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What is the Halo Mass Function in a Fuzzy Dark Matter Cosmology?: Fuzzy dark matter (FDM) or wave dark matter is an alternative theory designed
to solve the small-scale problems faced by the standard cold dark matter
proposal for the primary material component of the universe. It is made up of
ultra-light axions having mass $\sim 10^{-22}$ eV that typically have de
Broglie wavelength of several kpc, alleviating some of the apparent small-scale
discrepancies faced by the standard $\Lambda$CDM paradigm. In this paper, we
calculate the halo mass function for the fuzzy dark matter using a sharp-k
window function and compare it with one calculated using numerical simulations,
finding the peak mass at roughly $10^{10} {M_{\odot}}$ for a particle mass of
$2\times 10^{-22}$ eV. We also constrain the mass of FDM particle to be
$\gtrapprox 2\times10^{-22}$ eV using the observations of high-redshift ($z\sim
10$) lensed galaxies from CLASH survey. | Preparation to the CMB PLANCK data analysis, estimation of the
contamination due to the galactic polarized emissions: This work is point of the preparation to the analysis of the PLANCK satellite
data. The PLANCK satellite is an ESA mission which has been launched the 14th
of may 2009 and is dedicaced to the measurement of the Cosmic Microwave
Background (CMB) in temperature and polarization. The presence of diffuse
Galactic polarized emissions disturb the measurement of the CMB anisotropies,
in particular in polarization. Therefore a precise knowledge of these emissions
is needed to obtain the level of accuracy required for PLANCK. In this context,
we have developed and implemented a coherent 3D model of the two mains
polarized Galactic emissions : synchrotron and thermal dust. We have compared
these models to preexisting data: the 23 GHz band of the WMAP data, the 353 GHz
Archeops data and the 408 MHz all-sky continuum survey. We extrapolate these
models to the frequencies where the CMB dominates and we are able to estimate
the contribution of polarized foreground emissions to the polarized CMB
emission measured with PLANCK. |
A Primeval Magellanic Stream and Others: The Magellanic Stream might have grown out of tidal interactions at high
redshift, when the young galaxies were close together, rather than from later
interactions among the Magellanic Clouds and Milky Way. This is illustrated in
solutions for the orbits of Local Group galaxies under the cosmological
condition of growing peculiar velocities at high redshift. Massless test
particles initially near and moving with the Large Magellanic Cloud in these
solutions end up with distributions in angular position and redshift similar to
the Magellanic Stream, though with the usual overly prominent leading component
that the Milky Way corona might have suppressed. Another possible example of
the effect of conditions at high redshift is a model primeval stream around the
Local Group galaxy NGC 6822. Depending on the solution for Local Group dynamics
this primeval stream can end up with position angle similar to the HI around
this galaxy, and a redshift gradient in the observed direction. The gradient is
much smaller than observed, but might have been increased by dissipative
contraction. Presented also is an even more speculative illustration of the
possible effect of initial conditions, primeval stellar streams around M31. | The Ionized Absorber and Nuclear Environment of IRAS 13349+2438:
Multi-wavelength insights from coordinated Chandra HETGS, HST STIS, HET, and
Spitzer IRS: We present results from a coordinated IR-to-X-ray spectral campaign of the
QSO IRAS 13349+2438. Optical spectra reveal extreme Eigenvector-1
characteristics, but the H-beta line width argues against a NLS1
classification; we refine z=0.10853 based on [O III]. We estimate a BH
mass=10^9 Msun using 2 independent methods (H-beta line width & SED fits).
Blue-shifted absorption (-950km/s & -75km/s) is seen for the 1st time in STIS
UV spectra from Ly-alpha, NV, & CIV. The higher velocity UV lines are
coincident with the lower-ionisation (xi~1.6) X-ray warm absorber lines. A
dusty multiple ionization absorber blueshifted by 700-900km/s is required to
fit the X-ray data. Theoretical models comparing different ionising SEDs reveal
that a UV-inclusive (i.e., the accretion disc) ionising continuum strongly
impacts conclusions for the thermodynamic stability of the warm absorber.
Specific to IRAS13349, an Xray-UV ionising SED favors a continuous distribution
of ionisation states in a smooth flow (this paper), versus discrete clouds in
pressure equilibrium (work by others where UV is omitted). Direct dust
detections are seen in both the IR: PAH emission at (7.7 & 11.3)micron which
may also be blended with forsterite, and (10 & 18)micron silicate emission, and
X-rays: iron dust with a dust-to-gas ratio > 90%. We develop a geometrical
model whereby the QSO nuclear region is viewed through the upper atmosphere of
an obscuring torus. This sight line is obscured by dust that blocks a direct
view of the UV/optical emission region but is largely transparent in X-rays
since the gas is ionised. In our model, 20% of the intrinsic UV/optical
continuum is scattered into our sight line by the far wall of an obscuring
torus. An additional 2.4% of the direct light, which likely dominates the UV
emission, is Thomson-scattered into our line-of-sight by another off-plane
component of highly ionized gas. |
A Global ILC Approach in Pixel Space over Large Angular Scales of the
Sky using CMB Covariance Matrix: We propose a new internal linear combination (ILC) method in the pixel space,
applicable on large angular scales of the sky, to estimate a foreground
minimized Cosmic Microwave Background (CMB) temperature anisotropy map by
incorporating prior knowledge about the theoretical CMB covariance matrix.
Usual ILC method in pixel space, on the contrary, does not use any information
about the underlying CMB covariance matrix. The new approach complements the
usual pixel space ILC technique specifically at low multipole region, using
global information available from theoretical CMB covariance matrix as well as
from the data. Since we apply our method over the large scale on the sky
containing low multipoles we perform foreground minimization globally. We apply
our methods on low resolution Planck and WMAP foreground contaminated CMB maps
and validate the methodology by performing detailed Monte-Carlo simulations.
Our cleaned CMB map and its power spectrum have significantly less error than
those obtained following usual ILC technique at low resolution that does not
use CMB covariance information. Another very important advantage of our method
is that the cleaned power spectrum does not have any negative bias at the low
multipoles because of effective suppression of CMB-foreground chance
correlations on large angular scales of the sky. Our cleaned CMB map and its
power spectrum match well with those estimated by other research groups. | A close examination of cosmic microwave background mirror-parity after
Planck: Previous claims of significant evidence for mirror-parity in the large-scale
cosmic microwave background (CMB) data from the Wilkinson Microwave Anisotropy
Probe (WMAP) experiment have been recently echoed in the first study of
isotropy and statistics of CMB data from Planck. We revisit these claims with a
careful analysis of the latest data available. We construct statistical
estimators in both harmonic and pixel space, test them on simulated data with
and without mirror-parity symmetry, apply different Galactic masks, and study
the dependence of the results on arbitrary choices of free parameters. We
confirm that the data exhibit evidence for odd mirror-parity at a significance
which reaches as high as ~ 99 per cent C.L., under some circumstances. However,
given the inherent biases in the pixel-based statistic and the dependence of
both pixel and harmonic space statistics on the particular form of Galactic
masking and other a-posteriori choices, we conclude that these results are not
in significant tension with the predictions of the concordance cosmological
model. |
Multi-wavelength observations of a rich galaxy cluster at z ~ 1: the
HST/ACS colour-magnitude diagram: XMMU J1229+0151 is a rich galaxy cluster with redshift z=0.975, that was
serendipitously detected in X-rays within the scope of the XMM-Newton Distant
Cluster Project. HST/ACS observations in the i775 and z850 passbands, as well
as VLT/FORS2 spectroscopy were further obtained, in addition to follow-up
Near-Infrared (NIR) imaging in J- and Ks-bands with NTT/SOFI. We investigate
the photometric, structural and spectral properties of the early-type galaxies
in the high-redshift cluster XMMU J1229+0151. Source detection and aperture
photometry are performed in the optical and NIR imaging. Galaxy morphology is
inspected visually and by means of Sersic profile fitting to the 21
spectroscopically confirmed cluster members in the ACS field of view. The
i775-z850 colour-magnitude relation (CMR) is derived with a method based on
galaxy magnitudes obtained by fitting the surface brightness of the galaxies
with Sersic models. The i775-z850 CMR of the spectroscopic members shows a very
tight red-sequence with a zero point of 0.86+-0.04 mag and intrinsic scatter
equal to 0.039 mag. The CMR obtained with the galaxy models has similar
parameters. Stellar masses and formation ages of the cluster galaxies are
derived by fitting the observed spectral energy distributions (SED) with models
based on Bruzual & Charlot 2003. We obtain a star formation weighted age of 4.3
Gyr for a median mass of 7.4e10 Msun. Instead of an unambiguous brightest
cluster galaxy (BCG), we find three bright galaxies with a similar z850
magnitude, which are, in addition, the most massive cluster members, with ~
2e11 Msun. Our results strengthen the current evidence for a lack of
significant evolution of the scatter and slope of the red-sequence out to z~1. | Gravothermal collapse of isolated self-interacting dark matter haloes:
N-body simulation versus the fluid model: Self-Interacting Dark Matter (SIDM) is a collisional form of cold dark matter
(CDM), originally proposed to solve problems that arose when the collisionless
CDM theory of structure formation was compared with observations of galaxies on
small scales. The quantitative impact of the proposed elastic collisions on
structure formation has been estimated previously by Monte Carlo N-body
simulations and by a conducting fluid model, with apparently diverging results.
To improve this situation, we make direct comparisons between new Monte Carlo
N-body simulations and solutions of the conducting fluid model, for isolated
SIDM haloes of fixed mass. This allows us to separate cleanly the effects of
gravothermal relaxation from those of continuous mass accretion in an expanding
background universe. When these two methods were previously applied to halo
formation with cosmological boundary conditions, they disagreed by an order of
magnitude about the size of the scattering cross section required to solve the
so-called 'cusp-core problem.' We show here, however, that the methods agree
with each other within 20 per cent for isolated haloes. This suggests that the
two methods are consistent, and that their disagreement for cosmological haloes
is not caused by a breakdown of their validity.
The isolated haloes studied here undergo gravothermal collapse. We compare
the solutions calculated by these two methods for gravothermal collapse
starting from several initial conditions. This allows us to calibrate the heat
conduction which accounts for the effect of elastic hard-sphere scattering in
the fluid model. The amount of tuning of the thermal conductivity parameters
required to bring the two methods into close agreement for isolated haloes,
however, is too small to explain the discrepancy found previously in the
cosmological context. |
Using Host Galaxy Spectroscopy to Explore Systematics in the
Standardisation of Type Ia Supernovae: We use stacked spectra of the host galaxies of photometrically identified
type Ia supernovae (SNe Ia) from the Dark Energy Survey (DES) to search for
correlations between Hubble diagram residuals and the spectral properties of
the host galaxies. Utilising full spectrum fitting techniques on stacked
spectra binned by Hubble residual, we find no evidence for trends between
Hubble residuals and properties of the host galaxies that rely on spectral
absorption features ($< 1.3\sigma$), such as stellar population age,
metallicity, and mass-to-light ratio. However, we find significant trends
between the Hubble residuals and the strengths of [OII] ($4.4\sigma$) and the
Balmer emission lines ($3\sigma$). These trends are weaker than the well known
trend between Hubble residuals and host galaxy stellar mass ($7.2\sigma$) that
is derived from broad band photometry. After light curve corrections, we see
fainter SNe Ia residing in galaxies with larger line strengths. We also find a
trend (3$\sigma$) between Hubble residual and the Balmer decrement (a measure
of reddening by dust) using H${\beta}$ and H${\gamma}$. The trend, quantified
by correlation coefficients, is slightly more significant in the redder SNe Ia,
suggesting that bluer SNe Ia are relatively unaffected by dust in the
interstellar medium of the host and that dust contributes to current Hubble
diagram scatter impacting the measurement of cosmological parameters. | Primordial black holes from single-field inflation: a fine-tuning audit: All single-field inflationary models invoke varying degrees of tuning in
order to account for cosmological observations. Mechanisms that generate
primordial black holes (PBHs) from enhancement of primordial power at small
scales posit inflationary potentials that transiently break scale invariance
and possibly adiabaticity over a range of modes. This requires additional
tuning on top of that required to account for observations at scales probed by
cosmic microwave background (CMB) anisotropies. In this paper we study the
parametric dependence of various single-field models of inflation that enhance
power at small scales and quantify the degree to which coefficients in the
model construction have to be tuned in order for certain observables to lie
within specified ranges. We find significant tuning: changing the parameters of
the potentials by between one part in a hundred and one part in $10^8$
(depending on the model) is enough to change the power spectrum peak amplitude
by an order one factor. The fine-tuning of the PBH abundance is larger still by
1-2 orders of magnitude. We highlight the challenges imposed by this tuning on
any given model construction. Furthermore, polynomial potentials appear to
require significant additional fine-tuning to also match the CMB observations. |
A comparative study of radio halo occurrence in SZ and X-ray selected
galaxy cluster samples: We aim at an unbiased census of the radio halo population in galaxy clusters
and test whether current low number counts of radio halos have arisen from
selection biases. We construct near-complete samples based on X-ray and
Sunyaev-Zel'dovich (SZ) effect cluster catalogues and search for diffuse,
extended (Mpc-scale) emission near the cluster centers by analyzing data from
the National Radio Astronomy Observatory Very Large Array Sky Survey. We remove
compact sources using a matched filtering algorithm and model the diffuse
emission using two independent methods. The relation between radio halo power
at 1.4 GHz and mass observables is modelled using a power law, allowing for a
'dropout' population of clusters hosting no radio halo emission. An extensive
suite of simulations is used to check for biases in our methods. Our findings
suggest that the fraction of targets hosting radio halos may have to be revised
upwards for clusters selected using the SZ effect: while approximately 60 per
cent of the X-ray selected targets are found to contain no extended radio
emission, in agreement with previous findings, the corresponding fraction in
the SZ selected samples is roughly 20 per cent. We propose a simple explanation
for this selection difference based on the distinct time evolution of the SZ
and X-ray observables during cluster mergers, and a bias towards relaxed,
cool-core clusters in the X-ray selection. | Resonant Sterile Neutrino Dark Matter in the Local and High-z Universe: Sterile neutrinos comprise an entire class of dark matter models that,
depending on their production mechanism, can be hot, warm, or cold dark matter.
We simulate the Local Group and representative volumes of the Universe in a
variety of sterile neutrino models, all of which are consistent with the
possible existence of a radiative decay line at ~3.5 keV. We compare models of
production via resonances in the presence of a lepton asymmetry (suggested by
Shi & Fuller 1999) to "thermal" models. We find that properties in the highly
nonlinear regime - e.g., counts of satellites and internal properties of halos
and subhalos - are insensitive to the precise fall-off in power with
wavenumber, indicating that nonlinear evolution essentially washes away
differences in the initial (linear) matter power spectrum. In the quasi-linear
regime at higher redshifts, however, quantitative differences in the 3D matter
power spectra remain, raising the possibility that such models can be tested
with future observations of the Lyman-alpha forest. While many of the sterile
neutrino models largely eliminate multiple small-scale issues within the Cold
Dark Matter (CDM) paradigm, we show that these models may be ruled out in the
near future via discoveries of additional dwarf satellites in the Local Group. |
Constraints on the dark energy using multiple observations : snare of
principal component analysis: We explore snares in determining the equation of state of dark energy
($\omega$) when one uses the so-called principal component analysis for
multiple observations. We demonstrated drawbacks of principal component
analysis in an earlier paper. We used the Hubble parameter data generated from
a fiducial model using the so-called Chevallier-Polarski-Linder
parameterization. We extend our previous consideration to multiple
observations, the Hubble parameter and the luminosity distance. We find that
the principal component analysis produces the almost constant $\omega$ even
when a fiducial model is a rapidly varying $\omega$. Thus, resolution of
dynamical property of $\omega$ through PCA is degraded especially when one fits
to several observations. | Astrophysics from the Highly-Redshifted 21 cm Line: The cosmic dark ages and the epoch of reionization, during which the first
generations of stars and galaxies formed, are among the most compelling
frontiers of extragalactic astrophysics and cosmology. Here we describe an
exciting new probe of these eras: the 21 cm line of neutral hydrogen, which
will allow us to map the neutral intergalactic medium throughout the era of
first galaxy formation. In this white paper, we describe how these studies can
answer two key questions about galaxy formation: What were the properties of
high-redshift galaxies? How did they affect the Universe around them? |
Thermodynamics and Lemaitre-Tolman-Bondi void models: It has been argued in the literature that in order to make a matter dominated
Friedmann-Lemaitre-Robertson-Walker universe compatible with the generalized
second law of thermodynamics, one must invoke dark energy, or modified gravity.
In the present article we investigate if in a similar spirit, inhomogeneous
cosmological models can be motivated on thermodynamic grounds. We examine a
particular minimal void Lemaitre-Tolman-Bondi inhomogeneous model which agrees
well with observations. While on the one hand we find that the entropy
associated with the apparent horizon is not well-behaved thermodynamically, on
the other hand the canonical Weyl curvature entropy shows satisfactory
thermodynamic behavior. We suggest that evolution of canonical Weyl curvature
entropy might be a useful way to evaluate the thermodynamic viability of
inhomogeneous cosmologies. | Simple numerical implementation of general dark energy models: We present a formalism for the numerical implementation of general theories
of dark energy, combining the computational simplicity of the equation of state
for perturbations approach with the generality of the effective field theory
approach. An effective fluid description is employed, based on a general action
describing single-scalar field models. The formalism is developed from first
principles, and constructed keeping the goal of a simple implementation into
CAMB in mind. Benefits of this approach include its straightforward
implementation, the generality of the underlying theory, the fact that the
evolved variables are physical quantities, and that model-independent
phenomenological descriptions may be straightforwardly investigated. We hope
this formulation will provide a powerful tool for the comparison of theoretical
models of dark energy with observational data. |
A 189 MHz, 2400 square degree polarization survey with the Murchison
Widefield Array 32-element prototype: We present a Stokes I, Q and U survey at 189 MHz with the Murchison Widefield
Array 32-element prototype covering 2400 square degrees. The survey has a 15.6
arcmin angular resolution and achieves a noise level of 15 mJy/beam. We
demonstrate a novel interferometric data analysis that involves calibration of
drift scan data, integration through the co-addition of warped snapshot images
and deconvolution of the point spread function through forward modeling. We
present a point source catalogue down to a flux limit of 4 Jy. We detect
polarization from only one of the sources, PMN J0351-2744, at a level of 1.8
\pm 0.4%, whereas the remaining sources have a polarization fraction below 2%.
Compared to a reported average value of 7% at 1.4 GHz, the polarization
fraction of compact sources significantly decreases at low frequencies. We find
a wealth of diffuse polarized emission across a large area of the survey with a
maximum peak of ~13 K, primarily with positive rotation measure values smaller
than +10 rad/m^2. The small values observed indicate that the emission is
likely to have a local origin (closer than a few hundred parsecs). There is a
large sky area at 2^h30^m where the diffuse polarized emission rms is fainter
than 1 K. Within this area of low Galactic polarization we characterize the
foreground properties in a cold sky patch at $(\alpha,\delta) =
(4^h,-27^\circ.6)$ in terms of three dimensional power spectra | Limits on Cosmological Birefringence from the Ultraviolet Polarization
of Distant Radio Galaxies: We report on an update of the test on the rotation of the plane of linear
polarization for light traveling over cosmological distances, using a
comparison between the measured direction of the UV polarization in 8 radio
galaxies at z>2 and the direction predicted by the model of scattering of
anisotropic nuclear radiation, which explains the polarization. No rotation is
detected within a few degrees for each galaxy and, if the rotation does not
depend on direction, then the all-sky-average rotation is constrained to be
\theta = -0.8 +/- 2.2. We discuss the relevance of this result for constraining
cosmological birefringence, when this is caused by the interaction with a
cosmological pseudo-scalar field or by the presence of a Cherns-Simons term. |
The Axiverse Extended: Vacuum Destabilisation, Early Dark Energy and
Cosmological Collapse: A model is presented in the philosophy of the "String Axiverse" of Arvanitaki
et al (arXiv:0905.4720v2 [hep-th]) that incorporates a coupling of ultralight
axions to their corresponding moduli through the mass term. The light fields
roll in their potentials at late times and contribute to the dark sector energy
densities in the cosmological expansion. The addition of a coupling and extra
field greatly enrich the possible phenomenology of the axiverse. There are a
number of interesting phases where the axion and modulus components behave as
Dark Matter or Dark Energy and can have considerable and distinct effects on
the expansion history of the universe by modifying the equation of state in the
past or causing possible future collapse of the universe. In future such a
coupling may help to alleviate fine tuning problems for cosmological axions. We
motivate and present the model, and briefly explore its cosmological
consequences numerically. | Two-dimensional Topology of Cosmological Reionization: We study the two-dimensional topology of the 21-cm differential brightness
temperature for two hydrodynamic radiative transfer simulations and two
semi-numerical models. In each model, we calculate the two dimensional genus
curve for the early, middle and late epochs of reionization. It is found that
the genus curve depends strongly on the ionized fraction of hydrogen in each
model. The genus curves are significantly different for different reionization
scenarios even when the ionized faction is the same. We find that the
two-dimensional topology analysis method is a useful tool to constrain the
reionization models. Our method can be applied to the future observations such
as those of the Square Kilometer Array. |
Constraints on primordial magnetic fields from CMB distortions in the
axiverse: Measuring spectral distortions of the cosmic microwave background (CMB) is
attracting considerable attention as a probe of high energy particle physics in
the cosmological context, since PIXIE and PRISM have recently been proposed. In
this paper, CMB distortions due to resonant conversions between CMB photons and
light axion like particles (ALPs) are investigated, motivated by the string
axiverse scenario which suggests the presence of a plenitude of light axion
particles. Since these resonant conversions depend on the strength of
primordial magnetic fields, constraints on CMB distortions can provide an upper
limit on the product of the photon-ALP coupling constant g and the comoving
strength of primordial magnetic fields B. Potentially feasible constraints from
PIXIE/PRISM can set a limit g B < 10^{-16} GeV^{-1} nG for ALP mass, m_\phi <
10^{-14} eV. Although this result is not a direct constraint on g and B, it is
significantly tighter than the product of the current upper limits on g and B. | The contribution of non-central radio galaxies to AGN feedback in rich
galaxy clusters: We present a combined radio/X-ray study of six massive galaxy clusters, aimed
at determining the potential for heating of the intra-cluster medium (ICM) by
non-central radio galaxies. Since X-ray cavities associated with the radio
lobes of non-central galaxies are generally not detectable, we use Giant
Metrewave Radio Telescope 610~MHz observations to identify jet sources and
estimate their size, and Chandra data to estimate the pressure of the
surrounding ICM. In the radio, we detect 4.5% of galaxies above the
spectroscopic survey limit (M*K+2.0) of the Arizona cluster redshift survey
(ACReS) which covers five of our six clusters. Approximately one tenth of these
are extended radio sources. Using star formation (SF) rates determined from
mid-infrared data, we estimate the expected contribution to radio luminosity
from the stellar population of each galaxy, and find that most of the
unresolved or poorly-resolved radio sources are likely star formation
dominated. The relatively low frequency and good spatial resolution of our
radio data allows us to trace star formation emission down to galaxies of
stellar mass ~10^9.5 Msol. We estimate the enthalpy of the (AGN dominated)
jet/lobe and tailed sources, and place limits on the energy available from
unresolved radio jets. We find jet powers in the range ~10^43-10^46 erg/s,
comparable to those of brightest cluster galaxies. Our results suggest that
while cluster-central sources are the dominant factor balancing ICM cooling
over the long term, non-central sources may have a significant impact, and that
further investigation is possible and warranted. |
What sets the central structure of dark matter haloes?: Dark matter (DM) haloes forming near the thermal cut-off scale of the density
perturbations are unique, since they are the smallest objects and form through
monolithic gravitational collapse, while larger haloes contrastingly have
experienced mergers. While standard cold dark matter (CDM) simulations readily
produce haloes that follow the universal Navarro-Frenk-White (NFW) density
profile with an inner slope, $\rho \propto r^{-\alpha}$, with $\alpha=1$,
recent simulations have found that when the free-streaming cut-off expected for
the CDM model is resolved, the resulting haloes follow nearly power-law density
profiles of $\alpha\sim1.5$. In this paper, we study the formation of density
cusps in haloes using idealized $N$-body simulations of the collapse of
proto-haloes. When the proto-halo profile is initially cored due to particle
free-streaming at high redshift, we universally find $\sim r^{-1.5}$ profiles
irrespective of the proto-halo profile slope outside the core and large-scale
non-spherical perturbations. Quite in contrast, when the proto-halo has a
power-law profile, then we obtain profiles compatible with the NFW shape when
the density slope of the proto-halo patch is shallower than a critical value,
$\alpha_{\rm ini} \sim 0.3$, while the final slope can be steeper for
$\alpha_{\rm ini}\ga 0.3$. We further demonstrate that the $r^{-1.5}$ profiles
are sensitive to small scale noise, which gradually drives them towards an
inner slope of $-1$, where they become resilient to such perturbations. We
demonstrate that the $r^{-1.5}$ solutions are in hydrostatic equilibrium,
largely consistent with a simple analytic model, and provide arguments that
angular momentum appears to determine the inner slope. | Halo bias in mixed dark matter cosmologies: The large-scale distribution of cold dark matter halos is generally assumed
to trace the large-scale distribution of matter. In a universe with multiple
types of matter fluctuations, as is the case with massive neutrinos, the
relation between the halo field and the matter fluctuations may be more
complicated. We develop a method for calculating the bias factor relating
fluctuations in the halo number density to fluctuations in the mass density in
the presence of multiple fluctuating components of the energy density. In the
presence of massive neutrinos we find a small but pronounced feature in the
halo bias near the neutrino free-streaming scale. The neutrino feature is a
small step with amplitude that increases with halo mass and neutrino mass
density. The scale-dependent halo bias lessens the suppression of the
small-scale halo power spectrum and should therefore weaken constraints on
neutrino mass from the galaxy auto-power spectrum and correlation function. On
the other hand, the feature in the bias is itself a novel signature of massive
neutrinos that can be studied independently. |
The Effect of Massive Neutrinos on the Halo Spin Flip Phenomenon: The halo spin flip refers to the phenomenon that the spin axes of dark matter
halos with masses above a certain threshold tend to be preferentially aligned
perpendicular to the hosting large-scale filaments, while low-mass halos tend
to have their spin axes aligned parallel to such structures. Extensive work has
so far been conducted to understand this phenomenon under the assumption of
cold dark matter and suggested that its origin should be closely related to the
nonlinear evolution of the halo angular momentum in the anisotropic cosmic web.
We present, for the first time, a numerical examination of this phenomenon
assuming the presence of massive neutrinos, finding a clear and robust
dependence of the threshold mass for the spin flip on the total neutrino mass.
Our physical explanation is that the presence of more massive neutrinos retard
the nonlinear evolution of the cosmic web, which in turn allows the halo spin
vectors to better retain their memories of the initial tidal interactions in
the nonlinear regime. Our finding implies that the statistical alignment of
halo spins with the large-scale structures can be in principle used as a probe
of the total neutrino mass. | On the road to precision cosmology with high redshift HII galaxies: We report the first results of a programme aimed at studying the properties
of high redshift galaxies with on-going massive and dominant episodes of star
formation (HII galaxies). We use the $L(\mathrm{H}\beta) - \sigma$ distance
estimator based on the correlation between the ionized gas velocity dispersions
and Balmer emission line luminosities of HII galaxies and Giant HII regions to
trace the expansion of the Universe up to $z \sim 2.33$. This approach provides
an independent constraint on the equation of state of dark energy and its
possible evolution with look-back time.
Here we present high-dispersion (8,000 to 10,000 resolution) spectroscopy of
HII galaxies at redshifts between 0.6 and 2.33, obtained at the VLT using
XShooter. Using six of these HII galaxies we obtain broad constraints on the
plane $\Omega_m - w_0$. The addition of 19 high-z HII galaxies from the
literature improves the constraints and highlights the need for high quality
emission line profiles, fluxes and reddening corrections. The 25 high-z HII
galaxies plus our local compilation of 107 HII galaxies up to $z=0.16$ were
used to impose further constraints. Our results are consistent with recent
studies, although weaker due to the as yet small sample and low quality of the
literature data of high-z HII galaxies.
