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A new substantive proton to electron mass ratio constraint on rolling
scalar field cosmologies: New PKS1830-211 radio frequency observations of methanol at a redshift of
0.88582 have established the most stringent limits on changes in the proton to
electron mass ratio mu to date. The observations place the limit of (delta
mu)/mu </= (0.0 +/- 1.0) x 10^{-7} which is approximately a factor of four
lower than the previous lowest limit at a redshift of 0.6742. This stringent
limit at a look back time of roughly half the age of the universe has profound
implications for rolling scalar field cosmologies and the new physics that they
require. Many of these cosmologies invoke a scalar field phi that is also
coupled to the electromagnetic field causing the values of the fundamental
constants, mu and the fine structure constant alpha to roll with time. If the
lowest expected value of the coupling to mu, zeta_{mu}$ is invoked the new
limit requires a limit on the dark energy equation of state parameter w such
that w+1 </= 0.001 at a redshift of 0.88582. This eliminates almost all of the
expected parameter space for such cosmologies and new physics that have a
coupling to the electromagnetic field. In these cases the limit requires that w
must be extremely close to -1 for the last half of the age of the universe or
that the coupling of the rolling scalar field to mu and the electromagnetic
field be significantly below or at the limit of its expected range. The new
observations solidify the role of fundamental constants in providing probes of
the possible cosmologies and new physics to explain the acceleration of the
expansion of the universe. | The Optically Unbiased GRB Host (TOUGH) survey. IV. Lyman-alpha emitters: We report the results of a spectroscopic search for Lyman-alpha emission from
gamma-ray burst host galaxies. Based on the well-defined TOUGH sample of 69
X-ray selected Swift GRBs, we have targeted the hosts of a subsample of 20 GRBs
known from afterglow spectroscopy to be in the redshift range 1.8-4.5. We
detect Lya emission from 7 out of the 20 hosts, with the typical limiting
3sigma line flux being 8E-18 erg/cm2/s, corresponding to a Lya luminosity of
6E41 erg/s at z=3. The Lya luminosities for the 7 hosts in which we detect Lya
emission are in the range (0.6-2.3)E42 erg/s corresponding to star-formation
rates of 0.6-2.1 Msun/yr (not corrected for extinction). The rest-frame Lya
equivalent widths (EWs) for the 7 hosts are in the range 9-40A. For 6 of the 13
hosts for which Lya is not detected we place fairly strong 3sigma upper limits
on the EW (<20A), while for others the EW is either unconstrained or has a less
constraining upper limit. We find that the distribution of Lya EWs is
inconsistent with being drawn from the Lya EW distribution of bright Lyman
break galaxies at the 98.3% level, in the sense that the TOUGH hosts on average
have larger EWs than bright LBGs. We can exclude an early indication, based on
a smaller, heterogeneous sample of pre-Swift GRB hosts, that all GRB hosts are
Lya emitters. We find that the TOUGH hosts on average have lower EWs than the
pre-Swift GRB hosts, but the two samples are only inconsistent at the 92%
level. The velocity centroid of the Lya line is redshifted by 200-700 km/s with
respect to the systemic velocity, similar to what is seen for LBGs, possibly
indicating star-formation driven outflows from the host galaxies. There seems
to be a trend between the Lya EW and the optical to X-ray spectral index of the
afterglow (beta_OX), hinting that dust plays a role in the observed strength
and even presence of Lya emission. [ABRIDGED] |
MOND and the unique void galaxy KK246: MOND predictions are compared with the mass discrepancy, Gamma (the
dynamical-to-baryon mass ratio) deduced from the recently measured rotation
curve, for the gas-rich, dwarf galaxy KK246, "the only galaxy observed in the
local void". KK246 is special in at least two regards: a. It is, to my
knowledge, the record holder for the largest mass discrepancy deduced from a
rotation curve, Gamma= 15. b. It is very isolated, residing in a large, very
empty void. I also discuss another extreme case: Andromeda IV, a dwarf
considered here for the first time in light of MOND, with a very large mass
discrepancy, Gamma =12, also conforming accurately to the MOND prediction. In
both cases, MOND predicts Gamma, or the total dynamical mass at the last
observed radius, from only the knowledge of the small mass of baryons. If MOND
is accepted as the root of the mass discrepancy, these are just two more
expected, albeit reassuring, conformities. However, in the framework of the
dark-matter paradigm--where the mass discrepancy is strongly dependent on the
buildup history of a galaxy--every new such conformity with a tight law is
another difficult-to-understand surprise, and does carry a new import: What, in
the LCDM paradigm, would prevent such galactic baryons from residing in a halo
of half, or twice, the observed rotational velocities, instead of selecting
exactly the velocities predicted by MOND? This conundrum is especially poignant
for KK246, whose great isolation points to a relatively unique buildup history.
This note underscores the individual importance of each galaxy as a new test,
as opposed to the view of them all as a statistical ensemble. | Designing Horndeski and the effective fluid approach: We present a family of designer Horndeski models, i.e. models that have a
background exactly equal to that of the $\Lambda$CDM model but perturbations
given by the Horndeski theory. Then, we extend the effective fluid approach to
Horndeski theories, providing simple analytic formulae for the equivalent dark
energy effective fluid pressure, density and velocity. We implement the dark
energy effective fluid formulae in our code EFCLASS, a modified version of the
widely used Boltzmann solver CLASS, and compare the solution of the
perturbation equations with those of the code hi_CLASS which already includes
Horndeski models. We find that our simple modifications to the vanilla code are
accurate to the level of $\sim 0.1\%$ with respect to the more complicated
hi_CLASS code. Furthermore, we study the kinetic braiding model both on and off
the attractor and we find that even though the full case has a proper
$\Lambda$CDM model limit for large $n$, it is not appropriately smooth, thus
causing the quasistatic approximation to break down. Finally, we focus on our
designer model (HDES), which has both a smooth $\Lambda$CDM limit and
well-behaved perturbations, and we use it to perform Markov Chain Monte Carlo
analyses to constrain its parameters with the latest cosmological data. We find
that our HDES model can also alleviate the soft $2\sigma$ tension between the
growth data and Planck 18 due to a degeneracy between $\sigma_8$ and one of its
model parameters that indicates the deviation from the $\Lambda$CDM model. |
Superhorizon entanglement entropy from particle decay in inflation: In inflationary cosmology all particle states decay as a consequence of the
lack of kinematic thresholds. The decay of an initial single particle state
yields an \emph{entangled quantum state of the product particles}. We
generalize and extend a manifestly unitary field theoretical method to obtain
the time evolution of the quantum state. We consider the decay of a light
scalar field with mass $M\ll H$ with a cubic coupling in de Sitter space-time.
Radiative corrections feature an infrared enhancement manifest as poles in
$\Delta=M^2/3H^2$ and we obtain the quantum state in an expansion in $\Delta$.
To leading order in $\Delta$ the pure state density matrix describing the decay
of a particle with sub-horizon wavevector is dominated by the emission of
superhorizon quanta, describing \emph{entanglement between superhorizon and
subhorizon fluctuations and correlations across the horizon}. Tracing over the
superhorizon degrees of freedom yields a mixed state density matrix from which
we obtain the entanglement entropy. Asymptotically this entropy grows with the
\emph{physical} volume as a consequence of more modes of the decay products
crossing the Hubble radius. A generalization to localized wave packets is
provided. The cascade decay of single particle states into many particle states
is discussed. We conjecture on \emph{possible} impact of these results on
non-gaussianity and on the ``low multipole anomalies'' of the CMB. | Searching for Sterile Neutrino with X-ray Intensity Mapping: The cosmological X-ray emission associated to the possible radiative decay of
sterile neutrinos is composed by a collection of lines at different energies.
For a given mass, each line corresponds to a given redshift. In this work, we
cross correlate such line emission with catalogs of galaxies tracing the dark
matter distribution at different redshifts. We derive observational prospects
by correlating the X-ray sky that will be probed by the eROSITA and Athena
missions with current and near future photometric and spectroscopic galaxy
surveys. A relevant and unexplored fraction of the parameter space of sterile
neutrinos can be probed by this technique. |
Partially Acoustic Dark Matter Cosmology and Cosmological Constraints: Observations of the cosmic microwave background (CMB) together with weak
lensing measurements of the clustering of large scale cosmological structures
and local measurements of the Hubble constant pose a challenge to the standard
$\Lambda$CDM cosmological model. On one side CMB observations imply a Hubble
constant that is lower than local measurements and an amplitude of the lensing
signal that is higher than direct measurements from weak lensing surveys. We
investigate a way of relieving these tensions by adding dark radiation tightly
coupled to an acoustic part of the dark matter sector and compare it to massive
neutrino solutions. While these models offer a way of separately relieving the
Hubble and weak lensing tensions they are prevented from fully accommodating
both at the same time since the CMB requires additional cold dark matter when
adding acoustic dark matter or massive neutrinos to preserve the same sharpness
of the acoustic peaks which counteracts the desired growth suppression. | Ambiguities in gravitational lens models: the density field from the
source position transformation: Strong gravitational lensing is regarded as the most precise technique to
measure the mass in the inner region of galaxies or galaxy clusters. In
particular, the mass within one Einstein radius can be determined with an
accuracy of order of a few percent or better, depending on the image
configuration. For other radii, however, degeneracies exist between galaxy
density profiles, precluding an accurate determination of the enclosed mass.
The source position transformation (SPT), which includes the well-known
mass-sheet transformation (MST) as a special case, describes this degeneracy of
the lensing observables in a more general way. In this paper we explore
properties of an SPT, removing the MST to leading order, i.e., we consider
degeneracies which have not been described before. The deflection field
$\boldsymbol{\hat{\alpha}}(\boldsymbol{\theta})$ resulting from an SPT is not
curl-free in general, and thus not a deflection that can be obtained from a
lensing mass distribution. Starting from a variational principle, we construct
lensing potentials that give rise to a deflection field
$\boldsymbol{\tilde{\alpha}}$, which differs from $\boldsymbol{\hat{\alpha}}$
by less than an observationally motivated upper limit. The corresponding mass
distributions from these 'valid' SPTs are studied: their radial profiles are
modified relative to the original mass distribution in a significant and
non-trivial way, and originally axi-symmetric mass distributions can obtain a
finite ellipticity. These results indicate a significant effect of the SPT on
quantitative analyses of lens systems. We show that the mass inside the
Einstein radius of the original mass distribution is conserved by the SPT;
hence, as is the case for the MST, the SPT does not affect the mass
determination at the Einstein radius. [...] |
Ca II Absorbers in the Sloan Digital Sky Survey: Statistics: We present the results of a survey for CaII 3934,3969 absorption-line systems
culled from ~ 95,000 Sloan Digital Sky Survey (SDSS) Data Release 7 and Data
Release 9 quasar spectra. With 435 doublets identified in the catalog, this
list is the largest CaII catalog compiled to date, spanning redshifts z < 1.34,
which corresponds to the most recent ~ 8.9 Gyrs of the history of the Universe.
We derive statistics on the CaII rest equivalent width distribution (REW) and
incidence (number density per unit redshift). We find that the lambda3934 REW
distribution cannot be described by a single exponential function. A double
exponential function is required to produce a satisfactory description. The
function can be written as a sum of weak and strong components: dn/dW =
(N_wk*/W_wk*) exp(-W/W_wk*) + (N_str*/W_str*) exp(-W/W_str*). A maximum
likelihood fit to the unbinned data indicates: N_wk*=0.140 +/- 0.029,
W_wk*=0.165 +/- 0.020 A, N_str*=0.024 +/- 0.020, and W_str*=0.427 +/- 0.101 A.
This suggests that the CaII absorbers are composed of at least two distinct
populations. The incidence (product of integrated absorber cross section and
their co-moving number density) of the overall CaII absorber population does
not show evidence for evolution in the standard cosmology. The normalization of
the no-evolution curve, i.e., the value of the CaII incidence extrapolated to
redshift z=0, for lambda 3934 >= 0.3 A, is n_0=0.017 +/- 0.001. In comparison
to MgII surveys, we found that only 3% of MgII systems in the SDSS have CaII,
confirming that it is rare to identify CaII in quasar absorption-line surveys.
We also report on some preliminary investigations of the nature of the two
populations of CaII absorbers, and show that they can likely be distinguished
using their MgII properties. | Twinlike models for parametrized dark energy: We study cosmological models involving a single real scalar field that has an
equation of state parameter which evolves with cosmic time. We highlight some
common parametrizations for the equation of state as a function of redshift in
the context of twinlike theories. The procedure is used to introduce different
models that have the same acceleration parameter, with the very same energy
densities and pressure in flat spacetime. |
Correlations in the (Sub)millimeter background from ACTxBLAST: We present measurements of the auto- and cross-frequency correlation power
spectra of the cosmic (sub)millimeter background at: 250, 350, and 500 um
(1200, 860, and 600 GHz) from observations made with the Balloon-borne Large
Aperture Submillimeter Telescope, BLAST; and at 1380 and 2030 um (218 and 148
GHz) from observations made with the Atacama Cosmology Telescope, ACT. The
overlapping observations cover 8.6 deg^2 in an area relatively free of Galactic
dust near the south ecliptic pole (SEP). The ACT bands are sensitive to
radiation from the CMB, the Sunyaev-Zel'dovich (SZ) effect from galaxy
clusters, and to emission by radio and dusty star-forming galaxies (DSFGs),
while the dominant contribution to the BLAST bands is from DSFGs. We confirm
and extend the BLAST analysis of clustering with an independent pipeline, and
also detect correlations between the ACT and BLAST maps at over 25sigma
significance, which we interpret as a detection of the DSFGs in the ACT maps.
In addition to a Poisson component in the cross-frequency power spectra, we
detect a clustered signal at >4sigma, and using a model for the DSFG evolution
and number counts, we successfully fit all our spectra with a linear clustering
model and a bias that depends only on redshift and not on scale. Finally, the
data are compared to, and generally agree with, phenomenological models for the
DSFG population. This study represents a first of its kind, and demonstrates
the constraining power of the cross-frequency correlation technique to
constrain models for the DSFGs. Similar analyses with more data will impose
tight constraints on future models. | Global analysis of luminosity- and colour-dependent galaxy clustering in
the Sloan Digital Sky Survey: We present a Halo Occupation Distribution (HOD) analysis of the luminosity-
and colour-dependent galaxy clustering in the Sloan Digital Sky Survey. A
novelty of our technique is that it uses a combination of clustering
measurements in luminosity bins to perform a global likelihood analysis,
simultaneously constraining the HOD parameters for a range of luminosity
thresholds. We present simple, smooth fitting functions which accurately
describe the resulting luminosity dependence of the best-fit HOD parameters. To
minimise systematic halo modelling effects, we use theoretical halo 2-point
correlation functions directly measured and tabulated from a suite of $N$-body
simulations spanning a large enough dynamic range in halo mass and spatial
separation. Thus, our modelling correctly accounts for non-linear and
scale-dependent halo bias as well as any departure of halo profiles from
universality, and we additionally account for halo exclusion using the hard
sphere approximation. Using colour-dependent clustering information, we
constrain the satellite galaxy red fraction in a model-independent manner which
does not rely on any group-finding algorithm. We find that the resulting
luminosity dependence of the satellite red fraction is significantly shallower
than corresponding measurements from galaxy group catalogues, and we provide a
simple fitting function to describe this dependence. Our fitting functions are
readily usable in generating low-redshift mock galaxy catalogues, and we
discuss some potentially interesting applications as well as possible
extensions of our technique. |
The Fundamental Plane of Early-Type Galaxies as a Confounding
Correlation: Early-type galaxies are characterized by many scaling relations. One of them,
the so-called fundamental plane is a relatively tight correlation between three
variables, and has resisted a clear physical understanding despite many years
of intensive research. Here, we show that the correlation between the three
variables of the fundamental plane can be the artifact of the effect of another
parameter influencing all, so that the fundamental plane may be understood as a
confounding correlation. Indeed, the complexity of the physics of galaxies and
of their evolution suggests that the main confounding parameter must be related
to the level of diversification reached by the galaxies. Consequently, many
scaling relations for galaxies are probably evolutionary correlations. | Imprint of Accretion Disk-Induced Migration on Gravitational Waves from
Extreme Mass Ratio Inspirals: We study the effects of a thin gaseous accretion disk on the inspiral of a
stellar--mass black hole into a supermassive black hole. We construct a
phenomenological angular momentum transport equation that reproduces known disk
effects. Disk torques modify the gravitational wave phase evolution to
detectable levels with LISA for reasonable disk parameters. The Fourier
transform of disk-modified waveforms acquires a correction with a different
frequency trend than post-Newtonian vacuum terms. Such inspirals could be used
to detect accretion disks with LISA and to probe their physical parameters. |
Dark matter halo concentrations: a short review: This review analyzes the state and advancement of the dark matter halo
concentrations over the last two decades. It begins with presenting the article
that brought the field to the limelight and then follows through with other
research works that studied the concentrations of dark matter haloes over the
ages. Besides the discussion of the halo mass-concentration relation and its
evolution, we examine the effects of cosmology, subhaloes and environment on
the relation. In addition to theoretical halo concentrations, observational
dark matter halo concentrations are also considered. This review synthesizes
the progress in this field into a clear piece of article. | Relative distribution of dark matter, gas, and stars around cosmic
filaments in the IllustrisTNG simulation: We present a comprehensive study of the distribution of matter around
different populations of large-scale cosmic filaments, using the IllustrisTNG
simulation at z=0. We computed the dark matter (DM), gas, and stellar radial
density profiles of filaments, and we characterise the distribution of the
baryon fraction in these structures. We find that baryons exactly follow the
underlying DM distribution only down to r~7 Mpc to the filament spines. At
shorter distances (r<7 Mpc), the baryon fraction profile of filaments departs
from the cosmic value $\Omega_\mathrm{b} / \Omega_\mathrm{m}$. While in the
r~0.7-7 Mpc radial domain this departure is due to the radial accretion of the
warm-hot intergalactic medium (WHIM) towards the filament cores (creating an
excess of baryons with respect to the cosmic fraction), the cores of filaments
(r<0.7 Mpc) show a clear baryon depletion instead. The analysis of the
efficiency of active galactic nuclei (AGN) feedback events in filaments reveals
that they are potentially powerful enough to eject gas outside of the
gravitational potential wells of filaments. We show that the large-scale
environment (i.e. denser versus less dense, hotter versus colder regions) has a
non-negligible effect on the absolute values of the DM, gas, and stellar
densities around filaments. Nevertheless, the relative distribution of baryons
with respect to the underlying DM density field is found to be independent of
the filament population. Finally, we provide scaling relations between the gas
density, temperature, and pressure for the different populations of cosmic
filaments. We compare these relations to those pertaining to clusters of
galaxies, and find that these cosmic structures occupy separate regions of the
density-temperature and density-pressure planes. |
Voids and Halos in Voids statistics as a probe of the Expansion History
of the Universe: Structures in the Universe are arranged into the cosmic web. Distributions,
statistics, and evolutions of the structures can be used as probes for
cosmological models. We investigate the number density of voids and dark matter
halos-in-voids in the Excursion Set Theory (EST). We study the Markov and
non-Markov frameworks of EST in both spherical and ellipsoidal collapse models.
