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Propagating Speed of Primordial Gravitational Waves: Primordial Gravitational Waves, i.e. a background of metric perturbations
sourced by the quantum inflationary fluctuations, if measured, could both
provide a substantial evidence for primordial inflation and shed light on
physics at extremely high energy scales. In this work we focus on their
propagating speed. Using an effective field theory approach we introduce a
time-dependent propagating speed $c_{\rm T}(t)$ showing that also small
deviations from the General Relativity (GR) prediction $c_{\rm T}(t) = c$ can
lead to testable consequences. We derive a set of equations that relate the
propagating speed and its time dependence to the inflationary parameters and
that generalize the usual slow roll consistency relations. Imposing the new
generalized consistency relations and combining small and large scales data, we
derive model independent constraints on inflation with non-trivial primordial
tensor speed. In particular we constrain its scale dependence to be $d\log
c_{\rm T} / d\log k=0.082^{+0.047}_{-0.11}$ at 68% C.L. while we only derive
the lower bound $c_{\rm T}>0.22\,c$ at 95% C.L. . We also constrain the
tensor-to-scalar ratio at the pivot scale $k_*=0.05\rm{Mpc}^{-1}$ to be
$r<0.0599$ at 95% C.L. in agreement with the result provided by the Planck
collaboration. Thanks to a proper small scale parameterization of the tensor
spectrum we derive stringent constraints on the tensor tilt $n_{\rm
T}=-0.084^{+0.10}_{-0.047}$ at 68% C.L. and on its runnings $\alpha_{\rm
T}=d\,n_{\rm T}/d\log k=0.0141^{+0.0035}_{-0.021}$ and $\beta_{\rm
T}=d\,\alpha_{\rm T}/d\log k= -0.0061^{+0.010}_{-0.0014}$ both at 68% C.L. Our
results show a remarkable agreement with the standard slow roll predictions and
prove that current data can significantly constrain deviations from GR on the
inflationary energy scales. | astro-ph_CO |
Cosmological constraints on the velocity-dependent baryon-dark matter
coupling: We present the cosmological constraints on the cross section of baryon-dark
matter interactions for the dark matter mass below the MeV scale from the
Planck CMB (cosmic microwave background) and SDSS (Sloan Digital Sky Survey)
Lyman-$\alpha$ forest data. To explore the dark matter mass $m_{\chi}\lesssim
1$ MeV for which the dark matter's free-streaming effect can suppress the
observable small scale density fluctuations, in addition to the acoustic
oscillation damping in existence of the baryon-dark matter coupling, we apply
the approximated treatment of dark matter free-streaming analogous to that of
the conventional warm dark matter. We also demonstrate the mass dependence of
the baryon-dark matter cross section bounds (for the dark matter mass down to
$m_{\chi} \sim 5~{\rm keV}$), in contrast to the dark matter mass independence
of the cross section constraints for the light dark matter below the MeV scale
claimed in the previous literature. | astro-ph_CO |
On the apparent absence of broad iron lines in Seyfert galaxies: We present an analysis of XMM-Newton observations of eleven Seyfert galaxies
that appear to be missing a broad iron K alpha line. These objects represent a
challenge to the established paradigm for active galactic nuclei, where a
relatively cold accretion disc feeds the central black hole. In that paradigm,
X-ray illumination of the accretion disc should lead to continuum and
fluorescence emission from iron which is broadened and shifted by relativistic
effects close the hole. We extend the work of Nandra et al. (2007), who found
no evidence for such a component in an earlier analysis of these objects, by
testing a variety of more complex relativistic reflection models. Specifically,
we consider the possibility that the disc is highly ionised, and/or that the
the reflection is heavily blurred by strong relativistic effects in a Kerr
geometry. We find that in 8/11 of the observations with no apparent broad iron
line, the fit is significantly improved when an ionised or strongly blurred
reflector is included, and that all 11 observations allow for such a component.
The disc inclinations are found generally to be around 60 degrees, which when
combined with a steep emissivity profile results in strong relativistic
blurring of the reflection, rendering the K alpha line difficult to distinguish
from the underlying continuum. Nevertheless, relativistic reflection does
appear to be present, and the strength of the smeared reflection is similar to
that expected from a flat disc illuminated by a point source. Such blurred
reflection and the associated steep radial emissivity profiles are consistent
with the gravitational light bending of the continuum photons close to the
black hole. | astro-ph_CO |
Gravitational lensing effects on sub-millimetre galaxy counts: We study the effects on the number counts of sub-millimetre galaxies due to
gravitational lensing. We explore the effects on the magnification cross
section due to halo density profiles, ellipticity and cosmological parameter
(the power-spectrum normalisation $\sigma_8$). We show that the ellipticity
does not strongly affect the magnification cross section in gravitational
lensing while the halo radial profiles do. Since the baryonic cooling effect is
stronger in galaxies than clusters, galactic haloes are more concentrated. In
light of this, a new scenario of two halo population model is explored where
galaxies are modeled as a singular isothermal sphere profile and clusters as a
Navarro, Frenk and White (NFW) profile. We find the transition mass between the
two has modest effects on the lensing probability. The cosmological parameter
$\sigma_8$ alters the abundance of haloes and therefore affects our results.
Compared with other methods, our model is simpler and more realistic. The
conclusions of previous works is confirm that gravitational lensing is a
natural explanation for the number count excess at the bright end. | astro-ph_CO |
A fast and accurate method to compute the mass return from multiple
stellar populations: The mass returned to the ambient medium by aging stellar populations over
cosmological times sums up to a significant fraction (20% - 30% or more) of
their initial mass. This continuous mass injection plays a fundamental role in
phenomena such as galaxy formation and evolution, fueling of supermassive black
holes in galaxies and the consequent (negative and positive) feedback
phenomena, and the origin of multiple stellar populations in globular clusters.
In numerical simulations the calculation of the mass return can be time
consuming, since it requires at each time step the evaluation of a convolution
integral over the whole star formation history, so the computational time
increases quadratically with the number of time-steps. The situation can be
especially critical in hydrodynamical simulations, where different grid points
are characterized by different star formation histories, and the gas cooling
and heating times are shorter by orders of magnitude than the characteristic
stellar lifetimes. In this paper we present a fast and accurate method to
compute the mass return from stellar populations undergoing arbitrarily
complicated star formation histories. At each time-step the mass return is
calculated from its value at the previous time, and the star formation rate
over the last time-step only. Therefore in the new scheme there is no need to
store the whole star formation history, and the computational time increases
linearly with the number of time-steps. | astro-ph_CO |
The origin of dispersion in DLA metallicities: Recent chemical abundance measurements of damped Ly-alpha absorbers (DLAs)
revealed an intrinsic scatter in their metallicity of ~0.5 dex out to z~5. In
order to explore the origin of this scatter, we build a semi-analytic model
which traces the chemical evolution of the interstellar matter in small regions
of the Universe with different mean density, from over- to underdense regions.
We show that the different histories of structure formation in these regions,
namely halo abundance, mass and stellar content, is reflected in the chemical
properties of the protogalaxies, and in particular of DLAs. We calculate mean
metallicity-redshift relations and show that the metallicity dispersion arising
from this environmental effect amounts to ~0.25 dex and is an important
contributor to the observed overall intrinsic scatter. | astro-ph_CO |
Isotropy of low redshift type Ia Supernovae: A Bayesian analysis: The standard cosmology strongly relies upon the Cosmological Principle, which
consists on the hypotheses of large scale isotropy and homogeneity of the
Universe. Testing these assumptions is, therefore, crucial to determining if
there are deviations from the standard cosmological paradigm. In this paper, we
use the latest type Ia supernova compilations, namely JLA and Union2.1 to test
the cosmological isotropy at low redshift ranges ($z<0.1$). This is performed
through a Bayesian selection analysis, in which we compare the standard,
isotropic model, with another one including a dipole correction due to peculiar
velocities. We find that the Union2.1 sample favors the dipole-corrected model,
but the opposite happens for the JLA. Nonetheless, the velocity dipole results
are in good agreement with previous analyses carried out with both datasets. We
conclude that there are no significant indications for large anisotropic
signals from nearby supernova compilations, albeit this test should be greatly
improved with the upcoming cosmological surveys. | astro-ph_CO |
Optimal filtering of optical and weak lensing data to search for galaxy
clusters: application to the COSMOS field: Galaxy clusters are usually detected in blind optical surveys via suitable
filtering methods. We present an optimal matched filter which maximizes their
signal-to-noise ratio by taking advantage of the knowledge we have of their
intrinsic physical properties and of the data noise properties. In this paper
we restrict our application to galaxy magnitudes, positions and photometric
redshifts if available, and we also apply the filter separately to weak lensing
data. The method is suitable to be naturally extended to a multi-band approach
which could include not only additional optical bands but also observables with
different nature such as X-rays. For each detection, the filter provides its
significance, an estimate for the richness and for the redshift even if photo-z
are not given. The provided analytical error estimate is tested against
numerical simulations. We finally apply our method to the COSMOS field and
compare the results with previous cluster detections obtained with different
methods. Our catalogue contains 27 galaxy clusters with minimal threshold at
3-sigma level including both optical and weak-lensing information. | astro-ph_CO |
Clusters in the Disperse cosmic web: Galaxy cluster mass halos ("clusters") in a dark matter simulation are
matched to nodes in several different cosmic webs found using the Disperse
cosmic web finder. The webs have different simulation smoothings and Disperse
parameter choices; for each, 4 methods are considered for matching Disperse
nodes to clusters. For most of the webs, Disperse nodes outnumber clusters, but
not every cluster has a Disperse node match (and sometimes $>1$ cluster matches
to the same Disperse node). The clusters frequently lacking a matching Disperse
node have a different distribution of local shear trends and perhaps merger
histories. It might be interesting to see in what other ways, e.g.,
observational properties, these clusters differ. For the webs with smoothing
$\leq$ 2.5 $Mpc/h$, and all but the most restrictive matching criterion,
$\sim$3/4 of the clusters always have a Disperse node counterpart. The nearest
cluster to a given Disperse node and vice versa, within twice the smoothing
length, obey a cluster mass-Disperse node density relation. Cluster pairs where
both clusters match Disperse nodes can also be assigned the filaments between
those nodes, but as the web and matching methods are varied, most such
filaments do not remain. There is an enhancement of subhalo counts and halo
mass between cluster pairs, averaging over cluster pairs assigned Disperse
filaments increases the enhancement. The approach here also lends itself to
comparing nodes across many cosmic web constructions, using the fixed
underlying cluster distribution to make a correspondence. | astro-ph_CO |
Extraterrestrial Axion Search with the Breakthrough Listen Galactic
Center Survey: Axion dark matter (DM) may efficiently convert to photons in the
magnetospheres of neutron stars (NSs), producing nearly monochromatic radio
emission. This process is resonantly triggered when the plasma frequency
induced by the underlying charge distribution approximately matches the axion
mass. We search for evidence of this process using archival Green Bank
Telescope data collected in a survey of the Galactic Center in the C-Band by
the Breakthrough Listen project. While Breakthrough Listen aims to find
signatures of extraterrestrial life in the radio band, we show that their
high-frequency resolution spectral data of the Galactic Center region is ideal
for searching for axion-photon transitions generated by the population of NSs
in the inner pc of the Galaxy. We use data-driven models to capture the
distributions and properties of NSs in the inner Galaxy and compute the
expected radio flux from each NS using state-of-the-art ray tracing
simulations. We find no evidence for axion DM and set leading constraints on
the axion-photon coupling, excluding values down to the level $g_{a \gamma
\gamma} \sim 10^{-11}$ GeV$^{-1}$ for DM axions for masses between 15 and 35
$\mu$eV. | astro-ph_CO |
Is $w \neq -1$ evidence for a dynamical dark energy equation of state ?: Current constraints on the dark energy equation of state parameter, $w$, are
expected to be improved by more than one order of magnitude in the next decade.
If $|w-1| \gsim 0.01$ around the present time, but the dark energy dynamics is
sufficiently slow, it is possible that future constraints will rule out a
cosmological constant while being consistent with a time-independent equation
of state parameter. In this paper, we show that although models with such
behavior can be constructed, they do require significant fine-tuning.
Therefore, if the observed acceleration of the Universe is induced by a dark
energy component, then finding $w \neq -1$ would, on its own, constitute very
strong evidence for a dynamical dark energy equation of state. | astro-ph_CO |
Does a 'stochastic' background of gravitational waves exist in the
pulsar timing band?: We investigate the effects of gravitational waves (GWs) from a simulated
population of binary super-massive black holes (SMBHs) on pulsar timing array
datasets. We construct a distribution describing the binary SMBH population
from an existing semi-analytic galaxy formation model. Using realizations of
the binary SMBH population generated from this distribution, we simulate pulsar
timing datasets with GW-induced variations. We find that the statistics of
these variations do not correspond to an isotropic, stochastic GW background.
The "Hellings & Downs" correlations between simulated datasets for different
pulsars are recovered on average, though the scatter of the correlation
estimates is greater than expected for an isotropic, stochastic GW background.
These results are attributable to the fact that just a few GW sources dominate
the GW-induced variations in every Fourier frequency bin of a 5-year dataset.
Current constraints on the amplitude of the GW signal from binary SMBHs will be
biased. Individual binary systems are likely to be detectable in 5-year pulsar
timing array datasets where the noise is dominated by GW-induced variations.
Searches for GWs in pulsar timing array data therefore need to account for the
effects of individual sources of GWs. | astro-ph_CO |
Scale-invariant enhancement of gravitational waves during inflation: The inflationary 1-loop tensor power spectrum from an excited spectator
scalar field is calculated. Recent studies on primordial black holes suggest
that the inflationary curvature perturbation may be huge on small scales. An
enhanced curvature perturbation may arise from a drastic enhancement of
spectator scalar field fluctuations. In this letter, using the in-in formalism,
we calculate 1-loop quantum corrections to primordial gravitational waves by
such an excited spectator field with a sharp peak in momentum space. We find
scale-invariant loop corrections in this full quantum setup, in contrast to the
sharply peaked corrections in the previously calculated scalar-induced tensor
modes. Especially, on super Hubble scales, the primordial gravitational waves
are also amplified, which can be understood as a Bogolyubov transformation of
the vacuum due to the excited scalar field. This mechanism allows us to probe
the scalar field properties on extremely short-distance scales with the current
and future cosmic microwave background and gravitational wave experiments,
opening a novel window for inflationary cosmology. | astro-ph_CO |
Witnessing the Formation of a Brightest Cluster Galaxy in a Nearby X-ray
Cluster: The central dominant galaxies in galaxy clusters constitute the most massive
and luminous galaxies in the Universe. Despite this, the formation of these
brightest cluster galaxies (BCGs) and the impact of this on the surrounding
cluster environment remain poorly understood. Here we present multi-wavelength
observations of the nearby poor X-ray cluster MZ 10451, in which both processes
can be studied in unprecedented detail. Chandra observations of the
intracluster medium (ICM) in the cluster core, which harbors two optically
bright early-type galaxies in the process of merging, show that the system has
retained a cool core and a central metal excess. This suggests that any
merger-induced ICM heating and mixing remain modest at this stage. Tidally
stripped stars seen around either galaxy likely represent an emerging
intracluster light component, and the central ICM abundance enhancement may
have a prominent contribution from in situ enrichment provided by these stars.
