, central galaxies,
and in good agreement with that of dark matter halos in N-body simulations.
This suggests that red, central galaxies are well aligned with their host
halos, in quantitative agreement with previous studies based on the spatial
distribution of satellite galaxies. There is a luminosity and mass dependence
that brighter and more massive galaxies in filaments and sheets have stronger
alignment signals. We also find that the orientation of galaxies is aligned
with the eigenvector associated with the smallest eigenvalue of the tidal
tensor. These observational results indicate that galaxy formation is affected
by large-scale environments, and strongly suggests that galaxies are aligned
with each other over scales comparable to those of sheets and filaments in the
cosmic web. | Cosmological distances with general-relativistic ray tracing: framework
and comparison to cosmographic predictions: In this work we present the first results from a new ray-tracing tool to
calculate cosmological distances in the context of fully nonlinear general
relativity. We use this tool to study the ability of the general cosmographic
representation of luminosity distance, as truncated at third order in redshift,
to accurately capture anisotropies in the "true" luminosity distance. We use
numerical relativity simulations of cosmological large-scale structure
formation which are free from common simplifying assumptions in cosmology. We
find the general, third-order cosmography is accurate to within 1% for
redshifts to z\approx 0.034 when sampling scales strictly above 100 Mpc/h,
which is in agreement with an earlier prediction. We find the inclusion of
small-scale structure generally spoils the ability of the third-order
cosmography to accurately reproduce the full luminosity distance for wide
redshift intervals, as might be expected. For a simulation sampling small-scale
structures, we find a +/- 5% variance in the monopole of the ray-traced
luminosity distance at z \approx 0.02. Further, all 25 observers we study here
see a 9--20% variance in the luminosity distance across their sky at z \approx
0.03, which reduces to 2--5% by z \approx 0.1. These calculations are based on
simulations and ray tracing which adopt fully nonlinear general relativity, and
highlight the potential importance of fair sky-sampling in low-redshift
isotropic cosmological analysis. |
Finsler geometric perspective on the bulk flow in the universe: Astronomical observations showed that there may exist a bulk flow with
peculiar velocities in the universe, which contradicts with the (\Lambda)CDM
model. The bulk flow reveals that the observational universe is anisotropic at
large scales. In fact, a more reliable observation on the anisotropy of
spacetime comes from the CMB power spectra. The WMAP and Planck satellites both
show that there is a hemispherical power asymmetry at large-angular scales. In
this paper, we propose a "wind" scenario to the bulk flow (or the anisotropy of
spacetime). Under the influence of the "wind", the spacetime metric could
become a Finsler structure. By resolving the null geodesic equation, we obtain
the modified luminosity distance, which has a dipolar form at the leading
order. Thus, the "wind" describes well the bulk flow. In addition, we perform a
least-(\chi^2) fit to the data of type Ia supernovae (SNe Ia) in the Union2.1
compilation. The peculiar velocity of the bulk flow has an upper limit
(v_{bulk}\lesssim 4000 \rm{km/s}), which is compatible with all the existing
observational values. | Asymmetry and non-random orientation of the inflight effective beam
pattern in the WMAP Data: The anomaly against the Gaussianity in the WMAP data was alleged to be due to
insufficient handling of beam asymmetries. In this paper we investigate this
issue and develop a method to estimate the shape of the inflight effective
beam, particularly the asymmetry and azimuthal orientation. We divide the whole
map into square patches and exploit the information in the Fourier space. For
patches containing bright extra-galactic point sources, we can directly
estimate their shapes, from which the inflight effective beam manifests itself.
For those without, we estimate the pattern via perturbing the phases and
directly from the Fourier amplitudes. We show that the inflight effective beam
convolving the signal is indeed non-symmetric for most part of the sky, and
it's not randomly oriented. Around the ecliptic poles, however, the asymmetry
is smaller due to the averaging effect from different orientations of the beam
from the scan strategy. The effective beam with significant asymmetry is
combing with almost parallel fashion along the lines of Ecliptic longitude. In
the foreground-cleaned ILC map, however, the systematics caused by beam effect
is significantly lessened. |
Caustics in growing Cold Dark Matter Haloes: We simulate the growth of isolated dark matter haloes from self-similar and
spherically symmetric initial conditions. Our N-body code integrates the
geodesic deviation equation in order to track the streams and caustics
associated with individual simulation particles. The radial orbit instability
causes our haloes to develop major-to-minor axis ratios approaching 10 to 1 in
their inner regions. They grow similarly in time and have similar density
profiles to the spherical similarity solution, but their detailed structure is
very different. The higher dimensionality of the orbits causes their stream and
caustic densities to drop much more rapidly than in the similarity solution.
This results in a corresponding increase in the number of streams at each
point. At 1% of the turnaround radius (corresponding roughly to the Sun's
position in the Milky Way) we find of order 10^6 streams in our simulations, as
compared to 10^2 in the similarity solution. The number of caustics in the
inner halo increases by a factor of several, because a typical orbit has six
turning points rather than one, but caustic densities drop by a much larger
factor. This reduces the caustic contribution to the annihilation radiation.
For the region between 1% and 50% of the turnaround radius, this is 4% of the
total in our simulated haloes, as compared to 6.5% in the similarity solution.
Caustics contribute much less at smaller radii. These numbers assume a 100 GeV
c^-2 neutralino with present-day velocity dispersion 0.03 cm s^-1, but reducing
the dispersion by ten orders of magnitude only doubles the caustic luminosity.
We conclude that caustics will be unobservable in the inner parts of haloes.
Only the outermost caustic might potentially be detectable. | The rotation of Galaxy Clusters: The method for detection of the galaxy cluster rotation based on the study of
distribution of member galaxies with velocities lower and higher of the cluster
mean velocity over the cluster image is proposed. The search for rotation is
made for flat clusters with $a/b>1.8$ and BMI type clusters which are expected
to be rotating. For comparison there were studied also round clusters and
clusters of NBMI type, the second by brightness galaxy in which does not differ
significantly from the cluster cD galaxy. Seventeen out of studied 65 clusters
are found to be rotating. It was found that the detection rate is sufficiently
high for flat clusters, over 60\%, and clusters of BMI type with dominant cD
galaxy, ~ 35%. The obtained results show that clusters were formed from the
huge primordial gas clouds and preserved the rotation of the primordial clouds,
unless they did not have merging with other clusters and groups of galaxies, in
the result of which the rotation has been prevented. |
Complete Reionization Constraints from Planck 2015 Polarization: We conduct an analysis of the Planck 2015 data that is complete in
reionization observables from the large angle polarization $E$-mode spectrum in
the redshift range $6 < z < 30$. Based on 5 principal components, all of which
are constrained by the data, this single analysis can be used to infer
constraints on any model for reionization in the same range; we develop an
effective likelihood approach for applying these constraints to models. By
allowing for an arbitrary ionization history, this technique tests the
robustness of inferences on the total optical depth from the usual step-like
transition assumption, which is important for the interpretation of many other
cosmological parameters such as the dark energy and neutrino mass. The Planck
2015 data not only allow a high redshift $z>15$ component to the optical depth
but prefer it at the $2\sigma$ level. This preference is associated with excess
power in the multipole range $10 \lesssim \ell \lesssim 20$ and may indicate
high redshift ionization sources or unaccounted for systematics and foregrounds
in the 2015 data. | Theory MOND in a Friedmann-Robertson-Walker Cosmology as alternative to
the Nonbaryonic Dark Matter paradigm: Modified Newtonian Dynamics (MoND) is an empirically modification of
Newtonian gravity at largest scales in order to explain rotation curves of
galaxies, as an alternative to nonbaryonic dark matter. But MoND theories can
hardly connect themselves to the formalism of relativistic cosmology type
Friedmann-Robertson-Walker. The present work posits the possibility of building
this connection by postulating a Yukawa-like scalar potential, with non
gravitational origin. This potential comes from a simple reflection speculate
of the well-know potential of Yukawa and it is intended to describe the
following physics scenarios: null in very near solar system, slightly
attractive in ranges of interstellar distances, very attractive in distance
ranges comparable to galaxies cluster, and repulsive to cosmic scales. As a
result of introducing this potential into the typical Friedman equations we
found that the critical density of matter is consistent with the observed
density (without a dark matter assumption), besides this, MoND theory is
obtained for interstellar scales and consequently would explain rotation
curves. Also it is shown that Yukawa type inverse does not alter the
predictions of the Cosmic Microwave Background neither the primordial
nucleosinthesys in early universe; and can be useful to explain the large-scale
structure formation. |
Cosmological Equations for Interacting Energies: In this paper the coupling between dark energy and the other components of
the cosmological fluid has been studied. Firstly, it will be shown that the
application of general cosmological equations, deduced by the authors in a
previous work, to the known data of the Abell cluster A586 using the
Layzer-Irvine theory gives similar results compared to the work of other
authors. The aforesaid method present some problems: the application of an
approximate theory (Layzer-Irvine theory), it has only one experimental datum
and finally, it gives results that are a bit difficult to admit considering a
physical reasoning. In order to avoid the above-mentioned problems, a way to
study the coupling of dark energy with other Universe components has been
shown. The results obtained have a sensible physical behavior. They also fix
the required functionality of the product $w_\Lambda \Omega_\Lambda$ in order
to verify the main known properties of the Universe's behavior. Finally, these
results permit to make predictions about a set of different cosmological
properties. | Mass Varying Neutrinos With More Than One Species Of Neutrinos: In the context of Mass Varying Neutrinos(MaVaNs) we study a model in which a
scalar field is coupled to more than one species of neutrinos with different
masses. In general, adiabatic models of non-relativistic MaVaNs are heavily
constrained by their stability towards the formation of neutrino nuggets. These
constraints also apply to models with more than one neutrino species, and we
find that using the lightest neutrino, which is still relativistic, as an
explanation for dark energy does not work because of a feedback mechanism from
the heavier neutrinos. |
The circumnuclear environment of IRAS 20551-4250 a case study of
AGN/Starburst connection for JWST: We present a general review of the current knowledge of IRAS 20551-4250 and
its circumnuclear environment. This Ultraluminous Infrared Galaxy is one of the
most puzzling sources of its class in the nearby Universe: the near-IR spectrum
is typical of a galaxy experiencing a very intense starburst, but a highly
obscured active nucleus is identified beyond 5 micron and possibly dominates
the mid-IR energy output of the system. At longer wavelengths star formation is
again the main driver of the global spectral shape and features. We interpret
all the available IR diagnostics in the framework of simultaneous black hole
growth and star formation, and discuss the key properties that make this source
an ideal laboratory for the forthcoming James Webb Space Telescope. | Reconstructing the Initial Density Field of the Local Universe: Method
and Test with Mock Catalogs: Our research objective in this paper is to reconstruct an initial linear
density field, which follows the multivariate Gaussian distribution with
variances given by the linear power spectrum of the current CDM model and
evolves through gravitational instability to the present-day density field in
the local Universe. For this purpose, we develop a Hamiltonian Markov Chain
Monte Carlo method to obtain the linear density field from a posterior
probability function that consists of two components: a prior of a Gaussian
density field with a given linear spectrum, and a likelihood term that is given
by the current density field. The present-day density field can be
reconstructed from galaxy groups using the method developed in Wang et al.
(2009a). Using a realistic mock SDSS DR7, obtained by populating dark matter
haloes in the Millennium simulation with galaxies, we show that our method can
effectively and accurately recover both the amplitudes and phases of the
initial, linear density field. To examine the accuracy of our method, we use
$N$-body simulations to evolve these reconstructed initial conditions to the
present day. The resimulated density field thus obtained accurately matches the
original density field of the Millennium simulation in the density range 0.3 <=
rho/rho_mean <= 20 without any significant bias. Especially, the Fourier phases
of the resimulated density fields are tightly correlated with those of the
original simulation down to a scale corresponding to a wavenumber of ~ 1 h/Mpc,
much smaller than the translinear scale, which corresponds to a wavenumber of ~
0.15 h\Mpc. |
A possible analogy between the dynamics of a skydiver and a scalar
field: cosmological consequences: The cosmological consequences of a slow rolling scalar field with constant
kinetic term in analogy to the vertical movement of a skydiver after reaching
terminal velocity are investigated. It is shown that the terminal scalar field
hypothesis is quite realistic. In this approach, the scalar field potential is
given by a quadratic function of the field. This model provides solutions in
which the Universe was dominated in the past by a mixture of baryons and dark
matter, is currently accelerating (as indicated by type Ia supernovae data),
but will be followed by a contraction phase. The theoretical predictions of
this model are consistent with current observations, therefore, a terminal
scalar field is a viable candidate to dark energy. | Inferring halo masses with Graph Neural Networks: Understanding the halo-galaxy connection is fundamental in order to improve
our knowledge on the nature and properties of dark matter. In this work we
build a model that infers the mass of a halo given the positions, velocities,
stellar masses, and radii of the galaxies it hosts. In order to capture
information from correlations among galaxy properties and their phase-space, we
use Graph Neural Networks (GNNs), that are designed to work with irregular and
sparse data. We train our models on galaxies from more than 2,000
state-of-the-art simulations from the Cosmology and Astrophysics with MachinE
Learning Simulations (CAMELS) project. Our model, that accounts for
cosmological and astrophysical uncertainties, is able to constrain the masses
of the halos with a $\sim$0.2 dex accuracy. Furthermore, a GNN trained on a
suite of simulations is able to preserve part of its accuracy when tested on
simulations run with a different code that utilizes a distinct subgrid physics
model, showing the robustness of our method. The PyTorch Geometric
implementation of the GNN is publicly available on Github at
https://github.com/PabloVD/HaloGraphNet |
Non-local halo bias with and without massive neutrinos: Understanding the biasing between the clustering properties of halos and the
underlying dark matter distribution is important for extracting cosmological
information from ongoing and upcoming galaxy surveys. While on sufficiently
larges scales the halo overdensity is a local function of the mass density
fluctuations, on smaller scales the gravitational evolution generates non-local
terms in the halo density field. We characterize the magnitude of these
contributions at third-order in perturbation theory by identifying the
coefficients of the non-local invariant operators, and extend our calculation
to include non-local (Lagrangian) terms induced by a peak constraint. We apply
our results to describe the scale-dependence of halo bias in cosmologies with
massive neutrinos. The inclusion of gravity-induced non-local terms and,
especially, a Lagrangian $k^2$-contribution is essential to reproduce the
numerical data accurately. We use the peak-background split to derive the
numerical values of the various bias coefficients from the excursion set peak
mass function. For neutrino masses in the range $0\leq \sum_i m_{\nu_i} \leq
0.6$ eV, we are able to fit the data with a precision of a few percents up to
$k=0.3\, h {\rm \,Mpc^{-1}}$ without any free parameter. | Can Dark Matter be Geometry? A Case Study with Mimetic Dark Matter: We investigate the possibility of dark matter being a pure geometrical
effect, rather than a particle or a compact object, by exploring a specific
modified gravity model: mimetic dark matter. We present an alternative
formulation of the theory, closer to the standard cosmological perturbation
theory framework. We make manifest the presence of arbitrary parameters and
extra functions, both at background level and at first order in perturbation
theory. We present the full set of independent equations of motion for this
model, and we discuss the amount of tuning needed to match predictions of the
theory to actual data. By using the matter power spectrum and cosmic microwave
background angular power spectra as benchmark observables, we explicitly show
that since there is no natural mechanism to generate adiabatic initial
conditions in this specific model, extra fine-tuning is required. We modify the
publicly available Boltzmann code \texttt{CLASS} to make accurate predictions
for the observables in mimetic dark matter. Our modified version of
\texttt{CLASS} is available on GitHub. We have used mimetic dark matter as an
illustration of how much one is allowed to change the initial conditions before
contradicting observations when modifying the laws of gravity as described by
General Relativity but we point out that modifying gravity without providing a
natural mechanism to generate adiabatic initial conditions will always lead to
highly fine-tuned models. |
Examining the evidence for dynamical dark energy: We apply a new non-parametric Bayesian method for reconstructing the
evolution history of the equation-of-state $w$ of dark energy, based on
applying a correlated prior for $w(z)$, to a collection of cosmological data.
We combine the latest supernova (SNLS 3-year or Union2.1), cosmic microwave
background, redshift space distortion and the baryonic acoustic oscillation
measurements (including BOSS, WiggleZ and 6dF) and find that the cosmological
constant appears consistent with current data, but that a dynamical dark energy
model which evolves from $w<-1$ at $z\sim0.25$ to $w > -1$ at higher redshift
is mildly favored. Estimates of the Bayesian evidences show little preference
between the cosmological constant model and the dynamical model for a range of
correlated prior choices. Looking towards future data, we find that the best
fit models for current data could be well distinguished from the $\Lambda$CDM
model by observations such as Planck and Euclid-like surveys. | Photometric Redshift Calibration with Self Organising Maps: Accurate photometric redshift calibration is central to the robustness of all
cosmology constraints from cosmic shear surveys. Analyses of the KiDS
re-weighted training samples from all overlapping spectroscopic surveys to
provide a direct redshift calibration. Using self-organising maps (SOMs) we
demonstrate that this spectroscopic compilation is sufficiently complete for
KiDS, representing $99\%$ of the effective 2D cosmic shear sample. We use the
SOM to define a $100\%$ represented `gold' cosmic shear sample, per tomographic
bin. Using mock simulations of KiDS and the spectroscopic training set, we
estimate the uncertainty on the SOM redshift calibration, and find that
photometric noise, sample variance, and spectroscopic selection effects
(including redshift and magnitude incompleteness) induce a combined maximal
scatter on the bias of the redshift distribution reconstruction ($\Delta
\langle z \rangle=\langle z \rangle_{\rm est}-\langle z \rangle_{\rm true}$) of
$\sigma_{\Delta \langle z \rangle} \leq 0.006$ in all tomographic bins. We show
that the SOM calibration is unbiased in the cases of noiseless photometry and
perfectly representative spectroscopic datasets, as expected from theory. The
inclusion of both photometric noise and spectroscopic selection effects in our
mock data introduces a maximal bias of $\Delta \langle z \rangle
=0.013\pm0.006$, or $\Delta \langle z \rangle \leq 0.025$ at $97.5\%$
confidence, once quality flags have been applied to the SOM. The method
presented here represents a significant improvement over the previously adopted
direct redshift calibration implementation for KiDS, owing to its diagnostic
and quality assurance capabilities. The implementation of this method in future
cosmic shear studies will allow better diagnosis, examination, and mitigation
of systematic biases in photometric redshift calibration. |
In Pursuit of the Least Luminous Galaxies: The dwarf galaxy companions to the Milky Way are unique cosmological
laboratories. With luminosities as low as 10^-7 L_MW, they inhabit the lowest
mass dark matter halos known to host stars and are presently the most direct
tracers of the distribution, mass spectrum, and clustering scale of dark
matter. Their resolved stellar populations also facilitate detailed studies of
their history and mass content. To fully exploit this potential requires a
well-defined census of virtually invisible galaxies to the faintest possible
limits and to the largest possible distances. I review the past and present
impacts of survey astronomy on the census of Milky Way dwarf galaxy companions,
and discuss the future of finding ultra-faint dwarf galaxies around the Milky
Way and beyond in wide-field survey data. | Optimal 1D Ly$α$ Forest Power Spectrum Estimation -- II. KODIAQ,
SQUAD & XQ-100: We measure the 1D Ly$\,\alpha$ power spectrum $P_\mathrm{1D}$ from Keck
Observatory Database of Ionized Absorption toward Quasars (KODIAQ), The
Spectral Quasar Absorption Database (SQUAD) and XQ-100 quasars using the
optimal quadratic estimator. We combine KODIAQ and SQUAD at the spectrum level,
but perform a separate XQ-100 estimation to control its large resolution
corrections in check. Our final analysis measures $P_\mathrm{1D}$ at scales
$k<0.1\,$s$\,$km$^{-1}$ between redshifts $z=$ 2.0 -- 4.6 using 538 quasars.
This sample provides the largest number of high-resolution, high-S/N
observations; and combined with the power of optimal estimator it provides
exceptional precision at small scales. These small-scale modes ($k\gtrsim
0.02\,$s$\,$km$^{-1}$), unavailable in Sloan Digital Sky Survey (SDSS) and Dark
Energy Spectroscopic Instrument (DESI) analyses, are sensitive to the thermal
state and reionization history of the intergalactic medium, as well as the
nature of dark matter. As an example, a simple Fisher forecast analysis
estimates that our results can improve small-scale cut off sensitivity by more
than a factor of 2. |
Nuclear Star Clusters: The centers of most galaxies in the local universe are occupied by compact,
barely resolved sources. Based on their structural properties, position in the
fundamental plane, and integrated spectra, these sources clearly have a stellar
origin. They are therefore called "nuclear star clusters" (NCs) or "stellar
nuclei". NCs are found in galaxies of all Hubble types, suggesting that their
formation is intricately linked to galaxy evolution. Here, I review some recent
studies of NCs, describe ideas for their formation and subsequent growth, and
touch on their possible evolutionary connection with both supermassive black
holes and globular clusters. | Simultaneous determination of the cosmic birefringence and miscalibrated
polarisation angles from CMB experiments: We show that the cosmic birefringence and miscalibrated polarisation angles
can be determined simultaneously by cosmic microwave background (CMB)
experiments using the cross-correlation between $E$- and $B$-mode polarisation
data. This is possible because polarisation angles of the CMB are rotated by
both the cosmic birefringence and miscalibration effects,whereas those of the
Galactic foreground emission only by the latter. Our method does not require
prior knowledge of the $E$- and $B$-mode power spectra of the foreground
emission, but uses only the knowledge of the CMB polarisation spectra.
