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Cosmological Bardeen-Cooper-Schrieffer condensate as dark energy: We argue that the occurrence of late-time acceleration can conveniently be
described by first-order general relativity covariantly coupled to fermions.
Dark energy arises as a Bardeen-Cooper-Schrieffer condensate of fermions which
forms in the early universe. At late times, the gap and chemical potential
evolve to have an equation of state with effective negative pressure, thus
naturally leading to acceleration. | Stellar Mass and Velocity Functions of Galaxies: Backward evolution and
the fate of Milky Way siblings: We attempt in this paper to check the consistency of the observed Stellar
Mass Function (SMF), SFR functions and the cosmic star formation rate density
with simple backward evolutionary models. Starting from observed SMF for
star-forming galaxies, we use backwards models to predict the evolution of a
number of quantities, such as the SFR function, the cosmic SFR density and the
Velocity Function. The velocity being a parameter attached to a galaxy during
its history (contrary to the stellar mass), this approach allows us to quantify
the number density evolution of galaxies of a given velocity, e.g. of the Milky
Way siblings. Observations suggest that the SMF of star forming galaxies is
constant between redshift 0 and 1. In order to reproduce this result, we must
quench star formation in a number of star forming galaxies. The SMF of these
quenched galaxies is consistent with available data concerning the increase in
the population of quiescent galaxies in the same redshift interval. The SMF of
quiescent galaxies is then mainly determined by the distribution of active
galaxies that must stop star formation, with a modest mass redistribution
during mergers. The cosmic SFR density, and the evolution of the SFR functions
are relatively well recovered, although they provide some clue for a small
evolution of the SMF of star forming galaxies at the lowest redshifts. We thus
consider that we have obtained in a simple way a relatively consistent picture
of the evolution of galaxies at intermediate redshifts. We note that if this
picture is correct, 50 percent of the Milky-Way sisters (galaxies with the same
velocity as our Galaxy, i.e. 220 km/s) have quenched their star formation since
redshift 1 (and an even larger fraction for larger velocities). We discuss the
processes that might be responsible for this transformation. |
Axion astronomy with microwave cavity experiments: Terrestrial searches for the conversion of dark matter axions or axion-like
particles into photons inside magnetic fields are sensitive to the phase space
structure of the local Milky Way halo. We simulate signals in a hypothetical
future experiment based on the Axion Dark Matter eXperiment (ADMX) that could
be performed once the axion has been detected and a frequency range containing
the axion mass has been identified. We develop a statistical analysis to
extract astrophysical parameters, such as the halo velocity dispersion and
laboratory velocity, from such data and find that with only a few days
integration time a level of precision can be reached matching that of
astronomical observations. For longer experiments lasting up to a year in
duration we find that exploiting the modulation of the power spectrum in time
allows accurate measurements of the Solar peculiar velocity with an accuracy
that would improve upon astronomical observations. We also simulate signals
based on results from N-body simulations and find that finer substructure in
the form of tidal streams would show up prominently in future data, even if
only a subdominant contribution to the local dark matter distribution. In these
cases it would be possible to reconstruct all the properties of a dark matter
stream using the time and frequency dependence of the signal. Finally we
consider the detection prospects for a network of streams from tidally
disrupted axion miniclusters. These features appear much more prominently in
the resolved spectrum than suggested by calculations based on a scan over a
range of resonant frequencies, making the detection of axion minicluster
streams more viable than previously thought. These results confirm that
haloscope experiments in a post-discovery era are able to perform "axion
astronomy". | Two fundamental constants of gravity unifying the dark matter and the
dark energy: The common nature of the dark sector - dark energy and dark matter - as shown
in [1] follows readily from the consideration of generalized Newtonian
potential as a weak-field General Relativity. That generalized potential
satisfying the Newton's theorem on the equivalence of sphere's gravity and that
of a point-mass located in its center, contains an additional constant which
along with the gravitational constant is able to explain quantitatively both
the dark energy (cosmological constant) and dark matter. So, gravity is defined
not by one but two fundamental constants. We show that, the second constant is
dimensional-independent and matter-uncoupled and hence is even more universal
than the gravitational constant, thus affecting the strategy of observational
studies of dark energy and of the search of dark matter. |
Spatial distribution of stellar populations in the Magellanic Clouds:
Implementation to Gaia: The main goal of our project is to investigate the spatial distribution of
different stellar populations in the Magellanic Clouds. The results from
modelling the Magellanic Clouds can be useful, among others, for simulations
during the Gaia mission preparation. Isodensity contour maps have been used in
order to trace the morphology of the different stellar populations and estimate
the size of these structures. Moreover, star density maps are constructed
through star counts and projected radial density profiles are obtained. Fitting
exponential disk and King law curves to the spatial distribution allows us to
derive the structural parameters that describe these profiles. The
morphological structure and spatial distributions of various stellar components
in the Magellanic Clouds (young and intermediate age stars, carbon stars) along
with the overall spatial distribution in both Clouds are provided. | FERO (Finding Extreme Relativistic Objects): relativistic Iron K alpha
lines in type 1 AGN: The observational evidence for AGN relativistic Iron lines is very much
debated. To address this topic, the FERO project makes use of the largest
sample of X-ray spectra of radio quiet Type 1 AGN available in the XMM-Newton
archive. We perform a systematic fit of the individual sources using a full
relativistic code. Results on the first part of the project are presented here. |
Cosmological constraints and comparison of viable $f(R)$ models: In this paper we present cosmological constraints on several well-known
$f(R)$ models, but also on a new class of models that are variants of the
Hu-Sawicki one of the form $f(R)=R-\frac{2\Lambda}{1+b\;y(R,\Lambda)}$, that
interpolate between the cosmological constant model and a matter dominated
universe for different values of the parameter $b$, which is usually expected
to be small for viable models and which in practice measures the deviation from
General Relativity. We use the latest growth rate, Cosmic Microwave Background,
Baryon Acoustic Oscillations, Supernovae type Ia and Hubble parameter data to
place stringent constraints on the models and to compare them to the
cosmological constant model but also other viable $f(R)$ models such as the
Starobinsky or the degenerate hypergeometric models. We find that these kinds
of Hu-Sawicki variant parameterizations are in general compatible with the
currently available data and can provide useful toy models to explore the
available functional space of $f(R)$ models, something very useful with the
current and upcoming surveys that will test deviations from General Relativity. | Research Update on Extreme-Mass-Ratio Inspirals: The inspirals of stellar-mass mass compact objects into massive black holes
in the centres of galaxies are one of the most important sources of
gravitational radiation for space-based detectors like LISA or eLISA. These
extreme-mass-ratio inspirals (EMRIs) will enable an ambitious research program
with implications for astrophysics, cosmology, and fundamental physics. This
article is a summary of the talks delivered at the plenary session on EMRIs at
the 10th International LISA Symposium. It contains research updates on the
following topics: astrophysics of EMRIs; EMRI science potential; and EMRI
modeling. |
Constraining the cosmological parameters using gravitational wave
observations of massive black hole binaries and statistical redshift
information: Space-borne gravitational wave detectors like TianQin are expected to detect
GW signals emitted by the mergers of massive black hole binaries. Luminosity
distance information can be obtained from GW observations, and one can perform
cosmological inference if redshift information can also be extracted, which
would be straightforward if an electromagnetic counterpart exists. In this
paper, we concentrate on the conservative scenario where the EM counterparts
are not available, and comprehensively study if cosmological parameters can be
inferred through a statistical approach, utilizing the non-uniform distribution
of galaxies as well as the black hole mass-host galaxy bulge luminosity
relationship. By adopting different massive black hole binary merger models,
and assuming different detector configurations, we conclude that the
statistical inference of cosmological parameters is indeed possible. TianQin is
expected to constrain the Hubble constant to a relative error of about 4%-7%,
depending on the underlying model. The multidetector network of TianQin and
LISA can significantly improve the precision of cosmological parameters. In the
most favorable model, it is possible to achieve a level of 1.7% with a network
of TianQin and LISA. We find that without EM counterparts, constraints on all
other parameters need a larger number of events or more precise sky
localization of GW sources, which can be achieved by the multidetector network
or under a favorable model for massive black hole mergers. However, in the
optimistic case, where EM counterparts are available, one can obtain useful
constraints on all cosmological parameters in the Lambda-CDM cosmology,
regardless of the population model. Moreover, we can also constrain the
equation of state of the dark energy without the EM counterparts, and it is
even possible to study the evolution of EoS of the DE when the EM counterparts
are observed. | An empirical measurement of the Halo Mass Function from the combination
of GAMA DR4, SDSS DR12, and REFLEX II data: We construct the halo mass function (HMF) from the GAMA galaxy group
catalogue over the mass range 10^12.7M_sol to 10^15.5M_sol, and find good
agreement with the expectation from LambdaCDM. In comparison to previous
studies, this result extends the mass range over which the HMF has now been
measured over by an order of magnitude. We combine the GAMA DR4 HMF with
similar data from the SDSS DR12 and REFLEX II surveys, and fit a four-parameter
Murray-Robotham-Power (MRP) function, valid at z~0.1, yielding: a density
normalisation of: log10 (phi Mpc^3)=-3.96[+0.55,-0.82], a high mass turn-over
of: log10(M/M_sol)=14.13[+0.43,-0.40], a low mass power law slope of:
alpha=-1.68[+0.21,-0.24] , and a high mass softening parameter of: beta=
0.63[+0.25,-0.11]. If we fold in the constraint on Omega_M from Planck 2018
Cosmology, we are able to reduce these uncertainties further, but this relies
on the assumption that the power-law trend can be extrapolated from
10^12.7M_sol to zero mass. Throughout, we highlight the effort needed to
improve on our HMF measurement: improved halo mass estimates that do not rely
on calibration to simulations; reduced halo mass uncertainties needed to
mitigate the strong Eddington Bias that arises from the steepness of the HMF
low mass slope; and deeper wider area spectroscopic surveys. To our halo mass
limit of 10^12.7 M_sol, we are directly resolving (`seeing') 41+/-5 per cent of
the total mass density, i.e. Omega_[M>12.7]=0.128+/-0.016, opening the door for
the direct construction of 3D dark matter mass maps at Mpc resolution. |
COLA III. Radio Detection of AGN in Compact Moderate Luminosity
Infra-Red Galaxies: We present results from 4.8 GHz VLA and Global-VLBI observations of the
northern half of the moderate FIR luminosity (median L_IR = 10^11.01 L_Sol)
COLA sample of star-forming galaxies. VLBI sources are detected in a high
fraction (20/90) of the galaxies observed. The radio luminosities of these
cores (~10^21 W/Hz) are too large to be explained by radio supernovae or
supernova remnants and we argue that they are instead powered by AGN. These
sub-parsec scale radio cores are preferentially detected toward galaxies whose
VLA maps show bright 100-500 parsec scale nuclear radio components. Since these
latter structures tightly follow the FIR to radio-continuum correlation for
star-formation we conclude that the AGN powered VLBI sources are associated
with compact nuclear starburst environments. The implications for possible
starburst-AGN connections are discussed. The detected VLBI sources have a
relatively narrow range of radio luminosity consistent with models in which
intense compact Eddington-limited starbursts regulate the gas supply onto a
central super-massive black hole. The high incidence of AGN radio cores in
compact starbursts suggests little or no delay between the starburst phase and
the onset of AGN activity. | Polynomial $α$-attractors: Inflationary $\alpha$-attractor models can be naturally implemented in
supergravity with hyperbolic geometry. They have stable predictions for
observables, such as $n_s=1-{2/ N_e} $, assuming that the potential in terms of
the original geometric variables, as well as its derivatives, are not singular
at the boundary of the hyperbolic disk, or half-plane. In these models, the
potential in the canonically normalized inflaton field $\varphi$ has a plateau,
which is approached exponentially fast at large $\varphi$. We call them
exponential $\alpha$-attractors. We present a closely related class of models,
where the potential is not singular, but its derivative is singular at the
boundary. The resulting inflaton potential is also a plateau potential, but it
approaches the plateau polynomially. We call them polynomial
$\alpha$-attractors. Predictions of these two families of attractors completely
cover the sweet spot of the Planck/BICEP/Keck data. The exponential ones are on
the left, the polynomial are on the right. |
Characterizing the satellites of massive galaxies up to z~2: young
populations to build the outskirts of nearby massive galaxies: The accretion of minor satellites is currently proposed as the most likely
mechanism to explain the significant size evolution of the massive galaxies
during the last ~10 Gyr. In this paper we investigate the rest-frame colors and
the average stellar ages of satellites found around massive galaxies (Mstar
10^11Msun) since z~2. We find that the satellites have bluer colors than their
central galaxies. When exploring the stellar ages of the galaxies, we find that
the satellites have similar ages to the massive galaxies that host them at high
redshifts, while at lower redshifts they are, on average, ~1.5 Gyr younger. If
our satellite galaxies create the envelope of nearby massive galaxies, our
results would be compatible with the idea that the outskirts of those galaxies
are slightly younger, metal-poorer and with lower [alpha/Fe] abundance ratios
than their inner regions. | $f(Q)$-gravity and neutrino physics: Within the $f(Q)$-gravity framework we perform a phenomenological study of
the cosmological observables in light of the degeneracy between neutrinos
physics and the modified gravity parameter and we identify specific patterns
which allow to break such degeneracy. We also provide separately constraints on
the total mass of the neutrinos, $\Sigma m_{\nu}$, and on the effective number
of neutrino species, $N_{\rm eff}$, using cosmic microwave background (CMB),
baryon acoustic oscillation (BAO), redshift space distortion (RSD), supernovae
(SNIa), galaxy clustering (GC) and weak gravitational lensing (WL)
measurements. The strongest upper bound on the total mass of the neutrinos is
found for the combination of CMB+BAO+RSD+SNIa and it is $\Sigma m_\nu<0.277$ eV
at 95\% C.L. For the same combination of data we find $N_{\rm
eff}=2.93^{+0.31}_{-0.34}$ at 95\% C.L. We also find that all combinations of
data we consider, prefer a stronger gravitational interaction than
$\Lambda$CDM. Finally, we consider the $\chi^2$ and deviance information
criterion statistics and find the $f(Q)+\Sigma m_\nu$ model to be statistically
supported by data over the standard scenario. On the contrary $f(Q)+N_{\rm
eff}$ is supported by CMB+BAO+RSD+SNIa but a moderate evidence against it is
found with GC and WL data. |
AGN feedback and entropy injection in galaxy cluster cores: The non-gravitational energy feedback is of crucial importance in
modeling/simulating clusters to be used as cosmological probes. AGNs are,
arguably, of primary importance in injecting energy in the cluster cores. We
make the first estimate of non-gravitational energy {\it profiles} in galaxy
cluster cores (and beyond) from observational data. Comparing the observed
entropy profiles within $r_{500}$, from the Representative {\it XMM-Newton}
Cluster Structure Survey (REXCESS), to simulated entropy profiles from both AMR
and SPH non-radiative simulations, we estimate the amount of non-gravitational
energy, $E_{\rm ICM}$, contained in the ICM. Adding the radiative losses we
estimate the total energy feedback, $E_{\rm Feedback}$, into the clusters. The
profiles for the energy deposition, $\Delta E_{\rm ICM}(x)$, in the inner
regions differ for Cool-Core (CC) and Non Cool-Core (NCC) clusters, decreasing
after accounting for the radiative cooling. The total feedback energy scales
with the mean spectroscopic temperature as $E_{\rm Feedback} \propto T_{\rm
sp}^{2.52 \pm0.08}$ and $E_{\rm Feedback} \propto T_{\rm sp}^{2.17 \pm 0.11}$,
when compared with the baseline SPH and AMR profiles respectively. The scatter
in the two cases is 15% and 23%, respectively. The mean non-gravitational
energy per particle within $r_{500}$, is $\epsilon_{\rm ICM} = {2.8} \pm {0.8}$
keV for the SPH theoretical relation and $\epsilon_{\rm ICM} = {1.7} \pm {0.9}$
keV for the AMR theoretical relation. We use the {\it NRAO/VLA Sky Survey}
(NVSS) source catalog to determine the radio luminosity, $L_R$, at 1.4 GHz of
the central source(s) of our sample. For $T_{\rm sp} > 3$ keV, the $E_{\rm
Feedback}$ correlates with $L_R$. We show that AGNs could provide a significant
component of the feedback. (Abridged) | The Komatsu Spergel Wandelt estimator for oscillations in the cosmic
microwave background bispectrum: Oscillating shapes of the primordial bispectrum are present in many
inflationary models. The Planck experiment has recently published measurements
of oscillating shapes, which were however limited to the efficient frequency
range of the used analysis method. Here we study the KSW estimator for
oscillations in the CMB bispectrum, that allows to examine arbitrary
oscillation frequencies for separable oscillating bispectrum shapes. We study
the precision with which amplitude, phase and frequency can be determined with
our estimator. An examination of the 3-point function in real space gives
further insight into the estimator. |
Velocity and mass bias in the distribution of dark matter halos: The non-linear, scale-dependent bias in the mass distribution of galaxies and
the underlying dark matter is a key systematic affecting the extraction of
cosmological parameters from galaxy clustering. Using 95 million halos from the
Millennium-XXL N-body simulation, we find that the mass bias is scale
independent only for $k<0.1 h{\rm Mpc}^{-1}$ today ($z=0$) and for $k<0.2 h{\rm
Mpc}^{-1}$ at $z=0.7$. We test analytic halo bias models against our simulation
measurements and find that the model of Tinker et al. 2005 is accurate to
better then 5% at $z=0$. However, the simulation results are better fit by an
ellipsoidal collapse model at $z=0.7$. We highlight, for the first time,
another potentially serious systematic due to a sampling bias in the halo
velocity divergence power spectra which will affect the comparison between
observations and any redshift space distortion model which assumes dark matter
velocity statistics with no velocity bias. By measuring the velocity divergence
power spectra for different sized halo samples, we find that there is a
significant bias which increases with decreasing number density. This bias is
approximately 20% at $k=0.1h$Mpc$^{-1}$ for a halo sample of number density
$\bar{n} = 10^{-3} (h/$Mpc$)^3$ at both $z=0$ and $z=0.7$ for the velocity
divergence auto power spectrum. Given the importance of redshift space
distortions as a probe of dark energy and the on-going major effort to advance
models for the clustering signal in redshift space, our results show this
velocity bias introduces another systematic, alongside scale-dependent halo
mass bias, which cannot be neglected. | The Present and Future of Searching for Dark Matter with LUX and LZ: The LUX collaboration new results advance the search for dark matter
candidate particles in the 4 GeV/c^2 and higher mass range, with a maximal
spin-independent 90% C.L. limit of 2 x 10^-46 cm^2 at 50 GeV/c^2 for its 332
live-day run, following after 6 x 10^-46 cm^2 cross-section for 33 GeV/c^2 mass
from the re-analysis of its initial 95 live-day WIMP search data from December
2015. LUX has performed multiple advanced in situ neutron and beta/gamma
calibrations of light and charge yields down to 1.1 and 0.7 keV, respectively,
in nuclear recoil energy and 1.3 and 0.2 keV in units of electron recoil
energy, thereby bypassing the past practice of extrapolating yields from ex
situ calibrations or simulation models alone. For this conference proceedings,
consequences of the new calibrations for the limit on the interaction
cross-sections for low-mass WIMPs will be highlighted. Previous claims of a
WIMP signal, from other detectors, are now even more strongly disfavored,
assuming isospin invariance and the standard WIMP halo model. Both
spin-independent and spin-dependent limits will be discussed, including the
recent completion of LUX's 332-live-day blind run. Lastly, we highlight the
conceptual design and future plan for its 10-ton-scale, next-generation
successor LZ, which plans on achieving < 3 x 10^-48 cm^2 sensitivity for a WIMP
of mass 40 GeV/c^2. |
Imprints of Oscillatory Bispectra on Galaxy Clustering: Long-short mode coupling during inflation, encoded in the squeezed bispectrum
of curvature perturbations, induces a dependence of the local, small-scale
power spectrum on long-wavelength perturbations, leading to a scale-dependent
halo bias. While this scale dependence is absent in the large-scale limit for
single-field inflation models that satisfy the consistency relation, certain
models such as resonant non-Gaussianity show a peculiar behavior on
intermediate scales. We reconsider the predictions for the halo bias in this
model by working in Conformal Fermi Coordinates, which isolate the physical
effects of long-wavelength perturbations on short-scale physics. We find that
the bias oscillates with scale with an envelope similar to that of equilateral
non-Gaussianity. Moreover, the bias shows a peculiar modulation with the halo
mass. Unfortunately, we find that upcoming surveys will be unable to detect the
signal because of its very small amplitude. We also discuss non-Gaussianity due
to interactions between the inflaton and massive fields: our results for the
bias agree with those in the literature. | Using neural networks to estimate redshift distributions. An application
to CFHTLenS: We present a novel way of using neural networks (NN) to estimate the redshift
distribution of a galaxy sample. We are able to obtain a probability density
function (PDF) for each galaxy using a classification neural network. The
method is applied to 58714 galaxies in CFHTLenS that have spectroscopic
redshifts from DEEP2, VVDS and VIPERS. Using this data we show that the stacked
PDF's give an excellent representation of the true $N(z)$ using information
from 5, 4 or 3 photometric bands. We show that the fractional error due to
using N(z_(phot)) instead of N(z_(truth)) is <=1 on the lensing power spectrum
P_(kappa) in several tomographic bins. Further we investigate how well this
method performs when few training samples are available and show that in this
regime the neural network slightly overestimates the N(z) at high z. Finally
the case where the training sample is not representative of the full data set
is investigated. An IPython notebook accompanying this paper is made available
here: https://bitbucket.org/christopher_bonnett/nn_notebook |
The Persistence of Large Scale Structures I: Primordial non-Gaussianity: We develop an analysis pipeline for characterizing the topology of large
scale structure and extracting cosmological constraints based on persistent
homology. Persistent homology is a technique from topological data analysis
that quantifies the multiscale topology of a data set, in our context unifying
the contributions of clusters, filament loops, and cosmic voids to cosmological
constraints. We describe how this method captures the imprint of primordial
local non-Gaussianity on the late-time distribution of dark matter halos, using
a set of N-body simulations as a proxy for real data analysis. For our best
single statistic, running the pipeline on several cubic volumes of size
$40~(\rm{Gpc/h})^{3}$, we detect $f_{\rm NL}^{\rm loc}=10$ at $97.5\%$
confidence on $\sim 85\%$ of the volumes. Additionally we test our ability to
resolve degeneracies between the topological signature of $f_{\rm NL}^{\rm
loc}$ and variation of $\sigma_8$ and argue that correctly identifying nonzero
$f_{\rm NL}^{\rm loc}$ in this case is possible via an optimal template method.
Our method relies on information living at $\mathcal{O}(10)$ Mpc/h, a
complementary scale with respect to commonly used methods such as the
scale-dependent bias in the halo/galaxy power spectrum. Therefore, while still
requiring a large volume, our method does not require sampling long-wavelength
modes to constrain primordial non-Gaussianity. Moreover, our statistics are
interpretable: we are able to reproduce previous results in certain limits and
we make new predictions for unexplored observables, such as filament loops
formed by dark matter halos in a simulation box. | Quantifying the Importance of Ram Pressure Stripping in a Galaxy Group
at 100 Mpc: We examine two members of the NGC 4065 group of galaxies: a bent-double
(a.k.a. wide angle tail) radio source and an HI deficient spiral galaxy. Models
of the X-ray emitting intragroup gas and the bent-double radio source, NGC
4061, are used to probe the density of intergalactic gas in this group. HI
observations reveal an asymmetric, truncated distribution of neutral gas in
spiral galaxy, UGC 07049, and the accompanying radio continuum emission reveals
strong star formation. We examine the effectiveness of ram pressure stripping
as a gas removal mechanism and find that it alone cannot account for the HI
deficiency that is observed in UGC 07049 unless this galaxy has passed through
the core of the group with a velocity of ~800 km/s. A combination of tidal and
ram pressure stripping are necessary to produce the HI deficiency and asymmetry
in this galaxy. |
The dark matter assembly of the Local Group in constrained cosmological
simulations of a LambdaCDM universe: We make detailed theoretical predictions for the assembly properties of the
Local Group (LG) in the standard LambdaCDM cosmological model. We use three
cosmological N-body dark matter simulations from the CLUES project, which are
designed to reproduce the main dynamical features of the matter distribution
down to the scale of a few Mpc around the LG. Additionally, we use the results
of an unconstrained simulation with a sixty times larger volume to calibrate
the influence of cosmic variance. We characterize the Mass Aggregation History
(MAH) for each halo by three characteristic times, the formation, assembly and
last major merger times. A major merger is defined by a minimal mass ratio of
10:1. We find that the three LGs share a similar MAH with formation and last
major merger epochs placed on average \approx 10 - 12 Gyr ago. Between 12% and
17% of the halos in the mass range 5 x 10^11 Msol/h < M_h < 5 x 10^12 Msol/h
have a similar MAH. In a set of pairs of halos within the same mass range, a
fraction of 1% to 3% share similar formation properties as both halos in the
simulated LG. An unsolved question posed by our results is the dynamical origin
of the MAH of the LGs. The isolation criteria commonly used to define LG-like
halos in unconstrained simulations do not narrow down the halo population into
a set with quiet MAHs, nor does a further constraint to reside in a low density
environment. The quiet MAH of the LGs provides a favorable environment for the
formation of disk galaxies like the Milky Way and M31. The timing for the
beginning of the last major merger in the Milky Way dark matter halo matches
with the gas rich merger origin for the thick component in the galactic disk.
Our results support the view that the specific large and mid scale environment
around the Local Group play a critical role in shaping its MAH and hence its
baryonic structure at present. | Cosmological Evidence for Modified Gravity (MOG): Deviations from the standard $\Lambda$CDM model motivate an interpretation of
early universe cosmology using the Scalar-Tensor-Vector-Gravity (STVG) theory.
A constraint analysis carried out by Valentino, Melchiorri and Silk, revealed
deviations from the growth of structure predicted by General Relativity, and a
lensing anomaly in the angular CMB power spectrum data. The modified gravity
(MOG) theory resolves the lensing deviation from the standard model and
provides an explanation of the CMB and structure growth data. |
Strategies to Detect Dark-Matter Decays with Line-Intensity Mapping: The nature of dark matter is a longstanding mystery in cosmology, which can
be studied with laboratory or collider experiments, as well as astrophysical
and cosmological observations. In this work, we propose realistic and efficient
strategies to detect radiative products from dark-matter decays with
line-intensity mapping (LIM) experiments. This radiation will behave as a line
interloper for the atomic and molecular spectral lines targeted by LIM surveys.
The most distinctive signatures of the contribution from dark-matter radiative
decays are an extra anisotropy on the LIM power spectrum due to projection
effects, as well as a narrowing and a shift towards higher intensities of the
voxel intensity distribution. We forecast the minimum rate of decays into two
photons that LIM surveys will be sensitive to as function of the dark-matter
mass in the range $\sim 10^{-6}-10$ eV, and discuss how to reinterpret such
results for dark matter that decays into a photon and another particle. We find
that both the power spectrum and the voxel intensity distribution are expected
to be very sensitive to the dark-matter contribution, with the voxel intensity
distribution being more promising for most experiments considered. Interpreting
our results in terms of the axion, we show that LIM surveys will be extremely
competitive to detect its decay products, improving several orders of
magnitudes (depending on the mass) the sensitivity of laboratory and
astrophysical searches, especially in the mass range $\sim 1-10$ eV. | The Cluster-EAGLE project: a comparison of dynamical mass estimators
using simulated clusters: Forthcoming large-scale spectroscopic surveys will soon provide data on
thousands of galaxy clusters. It is important that the systematics of the
various mass estimation techniques are well understood and calibrated. We
compare three different dynamical mass estimators using the C-EAGLE galaxy
clusters, a set of high resolution simulations with resolved galaxies a median
total mass, $M_{200c} = 10^{14.7} \, \mathrm{M_\odot}$. We quantify the bias
and scatter of the Jeans, virial, and caustic mass estimators using all
galaxies with a stellar mass $M_*> 10^9 \, \mathrm{M_\odot}$, both in the ideal
3D case and in the more realistic projected case. On average we find our mass
estimates are unbiased, though relative to the true mass within $r_{200c}$ the
scatter is large with a range of $0.09$ - $0.15$ dex. We see a slight increase
in the scatter when projecting the clusters. Selecting galaxies using the same
criteria, we find no significant difference in the mass bias or scatter when
comparing results from hydrodynamical and dark matter only simulations.
However, selecting galaxies by stellar mass reduces the bias compared to
selecting by total mass. Comparing X-ray derived hydrostatic and dynamical
masses, the former are ${\sim} 30$ per cent lower. We find a slight dependence
between substructure, measured using two different metrics, and mass bias. In
conclusion, we find that dynamical mass estimators, when averaged together, are
unbiased with a scatter of $0.11 \pm 0.02$ dex when including interloper
galaxies and with no prior knowledge of $r_{200c}$. |
Comment on "Late Time Behavior of false Vacuum Decay: Possible
Implications for Cosmology and Metastable Inflating States": Comments on the paper "Late Time Behavior of false Vacuum Decay: Possible
Implications for Cosmology and Metastable Inflating States" [arXiv:0711.1821]
by L. M. Krauss and J. Dent are presented and the possible behavior of the
unstable false vacuum at very late times, where deviations from the exponential
decay law become to be dominant is analyzed. | Cosmological Parameter Estimation and Inference using Deep Summaries: The ability to obtain reliable point estimates of model parameters is of
crucial importance in many fields of physics. This is often a difficult task
given that the observed data can have a very high number of dimensions. In
order to address this problem, we propose a novel approach to construct
parameter estimators with a quantifiable bias using an order expansion of
highly compressed deep summary statistics of the observed data. These summary
statistics are learned automatically using an information maximising loss.