The smaller of the merging galaxies shows evidence for having retained a hot
gas halo, along with tentative evidence for some obscured star formation,
suggesting that not all BCG major mergers at low redshift are completely
dissipationless. Both galaxies are slightly offset from the peak of the ICM
emission, with all three lying on an axis that roughly coincides with the
large-scale elongation of the ICM. Our data are consistent with a picture in
which central BCGs are built up by mergers close to the cluster core, by
galaxies infalling on radial orbits aligned with the cosmological filaments
feeding the cluster. | astro-ph_CO |
The Cosmic Web of Baryons: Only about 10% of the baryons in the universe lie in galaxies as stars or
cold gas, with the remainder predicted to exist as a dilute gaseous filamentary
network known as the Cosmic Web. Some of this gas is detected through UV
absorption line studies, but half of the gas remains undetected. Growth of
structure simulations suggest that these "missing" baryons were shock heated in
unvirialized cosmic filaments to temperatures of 10^5.5-10^7 K, and that the
gas is chemically enriched by galactic superwinds. Most of the gas in this
temperature regime can be detected only by X-ray observations through
absorption and emission from the He-like and H-line ions of C, N, and O. This
white paper shows that an X-ray telescope such as IXO can test the most central
predictions of the Cosmic Web: the distribution of gas mass with temperature;
the dynamics of the gas and its relationship to nearby galaxies; and the
topology of the Cosmic Web material. | astro-ph_CO |
Mass-radius relation of Newtonian self-gravitating Bose-Einstein
condensates with short-range interactions: II. Numerical results: We develop the suggestion that dark matter could be a Bose-Einstein
condensate. We determine the mass-radius relation of a Newtonian
self-gravitating Bose-Einstein condensate with short-range interactions
described by the Gross-Pitaevskii-Poisson system. We numerically solve the
equation of hydrostatic equilibrium describing the balance between the
gravitational attraction and the pressure due to quantum effects (Heisenberg's
uncertainty principle) and short-range interactions (scattering). We connect
the non-interacting limit to the Thomas-Fermi limit. We also consider the case
of attractive self-interaction. We compare the exact mass-radius relation
obtained numerically with the approximate analytical relation obtained with a
Gaussian ansatz. An overall good agreement is found. | astro-ph_CO |
Primordial non-gaussianity from the bispectrum of 21-cm fluctuations in
the dark ages: A measurement of primordial non-gaussianity will be of paramount importance
to distinguish between different models of inflation. Cosmic microwave
background (CMB) anisotropy observations have set unprecedented bounds on the
non-gaussianity parameter f_NL but the interesting regime f_NL <~ 1 is beyond
their reach. Brightness-temperature fluctuations in the 21-cm line during the
dark ages (z ~ 30-100) are a promising successor to CMB studies, giving access
to a much larger number of modes. They are, however, intrinsically non-linear,
which results in secondary non-gaussianities orders of magnitude larger than
the sought-after primordial signal. In this paper we carefully compute the
primary and secondary bispectra of 21-cm fluctuations on small scales. We use
the flat-sky formalism, which greatly simplifies the analysis, while still
being very accurate on small angular scales. We show that the secondary
bispectrum is highly degenerate with the primordial one, and argue that even
percent-level uncertainties in the amplitude of the former lead to a bias of
order Delta f_NL ~ 10. To tackle this problem we carry out a detailed Fisher
analysis, marginalizing over the amplitudes of a few smooth redshift-dependent
coefficients characterizing the secondary bispectrum. We find that the
signal-to-noise ratio for a single redshift slice is reduced by a factor of ~5
in comparison to a case without secondary non-gaussianities. Setting aside
foreground contamination, we forecast that a cosmic-variance-limited experiment
observing 21-cm fluctuations over 30 < z < 100 with a 0.1-MHz bandwidth and
0.1-arcminute angular resolution could achieve a sensitivity of order
f_NL[local] ~ 0.03, f_NL[equilateral] ~ 0.04, and f_NL[orthogonal] ~ 0.03. | astro-ph_CO |
Is the expansion of the universe accelerating? All signs still point to
yes a local dipole anisotropy cannot explain dark energy: Type Ia supernovae (SNe Ia) provided the first strong evidence that the
expansion of the universe is accelerating. With SN samples now more than ten
times larger than those used for the original discovery and joined by other
cosmological probes, this discovery is on even firmer ground. Two recent,
related studies (Nielsen et al. 2016 and Colin et al. 2019, hereafter N16 and
C19, respectively) have claimed to undermine the statistical significance of
the SN Ia constraints. Rubin & Hayden (2016) (hereafter RH16) showed N16 made
an incorrect assumption about the distributions of SN Ia light-curve
parameters, while C19 also fails to remove the impact of the motion of the
solar system from the SN redshifts, interpreting the resulting errors as
evidence of a dipole in the deceleration parameter. Building on RH16, we
outline the errors C19 makes in their treatment of the data and inference on
cosmological parameters. Reproducing the C19 analysis with our proposed fixes,
we find that the dipole parameters have little effect on the inferred
cosmological parameters. We thus affirm the conclusion of RH16: the evidence
for acceleration is secure. | astro-ph_CO |
Bayesian evidence of the post-Planck curvaton: We perform a Bayesian model comparison for scenarios within the quadratic
curvaton model, determining the degree to which both are disfavoured with
respect to the $\Lambda$CDM concordance model and single-field quadratic
inflation, using the recent \emph{Planck} data release. Despite having three
additional model parameters, the simplest curvaton scenario is not disfavoured
relative to single-field quadratic inflation, and it becomes favoured against
this single-field model when we include the joint BICEP/Keck/\emph{Planck}
analysis. In all cases we assume an instantaneous inflaton decay and no
surviving isocurvature perturbations. Despite the success of \emph{Planck}
reaching its forecast measurement accuracy, we show that the current
constraints on local non-Gaussianity are insufficiently precise to have any
significant impact on the evidence ratios so far. We also determine the
precision $\sigma(f_{\mathrm{NL}})$ required by future measurements assuming a
fiducial value of $f_{\mathrm{NL}}=-5/4$ or $10.8$ to no longer disfavour the
curvaton against the $\Lambda$CDM parametrisation, and we discuss the effect
that the predicted increase in precision from future measurements on
$f_{\mathrm{NL}}$ may have. We show that our results are not very sensitive to
our choice of priors. | astro-ph_CO |
Introduction to Early Universe Cosmology: Observational cosmology is in its "golden age" with a vast amount of recent
data on the distribution of matter and light in the universe. This data can be
used to probe theories of the very early universe. It is small amplitude
cosmological fluctuations which encode the information about the very early
universe and relate it to current data. Hence, a central topic in these
lectures is the "theory of cosmological perturbations", the theory which
describes the generation of inhomogeneities in the very early universe and
their evolution until the current time. I will apply this theory to three
classes of models of the very early universe. The first is "Inflationary
Cosmology", the current paradigm for understanding the early evolution of the
universe. I will review the successes of inflationary cosmology, but will also
focus on some conceptual challenges which inflationary cosmology is facing,
challenges which motivate the search for possible alternatives. I will
introduce two alternative scenarios, the "Matter Bounce" model and "String Gas
Cosmology", and I will discuss how cosmological fluctuations which can explain
the current data are generated in those models. | astro-ph_CO |
A New Constraint on the Simulation of the Intergalactic Medium through
the Evolution of the Neutral Hydrogen Fraction in the Epoch of Reionization: The thermal history of the intergalactic medium is full of extremely useful
data in the field of astrophysics and cosmology. In other words, by examining
this environment in different redshifts, the effects of cosmology and
astrophysics can be observed side by side. Therefore, simulation is our very
powerful tool to reach a suitable model for the intergalactic medium, both in
terms of cosmology and astrophysics. In this work, we have simulated the
intergalactic medium with the help of the 21cmFAST code and compared the
evolution of the neutral hydrogen fraction in different initial conditions.
Considerable works arbitrarily determine many important effective parameters in
the thermal history of the intergalactic medium without any constraints, and
usually, there is a lot of flexibility for modeling. Nonetheless, in this work,
by focusing on the evolution of the neutral hydrogen fraction in different
models and comparing it with observational data, we have eliminated many models
and introduced only limited simulation models that could confirm the
observations with sufficient accuracy. This issue becomes thoroughly vital from
the point that, in addition to restricting the models through the neutral
hydrogen fraction, it can also impose restrictions on the parameters affecting
its changes. However, we hope that in future works, by enhancing the
observational data and increasing their accuracy, more compatible models with
the history of the intergalactic medium can be achieved. | astro-ph_CO |
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. | astro-ph_CO |
Vector field instability and the primordial tensor spectrum: It has recently been shown that the presence of a spectator pseudoscalar
field, coupled to photons through a Chern-Simons term, can amplify the
primordial tensor spectrum without observationally disrupting the primordial
scalar spectrum. The amplification occurs due to an instability that develops
for the vector fields. We consider the extension of previous studies to account
for the contribution arising from an inhomogeneous vector background which is
generated prior to the onset of inflation. We find that there may be
contributions in which net momentum is transferred between the inhomogeneous
vector background and the gravitons, which would give rise to a signature
different than in the absence of the semiclassical corrections. We discuss the
properties the classical vector field form must have in order for these
signatures to leave observable imprints, though we were unable to construct a
model for generating such a vector field. | astro-ph_CO |
The Epoch of Reionization in the R_h=ct Universe: The measured properties of the epoch of reionization (EoR) show that
reionization probably began around z ~ 12-15 and ended by z=6. In addition, a
careful analysis of the fluctuations in the cosmic microwave background
indicate a scattering optical depth tau ~ 0.066+/-0.012 through the EoR. In the
context of LCDM, galaxies at intermediate redshifts and dwarf galaxies at
higher redshifts now appear to be the principal sources of UV ionizing
radiation, but only for an inferred (ionizing) escape fraction f_ion ~ 0.2,
which is in tension with other observations that suggest a value as small as ~
0.05. In this paper, we examine how reionization might have progressed in the
alternative Friedmann-Robertson Walker cosmology known as the R_h=ct Universe,
and determine the value of f_ion required with this different rate of
expansion. We find that R_h=ct accounts quite well for the currently known
properties of the EoR, as long as its fractional baryon density falls within
the reasonable range 0.026 < Omega_b < 0.037. This model can also fit the EoR
data with f_ion ~ 0.05, but only if the Lyman continuum photon production is
highly efficient and Omega_b ~ 0.037. These results are still preliminary,
however, given their reliance on a particular form of the star-formation rate
density, which is still uncertain at very high redshifts. It will also be
helpful to reconsider the EoR in R_h=ct when complete structure formation
models become available. | astro-ph_CO |
The Spitzer Extragalactic Representative Volume Survey (SERVS): The
Environments of High-z SDSS Quasi-Stellar-Objects: This paper presents a study of the environments of SDSS Quasi-Stellar-Objects
(QSOs) in the Spitzer Extragalactic Representative Volume Survey (SERVS). We
concentrate on the high-redshift QSOs as these have not been studied in large
numbers with data of this depth before. We use the IRAC 3.6-4.5{\mu}m colour of
objects and ancillary r-band data to filter out as much foreground
contamination as possible. This technique allows us to find a significant (>
4-{\sigma}) over-density of galaxies around QSOs in a redshift bin centred on z
~ 2.0 and a (> 2-{\sigma}) over-density of galaxies around QSOs in a redshift
bin centred on z ~ 3.3. We compare our findings to the predictions of a
semi-analytic galaxy formation model, based on the {\Lambda}CDM millennium
simulation, and find for both redshift bins that the model predictions match
well the source-density we have measured from the SERVS data. | astro-ph_CO |
(Mis-)Interpreting supernovae observations in a lumpy universe: Light from `point sources' such as supernovae is observed with a beam width
of order of the sources' size - typically less than 1 AU. Such a beam probes
matter and curvature distributions that are very different from coarse-grained
representations in N-body simulations or perturbation theory, which are
smoothed on scales much larger than 1 AU. The beam typically travels through
unclustered dark matter and hydrogen with a mean density much less than the
cosmic mean, and through dark matter halos and hydrogen clouds. Using N-body
simulations, as well as a Press-Schechter approach, we quantify the density
probability distribution as a function of beam width and show that, even for
Gpc-length beams of 500 kpc diameter, most lines of sight are significantly
under-dense. From this we argue that modelling the probability distribution for
AU-diameter beams is absolutely critical. Standard analyses predict a huge
variance for such tiny beam sizes, and nonlinear corrections appear to be
non-trivial. It is not even clear whether under-dense regions lead to dimming
or brightening of sources, owing to the uncertainty in modelling the expansion
rate which we show is the dominant contribution. By considering different
reasonable approximations which yield very different cosmologies we argue that
modelling ultra-narrow beams accurately remains a critical problem for
precision cosmology. This could appear as a discordance between angular
diameter and luminosity distances when comparing SN observations to BAO or CMB
distances. | astro-ph_CO |
The Abundance Scatter in M33 from HII Regions: Is There Any Evidence for
Azimuthal Metallicity Variations?: Optical spectra of 25 H II regions in the inner two kpc of the M33 disk have
been obtained with the GMOS spectrograph at the Gemini North telescope. The
oxygen abundance gradient measured from the detection of the [O III]4363
auroral line displays a scatter of approximately 0.06 dex, a much smaller value
than recently reported by Rosolowsky & Simon in this galaxy. The analysis of
the abundances for a large sample of H II regions derived from the R23
strong-line indicator confirms that the scatter is small over the full disk of
M33, consistent with the measuring uncertainties, and comparable to what is
observed in other spiral galaxies. No evidence is therefore found for
significant azimuthal variations in the present-day metallicity of the
interstellar medium in this galaxy on spatial scales from ~100 pc to a few kpc.