Specifically, we relate the observed $EB$ correlation to the difference between
the $\mathit{observed}$ $E$- and $B$-mode spectra in the sky, and use different
multipole dependence of the CMB (given by theory) and foreground spectra (with
no assumption) to derive the likelihood for the miscalibration angle $\alpha$
and the birefringence angle $\beta$. We show that a future satellite mission
similar to LiteBIRD can determine $\beta$ with a precision of ten arcminutes. |
Reconstruction of halo power spectrum from redshift-space galaxy
distribution: cylinder-grouping method and halo exclusion effect: The peculiar velocity field measured by redshift-space distortions (RSD) in
galaxy surveys provides a unique probe of the growth of large-scale structure.
However, systematic effects arise when including satellite galaxies in the
clustering analysis. Since satellite galaxies tend to reside in massive halos
with a greater halo bias, the inclusion boosts the clustering power. In
addition, virial motions of the satellite galaxies cause a significant
suppression of the clustering power due to nonlinear RSD effects. We develop a
novel method to recover the redshift-space power spectrum of halos from the
observed galaxy distribution by minimizing the contamination of satellite
galaxies. The cylinder grouping method (CGM) we study effectively excludes
satellite galaxies from a galaxy sample. However, we find that this technique
produces apparent anisotropies in the reconstructed halo distribution over all
the scales which mimic RSD. On small scales, the apparent anisotropic
clustering is caused by exclusion of halos within the anisotropic cylinder used
by the CGM. On large scales, the misidentification of different halos in the
large-scale structures, aligned along the line-of-sight, into the same CGM
group, causes the apparent anisotropic clustering via their cross-correlation
with the CGM halos. We construct an empirical model for the CGM halo power
spectrum, which includes correction terms derived using the CGM window function
at small scales as well as the linear matter power spectrum multiplied by a
simple anisotropic function at large scales. We apply this model to a mock
galaxy catalog at z=0.5, designed to resemble SDSS-III BOSS CMASS galaxies, and
find that our model can predict both the monopole and quadrupole power spectra
of the host halos up to k<0.5 h/Mpc to within 5%. | Atmospheric neutrinos in a next-generation xenon dark matter experiment: We study the sensitivity of future xenon- and argon-based dark matter and
neutrino detection experiments to low-energy atmospheric neutrinos. Not
accounting for experimental backgrounds, the primary obstacle for identifying
nuclear recoils induced by atmospheric neutrinos is the tail of the electron
recoil distribution due to $pp$ solar neutrinos. We use the NEST code to model
the solar and atmospheric neutrino signals in a xenon detector and find that an
exposure of 700 tonne-years will produce a $5\sigma$ detection of atmospheric
neutrinos. We explore the effect of different detector properties and find that
a sufficiently long electron lifetime is essential to the success of such a
measurement. |
Efficient computation of the super-sample covariance for stage IV galaxy
surveys: Super-sample covariance (SSC) is an important effect for cosmological
analyses that use the deep structure of the cosmic web; it may, however, be
nontrivial to include it practically in a pipeline. We solve this difficulty by
presenting a formula for the precision (inverse covariance) matrix and show
applications to update likelihood or Fisher forecast pipelines. The formula has
several advantages in terms of speed, reliability, stability, and ease of
implementation. We present an analytical application to show the formal
equivalence between three approaches to SSC: (i) at the usual covariance level,
(ii) at the likelihood level, and (iii) with a quadratic estimator. We then
present an application of this computationally efficient framework for studying
the impact of inaccurate modelling of SSC responses for cosmological
constraints from stage IV surveys. We find that a weak-lensing-only analysis is
very sensitive to inaccurate modelling of the scale dependence of the response,
which needs to be calibrated at the $\sim15\%$ level. The sensitivity to this
scale dependence is less severe for the joint weak-lensing and galaxy
clustering analysis (also known as 3x2pt). Nevertheless, we find that both the
amplitude and scale-dependence of the responses have to be calibrated at better
than 30\%. | Breaking CMB degeneracy in dark energy through LSS: The cosmic microwave background and large scale structure are complementary
probes to investigate the early and late time universe. After the current
accomplishment of the high accuracies of CMB measurements, accompanying
precision cosmology from LSS data is emphasized. We investigate the dynamical
dark energy models which can produce the same CMB angular power spectra as that
of the LCDM model with less than a sub-percent level accuracy. If one adopts
the dynamical DE models using the so-called Chevallier-Polarski-Linder (CPL)
parametrization, w = w0 + wa(1-a), then one obtains models (w0,wa)=
(-0.8,-0.767), (-0.9,-0.375), (-1.1,0.355), (-1.2,0.688) named as M8, M9, M11,
and M12, respectively. The differences of the growth rate, f which is related
to the redshift space distortions (RSD) between different DE models and the
LCDM model are about 0.2% only at z=0. The difference of f between M8 (M9, M11,
M12) and the LCDM model becomes maximum at z ~ 0.25 with -2.4 (-1.2, 1.2,
2.5)%. This is a scale-independent quantity. One can investigate the one-loop
correction of the matter power spectrum of each model using the standard
perturbation theory in order to probe the scale-dependent quantity in the
quasi-linear regime ({\it i.e.} k < 0.4 h/Mpc). The differences in the matter
power spectra including the one-loop correction between M8 (M9, M11, M12) and
the LCDM model for k= 0.4 h/Mpc scale are 1.8 (0.9, 1.2, 3.0)% at z=0, 3.0
(1.6, 1.9, 4.2)% at z=0.5, and 3.2 (1.7, 2.0, 4.5)% at z=1.0. The bigger
departure from -1 of w0, the larger the difference in the power spectrum. Thus,
one should use both the RSD and the quasi-linear observable in order to
discriminate a viable DE model among a slew of models which are degenerated in
CMB. Also we obtain the lower limit on w0 > -1.5 from the CMB acoustic peaks
and this will provide the useful limitation on phantom models. |
The impact of global environment on galaxy mass functions at low
redshift: We study the galaxy stellar mass function in different environments in the
local Universe, considering both the total mass function and that of individual
galaxy morphological types. We compare the mass functions of galaxies with $\rm
log_{10} M_{\star}/M_{\odot} \geq 10.25$ in the general field and in galaxy
groups, binary and single galaxy systems from the Padova-Millennium Galaxy and
Group Catalogue at $z=0.04-0.1$ with the mass function of galaxy clusters of
the WIde-field Nearby Galaxy-Cluster Survey at $z=0.04-0.07$. Strikingly, the
variations of the mass function with global environment, overall, are small and
subtle. The shapes of the mass functions of the general field and clusters are
indistinguishable, and only small, statistically insignificant variations are
allowed in groups. Only the mass function of our single galaxies, representing
the least massive haloes and comprising less than a third of the general field
population, is proportionally richer in low-mass galaxies than other
environments. The most notable environmental effect is a progressive change in
the upper galaxy mass, with very massive galaxies found only in the most
massive environments. This environment-dependent mass cut-off is unable to
affect the Schechter parameters and the K-S test, and can only be revealed by
an ad-hoc analysis. Finally, we show how, in each given environment, the mass
function changes with morphological type, and that galaxies of the same
morphological type can have different mass functions in different environments. | Statistical Classification Techniques for Photometric Supernova Typing: Future photometric supernova surveys will produce vastly more candidates than
can be followed up spectroscopically, highlighting the need for effective
classification methods based on lightcurves alone. Here we introduce boosting
and kernel density estimation techniques which have minimal astrophysical
input, and compare their performance on 20,000 simulated Dark Energy Survey
lightcurves. We demonstrate that these methods are comparable to the best
template fitting methods currently used, and in particular do not require the
redshift of the host galaxy or candidate. However both methods require a
training sample that is representative of the full population, so typical
spectroscopic supernova subsamples will lead to poor performance. To enable the
full potential of such blind methods, we recommend that representative training
samples should be used and so specific attention should be given to their
creation in the design phase of future photometric surveys. |
Indicators of Intrinsic AGN Luminosity: a Multi-Wavelength Approach: We consider five indicators for intrinsic AGN luminosity: the luminosities of
the [OIII]$\lambda$5007 line, the [OIV]25.89$\mu$m line, the mid-infrared (MIR)
continuum emission by the torus, and the radio and hard X-ray (E $>$ 10keV)
continuum emission. We compare these different proxies using two complete
samples of low-redshift type 2 AGN selected in a homogeneous way based on
different indicators: an optically selected [OIII] sample and a mid-infrared
selected 12$\mu$m sample. We examine the correlations between all five
different proxies, and find better agreement for the [OIV], MIR, and [OIII]
luminosities than for the hard X-ray and radio luminosities. Next, we compare
the ratios of the fluxes of the different proxies to their values in unobscured
Type 1 AGN. The agreement is best for the ratio of the [OIV] and MIR fluxes,
while the ratios of the hard X-ray to [OIII], [OIV], and MIR fluxes are
systematically low by about an order-of-magnitude in the Type 2 AGN, indicating
that hard X-ray selected samples do not represent the full Type 2 AGN
population. In a similar spirit, we compare different optical and MIR
diagnostics of the relative energetic contributions of AGN and star formation
processes in our samples of Type 2 AGN. We find good agreement between the
various diagnostic parameters, such as the equivalent width of the MIR
polycyclic aromatic hydrocarbon features, the ratio of the MIR [OIV]/[NeII]
emission-lines, the spectral index of the MIR continuum, and the commonly used
optical emission-line ratios. Finally, we test whether the presence of cold gas
associated with star-formation leads to an enhanced conversion efficiency of
AGN ionizing radiation into [OIII] or [OIV] emission. We find that no
compelling evidence exists for this scenario for the luminosities represented
in this sample (L$_{bol}$ $\approx$ 10$^{9}$ - 8 $\times$ 10$^{11}$
L$_{\sun}$). (abridged) | The Sloan Lens ACS Survey. XI. Beyond Hubble resolution: size,
luminosity and stellar mass of compact lensed galaxies at intermediate
redshift: We exploit the strong lensing effect to explore the properties of
intrinsically faint and compact galaxies at intermediate redshift, at the
highest possible resolution at optical wavelengths. Our sample consists of 46
strongly-lensed emission line galaxies discovered by the Sloan Lens ACS (SLACS)
Survey. The galaxies have been imaged at high resolution with HST in three
bands (V_HST, I_814 and H_160), allowing us to infer their size, luminosity,
and stellar mass using stellar population synthesis models. Lens modeling is
performed using a new fast and robust code, klens, which we test extensively on
real and synthetic non-lensed galaxies, and also on simulated galaxies
multiply-imaged by SLACS- like galaxy-scale lenses. Our tests show that our
measurements of galaxy size, flux, and Sersic index are robust and accurate,
even for objects intrinsically smaller than the HST point spread function. The
median magnification is 8.8, with a long tail that extends to magnifications
above 40. Modeling the SLACS sources reveals a population of galaxies with
colors and Sersic indices (median n ~ 1) consistent with the objects detected
in the field with HST in the GEMS survey, but that are (typically) ~ 2
magnitudes fainter and ~ 5 times smaller in apparent size. The closest analog
are ultracompact emission line galaxies identified by HST grism surveys. The
lowest mass galaxies in our sample are comparable to the brightest Milky Way
satellites in stellar mass (10^7 solar masses) and have well-determined half
light radii of 0."05 (~0.3 kpc). |
Dark Matter Detection with Polarized Detectors: We consider the prospects to use polarized dark-matter detectors to
discriminate between various dark-matter models. If WIMPs are fermions and
participate in parity-violating interactions with ordinary matter, then the
recoil-direction and recoil-energy distributions of nuclei in detectors will
depend on the orientation of the initial nuclear spin with respect to the
velocity of the detector through the Galactic halo. If, however, WIMPS are
scalars, the only possible polarization-dependent interactions are extremely
velocity-suppressed and, therefore, unobservable. Since the amplitude of this
polarization modulation is fixed by the detector speed through the halo, in
units of the speed of light, exposures several times larger than those of
current experiments will be required to be probe this effect. | An X-ray View of Star Formation in the Central 3 kpc of NGC 2403: Archival Chandra observations are used to study the X-ray emission associated
with star formation in the central region of the nearby SAB(s)cd galaxy NGC
2403. The distribution of X-ray emission is compared to the morphology visible
at other wavelengths using complementary Spitzer, GALEX, and ground-based
Halpha imagery. In general, the brightest extended X-ray emission is associated
with HII regions and to other star-forming structures but is more pervasive;
existing also in regions devoid of strong Halpha and UV emission. This X-ray
emission has the spectral properties of diffuse hot gas (kT ~ 0.2keV) whose
likely origin is in gas shock-heated by stellar winds and supernovae with < 20%
coming from faint unresolved X-ray point sources. This hot gas may be
slowly-cooling extra-planar remnants of past outflow events, or a disk
component that either lingers after local star formation activity has ended or
that has vented from active star-forming regions into a porous interstellar
medium. |
Photometric Effects and Voronoi-diagrams as a mixed model for the
spatial distribution of galaxies: We review the model of the Voronoi Diagrams which allows to reproduce the
large-scale structures of our universe as given by the astronomical catalogs.
The observed number of galaxies in a given solid angle with a chosen
flux/magnitude versus the redshift presents a maximum that is a function of the
flux/magnitude ; it can be explained by a detailed analysis of the standard
luminosity function for galaxies as well by two new luminosity function for
galaxies. The current status of the research on the statistics of the Voronoi
Diagrams is reviewed. | The observed infall of galaxies towards the Virgo cluster: We examine the velocity field of galaxies around the Virgo cluster induced by
its overdensity. A sample of 1792 galaxies with distances from the Tip of the
Red Giant Branch, the Cepheid luminosity, the SNIa luminosity, the surface
brightness fluctuation method, and the Tully-Fisher relation has been used to
study the velocity-distance relation in the Virgocentric coordinates. Attention
was paid to some observational biases affected the Hubble flow around Virgo.
We estimate the radius of the zero-velocity surface for the Virgo cluster to
be within (5.0 - 7.5) Mpc corresponding to (17 - 26)^\circ at the mean cluster
distance of 17.0 Mpc. In the case of spherical symmetry with cosmological
parameter \Omega_m=0.24 and the age of the Universe T_0= 13.7 Gyr, it yields
the total mass of the Virgo cluster to be within M_T=(2.7 - 8.9) * 10^{14}
M_\sun in reasonable agreement with the existing virial mass estimates for the
cluster. |
Accurate classification of 28 objects detected in the 39 months Palermo
Swift/BAT hard X-ray catalogue: Through an optical campaign performed at 4 telescopes located in the northern
and the southern hemispheres, plus archival data from two on-line sky surveys,
we have obtained optical spectroscopy for 28 counterparts of unclassified or
poorly studied hard X-ray emitting objects detected with Swift/BAT and listed
in the 39 months Palermo Swift/BAT hard X-ray catalogue. We have been able to
pinpoint the optical counterpart of these high energy sources by means of X-ray
observations taken with Swift/XRT or XMM which allowed us to restrict the
positional uncertainty from few arcmin to few arcsec; satellite data also
provided information on the X-ray spectra of these objects. We find that 7
sources in our sample are Type 1 AGN while 20 are Type 2 AGN, with their
redshifts lying between 0.009 and 0.075; the remaining object is a Galactic
cataclysmic variable (CV). In this work we provide optical information for all
28 sources and the results of the soft X-ray analysis of 3 out of 5 AGN
observed with XMM/Newton. | Constraints on neutrino masses from WMAP5 and BBN in the lepton
asymmetric universe: In this paper, we put constraints on neutrino properties such as mass
$m_{\nu}$ and degeneracy parameters $\xi_i$ from WMAP5 data and light element
abundances by using a Markov chain Monte Carlo (MCMC) approach. In order to
take consistently into account the effects of the degeneracy parameters, we run
the Big Bang Nucleosynthesis code for each value of $\xi_i$ and the other
cosmological parameters to estimate the Helium abundance, which is then used to
calculate CMB anisotropy spectra instead of treating it as a free parameter. We
find that the constraint on $m_{\nu}$ is fairly robust and does not vary very
much even if the lepton asymmetry is allowed, and is given by $\sum m_\nu < 1.3
\rm eV$ ($95 % \rm C.L.$). |
HII Region Luminosity Function of the Interacting Galaxy M51: We present a study of HII regions in M51 using the Hubble Space Telescope ACS
images taken as part of the Hubble Heritage Program. We have catalogued about
19,600 HII regions in M51 with Ha luminosity in the range of L = 10^{35.5}
erg/s to 10^{39.0} erg/s. The Ha luminosity function of HII regions (HII LF) in
M51 is well represented by a double power law with its index alpha=-2.25\pm0.02
for the bright part and alpha=-1.42\pm0.01 for the faint part, separated at a
break point L= 10^{37.1} erg/s. This break was not found in previous studies of
M51 HII regions. Comparison with simulated HII LFs suggests that this break is
caused by the transition of HII region ionizing sources, from low mass clusters
(with ~ 10^3 M_sun, including several OB stars) to more massive clusters
(including several tens of OB stars). The HII LFs with L < 10^{37.1} erg/s are
found to have different slopes for different parts in M51: the HII LF for the
interarm region is steeper than those for the arm and the nuclear regions. This
observed difference in HII LFs can be explained by evolutionary effects that
HII regions in the interarm region are relatively older than those in the other
parts of M51. | A No-Go Theorem for Direct Collapse Black Holes Without a Strong
Ultraviolet Background: Explaining the existence of supermassive black holes (SMBHs) larger than
$\sim 10^9 M_\odot$ at redshifts $z >\sim 6$ remains an open theoretical
question. One possibility is that gas collapsing rapidly in pristine atomic
cooling halos ($T_{\rm vir} >\sim 10^4 \rm{K}$) produces $10^4-10^6 M_\odot$
black holes. Previous studies have shown that the formation of such a black
hole requires a strong UV background to prevent molecular hydrogen cooling and
gas fragmentation. Recently it has been proposed that a high UV background may
not be required for halos that accrete material extremely rapidly or for halos
where gas cooling is delayed due to a high baryon-dark matter streaming
velocity. In this work, we point out that building up a halo with $T_{\rm vir}
>\sim 10^4 \rm{K}$ before molecular cooling becomes efficient is not sufficient
for forming a direct collapse black hole (DCBH). Though molecular hydrogen
formation may be delayed, it will eventually form at high densities leading to
efficient cooling and fragmentation. The only obvious way that molecular
cooling could be avoided in the absence of strong UV radiation, is for gas to
reach high enough density to cause collisional dissociation of molecular
hydrogen ($\sim 10^4 ~ {\rm cm}^{-3}$) before cooling occurs. However, we argue
that the minimum core entropy, set by the entropy of the intergalactic medium
(IGM) when it decouples from the CMB, prevents this from occurring for
realistic halo masses. This is confirmed by hydrodynamical cosmological
simulations without radiative cooling. We explain the maximum density versus
halo mass in these simulations with simple entropy arguments. The low densities
found suggest that DCBH formation indeed requires a strong UV background. |
Morphology of the Local Volume: To study the global morphology of the galaxy distribution in our local
neighbourhood we calculate the Minkowski functionals for a sequence of volume
limited samples within a sphere of 8 Mpc centred on our galaxy. The well known
strong clustering of the galaxies and the dominance of voids and coherent
structures on larger scales is clearly visible in the Minkowski functionals.
The morphology of the galaxy distribution changes with the limiting absolute
magnitude. The samples, encompassing the more luminous galaxies, show emptier
voids and more pronounced coherent structures. Indeed there is a prominent peak
in the luminosity function of isolated galaxies for MB approx. -14, which at
least partly explains these morphological changes. We compare with halo samples
from a LambdaCDM simulation. Special care was taken to reproduce the observed
local neighbourhood as well as the observed luminosity function in these mock
samples. All in all the mock samples render the global morphology of the galaxy
distribution quite well. However the detailed morphological analysis reveals
that real galaxies cluster stronger, the observed voids are emptier and the
structures are more pronounced compared to the mock samples from the LambdaCDM
simulation. | Helium abundance (and $H_0$) in X-COP galaxy clusters: We present the constraints on the helium abundance in 12 X-ray luminous
galaxy clusters that have been mapped in their X-ray and Sunyaev-Zeldovich (SZ)
signals out to $R_{200}$ for the XMM-Newton Cluster Outskirts Project (X-COP).
The unprecedented precision available for the estimate of $H_0$ allows us to
investigate how much the reconstructed X-ray and SZ signals are consistent with
the expected ratio $x$ between helium and proton densities of 0.08-0.1. We find
that a $H_0$ around 70 km/s/Mpc is preferred from our measurements, with lower
values of $H_0$ as requested from the Planck collaboration (67 km/s/Mpc)
requiring a 34% higher value of $x$. On the other hand, higher values of $H_0$,
as obtained by measurements in the local universe, impose $x$, from the
primordial nucleosynthesis calculations and current solar abundances, reduced
by 37--44\%. |
Synthetic Galaxy Clusters and Observations Based on Dark Energy Survey
Year 3 Data: We develop a novel data-driven method for generating synthetic optical
observations of galaxy clusters. In cluster weak lensing, the interplay between
analysis choices and systematic effects related to source galaxy selection,
shape measurement and photometric redshift estimation can be best characterized
in end-to-end tests going from mock observations to recovered cluster masses.