Given an observation, we further show how one can use the constructed
estimators to obtain approximate Bayes computation (ABC) posterior estimates
and their corresponding uncertainties that can be used for parameter inference
using Gaussian process regression even if the likelihood is not tractable. We
validate our method with an application to the problem of cosmological
parameter inference of weak lensing mass maps. We show in that case that the
constructed estimators are unbiased and have an almost optimal variance, while
the posterior distribution obtained with the Gaussian process regression is
close to the true posterior and performs better or equally well than comparable
methods. |
Density fluctuations from warm inflation: Thermal fluctuations provide the main source of large scale density
perturbations in warm inflationary models of the early universe. For the first
time, general results are obtained for the power spectrum in the case when the
friction coefficient in the inflaton equation of motion depends on temperature.
A large increase in the amplitude of perturbations occurs when the friction
coefficient increases with temperature. This has to be taken into account when
constructing models of warm inflation. New results are also given for the
thermal fluctuations in the weak regime of warm inflation when the friction
coefficient is relatively small. | Radio Variability in Seyfert Nuclei: Comparison of 8.4-GHz radio images of a sample of 11 early-type Seyfert
galaxies with previous observations reveals possible variation in the nuclear
radio flux density in 5 of them over a 7-yr period. We find no correlation
between radio variability and nuclear radio luminosity or Seyfert nuclear type,
although the sample is small and dominated by type 2 Seyferts. Instead, a
possible correlation between the presence of nuclear radio variability and the
absence of ~100-pc-scale radio emission is seen. NGC2110 is the only source
with significant extended radio structure and strong nuclear variability (>38%
nuclear decline over seven years). Our results suggest that all Seyferts may
exhibit variation in their nuclear radio flux density at 8.4 GHz, but that
variability is more easily recognised in compact sources in which emission from
the variable nucleus is not diluted by unresolved, constant flux density
radio-jet emission within the central ~50 pc. If flares in radio light curves
correspond to ejection of new relativistic components or emergence of shocks in
the underlying flow, we suggest that radio jets may be intrinsically
non-relativistic during quiescence, but that Seyferts, as black-hole driven
AGN, have the capacity to accelerate relativistic jets during radio flares.
Taken together with the increased detection rate of flat spectrum radio nuclei
in Seyferts imaged at VLBI resolutions and the detection of variable water
megamaser emission, our results support the paradigm of intermittent periods of
quiescence and nuclear outburst across the Seyfert population. (Abridged). |
Spectroscopic Study of the HST/ACS PEARS Emission-Line Galaxies: We present spectroscopy of 76 emission-line galaxies (ELGs) in CDF-S taken
with the LDSS3 spectrograph on Magellan Telescope. These galaxies are selected
to have emission lines with ACS grism data in the Hubble Space Telescope
Probing Evolution and Reionization Spectroscopically (PEARS) grism Survey. The
ACS grism spectra cover the wavelength range 6000-9700 \AA\ and most PEARS
grism redshifts are based on a single emission line + photometric redshifts
from broad-band colors; the Magellan spectra cover a wavelength range from 4000
{\AA} to 9000 {\AA}, and provide a check on redshifts derived from PEARS data.
We find an accuracy of $\sigma_z$ = 0.006 for the ACS grism redshifts with only
one catastrophic outlier. We probe for AGN in our sample via several different
methods. In total we find 7 AGNs and AGN candidates out of 76 galaxies. Two
AGNs are identified from the X-ray full-band luminosity, $L_{X-ray,FB}>10^{43}$
erg$\;$s$^{-1}$, the line widths and the power-law continuum spectra. Two
unobscured faint AGN candidates are identified from the X-ray full-band
luminosity $L_{X-ray,FB}\sim10^{41}$ erg$\;$s$^{-1}$, the hardness ratio and
the column density, and the emission-line and X-ray derived SFRs. Two
candidates are classified based on the line ratio of [NII]\lambda6584/H$\alpha$
versus [OIII]$\lambda$5007/H$\beta$ (BPT diagram), which are between the
empirical and theoretical demarcation curves, i.e, the transition region from
star-forming galaxies to AGNs. One AGN candidate is identified from the
high-ionization emission line HeII{\AA}4686. | Weak Lensing with Sizes, Magnitudes and Shapes: Weak lensing can be observed through a number of effects on the images of
distant galaxies; their shapes are sheared, their sizes and fluxes (magnitudes)
are magnified and their positions on the sky are modified by the lensing field.
Galaxy shapes probe the shear field whilst size, magnitude and number density
probe the convergence field. Both contain cosmological information. In this
paper we are concerned with the magnification of the size and magnitude of
individual galaxies as a probe of cosmic convergence. We develop a Bayesian
approach for inferring the convergence field from a measured size, magnitude
and redshift and demonstrate that the inference on convergence requires
detailed knowledge of the joint distribution of intrinsic sizes and magnitudes.
We build a simple parameterised model for the size-magnitude distribution and
estimate this distribution for CFHTLenS galaxies. In light of the measured
distribution, we show that the typical dispersion on convergence estimation is
~0.8, compared to ~0.38 for shear. We discuss the possibility of physical
systematics for magnification (similar to intrinsic alignments for shear) and
compute the expected gains in the Dark Energy Figure-of-Merit (FoM) from
combining magnification with shear for different scenarios regarding
systematics: when accounting for intrinsic alignments but no systematics on the
magnification signal, including magnification could improve the FoM by upto a
factor of ~2.5, whilst when accounting for physical systematics in both shear
and magnification we anticipate a gain between ~25% and ~65%. In addition to
the statistical gains, the fact that cosmic shear and magnification are subject
to different systematics makes magnification an attractive complement to any
cosmic shear analysis. |
Numerical convergence of pre-initial conditions on dark matter halo
properties: Generating pre-initial conditions (or particle loads) is the very first step
to set up a cosmological N-body simulation. In this work, we revisit the
numerical convergence of pre-initial conditions on dark matter halo properties
using a set of simulations which only differs in initial particle loads, i.e.
grid, glass, and the newly introduced capacity constrained Voronoi tessellation
(CCVT). We find that the median halo properties agree fairly well (i.e. within
a convergence level of a few per cent) among simulations running from different
initial loads. We also notice that for some individual haloes cross-matched
among different simulations, the relative difference of their properties
sometimes can be several tens of per cent. By looking at the evolution history
of these poorly converged haloes, we find that they are usually merging haloes
or haloes have experienced recent merger events, and their merging processes in
different simulations are out-of-sync, making the convergence of halo
properties become poor temporarily. We show that, comparing to the simulation
starting with an anisotropic grid load, the simulation with an isotropic CCVT
load converges slightly better to the simulation with a glass load, which is
also isotropic. Among simulations with different pre-initial conditions, haloes
in higher density environments tend to have their properties converged slightly
better. Our results confirm that CCVT loads behave as well as the widely used
grid and glass loads at small scales, and for the first time we quantify the
convergence of two independent isotropic particle loads (i.e. glass and CCVT)
on halo properties. | Molecular hydrogen in the cosmic recombination epoch: The advent of precise measurements of the cosmic microwave background (CMB)
anisotropies has motivated correspondingly precise calculations of the cosmic
recombination history. Cosmic recombination proceeds far out of equilibrium
because of a "bottleneck" at the $n=2$ level of hydrogen: atoms can only reach
the ground state via slow processes: two-photon decay or Lyman-$\alpha$
resonance escape. However, even a small primordial abundance of molecules could
have a large effect on the interline opacity in the recombination epoch and
lead to an additional route for hydrogen recombination. Therefore, this paper
computes the abundance of the H$_2$ molecule during the cosmic recombination
epoch. Hydrogen molecules in the ground electronic levels X$^1\Sigma^+_g$ can
either form from the excited H$_2$ electronic levels B$^1\Sigma^+_u$ and
C$^1\Pi_u$ or through the charged particles H$_2^+$, HeH$^+$ and H$^-$. We
follow the transitions among all of these species, resolving the rotational and
vibrational sub-levels. Since the energies of the
X$^1\Sigma^+_g$--B$^1\Sigma^+_u$ (Lyman band) and X$^1\Sigma^+_g$-C$^1\Pi_u$
(Werner band) transitions are near the Lyman-$\alpha$ energy, the distortion of
the CMB spectrum caused by escaped H Lyman-line photons accelerates both the
formation and the destruction of H$_2$ due to this channel relative to the
thermal rates. This causes the populations of H$_2$ molecules in
X$^1\Sigma^+_g$ energy levels to deviate from their thermal equilibrium
abundances. We find that the resulting H$_2$ abundance is $10^{-17}$ at
$z=1200$ and $10^{-13}$ at $z=800$, which is too small to have any significant
influence on the recombination history. |
The Host Galaxies of Fast-Ejecta Core-Collapse Supernovae: Spectra of broad-lined Type Ic supernovae (SN Ic-BL), the only kind of SN
observed at the locations of long-duration gamma-ray bursts (LGRBs), exhibit
wide features indicative of high ejecta velocities (~0.1c). We study the host
galaxies of a sample of 245 low-redshift (z<0.2) core-collapse SN, including 17
SN Ic-BL, discovered by galaxy-untargeted searches, and 15 optically luminous
and dust-obscured z<1.2 LGRBs. We show that, in comparison with SDSS galaxies
having similar stellar masses, the hosts of low-redshift SN Ic-BL and z<1.2
LGRBs have high stellar-mass and star-formation-rate densities. Core-collapse
SN having typical ejecta velocities, in contrast, show no preference for such
galaxies. Moreover, we find that the hosts of SN Ic-BL, unlike those of SN
Ib/Ic and SN II, exhibit high gas velocity dispersions for their stellar
masses. The patterns likely reflect variations among star-forming environments,
and suggest that LGRBs can be used as probes of conditions in high-redshift
galaxies. They may be caused by efficient formation of massive binary
progenitors systems in densely star-forming regions, or, less probably, a
higher fraction of stars created with the initial masses required for a SN
Ic-BL or LGRB. Finally, we show that the preference of SN Ic-BL and LGRBs for
galaxies with high stellar-mass and star-formation-rate densities cannot be
attributed to a preference for low metal abundances but must reflect the
influence of a separate environmental factor. | Morphological transformation of NGC 205?: NGC 205 is a dwarf elliptical galaxy which shows many features that are more
typical of disk galaxies, and our recent study of the central stellar
population has added another peculiarity. In the central regions, star
formation has been on-going continuously for a few hundred Myr, until ca. 20
Myr ago, perhaps fed by gas funneled to the center in the course of
morphological transformation. In this contribution we use a deep, wide-field
image obtained at a scale of 2"/px to show that subtle structures can be
detected in and near the body of the dwarf galaxy. The southern tidal tail can
be mapped out to unprecedented distances from the center, and we suggest that
the northern tail is partially hidden behind a very extended dust lane, or
ring, belonging to M31. A spiral pattern emerges across the body of the galaxy,
but it might be explained by another M31 dust filament. |
A new pressure-parametric cosmological model: We put forward a pressure-parametric model to study the tiny deviation from
cosmological constant(CC) behavior of the dark sector accelerating the
expansion of the Universe. Data from cosmic microwave background (CMB)
anisotropies, baryonic acoustic oscillations (BAO), Type Ia supernovae (SN Ia)
observation are applied to constrict the model parameters. The constraint
results show that such model suffers with $H_0$ tension as well. To realize
this model more physically, we reconstruct it with the quintessence and phantom
scalar fields, and find out that although the model predicts a
quintessence-induced acceleration of the Universe at past and present, at some
moment of the future, dark energy's density have a disposition to increase. | Lensing Measurements of the Ellipticity of LRG Dark Matter Halos: Lensing measurements of the shapes of dark matter halos can provide tests of
gravity theories and possible dark matter interactions. We measure the
quadrupole weak lensing signal from the elliptical halos of 70,000 SDSS
Luminous Red Galaxies. We use a new estimator that nulls the spherical halo
lensing signal, isolating the shear due to anisotropy in the dark matter
distribution. One of the two Cartesian components of our estimator is
insensitive to the primary systematic, a spurious alignment of lens and source
ellipticities, allowing us to make robust measurements of halo ellipticity. Our
best-fit value for the ellipticity of the surface mass density is $0.24 \pm
0.06$, which translates to an axis ratio of 0.78. We rule out the hypothesis of
no ellipticity at the $4\sigma$ confidence level, and ellipticity < 0.12 (axis
ratio > 0.89) at the $2\sigma$ level. We discuss how our measurements of halo
ellipticity are revised to higher values using estimates of the misalignment of
mass and light from simulations. Finally, we apply the same techniques to a
smaller sample of redMaPPer galaxy clusters and obtain a $3\sigma$ measurement
of cluster ellipticity. We discuss how the improved signal to noise properties
of our estimator can enable studies of halo shapes for different galaxy
populations with upcoming surveys. |
Measuring Microlensing using Spectra of Multiply Lensed Quasars: We report on a program of spectroscopic observations of
gravitationally-lensed QSOs with multiple images. We seek to establish whether
microlensing is occurring in each QSO image using only single-epoch
observations. We calculate flux ratios for the cores of emission lines in image
pairs to set a baseline for no microlensing. The offset of the continuum flux
ratios relative to this baseline yields the microlensing magnification free
from extinction, as extinction affects the continuum and the lines equally.
When we find chromatic microlensing, we attempt to constrain the size of the
QSO accretion disk. SDSSJ1004+4112 and HE1104-1805 show chromatic microlensing
with amplitudes $0.2< |\Delta m| < 0.6$ and $0.2< |\Delta m| < 0.4$ mag,
respectively. Modeling the accretion disk with a Gaussian source ($I\propto
\exp(-R^2/2r_s^2)$) of size $r_s\propto \lambda^p$ and using magnification maps
to simulate microlensing we find $r_s(\lambda 3363)=7\pm3 light-days
(18.1\pm7.8 \times 10^{15} cm$) and $p=1.1\pm 0.4$ for SDSS1004+4112, and
$r_s(\lambda 3363)=6\pm2 light-days (15.5\pm5.2 \times 10^{15} cm$) and
$p=0.7\pm0.1$ for HE1104-1805. For SDSSJ1029+2623 we find strong chromaticity
of $\sim 0.4$ mag in the continuum flux ratio, which probably arises from
microlensing although not all the available data fit within this explanation.
For Q0957+561 we measure B-A magnitude differences of 0.4 mag, much greater
than the $\sim$0.05 mag amplitude usually inferred from lightcurve variability.
It may substantially modify the current interpretations of microlensing in this
system, likely favoring the hypothesis of smaller sources and/or larger
microdeflectors. For HS0818+1227, our data yield posible evidence of
microlensing. | Evidence for dark energy from the cosmic microwave background alone
using the Atacama Cosmology Telescope lensing measurements: For the first time, measurements of the cosmic microwave background radiation
(CMB) alone favor cosmologies with $w=-1$ dark energy over models without dark
energy at a 3.2-sigma level. We demonstrate this by combining the CMB lensing
deflection power spectrum from the Atacama Cosmology Telescope with temperature
and polarization power spectra from the Wilkinson Microwave Anisotropy Probe.
The lensing data break the geometric degeneracy of different cosmological
models with similar CMB temperature power spectra. Our CMB-only measurement of
the dark energy density $\Omega_\Lambda$ confirms other measurements from
supernovae, galaxy clusters and baryon acoustic oscillations, and demonstrates
the power of CMB lensing as a new cosmological tool. |
The Cherenkov radiation in the galaxy halo of dark matter: The effect of light refraction in a galaxy halo of dark matter, described by
profiles of Navarro-Frenk-White and Burkett, was considered. Powers of the
Cherenkov radiation for the refractive indexes of gravitational fields with
these profiles were calculated. It was shown that correspondent radiation
temperature in the X-rays range have the magnitude about some microKelvins. It
was also marked that its detection may be the criteria on choosing the
preferable dark matter density distribution in a galaxy. | Electroweak bubble wall expansion: gravitational waves and baryogenesis
in Standard Model-like thermal plasma: Computing the properties of the bubble wall of a cosmological first order
phase transition at electroweak scale is of paramount importance for the
correct prediction of the baryon asymmetry of the universe and the spectrum of
gravitational waves. By means of the semi-classical formalism we calculate the
velocity and thickness of the wall using as theoretical framework the scalar
singlet extension of the SM with a parity symmetry and the SM effective field
theory supplemented by a dimension six operator. We use these solutions to
carefully predict the baryon asymmetry and the gravitational wave signals. The
singlet scenario can easily accommodate the observed asymmetry but these
solutions do not lead to observable effects at future gravity wave experiments.
In contrast the effective field theory fails at explaining the baryon abundance
due to the strict constraints from electric dipole moment experiments, however,
the strongest solutions we found fall within the sensitivity of the LISA
experiment. We provide a simple analytical approximation for the wall velocity
which only requires calculation of the strength and temperature of the
transition and works reasonably well in all models tested. We find that
generically the weak transitions where the fluid approximation can be used to
calculate the wall velocity and verify baryogenesis produce signals too weak to
be observed in future gravitational wave experiments. Thus, we infer that GW
signals produced by simple SM extensions visible in future experiments are
likely to only be produced in strong transitions described by detonations with
highly relativistic wall velocities. |
Extragalactic millimeter-wave point source catalog, number counts and
statistics from 771 square degrees of the SPT-SZ Survey: We present a point source catalog from 771 square degrees of the South Pole
Telescope Sunyaev Zel'dovich (SPT-SZ) survey at 95, 150, and 220 GHz. We detect
1545 sources above 4.5 sigma significance in at least one band. Based on their
relative brightness between survey bands, we classify the sources into two
populations, one dominated by synchrotron emission from active galactic nuclei,
and one dominated by thermal emission from dust-enshrouded star-forming
galaxies. We find 1238 synchrotron and 307 dusty sources. We cross-match all
sources against external catalogs and find 189 unidentified synchrotron sources
and 189 unidentified dusty sources. The dusty sources without counterparts are
good candidates for high-redshift, strongly lensed submillimeter galaxies. We
derive number counts for each population from 1 Jy down to roughly 9, 5, and 11
mJy at 95, 150, and 220 GHz. We compare these counts with galaxy population
models and find that none of the models we consider for either population
provide a good fit to the measured counts in all three bands. The disparities
imply that these measurements will be an important input to the next generation
of millimeter-wave extragalactic source population models. | Was reionization complete by z ~ 5-6?: It is generally taken for granted that reionization has completed by z=6, due
to the detection of flux in the Lyman alpha forest at redshifts z<6. However,
since reionization is expected to be highly inhomogeneous, much of the spectra
pass through just the ionized component of the intergalactic medium (IGM) even
for non-negligible values of the volume-weighted mean neutral hydrogen
fraction, x_HI. We study the expected signature of an incomplete reionization
at z ~ 5--6, using very large-scale (2 Gpc) seminumeric simulations. We find
that ruling out an incomplete reionization is difficult at these redshifts
since: (1) quasars reside in biased regions of the ionization field, with fewer
surrounding HI patches than implied by the global mean, x_H; (2) absorption
from the residual neutral hydrogen inside the ionized IGM generally dominates
over the absorption from the remaining HI regions; (3) modeling the Lyman alpha
forest and its redshift evolution even in just the ionized IGM is very
difficult, and nearly impossible to do a priori. We propose using the fraction
of pixels which are dark as a simple, nearly model-independent upper limit on
x_HI. Alternately, the size distribution of regions with no detectable flux
(dark gaps) can be used to place a more model dependent constraint. Either way,
the current sample of quasars is statistically insufficient to constrain x_HI
at z~6 to even the 10 per cent level. At z~5, where there are more available
sightlines and the forest is less dark, constraining x_HI < 0.1 might be
possible given a large dynamic range from very deep spectra and/or the Lyman
beta forest. We conclude with the caution against over-interpreting the
observations. There is currently no direct evidence that reionization was
complete by z ~ 5-6. |
Stacking Redshifted 21cm Images of HII Regions Around High Redshift
Galaxies as a Probe of Early Reionization: A number of current and future experiments aim to detect the reionization of
neutral hydrogen by the first stars and galaxies in the Universe via the
redshifted 21cm line. Using the \textsc{BlueTides} simulation, we investigate
the measurement of an \textit{average} ionised region towards the beginning of
reionization by stacking redshifted 21cm images around optically identified
bright galaxies using mock observations. We find that with an SKA 1000 hour
observation, assuming perfect foreground subtraction, a $5\sigma$ detection of
a stacked HII region can be made with 30 images around some of the brightest
galaxies in \textsc{bluetides} (brighter than $M_{UV} < -22.75$) at $z=9$
(corresponding to a neutral fraction of 90.1 \% in our model). We present
simulated relationships between the UV magnitude of galaxies, the sizes of the
ionised regions they reside in, and the shape of the stacked profiles. These
mock observations can also distinguish between scenarios where the IGM is in
net emission or absorption of 21cm photons. Once 21cm foreground contamination
is included, we find that even with up to 200 images around these rare, bright
galaxies, only a tentative $> 1\sigma$ detection will be possible. However,
partial foreground subtraction substantially improves signal-to-noise. For
example, we predict that reducing the area of Fourier space dominated by
foregrounds by 50 (80) percent will allow $> 3\sigma$ ($> 5\sigma$) detections
of ionised regions at $z=9$. | Anisotropies in the Gravitational-Wave Stochastic Background: We consider anisotropies in the stochastic background of gravitational-waves
(SBGW) arising from random fluctuations in the number of gravitational-wave
sources. We first develop the general formalism which can be applied to
different cosmological or astrophysical scenarios. We then apply this formalism
to calculate the anisotropies of SBGW associated with the fluctuations in the
number of cosmic string loops, considering both cosmic string cusps and kinks.
We calculate the anisotropies as a function of angle and frequency. |
The trouble with Hubble: Local versus global expansion rates in
inhomogeneous cosmological simulations with numerical relativity: In a fully inhomogeneous, anisotropic cosmological simulation performed by
solving Einstein's equations with numerical relativity, we find a local
measurement of the effective Hubble parameter differs by less than 1\% compared
to the global value. This variance is consistent with predictions from
Newtonian gravity. We analyse the averaged local expansion rate on scales
comparable to Type 1a supernova surveys, and find that local variance cannot
resolve the tension between the \citet{riess2018b} and \citet{planck2018a}
measurements. | Dynamical dark energy: scalar fields and running vacuum: Recent analyses in the literature suggest that the concordance $\Lambda$CDM
model with rigid cosmological term, $\Lambda=$const., may not be the best
description of the cosmic acceleration. The class of "running vacuum models",
in which $\Lambda=\Lambda(H)$ evolves with the Hubble rate, has been shown to
fit the string of $SNIa+BAO+H(z)+LSS+CMB$ data significantly better than the
$\Lambda$CDM. Here we provide further evidence on the time-evolving nature of
the dark energy (DE) by fitting the same cosmological data in terms of scalar
fields. As a representative model we use the original Peebles & Ratra
potential, $V\propto\Phi^{-\alpha}$. We find clear signs of dynamical DE at
$\sim 4\sigma$ c.l., thus reconfirming through a nontrivial scalar field
approach the strong hints formerly found with other models and
parametrizations. |
Probing Primordial Black Holes and Dark Matter Clumps in the Solar
System with Gravimeter and GNSS Networks: We show that Global Navigation Satellite Systems (GNSS) and gravimeters on
Earth and in space can potentially offer the most accurate direct measurement
of local density of near-Earth asteroid-mass Primordial Black Holes (PBHs) and
Dark Matter (DM) clumps in the solar system by means of gravitational
influence. Using semi-analytical methods and Monte Carlo simulation, this paper
revisits the analysis of the trajectories of DM clumps in the solar system,
including both captured objects and hyperbolic trajectories. A link is thus
made between the frequency and distance of Earth overflights for a given mass
flux, and a direct measure of dark matter clump density in the solar system. We
then model the signature of a close flyby of a DM object on orbital data from
GNSS satellites and gravity measurements from gravimeters. We thus obtain a
first assessment of the single probe sensitivity. It paves the way for an
exhaustive statistical analysis of 28 years of gravimeters and GNSS data to
obtain observational constraints on the density of the PBHs and DM clumps
within the solar system, for the mass range $[10^8-10^{17}]$ kg. In addition,
our methodology offers a possibility of direct detection in cases where DM
clumps are endowed with an additional long-range clump-matter fifth-force
beyond gravity. | COSMOGRAIL XVII: Time delays for the quadruply imaged quasar PG 1115+080: We present time-delay estimates for the quadruply imaged quasar PG 1115+080.
Our resuls are based on almost daily observations for seven months at the ESO
MPIA 2.2m telescope at La Silla Observatory, reaching a signal-to-noise ratio
of about 1000 per quasar image. In addition, we re-analyse existing light
curves from the literature that we complete with an additional three seasons of
monitoring with the Mercator telescope at La Palma Observatory. When exploring
the possible source of bias we consider the so-called microlensing time delay,
a potential source of systematic error so far never directly accounted for in
previous time-delay publications. In fifteen years of data on PG 1115+080, we
find no strong evidence of microlensing time delay. Therefore not accounting
for this effect, our time-delay estimates on the individual data sets are in
good agreement with each other and with the literature. Combining the data
sets, we obtain the most precise time-delay estimates to date on PG 1115+080,
with Dt(AB) = 8.3+1.5-1.6 days (18.7% precision), Dt(AC) = 9.9+1.1-1.1 days
(11.1%) and Dt(BC) = 18.8+1.6-1.6 days (8.5%). Turning these time delays into
cosmological constraints is done in a companion paper that makes use of
ground-based Adaptive Optics (AO) with the Keck telescope. |
Using head-tail galaxies to constrain the intracluster magnetic field:
an in-depth study of PKS J0334-3900: We present a multi-wavelength study of the radio galaxy PKS J0334-3900 at the
centre of Abell 3135. The spectro-polarimetric radio observations are combined
with spectroscopic optical and X-ray data to illustrate the use of Head-Tail
radio galaxies to reveal properties of the intracluster medium. ATCA
observations at 1.4, 2.5, 4.6 & 8.6 GHz are presented with a detailed analysis
of the morphology and spectral indices giving physical parameters to constrain
the dynamical history of the galaxy. Using these constraints we produce a
simulation of PKS J0334-3900. We find that this Head-Tail morphology can be
induced via a combination of orbital motion due to a binary companion and
relative motion through the ICM. New Chandra images of A3135 are presented from
which we obtain a cluster electron density of n_(e,0) = (1.06 +/- 0.11 x
10^(-3) cm^(-3), a global temperature of 2.4 ^(+0.51)_(-0.38) keV and a lower
limit to the radio jet power of PKS J0334-3900 of 1.6 x 10^(44) erg/s. A new
redshift analysis of the cluster from available spectroscopic data shows A3135
to be comprised of galaxies with 0.058 < z < 0.066 and gives a new mean cluster
redshift of 0.06228 +/- 0.00015. We also uncovered a background subgroup
between 0.066 < z < 0.070. Stokes Q and U data of Abell 3135 were used to
obtain rotation measure values along the line of sight to PKS J0334-3900. Using
our simulation we are able to infer the distance between the jets to be 154 +/-
16 kpc, which when combined with the difference in rotation measure between the
jets provides a novel new way to estimate the average magnetic field within a
cluster. A lower limit to the cluster B-field was calculated to be 0.09 +/-
0.03 micro Gauss. We show observations of Head-Tail galaxies can be used to
infer information on the cluster environment, showing them to be an important
class of objects in next generation all sky surveys. | Degeneracy between warm and coupled cold dark matter: A clarifying note: Wei et al [PRD 88, 043510 (2013)] have proposed the existence of a
cosmological degeneracy between warm dark matter (WDM), modified gravity and
coupled cold dark matter (CDM) cosmologies at both the background expansion and
the growth of density perturbation levels, i.e., corresponding cosmological
data would not be able to differentiate such scenarios. Here, we will focus on
the specific indistinguishability between a warm dark matter plus cosmological
constant ($\Lambda$) and coupled scalar field-CDM scenarios. Although the
statement of Wei et al is true for very specific conditions we present a more
complete discussion on this issue and show in more detail that these models are
indeed distinguishable. We show that the degeneracy breaks down since coupled
models leave a specific signature in the redshift space distortion data which
is absent in the uncoupled warm dark matter cosmologies. Furthermore, we
complement our claim by providing the reasons which suggest that even at
nonlinear level a breaking of such apparent equivalence is also expected. |
Cosmological parameter constraints from CMB lensing with cosmic voids: We investigate the potential of using cosmic voids as a probe to constrain
cosmological parameters through the gravitational lensing effect of the cosmic
microwave background (CMB) and make predictions for the next generation
surveys. By assuming the detection of a series of $\approx 5 - 10$ voids along
a line of sight within a square-degree patch of the sky, we found that they can
be used to break the degeneracy direction of some of the cosmological parameter
constraints (for example $\omega_b$ and $\Omega_\Lambda$) in comparison with
the constraints from random CMB skies with the same size area for a survey with
extensive integration time. This analysis is based on our current knowledge of
the average void profile and analytical estimates of the void number function.
We also provide combined cosmological parameter constraints between a sky patch
where series of voids are detected and a patch without voids (a randomly
selected patch). The full potential of this technique relies on an accurate
determination of the void profile to $\approx 10$% level. For a small-area CMB
observation with extensive integration time and a high signal-to-noise ratio,
CMB lensing with such series of voids will provide a complementary route to
cosmological parameter constraints to the CMB observations. Example of
parameter constraints with a series of five voids on a $1.0^{\circ} \times
1.0^{\circ}$ patch of the sky are $100\omega_b = 2.20 \pm 0.27$, $\omega_c =
0.120 \pm 0.022$, $\Omega_\Lambda = 0.682 \pm 0.078$, $\Delta_{\mathcal{R}}^2 =
\left(2.22 \pm 7.79\right) \times 10^{-9}$, $n_s = 0.962 \pm 0.097$ and $\tau =
0.925 \pm 1.747$ at 68% C.L. | Gravitational lensing formalism in a curved arc basis: A continuous
description of observables and degeneracies from the weak to the strong
lensing regime: Gravitationally lensed curved arcs provide a wealth of information about the
underlying lensing distortions. Extracting precise lensing information from
extended sources is a key component in many studies aiming to answer
fundamental questions about the Universe. To maintain accuracy with increased
precision, it is of vital importance to characterize and understand the impact
of degeneracies inherent in lensing observables. In this work, we present a
formalism to describe the gravitational lensing distortion effects resulting in
curved extended arcs based on the eigenvectors and eigenvalues of the local
lensing Jacobian and their directional differentials. We identify a non-local
and non-linear extended deflector basis that inherits these local properties.