A considerable fraction of M33 H II regions with auroral line detections show
spectral features revealing sources of hard ionizing radiation (such as He II
emission and large [Ne III], [O III] line fluxes). Since R23 is shown to
severely underestimate the oxygen abundances in such cases, care must be taken
in chemical abundance studies of extragalactic H II regions based on this
strong-line indicator. | astro-ph_CO |
Reconstruction of Power Spectrum of Primordial Curvature Perturbations
on small scales from Primordial Black Hole Binaries scenario of LIGO/VIRGO
detection: As a candidate bound for the Binary Black Hole (BBH) merger events detected
by LIGO/Virgo, Primordial Black Holes (PBHs) provide a useful tool to
investigate the primordial curvature perturbations on small scales. Using the
GWTC-1 to GWTC-3 catalogs, under the scenario that PBHs originate from large
primordial curvature perturbations on small scales during inflationary epoch,
we for the first time reconstruct the power spectrum of primordial curvature
perturbations on small scales. It is found that the value of the amplitude of
the primordial power spectrum is enhanced to $\mathcal{O}(10^{-2})$ on scales
$\mathcal{O}(1)$ pc. This may imply the validity of PBH as a possible BBH
merger candidate. | astro-ph_CO |
Blue Fermi Flat Spectrum Radio Quasars: Many blazars detected by the Fermi satellite, observed spectroscopically in
the optical, are line-less, and have been classified as BL Lac objects.
Optical-UV photometry of nearly one hundred of them allowed to determine the
redshift for a handful of objects and redshift upper limits for the great
majority. A few of these are candidates to be "blue quasars", namely flat
spectrum radio quasars whose broad emission lines are hidden by an overwhelming
synchrotron emission peaking in the UV. This implies that the emitting
electrons have high energies. In turn, this requires relatively weak radiative
cooling, a condition that can be met if the main radiative dissipation of the
jet power occurs outside the broad line region. We confirm this hypothesis by
studying and modelling the spectral energy distributions of the 4 "blue
quasars" recently discovered. Furthermore, we discuss the distribution of Fermi
blazars in the gamma-ray spectral index -- gamma-ray luminosity plane, and
argue that "blue quasars" objects are a minority within the blazar populations. | astro-ph_CO |
Internal dynamics of Abell 1240: a galaxy cluster with symmetric double
radio relics: We aim to obtain new insights into the internal dynamics of the cluster Abell
1240, showing the presence of two roughly symmetric radio relics, separated by
~2 h_70^-1 Mpc. Our analysis is mainly based on redshift data for 145 galaxies
and on new photometric data. We also use X-ray data from the Chandra archive
and photometric data from the SDSS (DR7). We combine galaxy velocities and
positions to select 89 cluster galaxies and analyze the internal dynamics of
the Abell 1237 + Abell 1240 cluster complex. We estimate similar redshifts for
Abell 1237 and Abell 1240, <z>=0.1935 and <z>=0.1948, respectively. For Abell
1237 we estimate velocity dispersion sigma_v~740 km/s and a mass M~6 10^14
h_70^-1 M_sun. For Abell 1240 we estimate a LOS sigma_v~870 km/s and a mass
range M~0.9-1.9 10^15 h_70^-1 M_sun, which takes into account its complex
dynamics. Abell 1240 is shown to have a bimodal structure with two galaxy
clumps roughly defining the N-S direction, the same one defined by the
elongation of its X-ray surface brightness and by the axis of symmetry of the
relics. The two--body model agrees with the hypothesis that we are looking at a
cluster merger occurred largely in the plane of the sky, with the two galaxy
clumps separated by a rest-frame velocity difference V_rf~2000 km/s at a time
of 0.3 Gyrs after the crossing core, while Abell 1237 is still infalling onto
Abell 1240. Chandra archive data confirm the complex structure of Abell 1240
and allow us to estimate a global X-ray temperature T_X=6.0+-0.5 keV. In
agreement with the findings from radio data, our results for Abell 1240
strongly support the "outgoing merger shocks" model to explain the presence of
the relics. | astro-ph_CO |
Broadband Imaging Segregation of z ~ 3 Ly-alpha Emitting and Ly-alpha
Absorbing Galaxies: The spectral properties of Lyman break galaxies (LBGs) offer a means to
isolate pure samples displaying either dominant Ly-alpha in absorption or
Ly-alpha in emission using broadband information alone. We present criteria
developed using a large z ~ 3 LBG spectroscopic sample from the literature that
enables large numbers of each spectral type to be gathered in photometric data,
providing good statistics for multiple applications. In addition, we find that
the truncated faint, blue-end tail of z ~ 3 LBG population overlaps and leads
directly into an expected Ly-alpha emitter (LAE) population. As a result, we
present simple criteria to cleanly select large numbers of z ~ 3 LAEs in deep
broadband surveys. We present the spectroscopic results of 32 r' <~ 25.5 LBGs
and r' <~ 27.0 LAEs at z ~ 3 pre-selected in the Canada-France-Hawaii Telescope
Legacy Survey that confirm these criteria. | astro-ph_CO |
All-Sky Analysis of the General Relativistic Galaxy Power Spectrum: We perform an all-sky analysis of the general relativistic galaxy power
spectrum using the well-developed spherical Fourier decomposition. Spherical
Fourier analysis expresses the observed galaxy fluctuation in terms of the
spherical harmonics and spherical Bessel functions that are angular and radial
eigenfunctions of the Helmholtz equation, providing a natural orthogonal basis
for all-sky analysis of the large-scale mode measurements. Accounting for all
the relativistic effects in galaxy clustering, we compute the spherical power
spectrum and its covariance matrix and compare it to the standard
three-dimensional power spectrum to establish a connection. The spherical power
spectrum recovers the three-dimensional power spectrum at each wavenumber k
with its angular dependence mu_k encoded in angular multipole l, and the
contributions of the line-of-sight projection to galaxy clustering such as the
gravitational lensing effect can be readily accommodated in the spherical
Fourier analysis. A complete list of formulas for computing the relativistic
spherical galaxy power spectrum is also presented. | astro-ph_CO |
PNe as observational constraints in chemical evolution models for NGC
6822: Chemical evolution models are useful for understanding the formation and
evolution of stars and galaxies. Model predictions will be more robust as more
observational constraints are used. We present chemical evolution models for
the dwarf irregular galaxy NGC 6822 using chemical abundances of old and young
Planetary Nebulae (PNe) and \ion{H}{ii} regions as observational constraints.
Two sets of chemical abundances, one derived from collisionally excited lines
(CELs) and one, from recombination lines (RLs), are used. We try to use our
models as a tool to discriminate between both procedures for abundance
determinations. In our chemical evolution code, the chemical contribution of
low and intermediate mass stars is time delayed, while for the massive stars
the chemical contribution follows the instantaneous recycling approximation.
Our models have two main free parameters: the mass-loss rate of a well-mixed
outflow and the upper mass limit, $M_{up}$, of the initial mass function (IMF).
To reproduce the gaseous mass and the present-day O/H value we need to vary the
outflow rate and the $M_{up}$ value. | astro-ph_CO |
Non-Gaussianity from false vacuum inflation: Old curvaton scenario: We calculate the three-point correlation function of the comoving curvature
perturbation generated during an inflationary epoch driven by false vacuum
energy. We get a novel false vacuum shape bispectrum, which peaks in the
equilateral limit. Using this result, we propose a scenario which we call "old
curvaton". The shape of the resulting bispectrum lies between the local and the
false vacuum shapes. In addition we have a large running of the spectral index. | astro-ph_CO |
Utilizing Astroinformatics to Maximize the Science Return of the Next
Generation Virgo Cluster Survey: The Next Generation Virgo Cluster Survey is a 104 square degree survey of the
Virgo Cluster, carried out using the MegaPrime camera of the
Canada-France-Hawaii telescope, from semesters 2009A-2012A. The survey will
provide coverage of this nearby dense environment in the universe to
unprecedented depth, providing profound insights into galaxy formation and
evolution, including definitive measurements of the properties of galaxies in a
dense environment in the local universe, such as the luminosity function. The
limiting magnitude of the survey is g_AB = 25.7 (10 sigma point source), and
the 2 sigma surface brightness limit is g_AB ~ 29 mag arcsec^-2. The data
volume of the survey (approximately 50 terabytes of images), while large by
contemporary astronomical standards, is not intractable. This renders the
survey amenable to the methods of astroinformatics. The enormous dynamic range
of objects, from the giant elliptical galaxy M87 at M(B) = -21.6, to the
faintest dwarf ellipticals at M(B) ~ -6, combined with photometry in 5 broad
bands (u* g' r' i' z'), and unprecedented depth revealing many previously
unseen structures, creates new challenges in object detection and
classification. We present results from ongoing work on the survey, including
photometric redshifts, Virgo cluster membership, and the implementation of fast
data mining algorithms on the infrastructure of the Canadian Astronomy Data
Centre, as part of the Canadian Advanced Network for Astronomical Research
(CANFAR). | astro-ph_CO |
Steve: A hierarchical Bayesian model for Supernova Cosmology: We present a new Bayesian hierarchical model (BHM) named Steve for performing
type Ia supernova (SNIa) cosmology fits. This advances previous works by
including an improved treatment of Malmquist bias, accounting for additional
sources of systematic uncertainty, and increasing numerical efficiency. Given
light curve fit parameters, redshifts, and host-galaxy masses, we fit Steve
simultaneously for parameters describing cosmology, SNIa populations, and
systematic uncertainties. Selection effects are characterised using Monte-Carlo
simulations. We demonstrate its implementation by fitting realisations of SNIa
datasets where the SNIa model closely follows that used in Steve. Next, we
validate on more realistic SNANA simulations of SNIa samples from the Dark
Energy Survey and low-redshift surveys. These simulated datasets contain more
than $60\,000$ SNeIa, which we use to evaluate biases in the recovery of
cosmological parameters, specifically the equation-of-state of dark energy,
$w$. This is the most rigorous test of a BHM method applied to SNIa cosmology
fitting, and reveals small $w$-biases that depend on the simulated SNIa
properties, in particular the intrinsic SNIa scatter model. This $w$-bias is
less than $0.03$ on average, less than half the statistical uncertainty on
$w$.These simulation test results are a concern for BHM cosmology fitting
applications on large upcoming surveys, and therefore future development will
focus on minimising the sensitivity of Steve to the SNIa intrinsic scatter
model. | astro-ph_CO |
A fast empirical method for galaxy shape measurements in weak lensing
surveys: We describe a simple and fast method to correct ellipticity measurements of
galaxies from the distortion by the instrumental and atmospheric point spread
function (PSF), in view of weak lensing shear measurements. The method performs
a classification of galaxies and associated PSFs according to measured shape
parameters, and corrects the measured galaxy ellipticites by querying a large
lookup table (LUT), built by supervised learning. We have applied this new
method to the GREAT10 image analysis challenge, and present in this paper a
refined solution that obtains the competitive quality factor of Q = 104,
without any shear power spectrum denoising or training. Of particular interest
is the efficiency of the method, with a processing time below 3 ms per galaxy
on an ordinary CPU. | astro-ph_CO |
The Link Between the Hidden Broad Line Region and the Accretion Rate in
Seyfert 2 Galaxies: In the past few years more and more pieces of evidence have been presented
for a revision of the widely accepted Unified Model of Active Galactic Nuclei.
A model based solely on orientation cannot explain all the observed
phenomenology. In the following, we will present evidence that accretion rate
is also a key parameter for the presence of Hidden Broad Line Regions in
Seyfert 2 galaxies. Our sample consists of 21 sources with polarized Hidden
Broad Lines and 18 sources without Hidden Broad Lines. We use stellar velocity
dispersions from several studies on the CaII and Mg b triplets in Seyfert 2
galaxies, to estimate the mass of the central black holes via the
Mbh-{\sigma}\ast relation. The ratio between the bolometric luminosity, derived
from the intrinsic (i.e. unabsorbed) X-ray luminosity, and the Eddington
luminosity is a measure of the rate at which matter accretes onto the central
supermassive black hole. A separation between Compton-thin HBLR and non-HBLR
sources is clear, both in accretion rate (log Lbol/LEdd = -1.9) and in
luminosity (log Lbol = 43.90). When, properly luminosity-corrected,
Compton-thick sources are included, the separation between HBLR and non-HBLR is
less sharp but no HBLR source falls below the Eddington ratio threshold. We
speculate that non-HBLR Compton-thick sources with accretion rate higher than
the threshold, do possess a BLR, but something, probably related to their heavy
absorption, is preventing us from observing it even in polarized light. Our
results for Compton-thin sources support theoretical expectations. In a model
presented by Nicastro (2000), the presence of broad emission lines is
intrinsically connected with disk instabilities occuring in proximity of a
transition radius, which is a function of the accretion rate, becoming smaller
than the innermost stable orbit for very low accretion rates and therefore
luminosities. | astro-ph_CO |
IC10: the history of the nearest starburst galaxy through its Planetary
Nebula and HII region populations: We report the results of spectroscopic observations, obtained with the Gemini
North Multi-Object Spectrograph, of 9 planetary nebulae (PNe) and 15 \hii\
regions located in the 5.5\arcmin $\times$5.5\arcmin inner region of the nearby
starburst galaxy IC10. Twelve new candidate PNe have been discovered during our
pre-imaging phase. Nine of them have been spectroscopically confirmed. The
direct availability of the electron temperature diagnostics in several nebulae
allowed an accurate determination of the metallicity map of IC10 at two epochs:
the present-time from \hii regions and the old/intermediate-age from PNe. We
found a non-homogeneous distribution of metals at both epochs, but similar
average abundances were found for the two populations. The derived
age-metallicity relation shows a little global enrichment interpreted as the
loss of metals by SN winds and to differential gas outflows. Finally, we
analyzed the production of oxygen --through the third dredge-up-- in the
chemical abundance patterns of the PN populations belonging to several dwarf
irregular galaxies. We found that the third dredge-up of oxygen is a
metallicity dependent phenomenon occurring mainly for 12+$\log$(O/H)$\leq$7.7
and substantially absent in IC10 PNe. | astro-ph_CO |
The role of Dark Matter sub-halos in the non-thermal emission of galaxy
clusters: Annihilation of Dark Matter (DM) particles has been recognized as one of the
possible mechanisms for the production of non-thermal particles and radiation
in galaxy clusters. Previous studies have shown that, while DM models can
reproduce the spectral properties of the radio halo in the Coma cluster, they
fail in reproducing the shape of the radio halo surface brightness because they
produce a shape that is too concentrated towards the center of the cluster with
respect to the observed one. However, in previous studies the DM distribution
was modeled as a single spherically symmetric halo, while the DM distribution
in Coma is found to have a complex and elongated shape. In this work we
calculate a range of non-thermal emissions in the Coma cluster by using the
observed distribution of DM sub-halos. We find that, by including the observed
sub-halos in the DM model, we obtain a radio surface brightness with a shape
similar to the observed one, and that the sub-halos boost the radio emission by
a factor between 5 and 20%, thus allowing to reduce the gap between the
annihilation cross section required to reproduce the radio halo flux and the
upper limits derived from other observations, and that this gap can be
explained by realistic values of the boosting factor due to smaller
substructures. Models with neutralino mass of 9 GeV and composition $\tau^+
\tau^-$, and mass of 43 GeV and composition $b \bar b$ can fit the radio halo
spectrum using the observed properties of the magnetic field in Coma, and do
not predict a gamma-ray emission in excess compared to the recent Fermi-LAT
upper limits. These findings make these DM models viable candidate to explain
the origin of radio halos in galaxy clusters. [abridged] | astro-ph_CO |
Improved Cosmological Constraints from SDSS redMaPPer Clusters via X-ray
Follow-up of a Complete Subsample of Systems: We improve upon the cosmological constraints derived from the abundance and
weak-lensing data of redMaPPer clusters detected in the Sloan Digital Sky
Survey (SDSS). Specifically, we derive gas mass data using Chandra X-ray
follow-up of a complete sample of the 30 richest SDSS redMaPPer clusters with
$z\in[0.1,0.3]$, and use these additional data to improve upon the original
analysis by Costanzi et al. (2019b). We simultaneously fit for the parameters
of the richness-mass relation, the cluster gas mass-mass relation, and
cosmology. By including our X-ray cluster sample in the SDSS cluster cosmology
analysis, we measure $\Omega_{\rm m} = 0.25 \pm 0.04$ and $\sigma_8 =
0.85^{+0.06}_{-0.08}$. These constraints represent a 25.5% and 29.8% reduction
in the size of the 68% confidence intervals of $\Omega_{\rm m}$ and $\sigma_8$
respectively, relative to the constraints published in Costanzi et al. (2019b).