To create such test scenarios, we measure and model the photometric properties
of galaxy clusters and their sky environments from the Dark Energy Survey Year
3 (DES Y3) data in two bins of cluster richness $\lambda\in[30;\,45)$,
$\lambda\in[45;\,60)$ and three bins in cluster redshift ($z\in[0.3;\,0.35)$,
$z\in[0.45;\,0.5)$ and $z\in[0.6;\,0.65)$. Using deep-field imaging data we
extrapolate galaxy populations beyond the limiting magnitude of DES Y3 and
calculate the properties of cluster member galaxies via statistical background
subtraction. We construct mock galaxy clusters as random draws from a
distribution function, and render mock clusters and line-of-sight catalogs into
synthetic images in the same format as actual survey observations. Synthetic
galaxy clusters are generated from real observational data, and thus are
independent from the assumptions inherent to cosmological simulations. The
recipe can be straightforwardly modified to incorporate extra information, and
correct for survey incompleteness. New realizations of synthetic clusters can
be created at minimal cost, which will allow future analyses to generate the
large number of images needed to characterize systematic uncertainties in
cluster mass measurements. | Source Plane Reconstruction of The Bright Lensed Galaxy RCSGA
032727-132609: We present new HST/WFC3 imaging data of RCSGA 032727-132609, a bright lensed
galaxy at z=1.7 that is magnified and stretched by the lensing cluster RCS2
032727-132623. Using this new high-resolution imaging, we modify our previous
lens model (which was based on ground-based data) to fully understand the
lensing geometry, and use it to reconstruct the lensed galaxy in the source
plane. This giant arc represents a unique opportunity to peer into 100-pc scale
structures in a high-redshift galaxy. This new source reconstruction will be
crucial for a future analysis of the spatially-resolved rest-UV and
rest-optical spectra of the brightest parts of the arc. |
Optical Spectroscopic ATLAS of the MOJAVE/2cm AGN Sample (1): We present an optical spectroscopic atlas at intermediate resolution (8-15A)
for 123 core-dominated radio-loud active galactic nuclei with relativistic
jets, drawn from the MOJAVE/2cm sample at 15GHz. It is the first time that
spectroscopic and photometric parameters for a large sample of such type of AGN
are presented. The atlas includes spectral parameters for the emission lines
Hb, [O III] 5007, Mg II 2798 and/or C IV 1549 and corresponding data for the
continuum, as well as the luminosities and equivalent widths of the Fe II
UV/optical. It also contains the homogeneous photometric information in the
B-band for 242 sources of the sample, with a distribution peak at BJ=18.0 and a
magnitude interval of 11.1< BJ <23.7. | The real shape of non-Gaussianities: I review what bispectra and trispectra look like in real space, in terms of
the sign of particular shaped triangles and tetrahedrons. Having an equilateral
density bispectrum of positive sign corresponds to having concentrated
overdensities surrounded by larger weaker underdensities. In 3D these are
concentrated density filaments, as expected in large-scale structure. As the
shape changes from equilateral to flattened the concentrated overdensities
flatten into lines (3D planes). I then focus on squeezed bispectra, which can
be thought of as correlations of changes in small-scale power with large-scale
fields, and discuss the general non-perturbative form of the squeezed
bispectrum and its angular dependence. A general trispectrum has tetrahedral
form and I show examples of what this can look like in real space. Squeezed
trispectra are of particular interest and come in two forms, corresponding to
large-scale variance of small-scale power, and correlated modulations of an
equilateral-form bispectrum. Flattened trispectra can be produced by line-like
features in 2D, for example from cosmic strings, and randomly located features
also give a non-Gaussian signal. There are relationships between the squeezed
types of non-Gaussianity, and also a useful interpretation in terms of
statistical anisotropy. I discuss the various possible physical origins of
cosmological non-Gaussianities, both in terms of primordial perturbations and
late-time dynamical and geometric effects. |
Big Bang Nucleosynthesis with long-lived strongly interacting relic
particles: We study effects of relic long-lived strongly interacting massive particles
(X particles) on big bang nucleosynthesis (BBN). The X particle is assumed to
have existed during the BBN epoch, but decayed long before detected. The
interaction strength between an X and a nucleon is assumed to be similar to
that between nucleons. Rates of nuclear reactions and beta decay of X-nuclei
are calculated, and the BBN in the presence of neutral charged X^0 particles is
calculated taking account of captures of X^0 by nuclei. As a result, the X^0
particles form bound states with normal nuclei during a relatively early epoch
of BBN leading to the production of heavy elements. Constraints on the
abundance of X^0 are derived from observations of primordial light element
abundances. Particle models which predict long-lived colored particles with
lifetimes longer than about 200 s are rejected. This scenario prefers the
production of 9Be and 10B. There might, therefore, remain a signature of the X
particle on primordial abundances of those elements. Possible signatures left
on light element abundances expected in four different models are summarized. | Cosmic perturbations with running G and Lambda: Cosmologies with running cosmological term (Lambda) and gravitational
Newton's coupling (G) may naturally be expected if the evolution of the
universe can ultimately be derived from the first principles of Quantum Field
Theory or String Theory. In this paper, we derive the general cosmological
perturbation equations for models with variable G and Lambda in which the
fluctuations in both variables are explicitly included. We demonstrate that, if
matter is covariantly conserved, the late growth of matter density
perturbations is independent of the wavenumber. Furthermore, if Lambda is
negligible at high redshifts and G varies slowly, we find that these
cosmologies produce a matter power spectrum with the same shape as that of the
concordance LCDM model, thus predicting the same basic features on structure
formation. Despite this shape indistinguishability, the free parameters of the
variable G and Lambda models can still be effectively constrained from the
observational bounds on the spectrum amplitude. |
Concentrating the Dark Matter in Galaxy Clusters through Tidal Stripping
of Baryonically-Compressed Galactic Halos: Gravitational lensing observations of massive X-ray clusters imply a steep
characteristic density profile marked by a central concentration of dark
matter. The observed mass fraction within a projected radius of 150 kpc is
twice that found in state-of-the-art dark matter simulations of the standard
Lambda-CDM cosmology. A central baryon enhancement that could explain this
discrepancy is not observed, leaving a major puzzle. We propose a solution
based on the merger histories of clusters. A significant fraction of the final
dark matter content of a cluster halo originates within galaxy-sized halos, in
which gas can cool and compress the dark matter core to high densities. The
subsequent tidal stripping of this compressed dark matter occurs in denser
regions that are closer to the center of the cluster halo. Eventually, the
originally cooled gas must be dispersed into the intracluster medium through
feedback, for consistency with observations that do not find central baryon
enhancements in clusters. Still, the early adiabatic compression of the
galactic dark matter leaves a net effect on the cluster. Using a simple model
for this process, we show that the central cluster profile is substantially
modified, potentially explaining the observed discrepancy. | Accretion-Driven Evolution of Black Holes: Eddington Ratios, Duty
Cycles, and Active Galaxy Fractions: We develop semi-empirical models of the supermassive black hole and active
galactic nucleus (AGN) populations, which incorporate the black hole growth
implied by the observed AGN luminosity function assuming a radiative efficiency
\epsilon, and a distribution of Eddington ratios \lambda. By generalizing these
continuity-equation models to allow a distribution P(\lambda|mbh,z) we are able
to draw on constraints from observationally estimated P(\lambda) distributions
and active galaxy fractions while accounting for the luminosity thresholds of
observational samples. We consider models with a Gaussian distribution of log
\lambda, and Gaussians augmented with a power-law tail to low \lambda. Within
our framework, reproducing the high observed AGN fractions at low redshift
requires a characteristic Eddington ratio \lambda_c that declines at late
times, and matching observed Eddington ratio distributions requires P(\lambda)
that broadens at low redshift. To reproduce the observed increase of AGN
fraction with black hole or galaxy mass, we also require a \lambda_c that
decreases with increasing black hole mass, reducing the AGN luminosity
associated with the most massive black holes. Finally, achieving a good match
to the high mass end of the local black hole mass function requires an
increased radiative efficiency at high black hole mass. We discuss the
potential impact of black hole mergers or a \lambda-dependent bolometric
correction, and we compute evolutionary predictions for black hole and galaxy
specific accretion rates. Despite the flexibility of our framework, no one
model provides a good fit to all the data we consider. |
Primordial-black-hole mergers in dark-matter spikes: It has been suggested that primordial black holes (PBHs) of roughly 30 solar
masses could make up the dark matter and if so, might account for the recent
detections by LIGO involving binary black holes in this mass range. It has also
been argued that the super-massive black holes (SMBHs) that reside at galactic
centers may be surrounded by extremely-dense dark-matter (DM) spikes. Here we
show that the rate for PBH mergers in these spikes may well exceed the merger
rate considered before in galactic dark-matter halos, depending on the
magnitudes of two competing effects on the DM spikes: depletion of PBHs due to
relaxation and replenishment due to PBHs in loss cone. This may provide a
plausible explanation for the current rate of detection of mergers of
30-solar-mass black holes, even if PBHs make up a subdominant contribution to
the dark matter. The gravitational-wave signals from such events will always
originate in galactic centers, as opposed to those from halos, which are
expected to have little correlation with luminous-galaxy positions. | Galaxy Clusters Selected with the Sunyaev-Zel'dovich Effect from 2008
South Pole Telescope Observations: We present a detection-significance-limited catalog of 21 Sunyaev-Zel'dovich
selected galaxy clusters. These clusters, along with 1 unconfirmed candidate,
were identified in 178 deg^2 of sky surveyed in 2008 by the South Pole
Telescope to a depth of 18 uK-arcmin at 150 GHz. Optical imaging from the
Blanco Cosmology Survey (BCS) and Magellan telescopes provided photometric (and
in some cases spectroscopic) redshift estimates, with catalog redshifts ranging
from z=0.15 to z>1, with a median z = 0.74. Of the 21 confirmed galaxy
clusters, three were previously identified as Abell clusters, three were
presented as SPT discoveries in Staniszewski et al, 2009, and three were first
identified in a recent analysis of BCS data by Menanteau et al, 2010; the
remaining 12 clusters are presented for the first time in this work. Simulated
observations of the SPT fields predict the sample to be nearly 100% complete
above a mass threshold of M_200 ~ 5x10^14 M_sun/h at z = 0.6. This completeness
threshold pushes to lower mass with increasing redshift, dropping to ~4x10^14
M_sun/h at z=1. The size and redshift distribution of this catalog are in good
agreement with expectations based on our current understanding of galaxy
clusters and cosmology. In combination with other cosmological probes, we use
the cluster catalog to improve estimates of cosmological parameters. Assuming a
standard spatially flat wCDM cosmological model, the addition of our catalog to
the WMAP 7-year analysis yields sigma_8 = 0.81 +- 0.09 and w = -1.07 +- 0.29, a
~50% improvement in precision on both parameters over WMAP7 alone. |
Dark Halo or Bigravity?: Observations show that about the 20% of the Universe is composed by invisible
(dark) matter (DM), for which many candidates have been proposed. In
particular, the anomalous behavior of rotational curves of galaxies (i.e. the
flattening at large distance instead of the Keplerian fall) requires that this
matter is distributed in an extended halo around the galaxy. In order to
reproduce this matter density profiles in Newtonian gravity and in cold dark
matter (CDM) paradigm (in which the DM particles are collisionless), many
ad-hoc approximations are required. The flattening of rotational curves can be
explained by a suitable modification of gravitational force in bigravity
theories, together with mirror matter model that predicts the existence of a
dark sector in which DM has the same physical properties of visible matter. As
an additional result, the Newton constant is different at distances much less
and much greater than 20 kpc. | The effects of self-interacting dark matter on the stripping of galaxies
that fall into clusters: We use the Cluster-EAGLE (C-EAGLE) hydrodynamical simulations to investigate
the effects of self-interacting dark matter (SIDM) on galaxies as they fall
into clusters. We find that SIDM galaxies follow similar orbits to their Cold
Dark Matter (CDM) counterparts, but end up with ${\sim}$25 per cent less mass
by the present day. One in three SIDM galaxies are entirely disrupted, compared
to one in five CDM galaxies. However, the excess stripping will be harder to
observe than suggested by previous DM-only simulations because the most
stripped galaxies form cores and also lose stars: the most discriminating
objects become unobservable. The best test will be to measure the
stellar-to-halo mass relation (SHMR) for galaxies with stellar mass
$10^{10-11}\,\mathrm{M}_{\odot}$. This is 8 times higher in a cluster than in
the field for a CDM universe, but 13 times higher for an SIDM universe. Given
intrinsic scatter in the SHMR, these models could be distinguished with
noise-free galaxy-galaxy strong lensing of ${\sim}32$ cluster galaxies. |
Angular Power Spectra with Finite Counts: Angular anisotropy techniques for cosmic diffuse radiation maps are powerful
probes, even for quite small data sets. A popular observable is the angular
power spectrum; we present a detailed study applicable to any unbinned source
skymap S(n) from which N random, independent events are observed. Its exact
variance, which is due to the finite statistics, depends only on S(n) and N; we
also derive an unbiased estimator of the variance from the data. First-order
effects agree with previous analytic estimates. Importantly, heretofore
unidentified higher-order effects are found to contribute to the variance and
may cause the uncertainty to be significantly larger than previous analytic
estimates---potentially orders of magnitude larger. Neglect of these
higher-order terms, when significant, may result in a spurious detection of the
power spectrum. On the other hand, this would indicate the presence of
higher-order spatial correlations, such as a large bispectrum, providing new
clues about the sources. Numerical simulations are shown to support these
conclusions. Applying the formalism to an ensemble of Gaussian-distributed
skymaps, the noise-dominated part of the power spectrum uncertainty is
significantly increased at high multipoles by the new, higher-order effects.
This work is important for harmonic analyses of the distributions of diffuse
high-energy gamma-rays, neutrinos, and charged cosmic rays, as well as for
populations of sparse point sources such as active galactic nuclei. | Gravitational Wave Signatures from Warm Dark Energy: Motivated by some of the recent swampland conjectures, we study a model of
dark energy, in which a quintessence axion slowly rolls in a steep potential
due to its interactions with a U(1) or an SU(2) gauge field. The gauge fields
produced by this interaction can generate a stochastic gravitational wave
background with frequencies in the range $f \sim \left(10^{-16} -
10^{-14}\right)\; {\rm Hz}$. Gravitational waves in this range can in principle
be probed by CMB spectral distortions. We show that the amplitude of the signal
produced in this model is above the level for detectability only under very
favourable choices of parameters. |
Galaxy Zoo: A Catalog of Overlapping Galaxy Pairs for Dust Studies: Analysis of galaxies with overlapping images offers a direct way to probe the
distribution of dust extinction and its effects on the background light. We
present a catalog of 1990 such galaxy pairs selected from the Sloan Digital Sky
Survey (SDSS) by volunteers of the Galaxy Zoo project. We highlight subsamples
which are particularly useful for retrieving such properties of the dust
distribution as UV extinction, the extent perpendicular to the disk plane, and
extinction in the inner parts of disks. The sample spans wide ranges of
morphology and surface brightness, opening up the possibility of using this
technique to address systematic changes in dust extinction or distribution with
galaxy type. This sample will form the basis for forthcoming work on the ranges
of dust distributions in local disk galaxies, both for their astrophysical
implications and as the low-redshift part of a study of the evolution of dust
properties. Separate lists and figures show deep overlaps, where the inner
regions of the foreground galaxy are backlit, and the relatively small number
of previously-known overlapping pairs outside the SDSS DR7 sky coverage. | Stellar Structure and Tests of Modified Gravity: Theories that attempt to explain cosmic acceleration by modifying gravity
typically introduces a long-range scalar force that needs to be screened on
small scales. One common screening mechanism is the chameleon, where the scalar
force is screened in environments with a sufficiently deep gravitational
potential, but acts unimpeded in regions with a shallow gravitational
potential. This leads to a variation in the overall gravitational G with
environment. We show such a variation can occur within a star itself,
significantly affecting its evolution and structure, provided that the host
galaxy is unscreened. The effect is most pronounced for red giants, which would
be smaller by a factor of tens of percent and thus hotter by 100's of K,
depending on the parameters of the underlying scalar-tensor theory. Careful
measurements of these stars in suitable environments (nearby dwarf galaxies not
associated with groups or clusters) would provide constraints on the chameleon
mechanism that are four orders of magnitude better than current large scale
structure limits, and two orders of magnitude better than present solar system
tests. |
Internal dark matter structure of the most massive galaxy clusters since
redshift 1: We investigate the evolution of the dark matter density profiles of the most
massive galaxy clusters in the Universe. Using a `zoom-in' procedure on a large
suite of cosmological simulations of total comoving volume of $3\,(h^{-1}\,\rm
Gpc)^3$, we study the 25 most massive clusters in four redshift slices from
$z\sim 1$ to the present. The minimum mass is $M_{500} > 5.5 \times 10^{14}$
M$_{\odot}$ at $z=1$. Each system has more than two million particles within
$r_{500}$. Once scaled to the critical density at each redshift, the dark
matter profiles within $r_{500}$ are strikingly similar from $z\sim1$ to the
present day, exhibiting a low dispersion of 0.15 dex, and showing little
evolution with redshift in the radial logarithmic slope and scatter. They have
the running power law shape typical of the NFW-type profiles, and their inner
structure, resolved to $3.8\,h^{-1}$ comoving kpc at $z=1$, shows no signs of
converging to an asymptotic slope. Our results suggest that this type of
profile is already in place at $z>1$ in the highest-mass haloes in the
Universe, and that it remains exceptionally robust to merging activity. | Silicon detector results from the first five-tower run of CDMS II: We report results of a search for Weakly Interacting Massive Particles
(WIMPs) with the Si detectors of the CDMS II experiment. This report describes
a blind analysis of the first data taken with CDMS II's full complement of
detectors in 2006-2007; results from this exposure using the Ge detectors have
already been presented. We observed no candidate WIMP-scattering events in an
exposure of 55.9 kg-days before analysis cuts, with an expected background of
~1.1 events. The exposure of this analysis is equivalent to 10.3 kg-days over a
recoil energy range of 7-100 keV for an ideal Si detector and a WIMP mass of 10
GeV/c2. These data set an upper limit of 1.7x10-41 cm2 on the WIMP-nucleon
spin-independent cross section of a 10 GeV/c2 WIMP. These data exclude
parameter space for spin-independent WIMP-nucleon elastic scattering that is
relevant to recent searches for low-mass WIMPs. |
A uniform metallicity in the outskirts of massive, nearby galaxy
clusters: Suzaku measurements of a homogeneous metal distribution of $Z\sim0.3$ Solar
in the outskirts of the nearby Perseus cluster suggest that chemical elements
were deposited and mixed into the intergalactic medium before clusters formed,
likely over 10 billion years ago. A key prediction of this early enrichment
scenario is that the intracluster medium in all massive clusters should be
uniformly enriched to a similar level. Here, we confirm this prediction by
determining the iron abundances in the outskirts ($r>0.25r_{200}$) of a sample
of ten other nearby galaxy clusters observed with Suzaku for which robust
measurements based on the Fe-K lines can be made. Across our sample the iron
abundances are consistent with a constant value, $Z_{\rm Fe}=0.316\pm0.012$
Solar ($\chi^2=28.85$ for 25 degrees of freedom). This is remarkably similar to
the measurements for the Perseus cluster of $Z_{\rm Fe}=0.314\pm0.012$ Solar,
using the Solar abundance scale of Asplund et al. (2009). | Nuisance hardened data compression for fast likelihood-free inference: In this paper we show how nuisance parameter marginalized posteriors can be
inferred directly from simulations in a likelihood-free setting, without having
to jointly infer the higher-dimensional interesting and nuisance parameter
posterior first and marginalize a posteriori. The result is that for an
inference task with a given number of interesting parameters, the number of
simulations required to perform likelihood-free inference can be kept (roughly)
the same irrespective of the number of additional nuisances to be marginalized
over. To achieve this we introduce two extensions to the standard
likelihood-free inference set-up. Firstly we show how nuisance parameters can
be re-cast as latent variables and hence automatically marginalized over in the
likelihood-free framework. Secondly, we derive an asymptotically optimal
compression from $N$ data down to $n$ summaries -- one per interesting
parameter -- such that the Fisher information is (asymptotically) preserved,
but the summaries are insensitive (to leading order) to the nuisance
parameters. This means that the nuisance marginalized inference task involves
learning $n$ interesting parameters from $n$ "nuisance hardened" data
summaries, regardless of the presence or number of additional nuisance
parameters to be marginalized over. We validate our approach on two examples
from cosmology: supernovae and weak lensing data analyses with nuisance
parameterized systematics. For the supernova problem, high-fidelity posterior
inference of $\Omega_m$ and $w_0$ (marginalized over systematics) can be
obtained from just a few hundred data simulations. For the weak lensing
problem, six cosmological parameters can be inferred from $\mathcal{O}(10^3)$
simulations, irrespective of whether ten additional nuisance parameters are
included in the problem or not. |
Halo based reconstruction of the cosmic mass density field: We present the implementation of a halo based method for the reconstruction
of the cosmic mass density field. The method employs the mass density
distribution of dark matter haloes and its environments computed from
cosmological N-body simulations and convolves it with a halo catalog to
reconstruct the dark matter density field determined by the distribution of
haloes. We applied the method to the group catalog of Yang etal (2007) built
from the SDSS Data Release 4. As result we obtain reconstructions of the cosmic
mass density field that are independent on any explicit assumption of bias. We
describe in detail the implementation of the method, present a detailed
characterization of the reconstructed density field (mean mass density
distribution, correlation function and counts in cells) and the results of the
classification of large scale environments (filaments, voids, peaks and sheets)
in our reconstruction. Applications of the method include morphological studies
of the galaxy population on large scales and the realization of constrained
simulations. | Accretion disks around kicked black holes: Post-kick Dynamics: Numerical calculations of merging black hole binaries indicate that
asymmetric emission of gravitational radiation can kick the merged black hole
at up to thousands of km/s, and a number of systems have been observed recently
whose properties are consistent with an active galactic nucleus containing a
supermassive black hole moving with substantial velocity with respect to its
broader accretion disk. We study here the effect of an impulsive kick delivered
to a black hole on the dynamical evolution of its accretion disk using a
smoothed particle hydrodynamics code, focusing attention on the role played by
the kick angle with respect to the orbital angular momentum vector of the
pre-kicked disk. We find that for more vertical kicks, for which the angle
between the kick and the normal vector to the disk $\theta\lesssim 30^\circ$, a
gap remains present in the inner disk, in accordance with the prediction from
an analytic collisionless Keplerian disk model, while for more oblique kicks
with $\theta\gtrsim 45^\circ$, matter rapidly accretes toward the black hole.