Our parameterization is tightly linked to observable features in extended
sources and allows one to accurately extract the lensing information of
extended images without imposing an explicit global deflector model. We
quantify what degeneracies can be broken based on specific assumptions on the
local lensing nature and assumed intrinsic source shape. Our formalism is
applicable from the weak linear regime, the semi-linear regime all the way up
to the highly non-linear regime of highly magnified arcs of multiple images.
The methodology and implementation presented in this work provides a framework
to assessing systematics, to guide inference efforts in the right choices in
complexity based on the data at hand, and to quantify the lensing information
extracted in a model-independent way. |
Equilibrium Star Formation In A Constant Q Disk: Model Optimisation and
Initial Tests: We develop a model for the distribution of the ISM and star formation in
galaxies based on recent studies that indicate that galactic disks stabilise to
a constant stability parameter, which we combine with prescriptions of how the
phases of the ISM are determined and for the Star Formation Law (SFL). The
model predicts the gas surface mass density and star formation intensity of a
galaxy given its rotation curve, stellar surface mass density and the gas
velocity dispersion. This model is tested on radial profiles of neutral and
molecular ISM surface mass density and star formation intensity of 12 galaxies
selected from the THINGS sample. Our tests focus on intermediate radii.
Nevertheless, the model produces reasonable agreement with ISM mass and star
formation rate integrated over the central region in all but one case. To
optimise the model, we evaluate four recipes for the stability parameter, three
recipes for apportioning the ISM into molecular and neutral components, and
eight versions of the SFL. We find no clear-cut best prescription for the
two-fluid (gas and stars) stability parameter Q_2f and therefore for
simplicity, we use the Wang&Silk(1994) approximation (Q_WS). We found that an
empirical scaling between the molecular to neutral ISM ratio (R_mol) and the
stellar surface mass density proposed by Leroy et al. (2008) works marginally
better than the other two prescriptions for this ratio in predicting the ISM
profiles, and noticeably better in predicting star formation intensity from the
ISM profiles produced by our model with the SFLs we tested. Thus in the context
of our modeled ISM profiles, the linear molecular SFL and the two-component SFL
(Krumholz et al. 2009) work better than the other prescriptions we tested. We
incorporate these relations into our `Constant Q disk' (CQ-disk) model. | Number Counts and Dynamical Vacuum Cosmologies: We study non-linear structure formation in an interacting model of the dark
sector of the Universe in which the dark energy density decays linearly with
the Hubble parameter, $\rho_{\Lambda} \propto H$, leading to a constant-rate
creation of cold dark matter. We derive all relevant expressions to calculate
the mass function and the cluster number density using the Sheth-Torman
formalism and show that the effect of the interaction process is to increase
the number of bound structures of large masses ($M \gtrsim 10^{14}
M_{\odot}h^{-1}$) when compared to the standard $\Lambda$CDM model. Since these
models are not reducible to each other, this number counts signature can in
principle be tested in future surveys. |
Foregrounds for observations of the cosmological 21 cm line: I. First
Westerbork measurements of Galactic emission at 150 MHz in a low latitude
field: We present the first results from a series of observations conducted with the
Westerbork telescope in the 140--160 MHz range with a 2 arcmin resolution aimed
at characterizing the properties of the foregrounds for epoch of reionization
experiments. For the first time we have detected fluctuations in the Galactic
diffuse emission on scales greater than 13 arcmin at 150 MHz, in the low
Galactic latitude area known as Fan region. Those fluctuations have an $rms$ of
14 K. The total intensity power spectrum shows a power--law behaviour down to
$\ell \sim 900$ with slope $\beta^I_\ell = -2.2 \pm 0.3$. The detection of
diffuse emission at smaller angular scales is limited by residual point
sources. We measured an $rms$ confusion noise of $\sim$3 mJy beam$^{-1}$.
Diffuse polarized emission was also detected for the first time at this
frequency. The polarized signal shows complex structure both spatially and
along the line of sight. The polarization power spectrum shows a power--law
behaviour down to $\ell \sim 2700$ with slope $\beta^P_\ell = -1.65 \pm 0.15$.
The $rms$ of polarization fluctuations is 7.2 K on 4 arcmin scales. By
extrapolating the measured spectrum of total intensity emission, we find a
contamination on the cosmological signal of $\delta T= \sqrt{\ell (\ell+1)
C^I_\ell / 2\pi} \sim 5.7$ K on 5 arcmin scales and a corresponding $rms$ value
of $\sim$18.3 K at the same angular scale. The level of the polarization power
spectrum is $\delta T \sim 3.3$ K on 5 arcmin scales. Given its exceptionally
bright polarized signal, the Fan region is likely to represent an upper limit
on the sky brightness at moderate and high Galactic latitude. | Observational constraints on extended Proca-Nuevo gravity and cosmology: We confront massive Proca-Nuevo gravity with cosmological observations. The
former is a non-linear theory involving a massive spin-1 field, that can be
extended incorporating operators of the Generalized Proca class, and when
coupled to gravity it can be covariantized in a way that exhibits consistent
and ghost-free cosmological solutions, without experiencing instabilities and
superluminalities at the perturbative level. When applied at a cosmological
framework it induces extra terms in the Friedmann equations, however due to the
special non-linear construction the field is eliminated in favor of the Hubble
function. Thus, the resulting effective dark energy sector is dynamical, but
with just one model parameter, namely the energy scale that controls the
strength of the vector self-interactions. We use data from Supernovae Ia (SNIa)
and Cosmic Chronometers (CC) observations and we construct the corresponding
likelihood-contours for the free parameters. Interestingly enough, application
of various information criteria, such as AIC, BIC and DIC, shows that the
scenario of massive Proca-Nuevo gravity, although having exactly the same
number of free parameters with {\Lambda}CDM concordance model, is more
efficient in fitting the data. Finally, the reconstructed dark-energy
equation-of-state parameter shows statistical compatibility with the
model-independent, data-driven reconstructed one. |
Probing Cosmic Strings with Gravitational-Wave Fringe: Cosmic strings are important remnants of early-Universe phase transitions. We
show that they can be probed by Gravitational Waves (GWs) from compact binary
mergers. If such chirping GW passes by a cosmic string, it is gravitationally
lensed and left with a characteristic signal of the lensing -- the GW fringe.
It is observable naturally through the frequency chirping of GWs. This allows
to probe cosmic strings with small tension $\Delta = 8\pi G \mu = 10^{-6}
\text{ -- } 10^{-10}$, just below the current constraint, at high-frequency
LIGO-band and mid-band detectors. Although its detection rates are estimated to
be small, even a single detection can be used to identify a cosmic string.
Contrary to the stochastic GW produced from loop decays only in local $U(1)$
models, the GW fringe can directly probe straight strings model independently.
This is also complementary to the existing probes with the strong lensing of
light. | Circumnuclear star-forming regions in early type spiral galaxies:
dynamical masses: We present the measurements of gas and stellar velocity dispersions in 17
circumnuclear star-forming regions (CNSFRs) and the nuclei of three barred
spiral galaxies: NGC2903, NGC3310 and NGC3351 from high dispersion spectra. The
stellar dispersions have been obtained from the CaII triplet (CaT) lines at
8494, 8542, 8662A, while the gas velocity dispersions have been measured by
Gaussian fits to the Hbeta and to the [OIII]5007A\ lines. The CNSFRs, with
sizes of about 100 to 150pc in diameter, are seen to be composed of several
individual star clusters with sizes between 1.5 and 6.2pc on HST images. Using
the stellar velocity dispersions, we have derived dynamical masses for the
entire star-forming complexes and for the individual star clusters. Values of
the stellar velocity dispersions are between 31 and 73 km/s. Dynamical masses
for the whole CNSFRs are between 4.9x10^6 and 1.9x10^8 Mo and between 1.4x10^6
and 1.1x10^7 Mo for the individual star clusters. We have found indications for
the presence of two different kinematical components in the ionized gas of the
regions. The narrow component of the two-component Gaussian fits seem to have a
relatively constant value for all the studied CNSFRs, with estimated values
close to 25 km/s. This narrow component could be identified with ionized gas in
a rotating disc, while the stars and the fraction of the gas (responsible for
the broad component) related to the star-forming regions would be mostly
supported by dynamical pressure. |
Can Early Dark Energy be Probed by the High-Redshift Galaxy Abundance?: The Hubble tension and $\sigma_{8}$ tension are two of the major issues of
the standard $\Lambda$ Cold Dark Matter ($\Lambda$CDM) model. The analysis of
the Cosmic Microwave Background (CMB) data acquired by the Atacama Cosmology
Telescope (ACT) and the large-scale ($\ell\lesssim1300$) Planck Telescope
manifest their preference for the Early Dark Energy (EDE) theory, which was set
to alleviate the Hubble tension by decreasing the sound horizon $r_{s}$, and
gives $H_{0} \approx 72 \ km \ s^{-1} \ Mpc^{-1}$. However, the EDE model is
commonly questioned for exacerbating the $\sigma_8$ tension on top of the
$\Lambda$CDM model, and its lack of preference from the late-time matter power
spectrum observations, e.g., Baryon Oscillation Spectroscopic Survey (BOSS). In
light of the current obscurities, we inspect if the high redshift galaxy
abundance, i.e., Stellar Mass Function/Density (SMF/SMD) and Luminosity
Function (LF), can independently probe the EDE model and ameliorate the
challenges it encounters. Our result shows that the EDE model produces more
observable galaxies than $\Lambda$CDM at $z>8$. The LF and SMD, in particular,
are consistent with the recent unexpectedly high results observed by the James
Webb Space Telescope (JWST), which may posit another observational hint of EDE.
This result also implies an efficient suppression mechanism of the galaxy
formation rate that leads to the conversion between EDE- and $\Lambda$CDM-like
Universe around $z\sim7-10$, and that $\sigma_{8}$ tension could be more of a
tension of galaxy evolution than cosmology, hence diminishing its impact on EDE
or $\Lambda$CDM theory. | Some assembly required: assembly bias in massive dark matter halos: We study halo assembly bias for cluster-sized halos. Previous work has found
little evidence for correlations between large-scale bias and halo mass
assembly history for simulated cluster-sized halos, in contrast to the
significant correlation found between bias and concentration for halos of this
mass. This difference in behavior is surprising, given that both concentration
and assembly history are closely related to the same properties of the
linear-density peaks that collapse to form halos. Using publicly available
simulations, we show that significant assembly bias is indeed found in the most
massive halos with $M\sim 10^{15}M_\odot$, using essentially any definition of
halo age. For lower halo masses $M\sim 10^{14}M_\odot$, no correlation is found
between bias and the commonly used age indicator $a_{0.5}$, the half-mass time.
We show that this is a mere accident, and that significant assembly bias exists
for other definitions of halo age, including those based on the time when the
halo progenitor acquires some fraction $f$ of the ultimate mass at $z=0$. For
halos with $M_{\rm vir}\sim 10^{14}M_\odot$, the sense of assembly bias changes
sign at $f=0.5$. We explore the origin of this behavior, and argue that it
arises because standard definitions of halo mass in halo finders do not
correspond to the collapsed, virialized mass that appears in the spherical
collapse model used to predict large-scale clustering. Because bias depends
strongly on halo mass, these errors in mass definition can masquerade as or
even obscure the assembly bias that is physically present. More physically
motivated halo definitions using splashback should be free of this particular
defect of standard halo finders. |
Host Galaxy Properties and Hubble Residuals of Type Ia Supernovae from
the Nearby Supernova Factory: We examine the relationship between Type Ia Supernova (SN Ia) Hubble
residuals and the properties of their host galaxies using a sample of 115 SNe
Ia from the Nearby Supernova Factory (SNfactory). We use host galaxy stellar
masses and specific star-formation rates fitted from photometry for all hosts,
as well as gas-phase metallicities for a subset of 69 star-forming (non-AGN)
hosts, to show that the SN Ia Hubble residuals correlate with each of these
host properties. With these data we find new evidence for a correlation between
SN Ia intrinsic color and host metallicity. When we combine our data with those
of other published SN Ia surveys, we find the difference between mean SN Ia
brightnesses in low and high mass hosts is 0.077 +- 0.014 mag. When viewed in
narrow (0.2 dex) bins of host stellar mass, the data reveal apparent plateaus
of Hubble residuals at high and low host masses with a rapid transition over a
short mass range (9.8 <= log(M_*/M_Sun) <= 10.4). Although metallicity has been
a favored interpretation for the origin of the Hubble residual trend with host
mass, we illustrate how dust in star-forming galaxies and mean SN Ia progenitor
age both evolve along the galaxy mass sequence, thereby presenting equally
viable explanations for some or all of the observed SN Ia host bias. | On the determination of dark energy: I consider some of the issues we face in trying to understand dark energy.
Huge fluctuations in the unknown dark energy equation of state can be hidden in
distance data, so I argue that model-independent tests which signal if the
cosmological constant is wrong are valuable. These can be constructed to remove
degeneracies with the cosmological parameters. Gravitational effects can play
an important role. Even small inhomogeneity clouds our ability to say something
definite about dark energy. I discuss how the averaging problem confuses our
potential understanding of dark energy by considering the backreaction from
density perturbations to second-order in the concordance model: this effect
leads to at least a 10% increase in the dynamical value of the deceleration
parameter, and could be significantly higher. Large Hubble-scale inhomogeneity
has not been investigated in detail, and could conceivably be the cause of
apparent cosmic acceleration. I discuss void models which defy the Copernican
principle in our Hubble patch, and describe how we can potentially rule out
these models. |
New high-precision strong lensing modeling of Abell 2744. Preparing for
JWST observations: We present a new strong lensing (SL) model of the Hubble Frontier Fields
galaxy cluster Abell 2744, at z=0.3072, by exploiting archival Hubble Space
Telescope (HST) multi-band imaging and Multi Unit Spectroscopic Explorer (MUSE)
follow-up spectroscopy. The lens model considers 90 spectroscopically confirmed
multiple images (from 30 background sources), which represents the largest
secure sample for this cluster field prior to the recently acquired James Webb
Space Telescope observations. The inclusion of the sub-structures within
several extended sources as model constraints allows us to accurately
characterize the inner total mass distribution of the cluster and the position
of the cluster critical lines. We include the lensing contribution of 225
cluster members, 202 of which are spectroscopically confirmed. We also measure
the internal velocity dispersion of 85 cluster galaxies to independently
estimate the role of the subhalo mass component in the lens model. We
investigate the effect of the cluster environment on the total mass
reconstruction of the cluster core with two different mass parameterizations.
We consider the mass contribution from three external clumps, either based on
previous weak-lensing studies, or extended HST imaging of luminous members
around the cluster core. In the latter case, the observed positions of the
multiple images are better reproduced, with a remarkable accuracy of 0.37", a
factor of $\sim2$ smaller than previous lens models. We develop and make
publicly available a Strong Lensing Online Tool (SLOT) to exploit the
predictive power and the full statistical information of this and future
models, through a simple graphical interface. We plan to apply our
high-precision SL model to the first analysis of the GLASS-JWST-ERS program,
specifically to measure the intrinsic physical properties of high-$z$ galaxies
from robust magnification maps. | CMB Mode Coupling with Isotropic Polarization Rotation: We provide a new analysis technique to measure the effect of the isotropic
polarization rotation, induced by e.g. the isotropic cosmic birefringence from
axion-like particles and a miscalibration of CMB polarization angle, via mode
coupling in the cosmic microwave background (CMB). Several secondary effects
such as gravitational lensing and CMB optical-depth anisotropies lead to mode
coupling in observed CMB anisotropies, i.e., non-zero off-diagonal elements in
the observed CMB covariance. To derive the mode coupling, however, we usually
assume no parity violation in the observed CMB anisotropies. We first derive a
new contribution to the CMB mode coupling arising from parity violation in
observed CMB. Since the isotropic polarization rotation leads to parity
violation in the observed CMB anisotropies, we then discuss the use of the new
mode coupling for constraining the isotropic polarization angle. We find that
constraints on the isotropic polarization angle by measuring the new
mode-coupling contribution are comparable to that using the $EB$ cross-power
spectrum in future high-sensitivity polarization experiments such as CMB-S4 and
LiteBIRD. Thus, this technique can be used to cross-check results obtained by
the use of the $EB$ cross-power spectrum. |
Searching for Cross-Correlation Between Stochastic Gravitational Wave
Background and Galaxy Number Counts: Advanced LIGO and Advanced Virgo have recently published the upper limit
measurement of persistent directional stochastic gravitational wave background
(SGWB) based on data from their first and second observing runs (O1 and O2). In
this paper we investigate whether a correlation exists between this maximal
likelihood SGWB map and the electromagnetic tracers of matter structure in the
universe, such as galaxy number counts. The method we develop will improve the
sensitivity of future searches for anisotropy in the SGWB and expand the use of
SGWB anisotropy to probe the formation of structure in the universe. In order
to compute the cross-correlation, we used the spherical harmonic decomposition
of SGWB in multiple frequency bands and converted them into pixel-based sky
maps in HEALPix basis. For the electromagnetic (EM) part, we use the Sloan
Digital Sky Survey (SDSS) galaxy catalog and form HEALPix sky maps of galaxy
number counts at the same angular resolution as the SGWB maps. We compute the
pixel-based coherence between these SGWB and galaxy count maps. After
evaluating our results in different SGWB frequency bands and in different
galaxy redshift bins, we conclude that the coherence between the SGWB and
galaxy number count maps is dominated by the null measurement noise in the SGWB
maps, and therefore not statistically significant. We expect the results of
this analysis to be significantly improved by using the more sensitive upcoming
SGWB measurements based on the third observing run (O3) of Advanced LIGO and
Advanced Virgo. | Numerical resolution effects on simulations of massive black hole seeds: We have performed high-resolution numerical simulations with the
hydrodynamical AMR code Enzo to investigate the formation of massive seed black
holes in a sample of six dark matter haloes above the atomic cooling threshold.
The aim of this study is to illustrate the effects of varying the maximum
refinement level on the final object formed. The virial temperatures of the
simulated haloes range from $\rm{T} \sim 10000\ \rm{K} - 16000\ \rm{K}$ and
they have virial masses in the range $\rm{M} \sim 2 \times 10^7 \rm{M_{\odot}}$
to $\rm{M} \sim 7 \times 10^7 \rm{M_{\odot}}$ at $z \sim 15$. The outcome of
our six fiducial simulations is both generic and robust. A rotationally
supported, marginally gravitationally stable, disk forms with an exponential
profile. The mass and scale length of this disk depends strongly on the maximum
refinement level used. Varying the maximum refinement level by factors between
1 / 64 to 256 times the fiducial level illustrates the care that must be taken
in interpreting the results. The lower resolution simulations show tentative
evidence that the gas may become rotationally supported out to 20 pc while the
highest resolution simulations show only weak evidence of rotational support
due to the shorter dynamical times for which the simulation runs. The higher
resolution simulations do, however, point to fragmentation at small scales of
the order of $\sim 100$ AU. In the highest resolution simulations a central
object of a few times $10^2\ \rm{M_{\odot}}$ forms with multiple strongly
bound, Jeans unstable, clumps of $\sim 10\ \rm{M_{\odot}}$ and radii of 10 - 20
AU suggesting the formation of dense star clusters in these haloes. |
The Mass-Radius Relation for Star-Forming Galaxies at z ~ 1.5-3.0: We present early results from a Hubble Space Telescope (HST) WFC3/IR imaging
survey of star-forming galaxies in the redshift range 1.5 < z < 3.0. When
complete, this survey will consist of 42 orbits of F160W imaging distributed
amongst 10 survey fields on the line of sight to bright background QSOs,
covering 65 arcmin^2 to a depth of 27.9 AB with a PSF FWHM of 0.18". In this
contribution, we use a subset of these fields to explore the evolution of the
galactic stellar mass-radius relation for a magnitude-limited sample of 102
spectroscopically-confirmed star forming galaxies (<SFR> ~ 30 Msun/yr) with
stellar mass M* ~ 10^{10} Msun. Although the light profile of these galaxies
often has an irregular, multi-component morphology, it is typically possible to
describe the brightest component with a Sersic profile of index n ~ 1. The
circularized half-light radius r_e of the brightest component is on average
<r_e> = 1.66 \pm 0.79 kpc (i.e., ~ 50-70% the size of local late-type galaxies
with similar stellar mass), consistent with recent theoretical models that
incorporate strong feedback from star forming regions. The mean half-light
radius increases with stellar mass and, at fixed stellar mass, evolves with
cosmic time as ~ (1+z)^{-1.42}, suggesting that high redshift star forming
galaxies may evolve onto the local stellar mass-radius relation by redshift z ~
1. | A non-linear solution to the $S_8$ tension II: Analysis of DES Year 3
cosmic shear: Weak galaxy lensing surveys have consistently reported low values of the
$S_8$ parameter compared to the $\textit{Planck}\ \Lambda\rm{CDM}$ cosmology.
Amon & Efstathiou (2022) used KiDS-1000 cosmic shear measurements to propose
that this tension can be reconciled if the matter fluctuation spectrum is
suppressed more strongly on non-linear scales than assumed in state-of-the-art
hydrodynamical simulations. In this paper, we investigate cosmic shear data
from the Dark Energy Survey (DES) Year 3. The non-linear suppression of the
matter power spectrum required to resolve the $S_8$ tension between DES and the
$\textit{Planck}\ \Lambda\rm{CDM}$ model is not as strong as inferred using
KiDS data, but is still more extreme than predictions from recent numerical
simulations. An alternative possibility is that non-standard dark matter
contributes to the required suppression. We investigate the redshift and scale
dependence of the suppression of the matter power spectrum. If our proposed
explanation of the $S_8$ tension is correct, the required suppression must
extend into the mildly non-linear regime to wavenumbers $k\sim 0.2 h {\rm
Mpc}^{-1}$. In addition, all measures of $S_8$ using linear scales should agree
with the $\textit{Planck}\ \Lambda\rm{CDM}$ cosmology, an expectation that will
be testable to high precision in the near future. |
StarTrack predictions of the stochastic gravitational-wave background
from compact binary mergers: We model the gravitational-wave background created by double compact objects
from isolated binary evolution across cosmic time using the
\textbf{\textit{StarTrack}} binary population code. We include population I/II
stars as well as metal-free population III stars. Merging and non-merging
double compact object binaries are taken into account.
In order to model the low frequency signal in the band of the space antenna
LISA, we account for the evolution of the redshift and the eccentricity. We
find an energy density of $\Omega_{GW} \sim 1.0 \times 10^{-9}$ at the
reference frequency of 25 Hz for population I/II only, making the background
detectable at 3 $\sigma$ after about 7 years of observation with the current
generation of ground based detectors, such as LIGO, Virgo and Kagra, operating
at design sensitivity. The contribution from population III is one order of
magnitude below the population I/II for the total background, but dominates the
residual background, after detected sources have been removed, in 3G detectors.
It modifies the shape of the spectrum which starts deviating from the usual
power law $\Omega_{GW}(f) \sim f^{2/3}$ after $\sim 10$ Hz. The contribution
from the population of non merging binaries, on the other hand, is negligible,
being orders of magnitude below. Finally, we observe that the eccentricity has
no impact in the frequency band of LISA or ground based detectors. | Primordial black holes from inflaton and spectator field perturbations
in a matter-dominated era: We study production of primordial black holes (PBHs) during an early
matter-dominated phase. As a source of perturbations, we consider either the
inflaton field with a running spectral index or a spectator field that has a
blue spectrum and thus provides a significant contribution to the PBH
production at small scales. First, we identify the region of the parameter
space where a significant fraction of the observed dark matter can be produced,
taking into account all current PBH constraints. Then, we present constraints
on the amplitude and spectral index of the spectator field as a function of the
reheating temperature. We also derive constraints on the running of the
inflaton spectral index, ${\rm d}n/{\rm d}{\rm ln}k \lesssim -0.002$, which are
comparable to those from the Planck satellite for a scenario where the
spectator field is absent. |
WMAP 7 Constraints on Oscillations in the Primordial Power Spectrum: We use the WMAP 7 data to place constraints on oscillations supplementing an
almost scale-invariant primordial power spectrum. Such oscillations are
predicted by a variety of models, some of which amount to assuming there is
some non-trivial choice of the vacuum state at the onset of inflation. In this
paper we will explore data-driven constraints on two distinct models of initial
state modifications. In both models the frequency, phase and amplitude are
degrees of freedom of the theory for which the theoretical bounds are rather
weak: both the amplitude and frequency have allowed values ranging over several
orders of magnitude. This requires many computationally expensive evaluations
of the model CMB spectra and their goodness-of-fit, even in a Markov Chain
Monte Carlo (MCMC), normally the most efficient fitting method for such a
problem. To search more efficiently we first run a densely spaced grid, with
only 3 varying parameters; the frequency, the amplitude and the baryon density.
We obtain the optimal frequency and run an MCMC at the best fit frequency,
randomly varying all other relevant parameters. To reduce the computational
time of each power spectrum computation, we adjust both comoving momentum
integration and spline interpolation (in l) as a function of frequency and
amplitude of the primordial power spectrum. Applying this to the WMAP 7 data
allows us to improve existing constraints on the presence of oscillations. We
confirm earlier findings that certain frequencies can improve the fitting over
a model without oscillations. For those frequencies we compute the posterior
probability, allowing us to put some constraints on the primordial parameter
space of both models. | The radio structure of 3C 316, a galaxy with double-peaked narrow
optical emission lines: The galaxy 3C\,316 is the brightest in the radio band among the
optically-selected candidates exhibiting double-peaked narrow optical emission
lines. Observations with the Very Large Array (VLA), Multi-Element Remotely
Linked Interferometer Network (e-MERLIN), and the European VLBI Network (EVN)
at 5\,GHz have been used to study the radio structure of the source in order to
determine the nature of the nuclear components and to determine the presence of
radio cores. The e-MERLIN image of 3C 316 reveals a collimated coherent
east-west emission structure with a total extent of about 3 kpc. The EVN image
shows seven discrete compact knots on an S-shaped line. However, none of these
knots could be unambiguously identified as an AGN core. The observations
suggest that the majority of the radio structure belongs to a powerful radio
AGN, whose physical size and radio spectrum classify it as a compact
steep-spectrum source. Given the complex radio structure with radio blobs and
knots, the possibility of a kpc-separation dual AGN cannot be excluded if the
secondary is either a naked core or radio quiet. |
Constraints on the Extremely-high Energy Cosmic Neutrino Flux with the
IceCube 2008-2009 Data: We report on a search for extremely-high energy neutrinos with energies
greater than $10^6$ GeV using the data taken with the IceCube detector at the
South Pole. The data was collected between April 2008 and May 2009 with the
half completed IceCube array. The absence of signal candidate events in the
sample of 333.5 days of livetime significantly improves model independent limit
from previous searches and allows to place a limit on the diffuse flux of
cosmic neutrinos with an $E^{-2}$ spectrum in the energy range $2.0 \times
10^{6}$ $-$ $6.3 \times 10^{9}$ GeV to a level of $E^2 \phi \leq 3.6 \times
10^{-8}$ ${\rm GeV cm^{-2} sec^{-1}sr^{-1}}$. | Non-parametric study of the evolution of the cosmological equation of
state with SNeIa, BAO and high redshift GRBs: We study the dark energy equation of state as a function of redshift in a
non-parametric way, without imposing any {\it a priori} $w(z)$ (ratio of
pressure over energy density) functional form. As a check of the method, we
test our scheme through the use of synthetic data sets produced from different
input cosmological models which have the same relative errors and redshift
distribution as the real data. Using the luminosity-time $L_{X}-T_{a}$
correlation for GRB X-ray afterglows (the Dainotti et al. correlation), we are
able to utilize GRB sample from the {\it Swift} satellite as probes of the
expansion history of the Universe out to $z \approx 10$. Within the assumption
of a flat FLRW universe and combining SNeIa data with BAO constraints, the
resulting maximum likelihood solutions are close to a constant $w=-1$. If one
imposes the restriction of a constant $w$, we obtain $w=-0.99 \pm 0.06$
(consistent with a cosmological constant) with the present day Hubble constant
as $H_{0}=70.0 \pm 0.6$ ${\rm km} \, {\rm s}^{-1} {\rm Mpc}^{-1}$ and density
parameter as $\Omega_{\Lambda 0}=0.723 \pm 0.025$, while non-parametric $w(z)$
solutions give us a probability map which is centred at $H_{0}=70.04 \pm 1$
${\rm km} \, {\rm s}^{-1} {\rm Mpc}^{-1}$ and $\Omega_{\Lambda 0}=0.724 \pm
0.03$. Our chosen GRB data sample with full correlation matrix allows us to
estimate the amount, as well as quality (errors) of data, needed to constrain
$w(z)$ in the redshift range extending an order of magnitude in beyond the
farthest SNeIa measured. |
Recovery of 21 cm intensity maps with sparse component separation: 21 cm intensity mapping has emerged as a promising technique to map the
large-scale structure of the Universe. However, the presence of foregrounds
with amplitudes orders of magnitude larger than the cosmological signal
constitutes a critical challenge. Here, we test the sparsity-based algorithm
Generalised Morphological Component Analysis (GMCA) as a blind component
separation technique for this class of experiments. We test the GMCA
performance against realistic full-sky mock temperature maps that include,
besides astrophysical foregrounds, also a fraction of the polarized part of the
signal leaked into the unpolarized one, a very troublesome foreground to
subtract, usually referred to as polarization leakage. To our knowledge, this
is the first time the removal of such component is performed with no prior
assumption. We assess the success of the cleaning by comparing the true and
recovered power spectra, in the angular and radial directions. In the best
scenario looked at, GMCA is able to recover the input angular (radial) power
spectrum with an average bias of $\sim 5\%$ for $\ell>25$ ($20 - 30 \%$ for
$k_{\parallel} \gtrsim 0.02 \,h^{-1}$Mpc), in the presence of polarization
leakage. Our results are robust also when up to $40\%$ of channels are missing,
mimicking a Radio Frequency Interference (RFI) flagging of the data. Having
quantified the notable effect of polarisation leakage on our results, in
perspective we advocate the use of more realistic simulations when testing 21
cm intensity mapping capabilities. | Machine Learning methods to estimate observational properties of galaxy
clusters in large volume cosmological N-body simulations: In this paper we study the applicability of a set of supervised machine
learning (ML) models specifically trained to infer observed related properties
of the baryonic component (stars and gas) from a set of features of dark matter
only cluster-size halos. The training set is built from THE THREE HUNDRED
project which consists of a series of zoomed hydrodynamical simulations of
cluster-size regions extracted from the 1 Gpc volume MultiDark dark-matter only
simulation (MDPL2). We use as target variables a set of baryonic properties for
the intra cluster gas and stars derived from the hydrodynamical simulations and
correlate them with the properties of the dark matter halos from the MDPL2
N-body simulation. The different ML models are trained from this database and
subsequently used to infer the same baryonic properties for the whole range of
cluster-size halos identified in the MDPL2. We also test the robustness of the
predictions of the models against mass resolution of the dark matter halos and
conclude that their inferred baryonic properties are rather insensitive to
their DM properties which are resolved with almost an order of magnitude
smaller number of particles. We conclude that the ML models presented in this
paper can be used as an accurate and computationally efficient tool for
populating cluster-size halos with observational related baryonic properties in
large volume N-body simulations making them more valuable for comparison with
full sky galaxy cluster surveys at different wavelengths. We make the best ML
trained model publicly available. |
Spectral and polarization study of the double relics in Abell 3376 using
the GMRT and the VLA: Double radio relics in galaxy clusters are rare phenomena that trace shocks
in the outskirts of merging galaxy clusters. We have carried out a spectral and
polarization study of the spectacular double relics in the galaxy cluster A3376
using the Giant Metrewave Radio Telescope at 150 and 325 MHz and the Very Large
Array at 1400 MHz. The polarization study at 1400 MHz reveals a high degree of
polarization (~30%) and aligned magnetic field vectors (not corrected for
Faraday rotation) in the eastern relic. A highly polarized (>60%) filamentary
radio source of size ~300 kpc near the eastern relic and north of the bent-jet
radio galaxy is detected for the first time. The western relic is less
polarized and does not show aligned magnetic field vectors. The distribution of
spectral indices between 325 and 1400 MHz over the radio relics show steepening
from the outer to the inner edges of the relics. The spectral indices of the
eastern and the western relics imply Mach numbers in the range 2.2 to 3.3.