Afterward, we compare the number density of voids and halos-in-voids in the
standard $\Lambda$CDM and the reconstructed model. The reconstructed model is a
model-independent reconstruction based on background observations. This work
explores the effects of the collapse model barrier in the different EST
frameworks on the statistics of voids and the statistics of halos-in-voids.
Finally, we find the hint that cosmological models can be distinguished by the
number density of halos-in-voids in the $1.0-2.5$ redshift range. The maximum
difference is observed in $z\sim1.9$. | A brief review on cosmological analysis of galaxy surveys with multiple
tracers: Galaxy redshift surveys are one of the key probes in modern cosmology. In the
data analysis of galaxy surveys, the precision of the statistical measurement
is primarily limited by the cosmic variance on large scales. Fortunately, this
limitation can in principle be evaded by observing multiple types of biased
tracers. In this brief review, we present the idea of the multi-tracer method,
outline key steps in the data analysis, and show several worked examples based
on the GAMA, BOSS and eBOSS galaxy surveys. |
Probing High-Redshift Galaxy Formation at the Highest Luminosities: New
Insights from DEIMOS Spectroscopy: We present DEIMOS spectroscopic observations of the most UV-luminous
star-forming galaxies at 3.2<z<4.6. Our sample contains galaxies with
luminosities of L*<L<7L* and is one of the largest samples to date of the most
UV-luminous galaxies at these redshifts. Our data confirm 41 star-forming
galaxies at 3.2<z<4.6 and validate the clean selection of the photometric
candidates. We find that the fraction of Lya emitting galaxies increases with
decreasing UV luminosity. We find strong evidence of large-scale outflows,
transporting the neutral/ionized gas in the interstellar medium away from the
galaxy. Galaxies exhibiting both interstellar absorption and Lya emission lines
show a significant velocity offset between the two features (200-1140 km/s). We
find tentative evidence that this measure of the outflow velocity increases
with UV luminosity and/or stellar mass. The luminosity- and mass-dependent
outflow strengths suggest that the efficiency of feedback and enrichment of the
surrounding medium depend on these parameters. We present composite spectra of
the absorption-line-only and Lya-emitting subsets of the UV luminous galaxies
at z~3.7. The composite spectra are similar to those of lower-z and
lower-luminosity LBGs samples, but with some subtle differences. Analyses of
the composite spectra suggest that the UV luminous LBGs at z~3.7 may have a
higher covering fraction of absorbing gas, and may be older than their lower-z
and lower-luminosity counterparts. In addition, we have discovered 5 galaxies
that belong to a massive overdensity at z=3.78. Finally, two galaxies each show
two distinct sets of interstellar absorption features. The latter may be a sign
of a final stage of major merger, or clumpy disk formation. Their presence
implies that frequency of such sources among our luminous z~3.7 LBGs may be an
order of magnitude higher than in lower redshift and lower luminosity samples. | Bootstrapping Multi-Field Inflation: non-Gaussianities from light
scalars revisited: Primordial non-Gaussianities from multi-field inflation are a leading target
for cosmological observations, because of the possible large correlations
generated between long and short distances. These signatures are captured by
the local shape of the scalar bispectrum. In this paper, we revisit the
nonlinearities of the conversion process from additional light scalars into
curvature perturbations during inflation. We provide analytic templates for
correlation functions valid at any kinematical configuration, using the
cosmological bootstrap as a main computational tool. Our results include the
possibility of large breaking of boost symmetry, in the form of small speeds of
sound for both the inflaton and the mediators. We consider correlators coming
from the tree-level exchange of a massless scalar field. By introducing a
late-time cutoff, we identify that the symmetry constraints on the correlators
are modified. This leads to anomalous conformal Ward identities, and
consequently the bootstrap differential equations acquire a source term that
depends on this cutoff. The solutions to the differential equations are scalar
seed functions that incorporate these late-time growth effects. Applying
weight-shifting operators to auxiliary "seed" functions, we obtain a systematic
classification of shapes of non-Gaussianity coming from massless exchange. For
theories with de Sitter symmetry, we compare the resulting shapes with the ones
obtained via the $\delta N$ formalism, identifying missing contributions away
from the squeezed limit. For boost-breaking scenarios, we derive a novel class
of shape functions with phenomenologically distinct features. Specifically, the
new shape provides a simple extension of equilateral non-Gaussianity: the
signal peaks at a geometric configuration controlled by the ratio of the sound
speeds of the mediator and the inflaton. |
Primordial black holes from long-range scalar forces and scalar
radiative cooling: We describe a new scenario for the formation of primordial black holes
(PBHs). In the early Universe, the long-range forces mediated by the scalar
fields can lead to formation of halos of heavy particles even during the
radiation-dominated era. The same interactions result in the emission of scalar
radiation from the motion and close encounters of particles in such halos.
Radiative cooling due the scalar radiation allows the halos to collapse to
black holes. We illustrate this scenario on a simple model with fermions
interacting via the Yukawa forces. The abundance and the mass function of PBHs
are suitable to account for all dark matter, or for some gravitational wave
events detected by LIGO. The model relates the mass of the dark-sector
particles to the masses and abundance of dark matter PBHs in a way that can
explain why the dark matter and the ordinary matter have similar mass
densities. The model also predicts a small contribution to the number of
effective light degrees of freedom, which can help reconcile different
measurements of the Hubble constant. | $\texttt{fRevolution}$ $-$ Relativistic Cosmological Simulations in
$f(R)$ Gravity I: Methodology: We present the new relativistic cosmological particle-mesh code
$\texttt{fRevolution}$, based on $\texttt{gevolution}$, aimed at simulating
non-linear structure formation in $f(R)$ gravity. We introduce the general
framework and approximation scheme, and the set of equations used to solve for
the full set of gravitational perturbations. We show results for a point mass
field and for cosmological simulations in the Hu-Sawicki model, and compare
them to those of existing Newtonian codes. A more detailed analysis and
discussion of our solutions will be carried out in a following paper. |
Phenomenology of Gravitational Aether as a solution to the Old
Cosmological Constant Problem: One of the deepest and most long-standing mysteries in physics has been the
huge discrepancy between the observed vacuum density and our expectations from
theories of high energy physics, which has been dubbed the Old Cosmological
Constant problem. One proposal to address this puzzle at the semi-classical
level is to decouple quantum vacuum from space-time geometry via a modification
of gravity that includes an incompressible fluid, known as Gravitational
Aether. In this paper, we discuss classical predictions of this theory along
with its compatibility with cosmological and experimental tests of gravity. We
argue that deviations from General Relativity (GR) in this theory are sourced
by pressure or vorticity. In particular, the theory predicts that the
gravitational constant for radiation is 33% larger than that of
non-relativistic matter, which is preferred by (most) cosmic microwave
background (CMB), Lyman-Alpha forest, and Lithium-7 primordial abundance
observations, while being consistent with other cosmological tests at ~2-sigma
level. It is further shown that all Parametrized Post-Newtonian (PPN)
parameters have the standard GR values aside from the anomalous coupling to
pressure, which has not been directly measured. A more subtle prediction of
this model (assuming irrotational aether) is that the (intrinsic)
gravitomagnetic effect is 33% larger than GR prediction. This is consistent
with current limits from LAGEOS and Gravity Probe B at ~2-sigma level. | Resolving the nucleus of Centaurus A at mid-IR wavelengths: We have observed Centaurus A with the MID-infrared Interferometric instrument
(MIDI) at the Very Large Telescope Interferometer (VLTI) at resolutions of 7 -
15 mas (at 12.5 micron) and filled gaps in the (u,v) coverage in comparison to
earlier measurements. We are now able to describe the nuclear emission in terms
of geometric components and derive their parameters by fitting models to the
interferometric data. With simple geometrical models, the best fit is achieved
for an elongated disk with flat intensity profile with diameter 76 +/- 9 mas x
35 +/- 2 mas (1.41 +/- 0.17 pc x 0.65 +/- 0.03 pc) whose major axis is oriented
at a position angle (PA) of 10.1 +/- 2.2 degrees east of north. A point source
contributes 47 +/- 11 % of the nuclear emission at 12.5 micron. There is also
evidence that neither such a uniform nor a Gaussian disk are good fits to the
data. This indicates that we are resolving more complicated small-scale
structure in AGNs with MIDI, as has been seen in Seyfert galaxies previously
observed with MIDI. The PA and inferred inclination i = 62.6 +2.1/-2.6 degrees
of the dust emission are compared with observations of gas and dust at larger
scales. |
Cosmic Microwave Background anisotropies generated by domain wall
networks: We develop a numerical tool for the fast computation of the temperature and
polarization power spectra generated by domain wall networks, by extending the
publicly available CMBACT code --- that calculates the CMB signatures generated
by active sources --- to also describe domain wall networks. In order to
achieve this, we adapt the Unconnected Segment model for cosmic strings to also
describe domain wall networks, and use it to model the energy-momentum of
domain wall networks throughout their cosmological history. We use this new
tool to compute and study the TT, EE, TE and BB power spectra generated by
standard domain wall networks, and derive a conservative constraint on the
energy scale of the domain wall-forming phase transition of $\upeta
<0.92\,\,{\rm MeV}$ (which is a slight improvement over the original Zel'dovich
bound of $1\,\,{\rm MeV}$). | Bound Dark Energy: towards understanding the nature of the Dark Energy: We present a complete analysis of the observational constraints and
cosmological implications of our Bound Dark Energy (BDE) model aimed to explain
the late-time cosmic acceleration of the universe. BDE is derived from particle
physics and corresponds to the lightest meson field $\phi$ dynamically formed
at low energies due to the strong gauge coupling constant. The evolution of the
dark energy is determined by the scalar potential
$V(\phi)=\Lambda_c^{4+2/3}\phi^{-2/3}$ arising from non-perturbative effects at
a condensation scale $\Lambda_c$ and scale factor $a_c$, related each other by
$a_c\Lambda_c/\mathrm{eV}=1.0934\times 10^{-4}$. We present the full background
and perturbation evolution at a linear level. Using current observational data,
we obtain the constraints $a_c=(2.48 \pm 0.02)\times10^{-6}$ and
$\Lambda_c=(44.09 \pm 0.28) \textrm{ eV}$, which is in complete agreement with
our theoretical prediction $\Lambda_c^{th}=34^{+16}_{-11}\textrm{ eV}$. The
bounds on the equation of state today, the dark energy density and the
expansion rate are $w_\mathrm{BDE 0}=-0.929\pm 0.007$,
$\Omega_\mathrm{BDE0}=0.696\pm0.007$ and $H_0=67.82\pm 0.05$ km s$^{-1}$Mpc,
respectively. Even though the constraints on the six Planck base parameters are
consistent at the 1$\sigma$ level between BDE and the concordance $\Lambda$CDM
model, BDE improves the likelihood ratio by 2.1 of the Baryon Acoustic
Oscillations (BAO) measurements with respect to $\Lambda$CDM and has an
equivalent fit for type Ia supernovae and the Cosmic Microwave Background data.
We present the constraints on the different cosmological parameters, and
particularly we show the tension between BDE and $\Lambda$CDM in the BAO
distance ratio $r_\mathrm{BAO}$ vs $H_\mathrm{0}$ and the growth index $\gamma$
at different redshifts, as well as the dark matter density at present time
$\Omega_ch^2$ vs $H_0$. |
The quest for extragalactic magnetic fields: We review the observational and theoretical constraints on extragalactic
magnetic fields across cosmic environment. In the next decade, the combination
of sophisticated numerical simulations and various observational probes might
succeed in constraining the still elusive origin of magnetic fields on the
largest scales in the Universe. | Future Constraints on Primordial Black Holes from XGIS-THESEUS: Current observations allow Primordial Black Holes (PBHs) in asteroid mass
range $10^{17}-10^{22}$ g to constitute the entire dark matter (DM) energy
density (barring a small mass range constrained by 21 cm observations). In this
work, we explore the possibility of probing PBH with masses
$10^{17}-10^{19}\,{\rm g}$ via upcoming X and Gamma Imaging Spectrometer (XGIS)
telescope array on-board the Transient High-Energy Sky and Early Universe
Surveyor (THESEUS) mission. While our projected limits are comparable with
those proposed in the literature for $10^{16}\,{\rm
g}\,<\,M_{\mathrm{PBH}}\,<\,10^{17}\,{\rm g}$, we show that the XGIS-THESEUS
mission can potentially provide the strongest bound for $10^{17}
\mathrm{~g}<M_{\mathrm{PBH}} \lesssim 3\times 10^{18} \mathrm{~g}$ for
non-rotating PBHs. The bounds become more stringent by nearly an order of
magnitude for maximally rotating PBHs in the mass range $5\times10^{15}\,{\rm
g}\,<\,M_{\rm PBH}\,\lesssim\,10^{19}\,{\rm g}$. |
Scalar models for the generalized Chaplygin gas and the structure
formation constraints: The generalized Chaplygin gas model represents an attempt to unify dark
matter and dark energy. It is characterized by a fluid with an equation of
state $p = - A/\rho^\alpha$. It can be obtained from a generalization of the
DBI action for a scalar, tachyonic field. At background level, this model gives
very good results, but it suffers from many drawbacks at perturbative level. We
show that, while for background analysis it is possible to consider any value
for $\alpha$, the perturbative analysis must be restricted to positive values
of $\alpha$. This restriction can be circumvented if the origin of the
generalized Chaplygin gas is traced back to a self-interacting scalar field,
instead of the DBI action. But, in doing so, the predictions coming from
formation of large scale structures reduce the generalized Chaplygin gas model
to a kind of quintessence model, and the unification scenario is lost, if the
scalar field is the canonical one. However, if the unification condition is
imposed from the beginning as a prior, the model may remain competitive. More
interesting results, concerning the unification program, are obtained if a
non-canonical self-interacting scalar field, inspired by Rastall's theory of
gravity, is imposed. In this case, an agreement with the background tests is
possible. | A Novel Scheme for Dark Matter Annihilation Feedback in Cosmological
Simulations: We present a new self-consistent method for incorporating dark matter
annihilation feedback (DMAF) in cosmological N-body simulations. The power
generated by DMAF is evaluated at each dark matter (DM) particle which allows
for flexible energy injection into the surrounding gas based on the specific DM
annihilation model under consideration. Adaptive, individual time steps for gas
and DM particles are supported and a new time-step limiter, derived from the
propagation of a Sedov--Taylor blast wave, is introduced. We compare this
donor-based approach with a receiver-based approach used in recent studies and
illustrate the differences by means of a toy example. Furthermore, we consider
an isolated halo and a cosmological simulation and show that for these
realistic cases, both methods agree well with each other. The extension of our
implementation to scenarios such as non-local energy injection,
velocity-dependent annihilation cross-sections, and DM decay is
straightforward. |
Mid-Infrared Spectral Indicators of Star-Formation and AGN Activity in
Normal Galaxies: We investigate the use of mid-infrared PAH bands, continuum and emission
lines as probes of star-formation and AGN activity in a sample of 100 `normal'
and local (z~0.1) galaxies. The MIR spectra were obtained with the Spitzer IRS
as part of the Spitzer-SDSS-GALEX Spectroscopic Survey (SSGSS) which includes
multi-wavelength photometry from the UV to the FIR and optical spectroscopy.
The spectra were decomposed using PAHFIT (Smith et al. 2007), which we find to
yield PAH equivalent widths (EW) up to ~30 times larger than the commonly used
spline methods. Based on correlations between PAH, continuum and emission line
properties and optically derived physical properties (gas phase metallicity,
radiation field hardness), we revisit the diagnostic diagram relating PAH EWs
and [NeII]/[OIV] and find it more efficient as distinguishing weak AGNs from
star-forming galaxies than when spline decompositions are used. The luminosity
of individual MIR component (PAH, continuum, Ne and molecular hydrogen lines)
are found to be tightly correlated to the total IR luminosity and can be used
to estimate dust attenuation in the UV and in Ha lines based on energy balance
arguments. | GRB lensing parallax: Closing primordial black hole dark matter mass
window: The primordial black hole (PBH) comprising full dark matter (DM) abundance is
currently allowed if its mass lies between $10^{-16}M_{\odot} \lesssim M
\lesssim 10^{-11} M_{\odot}$. This lightest mass range is hard to be probed by
ongoing gravitational lensing observations. In this paper, we advocate that an
old idea of the lensing parallax of Gamma-ray bursts (GRBs), observed
simultaneously by spatially separated detectors, can probe the unconstrained
mass range; and that of nearby stars can probe a heavier mass range. In
addition to various good properties of GRBs, astrophysical separations
achievable around us --- $r_\oplus \text{--}$ AU --- is just large enough to
resolve the GRB lensing by lightest PBH DM. |
Pulsar timing array constraints on spin-2 ULDM: Ultra-light Dark Matter (ULDM) models are suitable candidates for the
cosmological Dark Matter that may leave characteristic imprints in many
observables. Among other probes, signatures of ULDM can be searched for in
pulsar timing data. In this work we describe the effects of spin-2 ULDM on
pulsar timing arrays, extending previous results on lower spins. Spin-2 ULDM is
universally coupled to standard matter with dimensionless strength $\alpha$. We
estimate that current data could constrain this coupling in the mass range
$m\lesssim4\times10^{-22}$ eV at the $10^{-5}$ to $10^{-6}$ level, which is the
most competitive constraint in this mass range. A crucial feature of the spin-2
ULDM effect on pulsar timing is its anisotropic, quadrupolar shape. This
feature can be instrumental in differentiating the effects sourced by spin-2
ULDM from, for instance, scalar ULDM, and the systematics of a PTA experiment. | X-ray properties expected from AGN feedback in elliptical galaxies: The ISM evolution of elliptical galaxies experiencing feedback from accretion
onto a central black hole was studied recently with high-resolution 1D
hydrodynamical simulations including radiative heating and pressure effects, a
RIAF-like radiative efficiency, mechanical input from AGN winds, and
accretion-driven starbursts. Here we focus on the observational properties of
the models in the X-ray band (nuclear luminosity; hot ISM luminosity and
temperature; temperature and brightness profiles during quiescence and during
outbursts). The nuclear bursts last for ~10^7 yr, with a duty-cycle of a few X
(10^-3-10^-2); the present epoch bolometric nuclear emission is very
sub-Eddington. The ISM thermal luminosity \lx oscillates in phase with the
nuclear one; this helps reproduce statistically the observed large \lx
variation. In quiescence the temperature profile has a negative gradient;
thanks to past outbursts, the brightness profile lacks the steep shape typical
of inflowing models. Outbursts produce disturbances in these profiles. Most
significantly, a hot bubble from shocked hot gas is inflated at the galaxy
center; the bubble would be conical in shape, and show radio emission. The ISM
resumes a smooth appearance on a time-scale of ~200 Myr; the duty-cycle of
perturbances in the ISM is of the order of 5-10%. From the present analysis,
additional input physics is important in the ISM-black hole coevolution, to
fully account for the properties of real galaxies, as a confining external
medium and a jet. The jet will reduce further the mass available for accretion
(and then the Eddington ratio $l$), and may help, together with an external
pressure, to produce flat or positive temperature gradient profiles (observed
in high density environments). Alternatively, $l$ can be reduced if the switch
from high to low radiative efficiency takes place at a larger $l$ than
routinely assumed. |
Black-hole masses of type 1 AGN in the XMM-Newton bright serendipitous
survey: We derive masses of the central super-massive black hole (SMBH) and accretion
rates for 154 type1 AGN belonging to a well-defined X-ray-selected sample, the
XMM-Newton Serendipitous Sample (XBS). To this end, we use the most recent
"single-epoch" relations, based on Hbeta and MgII2798A emission lines, to
derive the SMBH masses. We then use the bolometric luminosities, computed on
the basis of an SED-fitting procedure, to calculate the accretion rates, both
absolute and normalized to the Eddington luminosity (Eddington ratio). The
selected AGNs cover a range of masses from 10^7 to 10^10 Msun with a peak
around 8x10^8 Msun and a range of accretion rates from 0.01 to ~50 Msun/year
(assuming an efficiency of 0.1), with a peak at ~1 Msun/year. The values of
Eddington ratio range from 0.001 to ~0.5 and peak at 0.1. | Unveiling Neutrino Halos with CMB Lensing: The existence of a cosmic neutrino background has been inferred indirectly
from cosmological surveys through its effect on the linear-theory evolution of
primordial density perturbations, as well as from measurements of the
primordial abundances of light elements. Constraints on the masses of the three
neutrino species imply that at least two of them move non-relativistically
today. As a consequence, non-linear evolution of density perturbations results
in the formation of neutrino halos around dark-matter halos. We study whether
these neutrino halos can be detected in the foreseeable future through
measurements of weak gravitational lensing of the cosmic microwave background,
thus providing, possibly, the first beyond-linear-theory signature of cosmic
neutrinos. |
Intergalactic Dust Extinction in Hydrodynamic Cosmological Simulations: Recently Menard et al. detected a subtle but systematic change in the mean
color of quasars as a function of their projected separation from foreground
galaxies, extending to comoving separations of ~10Mpc/h, which they interpret
as a signature of reddening by intergalactic dust. We present theoretical
models of this remarkable observation, using SPH cosmological simulations of a
(50Mpc/h)^3 volume. Our primary model uses a simulation with galactic winds and
assumes that dust traces the intergalactic metals. The predicted galaxy-dust
correlation function is similar in form to the galaxy-mass correlation
function, and reproducing the MSFR data requires a dust-to-metal mass ratio of
0.24, about half the value in the Galactic ISM. Roughly half of the reddening
arises in dust that is more than 100Kpc/h from the nearest massive galaxy. We
also examine a simulation with no galactic winds, which predicts a much smaller
fraction of intergalactic metals (3% vs. 35%) and therefore requires an
unphysical dust-to-metal ratio of 2.18 to reproduce the MSFR data. In both
models, the signal is dominated by sightlines with E(g-i)=0.001-0.1. The
no-wind simulation can be reconciled with the data if we also allow reddening
to arise in galaxies up to several x 10^10 Msun. The wind model predicts a mean
visual extinction of A_V ~0.0133 mag out to z=0.5, with a
sightline-to-sightline dispersion similar to the mean, which could be
significant for future supernova cosmology studies. Reproducing the MSFR
results in these simulations requires that a large fraction of ISM dust survive
its expulsion from galaxies and its residence in the intergalactic medium.