Our cosmological constraints are in agreement with early universe results from
Planck. As a byproduct of our analysis, we also perform an independent
calibration of the amplitude of the $\langle M_{\rm gas}^{\rm true}|M_{\rm
500c}\rangle$ scaling relation. Our calibration is consistent with and of
comparable precision to that of Mantz et al. (2016b). | astro-ph_CO |
The zCOSMOS 20k Group Catalog: We present an optical group catalog between 0.1 < z < 1 based on 16,500
high-quality spectroscopic redshifts in the completed zCOSMOS-bright survey.
The catalog published herein contains 1498 groups in total and 192 groups with
more than five observed members. The catalog includes both group properties and
the identification of the member galaxies. Based on mock catalogs, the
completeness and purity of groups with three and more members should be both
about 83% with respect to all groups that should have been detectable within
the survey, and more than 75% of the groups should exhibit a one-to-one
correspondence to the "real" groups. Particularly at high redshift, there are
apparently more galaxies in groups in the COSMOS field than expected from mock
catalogs. We detect clear evidence for the growth of cosmic structure over the
last seven billion years in the sense that the fraction of galaxies that are
found in groups (in volume-limited samples) increases significantly with cosmic
time. In the second part of the paper, we develop a method for associating
galaxies that only have photo-z to our spectroscopically identified groups. We
show that this leads to improved definition of group centers, improved
identification of the most massive galaxies in the groups, and improved
identification of central and satellite galaxies, where we define the former to
be galaxies at the minimum of the gravitational potential wells. Subsamples of
centrals and satellites in the groups can be defined with purities up to 80%,
while a straight binary classification of all group and non-group galaxies into
centrals and satellites achieves purities of 85% and 75%, respectively, for the
spectroscopic sample. | astro-ph_CO |
An exploration of an early gravity transition in light of cosmological
tensions: We study a step-like transition in the value of the effective Planck mass (or
effective gravitational constant) on cosmological scales prior to
recombination. We employ CMB, BAO, and SNIa data and find they are sufficient
to strongly constrain our implementation of the Effective Field Theory of Dark
Energy and Modified Gravity, used to model the transition, to a limited
parameter space. The data prefer a $\sim 5\%$ shift in the value of the
effective Planck mass ($<10 \%$ at $2 \sigma$) prior to recombination. This
Transitional Planck Mass (TPM) model is free to undergo its transition at any
point over multiple decades of scale factor prior to recombination,
$\log_{10}(a) = -5.32^{+0.96}_{-0.72}$ (68\% CL). This lowers the sound horizon
at last scattering, which increases the Hubble constant to $71.09 \pm 0.75$ km
$\textrm{s}^{-1}\textrm{Mpc}^{-1}$ with a combination of local measurements as
prior and to $69.22^{+0.67}_{-0.86}$ km $\textrm{s}^{-1}\textrm{Mpc}^{-1}$ when
the prior is excluded. The TPM model improves $\chi^2$ with respect to
$\Lambda$CDM by $\Delta \chi^2 = -23.72$ with the $H_0$ prior and $\Delta
\chi^2 = -4.8$ without the prior. The model allows for both $H_0 > 70$
km$\textrm{s}^{-1}\textrm{Mpc}^{-1}$ and $S_8 < 0.80$ simultaneously with lower
values of $S_8$ due to a reduction in the matter density $\Omega_m$ to offset
the increase in $H_0$ relative to $\Lambda$CDM. While this is a particular
modified gravity model, studying other variants of modified gravity may be a
productive path for potentially resolving cosmological tensions, while avoiding
the need for a cosmological constant. | astro-ph_CO |
Is the misalignment of the Local Group velocity and the 2MASS Redshift
Survey dipole typical in a LambdaCDM model?: We predict the acceleration of the Local Group generated by the 2MASS
Redshift Survey within the framework of LambdaCDM and the halo model of
galaxies. We show that as the galaxy fluctuations derived from the halo model
have more power on small scales compared with the mass fluctuations, the
misalignment angle between the CMB velocity vector and the 2MRS dipole is in
reasonable agreement with the observed 21 degrees. This statistical analysis
suggests that it is not necessary to invoke a hypothetical nearby galaxy or a
distant cluster to explain this misalignment. | astro-ph_CO |
Instability in axion inflation with strong backreaction from gauge modes: We perform an analytical study of the stability of the background solution of
the model in which an inflaton, through an axionic coupling to a $U(1)$ gauge
field, causes an amplification of the gauge field modes that strongly backreact
on its dynamics. To this goal, we study the evolution of the gauge field modes
coupled to the inflaton zero mode, treating perturbatively the deviation of the
inflaton velocity from its mean-field value. As long as the system is in the
strong backreaction regime we find that the inflaton velocity performs
oscillations of increasing amplitude about the value it would have in the
approximation of constant velocity, confirming an instability that has been
observed in numerical studies. | astro-ph_CO |
Testable dark energy predictions from current data: Given a class of dark energy models, constraints from one set of cosmic
acceleration observables make predictions for other observables. Here we
present the allowed ranges for the expansion rate H(z), distances D(z), and the
linear growth function G(z) (as well as other, derived growth observables) from
the current combination of cosmological measurements of supernovae, the cosmic
microwave background, baryon acoustic oscillations, and the Hubble constant.
With a cosmological constant as the dark energy and assuming near-minimal
neutrino masses, the growth function is already predicted to better than 2%
precision at any redshift, with or without spatial curvature. Direct
measurements of growth that match this precision offer the opportunity to
stringently test and potentially rule out a cosmological constant. While
predictions in the broader class of quintessence models are weaker, it is
remarkable that they are typically within a factor of 2-3 of forecasts for
future space-based supernovae and Planck CMB measurements. In particular,
measurements of growth at any redshift, or the Hubble constant H_0, that exceed
LambdaCDM predictions by substantially more than 2% would rule out not only a
cosmological constant but also the whole quintessence class, with or without
curvature and early dark energy. Barring additional systematic errors hiding in
the data, such a discovery would require more exotic explanations of cosmic
acceleration such as phantom dark energy, dark energy clustering, or
modifications of gravity. | astro-ph_CO |
Probing Parity Violation in the Stochastic Gravitational Wave Background
with Astrometry: Astrometry holds the potential for testing fundamental physics through the
effects of the Stochastic Gravitational Wave Background (SGWB) in the $\sim
1-100$ nHz frequency band on precision measurements of stellar positions. Such
measurements are complementary to tests made possible by the detection of the
SGWB using Pulsar Timing Arrays. Here, the feasibility of using astrometry for
the identification of parity-violating signals within the SGWB is investigated.
This is achieved by defining and quantifying a non-vanishing $EB$ correlation
function within astrometric correlation functions, and investigating how one
might estimate the detectability of such signals. | astro-ph_CO |
Probing the anisotropic expansion history of the universe with cosmic
microwave background: We propose a simple technique to detect any anisotropic expansion stage in
the history of the universe starting from the inflationary stage to the surface
of last scattering from the CMBR data. We use the property that any anisotropic
expansion in the universe would deform the shapes of the primordial density
perturbations and this deformation can be detected in a shape analysis of
superhorizon fluctuations in CMBR. Using this analysis we obtain the constraint
on any previous anisotropic expansion of the universe to be less than about
35%. | astro-ph_CO |
Absence of concordance in a simple self-interacting neutrino cosmology: Some cosmic microwave background (CMB) data allow a cosmological scenario in
which the free streaming of neutrinos is delayed until close to
matter-radiation equality. Interestingly, recent analyses have revealed that
large-scale structure (LSS) data also align with this scenario, discarding the
possibility of an accidental feature in the CMB sky and calling for further
investigation into the free-streaming nature of neutrinos. By assuming a simple
representation of self-interacting neutrinos, we investigate whether this
nonstandard scenario can accommodate a consistent cosmology for both the CMB
power spectra and the large-scale distribution of galaxies simultaneously.
Employing three different approaches - a profile likelihood exploration, a
nested sampling method, and a heuristic Metropolis-Hasting approximation - we
exhaustively explore the parameter space and demonstrate that galaxy data
exacerbates the challenge already posed by the Planck polarization data for
this nonstandard scenario. We find that the most conservative value of the
Bayes factor disfavors the interactions among neutrinos over a $\Lambda$CDM +
$N_\mathrm{eff}$ + $\sum m_\nu$ model with odds of $23:1000$ and that the
difficulty of simultaneously fitting the galaxy and CMB data relates to the
so-called $S_8$ discrepancy. Our analysis not only emphasizes the need to
consider a broader range of phenomenologies in the early Universe but also
highlights significant numerical and theoretical challenges ahead in uncovering
the exact nature of the feature observed in the data or, ultimately, confirming
the standard chronological evolution of the Universe. | astro-ph_CO |
The role of Dark Matter sub-halos in the non-thermal emission of galaxy
clusters: Annihilation of Dark Matter (DM) particles has been recognized as one of the
possible mechanisms for the production of non-thermal particles and radiation
in galaxy clusters. Previous studies have shown that, while DM models can
reproduce the spectral properties of the radio halo in the Coma cluster, they
fail in reproducing the shape of the radio halo surface brightness because they
produce a shape that is too concentrated towards the center of the cluster with
respect to the observed one. However, in previous studies the DM distribution
was modeled as a single spherically symmetric halo, while the DM distribution
in Coma is found to have a complex and elongated shape. In this work we
calculate a range of non-thermal emissions in the Coma cluster by using the
observed distribution of DM sub-halos. We find that, by including the observed
sub-halos in the DM model, we obtain a radio surface brightness with a shape
similar to the observed one, and that the sub-halos boost the radio emission by
a factor between 5 and 20%, thus allowing to reduce the gap between the
annihilation cross section required to reproduce the radio halo flux and the
upper limits derived from other observations, and that this gap can be
explained by realistic values of the boosting factor due to smaller
substructures. Models with neutralino mass of 9 GeV and composition $\tau^+
\tau^-$, and mass of 43 GeV and composition $b \bar b$ can fit the radio halo
spectrum using the observed properties of the magnetic field in Coma, and do
not predict a gamma-ray emission in excess compared to the recent Fermi-LAT
upper limits. These findings make these DM models viable candidate to explain
the origin of radio halos in galaxy clusters. [abridged] | astro-ph_CO |
All sky angular power spectrum: I. Estimating brightness temperature
fluctuations using TGSS 150 MHz survey: Measurements of the Galactic synchrotron emission is relevant for the 21-cm
studies from the Epoch of Reionization. The study of the synchrotron emission
is also useful to quantify the fluctuations in the magnetic field and the
cosmic ray electron density of the turbulent interstellar medium (ISM) of our
Galaxy. Here, we present the all-sky angular power spectrum $(C_{\ell})$
measurements of the diffuse synchrotron emission using the TIFR GMRT Sky Survey
(TGSS) at 150 {\rm MHz}. We estimate $C_{\ell}$ using visibility data both
before and after subtracting the modelled point sources. The amplitude of the
measured $C_{\ell}$ falls significantly after subtracting the point sources,
and it is also slightly higher in the Galactic plane for the residual data. The
residual $C_{\ell}$ is most likely to be dominated by the Galactic synchrotron
emission. The amplitude of the residual $C_{\ell}$ falls significantly away
from the Galactic plane. We find the measurements are quite symmetric in the
Northern and Southern hemispheres except in the latitude range $15-30^{\circ}$
which is the transition region from the disk dominated to diffuse halo
dominated region. The comparison between this interferometric measurement with
the scaled version of the Haslam rms map at 150 {\rm MHz} shows that the
correlation coefficient $(r)$ is more than 0.5 for most of the latitude ranges
considered here. This signifies the TGSS survey is quite sensitive to the
diffuse Galactic synchrotron radiation. | astro-ph_CO |
Gödel-type universes and chronology protection in Horava-Lifshitz
gravity: In the attempts toward a quantum gravity theory, general relativity faces a
serious difficulty since it is non-renormalizable theory. Ho\v{r}ava-Lifshitz
gravity offers a framework to circumvent this difficulty, by sacrificing the
local Lorentz invariance at ultra-high energy scales in exchange of
power-counting renormalizability. The Lorentz symmetry is expected to be
recovered at low and medium energy scales. If gravitation is to be described by
a Ho\v{r}ava-Lifshitz gravity theory there are a number of issues that ought to
be reexamined in its context, including the question as to whether this gravity
incorporates a chronology protection, or particularly if it allows G\"odel-type
solutions with violation of causality. We show that Ho\v{r}ava-Lifshitz gravity
only allows hyperbolic G\"odel-type space-times whose essential parameters $m$
and $\omega$ are in the chronology respecting intervals, excluding therefore
any noncausal G\"odel-type space-times in the hyperbolic class. There emerges
from our results that the famous noncausal G\"odel model is not allowed in
Ho\v{r}ava-Lifshitz gravity. The question as to whether this quantum gravity
theory permits hyperbolic G\"odel-type solutions in the chronology preserving
interval of the essential parameters is also examined. We show that
Ho\v{r}ava-Lifshitz gravity not only excludes the noncausal G\"odel universe,
but also rules out any hyperbolic G\"odel-type solutions for physically
well-motivated perfect-fluid matter content. | astro-ph_CO |
A Bayesian analysis of redshifted 21-cm HI signal and foregrounds:
Simulations for LOFAR: Observations of the EoR with the 21-cm hyperfine emission of neutral hydrogen
(HI) promise to open an entirely new window onto the formation of the first
stars, galaxies and accreting black holes. In order to characterize the weak
21-cm signal, we need to develop imaging techniques which can reconstruct the
extended emission very precisely. Here, we present an inversion technique for
LOFAR baselines at NCP, based on a Bayesian formalism with optimal spatial
regularization, which is used to reconstruct the diffuse foreground map
directly from the simulated visibility data. We notice the spatial
regularization de-noises the images to a large extent, allowing one to recover
the 21-cm power-spectrum over a considerable $k_{\perp}-k_{\para}$ space in the
range of $0.03\,{\rm Mpc^{-1}}<k_{\perp}<0.19\,{\rm Mpc^{-1}}$ and $0.14\,{\rm
Mpc^{-1}}<k_{\para}<0.35\,{\rm Mpc^{-1}}$ without subtracting the noise
power-spectrum. We find that, in combination with using the GMCA, a
non-parametric foreground removal technique, we can mostly recover the
spherically average power-spectrum within $2\sigma$ statistical fluctuations
for an input Gaussian random rms noise level of $60 \, {\rm mK}$ in the maps
after 600 hrs of integration over a $10 \, {\rm MHz}$ bandwidth. | astro-ph_CO |
Structure in Galaxy Distribution. III. Fourier Transforming the Universe: We demonstrate the effectiveness of a relatively straightforward analysis of
the complex 3D Fourier transform of galaxy coordinates derived from redshift
surveys. Numerical demonstrations of this approach are carried out on a
volume-limited sample of the Sloan Digital Sky Survey redshift survey. The
direct unbinned transform yields a complex 3D data cube quite similar to that
from the Fast Fourier Transform (FFT) of finely binned galaxy positions. In
both cases deconvolution of the sampling window function yields estimates of
the true transform. Simple power spectrum estimates from these transforms are
roughly consistent with those using more elaborate methods. However we
concentrate on the less often studied Fourier phase spectrum, a simple and
general framework for characterizing non-Gaussianity, more easily interpretable
than the tangled, incomplete multi-point methods conventionally used. No
significant signature of non-Gaussianity has been found in the relatively small
data set analyzed, but we identify some threads of modern large scale inference
methodology that will presumably yield detections in new wider and deeper
surveys. | astro-ph_CO |
Simulations of helical inflationary magnetogenesis and gravitational
waves: Using numerical simulations of helical inflationary magnetogenesis in a low
reheating temperature scenario, we show that the magnetic energy spectrum is
strongly peaked at a particular wavenumber that depends on the reheating
temperature. Gravitational waves (GWs) are produced at frequencies between 3
nHz and 50 mHz for reheating temperatures between 150 MeV and 3x10^5 GeV,
respectively. At and below the peak frequency, the stress spectrum is always
found to be that of white noise. This implies a linear increase of GW energy
per logarithmic wavenumber interval, instead of a cubic one, as previously
thought. Both in the helical and nonhelical cases, the GW spectrum is followed
by a sharp drop for frequencies above the respective peak frequency. In this
magnetogenesis scenario, the presence of a helical term extends the peak of the
GW spectrum and therefore also the position of the aforementioned drop toward
larger frequencies compared to the case without helicity. This might make a
difference in it being detectable with space interferometers. The efficiency of
GW production is found to be almost the same as in the nonhelical case, and
independent of the reheating temperature, provided the electromagnetic energy
at the end of reheating is fixed to be a certain fraction of the radiation
energy density. Also, contrary to the case without helicity, the electric
energy is now less than the magnetic energy during reheating. The fractional
circular polarization is found to be nearly hundred per cent in a certain range
below the peak frequency range. | astro-ph_CO |
Inflation, Quantum Field Renormalization, and CMB Anisotropies: We point out that if quantum field renormalization is taken into account the
predictions of slow-roll inflation for both the scalar and tensorial power
spectra change significantly for wavelengths that today are at observable
scales | astro-ph_CO |
First measurement of the bulk flow of nearby galaxies using the cosmic
microwave background: Peculiar velocities in the nearby Universe can be measured via the kinetic
Sunyaev-Zel'dovich (kSZ) effect. Using a statistical method based on an
optimised cross-correlation with nearby galaxies, we extract the kSZ signal
generated by plasma halo of galaxies from the Cosmic Microwave Background (CMB)
temperature anisotropies observed by the Wilkinson Microwave Anisotropy Probe
(WMAP). Marginalising over the thermal Sunyaev-Zel'dovich contribution from
clusters of galaxies, possible unresolved point source contamination, and
Galactic foregrounds (dust, synchrotron and free-free emission), we report a
kSZ bulk flow signal present at the 90% confidence level in the seven-year WMAP
data. When only galaxies within 50 Mpc/h are included in the kSZ template we
find a bulk flow in the CMB frame of |V|=533 +/- 263 km/s, in the direction
l=324 +/- 27, b=-7 +/- 17, consistent with bulk flow measurements on a similar
scale using classical distance indicators. We show how this comparison
constrains the (ionised) baryonic budget in the local universe. On very large
(~ 500 Mpc/h) scales, we find a 95% upper limit of 470 km/s, inconsistent with
some analyses of bulk flow of clusters from the kSZ. We estimate that the
significance of the bulk flow signal may increase to 3-5 sigma using data from
the PLANCK probe. | astro-ph_CO |
All about baryons: revisiting SIDM predictions at small halo masses: We use cosmological hydrodynamic simulations to consistently compare the
assembly of dwarf galaxies in both $\Lambda$ dominated, Cold (CDM) and
Self--Interacting (SIDM) dark matter models. The SIDM model adopts a constant
cross section of 2 $cm^{2}/g$, a relatively large value to maximize its
effects. These are the first SIDM simulations that are combined with a
description of stellar feedback that naturally drives potential fluctuations
able to create dark matter cores. Remarkably, SIDM fails to significantly lower
the central dark matter density at halo peak velocities V$_{max}$ $<$ 30 Km/s.
This is due to the fact that the central regions of very low--mass field halos
have relatively low central velocity dispersion and densities, leading to time
scales for SIDM collisions greater than a Hubble time. CDM halos with V$_{max}$
$<$ 30 km/s have inefficient star formation, and hence weak supernova feedback.
At a fixed 2 cm2/g SIDM cross section, the DM content of very low mass CDM and
SIDM halos differs by no more than a factor of two within 100-200pc. At larger
halo masses ($\sim$ 10$^{10}$ solar masses), the introduction of baryonic
processes creates field dwarf galaxies with dark matter cores and central
DM$+$baryon distributions that are effectively indistinguishable between CDM
and SIDM. Both models are in broad agreement with observed Local Group field
galaxies across the range of masses explored. To significantly differentiate
SIDM from CDM at the scale of faint dwarf galaxies, a velocity dependent cross
section that rapidly increases to values larger than 2 $cm^{2}/g$ for halos
with V$_{max}$ < 25-30 Km/s needs to be introduced. | astro-ph_CO |
Calculation of the critical overdensity in the spherical-collapse
approximation: Critical overdensity $\delta_c$ is a key concept in estimating the number
count of halos for different redshift and halo-mass bins, and therefore, it is
a powerful tool to compare cosmological models to observations. There are
currently two different prescriptions in the literature for its calculation,
namely, the differential-radius and the constant-infinity methods. In this work
we show that the latter yields precise results {\it only} if we are careful in
the definition of the so-called numerical infinities. Although the subtleties
we point out are crucial ingredients for an accurate determination of
$\delta_c$ both in general relativity and in any other gravity theory, we focus
on $f(R)$ modified-gravity models in the metric approach; in particular, we use
the so-called large ($F=1/3$) and small-field ($F=0$) limits. For both of them,
we calculate the relative errors (between our method and the others) in the
critical density $\delta_c$, in the comoving number density of halos per
logarithmic mass interval $n_{\ln M}$ and in the number of clusters at a given
redshift in a given mass bin $N_{\rm bin}$, as functions of the redshift. We
have also derived an analytical expression for the density contrast in the
linear regime as a function of the collapse redshift $z_c$ and $\Omega_{m0}$
for any $F$. | astro-ph_CO |
The Atacama Cosmology Telescope (ACT): Beam Profiles and First SZ
Cluster Maps: The Atacama Cosmology Telescope (ACT) is currently observing the cosmic
microwave background with arcminute resolution at 148 GHz, 218 GHz, and 277
GHz. In this paper, we present ACT's first results. Data have been analyzed
using a maximum-likelihood map-making method which uses B-splines to model and
remove the atmospheric signal. It has been used to make high-precision beam
maps from which we determine the experiment's window functions. This beam
information directly impacts all subsequent analyses of the data. We also used
the method to map a sample of galaxy clusters via the Sunyaev-Zel'dovich (SZ)
effect, and show five clusters previously detected with X-ray or SZ
observations. We provide integrated Compton-y measurements for each cluster. Of
particular interest is our detection of the z = 0.44 component of A3128 and our
current non-detection of the low-redshift part, providing strong evidence that
the further cluster is more massive as suggested by X-ray measurements. This is
a compelling example of the redshift-independent mass selection of the SZ
effect. | astro-ph_CO |
Hot Gas, Cold Gas and Sub-Halos in a Lyman-alpha Blob at Redshift 2.38: We present integral field spectroscopy of a Lyman-alpha blob at redshift
2.38, with a spectral resolution three times better than previous published
work. As with previous observations, the blob has a chaotic velocity structure,
much of which breaks up into multiple components. Our spectroscopy shows,
however, that some of these multiple components are extremely narrow: they have
velocity widths of less than 100 km/s.
Combining these new data with previous observations, we argue that this
Lyman-alpha blob resides in a dark-matter halo of around 10^13 solar masses. At
the centre of this halo are two compact red massive galaxies. They are
surrounded by hot gas, probably a super-wind from merger-induced nuclear
starbursts. This hot gas has shut down star formation in the non-nuclear region
of these galaxies, leading to their red-and-dead colours.
A filament or lump of infalling cold gas is colliding with the hot gas phase
and being shocked to high temperatures, while still around 30kpc from the red
galaxies. The shock region is self-absorbed in Lyman-alpha but produces C IV
emission.
Further out still, the cold gas in a number of sub-halos is being lit up,
most likely by a combination of tidally triggered star formation, bow-shocks as
they plough through the hot halo medium, resonant scattering of Lyman-alpha
from the filament collision, and tidal stripping of gas which enhances the
Lyman-alpha escape fraction. The observed Lyman-alpha emission from the Blob is
dominated by the sum of the emission from these sub-halos.
On statistical grounds, we argue that Lyman-alpha blobs are not greatly
elongated in shape, and that most are not powered by ionisation or scattering
from a central active galactic nucleus or starburst. | astro-ph_CO |
Arbitrating the $S_8$ discrepancy with growth rate measurements from
Redshift-Space Distortions: Within the $\Lambda$CDM model, measurements from recent Cosmic Microwave
Background (CMB) and weak lensing (WL) surveys have uncovered a $\sim 3\sigma$
disagreement in the inferred value of the parameter $S_8 \equiv
\sigma_8\sqrt{\Omega_m/0.3}$, quantifying the amplitude of late-time matter
fluctuations. Before questioning whether the $S_8$ discrepancy calls for new
physics, it is important to assess the view of measurements other than CMB and
WL ones on the discrepancy. Here, we examine the role of measurements of the
growth rate $f(z)$ in arbitrating the $S_8$ discrepancy, considering
measurements of $f\sigma_8(z)$ from Redshift-Space Distortions (RSD). Our
baseline analysis combines RSD measurements with geometrical measurements from
Baryon Acoustic Oscillations (BAO) and Type Ia Supernovae (SNeIa), given the
key role of the latter in constraining $\Omega_m$. From this combination and
within the $\Lambda$CDM model we find $S_8 = 0.762^{+0.030}_{-0.025}$, and
quantify the agreement between RSD+BAO+SNeIa and \textit{Planck} to be at the
$2.2\sigma$ level: the mild disagreement is therefore compatible with a
statistical fluctuation. We discuss combinations of RSD measurements with other
datasets, including the $E_G$ statistic. This combination increases the
discrepancy with \textit{Planck}, but we deem it significantly less robust. Our
earlier results are stable against an extension where we allow the dark energy
equation of state $w$ to vary. We conclude that, from the point of view of
combined growth rate and geometrical measurements, there are hints, but no
strong evidence yet, for the \textit{Planck} $\Lambda$CDM cosmology
over-predicting the amplitude of matter fluctuations at redshifts $z \lesssim
1$. From this perspective, it might therefore still be premature to claim the
need for new physics from the $S_8$ discrepancy. | astro-ph_CO |
Extragalactic dark matter and direct detection experiments: Recent astronomical data strongly suggest that a significant part of the dark
matter, composing the Local Group and Virgo Supercluster, is not incorporated
into the galaxy haloes and forms diffuse components of these galaxy clusters.
Apparently, a portion of the particles from these components may penetrate into
the Milky Way and make an extragalactic contribution to the total dark matter
containment of our Galaxy.
We find that the particles of the diffuse component of the Local Group are
apt to contribute $\sim 12%$ to the total dark matter density near the Earth.
The particles of the extragalactic dark matter stand out because of their high
speed ($\sim 600$ {km/s}), i.e. they are much faster than the galactic dark
matter. In addition, their speed distribution is very narrow ($\sim 20$
{km/s}). The particles have isotropic velocity distribution (perhaps, in
contrast to the galactic dark matter). The extragalactic dark matter should
give a significant contribution to the direct detection signal. If the detector
is sensitive only to the fast particles ($v<450$ {km/s}), the signal may even
dominate.