Remarkable features such as the inward filament extending from the eastern
relic, the highly polarized filament, the complex polarization properties of
the western relic and the separation of the BCG from the ICM by a distance >900
kpc are noticed in the cluster. A comparison with simulated cluster mergers is
required to understand the complex properties of the double relics in the
context of the merger in A3376. An upper limit (log(P(1.4GHz) W/Hz < 23.0) on
the strength of a Mpc size radio halo in A3376 is estimated. | Extreme Feedback and the Epoch of Reionization: Clues in the Local
Universe: The source responsible for reionizing the universe at z > 6 remains
uncertain. While an energetically adequate population of star-forming galaxies
may be in place, it is unknown whether a large enough fraction of their
ionizing radiation can escape into the intergalactic medium. Attempts to
measure this escape-fraction in intensely star-forming galaxies at lower
redshifts have largely yielded upper limits. In this paper we present new HST
COS and archival FUSE far-UV spectroscopy of a sample of eleven Lyman Break
Analogs (LBAs), a rare population of local galaxies that strongly resemble the
high-z Lyman Break galaxies. We combine these data with SDSS optical spectra
and Spitzer photometry. We also analyze archival FUSE observations of fifteen
typical UV-bright local starbursts. We find evidence of small covering factors
for optically-thick neutral gas in 3 cases. This is based on two independent
pieces of evidence: a significant residual intensity in the cores of the
strongest interstellar absorption-lines tracing neutral gas and a small ratio
of extinction-corrected H-alpha to UV plus far-IR luminosities. These objects
represent three of the four LBAs that contain a young, very compact (~100pc),
and highly massive (~10^9 Mo) dominant central object (DCO). These three
objects also differ from the other galaxies in showing a significant amount of
blueshifted Ly-alpha emission, which may be related to the low covering factor
of neutral gas. All four LBAs with DCOs in our sample show extremely high
velocity outflows of interstellar gas, with line centroids blueshifted by about
700km/s and maximum outflow velocities reaching at least 1500km/s. We show that
these properties are consistent with an outflow driven by a powerful starburst
that is exceptionally compact. We speculate that such extreme feedback may be
required to enable the escape of ionizing radiation from star forming galaxies. |
Shell-like structures in our cosmic neighbourhood: Signatures of the processes in the early Universe are imprinted in the cosmic
web. Some of them may define shell-like structures characterised by typical
scales. We search for shell-like structures in the distribution of nearby rich
clusters of galaxies drawn from the SDSS DR8. We calculate the distance
distributions between rich clusters of galaxies, and groups and clusters of
various richness, look for the maxima in the distance distributions, and select
candidates of shell-like structures. We analyse the space distribution of
groups and clusters forming shell walls. We find six possible candidates of
shell-like structures, in which galaxy clusters have maxima in the distance
distribution to other galaxy groups and clusters at the distance of about 120
Mpc/h. The rich galaxy cluster A1795, the central cluster of the Bootes
supercluster, has the highest maximum in the distance distribution of other
groups and clusters around them at the distance of about 120 Mpc/h among our
rich cluster sample, and another maximum at the distance of about 240 Mpc/h.
The structures of galaxy systems causing the maxima at 120 Mpc/h form an almost
complete shell of galaxy groups, clusters and superclusters. The richest
systems in the nearby universe, the Sloan Great Wall, the Corona Borealis
supercluster and the Ursa Major supercluster are among them. The probability
that we obtain maxima like this from random distributions is lower than 0.001.
Our results confirm that shell-like structures can be found in the distribution
of nearby galaxies and their systems. The radii of the possible shells are
larger than expected for a BAO shell (approximately 109 Mpc/h versus
approximately 120 Mpc/h), and they are determined by very rich galaxy clusters
and superclusters with high density contrast while BAO shells are barely seen
in the galaxy distribution. We discuss possible consequences of these
differences. | The environmental dependence of the structure of outer galactic discs in
STAGES spiral galaxies: We present an analysis of V-band radial surface brightness profiles for
spiral galaxies from the field and cluster environments using Hubble Space
Telescope/Advanced Camera for Surveys imaging and data from the Space Telescope
A901/2 Galaxy Evolution Survey (STAGES). We use a large sample of ~330 face-on
to intermediately inclined spiral galaxies and assess the effect of the galaxy
environment on the azimuthally averaged radial surface brightness mu profiles
for each galaxy in the outer stellar disc (24 < mu < 26.5 mag per sq arcsec).
For galaxies with a purely exponential outer disc (~50 per cent), we determine
the significance of an environmental dependence on the outer disc scalelength
h_out. For galaxies with a broken exponential in their outer disc, either
down-bending (truncation, ~10 per cent) or up-bending (anti-truncation, ~40 per
cent), we measure the strength T (outer-to-inner scalelength ratio,
log_10(h_out/h_in) of the mu breaks and determine the significance of an
environmental dependence on break strength T. Surprisingly, we find no evidence
to suggest any such environmental dependence on either outer disc scalelength
h_out or break strength T, implying that the galaxy environment is not
affecting the stellar distribution in the outer stellar disc. We also find that
for galaxies with small effective radii (r_e < 3 kpc) there is a lack of outer
disc truncations in both the field and cluster environments. Our results
suggest that the stellar distribution in the outer disc of spiral galaxies is
not significantly affected by the galaxy environment. |
Estimating SI violation in CMB due to non-circular beam and complex scan
in minutes: Mild, unavoidable deviations from circular-symmetry of instrumental beams
along with scan strategy can give rise to measurable Statistical Isotropy (SI)
violation in Cosmic Microwave Background (CMB) experiments. If not accounted
properly, this spurious signal can complicate the extraction of other SI
violation signals (if any) in the data. However, estimation of this effect
through exact numerical simulation is computationally intensive and time
consuming. A generalized analytical formalism not only provides a quick way of
estimating this signal, but also gives a detailed understanding connecting the
leading beam anisotropy components to a measurable BipoSH characterisation of
SI violation. In this paper, we provide an approximate generic analytical
method for estimating the SI violation generated due to a non-circular (NC)
beam and arbitrary scan strategy, in terms of the Bipolar Spherical Harmonic
(BipoSH) spectra. Our analytical method can predict almost all the features
introduced by a NC beam in a complex scan and thus reduces the need for
extensive numerical simulation worth tens of thousands of CPU hours into
minutes long calculations. As an illustrative example, we use WMAP beams and
scanning strategy to demonstrate the easability, usability and efficiency of
our method. We test all our analytical results against that from exact
numerical simulations. | What Does a Submillimeter Galaxy Selection Actually Select? The
Dependence of Submillimeter Flux Density on Star Formation Rate and Dust Mass: We perform 3-D dust radiative transfer (RT) calculations on hydrodynamic
simulations of isolated and merging disk galaxies in order to quantitatively
study the dependence of observed-frame submillimeter (submm) flux density on
galaxy properties. We find that submm flux density and star formation rate
(SFR) are related in dramatically different ways for quiescently star-forming
galaxies and starbursts. Because the stars formed in the merger-induced
starburst do not dominate the bolometric luminosity and the rapid drop in dust
mass and more compact geometry cause a sharp increase in dust temperature
during the burst, starbursts are very inefficient at boosting submm flux
density (e.g., a $\ga16$x boost in SFR yields a $\la 2$x boost in submm flux
density). Moreover, the ratio of submm flux density to SFR differs
significantly between the two modes; thus one cannot assume that the galaxies
with highest submm flux density are necessarily those with the highest
bolometric luminosity or SFR. These results have important consequences for the
bright submillimeter-selected galaxy (SMG) population. Among them are: 1. The
SMG population is heterogeneous. In addition to merger-driven starbursts, there
is a subpopulation of galaxy pairs, where two disks undergoing a major merger
but not yet strongly interacting are blended into one submm source because of
the large ($\ga 15$", or $\sim 130$ kpc at $z = 2$) beam of single-dish submm
telescopes. 2. SMGs must be very massive ($M_{\star} \ga 6 \times 10^{10}
\msun$). 3. The infall phase makes the SMG duty cycle a factor of a few greater
than what is expected for a merger-driven starburst. (Abridged.) |
The dark matter content of the blue compact dwarf NGC 2915: NGC 2915 is a nearby blue compact dwarf with the HI properties of a late-type
spiral. Its large, rotating HI disk (extending out to R ~ 22 B-band scale
lengths) and apparent lack of stars in the outer HI disk make it a useful
candidate for dark matter studies. New HI synthesis observations of NGC 2915
have been obtained using the Australian Telescope Compact Array. These data are
combined with high-quality 3.6 $\mu$m imaging from the Spitzer Infrared Nearby
Galaxies Survey. The central regions of the HI disk are shown to consist of two
distinct HI concentrations with significantly non-Gaussian line profiles. We
fit a tilted ring model to the HI velocity field to derive a rotation curve.
This is used as input for mass models that determine the contributions from the
stellar and gas disks as well as the dark matter halo. The galaxy is
dark-matter-dominated at nearly all radii. At the last measured point of the
rotation curve, the total mass to blue light ratio is ~ 140 times solar, making
NGC 2915 one of the darkest galaxies known. We show that the stellar disk
cannot account for the steeply-rising portion of the observed rotation curve.
The best-fitting dark matter halo is a pseudo-isothermal sphere with a core
density $\rho_0\sim 0.17 \pm 0.03$ \msun pc$^{-3}$ and a core radius $r_c\sim
0.9 \pm 0.1$ kpc. | Cosmic Visions Dark Energy: Small Projects Portfolio: Understanding cosmic acceleration is one of the key science drivers for
astrophysics and high-energy physics in the coming decade (2014 P5 Report).
With the Large Synoptic Survey Telescope (LSST) and the Dark Energy
Spectroscopic Instrument (DESI) and other new facilities beginning operations
soon, we are entering an exciting phase during which we expect an order of
magnitude improvement in constraints on dark energy and the physics of the
accelerating Universe. This is a key moment for a matching Small Projects
portfolio that can (1) greatly enhance the science reach of these flagship
projects, (2) have immediate scientific impact, and (3) lay the groundwork for
the next stages of the Cosmic Frontier Dark Energy program. In this White
Paper, we outline a balanced portfolio that can accomplish these goals through
a combination of observational, experimental, and theory and simulation
efforts. |
Observing the very low-surface brightness dwarfs in a deep field in the
VIRGO cluster: constraints on Dark Matter scenarios: We report the discovery of 11 very faint (r< 23), low surface brightness
({\mu}_r< 27 mag/arcsec^2) dwarf galaxies in one deep field in the Virgo
cluster, obtained by the prime focus cameras (LBC) at the Large Binocular
Telescope (LBT). These extend our previous sample to reach a total number of 27
galaxies in a field of just of 0.17 deg^2 located at a median distance of 390
kpc from the cluster center. Their association with the Virgo cluster is
supported by their separate position in the central surface brightness - total
magnitude plane with respect to the background galaxies of similar total
magnitude. For a significant fraction (26\%) of the sample the association to
the cluster is confirmed by spectroscopic follow-up. We show that the mere
abundance of satellite galaxies corresponding to our observed number in the
target field provides extremely tight constraints on Dark Matter models with
suppressed power spectrum compared to the Cold Dark Matter case, independently
of the galaxy luminosity distribution. In particular, requiring the observed
number of satellite galaxies not to exceed the predicted abundance of Dark
Matter sub-halos yields a limit m_X >3 keV at 1-{\sigma} and m_X > 2.3 keV at
2-{\sigma} confidence level for the mass of thermal Warm Dark Matter particles.
Such a limit is competitive with other limits set by the abundance of
ultra-faint satellite galaxies in the Milky Way, is completely independent of
baryon physics involved in galaxy formation, and has the potentiality for
appreciable improvements with next observations. We extend our analysis to Dark
Matter models based on sterile neutrinos, showing that our observations set
tight constraints on the combination of sterile neutrino mass m_{\nu} and
mixing parameter sin^2(2{\theta}). We discuss the robustness of our results
with respect to systematics. | PINNferring the Hubble Function with Uncertainties: The Hubble function characterizes a given Friedmann-Robertson-Walker
spacetime and can be related to the densities of the cosmological fluids and
their equations of state. We show how physics-informed neural networks (PINNs)
emulate this dynamical system and provide fast predictions of the luminosity
distance for a given choice of densities and equations of state, as needed for
the analysis of supernova data. We use this emulator to perform a
model-independent and parameter-free reconstruction of the Hubble function on
the basis of supernova data. As part of this study, we develop and validate an
uncertainty treatment for PINNs using a heteroscedastic loss and repulsive
ensembles. |
Using correlations between CMB lensing and large-scale structure to
measure primordial non-Gaussianity: We apply a new method to measure primordial non-Gaussianity, using the
cross-correlation between galaxy surveys and the CMB lensing signal to measure
galaxy bias on very large scales, where local-type primordial non-Gaussianity
predicts a $k^2$ divergence. We use the CMB lensing map recently published by
the Planck collaboration, and measure its external correlations with a suite of
six galaxy catalogues spanning a broad redshift range. We then consistently
combine correlation functions to extend the recent analysis by Giannantonio et
al. (2013), where the density-density and the density-CMB temperature
correlations were used. Due to the intrinsic noise of the Planck lensing map,
which affects the largest scales most severely, we find that the constraints on
the galaxy bias are similar to the constraints from density-CMB temperature
correlations. Including lensing constraints only improves the previous
statistical measurement errors marginally, and we obtain $ f_{\mathrm{NL}} = 12
\pm 21 $ (1$\sigma$) from the combined data set. However, the lensing
measurements serve as an excellent test of systematic errors: we now have three
methods to measure the large-scale, scale-dependent bias from a galaxy survey:
auto-correlation, and cross-correlation with both CMB temperature and lensing.
As the publicly available Planck lensing maps have had their largest-scale
modes at multipoles $l<10$ removed, which are the most sensitive to the
scale-dependent bias, we consider mock CMB lensing data covering all
multipoles. We find that, while the effect of $f_{\mathrm{NL}}$ indeed
increases significantly on the largest scales, so do the contributions of both
cosmic variance and the intrinsic lensing noise, so that the improvement is
small. | Maximum entropy distributions of dark matter in $Λ$CDM cosmology: Small-scale challenges to $\Lambda$CDM cosmology require a deeper
understanding of dark matter physics.This paper aims to develop maximum entropy
distributions for dark matter particle velocity (denoted by $X$), speed
(denoted by $Z$), and energy (denoted by $E$) that are especially relevant on
small scales where system approaches full virialization. For systems involving
long-range interactions, a spectrum of halos of different sizes is required to
form to maximize system entropy. While velocity in halos can be Gaussian, the
velocity distribution throughout entire system, involving all halos of
different sizes, is non-Gaussian. With the virial theorem for mechanical
equilibrium, we applied maximum entropy principle to the statistical
equilibrium of entire system, such that maximum entropy distribution of
velocity (the $X$ distribution) could be analytically derived. The halo mass
function was not required in this formulation, but it did indeed result from
the maximum entropy. The predicted $X$ distribution involves a shape parameter
$\alpha$ and a velocity scale, $v_0$. The shape parameter $\alpha$ reflects the
nature of force ($\alpha\rightarrow0$ for long-range force or
$\alpha\rightarrow\infty$ for short-range force). Therefore, the distribution
approaches Laplacian with $\alpha\rightarrow0$ and Gaussian with
$\alpha\rightarrow\infty$. For an intermediate value of $\alpha$, the
distribution naturally exhibits a Gaussian core for $v\ll v_0$ and exponential
wings for $v\gg v_0$, as confirmed by N-body simulations. From this
distribution, the mean particle energy of all dark matter particles with a
given speed, $v$, follows a parabolic scaling for low speeds ($\propto v^2$ for
$v\ll v_0$ in halo core region, i.e., "Newtonian") and a linear scaling for
high speeds ($\propto v$ for $v\gg v_0$ in halo outskirt, i.e., exhibiting
"non-Newtonian" behavior in MOND due to long-range gravity). |
Gravitational waves from the evolution of magnetic field after
electroweak epoch: It was recently demonstrated that the evolution of helical magnetic field in
the primordial plasma at temperatures $T\gtrsim10$ MeV is affected by the
phenomenon of chiral quantum anomaly in the electroweak model, leading to a
possibility of self-sustained existence of magnetic field and chiral asymmetry
in the electronic distribution. This may serve as a mechanism for generating
primordial magnetic field in the early universe. Violent magnetic-field
generation may lead to production of gravitational waves which, regardless of
the fate of magnetic field itself, survive until today. We estimate the
threshold value of the initial chiral asymmetry above which the generated
gravitational waves would affect the big-bang nucleosynthesis and would show up
in the current and future experiments on gravitational-wave detection. | Sparse Bayesian mass-mapping with uncertainties: peak statistics and
feature locations: Weak lensing convergence maps - upon which higher order statistics can be
calculated - can be recovered from observations of the shear field by solving
the lensing inverse problem. For typical surveys this inverse problem is
ill-posed (often seriously) leading to substantial uncertainty on the recovered
convergence maps. In this paper we propose novel methods for quantifying the
Bayesian uncertainty in the location of recovered features and the uncertainty
in the cumulative peak statistic - the peak count as a function of signal to
noise ratio (SNR). We adopt the sparse hierarchical Bayesian mass-mapping
framework developed in previous work, which provides robust reconstructions and
principled statistical interpretation of reconstructed convergence maps without
the need to assume or impose Gaussianity. We demonstrate our uncertainty
quantification techniques on both Bolshoi N-body (cluster scale) and Buzzard
V-1.6 (large scale structure) N-body simulations. For the first time, this
methodology allows one to recover approximate Bayesian upper and lower limits
on the cumulative peak statistic at well defined confidence levels. |
Topology of large scale structure as test of modified gravity: The genus of the iso-density contours is a robust measure of the topology of
large scale structure, and it is relatively insensitive to nonlinear
gravitational evolution, galaxy bias and redshift-space distortion. We show
that the growth of density fluctuations is scale-dependent even in the linear
regime in some modified gravity theories, which opens a new possibility of
testing the theories observationally. We propose to use the genus of the
iso-density contours, an intrinsic measure of the topology of large scale
structure, as a statistic to be used in such tests. In Einstein's general
theory of relativity, density fluctuations are growing at the same rate on all
scales in the linear regime, and the genus per comoving volume is almost
conserved as structures are growing homologously, so we expect that the
genus-smoothing scale relation is basically time-independent. However, in some
modified gravity models where structures grow with different rates on different
scales, the genus-smoothing scale relation should change over time. This can be
used to test the gravity models with large scale structure observations. We
studied the case of the f(R) theory, DGP braneworld theory as well as the
parameterized post-Friedmann (PPF) models. We also forecast how the modified
gravity models can be constrained with optical/IR or redshifted 21cm radio
surveys in the near future. | CARPool: fast, accurate computation of large-scale structure statistics
by pairing costly and cheap cosmological simulations: To exploit the power of next-generation large-scale structure surveys,
ensembles of numerical simulations are necessary to give accurate theoretical
predictions of the statistics of observables. High-fidelity simulations come at
a towering computational cost. Therefore, approximate but fast simulations,
surrogates, are widely used to gain speed at the price of introducing model
error. We propose a general method that exploits the correlation between
simulations and surrogates to compute fast, reduced-variance statistics of
large-scale structure observables without model error at the cost of only a few
simulations. We call this approach Convergence Acceleration by Regression and
Pooling (CARPool). In numerical experiments with intentionally minimal tuning,
we apply CARPool to a handful of GADGET-III $N$-body simulations paired with
surrogates computed using COmoving Lagrangian Acceleration (COLA). We find
$\sim 100$-fold variance reduction even in the non-linear regime, up to
$k_\mathrm{max} \approx 1.2$ $h {\rm Mpc^{-1}}$ for the matter power spectrum.
CARPool realises similar improvements for the matter bispectrum. In the nearly
linear regime CARPool attains far larger sample variance reductions. By
comparing to the 15,000 simulations from the Quijote suite, we verify that the
CARPool estimates are unbiased, as guaranteed by construction, even though the
surrogate misses the simulation truth by up to $60\%$ at high $k$. Furthermore,
even with a fully configuration-space statistic like the non-linear matter
density probability density function, CARPool achieves unbiased variance
reduction factors of up to $\sim 10$, without any further tuning. Conversely,
CARPool can be used to remove model error from ensembles of fast surrogates by
combining them with a few high-accuracy simulations. |
The AKARI NEP-Deep survey: a mid-infrared source catalogue: We present a new catalogue of mid-IR sources using the AKARI NEP-Deep survey.
The InfraRed Camera (IRC) onboard AKARI has a comprehensive mid-IR wavelength
coverage with 9 photometric bands at 2 - 24 micron. We utilized all of these
bands to cover a nearly circular area adjacent to the North Ecliptic Pole
(NEP). We designed the catalogue to include most of sources detected in 7, 9,
11, 15 and 18 micron bands, and found 7284 sources in a 0.67 deg^2 area. From
our simulations, we estimate that the catalogue is ~80 per cent complete to 200
micro Jy at 15 - 18 micron, and ~10 per cent of sources are missed, owing to
source blending. Star-galaxy separation is conducted using only AKARI
photometry, as a result of which 10 per cent of catalogued sources are found to
be stars. The number counts at 11, 15, 18, and 24 micron are presented for both
stars and galaxies. A drastic increase in the source density is found in
between 11 and 15 micron at the flux level of ~300 micro Jy. This is likely due
to the redshifted PAH emission at 8 micron, given our rough estimate of
redshifts from an AKARI colour-colour plot. Along with the mid-IR source
catalogue, we present optical-NIR photometry for sources falling inside a
Subaru/Sprime-cam image covering part of the AKARI NEP-Deep field, which is
deep enough to detect most of AKARI mid-IR sources, and useful to study optical
characteristics of a complete mid-IR source sample. | Measuring the Properties of Dark Energy with Photometrically Classified
Pan-STARRS Supernovae. I. Systematic Uncertainty from Core-Collapse Supernova
Contamination: The Pan-STARRS (PS1) Medium Deep Survey discovered over 5,000 likely
supernovae (SNe) but obtained spectral classifications for just 10% of its SN
candidates. We measured spectroscopic host galaxy redshifts for 3,147 of these
likely SNe and estimate that $\sim$1,000 are Type Ia SNe (SNe Ia) with
light-curve quality sufficient for a cosmological analysis. We use these data
with simulations to determine the impact of core-collapse SN (CC SN)
contamination on measurements of the dark energy equation of state parameter,
$w$. Using the method of Bayesian Estimation Applied to Multiple Species
(BEAMS), distances to SNe Ia and the contaminating CC SN distribution are
simultaneously determined. We test light-curve based SN classification priors
for BEAMS as well as a new classification method that relies upon host galaxy
spectra and the association of SN type with host type. By testing several SN
classification methods and CC SN parameterizations on large SN simulations, we
estimate that CC SN contamination gives a systematic error on $w$
($\sigma_w^{CC}$) of 0.014, 29% of the statistical uncertainty. Our best method
gives $\sigma_w^{CC} = 0.004$, just 8% of the statistical uncertainty, but
could be affected by incomplete knowledge of the CC SN distribution. This
method determines the SALT2 color and shape coefficients, $\alpha$ and $\beta$,
with $\sim$3% bias. However, we find that some variants require $\alpha$ and
$\beta$ to be fixed to known values for BEAMS to yield accurate measurements of
$w$. Finally, the inferred abundance of bright CC SNe in our sample is greater
than expected based on measured CC SN rates and luminosity functions. |
The cosmic web in CosmoGrid void regions: We study the formation and evolution of the cosmic web, using the
high-resolution CosmoGrid \$\Lambda\$CDM simulation. In particular, we
investigate the evolution of the large-scale structure around void halo groups,
and compare this to observations of the VGS-31 galaxy group, which consists of
three interacting galaxies inside a large void. The structure around such
haloes shows a great deal of tenuous structure, with most of such systems being
embedded in intra-void filaments and walls. We use the Nexus+ algorithm to
detect walls and filaments in CosmoGrid, and find them to be present and
detectable at every scale. The void regions embed tenuous walls, which in turn
embed tenuous filaments. We hypothesize that the void galaxy group of VGS-31
formed in such an environment. | Soft band X/K luminosity ratios for gas-poor early-type galaxies: We aim to place upper limits on the combined X-ray emission from the
population of steady nuclear-burning white dwarfs in galaxies. In the framework
of the single-degenerate scenario these systems are believed to be likely
progenitors of Type Ia supernovae. From the Chandra archive, we selected normal
early-type galaxies with the point source detection sensitivity better than
10^37 erg/s to minimize the contribution of unresolved low-mass X-ray binaries.
The galaxies, contaminated by emission from ionized ISM, were identified based
on the analysis of radial surface brightness profiles and energy spectra. The
sample was complemented by the bulge of M31 and the data for the solar
neighborhood. To cover a broad range of ages, we also included NGC3377 and
NGC3585. Our final sample includes eight gas-poor galaxies for which we
determine L_X/L_K ratios in the 0.3-0.7 keV energy band. In computing the L_X
we included both unresolved emission and soft resolved sources with the color
temperature of kT_bb <= 200 eV. We find that the X/K luminosity ratios are in
the range of (1.7-3.2) x 10^27 erg/s/L_K,sun. The data show no obvious trends
with mass, age, or metallicity of the host galaxy, although a weak
anti-correlation with the Galactic NH appears to exist. It is much flatter than
predicted for a blackbody emission spectrum with temperature of ~50-75 eV,
suggesting that sources with such soft spectra contribute significantly less
than a half to the observed X/K ratios. However, the correlation of the X/K
ratios with NH has a significant scatter and in the strict statistical sense
cannot be adequately described by a superposition of a power law and a
blackbody components with reasonable parameters, thus precluding quantitative
constraints on the contribution from soft sources. (abbr.) |
Model Independent Tests of Cosmic Growth vs Expansion: We use Gaussian Processes to map the expansion history of the universe in a
model independent manner from the Union2.1 supernovae data and then apply these
reconstructed results to solve for the growth history. By comparing this to
BOSS and WiggleZ large scale structure data we examine whether growth is
determined wholly by expansion, with the measured gravitational growth index
testing gravity without assuming a model for dark energy. A further model
independent analysis looks for redshift dependent deviations of growth from the
general relativity solution without assuming the growth index form. Both
approaches give results consistent with general relativity. | Impact of nonlinear growth of the large-scale structure on CMB B-mode
delensing: We study the impact of the nonlinear growth of the large-scale structure
(LSS) on the removal of the gravitational lensing effect (delensing) in cosmic
microwave background (CMB) $B$ modes. The importance of the nonlinear growth of
the LSS in the gravitational lensing analysis of CMB has been recently
recognized by several works, while its impact on delensing is not yet explored.