Future observational studies that provide higher precision and measure the
dependence on galaxy type and environment will allow detailed tests for models
of enriched galactic outflows and the survival of IG dust. | Primordial Non-Gaussianity and the Statistics of Weak Lensing and other
Projected Density Fields: Estimators for weak lensing observables such as shear and convergence
generally have non-linear corrections, which, in principle, make weak lensing
power spectra sensitive to primordial non-Gaussianity. In this paper, we
quantitatively evaluate these contributions for weak lensing auto- and
cross-correlation power spectra, and show that they are strongly suppressed by
projection effects. This is a consequence of the central limit theorem, which
suppresses departures from Gaussianity when the projection reaches over several
correlation lengths of the density field, L_P~55 [Mpc/h]. Furthermore, the
typical scales that contribute to projected bispectra are generally smaller
than those that contribute to projected power spectra. Both of these effects
are not specific to lensing, and thus affect the statistics of non-linear
tracers (e.g., peaks) of any projected density field. Thus, the clustering of
biased tracers of the three-dimensional density field is generically more
sensitive to non-Gaussianity than observables constructed from projected
density fields. |
The dust energy balance in the edge-on spiral galaxy NGC 4565: We combine new dust continuum observations of the edge-on spiral galaxy NGC
4565 in all Herschel/SPIRE (250, 350, 500 micron) wavebands, obtained as part
of the Herschel Reference Survey, and a large set of ancillary data (Spitzer,
SDSS, GALEX) to analyze its dust energy balance. We fit a radiative transfer
model for the stars and dust to the optical maps with the fitting algorithm
FitSKIRT. To account for the observed UV and mid-infrared emission, this
initial model was supplemented with both obscured and unobscured star-forming
regions. Even though these star-forming complexes provide an additional heating
source for the dust, the far-infrared/submillimeter emission long wards of 100
micron is underestimated by a factor of 3-4. This inconsistency in the dust
energy budget of NGC 4565 suggests that a sizable fraction (two-thirds) of the
total dust reservoir (Mdust ~ 2.9e+8 Msun) consists of a clumpy distribution
with no associated young stellar sources. The distribution of those dense dust
clouds would be in such a way that they remain unresolved in current
far-infrared/submillimeter observations and hardly comtribute to the
attenuation at optical wavelengths. More than two-thirds of the dust heating in
NGC 4565 is powered by the old stellar population, with localized embedded
sources supplying the remaining dust heating in NGC 4565. The results from this
detailed dust energy balance study in NGC 4565 is consistent with that of
similar analyses of other edge-on spirals. | Effects of overlapping sources on cosmic shear estimation: Statistical
sensitivity and pixel-noise bias: In Stage-IV imaging surveys, a significant amount of the cosmologically
useful information is due to sources whose images overlap with those of other
sources on the sky. The cosmic shear signal is primarily encoded in the
estimated shapes of observed galaxies and thus directly impacted by overlaps.
We introduce a framework based on the Fisher formalism to analyze effects of
overlapping sources (blending) on the estimation of cosmic shear. For the Rubin
Observatory Legacy Survey of Space and Time (LSST), we present the expected
loss in statistical sensitivity for the ten-year survey due to blending. We
find that for approximately 62% of galaxies that are likely to be detected in
full-depth LSST images, at least 1% of the flux in their pixels is from
overlapping sources. We also find that the statistical correlations between
measures of overlapping galaxies and, to a much lesser extent the higher shot
noise level due to their presence, decrease the effective number density of
galaxies, $N_{eff}$, by $\sim$18%. We calculate an upper limit on $N_{eff}$ of
39.4 galaxies per arcmin$^2$ in $r$ band. We study the impact of varying
stellar density on $N_{eff}$ and illustrate the diminishing returns of
extending the survey into lower Galactic latitudes. We extend the Fisher
formalism to predict the increase in pixel-noise bias due to blending for
maximum-likelihood (ML) shape estimators. We find that noise bias is sensitive
to the particular shape estimator and measure of ensemble-average shape that is
used, and properties of the galaxy that include redshift-dependent quantities
such as size and luminosity. |
Dark energy with rigid voids versus relativistic voids alone: The standard model of cosmology is dominated - at the present epoch - by dark
energy. Its voids are rigid and Newtonian within a relativistic background. The
model prevents them from becoming hyperbolic. Observations of rapid velocity
flows out of voids are normally interpreted within the standard model that is
rigid in comoving coordinates, instead of allowing the voids' density parameter
to drop below critical and their curvature to become negative. Isn't it time to
advance beyond nineteenth century physics and relegate dark energy back to the
"no significant evidence" box? | The influence of the environment on bar formation: Galaxy mergers and interactions are mechanisms which could drive the
formation of bars. Therefore, we could expect that the fraction of barred
galaxies increases with the local density. Here we show the first results of an
extensive search for barred galaxies in different environments. We conclude
that the bar fraction on bright (L>L*) field, Virgo, and Coma cluster galaxies
is compatible. These results point towards an scenario where the formation
and/or evolution of bars depend mostly on internal galaxy processes rather than
external ones. |
Structure formation in inhomogeneous Early Dark Energy models: We study the impact of Early Dark Energy fluctuations in the linear and
non-linear regimes of structure formation. In these models the energy density
of dark energy is non-negligible at high redshifts and the fluctuations in the
dark energy component can have the same order of magnitude of dark matter
fluctuations. Since two basic approximations usually taken in the standard
scenario of quintessence models, that both dark energy density during the
matter dominated period and dark energy fluctuations on small scales are
negligible, are not valid in such models, we first study approximate analytical
solutions for dark matter and dark energy perturbations in the linear regime.
This study is helpful to find consistent initial conditions for the system of
equations and to analytically understand the effects of Early Dark Energy and
its fluctuations, which are also verified numerically. In the linear regime we
compute the matter growth and variation of the gravitational potential
associated with the Integrated Sachs-Wolf effect, showing that these
observables present important modifications due to Early Dark Energy
fluctuations, though making them more similar to $\Lambda$CDM model. We also
make use of the Spherical Collapse model to study the influence of Early Dark
Energy fluctuations in the nonlinear regime of structure formation, especially
on $\delta_c$ parameter, and their contribution to the halo mass, which we show
can be of the order of 10%. We finally compute how the number density of halos
is modified in comparison to $\Lambda$CDM model and address the problem of how
to correct the mass function in order to take into account the contribution of
clustered dark energy. We conclude that the inhomogeneous Early Dark Energy
models are more similar to $\Lambda$CDM model than its homogeneous
counterparts. | A circular polarimeter for the Cosmic Microwave Background: A primordial degree of circular polarization of the Cosmic Microwave
Background is not observationally excluded. The hypothesis of primordial
dichroism can be quantitatively falsified if the plasma is magnetized prior to
photon decoupling since the initial V-mode polarization affects the evolution
of the temperature fluctuations as well as the equations for the linear
polarization. The observed values of the temperature and polarization angular
power spectra are used to infer constraints on the amplitude and on the
spectral slope of the primordial V-mode. Prior to photon decoupling magnetic
fields play the role of polarimeters insofar as they unveil the circular
dichroism by coupling the V-mode power spectrum to the remaining brightness
perturbations. Conversely, for angular scales ranging between 4 deg and 10 deg
the joined bounds on the magnitude of circular polarization and on the magnetic
field intensity suggest that direct limits on the V-mode power spectrum in the
range of 0.01 mK could directly rule out pre-decoupling magnetic fields in the
range of 10-100 nG. The frequency dependence of the signal is located, for the
present purposes, in the GHz range. |
The precision and accuracy of early Epoch of Reionization foreground
models: comparing MWA and PAPER 32-antenna source catalogs: As observations of the Epoch of Reionization (EoR) in redshifted 21cm
emission begin, we asses the accuracy of the early catalog results from the
Precision Array for Probing the Epoch of Reionization (PAPER) and the Murchison
Widefield Array. The MWA EoR approach derives much of its sensitivity from
subtracting foregrounds to <1% precision while the PAPER approach relies on the
stability and symmetry of the primary beam. Both require an accurate flux
calibration to set the amplitude of the measured power spectrum. The two
instruments are very similar in resolution, sensitivity, sky coverage and
spectral range and have produced catalogs from nearly contemporaneous data. We
use a Bayesian MCMC fitting method to estimate that the two instruments are on
the same flux scale to within 20% and find that the images are mostly in good
agreement. We then investigate the source of the errors by comparing two
overlapping MWA facets where we find that the differences are primarily related
to an inaccurate model of the primary beam but also correlated errors in bright
sources due to CLEAN. We conclude with suggestions for mitigating and better
characterizing these effects. | Large-scale inhomogeneity of dark energy produced in the ancestor vacuum: We investigate large-scale inhomogeneity of dark energy in the bubble
nucleation scenario of the universe. In this scenario, the present universe was
created by a bubble nucleation due to quantum tunneling from a metastable
ancestor vacuum, followed by a primordial inflationary era. During the bubble
nucleation, supercurvature modes of some kind of a scalar field are produced,
and remain until present without decaying; thus they can play a role of the
dark energy, if the mass of the scalar field is sufficiently light in the
present universe. The supercurvature modes fluctuate at a very large spatial
scale, much longer than the Hubble length in the present universe. Thus they
create large-scale inhomogeneities of the dark energy, and generate large-scale
anisotropies in the cosmic microwave background (CMB) fluctuations. This is a
notable feature of this scenario, where quantum fluctuations of a scalar field
are responsible for the dark energy. In this paper, we calculate imprints of
the scenario on the CMB anisotropies through the integrated Sachs-Wolfe (ISW)
effect, and give observational constraints on the curvature parameter
$\Omega_K$ and on an additional parameter $\epsilon$ describing some properties
of the ancestor vacuum. |
Distinguishability of scalar field models of dark energy with time
variable equation of state parameter: The possibility of distinguishing of scalar field models of dark energy with
different Lagrangians and time variable equation of state parameter by
available observational data is analyzed. The multicomponent cosmological
models with the scalar field with either Klein-Gordon or Dirac-Born-Infeld
Lagrangians as dark energy and the monotonic decreasing and increasing equation
of state parameters are considered. It is concluded that scalar field models of
dark energy with decreasing and increasing EoS parameters should be
distinguishable at the accuracy level of forthcoming observational data. The
Lagrangians of scalar fields could be distinguished by expected observational
data (Planck, SDSS etc.) in the case of decreasing EoS parameter, but are
practically indistinguishable in the case of increasing one. | Primordial electric fields before recombination in the early Universe: This work is a supplement on the previous research about primordial
electromagnetic fields. In this work, three important problems are discussed:
the evolution of primordial electric fields, the electric and particle
densities' solitons in plasma before recombination and their influences on the
power spectra of cosmic microwave background. Detailed computations show that
the primordial electric fields dissipate by Landau damping effect on both large
scale and small scale and there is no impact on the spectrum. While, before
recombination, there exist solitary waves stably propagating in plasma whose
speed is significantly slower than that of baryonic acoustic oscillations,
working only at extremely small scale. On the other hand, the amplitude of
solitons is so weak that only a significantly small contribution on the phase
of baryon acoustic oscillations, so there merely exist the messages about such
electric solitary waves on the spectrum. In a word, as relevant monographs on
cosmology, neglecting the electromagnetic fields (electric fields at least) is
a reasonable treatment on the calculations of cosmic microwave background.
However, the protonic density fluctuations show a form of KdV equation while
its propagation as a stable solitary wave, leading a probability to the origin
of fluctuation promoting the generation and evolution of galaxies. |
Constraining axion inflation with gravitational waves from preheating: We study gravitational wave production from gauge preheating in a variety of
inflationary models, detailing its dependence on both the energy scale and the
shape of the potential. We show that preheating into Abelian gauge fields
generically leads to a large gravitational wave background that contributes
significantly to the effective number of relativistic degrees of freedom in the
early universe, $N_\mathrm{eff}$. We demonstrate that the efficiency of
gravitational wave production is correlated with the tensor-to-scalar ratio,
$r$. In particular, we show that efficient gauge preheating in models whose
tensor-to-scalar ratio would be detected by next-generation cosmic microwave
background experiments ($r \gtrsim 10^{-3}$) will be either detected through
its contribution to $N_\mathrm{eff}$ or ruled out. Furthermore, we show that
bounds on $N_\mathrm{eff}$ provide the most sensitive probe of the possible
axial coupling of the inflaton to gauge fields regardless of the potential. | Cosmology with Persistent Homology: a Fisher Forecast: Persistent homology naturally addresses the multi-scale topological
characteristics of the large-scale structure as a distribution of clusters,
loops, and voids. We apply this tool to the dark matter halo catalogs from the
Quijote simulations, and build a summary statistic for comparison with the
joint power spectrum and bispectrum statistic regarding their information
content on cosmological parameters and primordial non-Gaussianity. Through a
Fisher analysis, we find that constraints from persistent homology are tighter
for 8 out of the 10 parameters by margins of 13-50%. The complementarity of the
two statistics breaks parameter degeneracies, allowing for a further gain in
constraining power when combined. We run a series of consistency checks to
consolidate our results, and conclude that our findings motivate incorporating
persistent homology into inference pipelines for cosmological survey data. |
Stars throw their weight in old galaxies: The observation that old, massive galaxies have a larger fraction of low-mass
stars than their younger, lower-mass counterparts adds to mounting evidence
that star formation may have been different in the early Universe. | Recoiling black holes: electromagnetic signatures, candidates, and
astrophysical implications: Supermassive black holes (SMBHs) may not always reside right at the centers
of their host galaxies. This is a prediction of numerical relativity
simulations, which imply that the newly formed single SMBH, after binary
coalescence in a galaxy merger, can receive kick velocities up to several 1000
km/s due to anisotropic emission of gravitational waves. Long-lived
oscillations of the SMBHs in galaxy cores, and in rare cases even SMBH
ejections from their host galaxies, are the consequence. Observationally,
accreting recoiling SMBHs would appear as quasars spatially and/or
kinematically off-set from their host galaxies. The presence of the "kicks" has
a wide range of astrophysical implications which only now are beginning to be
explored, including consequences for black hole and galaxy assembly at the
epoch of structure formation, black hole feeding, and unified models of Active
Galactic Nuclei (AGN). Here, we review the observational signatures of
recoiling SMBHs and the properties of the first candidates which have emerged,
including follow-up studies of the candidate recoiling SMBH of
SDSSJ092712.65+294344.0. |
The population of Young Stellar Clusters throughout the disk of M33: The properties of young stellar clusters (YSCs) in M33, identified from the
center out to about twice the size of the bright star-forming disk,are
investigated. We find 915 discrete MIR sources as far as the extent of the
warped HI disk, i.e. 16 kpc from the galaxy center. Their surface density has a
steep radial decline beyond 4.5 kpc, and flattens out beyond the optical radius
at 8.5 kpc. We are able to identify YSCs out to 12 kpc. At large galactocentric
radii, the paucity of very luminous clusters and the relevance of hot dust
emission become evident from the analysis of the bolometric and MIR luminosity
functions. The YSC mass and size are correlated with a log-log slope of 2.09,
similar to that measured for giant molecular clouds in M33 and the Milky Way,
which represent the protocluster environment. Most of the YSCs in our sample
have low extinction and ages between 3 and 10 Myr. In the inner regions of M33
the clusters span a wide range of mass (10^2<M<3 10^5 msun) and luminosity
10^38<L{bol}<3 10^{41}erg/s, while at galactocentric radii larger than 4 kpc we
find a deficiency of massive clusters. Beyond 7 kpc, where the Halpha surface
brightness drops significantly, the dominant YSC population has M<10^3 msun and
a slightly older age (10 Myrs). This implies the occurrence of star formation
events about 10 Myr ago as far as 10-12 kpc from the center of M33. The cluster
L{FUV}--L{Halpha} relation is non-linear for L{FUV}<10^{39}erg/s, in agreement
with randomly sampled models of the IMF which, furthermore, shows no
appreciable variation throughout the M33 disk. | The joint evolution of baryons and dark matter haloes: We have studied the dark matter (DM) distribution in a approx 10^12 h^-1
M_sun mass halo extracted from a simulation consistent with the concordance
cosmology, where the physics regulating the transformation of gas into stars
was allowed to change producing galaxies with different morphologies. The
presence of baryons produces the concentration of the DM halo with respect to
its corresponding dissipationless run, but we found that this response does not
only depend on the amount of baryons gathered in the central region but also on
the way they have been assembled. DM and baryons affect each other in a complex
way so the formation history of a galaxy plays an important role on its final
total mass distribution. Supernova (SN) feedback regulates the star formation
and triggers galactic outflows not only in the central galaxy but also in its
satellites. Our results suggest that, as the effects of SN feedback get
stronger, satellites get less massive and can even be more easily disrupted by
dynamical friction, transferring less angular momentum. We found indications
that this angular momentum could be acquired not only by the outer part of the
DM halo but also by the inner ones and by the stellar component in the central
galaxy. The latter effect produces stellar migration which contributes to
change the inner potential well, probably working against further DM
contraction. As a consequence of the action of these processes, when the halo
hosts a galaxy with an important disc structure formed by smooth gas accretion,
it is more concentrated than when it hosts a spheroidal system which
experienced more massive mergers and interactions. (abridged) |
Real-time Cosmology with High Precision Spectroscopy and Astrometry: Breakthroughs in physics and astrophysics are often driven by technological
advances, with the recent detection of gravitational waves being one such
example. This white paper focuses upon how improved astrometric and
spectroscopic measurements from a new generation of precise, accurate, and
stable astronomical instrumentation can address two of the fundamental
mysteries of our time -- dark energy and dark matter -- and probe the nature of
spacetime. Instrumentation is now on the cusp of enabling new cosmological
measurements based on redshifts (cosmic redshift drift) and extremely precise
time-series measurements of accelerations, astrophysical source positions
(astrometry), and angles (cosmic parallax). These allow tests of the
fundamental framework of the universe (the Friedmann equations of general
relativity and whether cosmic expansion is physically accelerating) and its
contents (dark energy evolution and dark matter behavior), while also anchoring
the cosmic distance scale ($H_0$). | The local PNG bias of neutral Hydrogen, ${\rm H_I}$: We use separate universe simulations with the IllustrisTNG galaxy formation
model to predict the local PNG bias parameters $b_\phi$ and $b_{\phi\delta}$ of
atomic neutral hydrogen, ${\rm H_I}$. These parameters and their relation to
the linear density bias parameter $b_1$ play a key role in observational
constraints of the local PNG parameter $f_{\rm NL}$ using the ${\rm H_I}$ power
spectrum and bispectrum. Our results show that the popular calculation based on
the universality of the halo mass function overpredicts the $b_\phi(b_1)$ and
$b_{\phi\delta}(b_1)$ relations measured in the simulations. In particular, our
results show that at $z \lesssim 1$ the ${\rm H_I}$ power spectrum is more
sensitive to $f_{\rm NL}$ compared to previously thought ($b_\phi$ is more
negative), but is less sensitive at other epochs ($b_\phi$ is less positive).