There is a systematic trend for higher potential luminosities for more oblique
kick angles for a given black hole mass, disk mass and kick velocity, and we
find large amplitude oscillations in time in the case of a kick oriented
$60^\circ$ from the vertical. |
LOFAR and APERTIF surveys of the radio sky: probing shocks and magnetic
fields in galaxy clusters: At very low frequencies, the new pan-European radio telescope LOFAR is
opening the last unexplored window of the electromagnetic spectrum for
astrophysical studies. The revolutionary APERTIF phased arrays that are about
to be installed on the Westerbork radio telescope (WSRT) will dramatically
increase the survey speed for the WSRT. Combined surveys with these two
facilities will deeply chart the northern sky over almost two decades in radio
frequency from \sim 15 up to 1400 MHz. Here we briefly describe some of the
capabilities of these new facilities and what radio surveys are planned to
study fundamental issues related the formation and evolution of galaxies and
clusters of galaxies. In the second part we briefly review some recent
observational results directly showing that diffuse radio emission in clusters
traces shocks due to cluster mergers. As these diffuse radio sources are
relatively bright at low frequencies, LOFAR should be able to detect thousands
of such sources up to the epoch of cluster formation. This will allow
addressing many question about the origin and evolution of shocks and magnetic
fields in clusters. At the end we briefly review some of the first and very
preliminary LOFAR results on clusters. | Uncovering the deeply embedded AGN activity in the nuclear regions of
the interacting galaxy Arp299: We present mid-infrared (MIR) 8-13micron spectroscopy of the nuclear regions
of the interacting galaxy Arp299 (IC694+NGC3690) obtained with CanariCam (CC)
on the 10.4m Gran Telescopio Canarias (GTC). The high angular resolution
(~0.3-0.6arcsec) of the data allows us to probe nuclear physical scales between
60 and 120pc, which is a factor of 10 improvement over previous MIR
spectroscopic observations of this system. The GTC/CC spectroscopy displays
evidence of deeply embedded Active Galactic Nucleus (AGN) activity in both
nuclei. The GTC/CC nuclear spectrum of NGC3690/Arp299-B1 can be explained as
emission from AGN-heated dust in a clumpy torus with both a high covering
factor and high extinction along the line of sight. The estimated bolometric
luminosity of the AGN in NGC3690 is 3.2(+/-0.6)x10^44 erg/s. The nuclear GTC/CC
spectrum of IC694/Arp299-A shows 11.3micron polycyclic aromatic hydrocarbon
(PAH) emission stemming from a deeply embedded (A_V~24mag) region of less than
120pc in size. There is also a continuum-emitting dust component. If associated
with th putative AGN in IC694, we estimate that it would be approximately 5
times less luminous than the AGN in NGC3690. The presence of dual AGN activity
makes Arp299 a good example to study such phenomenon in the early coalescence
phase of interacting galaxies. |
Simulating Structure Formation of the Local Universe: In this work we present cosmological N-body simulations of the Local Universe
with initial conditions constrained by the Two-Micron Redshift Survey (2MRS)
within a cubic volume of 180 Mpc/h side-length centred at the Local Group. We
use a self-consistent Bayesian based approach to explore the joint parameter
space of primordial density fluctuations and peculiar velocity fields, which
are compatible with the 2MRS galaxy distribution after cosmic evolution. This
method (the KIGEN-code) includes the novel ALPT (Augmented Lagrangian
Perturbation Theory) structure formation model which combines second order LPT
(2LPT) on large scales with the spherical collapse model on small scales.
Furthermore we describe coherent flows with 2LPT and include a dispersion term
to model fingers-of-god (fogs). These implementations are crucial to avoid
artificial filamentary structures, which appear when using a structure
formation model with 2LPT and data with compressed fogs. We assume LCDM
cosmology throughout our method. The recovered initial Gaussian fields are used
to perform a set of 25 constrained simulations. Statistically this ensemble of
simulations is in agreement with a reference set of 25 simulations based on
randomly seeded Gaussian fluctuations in terms of matter statistics,
power-spectra and mass functions. Considering the entire volume, we obtain
correlation coefficients of about 98.3% for the comparison between the
simulated density fields and the galaxy density field in log-space with
Gaussian smoothing scales of r_S=3.5 Mpc/h (74% for r_S=1.4 Mpc/h). The cross
power-spectra show correlations with the galaxy distribution which weaken
towards smaller length scales until they vanish at scales of 2.2-3.0 Mpc/h. The
simulations we present provide a fully nonlinear density and velocity field
with a high level of correlation with the observed galaxy distribution at
scales of a few Mpc. | Thermalization, Fragmentation and Tidal Disruption: The Complex Galactic
Dynamics of Dark Matter Superfluidity: The idea of self-interacting bosonic dark matter capable of exhibiting
superfluidity is revisited. We show that the most interesting parameter space
of the theory corresponds to fully thermalized dark matter halos. As a result
the entire halo undergoes Bose-Einstein condensation due to high degeneracy.
Since it is observationally preferable for the dark matter density profile to
be similar to cold dark matter in the outskirts of the halo, we argue that the
Jeans wavelength must be at least few times shorter than the virial radius.
This entails that, upon condensation, a dark matter halo fragments into
superfluid clumps. However, we demonstrate that these would-be solitons
experience strong tidal disruption and behave as virialized weakly interacting
streams. An exception is the central soliton, which can be as large as few tens
of kiloparsecs in size without contradicting observational bounds. As a result,
in dwarf galaxies, the observed rotation curves can be completely contained
within the superfluid soliton. In this case, the dark matter distribution is
expected to be strongly sensitive to the baryonic density profile. We argue
that the diversity of rotation curves observed for dwarf galaxies is a natural
consequence of the superfluid dark matter scenario. |
Non-Gaussianities in multi-field DBI inflation with a waterfall phase
transition: We study multi-field DBI inflation models with a waterfall phase transition.
This transition happens for a D3 brane moving in the warped conifold if there
is an instability along angular directions. The transition converts the angular
perturbations into the curvature perturbation. Thanks to this conversion,
multi-field models can evade the stringent constraints that strongly disfavour
single field ultra-violet DBI inflation models in string theory. We explicitly
demonstrate that our model satisfies current observational constraints on the
spectral index and equilateral non-Gaussianity as well as the bound on the
tensor to scalar ratio imposed in string theory models. In addition we show
that large local type non-Gaussianity is generated together with equilateral
non-Gaussianity in this model. | DESI and other dark energy experiments in the era of neutrino mass
measurements: We present Fisher matrix projections for future cosmological parameter
measurements, including neutrino masses, dark energy, curvature, modified
gravity, the inflationary perturbation spectrum, non-Gaussianity, and dark
radiation. We focus on DESI and generally redshift surveys (BOSS, HETDEX,
eBOSS, Euclid, and WFIRST), but also include CMB (Planck) and weak
gravitational lensing (DES and LSST) constraints. The goal is to present a
consistent set of projections, for concrete experiments, which are otherwise
scattered throughout many papers and proposals. We include neutrino mass as a
free parameter in most projections, as it will inevitably be relevant -- DESI
and other experiments can measure the sum of neutrino masses to ~0.02 eV or
better, while the minimum possible sum is ~0.06 eV. We note that the BAO-only
use of galaxy clustering is substantially degraded as a dark energy probe in
the presence of neutrino mass uncertainty -- using broadband galaxy power is
critical, especially pushing it to as small a scale as possible, and big gains
are achieved by combining lensing survey constraints with redshift survey
constraints. We do not try to be especially innovative, e.g., in careful
treatments of potential systematic errors -- these projections are intended as
a straightforward baseline for comparison to more detailed analyses. |
Astrophysically Motivated Bulge-Disk Decompositions of SDSS Galaxies: We present a set of bulge-disk decompositions for a sample of 71,825 SDSS
main-sample galaxies in the redshift range 0.003<z<0.05. We have fit each
galaxy with either a de Vaucouleurs ('classical') or an exponential ('pseudo-')
bulge and an exponential disk. Two dimensional Sersic fits are performed when
the 2-component fits are not statistically significant or when the fits are
poor, even in the presence of high signal-to-noise. We study the robustness of
our 2-component fits by studying a bright subsample of galaxies and we study
the systematics of these fits with decreasing resolution and S/N. Only 30% of
our sample have been fit with two-component fits in which both components are
non-zero. The g-r and g-i colours of each component for the two-component
models are determined using linear templates derived from the r-band model. We
attempt a physical classification of types of fits into disk galaxies,
pseudo-bulges, classical bulges, and ellipticals. Our classification of
galaxies agrees well with previous large B+D decomposed samples. Using our
galaxy classifications, we find that Petrosian concentration is a good
indicator of B/T, while overall Sersic index is not. Additionally, we find that
the majority of green valley galaxies are bulge+disk galaxies. Furthermore, in
the transition from green to red B+D galaxies, the total galaxy colour is most
strongly correlated with the disk colour. | On the interpretation of the apparent existence of a preferred magnetic
polarity in extragalactic jet sources: Contopoulos et al. recently argued that there is observational evidence for a
preferred sense of the Faraday rotation-measure gradients across jets from
active galactic nuclei (AGNs). Such behaviour could arise if there were a
deterministic relationship between the polarity of the poloidal magnetic field
that threads the outflow and the sense of rotation of the outflow's source.
Based on this interpretation, Countopoulos et al. suggested that their finding
supports a model for the origin of cosmic magnetic fields in a
Poynting-Robertson process operating in AGN accretion discs. Here I point out
that an alternative explanation of such a relationship could be that the Hall
current plays a key role in the magnetohydrodynamics of the underlying disc. In
this picture, the measured Faraday rotation is dominated by the contribution of
a centrifugally driven wind that is launched from the weakly ionized outer
region of the disc. Additional observations are, however, needed to verify the
claimed behaviour. |
A Relic Star Cluster in the Sextans Dwarf Spheroidal Galaxy -
Implications for Early Star and Galaxy Formation: We present tentative evidence for the existence of a dissolved star cluster
in the Sextans dwarf spheroidal galaxy. In a sample of six stars, we identify
three (possibly four) stars around [Fe/H] =-2.7 that are highly clustered in a
multi-dimensional chemical abundance space. The estimated initial stellar mass
of the cluster is M*,init = 1.9^+1.5_-0.9 (1.6^+1.2_-0.8)*10^5 Msol assuming a
Salpeter (Kroupa) initial mass function (IMF). If corroborated by follow-up
spectroscopy, this ancient star cluster at [Fe/H] =-2.7 is the most metal-poor
system identified to date. Inspired by this finding, we also present a new way
to interpret the cumulative metallicity functions of dwarf galaxies. From
available observational data, we speculate that the ultra-faint dwarf galaxy
population, or a significant fraction thereof, and the more luminous, classical
dwarf spheroidal population were formed in different environments and would
thus be distinct in origin. | The Effect of Fluctuations on the Helium-Ionizing Background: Interpretation of He II Ly{\alpha} absorption spectra after the epoch of He
II reionization requires knowledge of the He II ionizing background. While past
work has modelled the evolution of the average background, the standard
cosmological radiative transfer technique assumes a uniform radiation field
despite the discrete nature of the (rare) bright quasars that dominate the
background. We implement a cosmological radiative transfer model that includes
the most recent constraints on the ionizing spectra and luminosity function of
quasars and the distribution of IGM absorbers. We also estimate, for the first
time, the effects of fluctuations on the evolving continuum opacity in two
ways: by incorporating the complete distribution of ionizing background
amplitudes into the standard approach, and by explicitly treating the quasars
as discrete -- but isolated -- sources. Our model results in a He II ionization
rate that evolves steeply with redshift, increasing by a factor ~2 from z=3.0
to z=2.5. This causes rapid evolution in the mean He II Ly{\alpha} optical
depth -- as recently observed -- without appealing to the reionization of He
II. The observed behaviour could instead result from rapid evolution in the
mean free path of ionizing photons as the helium in higher H I column density
absorbers becomes fully ionized. |
Loop corrections to primordial non-Gaussianity: We discuss quantum gravitational loop effects to observable quantities such
as curvature power spectrum and primordial non-Gaussianity of cosmic microwave
background (CMB) radiation. We first review the previously shown case where one
gets a time dependence for zeta-zeta correlator due to loop corrections. Then
we investigate the effect of loop corrections to primordial non-Gaussianity of
CMB. We conclude that, even with a single scalar inflaton, one might get a huge
value for non-Gaussianity which would exceed the observed value by at least 30
orders of magnitude. Finally we discuss the consequences of this result for
scalar driven inflationary models. | On the range of validity of perturbative models for galaxy clustering
and its uncertainty: We explore the reach of analytical models at one-loop in Perturbation Theory
(PT) to accurately describe measurements of the galaxy power spectrum from
numerical simulations in redshift space. We consider the validity range in
terms of three different diagnostics: 1) the goodness of fit; 2) a
figure-of-bias quantifying the error in recovering the fiducial value of a
cosmological parameter; 3) an internal consistency check of the theoretical
model quantifying the running of the model parameters with the scale cut. We
consider different sets of measurements corresponding to an increasing
cumulative simulation volume in redshift space. For each volume we define a
median value and the associated scatter for the largest wavenumber where the
model is valid (the $k$-reach of the model). We find, as a rather general
result, that the median value of the reach decreases with the simulation
volume, as expected since the smaller statistical errors provide a more
stringent test for the model. This is true for all the three definitions
considered, with the one given in terms of the figure-of-bias providing the
most stringent scale cut. More interestingly, we find as well that the error
associated with the $k$-reach value is quite large, with a significant
probability of being as low as 0.1$\, h \, {\rm Mpc}^{-1}$ (or, more generally,
up to 40% smaller than the median) for all the simulation volumes considered.
We explore as well the additional information on the growth rate parameter
encoded in the power spectrum hexadecapole, compared to the analysis of
monopole and quadrupole, as a function of simulation volume. While our analysis
is, in many ways, rather simplified, we find that the gain in the determination
of the growth rate is quite small in absolute value and well within the
statistical error on the corresponding figure of merit. |
Exotic energy injection in the early universe II: CMB spectral
distortions and constraints on light dark matter: We calculate the post-recombination contribution to the Cosmic Microwave
Background (CMB) spectral distortion due to general exotic energy injections,
including dark matter (DM) decaying or annihilating to Standard Model
particles. Upon subtracting the background distortion that would be present
even without such energy injections, we find residual distortions that are
still potentially large enough to be detectable by future experiments such as
PIXIE. The distortions also have a high-energy spectral feature that is a
unique signature of the injection of high-energy particles. We present a
calculation of the global ionization history in the presence of decaying dark
matter with sub-keV masses, and also show that previous calculations of the
global ionization history in the presence of energy injection are not
significantly modified by these additional spectral distortions. Our improved
treatment of low-energy electrons allows us to extend calculations of the CMB
anisotropy constraints for decaying DM down to arbitrarily low masses. We also
recast these bounds as constraints on the coupling of axion-like particles to
photons. | AzTEC/ASTE 1.1 mm survey of SSA22: Counterpart identification and
photometric redshift survey of submillimeter galaxies: We present the results from a 1.1 mm imaging survey of the SSA22 field, known
for having an overdensity of z=3.1 Lyman-alpha emitting galaxies (LAEs), taken
with the AzTEC camera on the Atacama Submillimeter Telescope Experiment (ASTE).
We imaged a 950 arcmin$^2$ field down to a 1 sigma sensitivity of 0.7-1.3
mJy/beam to find 125 submillimeter galaxies (SMGs) with a signal to noise ratio
>= 3.5. Counterpart identification using radio and near/mid-infrared data was
performed and one or more counterpart candidates were found for 59 SMGs.
Photometric redshifts based on optical to near-infrared images were evaluated
for 45 SMGs of these SMGs with Spitzer/IRAC data, and the median value is found
to be z=2.4. By combining these estimation with estimates from the literature
we determined that 10 SMGs might lie within the large-scale structure at z=3.1.
The two-point angular cross-correlation function between LAEs and SMGs
indicates that the positions of the SMGs are correlated with the z=3.1
protocluster. These results suggest that the SMGs were formed and evolved
selectively in the high dense environment of the high redshift universe. This
picture is consistent with the predictions of the standard model of
hierarchical structure formation. |
The strong environmental dependence of black hole scaling relations: We investigate how the scaling relations between central black hole mass
(Mbh) and host galaxy properties (velocity dispersion, bulge stellar mass and
bulge luminosity) depend on the large scale environment. For each of a sample
of 69 galaxies with dynamical black hole measurements we compile four
environmental measures (nearest neighbor distance, fixed aperture number
density, total halo mass, and central/satellite). We find that central and
satellite galaxies follow distinctly separate scalings in each of the three
relations we have examined. The Mbh - sigma relation of central galaxies is
significantly steeper (6.38 +/- 0.49) than that of satellite galaxies (4.91 +/-
0.49), but has a similar intercept. This behavior remains even after
restricting to a sample of only early type galaxies or after removing the 8
brightest cluster galaxies. The Mbh - sigma relation shows more modest
differences when splitting the sample based on the other environmental
indicators, suggesting that they are driven by the underlying satellite/central
fractions. Separate relations for centrals and satellites are also seen in the
power law scaling between black hole mass and bulge stellar mass or bulge
luminosity. We suggest that gas rich, low mass galaxies undergo a period of
rapid black hole growth in the process of becoming satellites. If central
galaxies on the current Mbh - sigma relation are representative progenitors of
the satellite population, the observations imply that a sigma = 120 km/s galaxy
must nearly triple its central black hole mass. The elevated black hole masses
of massive central galaxies are then a natural consequence of the accretion of
satellites. | The Covariance of Squeezed Bispectrum Configurations: We measure the halo bispectrum covariance in a large set of N-body
simulations and compare it with theoretical expectations. We find a large
correlation among (even mildly) squeezed halo bispectrum configurations. A
similarly large correlation can be found between squeezed triangles and the
long-wavelength halo power spectrum. This shows that the diagonal Gaussian
contribution fails to describe, even approximately, the full covariance in
these cases. We compare our numerical estimate with a model that includes, in
addition to the Gaussian one, only the non-Gaussian terms that are large for
squeezed configurations. We find that accounting for these large terms in the
modeling greatly improves the agreement of the full covariance with
simulations. We apply these results to a simple Fisher matrix forecast, and
find that constraints on primordial non-Gaussianity are degraded by a factor of
$\sim 2$ when a non-Gaussian covariance is assumed instead of the diagonal,
Gaussian approximation. |
Neutrino physics from Cosmology: In recent years precision cosmology has become an increasingly powerful probe
of particle physics. Perhaps the prime example of this is the very stringent
cosmological upper bound on the neutrino mass. However, other aspects of
neutrino physics, such as their decoupling history and possible non-standard
interactions, can also be probed using observations of cosmic structure. Here,
I review the current status of cosmological bounds on neutrino properties and
discuss the potential of future observations, for example by the recently
approved EUCLID mission, to precisely measure neutrino properties. | Planck intermediate results. VII. Statistical properties of infrared and
radio extragalactic sources from the Planck Early Release Compact Source
Catalogue at frequencies between 100 and 857 GHz: (abridged for arXiv) We make use of the Planck all-sky survey to derive
number counts and spectral indices of extragalactic sources -- infrared and
radio sources -- from the Planck Early Catalogue (ERCSC) at 100 to 857GHz. Our
sample contains, after the 80% completeness cut, between 122 and 452 and
sources, with flux densities above 0.3 and 1.9Jy at 100 and 857GHz, over about
31 to 40% of the sky. Using Planck HFI, all the sources have been classified as
either dust-dominated or synchrotron-dominated on the basis of their spectral
energy distributions (SED). Our sample is thus complete, flux-limited and
color-selected to differentiate between the two populations. We find an
approximately equal number of synchrotron and dusty sources between 217 and
353GHz; at 353GHz or higher (or 217GHz and lower) frequencies, the number is
dominated by dusty (synchrotron) sources, as expected. For most of the sources,
the spectral indices are also derived. We provide for the first time counts of
bright sources from 353 to 857GHz and the contributions from dusty and
synchrotron sources at all HFI frequencies in the key spectral range where
these spectra are crossing. The observed counts are in the Euclidean regime.
The number counts are compared to previously published data (earlier Planck,
Herschel, BLAST, SCUBA, LABOCA, SPT, and ACT) and models taking into account
both radio or infrared galaxies. We derive the multi-frequency Euclidean level
and compare it to WMAP, Spitzer and IRAS results. The submillimetre number
counts are not well reproduced by current evolution models of dusty galaxies,
whereas the millimetre part appears reasonably well fitted by the most recent
model for synchrotron-dominated sources. Finally we provide estimates of the
local luminosity density of dusty galaxies, providing the first such
measurements at 545 and 857GHz. |
Inferring Host Dark Matter Halo Masses of Individual Galaxies from
Neighboring Galaxy Counts: How well can we infer host dark matter halo masses of individual galaxies?
Based on the halo occupation distribution (HOD) framework, we analytically
compute the number of neighboring galaxies within a cylinder of some redshift
interval and radius in transverse comoving distance. The result is used to
derive the conditional probability distribution function (PDF) of the host halo
mass of a galaxy, given the neighboring galaxy counts. We compare our analytic
results with those obtained using a realistic mock galaxy catalog, finding
reasonable agreements. We find the optimal cylinder radius to be $\sim
0.5-1h^{-1}{\rm Mpc}$ for the inference of halo masses. The PDF is generally
broad, and sometimes has two peaks at low- and high-mass regimes, because of
the effect of chance projection along the line-of-sight. Potential applications
and extensions of the new theoretical framework developed herein are also
discussed. | Star formation in the extended gaseous disk of the isolated galaxy CIG
96: We study the Kennicutt-Schmidt star formation law and efficiency in the
gaseous disk of the isolated galaxy CIG 96 (NGC 864), with special emphasis on
its unusually large atomic gas (HI) disk (r_HI/r_25 = 3.5, r_25 = 1.'85). We
present deep GALEX near and far ultraviolet observations, used as a recent star
formation tracer, and we compare them with new, high resolution (16", or 1.6
kpc) VLA HI observations. The UV and HI maps show good spatial correlation
outside the inner 1', where the HI phase dominates over H_2. Star-forming
regions in the extended gaseous disk are mainly located along the enhanced HI
emission within two (relatively) symmetric giant gaseous spiral arm-like
features, which emulate a HI pseudo-ring at a r \simeq 3' . Inside such
structure, two smaller gaseous spiral arms extend from the NE and SW of the
optical disk and connect to the previously mentioned HI pseudo-ring.