We show that much better and competitive constraints can be obtained using a
larger sample of high redshift HII galaxies with high quality data that can be
easily obtained with present facilities like KMOS at the VLT. |
Groups and protocluster candidates in the CLAUDS and HSC-SSP joint deep
surveys: Using the extended halo-based group finder developed by Yang et al. (2021),
which is able to deal with galaxies via spectroscopic and photometric redshifts
simultaneously, we construct galaxy group and candidate protocluster catalogs
in a wide redshift range ($0 < z < 6$) from the joint CFHT Large Area $U$-band
Deep Survey (CLAUDS) and Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP)
deep data set. Based on a selection of 5,607,052 galaxies with $i$-band
magnitude $m_{i} < 26$ and a sky coverage of $34.41\ {\rm deg}^2$, we identify
a total of 2,232,134 groups, within which 402,947 groups have at least three
member galaxies. We have visually checked and discussed the general properties
of those richest groups at redshift $z>2.0$. By checking the galaxy number
distributions within a $5-7\ h^{-1}\mathrm{Mpc}$ projected separation and a
redshift difference $\Delta z \le 0.1$ around those richest groups at redshift
$z>2$, we identified a list of 761, 343 and 43 protocluster candidates in the
redshift bins $2\leq z<3$, $3\leq z<4$ and $z \geq 4$, respectively. In
general, these catalogs of galaxy groups and protocluster candidates will
provide useful environmental information in probing galaxy evolution along the
cosmic time. | Accelerated expansion from ghost-free bigravity: a statistical analysis
with improved generality: We study the background cosmology of the ghost-free, bimetric theory of
gravity. We perform an extensive statistical analysis of the model using both
frequentist and Bayesian frameworks and employ the constraints on the expansion
history of the Universe from the observations of supernovae, the cosmic
microwave background and the large scale structure to estimate the model's
parameters and test the goodness of the fits. We explore the parameter space of
the model with nested sampling to find the best-fit chi-square, obtain the
Bayesian evidence, and compute the marginalized posteriors and mean
likelihoods. We mainly focus on a class of sub-models with no explicit
cosmological constant (or vacuum energy) term to assess the ability of the
theory to dynamically cause a late-time accelerated expansion. The model
behaves as standard gravity without a cosmological constant at early times,
with an emergent extra contribution to the energy density that converges to a
cosmological constant in the far future. The model can in most cases yield very
good fits and is in perfect agreement with the data. This is because many
points in the parameter space of the model exist that give rise to
time-evolution equations that are effectively very similar to those of the
$\Lambda$CDM. This similarity makes the model compatible with observations as
in the $\Lambda$CDM case, at least at the background level. Even though our
results indicate a slightly better fit for the $\Lambda$CDM concordance model
in terms of the $p$-value and evidence, none of the models is statistically
preferred to the other. However, the parameters of the bigravity model are in
general degenerate. A similar but perturbative analysis of the model as well as
more data will be required to break the degeneracies and constrain the
parameters, in case the model will still be viable compared to the
$\Lambda$CDM. |
Constraint on the early Universe by relic gravitational waves: From
pulsar timing observations: Recent pulsar timing observations by the Parkers Pulsar Timing Array and
European Pulsar Timing Array teams obtained the constraint on the relic
gravitational waves at the frequency $f_*=1/{\rm yr}$, which provides the
opportunity to constrain $H_*$, the Hubble parameter when these waves crossed
the horizon during inflation. In this paper, we investigate this constraint by
considering the general scenario for the early Universe: we assume that the
effective (average) equation-of-state $w$ before the big bang nucleosynthesis
stage is a free parameter. In the standard hot big-bang scenario with $w=1/3$,
we find that the current PPTA result follows a bound $H_*\leq
1.15\times10^{-1}\mpl$, and the EPTA result follows $H_*\leq
6.92\times10^{-2}\mpl$. We also find that these bounds become much tighter in
the nonstandard scenarios with $w>1/3$. When $w=1$, the bounds become
$H_*\leq5.89\times10^{-3}\mpl$ for the current PPTA and
$H_*\leq3.39\times10^{-3}\mpl$ for the current EPTA. In contrast, in the
nonstandard scenario with $w=0$, the bound becomes $H_*\leq7.76\mpl$ for the
current PPTA. | Electromagnetic back-reaction from currents on a straight string: Charge carriers moving at the speed of light along a straight,
superconducting cosmic string carry with them a logarithmically divergent slab
of electromagnetic field energy. Thus no finite local input can induce a
current that travels unimpeded to infinity. Rather, electromagnetic
back-reaction must damp this current asymptotically to nothing. We compute this
back-reaction and find that the electromagnetic fields and currents decline
exactly as rapidly as necessary to prevent a divergence. We briefly discuss the
corresponding gravitational situation. |
Detection of Enhancement in Number Densities of Background Galaxies due
to Magnification by Massive Galaxy Clusters: We present a detection of the enhancement in the number densities of
background galaxies induced from lensing magnification and use it to test the
Sunyaev-Zel'dovich effect (SZE) inferred masses in a sample of 19 galaxy
clusters with median redshift $z\simeq0.42$ selected from the South Pole
Telescope SPT-SZ survey. Two background galaxy populations are selected for
this study through their photometric colours; they have median redshifts
${z}_{\mathrm{median}}\simeq0.9$ (low-$z$ background) and
${z}_{\mathrm{median}}\simeq1.8$ (high-$z$ background). Stacking these
populations, we detect the magnification bias effect at $3.3\sigma$ and
$1.3\sigma$ for the low- and high-$z$ backgrounds, respectively. We fit NFW
models simultaneously to all observed magnification bias profiles to estimate
the multiplicative factor $\eta$ that describes the ratio of the weak lensing
mass to the mass inferred from the SZE observable-mass relation. We further
quantify systematic uncertainties in $\eta$ resulting from the photometric
noise and bias, the cluster galaxy contamination and the estimations of the
background properties. The resulting $\eta$ for the combined background
populations with $1\sigma$ uncertainties is
$0.83\pm0.24\mathrm{(stat)}\pm0.074\mathrm{(sys)}$, indicating good consistency
between the lensing and the SZE-inferred masses. We use our best-fit $\eta$ to
predict the weak lensing shear profiles and compare these predictions with
observations, showing agreement between the magnification and shear mass
constraints. This work demonstrates the promise of using the magnification as a
complementary method to estimate cluster masses in large surveys. | On the Cluster Physics of Sunyaev-Zel'dovich Surveys I: The Influence of
Feedback, Non-thermal Pressure and Cluster Shapes on Y-M Scaling Relations: The utility of large Sunyaev Zel'dovich (SZ) surveys for determining
cosmological parameters from cluster abundances is limited by the theoretical
uncertainties in the integrated SZ-flux-to-mass relation, Y-M. We explore how
non-thermal pressure and the anisotropic shape of the gas distribution of the
intracluster medium (ICM) impacts Y-M scaling using a suite of SPH simulations
of the cosmic web. We contrast results for models with different treatments of
entropy injection and transport, varying radiative cooling, star formation and
accompanying supernova feedback, cosmic rays, and energetic feedback from
active galactic nuclei (AGN). We find that the gas kinetic-to-thermal pressure
ratio from internal bulk motions depends on the cluster mass, and increases in
the outer-cluster due to enhanced substructure, as does the asphericity of the
ICM gas. With only a ~5-10% correction to projected (observable) ellipticities,
we can infer the 3D ellipticities. Our simulated Y-M-slope roughly follows the
self-similar prediction, except for a steepening due to a deficit of gas in
lower mass clusters at low redshift in our AGN-feedback simulations. AGN
feedback enhances slightly the overall Y-M-scatter, from ~11% to ~13%, a
reflection of accretion history variations due to cluster merging. If we split
the cluster system into lower, middle and upper bands of both P_kin/P_th and
long-to-short axis ratio, we find a ~10% effect on Y-M. Identifying observable
second parameters related to internal bulk flows and anisotropy for
cluster-selection to minimize Y-M scatter in a "fundamental plane" would allow
tighter cosmological parameter constraints. |
Massive star formation in Wolf-Rayet galaxies. IV: Colours, chemical
composition analysis and metallicity-luminosity relations: (Abridged) We performed a multiwavelength analysis of a sample of starburst
galaxies that show the presence of a substantial population of very young
massive (WR) stars. Here we present the global analysis of the derived
photometric and chemical properties. We compare optical/NIR colours and the
physical properties (reddening coefficient, equivalent widths of the emission
and underlying absorption lines, ionization degree, electron density, and
electron temperature) and chemical properties with previous observations and
galaxy evolution models. Attending to their absolute B-magnitude many of them
are not dwarf galaxies, but they should be during their quiescent phase. We
found that both C(Hb) and Wabs increase with increasing metallicity. We
detected a high N/O ratio in objects showing strong WR features. The ejecta of
the WR stars may be the origin of the N enrichment in these galaxies. We
compared the abundances provided by the direct method with those obtained using
empirical calibrations, finding that (i) the Pilyugin method is the best
suitable empirical calibration, (ii) the relations between the oxygen abundance
and the N2 or the O3N2 parameters provided by Pettini & Pagel (2004) give
acceptable results for objects with 12+log(O/H)>8.0, and (iii) the results
provided by empirical calibrations based on photoionization models are
systematically 0.2-0.3 dex higher than the values derived from the direct
method. The O and N abundances and the N/O ratios are related to the
optical/NIR luminosity; the dispersion is consequence of the differences in the
star-formation histories. Galaxies with redder colours tend to have higher
oxygen and nitrogen abundances. Our detailed analysis is fundamental to
understand the nature of galaxies showing strong starbursts, as well as to know
their star formation history and the relationships with the environment. | Simulating the Cosmic Neutrino Background using Collisionless
Hydrodynamics: The cosmic neutrino background is an important component of the Universe that
is difficult to include in cosmological simulations due to the extremely large
velocity dispersion of neutrino particles. We develop a new approach to
simulate cosmic neutrinos that decomposes the Fermi-Dirac phase space into
shells of constant speed and then evolves those shells using hydrodynamic
equations. These collisionless hydrodynamic equations are chosen to match
linear theory, free particle evolution and allow for superposition. We
implement this method into the information-optimized cosmological $N$-body code
CUBE and demonstrate that neutrino perturbations can be accurately resolved to
at least $k\sim1\ h/$Mpc. This technique allows for neutrino memory
requirements to be decreased by up to $\sim 10^3$ compared to traditional
$N$-body methods. |
The DESI One-Percent survey: exploring the Halo Occupation Distribution
of Emission Line Galaxies with AbacusSummit simulations: The One-Percent survey of the Dark Energy Spectroscopic Instrument collected
~ 270k emission line galaxies (ELGs) at 0.8 < z < 1.6. The high completeness of
the sample allowed the clustering to be measured down to scales never probed
before, 0.04 Mpc/h in rp for the projected 2-point correlation function (2PCF)
and 0.17 Mpc/h in galaxy pair separation s for the 2PCF monopole and
quadrupole. The most striking feature of the measurements is a strong signal at
the smallest scales, below 0.2 Mpc/h in rp and 1 Mpc/h in s. We analyze these
data in the halo occupation distribution framework. We consider different
distributions for central galaxies, a standard power law for satellites with no
condition on the presence of a central galaxy and explore several extensions of
these models. For all considered models, the mean halo mass of the sample is
found to be log10 <Mh> ~ 11.9. We obtain a satellite mean occupation function
which agrees with physically motivated ELG models only if we introduce
central-satellite conformity, meaning that the satellite occupation is
conditioned by the presence of central galaxies of the same type. To achieve in
addition a good modeling of the clustering between 0.1 and 1 Mpc/h in rp, we
allow for ELG positioning outside of the halo virial radius and find 0.5% of
ELGs residing in the outskirts of halos. Furthermore, the satellite velocity
dispersion inside halos is found to be ~ 30% larger than that of the halo dark
matter particles. These are the main findings of our work. We investigate
assembly bias as a function of halo concentration, local density or local
density anisotropies and observe no significant change in our results. We split
the data sample in two redshift bins and report no significant evolution with
redshift. Lastly, changing the cosmology in the modeling impacts only slightly
our results. | Dust and Ionized Gas Association in E/S0 Galaxies with Dust Lanes: Clues
to their Origin: We present results from an on-going programme to study the dust and ionized
gas in E/S0 galaxies with dust lanes. Our data, together with results from
previous studies of E/S0 galaxies, are used to demonstrate the tight
relationship between these two components. This relationship is discussed in
light of our current understanding of the nature and origin of the interstellar
medium (ISM), and in particular in the context of the interplay between the
different multi-temperature components. We show that focusing on dust obscured
regions as tracers of the ISM, and on their properties, serves as independent
evidence for the external origin of the dust and ionized gas. |
Constraints on non-resonant photon-axion conversion from the Planck
satellite data: The non-resonant conversion of Cosmic Microwave Background (CMB) photons into
scalar as well as light pseudoscalar particles such as axion-like particles
(ALPs) in the presence of turbulent magnetic fields can cause a unique,
spatially fluctuating spectral distortion in the CMB. We use the publicly
available Planck temperature maps for the frequency channels (70-545 GHz) to
obtain the first ALP distortion map using $45\%$ clean part of the sky. The
$95^{th}$ percentile upper limit on the RMS fluctuation of ALP distortions from
the cleanest part of the CMB sky at $15$ arcmin angular resolution is $18.5
\times 10^{-6}$. The RMS fluctuation in the distortion map is also consistent
with different combinations of frequency channels and sky-fractions. | Cosmological Forecast for non-Gaussian Statistics in large-scale weak
Lensing Surveys: Cosmic shear data contains a large amount of cosmological information
encapsulated in the non-Gaussian features of the weak lensing mass maps. This
information can be extracted using non-Gaussian statistics. We compare the
constraining power in the $\Omega_{\mathrm{m}} - \sigma_8$ plane of three
map-based non-Gaussian statistics with the angular power spectrum, namely;
peak/minimum counts and Minkowski functionals. We further analyze the impact of
tomography and systematic effects originating from galaxy intrinsic alignments,
multiplicative shear bias and photometric redshift systematics. We forecast the
performance of the statistics for a stage-3-like weak lensing survey and
restrict ourselves to scales $\geq$ 10 arcmin. We find, that in our setup, the
considered non-Gaussian statistics provide tighter constraints than the angular
power spectrum. The peak counts show the greatest potential, increasing the
Figure-of-Merit (FoM) in the $\Omega_{\mathrm{m}} - \sigma_8$ plane by a factor
of about 4. A combined analysis using all non-Gaussian statistics in addition
to the power spectrum increases the FoM by a factor of 5 and reduces the error
on $S_8$ by $\approx$ 25\%. We find that the importance of tomography is
diminished when combining non-Gaussian statistics with the angular power
spectrum. The non-Gaussian statistics indeed profit less from tomography and
the minimum counts and Minkowski functionals add some robustness against galaxy
intrinsic alignment in a non-tomographic setting. We further find that a
combination of the angular power spectrum and the non-Gaussian statistics
allows us to apply conservative scale cuts in the analysis, thus helping to
minimize the impact of baryonic and relativistic effects, while conserving the
cosmological constraining power. We make the code that was used to conduct this
analysis publicly available. |
Lensing Without Borders. I. A Blind Comparison of the Amplitude of
Galaxy-Galaxy Lensing Between Independent Imaging Surveys: Lensing Without Borders is a cross-survey collaboration created to assess the
consistency of galaxy-galaxy lensing signals ($\Delta\Sigma$) across different
data-sets and to carry out end-to-end tests of systematic errors. We perform a
blind comparison of the amplitude of $\Delta\Sigma$ using lens samples from
BOSS and six independent lensing surveys. We find good agreement between
empirically estimated and reported systematic errors which agree to better than
2.3$\sigma$ in four lens bins and three radial ranges. For lenses with $z_{\rm
L}>0.43$ and considering statistical errors, we detect a 3-4$\sigma$
correlation between lensing amplitude and survey depth. This correlation could
arise from the increasing impact at higher redshift of unrecognised galaxy
blends on shear calibration and imperfections in photometric redshift
calibration. At $z_{\rm L}>0.54$ amplitudes may additionally correlate with
foreground stellar density. The amplitude of these trends is within
survey-defined systematic error budgets which are designed to include known
shear and redshift calibration uncertainty. Using a fully empirical and
conservative method, we do not find evidence for large unknown systematics.
Systematic errors greater than 15% (25%) ruled out in three lens bins at 68%
(95%) confidence at $z<0.54$. Differences with respect to predictions based on
clustering are observed to be at the 20-30% level. Our results therefore
suggest that lensing systematics alone are unlikely to fully explain the
"lensing is low" effect at $z<0.54$. This analysis demonstrates the power of
cross-survey comparisons and provides a promising path for identifying and
reducing systematics in future lensing analyses. | Beyond $Λ$CDM: Problems, solutions, and the road ahead: Despite its continued observational successes, there is a persistent (and
growing) interest in extending cosmology beyond the standard model,
$\Lambda$CDM. This is motivated by a range of apparently serious theoretical
issues, involving such questions as the cosmological constant problem, the
particle nature of dark matter, the validity of general relativity on large
scales, the existence of anomalies in the CMB and on small scales, and the
predictivity and testability of the inflationary paradigm. In this paper, we
summarize the current status of $\Lambda$CDM as a physical theory, and review
investigations into possible alternatives along a number of different lines,
with a particular focus on highlighting the most promising directions. While
the fundamental problems are proving reluctant to yield, the study of
alternative cosmologies has led to considerable progress, with much more to
come if hopes about forthcoming high-precision observations and new theoretical
ideas are fulfilled. |
Cosmological simulation in tides: power spectra and halo shape
responses, and shape assembly bias: The well-developed separate universe technique enables accurate calibration
of the response of any observable to an isotropic long-wavelength density
fluctuation. The large-scale environment also hosts tidal modes that perturb
all observables anisotropically. As in the separate universe, both the long
tidal and density modes can be absorbed by an effective anisotropic background,
on which the interaction and evolution of the short modes change accordingly.
We further develop the tidal simulation method, including proper corrections to
the second order Lagrangian perturbation theory (2LPT) to generate initial
conditions of the simulations. We measure the linear tidal responses of the
matter power spectrum, at high redshift from our modified 2LPT, and at low
redshift from the tidal simulations. Our results agree qualitatively with
previous works, but exhibit quantitative differences in both cases. We also
measure the linear tidal response of the halo shapes, or the shape bias, and
find its universal relation with the linear halo bias, for which we provide a
fitting formula. Furthermore, analogous to the assembly bias, we study the
secondary dependence of the shape bias, and discover for the first time
dependence on halo concentration and axis ratio. Our results provide useful
insights for studies of the intrinsic alignment as source of either
contamination or information. These effects need to be correctly taken into
account when one uses intrinsic alignments of galaxy shapes as a precision
cosmological tool. | The $S_8$ Tension in Light of Updated Redshift-Space Distortion Data and
PAge Approximation: One of the most prominent challenges to the standard Lambda cold dark matter
($\Lambda$CDM) cosmology is the tension between the structure growth parameter
$S_8$ constrained by the cosmic microwave background (CMB) data and the smaller
one suggested by the cosmic shear data. Recent studies show that, for
$\Lambda$CDM cosmology, redshift-space distortion (RSD) data also prefers a
smaller $S_8$ that is $\sim 2$-$3\sigma$ lower than the CMB value, but the
result is sensitive to the cosmological model. In the present work we update
the RSD constraint on $S_8$ with the most up-to-date RSD data set where the
correlation between data points are properly taken into account. To reduce the
model dependence, we add in our Monte Carlo Markov Chain calculation the most
up-to-date data sets of Type Ia supernovae (SN) and baryon acoustic
oscillations (BAO), whose correlation with RSD is also taken into account, to
constrain the background geometry. For $\Lambda$CDM cosmology we find $S_8=
0.812 \pm 0.026$, which is $\sim 2\sigma$ larger than previous studies, and
hence is consistent with the CMB constraint. By replacing $\Lambda$CDM with the
Parameterization based on cosmic Age (PAge), an almost model-independent
description of the late universe, we find that the RSD + SN + BAO constraint on
$S_8$ is insensitive to the cosmological model. |
Interacting Dark Energy -- constraints and degeneracies: In standard cosmologies, dark energy interacts only gravitationally with dark
matter. There could be a non-gravitational interaction in the dark sector,
leading to changes in the effective DE equation of state, in the redshift
dependence of the DM density and in structure formation. We use CMB, BAO and
SNIa data to constrain a model where the energy transfer in the dark sector is
proportional to the DE density. There are two subclasses, defined by the
vanishing of momentum transfer either in the DM or the DE frame. We conduct a
Markov-Chain Monte-Carlo analysis to obtain best-fit parameters. The background
evolution allows large interaction strengths, and the constraints from CMB
anisotropies are weak. The growth of DM density perturbations is much more
sensitive to the interaction, and can deviate strongly from the standard case.
However, the deviations are degenerate with galaxy bias and thus more difficult
to constrain. Interestingly, the ISW signature is suppressed since the
non-standard background evolution can compensate for high growth rates. We also
discuss the partial degeneracy between interacting DE and modified gravity, and
how this can be broken. | Investigating Cosmological Models and the Hubble Tension using Localized
Fast Radio Bursts: We use the dispersion measure (DM) and redshift measurements of 24 localized
fast radio bursts (FRBs) to compare cosmological models and investigate the
Hubble tension. Setting a flat prior on the DM contribution from the Milky
Way's halo, $\mathrm{DM_{halo}^{MW}}\in[5,\;80]\;\mathrm{pc\;cm^{-3}}$, the
best fit for flat $\Lambda$CDM is obtained with a Hubble constant
$H_0=95.8^{+7.8}_{-9.2}\;\mathrm{km\;s^{-1}\;Mpc^{-1}}$ and a median matter
density $\Omega_{\mathrm{m}}\approx0.66$. The best fit for the
$R_{\mathrm{h}}=ct$ universe is realized with
$H_0=94.2^{+5.6}_{-6.2}\;\mathrm{km\;s^{-1}\;Mpc^{-1}}$. We emphasize that the
$H_0$ measurement depends sensitively on the $\mathrm{DM_{halo}^{MW}}$ prior.
Since flat $\Lambda$CDM has one more free parameter, $R_{\mathrm{h}}=ct$ is
favored by the Bayesian Information Criterion (BIC) with a likelihood of
$\sim73\%$ versus $\sim27\%$. Through simulations, we find that if the real
cosmology is $\Lambda$CDM, a sample of $\sim1,150$ FRBs in the redshift range
$0<z<3$ would be sufficient to rule out $R_{\mathrm{h}}=ct$ at a $3\sigma$
confidence level, while $\sim550$ FRBs would be necessary to rule out
$\Lambda$CDM if the real cosmology is instead $R_{\mathrm{h}}=ct$. The required
sample sizes are different, reflecting the fact that the BIC imposes a severe
penalty on the model with more free parameters. We further adopt a
straightforward method of deriving an upper limit to $H_{0}$, without needing
to consider the poorly known probability distribution of the DM contributed by
the host galaxy. The theoretical DM contribution from the intergalactic medium
($\mathrm{DM_{IGM}}$) at any $z$ is proportional to $H_0$. Thus, requiring the
extragalactic $\mathrm{DM_{ext}}$ to be larger than $\mathrm{DM_{IGM}}$
delimits $H_0$ to the upside. Assuming flat $\Lambda$CDM, we have
$H_0<89.0\;\mathrm{km\;s^{-1}\;Mpc^{-1}}$ at a 95\% confidence level. |
The impact of super-survey modes on cosmological constraints from cosmic
shear fields: Owing to the mass-sheet degeneracy, cosmic shear maps do not probe directly
the Fourier modes of the underlying mass distribution on scales comparable to
the survey size and larger. To assess the corresponding effect on attainable
cosmological parameter constraints, we quantify the information on super-survey
modes in a lognormal model and, when interpreted as nuisance parameters, their
degeneracies to cosmological parameters. Our analytical and numerical
calculations clarify the central role of super-sample covariance (SSC) in
shaping the statistical power of cosmological observables. Reconstructing the
background modes from their non-Gaussian statistical dependence to small scales
modes yields the renormalized convergence. This diagonalizes the spectrum
covariance matrix, and the information content of the corresponding power
spectrum is increased by a factor of two over standard methods. Unfortunately,
careful calculation of the Cramer-Rao bound shows that the information recovery
can never be made complete, any observable built from shear fields, including
optimal sufficient statistics, are subject to severe information loss,
typically $80\%$ to $90\%$ below $\ell \sim 3000$ for generic cosmological
parameters. The lost information can only be recovered from additional,
non-shear based data. Our predictions hold just as well for a tomographic
analysis, and/or full sky surveys. | Cosmological Collider Signatures of Massive Vectors from Non-Gaussian
Gravitational Waves: The cosmological collider provides a model-independent probe of particle
physics during inflation. We extend the study of cosmological collider physics
to much smaller scales through gravitational wave (GW) probes. With a
Chern-Simons interaction, a massive vector field can obtain a chemical
potential and its particle production can cause significant non-Gaussian GW
signals. We calculate the mass and spin dependences of the induced GW 3-point
correlation function in the squeezed limit, and estimate its amplitude. Such
signals may be detectable in the current and upcoming GW interferometer
experiments. |
Extragalactic number counts at 100 um, free from cosmic variance: We use data from the Disc Emission via a Bias-free Reconnaissance in the
Infrared/Submillimetre (DEBRIS) survey, taken at 100 um with the Photoconductor
Array Camera and Spectrometer instrument on board the Herschel Space
Observatory, to make a cosmic variance independent measurement of the
extragalactic number counts. These data consist of 323 small-area mapping
observations performed uniformly across the sky, and thus represent a sparse
sampling of the astronomical sky with an effective coverage of ~2.5 deg^2.
We find our cosmic variance independent analysis to be consistent with
previous count measurements made using relatively small area surveys.
Furthermore, we find no statistically significant cosmic variance on any scale
within the errors of our data. Finally, we interpret these results to estimate
the probability of galaxy source confusion in the study of debris discs. | Sterile neutrino dark matter: A tale of weak interactions in the strong
coupling epoch: We perform a detailed study of the weak interactions of standard model
neutrinos with the primordial plasma and their effect on the resonant
production of sterile neutrino dark matter. Motivated by issues in cosmological
structure formation on small scales, and reported X-ray signals that could be
due to sterile neutrino decay, we consider $7$ keV-scale sterile neutrinos.
Oscillation-driven production of such sterile neutrinos occurs at temperatures
$T \gtrsim 100$ MeV, where we study two significant effects of weakly charged
species in the primordial plasma: (1) the redistribution of an input lepton
asymmetry; (2) the opacity for active neutrinos. We calculate the
redistribution analytically above and below the quark-hadron transition, and
match with lattice QCD calculations through the transition. We estimate
opacities due to tree level processes involving leptons and quarks above the
quark-hadron transition, and the most important mesons below the transition. We
report final sterile neutrino dark matter phase space densities that are
significantly influenced by these effects, and yet relatively robust to
remaining uncertainties in the nature of the quark-hadron transition. We also
provide transfer functions for cosmological density fluctuations with cutoffs
at $k \simeq 10 \ h \ {\rm Mpc}^{-1}$, that are relevant to galactic structure
formation. |
I. Apples to apples $A^2$: realistic galaxy simulated catalogs and
photometric redshift predictions for next-generation surveys: We present new mock catalogues for two of the largest stage-IV
next-generation surveys in the optical and infrared: LSST and Euclid, based on
an N-body simulation+semi-analytical cone with a posterior modification with
\texttt{PhotReal}. This technique modifies the original photometry by using an
empirical library of spectral templates to make it more realistic. The
reliability of the catalogues is confirmed by comparing the obtained
color-magnitude relation, the luminosity and mass function and the angular
correlation function with those of real data.
Consistent comparisons between the expected photometric redshifts for
different surveys are also provided. Very deep near infrared surveys such as
Euclid will provide very good performance ($\Delta z/(1+z) \sim 0.025-0.053$)
down to $H\sim24$ AB mag and up to $z\sim3$ depending on the optical
observations available from the ground whereas extremely deep optical surveys
such as LSST will obtain an overall lower photometric redshift resolution
($\Delta z/(1+z) \sim 0.045$) down to $i\sim27.5$ AB mag, being considerably
improved ($\Delta z/(1+z) \sim 0.035$) if we restrict the sample down to
i$\sim$24 AB mag. Those numbers can be substantially upgraded by selecting a
subsample of galaxies with the best quality photometric redshifts. We finally
discuss the impact that these surveys will have for the community in terms of
photometric redshift legacy.