We discuss how this can be explained by the competition of physical effects
such as that large-scale gravitational potentials with local PNG (i) accelerate
the conversion of hydrogen to heavy elements by star formation, (ii) enhance
the effects of baryonic feedback that eject the gas to regions more exposed to
ionizing radiation, and (iii) promote the formation of denser structures that
shield the ${\rm H_I}$ more efficiently. Our numerical results can be used to
revise existing forecast studies on $f_{\rm NL}$ using 21cm line-intensity
mapping data. Despite this first step towards predictions for the local PNG
bias parameters of ${\rm H_I}$, we emphasize that more work is needed to assess
their sensitivity on the assumed galaxy formation physics and ${\rm H_I}$
modeling strategy. |
Fingerprints of Primordial Universe Paradigms as Features in Density
Perturbations: Experimentally distinguishing different primordial universe paradigms that
lead to the Big Bang model is an outstanding challenge in modern cosmology and
astrophysics. We show that a generic type of signals that exist in primordial
universe models can be used for such purpose. These signals are induced by tiny
oscillations of massive fields and manifest as features in primordial density
perturbations. They are capable of recording the time-dependence of the scale
factor of the primordial universe, and therefore provide direct evidence for
specific paradigm. | Weak lensing using only galaxy position angles: We develop a method for performing a weak lensing analysis using only
measurements of galaxy position angles. By analysing the statistical properties
of the galaxy orientations given a known intrinsic ellipticity distribution, we
show that it is possible to obtain estimates of the shear by minimizing a
$\chi^2$ statistic. The method is demonstrated using simulations where the
components of the intrinsic ellipticity are taken to be Gaussian distributed.
Uncertainties in the position angle measurements introduce a bias into the
shear estimates which can be reduced to negligible levels by introducing a
correction term into the formalism. We generalize our approach by developing an
algorithm to obtain direct shear estimators given any azimuthally symmetric
intrinsic ellipticity distribution. We introduce a method of measuring the
position angles of the galaxies from noisy pixelized images, and propose a
method to correct for biases which arise due to pixelization and correlations
between measurement errors and galaxy ellipticities. We also develop a method
to constrain the sample of galaxies used to obtain an estimate of the intrinsic
ellipticity distribution such that fractional biases in the resulting shear
estimates are below a given threshold value. We demonstrate the angle only
method by applying it to simulations where the ellipticities are taken to
follow a log-normal distribution. We compare the performance of the position
angle only method with the standard method based on full ellipticity
measurements by reconstructing lensing convergence maps from both numerical
simulations and from the CFHTLenS data. We find that the difference between the
convergence maps reconstructed using the two methods is consistent with noise. |
On the nature of sodium excess objects. I. Data and observed trends: Several studies have reported the presence of sodium excess objects that have
neutral atomic absorption lines at 5895A (NaD) and 8190A that are deeper than
expected based on stellar population models. van Dokkum & Conroy proposed that
low-mass stars are more prevalent in massive early-type galaxies, which may
lead to a strong NaI8190 line strength. It is, however, necessary to test this
prediction against other prominent line indices in optical wavelengths. We
newly identified roughly a thousand NaD excess objects (NEOs) based on the NaD
line strength in the redshift range 0.00<z<0.08 from the SDSS DR7. The novelty
of this work is that galaxies were carefully identified through direct visual
inspection of SDSS images, and we systematically compared the properties of
NEOs and those of a control sample of normal galaxies. Note that the majority
of galaxies with high velocity dispersion (>250km/s) show NaD excess. Most
late-type NEOs have strong Hb line strengths and significant emission lines.
This implies that the presence of ISM and/or dust contributes to the increase
in NaD line strengths observed for these galaxies. In contrast, the majority of
early-type NEOs are predominantly luminous and massive systems. However, we
find that models used to reproduce the NaI8190 line strengths that adopt a
bottom-heavy IMF are not able to reproduce the observed NaD line strengths. By
comparing the observed NaD, Mgb and Fe5270 line strengths with those of the
models, we identify a plausible range of parameters. In these models, the
majority of early-type NEOs are alpha-enhanced ([a/Fe]~0.3), metal-rich
([Z/H]~0.3) and especially Na-enhanced ([Na/Fe]~0.3). Enhanced Na abundance is
a particularly compelling hypothesis for the increase in the strength of the
NaD line index in our early-type NEOs that appear devoid of dust, both in their
SDSS images and spectra. | A New Method to Calculate the Stochastic Background of Gravitational
Waves Generated by Compact Binaries: In the study of gravitational waves (GWs), the stochastic background
generated by compact binary systems are among the most important kinds of
signals. The reason for such an importance has to do with their probable
detection by the interferometric detectors [such as the Advanced LIGO (ALIGO)
and Einstein Telescope (ET)] in the near future. In this paper we are concerned
with, in particular, the stochastic background of GWs generated by double
neutron star (DNS) systems in circular orbits during their periodic and
quasi--periodic phases. Our aim here is to describe a new method to calculate
such spectra, which is based on an analogy with a problem of Statistical
Mechanics. Besides, an important characteristic of our method is to consider
the time evolution of the orbital parameters. |
Modeling Post-Reionization HI Distributions in Fuzzy Dark Matter
Cosmologies Using Conditional Normalizing Flows: Upcoming 21 cm intensity mapping experiments like the Square Kilometer Array
(SKA) hold significant potential to constrain the properties of dark matter. In
this work, we model neutral hydrogen (HI) distributions using high-resolution
hydrodynamical $N$-body simulations of both cold dark matter (CDM) and fuzzy
dark matter (FDM) cosmologies in the post-reionization redshift range of
$z=3.42-4.94$. We show that the HI abundance decreases in FDM-like cosmologies.
Extreme FDM models with $m\sim 10^{-22}$ eV are at odds with a range of
measurements. Due to the increased halo bias, the HI bias increases, paralleled
by the damped Lyman-$\alpha$ (DLA) bias which we infer from the cross-section
of DLAs. The distribution of the latter in extreme FDM models has a high median
at the low-mass end, which can be traced to the high column density of cosmic
filaments. FDM models exhibit a very similar abundance of DLAs compared to CDM
while sub-DLAs are already less abundant. We study the prospects of detecting
the brightest HI peaks with SKA1-Low at $z=4.94$, indicating moderate
signal-to-noise ratios (SNR) at angular resolution $\theta_A = 2^{\prime}$ with
a rapidly declining SNR for lower values of $\theta_{A}$. After training the
conditional normalizing flow network HIGlow on 2D HI maps, we interpolate its
latent space of axion masses to predict the peak flux for a new, synthetic FDM
cosmology, finding good agreement with expectations. This work thus underscores
the potential of normalizing flows in capturing complex, non-linear structures
within HI maps, offering a versatile tool for conditional sample generation and
prediction tasks. | Growth Rate in the Dynamical Dark Energy Models: Dark Energy models with slowly-rolling cosmological scalar field provide a
popular alternative to the standard, time-independent cosmological constant
model. We study simultaneous evolution of background expansion and growth in
the scalar field model with the Ratra-Peebles self-interaction potential. We
use recent measurements of the linear growth rate and the baryon acoustic
oscillation peak positions to constrain the model parameter $\alpha$ that
describes the steepness of the scalar field potential. |
Upcoming SKA precursor surveys and sensitivity to HI mass function: We describe a simulation for the distribution of galaxies focusing on the
atomic Hydrogen content. We aim to make predictions for surveys of galaxies
using the redshifted 21 cm line emission. We take the expected distribution of
HI masses, circular velocities, sizes of galaxies and orientations into account
for this simulation. We use the sensitivity of ASKAP and MeeKAT radio
telescopes to estimate the number of detections of HI galaxies in upcoming
surveys. We validate our simulation with earlier estimates carried out by using
some of these considerations. We show that unlike earlier simulations that take
some of the factors into account, the predicted number of galaxies and their
distribution across masses changes significantly when all of these are
accounted for. We describe our predictions for the MIGHTEE-HI and WALLABY
surveys for blind detection of galaxies using the redshifted 21 cm radiation.
We study the dependence of the predicted number of detections on the HI mass
function. We also describe our future plans for improving the simulation. | A loophole to the universal photon spectrum in electromagnetic cascades:
application to the "cosmological lithium problem": The standard theory of electromagnetic cascades onto a photon background
predicts a quasi-universal shape for the resulting non-thermal photon spectrum.
This has been applied to very disparate fields, including non-thermal big bang
nucleosynthesis (BBN). However, once the energy of the injected photons falls
below the pair-production threshold the spectral shape is very different, a
fact that has been overlooked in past literature. This loophole may have
important phenomenological consequences, since it generically alters the BBN
bounds on non-thermal relics: for instance it allows to re-open the possibility
of purely electromagnetic solutions to the so-called "cosmological lithium
problem", which were thought to be excluded by other cosmological constraints.
We show this with a proof-of-principle example and a simple particle physics
model, compared with previous literature. |
The Abell 3391/95 galaxy cluster system: A 15 Mpc intergalactic medium
emission filament, a warm gas bridge, infalling matter clumps, and (re-)
accelerated plasma discovered by combining SRG/eROSITA data with ASKAP/EMU
and DECam data: We used dedicated SRG/eROSITA X-ray, ASKAP/EMU radio, and DECam optical
observations of a 15 sq.deg region around the interacting galaxy cluster system
A3391/95 to study the warm-hot gas in cluster outskirts and filaments, the
surrounding large-scale structure and its formation process. We relate the
observations to expectations from cosmological hydrodynamic simulations from
the Magneticum suite.
We trace the irregular morphology of warm-hot gas of the main clusters from
their centers out to well beyond their characteristic radii, $r_{200}$. Between
the two main cluster systems, we observe an emission bridge; thanks to
eROSITA's unique soft response and large field of view, we discover tantalizing
hints for warm gas. Several matter clumps physically surrounding the system are
detected. For the "Northern Clump," we provide evidence that it is falling
towards A3391 from the hot gas morphology and radio lobe structure of its
central AGN. Many of the extended sources in the field detected by eROSITA are
known clusters or new clusters in the background, including a known SZ cluster
at redshift z=1. We discover an emission filament north of the virial radius,
$r_{100}$, of A3391 connecting to the Northern Clump and extending south of
A3395 towards another galaxy cluster. The total projected length of this
continuous warm-hot emission filament is 15 Mpc, running almost 4 degrees
across the entire eROSITA observation. The DECam galaxy density map shows
galaxy overdensities in the same regions. The new datasets provide impressive
confirmation of the theoretically expected structure formation processes on the
individual system level, including the surrounding warm-hot intergalactic
medium distribution compared to the Magneticum simulation. Our spatially
resolved findings show that baryons indeed reside in large-scale warm-hot gas
filaments with a clumpy structure. | HALOGAS: Extraplanar gas in NGC 3198: We present the analysis of new, deep HI observations of the spiral galaxy NGC
3198, as part of the HALOGAS (Westerbork Hydrogen Accretion in LOcal GAlaxieS)
survey, with the main aim of investigating the presence, amount, morphology and
kinematics of extraplanar gas. We present models of the HI observations of NGC
3198: the model that matches best the observed data cube features a thick disk
with a scale height of ~3 kpc and an HI mass of about 15% of the total HI mass;
this thick disk also has a decrease in rotation velocity as a function of
height (lag) of 7-15 km/s/kpc (though with large uncertainties). This
extraplanar gas is detected for the first time in NGC 3198. Radially, this gas
appears to extend slightly beyond the actively star-forming body of the galaxy
(as traced by the Halpha emission), but it is not more radially extended than
the outer, fainter parts of the stellar disk. Compared to previous studies,
thanks to the improved sensitivity we trace the rotation curve out to larger
radii. We model the rotation curve in the framework of MOND (Modified Newtonian
Dynamics) and we confirm that, with the allowed distance range we assumed, fit
quality is modest in this galaxy, but the new outer parts are explained in a
satisfactory way. |
Reconstructing the three-dimensional local dark matter velocity
distribution: Directionally sensitive dark matter (DM) direct detection experiments present
the only way to observe the full three-dimensional velocity distribution of the
Milky Way halo local to Earth. In this work we compare methods for extracting
information about the local DM velocity distribution from a set of recoil
directions and energies in a range of hypothetical directional and
non-directional experiments. We compare a model independent empirical
parameterisation of the velocity distribution based on an angular
discretisation with a model dependent approach which assumes knowledge of the
functional form of the distribution. The methods are tested under three
distinct halo models which cover a range of possible phase space structures for
the local velocity distribution: a smooth Maxwellian halo, a tidal stream and a
debris flow. In each case we use simulated directional data to attempt to
reconstruct the shape and parameters describing each model as well as the DM
particle properties. We find that the empirical parametrisation is able to make
accurate unbiased reconstructions of the DM mass and cross section as well as
capture features in the underlying velocity distribution in certain directions
without any assumptions about its true functional form. We also find that by
extracting directionally averaged velocity parameters with this method one can
discriminate between halo models with different classes of substructure. | Detecting high-$z$ galaxies in the Near Infrared Background: Emission from high-$z$ galaxies must unquestionably contribute to the
near-infrared background (NIRB). However, this contribution has so far proven
difficult to isolate even after subtracting the resolved galaxies to deep
levels. Remaining NIRB fluctuations are dominated by unresolved low-$z$
galaxies on small angular scales, and by an unidentified component with unclear
origin on large scales ($\approx 1000''$). In this paper, by analyzing mock
maps generated from semi-numerical simulations and empirically determined
$L_{\rm UV} - M_{\rm h}$ relations, we find that fluctuations associated with
galaxies at $5 < z < 10$ amount to several percent of the unresolved NIRB flux
fluctuations. We investigate the properties of this component for different
survey areas and limiting magnitudes. In all cases, we show that this signal
can be efficiently, and most easily at small angular scales, isolated by
cross-correlating the source-subtracted NIRB with Lyman Break Galaxies (LBGs)
detected in the same field by {\tt HST} surveys. This result provides a fresh
insight into the properties of reionization sources. |
BBN And The CMB Constrain Light, Electromagnetically Coupled WIMPs: (Abridged) In the presence of a light WIMP (< 30 MeV), there are degeneracies
among the nature of the WIMP, its couplings to standard model particles, its
mass m_chi, and the number of equivalent neutrinos beyond the standard model,
Delta N_nu. These degeneracies cannot be broken by the CMB constraint on the
effective number of neutrinos, N_eff. However, big bang nucleosynthesis (BBN)
is affected by a light WIMP and equivalent neutrinos, so the combination of BBN
and CMB can break some of the degeneracies. Here, BBN predictions for
abundances in the presence of a light WIMP and equivalent neutrinos are
explored, and estimates of their observationally determined relic abundances
are used to limit m_chi, Delta N_nu, and the present Universe baryon density
(Omega_B h^2). These constraints are explored for Majorana and Dirac fermion
WIMPs, as well as for real and complex scalar WIMPs that couple to electrons,
positrons, and photons. In a separate paper this analysis is repeated for WIMPs
that couple only to the standard model neutrinos, and constraints for the two
cases are contrasted. Without a light WIMP but allowing for equivalent
neutrinos, the combined BBN and CMB constraints favor N_eff = 3.46 +/- 0.17,
Omega_B h^2 = 0.0224 +/- 0.0003, and Delta N_nu = 0.40 +/- 0.17. In this case,
standard BBN (Delta N_nu = 0) is disfavored at ~98% confidence, and the
presence of one sterile neutrino (Delta N_nu = 1) is disfavored at > 99%
confidence. Allowing a light WIMP and Delta N_nu equivalent neutrinos together,
the combined BBN and CMB data provide lower limits to the WIMP masses (> 0.5 -
5 MeV) that depend on the nature of the WIMP, favor m_chi ~8 MeV slightly over
no WIMP, and loosen constraints on equivalent neutrinos, Delta N_nu =
0.65+0.46-0.35. While Delta N_nu = 0 is still disfavored at ~95% confidence
with a light WIMP, Delta N_nu = 1 is now allowed. | Limit on graviton mass using stacked galaxy cluster catalogs from
SPT-SZ, Planck-SZ and SDSS-redMaPPer: In the last few years, there has been a resurgence of interest in obtaining
observational bounds on the graviton mass, following the detection of
gravitational waves, because of the versatility of massive graviton theories in
resolving multiple problems in cosmology and fundamental physics. In this work,
we apply the method proposed in Rana et al.(arXiv:1801.03309), which consists
of looking for Yukawa-like fall off in the gravitational potential, to stacked
galaxy cluster catalogs from three disparate surveys. These include catalogs
from 2500 sq. degree SPT-SZ survey, the Planck all-sky SZ catalog, and a
redMaPPer selected catalog from 10,000 sq. degree of SDSS-DR8 data. The 90\%
c.l. limits which we obtained on the graviton mass using SPT, Planck and SDSS
are: $m_g < 4.73 \times 10^{-30}$ eV, $3.0 \times 10^{-30}$ eV, and $1.27
\times 10^{-30}$ eV respectively; or in terms of Compton wavelength are
$\lambda_g >2.62 \times 10^{20}$ km, $4.12 \times 10^{20}$ km, $9.76 \times
10^{20}$ km. These limits are about five times more stringent than the previous
best bound from galaxy clusters. |
MultiDark-Clusters: Galaxy Cluster Mock Light-Cones, eROSITA and the
Cluster Power Spectrum: Cosmological simulations are fundamental tools to study structure formation
and the astrophysics of evolving structures, in particular clusters of
galaxies. While hydrodynamical simulations cannot sample efficiently large
volumes and explore different cosmologies at the same time, N-body simulations
lack the baryonic physics that is crucial to determine the observed properties
of clusters. One solution is to use (semi-)analytical models to implement the
needed baryonic physics. In this way, we can generate the many mock universes
that will be required to fully exploit future large sky surveys, such as that
from the upcoming eROSITA X-ray telescope. We developed a phenomenological
model based on observations of clusters to implement gas density and
temperature information on the dark-matter-only halos of the MultiDark
simulations. We generate several full-sky mock light-cones of clusters for the
WMAP and Planck cosmologies, adopting different parameters in our
phenomenological model of the intra-cluster medium. For one of these
simulations and models, we also generate 100 light-cones corresponding to 100
random observers and explore the variance among them in several quantities. In
this first paper on MultiDark mock galaxy cluster light-cones, we focus on
presenting our methodology and discuss predictions for eROSITA, in particular,
exploring the potential of angular power spectrum analyses of its detected (and
undetected) cluster population to study X-ray scaling relations, the
intra-cluster medium, and the composition of the cosmic X-ray background. We
make publicly available on-line more than 400 GB of light-cones, which include
the expected eROSITA count rate, on Skies & Universes
(http://www.skiesanduniverses.org). | New Image Statistics for Detecting Disturbed Galaxy Morphologies at High
Redshift: Testing theories of hierarchical structure formation requires estimating the
distribution of galaxy morphologies and its change with redshift. One aspect of
this investigation involves identifying galaxies with disturbed morphologies
(e.g., merging galaxies). This is often done by summarizing galaxy images
using, e.g., the CAS and Gini-M20 statistics of Conselice (2003) and Lotz et
al. (2004), respectively, and associating particular statistic values with
disturbance. We introduce three statistics that enhance detection of disturbed
morphologies at high-redshift (z ~ 2): the multi-mode (M), intensity (I), and
deviation (D) statistics. We show their effectiveness by training a
machine-learning classifier, random forest, using 1,639 galaxies observed in
the H band by the Hubble Space Telescope WFC3, galaxies that had been
previously classified by eye by the CANDELS collaboration (Grogin et al. 2011,
Koekemoer et al. 2011). We find that the MID statistics (and the A statistic of
Conselice 2003) are the most useful for identifying disturbed morphologies.