Interestingly, we find that the (atomic) Kennicutt-Schmidt power law index
systematically decreases with radius, from N \simeq 3.0 +- 0.3 in the inner
disk (0.'8 - 1.'7) to N = 1.6 +- 0.5 in the outskirts of the gaseous disk (3.'3
- 4.'2). Although the star formation efficiency (SFE), the star formation rate
per unit of gas, decreases with radius where the HI component dominates as is
common in galaxies, we find that there is a break of the correlation at r = 1.5
r_25. At radii 1.5 r_25 < r < 3.5 r_25, mostly within the HI pseudo-ring
structure, there exist regions whose SFE remains nearly constant, SFE \simeq
10^-11 yr^-1. We discuss about possible mechanisms that might be triggering the
star formation in the outskirts of this galaxy, and we suggest that the
constant SFE for such large radii r > 2 r_25 and at such low surface densities
might be a common characteristic in extended UV disk galaxies. |
Search for transient variations of the fine structure constant and dark
matter using fiber-linked optical atomic clocks: We search for transient variations of the fine structure constant using data
from a European network of fiber-linked optical atomic clocks. By searching for
coherent variations in the recorded clock frequency comparisons across the
network, we significantly improve the constraints on transient variations of
the fine structure constant. For example, we constrain the variation in alpha
to <5*10^-17 for transients of duration 10^3 s. This analysis also presents a
possibility to search for dark matter, the mysterious substance hypothesised to
explain galaxy dynamics and other astrophysical phenomena that is thought to
dominate the matter density of the universe. At the current sensitivity level,
we find no evidence for dark matter in the form of topological defects (or,
more generally, any macroscopic objects), and we thus place constraints on
certain potential couplings between the dark matter and standard model
particles, substantially improving upon the existing constraints, particularly
for large (>~10^4 km) objects. | Probing the primordial Universe from the low-multipole CMB data: Since the temperature fluctuations in cosmic microwave background (CMB) on
large-angular scales probe length scales that were super-horizon sized at
photon decoupling and hence insensitive to microphysical processes, the
low-multipole CMB data are supposed to be a good probe to the physics of the
primordial Universe. In this letter we will constrain the cosmological
parameters in the base $\Lambda$CDM model with tensor perturbations by only
using low-multipole CMB data, including Background Imaging of Cosmic
Extragalactic Polarization (B2), Planck released in 2013 (P13) and Wilkinson
Microwaves Anisotropy Probe 9-year data (W9). We find that a red tilted power
spectrum of relic gravitational waves is compatible with the data, but a blue
tilted power spectrum of scalar perturbations on the large scales is preferred
at around $2\sigma$ confidence level. |
Radio and Millimeter Continuum Surveys and their Astrophysical
Implications: We review the statistical properties of the main populations of radio
sources, as emerging from radio and millimeter sky surveys. Recent
determinations of local luminosity functions are presented and compared with
earlier estimates still in widespread use. A number of unresolved issues are
discussed. These include: the (possibly luminosity-dependent) decline of source
space densities at high redshifts; the possible dichotomies between
evolutionary properties of low- versus high-luminosity and of flat- versus
steep-spectrum AGN-powered radio sources; and the nature of sources accounting
for the upturn of source counts at sub-mJy levels. It is shown that
straightforward extrapolations of evolutionary models, accounting for both the
far-IR counts and redshift distributions of star-forming galaxies, match the
radio source counts at flux-density levels of tens of microJy remarkably well.
We consider the statistical properties of rare but physically very interesting
classes of sources, such as GHz Peak Spectrum and ADAF/ADIOS sources, and radio
afterglows of gamma-ray bursts. We also discuss the exploitation of large-area
radio surveys to investigate large scale structure through studies of
clustering and the Integrated Sachs-Wolfe effect. Finally we briefly describe
the potential of the new and forthcoming generations of radio telescopes. A
compendium of source counts at different frequencies is given in an appendix. | Median Statistics Analysis of Deuterium Abundance Measurements and
Spatial Curvature Constraints: Zavarygin et al. (2018) compiled a list of 15 deuterium abundance
measurements, discarded two because the remaining 13 measurements are then
consistent with gaussianity, and found that the weighted mean baryon density
(Omega_b h^2) determined from the 13 measurements is mildly discrepant
(1.6sigma) with that determined from the Planck 2015 cosmic microwave
background anisotropy data in a flat cosmogony. We find that a median statistic
central estimate of Omega_b h^2 from all 15 deuterium abundance measurements is
a more accurate estimate, is very consistent with Omega_b h^2 estimated from
Planck 2015 data in a flat cosmogony, but is about 2sigma lower than that found
in a closed cosmogonical model from the Planck 2015 data. |
Cosmic vorticity and the origin of halo spins: In the standard model of cosmology, structure emerges out of non-rotational
flow and the angular momentum of collapsing halos is induced by tidal torques.
The growth of halo angular momentum in the linear and quasi-linear phases is
associated with a shear, curl-free, flow and it is well described within the
linear framework of tidal torque theory (TTT). However, TTT is rendered
irrelevant as haloes approach turn around and virialization. At that stage the
flow field around halos has non-zero vorticity. Using a cosmological
simulation, we have examined the importance of the curl of the velocity field
(vorticity) in determining halo spin, finding a strong alignment between the
two. We have also examined the alignment of vorticity with the principle axes
of the shear tensor, finding that it tends to be perpendicular to the axis
along which material is collapsing fastest (e1). This behavior is independent
of halo masses and cosmic web environment. Our results agree with previous
findings on the tendency of halo spin to be perpendicular to e1, and of the
spin of (simulated) halos and (observed) galaxies to be aligned with the
large-scale structure. Our results imply that angular momentum growth proceeds
in two distinct phases. In the first phase angular momentum emerges out of a
shear, curl-free, potential flow, as described by TTT. In the second phase, in
which haloes approach virialization, the angular momentum emerges out of a
vortical flow and halo spin becomes strongly aligned with the vorticity of the
ambient flow field. | Application of the Kolmogorov-Smirnov test to CMB data: Is the universe
really weakly random?: A recent application of the Kolmogorov-Smirnov test to the WMAP 7 year W-band
maps claims evidence that the CMB is "weakly random", and that only 20% of the
signal can be explained as a random Gaussian field. I here repeat this
analysis, and in contrast to the original result find no evidence for deviation
from the standard {\Lambda}CDM model. Instead, the results of the original
analysis are consistent with not properly taking into account the correlations
of the {\Lambda}CDM power spectrum. |
What is flat ΛCDM, and may we choose it?: The Universe is neither homogeneous nor isotropic, but it is close enough
that we can reasonably approximate it as such on suitably large scales. The
inflationary-$\Lambda$-Cold Dark Matter ($\Lambda$CDM) concordance cosmology
builds on these assumptions to describe the origin and evolution of
fluctuations. With standard assumptions about stress-energy sources, this
system is specified by just seven phenomenological parameters, whose precise
relations to underlying fundamental theories are complicated and may depend on
details of those fields. Nevertheless, it is common practice to set the
parameter that characterizes the spatial curvature, $\Omega_K$, exactly to
zero. This parameter-fixed $\Lambda$CDM is awarded distinguished status as
separate model, "flat $\Lambda$CDM.'' Ipso facto this places the onus on
proponents of "curved $\Lambda$CDM'' to present sufficient evidence that
$\Omega_K\neq0$, and is needed as a parameter. While certain inflationary model
Lagrangians, with certain values of their parameters, and certain initial
conditions, will lead to a present-day universe well-described as containing
zero curvature, this does not justify distinguishing that subset of
Lagrangians, parameters and initial conditions into a separate model. Absent
any theoretical arguments, we cannot use observations that suggest small
$\Omega_K$ to enforce $\Omega_K=0$. Our track record in picking inflationary
models and their parameters a priori makes such a choice dubious, and concerns
about tensions in cosmological parameters and large-angle
cosmic-microwave-background anomalies strengthens arguments against this
choice. We argue that $\Omega_K$ must not be set to zero, and that $\Lambda$CDM
remains a phenomenological model with at least 7 parameters. | Galaxy Evolution in Cosmological Simulations With Outflows I: Stellar
Masses and Star Formation Rates: We examine the growth of the stellar content of galaxies from z=3-0 in
cosmological hydrodynamic simulations incorporating parameterised galactic
outflows. Without outflows, galaxies overproduce stellar masses (M*) and star
formation rates (SFRs) compared to observations. Winds introduce a three-tier
form for the galaxy stellar mass and star formation rate functions, where the
middle tier depends on differential (i.e. mass-dependent) recycling of ejected
wind material back into galaxies. A tight M*-SFR relation is a generic outcome
of all these simulations, and its evolution is well-described as being powered
by cold accretion, although current observations at z>2 suggest that star
formation in small early galaxies must be highly suppressed. Roughly one-third
of z=0 galaxies at masses below M^* are satellites, and star formation in
satellites is not much burstier than in centrals. All models fail to suppress
star formation and stellar mass growth in massive galaxies at z<2, indicating
the need for an external quenching mechanism such as black hole feedback. All
models also fail to produce dwarfs as young and rapidly star-forming as
observed. An outflow model following scalings expected for momentum-driven
winds broadly matches observed galaxy evolution around M^* from z=0-3, which is
a significant success since these galaxies dominate cosmic star formation, but
the failures at higher and lower masses highlight the challenges still faced by
this class of models. We argue that central star-forming galaxies are
well-described as living in a slowly-evolving equilibrium between inflows from
gravity and recycled winds, star formation, and strong and ubiquitous outflows
that regulate how much inflow forms into stars. Star-forming galaxy evolution
is thus primarily governed by the continual cycling of baryons between galaxies
and intergalactic gas. |
The Projected Dark and Baryonic Ellipsoidal Structure of 20 CLASH Galaxy
Clusters: We reconstruct the two-dimensional (2D) matter distributions in 20 high-mass
galaxy clusters selected from the CLASH survey by using the new approach of
performing a joint weak lensing analysis of 2D shear and azimuthally averaged
magnification measurements. This combination allows for a complete analysis of
the field, effectively breaking the mass-sheet degeneracy. In a Bayesian
framework, we simultaneously constrain the mass profile and morphology of each
individual cluster assuming an elliptical Navarro-Frenk-White halo
characterized by the mass, concentration, projected axis ratio, and position
angle of the projected major axis.. We find that spherical mass estimates of
the clusters from azimuthally averaged weak-lensing measurements in previous
work are in excellent agreement with our results from a full 2D analysis.
Combining all 20 clusters in our sample, we detect the elliptical shape of
weak-lensing halos at the $5\sigma$ significance level within a scale of
2Mpc$/h$. The median projected axis ratio is $0.67\pm 0.07$ at a virial mass of
$M_\mathrm{vir}=(15.2\pm 2.8) \times 10^{14} M_\odot$, which is in agreement
with theoretical predictions of the standard collisionless cold dark matter
model. We also study misalignment statistics of the brightest cluster galaxy,
X-ray, thermal Sunyaev-Zel'dovich effect, and strong-lensing morphologies with
respect to the weak-lensing signal. Among the three baryonic tracers studied
here, we find that the X-ray morphology is best aligned with the weak-lensing
mass distribution, with a median misalignment angle of $21\pm 7$ degrees. We
also conduct a stacked quadrupole shear analysis assuming that the X-ray major
axis is aligned with that of the projected mass distribution. This yields a
consistent axis ratio of $0.67\pm 0.10$, suggesting again a tight alignment
between the intracluster gas and dark matter. | Angular Power Spectrum of B-mode Polarization from Cosmic String Wakes: Cosmic string wakes produce direct B-mode polarization at leading order in
cosmological perturbation theory, as worked out in a previous publication
\cite{BDH} in the case of a single string wake. Here we compute the angular
power spectrum of B-mode polarization from a scaling distribution of string
wakes. We find that the averaging which enters in computing the power spectrum
renders the signal, which is distinctive in position space maps, too small in
amplitude to be detectable with the first generation B-mode surveys. In
addition, the spectral shape is similar to that of gravitational lensing,
making it additionally difficult to detect the cosmic string signal from the
angular power spectrum. Hence, a more promising way to constrain cosmic strings
using B-mode polarization is by analyzing position space maps using novel
algorithms such as the Canny algorithm. |
The relation between surface star formation rate density and spiral arms
in NGC 5236 (M83): For a long time the consensus has been that star formation rates are higher
in the interior of spiral arms in galaxies, compared to inter-arm regions.
However, recent studies have found that the star formation inside the arms is
not more efficient than elsewhere in the galaxy. Previous studies have based
their conclusion mainly on integrated light. We use resolved stellar
populations to investigate the star formation rates throughout the nearby
spiral galaxy NGC 5236. We aim to investigate how the star formation rate
varies in the spiral arms compared to the inter-arm regions, using optical
space-based observations of NGC 5236. Using ground-based H\alpha images we
traced regions of recent star formation, and reconstructed the arms of the
galaxy. Using HST/ACS images we estimate star formation histories by means of
the synthetic CMD method. Arms based on H\alpha images showed to follow the
regions where stellar crowding is higher. Star formation rates for individual
arms over the fields covered were estimated between 10 to 100 Myr, where the
stellar photometry is less affected by incompleteness. Comparison between arms
and inter-arm surface star formation rate densities (\Sigma$_{SFR}$) suggested
higher values in the arms (\sim0.6 dex). Over a small fraction of one arm we
checked how the \Sigma$_{SFR}$ changes for the trailing and leading part. The
leading part of the arm showed to have a higher \Sigma$_{SFR}$ in the age range
10-100 Myr. Predictions from the density wave theory of a rapid increase in the
star formation at the edge where the stars and the gas enter the density wave
are confirmed. The \Sigma$_{SFR}$ presents a steep decrease with distance from
the center of the arms through the inter-arm regions. | CMB Shadows: The Effect of Interstellar Extinction on Cosmic Microwave
Background Polarization and Temperature Anisotropy: We evaluate the degradation of the accuracy of the component separation
between the cosmic microwave background (CMB) and foreground components caused
by neglect of absorption of the monopole component of the CMB by the galactic
interstellar matter. The amplitude of the temperature anisotropy caused by the
CMB shadow, due to dust components, is about 1 uK. This value is comparable to
the required noise level necessary to probe non-Gaussianity studies with
upcoming CMB experiments. In addition, the amplitude of the polarization caused
by the CMB shadow due to dust is comparable to or larger than the RMS value of
the CMB B-mode polarization, imprinted by primordial gravitational waves. We
show that applying a single-power law model as the dust spectrum to observed
multifrequency data introduces systematic errors, which are comparable to or
larger than the required noise level for forthcoming CMB B-mode polarization
experiments. Deducing the intrinsic spectrum of dust emission from the
submillimeter waveband data reduces systematic error below the required noise
level. However, this method requires dust temperature measurements with an
accuracy of better than a few percent. We conclude that the CMB shadow due to
dust must be considered in future CMB missions for achieving their targeted
sensitivity. Our results will be important to detect the primordial CMB B-mode
polarization, with the amplitude of the tensor-to-scalar ratio of r=10^{-3}. |
Search of sub-parsec massive binary black holes through line diagnosis
II: Massive black hole binaries at sub-parsec separations may display in their
spectra anomalously small flux ratios between the MgII and CIV broad emission
lines, i.e. F_MgII/F_CIV <~ 0.1, due to the erosion of the broad line region
around the active, secondary black hole, by the tidal field of the primary. In
Paper I by Montuori et al. (2011), we focussed on broad lines emitted by gas
bound to the lighter accreting member of a binary when the binary is at the
center of a hollow density region (the gap) inside a circum-binary disc. The
main aim of this new study is at exploring the potential contribution to the
broad line emission by the circum-binary disc and by gaseous streams flowing
toward the black hole through the gap. We carry out a post-process analysis of
data extracted from a SPH simulation of a circum-binary disc around a black
hole binary. Our main result is that the MgII to CIV flux ratio can be reduced
to ~ 0.1 within an interval of sub-pc binary separations of the order of a ~
(0.01-0.2)(f_Edd/0.1)^(1/2) pc corresponding to orbital periods of ~ (20-200)
(f_Edd/0.1)^(3/4) years for a secondary BH mass in the range M_2 ~ 10^7-10^9
M_sun and a binary mass ratio of 0.3. At even closer separations this ratio
returns to increase to values that are indistinguishable from the case of a
single AGN (typically F_MgII/F_CIV ~ 0.3-0.4) because of the contribution to
the MgII line from gas in the circum-binary disc. | Primordial Gravitational Waves in Running Vacuum Cosmologies: We investigate the cosmological production of gravitational waves in a
nonsingular flat cosmology powered by a "running vacuum" energy density
described by $\rho_{\Lambda}\equiv\rho_{\Lambda}(H)$, a phenomenological
expression potentially linked with the renormalization group approach in
quantum field theory in curved spacetimes. The model can be interpreted as a
particular case of the class recently discussed by Perico et al. (Phys. Rev. D
{\bf 88}, 063531, 2013) which is termed complete in the sense that the cosmic
evolution occurs between two extreme de Sitter stages (early and late time de
Sitter phases). {The gravitational wave equation is derived and its
time-dependent part numerically integrated since the primordial de Sitter
stage. The generated spectrum of gravitons is also compared with the standard
calculations where an abrupt transition, from the early de Sitter to the
radiation phase, is usually assumed.} It is found that the stochastic
background of gravitons is very similar to the one predicted by the cosmic
concordance model plus inflation except at higher frequencies ($\nu \gtrsim
100$ kHz). This remarkable signature of a "running vacuum" cosmology combined
with the proposed high frequency gravitational wave detectors and measurements
of the CMB polarization (B-modes) may provide a new window to confront more
conventional models of inflation. |
A new coupled three-form dark energy model and implications for the
$H_0$ tension: We propose a new coupled three-form dark energy model to relieve the Hubble
tension in this paper. Firstly, by performing a dynamical analysis with the
coupled three-form dark energy model, we obtain four fixed points, including a
saddle point representing a radiation dominated Universe, a saddle point
representing a matter dominated Universe, and two attractors representing two
saturated de Sitter Universes. Secondly, by confronting the coupled three-form
dark energy model and the $\Lambda$ cold dark matter model (the $\Lambda$CDM
model) with cosmic microwave background (CMB), baryonic acoustic oscillations
(BAO), Type Ia supernovae (SN Ia) observations, we obtain $H_0=
67.8_{-0.6}^{+0.7}$($1\sigma$ level) km/s/Mpc for the coupled three-form dark
energy model and $H_0=67.6_{-0.5}^{+0.5}$($1\sigma$ level) km/s/Mpc for the
$\Lambda$CDM model, the former is in strong tension with the latest local
measured $H_0$ value at $4.3\sigma$ confidence level, while the latter is in
strong tension with the latest local measured $H_0$ value at $5.1\sigma$ level. | AGN feedback in clusters: shock and sound heating: Observations support the view that feedback, in the form of radio outbursts
from active nuclei in central galaxies, prevents catastrophic cooling of gas
and rapid star formation in many groups and clusters of galaxies. Variations in
jet power drive a succession of weak shocks that can heat regions close to the
active galactic nuclei (AGN). On larger scales, shocks fade into sound waves.
The Braginskii viscosity determines a well-defined sound damping rate in the
weakly magnetized intracluster medium (ICM) that can provide sufficient heating
on larger scales. It is argued that weak shocks and sound dissipation are the
main means by which radio AGN heat the ICM, in which case, the power spectrum
of AGN outbursts plays a central role in AGN feedback. |
A new approach for obtaining cosmological constraints from Type Ia
Supernovae using Approximate Bayesian Computation: Cosmological parameter estimation techniques that robustly account for
systematic measurement uncertainties will be crucial for the next generation of
cosmological surveys. We present a new analysis method, superABC, for obtaining
cosmological constraints from Type Ia supernova (SN Ia) light curves using
Approximate Bayesian Computation (ABC) without any likelihood assumptions. The
ABC method works by using a forward model simulation of the data where
systematic uncertainties can be simulated and marginalized over. A key feature
of the method presented here is the use of two distinct metrics, the `Tripp'
and `Light Curve' metrics, which allow us to compare the simulated data to the
observed data set. The Tripp metric takes as input the parameters of models fit
to each light curve with the SALT-II method, whereas the Light Curve metric
uses the measured fluxes directly without model fitting. We apply the superABC
sampler to a simulated data set of $\sim$1000 SNe corresponding to the first
season of the Dark Energy Survey Supernova Program. Varying $\Omega_m, w_0,
\alpha$ and $\beta$ and a magnitude offset parameter, with no systematics we
obtain $\Delta(w_0) = w_0^{\rm true} - w_0^{\rm best \, fit} = -0.036\pm0.109$
(a $\sim11$% 1$\sigma$ uncertainty) using the Tripp metric and $\Delta(w_0) =
-0.055\pm0.068$ (a $\sim7$% 1$\sigma$ uncertainty) using the Light Curve
metric. Including 1% calibration uncertainties in four passbands, adding 4 more
parameters, we obtain $\Delta(w_0) = -0.062\pm0.132$ (a $\sim14$% 1$\sigma$
uncertainty) using the Tripp metric. Overall we find a $17$% increase in the
uncertainty on $w_0$ with systematics compared to without. We contrast this
with a MCMC approach where systematic effects are approximately included. We
find that the MCMC method slightly underestimates the impact of calibration
uncertainties for this simulated data set. | Shear measurement bias II: a fast machine learning calibration method: We present a new shear calibration method based on machine learning. The
method estimates the individual shear responses of the objects from the
combination of several measured properties on the images using supervised
learning. The supervised learning uses the true individual shear responses
obtained from copies of the image simulations with different shear values. On
simulated GREAT3data, we obtain a residual bias after the calibration
compatible with 0 and beyond Euclid requirements for a signal-to-noise ratio >
20 within ~15 CPU hours of training using only ~10^5 objects. This efficient
machine-learning approach can use a smaller data set because the method avoids
the contribution from shape noise. The low dimensionality of the input data
also leads to simple neural network architectures. We compare it to the
recently described method Metacalibration, which shows similar performances.