This is the first of a series of papers where we set a framework for
comparability between mock catalogues and observations with a particular focus
on cluster surveys. The Euclid and LSST mocks are made publicly available in
the following link: http://photmocks.obspm.fr/. | Probing the sign-changeable interaction between dark energy and dark
matter with current observations: We consider the models of vacuum energy interacting with cold dark matter in
this study, in which the coupling can change sigh during the cosmological
evolution. We parameterize the running coupling $b$ by the form
$b(a)=b_0a+b_e(1-a)$, where at the early-time the coupling is given by a
constant $b_{e}$ and today the coupling is described by another constant
$b_{0}$. We explore six specific models with (i) $Q(a)=b(a)H_0\rho_0$, (ii)
$Q(a)=b(a)H_0\rho_{\rm de}$, (iii) $Q(a)=b(a)H_0\rho_{\rm c}$, (iv)
$Q(a)=b(a)H\rho_0$, (v) $Q(a)=b(a)H\rho_{\rm de}$, and (vi)
$Q(a)=b(a)H\rho_{\rm c}$. The current observational data sets we use to
constrain the models include the JLA compilation of type Ia supernova data, the
Planck 2015 distance priors data of cosmic microwave background observation,
the baryon acoustic oscillations measurements, and the Hubble constant direct
measurement. We find that, for all the models, we have $b_0<0$ and $b_e>0$ at
around the 1$\sigma$ level, and $b_0$ and $b_e$ are in extremely strong
anti-correlation. Our results show that the coupling changes sign during the
evolution at about the 1$\sigma$ level, i.e., the energy transfer is from dark
matter to dark energy when dark matter dominates the universe and the energy
transfer is from dark energy to dark matter when dark energy dominates the
universe. |
We do not live in the R_h = c t universe: We analyse the possibility that our Universe could be described by the model
recently proposed by Melia & Shevchuk (2012), where the Hubble scale R_h=c/H is
at all times equal to the distance ct that light has travelled since the Big
Bang. In such a model, the scale factor is proportional to cosmic time and
there is neither acceleration nor deceleration of the expansion. We first point
out problems with the very foundations of the model and its consequences for
the evolution of the Universe. Next, we compare predictions of the model with
observational data. As probes of the expansion we use distance data of
supernovae type Ia, as well as Hubble rate data obtained from cosmic
chronometers and radial baryon acoustic oscillations. We analyse the redshift
evolution of the Hubble parameter and its redshift derivatives, together with
the so-called O_m diagnostic and the deceleration parameter. To reliably
estimate smooth functions and their derivatives from discrete data, we use the
recently developed Gaussian Processes in Python package (GaPP). Our general
conclusion is that the discussed model is strongly disfavoured by observations,
especially at low redshifts (z<0.5). In particular, it predicts specific
constant values for the deceleration parameter and for redshift derivatives of
the Hubble parameter, which is ruled out by the data. | Inelastic dark matter with spin-dependent couplings to protons and large
modulation fractions in DAMA: We discuss a scenario where the DAMA modulation effect is explained by a
Weakly Interacting Massive Particle (WIMP) which upscatters inelastically to a
heavier state and predominantly couples to the spin of protons. In this
scenario constraints from xenon and germanium targets are evaded dynamically,
due to the suppression of the WIMP coupling to neutrons, while those from
fluorine targets are evaded kinematically, because the minimal WIMP incoming
speed required to trigger upscatters off fluorine exceeds the maximal WIMP
velocity in the Galaxy, or is very close to it. In this scenario WIMP
scatterings off sodium are usually sensitive to the large-speed tail of the
WIMP velocity distribution and modulated fractions of the signal close to unity
arise in a natural way. On the other hand, a halo-independent analysis with
more conservative assumptions about the WIMP velocity distribution allows to
extend the viable parameter space to configurations where large modulated
fractions are not strictly necessary. We discuss large modulated fractions in
the Maxwellian case showing that they imply a departure from the usual cosine
time dependence of the expected signal in DAMA. However we explicitly show that
the DAMA data is not sensitive to this distortion, both in time and frequency
space, even in the extreme case of a 100 % modulated fraction. Moreover the
same scenario provides an explanation of the maximum in the energy spectrum of
the modulation amplitude detected by DAMA in terms of WIMPs whose minimal
incoming speed matches the kinematic threshold for inelastic upscatters. For
the elastic case the detection of such maximum suggests an inversion of the
modulation phase below the present DAMA energy threshold, while this is not
expected for inelastic scattering. This may allow to discriminate between the
two scenarios in a future low-threshold analysis of the DAMA data. |
WIMP physics with ensembles of direct-detection experiments: The search for weakly-interacting massive particle (WIMP) dark matter is
multi-pronged. Ultimately, the WIMP-dark-matter picture will only be confirmed
if different classes of experiments see consistent signals and infer the same
WIMP properties. In this work, we review the ideas, methods, and status of
direct-detection searches. We focus in particular on extracting WIMP physics
(WIMP interactions and phase-space distribution) from direct-detection data in
the early discovery days when multiple experiments see of order dozens to
hundreds of events. To demonstrate the essential complementarity of different
direct-detection experiments in this context, we create mock data intended to
represent the data from the near-future Generation 2 experiments. We consider
both conventional supersymmetry-inspired benchmark points (with
spin-independent and -dependent elastic cross sections just below current
limits), as well as benchmark points for other classes of models (inelastic and
effective-operator paradigms). We also investigate the effect on parameter
estimation of loosening or dropping the assumptions about the local WIMP
phase-space distribution. We arrive at two main conclusions. Firstly, teasing
out WIMP physics with experiments depends critically on having a wide set of
detector target materials, spanning a large range of target nuclear masses and
spin-dependent sensitivity. It is also highly desirable to obtain data from
low-threshold experiments. Secondly, a general reconstruction of the local WIMP
velocity distribution, which will only be achieved if there are multiple
experiments using different target materials, is critical to obtaining a robust
and unbiased estimate of the WIMP mass. | Photometric redshift estimation of strongly lensed galaxies: Around $10^5$ strongly lensed galaxies are expected to be discovered with
Euclid and the LSST. Utilising these large samples to study the inner structure
of lens galaxies requires source redshifts, to turn lens models into mass
measurements. However, obtaining spectroscopic source redshifts for large lens
samples is prohibitive with the capacity of spectroscopic facilities.
Alternatively, we study the possibility of obtaining source photometric
redshifts (photo-zs) for large lens samples. Our strategy consists of
deblending the source and lens light by simultaneously modelling the lens and
background source in all available photometric bands, and feeding the derived
source colours to a template-fitting photo-z algorithm. We describe the lens
and source light with a Sersic profile, and the lens mass with a Singular
Isothermal Ellipsoid. We test our approach on a simulated and a real sample of
lenses, both in broad-band photometry of the Hyper Suprime-Cam survey. We
identify the deviations of the lens light from a Sersic profile and the
contrast between the lens and source image as the main drivers of the source
colour measurement error. We split the real sample based on the ratio $\Lambda$
of the lens to source surface brightness measured at the image locations. In
the $\Lambda<1$ regime, the photo-z outlier fraction is $20\%$, and the
accuracy of photo-z estimation is limited by the performance of
template-fitting process. In the opposite regime, the photo-z outlier fraction
is $75\%$, and the errors from the source colour measurements dominate the
photo-z uncertainty. Measuring source photo-zs for lenses with $\Lambda<1$
poses no particular challenges, compared to isolated galaxies. For systems with
significant lens light contamination, however, improving the description of the
surface brightness distribution of the lens is required: a single Sersic model
is not sufficiently accurate. |
The SRG/eROSITA All-Sky Survey: The first catalog of galaxy clusters and
groups in the Western Galactic Hemisphere: Clusters of galaxies can be used as powerful probes to study astrophysical
processes on large scales, test theories of the growth of structure, and
constrain cosmological models. The driving science goal of the SRG/eROSITA
All-Sky Survey (eRASS) is to assemble a large sample of X-ray-selected clusters
with a well-defined selection function to determine the evolution of the mass
function and, hence, the cosmological parameters. We present here a catalog of
12247 optically confirmed galaxy groups and clusters detected in the 0.2-2.3
keV as extended X-ray sources in a 13,116deg$^2$ region in the western Galactic
hemisphere of the sky, which eROSITA surveyed in its first six months of
operation. The clusters in the sample span the redshift range $0.003<z<1.32$.
The majority (68%) of these clusters, 8361 sources, represent new discoveries
without known counterparts in the literature. The mass range of the sample
covers three orders of magnitude from $5\times10^{12}M_{\rm sun}$ to
$2\times10^{15}M_{\rm sun}$. We construct a sample for cosmology with a higher
purity level (~95%) than the primary sample, comprising 5259 securely detected
and confirmed clusters in the 12791deg$^{2}$ common footprint with the DESI
Legacy Survey DR10. We characterize the X-ray properties of each cluster,
including their flux, luminosity and temperature, the total mass, gas mass, gas
mass fraction, and mass proxy $Y_{X}$. These are determined within two
apertures, 300 kpc, and the overdensity radius $R_{500}$, and are calculated by
applying a forward modeling approach with a rigorous X-ray background
treatment, K-factor, and the Galactic absorption corrections. Population
studies utilizing LogN-LogS, the number of clusters detected above a given flux
limit, and the luminosity function show overall agreement with the previous
X-ray surveys after accounting for the survey completeness and purity
(ABRIDGED) | Galaxy Stellar Mass Assembly between 0.2<z<2 from the S-COSMOS survey: We follow the galaxy stellar mass assembly by morphological and spectral type
in the COSMOS 2-deg^2 field. We derive the stellar mass functions and stellar
mass densities from z=2 to z=0.2 using 196,000 galaxies selected at F(3.6
micron) > 1 microJy with accurate photometric redshifts
(sigma_((zp-zs)/(1+zs))=0.008 at i<22.5). Using a spectral classification, we
find that z~1 is an epoch of transition in the stellar mass assembly of
quiescent galaxies. Their stellar mass density increases by 1.1 dex between
z=1.5-2 and z=0.8-1 (Delta t ~2.5 Gyr), but only by 0.3 dex between z=0.8-1 and
z~0.1 (Delta t ~ 6 Gyr). Then, we add the morphological information and find
that 80-90% of the massive quiescent galaxies (log(M)~11) have an elliptical
morphology at z<0.8. Therefore, a dominant mechanism links the shutdown of star
formation and the acquisition of an elliptical morphology in massive galaxies.
Still, a significant fraction of quiescent galaxies present a Spi/Irr
morphology at low mass (40-60% at log(M)~9.5), but this fraction is smaller
than predicted by semi-analytical models using a ``halo quenching'' recipe. We
also analyze the evolution of star-forming galaxies and split them into
``intermediate activity'' and ``high activity'' galaxies. We find that the most
massive ``high activity'' galaxies end their high star formation rate phase
first. Finally, the space density of massive star-forming galaxies becomes
lower than the space density of massive elliptical galaxies at z<1. As a
consequence, the rate of ``wet mergers'' involved in the formation of the most
massive ellipticals must decline very rapidly at z<1, which could explain the
observed slow down in the assembly of these quiescent and massive sources. |
CMB spectra and bispectra calculations: making the flat-sky
approximation rigorous: This article constructs flat-sky approximations in a controlled way in the
context of the cosmic microwave background observations for the computation of
both spectra and bispectra. For angular spectra, it is explicitly shown that
there exists a whole family of flat-sky approximations of similar accuracy for
which the expression and amplitude of next to leading order terms can be
explicitly computed. It is noted that in this context two limiting cases can be
encountered for which the expressions can be further simplified. They
correspond to cases where either the sources are localized in a narrow region
(thin-shell approximation) or are slowly varying over a large distance (which
leads to the so-called Limber approximation). Applying this to the calculation
of the spectra it is shown that, as long as the late integrated Sachs-Wolfe
contribution is neglected, the flat-sky approximation at leading order is
accurate at 1% level for any multipole. Generalization of this construction
scheme to the bispectra led to the introduction of an alternative description
of the bispectra for which the flat-sky approximation is well controlled. This
is not the case for the usual description of the bispectrum in terms of reduced
bispectrum for which a flat-sky approximation is proposed but the
next-to-leading order terms of which remain obscure. | On Identifying the Progenitors of Type Ia Supernovae: We propose two new means of identifying the main class of progenitors of Type
Ia supernovae--single or double degenerate: (i) If the range of supernova
properties is significantly determined by the range of viewing angles of
non-spherically symmetric explosions, then the nature of the correlation
between polarization and another property (for example, the velocity gradient)
can be used to determine the geometry of the asymmetry and hence the nature of
the progenitor, and (ii) in the double- but not in the single-degenerate case,
the range in the observed properties (e.g., velocity gradients) is likely to
increase with the amount of carbon seen in the ejecta. |
Weak Lensing Measurement of the Mass--Richness Relation of SDSS
redMaPPer Clusters: We perform a measurement of the mass--richness relation of the redMaPPer
galaxy cluster catalogue using weak lensing data from the Sloan Digital Sky
Survey. We have carefully characterized a broad range of systematic
uncertainties, including shear calibration errors, photo-$z$ biases, dilution
by member galaxies, source obscuration, magnification bias, incorrect
assumptions about cluster mass profiles, cluster centering, halo triaxiality,
and projection effects. We also compare measurements of the lensing signal from
two independently-produced shear and photometric redshift catalogues to
characterize systematic errors in the lensing signal itself. Using a sample of
5,570 clusters from $0.1\le z\le 0.33$, the normalization of our power-law mass
vs.\ $\lambda$ relation is $\log_{10}[M_{200m}/h^{-1}\ M_{\odot}]$ = $14.344
\pm 0.021$ (statistical) $\pm 0.023$ (systematic) at a richness $\lambda=40$, a
7 per cent calibration uncertainty, with a power-law index of
$1.33^{+0.09}_{-0.10}$ ($1\sigma$). The detailed systematics characterization
in this work renders it the definitive weak lensing mass calibration for SDSS
redMaPPer clusters at this time. | Cosmic acceleration a new review: Recent observations of near supernova show that the acceleration expansion of
Universe decreases. This phenomenon is called the transient acceleration. In
the second part of work we consider the 3-component Universe composed of a
scalar field, interacting with the dark matter on the agegraphic dark energy
background. We show that the transient acceleration appears in frame of such a
model. The obtained results agree with the latest cosmological observations,
namely, the 557 SNIa sample (Union2) was released by the Supernova Cosmology
Project (SCP) Collaboration. |
Turnaround density as a probe of the cosmological constant: Spherical collapse predicts that a single value of the turnaround density
(average matter density within the scale on which a structure detaches from the
Hubble flow) characterizes all cosmic structures at the same redshift. It has
been recently shown by Korkidis et al. that this feature persists in complex
non-spherical galaxy clusters identified in N-body simulations. Here we show
that the low-redshift evolution of the turnaround density constrains the
cosmological parameters, and that it can be used to derive a local constraint
on $\Omega_\Lambda$ alone, independent of $\Omega_m$. The turnaround density
thus provides a promising new way to exploit upcoming large cosmological
datasets. | Evolution of the cosmic matter density field with a primordial magnetic
field: A cosmological magnetic field affects the time evolution of the cosmic matter
density field. The squared Alfven velocity of the cosmic fluid is proportional
to an ensemble average energy density of a primordial magnetic field (PMF), and
it prevents the matter density field from collapsing in the horizon scale. The
matter-radiation equality time also is delayed by the presence of an ensemble
average energy density of a PMF. The ensemble average energy density of the PMF
also affects the matter power spectrum (MPS) through the Meszaros effect and
the potential decay. Since the ensemble average energy density of the PMF is
not a first order perturbation but a zero order source in the linear
perturbation equations for the cosmology, to correctly understand the overall
effects of the PMF on the MPS, we should significantly revise previous
approaches to research for the MPS with the PMF by considering both the effects
of the zero and first order sources from the PMF in the linear perturbation
theory. We apply the effects of the zero order sources from the PMF to
theoretical computations of the MPS for the first time. We also analyze the
overall PMF effects on the MPS. The CMB polarizations are affected the weak
lensing. The weak lensing is determined by the MPS. Therefore, we have to
consider the zero order sources of the PMF to gain a correct understanding not
only of the MPS but also the CMB polarization. |
On Cosmological Low Entropy After the Big Bang: Universal Expansion and
Nucleosynthesis: We investigate the sensitivity of a universe's nuclear entropy after Big Bang
nucleosynthesis (BBN) to variations in both the baryon-to-photon ratio and the
temporal evolution of cosmological expansion. Specifically, we construct
counterfactual cosmologies to quantify the degree by which these two parameters
must vary from those in our Universe before we observe a substantial change in
the degree of fusion, and thus nuclear entropy, during BBN. We find that, while
the post-BBN nuclear entropy is indeed linked to baryogenesis and the
Universe's expansion history, the requirement of leftover light elements does
not place strong constraints on the properties of these two cosmological
processes. | Constraints on the origin of the radio synchrotron background via
angular correlations: The origin of the radio synchrotron background (RSB) is currently unknown.
Its understanding might have profound implications in fundamental physics or
might reveal a new class of radio emitters. In this work, we consider the
scenario in which the RSB is due to extragalactic radio sources and measure the
angular cross-correlation of LOFAR images of the diffuse radio sky with matter
tracers at different redshifts, provided by galaxy catalogs and CMB lensing. We
compare these measured cross-correlations to those expected for models of RSB
sources. We find that low-redshift populations of discrete sources are excluded
by the data, while higher redshift explanations are compatible with available
observations. We also conclude that at least 20\% of the RSB surface brightness
level must originate from populations tracing the large-scale distribution of
matter in the universe, indicating that at least this fraction of the RSB is of
extragalactic origin. Future measurements of the correlation between the RSB
and tracers of high-redshift sources will be crucial to constraining the source
population of the RSB. |
Tidal stirring of Milky Way satellites: a simple picture with the
integrated tidal force: Most of dwarf spheroidal galaxies in the Local Group were probably formed via
environmental processes like the tidal interaction with the Milky Way. We study
this process via N-body simulations of dwarf galaxies evolving on seven
different orbits around the Galaxy. The dwarf galaxy is initially composed of a
rotating stellar disk and a dark matter halo. Due to the action of tidal forces
it loses mass and the disk gradually transforms into a spheroid while stellar
motions become increasingly random. We measure the characteristic scale-length
of the dwarf, its maximum circular velocity, mass, shape and kinematics as a
function of the integrated tidal force along the orbit. The final properties of
the evolved dwarfs are remarkably similar if the total tidal force they
experienced was the same, independently of the actual size and eccentricity of
the orbit. | Robustness of direct measurements of the mean free path of ionizing
photons in the epoch of reionization: Measurements of the mean free path of Lyman-continuum photons in the
intergalactic medium during the epoch of reionization can help constrain the
nature of the sources as well as sinks of hydrogen-ionizing radiation. A recent
approach to this measurement has been to utilize composite spectra of multiple
quasars at $z\sim 6$, and infer the mean free path after correcting the spectra
for the presence of quasar proximity zones. This has revealed not only a steep
drop in the mean free path from $z=5$ to $z=6$, but also potentially a mild
tension with reionization simulations. We critically examine such direct
measurements of the mean free path for biases due to quasar environment,
incomplete reionization, and quasar proximity zones. Using cosmological
radiative transfer simulations of reionization combined with one-dimensional
radiative transfer calculations of quasar proximity zones, we find that the
bias in the mean free path due to overdensities around quasars is minimal at
$z\sim 6$. Patchiness of reionization at this redshift also does not affect the
measurements significantly. Fitting our model to the data results in a mean
free path of $\lambda_{\mathrm{mfp}}=0.90^{+0.66}_{-0.40}$ pMpc at $z=6$, which
is consistent with the recent measurements in the literature, indicating
robustness with respect to the modelling of quasar proximity zones. We also
compare various ways in which the mean free path has been defined in
simulations before the end of reionization. Overall, our finding is that recent
measurements of the mean free path appear to be robust relative to several
sources of potential bias. |
The Decay of the Standard Model Higgs after Inflation: We study the nonperturbative dynamics of the Standard Model (SM) after
inflation, in the regime where the SM is decoupled from (or weakly coupled to)
the inflationary sector. We use classical lattice simulations in an expanding
box in (3+1) dimensions, modeling the SM gauge interactions with both global
and Abelian-Higgs analogue scenarios. We consider different post-inflationary
expansion rates. During inflation, the Higgs forms a condensate, which starts
oscillating soon after inflation ends. Via nonperturbative effects, the
oscillations lead to a fast decay of the Higgs into the SM species,
transferring most of the energy into $Z$ and $W^{\pm}$ bosons. All species are
initially excited far away from equilibrium, but their interactions lead them
into a stationary stage, with exact equipartition among the different energy
components. From there on the system eventually reaches equilibrium. We have
characterized in detail, in the different expansion histories considered, the
evolution of the Higgs and of its dominant decay products, until equipartition
is established. We provide a useful mapping between simulations with different
parameters, from where we derive a master formula for the Higgs decay time, as
a function of the coupling constants, Higgs initial amplitude and
postinflationary expansion rate. | Lyman-$α$ polarization from cosmological ionization fronts: II.
Implications for intensity mapping: This is the second paper in a series whose aim is to predict the power
spectrum of intensity and polarized intensity from cosmic reionization fronts.
After building the analytic models for intensity and polarized intensity
calculations in paper I, here we apply these models to simulations of
reionization. We construct a geometric model for identifying front boundaries,
calculate the intensity and polarized intensity for each front, and compute a
power spectrum of these results. This method was applied to different
simulation sizes and resolutions, so we ensure that our results are convergent.
We find that the power spectrum of fluctuations at $z=8$ in a bin of width
$\Delta z=0.5$ ($\lambda/\Delta\lambda=18$) is $\Delta_\ell \equiv
[\ell(\ell+1)C_\ell/2\pi]^{1/2}$ is $3.2\times 10^{-11}$ erg s$^{-1}$ cm$^{-2}$
sr$^{-1}$ for the intensity $I$, $7.6\times10^{-13}$ erg s$^{-1}$ cm$^{-2}$
sr$^{-1}$ for the $E$-mode polarization, and $5.8\times10^{-13}$ erg s$^{-1}$
cm$^{-2}$ sr$^{-1}$ for the $B$-mode polarization at $\ell=1.5\times10^4$.
After computing the power spectrum, we compare results to detectable scales and
discuss implications for observing this signal based on a proposed experiment.
We find that, while fundamental physics does not exclude this kind of mapping
from being attainable, an experiment would need to be highly ambitious and
require significant advances to make mapping Lyman-$\alpha$ polarization from
cosmic reionization fronts a feasible goal. |
CMB spectral distortions constraints on primordial black holes, cosmic
strings and long lived unstable particles revisited: We calculate the spectral distortions from Hawking evaporation of primordial
black holes before the epoch of recombination, taking into account emission of
all standard model particles, including quark and gluons, and evolving the
resulting particle cascades in the expanding Universe. We show that the
constraints on the abundance of primordial black holes are stronger by more
than an order of magnitude compared to the previous calculations which take
only the primary photon emission into account. We also show that the shapes of
the spectral distortions is different from the $y$ or $i$-type distortions and
are sensitive to the mass of the primordial black holes. We also extend
previous constraints on the decay of long lived unstable particles before
recombination to additional decay channels. We show that for dark matter mass
$\lesssim$ 1 GeV, the spectral distortion shape is a function of the dark
matter mass as well as the decay channel to standard model particles. We also
provide new spectral distortion constraints on superconducting cosmic string
decay. We explicitly show that consideration of emitted photon spectrum from
string decay is not only important for the future experiments but also for
already available COBE-FIRAS data. | Higgs inflation with the Holst and the Nieh-Yan term: The action of loop quantum gravity includes the Holst term and/or the
Nieh-Yan term in addition to the Ricci scalar. These terms are expected to
couple non-minimally to the Higgs. Thus the Holst and Nieh-Yan terms contribute
to the classical equations of motion, and they can have a significant impact on
inflation.
We derive inflationary predictions in the parameter space of the non-minimal
couplings, including non-minimally coupled terms up to dimension 4. Successful
inflation is possible even with zero or negative coupling of the Ricci scalar.
Notably, inflation supported by the non-minimally coupled Holst term alone
gives almost the same observables as the original metric formulation plateau
Higgs inflation. A non-minimally coupled Nieh-Yan term alone cannot give
successful inflation. When all three terms are considered, the predictions for
the spectral index and tensor-to-scalar ratio span almost the whole range
probed by upcoming experiments. This is not true for the running of the
spectral index, and many cases are highly tuned. |
Foreground contamination in Ly-alpha intensity mapping during the epoch
of reionization: The intensity mapping of Ly-alpha emission during the epoch of reionization
(EoR) will be contaminated by foreground emission lines from lower redshifts.
We calculate the mean intensity and power spectrum of Ly-alpha emission at z~7,
and estimate the uncertainties according to the relevant astrophysical
processes. We find that the low-redshift emission lines from 6563 A H-alpha,
5007 A [OIII] and 3727 A [OII] will be the strong contaminants on the observed
Ly-alpha power spectrum. We make use of both the star formation rate (SFR) and
luminosity functions (LF) to estimate the mean intensity and power spectra of
the three foreground lines at z~0.5 for H-alpha, z~0.9 for [OIII] and z~1.6 for
[OII], as they will contaminate the Ly-alpha emission at z~7. The [OII] line is
found to be the strongest. We analyze the masking of the bright survey pixels
with a foreground line above some line intensity threshold as a way to reduce
the contamination in the intensity mapping survey. We find that the foreground
contamination can be neglected if we remove the pixels with fluxes above
1.4x10^-20 W/m^2. | Dark Energy after GW170817: dead ends and the road ahead: Multi-messenger gravitational wave (GW) astronomy has commenced with the
detection of the binary neutron star merger GW170817 and its associated
electromagnetic counterparts. The almost coincident observation of both signals
places an exquisite bound on the GW speed $|c_g/c-1|\leq5\cdot10^{-16}$. We use
this result to probe the nature of dark energy (DE), showing that a large class
of scalar-tensor theories and DE models are highly disfavored. As an example we
consider the covariant Galileon, a cosmologically viable, well motivated
gravity theory which predicts a variable GW speed at low redshift. Our results
eliminate any late-universe application of these models, as well as their
Horndeski and most of their beyond Horndeski generalizations. Three
alternatives (and their combinations) emerge as the only possible scalar-tensor
DE models: 1) restricting Horndeski's action to its simplest terms, 2) applying
a conformal transformation which preserves the causal structure and 3)
compensating the different terms that modify the GW speed (to be robust, the
compensation has to be independent on the background on which GWs propagate).
Our conclusions extend to any other gravity theory predicting varying $c_g$
such as Einstein-Aether, Ho\v{r}ava gravity, Generalized Proca, TeVeS and other
MOND-like gravities. |
An 8.0\% Determination of the Baryon Fraction in the Intergalactic
Medium from Localized Fast Radio Bursts: The dispersion measure (DM)--redshift relation of fast radio bursts (FRBs)
has been proposed as a potential new tool for probing intergalactic medium
(IGM) and for studying cosmology. However, the poor knowledge of the baryon
fraction in the IGM ($f_{\mathrm{IGM}}$) and its degeneracy with cosmological
parameters impose restrictions on the cosmological applications of FRBs.
Furthermore, DMs contributed by the IGM ($\mathrm{DM_{IGM}}$) and host galaxy
($\mathrm{DM_{host}}$), important cosmological quantities, cannot be exactly
extracted from observations, which would bring uncontrolled systematic
uncertainties in FRB cosmology. In this work, we use seventeen localized FRBs
to constrain $f_{\mathrm{IGM}}$ and its possible redshift evolution. Other
cosmological probes such as type Ia supernovae, baryon acoustic oscillations,
and cosmic microwave background radiation are combined to break parameter
degeneracy. Taking into account the probability distributions of
$\mathrm{DM_{IGM}}$ and $\mathrm{DM_{host}}$ derived from the the IllustrisTNG
simulation, we obtain a robust measurement of $f_{\mathrm{IGM}}=0.927\pm0.075$,
representing a precision of 8.0\%. We find that there is no strong evidence for
the redshift dependence of $f_{\mathrm{IGM}}$ at the current observational data
level. The rapid progress in localizing FRBs will significantly improve the
constraints on $f_{\mathrm{IGM}}$. | Background of radio photons from primordial black holes: We compute the isotropic radiation background due to Hawking emission from
primordial black holes (PBHs), and examine if this background is a viable
option in explaining the excess radiowave background observed by the ARCADE2
and LWA1 experiments at $\lesssim 1\,$GHz. We find that even under the extreme
assumption that all of the dark matter is in the form of PBHs, the radio
brightness temperature induced by Hawking evaporation of PBHs is
$\mathcal{O}(10^{-46})\,$K, highly subdominant compared to the cosmic microwave
background. The main reason for this is that for PBHs in the mass range
$\sim10^{12}$-$10^{14}\,$kg, which can be constrained by Hawking emission, the
spectrum peaks at $10^7$ to $10^5\,$eV. As the Hawking spectrum is power law
suppressed towards lower energies, negligible flux of $\mu$eV photons is
obtained. The peak of the Hawking spectrum shifts to lower energies for higher
masses, but the number density is low and so is the specific intensity. Because
Hawking emission from PBHs is thus unable to explain the observed excess radio
background, we also consider the alternative possibility of radio emission from
gas accretion onto supermassive PBHs. These PBHs can readily produce strong
radio emission that could easily explain the ARCADE2/LWA1 excess. |
Quasar Absorption Lines from Radiative Shocks: Implications for
Multiphase Outflows and Feedback: Photoionization modeling of certain low-ionization broad absorption lines in
quasars implies very compact (Delta R~0.01 pc), galaxy-scale (R kpc) absorbers
blueshifted by several 1000 km s^-1. While these are likely signatures of
quasar outflows, the lifetimes of such compact absorbers are too short for them
to be direct ejecta from a nuclear wind. Instead, I argue that the absorbing
clouds must be transient and created in situ. Following arguments detailed by
Faucher-Giguere, Quataert, & Murray (2011), I show that a model in which the
cool absorbers form in radiative shocks arising when a quasar blast wave
impacts an interstellar cloud along the line of sight successfully explains the
key observed properties. Using this radiative shock model, the outflow kinetic
luminosities for three luminous quasars are estimated to be Edot,k~2-5% L_AGN
(with corresponding momentum fluxes Pdot~2-15 L_AGN/c), consistent with
feedback models of the M-sigma relation. These energetics are similar to those
recently inferred of molecular outflows in local ultra-luminous infrared
galaxies and in post-starburt winds, suggesting that active galactic nuclei
(AGN) are capable of driving such outflows. Radiative shocks probably affect
the multiphase structure of outflows in a range of other systems, including
narrower and higher-ionization quasar absorption lines, and compact
intergalactic absorbers ejected by star formation and AGN activity. | The morphology of the redshifted 21-cm signal from the Cosmic Dawn: The spatial fluctuations in the tomographic maps of the redshifted 21-cm
signal from the Cosmic Dawn (CD) crucially depend on the size and distribution
of the regions with gas temperatures larger than the radio background
temperature. In this article, we study the morphological characteristics of
such emission regions and their absorption counterparts using the shape
diagnostic tool {\sc surfgen2}. Using simulated CD brightness temperature cubes
of the 21-cm signal, we find that the emission regions percolate at stages with
the filling factor of the emission regions $FF_{\rm emi}\gtrsim 0.15$.