We also explore whether human annotators are useful for identifying disturbed
morphologies. We demonstrate that they show limited ability to detect
disturbance at high redshift, and that increasing their number beyond
approximately 10 does not provably yield better classification performance. We
propose a simulation-based model-fitting algorithm that mitigates these issues
by bypassing annotation. |
Does small scale structure significantly affect cosmological dynamics?: The large-scale homogeneity and isotropy of the universe is generally thought
to imply a well defined background cosmological model. It may not. Smoothing
over structure adds in an extra contribution, transferring power from small
scales up to large. Second-order perturbation theory implies that the effect is
small, but suggests that formally the perturbation series may not converge. The
amplitude of the effect is actually determined by the ratio of the Hubble
scales at matter-radiation equality and today - which are entirely unrelated.
This implies that a universe with significantly lower temperature today could
have significant backreaction from more power on small scales, and so provides
the ideal testing ground for understanding backreaction. We investigate this
using two different N-body numerical simulations - a 3D Newtonian and a 1D
simulation which includes all relevant relativistic effects. We show that while
perturbation theory predicts an increasing backreaction as more initial
small-scale power is added, in fact the virialisation of structure saturates
the backreaction effect at the same level independently of the equality scale.
This implies that backreaction is a small effect independently of initial
conditions. Nevertheless, it may still contribute at the percent level to
certain cosmological observables and therefore it cannot be neglected in
precision cosmology. | The VIRUS-P Exploration of Nearby Galaxies (VENGA): Survey Design, Data
Processing, and Spectral Analysis Methods: We present the survey design, data reduction, and spectral fitting pipeline
for the VIRUS-P Exploration of Nearby Galaxies (VENGA). VENGA is an integral
field spectroscopic survey, which maps the disks of 30 nearby spiral galaxies.
Targets span a wide range in Hubble type, star formation activity, morphology,
and inclination. The VENGA data-cubes have 5.6'' FWHM spatial resolution, ~5A
FWHM spectral resolution, sample the 3600A-6800A range, and cover large areas
typically sampling galaxies out to ~0.7 R_25. These data-cubes can be used to
produce 2D maps of the star formation rate, dust extinction, electron density,
stellar population parameters, the kinematics and chemical abundances of both
stars and ionized gas, and other physical quantities derived from the fitting
of the stellar spectrum and the measurement of nebular emission lines. To
exemplify our methods and the quality of the data, we present the VENGA
data-cube on the face-on Sc galaxy NGC 628 (a.k.a. M 74). The VENGA
observations of NGC 628 are described, as well as the construction of the
data-cube, our spectral fitting method, and the fitting of the stellar and
ionized gas velocity fields. We also propose a new method to measure the
inclination of nearly face-on systems based on the matching of the stellar and
gas rotation curves using asymmetric drift corrections. VENGA will measure
relevant physical parameters across different environments within these
galaxies, allowing a series of studies on star formation, structure assembly,
stellar populations, chemical evolution, galactic feedback, nuclear activity,
and the properties of the interstellar medium in massive disk galaxies. |
Ultra deep AKARI observations of Abell 2218: resolving the 15 um
extragalactic background light: We present extragalactic number counts and a lower limit estimate for the
cosmic infrared background at 15 um from AKARI ultra deep mapping of the
gravitational lensing cluster Abell 2218. This data is the deepest taken by any
facility at this wavelength, and uniquely samples the normal galaxy population.
We have de-blended our sources, to resolve photometric confusion, and de-lensed
our photometry to probe beyond AKARI's blank-field sensitivity. We estimate a
de-blended 5 sigma sensitivity of 28.7 uJy. The resulting 15 um galaxy number
counts are a factor of three fainter than previous results, extending to a
depth of ~ 0.01 mJy and providing a stronger lower limit constraint on the
cosmic infrared background at 15 um of 1.9 +/- 0.5 nW m^-2 sr^-1. | Physics-informed neural networks in the recreation of hydrodynamic
simulations from dark matter: Physics-informed neural networks have emerged as a coherent framework for
building predictive models that combine statistical patterns with domain
knowledge. The underlying notion is to enrich the optimization loss function
with known relationships to constrain the space of possible solutions.
Hydrodynamic simulations are a core constituent of modern cosmology, while the
required computations are both expensive and time-consuming. At the same time,
the comparatively fast simulation of dark matter requires fewer resources,
which has led to the emergence of machine learning algorithms for baryon
inpainting as an active area of research; here, recreating the scatter found in
hydrodynamic simulations is an ongoing challenge. This paper presents the first
application of physics-informed neural networks to baryon inpainting by
combining advances in neural network architectures with physical constraints,
injecting theory on baryon conversion efficiency into the model loss function.
We also introduce a punitive prediction comparison based on the
Kullback-Leibler divergence, which enforces scatter reproduction. By
simultaneously extracting the complete set of baryonic properties for the Simba
suite of cosmological simulations, our results demonstrate improved accuracy of
baryonic predictions based on dark matter halo properties, successful recovery
of the fundamental metallicity relation, and retrieve scatter that traces the
target simulation's distribution. |
A variation of the fraction of stars that form in bound clusters within
M83: Recent observations, as well as theoretical studies, have suggested that
stellar cluster formation may depend on local and global environmental
properties. In particular, the fraction of stars that form within long-lived
bound clusters (\Gamma) may depend on environment, with indications that it may
be higher in the more extreme environments of high star-formation rate density
galaxies. How \Gamma varies has important implications on the use of clusters
to determine the star-formation histories of galaxies as well as our
understanding of the star-formation process itself. Previous studies have
estimated \Gamma over full galaxies, making it difficult to discern the
physical cause of the reported variations. Here, we use existing star cluster
catalogues and HST-WFC3 V and I images of the grand design, face-on spiral
galaxy M83 in order to see if and how \Gamma varies within a single galaxy. We
find that \Gamma decreases strongly as a function of galactocentric radius, by
a factor of ~5 over the inner ~6kpc, in agreement with recent theoretical
predictions and decreasing trends observed in the gas surface density of the
galaxy. | Reducing Noise in Cosmological N-body Simulations with Neutrinos: We present a new method for generating initial conditions for numerical
cosmological simulations in which massive neutrinos are treated as an extra set
of N-body (collisionless) particles. It allows us to accurately follow the
density field for both Cold Dark Matter (CDM) and neutrinos at both high and
low redshifts. At high redshifts, the new method is able to reduce the shot
noise in the neutrino power spectrum by a factor of more than $10^7$ compared
to previous methods, where the power spectrum was dominated by shot noise at
all scales. We find that our new approach also helps to reduce the noise on the
total matter power spectrum on large scales, whereas on small scales the
results agree with previous simulations. Our new method also allows for a
systematic study of clustering of the low velocity tail of the distribution
function of neutrinos. This method also allows for the study of the evolution
of the overall velocity distribution as a function of the environment
determined by the CDM field. |
Geometrical Constraint on Curvature with BAO experiments: The spatial curvature ($K$ or $\Omega_K$) is one of the most fundamental
parameters of an isotropic and homogeneous universe and has a close link to the
physics of the early Universe. Combining the radial and angular diameter
distances measured via the baryon acoustic oscillation (BAO) experiments allows
us to unambiguously constrain the curvature. The method is primarily based on
the metric theory, but is less sensitive to the theory of structure formation
other than the existence of the BAO scale and is free of any model of dark
energy. In this paper, we estimate a best achievable accuracy of constraining
the curvature with the BAO experiments. We show that an all-sky,
cosmic-variance-limited galaxy survey covering the Universe up to $z> 4$
enables a precise determination of the curvature to an accuracy of
$\sigma(\Omega_K)\simeq 10^{-3}$. When we assume a model of dark energy -
either the cosmological constant or the $(w_0,w_a)$ model - it can achieve a
precision of $\sigma(\Omega_K)\simeq \mbox{a few}\times 10^{-4}$. These
forecasts require a high sampling density of galaxies, and are degraded by up
to a factor of a few for a survey with a finite number density of $\sim
10^{-3}(h/{\rm Mpc})^3$. | Towards accurate rescaling of a halo mass function: We investigate the precision within which a simulated dark matter halo mass
function can be rescaled to a different set of cosmological parameters. Our
tests show that the accuracy almost linearly depends on the difference of the
cosmological parameters and amounts to few percent in the case of WMAP5 and
PLANCK parameters. The rescaling allows thus to obtain a mass function with
better precision than the one given by Sheth-Mo-Tormen approximation and even
more modern fits currently used in literature. |
New constraints on cosmological modified gravity theories from
anisotropic three-point correlation functions of BOSS DR12 galaxies: We report a new test of modified gravity theories using the large-scale
structure of the Universe. This paper is the first attempt to (1) apply a joint
analysis of the anisotropic components of galaxy two- and three-point
correlation functions (2 and 3PCFs) to actual galaxy data and (2) constrain the
nonlinear effects of degenerate higher-order scalar-tensor (DHOST) theories on
cosmological scales. Applying this analysis to the Baryon Oscillation
Spectroscopic Survey (BOSS) data release 12, we obtain the lower bounds of
$-1.655 < \xi_{\rm t}$ and $-0.504 < \xi_{\rm s}$ at the $95\%$ confidence
level on the parameters characterising the time evolution of the tidal and
shift terms of the second-order velocity field. These constraints are
consistent with GR predictions of $\xi_{\rm t}=15/1144$ and $\xi_{\rm s}=0$.
Moreover, they represent a $35$-fold and $20$-fold improvement, respectively,
over the joint analysis with only the isotropic 3PCF. We ensure the validity of
our results by investigating various quantities, including theoretical models
of the 3PCF, window function corrections, cumulative ${\rm S/N}$, Fisher
matrices, and statistical scattering effects of mock simulation data. We also
find statistically significant discrepancies between the BOSS data and the
Patchy mocks for the 3PCF measurement. Finally, we package all of our 3PCF
analysis codes under the name \textsc{HITOMI} and make them publicly available
so that readers can reproduce all the results of this paper and easily apply
them to ongoing future galaxy surveys. | Determining the Neutrino Mass Hierarchy with Cosmology: The combination of current large scale structure and cosmic microwave
background (CMB) anisotropies data can place strong constraints on the sum of
the neutrino masses. Here we show that future cosmic shear experiments, in
combination with CMB constraints, can provide the statistical accuracy required
to answer questions about differences in the mass of individual neutrino
species. Allowing for the possibility that masses are non-degenerate we combine
Fisher matrix forecasts for a weak lensing survey like Euclid with those for
the forthcoming Planck experiment. Under the assumption that neutrino mass
splitting is described by a normal hierarchy we find that the combination
Planck and Euclid will possibly reach enough sensitivity to put a constraint on
the mass of a single species. Using a Bayesian evidence calculation we find
that such future experiments could provide strong evidence for either a normal
or an inverted neutrino hierachy. Finally we show that if a particular neutrino
hierachy is assumed then this could bias cosmological parameter constraints,
for example the dark energy equation of state parameter, by > 1\sigma, and the
sum of masses by 2.3\sigma. |
Double-Barred Galaxies: I present a brief review of what is known about double-barred galaxies, where
a small ("inner") bar is nested inside a larger ("outer") bar; the review is
focused primarily on their demographics and photometric properties. Roughly 20%
of S0--Sb galaxies are double-barred; they may be rarer in later Hubble types.
Inner bars are typically ~ 500 pc in radius (~ 12% the size of outer bars), but
sizes range from ~ 100 pc to > 1 kpc. The structure of at least some inner bars
appears very similar to that of outer bars (and single large-scale bars).
Direct and indirect evidence all support the hypothesis that inner bars rotate
independently of outer bars, although actual pattern speeds for inner bars are
poorly constrained. Finally, I note that inner bars do not appear to promote
nuclear activity. | What is the Physical Origin of Strong Lya Emission? I. Demographics of
Lya Emitter Structures: We present the results of structure analyses for a large sample of 426 Lya
emitters (LAEs) at z~2.2 that are observed with HST/ACS and WFC3-IR by deep
extra-galactic legacy surveys. We confirm that the merger fraction and the
average ellipticity of LAE's stellar component are 10-30 % and 0.4-0.6,
respectively, that are comparable with previous study results. We successfully
identify that some LAEs have a spatial offset between Lya and stellar-continuum
emission peaks, d_Lya, by ~2.5-4 kpc beyond our statistical errors. To uncover
the physical origin of strong Lya emission found in LAEs, we investigate Lya
equivalent width (EW) dependences of these three structural parameters, merger
fraction, d_Lya, and ellipticity of stellar distribution in the range of
EW(Lya)=20-250A. Contrary to expectations, we find that merger fraction does
not significantly increase with Lya EW. We reveal an anti-correlation between
d_Lya and EW(Lya) by Kolmogorov-Smirnov (KS) test. There is a trend that the
LAEs with a large Lya EW have a small ellipticity. This is consistent with the
recent theoretical claims that Lya photons can more easily escape from face-on
disks having a small ellipticity, due to less inter-stellar gas along the line
of sight, although our KS test indicates that this trend is not statistically
significant. Our results of Lya-EW dependence generally support the idea that
an HI column density is a key quantity determining Lya emissivity. |
Probing Dark Energy with Neutrino Number: From measurements of the cosmic microwave background (CMB), the effective
number of neutrino is found to be close to the standard model value Neff =
3.046 for the \LambdaCDM cosmology. One can obtain the same CMB angular power
spectrum as that of \LambdaCDM for the different value of Neff by using the
different dark energy model (i.e. for the different value of w). This
degeneracy between Neff and w in CMB can be broken from future galaxy survey
using the matter power spectrum. | The squeezed matter bispectrum covariance with responses: We present a calculation of the angle-averaged squeezed matter bispectrum
covariance ${\rm Cov}\left(B_{m}(k_1, k_1', s_1), B_{m}(k_2, k_2',
s_2)\right)$, $s_i \ll k_i,k_i'$ ($i=1,2$), that uses matter power spectrum
responses to describe the coupling of large- to short-scale modes in the
nonlinear regime. The covariance is given by a certain configuration of the
6-point function, which we show is dominated by response-type mode-coupling
terms in the squeezed bispectrum limit. The terms that are not captured by
responses are small, effectively rendering our calculation complete and
predictive for linear $s_1,s_2$ values and any nonlinear values of
$k_1,k_1',k_2,k_2'$. Our numerical results show that the squeezed bispectrum
super-sample covariance is only a negligible contribution. We also compute the
power spectrum-bispectrum cross-covariance using responses. Our derivation for
the squeezed matter bispectrum is the starting point to calculate analytical
covariances for more realistic galaxy clustering and weak-lensing applications.
It can also be used in cross-checks of numerical ensemble estimates of the
general bispectrum covariance, given that it is effectively noise-free and
complete in the squeezed limit. |
A tight correlation between the enclosed gravitational mass and hot gas
mass in galaxy clusters at intermediate radii: Many studies point out that there exists some tight correlations between dark
matter and baryonic matter at different radii in galaxies. However, similar
tight correlations can only be found in galaxy clusters for large radii. Here
we report extremely tight correlations between the gravitational mass $M_{\rm
grav}$ and hot gas mass $M_{\rm gas}$ in galaxy clusters at the hot gas core
radius $r_c$ and at $2r_c$ (i.e. $M_{\rm grav}(r_c)$ vs $M_{\rm gas}(r_c)$ and
$M_{\rm grav}(2r_c)$ vs $M_{\rm gas}(2r_c)$). By using the X-ray data of 64
large galaxy clusters with different sizes and masses, we find that the
correlations can be described by a single relation $\log(M_{\rm
grav}/M_{\odot})=(0.74 \pm 0.02) \log(M_{\rm gas}/M_{\odot})+(4.47 \pm 0.23)$
for a wide range of hot gas mass ($10^{11}M_{\odot}-10^{14}M_{\odot}$). The
corresponding correlation coefficient and scatter are 0.97 and 0.10 dex
respectively. This would be the first tight correlation with very small scatter
between the enclosed gravitational mass and hot gas mass for galaxy clusters
within intermediate radii ($\sim 100-1000$ kpc) and it provides a new kind of
observational evidence to support the universality of correlation between dark
matter and baryons. | Bulk flow and shear in the local Universe: 2MTF and COSMICFLOWS-3: The low-order kinematic moments of galaxies, namely bulk flow and shear,
enables us to test whether theoretical models can accurately describe the
evolution of the mass density field in the nearby Universe. We use the
so-called etaMLE maximum likelihood estimator in logdistance space to measure
thesemoments from a combined sample of the 2MASS Tully-Fisher (2MTF) survey and
the COSMICFLOWS-3 (CF3) compilation. Galaxies common between 2MTF and CF3
demonstrate a small zero-point difference of -0.016+-0.002 dex.We test the
etaMLE on 16 mock 2MTF survey catalogues in order to explore how well the
etaMLE recovers the true moments, and the effect of sample anisotropy. On the
scale size of 37 Mpc/h, we find that the bulk flow of the local Universe is 259
+- 15 km/h in the direction is (l,b)=(300+-4, 23+-3) (Galactic coordinates).