The different methods and systematics suggest that the two methods are very
good complementary methods. Our method can therefore be applied without much
effort to any survey such as Euclid or the Vera C. Rubin Observatory, with
fewer than a million images to simulate to learn the calibration function. |
Stability analysis of chromo-natural inflation and possible evasion of
Lyth's bound: We perform the complete stability study of the model of chromo-natural
inflation (Adshead and Wyman '12), where, due to its coupling to a SU(2)
vector, a pseudo-scalar inflaton chi slowly rolls on a steep potential. As a
typical example, one can consider an axion with a sub-Planckian decay constant
f. The phenomenology of the model was recently studied (Dimastrogiovanni,
Fasiello, and Tolley '12) in the m_g >> H limit, where m_g is the mass of the
fluctuations of the vector field, and H the Hubble rate. We show that the
inflationary solution is stable for m_g > 2 H, while it otherwise experiences a
strong instability due to scalar perturbations in the sub-horizon regime. The
tensor perturbations are instead standard, and the vector ones remain
perturbatively small. Depending on the parameters, this model can give a
gravity wave signal that can be detected in ongoing or forthcoming CMB
experiments. This detection can occur even if, during inflation, the inflaton
spans an interval of size Delta chi = O (f) which is some orders of magnitude
below the Planck scale, evading a well known bound that holds for a free
inflaton (Lyth '97). | Sunyaev-Zel'dovich Cluster Profiles Measured with the South Pole
Telescope: We present Sunyaev-Zel'dovich measurements of 15 massive X-ray selected
galaxy clusters obtained with the South Pole Telescope. The Sunyaev-Zel'dovich
(SZ) cluster signals are measured at 150 GHz, and concurrent 220 GHz data are
used to reduce astrophysical contamination. Radial profiles are computed using
a technique that takes into account the effects of the beams and filtering. In
several clusters, significant SZ decrements are detected out to a substantial
fraction of the virial radius. The profiles are fit to the beta model and to a
generalized NFW pressure profile, and are scaled and stacked to probe their
average behavior. We find model parameters that are consistent with previous
studies: beta=0.86 and r_core/r_500 = 0.20 for the beta model, and (alpha,
beta, gamma, c_500)=(1.0,5.5,0.5,1.0) for the generalized NFW model. Both
models fit the SPT data comparably well, and both are consistent with the
average SZ profile out to the virial radius. The integrated Compton-y parameter
Y_SZ is computed for each cluster using both model-dependent and
model-independent techniques, and the results are compared to X-ray estimates
of cluster parameters. We find that Y_SZ scales with Y_X and gas mass with low
scatter. Since these observables have been found to scale with total mass, our
results point to a tight mass-observable relation for the SPT cluster survey. |
The Dense Stellar Systems Around Galactic Massive Black Holes: The central regions of galaxies show the presence of massive black holes
and/or dense stellar systems. The question about their modes of formation is
still under debate. A likely explanation of the formation of the central dense
stellar systems in both spiral and elliptical galaxies is based on the orbital
decay of massive globular clusters in the central region of galaxies due to
kinetic energy dissipation by dynamical friction. Their merging leads to the
formation of a nuclear star cluster, like that of the Milky Way, where a
massive black hole (Sgr A*) is also present. Actually, high precision N-body
simulations (Antonini, Capuzzo-Dolcetta et al. 2012, ApJ, 750, 111) show a good
fit to the observational characteristics of the Milky Way nuclear cluster,
giving further reliability to the cited `migratory' model for the formation of
compact systems in the inner galaxy regions. | A study on Cubic Galileon Gravity Using N-body Simulations: We use N-body simulation to study the structure formation in the Cubic
Galileon Gravity model where along with the usual kinetic and potential term we
also have a higher derivative self-interaction term. We find that the large
scale structure provides a unique constraining power for this model. The matter
power spectrum, halo mass function, galaxy-galaxy weak lensing signal, marked
density power spectrum as well as count in cell are measured. The simulations
show that there are less massive halos in the Cubic Galileon Gravity model than
corresponding $\Lambda$CDM model and the marked density power spectrum in these
two models are different by more than $10\%$. Furthermore, the Cubic Galileon
model shows significant differences in voids compared to $\Lambda$CDM. The
number of low density cells is far higher in the Cubic Galileon model than that
in the $\Lambda$CDM model. Therefore, it would be interesting to put
constraints on this model using future large scale structure observations,
especially in void regions. |
Observational constraints on nonlinear matter extensions of general
relativity: We present a phenomenological analysis of current observational constraints
on classes of FLRW cosmological models in which the matter side of Einstein's
equations includes, in addition to the canonical term, a term proportional to
some function of the energy-momentum tensor
($T^2=T_{\alpha\beta}T^{\alpha\beta}=\rho^2+3p^2$), or of its trace
($T=\rho-3p$). Qualitatively, one may think of these models as extensions of
general relativity with a nonlinear matter Lagrangian. As such they are
somewhat different from the usual dynamical dark energy or modified gravity
models: in the former class of models one adds further dynamical degrees of
freedom to the Lagrangian (often in the form of scalar fields), while in the
latter the gravitational part of the Lagrangian is changed. We study both of
these models under two different scenarios: (1) as phenomenological
two-parameter or three-parameter extensions of the standard $\Lambda$CDM, in
which case the model still has a cosmological constant but the nonlinear matter
Lagrangian leads to additional terms in Einstein's equations, which
cosmological observations tightly constrain, and (2) as alternatives to
$\Lambda$CDM, where there is no cosmological constant, and the nonlinear matter
term would have to provide the acceleration (which would be somewhat closer in
spirit to the usual modified gravity models). A comparative analysis of the
observational constraints obtained in the various cases provides some insight
on the level of robustness of the $\Lambda$ model and on the parameter space
still available for phenomenological alternatives. | Anisotropic Jeans models of stellar kinematics: second moments including
proper motions and radial velocities: This is an addendum to the paper by Cappellari (2008, MNRAS, 390, 71), which
presented a simple and efficient method to model the stellar kinematics of
axisymmetric stellar systems. The technique reproduces well the integral-field
kinematics of real galaxies. It allows for orbital anisotropy (three-integral
distribution function), multiple kinematic components, supermassive black holes
and dark matter. The paper described the derivation of the projected second
moments and we provided a reference software implementation. However only the
line-of-sight component was given in the paper. For completeness we provide
here all the six projected second moments, including radial velocities and
proper motions. We present a test against realistic N-body galaxy simulations. |
XMM-Newton observations of SDSS J143030.22$-$001115.1: an unusually flat
spectrum AGN: We present XMM observations of the AGN SDSS 1430-0011. The low S/N spectrum
of this source obtained in a snap shot Chandra observation showed an unusually
flat continuum. With the follow up XMM observations we find that the source
spectrum is complex; it either has an ionized absorber or a partially covering
absorber. The underlying power-law is in the normal range observed for AGNs.
The low luminosity of the source during Chandra observations can be understood
in terms of variations in the absorber properties. The X-ray and optical
properties of this source are such that it cannot be securely classified as
either a narrow line Seyfert 1 or a broad line Seyfert 1 galaxy. | Constraining the dark energy models with H(z) data: an approach
independent of $H_{0}$: We study the performance of the latest $H(z)$ data in constraining the
cosmological parameters of different cosmological models, including that of
Chevalier-Polarski-Linder $w_{0}w_{1}$ parametrization. First, we introduce a
statistical procedure in which the chi-square estimator is not affected by the
value of the Hubble constant. As a result, we find that the $H(z)$ data do not
rule out the possibility of either non-flat models or dynamical dark energy
cosmological models. However, we verify that the time varying equation of state
parameter $w(z)$ is not constrained by the current expansion data. Combining
the $H(z)$ and the Type Ia supernova data we find that the $H(z)$/SNIa overall
statistical analysis provides a substantial improvement of the cosmological
constraints with respect to those of the $H(z)$ analysis. Moreover, the
$w_{0}-w_{1}$ parameter space provided by the $H(z)$/SNIa joint analysis is in
a very good agreement with that of Planck 2015, which confirms that the present
analysis with the $H(z)$ and SNIa probes correctly reveals the expansion of the
Universe as found by the team of Planck. Finally, we generate sets of Monte
Carlo realizations in order to quantify the ability of the $H(z)$ data to
provide strong constraints on the dark energy model parameters. The Monte Carlo
approach shows significant improvement of the constraints, when increasing the
sample to 100 $H(z)$ measurements. Such a goal can be achieved in the future,
especially in the light of the next generation of surveys. |
Impact of Instrumental Systematic Contamination on the Lensing Mass
Reconstruction using the CMB Polarization: In this paper, we study the effects of instrumental systematics on the
reconstruction of the deflection angle power spectrum from weak lensing of
Cosmic Microwave Background (CMB) temperature and polarization observations. We
consider seven types of effects which are related to known instrumental
systematics: calibration, rotation, pointing, spin-flip, monopole leakage,
dipole leakage and quadrupole leakage. These effects can be characterized by 11
distortion fields. Each of these systematic effects can mimic the effective
projected matter power spectrum and hence contaminate the lensing
reconstruction. To demonstrate the effect of these instrumental systematics, we
consider two types of experiments, one with a detector noise level for
polarization of 9.6 uK-arcmin and FWHM of 8.0', typical of upcoming ground and
balloon-based CMB experiments, and a CMBPol-like instrument with a detector
noise level for polarization of 2.0 uK-arcmin and FWHM of 4.0', typical of
future space-based CMB experiments. For each systematics, we consider various
choices of coherence scale. Among all the 11 systematic parameters, rotation
and monopole leakage place the most stringent requirements, while quadrupole
leakage, pointing error, and calibration are among the least demanding. The
requirements from lensing extraction are about 1-2 orders of magnitude less
stringent than the requirements to measure the primordial B-modes with
inflationary energy scale of 1.0*10^{16} GeV. On the other hand the
requirements for lensing reconstruction are comparable or even more stringent
for some systematic parameters than the requirements to detect primordial
B-modes with inflationary scale E_i = 3.0*10^{16} GeV. | Euclid: Forecasts from the void-lensing cross-correlation: The Euclid space telescope will survey a large dataset of cosmic voids traced
by dense samples of galaxies. In this work we estimate its expected performance
when exploiting angular photometric void clustering, galaxy weak lensing and
their cross-correlation. To this aim, we implement a Fisher matrix approach
tailored for voids from the Euclid photometric dataset and present the first
forecasts on cosmological parameters that include the void-lensing correlation.
We examine two different probe settings, pessimistic and optimistic, both for
void clustering and galaxy lensing. We carry out forecast analyses in four
model cosmologies, accounting for a varying total neutrino mass, $M_\nu$, and a
dynamical dark energy (DE) equation of state, $w(z)$, described by the CPL
parametrisation. We find that void clustering constraints on $h$ and $\Omega_b$
are competitive with galaxy lensing alone, while errors on $n_s$ decrease
thanks to the orthogonality of the two probes in the 2D-projected parameter
space. We also note that, as a whole, the inclusion of the void-lensing
cross-correlation signal improves parameter constraints by $10-15\%$, and
enhances the joint void clustering and galaxy lensing Figure of Merit (FoM) by
$10\%$ and $25\%$, in the pessimistic and optimistic scenarios, respectively.
Finally, when further combining with the spectroscopic galaxy clustering,
assumed as an independent probe, we find that, in the most competitive case,
the FoM increases by a factor of 4 with respect to the combination of weak
lensing and spectroscopic galaxy clustering taken as independent probes. The
forecasts presented in this work show that photometric void-clustering and its
cross-correlation with galaxy lensing deserve to be exploited in the data
analysis of the Euclid galaxy survey and promise to improve its constraining
power, especially on $h$, $\Omega_b$, the neutrino mass, and the DE evolution. |
Effective $J$-factors for Milky Way dwarf spheroidal galaxies with
velocity-dependent annihilation: We calculate the effective $J$-factors, which determine the strength of
indirect detection signals from dark matter annihilation, for 25 dwarf
spheroidal galaxies (dSphs). We consider several well-motivated assumptions for
the relative velocity dependence of the dark matter annihilation cross section:
$\sigma_A v$: $s$-wave (velocity independent), $p$-wave ($\sigma_A v \propto
v^2$), $d$-wave ($\sigma_A v \propto v^4$), and Sommerfeld-enhancement in the
Coulomb limit ($\sigma_A v \propto 1/v$). As a result we provide the largest
and most updated sample of J-factors for velocity-dependent annihilation
models. For each scenario, we use Fermi-LAT gamma-ray data to constrain the
annihilation cross section. Due to the assumptions made in our gamma-ray data
analysis, our bounds are comparable to previous bounds on both the $p$-wave and
Sommerfeld-enhanced cross sections using dSphs. Our bounds on the $d$-wave
cross section are the first such bounds using indirect detection data. | The cosmic web connection to the dark matter halo distribution through
gravity: This work investigates the connection between the cosmic web and the halo
distribution through the gravitational potential at the field level. We combine
three fields of research, cosmic web classification, perturbation theory
expansions of the halo bias, and halo (galaxy) mock catalogue making methods.
In particular, we use the invariants of the tidal field and the velocity shear
tensor as generating functions to reproduce the halo number counts of a
reference catalogue from full gravity calculations, populating the dark matter
field on a mesh well into the non-linear regime ($3\,h^{-1}\,{\rm Mpc}$
scales). Our results show an unprecedented agreement with the reference power
spectrum within 1% up to $k=0.72\,h\,{\rm Mpc}^{-1}$. By analysing the
three-point statistics on large scales (configurations of up to $k=0.2\,h\,{\rm
Mpc}^{-1}$), we find evidence for non-local bias at the 4.8 $\sigma$ confidence
level, being compatible with the reference catalogue. In particular, we find
that a detailed description of tidal anisotropic clustering on large scales is
crucial to achieve this accuracy at the field level. These findings can be
particularly important for the analysis of the next generation of galaxy
surveys in mock galaxy production. |
Correlations between SNe Ia Rates and Host Galaxy Properties: Studying the correlation of type Ia supernova rates (SNR) with host galaxy
properties is an important step in understanding the exact nature of type Ia
supernovae. We use SNe Ia from the SDSS-II sample, spectroscopically determined
masses and star formation rates, and a new maximum likelihood method, to fit
the Scannapieco and Bildsten rate model $SNR = A{\times}M + B{\times}SFR$,
where $M$ is galaxy mass and $SFR$ is star formation rate. We find $A =
3.5^{+0.9}_{-0.7}\times10^{-14}(\text{SNe/yr})(M_{\odot})^{-1}$ and $B
=1.3^{+0.4}_{-0.3}\times10^{-3}(\text{SNe/yr})(M_{\odot}$yr$^{-1})^{-1}$,
assuming overall efficiency of 0.5. This is in reasonable agreement with other
determinations. However we find strong evidence that this model is a poor fit
to other projections of the data: it fails to correctly predict the
distribution of supernovae with host mass or SFR. An additional model parameter
is required; most likely this parameter is related to host galaxy mass. Some
implications of this result are discussed. | The MOND phenomenology: The Lambda-CDM cosmological model is succesful at reproducing various
independent sets of observations concerning the large-scale Universe. This
model is however currently, and actually in principle, unable to predict the
gravitational field of a galaxy from it observed baryons alone. Indeed the
gravitational field should depend on the relative contribution of the particle
dark matter distribution to the baryonic one, itself depending on the
individual assembly history and environment of the galaxy, including a lot of
complex feedback mechanisms. However, for the last thirty years, Milgrom's
formula, at the heart of the MOND paradigm, has been consistently succesful at
predicting rotation curves from baryons alone, and has been resilient to all
sorts of observational tests on galaxy scales. We show that the few individual
galaxy rotation curves that have been claimed to be highly problematic for the
predictions of Milgrom's formula, such as Holmberg II or NGC 3109, are actually
false alarms. We argue that the fact that it is actually possible to predict
the gravitational field of galaxies from baryons alone presents a challenge to
the current Lambda-CDM model, and may indicate a breakdown of our understanding
of gravitation and dynamics, and/or that the actual lagrangian of the dark
sector is very different and richer than currently assumed. On the other hand,
it is obvious that any alternative must also, in fine, reproduce the successes
of the Lambda-CDM model on large scales, where this model is so well-tested
that it presents by itself a challenge to any such alternative. |
Core Mass Estimates in Strong Lensing Galaxy Clusters: a Comparison
Between Masses Obtained from Detailed Lens Models, Single-Halo Lens Models,
and Einstein Radii: The core mass of galaxy clusters is both an important anchor of the radial
mass distribution profile and probe of structure formation. With thousands of
strong lensing galaxy clusters being discovered by current and upcoming
surveys, timely, efficient, and accurate core mass estimates are needed. We
assess the results of two efficient methods to estimate the core mass of strong
lensing clusters: the mass enclosed by the Einstein radius
($M_{corr}(<\theta_E)$ where $\theta_{\rm E}$ is approximated from arc
positions; Remolina Gonz\'{a}lez et al. 2020), and single-halo lens model
($M_{\rm{SHM}}(<\rm{e}\theta_{\rm{E}})$; Remolina Gonz\'{a}lez et al. 2021),
against measurements from publicly available detailed lens models
($M_{\rm{DLM}}$) of the same clusters. We use data from the Sloan Giant Arc
Survey, the Reionization Lensing Cluster Survey, the \Hubble\ Frontier Fields,
and the Cluster Lensing and Supernova Survey with \Hubble. We find a scatter of
$18.3\%$ ($8.4\%$) with a bias of $-7.5\%$ ($0.4\%$) between
$M_{corr}(<\theta_E)$ ($M_{\rm{SHM}}(<\rm{e}\theta_{\rm{E}})$) and
$M_{\rm{DLM}}$. Last, we compare the statistical uncertainties measured in this
work to those from simulations. This work demonstrates the successful
application of these methods to observational data. As the effort to
efficiently model the mass distribution of strong lensing galaxy clusters
continues, we need fast, reliable methods to advance the field. | Application of Bayesian model averaging to measurements of the
primordial power spectrum: Cosmological parameter uncertainties are often stated assuming a particular
model, neglecting the model uncertainty, even when Bayesian model selection is
unable to identify a conclusive best model. Bayesian model averaging is a
method for assessing parameter uncertainties in situations where there is also
uncertainty in the underlying model. We apply model averaging to the estimation
of the parameters associated with the primordial power spectra of curvature and
tensor perturbations. We use CosmoNest and MultiNest to compute the model
Evidences and posteriors, using cosmic microwave data from WMAP, ACBAR,
BOOMERanG and CBI, plus large-scale structure data from the SDSS DR7. We find
that the model-averaged 95% credible interval for the spectral index using all
of the data is 0.940 < n_s < 1.000, where n_s is specified at a pivot scale
0.015 Mpc^{-1}. For the tensors model averaging can tighten the credible upper
limit, depending on prior assumptions. |
The nature of HI absorbers in GRB afterglows: clues from hydrodynamic
simulations: In recent work, we have shown that it is possible to link quantitatively many
aspects of damped Lyman alpha (DLA) absorbers in the spectra of quasars to high
resolution simulations of galaxy formation. Using runs from the same series of
hydrodynamic numerical studies, we consider the expected properties of Lyman
alpha absorbers seen in the spectra of high redshift (z>2) gamma ray burst
afterglows (GRB-DLAs). If GRBs are associated with the death of massive stars,
their afterglows provide insights into otherwise unprobed regions of
protogalactic objects, but detailed physical interpretations are currently
embryonic.
We find that median impact parameters (measured from the potential minimum)
are approximately 1 kpc for GRBs compared with 4 kpc for QSO-DLAs. However, an
equally important difference is that GRB-DLAs are predominantly associated with
halos of mass 10^10<M_vir/M_sol<10^12, an order of magnitude larger than the
hosts of QSO-DLAs. Accordingly, there are differences in the stellar properties
of hosts.
Our simulations accurately predict the form of the GRB-DLA HI column density
distribution, producing quantitative agreement for N_HI>10^19 cm^-2, but they
somewhat underpredict the incidence of low column densities N_HI<10^19 cm^-2.