Percolation of the absorption regions occurs for $FF_{\rm abs}\gtrsim 0.05$.
The largest emission and absorption regions are topologically complex and
highly filamentary for most parts of the CD. The number density of these
regions as a function of the volume shows the power-law nature with the
power-law indexes $\approx -2$ and $-1.6$ for the emission and absorption
regions, respectively. Overall, the planarity, filamentarity and genus increase
with the increase of the volume of both emission and absorption regions. |
Cosmology with 21cm intensity mapping: The nature of the most abundant components of the Universe, dark energy and
dark matter, is still to be uncovered. I tackle this subject considering a
novel cosmological probe: the neutral hydrogen emitted 21cm radiation, observed
with the intensity mapping technique. I analyse competitive and realistic dark
energy and dark matter models and show how they produce distinctive and
detectable effects on the 21cm signal. Moreover, I provide radio telescope
forecasts showing how these models will be distinguishable in an unprecedented
way. | 3D Spherical Analysis of Baryon Acoustic Oscillations: Baryon Acoustic Oscillations (BAOs) are oscillatory features in the galaxy
power spectrum and are a standard rod to measure the cosmological expansion.
These have been studied in Cartesian space (Fourier or real space) or in
Spherical Harmonic (SH) space in thin shells. Future wide-field surveys will
cover both wide and deep regions of the sky and thus require a simultaneous
treatment of the spherical sky and of an extended radial coverage. The
Spherical Fourier-Bessel (SFB) decomposition is a natural basis for the
analysis of fields in this geometry and facilitates the combination of BAO
surveys with other cosmological probes readily described in this basis. We
present here a new way to analyse BAOs by studying the BAO wiggles from the SFB
power spectrum. In SFB space, the power spectrum generally has both a radial
(k) and tangential (l) dependence and so do the BAOs. In the deep survey limit
and ignoring evolution, the SFB power spectrum becomes radial and reduces to
the Cartesian Fourier power spectrum. In the limit of a thin shell, all the
information is contained in the tangential modes described by the 2D SH power
spectrum. We find that the radialisation of the SFB power spectrum is still a
good approximation even when considering an evolving and biased galaxy field
with a finite selection function. This effect can be observed by all-sky
surveys with depths comparable to current surveys. We find that the BAOs
radialise more rapidly than the full SFB power spectrum. Our results suggest
the first peak of the BAOs in SFB space becomes radial out to l ~ 10 for
all-sky surveys with the same depth as SDSS or 2dF, and out to l ~ 70 for an
all-sky stage IV survey. Subsequent BAO peaks also become radial, but for
shallow surveys these may be in the non-linear regime. For modes that have
become radial, measurements at different l's are useful in practice to reduce
measurement errors. |
Measuring Cosmological Distances Using Cluster Edges as a Standard Ruler: The line-of-sight velocity dispersion profile of galaxy clusters exhibits a
"kink" corresponding to the spatial extent of orbiting galaxies. Because the
spatial extent of a cluster is correlated with the amplitude of the velocity
dispersion profile, we can utilise this feature as a gravity-calibrated
standard ruler. Specifically, the amplitude of the velocity dispersion data
allows us to infer the physical cluster size. Consequently, observations of the
angular scale of the "kink" in the profile can be translated into a distance
measurement to the cluster. Assuming the relation between cluster radius and
cluster velocity dispersion can be calibrated from simulations, we forecast
that with existing data from the Sloan Digital Sky Survey (SDSS) we will be
able to measure the Hubble constant with $3\%$ precision. Implementing our
method with data from the Dark Energy Spectroscopic Instrument (DESI) will
result in a $1.3\%$ measurement of the Hubble constant. Adding cosmological
supernova data improves the uncertainty of the DESI measurement to $0.7\%$. | CMB constraints on monodromy inflation at strong coupling: We carry out a thorough numerical examination of field theory monodromy
inflation at strong coupling. We perform an MCMC analysis using a Gaussian
likelihood, fitting multiparameter models using CMB constraints on the spectral
index and the tensor to scalar ratio. We show that models with uniquely
positive Wilson coefficients are ruled out. If there are coefficients that can
take on both signs, there can be a cancellation of terms that flattens the
potentials and allows one to satisfy current data, and forecasts with strong
constraints on the tensor to scalar ratio. Models of field theory monodromy are
naturally enhanced to include a mechanism for canceling off radiative
corrections to vacuum energy, via vacuum energy sequestering (VES). Although
they include a much larger parameter space, we find that a similar numerical
examination yields no significant change in the Bayesian evidence for VES
enhanced models, with naturalness considerations making them more attractive
from a theoretical perspective. |
Classical Cosmological Tests for Galaxies of the Hubble Ultra Deep Field: Images of the Hubble Ultra Deep Field are analyzed to obtain a catalog of
galaxies for which the angular sizes, surface brightness, photometric
redshifts, and absolute magnitudes are found. The catalog contains a total of
about 4000 galaxies identified at a high signal-to-noise ratio, which allows
the cosmological relations angular size{redshift and surface
brightness-redshift to be analyzed. The parameters of the evolution of linear
sizes and surface brightness of distant galaxies in the redshift interval
0.5-6.5 are estimated in terms of a grid of cosmological models with different
density parameters. The distribution of photometric redshifts of galaxies is
analyzed and possible superlarge inhomogeneities in the radial distribution of
galaxies are found with scale lengths as large as 2000 Mpc. | Groups of Galaxies at Intermediate Redshift: Galaxy groups are key tracers of galaxy evolution, cluster evolution, and
structure formation, yet they are difficult to study at even moderate redshift.
We have undertaken a project to observe a flux-limited sample of
intermediate-redshift (0.1 < z < 0.5) group candidates identified by the
XBootes Chandra survey. When complete, this project will nearly triple the
current number of groups with measured temperatures in this redshift range.
Here we present deep Suzaku/XIS and Chandra/ACIS follow-up observations of the
first 10 targets in this project; all are confirmed sources of diffuse, thermal
emission with derived temperatures and luminosities indicative of rich
groups/poor clusters. By exploiting the multi-wavelength coverage of the
XBootes/NOAO Deep Wide Field Survey (NDWFS) field, we aim to (1) constrain
non-gravitational effects that alter the energetics of the intragroup medium,
and (2) understand the physical connection between the X-ray and optical
properties of groups. We discuss the properties of the current group sample in
the context of observed cluster scaling relations and group and cluster
evolution and outline the future plans for this project. |
Specific heat and entropy of tachyon Fermi gas: We consider an ideal Fermi gas of tachyons and derive a low temperature
expansion of its thermodynamical functions. The tachyonic specific heat is
linear dependent on temperature $C_V=\epsilon_Fk_FT$ and formally coincides
with the specific heat of electron gas if the tachyon Fermi energy is defined
as $\epsilon_F=\sqrt{k_F-m^2}$. | Searching for Neutral Hydrogen Halos around z ~ 2.1 and z ~ 3.1 Ly-alpha
Emitting Galaxies: We search for evidence of diffuse Ly-alpha emission from extended neutral
hydrogen surrounding Ly-alpha emitting galaxies (LAEs) using deep narrow-band
images of the Extended Chandra Deep Field South. By stacking the profiles of
187 LAEs at z = 2.06, 241 LAEs at z = 3.10, and 179 LAEs at z = 3.12, and
carefully performing low-surface brightness photometry, we obtain mean surface
brightness maps that reach 9.9, 8.7, and 6.2 * 10^{-19} ergs cm^{-2} s^{-1}
arcsec^{-2} in the emission line. We undertake a thorough investigation of
systematic uncertainties in our surface brightness measurements, and find that
our limits are 5--10 times larger than would be expected from Poisson
background fluctuations; these uncertainties are often underestimated in the
literature. At z ~ 3.1, we find evidence for extended halos with small scale
lengths of 5--8 kpc in some, but not all of our sub-samples. We demonstrate
that sub-samples of LAEs with low equivalent widths and brighter continuum
magnitudes are more likely to possess such halos. At z ~ 2.1, we find no
evidence of extended Ly-alpha emission down to our detection limits. Through
Monte-Carlo simulations, we also show that we would have detected large diffuse
LAE halos if they were present in our data sets. We compare these findings to
other measurements in the literature, and discuss possible instrumental and
astrophysical reasons for the discrepancies. |
Constraining sterile neutrino cosmologies with strong gravitational
lensing observations at redshift z~0.2: We use the observed amount of subhaloes and line-of-sight dark matter haloes
in a sample of 11 gravitational lens systems from the Sloan Lens ACS Survey to
constrain the free-streaming properties of the dark matter particles. In
particular, we combine the detection of a small-mass dark matter halo by
Vegetti et al. 2010 with the non-detections by Vegetti et al. 2014 and compare
the derived subhalo and halo mass functions with expectations from cold dark
matter (CDM) and resonantly produced sterile neutrino models. We constrain the
half-mode mass, i.e. the mass scale at which the linear matter power spectrum
is reduced by 50 per cent relatively to the CDM model, to be $\log M_{\rm{hm}}
\left[M_\odot\right] < 12.0$ (equivalent thermal relic mass $m_{\rm th} > 0.3$
keV) at the 2$\sigma$ level. This excludes sterile neutrino models with
neutrino masses $m_{\rm s} < 0.8$ keV at any value of $L_{\rm 6}$. Our
constraints are weaker than currently provided by the number of Milky Way
satellites, observations of the 3.5 keV X-ray line, and the Lyman $\alpha$
forest. However, they are more robust than the former as they are less affected
by baryonic processes. Moreover, unlike the latter, they are not affected by
assumptions on the thermal histories for the intergalactic medium.
Gravitational lens systems with higher data quality and higher source and lens
redshift are required to obtain tighter constraints. | Etherington duality breaking: gravitational lensing in non-metric
spacetimes versus intrinsic alignments: The Etherington distance duality relation is well-established for metric
theories of gravity, and confirms the duality between the luminosity distance
and the angular diameter distance through the conservation of surface
brightness. A violation of the Etherington distance duality due to lensing in a
non-metric spacetime would lead to fluctuations in surface brightness of
galaxies. Likewise, fluctuations of the surface brightness can arise in
classical astrophysics as a consequence of intrinsic tidal interaction of
galaxies with their environment. Therefore, we study these in two cases in
detail: Firstly, for intrinsic size fluctuations and the resulting changes in
surface brightness, and secondly, for an area-metric spacetime as an example of
a non-metric spacetime where the distance duality relation itself acquires
modifications. The aim of this work is to quantify whether a surface brightness
fluctuation effect due to area-metric gravity would be resolvable compared to
the similar effect caused by intrinsic alignment. We thus compare the auto- and
cross-correlations of the angular spectra in these two cases and show that the
fluctuations in intrinsic brightness can potentially be measured with a
cumulative signal-to-noise ratio $\Sigma(\ell) \geq 3$ in a Euclid-like survey.
The measurement in area-metric spacetimes, however, depends on the specific
parameter choices, which also determine the shape and amplitude of the spectra.
While lensing surveys do have sensitivity to lensing-induced surface brightness
fluctuations in area-metric spacetimes, the measurement does not seem to be
possible for natural values of the Etherington-breaking parameters. |
The clustering of $z > 7$ galaxies: Predictions from the BLUETIDES
simulation: We study the clustering of the highest-z galaxies (from ~ $0.1$ to a few tens
Mpc scales) using the BLUETIDES simulation and compare it to current
observational constraints from Hubble legacy and Hyper Suprime Cam (HSC) fields
(at $z=6-7.2$). With a box length of $400$ $Mpc/h$ on each side and $0.7$
trillion particles, BLUETIDES is the largest high resolution cosmological
hydrodynamic simulation to date ideally suited for studies of high-z galaxies.
We find that galaxies with magnitude $m_{UV}<27.7$ have a bias ($b_g$) of
$8.1\pm 1.2$ at $z=8$, and typical halo masses $M_H \gtrsim 6\times10^{10}
M_{\odot}$. Given the redshift evolution between $z=8$ to $z=10$
($b_g\propto(1+z)^{1.6}$), our inferred values of the bias and halo masses are
consistent with measured angular clustering at $z \sim 6.8$ from these brighter
samples. The bias of fainter galaxies (in the Hubble legacy field at $H_{160}
\lesssim29.5$) is $5.9\pm0.9$ at $z=8$ corresponding to halo masses $M_H
\gtrsim 10^{10} M_{\odot}$. We investigate directly the 1-halo term inthe
clustering and show that it dominates on scales $r \lesssim 0.1$ Mpc/$h$
($\Theta \lesssim 3"$) with non-linear effect at transition scales between the
1-halo and 2-halo term affecting scales 0.1 $\lesssim r \lesssim $ 20 Mpc/$h$
($3"\lesssim \Theta \lesssim 90"$). Current clustering measurements probe down
to the scales in the transition between 1-halo to 2-halo regime where
non-linear effects are important. The amplitude of the 1-halo term implies that
occupation numbers for satellites in \texttt{BLUETIDES} are somewhat higher
than standard HODs adopted in these analyses (which predict amplitudes in the
1-halo regime suppressed by a factor 2-3). That possibly implies a higher
number of galaxies detected by JWST (at small scales and even fainter
magnitudes) observing these fields. | A consistent determination of the temperature of the intergalactic
medium at redshift z=2.4: We present new measurements of the thermal state of the intergalactic medium
(IGM) at $z\sim2.4$ derived from absorption line profiles in the Ly$\alpha$
forest. We use a large set of high-resolution hydrodynamical simulations to
calibrate the relationship between the temperature-density ($T$--$\Delta$)
relation in the IGM and the distribution of HI column densities, $N_{\rm HI}$,
and velocity widths, $b_{\rm HI}$, of discrete Ly$\alpha$ forest absorbers.
This calibration is then applied to the measurement of the lower cut-off of the
$b_{\rm HI}$--$N_{\rm HI}$ distribution recently presented by Rudie et al.
(2012). We infer a power-law $T$--$\Delta$ relation,
$T=T_{0}\Delta^{\gamma-1}$, with a temperature at mean density,
$T_{0}=[1.00^{+0.32}_{-0.21}]\times10^{4}\rm\,K$ and slope
$(\gamma-1)=0.54\pm0.11$. The slope is fully consistent with that advocated by
the analysis of Rudie et al (2012); however, the temperature at mean density is
lower by almost a factor of two, primarily due to an adjustment in the
relationship between column density and physical density assumed by these
authors. These new results are in excellent agreement with the recent
temperature measurements of Becker et al. (2011), based on the curvature of the
transmitted flux in the Ly$\alpha$ forest. This suggests that the thermal state
of the IGM at this redshift is reasonably well characterised over the range of
densities probed by these methods. |
High Precision Analyses of Lyman alpha Damping Wing of Gamma-Ray Bursts
in the Reionization Era: On the Controversial Results from GRB 130606A at z =
5.91: The unprecedentedly bright afterglow of Swift GRB 130606A at z = 5.91 gave us
a unique opportunity to probe the reionization era by high precision analyses
of the redward damping wing of Ly alpha absorption, but the reported
constraints on the neutral hydrogen fraction (f_HI) in intergalactic medium
(IGM) derived from spectra taken by different telescopes are in contradiction.
Here we examine the origin of this discrepancy by analyzing the spectrum taken
by VLT with our own analysis code previously used to fit the Subaru spectrum.
Though the VLT team reported no evidence for IGM HI using the VLT spectrum, we
confirmed our previous result of preferring non-zero IGM HI (the best-fit f_HI
~ 0.06, when IGM HI extends to the GRB redshift). The fit residuals of the VLT
spectrum by the model without IGM HI show the same systematic trend as the
Subaru spectrum. We consider that the likely origin of the discrepancy between
the two teams is the difference of the wavelength ranges adopted in the
fittings; our wavelength range is wider than that of the VLT team, and also we
avoided the shortest wavelength range of deep Ly alpha absorption (lambda_obs <
8426 A), because this region is dominated by HI in the host galaxy and the
systematic uncertainty about host HI velocity distribution is large. We also
study the sensitivity of these results to the adopted Ly alpha cross section
formulae, ranging from the classical Lorentzian function to the most recent one
taking into account fully quantum mechanical scattering. It is found that the
preference for non-zero IGM HI is robust against the choice of the cross
section formulae, but it is quantitatively not negligible and hence one should
be careful in future analyses. | Ram pressure stripping in elliptical galaxies: I. the impact of the
interstellar medium turbulence: Elliptical galaxies contain X-ray emitting gas that is subject to continuous
ram pressure stripping over timescales comparable to cluster ages. The gas in
these galaxies is not in perfect hydrostatic equilibrium. Supernova feedback,
stellar winds, or active galactic nuclei (AGN) feedback can significantly
perturb the interstellar medium (ISM). Using hydrodynamical simulations, we
investigate the effect of subsonic turbulence in the hot ISM on the ram
pressure stripping process in early-type galaxies. We find that galaxies with
more turbulent ISM produce longer, wider, and more smoothly distributed tails
of the stripped ISM than those characterised by weaker ISM turbulence. Our main
conclusion is that even very weak internal turbulence, at the level of <15% of
the average ISM sound speed, can significantly accelerate the gas removal from
galaxies via ram pressure stripping. The magnitude of this effect increases
sharply with the strength of turbulence. As most of the gas stripping takes
place near the boundary between the ISM and the intraclustermedium (ICM), the
boost in the ISM stripping rate is due to the "random walk" of the ISM from the
central regions of the galactic potential well to larger distances, where the
ram pressure is able to permanently remove the gas from galaxies. The ICM can
be temporarily trapped inside the galactic potential well due to the mixing of
the turbulent ISM with the ICM. The galaxies with more turbulent ISM, yet still
characterised by very weak turbulence, can hold larger amounts of the ICM.
[Abridged] |
On the mass-to-light ratios of fossil groups. Are they simply dark
clusters?: Defined as X-ray bright galaxy groups with large differences between the
luminosities of their brightest and second brightest galaxies, "fossil groups"
are believed to be some of the oldest galaxy systems in the universe. They have
therefore been the subject of much recent research.
In this work we present a study of 10 fossil group candidates with an average
of 33 spectroscopically confirmed members per group, making this the deepest
study of its type to-date. We also use this data to perform an analysis of the
luminosity function of our sample of fossil groups.
We confirm the high masses previously reported for many of fossil systems,
finding values more similar to those of clusters than of groups. We also
confirm the high dynamical mass-to-light ratios reported in many previous
studies. While our results are consistent with previous studies in many ways,
our interpretation is not. This is because we show that, while the luminosities
of the BCGs in these systems are consistent with their high dynamical masses,
their richnesses (total number of galaxies above some canonical value) are
extremely low. This leads us to suggest a new interpretation of fossil systems
in which the large differences between the luminosities of their brightest and
second brightest galaxies are simply the result the high BCG luminosities and
low richnesses, while the high masses and low richnesses also explain the high
mass-to-light ratios. Our results therefore suggest that fossil systems can be
characterised as cluster-like in their masses and BCG luminosities, but
possessing the richnesses and optical luminosities of relatively poor groups.
These findings are not predicted by any of the current models for the formation
of fossil groups. Therefore, if this picture is confirmed, current ideas about
the formation and evolution of fossil systems will need to be reformulated. | Cosmic Strings and the Origin of Globular Clusters: We hypothesize that cosmic string loops are the seeds about which globular
clusters accrete. Fixing the cosmic string tension by demanding that the peak
in the distribution of masses of objects accreting onto string loops agrees
with the peak in the observed mass distribution of globular clusters in our
Milky Way galaxy, we then compute the expected number density and mass function
of globular clusters, and compare with observations. Our hypothesis naturally
explains why globular clusters are the oldest and most dense objects in a
galaxy, and why they are found in the halo of the galaxy. |
Impact of big bang nucleosynthesis on the H0 tension: We investigate the impact of big bang nucleosynthesis (BBN) on the Hubble
tension, focusing on how the treatment of the reaction rate and observational
data affect the evaluation of the tension. We show that the significance of the
tension can vary by $0.8 \sigma$ in some early dark energy model, depending on
the treatment of the reaction rate and observational data. This indicates that
how we include the BBN data in the analysis can give a significant impact on
the Hubble tension, and we need to carefully consider the assumptions of the
analysis to evaluate the significance of the tension when the BBN data is used. | Exploring Two-Field Inflation in the Wess-Zumino Model: We explore inflation via the effective potential of the minimal Wess-Zumino
model, considering both the real and imaginary components of the complex field.
Using transport techniques, we calculate the full allowed range of $n_s$, $r$
and $f_{\rm NL}$ for different choices of the single free parameter, $v$, and
present the probability distribution of these signatures given a simple choice
for the prior distribution of initial conditions. Our work provides a case
study of multi-field inflation in a simple but realistic setting, with
important lessons that are likely to apply more generally. For example, we find
that there are initial conditions consistent with observations of $n_s$ and $r$
for values of $v$ that would be excluded if only evolutions in the real field
direction were to be considered, and that these may yield enhanced values of
$f_{\rm NL}$. Moreover, we find that initial conditions fixed at high energy
density, where the potential is close to quartic in form, can still lead to
evolutions in a concave region of the potential during the observable number of
e-folds, as preferred by present data. The Wess-Zumino model therefore provides
an illustration that multi-field dynamics must be taken into account when
seeking to understand fully the phenomenology of such models of inflation. |
Deep radio observations of the radio halo of the bullet cluster 1E
0657-55.8: We present deep 1.1-3.1 GHz Australia Telescope Compact Array observations of
the radio halo of the bullet cluster, 1E 0657-55.8. In comparison to existing
images of this radio halo the detection in our images is at higher
significance. The radio halo is as extended as the X-ray emission in the
direction of cluster merger but is significantly less extended than the X-ray
emission in the perpendicular direction. At low significance we detect a faint
second peak in the radio halo close to the X-ray centroid of the smaller
sub-cluster (the bullet) suggesting that, similarly to the X-ray emission, the
radio halo may consist of two components. Finally, we find that the distinctive
shape of the western edge of the radio halo traces out the X-ray detected bow
shock. The radio halo morphology and the lack of strong point-to-point
correlations between radio, X-ray and weak-lensing properties suggests that the
radio halo is still being formed. The colocation of the X-ray shock with a
distinctive radio brightness edge illustrates that the shock is influencing the
structure of the radio halo. These observations support the theory that shocks
and turbulence influence the formation and evolution of radio halo synchrotron
emission. | On the Hydrodynamic Interplay Between a Young Nuclear Starburst and a
Central Super Massive Black Hole: We present 1D numerical simulations, which consider the effects of radiative
cooling and gravity on the hydrodynamics of the matter reinserted by stellar
winds and supernovae within young nuclear starbursts with a central
supermassive black hole (SMBH). The simulations confirm our previous
semi-analytic results for low energetic starbursts, evolving in a
quasi-adiabatic regime, and extend them to more powerful starbursts evolving in
the catastrophic cooling regime. The simulations show a bimodal hydrodynamic
solution in all cases. They present a quasi-stationary accretion flow onto the
black hole, defined by the matter reinserted by massive stars within the
stagnation volume and a stationary starburst wind, driven by the high thermal
pressure acquired in the region between the stagnation and the starburst radii.
In the catastrophic cooling regime, the stagnation radius rapidly approaches
the surface of the starburst region, as one considers more massive starbursts.
This leads to larger accretion rates onto the SMBH and concurrently to powerful
winds able to inhibit interstellar matter from approaching the nuclear
starburst.
Our self-consistent model thus establishes a direct physical link between the
SMBH accretion rate and the nuclear star formation activity of the host galaxy
and provides a good upper limit to the accretion rate onto the central black
hole. |
Examining Temporal Variation of the Fermi Coupling Constant using SNe Ia
Light Curves: In standard model, the Fermi coupling constant, $G_F$, sets the strength of
electroweak decay. We attempt an approach to constrain the temporal variation
of the Fermi coupling constant $G_F$. To probe it, Type Ia supernovae (SNe Ia)
light curves are being used as a source of reliable primordial nucleosynthesis
events across the redshifts. We utilized studies suggesting that in the initial
phase after the SNe Ia explosion, the electroweak decay of $^{56}Ni \rightarrow
^{56}Co \rightarrow ^{56}Fe$ is the key contributor to powering the SNe Ia
light curve. We hence used the Pan-STARRS supernovae catalog having 1169
supernovae light curves in $g$, $r$, $i$, and $z$ spectral filters. The
post-peak decrease in the apparent magnitude of light curves (in the rest frame
of SNe) was related to the electroweak decay rate of primordial
nucleosynthesis. Further, the decay rate relates to $G_F$. To keep the analysis
independent of the cosmological model, we used the Hubble parameter measurement
and a non-parametric statistical method, the Gaussian Process. Our study
suggests a small yet finite temporal variation of $G_F$ and puts a strong upper
bound on the present value of the fractional change in the Fermi coupling
constant i.e; $\dfrac{\dot G_F}{G_F}\big\rvert_{z=0} \approx 10^{-11} yr^{-1}$
using datasets spread over a redshift range $0<z<0.75$. | The X-CLASS - redMaPPer galaxy cluster comparison: I. Identification
procedures: We performed a detailed and, for a large part interactive, analysis of the
matching output between the X-CLASS and redMaPPer cluster catalogues. The
overlap between the two catalogues has been accurately determined and possible
cluster positional errors were manually recovered. The final samples comprise
270 and 355 redMaPPer and X-CLASS clusters respectively. X-ray cluster matching
rates were analysed as a function of optical richness. In a second step, the
redMaPPer clusters were correlated with the entire X-ray catalogue, containing
point and uncharacterised sources (down to a few 10^{-15} erg s^{-1} cm^{-2} in
the [0.5-2] keV band). A stacking analysis was performed for the remaining
undetected optical clusters. Main results show that neither of the wavebands
misses any massive cluster (as coded by X-ray luminosity or optical richness).