The average shear amplitude is 1.7+-0.4 h km/s/Mpc. We use a variable window
function to explore the bulk and shear moments as a function of depth. In all
cases, the measurements are consistent with the predictions of the L cold dark
matter (LCDM) model. |
SPIDER: a balloon-borne CMB polarimeter for large angular scales: We describe SPIDER, a balloon-borne instrument to map the polarization of the
millimeter-wave sky with degree angular resolution. Spider consists of six
monochromatic refracting telescopes, each illuminating a focal plane of
large-format antenna-coupled bolometer arrays. A total of 2,624 superconducting
transition-edge sensors are distributed among three observing bands centered at
90, 150, and 280 GHz. A cold half-wave plate at the aperture of each telescope
modulates the polarization of incoming light to control systematics. Spider's
first flight will be a 20-30-day Antarctic balloon campaign in December 2011.
This flight will map \sim8% of the sky to achieve unprecedented sensitivity to
the polarization signature of the gravitational wave background predicted by
inflationary cosmology. The Spider mission will also serve as a proving ground
for these detector technologies in preparation for a future satellite mission. | Towards reconstruction of unlensed, intrinsic CMB power spectra from
lensed map: We propose a method to extract the unlensed, intrinsic CMB temperature and
polarization power spectra from the observed (i.e., lensed) spectra. Using a
matrix inversion technique, we demonstrate how one can reconstruct the
intrinsic CMB power spectra directly from lensed data for both flat sky and
full sky analyses. The delensed spectra obtained by the technique are
calibrated against the Code for Anisotropies in the Microwave Background (CAMB)
using WMAP 7-year best-fit data and applied to WMAP 9-year unbinned data as
well. In principle, our methodology may help in subtracting out the E-mode
lensing contribution in order to obtain the intrinsic B-mode power. |
The Cosmic Dawn and Epoch of Reionization with the Square Kilometre
Array: Concerted effort is currently ongoing to open up the Epoch of Reionization
(EoR) ($z\sim$15-6) for studies with IR and radio telescopes. Whereas IR
detections have been made of sources (Lyman-$\alpha$ emitters, quasars and
drop-outs) in this redshift regime in relatively small fields of view, no
direct detection of neutral hydrogen, via the redshifted 21-cm line, has yet
been established. Such a direct detection is expected in the coming years, with
ongoing surveys, and could open up the entire universe from $z\sim$6-200 for
astrophysical and cosmological studies, opening not only the EoR, but also its
preceding Cosmic Dawn ($z\sim$30-15) and possibly even the later phases of the
Dark Ages ($z\sim$200-30). All currently ongoing experiments attempt
statistical detections of the 21-cm signal during the EoR, with limited
signal-to-noise. Direct imaging, except maybe on the largest (degree) scales at
lower redshifts, as well as higher redshifts will remain out of reach. The
Square Kilometre Array(SKA) will revolutionize the field, allowing direct
imaging of neutral hydrogen from scales of arc-minutes to degrees over most of
the redshift range $z\sim$6-28 with SKA1-LOW, and possibly even higher
redshifts with the SKA2-LOW. In this SKA will be unique, and in parallel
provide enormous potential of synergy with other upcoming facilities (e.g.
JWST). In this chapter we summarize the physics of 21-cm emission, the
different phases the universe is thought to go through, and the observables
that the SKA can probe, referring where needed to detailed chapters in this
volume (Abridged). | Dark Energy Cosmology with the Alternative Cosmic Microwave Background
Data: Recently, in a series of works by Liu and Li (L&L), they claimed that there
exists a timing asynchrony of $-25.6\,$ms between the spacecraft attitude and
radiometer output timestamps in the original raw WMAP time-ordered data (TOD).
L&L reprocessed the WMAP data while the aforementioned timing asynchrony has
been corrected, and they obtained an alternative CMB map in which the
quadrupole dropped to nearly zero. In the present work, we try to see the
implications to dark energy cosmology if L&L are right. While L&L claimed that
there is a bug in the WMAP pipeline which leads to significantly different
cosmological parameters, an interesting question naturally arises, namely, how
robust is the current dark energy cosmology with respect to systematic errors
and bugs? So, in this work, we adopt the alternative CMB data of L&L as a
strawman to study the robustness of dark energy predictions. |
The SDSS DR7 Galaxy Angular Power Spectrum: We calculate the angular power spectrum of galaxies selected from the Sloan
Digital Sky Survey (SDSS) Data Release 7 (DR7) by using a quadratic estimation
method with KL-compression. The primary data sample includes over 18 million
galaxies covering more than 5,700 square degrees after masking areas with
bright objects, reddening greater than 0.2 magnitudes, and seeing of more than
1.5 arcseconds. We test for systematic effects by calculating the angular power
spectrum by SDSS stripe and find that these measurements are minimally affected
by seeing and reddening. We calculate the angular power spectrum for l \leq 200
multipoles by using 40 bandpowers for the full sample, and l \leq 1000
multipoles using 50 bandpowers for individual stripes. We also calculate the
angular power spectrum for this sample separated into 3 magnitude bins with
mean redshifts of z = 0.171, z = 0.217, and z = 0.261 to examine the evolution
of the angular power spectrum. We determine the theoretical linear angular
power spectrum by projecting the 3D power spectrum to two dimensions for a
basic comparison to our observational results. By minimizing the {\chi}^2 fit
between these data and the theoretical linear angular power spectrum we measure
a loosely-constrained fit of {\Omega}_m = 0.31^{+0.18}_{-0.11} with a linear
bias of b = 0.94 \pm 0.04. | Galaxy and Mass Assembly (GAMA): survey diagnostics and core data
release: The Galaxy And Mass Assembly (GAMA) survey has been operating since February
2008 on the 3.9-m Anglo-Australian Telescope using the AAOmega fibre-fed
spectrograph facility to acquire spectra with a resolution of R~1300 for
120,862 SDSS selected galaxies. The target catalogue constitutes three
contiguous equatorial regions centred at 9h (G09), 12h (G12) and 14.5h (G15)
each of 12 x 4 sq.deg to limiting fluxes of r < 19.4, r < 19.8, and r < 19.4
mag respectively (and additional limits at other wavelengths). Spectra and
reliable redshifts have been acquired for over 98 per cent of the galaxies
within these limits. Here we present the survey footprint, progression, data
reduction, redshifting, re-redshifting, an assessment of data quality after 3
years, additional image analysis products (including ugrizYJHK photometry,
Sersic profiles and photometric redshifts), observing mask, and construction of
our core survey catalogue (GamaCore). From this we create three science ready
catalogues: GamaCoreDR1 for public release, which includes data acquired during
year 1 of operations within specified magnitude limits (February 2008 to April
2008); GamaCoreMainSurvey containing all data above our survey limits for use
by the GAMA team and collaborators; and GamaCoreAtlasSv containing year 1, 2
and 3 data matched to Herschel-ATLAS Science Demonstration data. These
catalogues along with the associated spectra, stamps and profiles can be
accessed via the GAMA website: http://www.gama-survey.org/ |
Magnetic field evolution in simulations with Euler potentials: Using two- and three-dimensional hydromagnetic simulations for a range of
different flows, including laminar and turbulent ones, it is shown that
solutions expressing the field in terms of Euler potentials (EP) are in general
incorrect if the EP are evolved with an artificial diffusion term. In three
dimensions, standard methods using the magnetic vector potential are found to
permit dynamo action when the EP give decaying solutions. With an imposed
field, the EP method yields excessive power at small scales. This effect is
more exaggerated in the dynamic case, suggesting an unrealistically reduced
feedback from the Lorentz force. The EP approach agrees with standard methods
only at early times when magnetic diffusivity did not have time to act. It is
demonstrated that the usage of EP with even a small artificial magnetic
diffusivity does not converge to a proper solution of hydromagnetic turbulence.
The source of this disagreement is not connected with magnetic helicity or the
three-dimensionality of the magnetic field, but is simply due to the fact that
the nonlinear representation of the magnetic field in terms of EP that depend
on the same coordinates is incompatible with the linear diffusion operator in
the induction equation. | The Rise and Fall of Passive Disk Galaxies: Morphological Evolution
Along the Red Sequence Revealed by COSMOS: The increasing abundance of passive "red-sequence" galaxies since z=1-2 is
mirrored by a coincident rise in the number of galaxies with spheroidal
morphologies. In this paper, however, we show that in detail the correspondence
between galaxy morphology and color is not perfect, providing insight into the
physical origin of this evolution. Using the COSMOS survey, we study a
significant population of red sequence galaxies with disk-like morphologies.
These passive disks typically have Sa-Sb morphological types with large bulges,
but they are not confined to dense environments. They represent nearly one-half
of all red-sequence galaxies and dominate at lower masses (log Mstar < 10)
where they are increasingly disk-dominated. As a function of time, the
abundance of passive disks with log Mstar < 11 increases, but not as fast as
red-sequence spheroidals in the same mass range. At higher mass, the passive
disk population has declined since z~1, likely because they transform into
spheroidals. We estimate that as much as 60% of galaxies transitioning onto the
red sequence evolve through a passive disk phase. The origin of passive disks
therefore has broad implications for understanding how star formation shuts
down. Because passive disks tend to be more bulge-dominated than their
star-forming counterparts, a simple fading of blue disks does not fully explain
their origin. We explore several more sophisticated explanations, including
environmental effects, internal stabilization, and disk regrowth during
gas-rich mergers. While previous work has sought to explain color and
morphological transformations with a single process, these observations open
the way to new insight by highlighting the fact that galaxy evolution may
actually proceed through several separate stages. |
On the galaxy 3-point correlation function in Modified Gravity: The next generation of galaxy surveys will provide highly accurate
measurements of the large-scale structure of the Universe, allowing for more
stringent tests of gravity on cosmological scales. Higher order statistics are
a valuable tool to study the non-Gaussianities in the matter field and to break
degeneracies between modified gravity and other physical or nuisance
parameters. However, understanding from first principles the behaviour of these
correlations is essential to characterise deviations from General Relativity
(GR), and the purpose of this work. This work uses contemporary ideas of
Standard Perturbation Theory on biased tracers to characterize the three point
correlation function (3PCF) at tree level for Modified Gravity models with a
scale-dependent gravitational strength, and applies the theory to two specific
models ($f(R)$ and DGP) that are representative for Chameleon and Vainshtein
screening mechanisms. Additionally, we use a multipole decomposition, which
apart from speeding up the algorithm to extract the signal from data, also
helps to visualize and characterize GR deviations. | The L-sigma Relation of Local HII Galaxies: We present for the first time a new data set of emission line widths for 118
star-forming regions in HII galaxies (HIIGs). This homogeneous set is used to
investigate the L-sigma relation in conjunction with optical spectrophotometric
observations. Peculiarities in the line profiles such as sharp lines, wings,
asymmetries, and in some cases more than one component in emission were
verified. From a new independent homogeneous set of spectrophotometric data we
derived physical condition parameters and performed the statistical principal
component analysis. We have investigated the potential role of metallicity
(O/H), Hbeta equivalent width (WHbeta) and ionization ratio [OIII]/[OII] to
account for the observational scatter of L-sigma relation. Our results indicate
that the L-sigma relation for HIIGs is more sensitive to the evolution of the
current starburst event (short-term evolution) and dated by WHbeta or even the
[OIII]/[OII] ratio. The long-term evolution measured by O/H also plays a
potential role in determining the luminosity of the current burst for a given
velocity dispersion and age as previously suggested. Additionally, galaxies
showing Gaussian line profiles present more tight correlations indicating that
they are best targets for the application of the parametric relations as an
extragalactic cosmological distance indicator. Best fits for a restricted
homogeneous sample of 45 HIIGs provide us a set of new extragalactic distance
indicators with an RMS scatter compatible with observational errors of
Delta_log(LHalpha) = 0.2 dex or 0.5 mag. Improvements may still come from
future optimized observational programs to reduce the observational
uncertainties on the predicted luminosities of HIIGs in order to achieve the
precision required for the application of these relations as tests of
cosmological models. |
A type IIn supernova with coronal lines in the low-metallicity compact
dwarf galaxy J1320+2155: We report the discovery of a type IIn supernova in the low-metallicity dwarf
galaxy J1320+2155, with an oxygen abundance 12+logO/H = 8.0+/-0.2. This finding
is based on SDSS (February 2008) and 3.5m Apache Point Observatory (February
2009) spectra taken one year apart, and on the observations that: the Hbeta and
Halpha emission lines show broad components corresponding to gas expansion
velocities of ~1600 km/s; the Balmer decrement is exceeedingly high: the
Halpha/Hbeta flux ratio, being more than 30, implies a very dense environment
(>10^7 cm^-3); and the Halpha broad luminosity decreases slowly, by only a
factor of ~1.8 over the course of a year, typical of the slow luminosity
evolution of a type IIn supernova. Several weak coronal lines of [Fe VII] and
[Fe X] are also seen in the SDSS spectrum, implying ionization of the pre-shock
circumstellar medium by shock-induced X-ray emission. The galaxy J1320+2155 is
the first dwarf system ever to be discovered with a type IIn supernova
exhibiting coronal lines in its spectrum. | Imaging an Event Horizon: submm-VLBI of a Super Massive Black Hole: A long standing goal in astrophysics is to directly observe the immediate
environment of a black hole with angular resolution comparable to the event
horizon. Realizing this goal would open a new window on the study of General
Relativity in the strong field regime, accretion and outflow processes at the
edge of a black hole, the existence of an event horizon, and fundamental black
hole physics (e.g., spin). Steady long-term progress on improving the
capability of Very Long Baseline Interferometry (VLBI) at short wavelengths has
now made it extremely likely that this goal will be achieved within the next
decade. The most compelling evidence for this is the recent observation by
1.3mm VLBI of Schwarzschild radius scale structure in SgrA*, the compact source
of radio, submm, NIR and xrays at the center of the Milky Way. SgrA* is thought
to mark the position of a ~4 million solar mass black hole, and because of its
proximity and estimated mass presents the largest apparent event horizon size
of any black hole candidate in the Universe. Over the next decade, existing and
planned mm/submm facilities will be combined into a high sensitivity, high
angular resolution "Event Horizon Telescope" that will bring us as close to the
edge of black hole as we will come for decades. This white paper describes the
science case for mm/submm VLBI observations of both SgrA* and M87 (a radio loud
AGN of a much more luminous class that SgrA*). We emphasize that while there is
development and procurement involved, the technical path forward is clear, and
the recent successful observations have removed much of the risk that would
normally be associated with such an ambitious project. |
Properties of dust and PAHs in the hot plasma of the elliptical galaxy
NGC4125 revealed with AKARI and Spitzer: We present the spatial distributions of dust and polycyclic aromatic
hydrocarbons (PAHs) in the elliptical galaxy NGC4125, revealed by AKARI and
Spitzer. NGC4125 is relatively bright in the dust and the PAH emision for
elliptical galaxies, although it certainly possesses diffuse interstellar hot
plasma indicated by the high spatial resolution X-ray data of Chandra. We
investigate how the dust and PAHs interact with the X-ray plasma or avoid the
interaction by comparing their spatial distributions. We find that the
distributions of the PAHs and dust are different from each other, both showing
a significant deviation from a smooth stellar distribution. The PAH emission
predominantly comes from a dust lane, a compact dense molecular gas region in
the galactic center, where the PAHs are likely to have been protected from the
interaction with the X-ray plasma. The dust emission has more extended
structures similar to the distribution of the X-ray plasma, suggesting their
interaction to some extent. We also discuss a possible origin of the dust and
PAHs in the galaxy. | Peculiar Velocity Decomposition, Redshift Space Distortion and Velocity
Reconstruction in Redshift Surveys. II. Dark Matter Velocity Statistics: Massive spectroscopic redshift surveys open a promising window to accurately
measure peculiar velocity at cosmological distances through redshift space
distortion (RSD). In paper I of this series of work we proposed to decompose
peculiar velocity into three eigen-modes (v_\delta, v_S and v_B) in order to
facilitate the RSD modeling and peculiar velocity reconstruction. In the
current paper we measure the dark matter RSD related statistics of the velocity
eigen-modes through a set of N-body simulations, including the velocity power
spectra, correlation functions, one-point probability distribution functions,
cumulants and the damping functions describing the Finger of God effect. (1)
The power spectrum measurement shows that these velocity components have
distinctly different spatial distribution and redshift evolution. In
particular, we measure the window function \tilde{W}(k,z), which describes the
impact of nonlinear evolution on the v_\delta-density relation. We confirm that
it can induce a significant systematic error of O(10%) in RSD cosmology. We
demonstrate that \tilde{W} can be accurately described by a simple fitting
formula with one or two free parameters. (2) The correlation function
measurement shows that the correlation length is O(100), O(10) and O(1) Mpc for
v_\delta, v_S and v_B respectively. These correlation lengths determine where
we can treat the velocity fields as spatially uncorrelated. (3) The velocity
PDFs and cumulants quantify non-Gaussianities of the velocity fields. We
confirm speculation in paper I that v_\delta is largely Gaussian, nevertheless
with non-negligible non-Gaussianity, v_B is significantly non-Gaussian. We also
measure the damping functions. Despite the observed non-Gaussianities, the
damping functions and hence the FOG effect are all well approximated as
Gaussian ones at scales of interest. |
The power spectrum of systematics in cosmic shear tomography and the
bias on cosmological parameters: Cosmic shear tomography has emerged as one of the most promising tools to
both investigate the nature of dark energy and discriminate between General
Relativity and modified gravity theories. In order to successfully achieve
these goals, systematics in shear measurements have to be taken into account;
their impact on the weak lensing power spectrum has to be carefully
investigated in order to estimate the bias induced on the inferred cosmological
parameters. To this end, we develop here an efficient tool to compute the power
spectrum of systematics by propagating, in a realistic way, shear measurement,
source properties and survey setup uncertainties. Starting from analytical
results for unweighted moments and general assumptions on the relation between
measured and actual shear, we derive analytical expressions for the
multiplicative and additive bias, showing how these terms depend not only on
the shape measurement errors, but also on the properties of the source galaxies
(namely, size, magnitude and spectral energy distribution). We are then able to
compute the amplitude of the systematics power spectrum and its scaling with
redshift, while we propose a multigaussian expansion to model in a
non-parametric way its angular scale dependence. Our method allows to
self-consistently propagate the systematics uncertainties to the finally
observed shear power spectrum, thus allowing us to quantify the departures from
the actual spectrum. We show that even a modest level of systematics can induce
non-negligible deviations, thus leading to a significant bias on the recovered
cosmological parameters. | Gravitational Redshift of Galaxies in Clusters from the Sloan Digital
Sky Survey and the Baryon Oscillation Spectroscopic Survey: The gravitational redshift effect allows one to directly probe the
gravitational potential in clusters of galaxies. Following up on Wojtak et al.