Line-of-sight neutral gas metallicities predicted by our simulations (10^-2 <
Z/Z_sol < 1) are consistent with the modest observational constraints. Because
of large internal dispersions in gas metallicities, this agreement is not
significantly compromised by imposing a cut-off on the metallicity of stars
able to launch GRBs (Z_star<Z_sol/3), confounding claims that the observed
metallicity of GRB-DLAs poses a challenge to current GRB models. (Abridged.) | Unusually High Metallicity Host Of The Dark LGRB 051022: We present spectroscopy of the host of GRB 051022 with GMOS nod and shuffle
on Gemini South and NIRSPEC on Keck II. We determine a metallicity for the host
of log(O/H)+12 = 8.77 using the R23 method (Kobulnicky & Kewley 2004 scale)
making this the highest metallicity long burst host yet observed. The galaxy
itself is unusually luminous for a LGRB host with a rest frame B band absolute
magnitude -21.5 and has the spectrum of a rapidly star-forming galaxy. Our work
raises the question of whether other dark burst hosts will show high
metallicities. |
The hyperfine transition of 3He+ as a probe of the intergalactic medium: We explore the prospects of using the hyperfine transition of 3He+ as a probe
of the intergalactic medium. The emission signal from ionized regions during
reionization is expected to be anti-correlated with 21cm maps. The predicted
emission signal from Lyman-alpha blobs at lower redshifts is detectable with
future radio observatories. | New Inflation in the Landscape and Typicality of the Observed Cosmic
Perturbation: We investigate if the observed small and nearly scale-invariant primordial
cosmic perturbation, i.e. the perturbation amplitude $P_\zeta\sim10^{-9}$ and
the spectral index $n_s \simeq 0.965$, is typical in the landscape of vacua
after imposing anthropic selections on them. We consider the situation where
the universe begins from a metastable vacuum driving a precedent inflation, a
curvature-dominated open universe is created by tunneling, and the curvature
energy is inflated away by new inflation. We argue that the initial inflaton
field value is homogeneous but typically non-zero because of the quantum
fluctuation of long wavelength modes created during the precedent inflation,
and only the universe which accidentally has a small inflaton field value is
anthropically selected. We show that this bias, together with certain
distributions of inflation model parameters that are physically well-motivated,
makes the observed small and nearly scale-invariant spectrum typical. |
The stellar mass function of star-forming galaxies and the
mass-dependent SFR function since z=2.23 from HiZELS: We explore a large uniformly selected sample of H${\alpha}$ selected
star-forming galaxies (SFGs) at z=0.40,0.84,1.47,2.23 to unveil the evolution
of the star formation rate (SFR) function and the stellar mass function. We
find strong evolution in the SFR function, with the typical SFR of SFGs
declining exponentially with time in the last 11Gyrs as
SFR$^*$(T[Gyr])=10$^{4.23/T+0.37}$ M$_{\odot}$yr$^{-1}$, but with no evolution
in the faint-end slope, ${\alpha}\approx$-1.6. The stellar mass function of
SFGs, however, reveals little evolution: ${\alpha} \approx$-1.4,
M$^*$$\approx$10$^{11.2\pm0.2}$ M$_{\odot}$ and just a slight increase of
$\approx$2.3x in ${\Phi}^*$ from z=2.23 to z=0.4. The stellar mass density
within SFGs has been roughly constant since z=2.23 at
$\approx$10$^{7.65\pm0.08}$ M$_{\odot}$Mpc$^{-3}$, comprising $\approx$100% of
the stellar mass density in all galaxies at z=2.23, and declining to
$\approx$20% by z=0.4, driven by the rise of the passive population. We find
that SFGs with M$\approx$10$^{10.0\pm0.2}$ M$_{\odot}$ contribute most to the
SFR density (${\rho}_{\rm SFR}$) per dlog$_{10}$M, and that there is no
significant evolution in the fractional contribution from SFGs of different
masses to ${\rho}_{\rm SFR}$ or ${\rho}_{\rm SFR}$(dlog$_{10}$M)$^{-1}$ since
z=2.23. Instead, we show that the decline of SFR$^*$ and of ${\rho}_{\rm SFR}$
are primarily driven by an exponential decline in SFRs at all masses. Our
results have important implications not only on how SFGs need to be quenched
across cosmic time, but also on the driver(s) of the exponential decline in
SFR$^*$ from $\approx$66 M$_{\odot}$yr$^{-1}$ to $\approx$5
M$_{\odot}$yr$^{-1}$ since z=2.23. | A clear and measurable signature of modified gravity in the galaxy
velocity field: The velocity field of dark matter and galaxies reflects the continued action
of gravity throughout cosmic history. We show that the low-order moments of the
pairwise velocity distribution, $v_{12}$, are a powerful diagnostic of the laws
of gravity on cosmological scales. In particular, the projected line-of-sight
galaxy pairwise velocity dispersion, $\sigma_{12}(r)$, is very sensitive to the
presence of modified gravity. Using a set of high-resolution N-body simulations
we compute the pairwise velocity distribution and its projected line-of-sight
dispersion for a class of modified gravity theories: the chameleon \fR gravity
and Galileon gravity (cubic and quartic). The velocities of dark matter halos
with a wide range of masses would exhibit deviations from General Relativity at
the $(5-10)\sigma$ level. We examine strategies for detecting these deviations
in galaxy redshift and peculiar velocity surveys. If detected, this signature
would be a "smoking gun" for modified gravity. |
Computing the Three-Point Correlation Function of Galaxies in
$\mathcal{O}(N^2)$ Time: We present an algorithm that computes the multipole coefficients of the
galaxy three-point correlation function (3PCF) without explicitly considering
triplets of galaxies. Rather, centering on each galaxy in the survey, it
expands the radially-binned density field in spherical harmonics and combines
these to form the multipoles without ever requiring the relative angle between
a pair about the central. This approach scales with number and number density
in the same way as the two-point correlation function, allowing runtimes that
are comparable, and 500 times faster than a naive triplet count. It is exact in
angle and easily handles edge correction. We demonstrate the algorithm on the
LasDamas SDSS-DR7 mock catalogs, computing an edge corrected 3PCF out to
$90\;{\rm Mpc}/h$ in under an hour on modest computing resources. We expect
this algorithm will render it possible to obtain the large-scale 3PCF for
upcoming surveys such as Euclid, LSST, and DESI. | Revealing reionization with the thermal history of the intergalactic
medium: new constraints from the Lyman-$α$ flux power spectrum: We present a new investigation of the thermal history of the intergalactic
medium (IGM) during and after reionization using the Lyman-$\alpha$ forest flux
power spectrum at $4.0\lesssim z\lesssim5.2$. Using a sample of 15
high-resolution spectra, we measure the flux power down to the smallest scales
ever probed at these redshifts ($-1\lesssim \log(k/$km$^{-1}$s)$\lesssim
-0.7$). These scales are highly sensitive to both the instantaneous temperature
of the IGM and the total energy injected per unit mass during and after
reionization. We measure temperatures at the mean density of
$T_{0}\sim7000$-8000 K, consistent with no significant temperature evolution
for redshifts $4.2\lesssim z\lesssim5.0$. We also present the first
observational constraints on the integrated IGM thermal history, finding that
the total energy input per unit mass increases from $u_{0}\sim4.6$ ${\rm eV}$
$m_{\rm p}^{-1}$ to 7.3 eV $m_{\rm p}^{-1}$ from $z\sim 6$ to $4.2$ assuming a
$\Lambda$-CDM cosmology. We show how these results can be used simultaneously
to obtain information on the timing and the sources of the reionization
process. Our first proof of concept using simplistic models of instantaneous
reionization produces results comparable to and consistent with the recent
Planck constraints, favoring models with $z_{\rm rei}\sim 8.5^{+1.1}_{-0.8}$. |
On the multiplicity of supernovae within host galaxies: We investigate the nature of multiple supernova hosting galaxies, and the
types of events which they produce. Using all known historical supernovae, we
split host galaxies into samples containing single or multiple events. These
samples are then characterised in terms of their relative supernova fractions,
and host properties. In multiple supernova hosts the ratio of type Ia to
core-collapse events is lower than in single supernova hosts. For core-collapse
events there is a suggestion that the ratio of types Ibc to type II events is
higher in multiples than within single supernova hosts. This second increase is
dominated by an increase in the number of SNIb. Within multiple supernova
hosts, supernovae of any given type appear to 'prefer' to explode in galaxies
that are host to the same type of SN. We also find that multiple SN hosts have
higher T-type morphologies. While our results suffer from low number
statistics, we speculate that their simplest interpretation is that star
formation within galaxies is generally of an episodic and bursty nature. This
leads to the supernovae detected within any particular galaxy to be dominated
by those with progenitors of a specific age, rather than a random selection
from standard relative supernova rates, as the latter would be expected if star
formation was of a long-term continuous nature. We further discuss the
supernova progenitor and star formation properties that may be important for
understanding these trends, and also comment on a range of important selection
effects within our sample. | The Compton-thick AGN in the CDF-N: We present X-ray spectral analysis of the brightest sources (f_{2-10
keV}>10^{-15}$ cgs) in the Chandra Deep Field North. Our sample consists of 222
sources; for the vast majority (171) either a spectroscopic or a photometric
redshift is available. Our goal is to discover the Compton-thick AGN in a
direct way i.e. through their X-ray spectra. Compton-thick AGN give away their
presence in X-rays either directly through the absorption turnover redshifted
in the Chandra passband, or through a flat, reflection-dominated, spectrum. The
above selection criteria yield 10 Compton-thick AGN candidates of which the
nine are reflection dominated. The IR or sub-mm data where available,
corroborate the presence of a heavily obscured nucleus in most cases. All the
five candidate Compton-thick sources with available 24 micron data present very
high values of the f_{24}/f_R flux ratio suggesting that they are dust obscured
galaxies. The low f_x/f_{IR} ratio also suggest the presence of obscured nuclei
in many cases. Four of the candidate Compton-thick sources are associated with
sub-mm galaxies at high redshifts z$\sim2$. The number count vs. flux
distribution of the candidate Compton-thick AGN as well as their distribution
with redshift agree reasonably well with the predictions of the X-ray
background synthesis models of Gilli et al. |
Baryon acoustic oscillation methods for generic curvature: Application
to the SDSS-III Baryon Oscillation Spectroscopic Survey: We develop methods for investigating baryon acoustic oscillation (BAO)
features in cosmological models with non-trivial (but slowly varying) averaged
spatial curvature: models that are not necessarily flat, close to flat, nor
with constant spatial curvature. The class of models to which our methods apply
include Lemaitre-Tolman-Bondi models, modified gravity cosmologies, and
inhomogeneous cosmologies with backreaction - in which we do not have a
prediction of the shape of the spatial 2-point correlation function, but where
we nevertheless expect to see a BAO feature in the present-day galaxy
distribution, in form of an excess in the galaxy 2-point correlation function.
We apply our methods to the Baryon Oscillation Spectroscopic Survey (BOSS)
dataset, investigating both the Lambda Cold Dark Matter ($\Lambda$CDM) and
timescape cosmological models as case studies. The correlation functions
measured in the two fiducial models contain a similarly-pronounced BAO feature.
We use the relative tangential and radial BAO scales to measure the anisotropic
Alcock-Paczy\'nski distortion parameter, $\epsilon$, which is independent of
the underlying BAO preferred scale. We find that $\epsilon$ is consistent with
zero in both fiducial cosmologies, indicating that models with a different
spatial curvature behaviour can account for the relative positions of the
tangential and radial BAO scale. We validate our methods using $\Lambda$CDM
mocks. | The Parkes Galactic Meridian Survey (PGMS): observations and CMB
polarization foreground analysis: We present observations and CMB foreground analysis of the Parkes Galactic
Meridian Survey (PGMS), an investigation of the Galactic latitude behaviour of
the polarized synchrotron emission at 2.3 GHz with the Parkes Radio Telescope.
The survey consists of a 5-deg wide strip along the Galactic meridian l=254-deg
extending from Galactic plane to South Galactic pole. We identify three zones
distinguished by polarized emission properties: the disc, the halo, and a
transition region connecting them. The halo section lies at latitudes |b| >
40-deg and has weak and smooth polarized emission mostly at large scale with
steep angular power spectra of median slope $\beta_{\rm med} \sim -2.6$. The
disc region covers the latitudes |b|<20-deg and has a brighter, more complex
emission dominated by the small scales with flatter spectra of median slope
$\beta_{\rm med} = -1.8$. The transition region has steep spectra as in the
halo, but the emission increases toward the Galactic plane from halo to disc
levels. The change of slope and emission structure at $b \sim -20\degr$ is
sudden, indicating a sharp disc-halo transition. The whole halo section is just
one environment extended over 50-deg with very low emission which, once scaled
to 70GHz, is equivalent to the CMB B-Mode emission for a tensor-to-scalar
perturbation power ratio r_halo = 3.3 +/- 0.4 x 10^{-3}. Applying a
conservative cleaning procedure, we estimate an r detection limit of $\delta r
\sim 2\times 10^{-3}$ at 70~GHz (3-sigma C.L.) and, assuming a dust polariztion
fraction <12%, $\delta r \sim 1\times 10^{-2}$ at 150~GHz. The 150-GHz limit
matches the goals of planned sub-orbital experiments, which can therefore be
conducted at this high frequency. The 70-GHz limit is close to the goal of
proposed next generation space missions, which thus might not strictly require
space-based platforms. |
Efficient gravitational lens optical scalars calculation of black holes
with angular momentum: We provide new very simple and compact expressions for the efficient
calculation of gravitational lens optical scalars for Kerr spacetime which are
exact along any null geodesic. These new results are obtained recurring to well
known results on geodesic motion that exploit obvious and hidden symmetries of
Kerr spacetime and contrast with the rather long and cumbersome expressions
previously reported in the literature, providing a helpful improvement for the
sake of an efficient integration of the geodesic deviation equation on Kerr
geometry. We also introduce a prescription for the observer frame which
captures a new notion of \emph{center of the black hole} which can be used for
any position of the observer, including those near the black hole. We compare
the efficient calculation of weak lens optical scalars with the exact
equations; finding an excellent agreement. | Disentangling the stellar populations in the counter-rotating disc
galaxy NGC 4550: In order to try and understand its origins, we present high-quality long-slit
spectral observations of the counter-rotating stellar discs in the strange S0
galaxy NGC 4550. We kinematically decompose the spectra into two
counter-rotating stellar components (plus a gaseous component), in order to
study both their kinematics and their populations. The derived kinematics
largely confirm what was known previously about the stellar discs, but trace
them to larger radii with smaller errors; the fitted gaseous component allows
us to trace the hydrogen emission lines for the first time, which are found to
follow the same rather strange kinematics previously seen in the [OIII] line.
Analysis of the populations of the two separate stellar components shows that
the secondary disc has a significantly younger mean age than the primary disc,
consistent with later star formation from the associated gaseous material. In
addition, the secondary disc is somewhat brighter, also consistent with such
additional star formation. However, these measurements cannot be
self-consistently modelled by a scenario in which extra stars have been added
to initially-identical counter-rotating stellar discs, which rules out Evans &
Collett's (1994) elegant "separatrix-crossing" model for the formation of such
massive counter-rotating discs from a single galaxy, leaving some form of
unusual gas accretion history as the most likely formation mechanism. |
CMB lensing and primordial non-Gaussianity: We study the effects of gravitational lensing on the estimation of
non-Gaussianity from the bispectrum of the cosmic microwave background (CMB)
temperature anisotropies. We find that the effect of lensing on the bispectrum
may qualitatively be described as a smoothing of the acoustic features
analogous to the temperature power spectrum. In contrast to previous results,
for a Planck-like experiment which is cosmic-variance limited to L=2000, we
find that lensing causes no significant degradation of our ability to constrain
the non-Gaussianity amplitude fNL for both local and equilateral
configurations, provided that the biases due to the cross correlation between
the lensing potential and the integrated-Sachs-Wolfe (ISW) contribution to the
CMB temperature are adequately understood. With numerical simulations, we also
verify that low-order Taylor approximations to the lensed bispectrum and
ISW-lensing biases are accurate. | Tightening geometric and dynamical constraints on dark energy and
gravity: galaxy clustering, intrinsic alignment and kinetic
Sunyaev-Zel'dovich effect: Conventionally, in galaxy surveys, cosmological constraints on the growth and
expansion history of the universe have been obtained from the measurements of
redshift-space distortions and baryon acoustic oscillations embedded in the
large-scale galaxy density field. In this paper, we study how well one can
improve the cosmological constraints from the combination of the galaxy density
field with velocity and tidal fields, which are observed via the kinetic
Sunyaev-Zel'dovich (kSZ) and galaxy intrinsic alignment (IA) effects,
respectively. For illustration, we consider the deep galaxy survey by Subaru
Prime Focus Spectrograph, whose survey footprint perfectly overlaps with the
imaging survey of the Hyper Suprime-Cam and the CMB-S4 experiment. We find that
adding the kSZ and IA effects significantly improves cosmological constraints,
particularly when we adopt the non-flat cold dark matter model which allows
both time variation of the dark energy equation-of-state and deviation of the
gravity law from general relativity. Under this model, we achieve $31\%$
improvement for the growth index $\gamma$ and $>35\%$ improvement for other
parameters except for the curvature parameter, compared to the case of the
conventional galaxy-clustering-only analysis. As another example, we also
consider the wide galaxy survey by the {\it Euclid} satellite, in which shapes
of galaxies are noisier but the survey volume is much larger. We demonstrate
that when the above model is adopted, the clustering analysis combined with kSZ
and IA from the deep survey can achieve tighter cosmological constraints than
the clustering-only analysis from the wide survey. |
Imprints of a hemispherical power asymmetry in the seven-year WMAP data
due to non-commutativity of space-time: Non-commutative geometry at inflation can give arise to parity violating
modulations of the primordial power spectrum. We develop the statistical tools
needed for investigating whether these modulations are evident in the Cosmic
Microwave Background (CMB). The free parameters of the models are two
directional parameters (theta,phi), the signal amplitude A*, and a tilt
parameter n* that modulates correlation power on different scales. The
signature of the model corresponds to a kind of hemispherical power asymmetry.
When analyzing the 7-year WMAP data we find a weak signature for a preferred
direction in the Q-, V-, and W bands with direction (l,b) = (-225 deg,-25 deg)
+- (20 deg, 20 deg), which is close to another previously discovered
hemispherical power asymmetry. Although these results are intriguing, the
significance of the detection in the W-, V- and Q-bands are nonzero at about 2
sigma, suggesting that the simplest parameterization of the leading correction
represents only partially the effects of the space-time non-commutativity
possibly responsible for the hemispherical asymmetry. Our constraints on the
presence of a dipole are independent of its physical origin and prefer a
blue-tilted spectral index n* ~ 0 with the amplitude A* ~ 0.18. | The MUSIC of Galaxy Clusters I: Baryon properties and Scaling Relations
of the thermal Sunyaev-Zel'dovich Effect: We introduce the Marenostrum-MultiDark SImulations of galaxy Clusters (MUSIC)
Dataset, one of the largest sample of hydrodynamically simulated galaxy
clusters with more than 500 clusters and 2000 groups. The objects have been
selected from two large N-body simulations and have been resimulated at high
resolution using SPH together with relevant physical processes (cooling, UV
photoionization, star formation and different feedback processes). We focus on
the analysis of the baryon content (gas and star) of clusters in the MUSIC
dataset both as a function of aperture radius and redshift. The results from
our simulations are compared with the most recent observational estimates of
the gas fraction in galaxy clusters at different overdensity radii. When the
effects of cooling and stellar feedbacks are included, the MUSIC clusters show
a good agreement with the most recent observed gas fractions quoted in the
literature. A clear dependence of the gas fractions with the total cluster mass
is also evident. The impact of the aperture radius choice, when comparing
integrated quantities at different redshifts, is tested: the standard
definition of radius at a fixed overdensity with respect to critical density is
compared with a definition based on the redshift dependent overdensity with
respect to background density. We also present a detailed analysis of the
scaling relations of the thermal SZ (Sunyaev Zel'dovich) Effect derived from
MUSIC clusters. The integrated SZ brightness, Y, is related to the cluster
total mass, M, as well as, the M-Y counterpart, more suitable for observational
applications. Both laws are consistent with predictions from the self-similar
model, showing a very low scatter. The effects of the gas fraction on the Y-M
scaling and the presence of a possible redshift dependence on the Y-M scaling
relation are also explored. |
Local Tadpole Galaxies: Tadpole galaxies have a giant star-forming region at the end of an elongated
intensity distribution. Here we use SDSS data to determine the ages, masses,
and surface densities of the heads and tails in 14 local tadpoles selected from
the Kiso and Michigan surveys of UV-bright galaxies, and we compare them to
tadpoles previously studied in the Hubble Ultra Deep Field. The young stellar
mass in the head scales linearly with restframe galaxy luminosity, ranging from
~10^5 M_solar at galaxy absolute magnitude U=-13 mag to 10^9 M_solar at U=-20
mag. The corresponding head surface density increases from several M_solar
pc^{-2} locally to 10-100 M_solar pc^{-2} at high redshift, and the star
formation rate per unit area in the head increases from ~0.01 M_solar yr^{-1}
kpc^{-2} locally to ~1 M_solar yr^{-1} kpc^{-2} at high z. These local values
are normal for star-forming regions, and the increases with redshift are
consistent with other cosmological star formation rates, most likely reflecting
an increase in gas abundance. The tails in the local sample look like
bulge-free galaxy disks. Their photometric ages decrease from several Gyr to
several hundred Myr with increasing z, and their surface densities are more
constant than the surface densities of the heads. The far outer intensity
profiles in the local sample are symmetric and exponential. We suggest that
most local tadpoles are bulge-free galaxy disks with lopsided star formation,
perhaps from environmental effects such as ram pressure or disk impacts, or
from a Jeans length comparable to half the disk size. | Gravitational lensing evidence against extended dark matter halos: It is generally thought that galaxies are embedded in dark matter halos
extending well beyond their luminous matter. The existence of these galactic
halos is mainly derived from the larger than expected velocities of stars and
gas in the outskirts of spiral galaxies. Much less is known about dark matter
around early-type (elliptical or lenticular) galaxies. We use gravitational
lensing to derive the masses of early-type galaxies deflecting light of
background quasars. This provides a robust measurement of the total mass within
the Einstein ring, a circle whose diameter is comparable to the separation of
the different quasar images. We find that the mass-to-light ratio of the
lensing galaxies does not depend on radius, from inner galactic regions out to
several half-light radii. Moreover, its value does not exceed the value
predicted by stellar population models by more than a factor two, which may be
explained by baryonic dark matter alone, without any need for exotic matter.