After correcting for obvious pipeline short-comings (about 10% of the cases
both in optical and X-ray), ~50% of the redMaPPer (down to a richness of 20)
are found to coincide with an X-CLASS cluster; when considering X-ray sources
of any type, this fraction increases to ~ 80%; for the remaining objects, the
stacking analysis finds a weak signal within 0.5 Mpc around the cluster optical
centers. The fraction of clusters totally dominated by AGN-type emission
appears to be of the order of a few percent. Conversely ~ 40% of the X-CLASS
clusters are identified with a redMaPPer (down to a richness of 20) - part of
the non-matches being due to the fact that the X-CLASS sample extends further
out than redMaPPer (z<1 vs z<0.6); extending the correlation down to a richness
of 5, raises the matching rate to ~ 65%. |
Prospects of strongly lensed fast radio bursts: Simultaneous measurement
of post-Newtonian parameter and Hubble constant: Strong gravitational lensing effect is a powerful tool to probe cosmological
models and gravity theories. Recently, the time-delay cosmography from strong
lensing and the stellar kinematics of the deflector, which encode the Hubble
constant and the post-Newtonian parameter via two distance ratios reflecting
the lensing mass and dynamical mass respectively, have been proposed to
investigate these two parameters simultaneously. Among strong lensing systems
with different sources, strongly lensed fast radio bursts (FRBs) have been
proposed as precision probes of the universe since the time delay $\sim$ 10
days between images could be measured extremely precisely because of their
short duration of a few milliseconds. In this work, we investigate the ability
of strongly lensed FRBs on simultaneously estimating these two parameters via
simulations. Take the expected FRB detection rate of upcoming facilities and
lensing probability into consideration, it is likely to accumulate 10 lensed
FRBs in several years and we find that $H_0$ could be determined to a
$\sim1.5\%$ precision and $\gamma_{\rm PPN}$ could be constrained to a
$\sim8.7\%$ precision simultaneously from them. These simultaneous estimations
will be helpful for properly reflecting the possible correlation between these
two fundamental parameters. | Modelling the environmental dependence of the growth rate: The growth rate of cosmic structure is a powerful cosmological probe for
extracting information on the gravitational interactions and dark energy. In
the late time Universe, the growth rate becomes non-linear and is usually
probed by measuring the two point statistics of galaxy clustering in redshift
space up to a limited scale, retaining the constraint on the linear growth rate
f. In this letter, we present an alternative method to analyse the growth of
structure in terms of local densities, i.e. f(Delta). Using N-body simulations,
we measure the function of f(Delta) and show that structure grows faster in
high density regions and slower in low density regions. We demonstrate that
f(Delta) can be modelled using a log-normal Monte Carlo Random Walk approach,
which provides a means to extract cosmological information from f(Delta). We
discuss prospects for applying this approach to galaxy surveys. |
Complementarity of Weak Lensing and Peculiar Velocity Measurements in
Testing General Relativity: We explore the complementarity of weak lensing and galaxy peculiar velocity
measurements to better constrain modifications to General Relativity. We find
no evidence for deviations from GR on cosmological scales from a combination of
peculiar velocity measurements (for Luminous Red Galaxies in the Sloan Digital
Sky Survey) with weak lensing measurements (from the CFHT Legacy Survey). We
provide a Fisher error forecast for a Euclid-like space-based survey including
both lensing and peculiar velocity measurements, and show that the expected
constraints on modified gravity will be at least an order of magnitude better
than with present data, i.e. we will obtain 5% errors on the modified gravity
parametrization described here. We also present a model--independent method for
constraining modified gravity parameters using tomographic peculiar velocity
information, and apply this methodology to the present dataset. | Colour gradients of high-redshift Early-Type Galaxies from
hydrodynamical monolithic models: We analyze the evolution of colour gradients predicted by the hydrodynamical
models of early type galaxies (ETGs) in Pipino et al. (2008), which reproduce
fairly well the chemical abundance pattern and the metallicity gradients of
local ETGs. We convert the star formation (SF) and metal content into colours
by means of stellar population synthetic model and investigate the role of
different physical ingredients, as the initial gas distribution and content,
and eps_SF, i.e. the normalization of SF rate. From the comparison with high
redshift data, a full agreement with optical rest-frame observations at z < 1
is found, for models with low eps_SF, whereas some discrepancies emerge at 1 <
z < 2, despite our models reproduce quite well the data scatter at these
redshifts. To reconcile the prediction of these high eps_SF systems with the
shallower colour gradients observed at lower z we suggest intervention of 1-2
dry mergers. We suggest that future studies should explore the impact of wet
galaxy mergings, interactions with environment, dust content and a variation of
the Initial Mass Function from the galactic centers to the peripheries. |
The Burst Cluster: Dark Matter in a Cluster Merger Associated with the
Short Gamma Ray Burst, GRB 050509B: We have identified a merging galaxy cluster with evidence of two distinct
sub-clusters. The X-ray and optical data suggest that the subclusters are
moving away from each other after closest approach. This cluster merger was
discovered from observations of the well localized short-duration gamma-ray
burst (GRB), GRB 050509B. The Swift/Burst Alert Telescope (BAT) source position
is coincident with a cluster of galaxies ZwCl 1234.0+02916. The subsequent
Swift/X-Ray Telescope (XRT) localization of the X-ray afterglow found the GRB
coincident with 2MASX J12361286+2858580, a giant red elliptical galaxy in the
cluster. Deep multi-epoch optical images were obtained to constrain the
evolution of the GRB afterglow, including a 27480s exposure in the F814W band
with Hubble Space Telescope Advanced Camera for Surveys (ACS), among the
deepest imaging ever obtained towards a known galaxy cluster in a single
passband. We perform a weak gravitational lensing analysis, including mapping
the total mass distribution of the merger system. Combined with Chandra X-ray
Observatory and Swift/XRT observations, we investigate the dynamical state of
the merger to probe the nature of the dark matter component. Our weak
gravitational lensing measurements reveal a separation of the X-ray centroid of
the western subcluster from the center of the mass and galaxy light
distributions, similar to that of the famous "Bullet cluster". We conclude that
the "Burst cluster" is another candidate merger system for determining the
nature of dark matter and for studying the environment of short GRBs. We
discuss connections between the cluster dynamical state and/or matter
composition and compact object mergers, the leading model for the origin of
short GRBs. Finally, we present results from a weak lensing survey based on
archival Very Large Telescope (VLT) images in the areas of 5 other short GRBs. | The Evolution of Ly-alpha Emitting Galaxies Between z = 2.1 and z = 3.1: We describe the results of a new, wide-field survey for z=3.1 Ly-alpha
emission-line galaxies (LAEs) in the Extended Chandra Deep Field South
(ECDF-S). By using a nearly top-hat 5010 Angstrom filter and complementary
broadband photometry from the MUSYC survey, we identify a complete sample of
141 objects with monochromatic fluxes brighter than 2.4E-17 ergs/cm^2/s and
observers-frame equivalent widths greater than ~ 80 Angstroms (i.e., 20
Angstroms in the rest-frame of Ly-alpha). The bright-end of this dataset is
dominated by x-ray sources and foreground objects with GALEX detections, but
when these interlopers are removed, we are still left with a sample of 130 LAE
candidates, 39 of which have spectroscopic confirmations. This sample overlaps
the set of objects found in an earlier ECDF-S survey, but due to our filter's
redder bandpass, it also includes 68 previously uncataloged sources. We confirm
earlier measurements of the z=3.1 LAE emission-line luminosity function, and
show that an apparent anti-correlation between equivalent width and continuum
brightness is likely due to the effect of correlated errors in our
heteroskedastic dataset. Finally, we compare the properties of z=3.1 LAEs to
LAEs found at z=2.1. We show that in the ~1 Gyr after z~3, the LAE luminosity
function evolved significantly, with L* fading by ~0.4 mag, the number density
of sources with L > 1.5E42 ergs/s declining by ~50%, and the equivalent width
scale-length contracting from 70^{+7}_{-5} Angstroms to 50^{+9}_{-6} Angstroms.
When combined with literature results, our observations demonstrate that over
the redshift range z~0 to z~4, LAEs contain less than ~10% of the
star-formation rate density of the universe. |
Cross-correlations as a Diagnostic Tool for Primordial Gravitational
Waves: We explore and corroborate, by working out explicit examples, the
effectiveness of cross-correlating stochastic gravitational wave background
anisotropies with CMB temperature fluctuations as a way to establish the
primordial nature of a given gravitational wave signal. We consider the case of
gravitational wave anisotropies induced by scalar-tensor-tensor primordial
non-Gaussianity. Our analysis spans anisotropies exhibiting different angular
behaviours, including a quadrupolar dependence. We calculate the expected
uncertainty on the non-linearity parameter $F_{\rm NL}$ obtained as a result of
cross-correlation measurements for several proposed experiments such as the
ground-based Einstein Telescope, Cosmic Explorer, and the space-based Big-Bang
Observer. As a benchmark for future survey planning, we also calculate the
theoretical, cosmic-variance-limited, error on the non-linearity parameter. | COFFE: a code for the full-sky relativistic galaxy correlation function: We present a public version of the code COFFE (COrrelation Function Full-sky
Estimator) available at https://github.com/JCGoran/coffe. The code computes the
galaxy two-point correlation function and its multipoles in linear perturbation
theory, including all relativistic and wide angle corrections. COFFE also
calculates the covariance matrix for two physically relevant estimators of the
correlation function multipoles. We illustrate the usefulness of our code by a
simple but relevant example: a forecast of the detectability of the lensing
signal in the multipoles of the two-point function. In particular, we show that
lensing should be detectable in the multipoles of the two-point function, with
a signal-to-noise larger than 10, in future surveys like Euclid or the SKA. |
Strong Lensing with Finite Temperature Scalar Field Dark Matter: We investigate the gravitational constraints imposed to dark matter halos in
the context of finite temperature scalar field dark matter. We find constraints
to produce multiple images by dark matter only, we show that there are
differences with respect to the full Bose Einstein condensate halo when the
temperature of the scalar field in dark matter halos is taken into account. The
non zero temperature allows the scalar field to be in excited states and
recently, their existence has proved to be necessary to fit rotation curves of
dark matter dominated galaxies of all sizes, it also explained the non
universality of the halo density profiles. Therefore, we expect that combining
observations of rotation curves and strong lensing systems can give us a clue
to the nature of dark matter. Finally, we propose a method to identify the
excited state of a strong lens halo, knowing various halo excited states can
provide information of the scalar field dark matter halo evolution which can be
tested using numerical simulations. | On the influence of high energy electron populations on metal abundance
estimates in galaxy groups and clusters: Spectral line emissivities have usually been calculated for a Maxwellian
electron distribution. But many theoretical works on galaxy groups and clusters
and on the solar corona suggest to consider modified Maxwellian electron
distribution functions to fit observed X-ray spectra. Here we examine the
influence of high energy electron populations on measurements of metal
abundances. A generalized approach which was proposed in the paper by Prokhorov
et al. (2009) is used to calculate the line emissivities for a modified
Maxwellian distribution. We study metal abundances in galaxy groups and
clusters where hard X-ray excess emission was observed. We found that for
modified Maxwellian distributions the argon abundance decreases for the HCG 62
group, the iron abundance decreases for the Centaurus cluster and the oxygen
abundance decreases for the solar corona with respect to the case of a
Maxwellian distribution. Therefore, metal abundance measurements are a
promising tool to test the presence of high energy electron populations. |
Hubble-rate-dependent Dark Energy in Brans-Dicke Cosmology: Three general cases of dynamical interacting dark energy models
($\mathcal{D}$-class) are investigated in the context of Brans-Dicke cosmology.
Some of important cosmological quantities are calculated for every cases as a
function of redshift parameter. The most important part of this paper deals
with fitting models with two different expansion history:
(SNIa+BAO$_A$+$Omh^{2}$ and SNIa+BAO$_A$+H(z)) and with two different sets of
data for Hubble parameter. This provides a remarkable feature to could
analytically see the effects of each analyzes and each data sets on final
results. The best fitted values of parameters according to these analyzes and
data points, $\chi_{tot}^2/dof$, AIC and BIC are reported. By these diagnostic
tools we found that some of these models have no chance against $\Lambda$CDM,
even without need to study the structure formation, and could be ruled out.
While some (e.g. $\mathcal{BD-D}C2$ and $\mathcal{BD-D}A^*$) render the best
fit quality,i.e. the value of AIC and BIC and figures show that they fit
perfectly with overall data and reveals a strong evidence in favor of these two
models against $\Lambda$CDM. | Effect of clustering on primordial black hole microlensing constraints: Stellar microlensing observations tightly constrain compact object dark
matter in the mass range $(10^{-11} - 10^{3}) M_{\odot}$. Primordial Black
Holes (PBHs) form clusters, and it has been argued that these microlensing
constraints are consequently weakened or evaded. For the most commonly studied
PBH formation mechanism, the collapse of large gaussian curvature perturbations
generated by inflation, the clusters are sufficiently extended that the PBHs
within them act as individual lenses. We find that if the typical mass of the
clusters is sufficiently large, $ \gtrsim 10^{6} M_{\odot}$, then the event
duration distribution can deviate significantly from that produced by a smooth
dark matter distribution, in particular at the shortest durations. As a
consequence of this, the probability distribution of the number of observed
events is non-Poissonian, peaking at a lower value, with an extended tail to
large numbers of events. However, for PBHs formed from the collapse of large
inflationary perturbations, the typical cluster is expected to contain $\sim
10^{3}$ PBHs. In this case the effect of clustering is negligibly small, apart
from for the most massive PBHs probed by decade-long stellar microlensing
surveys ($M_{\rm PBH} \sim 10^{3} M_{\odot}$). |
Looking for dark matter trails in colliding galaxy clusters: If dark matter interacts, even weakly, via non-gravitational forces,
simulations predict that it will be preferentially scattered towards the
trailing edge of the halo during collisions between galaxy clusters. This will
temporarily create a non-symmetric mass profile, with a trailing over-density
along the direction of motion. To test this hypothesis, we fit (and subtract)
symmetric halos to the weak gravitational data of 72 merging galaxy clusters
observed with the Hubble Space Telescope. We convert the shear directly into
excess {\kappa} and project in to a one dimensional profile. We generate
numerical simulations and find that the one dimensional profile is well
described with simple Gaussian approximations. We detect the weak lensing
signal of trailing gas at a 4{\sigma} confidence, finding a mean gas fraction
of Mgas/Mdm = 0.13 +/- 0.035. We find no evidence for scattered dark matter
particles with a estimated scattering fraction of f = 0.03 +/- 0.05. Finally we
find that if we can reduce the statistical error on the positional estimate of
a single dark matter halo to <2.5", then we will be able to detect a scattering
fraction of 10% at the 3{\sigma} level with current surveys. This poten- tially
interesting new method can provide an important independent test for other
complimentary studies of the self-interaction cross-section of dark matter. | Effect of lensing magnification on type Ia supernova cosmology: Effect of gravitational magnification on the measurement of distance modulus
of type Ia supernovae is presented. We investigate a correlation between
magnification and Hubble residual to explore how the magnification affects the
estimation of cosmological parameters. We estimate magnification of type Ia
supernovae in two distinct methods: one is based on convergence mass
reconstruction under the weak lensing limit and the other is based on the
direct measurement from galaxies distribution. Both magnification measurements
are measured from Subaru Hyper Suprime-Cam survey catalogue. For both
measurements, we find no significant correlation between Hubble residual and
magnification. Furthermore, we correct for the apparent supernovae fluxes
obtained by Supernova Legacy Survey 3-year sample using direct measurement of
the magnification. We find $\Omega_{\rm m0} = 0.287 ^{+0.104} _{-0.085}$ and $w
= -1.161 ^{+0.595}_{-0.358}$ for supernovae samples corrected for lensing
magnification when we use photometric redshift catalogue of Mizuki, while
$\Omega_{\rm m0} = 0.253 ^{+0.113} _{-0.087}$ and $w = -1.078 ^{+0.498}
_{-0.297}$ for DEmP photo-z catalogue. Therefore, we conclude that the effect
of magnification on the supernova cosmology is negligibly small for the current
surveys; however, it has to be considered for the future supernova survey like
LSST. |
Testing cosmic acceleration for $w(z)$ parameterizations using $f_{gas}$
measurements in galaxy clusters: In this paper we study the cosmic acceleration for five dynamical dark energy
models whose equation of state varies with redshift. The cosmological
parameters of these models are constrained by performing a MCMC analysis using
mainly gas mass fraction, $f_{gas}$, measurements in two samples of galaxy
clusters: one reported by Allen et al. (2004), which consists of $42$ points
spanning the redshift range $0.05<z<1.1$, and the other by Hasselfield et al.
(2013) from the Atacama Cosmology Telescope survey, which consists of $91$ data
points in the redshift range $0.118 < \mathrm{z} < 1.36$. In addition, we
perform a joint analysis with the measurements of the Hubble parameter $H(z)$,
baryon acoustic oscillations and the cosmic microwave background radiation from
WMAP and Planck measurements to estimate the equation of state parameters. We
obtained that both $f_{gas}$ samples provide consistent constraints on the
cosmological parameters. We found that the $f_{gas}$ data is consistent at the
$2\sigma$ confidence level with a cosmic slowing down of the acceleration at
late times for most of the parameterizations. The constraints of the joint
analysis using WMAP and Planck measurements show that this trend disappears. We
have confirmed that the $f_{gas}$ probe provides competitive constraints on the
dark energy parameters when a $w(z)$ is assumed. | Cosmological constraints from Sunyaev-Zeldovich cluster counts: an
approach to account for missing redshifts: The accumulation of redshifts provides a significant observational bottleneck
when using galaxy cluster surveys to constrain cosmological parameters. We
propose a simple method to allow the use of samples where there is a fraction
of the redshifts that are not known. The simplest assumption is that the
missing redshifts are randomly extracted from the catalogue, but the method
also allows one to take into account known selection effects in the
accumulation of redshifts. We quantify the reduction in statistical precision
of cosmological parameter constraints as a function of the fraction of missing
redshifts for simulated surveys, and also investigate the impact of making an
incorrect assumption for the distribution of missing redshifts. |
Supernovae-induced accretion and star formation in the inner kiloparsec
of a gaseous disk: We consider the effects of supernovae (SNe) on accretion and star formation
in a massive gaseous disk in a large primeval galaxy. The gaseous disk we
envisage, roughly 1 kiloparsec (kpc) in size with >~ 10^8 M_Sun of gas, could
have formed as a result of galaxy mergers where tidal interactions removed
angular momentum from gas at larger radius and thereby concentrated it within
the central ~ 1 kpc region. We find that SNe lead to accretion in the disk at a
rate of roughly 0.1 - 1 M_Sun per year and induce star formation at a rate of ~
10 - 100 M_Sun per year which contributes to the formation of a bulge; a part
of the stellar velocity dispersion is due to the speed of SNa shells from which
stars are formed and a part due to the repeated action of the stochastic
gravitational field of the network of SNa remnants on stars. The rate of SNe in
the inner kpc is shown to be self- regulating, and it cycles through phases of
low and high activity. The supernova-assisted accretion transports gas from
about one kpc to within a few pc of the center. If this accretion were to
continue down to the central black hole (BH) then the resulting ratio of BH
mass to the stellar mass in the bulge would be of order ~ 10^-2 - 10^-3, in
line with the observed Magorrian relation. | The effects of alignment and ellipticity on the clustering of galaxies: We investigate the effects of halo ellipticity and alignment with
larger-scale structure on the galaxy correlation function. We base our analysis
on the galaxy formation models of Guo et al. (2011), run on the Millennium
Simulations. We quantify the importance of these properties of the galaxy
distribution by randomizing the angular positions of satellite galaxies within
haloes, either coherently or individually, while keeping the distance to their
respective central galaxies fixed. We find that the effect of disrupting the
alignment with larger-scale structure is a ~2 per cent decrease in the galaxy
correlation function around r=1.8 Mpc/h. Sphericalizing the ellipsoidal
distributions of galaxies within haloes decreases the correlation function by
up to 20 per cent for r<1 Mpc/h. Similar results apply to power spectra and
redshift-space correlation functions. Models such as those based on the Halo
Occupation Distribution, which adopt a spherically averaged profile for the
galaxy distributions within haloes, will therefore significantly underestimate
the clustering on sub-Mpc scales. |
A proposal to improve the accuracy of cosmological observables and
address the Hubble tension problem: Cosmological observational programs often compare their data not only with
$\Lambda$CDM, but also with dark energy (DE) models, whose time-dependent
equations of state (EoS) differ from a cosmological constant. We identified a
generic issue in the standard procedure of computing the expansion history for
models with time-dependent EoS, which leads to bias in the interpretation of
the results. In order to compute the evolution of models with time-dependent
EoS parameter $w$ in a consistent manner, we introduce an enhanced
computational procedure, which accounts for the correct choice of initial
conditions in the respective backward-in-time and forward-in-time evolution of
the equations of motion. We implement our enhanced procedure in an amended
version of the code CLASS, where we focus on exemplary DE models which are
based on the CPL parameterization, studying cases with monotonically increasing
and decreasing $w$ over cosmic time. Our results reveal that a cosmological DE
model with a decreasing $w$ of the form $w(a)=-0.9 + 0.1(1-a)$ could provide a
resolution to the Hubble tension problem. Moreover, we find characteristic
signatures in the late expansion histories of models, allowing a
phenomenological discrimination of DE candidates. Finally, we argue that our
enhanced scheme should be implemented as a novel consistency check for
cosmological models within current Monte-Carlo-Markov-Chain (MCMC) methods. Our
enhanced computational procedure avoids the interpretational bias to which the
standard procedure is unwittingly exposed. As a result, DE models can be better
constrained. If implemented into MCMC codes, we expect that our scheme will
contribute to providing a significant improvement in the determined accuracy of
cosmological model parameters. | Physical Conditions in the Interstellar Medium of High-Redshift
Galaxies: Mass Budget and Gas Excitation: Following the first pioneering efforts in the 1990s that have focused on the
detection of the molecular interstellar medium in high redshift galaxies,
recent years have brought great advances in our understanding of the actual
physical properties of the gas that set the conditions for star formation.
Observations of the ground-state CO J=1-0 line have furnished crucial
information on the total masses of the gas reservoirs, as well as reliable
dynamical mass and size estimates. Detailed studies of rotational ladders of CO
have provided insight on the temperature and density of the gas. Investigations
of the very dense gas associated with actively star-forming regions in the
interstellar medium, most prominently through HCN and HCO+, have enabled a
better understanding of the nature of the extreme starbursts found in many
high-redshift galaxies, which exceed the star formation rates of their most
active present-day counterparts by an order of magnitude. Key progress in this
area has been made through targeted studies of few, well-selected systems with
current facilities. With the completion of the Karl G. Jansky Very Large Array
and the Atacama Large (sub)Millimeter Array, it will become possible to develop
a more general framework for the interpretation of these investigations based
on unbiased studies of "normal" star-forming galaxies back to the earliest
cosmic epochs. |
Luminous Starbursts in the Redshift Desert at z~1-2: Star Formation
Rates, Masses & Evidence for Outflows: We present a spectroscopic catalogue of 40 luminous starburst galaxies at
z=0.7--1.7 (median z=1.3). 19 of these are submillimetre galaxies (SMGs) and 21
are submillimetre-faint radio galaxies (SFRGs). This sample helps to fill in
the redshift desert at z=1.2--1.7 in previous studies as well as probing a
lower luminosity population of galaxies. Radio fluxes are used to determine
star-formation rates for our sample which range from around 50 to 500 M$_\odot$
yr$^{-1}$ and are generally lower than those in z$\sim$2 SMGs. We identify
nebular [OII] 3727 emission in the rest-UV spectra and use the linewidths to
show that SMGs and SFRGs in our sample have larger linewidths and therefore
dynamical masses than optically selected star-forming galaxies at similar
redshifts. The linewidths are indistinguishable from those measured in the
z$\sim$2 SMG populations suggesting little evolution in the dynamical masses of
the galaxies between redshift 1--2. [NeV] and [NeIII] emission lines are
identified in a subset of the spectra indicating the presence of an active
galactic nucleus (AGN). In addition, a host of interstellar absorption lines
corresponding to transitions of MgII and FeII ions are also detected. These
features show up prominently in composite spectra and we use these composites
to demonstrate that the absorption lines are present at an average blueshift of
$-240\pm$50 kms$^{-1}$ relative to the systemic velocities of the galaxies
derived from [OII]. This indicates the presence of large-scale outflowing
interstellar gas in these systems (Abridged) | Phenomenological consequences of superfluid dark matter with
baryon-phonon coupling: Recently, a new form of dark matter has been suggested to naturally reproduce
the empirically successful aspects of Milgrom's law in galaxies. The dark
matter particle candidates are axion-like, with masses of order eV and strong
self-interactions. They Bose-Einstein condense into a superfluid phase in the
central regions of galaxy halos. The superfluid phonon excitations in turn
couple to baryons and mediate an additional long-range force. For a suitable
choice of the superfluid equation of state, this force can mimic Milgrom's law.
In this paper we develop in detail some of the main phenomenological
consequences of such a formalism, by revisiting the expected dark matter halo
profile in the presence of an extended baryon distribution. In particular, we
show how rotation curves of both high and low surface brightness galaxies can
be reproduced, with a slightly rising rotation curve at large radii in massive
high surface brightness galaxies, thus subtly different from Milgrom's law. We
finally point out other expected differences with Milgrom's law, in particular
in dwarf spheroidal satellite galaxies, tidal dwarf galaxies, and globular
clusters, whose Milgromian or Newtonian behavior depends on the position with
respect to the superfluid core of the host galaxy. We also expect ultra-diffuse
galaxies within galaxy clusters to have velocities slightly above the baryonic
Tully-Fisher relation. Finally, we note that, in this framework, photons and
gravitons follow the same geodesics, and that galaxy-galaxy lensing, probing
larger distances within galaxy halos than rotation curves, should follow
predictions closer to the standard cosmological model than those of Milgrom's
law. |
Future detectability of gravitational-wave induced lensing from
high-sensitivity CMB experiments: We discuss the future detectability of gravitational-wave induced lensing
from high-sensitivity cosmic microwave background (CMB) experiments.
Gravitational waves can induce a rotational component of the weak-lensing
deflection angle, usually referred to as the curl mode, which would be
imprinted on the CMB maps. Using the technique of reconstructing lensing
signals involved in CMB maps, this curl mode can be measured in an unbiased
manner, offering an independent confirmation of the gravitational waves
complementary to the B-mode polarization experiments. Based on the Fisher
matrix analysis, we first show that with the noise levels necessary to confirm
the consistency relation for the primordial gravitational waves, the future CMB
experiments will be able to detect the gravitational-wave induced lensing
signals. For a tensor-to-scalar ratio of $r < 0.1$, even if the consistency
relation is difficult to confirm with a high significance, the
gravitational-wave induced lensing would be detected at more than $3\,\sigma$
significance level. Further, we point out that high-sensitivity experiments
will be also powerful to constrain the gravitational waves generated after the
recombination epoch. Compared to the B-mode polarization, the curl mode is
particularly sensitive to gravitational waves generated at low redshifts ($z <
10$) with a low frequency ($k < 10^{-3}$ Mpc$^{-1}$), and it could give a much
tighter constraint on their energy density $\Omega_{\rm GW}$ by more than three
orders of magnitude. | Observational constraints on the tilted flat-XCDM and the untilted
nonflat XCDM dynamical dark energy inflation parameterizations: We constrain tilted spatially-flat and untilted nonflat XCDM dynamical dark
energy inflation parameterizations using Planck 2015 cosmic microwave
background (CMB) anisotropy data and recent baryonic acoustic oscillations
distance measurements, Type Ia supernovae data, Hubble parameter observations,
and growth rate measurements. Inclusion of the four non-CMB data sets results
in a significant strengthening of the evidence for nonflatness in the nonflat
XCDM model from 1.1$\sigma$ for the CMB data alone to 3.4$\sigma$ for the full
data combination. In this untilted nonflat XCDM case the data favor a
spatially-closed model in which spatial curvature contributes a little less
than a percent of the current cosmological energy budget; they also mildly
favor dynamical dark energy over a cosmological constant at 1.2$\sigma$. These
data are also better fit by the flat-XCDM parameterization than by the standard
$\Lambda$CDM model, but only at 0.3$\sigma$ significance. Current data is
unable to rule out dark energy dynamics. The nonflat XCDM parameterization is
compatible with the Dark Energy Survey limits on the present value of the rms
mass fluctuations amplitude ($\sigma_8$) as a function of the present value of
the nonrelativistic matter density parameter ($\Omega_m$), however it does not
provide as good a fit to the higher multipole CMB temperature anisotropy data
as does the standard tilted flat-$\Lambda$CDM model. A number of measured
cosmological parameter values differ significantly when determined using the
tilted flat-XCDM and the nonflat XCDM parameterizations, including the baryonic
matter density parameter and the reionization optical depth. |
Photometric selection of Type Ia supernovae in the Supernova Legacy
Survey: We present a sample of 485 photometrically identified Type Ia supernova
candidates mined from the first three years of data of the CFHT SuperNova
Legacy Survey (SNLS). The images were submitted to a deferred processing
independent of the SNLS real-time detection pipeline. Light curves of all
transient events were reconstructed in the g_M, r_M, i_M and z_M filters and
submitted to automated sequential cuts in order to identify possible
supernovae. Pure noise and long-term variable events were rejected by light
curve shape criteria. Type Ia supernova identification relied on event
characteristics fitted to their light curves assuming the events to be normal
SNe Ia. The light curve fitter SALT2 was used for this purpose, assigning host
galaxy photometric redshifts to the tested events. The selected sample of 485
candidates is one magnitude deeper than that allowed by the SNLS spectroscopic
identification. The contamination by supernovae of other types is estimated to
be 4%. Testing Hubble diagram residuals with this enlarged sample allows us to
measure the Malmquist bias due to spectroscopic selections directly. The result
is fully consistent with the precise Monte Carlo based estimate used to correct
SN Ia distance moduli in the SNLS 3-year cosmological analyses. This paper
demonstrates the feasibility of a photometric selection of high redshift
supernovae with known host galaxy redshifts, opening interesting prospects for
cosmological analyses from future large photometric SN Ia surveys. | A2163: Merger events in the hottest Abell galaxy cluster II. Subcluster
accretion with galaxy-gas separation: Located at z = 0.203, A2163 is a rich galaxy cluster with an intra-cluster
medium (ICM) that exhibits extraordinary properties, including an exceptionally
high X-ray luminosity, average temperature, and a powerful and extended radio
halo. The irregular and complex morphology of its gas and galaxy structure
suggests that this cluster has recently undergone major merger events that
involve two or more cluster components. In this paper, we study the gas
structure and dynamics by means of spectral-imaging analysis of X-ray data
obtained from XMM-Newton and Chandra observations. From the evidence of a cold
front, we infer the westward motion of a cool core across the E-W elongated
atmosphere of the main cluster A2163-A. Located close to a galaxy over-density,
this gas 'bullet' appears to have been spatially separated from its galaxy (and
presumably dark matter component) as a result of high-velocity accretion.