[Nature (London) 477, 567 (2011)], we present a new measurement. We take
advantage of new data from the tenth data release of the Sloan Digital Sky
Survey and the Baryon Oscillation Spectroscopic Survey. We compare the
spectroscopic redshift of the brightest cluster galaxies (BCGs) with that of
galaxies at the outskirts of clusters, using a sample with an average cluster
mass of $10^{14} M_{\odot}$. We find that these galaxies have an average
relative redshift of -11 km/s compared with that of BCGs, with a standard
deviation of +7 and -5 km/s. Our measurement is consistent with that of Wojtak
et al. However, our derived standard deviation is larger, as we take into
account various systematic effects, beyond the size of the dataset. The result
is in good agreement with the predictions from general relativity. |
Planck 2018 results. III. High Frequency Instrument data processing and
frequency maps: This paper presents the High Frequency Instrument (HFI) data processing
procedures for the Planck 2018 release. Major improvements in mapmaking have
been achieved since the previous 2015 release. They enabled the first
significant measurement of the reionization optical depth parameter using HFI
data. This paper presents an extensive analysis of systematic effects,
including the use of simulations to facilitate their removal and characterize
the residuals. The polarized data, which presented a number of known problems
in the 2015 Planck release, are very significantly improved. Calibration, based
on the CMB dipole, is now extremely accurate and in the frequency range 100 to
353 GHz reduces intensity-to-polarization leakage caused by calibration
mismatch. The Solar dipole direction has been determined in the three lowest
HFI frequency channels to within one arc minute, and its amplitude has an
absolute uncertainty smaller than $0.35\mu$K, an accuracy of order $10^{-4}$.
This is a major legacy from the HFI for future CMB experiments. The removal of
bandpass leakage has been improved by extracting the bandpass-mismatch
coefficients for each detector as part of the mapmaking process; these values
in turn improve the intensity maps. This is a major change in the philosophy of
"frequency maps", which are now computed from single detector data, all
adjusted to the same average bandpass response for the main foregrounds.
Simulations reproduce very well the relative gain calibration of detectors, as
well as drifts within a frequency induced by the residuals of the main
systematic effect. Using these simulations, we measure and correct the small
frequency calibration bias induced by this systematic effect at the $10^{-4}$
level. There is no detectable sign of a residual calibration bias between the
first and second acoustic peaks in the CMB channels, at the $10^{-3}$ level. | BL Lacertae objects beyond redshift 1.3 - UV-to-NIR photometry and
photometric redshift for Fermi/LAT blazars: Observations of the gamma-ray sky with Fermi led to significant advances
towards understanding blazars, the most extreme class of Active Galactic
Nuclei. A large fraction of the population detected by Fermi is formed by BL
Lacertae (BL Lac) objects, whose sample has always suffered from a severe
redshift incompleteness due to the quasi-featureless optical spectra. Our goal
is to provide a significant increase of the number of confirmed high-redshift
BL Lac objects contained in the 2 LAC Fermi/LAT catalog. For 103 Fermi/LAT
blazars, photometric redshifts using spectral energy distribution fitting have
been obtained. The photometry includes 13 broad-band filters from the far
ultraviolet to the near-IR observed with Swift/UVOT and the multi-channel
imager GROND at the MPG/ESO 2.2m telescope. Data have been taken
quasi-simultaneously and the remaining source-intrinsic variability has been
corrected for. We release the UV-to-near-IR 13-band photometry for all 103
sources and provide redshift constraints for 75 sources without previously
known redshift. Out of those, eight have reliable photometric redshifts at
z>1.3, while for the other 67 sources we provide upper limits. Six of the
former eight are BL Lac objects, which quadruples the sample of confirmed
high-redshift BL Lac. This includes three sources with redshifts higher than
the previous record for BL Lac, including CRATES J0402-2615 with the best-fit
solution at z~1.9. |
Cosmological tests of an axiverse-inspired quintessence field: Inspired by the string axiverse idea, it has been suggested that the recent
transition from decelerated to accelerated cosmic expansion is driven by an
axion-like quintessence field with a sub-Planckian decay constant. The scenario
requires that the axion field be rather near the maximum of its potential, but
is less finely tuned than other explanations of cosmic acceleration. The model
is parametrized by an axion decay constant $f$, the axion mass $m$, and an
initial misalignment angle $|\theta_i|$ which is close to $\pi$. In order to
determine the $m$ and $\theta_{i}$ values consistent with observations, these
parameters are mapped onto observables: the Hubble parameter $H(z)$ at and
angular diameter distance $d_{A}(z)$ to redshift $z= 0.57$, as well as the
angular sound horizon of the cosmic microwave background (CMB). Measurements of
the baryon acoustic oscillation (BAO) scale at $z\simeq 0.57$ by the BOSS
survey and Planck measurements of CMB temperature anisotropies are then used to
probe the $\left\{m,f,\theta_i\right\}$ parameter space. With current data, CMB
constraints are the most powerful, allowing a fraction of only $\sim 0.2$ of
the parameter-space volume. Measurements of the BAO scale made using the
SPHEREx or SKA experiments could go further, observationally distinguishing all
but $\sim 10^{-2}$ or $\sim 10^{-5}$ of the parameter-space volume (allowed by
simple priors) from the $\Lambda$CDM model. | The eROSITA Final Equatorial-Depth Survey (eFEDS): X-ray Properties and
Scaling Relations of Galaxy Clusters and Groups: We investigate the scaling relations between X-ray observables of the
clusters detected in the eFEDS field using Spectrum-Roentgen-Gamma/eROSITA
observations taking into account the selection effects and the distributions of
observables with cosmic time. We extract X-ray observables (Lx, Lbol, T, Mgas,
Yx) within R500 for the sample of 542 clusters in the eFEDS field. By applying
detection and extent likelihoods, we construct a subsample of 265 clusters with
a contamination level of <10% (including AGNs and spurious fluctuations) to be
utilized in the scaling relation analysis. The selection function based on the
state-of-the-art simulations of the eROSITA sky is fully accounted for in our
work. We provide the X-ray observables in the core-included <R500 and
core-excised 0.15*R500-R500 apertures for 542 galaxy clusters and groups
detected in the eFEDS field. Additionally, we present our best-fit results for
the normalization, slope, redshift evolution and intrinsic scatter parameters
of the X-ray scaling relations between Lx-T, Lx-Mgas, Lx-Yx, Lbol-T, Lbol-Mgas,
Lbol-Yx and Mgas-T. We find that the best-fit slopes significantly deviate from
the self-similar model at a >3sigma confidence level however, our results are
in good agreement with the simulations including non-gravitational physics and
the recent results that take into account selection effects. Strong deviations
we find from the self-similar scenario indicate that the non-gravitational
effects play an important role in shaping the observed physical state of
clusters. This work extends the scaling relations to low mass, low luminosity
galaxy cluster and group regime using eFEDS observations, demonstrating
eROSITA's ability to measure ICM emission out to R500 with survey-depth
exposures and constrain the scaling relations in a wide
mass-luminosity-redshift range. |
The integrated Sachs-Wolfe imprints of cosmic superstructures: a problem
for ΛCDM: A crucial diagnostic of the \Lambda CDM cosmological model is the integrated
Sachs-Wolfe (ISW) effect of large-scale structure on the cosmic microwave
background (CMB). The ISW imprint of superstructures of size \sim100\;h^{-1}
Mpc at redshift $z\sim0.5$ has been detected with $>4\sigma$ significance,
however it has been noted that the signal is much larger than expected. We
revisit the calculation using linear theory predictions in \Lambda CDM
cosmology for the number density of superstructures and their radial density
profile, and take possible selection effects into account. While our expected
signal is larger than previous estimates, it is still inconsistent by
$>3\sigma$ with the observation. If the observed signal is indeed due to the
ISW effect then huge, extremely underdense voids are far more common in the
observed universe than predicted by \Lambda CDM. | Magnetogenesis from axion inflation: In this work we compute the production of magnetic fields in models of axion
inflation coupled to the hypercharge sector of the Standard Model through a
Chern-Simons interaction term. We make the simplest choice of a quadratic
inflationary potential and use lattice simulations to calculate the magnetic
field strength, helicity and correlation length at the end of inflation. For
small values of the axion-gauge field coupling strength the results agree with
no-backreaction calculations and estimates found in the literature. For larger
couplings the helicity of the magnetic field differs from the no-backreaction
estimate and depends strongly on the comoving wavenumber. We estimate the
post-inflationary evolution of the magnetic field based on known results for
the evolution of helical and non-helical magnetic fields. The magnetic fields
produced by axion inflation with large couplings to $U(1)_Y$ can reach $B_{\rm
eff} \gtrsim 10^{-16}\, {\rm G}$, exhibiting a field strength $B_{\rm phys}
\approx 10^{-13}\, {\rm G}$ and a correlation length $\lambda_{\rm
phys}\approx10\, {\rm pc}$. This result is insensitive to the exact value of
the coupling, as long as the coupling is large enough to allow for
instantaneous preheating. Depending on the assumptions for the physical
processes that determine blazar properties, these fields can be found
consistent with blazar observations based on the value of $B_{\rm eff}$.
Finally, the intensity of the magnetic field for large coupling can be enough
to satisfy the requirements for a recently proposed baryogenesis mechanism,
which utilizes the chiral anomaly of the Standard Model. |
A KAT-7 view of a low-mass sample of galaxy clusters: Radio observations over the last two decades have provided evidence that
diffuse synchrotron emission in the form of megaparsec-scale radio halos in
galaxy clusters is likely tracing regions of the intracluster medium where
relativistic particles are accelerated during cluster mergers. In this paper we
present results of a survey of 14 galaxy clusters carried out with the
7-element Karoo Array Telescope at 1.86 GHz, aimed to extend the current
studies of radio halo occurrence to systems with lower masses (M$_{\rm 500} >
4\times10^{14}$ M${_\odot}$). We found upper limits at the $0.6 - 1.9 \times
10^{24}$ Watt Hz$^{-1}$ level for $\sim 50\%$ of the sample, confirming that
bright radio halos in less massive galaxy clusters are statistically rare. | Dark Matter Substructure Detection Using Spatially Resolved Spectroscopy
of Lensed Dusty Galaxies: We investigate how strong lensing of dusty, star-forming galaxies by
foreground galaxies can be used as a probe of dark matter halo substructure. We
find that spatially resolved spectroscopy of lensed sources allows dramatic
improvements to measurements of lens parameters. In particular we find that
modeling of the full, three-dimensional (angular position and radial velocity)
data can significantly facilitate substructure detection, increasing the
sensitivity of observables to lower mass subhalos. We carry out simulations of
lensed dusty sources observed by early ALMA (Cycle 1) and use a Fisher matrix
analysis to study the parameter degeneracies and mass detection limits of this
method. We find that, even with conservative assumptions, it is possible to
detect galactic dark matter subhalos of ~ 10^8 M_{\odot} with high significance
in most lensed DSFGs. Specifically, we find that in typical DSFG lenses, there
is a ~ 55 % probability of detecting a substructure with M>10^8 M_{\odot} with
more than 5 sigma detection significance in each lens, if the abundance of
substructure is consistent with previous lensing results. The full ALMA array,
with its significantly enhanced sensitivity and resolution, should improve
these estimates considerably. Given the sample of ~100 lenses provided by
surveys like the South Pole Telescope, our understanding of dark matter
substructure in typical galaxy halos is poised to improve dramatically over the
next few years. |
Testing Two-Field Inflation: We derive semi-analytic formulae for the power spectra of two-field inflation
assuming an arbitrary potential and non-canonical kinetic terms, and we use
them both to build phenomenological intuition and to constrain classes of
two-field models using WMAP data. Using covariant formalism, we first develop a
framework for understanding the background field kinematics and introduce a
"slow-turn" approximation. Next, we find covariant expressions for the
evolution of the adiabatic/curvature and entropy/isocurvature modes, and we
discuss how the mode evolution can be inferred directly from the background
kinematics and the geometry of the field manifold. From these expressions, we
derive semi-analytic formulae for the curvature, isocurvature, and cross
spectra, and the spectral observables, all to second-order in the slow-roll and
slow-turn approximations. In tandem, we show how our covariant formalism
provides useful intuition into how the characteristics of the inflationary
Lagrangian translate into distinct features in the power spectra. In
particular, we find that key features of the power spectra can be directly read
off of the nature of the roll path, the curve the field vector rolls along with
respect to the field manifold. For example, models whose roll path makes a
sharp turn 60 e-folds before inflation ends tend to be ruled out because they
produce strong departures from scale invariance. Finally, we apply our
formalism to confront four classes of two-field models with WMAP data,
including doubly quadratic and quartic potentials and non-standard kinetic
terms, showing how whether a model is ruled out depends not only on certain
features of the inflationary Lagrangian, but also on the initial conditions.
Ultimately, models must possess the right balance of kinematical and dynamical
behaviors, which we capture in a set of functions that can be reconstructed
from spectral observables. | The evolution of a primordial binary black hole due to interaction with
cold dark matter and the formation rate of gravitational wave events: In this Paper we consider a problem of formation and evolution of orbital
parameters of a binary primordial black hole (PBH) due to gravitational
interaction with clustering cold dark matter (CDM). Mass and initial separation
have values, which are appropriate for the problem of explanation of the
LIGO/Virgo events by coalescing binary PBHs. We consider both radiation
dominated and CDM dominated stages of the evolution using numerical and
semi-analytical means. We show that at the end time of our numerical
simulations binary's semimajor axis decreases by approximately one hundred
times, while its angular momentum decreases by ten times, in comparison to the
standard values, which do not take into account effects associated with CDM
clustering. We check that our conclusions are hardly affected by numerical
artefacts. We estimate the merger rate of binary PBHs due to emission of
gravitational wave at the present time both in the standard case when the
effects associated with clustering are neglected and in the case when they are
taken into account and show, that these effects could increase the merger rate
at least by $6-8$ times in comparison to the standard estimate. This, in turn,
means, that a mass fraction of PBHs, $f$, should be smaller than it was assumed
before. |
The Spitzer discovery of a galaxy with infrared emission solely due to
AGN activity: We present a galaxy (SAGE1CJ053634.78-722658.5) at a redshift of 0.14 of
which the IR is entirely dominated by emission associated with the AGN. We
present the 5-37 um Spitzer/IRS spectrum and broad wavelength SED of
SAGE1CJ053634, an IR point-source detected by Spitzer/SAGE (Meixner et al
2006). The source was observed in the SAGE-Spec program (Kemper et al., 2010)
and was included to determine the nature of sources with deviant IR colours.
The spectrum shows a redshifted (z=0.14+-0.005) silicate emission feature with
an exceptionally high feature-to-continuum ratio and weak polycyclic aromatic
hydrocarbon (PAH) bands. We compare the source with models of emission from
dusty tori around AGNs from Nenkova et al. (2008). We present a diagnostic
diagram that will help to identify similar sources based on Spitzer/MIPS and
Herschel/PACS photometry. The SED of SAGE1CJ053634 is peculiar because it lacks
far-IR emission and a clear stellar counterpart. We find that the SED and the
IR spectrum can be understood as emission originating from the inner ~10 pc
around an accreting black hole. There is no need to invoke emission from the
host galaxy, either from the stars or from the interstellar medium, although a
possible early-type host galaxy cannot be excluded based on the SED analysis.
The hot dust around the accretion disk gives rise to a continuum, which peaks
at 4 um, whereas the strong silicate features may arise from optically thin
emission of dusty clouds within ~10 pc around the black hole. The weak PAH
emission does not appear to be linked to star formation, as star formation
templates strongly over-predict the measured far-IR flux levels. The SED of
SAGE1CJ053634 is rare in the local universe but may be more common in the more
distant universe. The conspicuous absence of host-galaxy IR emission places
limits on the far-IR emission arising from the dusty torus alone. | Host Galaxies of Luminous Type 2 Quasars at z ~ 0.5: We present deep Gemini GMOS optical spectroscopy of nine luminous quasars at
redshifts z ~ 0.5, drawn from the SDSS type 2 quasar sample. Our targets were
selected to have high intrinsic luminosities (M_V < -26 mag) as indicated by
the [O III] 5007 A emission-line luminosity (L_[O III]). Our sample has a
median black hole mass of ~ 10^8.8 M_sun inferred assuming the local
M_BH-sigma_* relation and a median Eddington ratio of ~ 0.7, using stellar
velocity dispersions sigma_* measured from the G band. We estimate the
contamination of the stellar continuum from scattered quasar light based on the
strength of broad H-beta, and provide an empirical calibration of the
contamination as a function of L_[O III]; the scattered light fraction is ~ 30%
of L_5100 for objects with L_[O III] = 10^9.5 L_sun. Population synthesis
indicates that young post-starburst populations (< 0.1 Gyr) are prevalent in
luminous type 2 quasars, in addition to a relatively old population (> 1 Gyr)
which dominates the stellar mass. Broad emission complexes around He II 4686 A
with luminosities up to 10^8.3 L_sun are unambiguously detected in three out of
the nine targets, indicative of Wolf-Rayet populations. Population synthesis
shows that ~ 5-Myr post-starburst populations contribute substantially to the
luminosities (> 50% of L_5100) of all three objects with Wolf-Rayet detections.