The density of other possible types of the extragalactic dark matter (for
instance, of the diffuse component of the Virgo Supercluster) should be
relatively small and comparable with the average dark matter density of the
Universe. However, these particles can generate anomaly high energy collisions
in direct dark matter detectors. | astro-ph_CO |
A general framework to test gravity using galaxy clusters III:
Observable-mass scaling relations in $f(R)$ gravity: We test two methods, including one that is newly proposed in this work, for
correcting for the effects of chameleon $f(R)$ gravity on the scaling relations
between the galaxy cluster mass and four observable proxies. Using the first
suite of cosmological simulations that simultaneously incorporate both full
physics of galaxy formation and Hu-Sawicki $f(R)$ gravity, we find that these
rescaling methods work with a very high accuracy for the gas temperature, the
Compton $Y$-parameter of the Sunyaev-Zel'dovich (SZ) effect and the X-ray
analogue of the $Y$-parameter. This allows the scaling relations in $f(R)$
gravity to be mapped to their $\Lambda$CDM counterparts to within a few
percent. We confirm that a simple analytical tanh formula for the ratio between
the dynamical and true masses of haloes in chameleon $f(R)$ gravity, proposed
and calibrated using dark-matter-only simulations in a previous work, works
equally well for haloes identified in simulations with two very different --
full-physics and non-radiative -- baryonic models. The mappings of scaling
relations can be computed using this tanh formula, which depends on the halo
mass, redshift and size of the background scalar field, also at a very good
accuracy. Our results can be used for accurate determination of the cluster
mass using SZ and X-ray observables, and will form part of a general framework
for unbiased and self-consistent tests of gravity using data from present and
upcoming galaxy cluster surveys. We also propose an alternative test of
gravity, using the $Y_{\rm X}$-temperature relation, which does not involve
mass calibration. | astro-ph_CO |
Testing theories in barred spiral galaxies: According to one version of the recently proposed "manifold" theory that
explains the origin of spirals and rings in relation to chaotic orbits,
galaxies with stronger bars should have a higher spiral arms pitch angle when
compared to galaxies with weaker bars. A sub-sample of barred-spiral galaxies
in the Ohio State University Bright Galaxy Survey, was used to analyze the
spiral arms pitch angle. These were compared with bar strengths taken from the
literature. It was found that the galaxies in which the spiral arms maintain a
logarithmic shape for more than 70$\degr$ seem to corroborate the predicted
trend. | astro-ph_CO |
Probing below the neutrino floor with the first generation of stars: We show that the mere observation of the first stars (Pop III stars) in the
universe can be used to place tight constraints on the strength of the
interaction between dark matter and regular, baryonic matter. We apply this
technique to a candidate Pop III stellar complex discovered with the Hubble
Space Telescope at $z \sim 7$ and find bounds that are competitive with, or
even stronger than, current direct detection experiments, such as XENON1T, for
dark matter particles with mass ($m_X$) larger than about $100$ GeV. We also
show that the discovery of sufficiently massive Pop III stars could be used to
bypass the main limitations of direct detection experiments: the neutrino
background to which they will be soon sensitive. | astro-ph_CO |
Absence of a Periodic Component in Quasar z-Distribution: Since the discovery of quasars in papers often appeared and appear the
assertions that the redshift quasar distribution includes a periodic component
with the period $\Delta z = 0.063$ or 0.11. A statement of such kind, if it is
correct, may manifest the existence of a far order in quasar distribution in
cosmological time, that might lead to a fundamental revision all the
cosmological paradigm. In the present time there is a unique opportunity to
check this statement with a high precision, using the rich statictics of 2dF
and SDSS catalogues (about 85000 quasars). Our analysis indicates that the
periodic component in distribution of quasar redshifts is absent at high
confidence level. | astro-ph_CO |
An Improved Calculation of the Non-Gaussian Halo Mass Function: The abundance of collapsed objects in the universe, or halo mass function, is
an important theoretical tool in studying the effects of primordially generated
non-Gaussianities on the large scale structure. The non-Gaussian mass function
has been calculated by several authors in different ways, typically by
exploiting the smallness of certain parameters which naturally appear in the
calculation, to set up a perturbative expansion. We improve upon the existing
results for the mass function by combining path integral methods and saddle
point techniques (which have been separately applied in previous approaches).
Additionally, we carefully account for the various scale dependent combinations
of small parameters which appear. Some of these combinations in fact become of
order unity for large mass scales and at high redshifts, and must therefore be
treated non-perturbatively. Our approach allows us to do this, and to also
account for multi-scale density correlations which appear in the calculation.
We thus derive an accurate expression for the mass function which is based on
approximations that are valid over a larger range of mass scales and redshifts
than those of other authors. By tracking the terms ignored in the analysis, we
estimate theoretical errors for our result and also for the results of others.
We also discuss the complications introduced by the choice of smoothing filter
function, which we take to be a top-hat in real space, and which leads to the
dominant errors in our expression. Finally, we present a detailed comparison
between the various expressions for the mass functions, exploring the accuracy
and range of validity of each. | astro-ph_CO |
A new analysis of fine-structure constant measurements and modelling
errors from quasar absorption lines: We present an analysis of 23 absorption systems along the lines of sight
towards 18 quasars in the redshift range of $0.4 \leq z_{abs} \leq 2.3$
observed on the Very Large Telescope (VLT) using the Ultraviolet and Visual
Echelle Spectrograph (UVES). Considering both statistical and systematic error
contributions we find a robust estimate of the weighted mean deviation of the
fine-structure constant from its current, laboratory value of
$\Delta\alpha/\alpha=\left(0.22\pm0.23\right)\times10^{-5}$, consistent with
the dipole variation reported in Webb et al. and King et al. This paper also
examines modelling methodologies and systematic effects. In particular we focus
on the consequences of fitting quasar absorption systems with too few absorbing
components and of selectively fitting only the stronger components in an
absorption complex. We show that using insufficient continuum regions around an
absorption complex causes a significant increase in the scatter of a sample of
$\Delta\alpha/\alpha$ measurements, thus unnecessarily reducing the overall
precision. We further show that fitting absorption systems with too few
velocity components also results in a significant increase in the scatter of
$\Delta\alpha/\alpha$ measurements, and in addition causes
$\Delta\alpha/\alpha$ error estimates to be systematically underestimated.
These results thus identify some of the potential pitfalls in analysis
techniques and provide a guide for future analyses. | astro-ph_CO |
Photodissociation chemistry footprints in the Starburst galaxy NGC 253: We report the first detection of PDR molecular tracers, namely HOC+, and CO+,
and confirm the detection of the also PDR tracer HCO towards the starburst
galaxy NGC 253, claimed to be mainly dominated by shock heating and in an
earlier stage of evolution than M 82, the prototypical extragalactic PDR. Our
CO+ detection suffers from significant blending to a group of transitions of
13CH3OH, tentatively detected for the first time in the extragalactic
interstellar medium. These species are efficiently formed in the highly UV
irradiated outer layers of molecular clouds, as observed in the late stage
nuclear starburst in M 82. The molecular abundance ratios we derive for these
molecules are very similar to those found in M 82. This strongly supports the
idea that these molecules are tracing the PDR component associated with the
starburst in the nuclear region of NGC 253. A comparison with the predictions
of chemical models for PDRs shows that the observed molecular ratios are
tracing the outer layers of UV illuminated clouds up to two magnitudes of
visual extinction. Chemical models, which include grain formation and
photodissociation of HNCO, support the scenario of a photo-dominated chemistry
as an explanation to the abundances of the observed species. From this
comparison we conclude that the molecular clouds in NGC 253 are more massive
and with larger column densities than those in M 82, as expected from the
evolutionary stage of the starbursts in both galaxies. | astro-ph_CO |
$H_0$ Tension, Phantom Dark Energy and Cosmological Parameter
Degeneracies: Phantom dark energy can produce amplified cosmic acceleration at late times,
thus increasing the value of $H_0$ favored by CMB data and releasing the
tension with local measurements of $H_0$. We show that the best fit value of
$H_0$ in the context of the CMB power spectrum is degenerate with a constant
equation of state parameter $w$, in accordance with the approximate effective
linear equation $H_0 + 30.93\; w - 36.47 = 0$ ($H_0$ in $km \; sec^{-1} \;
Mpc^{-1}$). This equation is derived by assuming that both $\Omega_{0 \rm
m}h^2$ and $d_A=\int_0^{z_{rec}}\frac{dz}{H(z)}$ remain constant (for invariant
CMB spectrum) and equal to their best fit Planck/$\Lambda$CDM values as $H_0$,
$\Omega_{0 \rm m}$ and $w$ vary. For $w=-1$, this linear degeneracy equation
leads to the best fit $H_0=67.4 \; km \; sec^{-1} \; Mpc^{-1}$ as expected. For
$w=-1.22$ the corresponding predicted CMB best fit Hubble constant is $H_0=74
\; km \; sec^{-1} \; Mpc^{-1}$ which is identical with the value obtained by
local distance ladder measurements while the best fit matter density parameter
is predicted to decrease since $\Omega_{0 \rm m}h^2$ is fixed. We verify the
above $H_0-w$ degeneracy equation by fitting a $w$CDM model with fixed values
of $w$ to the Planck TT spectrum showing also that the quality of fit
($\chi^2$) is similar to that of $\Lambda$CDM. However, when including SnIa,
BAO or growth data the quality of fit becomes worse than $\Lambda$CDM when $w<
-1$. Finally, we generalize the $H_0-w(z)$ degeneracy equation for
$w(z)=w_0+w_1\; z/(1+z)$ and identify analytically the full $w_0-w_1$ parameter
region that leads to a best fit $H_0=74\; km \; sec^{-1} \; Mpc^{-1}$ in the
context of the Planck CMB spectrum. This exploitation of $H_0-w(z)$ degeneracy
can lead to immediate identification of all parameter values of a given $w(z)$
parametrization that can potentially resolve the $H_0$ tension. | astro-ph_CO |
Velocity waves in the Hubble diagram: signature of local galaxy clusters: The Universe expansion rate is modulated around local inhomogeneities due to
their gravitational potential. Velocity waves are then observed around galaxy
clusters in the Hubble diagram. This paper studies them in a ~738 Mpc wide,
with 2048^3 particles, cosmological simulation of our cosmic environment
(a.k.a. CLONE: Constrained LOcal & Nesting Environment Simulation). For the
first time, the simulation shows that velocity waves that arise in the
lines-of-sight of the most massive dark matter halos agree with those observed
in local galaxy velocity catalogs in the lines-of-sight of Coma and several
other local (Abell) clusters. For the best-constrained clusters such as Virgo
and Centaurus, i.e. those closest to us, secondary waves caused by galaxy
groups, further into the non-linear regime, also stand out. This match is not
utterly expected given that before being evolved into a fully non-linear z=0
state, assuming $\Lambda$CDM, CLONE initial conditions are constrained with
solely linear theory, power spectrum and highly uncertain and sparse local
peculiar velocities. Additionally, Gaussian fits to velocity wave envelopes
show that wave properties are tightly tangled with cluster masses. This link is
complex though and involves the environment and formation history of the
clusters. Using machine learning techniques to grasp more thoroughly the
complex wave-mass relation, velocity waves could in the near future be used to
provide additional and independent mass estimates from galaxy dynamics within
large cluster radii. | astro-ph_CO |
How clustering dark energy affects matter perturbations: The rate of structure formation in the Universe is different in homogeneous
and clustered dark energy models. The degree of dark energy clustering depends
on the magnitude of its effective sound speed $c^{2}_{\rm eff}$ and for $c_{\rm
eff}=0$ dark energy clusters in a similar fashion to dark matter while for
$c_{\rm eff}=1$ it stays (approximately) homogeneous. In this paper we consider
two distinct equations of state for the dark energy component, $w_{\rm
d}=const$ and $w_{\rm d}=w_0+w_1\left(\frac{z}{1+z}\right)$ with $c_{\rm eff}$
as a free parameter and we try to constrain the dark energy effective sound
speed using current available data including SnIa, Baryon Acoustic Oscillation,
CMB shift parameter ({\em Planck} and {\em WMAP}), Hubble parameter, Big Bang
Nucleosynthesis and the growth rate of structures $f\sigma_{8}(z)$. At first we
derive the most general form of the equations governing dark matter and dark
energy clustering under the assumption that $c_{\rm eff}=const$.
Finally, performing an overall likelihood analysis we find that the
likelihood function peaks at $c_{\rm eff}=0$, however the dark energy sound
speed is degenerate with respect to the cosmological parameters, namely
$\Omega_{\rm m}$ and $w_{\rm d}$. | astro-ph_CO |
Newtonian acceleration scales in spiral galaxies: We revisit the issue of the constancy of the dark matter (DM) and baryonic
Newtonian acceleration scales within the DM scale radius by considering a large
sample of late - type galaxies. We rely on a Markov Chain Monte Carlo (MCMC)
method to estimate the parameters of the halo model and the stellar mass - to -
light ratio and then propagate the uncertainties from the rotation curve data
to the estimate of the acceleration scales. This procedure allows us to compile
a catalog of 58 objects with estimated values of the $B$ band absolute
magnitude $M_B$, the virial mass $M_{vir}$, the DM and baryonic Newtonian
accelerations (denoted as $g_{DM}(r_0)$ and $g_{bar}(r_0)$, respectively)
within the scale radius $r_0$ which we use to investigate whether it is
possible to define a universal acceleration scale. We find a weak but
statistically meaningful correlation with $M_{vir}$ thus making us argue
against the universality of the acceleration scales. However, the results
somewhat depend on the sample adopted so that a careful analysis of selection
effects should be carried out before any definitive conclusion can be drawn. | astro-ph_CO |
New Strong Line Abundance Diagnostics for \HII Regions: Effects of
$κ$-Distributed Electron Energies and New Atomic Data: Recently, \citet{Nicholls12}, inspired by \emph{in situ} observations of
solar system astrophysical plasmas, suggested that the electrons in \HII
regions are characterised by a $\kappa$-distribution of electron energies
rather than by a simple Maxwell-Boltzmann distribution. Here we have collected
together the new atomic data within a modified photoionisation code to explore
the effects of both the new atomic data and the $\kappa$-distribution on the
strong-line techniques used to determine chemical abundances in \HII regions.
By comparing the recombination temperatures ($T_{\rm rec}$) with the forbidden
line temperatures ($T_{\rm FL}$) we conclude that $ \kappa \sim 20$. While
representing only a mild deviation from equilibrium, this is sufficient to
strongly influence abundances determined using methods which depend on
measurements of the electron temperature from forbidden lines. We present a
number of new emission line ratio diagnostics which cleanly separate the two
parameters determining the optical spectrum of \HII regions - the ionisation
parameter $q$ or $\cal{U}$ and the chemical abundance; 12+log(O/H). An
automated code to extract these parameters is presented. Using the homogeneous
dataset from \citet{vanZee98}, we find self-consistent results between all
these different diagnostics. The systematic errors between different line ratio
diagnostics are much smaller than was found in the earlier strong line work.