From gas brightness and temperature profile analysis performed in two
opposite regions of the main cluster, we show that the ICM has been
adiabatically compressed behind the crossing 'bullet' possibly because of shock
heating, leading to a strong departure of the ICM from hydrostatic equilibrium
in this region. Assuming that the mass estimated from the Yx proxy best
indicates the overall mass of the system and that the western cluster sector is
in approximate hydrostatic equilibrium before subcluster accretion, we infer a
merger scenario between two subunits of mass ratio 1:4, leading to a present
total system mass of M500 $\propto 1.9 \times 1015 M_{\odot}$. The exceptional
properties of A2163 present various similarities with those of 1E0657-56, the
so-called 'bullet-cluster'. These similarities are likely to be related to a
comparable merger scenario. |
Image Analysis for Cosmology: Shape Measurement Challenge Review &
Results from the Mapping Dark Matter Challenge: In this paper we present results from the Mapping Dark Matter competition
that expressed the weak lensing shape measurement task in its simplest form and
as a result attracted over 700 submissions in 2 months and a factor of 3
improvement in shape measurement accuracy on high signal to noise galaxies,
over previously published results, and a factor 10 improvement over methods
tested on constant shear blind simulations. We also review weak lensing shape
measurement challenges, including the Shear TEsting Programmes (STEP1 and
STEP2) and the GRavitational lEnsing Accuracy Testing competitions (GREAT08 and
GREAT10). | Baryon Content in a Sample of 91 Galaxy Clusters Selected by the South
Pole Telescope at 0.2 < z < 1.25: We estimate total mass ($M_{500}$), intracluster medium (ICM) mass
($M_{\mathrm{ICM}}$) and stellar mass ($M_{\star}$) in a Sunyaev-Zel'dovich
effect (SZE) selected sample of 91 galaxy clusters with masses
$M_{500}\gtrsim2.5\times10^{14}M_{\odot}$ and redshift $0.2 < z < 1.25$ from
the 2500 deg$^2$ South Pole Telescope SPT-SZ survey. The total masses $M_{500}$
are estimated from the SZE observable, the ICM masses $M_{\mathrm{ICM}}$ are
obtained from the analysis of $Chandra$ X-ray observations, and the stellar
masses $M_{\star}$ are derived by fitting spectral energy distribution
templates to Dark Energy Survey (DES) $griz$ optical photometry and $WISE$ or
$Spitzer$ near-infrared photometry. We study trends in the stellar mass, the
ICM mass, the total baryonic mass and the cold baryonic fraction with cluster
mass and redshift. We find significant departures from self-similarity in the
mass scaling for all quantities, while the redshift trends are all
statistically consistent with zero, indicating that the baryon content of
clusters at fixed mass has changed remarkably little over the past $\approx9$
Gyr. We compare our results to the mean baryon fraction (and the stellar mass
fraction) in the field, finding that these values lie above (below) those in
cluster virial regions in all but the most massive clusters at low redshift.
Using a simple model of the matter assembly of clusters from infalling groups
with lower masses and from infalling material from the low density environment
or field surrounding the parent halos, we show that the measured mass trends
without strong redshift trends in the stellar mass scaling relation could be
explained by a mass and redshift dependent fractional contribution from field
material. Similar analyses of the ICM and baryon mass scaling relations provide
evidence for the so-called "missing baryons" outside cluster virial regions. |
How do galaxy properties affect void statistics?: Using a mapping from dark matter halos to galaxy properties based on
hydrodynamical simulations, we explore the impact of galaxy properties on the
void size function and the void-galaxy correlation function. We replicate the
properties of galaxies from Illustris on MassiveNus halos, to perform both
luminosity and star formation rate cuts on MassiveNus halos. We compare the
impact of such cuts on voids properties with respect to cuts on halo mass (as
usually performed on halo catalogs driven from N-body simulations). We find
that void catalogs built from luminosity-selected galaxies and halos are
consistent within errors, while void catalogs built from star formation rate
selected galaxies differ from void catalogs built on halos. We investigate the
reason for this difference. Our work suggests that voids built on galaxy
catalogs (selected through luminosity cut) can be reliably studied by using
halos in dark matter simulations. | A Comprehensive GALEX Ultraviolet Catalog of Star Clusters in M31 and a
Study of the Young Clusters: We present a comprehensive catalog of 700 confirmed star clusters in the
field of M31 compiled from three major existing catalogs. We detect 418 and 257
star clusters in Galaxy Evolution Explorer (GALEX) near-ultraviolet (NUV) and
far-ultraviolet (FUV) imaging, respectively. Our final catalog includes
photometry of star clusters in up to 16 passbands ranging from FUV to NIR as
well as ancillary information such as reddening, metallicity, and radial
velocities. In particular, this is the most extensive and updated catalog of UV
integrated photometry for M31 star clusters. Ages and masses of star clusters
are derived by fitting the multi-band photometry with model spectral energy
distribution (SED); UV photometry enables more accurate age estimation of young
clusters. Our catalog includes 182 young clusters with ages less than 1 Gyr.
Our estimated ages and masses of young clusters are in good agreement with
previously determined values in the literature. The mean age and mass of young
clusters are about 300 Myr and 10^4 M_sun, respectively. We found that the
compiled [Fe/H] values of young clusters included in our catalog are
systematically lower (by more than 1 dex) than those from recent high-quality
spectroscopic data and our SED fitting result. We confirm that most of the
young clusters kinematics show systematic rotation around the minor axis and
association with the thin disk of M31. The young clusters distribution exhibits
a distinct peak in the M31 disk around 10 - 12 kpc from the center and follow a
spatial distributions similar to other tracers of disk structure such as OB
stars, UV star-forming regions, and dust. Some young clusters also show
concentration around the ring splitting regions found in the southern part of
the M31 disk and most of them have systematically younger (< 100 Myr) ages. |
The kinematic dipole in galaxy redshift surveys: In the concordance model of the Universe, the matter distribution - as
observed in galaxy number counts or the intensity of line emission (such as the
21cm line of neutral hydrogen) - should have a kinematic dipole due to the
Sun's motion relative to the CMB rest-frame. This dipole should be aligned with
the kinematic dipole in the CMB temperature. Accurate measurement of the
direction of the matter dipole will become possible with future galaxy surveys,
and this will be a critical test of the foundations of the concordance model.
The amplitude of the matter dipole is also a potential cosmological probe. We
derive formulas for the amplitude of the kinematic dipole in galaxy redshift
and intensity mapping surveys, taking into account the Doppler, aberration and
other relativistic effects. The amplitude of the matter dipole can be
significantly larger than that of the CMB dipole. Its redshift dependence
encodes information on the evolution of the Universe and on the tracers, and we
discuss possible ways to determine the amplitude. | Absence of torsion : Clue from Starobinsky model of f(R) gravity: One of the surprising aspects of the present Universe, is the absence of any
noticeable observable effects of higher-rank anti-symmetric tensor fields, such
as space-time torsion, in any natural phenomena. Here we address the possible
explanation of torsion, which may often be identified with the field strength
tensor of the second rank antisymmetric Kalb-Ramond field. Within the framework
of f(R) gravity, we explore the cosmological evolution of the scalar degrees of
freedom associated with higher curvature term in a general higher curvature
model $f (R) = R +\alpha_n R^n$. We show that while the values of different
cosmological parameters follow acceptable values in the framework of standard
cosmology at different epochs for different forms of higher curvature gravity
(i.e. different values of n ), only for Starobinsky model (n = 2), the Kalb
Ramond field gets naturally suppressed with cosmological evolution. In
contrast, for other models (n both positive and negative), despite their
agreement with standard cosmology, the scalar field associated with the higher
derivative degree of freedom induces an enhancement in Kalb-Ramond field and
thereby contradicts the observation. The result does note change even if we
include the Cosmological Constant. Thus our result reveals that among different
$f(R)$ models, Starobinsky model successfully explains the suppression of
space-time torsion along with a consistent cosmological evolution. |
The duty cycle of radio-mode feedback in complete samples of clusters: The Chandra X-ray Observatory has revealed X-ray bubbles in the intracluster
medium (ICM) of many nearby cooling flow clusters. The bubbles trace feedback
that is thought to couple the central active galactic nucleus (AGN) to the ICM,
helping to stabilize cooling flows and govern the evolution of massive
galaxies. However, the prevalence and duty cycle of such AGN outbursts is not
well understood. To this end, we study how cooling is balanced by bubble
heating for complete samples of clusters (the Brightest 55 clusters of
galaxies, hereafter B55, and the HIghest X-ray FLUx Galaxy Cluster Sample,
HIFLUGCS). We find that the radio luminosity of the central galaxy only exceeds
2.5 x 10^30 erg s^-1 Hz^-1 in cooling flow clusters. This result implies a
connection between the central radio source and the ICM, as expected if AGN
feedback is operating. Additionally, we find a duty cycle for radio mode
feedback, the fraction of time that a system possesses bubbles inflated by its
central radio source, of > 69 per cent for B55 and > 63 per cent for HIFLUGCS.
These duty cycles are lower limits since some bubbles are likely missed in
existing images. We used simulations to constrain the bubble power that might
be present and remain undetected in the cooling flow systems without detected
bubbles. Among theses systems, almost all could have significant bubble power.
Therefore, our results imply that the duty cycle of AGN outbursts with the
potential to heat the gas significantly in cooling flow clusters is at least 60
per cent and could approach 100 per cent. | A deep radio survey of the AKARI North Ecliptic Pole Field - WSRT 20 cm
Radio survey description, observations and data reduction: The Westerbork Radio Synthesis Telescope, WSRT, has been used to make a deep
radio survey of an ~ 1.7 sq degree field coinciding with the AKARI North
Ecliptic Pole Deep Field. The observations, data reduction and source count
analysis are presented, along with a description of the overall scientific
objectives. The survey consisted of 10 pointings, mosaiced with enough overlap
to maintain a similar sensitivity across the central region that reached as low
as 21 microJy per beam at 1.4 GHz. A catalogue containing 462 sources detected
with a resolution of 17"x15" is presented. The differential source counts
calculated from the WSRT data have been compared with those from the shallow
VLA-NEP survey of Kollgaard et al 1994, and show a pronounced excess for
sources fainter than ~ 1 mJy, consistent with the presence of a population of
star forming galaxies at sub-mJy flux levels. The AKARI North Ecliptic Pole
Deep field is the focus of a major observing campaign conducted across the
entire spectral region. The combination of these data sets, along with the deep
nature of the radio observations will allow unique studies of a large range of
topics including the redshift evolution of the luminosity function of radio
sources, the clustering environment of radio galaxies, the nature of obscured
radio-loud active galactic nuclei, and the radio/far-infrared correlation for
distant galaxies. This catalogue provides the basic data set for a future
series of paper dealing with source identifications, morphologies, and the
associated properties of the identified radio sources. |
Photometric Properties of Six Local Volume Dwarf Galaxies from Deep
Near-Infrared Observations: We have obtained deep near-infrared $J$- (1.25 $\mu$m), $H$- (1.65$ \mu$m)
and $K_s$-band (2.15 $\mu$m) imaging for a sample of six dwarf galaxies
($M_B\ga-17$ mag) in the Local Volume (LV, $D\la10$ Mpc). The sample consists
mainly of early-type dwarf galaxies found in various environments in the LV.
Two galaxies (LEDA 166099 and UGCA 200) in the sample are detected in the
near-infrared for the first time. The deep near-infrared images allow for a
detailed study of the photometric and structural properties of each galaxy. The
surface brightness profiles of the galaxies are detected down to the ~$24 mag
arcsec^{-2}$ isophote in the $J$- and $H$-bands, and $23 mag arcsec^{-2}$ in
the $K_s$-band. The total magnitudes of the galaxies are derived in the three
wavelength bands. For the brightest galaxies ($M_B\la-15.5$ mag) in the sample,
we find that the Two Micron All Sky Survey (2MASS) underestimates the total
magnitudes of these systems by up to $\la0.5$ mag. The radial surface
brightness profiles of the galaxies are fitted with an exponential (for those
galaxies having a stellar disk) or S\'ersic law to derive the structure of the
underlying stellar component. In particular, the effective surface brightness
($\mu_e$) and effective radius ($r_e$) are determined from the analytic fits to
the surface brightness profile. The $J$-$K_s$ colours for the galaxies have
been measured to explore the luminosity-metallicity relation for early-type
dwarfs. In addition, the $B$-$K_s$ colours of the galaxies are used to assess
their evolutionary state relative to other galaxy morphologies. The total
stellar masses of the dwarf galaxies are derived from the $H$-band photometric
measurements. These will later be compared to the dynamical mass estimates for
the galaxies to determine their dark matter content. | Radiative transfer of energetic photons: X-rays and helium ionization in
C2-Ray: We present an extension to the short-characteristic ray-tracing and
non-equilibrium photon-ionization code C2Ray. The new version includes the
effects of helium and improved multi-frequency heating. The motivation for this
work is to be able to deal with harder ionizing spectra, such as for example
from quasar-like sources during cosmic reionization. We review the basic
algorithmic ingredients of C2-Ray before describing the changes implemented,
which include a treatment of the full on the spot (OTS) approximation,
secondary ionization, and multi-frequency photo-ionization and heating. We
performed a series of tests against equilibrium solutions from CLOUDY as well
as comparisons to the hydrogen only solutions by C2-Ray in the extensive code
comparison in Iliev et al. (2006). We show that the full, coupled OTS
approximation is more accurate than the simplified, uncoupled one. We find that
also with helium and a multi-frequency set up, long timesteps (up to ~10% of
the recombination time) still give accurate results for the ionization
fractions. On the other hand, accurate results for the temperature set strong
constrains on the timestep. The details of these constraints depend however on
the optical depth of the cells. We use the new version of the code to confirm
that the assumption made in many reionization simulations, namely that helium
is singly ionized everywhere were hydrogen is, is indeed valid when the sources
have stellar-like spectra. |
Primordial Non-Gaussianities from the Trispectra in Multiple Field
Inflationary Models: We investigate the primordial non-Gaussianities from the trispectra in
multi-field inflation models, which can be seen as generalization of
multi-field $k$-inflation and multi-DBI inflation. We derive the full
fourth-order perturbation action for the inflaton fields and evaluate the
four-point correlation functions for the perturbations in the limit $\ca \ll 1$
and $\ce \ll1$. There are three types of momentum-dependent shape functions
which arise from three types of four-point interaction vertices. The final
trispectrum of the curvature perturbation can be expressed in terms of the
deformations and permutations of these three shape functions, and is determined
by $\ca$, $\ce$, $\lambda$, $\Pi$ which depend on the non-linear structure of
the model and also the transfer function $T_{\Rc\Sc}$. We also discuss the
parameter space for the trispectrum and plot the shape diagrams for the
trispectrum both for visualization and for distinguishing different shapes from
each other. | XMM-Newton first X-ray detection of the LoBAL quasar PG 1700+518: We report the first high-energy detection of PG 1700+518, a well-known
low-ionization broad absorption line quasar (QSO). Due to previous X-ray
non-detection, it was classified as soft X-ray weak QSO. We observed PG
1700+518 with XMM-Newton for about 60 ksec divided in three exposures. The
spectrum below 2 keV is very steep, Gamma ~ 2.4-3.8, while at higher energies
the extremely flat emission (photon index Gamma ~ 0.15, when modelled with a
power law) suggests the presence of strong absorption (NH,pl ~ 2\times10^23
cm-2, Gamma fixed to 1.8), or a reflection-dominated continuum. The broad-band
flux is consistent with previous non-detection. Simultaneous EPIC and OM data
confirm its X-ray weakness (alpha_ox = -2.2). The level of obscuration derived
from the X-ray spectra of PG 1700+518 cannot explain its soft X-ray nuclear
weakness unless a column density of NH >~ 2\times10^24 cm-2 is present. |
A dark siren measurement of the Hubble constant with the LIGO/Virgo
gravitational wave event GW190412 and DESI galaxies: We present a measurement of the Hubble Constant $H_0$ using the gravitational
wave event GW190412, an asymmetric binary black hole merger detected by
LIGO/Virgo, as a dark standard siren. This event does not have an
electromagnetic counterpart, so we use the statistical standard siren method
and marginalize over potential host galaxies from the Dark Energy Spectroscopic
Instrument (DESI) survey. GW190412 is well-localized to 12 deg$^2$ (90%
credible interval), so it is promising for a dark siren analysis. The dark
siren value for $H_0=85.4_{-33.9}^{+29.1}$ km/s/Mpc, with a posterior shape
that is consistent with redshift overdensities. When combined with the bright
standard siren measurement from GW170817 we recover $H_0=77.96_{-5.03}^{+23.0}$
km/s/Mpc, consistent with both early and late-time Universe measurements of
$H_0$. This work represents the first standard siren analysis performed with
DESI data, and includes the most complete spectroscopic sample used in a dark
siren analysis to date. | Measuring cosmological parameters with Gamma-Ray Bursts: In a few dozen seconds gamma ray bursts (GRBs) emit up to 10^54 erg in terms
of an equivalent isotropically radiated energy Eiso, so they can be observed up
to z ~10. Thus, these phenomena appear to be very promising tools to describe
the expansion rate history of the universe. Here we review the use of the Ep,i
- Eiso correlation of GRBs to measure the cosmological density parameter
Omega_M. We show that the present data set of Gamma-Ray Bursts, coupled with
the assumption that we live in a flat universe, can provide independent
evidence, from other probes, that Omega_M ~0.3. We show that current (e.g.,
Swift, Fermi/GBM, Konus-WIND) and forthcoming GRB experiments (e.g., CALET/GBM,
SVOM, Lomonosov/UFFO, LOFT/WFM) will allow us to constrain Omega_M with an
accuracy comparable to that currently exhibited by Type Ia supernovae and to
study the properties of dark energy and their evolution with time. |
H0LiCOW IV. Lens mass model of HE 0435-1223 and blind measurement of its
time-delay distance for cosmology: Strong gravitational lenses with measured time delays between the multiple
images allow a direct measurement of the time-delay distance to the lens, and
thus a measure of cosmological parameters, particularly the Hubble constant,
$H_{0}$. We present a blind lens model analysis of the quadruply-imaged quasar
lens HE 0435-1223 using deep Hubble Space Telescope imaging, updated time-delay
measurements from the COSmological MOnitoring of GRAvItational Lenses
(COSMOGRAIL), a measurement of the velocity dispersion of the lens galaxy based
on Keck data, and a characterization of the mass distribution along the line of
sight. HE 0435-1223 is the third lens analyzed as a part of the $H_{0}$ Lenses
in COSMOGRAIL's Wellspring (H0LiCOW) project. We account for various sources of
systematic uncertainty, including the detailed treatment of nearby perturbers,
the parameterization of the galaxy light and mass profile, and the regions used
for lens modeling. We constrain the effective time-delay distance to be
$D_{\Delta t} = 2612_{-191}^{+208}~\mathrm{Mpc}$, a precision of 7.6%. From HE
0435-1223 alone, we infer a Hubble constant of $H_{0} =
73.1_{-6.0}^{+5.7}~\mathrm{km~s^{-1}~Mpc^{-1}}$ assuming a flat $\Lambda$CDM
cosmology. The cosmographic inference based on the three lenses analyzed by
H0LiCOW to date is presented in a companion paper (H0LiCOW Paper V). | $γ$ gravity: Steepness control: We investigate a simple generalization of the metric exponential $f(R)$
gravity theory that is cosmologically viable and compatible with solar system
tests of gravity. We show that, as compared to other viable $f(R)$ theories,
its steep dependence on the Ricci scalar $R$ facilitates agreement with
structure constraints, opening the possibility of $f(R)$ models with
equation-of-state parameter that could be differentiated from a cosmological
constant ($w_{de}=-1$) with future surveys at both background and perturbative
levels. |
Cosmic Feedback from AGN: Accretion onto the massive black hole at the centre of a galaxy can feed
energy and momentum into its surroundings via radiation, winds and jets.
Feedback due to radiation pressure can lock the mass of the black hole onto the
M-sigma relation, and shape the final stellar bulge of the galaxy. Feedback due
to the kinetic power of jets can prevent massive galaxies greatly increasing
their stellar mass, by heating gas which would otherwise cool radiatively. The
mechanisms involved in cosmic feedback are discussed and illustrated with
observations. | Conformal Cosmology and the Pioneer Anomaly: We review the fundamental results of a new cosmological model, based on
conformal gravity, and apply them to the analysis of the early data of the
Pioneer anomaly. We show that our conformal cosmology can naturally explain the
anomalous acceleration of the Pioneer 10 and 11 spacecraft, in terms of a local
blueshift region extending around the solar system and therefore affecting the
frequencies of the navigational radio signals exchanged between Earth and the
spacecraft. On the contrary, conformal gravity corrections alone would not be
able to account for dynamical effects of such magnitude to be capable of
producing the observed Pioneer acceleration. By using our model, we explain the
numerical coincidence between the value of the anomalous acceleration and the
Hubble constant at the present epoch and also confirm our previous
determination of the cosmological parameters gamma ~ 10^(-28) cm^(-1) and delta
~ 10^(-4) - 10^(-5). New Pioneer data are expected to be publicly available in
the near future, which might enable more precise evaluations of these
parameters. |
Growth and Geometry Split in Light of the DES-Y3 Survey: We test the smooth dark energy paradigm using Dark Energy Survey (DES) Year 1
and Year 3 weak lensing and galaxy clustering data. Within the $\Lambda$CDM and
$w$CDM model we separate the expansion and structure growth history by
splitting $\Omega_\mathrm{m}$ (and $w$) into two meta-parameters that allow for
different evolution of growth and geometry in the Universe. We consider three
different combinations of priors on geometry from CMB, SNIa, BAO, BBN that
differ in constraining power but have been designed such that the growth
information comes solely from the DES weak lensing and galaxy clustering. For
the DES-Y1 data we find no detectable tension between growth and geometry
meta-parameters in both the $\Lambda$CDM and $w$CDM parameter space. This
statement also holds for DES-Y3 cosmic shear and 3x2pt analyses. For the
combination of DES-Y3 galaxy-galaxy lensing and galaxy clustering (2x2pt) we
measure a tension between our growth and geometry meta-parameters of
2.6$\sigma$ in the $\Lambda$CDM and 4.48$\sigma$ in the $w$CDM model space,
respectively. We attribute this tension to residual systematics in the DES-Y3
RedMagic galaxy sample rather than to new physics. We plan to investigate our
findings further using alternative lens samples in DES-Y3 and future weak
lensing and galaxy clustering datasets. | The eROSITA Final Equatorial-Depth Survey (eFEDS): Characterization of
Morphological Properties of Galaxy Groups and Clusters: Understanding the cluster population of clusters of galaxies is of the utmost
importance for using cluster samples in both astrophysical and cosmological
studies. We present an in-depth analysis of the X-ray morphological parameters
of the galaxy clusters and groups detected in the eROSITA Final
Equatorial-Depth Survey (eFEDS). We study the eROSITA X-ray imaging data for a
sample of 325 clusters and groups that are significantly detected in the eFEDS
field. We characterize their dynamical properties by measuring a number of
dynamical estimators: concentration, central density, cuspiness, ellipticity,
power-ratios, photon asymmetry, and Gini coefficient. The galaxy clusters and
groups detected in eFEDS, covering a luminosity range of more than three orders
of magnitude and large redshift range out to 1.2 provide an ideal sample for
studying the redshift and luminosity evolution of the morphological parameters
and characterization of the underlying dynamical state of the sample. Based on
these measurements we construct a new dynamical indicator, relaxation score,
for all the clusters in the sample. We find no evidence for bimodality in the
distribution of morphological parameters of our clusters, rather we observe a
smooth transition from the cool-core to non-cool-core and from relaxed to
disturbed states. A significant evolution in redshift and luminosity is also
observed in the morphological parameters examined in this study after carefully
taking into account the selection effects. We determine that our eFEDS-selected
cluster sample, differently than ROSAT-based cluster samples, is not biased
toward relaxed clusters, but contains a similar fraction of disturbed as SZ
surveys. |
On the relative Contribution of high-redshift Galaxies and Active
Galactic Nuclei to Reionization: In this paper we discuss the contribution of different astrophysical sources
to the ionization of neutral hydrogen at different redshifts. We critically
revise the arguments in favour/against a substantial contribution of Active
Galactic Nuclei (AGNs) and/or Lyman Break Galaxies (LBGs) to the reionization
of the Universe at z>5. We consider extrapolations of the high-z QSO and LBG
luminosity functions and their redshift evolution as well as indirect
constraints on the space density of lower luminosity Active Galactic Nuclei
based on the galaxy stellar mass function. Since the hypothesis of a
reionization due to LBGs alone requires a significant contribution of faint
dwarf galaxies and a LyC photon escape fraction (f_esc) of the order of ~20%,
in tension with present observational constraints, we examine under which
hypothesis AGNs and LBGs may provide a combined relevant contribution to the
reionization. We show that a relatively steep faint-end of the AGN luminosity
function, consistent with present constraints, provides a relevant (although
sub-dominant) contribution, thus allowing us to recover the required ionizing
photon rates with f_esc~5% up to z~7. At higher redshifts, we test the case for
a luminosity-dependent f_esc scenario and we conclude that, if the observed
LBGs are indeed characterized by very low f_esc, values of the order of
f_esc~70% are needed for objects below our detection threshold, for this galaxy
population to provide a substantial contribution to reionization. Clearly, the
study of the properties of faint sources (both AGNs and LBGs) is crucial. | Partition function approach to non-Gaussian likelihoods: physically
motivated convergence criteria for Markov-chains: Non-Gaussian distributions in cosmology are commonly evaluated with Monte
Carlo Markov-chain methods, as the Fisher-matrix formalism is restricted to the
Gaussian case. The Metropolis-Hastings algorithm will provide samples from the
posterior distribution after a burn-in period, and the corresponding
convergence is usually quantified with the Gelman-Rubin criterion. In this
paper, we investigate the convergence of the Metropolis-Hastings algorithm by
drawing analogies to statistical Hamiltonian systems in thermal equilibrium for
which a canonical partition sum exists. Specifically, we quantify
virialisation, equipartition and thermalisation of Hamiltonian Monte Carlo
Markov-chains for a toy-model and for the likelihood evaluation for a simple
dark energy model constructed from supernova data. We follow the convergence of
these criteria to the values expected in thermal equilibrium, in comparison to
the Gelman-Rubin criterion. We find that there is a much larger class of
physically motivated convergence criteria with clearly defined target values
indicating convergence. As a numerical tool, we employ physics-informed neural
networks for speeding up the sampling process. |
A model-independent characterisation of strong gravitational lensing by
observables: When light from a distant source object, like a galaxy or a supernova,
travels towards us, it is deflected by massive objects that lie on its path.
When the mass density of the deflecting object exceeds a certain threshold,
multiple, highly distorted images of the source are observed. This strong
gravitational lensing effect has so far been treated as a model-fitting
problem. Using the observed multiple images as constraints yields a
self-consistent model of the deflecting mass density and the source object. As
several models meet the constraints equally well, we develop a lens
characterisation that separates data-based information from model assumptions.
The observed multiple images allow us to determine local properties of the
deflecting mass distribution on any mass scale from one simple set of
equations. Their solution is unique and free of model-dependent degeneracies.
The reconstruction of source objects can be performed completely
model-independently, enabling us to study galaxy evolution without a lens-model
bias. Our approach reduces the lens and source description to its data-based
evidence that all models agree upon, simplifies an automated treatment of large
datasets, and allows for an extrapolation to a global description resembling
model-based descriptions. | Gravitational lensing from clusters of galaxies to test Disformal
Couplings Theories: In this study, we investigate the potential existence of a non-minimal
coupling between dark matter and gravity using a compilation of galaxy
clusters. We focus on the disformal scenario of a non-minimal model with an
associated coupling length $L$. Within the Newtonian approximation, this model
introduces a modification to the Poisson equation, characterized by a term
proportional to $L^2 \nabla^2 \rho$, where $\rho$ represents the density of the
DM field. We have tested the model by examining strong and weak gravitational
lensing data available for a selection of 19 high-mass galaxy clusters observed
by the CLASH survey. We have employed a Markov Chain Monte Carlo code to
explore the parameter space, and two different statistical approaches to
analyse our results: a standard marginalisation and a profile distribution
method. Notably, the profile distribution analysis helps out to bypass some
volume-effects in the posterior distribution, and reveals lower
Navarro--Frenk--White concentrations and masses in the non-minimal coupling
model compared to general relativity case. We also found a nearly perfect
correlation between the coupling constant $L$ and the standard
Navarro--Frenk--White scale parameter $r_s$, hinting at a compelling link
between these two lengths. |
Probing Time-Dependent Dark Energy with the Flux Power Spectrum of the
Lyman $α$ Forest: We present new simulations of the flux power spectrum of the Lyman $\alpha$
forest as a means to investigate the effects of time-dependent dark energy on
structure formation. We use a linearized parameterization of the
time-dependence of the dark energy equation of state and sample the parameters
($w_0,w_a$) from the the extrema of the allowed observational values as
determined by the Planck results. Each chosen ($w_0,w_a$) pair is then used in
a high-resolution, large-scale cosmological simulation run with a modified
version of the publicly available SPH code {\tt GADGET-2}. From each of these
simulations we extract synthetic Lyman $\alpha$ forest spectra and calculate
the flux power spectrum. We use the k-sample Anderson-Darling test to analyze
the effects of dark energy on the Lyman $\alpha$ forest. We compare each dark
energy power spectrum to that due to a cosmological constant power spectrum. We
find, however, that there is only a marginal effect of the choice of allowed
dark energy models on the flux power spectrum. | Estimation of the Hubble Constant and Constraint on Descriptions of Dark
Energy: Joint analysis of Cosmic Microwave Background, Baryon Acoustic Oscillation,
and supernova data has enabled precision estimation of cosmological parameters.