The delensing using mass-tracers such as galaxies and cosmic infrared
background (CIB) could be also affected by the nonlinear growth. We find that
the nonlinear growth of the LSS leads to $\sim 0.3\%$ corrections to $B$-mode
spectrum after delensing with a high-$z$ mass tracer ($z_m\sim 2$) at
$\ell=1000$-$2000$. The off-diagonal correlation coefficients of the lensing
$B$-mode template spectrum become significant for delensing with low-$z$
tracers ($z_m\lesssim 0.5$), but are negligible with high-$z$ tracers (such as
CIB). On the other hand, the power spectrum covariance of the delensed $B$ mode
is not significantly affected by the nonlinear growth of the LSS, and the
delensing efficiency is not significantly changed even if we use low-$z$
tracers. The CMB $B$-mode internal delensing is also not significantly affected
by the nonlinear growth. |
Stellar Clusters in M31 from PHAT: Survey Overview and First Results: The Panchromatic Hubble Andromeda Treasury (PHAT) is an on-going Hubble Space
Telescope (HST) multi-cycle program that will image one-third of the M31 disk
at high resolution, with wavelength coverage from the ultraviolet through the
near-infrared. This dataset will allow for the construction of the most
complete catalog of stellar clusters obtained for a spiral galaxy. Here, we
provide an overview of the PHAT survey, a progress report on the status of
observations and analysis, and preliminary results from the PHAT cluster
program. Although only ~20% of the survey is complete, the superior resolution
of HST has allowed us to identify hundreds of new intermediate and low mass
clusters. As a result, the size of the cluster sample within the Year 1 survey
footprint has grown by a factor of three relative to previous catalogs. | Kinematic classification of non-interacting spiral galaxies: Using neutral hydrogen (HI) rotation curves of 79 galaxies, culled from the
literature, as well as measured from HI data, we present a method for
classifying disk galaxies by their kinematics. In order to investigate
fundamental kinematic properties we concentrate on non-interacting spiral
galaxies. We employ a simple parameterized form for the rotation curve in order
to derive the three parameters: the maximum rotational velocity, the turnover
radius and a measure of the slope of the rotation curve beyond the turnover
radius. Our approach uses the statistical Hierarchical Clustering method to
guide our division of the resultant 3D distribution of galaxies into five
classes. Comparing the kinematic classes in this preliminary classification
scheme to a number of galaxy properties we find that our class containing
galaxies with the largest rotational velocities has a mean morphological type
of Sb/Sbc while the other classes tend to later types. Other trends also
generally agree with those described by previous researchers. In particular we
confirm correlations between increasing maximum rotational velocity and the
following observed properties: increasing brightness in B-band, increasing size
of the optical disk (D_25) and increasing star formation rate (as derived using
radio continuum data). Our analysis also suggests that lower velocities are
associated with a higher ratio of the HI mass over the dynamical mass.
Additionally, three galaxies exhibit a drop in rotational velocity amplitude of
>~ 20% after the turnover radius. However recent investigations suggest that
they have interacted with minor companions which is a common cause for
declining rotation curves. (Figures 12, 14, 16 and 17 are interactive in the
electronic pdf version of this paper.) |
Formation of Massive and Wide First-star Binaries in Radiation
Hydrodynamics Simulations: We study the formation of Pop III stars by performing radiation hydrodynamics
simulations for three different initial clouds extracted from cosmological
hydrodynamics simulations. Starting from the cloud collapse stage, we follow
the growth of protostars by accretion for $\sim 10^5$ yr until the radiative
feedback from the protostars suppresses the accretion and the stellar
properties are nearly fixed. We find that the Pop III stars form in massive and
wide binaries/small-multiple stellar systems, with masses $>30\,M_\odot$ and
separations $>2000$ au. We also find that the properties of the final stellar
system correlate with those of the initial clouds: the total mass increases
with the cloud-scale accretion rate, and the angular momentum of the binary
orbit matches that of the initial cloud. While the total mass of the system in
our simulations is consistent with our previous single-star formation
simulations, individual masses are lower due to mass sharing, suggesting
potential modification in the extent of feedback from Pop III stars in the
subsequent evolution of the Universe. We also identify such systems as
mini-binaries embedded in a wider outer multiple-star system, which could
evolve into progenitors for observed gravitational wave events. | NIKA2: a mm camera for cluster cosmology: Galaxy clusters constitute a major cosmological probe. However, Planck 2015
results have shown a weak tension between CMB-derived and cluster-derived
cosmological parameters. This tension might be due to poor knowledge of the
cluster mass and observable relationship.
As for now, arcmin resolution Sunyaev-Zeldovich (SZ) observations ({\it e.g.}
SPT, ACT and Planck) only allowed detailed studies of the intra cluster medium
for low redshift clusters ($z<0.2$). For high redshift clusters ($z>0.5$) high
resolution and high sensitivity SZ observations are needed. With both a wide
field of view (6.5 arcmin) and a high angular resolution (17.7 and 11.2 arcsec
at 150 and 260 GHz), the NIKA2 camera installed at the IRAM 30-m telescope
(Pico Veleta, Spain) is particularly well adapted for these observations. The
NIKA2 SZ observation program will map a large sample of clusters (50) at
redshifts between 0.5 and 0.9. As a pilot study for NIKA2, several clusters of
galaxies have been observed with the pathfinder, NIKA, at the IRAM 30-m
telescope to cover the various configurations and observation conditions
expected for NIKA2.} |
Non-thermal WIMPs as Dark Radiation: It has been thought that only light species could behave as radiation and
account for the dark radiation observed recently by Planck, WMAP9, South Pole
and ATACAMA telescopes. In this work we will show that GeV scale WIMPs can
plausibly account for the dark radiation as well. Heavy WIMPs might mimic the
effect of a half neutrino species if some of their fraction were produced
non-thermally after the thermal freeze-out. In addition, we will show how BBN,
CMB and Structure Formation bounds might be circumvented. | Unraveling Cosmological Anisotropies within Stochastic Gravitational
Wave Backgrounds: Identifying the anisotropies in a cosmologically sourced stochastic
gravitational wave background (SGWB) would be of significance in shedding light
on the nature of primordial inhomogeneities. For example, if SGWB carries
isocurvature fluctuations, it would provide evidence for a multi-field
inflationary origin of these inhomogeneities. However, this is challenging in
practice due to finite detector sensitivity and also the presence of the
astrophysical foregrounds that can compete with the cosmological signal. In
this work, we explore the prospects for measuring cosmological SGWB
anisotropies in the presence of an astrophysical counterpart and detector
noise. To illustrate the main idea, we perform a Fisher analysis using a
well-motivated cosmological SGWB template corresponding to a first order phase
transition, and an astrophysical SGWB template corresponding to extra-galactic
binary mergers, and compute the uncertainty with which various parameters
characterizing the isotropic and anisotropic components can be extracted. We
also discuss some subtleties and caveats involving shot noise in the
astrophysical foreground. Overall, we show that upcoming experiments, e.g.,
LISA, Taiji, Einstein Telescope, Cosmic Explorer, and BBO, can all be effective
in discovering plausible anisotropic cosmological SGWBs. |
Polytropic spheres modelling dark matter halos of dwarf galaxies: Dwarf galaxies and their dark matter (DM) halos have the velocity curves of a
different character than those in large galaxies. They are modelled by a simple
pseudo iso-thermal model containing only two parameters that do not allow to
obtain insight into physics of the DM halo. We would like to obtain some
insight into the physical conditions in DM halos of dwarf galaxies by using a
simple physically based model of DM halos. In order to treat a diversity of the
dwarf galaxy velocity profiles in a unifying framework, we apply the polytropic
spheres characterised by the polytropic index $n$ and the relativistic
parameter $\sigma$ as a model of dwarf-galaxy DM halos and match the velocity
of circular geodesics of the polytropes to the velocity curves observed in the
dwarf galaxies from the LITTLE THINGS ensemble. We introduce three classes of
the LITTLE THINGS dwarf galaxies in accord with the polytrope models, due to
the different character of the velocity profile. The first class corresponds to
polytropes having $n < 1$ with linearly increasing velocity along with the
whole profile, the second class has $1 < n < 2$ and the velocity profile
becomes flat in the external region, the third class has $n > 2$ and the
velocity profile reaches a maximum and demonstrated a decline in the external
region. The $\sigma$ parameter has to be strongly non-relativistic ($\sigma <
10^{-8}$) for all dwarf galaxy models -- it varies for the models of each
class, but these variations have a negligible influence on the character of the
velocity profile. Our results indicate the possibility that at least two
different kinds of dark matter are behind the composition of DM halos. The
matches of the observational velocity curves are of the same quality as those
obtained by the pseudo-isothermal, core-like models of dwarf galaxy DM halos. | Accelerating BAO Scale Fitting Using Taylor Series: The Universe is currently undergoing accelerated expansion driven by dark
energy. Dark energy's essential nature remains mysterious: one means of
revealing it is by measuring the Universe's size at different redshifts. This
may be done using the Baryon Acoustic Oscillation (BAO) feature, a standard
ruler in the galaxy 2-Point Correlation Function (2PCF). In order to measure
the distance scale, one dilates and contracts a template for the 2PCF in a
fiducial cosmology, using a scaling factor $\alpha$. The standard method for
finding the best-fit $\alpha$ is to compute the likelihood over a grid of
roughly 100 values of it. This approach is slow; in this work, we propose a
significantly faster way. Our method writes the 2PCF as a polynomial in
$\alpha$ by Taylor-expanding it about $\alpha = 1$, exploiting that we know the
fiducial cosmology sufficiently well that $\alpha$ is within a few percent of
unity. The likelihood resulting from this expansion may then be analytically
solved for the best-fit $\alpha$. Our method is 48-85$\times$ faster than a
directly comparable approach in which we numerically minimize $\alpha$, and
$\sim$$12,000 \times$ faster than the standard iterative method. Our work will
be highly enabling for upcoming large-scale structure redshift surveys such as
that by Dark Energy Spectroscopic Instrument (DESI). |
Markarian 6: shocking the environment of an intermediate Seyfert: Markarian 6 is a nearby (D~78 Mpc) Seyfert 1.5, early-type galaxy, with a
double set of radio bubbles. The outer set spans ~7.5 kpc and is expanding into
the halo regions of the host galaxy. We present an analysis of our new Chandra
observation, together with archival XMM-Newton data, to look for evidence of
emission from shocked gas around the external radio bubbles, both from
spatially resolved regions in Chandra and from spectral analysis of the XMM
data. We also look for evidence of a variable absorbing column along our line
of sight to Mrk 6, to explain the evident differences seen in the AGN spectra
from the various, non-contemporaneous, observations.
We find that the variable absorption hypothesis explains the differences
between the Chandra and XMM spectra, with the Chandra spectrum being heavily
absorbed. The intrinsic N_H varies from ~8x10^{21} atoms*cm^{-2} to ~3x10^{23}
atoms*cm^{-2} on short timescales (2-6 years). The past evolution of the source
suggests this is probably caused by a clump of gas close to the central AGN,
passing in front of us at the moment of the observation. Shells of thermal
X-ray emission are detected around the radio bubbles, with a temperature of
~0.9 keV. We estimate a temperature of ~0.2 keV for the external medium using
luminosity constraints from our Chandra image. We analyse these results using
the Rankine-Hugoniot shock jump conditions, and obtain a Mach number of ~3.9,
compatible with a scenario in which the gas in the shells is inducing a strong
shock in the surrounding ISM. This could be the third clear detection of strong
shocks produced by a radio-powerful Seyfert galaxy. These results are
compatible with previous findings on Centaurus A and NGC 3801, supporting a
picture in which these AGN-driven outflows play an important role in the
environment and evolution of the host galaxy. | The Low-Luminosity End of the Radius-Luminosity Relationship for Active
Galactic Nuclei: We present an updated and revised analysis of the relationship between the
Hbeta broad-line region (BLR) radius and the luminosity of the active galactic
nucleus (AGN). Specifically, we have carried out two-dimensional surface
brightness decompositions of the host galaxies of 9 new AGNs imaged with the
Hubble Space Telescope Wide Field Camera 3. The surface brightness
decompositions allow us to create "AGN-free" images of the galaxies, from which
we measure the starlight contribution to the optical luminosity measured
through the ground-based spectroscopic aperture. We also incorporate 20 new
reverberation-mapping measurements of the Hbeta time lag, which is assumed to
yield the average Hbeta BLR radius. The final sample includes 41 AGNs covering
four orders of magnitude in luminosity. The additions and updates incorporated
here primarily affect the low-luminosity end of the R-L relationship. The best
fit to the relationship using a Bayesian analysis finds a slope of alpha =
0.533 (+0.035/-0.033), consistent with previous work and with simple
photoionization arguments. Only two AGNs appear to be outliers from the
relationship, but both of them have monitoring light curves that raise doubt
regarding the accuracy of their reported time lags. The scatter around the
relationship is found to be 0.19(+/-0.02) dex, but would be decreased to 0.13
dex by the removal of these two suspect measurements. A large fraction of the
remaining scatter in the relationship is likely due to the inaccurate distances
to the AGN host galaxies. Our results help support the possibility that the R-L
relationship could potentially be used to turn the BLRs of AGNs into
standardizable candles. This would allow the cosmological expansion of the
Universe to be probed by a separate population of objects, and over a larger
range of redshifts. |
Running Spectral Index and Formation of Primordial Black Hole in Single
Field Inflation Models: A broad range of single field models of inflation are analyzed in light of
all relevant recent cosmological data, checking whether they can lead to the
formation of long-lived Primordial Black Holes (PBHs). To that end we calculate
the spectral index of the power spectrum of primordial perturbations as well as
its first and second derivatives. PBH formation is possible only if the
spectral index increases significantly at small scales, i.e. large wave number
$k$. Since current data indicate that the first derivative $\alpha_S$ of the
spectral index $n_S(k_0)$ is negative at the pivot scale $k_0$, PBH formation
is only possible in the presence of a sizable and positive second derivative
("running of the running") $\beta_S$. Among the three small-field and five
large-field models we analyze, only one small-field model, the "running mass"
model, allows PBH formation, for a narrow range of parameters. We also note
that none of the models we analyze can accord for a large and negative value of
$\alpha_S$, which is weakly preferred by current data. | The $Λ$CDM growth rate of structure revisited: We re-examine the growth index of the concordance $\Lambda$ cosmology in the
light of the latest 6dF and {\em WiggleZ} data. In particular, we investigate
five different models for the growth index $\gamma$, by comparing their
cosmological evolution using observational data of the growth rate of structure
formation at different redshifts. Performing a joint likelihood analysis of the
recent supernovae type Ia data, the Cosmic Microwave Background shift
parameter, Baryonic Acoustic Oscillations and the growth rate data, we
determine the free parameters of the $\gamma(z)$ parametrizations and we
statistically quantify their ability to represent the observations. We find
that the addition of the 6dF and {\em WiggleZ} growth data in the likelihood
analysis improves significantly the statistical results. As an example,
considering a constant growth index we find $\Omega_{m0}=0.273\pm 0.011$ and
$\gamma=0.586^{+0.079}_{-0.074}$. |
Impact of thermal SZ effect on cross-correlations between Planck CMB
lensing and SDSS galaxy density fields: Residual foreground contamination by thermal Sunyaev-Zeldovich (tSZ) effect
from galaxy clusters in cosmic microwave background (CMB) maps propagates into
the reconstructed CMB lensing field, and thus biases the intrinsic
cross-correlation between CMB lensing and large-scale structure (LSS). Through
stacking analysis, we show that residual tSZ contamination causes an increment
of lensing convergence in the central part of the clusters and a decrement of
lensing convergence in the cluster outskirts. We quantify the impact of
residual tSZ contamination on cross-correlations between the Planck 2018 CMB
lensing convergence maps and the SDSS-IV galaxy density data through
cross-power spectrum computation. In contrast with the Planck 2018
tSZ-deprojected SMICA lensing map, our analysis using the tSZ-contaminated
SMICA lensing map measures a $\sim2.5\%$ negative bias at multipoles
$\ell\lesssim 500$ and transits to a $\sim9\%$ positive bias at
$\ell\gtrsim1500$, which validates earlier theoretical predictions of the
overall shape of such tSZ-induced spurious cross-correlation. The tSZ-induced
lensing convergence field in Planck CMB data is detected with more than
$1\sigma$ significance at $\ell\lesssim 500$ and more than $14\sigma$
significance at $\ell\gtrsim1500$, yielding an overall $14.8\sigma$ detection.
We also show that masking galaxy clusters in CMB data is not sufficient to
eliminate the spurious lensing signal, still detecting a non-negligible bias
with $5.5\sigma$ significance on cross-correlations with galaxy density fields.
Our results emphasize how essential it is to deproject the tSZ effect from CMB
maps at the component separation stage and adopt tSZ-free CMB lensing maps for
cross-correlations with LSS data. | On the influence of physical galaxy properties on Lyman-alpha escape in
star-forming galaxies: [abridged] Among the different observational techniques used to select
high-redshift galaxies, the hydrogen recombination line Lyman-alpha (Lya) is of
particular interest as it gives access to the measurement of cosmological
quantities such as the star formation rate of distant galaxy populations.
However, the interpretation of this line and the calibration of such
observables is still subject to serious uncertainties. Therefore, it important
to understand under what conditions the Lya line can be used as a reliable star
formation diagnostic tool. We use a sample of 24 Lya emitters at z ~ 0.3 with
an optical spectroscopic follow-up to calculate the Lya escape fraction and its
dependency upon different physical properties. We also examine the reliability
of Lya as a star formation rate indicator. We combine these observations with a
compilation of Lya emitters selected at z = 0 - 0.3 to assemble a larger
sample. The Lya escape fraction depends clearly on the dust extinction
following the relation fesc(Lya) = C(Lya) x 10^(-0.4 E(B-V) k(Lya)), but with a
shallower slope than previously reported, with k(Lya) ~ 6.67 and C(Lya) = 0.22.
However, the correlation does not follow the expected curve for a simple dust
attenuation. We explore the various mechanisms than lead to fesc(Lya) values
above the continuum extinction curve, i.e. to an enhancement of the Lya output.
We also observe that the strength of Lya and the escape fraction appear
unrelated to the galaxy metallicity. Regarding the reliability of Lya as a star
formation rate (SFR) indicator, we show that the deviation of SFR(Lya) from the
true SFR (as traced by the UV continuum) is a function of the observed SFR(UV),
which can be seen as the decrease of fesc(Lya) with increasing UV luminosity.
Moreover, we observe a redshift-dependence of this relationship revealing the
underlying evolution of fesc(Lya) with redshift. |
Supernova constraints on Multi-coupled Dark Energy: The persisting consistency of ever more accurate observational data with the
predictions of the standard LCDM cosmological model puts severe constraints on
possible alternative scenarios, but still does not shed any light on the
fundamental nature of the cosmic dark sector.As large deviations from a LCDM
cosmology are ruled out by data, the path to detect possible features of
alternative models goes necessarily through the definition of cosmological
scenarios that leave almost unaffected the background and -- to a lesser extent
-- the linear perturbations evolution of the universe. In this context,the
Multi-coupled DE (McDE) model was proposed by Baldi 2012 as a particular
realization of an interacting Dark Energy field characterized by an effective
screening mechanism capable of suppressing the effects of the coupling at the
background and linear perturbation level. In the present paper, for the first
time, we challenge the McDE scenario through a direct comparison with real
data, in particular with the luminosity distance of Type Ia supernovae. By
studying the existence and stability conditions of the critical points of the
associated background dynamical system, we select only the cosmologically
consistent solutions, and confront their background expansion history with
data. Confirming previous qualitative results, the McDE scenario appears to be
fully consistent with the adopted sample of Type Ia supernovae, even for
coupling values corresponding to an associated scalar fifth-force about four
orders of magnitude stronger than standard gravity. Our analysis demonstrates
the effectiveness of the McDE background screening, and shows some new
non-trivial asymptotic solutions for the future evolution of the universe. Our
results show how the background expansion history might be highly insensitive
to the fundamental nature and to the internal complexity of the dark sector.
[Abridged] | Differential Microlensing Measurements of Quasar Broad Line Kinematics
in Q2237+0305: The detailed workings of the central engines of powerful quasars remain a
mystery. This is primarily due to the fact that, at their cosmological
distances, the inner regions of these quasars are spatially unresolvable.
Reverberation mapping is now beginning to unlock the physics of the Broad
Emission Line Region (BELR) in nearby, low-luminosity quasars, however it is
still unknown whether this gas is dominated by virial motion, by outflows, or
infall. The challenge is greater for more distant, powerful sources due to the
very long response time of the BELR to changes in the continuum. We present a
new technique for probing the kinematic properties of the BELR and accretion
disk of high-z quasars using differential microlensing, and show how
substantial information can be gained through a single observation of a
strongly-lensed quasar using integral field spectroscopy. We apply this
technique to GMOS IFU observations of the multiply-imaged quasar Q2237+0305,
and find that the observed microlensing signature in the CIII] broad emission
line favours gravitationally-dominated dynamics over an accelerating outflow. |
What Shapes the Galaxy Mass Function? Exploring the Roles of
Supernova-Driven Winds and AGN: The observed stellar mass function (SMF) is very different to the halo mass
function predicted by Lambda-CDM, and it is widely accepted that this is due to
energy feedback from supernovae and black holes. However, the strength and form
of this feedback is not understood. In this paper, we use the phenomenological
model GALFORM to explore how galaxy formation depends on the strength and halo
mass dependence of feedback. We focus on 'expulsion' models in which the wind
mass loading, beta, is proportional to 1/\vdisk^n, with n=0,1,2 and contrast
these models with the successful Bower et al.\ 2008 model (B8W7). A crucial
development is that our code explicitly accounts for the recapture of expelled
gas as the system's halo mass (and thus gravitational potential) increases. We
find that a model with modest wind speed but high mass loading matches the flat
portion of the SMF. When combined with AGN feedback, the model provides a good
description of the observed SMF above 10^9 h^-1 Msol. However, in the expulsion
models, the brightest galaxies are assembled more recently than in B8W7, and
the specific star formation rates of galaxies decrease strongly with decreasing
stellar mass. The expulsion models also tend to have a cosmic star formation
density that is dominated by lower mass galaxies at z=1-3, and dominated high
mass galaxies at low redshift. These trends are in conflict with observational
data, but the comparison highlights some deficiencies of the B8W7 model also.
The experiments in this paper give us important physical insight to the impact
of the feedback process on the formation histories of galaxies, but the strong
mass dependence of feedback adopted in B8W7 still appears to provide the most
promising description of the observed universe. | The Primordial Magnetic Field (PMF) Generated in Large Field Inflation
(LFI), Natural Inflation (NI) and $R^2$-Inflation by $f^{2}FF$ Model: Large scale magnetic fields seem to be present in almost all astrophysical
systems and scales from planets to superclusters of galaxies and in very low
density intergalactic media. The upper limit of primordial magnetic fields
(PMF) has been set by recent observations by the Planck observatory (2015) to
be of the order of a few nG. The simple model ${f^2}FF$ used to generate the
PMF during the inflation era. It is based on the breaking of conformal symmetry
of electromagnetism during inflation. It is attractive because it is stable
under perturbations and leads to a scale invariant PMF. However, it may suffer
from two problems: Backreaction and strong coupling. In the first case, the
electromagnetic energy may exceed the energy of inflation, ${\rho
_{{\rm{Inf}}}}$. In the second case, the effective electric charges become
excessively large if we want to retrieve the standard electromagnetism at the
end of inflation. In this research, we investigate the generation of PMF under
three different models of inflation in order to avoid the backreaction problem.
We compute magnetic and electric spectra generated by the ${f^2}FF$ model in
the context of large field inflation (LFI), natural inflation (NI) and
${R^2}$-inflation, for all possible values of model parameters for de Sitter
and power law expansion of inflation. The results of the research show that the
scale invariant PMF can be generated in these models and the problem of
backreaction may be avoided in some observational ranges. In $R^2$-inflation,
which is preferred by the recent results of Planck 2015, we calculate the upper
of the scale invariant PMF generated by ${f^2}FF$ and in turns we find that the
upper limit of present magnetic field, ${B_0} < 8.058 \times {10^{ -
9}}{\rm{G}}$. It is in the same order of magnitude of PMF, reported by Planck,
2015. |
Singling out modified gravity parameters and datasets reveals a
dichotomy between Planck and lensing: An important route to testing General Relativity (GR) at cosmological scales
is usually done by constraining modified gravity (MG) parameters added to the
Einstein perturbed equations. Most studies have analyzed so far constraints on
pairs of MG parameters, but here, we explore constraints on one parameter at a
time while fixing the other at its GR value. This allows us to analyze various
models while benefiting from a stronger constraining power from the data. We
also explore which specific datasets are in tension with GR. We find that
models with ($\mu=1$, $\eta$) and ($\mu$, $\eta=1$) exhibit a 3.9-$\sigma$ and
3.8-$\sigma$ departure from GR when using Planck18+SNe+BAO, while ($\mu$,
$\eta$) shows a tension of 3.4-$\sigma$. We find no tension with GR for models
with the MG parameter $\Sigma$ fixed to its GR value. Using a Bayesian model
selection analysis, we find that some one-parameter MG models are moderately
favored over $\Lambda$CDM when using all dataset combinations except Planck CMB
Lensing and DES data. Namely, Planck18 shows a moderate tension with GR that
only increases when adding any combination of RSD, SNe, or BAO. However, adding
lensing diminishes or removes these tensions, which can be attributed to the
ability of lensing in constraining the MG parameter $\Sigma$. The two overall
groups of datasets are found to have a dichotomy when performing consistency
tests with GR, which may be due to systematic effects, lack of constraining
power, or modelling. These findings warrant further investigation using more
precise data from ongoing and future surveys. | The Relationships Among Compact Stellar Systems: A Fresh View of Ultra
Compact Dwarfs: We use a combined imaging and spectroscopic survey of the nearby central
cluster galaxy, M87, to assemble a sample of 34 confirmed ultra compact dwarfs
(UCDs) with half-light radii of >~ 10 pc measured from Hubble Space Telescope
images. This doubles the existing sample in M87, making it the largest such
sample for any galaxy, while extending the detection of UCDs to unprecedentedly
low luminosities (MV = -9). With this expanded sample, we find no correlation
between size and luminosity, in contrast to previous suggestions, and no
general correlation between size and galactocentric distance. We explore the
relationships between UCDs, less luminous extended clusters (including faint
fuzzies), globular clusters (GCs), as well as early-type galaxies and their
nuclei, assembling an extensive new catalog of sizes and luminosities for
stellar systems. Most of the M87 UCDs follow a tight color-magnitude relation,
offset from the metal-poor GCs. This, along with kinematical differences,
demonstrates that most UCDs are a distinct population from normal GCs, and not
simply a continuation to larger sizes and higher luminosities. The UCD
color-magnitude trend couples closely with that for Virgo dwarf elliptical
nuclei. We conclude that the M87 UCDs are predominantly stripped nuclei. The
brightest and reddest UCDs may be the remnant nuclei of more massive galaxies
while a subset of the faintest UCDs may be tidally limited and related to more
compact star clusters. In the broader context of galaxy assembly, blue UCDs may
trace halo build-up by accretion of low-mass satellites, while red UCDs may be
markers of metal-rich bulge formation in larger galaxies. |
The dynamical state of brightest cluster galaxies and the formation of
clusters: A large sample of Abell clusters of galaxies, selected for the likely
presence of a dominant galaxy, is used to study the dynamical properties of
brightest cluster members (BCMs). From visual inspection of Digitized Sky
Survey images combined with redshift data we identify 1426 candidate BCMs in
1221 redshift components in 1169 different Abell clusters, the largest such
sample published so far. By our own morphological classification we find ~92%
of these BCMs to be early-type galaxies, and 48% of cD type. We confirm
previous findings based on much smaller samples, namely that a large fraction
of BCMs have significant peculiar velocities. For a subsample of 452 clusters
with at least 10 measured radial velocities, we find a median BCM peculiar
velocity of 32% of their host clusters' radial velocity dispersion. This
suggests that most BCMs are not at rest in the potential well of their
clusters, and that the phenomenon is thus not a special trait of clusters
hosting cD galaxies. We show that the peculiar velocity of the BCM is
independent of cluster richness and only slightly dependent on the Bautz-Morgan
type. We also find a weak trend for the peculiar velocity to rise with the
cluster velocity dispersion. The strongest dependence is with the morphological
type of the BCM: cD galaxies tend to have lower relative peculiar velocities
than elliptical galaxies. This result points to a connection between the
formation of the BCMs and that of their clusters. Our data are qualitatively
consistent with the merging-groups scenario, where BCMs in clusters formed
first in smaller subsystems comparable to compact groups of galaxies. In this
scenario, clusters would have formed recently from the mergers of many such
groups and would still be in a dynamically unrelaxed state. | Clusters, Groups, and Filaments in the Chandra Deep Field-South up to
Redshift 1: We present a comprehensive structure detection analysis of the 0.3 square
degree area of the MUSYC-ACES field which covers the Chandra Deep Field-South
(CDFS). Using a density-based clustering algorithm on the MUSYC and ACES
photometric and spectroscopic catalogues we find 62 over-dense regions up to
redshifts of 1, including, clusters, groups and filaments. All structures are
confirmed using the DBSCAN method, including the detection of nine structures
previously reported in the literature. We present a catalogue of all structures
present including their central position, mean redshift, velocity dispersions,
and classification based on their morphological and spectroscopic
distributions. In particular we find 13 galaxy clusters and 6 large
groups/small clusters. Comparison of these massive structures with published
XMM-Newton imaging (where available) shows that $80\%$ of these structures are
associated with diffuse, soft-band (0.4 - 1 keV) X-ray emission including
$90\%$ of all objects classified as clusters. The presence of soft-band X-ray
emission in these massive structures (${\rm M}_{200} \geq 4.9 \times 10^{13}
{\rm M}_{\odot}$) provides a strong independent confirmation of our methodology
and classification scheme. Nearly $60\%$ of the clusters, groups and filaments
are detected in the known enhanced density regions of the CDFS at
$z\simeq0.13$, $z\simeq0.52$, $0.68$, and $0.73$. Additionally, all of the
clusters, bar the most distant, are found in these over-dense redshifts
regions. Many of the clusters and groups exhibit signs of on-going formation
seen in their velocity distributions, position within the detected cosmic web
and in one case through the presence of tidally disrupted central galaxies
exhibiting trails of stars. These results all provide strong support for
hierarchical structure formation up to redshifts of 1. |
The Space Density of Extended Ultraviolet (XUV) Disks in the Local
Universe and Implications for Gas Accretion on to Galaxies: We present results of the first unbiased search for extended UV (XUV)-disk
galaxies undertaken to determine the space density of such galaxies. Our sample
contains 561 local (0.001 < z < 0.05) galaxies that lie in the intersection of
available GALEX deep imaging (exposure time > 1.5 x 10^4 s) and SDSS DR7
footprints. We explore modifications to the standard classification scheme for
our sample that includes both disk- and bulge-dominated galaxies. Visual
classification of each galaxy in the sample reveals an XUV-disk frequency of up
to 20% for the most nearby portion of our sample. On average over the entire
sample (out to z=0.05) the frequency ranges from a hard limit of 4% to 14%. The
GALEX imaging allows us to detect XUV-disks beyond 100 Mpc. The XUV regions
around XUV-disk galaxies are consistently bluer than the main bodies. We find a
surprisingly high frequency of XUV emission around luminous red (NUV-r > 5) and
green valley (3 < NUV-r < 5) galaxies. The XUV-disk space density in the local
universe is > 1.5-4.2 x 10^-3 Mpc^-3. Using the XUV emission as an indicator of
recent gas accretion, we estimate that the cold gas accretion rate onto these
galaxies is > 1.7-4.6 x 10^-3 Msun Mpc^-3 yr^-1. The number of XUV-disks in the
green valley and the estimated accretion rate onto such galaxies points to the
intriguing possibility that 7%-18% of galaxies in this population are
transitioning away from the red sequence. | The analytic radial acceleration relation for galaxy clusters: Recently, a tight correlation between the dynamical radial acceleration and
the baryonic radial acceleration in galaxies - the radial acceleration relation
- has been discovered. This has been claimed as an indirect support of the
modified gravity theories. However, whether the radial acceleration relation
could also be found in galaxy clusters is controversial. In this article, we
derive and present an analytic radial acceleration relation for the central
region of galaxy clusters. We examine the data of some large galaxy clusters
and we find that the resulting radial acceleration relation has a very large
scatter. Moreover, although the radial acceleration relation for galaxy
clusters shows some agreement with the one discovered in galaxies for a certain
range of baryonic radial acceleration, their functional forms are somewhat
different from each other. This suggests that the radial acceleration relation
may not be a universal relation in general. |
Quantifying Density-Ionization Correlations with the 21cm Power Spectrum: The Epoch of Reionization (EoR)---when neutral hydrogen in the intergalactic
medium was systematically ionized---is a period in our Universe's history that
is currently poorly understood. However, a key prediction of most models is a
correlation between the density and ionization field during the EoR. This has
consequences for the 21cm power spectrum. Here, we propose a parametrization
for the density-ionization correlation and study the dependence of the 21cm
power spectrum on this parameterization. We use this formalism to forecast the
ability of current and future observations to constrain these correlations. We
find that upper limits on the dimensionless power spectrum at redshifts $7.5 <
z < 8.5$ using $k$ bins between $0.1\,\textrm{Mpc}^{-1} < k <
0.75\,\textrm{Mpc}^{-1}$ with error bars at the level of
$\sim\!\!20\,\textrm{mK}^2$ about our fiducial model would rule out
uncorrelated reionization at $99\%$ credibility. Beyond upper limits, we find
that at its full sensitivity, the Hydrogen Epoch of Reionization Array (HERA)
will be able to place strong constraints on the sign and magnitude of
density-ionization correlations. | The Biggest Explosions in the Universe: Supermassive primordial stars are expected to form in a small fraction of
massive protogalaxies in the early universe, and are generally conceived of as
the progenitors of the seeds of supermassive black holes (BHs). Supermassive
stars with masses of ~55,000 M_Sun, however, have been found to explode and
completely disrupt in a supernova (SN) with an energy of up to ~10^55 erg
instead of collapsing to a BH. Such events, ~10,000 times more energetic than
typical SNe today, would be among the biggest explosions in the history of the
universe. Here we present a simulation of such a SN in two stages. Using the
RAGE radiation hydrodynamics code we first evolve the explosion from an early
stage through the breakout of the shock from the surface of the star until the
blast wave has propagated out to several parsecs from the explosion site, which
lies deep within an atomic cooling dark matter (DM) halo at z ~ 15. Then, using
the GADGET cosmological hydrodynamics code we evolve the explosion out to
several kiloparsecs from the explosion site, far into the low-density
intergalactic medium. The host DM halo, with a total mass of 4 x 10^7 M_Sun,
much more massive than typical primordial star-forming halos, is completely
evacuated of high density gas after < 10 Myr, although dense metal-enriched gas
recollapses into the halo, where it will likely form second-generation stars
with metallicities of ~ 0.05 Z_Sun after > 70 Myr. The chemical signature of
supermassive star explosions may be found in such long-lived second-generation
stars today. |
Exact black hole solution for scale dependent gravitational couplings
and the corresponding coupling flow: We study a black hole solution for the generalized Einstein Hilbert action
with scale dependent couplings G(r) and Lambda(r). The form of the couplings is
not imposed, but rather deduced from the existence of a non trivial symmetrical
solution. A classical-like choice of the integration constants is found.