Overall the effect of the $\kappa$-distribution on the strong line abundances
derived solely on the basis of theoretical models is rather small. | astro-ph_CO |
Cosmology-marginalized approaches in Bayesian model comparison: the
neutrino mass as a case study: We propose here a \emph{novel} method which singles out the \emph{a priori}
unavoidable dependence on the underlying cosmological model when extracting
parameter constraints, providing robust limits which only depend on the
considered dataset. Interestingly, when dealing with several possible
cosmologies and interpreting the Bayesian preference in terms of the Gaussian
statistical evidence, the preferred model is much less favored than when only
two cases are compared. As a working example, we apply our approach to the
cosmological neutrino mass bounds, which play a fundamental role not only in
establishing the contribution of relic neutrinos to the dark matter of the
Universe, but also in the planning of future experimental searches of the
neutrino character and of the neutrino mass ordering. | astro-ph_CO |
Measuring the global 21-cm signal with the MWA-I: improved measurements
of the Galactic synchrotron background using lunar occultation: We present early results from a project to measure the sky-averaged (global),
redshifted $21\,$cm signal from the Epoch of Reionisation (EoR), using the
Murchison Widefield Array (MWA) telescope. Because interferometers are not
sensitive to a spatially-invariant global average, they cannot be used to
detect this signal using standard techniques. However, lunar occultation of the
radio sky imprints a spatial structure on the global signal, allowing us to
measure the average brightness temperature of the patch of sky immediately
surrounding the Moon. In this paper we present one night of Moon observations
with the MWA between 72 - 230 MHz and verify our techniques to extract the
background sky temperature from measurements of the Moon's flux density. We
improve upon previous work using the lunar occultation technique by using a
more sophisticated model for reflected `earthshine' and by employing image
differencing to remove imaging artefacts. We leave the Moon's (constant) radio
brightness temperature as a free parameter in our fit to the data and as a
result, measure $T_{\rm{moon}} = 180 \pm 12 $ K and a Galactic synchrotron
spectral index of $-2.64\pm0.14$, at the position of the Moon. Finally, we
evaluate the prospects of the lunar occultation technique for a global EoR
detection and map out a way forward for future work with the MWA. | astro-ph_CO |
Constraints on the abundance of primordial black holes with different
mass distributions from lensing of fast radio bursts: Primordial black holes (PBHs) has been considered to form a part of dark
matter for a long time but the possibility has been poorly constrained over a
wide mass range, including the stellar mass range ($1-100~M_{\odot}$). However,
due to the discovery of merger events of black hole binaries by LIGO-Virgo
gravitational wave observatories, the interest for PBHs in the stellar mass
window has been aroused again. Fast radio bursts (FRBs) are bright radio
transients with millisecond duration and very high all-sky occurrence rate.
Lensing effect of these bursts has been proposed as one of the optimal probes
for constraining the abundance of PBHs in the stellar mass range. In this
paper, we first investigate constraints on the abundance of PBHs from the
latest $593$ FRB observations for both the monochromatic mass distribution and
three other popular extended mass distributions related to different formation
mechanisms of PBHs. It is found that constraints from currently public FRB
observations are relatively weaker than those from existing gravitational wave
detections. Furthermore, we forecast constraining power of future FRB
observations on the abundance of PBHs with different mass distributions of PBHs
and different redshift distributions of FRBs taken into account. Finally, We
find that constraints of parameter space on extended mass distributions from
$\sim10^5$ FRBs with $\overline{\Delta t}\leq1 ~\rm ms$ would be comparable
with what can be constrained from gravitational wave events. It is foreseen
that upcoming complementary multi-messenger observations will yield
considerable constraints on the possibilities of PBHs in this intriguing mass
window. | astro-ph_CO |
Evolution of X-ray Cavities in Galaxy Clusters: The physics of X-ray cavities in galaxy clusters is constrained by their
observed morphological evolution, which depends on such poorly-understood
properties as the turbulent density field and magnetic fields. Here we combine
numerical simulations that include subgrid turbulence and software that
produces synthetic X-ray observations to examine the evolution of X-ray
cavities in the the absence of magnetic fields. Our results reveal an
anisotropic size evolution that is very different from simplified, analytical
predictions. These differences highlight some of the key issues that must be
accurately quantified when studying AGN-driven cavities, and help to explain
why the inferred pV energy in these regions appears to be correlated with their
distance from the cluster center. Interpreting X-ray observations will require
detailed modeling of effects including mass-entrainment, distortion by drag
forces, and projection. Current limitations do not allow a discrimination
between purely hydrodynamic and magnetically-dominated models for X-ray
cavities. | astro-ph_CO |
A Redshift Survey of Herschel Far-Infrared Selected Starbursts and
Implications for Obscured Star Formation: We present Keck spectroscopic observations and redshifts for a sample of 767
Herschel-SPIRE selected galaxies (HSGs) at 250, 350, and 500um, taken with the
Keck I Low Resolution Imaging Spectrometer (LRIS) and the Keck II DEep Imaging
Multi-Object Spectrograph (DEIMOS). The redshift distribution of these SPIRE
sources from the Herschel Multitiered Extragalactic Survey (HerMES) peaks at
z=0.85, with 731 sources at z<2 and a tail of sources out to z~5. We measure
more significant disagreement between photometric and spectroscopic redshifts
(<delta_z>/(1+z)>=0.29) than is seen in non-infrared selected samples, likely
due to enhanced star formation rates and dust obscuration in infrared-selected
galaxies. We estimate that the vast majority (72-83%) of z<2 Herschel-selected
galaxies would drop out of traditional submillimeter surveys at 0.85-1mm. We
estimate the luminosity function and implied star-formation rate density
contribution of HSGs at z<1.6 and find overall agreement with work based on
24um extrapolations of the LIRG, ULIRG and total infrared contributions. This
work significantly increased the number of spectroscopically confirmed
infrared-luminous galaxies at z>>0 and demonstrates the growing importance of
dusty starbursts for galaxy evolution studies and the build-up of stellar mass
throughout cosmic time. [abridged] | astro-ph_CO |
A new gravitational N-body simulation algorithm for investigation of
cosmological chaotic advection: Recently alternative approaches in cosmology seeks to explain the nature of
dark matter as a direct result of the non-linear spacetime curvature due to
different types of deformation potentials. In this context, a key test for this
hypothesis is to examine the effects of deformation on the evolution of large
scales structures. An important requirement for the fine analysis of this pure
gravitational signature (without dark matter elements) is to characterize the
position of a galaxy during its trajectory to the gravitational collapse of
super clusters at low redshifts. In this context, each element in an
gravitational N-body simulation behaves as a tracer of collapse governed by the
process known as chaotic advection (or lagrangian turbulence). In order to
develop a detailed study of this new approach we develop the COsmic LAgrangian
TUrbulence Simulator (COLATUS) to perform gravitational N-body simulations
based on Compute Unified Device Architecture (CUDA) for graphics processing
units (GPUs). In this paper we report the first robust results obtained from
COLATUS. | astro-ph_CO |
The evolution of galaxy intrinsic alignments in the MassiveBlack II
universe: We investigate the redshift evolution of the intrinsic alignments (IA) of
galaxies in the \texttt{MassiveBlackII} (MBII) simulation. We select galaxy
samples above fixed subhalo mass cuts ($M_h>10^{11,12,13}~M_{\odot}/h$) at
$z=0.6$ and trace their progenitors to $z=3$ along their merger trees. Dark
matter components of $z=0.6$ galaxies are more spherical than their progenitors
while stellar matter components tend to be less spherical than their
progenitors. The distribution of the galaxy-subhalo misalignment angle peaks at
$\sim10~\mathrm{deg}$ with a mild increase with time. The evolution of the
ellipticity-direction~(ED) correlation amplitude $\omega(r)$ of galaxies (which
quantifies the tendency of galaxies to preferentially point towards surrounding
matter overdensities) is governed by the evolution in the alignment of
underlying dark matter~(DM) subhaloes to the matter density of field, as well
as the alignment between galaxies and their DM subhaloes. At scales
$\sim1~\mathrm{cMpc}/h$, the alignment between DM subhaloes and matter
overdensity gets suppressed with time, whereas the alignment between galaxies
and DM subhaloes is enhanced. These competing tendencies lead to a complex
redshift evolution of $\omega(r)$ for galaxies at $\sim1~\mathrm{cMpc}/h$. At
scales $>1~\mathrm{cMpc}/h$, alignment between DM subhaloes and matter
overdensity does not evolve significantly; the evolution of the galaxy-subhalo
misalignment therefore leads to an increase in $\omega(r)$ for galaxies by a
factor of $\sim4$ from $z=3$ to $0.6$ at scales $>1~\mathrm{cMpc}/h$. The
balance between competing physical effects is scale dependant, leading to
different conclusions at much smaller scales($\sim0.1~\mathrm{Mpc}/h$). | astro-ph_CO |
The (black hole mass)-(host spheroid luminosity) relation at high and
low masses, the quadratic growth of black holes, and intermediate-mass black
hole candidates: From a sample of 72 galaxies with reliable supermassive black hole masses
M_(bh), we derive the M_(bh)-(host spheroid luminosity, L) relation for (i) the
subsample of 24 core-Sersic galaxies with partially depleted cores, and (ii)
the remaining subsample of 48 Sersic galaxies. Using (K_s)-band 2MASS data, we
find the near-linear relation M_(bh) ~ L_(K_s)^(1.10+/-0.20) for the
core-Sersic spheroids thought to be built in additive dry merger events, while
M_(bh) ~ L_(K_s)^(2.73+/-0.55) for the Sersic spheroids built from gas-rich
processes. After converting literature B-band disk galaxy magnitudes into
inclination- and dust-corrected bulge magnitudes, via a useful new equation
presented herein, we obtain a similar result. Unlike with the M_(bh)-sigma
diagram, which is also updated here using the same galaxy sample, it remains
unknown whether barred and non-barred Sersic galaxies are offset from each
other in the M_(bh)-L diagram.
While black hole feedback has typically been invoked to explain what was
previously thought to be a nearly constant M_bh/M_sph mass ratio of ~0.2%, we
advocate that the near-linear M_bh-L and M_bh-M_sph relations observed at high
masses may have instead largely arisen from the additive dry merging of
galaxies. We argue that feedback results in a dramatically different scaling
relation, such that black hole mass scales roughly quadratically with the
spheroid mass in Sersic galaxies. We therefore introduce a revised cold-gas
'quasar' mode feeding equation for semi-analytical models to reflect what we
dub the "quadratic growth" of black holes in Sersic galaxies built amidst
gas-rich processes. Finally, we use our new Sersic M_bh-L equations to predict
the masses of candidate `intermediate mass' black holes in almost 50 low
luminosity spheroids containing AGN, finding many masses between that of
stellar mass black holes and supermassive black holes. | astro-ph_CO |
The eROSITA Final Equatorial-Depth Survey (eFEDS): Characterization of
Morphological Properties of Galaxy Groups and Clusters: Understanding the cluster population of clusters of galaxies is of the utmost
importance for using cluster samples in both astrophysical and cosmological
studies. We present an in-depth analysis of the X-ray morphological parameters
of the galaxy clusters and groups detected in the eROSITA Final
Equatorial-Depth Survey (eFEDS). We study the eROSITA X-ray imaging data for a
sample of 325 clusters and groups that are significantly detected in the eFEDS
field. We characterize their dynamical properties by measuring a number of
dynamical estimators: concentration, central density, cuspiness, ellipticity,
power-ratios, photon asymmetry, and Gini coefficient. The galaxy clusters and
groups detected in eFEDS, covering a luminosity range of more than three orders
of magnitude and large redshift range out to 1.2 provide an ideal sample for
studying the redshift and luminosity evolution of the morphological parameters
and characterization of the underlying dynamical state of the sample. Based on
these measurements we construct a new dynamical indicator, relaxation score,
for all the clusters in the sample. We find no evidence for bimodality in the
distribution of morphological parameters of our clusters, rather we observe a
smooth transition from the cool-core to non-cool-core and from relaxed to
disturbed states. A significant evolution in redshift and luminosity is also
observed in the morphological parameters examined in this study after carefully
taking into account the selection effects. We determine that our eFEDS-selected
cluster sample, differently than ROSAT-based cluster samples, is not biased
toward relaxed clusters, but contains a similar fraction of disturbed as SZ
surveys. | astro-ph_CO |
Relativistic and non-Gaussianity contributions to the one-loop power
spectrum: We compute the one-loop density power spectrum including Newtonian and
relativistic contributions, as well as the primordial non-Gaussianity
contributions from $f_{\rm NL}$ and $g_{\rm NL}$ in the local configuration. To
this end we take solutions to the Einstein equations in the long-wavelength
approximation and provide expressions for the matter density perturbation at
second and third order. These solutions have shown to be complementary to the
usual Newtonian cosmological perturbations. We confirm a sub-dominant effect
from pure relativistic terms, manifested at scales dominated by cosmic
variance, but find that a sizable effect of order one comes from $g_{\rm NL}$
values allowed by Planck-2018 constraints, manifested at scales probed by
forthcoming galaxy surveys like DESI and Euclid. As a complement, we present
the matter bispectrum at the tree-level including the mentioned contributions. | astro-ph_CO |
Hunting WIMPs with LISA: Correlating dark matter and gravitational wave
signals: The thermal freeze-out mechanism in its classical form is tightly connected
to physics beyond the Standard Model around the electroweak scale, which has
been the target of enormous experimental efforts. In this work we study a dark
matter model in which freeze-out is triggered by a strong first-order phase
transition in a dark sector, and show that this phase transition must also
happen close to the electroweak scale, i.e. in the temperature range relevant
for gravitational wave searches with the LISA mission. Specifically, we
consider the spontaneous breaking of a $U(1)^\prime$ gauge symmetry through the
vacuum expectation value of a scalar field, which generates the mass of a
fermionic dark matter candidate that subsequently annihilates into dark Higgs
and gauge bosons. In this set-up the peak frequency of the gravitational wave
background is tightly correlated with the dark matter relic abundance, and
imposing the observed value for the latter implies that the former must lie in
the milli-Hertz range. A peculiar feature of our set-up is that the dark sector
is not necessarily in thermal equilibrium with the Standard Model during the
phase transition, and hence the temperatures of the two sectors evolve
independently. Nevertheless, the requirement that the universe does not enter
an extended period of matter domination after the phase transition, which would
strongly dilute any gravitational wave signal, places a lower bound on the
portal coupling that governs the entropy transfer between the two sectors. As a
result, the predictions for the peak frequency of gravitational waves in the
LISA band are robust, while the amplitude can change depending on the initial
dark sector temperature. | astro-ph_CO |
Intrinsic Shapes of Very Flat Elliptical Galaxies: Photometric data from the literature is combined with triaxial mass models to
derive variation in the intrinsic shapes of the light distribution of
elliptical galaxies NGC 720, 2768 and 3605. The inferred shape variation in
given by a Bayesian probability distribution, assuming a uniform prior. The
likelihood of obtaining the data is calculated by using ensemble of triaxial
models. We apply the method to infer the shape variation of a galaxy, using the
ellipticities and the difference in the position angles at two suitably chosen
points from the profiles of the photometric data. Best constrained shape