Our results thus suggest that, if dark matter is present in early-type
galaxies, its amount does not exceed the amount of luminous matter and its
density follows that of luminous matter, in sharp contrast to what is found
from rotation curves of spiral galaxies. |
Cosmological Model with a Local Void: New Supernova Constraints: A simple inhomogeneous cosmological model with a local void is constrained
with the latest Union supernova compilation. To fit the supernova data, a large
local void on the scales of 1 Gpc is found, contrary to the small scales of 200
Mpc in the previous finding. A more realistic inhomogeneous cosmological model
may be required to fit the supernova data. Alternatively, a clumpy universe
with clumpiness parameter < 1 can fit the supernova data with reduced local
void scales. | Gravitational Waves produced by Compressible MHD Turbulence from
Cosmological Phase Transitions: We calculate the gravitational wave spectrum produced by magneto-hydrodynamic
turbulence in a first order phase transitions. We focus in particular on the
role of decorrelation of incompressible (solenoidal) homogeneous isotropic
turbulence, which is dominated by the sweeping effect. The sweeping effect
describes that turbulent decorrelation is primarily due to the small scale
eddies being swept with by large scale eddies in a stochastic manner. This
effect reduces the gravitational wave signal produced by incompressible MHD
turbulence by around an order of magnitude compared to previous studies.
Additionally, we find a more complicated dependence for the spectral shape of
the gravitational wave spectrum on the energy density sourced by solenoidal
modes (magnetic and kinetic). The high frequency tail follows either a
$k^{-5/3}$ or a $k^{-8/3}$ power law for large and small solenoidal turbulence
density parameter, respectively. Further, magnetic helicity tends to increase
the gravitational wave energy at low frequencies. Moreover, we show how
solenoidal modes might impact the gravitational wave spectrum from dilatational
modes e.g. sound waves. We find that solenoidal modes greatly affect the shape
of the gravitational wave spectrum due to the sweeping effect on the
dilatational modes. For a high velocity flow, one expects a $k^{-2}$ high
frequency tail, due to sweeping. In contrast, for a low velocity flow and a
sound wave dominated flow, we expect a $k^{-3}$ high frequency tail. If neither
of these limiting cases is realized, the gravitational wave spectrum may be a
broken power law with index between -2 and -3, extending up to the frequency at
which the source is damped by viscous dissipation. |
Can $f(R)$ gravity relieve $H_0$ and $σ_8$ tensions?: To investigate whether $f(R)$ gravity can relieve current $H_0$ and
$\sigma_8$ tensions, we constrain the Hu-Sawicki $f(R)$ gravity with
Planck-2018 cosmic microwave background and redshift space distortions
observations. We find that this model fails to relieve both $H_0$ and
$\sigma_8$ tensions, and that its two typical parameters $\log_{10}f_{R0}$ and
$n$ are insensitive to other cosmological parameters. Combining the cosmic
microwave background, baryon acoustic oscillations, Type Ia supernovae, cosmic
chronometers with redshift space distortions observations, we give our best
constraint $\log_{10}f_{R0}<-6.75$ at the $2\sigma$ confidence level. | Galaxy Zoo: Dust in Spirals: We investigate the effect of dust on spiral galaxies by measuring the
inclination-dependence of optical colours for 24,276 well-resolved SDSS
galaxies visually classified in Galaxy Zoo. We find clear trends of reddening
with inclination which imply a total extinction from face-on to edge-on of 0.7,
0.6, 0.5 and 0.4 magnitudes for the ugri passbands. We split the sample into
"bulgy" (early-type) and "disky" (late-type) spirals using the SDSS fracdeV (or
f_DeV) parameter and show that the average face-on colour of "bulgy" spirals is
redder than the average edge-on colour of "disky" spirals. This shows that the
observed optical colour of a spiral galaxy is determined almost equally by the
spiral type (via the bulge-disk ratio and stellar populations), and reddening
due to dust. We find that both luminosity and spiral type affect the total
amount of extinction, with "disky" spirals at M_r ~ -21.5 mags having the most
reddening. This decrease of reddening for the most luminous spirals has not
been observed before and may be related to their lower levels of recent star
formation. We compare our results with the latest dust attenuation models of
Tuffs et al. We find that the model reproduces the observed trends reasonably
well but overpredicts the amount of u-band attenuation in edge-on galaxies. We
end by discussing the effects of dust on large galaxy surveys and emphasize
that these effects will become important as we push to higher precision
measurements of galaxy properties and their clustering. |
Probing recent star formation with absorption-line strengths in
hierarchical models and observations: Stellar population parameters derived from spectral line-strengths provide a
powerful probe of galaxy properties and formation histories. We implement the
machinery for extracting single-stellar-population-equivalent stellar
population parameters from synthetic spectra generated by a hierarchical galaxy
formation model. We find that the SSP-equivalent age is related to the
light-weighted age in a complicated fashion that reflects the influence of
recently-formed stars and is poorly correlated with the mass-weighted age. The
tendency for SSP-equivalent ages to be biased young means that archaeological
downsizing overstates the mass-weighted downsizing in age with mass. We find
that the SSP-equivalent metallicity closely tracks the mass- and light-weighted
metallicities, so that observed mass--metallicity relations for old galaxies
closely reflect the underlying trends. We construct mock catalogues of
early-type galaxies in a Coma cluster-sized halo and compare them directly to
observations of early-type galaxies in the Coma cluster. The similarity of the
SSP-equivalent ages in the observational samples and the mock catalogues gives
us confidence that the star-formation quenching implemented in the hierarchical
galaxy formation model produces roughly the correct amount of recent star
formation. The SSP-equivalent metallicities are however too low and have the
wrong slope as a function of velocity dispersion, and the SSP-equivalent ages
of the model galaxies may have an incorrect slope as a function of velocity
dispersion. (Abridged) | Slaying Axion-Like Particles via Gravitational Waves and Primordial
Black Holes from Supercooled Phase Transition: We study the formation of primordial black holes (PBHs) from density
fluctuations due to supercooled phase transitions (PTs) triggered in an
axion-like particle (ALP) model. We find that the mass of the PBHs is inversely
correlated with the ALP decay constant $f_a$. For instance, for $f_a$ varying
from ${\cal O}$(100 MeV) to ${\cal O}$($10^{12}$ GeV), the PBH mass varies
between $(10^{3} - 10^{-24}) M_{\odot}$. We then identify the ALP parameter
space where the PBH can account for the entire (or partial) dark matter
fraction of the Universe, in a single (multi-component) dark matter scenario,
with the ALP being the other dark matter candidate. The PBH parameter space
ruled out by current cosmological and microlensing observations can thus be
directly mapped onto the ALP parameter space, thus providing new bounds on
ALPs, complementary to the laboratory and astrophysical ALP constraints.
Similarly, depending on the ALP couplings to other Standard Model particles,
the ALP constraints on $f_a$ can be translated into a lower bound on the PBH
mass scale. Moreover, the supercooled PT leads to a potentially observable
stochastic gravitational wave (GW) signal at future GW observatories, such as
aLIGO, LISA and ET, that acts as another complementary probe of the ALPs, as
well as of the PBH dark matter. Finally, we show that the recent NANOGrav
signal of stochastic GW in the nHz frequency range can be explained in our
model with $f_a\simeq (10~{\rm GeV}-1~{\rm TeV})$. |
Spot the difference. Impact of different selection criteria on observed
properties of passive galaxies in zCOSMOS 20-k sample: We present the analysis of photometric, spectroscopic, and morphological
properties for differently selected samples of passive galaxies up to z=1
extracted from the zCOSMOS-20k spectroscopic survey. This analysis intends to
explore the dependence of galaxy properties on the selection criterion adopted,
study the degree of contamination due to star-forming outliers, and provide a
comparison between different commonly used selection criteria. We extracted
from the zCOSMOS-20k catalog six different samples of passive galaxies, based
on morphology, optical colors, specific star-formation rate, a best fit to the
observed spectral energy distribution, and a criterion that combines
morphological, spectroscopic, and photometric information. The morphological
sample has the higher percentage of contamination in colors, specific star
formation rate and presence of emission lines, while the red & passive ETGs
sample is the purest, with properties mostly compatible with no star formation
activity; however, it is also the less economic criterion in terms of
information used. The best performing among the other criteria are the red SED
and the quiescent ones, providing a percentage of contamination only slightly
higher than the red & passive ETGs criterion (on average of a factor of ~2) but
with absolute values of the properties of contaminants still compatible with a
red, passively evolving population. We also provided two revised definitions of
early type galaxies based on restframe color-color and color-mass criteria,
that better reproduce the observed bimodalities. The analysis of the number
densities shows evidences of mass-assembly downsizing, with galaxies at
10.25<log(M/Msun)<10.75 increasing their number by a factor ~2-4 from z=0.6 to
z=0.2, by a factor ~2-3 from z=1 to z=0.2 at 10.75<log(M/Msun)<11, and by only
~10-50% from z=1 to z=0.2 at 11<log(M/Msun)<11.5. | On the electron temperatures in high-metallicity HII regions: The electron temperatures of high-metallicity (12+log(O/H) > 8.2) HII regions
have been studied. The empirical ff relations which express the nebular-to-
auroral [OIII] line ratio Q_3,O (as well as the nebular-to-auroral [OII] line
ratio Q_2,O, and the nebular-to-auroral [NII] line ratio Q_2,N) in terms of the
nebular R_3 and R_2 line fluxes in spectra of high-metallicity HII regions are
derived, and the electron temperatures t_3,O, t_2,O, and t_2,N in a number of
extragalactic HII regions are also determined. Furthermore, the t_2 - t_3
diagram is discussed. It is found that there is a one-to-one correspondence
between t_2 and t_3 electron temperatures for HII regions with a weak nebular
R_3 lines (logR_ < 0.5). The derived t_2,N - t_3,O relation for these HII
regions is similar to commonly used t_2 - t_3 relations. The HII regions with a
strong nebular R_3 line flux (logR_3 > 0.5) do not follow this relation. A
discrepancy between t_2,N and t_2,O temperatures is found, being the t_2,N
temperatures systematically lower than t_2,O ones. The differences are small at
low electron temperatures and increases with increasing electron temperatures
up to 10% at t=1. The uncertainties in the atomic data may be the cause of this
discrepancy. |
Numerical approaches to star formation and SuperNovae energy feedback in
simulations of galaxy clusters: The goal of this work is to to investigate different numerical approaches and
to introduce a new, physically-based sub-grid model for the ISM physics,
including a treatment of star formation and Type II supernovae energy feedback
(MUPPI, MUlti-Phase Particle Integrator). Our model follows the ISM physics
using a system of ordinary differential equations, describing mass and energy
flows among the different gas phases in the ISM inside each gas particle. The
model also includes the treatment of SNe energy transfer from star-forming
particles to their neighbours. We will show in this Thesis how this model is
able to reproduce observed ISM properties, while also providing an effective
thermal energy feedback and responding to variations in the local
hydrodynamical properties of the gas, e.g. crossing of a spiral density wave in
a galaxy disk. We believe the model we presented here will be particularly
useful in cosmological simulations of formation and evolution of isolated
galaxies and galaxy clusters. For this reason, the first application of the
present Ph.D. work will therefore be to apply MUPPI to cosmological
simulations, with the aim of determine how an improved treatment of star
formation and feedback astrophysical processes impacts on many open issues,
from the properties of simulated disk galaxies to the properties of cold
baryons (galaxies and diffuse stellar component) in galaxy clusters, to the
properties of the Intra-Cluster Medium in presence of an effective supernovae
thermal feedback. | Removing the Impact of Correlated PSF Uncertainties in Weak Lensing: Accurate reconstruction of the spatial distributions of the Point Spread
Function (PSF) is crucial for high precision cosmic shear measurements.
Nevertheless, current methods are not good at recovering the PSF fluctuations
of high spatial frequencies. In general, the residual PSF fluctuations are
spatially correlated, therefore can significantly contaminate the correlation
functions of the weak lensing signals. We propose a method to correct for this
contamination statistically, without any assumptions on the PSF and galaxy
morphologies or their spatial distribution. We demonstrate our idea with the
data from the W2 field of CFHTLenS. |
Formation of slowly rotating early-type galaxies via major mergers: a
Resolution Study: We study resolution effects in numerical simulations of gas-rich and gas-poor
major mergers, and show that the formation of slowly-rotating elliptical
galaxies often requires a resolution that is beyond the present-day standards
to be properly modelled. Our sample of equal-mass merger models encompasses
various masses and spatial resolutions, ranging from about 200pc and 10^5
particles per component, typical of some recently published major merger
simulations, to up to 32pc and 10^3 M_sun in simulations using 2.4 x 10^7
collisionless particles and 1.2 x 10^7 gas particles, among the highest
resolutions reached so far for gas-rich major merger of massive disc galaxies.
We find that the formation of fast-rotating early-type galaxies, that are
flattened by a significant residual rotation, is overall correctly reproduced
at all such resolutions. However, the formation of slow-rotating early-type
galaxies, which have a low residual angular momentum and are supported mostly
by anisotropic velocity dispersions, is strongly resolution-dependent. The
evacuation of angular momentum from the main stellar body is largely missed at
standard resolution, and systems that should be slow rotators are then found to
be fast rotators. The effect is most important for gas-rich mergers, but is
also witnessed in mergers with an absent or modest gas component. The effect is
robust with respect to our initial conditions and interaction orbits, and
originates in the physical treatment of the relaxation process during the
coalescence of the galaxies. Our findings show that a high-enough resolution is
required to accurately model the global properties of merger remnants and the
evolution of their angular momentum. The role of gas-rich mergers of spiral
galaxies in the formation of slow-rotating ellipticals may therefore have been
underestimated. | Constraints on the redshift evolution of astrophysical feedback with
Sunyaev-Zeldovich effect cross-correlations: An understanding of astrophysical feedback is important for constraining
models of galaxy formation and for extracting cosmological information from
current and future weak lensing surveys. The thermal Sunyaev-Zel'dovich effect,
quantified via the Compton-$y$ parameter, is a powerful tool for studying
feedback, because it directly probes the pressure of the hot, ionized gas
residing in dark matter halos. Cross-correlations between galaxies and maps of
Compton-$y$ obtained from cosmic microwave background surveys are sensitive to
the redshift evolution of the gas pressure, and its dependence on halo mass. In
this work, we use galaxies identified in year one data from the Dark Energy
Survey and Compton-$y$ maps constructed from Planck observations. We find
highly significant (roughly $12\sigma$) detections of galaxy-$y$
cross-correlation in multiple redshift bins. By jointly fitting these
measurements as well as measurements of galaxy clustering, we constrain the
halo bias-weighted, gas pressure of the Universe as a function of redshift
between $0.15 \lesssim z \lesssim 0.75$. We compare these measurements to
predictions from hydrodynamical simulations, allowing us to constrain the
amount of thermal energy in the halo gas relative to that resulting from
gravitational collapse. |
Shortcomings of New Parametrizations of Inflation: In the hope of avoiding model dependence of the cosmological observables,
phenomenological parametrizations of Cosmic Inflation have recently been
proposed. Typically, they are expressed in terms of two parameters associated
with an expansion of the inflationary quantities matching the belief that
inflation is characterized by two numbers only, the tensor-to-scalar ratio and
the scalar spectral index. We give different arguments and examples showing
that these new approaches are either not generic or insufficient to make
predictions at the accuracy level needed by the cosmological data. We conclude
that disconnecting inflation from high energy physics and gravity might not be
the most promising way to learn about the physics of the early Universe. | The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey:
BAO and RSD measurements from the anisotropic power spectrum of the Quasar
sample between redshift 0.8 and 2.2: We measure the clustering of quasars of the final data release (DR16) of
eBOSS. The sample contains $343\,708$ quasars between redshifts $0.8\leq
z\leq2.2$ over $4699\,\mathrm{deg}^2$. We calculate the Legendre multipoles
(0,2,4) of the anisotropic power spectrum and perform a BAO and a Full-Shape
(FS) analysis at the effective redshift $z{\rm eff}=1.480$. The errors include
systematic errors that amount to 1/3 of the statistical error. The systematic
errors comprise a modelling part studied using a blind N-Body mock challenge
and observational effects studied with approximate mocks to account for various
types of redshift smearing and fibre collisions. For the BAO analysis, we
measure the transverse comoving distance $D_{\rm M}(z_{\rm eff})/r_{\rm
drag}=30.60\pm{0.90}$ and the Hubble distance $D_{\rm H}(z_{\rm eff})/r_{\rm
drag}=13.34\pm{0.60}$. This agrees with the configuration space analysis, and
the consensus yields: $D_{\rm M}(z_{\rm eff})/r_{\rm drag}=30.69\pm{0.80}$ and
$D_{\rm H}(z_{\rm eff})/r_{\rm drag}=13.26\pm{0.55}$. In the FS analysis, we
fit the power spectrum using a model based on Regularised Perturbation Theory,
which includes Redshift Space Distortions and the Alcock-Paczynski effect. The
results are $D_{\rm M}(z_{\rm eff})/r_{\rm drag}=30.68\pm{0.90}$ and $D_{\rm
H}(z_{\rm eff})/r_{\rm drag}=13.52\pm{0.51}$ and we constrain the linear growth
rate of structure $f(z_{\rm eff})\sigma_8(z_{\rm eff})=0.476\pm{0.047}$. Our
results agree with the configuration space analysis. The consensus analysis of
the eBOSS quasar sample yields: $D_{\rm M}(z_{\rm eff})/r_{\rm
drag}=30.21\pm{0.79}$, $D_{\rm H}(z_{\rm eff})/r_{\rm drag}=3.23\pm{0.47}$ and
$f(z_{\rm eff})\sigma_8(z_{\rm eff})=0.462\pm{0.045}$ and is consistent with a
flat $\Lambda {\rm CDM}$ cosmological model using Planck results. |
Nonlinear Behavior of Baryon Acoustic Oscillations from the Zel'dovich
Approximation Using a Non-Fourier Perturbation Approach: Baryon acoustic oscillations are an excellent technique to constrain the
properties of dark energy in the Universe. In order to accurately characterize
the dark energy equation of state, we must understand the effects of both the
nonlinearities and redshift space distortions on the location and shape of the
acoustic peak. In this paper, we consider these effects using the Zel'dovich
approximation and a novel approach to 2nd order perturbation theory. The second
order term of the Zel'dovich power spectrum is built from convolutions of the
linear power spectrum with polynomial kernels in Fourier space, suggesting that
the corresponding term of the the Zel'dovich correlation function can be
written as a sum of quadratic products of a broader class of correlation
functions, expressed through simple spherical Bessel transforms of the linear
power spectrum. We show how to systematically perform such a computation. We
explicitly prove that our result is the Fourier transform of the Zel'dovich
power spectrum, and compare our expressions to numerical simulations. Finally,
we highlight the advantages of writing the nonlinear expansion in configuration
space, as this calculation is easily extended to redshift space, and the higher
order terms are mathematically simpler than their Fourier counterparts. | Birth, life and survival of Tidal Dwarf Galaxies: Advances on the formation and survival of the so-called Tidal Dwarf Galaxies
(TDGs) are reviewed. The understanding on how objects of the mass of dwarf
galaxies may form in debris of galactic collisions has recently benefited from
the coupling of multi-wavelength observations with numerical simulations of
galaxy mergers. Nonetheless, no consensual scenario has yet emerged and as a
matter of fact the very definition of TDGs remains elusive. Their real
cosmological importance is also a matter of debate, their presence in our Local
Group of galaxies as well. Identifying old, evolved, TDGs among the population
of regular dwarf galaxies and satellites may not be straightforward. However a
number of specific properties (location, dark matter and metal content) that
objects of tidal origin should have are reminded here. Examples of newly
discovered genuine old TDGs around a nearby elliptical galaxy are finally
presented. |
Chandra X-Ray Observations of Two Unusual BAL Quasars: We report sensitive Chandra X-ray non-detections of two unusual, luminous
Iron Low-Ionization Broad Absorption Line Quasars (FeLoBALs). The observations
do detect a non-BAL, wide-binary companion quasar to one of the FeLoBAL
quasars. We combine X-ray-derived column density lower limits (assuming solar
metallicity) with column densities measured from ultraviolet spectra and CLOUDY
photoionization simulations to explore whether constant density slabs at broad
line region densities can match the physical parameters of these two BAL
outflows, and find that they cannot. In the "overlapping-trough" object SDSS
J0300+0048, we measure the column density of the X-ray absorbing gas to be N_H
>= 1.8 x 1024 cm-2. From the presence of Fe II UV78 absorption but lack of Fe
II UV195/UV196 absorption, we infer the density in that part of the absorbing
region to be n_e ~ 106 cm-3. We do find that a slab of gas at that density
might be able to explain this object's absorption. In the Fe III-dominant
object SDSS J2215-0045, the X-ray absorbing column density of N_H >= 3.4 x 1024
cm-2 is consistent with the Fe III-derived N_H >= 2 x 1022 cm-2 provided the
ionization parameter is log U > 1.0 for both the n_e = 1011 cm-3 and n_e = 1012
cm-3 scenarios considered (such densities are required to produce Fe III
absorption without Fe II absorption). However, the velocity width of the
absorption rules out its being concentrated in a single slab at these
densities. Instead, this object's spectrum can be explained by a low density,
high ionization and high temperature disk wind that encounters and ablates
higher density, lower ionization Fe III-emitting clumps. | Accurate field-level weak lensing inference for precision cosmology: We present $\texttt{Miko}$, a catalog-to-cosmology pipeline for general
flat-sky field-level inference, which provides access to cosmological
information beyond the two-point statistics. In the context of weak lensing, we
identify several new field-level analysis systematics (such as aliasing,
Fourier mode-coupling, and density-induced shape noise), quantify their impact
on cosmological constraints, and correct the biases to a percent level. Next,
we find that model mis-specification can lead to both absolute bias and
incorrect uncertainty quantification for the inferred cosmological parameters
in realistic simulations. The Gaussian map prior infers unbiased cosmological
parameters, regardless of the true data distribution, but it yields
over-confident uncertainties. The log-normal map prior quantifies the
uncertainties accurately, although it requires careful calibration of the shift
parameters for unbiased cosmological parameters. We demonstrate systematics
control down to the $2\%$ level for both models, making them suitable for
ongoing weak lensing surveys. |
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