Finally, the induced flow of the couplings is derived and compared to the flow
that is obtained in the context of the exact renormalization group approach. | GRB spectral parameter modeling: Fireball model of the gamma-ray bursts (GRBs) predicts generation of numerous
internal shocks, which efficiently accelerate charged particles and generate
relatively small-scale stochastic magnetic and electric fields. The accelerated
particles diffuse in space due to interaction with the random waves and so emit
so called Diffusive Synchrotron Radiation (DSR) in contrast to standard
synchrotron radiation they would produce in a large-scale regular magnetic
fields. In this contribution we present key results of detailed modeling of the
GRB spectral parameters, which demonstrate that the non-perturbative DSR
emission mechanism in a strong random magnetic field is consistent with
observed distributions of the Band parameters and also with cross-correlations
between them. |
Resurrecting the Power-law, Intermediate, and Logamediate Inflations in
the DBI Scenario with Constant Sound Speed: We investigate the power-law, intermediate, and logamediate inflationary
models in the framework of DBI non-canonical scalar field with constant sound
speed. In the DBI setting, we first represent the power spectrum of both scalar
density and tensor gravitational perturbations. Then, we derive different
inflationary observables including the scalar spectral index $n_s$, the running
of the scalar spectral index $dn_s/d\ln k$, and the tensor-to-scalar ratio $r$.
We show that the 95\% CL constraint of the Planck 2015 T+E data on the
non-Gaussianity parameter $f_{{\rm NL}}^{{\rm DBI}}$ leads to the sound speed
bound $c_{s}\geq0.087$ in the DBI inflation. Moreover, our results imply that,
although the predictions of the power-law, intermediate, and logamediate
inflations in the standard canonical framework ($c_s=1$) are not consistent
with the Planck 2015 data, in the DBI scenario with constant sound speed
$c_s<1$, the result of the $r-n_s$ diagram for these models can lie inside the
68\% CL region favored by the Planck 2015 TT,TE,EE+lowP data. We also specify
the parameter space of the power-law, intermediate, and logamediate inflations
for which our models are compatible with the 68\% or 95\% CL regions of the
Planck 2015 TT,TE,EE+lowP data. Using the allowed ranges of the parameter space
of the intermediate and logamediate inflationary models, we estimate the
running of the scalar spectral index and find that it is compatible with the
95\% CL constraint from the Planck 2015 TT,TE,EE+lowP data. | Constraining scalar fields with stellar kinematics and collisional dark
matter: The existence and detection of scalar fields could provide solutions to
long-standing puzzles about the nature of dark matter, the dark compact objects
at the centre of most galaxies, and other phenomena. Yet, self-interacting
scalar fields are very poorly constrained by astronomical observations, leading
to great uncertainties in estimates of the mass $m_\phi$ and the
self-interacting coupling constant $\lambda$ of these fields. To counter this,
we have systematically employed available astronomical observations to develop
new constraints, considerably restricting this parameter space. In particular,
by exploiting precise observations of stellar dynamics at the centre of our
Galaxy and assuming that these dynamics can be explained by a single boson
star, we determine an upper limit for the boson star compactness and impose
significant limits on the values of the properties of possible scalar fields.
Requiring the scalar field particle to follow a collisional dark matter model
further narrows these constraints. Most importantly, we find that if a scalar
dark matter particle does exist, then it cannot account for both the
dark-matter halos and the existence of dark compact objects in galactic nuclei |
Physical Properties of Jets in AGN: I review constraints on the physical properties of AGN jets revealed through
Very Long Baseline Interferometry (VLBI) studies of the structure and
time-evolution of parsec-scale jets, including recent results from the MOJAVE
program. In particular I focus on constraints available from very long time
baseline studies which probe a wide range of jet behavior over many outbursts.
Kinematic studies of propagating jet features find an apparent speed
distribution that peaks around 10c for blazars, with speeds up to 50c observed.
These observed speeds require Lorentz factors at least as large, implying that
parsec-scale Lorentz factors up to 10-20 are common for blazars with a tail up
to ~ 50. Jet flows are still becoming organized on these scales as evidenced by
the high incidence of non-radial motions and/or accelerations of jet features
(including increases and decreases in apparent speed and direction). Changes in
Lorentz factors of propagating jet features appear to play a significant role
in the observed accelerations, and while the connection between acceleration of
jet features and the underlying flow is not clear, the pattern of observed
accelerations suggest the flow may increase in speed near the base of the jet
and decrease further out. In some jets, ejections of new features span a range
of ejection angles over many epochs, tracing out wider opening angles on
parsec-scales than are apparent in single epoch observations. | Cosmological Constraint on $Ω_m$ and $σ_8$ from Cluster
Abundances using the $\mathtt{GalWCat19}$ Optical-Spectroscopic SDSS Catalog: We derive cosmological constraints on the matter density, \om, and the
amplitude of fluctuations, \sig, using $\mathtt{GalWCat19}$, a catalog of 1800
galaxy clusters we identified in the Sloan Digital Sky Survey-DR13
spectroscopic data set using our GalWeight technique to determine cluster
membership \citep{Abdullah18,Abdullah19}. By analyzing a subsample of 756
clusters in a redshift range of $0.045\leq z \leq 0.125$ and virial masses of
$M\geq 0.8\times10^{14}$ \hm ~with mean redshift of $z = 0.085$, we obtain \om
~$=0.310^{+0.023}_{-0.027} \pm 0.041$ (systematic) and \sig
~$=0.810^{+0.031}_{-0.036}\pm 0.035$ (systematic), with a cluster normalization
relation of $\sigma_8= 0.43 \Omega_m^{-0.55}$. There are several unique aspects
to our approach: we use the largest spectroscopic data set currently available,
and we assign membership using the GalWeight technique which we have shown to
be very effective at simultaneously maximizing the number of {\it{bona fide}}
cluster members while minimizing the number of contaminating interlopers.
Moreover, rather than employing scaling relations, we calculate cluster masses
individually using the virial mass estimator. Since $\mathtt{GalWCat19}$ is a
low-redshift cluster catalog we do not need to make any assumptions about
evolution either in cosmological parameters or in the properties of the
clusters themselves. Our constraints on \om ~and \sig ~are consistent and very
competitive with those obtained from non-cluster abundance cosmological probes
such as Cosmic Microwave Background (CMB), Baryonic Acoustic Oscillation (BAO),
and supernovae (SNe). The joint analysis of our cluster data with
Planck18+BAO+Pantheon gives \om ~$=0.315^{+0.013}_{-0.011}$ and \sig
~$=0.810^{+0.011}_{-0.010}$. |
The cosmological size and velocity dispersion evolution of massive
early-type galaxies: We analyze 40 cosmological re-simulations of individual massive galaxies with
present-day stellar masses of $M_{*} > 6.3 \times 10^{10} M_{\odot}$ in order
to investigate the physical origin of the observed strong increase in galaxy
sizes and the decrease of the stellar velocity dispersions since redshift $z
\approx 2$. At present 25 out of 40 galaxies are quiescent with structural
parameters (sizes and velocity dispersions) in agreement with local early type
galaxies. At z=2 all simulated galaxies with $M_* \gtrsim 10^{11}M_{\odot}$ (11
out of 40) at z=2 are compact with projected half-mass radii of $\approx$ 0.77
($\pm$0.24) kpc and line-of-sight velocity dispersions within the projected
half-mass radius of $\approx$ 262 ($\pm$28) kms$^{-1}$ (3 out of 11 are already
quiescent). Similar to observed compact early-type galaxies at high redshift
the simulated galaxies are clearly offset from the local mass-size and
mass-velocity dispersion relations. Towards redshift zero the sizes increase by
a factor of $\sim 5-6$, following $R_{1/2} \propto (1+z)^{\alpha}$ with $\alpha
= -1.44$ for quiescent galaxies ($\alpha = -1.12$ for all galaxies). The
velocity dispersions drop by about one-third since $z \approx 2$, following
$\sigma_{1/2} \propto (1+z)^{\beta}$ with $\beta = 0.44$ for the quiescent
galaxies ($\beta = 0.37$ for all galaxies). The simulated size and dispersion
evolution is in good agreement with observations and results from the
subsequent accretion and merging of stellar systems at $z\lesssim 2$ which is a
natural consequence of the hierarchical structure formation. A significant
number of the simulated massive galaxies (7 out of 40) experience no merger
more massive than 1:4 (usually considered as major mergers). On average, the
dominant accretion mode is stellar minor mergers with a mass-weighted
mass-ratio of 1:5. (abridged) | Model-independent Gamma-Ray Bursts Constraints on Cosmological Models
Using Machine Learning: In this paper, we calibrate the luminosity relation of gamma-ray bursts
(GRBs) with the machine learning (ML) methods for reconstructing
distance-redshift relation from the Pantheon+ sample of type Ia supernovae (SNe
Ia) in a cosmology-independent way. The A219 GRB data set at low redshift are
used to calibrate the Amati relation ($E_{\rm p}$-$E_{\rm iso}$) relation by
the ML methods selected with the best performance %and the calibrated results
are extrapolated to the high redshift data to construct the Hubble diagram at
high redshift. We constrain cosmological models via the Markov Chain Monte
Carlo numerical method with the GRBs at high redshift and the latest
observational Hubble data (OHD). By the K-Nearest Neighbors (KNN) methods, we
obtain $\Omega_{\rm m}$ = $0.29^{+0.09}_{-0.06}$, $h$ = $0.66^{+0.04}_{-0.07}$
, $w_0$ = $-0.83^{+0.66}_{-0.31}$, $w_a$ = $-0.91^{+0.87}_{-0.46}$ at
1-$\sigma$ confidence level for the Chevallier-Polarski-Linder (CPL) model in a
flat space, which favor the dark energy with a possible evolution ($w_a\neq0$)
at 1-$\sigma$. These results are consistent with those obtained from GRBs
calibrated via the Gaussian Process. |
Evolution of the Cosmological Horizons in a Universe with Countably
Infinitely Many State Equations: This paper is the second of two papers devoted to the study of the evolution
of the cosmological horizons (particle and event horizons). Specifically, in
this paper we consider the extremely general case of an accelerated universe
with countably infinitely many constant state equations, and we obtain simple
expressions in terms of their respective recession velocities that generalize
the previous results for one and two state equations. We also provide a
qualitative study of the values of the horizons and their velocities at the
origin of the universe and at the far future, and we prove that these values
only depend on one dominant state equation. Finally, we compare both horizons
and determine when one is larger that the other. | The Quantum Field Theory of K-mouflage: We consider K-mouflage models which are K-essence theories coupled to matter.
We analyse their quantum properties and in particular the quantum corrections
to the classical Lagrangian. We setup the renormalisation programme for these
models and show that K-mouflage theories involve a recursive construction
whereby each set of counter-terms introduces new divergent quantum
contributions which in turn must be subtracted by new counter-terms. This tower
of counter-terms can be constructed by recursion and allows one to calculate
the finite renormalised action of the model. In particular, the classical
action is not renormalised and the finite corrections to the renormalised
action contain only higher derivative operators. We establish an operational
criterion for classicality, where the corrections to the classical action are
negligible, and show that this is satisfied in cosmological and astrophysical
situations for (healthy) K-mouflage models which pass the solar system tests.
We also find that these models are quantum stable around astrophysical and
cosmological backgrounds. We then consider the possible embedding of the
K-mouflage models in an Ultra-Violet completion. We find that the healthy
models which pass the solar system tests all violate the positivity constraint
which would follow from the unitarity of the putative UV completion, implying
that these healthy K-mouflage theories have no UV completion. We then analyse
their behaviour at high energy and we find that the classicality criterion is
satisfied in the vicinity of a high energy collision implying that the
classical K-mouflage theory can be applied in this context. Moreover, the
classical description becomes more accurate as the energy increases, in a way
compatible with the classicalisation concept. |
Barrow Entropy Cosmology: an observational approach with a hint of
stability analysis: In this work, we use an observational approach and dynamical system analysis
to study the cosmological model recently proposed by Saridakis (2020), which is
based on the modification of the entropy-area black hole relation proposed by
Barrow (2020). The Friedmann equations governing the dynamics of the Universe
under this entropy modification can be calculated through the
gravity-thermodynamics conjecture. We investigate two models, one considering
only a matter component and the other including matter and radiation, which
have new terms compared to the standard model sourcing the late cosmic
acceleration. A Bayesian analysis is performed in which we use five
cosmological observations (observational Hubble data, type Ia supernovae, HII
galaxies, strong lensing systems, and baryon acoustic oscillations) to
constrain the free parameters of both models. From a joint analysis, we obtain
constraints that are consistent with the standard cosmological paradigm within
$2\sigma$ confidence level. In addition, a complementary dynamical system
analysis using local and global variables is developed which allows obtaining a
qualitative description of the cosmology. As expected, we found that the
dynamical equations have a de Sitter solution at late times. | Resonant Destruction as a Possible Solution to the Cosmological Lithium
Problem: We explore a nuclear physics resolution to the discrepancy between the
predicted standard big-bang nucleosynthesis (BBN) abundance of 7Li and its
observational determination in metal-poor stars. The theoretical 7Li abundance
is 3-4 times greater than the observational values, assuming the
baryon-to-photon ratio, eta_wmap, determined by WMAP. The 7Li problem could be
resolved within the standard BBN picture if additional destruction of A=7
isotopes occurs due to new nuclear reaction channels or upward corrections to
existing channels. This could be achieved via missed resonant nuclear
reactions, which is the possibility we consider here. We find some potential
candidate resonances which can solve the lithium problem and specify their
required resonant energies and widths. For example, a 1^- or 2^- excited state
of 10C sitting at approximately 15.0 MeV above its ground state with an
effective width of order 10 keV could resolve the 7Li problem; the existence of
this excited state needs experimental verification. Other examples using known
states include 7Be+t \rightarrow 10B(18.80 MeV), and 7Be+d \rightarrow 9B(16.71
MeV). For all of these states, a large channel radius (a > 10 fm) is needed to
give sufficiently large widths. Experimental determination of these reaction
strengths is needed to rule out or confirm these nuclear physics solutions to
the lithium problem. |
21 cm Angular Spectrum of Cosmic String Loops: The 21 cm signatures induced by moving cosmic string loops are investigated.
Moving cosmic string loops seed filamentary nonlinear objects. We analytically
evaluate the differential 21 cm brightness temperature from these objects. We
show that the brightness temperature reaches 200 mK for a loop whose tension is
about the current upper limit, $G\mu\sim10^{-7}$. We also calculate the angular
power spectrum, assuming scaling in loop distribution. We find that the angular
power spectrum for $G\mu>10^{-8}$ at $z=30$ or $G\mu>10^{-10}$ at $z=20$ can
dominate the spectrum of the primordial density fluctuations. Finally we show
that a future SKA-like observation has the potential to detect the power
spectrum due to loops with $G\mu=10^{-8}$ at $z=20$. | Coupled Multi Scalar Field Dark Energy: The main aim of this paper is to present the multi scalar field components as
candidates to be the dark energy of the universe and their observational
constraints. We start with the canonical Quintessence and Phantom fields with
quadratic potentials and show that a more complex model should bear in mind to
satisfy current cosmological observations. Then we present some implications
for a combination of two fields, named as Quintom models. We consider two types
of models, one as the sum of the quintessence and phantom potentials and other
including an interacting term between fields. We find that adding one extra
degree of freedom, by the interacting term, the dynamics enriches considerably
and could lead to an improvement in the fit of $-2\ln\Delta \Like_{\rm max}=
5.19$, compared to $\Lambda$CDM. The resultant effective equation of state is
now able to cross the phantom divide line, and in several cases present an
oscillatory or discontinuous behavior, depending on the interaction value. The
parameter constraints of the scalar field models (quintessence, phantom,
quintom and interacting quintom) were performed using Cosmic Chronometers,
Supernovae Ia and Baryon Acoustic Oscillations data; and the Log-Bayes factors
were computed to compare the performance of the models. We show that single
scalar fields may face serious troubles and hence the necessity of a more
complex models, i.e. multiple fields. |
Smallest Remnants of Early Matter Domination: The evolution of the universe prior to Big Bang Nucleosynthesis could have
gone through a phase of early matter domination (EMD) which enhanced the growth
of small-scale dark matter structure. If EMD was long enough, self-gravitating
objects formed prior to reheating. We study the evolution of these dense early
halos (EHs) through reheating. At the end of EMD, EHs undergo rapid expansion
and eventually eject their matter. We find that this process washes out
structure on scales much larger than naively expected from the size of the
original halos. We compute the density profiles of the EH remnants and use them
to construct late-time power spectra that include these non-linear effects. EH
dynamics limits the maximum enhancement that can be generated by EMD in a way
that is independent of the dark matter microphysics. We evolve an extrapolated
$\Lambda$CDM power spectrum to estimate the properties of microhalos that would
form after matter-radiation equality. Surprisingly, cosmologies with a short
period of EMD lead to an earlier onset of microhalo formation compared to those
with a long period of EMD. In either case, dark matter structure formation
begins much earlier than in the standard cosmology, with most DM bound in
microhalos. | Constraining dark energy with gamma-ray bursts: We use the measurement of gamma-ray burst (GRB) distances to constrain dark
energy cosmological model parameters. We employ two methods for analyzing GRB
data - fitting luminosity relation of GRBs in each cosmology and using distance
measures computed from binned GRB data. Current GRB data alone cannot tightly
constrain cosmological parameters and allow for a wide range of dark energy
models. |
Simulating the Large-Scale Structure of HI Intensity Maps: Intensity mapping of neutral hydrogen (HI) is a promising observational probe
of cosmology and large-scale structure. We present wide field simulations of HI
intensity maps based on N-body simulations of a $2.6\, {\rm Gpc / h}$ box with
$2048^3$ particles (particle mass $1.6 \times 10^{11}\, {\rm M_\odot / h}$).
Using a conditional mass function to populate the simulated dark matter density
field with halos below the mass resolution of the simulation ($10^{8}\, {\rm
M_\odot / h} < M_{\rm halo} < 10^{13}\, {\rm M_\odot / h}$), we assign HI to
those halos according to a phenomenological halo to HI mass relation. The
simulations span a redshift range of 0.35 < z < 0.9 in redshift bins of width
$\Delta z \approx 0.05$ and cover a quarter of the sky at an angular resolution
of about 7'. We use the simulated intensity maps to study the impact of
non-linear effects and redshift space distortions on the angular clustering of
HI. Focusing on the autocorrelations of the maps, we apply and compare several
estimators for the angular power spectrum and its covariance. We verify that
these estimators agree with analytic predictions on large scales and study the
validity of approximations based on Gaussian random fields, particularly in the
context of the covariance. We discuss how our results and the simulated maps
can be useful for planning and interpreting future HI intensity mapping
surveys. | Towards optimal extraction of cosmological information from nonlinear
data: One of the main unsolved problems of cosmology is how to maximize the
extraction of information from nonlinear data. If the data are nonlinear the
usual approach is to employ a sequence of statistics (N-point statistics,
counting statistics of clusters, density peaks or voids etc.), along with the
corresponding covariance matrices. However, this approach is computationally
prohibitive and has not been shown to be exhaustive in terms of information
content. Here we instead develop a Bayesian approach, expanding the likelihood
around the maximum posterior of linear modes, which we solve for using
optimization methods. By integrating out the modes using perturbative expansion
of the likelihood we construct an initial power spectrum estimator, which for a
fixed forward model contains all the cosmological information if the initial
modes are gaussian distributed. We develop a method to construct the window and
covariance matrix such that the estimator is explicitly unbiased and nearly
optimal. We then generalize the method to include the forward model parameters,
including cosmological and nuisance parameters, and primordial non-gaussianity.
We apply the method in the simplified context of nonlinear structure formation,
using either simplified 2-LPT dynamics or N-body simulations as the nonlinear
mapping between linear and nonlinear density, and 2-LPT dynamics in the
optimization steps used to reconstruct the initial density modes. We
demonstrate that the method gives an unbiased estimator of the initial power
spectrum, providing among other a near optimal reconstruction of linear
baryonic acoustic oscillations. |
Cosmological implications of baryon acoustic oscillation (BAO)
measurements: We derive constraints on cosmological parameters and tests of dark energy
models from the combination of baryon acoustic oscillation (BAO) measurements
with cosmic microwave background (CMB) and Type Ia supernova (SN) data. We take
advantage of high-precision BAO measurements from galaxy clustering and the
Ly-alpha forest (LyaF) in the BOSS survey of SDSS-III. BAO data alone yield a
high confidence detection of dark energy, and in combination with the CMB
angular acoustic scale they further imply a nearly flat universe. Combining BAO
and SN data into an "inverse distance ladder" yields a 1.7% measurement of
$H_0=67.3 \pm1.1$ km/s/Mpc. This measurement assumes standard pre-recombination
physics but is insensitive to assumptions about dark energy or space curvature,
so agreement with CMB-based estimates that assume a flat LCDM cosmology is an
important corroboration of this minimal cosmological model. For open LCDM, our
BAO+SN+CMB combination yields $\Omega_m=0.301 \pm 0.008$ and curvature
$\Omega_k=-0.003 \pm 0.003$. When we allow more general forms of evolving dark
energy, the BAO+SN+CMB parameter constraints remain consistent with flat LCDM.
While the overall $\chi^2$ of model fits is satisfactory, the LyaF BAO
measurements are in moderate (2-2.5 sigma) tension with model predictions.
Models with early dark energy that tracks the dominant energy component at high
redshifts remain consistent with our constraints. Expansion history alone
yields an upper limit of 0.56 eV on the summed mass of neutrino species,
improving to 0.26 eV if we include Planck CMB lensing. Standard dark energy
models constrained by our data predict a level of matter clustering that is
high compared to most, but not all, observational estimates. (Abridged) | Systematic investigation of the expected gravitational wave signal from
supermassive black hole binaries in the pulsar timing band: In this letter we carry out the first systematic investigation of the
expected gravitational wave (GW) background generated by supermassive black
hole (SMBH) binaries in the nHz frequency band accessible to pulsar timing
arrays (PTAs). We take from the literature several estimates of the redshift
dependent galaxy mass function and of the fraction of close galaxy pairs to
derive a wide range of galaxy merger rates. We then exploit empirical black
hole-host relations to populate merging galaxies with SMBHs. The result of our
procedure is a collection of a large number of phenomenological SMBH binary
merger rates consistent with current observational constraints on the galaxy
assembly at z<1.5. For each merger rate we compute the associated GW signal,
eventually producing a large set of estimates of the nHz GW background that we
use to infer confidence intervals of its expected amplitude. When considering
the most recent SMBH-host relations, accounting for ultra-massive black holes
in brightest cluster galaxies, we find that the nominal $1\sigma$ interval of
the expected GW signal is only a factor of 3-to-10 below current PTA limits,
implying a non negligible chance of detection in the next few years. |
Evolving Starburst Modeling of FIR/sub-mm/mm Line Emission. II.
Application to M 82: We present starburst models for far-infrared/sub-millimeter/millimeter
(FIR/sub-mm/mm) line emission of molecular and atomic gas in an evolving
starburst region, which is treated as an ensemble of non-interacting hot
bubbles which drive spherical shells of swept-up gas into a surrounding uniform
gas medium. These bubbles and shells are driven by stellar winds and supernovae
within massive star clusters formed during an instantaneous starburst. The
underlying stellar radiation from the evolving clusters affects the properties
and structure of photodissociation regions (PDRs) in the shells, and hence the
spectral energy distributions (SEDs) of the molecular and atomic line emission
from these swept-up shells and the associated parent giant molecular clouds
(GMCs) contains a signature of the stage of evolution of the starburst. The
physical and chemical properties of the shells and their structure are computed
using a a simple well known similarity solution for the shell expansion, a
stellar population synthesis code, and a time-dependent PDR chemistry model.