New programs will push to 1% uncertainty in the dark energy equation of state
and tightened constraint on curvature, requiring close attention to
systematics. Direct 1% measurement of the Hubble constant (H0) would provide a
new constraint. It can be obtained without overlapping systematics directly
from recessional velocities and geometric distance estimates for galaxies via
the mapping of water maser emission that traces the accretion disks of nuclear
black holes. We identify redshifts 0.02<z<0.06 as best for small samples, e.g.,
10 widely distributed galaxies, each with 3% distance uncertainty. Knowledge of
peculiar radial motion is also required. Mapping requires very long baseline
interferometry (VLBI) with the finest angular resolution, sensitivity to
individual lines of a few mJy-km/s, and baselines that can detect a complex of
~10 mJy lines (peak) in < 1 min. For 2010-2020, large ground apertures (50-100m
diameter) augmenting the VLBA are critical, such as EVLA, GBT, Effelsberg, and
the Large Millimeter Telescope, for which we propose a 22 GHz receiver and VLBI
instrumentation. A space-VLBI aperture may be required, thus motivating US
participation in the Japanese VSOP-2 mission (launch c.2013). This will provide
3-4x longer baselines and ~5x improvement in distance uncertainty. There are
now 5 good targets at z>0.02, out of ~100 known masers. A single-dish discovery
survey of >10,000 nuclei (>2500 hours on the GBT) would build a sample of tens
of potential distance anchors. Beyond 2020, a high-frequency SKA could provide
larger maser samples, enabling estimation of H0 from individually less accurate
distances, and possibly without the need for peculiar motion corrections. |
Satellites around massive galaxies since z~2: Accretion of minor satellites has been postulated as the most likely
mechanism to explain the significant size evolution of the massive galaxies
over cosmic time. Using a sample of 629 massive (Mstar~10^11 Msun) galaxies
from the near-infrared Palomar/DEEP-2 survey, we explore which fraction of
these objects has satellites with 0.01 Msat < Mcentral < 1 (1:100) up to z=1
and which fraction has satellites with 0.1 Msat < Mcentral < 1 (1:10) up to z=2
within a projected radial distance of 100 kpc. We find that the fraction of
massive galaxies with satellites, after the background correction, remains
basically constant and close to ~30% for satellites with a mass ratio down to
1:100 up to z=1, and ~15% for satellites with a 1:10 mass ratio up to z=2. The
family of spheroid-like massive galaxies presents a 2-3 times larger fraction
of objects with satellites than the group of disk-like massive galaxies. A
crude estimation of the number of 1:3 mergers a massive spheroid-like galaxy
experiences since z~2 is around 2. For a disk-like galaxy this number decreases
to ~1. | CLASH: The enhanced lensing efficiency of the highly elongated merging
cluster MACS J0416.1-2403: We perform a strong-lensing analysis of the merging galaxy cluster MACS
J0416.1-2403 (M0416; z=0.42) in recent CLASH/HST observations. We identify 70
new multiple images and candidates of 23 background sources in the range
0.7<z_{phot}<6.14 including two probable high-redshift dropouts, revealing a
highly elongated lens with axis ratio ~5:1, and a major axis of ~100\arcsec
(z_{s}~2). Compared to other well-studied clusters, M0416 shows an enhanced
lensing efficiency. Although the critical area is not particularly large (~0.6
\square\arcmin; z_{s}~2), the number of multiple images, per critical area, is
anomalously high. We calculate that the observed elongation boosts the number
of multiple images, \emph{per critical area}, by a factor of ~2.5\times, due to
the increased ratio of the caustic area relative to the critical area.
Additionally, we find that the observed separation between the two main mass
components enlarges the critical area by a factor of ~2. These geometrical
effects can account for the high number (density) of multiple images observed.
We find in numerical simulations, that only ~4% of the clusters (with M_{vir}>6
x 10^{14} h^{-1}M_{\odot}) exhibit as elongated critical curves as M0416. |
First test of the consistency relation for the large-scale structure
using the anisotropic three-point correlation function of BOSS DR12 galaxies
(An explanatory video is available at https://youtu.be/Zi36ooLPhss.): We present, for the first time, an observational test of the consistency
relation for the large-scale structure (LSS) of the Universe through a joint
analysis of the anisotropic two- and three-point correlation functions (2PCF
and 3PCF) of galaxies. We parameterise the breakdown of the LSS consistency
relation in the squeezed limit by $E_{\rm s}$, which represents the ratio of
the coefficients of the shift terms in the second-order density and velocity
fluctuations. $E_{\rm s}\neq1$ is a sufficient condition under which the LSS
consistency relation is violated. A novel aspect of this work is that we
constrain $E_{\rm s}$ by obtaining information about the nonlinear velocity
field from the quadrupole component of the 3PCF without taking the squeezed
limit. Using the galaxy catalogues in the Baryon Oscillation Spectroscopic
Survey (BOSS) Data Release 12, we obtain $E_{\rm s} = -0.92_{-3.26}^{+3.13}$,
indicating that there is no violation of the LSS consistency relation in our
analysis within the statistical errors. Our parameterisation is general enough
that our constraint can be applied to a wide range of theories, such as
multicomponent fluids, modified gravity theories, and their associated galaxy
bias effects. Our analysis opens a new observational window to test the
fundamental physics using the anisotropic higher-order correlation functions of
galaxy clustering. | Candidate Clusters of Galaxies at $z>1.3$ Identified in the Spitzer SPT
Deep Field Survey: We present 279 galaxy cluster candidates at $z > 1.3$ selected from the 94
deg$^{2}$ Spitzer South Pole Telescope Deep Field (SSDF) survey. We use a
simple algorithm to select candidate high-redshift clusters of galaxies based
on Spitzer/IRAC mid-infrared data combined with shallow all-sky optical data.
We identify distant cluster candidates in SSDF adopting an overdensity
threshold that results in a high purity (80%) cluster sample based on tests in
the Spitzer Deep, Wide-Field Survey of the Bo\"otes field. Our simple algorithm
detects all three $1.4 < z \leq 1.75$ X-ray detected clusters in the Bo\"otes
field. The uniqueness of the SSDF survey resides not just in its area, one of
the largest contiguous extragalactic fields observed with Spitzer, but also in
its deep, multi-wavelength coverage by the South Pole Telescope (SPT),
Herschel/SPIRE and XMM-Newton. This rich dataset will allow direct or stacked
measurements of Sunyaev-Zel'dovich effect decrements or X-ray masses for many
of the SSDF clusters presented here, and enable systematic study of the most
distant clusters on an unprecedented scale. We measure the angular correlation
function of our sample and find that these candidates show strong clustering.
Employing the COSMOS/UltraVista photometric catalog in order to infer the
redshift distribution of our cluster selection, we find that these clusters
have a comoving number density $n_c = (0.7^{+6.3}_{-0.6}) \times 10^{-7} h^{3}
\mathrm{Mpc}^{-3}$ and a spatial clustering correlation scale length $r_0 = (32
\pm 7) h^{-1} \rm{Mpc}$. Assuming our sample is comprised of dark matter halos
above a characteristic minimum mass, $M_{{\rm min}}$, we derive that at $z=1.5$
these clusters reside in halos larger than $M_{{\rm min}} = 1.5^{+0.9}_{-0.7}
\times 10^{14} h^{-1} M_{\odot}$. (abridged) |
Constraints on smoothness parameter and dark energy using observational
$H(z)$ data: The universe, with large-scale homogeneity, is locally inhomogeneous,
clustering into stars, galaxies and larger structures. Such property is
described by the smoothness parameter $\alpha$ which is defined as the
proportion of matter in the form of intergalactic medium. If we take
consideration of the inhomogeneities in small scale, there should be
modifications of the cosmological distances compared to a homogenous model.
Dyer and Roeder developed a second-order ordinary differential equation (D-R
equation) that describes the angular diameter distance-redshift relation for
inhomogeneous cosmological models. Furthermore, we may obtain the D-R equation
for observational $H(z)$ data (OHD). The density-parameter $\Omega_{\rm M}$,
the state of dark energy $\omega$, and the smoothness-parameter $\alpha$ are
constrained by a set of OHD in a spatially flat $\Lambda$CDM universe as well
as a spatially flat XCDM universe. By using of $\chi^2$ minimization method we
get $\alpha=0.81^{+0.19}_{-0.20}$ and $\Omega_{\rm M}=0.32^{+0.12}_{-0.06}$ at
$1\sigma$ confidence level. If we assume a Gaussian prior of $\Omega_{\rm
M}=0.26\pm0.1$, we get $\alpha=0.93^{+0.07}_{-0.19}$ and $\Omega_{\rm
M}=0.31^{+0.06}_{-0.05}$. For XCDM model, $\alpha$ is constrained to
$\alpha\geq0.80$ but $\omega$ is weakly constrained around -1, where $\omega$
describes the equation of the state of the dark energy ($p_{\rm
X}=\omega\rho_{\rm X}$). We conclude that OHD constrains the smoothness
parameter more effectively than the data of SNe Ia and compact radio sources. | Optimal bispectrum estimator and simulations of the the CMB Lensing-ISW
non-Gaussian signal: In this paper we present the tools to optimally extract the
Lensing-Integrated Sachs Wolfe (L-ISW) bispectrum signal from future CMB data.
We implement two different methods to simulate the non-Gaussian CMB maps with
the L-ISW signal: a non-perturbative method based on the FLINTS lensing code
and the separable mode expansion method. We implement the Komatsu, Spergel and
Wandelt (KSW) optimal estimator analysis for the Lensing-ISW bispectrum and we
test it on the non-Gaussian simulations in the case of a realistic CMB
experimental settings with an inhomogeneous sky coverage. We show that the
estimator approaches the Cramer-Rao bound and that Wiener filtering the L-ISW
simulations gives a slight improvement on the estimate of $f_{NL}^{L-ISW}$ of
$\leq 10%$. For a realistic CMB experimental setting accounting for anisotropic
noise and masked sky, we show that the linear term of the estimator is highly
correlated to the cubic term and it is necessary to recover the signal and the
optimal error bars. We also show that the L-ISW bispectrum, if not correctly
accounted for, yields an underestimation of the $f_{NL}^{local}$ error bars of
$\simeq 4%$. A joint analysis of the non-Gaussian shapes and/or L-ISW template
subtraction is needed in order to recover unbiased results of the primordial
non-Gaussian signal from ongoing and future CMB experiments. |
Machine learning unveils the linear matter power spectrum of modified
gravity: The matter power spectrum $P(k)$ is one of the main quantities connecting
observational and theoretical cosmology. Although for a fixed redshift this can
be numerically computed very efficiently by Boltzmann solvers, an analytical
description is always desirable. However, accurate fitting functions for $P(k)$
are only available for the concordance model. Taking into account that
forthcoming surveys will further constrain the parameter space of cosmological
models, it is also of interest to have analytical formulations for $P(k)$ when
alternative models are considered. Here, we use the genetic algorithms, a
machine learning technique, to find a parametric function for $P(k)$
considering several possible effects imprinted by modifications of gravity. Our
expression for the $P(k)$ of modified gravity shows a mean accuracy of around
1-2% when compared with numerical data obtained via modified versions of the
Boltzmann solver CLASS, and thus it represents a competitive formulation given
the target accuracy of forthcoming surveys. | CO line emission in the halo of a radio galaxy at z=2.6: We report the detection of luminous CO(3-2) line emission in the halo of the
z=2.6 radio galaxy (HzRG) TXS0828+193, which has no detected counterpart at
optical to mid-infrared wavelengths implying a stellar mass < few x10^9 M_sun
and relatively low star-formation rates. With the IRAM PdBI we find two CO
emission line components at the same position at ~80 kpc distance from the HzRG
along the axis of the radio jet, with different blueshifts of few 100 km s^-1
relative to the HzRG and a total luminosity of ~2x10^10 K km s^-1 pc^2 detected
at 8 sigma significance. HzRGs have significant galaxy overdensities and
extended halos of metal-enriched gas often with embedded clouds or filaments of
denser material, and likely trace very massive dark-matter halos. The CO
emission may be associated with a gas-rich, low-mass satellite galaxy with
little on-going star formation, in contrast to all previous CO detections of
galaxies at similar redshifts. Alternatively, the CO may be related to a gas
cloud or filament and perhaps jet-induced gas cooling in the outer halo,
somewhat in analogy with extended CO emission found in low-redshift galaxy
clusters. |
The Hydrogen Epoch of Reionization Array Dish II: Characterization of
Spectral Structure with Electromagnetic Simulations and its science
Implications: We use time-domain electromagnetic simulations to determine the spectral
characteristics of the Hydrogen Epoch of Reionization Arrays (HERA) antenna.
These simulations are part of a multi-faceted campaign to determine the
effectiveness of the dish's design for obtaining a detection of redshifted 21
cm emission from the epoch of reionization. Our simulations show the existence
of reflections between HERA's suspended feed and its parabolic dish reflector
that fall below -40 dB at 150 ns and, for reasonable impedance matches, have a
negligible impact on HERA's ability to constrain EoR parameters. It follows
that despite the reflections they introduce, dishes are effective for
increasing the sensitivity of EoR experiments at relatively low cost. We find
that electromagnetic resonances in the HERA feed's cylindrical skirt, which is
intended to reduce cross coupling and beam ellipticity, introduces significant
power at large delays ($-40$ dB at 200 ns) which can lead to some loss of
measurable Fourier modes and a modest reduction in sensitivity. Even in the
presence of this structure, we find that the spectral response of the antenna
is sufficiently smooth for delay filtering to contain foreground emission at
line-of-sight wave numbers below $k_\parallel \lesssim 0.2$ $h$Mpc$^{-1}$, in
the region where the current PAPER experiment operates. Incorporating these
results into a Fisher Matrix analysis, we find that the spectral structure
observed in our simulations has only a small effect on the tight constraints
HERA can achieve on parameters associated with the astrophysics of
reionization. | [CII] line emission in massive star-forming galaxies at z=4.7: We present Atacama Large Millimeter/submillimeter Array (ALMA) observations
of the [CII] 157.7micron fine structure line and thermal dust continuum
emission from a pair of gas-rich galaxies at z=4.7, BR1202-0725. This system
consists of a luminous quasar host galaxy and a bright submm galaxy (SMG),
while a fainter star-forming galaxy is also spatially coincident within a 4"
(25 kpc) region. All three galaxies are detected in the submm continuum,
indicating FIR luminosities in excess of 10^13 Lsun for the two most luminous
objects. The SMG and the quasar host galaxy are both detected in [CII] line
emission with luminosities, L([CII]) = (10.0 +/- 1.5)x10^9 Lsun and L([CII]) =
(6.5+/-1.0)x10^9 Lsun, respectively. We estimate a luminosity ratio,
L([CII])/L(FIR) = (8.3+/-1.2)x10^-4 for the starburst SMG to the North, and
L([CII])/L(FIR) = (2.5+/-0.4)x10^-4 for the quasar host galaxy, in agreement
with previous high-redshift studies that suggest lower [CII]-to-FIR luminosity
ratios in quasars than in starburst galaxies. The third fainter object with a
flux density, S(340GHz) = 1.9+/-0.3 mJy, is coincident with a Ly-Alpha emitter
and is detected in HST ACS F775W and F814W images but has no clear counterpart
in the H-band. Even if this third companion does not lie at a similar redshift
to BR1202-0725, the quasar and the SMG represent an overdensity of massive,
infrared luminous star-forming galaxies within 1.3 Gyr of the Big Bang. |
Recovering the Missing Large-Scale Density Modes in 21cm Intensity Map
from the Scalar-Type Clustering Fossils: Revealing the large-scale structure from the 21cm intensity mapping surveys
is only possible after the foreground cleaning. However, most current cleaning
techniques relying on the smoothness of the foreground spectrum lead to a
severe side effect of removing the large-scale structure signal along the line
of sight. On the other hand, the clustering fossil, a coherent variation of the
small-scale clustering over large scales, allows us to recover the
long-wavelength density modes from the off-diagonal correlation between
short-wavelength modes. In this paper, we study the requirements for an
unbiased and optimal clustering-fossil estimator and show that (A) the
estimator is unbiased only when using an accurate bispectrum model for the
long-short-short mode coupling and (B) including the connected four-point
correlation functions is essential for characterizing the noise power spectrum
of the estimated long mode. The clustering fossil estimator based upon the
leading-order bispectrum yields an unbiased estimation of the long-wavelength
($k\lesssim 0.01~[h/{\rm Mpc}]$) modes with the cross-correlation coefficient
of $0.7$ at redshifts $z=0$ to $3$. | Simulations of Early Baryonic Structure Formation with Stream Velocity:
I. Halo Abundance: It has been recently shown that the relative velocity between the dark matter
and the baryons (vbc) at the time of recombination can affect the structure
formation in the early universe (Tseliakhovich & Hirata 2010). We statistically
quantify this effect using large cosmological simulations. We use three
different high resolution sets of simulations (with separate transfer functions
for baryons and dark matter) that vary in box size, particle number, and the
value of the relative velocity between dark matter and baryons. We show that
the total number density of halos is suppressed by ~ 20% at z = 25 for vbc =
1{\sigma}(vbc), where {\sigma}(vbc) is the variance of the relative velocity,
while for vbc = 3.4{\sigma}(vbc) the relative suppression at the same redshift
reaches 50%, remaining at or above the 30% level all the way to z = 11. We also
find high abundance of "empty halos", i.e., halos that have gas fraction below
half of the cosmic mean baryonic fraction fb. Specifically we find that for vbc
= 1{\sigma}(vbc) all halos below 10^5M\odot are empty at z \geq 19. The high
abundance of empty halos results in significant delay in the formation of gas
rich mini-halos and the first galaxies. |
Galaxy assembly bias and large-scale distribution: a comparison between
IllustrisTNG and a semi-analytic model: In this work, we compare large scale structure observables for stellar mass
selected samples at $z=0$, as predicted by two galaxy models, the
hydrodynamical simulation IllustrisTNG and the Santa-Cruz semi-analytic model
(SC-SAM). Although both models have been independently calibrated to match
observations, rather than each other, we find good agreement between the two
models for two-point clustering and galaxy assembly bias signatures. The models
also show a qualitatively similar response of occupancy and clustering to
secondary halo paramaters other than mass, such as formation history and
concentration, although with some quantitative differences. Thus, our results
demonstrate that the galaxy-halo relationships in SC-SAM and TNG are quite
similar to first order. However, we also find areas in which the models differ.
For example, we note a strong correlation between halo gas content and
environment in TNG, which is lacking in the SC-SAM, as well as differences in
the occupancy predictions for low-mass haloes. Moreover, we show that
higher-order statistics, such as cumulants of the density field, help to
accurately describe the galaxy distribution and discriminate between models
that show degenerate behavior for two-point statistics. Our results suggest
that SAMs are a promising cost-effective and intuitive method for generating
mock catalogues for next generation cosmological surveys. | Optical circular polarization in quasars: We present new optical circular polarization measurements with typical
uncertainties < 0.1% for a sample of 21 quasars. All but two objects have null
circular polarization. We use this result to constrain the polarization due to
photon-pseudoscalar mixing along the line of sight. We detect significant (> 3
sigma) circular polarization in two blazars with high linear polarization and
discuss the implications of this result for quasar physics. In particular, the
recorded polarization degrees may be indicative of magnetic fields as strong as
1 kG or a significant contribution of inverse Compton scattering to the optical
continuum. |
On the observed distributions of black hole masses and Eddington ratios
from radiation pressure corrected virial indicators: The application of the virial theorem to the Broad Line Region of Active
Galactic Nuclei allows Black Hole mass estimates for large samples of objects
at all redshifts. In a recent paper we showed that ionizing radiation pressure
onto BLR clouds affects virial BH mass estimates and we provided empirically
calibrated corrections. More recently, a new test of the importance of
radiation forces has been proposed: the MBH-sigma relation has been used to
estimate MBH for a sample of type-2 AGN and virial relations (with and without
radiation pressure) for a sample of type-1 AGN extracted from the same parent
population. The observed L/LEdd distribution based on virial BH masses is in
good agreement with that based on MBH-sigma only if radiation pressure effects
are negligible, otherwise significant discrepancies are observed. In this paper
we investigate the effects of intrinsic dispersions associated to the virial
relations providing MBH, and we show that they explain the discrepancies
between the observed L/LEdd distributions of type-1 and type-2 AGN. These
discrepancies in the L/LEdd distributions are present regardless of the general
importance of radiation forces, which must be negligible only for a small
fraction of sources with large L/LEdd. Average radiation pressure corrections
should then be applied in virial MBH estimators until their dependence on
observed source physical properties has been fully calibrated. Finally, the
comparison between MBH and L/LEdd distributions derived from sigma-based and
virial estimators can constrain the variance of BLR physical properties in AGN. | A candidate polar-ring galaxy in the Subaru Deep Field: We discuss the properties of an object in the Subaru Deep Field (SDF)
classified as a galaxy in on-line data bases and revealed on the Subaru images
as a genuine polar-ring galaxy (PRG) candidate. We analyse available
photometric data and conclude that this object consists of a >5 Gyr old
early-type central body surrounded by a faint, narrow inner ring tilted at a
~25 deg angle relative to the polar axis of the host galaxy. The halo
surrounding the main stellar body exhibits a diversity of spatially extended
stellar features of low surface brightness, including a faint asymmetric
stellar cloud and two prominent loops. These faint features, together with the
unperturbed morphology of the central host, are clear signs of a recent
coalescence of two highly unequal mass galaxies, most likely a pre-existing
early-type galaxy and a close-by gas-rich dwarf galaxy. The presumed stellar
remnants observed near the edges of the ring, including possibly the surviving
captured companion itself, indicate that the merger is still taking place. |
Multi-band constraints on the nature of emission line galaxies: Our aim is to explore the nature of emission line galaxies by combining
high-resolution observations obtained in different bands to understand which
objects are powered by an Active Galactic Nucleus(AGN). From the spectroscopic
Palomar survey of nearby bright galaxies, we selected a sample of 18 objects
observed with HST, Chandra, and VLA.
No connection is found between X-ray and emission line luminosities from
ground-based data, unlike what is found for brighter AGN. Conversely, a strong
correlation emerges when using the HST spectroscopic data, which are extracted
on a much smaller aperture. This suggests that the HST data better isolate the
AGN component when one is present, while ground-based line measurements are
affected by diffuse emission from the host galaxies.
The sample separates into two populations. The 11 objects belonging to the
first class have an equivalent width of the [OIII] emission line measured from
HST data EW([OIII])>~2 A and are associated with an X-ray nuclear source; in
the second group we find seven galaxies with EW([OIII])<~1 A that generally do
not show any emission related to an active nucleus (emission lines, X-ray, or
radio sources). This latter group includes about half of the Low Ionization
Nuclear Emission-line region (LINERs) or transition galaxies of the sample, all
of which are objects of low [OIII] line luminosity (<~1E38 erg s-1) and low
equivalent width (<~1 A) in ground-based observations. These results strengthen
the suggestion that the EW([OIII]) value is a robust predictor of the nature of
an emission line galaxy. | Minimization of Biases in Galaxy Peculiar Velocity Catalogs: Galaxy distances and derived radial peculiar velocity catalogs constitute
valuable datasets to study the dynamics of the Local Universe. However, such
catalogs suffer from biases whose effects increase with the distance. Malmquist
biases and lognormal error distribution affect the catalogs. Velocity fields of
the Local Universe reconstructed with these catalogs present a spurious overall
infall onto the Local Volume if they are not corrected for biases. Such an
infall is observed in the reconstructed velocity field obtained when applying
the BayesianWiener-Filter technique to the raw second radial peculiar velocity
catalog of the Cosmicflows project. In this paper, an iterative method to
reduce spurious non-Gaussianities in the radial peculiar velocity distribution,
to retroactively derive overall better distance estimates resulting in a
minimization of the effects of biases, is presented. This method is tested with
mock catalogs. To control the cosmic variance, mocks are built out of different
cosmological constrained simulations which resemble the Local Universe. To
realistically reproduce the effects of biases, the mocks are constructed to be
look-alikes of the second data release of the Cosmicflows project, with respect
to the size, distribution of data and distribution of errors. Using a suite of
mock catalogs, the outcome of the correction is verified to be affected neither
by the added error realization, nor by the datapoint selection, nor by the
constrained simulation. Results are similar for the different tested mocks.
After correction, the general infall is satisfactorily suppressed. The method
allows us to obtained catalogs which together with the Wiener-Filter technique
give reconstructions approximating non biased velocity fields at 100-150 km/s
(2-3 Mpc/h in terms of linear displacement), the linear theory threshold. |
Cosmological Tests With Strong Gravitational Lenses using Gaussian
Processes: Strong gravitational lenses provide source/lens distance ratios D_obs useful
in cosmological tests. Previously, a catalog of 69 such systems was used in a
one-on-one comparison between the standard model, LCDM, and the R_h=ct
universe, which has thus far been favored by the application of model selection
tools to many other kinds of data. But in that work, the use of model
parametric fits to the observations could not easily distinguish between these
two cosmologies, in part due to the limited measurement precision. Here, we
instead use recently developed methods based on Gaussian Processes (GP), in
which D_obs may be reconstructed directly from the data without assuming any
parametric form. This approach not only smooths out the reconstructed function
representing the data, but also reduces the size of the 1-sigma confidence
regions, thereby providing greater power to discern between different models.
With the current sample size, we show that analyzing strong lenses with a GP
approach can definitely improve the model comparisons, producing probability
differences in the range ~10-30%. These results are still marginal, however,
given the relatively small sample. Nonetheless, we conclude that the
probability of R_h=ct being the correct cosmology is somewhat higher than that
of LCDM, with a degree of significance that grows with the number of sources in
the subsamples we consider. Future surveys will significantly grow the catalog
of strong lenses and will therefore benefit considerably from the GP method we
describe here. In addition, we point out that if the R_h=ct universe is
eventually shown to be the correct cosmology, the lack of free parameters in
the study of strong lenses should provide a remarkably powerful tool for
uncovering the mass structure in lensing galaxies. | Optical observational biases in the GRB redshift: The measured redshifts of gamma-ray bursts (GRBs), which were first detected
by the Swift satellite, seem to be bigger on average than the redshifts of GRBs
detected by other satellites. We analyzed the redshift distribution of GRBs
triggered and observed by different satellites (Swift, HETE2, BeppoSax,
Ulyssses). After considering the possible biases {significant difference was
found at the p=95.70% level in the redshift distributions of GRBs measured by
HETE and the Swift. |
A Model for Multi-property Galaxy Cluster Statistics: The massive dark matter halos that host groups and clusters of galaxies have
observable properties that appear to be log-normally distributed about
power-law mean scaling relations in halo mass. Coupling this assumption with
either quadratic or cubic approximations to the mass function in log space, we
derive closed-form expressions for the space density of halos as a function of
multiple observables as well as forms for the low-order moments of properties
of observable-selected samples. Using a Tinker mass function in a {\Lambda}CDM
cosmology, we show that the cubic analytic model reproduces results obtained
from direct, numerical convolution at the 10 percent level or better over
nearly the full range of observables covered by current observations and for
redshifts extending to z = 1.5. The model provides an efficient framework for
estimating effects arising from selection and covariance among observable
properties in survey samples. | General relativistic corrections to $N$-body simulations and the
Zel'dovich approximation: The initial conditions for Newtonian $N$-body simulations are usually
generated by applying the Zel'dovich approximation to the initial displacements
of the particles using an initial power spectrum of density fluctuations
generated by an Einstein-Boltzmann solver. We show that in most gauges the
initial displacements generated in this way receive a first-order relativistic
correction. We define a new gauge, the $N$-body gauge, in which this
relativistic correction vanishes and show that a conventional Newtonian
$N$-body simulation includes all first-order relativistic contributions (in the
absence of radiation) if we identify the coordinates in Newtonian simulations
with those in the relativistic $N$-body gauge. |
Constraints on Warm Dark Matter models from high-redshift long gamma-ray
bursts: Structures in Warm Dark Matter (WDM) models are exponentially suppressed
below a certain scale, characterized by the dark matter particle mass, $m_{\rm
x}$. Since structures form hierarchically, the presence of collapsed objects at
high-redshifts can set strong lower limits on $m_{\rm x}$. We place robust
constraints on $m_{\rm x}$ using recent results from the {\it Swift} database
of high-redshift gamma-ray bursts (GRBs). We parameterize the redshift
evolution of the ratio between the cosmic GRB rate and star formation rate
(SFR) as $\propto (1+z)^\alpha$, thereby allowing astrophysical uncertainties
to partially mimic the cosmological suppression of structures in WDM models.
Using a maximum likelihood estimator on two different $z>4$ GRB subsamples
(including two bursts at $z>8$), we constrain $m_{\rm x} \gtrsim 1.6$-1.8 keV
at 95% C.L., when marginalized over a flat prior in $\alpha$. We further
estimate that 5 years of a SVOM-like mission would tighten these constraints to
$m_{\rm x} \gtrsim 2.3 $ keV. Our results show that GRBs are a powerful probe
of high-redshift structures, providing robust and competitive constraints on
$m_{\rm x}$. | The bolometric output and host-galaxy properties of obscured AGN in the
XMM-COSMOS survey: We present a study of the multi-wavelength properties, from the mid-infrared
to the hard X-rays, of a sample of 255 spectroscopically identified X-ray
selected Type-2 AGN from the XMM-COSMOS survey. Most of them are obscured the
X-ray absorbing column density is determined by either X-ray spectral analyses
(for the 45% of the sample), or from hardness ratios. Spectral Energy
Distributions (SEDs) are computed for all sources in the sample. The average
SEDs in the optical band is dominated by the host-galaxy light, especially at
low X-ray luminosities and redshifts. There is also a trend between X-ray and
mid-infrared luminosity: the AGN contribution in the infrared is higher at
higher X-ray luminosities. We calculate bolometric luminosities, bolometric
corrections, stellar masses and star formation rates (SFRs) for these sources
using a multi-component modeling to properly disentangle the emission
associated to stellar light from that due to black hole accretion. For 90% of
the sample we also have the morphological classifications obtained with an
upgraded version of the Zurich Estimator of Structural Types (ZEST+). We find
that on average Type-2 AGN have lower bolometric corrections than Type-1 AGN.