parameters are found to be the short to long axial ratios at small and large
radii, and the absolute values of the triaxiallity difference between these
radii. | astro-ph_CO |
Inflationary tensor fossils in large-scale structure: Inflation models make specific predictions for a tensor-scalar-scalar
three-point correlation, or bispectrum, between one gravitational-wave (tensor)
mode and two density-perturbation (scalar) modes. This tensor-scalar-scalar
correlation leads to a local power quadrupole, an apparent departure from
statistical isotropy in our Universe, as well as characteristic four-point
correlations in the current mass distribution in the Universe. So far, the
predictions for these observables have been worked out only for single-clock
models in which certain consistency conditions between the tensor-scalar-scalar
correlation and tensor and scalar power spectra are satisfied. Here we review
the requirements on inflation models for these consistency conditions to be
satisfied. We then consider several examples of inflation models, such as
non-attractor and solid inflation models, in which these conditions are put to
the test. In solid inflation the simplest consistency conditions are already
violated whilst in the non-attractor model we find that, contrary to the
standard scenario, the tensor-scalar-scalar correlator probes directly relevant
model-dependent information. We work out the predictions for observables in
these models. For non-attractor inflation we find an apparent local quadrupolar
departure from statistical isotropy in large-scale structure but that this
power quadrupole decreases very rapidly at smaller scales. The consistency of
the CMB quadrupole with statistical isotropy then constrains the distance scale
that corresponds to the transition from the non-attractor to attractor phase of
inflation to be larger than the currently observable horizon. Solid inflation
predicts clustering fossils signatures in the current galaxy distribution that
may be large enough to be detectable with forthcoming, and possibly even
current, galaxy surveys. | astro-ph_CO |
The 6x2pt method: supernova velocities meet multiple tracers: We present a new methodology to analyse in a comprehensive way large-scale
and supernovae (or any other distance indicator) surveys. Our approach combines
galaxy and supernova position and redshift data with supernova peculiar
velocities, obtained through their magnitude scatter, to construct a 6x2pt
analysis which includes six power spectra. The 3x3 correlation matrix of these
spectra expresses exhaustively the information content of the surveys at the
linear level. We proceed then to forecast the performance of future surveys
like LSST and 4MOST with a Fisher Matrix analysis, adopting both a
model-dependent and a model-independent approach. We compare the performance of
the 6x2pt approach to the traditional one using only galaxy clustering and some
recently proposed combinations of galaxy and supernovae data and quantify the
possible gains by optimally extracting the linear information. We show that the
6x2pt method shrinks the uncertainty area in the $\sigma_8, \gamma$ plane by
more than half when compared to the traditional method. The combined clustering
and velocity data on the growth of structures has uncertainties at similar
levels to those of the CMB but exhibit orthogonal degeneracies, and the
combined constraints yield improvements of factors of 5 in each of the five
cosmological parameters here considered. Concerning the model-independent
results, we find that our method can improve the constraints on $H(z)/H_0$ in
all redshift bins by more than 70% with respect to the galaxy clustering alone
and by 30% when supernova velocities (but not clustering) are considered,
reaching a precision of 3-4% at high redshifts. | astro-ph_CO |
Evidence for Three Accreting Black Holes in a Galaxy at z~1.35: A
Snapshot of Recently Formed Black Hole Seeds?: One of the key open questions in cosmology today pertains to understanding
when, where and how super massive black holes form, while it is clear that
mergers likely play a significant role in the growth cycles of black holes, how
supermassive black holes form, and how galaxies grow around them. Here, we
present Hubble Space Telescope WFC3/IR grism observations of a clumpy galaxy at
z=1.35, with evidence for 10^6 - 10^7 Msun rapidly growing black holes in
separate sub-components of the host galaxy. These black holes could have been
brought into close proximity as a consequence of a rare multiple galaxy merger
or they could have formed in situ. Such holes would eventually merge into a
central black hole as the stellar clumps/components presumably coalesce to form
a galaxy bulge. If we are witnessing the in-situ formation of multiple black
holes, their properties can inform seed formation models and raise the
possibility that massive black holes can continue to emerge in star-forming
galaxies as late as z=1.35 (4.8 Gyr after the Big Bang). | astro-ph_CO |
Contamination of the Epoch of Reionization power spectrum in the
presence of foregrounds: We construct foreground simulations comprising spatially correlated
extragalactic and diffuse Galactic emission components and calculate the
`intrinsic' (instrument-free) two-dimensional spatial power spectrum and the
cylindrically and spherically averaged three-dimensional k-space power spectra
of the Epoch of Reionization (EoR) and our foreground simulations using a
Bayesian power spectral estimation framework. This leads us to identify a model
dependent region of optimal signal estimation for our foreground and EoR
models, within which the spatial power in the EoR signal relative to
foregrounds is maximised. We identify a target field dependent region, in
k-space, of intrinsic foreground power spectral contamination at low k_perp and
k_parallel and a transition to a relatively foreground-free intrinsic EoR
window in the complement to this region. The contaminated region of k-space
demonstrates that simultaneous estimation of the EoR and foregrounds is
important for obtaining statistically robust estimates of the EoR power
spectrum; biased results will be obtained from methodologies that ignore their
covariance. Using simulated observations with frequency dependent uv-coverage
and primary beam, with the former derived for HERA in 37-antenna and
331-antenna configuration, we recover instrumental power spectra consistent
with their intrinsic counterparts. We discuss the implications of these results
for optimal strategies for unbiased estimation of the EoR power spectrum. | astro-ph_CO |
Induced Gravity and the Attractor Dynamics of Dark Energy/Dark Matter: Attractor solutions that give dynamical reasons for dark energy to act like
the cosmological constant, or behavior close to it, are interesting
possibilities to explain cosmic acceleration. Coupling the scalar field to
matter or to gravity enlarges the dynamical behavior; we consider both
couplings together, which can ameliorate some problems for each individually.
Such theories have also been proposed in a Higgs-like fashion to induce gravity
and unify dark energy and dark matter origins. We explore restrictions on such
theories due to their dynamical behavior compared to observations of the cosmic
expansion. Quartic potentials in particular have viable stability properties
and asymptotically approach general relativity. | astro-ph_CO |
A Survey of z~6 Quasars in the SDSS Deep Stripe. II. Discovery of Six
Quasars at z_{AB}>21: We present the discovery of six new quasars at z~6 selected from the Sloan
Digital Sky Survey (SDSS) southern survey, a deep imaging survey obtained by
repeatedly scanning a stripe along the celestial equator. The six quasars are
about two magnitudes fainter than the luminous z~6 quasars found in the SDSS
main survey and one magnitude fainter than the quasars reported in Paper I
(Jiang et al. 2008). Four of them comprise a complete flux-limited sample at
21<z_AB<21.8 over an effective area of 195 deg^2. The other two quasars are
fainter than z_AB=22 and are not part of the complete sample. The quasar
luminosity function at z~6 is well described as a single power law
\Phi(L_{1450}) \propto L_{1450}^{\beta} over the luminosity range
-28<M_{1450}<-25. The best-fitting slope \beta varies from -2.6 to -3.1,
depending on the quasar samples used, with a statistical error of 0.3-0.4.
About 40% of the quasars discovered in the SDSS southern survey have very
narrow Lya emission lines, which may indicate small black hole masses and high
Eddington luminosity ratios, and therefore short black hole growth time scales
for these faint quasars at early epochs. | astro-ph_CO |
Accurate photometric redshift probability density estimation - method
comparison and application: We introduce an ordinal classification algorithm for photometric redshift
estimation, which significantly improves the reconstruction of photometric
redshift probability density functions (PDFs) for individual galaxies and
galaxy samples. As a use case we apply our method to CFHTLS galaxies. The
ordinal classification algorithm treats distinct redshift bins as ordered
values, which improves the quality of photometric redshift PDFs, compared with
non-ordinal classification architectures. We also propose a new single value
point estimate of the galaxy redshift, that can be used to estimate the full
redshift PDF of a galaxy sample. This method is competitive in terms of
accuracy with contemporary algorithms, which stack the full redshift PDFs of
all galaxies in the sample, but requires orders of magnitudes less storage
space.
The methods described in this paper greatly improve the log-likelihood of
individual object redshift PDFs, when compared with a popular Neural Network
code (ANNz). In our use case, this improvement reaches 50\% for high redshift
objects ($z \geq 0.75$).
We show that using these more accurate photometric redshift PDFs will lead to
a reduction in the systematic biases by up to a factor of four, when compared
with less accurate PDFs obtained from commonly used methods. The cosmological
analyses we examine and find improvement upon are the following: gravitational
lensing cluster mass estimates, modelling of angular correlation functions, and
modelling of cosmic shear correlation functions. | astro-ph_CO |
Testing physical models for dipolar asymmetry with CMB polarization: The cosmic microwave background (CMB) temperature anisotropies exhibit a
large-scale dipolar power asymmetry. To determine whether this is due to a
real, physical modulation or is simply a large statistical fluctuation requires
the measurement of new modes. Here we forecast how well CMB polarization data
from \Planck\ and future experiments will be able to confirm or constrain
physical models for modulation. Fitting several such models to the \Planck\
temperature data allows us to provide predictions for polarization asymmetry.
While for some models and parameters \Planck\ polarization will decrease error
bars on the modulation amplitude by only a small percentage, we show,
importantly, that cosmic-variance-limited (and in some cases even \Planck)
polarization data can decrease the errors by considerably better than the
expectation of $\sqrt 2$ based on simple $\ell$-space arguments. We project
that if the primordial fluctuations are truly modulated (with parameters as
indicated by \Planck\ temperature data) then \Planck\ will be able to make a
2$\sigma$ detection of the modulation model with 20--75\% probability,
increasing to 45--99\% when cosmic-variance-limited polarization is considered.
We stress that these results are quite model dependent. Cosmic variance in
temperature is important: combining statistically isotropic polarization with
temperature data will spuriously increase the significance of the temperature
signal with 30\% probability for \Planck. | astro-ph_CO |
Curvature Perturbations and non-Gaussianities from Waterfall Phase
Transition during Inflation: We consider a variant of hybrid inflation where the waterfall phase
transition happens during inflation. By adjusting the parameters associated
with the mass of the waterfall field we arrange that the phase transition is
not sharp so inflation can proceed for about 50-60 e-folds after the waterfall
phase transition. We show that one can work in the limit where the quantum
back-reactions are subdominant compared to the classical back-reactions. It is
shown that significant amount of large scale curvature perturbations are
induced from the entropy perturbations. The curvature perturbations spectral
index is either blue or red depending on whether the mode of interest leaves
the horizon before the phase transition or after the phase transition. This can
have interesting observational consequences on CMB. The non-Gaussianity
parameter $f_{NL}$ is calculated to be $\lesssim 1$ but much bigger than the
slow-roll parameters. | astro-ph_CO |
Observational constraints on the metagalactic Ly$α$ photon
scattering rate at high redshift: The scattering of Ly$\alpha$ photons from the first radiating sources in the
Universe plays a pivotal role in 21-cm radio detections of Cosmic Dawn and the
Epoch of Reionization through the Wouthuysen-Field effect. New data from JWST
show the Ly$\alpha$ photon scattering rate exceeds that required to decouple
the intergalactic hydrogen spin temperature from that of the Cosmic Microwave
Background up to $z\sim14$ and render the neutral hydrogen visible over the
main redshift range expected for the Epoch of Reionization. | astro-ph_CO |
Discovery of a diffuse optical line emitting halo in the core of the
Centaurus cluster of galaxies: Line emission outside the protection of the
filaments: We present the discovery of diffuse optical line emission in the Centaurus
cluster seen with the MUSE IFU. The unparalleled sensitivity of MUSE allows us
to detect the faint emission from these structures which extend well beyond the
bounds of the previously known filaments. Diffuse structures (emission
surrounding the filaments, a northern shell and an extended Halo) are detected
in many lines typical of the nebulae in cluster cores ([NII]$_{\lambda
6548\&6583}$ ,[SII]$_{\lambda 6716\&6731}$, [OI]$_{\lambda 6300}$,
[OIII]$_{\lambda 4959\&5007}$ etc.) but are more than an order of magnitude
fainter than the filaments, with the faint halo only detected through the
brightest line in the spectrum ([NII]$_{\lambda 6583}$). These structures are
shown to be kinematically distinct from the stars in the central galaxy and
have different physical and excitation states to the filaments. Possible
origins are discussed for each structure in turn and we conclude that shocks
and/or pressure imbalances are resulting in gas dispersed throughout the
cluster core, formed from either disrupted filaments or direct cooling, which
is not confined to the bright filaments. | astro-ph_CO |
Multiwavelength study of nearly face-on low surface brightness disk
galaxies: We study the ages of a large sample (1,802) of nearly face-on disk low
surface brightness galaxies (LSBGs) by using the evolutionary population
synthesis (EPS) model PEGASE with exponential decreasing star formation rate to
fit their multiwavelength spectral energy distributions (SEDs) from
far-ultraviolet (FUV) to near-infrared (NIR). The derived ages of LSBGs are 1-5
Gyr for most of the sample no matter the constant or varying dust extinction is
adopted, which are similar to most of the previous studies on smaller samples.
This means that these LSBGs formed their majority of stars quite recently.
However, a small part of the sample (~2-3%) have larger ages as 5-8 Gyr,
meaning their major star forming process may occur earlier. At the same time, a
large sample (5,886) of high surface brightness galaxies (HSBGs) are selected
and studied in the same method for comparisons. The derived ages are 1-5 Gyr
for most of the sample (97%) as well. These may mean that probably these LSBGs
have no much different star formation history from their HSBGs counterparts.
But we should notice that the HSBGs are about 0.2 Gyr younger generally, which
could mean that the HSBGs may have more recent star forming activities than the
LSBGs. | astro-ph_CO |
Large-Scale Clustering of Cosmic Voids: We study the clustering of voids using $N$-body simulations and simple
theoretical models. The excursion-set formalism describes fairly well the
abundance of voids identified with the watershed algorithm, although the void
formation threshold required is quite different from the spherical collapse
value. The void cross bias $b_{\rm c} $ is measured and its large-scale value
is found to be consistent with the peak background split results. A simple
fitting formula for $b_{\rm c} $ is found. We model the void auto-power
spectrum taking into account the void biasing and exclusion effect. A good fit
to the simulation data is obtained for voids with radii $\gtrsim$ 30 Mpc/$h$,
especially when the void biasing model is extended to 1-loop order. However,
the best-fit bias parameters do not agree well with the peak-background split
results. Being able to fit the void auto-power spectrum is particularly
important not only because it is the direct observable in galaxy surveys, but
also our method enables us to treat the bias parameters as nuisance parameters,
which are sensitive to the techniques used to identify voids. | astro-ph_CO |
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