The SEDs for several molecular and atomic lines ($^{12}$CO and its isotope
$^{13}$CO, HCN, HCO$^+$, C, O, and C$^+$) are computed using a non-local
thermodynamic equilibrium (non-LTE) line radiative transfer model. By comparing
our models with the available observed data of nearby infrared bright galaxies,
especially M 82, we constrain the models and in the case of M 82, we provide
estimates for the ages (5 - 6 Myr, 10 Myr) of recent starburst activity. We
also derive a total H$_2$ gas mass of $\sim$ 2 - 3.4 $\times$ 10$^8$
M$_{\odot}$ for the observed regions of the central 1 kpc starburst disk of M
82. | Feedback from Mass Outflows in Nearby Active Galactic Nuclei I. UV and
X-ray Absorbers: We present an investigation into the impact of feedback from outflowing UV
and X-ray absorbers in nearby z < 0.04 AGN. From studies of the kinematics,
physical conditions, and variability of the absorbers in the literature, we
calculate the possible ranges in total mass outflow rate and kinetic luminosity
for each AGN, summed over all of its absorbers. These calculations make use of
values (or limits) for the radial locations of the absorbers determined from
variability, excited-state absorption, and other considerations. From a sample
of 10 Seyfert 1 galaxies with detailed photoionization models for their
absorbers, we find that 7 have sufficient constraints on the absorber locations
to determine feedback parameters. For the low-luminosity AGN NGC 4395, these
values are low, although we do not have sufficient constraints on the X-ray
absorbers to make definitive conclusions. At least 5 of the 6 Seyfert 1s with
moderate bolometric luminosities have mass outflow rates that are 10 - 1000
times the mass accretion rates needed to generate their observed luminosities,
indicating that most of the mass outflow originates from outside the inner
accretion disk. Three of these (NGC 4051, NGC 3516, and NGC 3783) have kinetic
luminosities in the range 0.5 to 5% bolometric, which is the range typically
required by feedback models for efficient self-regulation of black-hole and
galactic bulge growth. At least 2 of the other 3 (NGC 5548, NGC 4151, and NGC
7469) have kinetic luminosities > 0.1% bolometric, although these values may
increase if radial locations can be determined for more of the absorbers. We
conclude that the outflowing UV and X-ray absorbers in moderate-luminosity AGN
have the potential to deliver significant feedback to their environments. |
The bispectrum of cosmic string temperature fluctuations including
recombination effects: We calculate the cosmic microwave background temperature bispectrum from
cosmic strings, for the first time including the contributions from the last
scattering surface, using a well-established Gaussian model for the string
energy-momentum correlation functions, and a simplified model for the cosmic
fluid. We check our approximation for the integrated Sachs-Wolfe (ISW)
contribution against the bispectrum obtained from the full sky map of the
cosmic string ISW signal used by the Planck team, obtaining good agreement. We
validate our model for the last scattering surface contribution by comparing
the predicted temperature power spectrum with that obtained from a full
Boltzmann code treatment applied to the Unconnected Segment Model of a string
network. We find that including the last scattering contribution has only a
small impact on the upper limit on the string tension resulting from the
bispectrum at Planck resolutions, and argue that the bispectrum is unlikely to
be competitive with the power spectrum at any resolution. | Nearest Neighbor Analysis as a New Probe for Fuzzy Dark Matter: Fuzzy dark matter (FDM) is a promising candidate for dark matter,
characterized by its ultra-light mass, which gives rise to wave effects at
astrophysical scales. These effects offer potential solutions to the
small-scale issues encountered within the standard cold dark matter (CDM)
paradigm. In this paper, we investigate the large-scale structure of the cosmic
web using FDM simulations, comparing them to CDM-only simulations and a
simulation incorporating baryonic effects. Our study employs the nearest
neighbor (NN) analysis as a new statistical tool for examining the structure
and statistics of the cosmic web in an FDM universe. This analysis could
capture the information absent in the two-point correlation functions. In
particular, we analyze data related to the spherical contact, nearest neighbor
distances, and the angle between the first and second nearest neighbors of
halos. Specifically, we utilize probability distribution functions, statistical
moments, and fitting parameters, as well as G(x), F(x), and J(x) functions to
analyze the above data. Remarkably, the results from the FDM simulations differ
significantly from the others across these analyses, while no noticeable
distinction is observed between the baryonic and CDM-only simulations.
Moreover, the lower FDM mass leads to more significant deviations from the CDM
simulations. These compelling results highlight the efficiency of the NN
analysis - mainly through the use of the J(x) function, $s_3$, $l_{3}$ and
$a_4$ parameters - as a prominent new tool for investigating FDM on large
scales and making observational predictions. |
A new mechanism for dark matter generation from an interacting
cosmological constant: We propose an alternative scenario for the dark matter generation from an
evolving cosmological constant which interacts with the dominant background in
certain intermediate phase of the universe, and relaxes to the observed small
value at present. In this way, it is shown that the interaction of the
cosmological constant with the radiation or matter might generate the dark
matter densities with a varied mass spectrum in the universe with their
characteristic arc-like frozen signatures on the Cosmic Microwave Background
Radiation (CMBR). This approach also suggests a possible solution to the long
standing cosmological constant problem. | Relative baryon-dark matter velocities in cosmological zoom simulations: Supersonic relative motion between baryons and dark matter due to the
decoupling of baryons from the primordial plasma after recombination affects
the growth of the first small-scale structures. Large box sizes (greater than a
few hundred Mpc) are required to sample the full range of scales pertinent to
the relative velocity, while the effect of the relative velocity is strongest
on small scales (less than a few hundred kpc). This separation of scales
naturally lends itself to the use of `zoom' simulations, and here we present
our methodology to self-consistently incorporate the relative velocity in zoom
simulations, including its cumulative effect from recombination through to the
start time of the simulation. We apply our methodology to a large-scale
cosmological zoom simulation, finding that the inclusion of relative velocities
suppresses the halo baryon fraction by $46$--$23$ per cent between $z=13.6$ and
$11.2$, in qualitative agreement with previous works. In addition, we find that
including the relative velocity delays the formation of star particles by $\sim
20 {~\rm Myr}$ Myr on average (of the order of the lifetime of a $\sim 9~{\rm
M}_\odot$ Population III star) and suppresses the final stellar mass by as much
as $79$ per cent at $z=11.2$. |
SAO-6m Telescope Spectroscopic Observations of Globular Clusters in
Nearby Galaxies: We present the results of medium-resolution spectroscopy of 28 globular
clusters (GCs) in six nearby galaxies of different luminosities and
morphological types, situated in: M33 (15 objects), M31 (3), IC10 (4), UGCA86
(4), HolmbergIX (1), and DDO71 (1) obtained at the Special Astrophysical
Observatory 6-meter telescope. Measurements of Lick absorption-line indices and
comparison with SSP models enabled us to obtain their spectroscopic ages,
metallicities and alpha-element to Fe abundance ratios. We found that all old
and intermediate-age GCs in our sample have low metallicities [Z/H] < -0.8 dex.
Metal-rich clusters are young and are preferentially found in galaxies more
massive than ~10^9 M_sun. The least massive dwarfs of our sample, DDO71 and
HolmbergIX, host one massive intermediate-age and one massive young metal-poor
GC, respectively. [a/Fe] abundance ratios tend to be enhanced but closer to
solar values for dwarf galaxies compared to GCs in more massive galaxies. We
analyse the age-metallicity relation for GCs in our galaxy sample and others
from the literature, and find, that 1) there is a general trend for GCs in low
surface brightness dwarf galaxies to be more metal-poor at a given age than GCs
in more massive galaxies; 2) the GC metallicity spread is wider for more
massive galaxies; 3) intermediate-age GCs in early-type dwarf galaxies are more
metal-rich at any given age than those in irregular galaxies of similar
luminosity. | Cosmological Constraint on the Light Gravitino Mass from CMB Lensing and
Cosmic Shear: Light gravitinos of mass $\lesssim \mathcal{O} (10)$ eV are of particular
interest in cosmology, offering various baryogenesis scenarios without
suffering from the cosmological gravitino problem. The gravitino may contribute
considerably to the total matter content of the Universe and affect structure
formation from early to present epochs. After the gravitinos decouple from
other particles in the early Universe, they free-stream and consequently
suppress density fluctuations of (sub-)galactic length scales. Observations of
structure at the relevant length-scales can be used to infer or constrain the
mass and the abundance of light gravitinos. We derive constraints on the light
gravitino mass using the data of cosmic microwave background (CMB) lensing from
Planck and of cosmic shear from the Canada France Hawaii Lensing Survey,
combined with analyses of the primary CMB anisotropies and the signature of
baryon acoustic oscillations in galaxy distributions. The obtained constraint
on the gravitino mass is $m_{3/2} < 4.7$ eV (95% C.L.), which is substantially
tighter than the previous constraint from clustering analysis of Ly-$\alpha$
forests. |
Non-minimally coupled curvaton: We investigate two-field inflationary models in which scalar cosmological
pertubations are generated via a spectator field nonminimally coupled to
gravity, with the particular emphasis on curvaton scenarios. The principal
advantage of these models is in the possibility to tune the spectator spectral
index via the nonminimal coupling. Our models naturally yield red spectrum of
the adiabatic perturbation demanded by observations. We study how the
nonminimal coupling affects the spectrum of the curvature perturbation
generated in the curvaton scenarios. In particular we find that for small,
negative nonminimal couplings the spectral index gets a contribution that is
negative and linear in the nonminimal coupling. Since in this way the curvature
spectrum becomes redder, some of curvaton scenarios can be saved, which would
otherwise be ruled out. In the power law inflation we find that a large
nonminimal coupling is excluded since it gives the principal slow roll
parameter that is of the order of unity. Finally, we point out that nonminimal
coupling can affect the postinflationary growth of the spectator perturbation,
and in this way the effectiveness of the curvaton mechanism. | Late time acceleration in a slow moving galileon field: In this paper, we examine the cosmological viability of a slow moving
galileon field in a potential. The Lagrangian $\cal{L}$ $
=-\frac{1}{2}g^{\mu\nu}\pi_{;\mu}\pi_{;\nu}
+\frac{G^{\mu\nu}}{2M^2}\pi_{;\mu}\pi_{;\nu}$ respects the galileon symmetry in
curved space time.
We carry out detailed investigations of the underlying dynamics of this
Lagrangian with Einstein-Hilbert term and a potential. We demonstrate that the
model can give rise to a viable ghost free late time acceleration of universe.
Furthermore we study the cosmological perturbation of the model and see that
the model gives different BBN constraints at early times. We also carry out the
observational analysis of the model and use observational data from growth,
Type Ia Supernovae (SNIa), Baryon Acoustic Oscillations (BAO) and Cosmic
Microwave Background (CMB) to constrain the parameters of the theory. |
Multicomponent multiscatter capture of Dark Matter: In recent years, the usefulness of astrophysical objects as Dark Matter (DM)
probes has become more and more evident, especially in view of null results
from direct detection and particle production experiments. The potentially
observable signatures of DM gravitationally trapped inside a star, or another
compact astrophysical object, have been used to forecast stringent constraints
on the nucleon-Dark Matter interaction cross section. Currently, the probes of
interest are: at high red-shifts, Population III stars that form in isolation,
or in small numbers, in very dense DM minihalos at $z\sim 15-40$, and, in our
own Milky Way, neutron stars, white dwarfs, brown dwarfs, exoplanets, etc. Of
those, only neutron stars are single-component objects, and, as such, they are
the only objects for which the common assumption made in the literature of
single-component capture, i.e. capture of DM by multiple scatterings with one
single type of nucleus inside the object, is valid. In this paper, we present
an extension of this formalism to multi-component objects and apply it to Pop
III stars, thereby investigating the role of He on the capture rates of Pop III
stars. As expected, we find that the inclusion of the heavier He nuclei leads
to an enhancement of the overall capture rates, further improving the potential
of Pop III stars as Dark Matter probes. | Imaging the redshifted 21-cm pattern around the first sources during the
cosmic dawn using the SKA: Understanding properties of the first sources in the Universe using the
redshifted \HI ~21-cm signal is one of the major aims of present and upcoming
low-frequency experiments. We investigate the possibility of imaging the
redshifted 21-cm pattern around the first sources during the cosmic dawn using
the SKA1-low. We model the \HI ~21-cm image maps, appropriate for the SKA1-low,
around the first sources consisting of stars and X-ray sources within galaxies.
In addition to the system noise, we account also for the astrophysical
foregrounds by adding them to the signal maps. We find that after subtracting
the foregrounds using a polynomial fit and suppressing the noise by smoothing
the maps over $10^{'} - 30^{'}$ angular scale, the isolated sources at $z \sim
15$ are detectable with $\sim 4 - 9 \, \sigma$ confidence level in 2000 h of
observation with the SKA1-low. Although the 21-cm profiles around the sources
get altered because of the Gaussian smoothing, the images can still be used to
extract some of the source properties. We account for overlaps in the patterns
of the individual sources by generating realistic \HI ~21-cm maps of the cosmic
dawn that are based on $N$-body simulations and a one-dimensional radiative
transfer code. We find that these sources should be detectable in the SKA1-low
images at $z = 15$ with an SNR of $\sim 14 (4)$ in 2000 (200) h of
observations. One possible observational strategy thus could be to observe
multiple fields for shorter observation times, identify fields with SNR
$\gtrsim 3$ and observe these fields for much longer duration. Such
observations are expected to be useful in constraining the parameters related
to the first sources. |
Mass dependent Evolution of Field Early-Type Galaxies Since z=1: We present the Fundamental Plane (FP) of field early-type galaxies at
0.5<z<1.0. Our project is a continuation of our efforts to understand the
formation and evolution of early-type galaxies in different environments. The
target galaxies were selected from the comprehensive and homogeneous data set
of the Gemini/HST Galaxy Cluster Project. The distant field early-type galaxies
follow a steeper FP relation compared to the local FP. The change in the slope
of the FP can be interpreted as a mass-dependent evolution. Similar results
have been found for cluster early-type galaxies in high redshift galaxy
clusters at 0.8<z<1. Therefore, the slope change of the FP appears to be
independent of the environment of the galaxies. | Discordance of the unified scheme with observed properties of quasars
and high-excitation galaxies in the 3CRR sample: We examine the consistency of the unified scheme of FR II-type radio galaxies
and quasars with their observed number and size distributions in the 3CRR
sample. We separate the low-excitation galaxies from the high-excitation ones,
as the former might not harbor a quasar within and thus may not be partaking in
the unified scheme models. In the updated 3CRR sample, at low redshifts
(z<0.5), the relative number and luminosity distributions of high-excitation
galaxies and quasars do roughly match the expectations from the
orientation-based unified scheme model. However, a foreshortening in the
observed sizes of quasars, a must in the orientation-based model, is not seen
with respect to radio galaxies even when the low-excitation galaxies are
excluded. This dashes the hope that the unified scheme might still work if one
includes only the high-excitation galaxies. |
Model-independent reconstruction of $f(T)$ gravity from Gaussian
Processes: We apply Gaussian processes and Hubble function data in $f(T)$ cosmology, to
reconstruct for the first time the $f(T)$ form in a model-independent way. In
particular, using $H(z)$ datasets coming from cosmic chronometers as well as
from the radial BAO method, alongside the latest released local value $H_{0} =
73.52 \pm 1.62$ km/s/Mpc, we reconstruct $H(z)$ and its derivatives, resulting
eventually in a reconstructed region for $f(T)$, without any assumption.
Although the cosmological constant lies in the central part of the
reconstructed region, the obtained mean curve follows a quadratic function.
Inspired by this we propose a new $f(T)$ parametrization, i.e. $f(T) =
-2\Lambda +\xi T^2$, with $\xi$ the sole free parameter that quantifies the
deviation from $\Lambda$CDM cosmology. Additionally, we confront three viable
one-parameter $f(T)$ models of the literature, which respectively are the
power-law, the square-root exponential, and the exponential one, with the
reconstructed $f(T)$ region, and then we extract significantly improved
constraints for their model parameters, comparing to the constraints that arise
from usual observational analysis. Finally, we argue that since we are using
the direct Hubble measurements and the local value for $H_0$ in our analysis,
with the above reconstruction of $f(T)$, the $H_0$ tension can be efficiently
alleviated. | Submillimeter Interferometry of the Luminous Infrared Galaxy NGC 4418: A
Hidden Hot Nucleus with an Inflow and an Outflow: We have observed the nucleus of the nearby luminous infrared galaxy NGC 4418
with subarcsec resolution at 860 and 450 micron for the first time to
characterize its hidden power source. A ~20 pc (0.1") hot dusty core was found
inside a 100 pc scale concentration of molecular gas at the galactic center.
The 860 micron continuum core has a deconvolved (peak) brightness temperature
of 120-210 K. The CO(3-2) peak brightness temperature there is as high as 90 K
at 50 pc resolution. The core has a bolometric luminosity of about 10^{11}
Lsun, which accounts for most of the galaxy luminosity. It is Compton thick
(N_H >~ 10^{25} cm^{-2}) and has a high luminosity-to-mass ratio ~500 Lsun/Msun
as well as a high luminosity surface density 10^{8.5+-0.5} Lsun pc^{-2}. These
parameters are consistent with an AGN to be the main luminosity source (with an
Eddington ratio about 0.3) while they can be also due to a young starburst near
its maximum L/M. We also found an optical color (reddening) feature that we
attribute to an outflow cone emanating from the nucleus. The hidden hot nucleus
thus shows evidence of both an inflow, previously seen with absorption lines,
and the new outflow reported here in a different direction. The nucleus must be
rapidly evolving with these gas flows. |
Synergistic Astrophysics in the Ultraviolet using Active Galactic Nuclei: Observing programs comprising multiple scientific objectives will enhance the
productivity of NASA's next UV/Visible mission. Studying active galactic nuclei
(AGN) is intrinsically important for understanding how black holes accrete
matter, grow through cosmic time, and influence their host galaxies. At the
same time, the bright UV continuum of AGN serves as an ideal background light
source for studying foreground gas in the intergalactic medium (IGM), the
circumgalactic medium (CGM) of individual galaxies, and the interstellar medium
(ISM) and halo of the Milky Way. A well chosen sample of AGN can serve as the
observational backbone for multiple spectroscopic investigations including
quantitative measurements of outflows from AGN, the structure of their
accretion disks, and the mass of the central black hole. | A problem with the analysis of type Ia supernovae: Type Ia supernovae have light curves that have widths and magnitudes that can
be used for testing cosmologies and they provide one of the few direct
measurements of time dilation. It is shown that the standard analysis that
calibrates the light curve against a rest-frame average (such as SALT2) removes
all the cosmological information from the calibrated light curves. Consequently
type Ia supernovae calibrated with these methods cannot be used to investigate
cosmology. The major evidence that supports the hypothesis of a static universe
is that the measurements of the widths of the raw light curves of type Ia
supernovae do not show any time dilation. The intrinsic wavelength dependence
shown by the SALT2 calibration templates is also consistent with no time
dilation. Using a static cosmological model the peak absolute magnitudes of raw
type Ia supernovae observations are also independent of redshift. These results
support the hypothesis of a static universe. |
The future of cosmology and the role of non-linear perturbations: Cosmological perturbation theory is a key tool to study the universe. The
linear or first order theory is well understood, however, developing and
applying the theory beyond linear order is at the cutting edge of current
research in theoretical cosmology. In this article, I will describe some
signatures of non-linear perturbation theory that do not exist at linear order,
focusing on vorticity generation at second order. In doing so, we discuss why
this, among other features such as induced gravitational waves and
non-Gaussianities, shows that cosmological perturbation theory is crucial for
testing models of the universe. | Investigating the velocity structure and X-ray observable properties of
simulated galaxy clusters with PHOX: Non-thermal motions in the intra-cluster medium (ICM) are believed to play a
non-negligible role in the pressure support to the total gravitating mass of
galaxy clusters. Future X-ray missions, such as ASTRO-H and ATHENA, will
eventually allow us to directly detect the signature of these motions from
high-resolution spectra of the ICM. In this paper, we present a study on a set
of clusters extracted from a cosmological hydrodynamical simulation, devoted to
explore the role of non-thermal velocity amplitude in characterising the
cluster state and the relation between observed X-ray properties. In order to
reach this goal, we apply the X-ray virtual telescope PHOX to generate
synthetic observations of the simulated clusters with both Chandra and ATHENA,
the latter used as an example for the performance of very high-resolution X-ray
telescopes. From Chandra spectra we extract global properties, e.g. luminosity
and temperature, and from ATHENA spectra we estimate the gas velocity
dispersion along the line of sight from the broadening of heavy-ion emission
lines (e.g. Fe). We further extend the analysis to the relation between
non-thermal velocity dispersion of the gas and the L_X-T scaling law for the
simulated clusters. Interestingly, we find a clear dependence of slope and
scatter on the selection criterion for the clusters, based on the level of
significance of non-thermal motions. Namely, the scatter in the relation is
significantly reduced by the exclusion of the clusters, for which we estimate
the highest turbulent velocities. Such velocity diagnostics appears therefore
as a promising independent way to identify disturbed clusters, in addition to
the commonly used morphological inspection. |
Weak-lensing calibration of a stellar mass-based mass proxy for
redMaPPer and Voronoi Tessellation clusters in SDSS Stripe 82: We present the first weak lensing calibration of $\mu_{\star}$, a new galaxy
cluster mass proxy corresponding to the total stellar mass of red and blue
members, in two cluster samples selected from the SDSS Stripe 82 data: 230
redMaPPer clusters at redshift $0.1\leq z<0.33$ and 136 Voronoi Tessellation
(VT) clusters at $0.1 \leq z < 0.6$. We use the CS82 shear catalog and stack
the clusters in $\mu_{\star}$ bins to measure a mass-observable power law
relation. For redMaPPer clusters we obtain $M_0 = (1.77 \pm 0.36) \times
10^{14}h^{-1} M_{\odot}$, $\alpha = 1.74 \pm 0.62$. For VT clusters, we find
$M_0 = (4.31 \pm 0.89) \times 10^{14}h^{-1} M_{\odot}$, $\alpha = 0.59 \pm
0.54$ and $M_0 = (3.67 \pm 0.56) \times 10^{14}h^{-1} M_{\odot}$, $\alpha =
0.68 \pm 0.49$ for a low and a high redshift bin, respectively. Our results are
consistent, internally and with the literature, indicating that our method can
be applied to any cluster finding algorithm. In particular, we recommend that
$\mu_{\star}$ be used as the mass proxy for VT clusters. Catalogs including
$\mu_{\star}$ measurements will enable its use in studies of galaxy evolution
in clusters and cluster cosmology. | Be It Unresolved: Measuring Time Delays from Lensed Supernovae: Gravitationally lensed Type Ia supernovae may be the next frontier in cosmic
probes, able to deliver independent constraints on dark energy, spatial
curvature, and the Hubble constant. Measurements of time delays between the
multiple images become more incisive due to the standardized candle nature of
the source, monitoring for months rather than years, and partial immunity to
microlensing. While currently extremely rare, hundreds of such systems should
be detected by upcoming time domain surveys. Even more will have the images
spatially unresolved, with the observed lightcurve a superposition of time
delayed image fluxes. We investigate whether unresolved images can be
recognized as lensed sources given only lightcurve information, and whether
time delays can be extracted robustly. We develop a method that successfully
identifies such systems, with a false positive rate of $\lesssim 5\%$, and
measures the time delays with a completeness of $\gtrsim 93\%$ and with a bias
of $\lesssim 0.5\%$ for $\Delta t_{\rm fit} \gtrsim 10$ days. |
Reconstructing the radial velocity profile of cosmic voids with
kinematic Sunyaev-Zeldovich Effect: We develop an estimator to extract the mean radial velocity profile of cosmic
voids via the kinematic Sunyaev-Zeldovich effect of pairs of galaxies
surrounding them. The estimator is tested with simulated pure kSZ map and void
catalogue data from the same simulation. The results show that the recovered
signal could be attenuated by low angular resolution of the map or large
aperture photometry filter radius size, but the mean radial velocity profile
can be fully recovered with our estimator. By applying the estimator to the
Planck 2D-ILC CMB map, with galaxy and void catalogues from BOSS DR12, we find
that the estimated void velocity profile is $3.31\sigma$ apart from null
detection for for voids with continuously rising density profiles asymptoting
to the mean density; and $1.75\sigma$ for voids with positive density contrast
shell surrounded. By fitting the reconstructed data to the theoretical profile,
we find the reduced $\chi^{2}$ to be $1.19$ and $0.62$ for the two types of
void, respectively, indicating a good fit of the model to the data. We then
forecast the detectability of the radial velocity profile of cosmic voids with
future CMB surveys, including SPT-3G, AdvACT, and Simons Observatory. We find
that the contamination effect from CMB residuals is negligible with survey area
over $2,000~{\rm deg}^2$, especially with aperture photometry size less than
$1\,{\rm arcmin}$. But the effect from instrumental noise is non-negligible.
For future SPT-3G, AdvACT and Simons Observatory, the detection is potentially
achievable from $3\sigma$ to $10\sigma$ C.L., depending on specific
instrumental parameters. This opens a new window of probing dynamics of the
cosmic structures from the kinematic Sunyaev-Zeldovich effect. | Imprints of Chameleon f(R) Gravity on Galaxy Rotation Curves: Current constraints on gravity are relatively weak on galactic and
intergalactic scales. Screened modified gravity models can exhibit complex
behaviour there without violating stringent tests of gravity within our Solar
System. They might hence provide viable extensions of the theory of gravity.
Here, we use galaxy kinematics to constrain screened modified gravity models.
We focus on chameleon $f(R)$ gravity and predict its impact on galaxy rotation
curves and radial acceleration relations. This is achieved by post-processing
state-of-the-art galaxy formation simulations from the \textsc{auriga project},
using the \textsc{mg-gadget} code. For a given galaxy, the surface dividing
screened and un-screened regions adopts an oblate shape, reflecting the disc
morphology of the galaxy's mass distribution. At the `screening radius'---the
radius at which screening is triggered in the disc plane---characteristic
`upturns' are present in both rotation curves and radial acceleration
relations. The locations of these features depend on various factors, such as
the galaxy mass, the concentration of the density profile and the value of the
background field amplitude $f_{R0}$. Self-screening of stars and environmental
screening also play a role. For Milky Way-size galaxies, we find that a model
with $|f_{R0}|=10^{-7}$ results in rotation curves that are indistinguishable
from $\Lambda$CDM, while for $|f_{R0}| \geq 2 \times 10^{-6}$ the simulated
galaxies are entirely unscreened, violating Solar System constraints. For
intermediate values, distinct upturns are present. With a careful statistical
analysis of existing samples of observed rotation curves, including lower mass
objects, constraints on $f(R)$ gravity with a sensitivity down to
$|f_{R0}|\sim10^{-7}$ should be possible. |
Herschel-ATLAS/GAMA: a difference between star-formation rates in
strong-line and weak-line radio galaxies: We have constructed a sample of radio-loud objects with optical spectroscopy
from the Galaxy and Mass Assembly (GAMA) project over the Herschel-ATLAS Phase
1 fields. Classifying the radio sources in terms of their optical spectra, we
find that strong-emission-line sources (`high-excitation radio galaxies') have,
on average, a factor ~4 higher 250-micron Herschel luminosity than weak-line
(`low-excitation') radio galaxies and are also more luminous than
magnitude-matched radio-quiet galaxies at the same redshift. Using all five
H-ATLAS bands, we show that this difference in luminosity between the
emission-line classes arises mostly from a difference in the average dust
temperature; strong-emission-line sources tend to have comparable dust masses
to, but higher dust temperatures than, radio galaxies with weak emission lines.
We interpret this as showing that radio galaxies with strong nuclear emission
lines are much more likely to be associated with star formation in their host
galaxy, although there is certainly not a one-to-one relationship between star
formation and strong-line AGN activity. The strong-line sources are estimated
to have star-formation rates at least a factor 3-4 higher than those in the
weak-line objects. Our conclusion is consistent with earlier work, generally
carried out using much smaller samples, and reinforces the general picture of
high-excitation radio galaxies as being located in lower-mass, less evolved
host galaxies than their low-excitation counterparts. | Alignments of parity even/odd-only multipoles in CMB: We compare the statistics of parity even and odd multipoles of the cosmic
microwave background (CMB) sky from PLANCK full mission temperature
measurements. An excess power in odd multipoles compared to even multipoles has
previously been found on large angular scales. Motivated by this apparent
parity asymmetry, we evaluate directional statistics associated with even
compared to odd multipoles, along with their significances. Primary tools are
the \emph{Power Tensor} and \emph{Alignment Tensor} statistics. We limit our
analysis to the first sixty multipoles i.e., $l=[2,61]$. We find no evidence
for statistically unusual alignments of even parity multipoles. More than one
independent statistic finds evidence for alignments of anisotropy axes of odd
multipoles, with a significance equivalent to $\sim 2 \sigma$ or more. The
robustness of alignment axes is tested by making galactic cuts and varying the
multipole range. Very interestingly, the region spanned by the (a)symmetry axes
is found to broadly contain other parity (a)symmetry axes previously observed
in the literature. |
The Sloan Digital Sky Survey Quasar Lens Search. VI. Constraints on Dark
Energy and the Evolution of Massive Galaxies: We present a statistical analysis of the final lens sample from the Sloan
Digital Sky Survey Quasar Lens Search (SQLS). The number distribution of a
complete subsample of 19 lensed quasars selected from 50,836 source quasars is
compared with theoretical expectations, with particular attention to the
selection function. Assuming that the velocity function of galaxies does not
evolve with redshift, the SQLS sample constrains the cosmological constant to
\Omega_\Lambda=0.79^{+0.06}_{-0.07}(stat.)^{+0.06}_{-0.06}(syst.) for a flat
universe. The dark energy equation of state is found to be consistent with w=-1
when the SQLS is combined with constraints from baryon acoustic oscillation
(BAO) measurements or results from the Wilkinson Microwave Anisotropy Probe
(WMAP). We also obtain simultaneous constraints on cosmological parameters and
redshift evolution of the galaxy velocity function, finding no evidence for
redshift evolution at z<1 in any combinations of constraints. For instance,
number density evolution quantified as \nu_n=d\ln\phi_*/d\ln(1+z) and the
velocity dispersion evolution \nu_\sigma=d\ln\sigma_*/d\ln(1+z) are constrained
to \nu_n=1.06^{+1.36}_{-1.39}(stat.)^{+0.33}_{-0.64}(syst.) and
\nu_\sigma=-0.05^{+0.19}_{-0.16}(stat.)^{+0.03}_{-0.03}(syst.) respectively
when the SQLS result is combined with BAO and WMAP for flat models with a
cosmological constant. We find that a significant amount of dark energy is
preferred even after fully marginalizing over the galaxy evolution parameters.