Moreover, we confirm that the morphologies of AGN host-galaxies indicate that
there is a preference for these Type-2 AGN to be hosted in bulge-dominated
galaxies with stellar masses greater than 10^10 solar masses. |
21-cm line Anomaly: A brief Status: In this short review I present the status of the global 21-cm signal detected
by EDGES in March 2018. It is organized in three parts. First, I present the
EDGES experiment and the fitting procedure used by the collaboration to extract
the tiny 21-cm signal from large foregrounds of galactic synchrotron emission.
Then, I review the physics behind the global 21-cm signature and I explain why
the measured absorption feature is anomalous with respect to the predictions
from standard astrophysics. I conclude with the implications for Beyond
Standard Model (BSM) physics coming from the EDGES discovery. | The Atacama Cosmology Telescope: A Measurement of the 600< ell <8000
Cosmic Microwave Background Power Spectrum at 148 GHz: We present a measurement of the angular power spectrum of the cosmic
microwave background (CMB) radiation observed at 148 GHz. The measurement uses
maps with 1.4' angular resolution made with data from the Atacama Cosmology
Telescope (ACT). The observations cover 228 square degrees of the southern sky,
in a 4.2-degree-wide strip centered on declination 53 degrees South. The CMB at
arcminute angular scales is particularly sensitive to the Silk damping scale,
to the Sunyaev-Zel'dovich (SZ) effect from galaxy clusters, and to emission by
radio sources and dusty galaxies. After masking the 108 brightest point sources
in our maps, we estimate the power spectrum between 600 < \ell < 8000 using the
adaptive multi-taper method to minimize spectral leakage and maximize use of
the full data set. Our absolute calibration is based on observations of Uranus.
To verify the calibration and test the fidelity of our map at large angular
scales, we cross-correlate the ACT map to the WMAP map and recover the WMAP
power spectrum from 250 < ell < 1150. The power beyond the Silk damping tail of
the CMB is consistent with models of the emission from point sources. We
quantify the contribution of SZ clusters to the power spectrum by fitting to a
model normalized at sigma8 = 0.8. We constrain the model's amplitude ASZ < 1.63
(95% CL). If interpreted as a measurement of sigma8, this implies sigma8^SZ <
0.86 (95% CL) given our SZ model. A fit of ACT and WMAP five-year data jointly
to a 6-parameter LCDM model plus terms for point sources and the SZ effect is
consistent with these results. |
A Catalog of Detailed Visual Morphological Classifications for 14034
Galaxies in the Sloan Digital Sky Survey: We present a catalog of detailed visual classifications for 14034 galaxies in
the Sloan Digital Sky Survey (SDSS) Data Release 4 (DR4). Our sample includes
nearly all spectroscopically-targeted galaxies in the redshift range 0.01<z<0.1
down to an apparent extinction-corrected limit of g<16 mag. In addition to
T-Types we record the existence of bars, rings, lenses, tails, warps, dust
lanes, arm flocculence and multiplicity. This sample defines a comprehensive
local galaxy sample which we will use in future papers to study low redshift
morphology. It will also prove useful for calibrating automated galaxy
classification algorithms. In this paper we describe the classification
methodology used, detail the systematics and biases of our sample and summarize
the overall statistical properties of the sample, noting the most obvious
trends that are relevant for general comparisons of our catalog with previously
published work. | Plasma lensing with magnetic field and a small correction to the Faraday
rotation measurement: Plasma lensing displays interesting characteristics that set it apart from
gravitational lensing. The magnetised medium induces birefringence in the two
polarisation modes. As the lensing deflection grows stronger, e.g. when images
form near the critical curve, the geometric delay of the signal can cause
rotation in linear polarisation, in addition to Faraday rotation. This rotation
has a frequency dependence to the power of four. We study the geometric
rotation of the lensed image in a Gaussian density model and find that it is
necessary to take into account the geometric rotation when estimating
magnetised media, especially in the under-dense lens. At frequencies of $\sim
1$ GHz or lower, the geometric rotation can dominate. We simulate the flux of
lensed images and find that when the image forms near the lensing critical
curve, the birefringence can convert the linear polarisation and
un-polarisation pulse into a circular mode. The lensing magnification has the
potential to increase the probability of detecting such events. |
The Cosmic Evolution of Gamma-Ray Burst Host Galaxies: Due to their extreme luminosities, gamma-ray bursts (GRBs) can be detected in
hostile regions of galaxies, nearby and at very high redshift, making them
important cosmological probes. The investigation of galaxies hosting
long-duration GRBs (whose progenitor is a massive star) demonstrated their
connection to star formation. Still, the link to the total galaxy population is
controversial, mainly because of the small-number statistics: ~ 1,100 are the
GRBs detected so far, ~ 280 those with measured redshift, and ~ 70 the hosts
studied in detail. These are typically low-redshift (z < 1.5), low luminosity,
metal poor, and star-forming galaxes. On the other hand, at 1.5< z <4, massive,
metal rich and dusty, interacting galaxies are not uncommon. The most distant
population (z > 4) is poorly explored, but the deep limits reached point
towards very small and star-forming objects, similar to the low-z population.
This `back to the future' behavior is a natural consequence of the connection
of long GRBs to star formation in young regions of the universe. | Beyond the $Λ$CDM cosmology: complex composition of dark matter: The mass and composition of dark matter (DM) particles and the shape and
damping scales of the power spectrum of density perturbations can be estimated
from recent observations of the DM dominated relaxed objects -- dwarf galaxies
and clusters of galaxies. We confirm that the observed velocity dispersion of
dSph galaxies agrees with the possible existence of DM particles with mass
$m_w\sim 15 - 20keV$. More complex analysis utilizes the well known semi
analytical model of formation of DM halos in order to describe the basic
properties of corresponding objects and to estimate their redshifts of
formation. For the DM halos this redshift is determined by their masses and the
initial power spectrum of density perturbations. This correlation allows us to
partly reconstruct the small scale spectrum of perturbations. We consider the
available sample of suitable observed objects that includes $\sim 40$ DM
dominated galaxies and $\sim 40$ clusters of galaxies and we show that the
observed characteristics of these objects are inconsistent with expectations of
the standard $\Lambda$CDM cosmological model. However, they are consistent with
a more complex DM model with a significant contribution of the hot DM--like
power spectrum with relatively large damping scale ($\sim 10 - 30Mpc$). The HDM
component of DM decelerates but does not prevent formation of low mass objects.
These preliminary inferences require confirmation by a more representative
observational data that should include -- if possible -- DM dominated objects
with intermediate masses $M\sim 10^{10} - 10^{12} M_\odot$. Comparison of
observed properties of such objects with numerical simulations will provide
more detailed picture of the process of formation of DM halos. |
General Cosmography Model with Spatial Curvature: The cosmographic approach is adopted to determine the spatial curvature
(i.e., $\Omega_K$) combining the latest released cosmic chronometers data (CC),
the Pantheon sample of type Ia supernovae observations, and the baryon acoustic
oscillation measurements. We use the expanded transverse comoving distance
$D_M(z)$ as a basic function for deriving $H(z)$ and the other cosmic
distances. In this scenario, $\Omega_K$ can be constrained only by CC data. To
overcome the convergence issues at high-redshift domains, two methods are
applied: the Pad\'{e} approximants and the Taylor series in terms of the new
redshift $y=z/(1+z)$. Adopting the Bayesian evidence, we find that there is
positive evidence for the Pad\'{e} approximant up to order ($2,2$) and weak
evidence for the Taylor series up to 3-rd order against
$\Lambda\text{CDM}+\Omega_K$ model. The constraint results show that a closed
universe is preferred by the present observations under all the approximants
used in this study. And the tension level of the Hubble constant $H_0$ is less
than $2\sigma$ significance between different approximants and the local
distance ladder determination. For each assumed approximant, $H_0$ is
anti-correlated with $\Omega_K$ and the sound horizon at the end of the
radiation drag epoch, which indicates that the $H_0$ tension problem can be
slightly relaxed by introducing $\Omega_K$ or any new physics which can reduce
the sound horizon in the early universe. | An ultra-deep near-infrared spectrum of a compact quiescent galaxy at
z=2.2: Several recent studies have shown that about half of the massive galaxies at
z~2 are in a quiescent phase. Moreover, these galaxies are commonly found to be
ultra-compact with half-light radii of ~1 kpc. We have obtained a ~29 hr
spectrum of a typical quiescent, ultra-dense galaxy at z=2.1865 with the Gemini
Near-Infrared Spectrograph. The spectrum exhibits a strong optical break and
several absorption features, which have not previously been detected in z>2
quiescent galaxies. Comparison of the spectral energy distribution with stellar
population synthesis models implies a low star formation rate (SFR) of 1-3
Msol/yr, an age of 1.3-2.2 Gyr, and a stellar mass of ~2x10^11 Msol. We detect
several faint emission lines, with emission-line ratios of [NII]/Halpha,
[SII]/Halpha and [OII]/[OIII] typical of low-ionization nuclear emission-line
regions. Thus, neither the stellar continuum nor the nebular emission implies
active star formation. The current SFR is <1% of the past average SFR. If this
galaxy is representative of compact quiescent galaxies beyond z=2, it implies
that quenching of star formation is extremely efficient and also indicates that
low luminosity active galactic nuclei (AGNs) could be common in these objects.
Nuclear emission is a potential concern for the size measurement. However, we
show that the AGN contributes <8% to the rest-frame optical emission. A
possible post-starburst population may affect size measurements more strongly;
although a 0.5 Gyr old stellar population can make up <10% of the total stellar
mass, it could account for up to ~40% of the optical light. Nevertheless, this
spectrum shows that this compact galaxy is dominated by an evolved stellar
population. |
Beyond Einstein: Cosmological Tests of Model Independent Modified
Gravity: Model-independent parametrisations of modified gravity have attracted a lot
of attention over the past few years; numerous combinations of experiments and
observables have been suggested to constrain these parameterisations, and
future surveys look very promising. Galaxy Clusters have been mentioned, but
not looked at as extensively in the literature as some other probes. Here we
look at adding Galaxy Clusters into the mix of observables and examine whether
they could improve the constraints on the modified gravity parameters. In
particular, we forecast the constraints from combining the Planck CMB spectrum
and SZ cluster catalogue and a DES-like Weak Lensing survey. We've found that
adding cluster counts improves the constraints obtained from combining CMB and
WL data. | Perturbation level interacting dark energy model and its consequence on
late-time cosmological parameters: In the present paper, we study the capability of interacting dark energy
model with pure momentum transfer in the dark sector to reconcile tensions
between low redshift observations and cosmic microwave background (CMB)
results. This class of interacting model with pure momentum exchange introduces
modifications to the standard model in the level of perturbation. We
investigate the model by comparing to observational data, including integrated
Sachs-Wolfe-galaxy cross-correlation, galaxy power spectrum, $f \sigma_8$, and
CMB data. It is shown that this model can alleviate the observed tension
between local and global measurements of $\sigma_8$. According to our results,
the best fit value of $\sigma_8$ for interacting model is $0.700$, which is
lower than the one for $\Lambda$CDM model and also is consistent with low
redshift observations. Furthermore, we perform a forecast analysis to find the
constraints on parameters of the interacting model from future experiments. |
Inflationary Magnetogenesis in $R^{2}$-Inflation after Planck 2015: We study the primordial magnetic field generated by the simple model $f^2 FF$
in Starobinsky, $R^2$-inflationary, model. The scale invariant PMF is achieved
at relatively high power index of the coupling function, $\left| \alpha \right|
\approx 7.44$. This model does not suffer from the backreaction problem as long
as, the rate of inflationary expansion, $H$, is in the order of or less than
the upper bound reported by Planck ($\le 3.6 \times 10^{-5} M_\rm{Pl}$) in both
de Sitter and power law expansion, which show similar results. We calculate the
lower limit of the reheating parameter, $R_\rm{rad} > 6.888$ in
$R^2$-inflation. Based on the upper limit obtained from CMB, we find that the
upper limits of magnetic field and reheating energy density as,
$\left(\rho_{B_\rm{end}} \right)_\rm{CMB} < 1.184 \times 10^{-20} M_\rm{Pl}^4$
and $\left(\rho_\rm{reh} \right)_\rm{CMB} < 8.480 \times 10^{-22} M_\rm{Pl}^4$.
All of foregoing results are well more than the lower limit derived from WMAP7
for both large and small field inflation. By using the Planck inflationary
constraints, 2015 in the context of ${R^2}$-inflation, the upper limit of
reheating temperature and energy density for all possible values of $w
_\rm{reh}$ are respectively constrained as, $T_\rm{reh} < 4.32 \times 10^{13}
\rm{GeV}$ and $\rho_\rm{reh} < 3.259 \times 10^{-18} M_\rm{Pl}^4$ at $n_\rm{s}
\approx 0.9674$. This value of spectral index is well consistent with Planck,
2015 results. Adopting $T_\rm{reh}$, enables us to constrain the reheating
e-folds number, $N_\rm{reh}$ on the range $1 < N_\rm{reh} < 8.3$, for $- 1/3 <
w_\rm{reh} < 1$. By using the scale invariant PMF generated by $f^2 FF$, we
find that the upper limit of present magnetic field, $B_0 < 8.058 \times
10^{-9} \rm{G}$. | Measuring the distances to quasars at high redshifts with strong lensing: Strongly lensed quasars with time-delay measurements are well known to
provide the "time-delay distances" $D_{\Delta t}=(1+z_L)D_LD_S/D_{LS}$ and the
angular diameter distances to lens galaxies $D_L$. These two kinds of distances
give stringent constraints on cosmological parameters. In this work, we explore
a different use of time-delay observables: Under the assumption of a flat
Universe, strong lensing observations can accurately measure the angular
diameter distances to sources $D_S$. The corresponding redshifts of quasars may
be up to $z_S\sim4$ according to the forecast. The high-redshift distances
would sample the Hubble diagram between SNe Ia and CMB,
cosmological-model-independently providing direct information on the evolution
of the nature of our Universe, for example, the dark energy Equation-of-State
parameter $w(z)$. We apply our method to the existing lensing system SDSS
1206+4332 and get $D_S=2388_{-978}^{+2632}Mpc$ at $z_S=1.789$. We also make a
forecast for the era of LSST. The uncertainty of $D_S$ depends on the redshifts
of lens and source, the uncertainties of $D_{\Delta t}$ and $D_L$, and the
correlation between $D_{\Delta t}$ and $D_L$ as well. Larger correlation would
result in tighter $D_S$ determination. |
Cosmological correlation functions in scalar and vector inflationary
models: This thesis is centered on three main subjects within the theory of inflation
and cosmological perturbations: loop corrections to the power spectrum of
curvature fluctuations generated during inflation; evolution of cosmological
fluctuations in anisotropic pre-inflationary cosmologies; statistical
anisotropy and non-Gaussianity predictions of models of inflation populated
with vector fields. Currently, what makes even more interesting the study of
2-nd and higher order corrections to cosmological correlation functions as well
as the computation of higher-than-two order correlators, is the almost
unprecedented chance to confront theories with new and increasingly accurate
experimental data that will shed more light in the physics of the early
Universe. In the context of loop calculations, we have computed the corrections
arising from scalar-tensor interactions in models of single-field inflation
(both for the standard slow-roll model and for models described by Lagrangians
with non-canonical kinetic terms). In the context of anisotropic cosmologies,
also motivated by the observation of "anomalies" in the Cosmic Microwave
Background (CMB) fluctuations, we have computed the bispectrum and the
trispectrum of the curvature fluctuations in inflationary models with SU(2)
vector fields, analyzing the statistical anisotropy features of the correlators
in these models; finally, we have studied cosmological perturbations for a
Universe with a Bianchi type-I background metric, with an energy density
dominated by a pressureless fluid and in the presence of a cosmological
constant. | CMB-HD: Astro2020 RFI Response: CMB-HD is a proposed ultra-deep (0.5 uk-arcmin), high-resolution (15
arcseconds) millimeter-wave survey over half the sky that would answer many
outstanding questions in both fundamental physics of the Universe and
astrophysics. This survey would be delivered in 7.5 years of observing 20,000
square degrees, using two new 30-meter-class off-axis cross-Dragone telescopes
to be located at Cerro Toco in the Atacama Desert. Each telescope would field
800,000 detectors (200,000 pixels), for a total of 1.6 million detectors. |
Minimal dark energy: key to sterile neutrino and Hubble constant
tensions?: Minimal dark energy models, described by the same number of free parameters
of the standard cosmological model with cold dark matter plus a cosmological
constant to parameterize the dark energy component, constitute very appealing
scenarios which may solve long-standing, pending tensions. On the one hand,
they alleviate significantly the tension between cosmological observations and
the presence of one sterile neutrino motivated by the short-baseline anomalies:
we obtain a $95\%$ CL cosmological bound on the mass of a fully thermalized
fourth sterile neutrino ($N_{\rm eff}=4$) equal to $m_s<0.65\ (1.3)$~eV within
the PEDE (VM) scenarios under consideration. Interestingly, these limits are in
agreement with the observations at short-baseline experiments, and the PEDE
scenario is favored with respect to the $\Lambda$CDM case when the full data
combination is considered. On the other hand, the Hubble tension is
satisfactorily solved in almost all the minimal dark energy schemes explored
here. These phenomenological scenarios may therefore shed light on differences
arising from near and far universe probes, and also on discrepancies between
cosmological and laboratory sterile neutrino searches. | Magnetogenesis and the Cosmic Web: a joint challenge for radio
observations and numerical simulations: The detection of the radio signal from filaments in the cosmic web is crucial
to distinguish possible magnetogenesis scenarios. We review the status of the
different attempts to detect the cosmic web at radio wavelengths. This is put
into the context of the advanced simulations of cosmic magnetism carried out in
the last few years by our {\magcow} project. While first attempts of imaging
the cosmic web with the MWA and LOFAR have been encouraging and could discard
some magnetogenesis models, the complexity behind such observations makes a
definitive answer still uncertain. A combination of total intensity and
polarimetric data at low radio frequencies that the SKA and LOFAR2.0 will
achieve is key to removing the existing uncertainties related to the
contribution of many possible sources of signal along deep lines of sight. This
will make it possible to isolate the contribution from filaments, and expose
its deep physical connection with the origin of extragalactic magnetism. |
Dark-Ages Reionisation & Galaxy Formation Simulation XVI: The Thermal
Memory of Reionisation: Intergalactic medium temperature is a powerful probe of the epoch of
reionisation, as information is retained long after reionisation itself.
However, mean temperatures are highly degenerate with the timing of
reionisation, with the amount heat injected during the epoch, and with the
subsequent cooling rates. We post-process a suite of semi-analytic galaxy
formation models to characterise how different thermal statistics of the
intergalactic medium can be used to constrain reionisation. Temperature is
highly correlated with redshift of reionisation for a period of time after the
gas is heated. However as the gas cools, thermal memory of reionisation is
lost, and a power-law temperature-density relation is formed, $T =
T_0(1+\delta)^{1-\gamma}$ with $\gamma \approx 1.5$. Constraining our model
against observations of electron optical depth and temperature at mean density,
we find that reionisation likely finished at $z_{\rm{reion}} = 6.8 ^{+ 0.5}
_{-0.8}$ with a soft spectral slope of $\alpha = 2.8 ^{+ 1.2} _{-1.0}$. By
restricting spectral slope to the range $[0.5,2.5]$ motivated by population II
synthesis models, reionisation timing is further constrained to $z_{\rm{reion}}
= 6.9 ^{+ 0.4} _{-0.5}$. We find that, in the future, the degeneracies between
reionisation timing and background spectrum can be broken using the scatter in
temperatures and integrated thermal history. | General conditions for scale-invariant perturbations in an expanding
universe: We investigate the general properties of expanding cosmological models which
generate scale-invariant curvature perturbations in the presence of a variable
speed of sound. We show that in an expanding universe, generation of a
super-Hubble, nearly scale-invariant spectrum of perturbations over a range of
wavelengths consistent with observation requires at least one of three
conditions: (1) accelerating expansion, (2) a speed of sound faster than the
speed of light, or (3) super-Planckian energy density. |
On the diversity and complexity of absorption line profiles produced by
outflows in Active Galactic Nuclei: Understanding the origin of AGN absorption line profiles and their diversity
could help to explain the physical structure of the accretion flow, and also to
assess the impact of accretion on the evolution of the AGN host galaxies. Here
we present our first attempt to systematically address the issue of the origin
of the complexities observed in absorption profiles. Using a simple method, we
compute absorption line profiles against a continuum point source for several
simulations of accretion disk winds. We investigate the geometrical,
ionization, and dynamical effects on the absorption line shapes. We find that
significant complexity and diversity of the absorption line profile shapes can
be produced by the non-monotonic distribution of the wind velocity, density,
and ionization state. Non-monotonic distributions of such quantities are
present even in steady-state, smooth disk winds, and naturally lead to the
formation of multiple and detached absorption troughs. These results
demonstrate that the part of a wind where an absorption line is formed is not
representative of the entire wind. Thus, the information contained in the
absorption line is incomplete if not even insufficient to well estimate gross
properties of the wind such as the total mass and energy fluxes. In addition,
the highly dynamical nature of certain portions of disk winds can have
important effects on the estimates of the wind properties. For example, the
mass outflow rates can be off up to two orders of magnitude with respect to
estimates based on a spherically symmetric, homogeneous, constant velocity
wind. | Constraint on the abundance of primordial black holes in dark matter
from Planck data: We use Planck data released in 2015 to constrain the abundance of primordial
black holes (PBHs) in dark matter in two different reionization models (one is
the instantaneous reionization and the other is the asymmetric reionization),
and significantly improve the upper limits on the abundance of PBHs from WMAP
3-year data by around two orders of magnitude. Furthermore, these new limits
imply that the event rates of mergers of PBH binaries (Gpc$^{-3}$ yr$^{-1}$)
are less than $0.002$ for $M_\text{pbh}=30M_\odot$, $5$ for
$M_\text{pbh}=10M_\odot$ and $2000$ for $M_\text{pbh}=2M_\odot$ at $95\%$
confidence level (C.L.), and thus GW150914 seems very unlikely produced by the
merger of a PBH binary. |
Can the Distance-Redshift Relation Be Determined from Correlations
Between Luminosities?: We explore whether an independent determination of the distance-redshift
relation, and hence cosmological model parameters, can be obtained from the
apparent correlations between two different waveband luminosities or fluxes, as
has been claimed in recent works using the X-ray and ultraviolet luminosities
and fluxes of quasars. We show that such an independent determination is
possible only if the correlation between luminosities is obtained independent
of the cosmological model, and measured fluxes and redshifts; for example,
being based on sound theoretical models or unrelated observations. In
particular, we show that if the correlation is determined empirically from two
luminosities obtained from fluxes and redshifts, then the method suffers from
circularity. In case, as claimed in recent works, the observed correlation
between fluxes in very narrow redshift bins are used as proxy for the
luminosity correlation, then we show that one is dealing with a pure tautology
with no information on distances and cosmological model. We argue that the
problem arises because of the incomplete treatment of the correlation and we
use numerical methods with a joint X-ray and ultraviolet quasar data set to
demonstrate this shortcoming. | CMB Spectral Distortion Constraints on Thermal Inflation: Thermal inflation is a second epoch of exponential expansion at typical
energy scales $V^{1/4} \sim 10^{6 \sim 8} \mathrm{GeV}$. If the usual
primordial inflation is followed by thermal inflation, the primordial power
spectrum is only modestly redshifted on large scales, but strongly suppressed
on scales smaller than the horizon size at the beginning of thermal inflation,
$k > k_{\rm b} = a_{\rm b} H_{\rm b}$. We calculate the spectral distortion of
the cosmic microwave background generated by the dissipation of acoustic waves
in this context. For $k_{\rm b} \ll 10^3 \mathrm{Mpc}^{-1}$, thermal inflation
results in a large suppression of the $\mu$-distortion amplitude, predicting
that it falls well below the standard value of $\mu \simeq 2\times 10^{-8}$.
Thus, future spectral distortion experiments, similar to PIXIE, can place new
limits on the thermal inflation scenario, constraining $k_{\rm b} \gtrsim 10^3
\mathrm{Mpc}^{-1}$ if $\mu \simeq 2\times 10^{-8}$ were found. |
Magnification of Photometric LRGs by Foreground LRGs and Clusters in
SDSS: The magnification effect of gravitational lensing is a powerful probe of the
distribution of matter in the universe, yet it is frequently overlooked due to
the fact that its signal to noise is smaller than that of lensing shear.
Because its systematic errors are quite different from those of shear,
magnification is nevertheless an important approach with which to study the
distribution of large scale structure. We present lensing mass profiles of
spectroscopic luminous red galaxies (LRGs) and galaxy clusters determined
through measurements of the weak lensing magnification of photometric LRGs in
their background. We measure the change in detected galaxy counts as well as
the increased average galaxy flux behind the lenses. In addition, we examine
the average change in source color due to extinction by dust in the lenses. By
simultaneously fitting these three probes we constrain the mass profiles and
dust-to-mass ratios of the lenses in six bins of lens richness. For each
richness bin we fit an NFW halo mass, brightest cluster galaxy (BCG) mass,
second halo term, and dust-to-mass ratio. The resulting mass-richness relation
is consistent with previous analyses of the catalogs, and limits on the
dust-to-mass ratio in the lenses are in agreement with expectations. We explore
the effects of including the (low signal-to-noise) flux magnification and
reddening measurements in the analysis compared to using only the counts
magnification data; the additional probes significantly improve the agreement
between our measured mass-richness relation and previous results. | A study of relative velocity statistics in Lagrangian perturbation
theory with PINOCCHIO: Subject of this paper is a detailed analysis of the PINOCCHIO algorithm for
studying the relative velocity statistics of merging haloes in Lagrangian
perturbation theory. Given a cosmological background model, a power spectrum of
fluctuations as well as a Gaussian linear density contrast field $\delta_{\rm
l}$ is generated on a cubic grid, which is then smoothed repeatedly with
Gaussian filters. For each Lagrangian particle at position $\bmath{q}$ and each
smoothing radius $R$, the collapse time, the velocities and ellipsoidal
truncation are computed using Lagrangian Perturbation Theory. The collapsed
medium is then fragmented into isolated objects by an algorithm designed to
mimic the accretion and merger events of hierarchical collapse. Directly after
the fragmentation process the mass function, merger histories of haloes and the
statistics of the relative velocities at merging are evaluated. We
reimplemented the algorithm in C++, recovered the mass function and optimised
the construction of halo merging histories. Comparing our results with the
output of the Millennium simulation suggests that PINOCCHIO is well suited for
studying relative velocities of merging haloes and is able to reproduce the
pairwise velocity distribution. |
The Characteristic Shape of Damping Wings During Reionization: Spectroscopic analysis of Ly$\alpha$ damping wings of bright sources at $z>6$
is a promising way to measure the reionization history of the universe.
However, the theoretical interpretation of the damping wings is challenging due
to the inhomogeneous nature of the reionization process and the proximity
effect of bright sources. In this Letter, we analyze the damping wings arising
from the neutral patches in the radiative transfer cosmological simulation
suite Cosmic Reionization on Computers (CROC). We find that the damping wing
profile remains a tight function of volume-weighted neutral fraction $\left<
x_{\rm HI} \right>_{\rm v}$, especially when $\left< x_{\rm HI} \right>_{\rm
v}>0.5$, despite the patchy nature of reionization and the proximity effect.
This small scatter indicates that with a well-measured damping wing profile, we
could constrain the volume-weighted neutral fraction as precise as $\Delta
\left< x_{\rm HI} \right>_{\rm v} \lesssim 0.1$ in the first half of
reionization. | Joint resonant CMB power spectrum and bispectrum estimation: We develop the tools necessary to assess the statistical significance of
resonant features in the CMB correlation functions, combining power spectrum
and bispectrum measurements. This significance is typically addressed by
running a large number of simulations to derive the probability density
function (PDF) of the feature-amplitude in the Gaussian case. Although these
simulations are tractable for the power spectrum, for the bispectrum they
require significant computational resources. We show that, by assuming that the
PDF is given by a multi-variate Gaussian where the covariance is determined by
the Fisher matrix of the sine and cosine terms, we can efficiently produce
spectra that are statistically close to those derived from full simulations. By
drawing a large number of spectra from this PDF, both for the power spectrum
and the bispectrum, we can quickly determine the statistical significance of
candidate signatures in the CMB, considering both single frequency and
multi-frequency estimators. We show that for resonance models, cosmology and
foreground parameters have little influence on the estimated amplitude, which
allows to simplify the analysis considerably. A more precise likelihood
treatment can then be applied to candidate signatures only. We also discuss a
modal expansion approach for the power spectrum, aimed at quickly scanning
through large families of oscillating models. |
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