Thus the statistics of lensed quasars robustly confirm the accelerated cosmic
expansion. | An ALMA Survey of Submillimeter Galaxies in the Extended Chandra Deep
Field South: The Redshift Distribution and Evolution of Submillimeter
Galaxies: We present the first photometric redshift distribution for a large unbiased
sample of 870um selected submillimeter galaxies (SMGs) with robust
identifications based on observations with the Atacama Large Millimeter Array
(ALMA). In our analysis we consider 96 SMGs in the Extended Chandra Deep Field
South, 77 of which have 4-19 band, optical-near-infrared, photometry. We model
the Spectral Energy Distributions (SEDs) for these 77 SMGs, deriving a median
photometric redshift of z=2.3+/-0.1. The remaining 19 SMGs have insufficient
optical or near-infrared photometry to derive photometric redshifts, but a
stacking analysis of IRAC and Herschel observations confirms they are not
spurious. Assuming these sources have an absolute H-band magnitude distribution
comparable to that of a complete sample of z~1-2 SMGs, we demonstrate that the
undetected SMGs lie at higher redshifts, raising the median redshift for SMGs
to z=2.5+/-0.2. More critically we show that the proportion of galaxies
undergoing an SMG phase at z>3 is 35+/-5% of the total population. We derive a
median stellar mass for SMGs of Mstar=(8+/-1)x10^10Mo, but caution that there
are significant systematic uncertainties in our stellar mass estimate, up to x5
for individual sources. We compare our sample of SMGs to a volume-limited,
morphologically classified sample of ellipticals in the local Universe.
Assuming the star formation activity in SMGs has a timescale of ~100Myr we show
that their descendants at z~0 would have a space density and M_H distribution
which are in good agreement with those of local ellipticals. In addition the
inferred mass-weighted ages of the local ellipticals broadly agree with the
look-back times of the SMG events. Taken together, these results are consistent
with a simple model that identifies SMGs as events that form most of the stars
seen in the majority of luminous elliptical galaxies at the present day. |
Perturbation of FRW Spacetime in NP Formalism: Perturbation of FRW spacetime is carried out in NP formalism. The equation
governing the scalar, vector and tensor modes take on a very simple and
transparent form. All of them can be combined in one master equation for all
helicities. The solutions for the closed, flat and open FRW are analytic
continuation of the same functions, so only the solutions in the closed model
are described. The scalar equation is the same as that of the conformally
coupled massless Klein-Gordon field, the vectorial ones are the same as Maxwell
equations, and the tensorial ones are for spin-2 fields. The corresponding
eigen-functions are all determined, and in particular, the Green's function and
the Lienard-Wiechert type potential also solved. These solutions reduce to the
familiar form in flat space. | Stochastic gravitational waves from a new type of modified Chaplygin gas: We propose a new scenario for the early universe where there is a smooth
transition between an early de Sitter-like phase and a radiation dominated era.
In this model, the matter content is modelled by a new type of generalised
Chaplygin gas for the early universe, with an underlying scalar field
description. We study the gravitational waves generated by the quantum
fluctuations. In particular, we calculate the gravitational wave power
spectrum, as it would be measured today, following the method of the Bogoliubov
coefficients. We show that the high frequencies region of the spectrum depends
strongly on one of the parameters of the model. On the other hand, we use the
number of e-folds, along with the power spectra and spectral index of the
scalar perturbations, to constrain the model observationally. |
Iron in X-COP: tracing enrichment in cluster outskirts with high
accuracy abundance profiles: We present the first metal abundance profiles for a representative sample of
massive clusters. Our measures extend to $R_{500}$ and are corrected for a
systematic error plaguing previous outskirt estimates. Our profiles flatten out
at large radii, admittedly not a new result, however the radial range and
representative nature of our sample extends its import well beyond previous
findings. We find no evidence of segregation between cool-core and
non-cool-core systems beyond $\sim 0.3 R_{500}$, implying that, as was found
for thermodynamic properties (Ghirardini et al, 2019), the physical state of
the core does not affect global cluster properties. Our mean abundance within
$R_{500}$ shows a very modest scatter, $< $15%, suggesting the enrichment
process must be quite similar in all these massive systems. This is a new
finding and has significant implications on feedback processes. Together with
results from thermodynamic properties presented in a previous X-COP paper, it
affords a coherent picture where feedback effects do not vary significantly
from one system to another. By combing ICM with stellar measurements we have
found the amount of Fe diffused in the ICM to be about ten times higher than
that locked in stars. Although our estimates suggest, with some strength, that
the measured iron mass in clusters is well in excess of the predicted one,
systematic errors prevent us from making a definitive statement. Further
advancements will only be possible when systematic uncertainties, principally
those associated to stellar masses, both within and beyond $R_{500}$, can be
reduced. | The first magnetic fields in the universe: We show that the first structures that form in the universe should
spontaneously generate magnetic fields. No primordial seed field is required
for this "first dynamo".
Although the first dynamo starts with kinetic plasma instabilities, we argue
that an adequate magnetohydrodynamic description might be possible via a simple
trick. This should allow a numerical study of the effect of the first magnetic
fields on the first baryonic objects. |
Measuring turbulence and gas motions in galaxy clusters via synthetic
Athena X-IFU observations: The X-ray Integral Field Unit (X-IFU) that will be on board the Athena
telescope will provide an unprecedented view of the intracluster medium (ICM)
kinematics through the observation of gas velocity, $v$, and velocity
dispersion, $w$, via centroid-shift and broadening of emission lines,
respectively. The improvement of data quality and quantity requires an
assessment of the systematics associated with this new data analysis, namely
biases, statistical and systematic errors, and possible correlations between
the different measured quantities. We have developed an end-to-end X-IFU
simulator that mimics a full X-ray spectral fitting analysis on a set of mock
event lists, obtained using SIXTE. We have applied it to three hydrodynamical
simulations of a Coma-like cluster that include the injection of turbulence.
This allowed us to assess the ability of X-IFU to map five physical quantities
in the cluster core: emission measure, temperature, metal abundance, velocity
and velocity dispersion. Finally, starting from our measurements maps, we
computed the 2D structure function (SF) of emission measure fluctuations, $v$
and $w$ and compared them with those derived directly from the simulations. All
quantities match with the input projected values without bias; the systematic
errors were below 5%, except for velocity dispersion whose error reaches about
15%. Moreover, all measurements prove to be statistically independent,
indicating the robustness of the fitting method. Most importantly, we recover
the slope of the SFs in the inertial regime with excellent accuracy, but we
observe a systematic excess in the normalization of both SF$_v$ and SF$_w$
ascribed to the simplistic assumption of uniform and (bi-)Gaussian measurement
errors. Our work highlights the excellent capabilities of Athena X-IFU in
probing the thermodynamic and kinematic properties of the ICM. (abridged) | A Method for Measuring Variations in the Stellar Initial Mass Function: We present a method for investigating variations in the upper end of the
stellar Initial Mass Function (IMF) by probing the production rate of ionizing
photons in unresolved, compact star clusters with ages <~10 Myr and with
different masses. We test this method by performing a pilot study on the young
cluster population in the nearby galaxy NGC5194 (M51a), for which
multi-wavelength observations from the Hubble Space Telescope are available.
Our results indicate that the proposed method can probe the upper end of the
IMF in galaxies located out to at least ~10 Mpc, i.e., a factor ~200 further
away than possible by counting individual stars in young compact clusters. Our
results for NGC5194 show no obvious dependence of the upper mass end of the IMF
on the mass of the star cluster down to ~1000 M_sun, although more extensive
analyses involving lower mass clusters and other galaxies are needed to confirm
this conclusion. |
Cosmology with Hypervelocity Stars: In the standard cosmological model, the merger remnant of the Milky Way and
Andromeda (Milkomeda) will be the only galaxy remaining within our event
horizon once the Universe has aged by another factor of ten, ~10^{11} years
after the Big Bang. After that time, the only extragalactic sources of light in
the observable cosmic volume will be hypervelocity stars being ejected
continuously from Milkomeda. Spectroscopic detection of the velocity-distance
relation or the evolution in the Doppler shifts of these stars will allow a
precise measurement of the vacuum mass density as well as the local matter
distribution. Already in the near future, the next generation of large
telescopes will allow photometric detection of individual stars out to the edge
of the Local Group, and may target the ~10^{5+-1} hypervelocity stars that
originated in it as cosmological tracers. | Dark Energy with Phantom Crossing and the $H_0$ tension: We investigate the possibility of phantom crossing in the dark energy sector
and solution for the Hubble tension between early and late universe
observations. We use robust combinations of different cosmological
observations, namely the CMB, local measurement of Hubble constant ($H_0$), BAO
and SnIa for this purpose. For a combination of CMB+BAO data which is related
to early Universe physics, phantom crossing in the dark energy sector is
confirmed at $95$\% confidence level and we obtain the constraint
$H_0=71.0^{+2.9}_{-3.8}$ km/s/Mpc at 68\% confidence level which is in perfect
agreement with the local measurement by Riess et al. We show that constraints
from different combination of data are consistent with each other and all of
them are consistent with phantom crossing in the dark energy sector. For the
combination of all data considered, we obtain the constraint $H_0=70.25\pm
0.78$ km/s/Mpc at 68\% confidence level and the phantom crossing happening at
the scale factor $a_m=0.851^{+0.048}_{-0.031}$ at 68\% confidence level. |
The LoReLi database: 21 cm signal inference with 3D radiative
hydrodynamics simulations: The Square Kilometer array is expected to measure the 21cm signal from the
Epoch of Reionization (EoR) in the coming decade, and its pathfinders may
provide a statistical detection even earlier. The currently reported upper
limits provide tentative constraints on the astrophysical parameters of the
models of the EoR.
In order to interpret such data with 3D radiative hydrodynamics simulations
using Bayesian inference, we present the latest developments of the
\textsc{Licorice} code. Relying on an implementation of the halo conditional
mass function to account for unresolved star formation, this code now allows
accurate simulations of the EoR at $256^3$ resolution. We use this version of
\textsc{Licorice} to produce the first iteration of \textsc{LoReLi}, a public
dataset now containing hundreds of 21cm signals computed from radiative
hydrodynamics simulations. We train a neural network on \textsc{LoReLi} to
provide a fast emulator of the \textsc{Licorice} power spectra,
\textsc{LorEMU}, which has $\sim 5\%$ rms error relative to the simulated
signals. \textsc{LorEMU} is used in a Markov Chain Monte Carlo framework to
perform Bayesian inference, first on a mock observation composed of a simulated
signal and thermal noise corresponding to 100h observations with the SKA. We
then apply our inference pipeline to the latest measurements from the HERA
interferometer. We report constraints on the X-ray emissivity, and confirm that
cold reionization scenarios are unlikely to accurately represent our Universe. | There was movement that was stationary, for the four-velocity had passed
around: Is the Doppler interpretation of galaxy redshifts in a
Friedmann-Lemaitre-Robertson-Walker (FLRW) model valid in the context of the
approach to comoving spatial sections pioneered by de Sitter, Friedmann,
Lemaitre and Robertson, i.e. according to which the 3-manifold of comoving
space is characterised by both its curvature and topology? Holonomy
transformations for flat, spherical and hyperbolic FLRW spatial sections are
proposed. By quotienting a simply-connected FLRW spatial section by an
appropriate group of holonomy transformations, the Doppler interpretation in a
non-expanding Minkowski space-time, obtained via four-velocity parallel
transport along a photon path, is found to imply that an inertial observer is
receding from herself at a speed greater than zero, implying contradictory
world-lines. The contradiction in the multiply-connected case occurs for
arbitrary redshifts in the flat and spherical cases, and for certain large
redshifts in the hyperbolic case. The link between the Doppler interpretation
of redshifts and cosmic topology can be understood physically as the link
between parallel transport along a photon path and the fact that the comoving
spatial geodesic corresponding to a photon's path can be a closed loop in an
FLRW model of any curvature. Closed comoving spatial loops are fundamental to
cosmic topology. |
Parameterization of temperature and spectral distortions in future CMB
experiments: CMB spectral distortions are induced by Compton collisions with electrons. We
review the various schemes to characterize the anisotropic CMB with a
non-Planckian spectrum. We advocate using logarithmically averaged temperature
moments as the preferred language to describe these spectral distortions, both
for theoretical modeling and observations. Numerical modeling is simpler, the
moments are frame-independent, and in terms of scattering the mode truncation
is exact. | The SWELLS survey - V. A Salpeter stellar initial mass function in the
bulges of massive spiral galaxies: Recent work has suggested that the stellar initial mass function (IMF) is not
universal, but rather is correlated with galaxy stellar mass, stellar velocity
dispersion, or morphological type. In this paper, we investigate variations of
the IMF within individual galaxies. For this purpose, we use strong lensing and
gas kinematics to measure independently the normalisation of the IMF of the
bulge and disk components of a sample of 5 massive spiral galaxies with
substantial bulge components taken from the SWELLS survey. We find that the
stellar mass of the bulges are tightly constrained by the lensing and kinematic
data. A comparison with masses based on stellar population synthesis models
fitted to optical and near infrared photometry favors a Salpeter-like
normalisation of the IMF. Conversely, the disk masses are less well constrained
due to degeneracies with the dark matter halo, but are consistent with Milky
Way type IMFs in agreement with previous studies. The disks are submaximal at
2.2 disk scale lengths, but due to the contribution of the bulges, the galaxies
are baryon dominated at 2.2 disk scale lengths. Globally, our inferred IMF
normalisation is consistent with that found for early-type galaxies of
comparable stellar mass (> 10^11 M_sun). Our results suggest a non-universal
IMF within the different components of spiral galaxies, adding to the
well-known differences in stellar populations between disks and bulges. |
Effects of supermassive binary black holes on gravitational lenses: Recent observations indicate that many if not all galaxies host massive
central black holes (BHs). In this paper we explore the influence of
supermassive binary black holes (SMBBHs) on their actions as gravitational
lenses. When lenses are modelled as singular isothermal ellipsoids, binary
black holes change the critical curves and caustics differently as a function
of distance. Each black hole can in principle create at least one additional
image, which, if observed, provides evidence of black holes. By studying how
SMBBHs affect the cumulative distribution of magnification for images created
by black holes, we find that the cross section for at least one such additional
image to have a magnification larger than $10^{-5}$ is comparable to the cross
section for producing multiple-images in singular isothermal lenses. Such
additional images may be detectable with high-resolution and large dynamic
range maps of multiply-imaged systems from future facilities, such as the SKA.
The probability of detecting at least one image (two images) with magnification
above $10^{-3}$ is $\sim 0.2 \fBH$ ($\sim 0.05 \fBH$) in a multiply-imaged lens
system, where $\fBH$ is the fraction of galaxies housing binary black holes. We
also study the effects of SMBBHs on the core images when galaxies have
shallower central density profiles (modelled as non-singular isothermal
ellipsoids). We find that the cross section of the usually faint core images is
further suppressed by SMBBHs. Thus their presence should also be taken into
account when one constrains the core radius from the lack of central images in
gravitational lenses. | On the relative abundance of LiH and LiH+ molecules in the early
universe: new results from quantum reactions: The relative efficiencies of the chemical pathways that can lead to the
destruction of LiH and LiH+ molecules, conjectured to be present in the
primordial gas and to control molecular cooling processes in the gravitational
collapse of the post-recombination era, are revisited by using accurate quantum
calculations for the several reactions involved. The new rates are employed to
survey the behavior of the relative abundance of these molecules at redshifts
of interest for early universe conditions. We find significant differences with
respect to previous calculations, the present ones yielding LIH abundances
higher than LiH+ at all redshifts. |
Nonlinear power spectrum in clustering and smooth dark energy models
beyond the BAO scale: We study the nonlinear effects of the clustering and smooth quintessence. We
present numerical and also approximate semi-analytical expressions of nonlinear
power spectrum both for clustering and smooth dark energy models beyond the
Baryon Acoustic Oscillations (BAO) scale. This approximation is motivated by
the extension of the resummation method of Anselmi $\&$ Pietroni (J Cosmol
Astro-Part Phys 12:13, 2012. \url{arXiv:1205.2235}) for the dark energy models
with evolving equation of state. The results of this scheme allow us for the
prediction of the nonlinear power spectrum in the mildly nonlinear regime up to
few percentage accuracies compared to the other available tools to compute the
nonlinear power spectrum for the evolving dark energy models. | Uncovering Mass Segregation with Galaxy Analogues in Dark Matter
Simulations: We investigate mass segregation in group and cluster environments by
identifying galaxy analogues in high-resolution dark matter simulations.
Subhalos identified by the AHF and ROCKSTAR halo finders have similar mass
functions, independent of resolution, but different radial distributions due to
significantly different subhalo hierarchies. We propose a simple way to
classify subhalos as galaxy analogues. The radial distributions of galaxy
analogues agree well at large halo-centric radii for both AHF and ROCKSTAR but
disagree near parent halo centres where the phase-space information used by
ROCKSTAR is essential.
We see clear mass segregation at small radii (within $0.5\,r_{vir}$) with
average galaxy analogue mass decreasing with radius. Beyond the virial radius,
we find a mild trend where the average galaxy analogue mass increases with
radius. These mass segregation trends are strongest in small groups and
dominated by the segregation of low mass analogues. The lack of mass
segregation in massive galaxy analogues suggests that the observed trends are
driven by the complex accretion histories of the parent halos rather than
dynamical friction. |
The Space Density of Compton Thick AGN and the X-ray Background: We constrain the number density and evolution of Compton-thick Active
Galactic Nuclei (AGN). In the local Universe we use the wide area surveys from
the Swift and INTEGRAL satellites, while for high redshifts we explore
candidate selections based on a combination of X-ray and mid-IR parameters. We
find a significantly lower space density of Compton-thick AGN in the local
Universe than expected from published AGN population synthesis models to
explain the X-ray background. This can be explained by the numerous
degeneracies in the parameters of those models; we use the high-energy surveys
described here to remove those degeneracies. We show that only direct
observations of CT AGN can currently constrain the number of heavily-obscured
supermassive black holes. At high redshift, the inclusion of IR-selected
Compton-thick AGN candidates leads to a much higher space density, implying (a)
a different (steeper) evolution for these sources compared to less-obscured
AGN, (b) that the IR selection includes a large number of interlopers, and/or
(c) that there is a large number of reflection-dominated AGN missed in the
INTEGRAL and Swift observations. The contribution of CT AGN to the X-ray
background is small, ~9%, with a comparable contribution to the total cosmic
accretion, unless reflection-dominated CT AGN significantly outnumber
transmission-dominated CT AGN, in which case their contribution can be much
higher. Using estimates derived here for the accretion luminosity over cosmic
time we estimate the local mass density in supermassive black holes and find a
good agreement with available constraints for an accretion efficiency of ~10%.
Transmission-dominated CT AGN contribute only ~8% to total black hole growth. | CMB Constraints on Reheating Models with Varying Equation of State: The temperature at the end of reheating and the length of this cosmological
phase can be bound to the inflationary observables if one considers the
cosmological evolution from the time of Hubble crossing until today. There are
many examples in the literature where it is made for single-field inflationary
models and a constant equation of state during reheating. We adopt two simple
varying equation of state parameters during reheating, combine the allowed
range of the reheating parameters with the observational limits of the scalar
perturbations spectral index and compare the constraints of some inflationary
models with the case of a constant equation of state parameter during
reheating. |
Measuring the Reduced Shear: Neglecting the second order corrections in weak lensing measurements can lead
to a few percent uncertainties on cosmic shears, and becomes more important for
cluster lensing mass reconstructions. Existing methods which claim to measure
the reduced shears are not necessarily accurate to the second order when a
point spread function (PSF) is present. We show that the method of Zhang (2008)
exactly measures the reduced shears at the second order level in the presence
of PSF. A simple theorem is provided for further confirming our calculation,
and for judging the accuracy of any shear measurement method at the second
order based on its properties at the first order. The method of Zhang (2008) is
well defined mathematically. It does not require assumptions on the
morphologies of galaxies and the PSF. To reach a sub-percent level accuracy,
the CCD pixel size is required to be not larger than 1/3 of the Full Width at
Half Maximum (FWHM) of the PSF. Using a large ensemble (> 10^7) of mock
galaxies of unrestricted morphologies, we find that contaminations to the shear
signals from the noise of background photons can be removed in a well defined
way because they are not correlated with the source shapes. The residual shear
measurement errors due to background noise are consistent with zero at the
sub-percent level even when the amplitude of such noise reaches about 1/10 of
the source flux within the half-light radius of the source. This limit can in
principle be extended further with a larger galaxy ensemble in our simulations.
On the other hand, the source Poisson noise remains to be a cause of systematic
errors. For a sub-percent level accuracy, our method requires the amplitude of
the source Poisson noise to be less than 1/80 ~ 1/100 of the source flux within
the half-light radius of the source, corresponding to collecting roughly 10^4
source photons. | Regularizing made-to-measure particle models of galaxies: Made-to-measure methods such as the parallel code NMAGIC are powerful tools
to build galaxy models reproducing observational data. They work by adapting
the particle weights in an N-body system until the target observables are well
matched. Here we introduce a moving prior regularization (MPR) method for such
particle models. It is based on determining from the particles a distribution
of priors in phase-space, which are updated in parallel with the weight
adaptation. This method allows one to construct smooth models from noisy data
without erasing global phase-space gradients. We first apply MPR to a spherical
system for which the distribution function can in theory be uniquely recovered
from idealized data. We show that NMAGIC with MPR indeed converges to the true
solution with very good accuracy, independent of the initial particle model.
Compared to the standard weight entropy regularization, biases in the
anisotropy structure are removed and local fluctuations in the intrinsic
distribution function are reduced. We then investigate how the uncertainties in
the inferred dynamical structure increase with less complete and noisier
kinematic data, and how the dependence on the initial particle model also
increases. Finally, we apply the MPR technique to the two
intermediate-luminosity elliptical galaxies NGC 4697 and NGC 3379, obtaining
smoother dynamical models in luminous and dark matter potentials. |
Cosmological Model-independent Gamma-ray Bursts Calibration and its
Cosmological Constraint to Dark Energy: As so far, the redshift of Gamma-ray bursts (GRBs) can extend to $z\sim 8$
which makes it as a complementary probe of dark energy to supernova Ia (SN Ia).
However, the calibration of GRBs is still a big challenge when they are used to
constrain cosmological models. Though, the absolute magnitude of GRBs is still
unknown, the slopes of GRBs correlations can be used as a useful constraint to
dark energy in a completely cosmological model independent way. In this paper,
we follow Wang's model-independent distance measurement method and calculate
their values by using 109 GRBs events via the so-called Amati relation. Then,
we use the obtained model-independent distances to constrain $\Lambda$CDM model
as an example. | Galaxy Clusters Discovered via the Sunyaev-Zel'dovich Effect in the
2500-square-degree SPT-SZ survey: We present a catalog of galaxy clusters selected via their Sunyaev-Zel'dovich
(SZ) effect signature from 2500 deg$^2$ of South Pole Telescope (SPT) data.
This work represents the complete sample of clusters detected at high
significance in the 2500-square-degree SPT-SZ survey, which was completed in
2011. A total of 677 (409) cluster candidates are identified above a
signal-to-noise threshold of $\xi$ =4.5 (5.0). Ground- and space-based optical
and near-infrared (NIR) imaging confirms overdensities of similarly colored
galaxies in the direction of 516 (or 76%) of the $\xi$>4.5 candidates and 387
(or 95%) of the $\xi$>5 candidates; the measured purity is consistent with
expectations from simulations. Of these confirmed clusters, 415 were first
identified in SPT data, including 251 new discoveries reported in this work. We
estimate photometric redshifts for all candidates with identified optical
and/or NIR counterparts; we additionally report redshifts derived from
spectroscopic observations for 141 of these systems. The mass threshold of the
catalog is roughly independent of redshift above $z$~0.25 leading to a sample
of massive clusters that extends to high redshift. The median mass of the
sample is $M_{\scriptsize 500c}(\rho_\mathrm{crit})$ ~ 3.5 x 10$^{14} M_\odot
h^{-1}$, the median redshift is $z_{med}$ =0.55, and the highest-redshift
systems are at $z$>1.4. The combination of large redshift extent, clean
selection, and high typical mass makes this cluster sample of particular
interest for cosmological analyses and studies of cluster formation and
evolution. |
On the Origin of the Galaxy Star-Formation-Rate Sequence: Evolution and
Scatter: We use a semi-analytic model for disk galaxies to explore the origin of the
time evolution and small scatter of the galaxy SFR sequence -- the tight
correlation between star-formation rate (SFR) and stellar mass (M_star). The
steep decline of SFR from z~2 to the present, at fixed M_star, is a consequence
of the following: First, disk galaxies are in a steady state with the SFR
following the net (i.e., inflow minus outflow) gas accretion rate. The
evolution of the SFR sequence is determined by evolution in the cosmological
specific accretion rates, \propto (1+z)^{2.25}, but is found to be independent
of feedback. Although feedback determines the outflow rates, it shifts galaxies
along the SFR sequence, leaving its zero point invariant. Second, the
conversion of accretion rate to SFR is materialized through gas density, not
gas mass. Although the model SFR is an increasing function of both gas mass
fraction and gas density, only the gas densities are predicted to evolve
significantly with redshift. Third, star formation is fueled by molecular gas.
Since the molecular gas fraction increases monotonically with increasing gas
density, the model predicts strong evolution in the molecular gas fractions,
increasing by an order of magnitude from z=0 to z~2. On the other hand, the
model predicts that the effective surface density of atomic gas is ~10 M_sun
pc^{-2}, independent of redshift, stellar mass or feedback. Our model suggests
that the scatter in the SFR sequence reflects variations in the gas accretion
history, and thus is insensitive to stellar mass, redshift or feedback. The
large scatter in halo spin contributes negligibly, because it scatters galaxies
along the SFR sequence. An observational consequence of this is that the
scatter in the SFR sequence is independent of the size (both stellar and
gaseous) of galaxy disks. | YOLO-CL: Galaxy cluster detection in the SDSS with deep machine learning: (Abridged) Galaxy clusters are a powerful probe of cosmological models. Next
generation large-scale optical and infrared surveys will reach unprecedented
depths over large areas and require highly complete and pure cluster catalogs,
with a well defined selection function. We have developed a new cluster
detection algorithm YOLO-CL, which is a modified version of the
state-of-the-art object detection deep convolutional network YOLO, optimized
for the detection of galaxy clusters. We trained YOLO-CL on color images of the
redMaPPer cluster detections in the SDSS. We find that YOLO-CL detects
$95-98\%$ of the redMaPPer clusters, with a purity of $95-98\%$ calculated by
applying the network to SDSS blank fields. When compared to the MCXC2021 X-ray
catalog in the SDSS footprint,YOLO-CL is more complete then redMaPPer, which
means that the neural network improved the cluster detection efficiency of its
training sample. The YOLO-CL selection function is approximately constant with
redshift, with respect to the MCXC2021 cluster mean X-ray surface brightness.
YOLO-CL shows high performance when compared to traditional detection
algorithms applied to SDSS. Deep learning networks benefit from a strong
advantage over traditional galaxy cluster detection techniques because they do
not need galaxy photometric and photometric redshift catalogs. This eliminates
systematic uncertainties that can be introduced during source detection, and
photometry and photometric redshift measurements. Our results show that YOLO-CL
is an efficient alternative to traditional cluster detection methods. In
general, this work shows that it is worth exploring the performance of deep
convolution networks for future cosmological cluster surveys, such as the
Rubin/LSST, Euclid or the Roman Space Telescope surveys. |
JWST lensed quasar dark matter survey I: Description and First Results: The flux ratios of gravitationally lensed quasars provide a powerful probe of
the nature of dark matter. Importantly, these ratios are sensitive to
small-scale structure, irrespective of the presence of baryons. This
sensitivity may allow us to study the halo mass function even below the scales
where galaxies form observable stars. For accurate measurements, it is
essential that the quasar's light is emitted from a physical region of the
quasar with an angular scale of milli-arcseconds or larger; this minimizes
microlensing effects by stars within the deflector. The warm dust region of
quasars fits this criterion, as it has parsec-size physical scales and
dominates the spectral energy distribution of quasars at wavelengths greater
than 10$\mu$m. The JWST Mid-Infrared Instrument (MIRI) is adept at detecting
redshifted light in this wavelength range, offering both the spatial resolution
and sensitivity required for accurate gravitational lensing flux ratio
measurements. Here, we introduce our survey designed to measure the warm dust
flux ratios of 31 lensed quasars. We discuss the flux-ratio measurement
technique and present results for the first target, DES J0405-3308. We find
that we can measure the quasar warm dust flux ratios with 3% precision. Our
simulations suggest that this precision makes it feasible to detect the
presence of 10$^7$ M$_\odot$ dark matter halos at cosmological distances. Such
halos are expected to be completely dark in Cold Dark Matter models. | Co-evolution of AGN and Star-forming Galaxies in the Australia Telescope
Large Area Survey: ATLAS (Australia Telescope Large Area Survey) is a wide deep radio survey
which is distinguished by its comprehensive multi-wavelength approach. ATLAS is
creating a large dataset of radio-selected galaxies for studying the evolution
and inter-relationship of star-forming and active galaxies. Although the
project is far from complete, we are already starting to answer some of these
questions, and have stumbled across three surprises along the way: * FRI/FRII
radio-loud AGN embedded within spiral galaxies, * radio-bright AGN which are
unexpectedly faint in the infrared, and which may be at high redshift *
IR-luminous radio-quiet AGN which are partly responsible for the wide
variations in reported values of the radio-infrared ratio These and other
observations suggest that the AGN activity and star formation become
increasingly inter-dependent at high redshifts. |
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