We find two objects with double cores and four with close companions. Our
results may suggest that luminous type 2 quasars trace an early stage of galaxy
interaction, perhaps responsible for both the quasar and the starburst
activity. |
Simulating the Anisotropic Clustering of Luminous Red Galaxies with
Subhalos: A Direct Confrontation with Observation and Cosmological
Implications: We model the apparent clustering anisotropy of Luminous Red Galaxies (LRGs)
in the Sloan Digital Sky Survey using subhalos identified in cosmological
$N$-body simulations. We first conduct a Markov-chain Monte Carlo analysis on
the parameters characterizing subhalos hosting LRGs assuming a specific
$\Lambda$CDM cosmology on which we run the simulations. We show that simple
models with central and satellite subhalos can explain the observed multipole
moments of the power spectrum up to hexadecapole on large scales
($k\lesssim0.3~h\mathrm{Mpc}^{-1}$). A satellite fraction of $20$ to $30$ per
cent is favored weakly depending on the detail of the model. The fraction is
shown to be robust when we adopt a more refined model based on the halo
occupation number from the literature. We then vary cosmological parameters
controlling the anisotropy in redshift-space effectively by deforming the
simulation box (the Alcock-Paczynski effect) and changing the amplitude of the
velocities (the redshift-space distortions). We demonstrate that we can
constrain the geometry of the universe, the structure growth rate, and the
parameters characterizing LRGs simultaneously. This is a step toward
cosmological analysis with realistic bias description beyond empirical bias
functions with nuisance parameters. | Information Content of Higher-Order Galaxy Correlation Functions: The shapes of galaxy N-point correlation functions can be used as standard
rulers to constrain the distance-redshift relationship and thence the expansion
rate of the Universe. The cosmological density fields traced by late-time
galaxy formation are initially nearly Gaussian, and hence all the cosmological
information can be extracted from their 2-Point Correlation Function (2PCF) or
its Fourier-space analog the power spectrum. Subsequent nonlinear evolution
under gravity, as well as halo and then galaxy formation, generate higher-order
correlation functions. Since the mapping of the initial to the final density
field is, on large scales, invertible, it is often claimed that the information
content of the initial field's power spectrum is equal to that of all the
higher-order functions of the final, nonlinear field. This claim implies that
reconstruction of the initial density field from the nonlinear field renders
analysis of higher-order correlation functions of the latter superfluous. We
here show that this claim is false when the N-point functions are used as
standard rulers. Constraints available from joint analysis of the galaxy power
spectrum and bispectrum (Fourier-space analog of the 3-Point Correlation
Function) can, in some cases, exceed those offered by the initial power
spectrum even when the reconstruction is perfect. We provide a mathematical
justification for this claim and also demonstrate it using a large suite of
N-body simulations. In particular, we show that for the z = 0 real-space matter
field in the limit of vanishing shot noise, taking modes up to k_max = 0.2
h/Mpc, using the bispectrum alone offers a factor of two reduction in the
variance on the cosmic distance scale relative to that available from the power
spectrum. |
Direct Dark Matter Search with the CRESST II Experiment: The quest for the particle nature of dark matter is one of the big open
questions of modern physics. A well motivated candidate for dark matter is the
so-called WIMP - a weakly interacting massive particle. Recently several
theoretically well-motivated models with dark matter candidates in a mass
region below the WIMP mass-scale gained also a lot of interest, theoretically
and experimentally. The CRESST II experiment located at the Gran Sasso
laboratory in Italy is optimised for the detection of the elastic scattering of
these low-mass dark matter particles with ordinary matter. We show the results
obtained with an improved detector setup with increased radio purity and
enhanced background rejection and the results obtained with a dedicated
low-threshold analysis of a single conventional detector module. The limit
achieved is the most stringent limit achieved for direct dark matter
experiments in the mass region below 1.8 GeV/$c^{2}$. We will discuss the
expected performance for new small CRESST-type detectors to be used during the
next data taking phase. We conclude with an outlook of the future potential for
direct dark matter detection using further improved CRESST CaWO$_{4}$ cryogenic
detectors. | A revision of the X-ray absorption nature of the BALQSOs: Broad absorption line quasars (BALQSOs) are key objects for studying the
structure and emission/absorption properties of AGN. However, despite their
fundamental importance, the properties of BALQSOs are still not well
understood. In order to investigate the X-ray nature of these sources, as well
as the correlations between X-ray and rest-frame UV properties, we compile a
large sample of 88 BALQSOs observed by XMM-Newton. We performed a full X-ray
spectral analysis on a sample of 39 sources with higher X-ray spectral quality,
and an approximate HR analysis on the remaining sources. Using available
optical spectra, we calculate the BALnicity index and investigate the
dependence between this optical parameter and different X-ray properties.
Using the neutral absorption model, we found that 36% of our BALQSOs have NH
< 5x10^21 cm^-2, lower than the expected X-ray absorption for such objects.
However, when we used a physically-motivated model for the X-ray absorption in
BALQSOs, i.e. ionized absorption, \sim 90% of the objects are absorbed. The
absorption properties also suggest that LoBALs may be physically different
objects from HiBALs. In addition, we report on a correlation between the
ionized absorption column density and BAL parameters. There is evidence (at 98%
level) that the amount of X-ray absorption is correlated with the strength of
high-ionization UV absorption. This correlation, not previously reported, can
be naturally understood in virtually all BALQSO models, as driven by the total
amount of gas mass flowing towards the observer. |
Overdensities of 24um Sources in the Vicinities of High-Redshift Radio
Galaxies: We present a statistical study of the environments of 63 high-redshift radio
galaxies (HzRGs) between redshifts 1<z<5.2, using the 24um, waveband of the
MIPS instrument aboard the Spitzer Space Telescope. Using a counts-in-cell
analysis, a statistically significant source overdensity is found in 1.75arcmin
radius circular cells centred on the HzRGs when compared to reference fields.
We report an average overdensity of delta (= {N}_{targets} / {N}_{reference}) =
2.2 +/- 1.2 at a flux density cut of f24um=0.3mJy. This result implies that
HzRGs are likely to lie in protoclusters of active and star-forming galaxies at
high redshift. Over 95% of our targeted HzRGs lie in higher than average
density fields. Further, 20 (32%) of our selected fields are found to be
overdense to at least a 3sigma significance, of which 9 are newly identified
protocluster candidates. We observe a weak correlation between redshift and
24um, source density, and discuss the populations being probed at different
redshifts. In our uniformly selected sample, which was designed to cover two
orders of magnitude in radio luminosity throughout z=1-4, we find that the
24um, source density does not depend on radio luminosity. We also compare this
result with recent work describing IRAC source overdensities around the same
HzRGs and find correlations between the results. | Improved constraint on primordial gravitational waves in light of the
Hubble tension and BICEP/Keck: The Hubble tension that the standard $\Lambda$CDM model is suffering from can
be resolved with pre-recombination early dark energy. We present the first
constraint on the tensor-to-scalar ratio $r$ in corresponding
Hubble-tension-free cosmologies using the most recent BICEP/Keck cosmic
microwave background (CMB) B-mode polarization data. We find, combining
BICEP/Keck with Planck18 CMB and baryon acoustic oscillation data, that the
models with larger Hubble constant $H_0$ will have tighter upper bound on $r$,
and resolution $H_0\sim73$ km/s/Mpc of the Hubble tension tightens the upper
bound to $r<0.028\ (95\%\text{C.L.})$, $25\%$ tighter than the $\Lambda$CDM
constraint $r<0.036$. We clarify the origin of this tightening bound. |
Phenomenology of BAO evolution from Lagrangian to Eulerian Space: The baryon acoustic oscillation (BAO) feature provides an important distance
scale for the measurement of the expansion history of the Universe. Theoretical
models of the BAO in the distribution of biased tracers of the large scale
structure usually rely on an initially linear BAO. With aid of N-body
simulations, we demonstrate that the BAO in the initial (Lagrangian) halo
2-point function is significantly sharper than in the linear matter
distribution, in agreement with peak theory. Using this approach, we delineate
the scale-dependence induced by the higher-derivative and velocity bias before
assessing how much of the initial BAO enhancement survives until the collapse
epoch. Finally, we discuss the extent to which the velocity or gravity bias,
which is also imprinted in the displacement field of halos, affects the
contrast of the BAO obtained with a reconstruction. | The accretion of a solar mass per day by a 17-billion solar mass black
hole: Around a million quasars have been catalogued in the Universe by probing
deeper and using new methods for discovery. However, the hardest ones to find
seem to be the rarest and brightest specimen. In this work, we study the
properties of the most luminous of all quasars found so far. It has been
overlooked until recently, which demonstrates that modern all-sky surveys have
much to reveal. The black hole in this quasar accretes around one solar mass
per day onto an existing mass of $\sim$17 billion solar masses. In this process
its accretion disc alone releases a radiative energy of $2\times 10^{41}$
Watts. If the quasar is not strongly gravitationally lensed, then its broad
line region (BLR) is expected to have the largest physical and angular diameter
occurring in the Universe, and will allow the Very Large Telescope
Interferometer to image its rotation and measure its black hole mass directly.
This will be an important test for BLR size-luminosity relations, whose
extrapolation has underpinned common black-hole mass estimates at high
redshift. |
The key role of the Calan/Tololo project in the discovery of the
accelerating Universe: The Nobel Prize in Physics 2011 has just been awarded to three astronomers:
Saul Perlmutter, Brian Schmidt, and Adam Riess, for their amazing discovery of
the accelerating expansion of the Universe. Without diminishing the achievement
of our community's laureates, here I elaborate on the role of the C&T project
in this discovery. | Measuring BAO and non-Gaussianity via QSO clustering: Our goals are (i) to search for BAO and large-scale structure in current QSO
survey data and (ii) to use these and simulation/forecast results to assess the
science case for a new, >10x larger, QSO survey. We first combine the SDSS, 2QZ
and 2SLAQ surveys to form a survey of ~60000 QSOs. We find a hint of a peak in
the QSO 2-point correlation function, xi(s), at the same scale (~105h^-1 Mpc)
as detected by Eisenstein et al (2005) in their sample of DR5 LRGs but only at
low statistical significance. We then compare these data with QSO mock
catalogues from the Hubble Volume simulation used by Hoyle et al (2002) and
find that both routes give statistical error estimates that are consistent at
~100h^-1 Mpc scales. Mock catalogues are then used to estimate the nominal
survey size needed for a 3-4 sigma detection of the BAO peak. We find that a
redshift survey of ~250000 z<2.2 QSOs is required over ~3000 deg^2. This is
further confirmed by static log-normal simulations where the BAO are clearly
detectable in the QSO power spectrum and correlation function. The nominal
survey would on its own produce the first detection of, for example,
discontinuous dark energy evolution in the so far uncharted 1<z<2.2 redshift
range. A survey with ~50% higher QSO sky densities and 50% bigger area will
give an ~6sigma BAO detection, leading to an error ~60% of the size of the BOSS
error on the dark energy evolution parameter, w_a.
Another important aim for a QSO survey is to place new limits on primordial
non-Gaussianity at large scales, testing tentative evidence we have found for
the evolution of the linear form of the combined QSO xi(s) at z~1.6. Such a QSO
survey will also determine the gravitational growth rate at z~1.6 via z-space
distortions, allow lensing tomography via QSO magnification bias while also
measuring the exact luminosity dependence of small-scale QSO clustering. |
Stochastic bias of colour-selected BAO tracers by joint clustering-weak
lensing analysis: The baryon acoustic oscillation (BAO) feature in the two-point correlation
function of galaxies supplies a standard ruler to probe the expansion history
of the Universe. We study here several galaxy selection schemes, aiming at
building an emission-line galaxy (ELG) sample in the redshift range
$0.6<z<1.7$, that would be suitable for future BAO studies, providing a highly
biased galaxy sample. We analyse the angular galaxy clustering of galaxy
selections at the redshifts 0.5, 0.7, 0.8, 1 and 1.2 and we combine this
analysis with a halo occupation distribution (HOD) model to derive the
properties of the haloes these galaxies inhabit, in particular the galaxy bias
on large scales. We also perform a weak lensing analysis (aperture statistics)
to extract the galaxy bias and the cross-correlation coefficient and compare to
the HOD prediction.
We apply this analysis on a data set composed of the photometry of the deep
co-addition on Sloan Digital Sky Survey (SDSS) Stripe 82 (225 deg$^2$), of
Canda-France-Hawai Telescope/Stripe 82 deep \emph{i}-band weak lensing survey
and of the {\it Wide-Field Infrared Survey Explorer}infrared photometric band
W1.
The analysis on the SDSS-III/constant mass galaxies selection at $z=0.5$ is
in agreement with previous studies on the tracer, moreover we measure its
cross-correlation coefficient $r=1.16\pm0.35$. For the higher redshift bins, we
confirm the trends that the brightest galaxy populations selected are strongly
biased ($b>1.5$), but we are limited by current data sets depth to derive
precise values of the galaxy bias. A survey using such tracers of the mass
field will guarantee a high significance detection of the BAO. | Disentangling Resonant Scattering and Gas Motions in Galaxy Cluster
Emission Line Profiles: Future high spectral resolution telescopes will enable us to place tight
constraints on turbulence in the intra-cluster medium through the line widths
of strong emission lines. At the same time, these bright lines are the most
prone to be optically thick. This requires us to separate the effects of
resonant scattering from turbulence, both of which could broaden the lines. How
this can be achieved has yet not been quantitatively addressed. In this paper,
we propose a flexible new parametrization for the line profile, which allows
these effects to be distinguished. The model has only 3 free parameters, which
we calibrate with Monte-Carlo radiative transfer simulations. We provide
fitting functions and tables that allow the results of these calculations to be
easily incorporated into a fast spectral fitting package. In a mock spectral
fit, we explicitly show that this parameterization allows us to correctly
estimate the turbulent amplitude and metallicity of a cluster such as Perseus,
which would otherwise give significantly biased results. We also show how the
physical origin of the line shape can be understood analytically. |
Non-thermal neutrino-like hot dark matter in light of the $S_8$ tension: The $\Lambda$CDM prediction of $S_8\equiv\sigma_8(\Omega_m/0.3)^{0.5}$ --
where $\sigma_8$ is the root mean square of matter fluctuations on a 8
$h^{-1}$Mpc scale -- once calibrated on Planck CMB data is $2-3\sigma$ lower
than its direct estimate by a number of weak lensing surveys. In this paper, we
explore the possibility that the '$S_8$-tension' is due to a non-thermal hot
dark matter (HDM) fractional contribution to the universe energy density
leading to a power suppression at small-scales in the matter power spectrum.
Any HDM models can be characterized by its effective mass $ m_{sp}^{\rm eff}$
and its contribution to the relativistic degrees of freedom at CMB decoupling
$\Delta N_{\rm eff}$. Taking the specific example of a sterile particle
produced from the decay of the inflaton during a matter dominated era, we find
that from Planck only the tension can be reduced below $2\sigma$, but Planck
does not favor a non-zero ${m_{sp}^{\rm eff},\Delta N_{\rm eff}}$. In
combination with a measurement of $S_8$ from KIDS1000+BOSS+2dfLenS, the
$S_8$-tension would hint at the existence of a particle of mass $ m_{sp}^{\rm
eff} \simeq 0.67_{-0.48}^{+0.26}$ ${\rm eV}$ with a contribution to $\Delta
N_{\rm eff} \simeq0.06\pm0.05$. However, Pantheon and BOSS BAO/$f\sigma_8$ data
restricts the particle mass to $m_{sp}^{\rm eff} \simeq 0.48_{-0.36}^{+0.17}$
and contribution to $\Delta N_{\rm eff} \simeq 0.046_{-0.031}^{+0.004}$. We
discuss implications of our results for other canonical non-thermal HDM models
-- the Dodelson-Widrow model and a thermal sterile particle with a different
temperature in the hidden sector. We report competitive results on such hidden
sector temperature which might have interesting implications for particle
physics model building, in particular connecting the $S_8$-tension to the
longstanding short baseline oscillation anomaly. | A new measurement of the Hubble constant using Type Ia supernovae
calibrated with surface brightness fluctuations: We present a new calibration of the peak absolute magnitude of SNe Type Ia
based on the Surface Brightness Fluctuations (SBF) method, aimed at measuring
the value of the Hubble constant. We build a sample of calibrating anchors
consisting of 24 SNe hosted in galaxies having SBF distance measurements.
Applying a hierarchical Bayesian approach, we calibrate the SNe luminosity and
extend it into the Hubble flow by using a sample of 96 SNe Ia in the redshift
range $0.02 < z < 0.075$, extracted from the Combined Pantheon Sample. We
estimate a value of $H_0 = 70.50 \pm 2.37(stat) \pm 3.38(sys)$ $\text{km}\
\text{s}^{-1}\ \text{Mpc}^{-1}$ (i.e. $3.4\% stat, 4.8\% sys$), which is in
agreement with the value obtained using the tip of the red giant branch
calibration, and consistent within the errors with the value obtained from SNe
Type Ia calibrated with Cepheids and the one inferred from the analysis of the
cosmic microwave background. We find that the SNe Ia distance moduli calibrated
with SBF are on average larger by 0.07 mag than the ones calibrated with
Cepheids. Our results point to possible differences among SNe in different
types of galaxies, which could originate from different local environments
and/or SNe Ia progenitor properties. Sampling different host galaxy type, SBF
offers a complementary approach to Cepheids which is important in addressing
possible systematics. As the SBF method has the ability to reach larger
distances than Cepheids, the impending entry of LSST and JWST into operation
will increase the number of SNe Ia hosted in galaxies where SBF distances can
be measured, making SBF measurements attractive for improving the calibration
of SNe Ia, and in the estimation of $H_0$. |
Scaling relations of clusters and groups, and their evolution: X-ray observations of the hot intra-cluster medium (ICM) in galaxy groups and
clusters provide quantities such as their gas mass, X-ray luminosity, and
temperature. The analysis of the scaling relations between these observable
properties gives considerable insight into the physical processes taking place
in the ICM. Furthermore, an understanding of the scaling relations between ICM
properties and the total cluster mass is essential for cosmological studies
with clusters. For these reasons, the X-ray scaling relations of groups and
clusters have been a major focus of research over the past several decades. In
this Chapter, after presenting the expectations from the self-similar model,
based on the assumption that only gravity drives the evolution of the ICM, we
discuss how the processes of gas cooling and non-gravitational heating are
believed to be responsible for the observed deviations from the self-similar
scenario. We also describe important complications that must be considered when
measuring and interpreting the scaling relations. | Grid-based calculations of redshift-space matter fluctuations from
perturbation theory: UV sensitivity and convergence at the field level: Perturbation theory (PT) has been used to interpret the observed nonlinear
large-scale structure statistics at the quasi-linear regime. To facilitate the
PT-based analysis, we have presented the GridSPT algorithm, a grid-based method
to compute the nonlinear density and velocity fields in standard perturbation
theory (SPT) from a given linear power spectrum. Here, we further put forward
the approach by taking the redshift-space distortions into account. With the
new implementation, we have, for the first time, generated the redshift-space
density field to the fifth order and computed the next-to-next-to-leading order
(2 loop) power spectrum and the next-to-leading order (1 loop) bispectrum of
matter clustering in redshift space. By comparing the result with corresponding
analytical SPT calculation and $N$-body simulations, we find that the SPT
calculation (A) suffers much more from the UV sensitivity due to the
higher-derivative operators and (B) deviates from the $N$-body results from the
Fourier wavenumber smaller than real space $k_{\rm max}$. Finally, we have
shown that while Pad\'e approximation removes spurious features in morphology,
it does not improve the modeling of power spectrum and bispectrum. |
The Fermi blazars divide: Flat Spectrum Radio Quasars (FSRQs) and BL Lac objects detected in the first
three months of the Fermi survey neatly separate in the gamma-ray spectral
index vs gamma-ray luminosity plane. BL Lac objects are less luminous and have
harder spectra than broad line blazars. We suggest that this division has its
origin in the different accretion regimes of the two classes of objects. Using
the gamma-ray luminosity as a proxy for the observed bolometric one we show
that the boundary between the two subclasses of blazars can be associated with
the threshold between the regimes of optically thick accretion disks and of
radiatively inefficient accretion flows, which lies at an accretion rate of the
order of 0.01 the Eddington rate. The spectral separation in hard (BL Lacs) and
soft (FSRQs) objects can then result from the different radiative cooling
suffered by the relativistic electrons in jets propagating in different
ambients. We argue that the bulk of the most luminous blazars alread detected
by Fermi should be characterised by large black hole masses, around 10^9 solar
masses, and predict that lowering the gamma-ray flux threshold the region of
the alpha_gamma-L_gamma plane corresponding to steep spectral indices and lower
luminosities will be progressively populated by FSRQs with lower mass black
holes, while the region of hard spectra and large luminosities will remain
forbidden. | The SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Quasar
Target Selection: As part of the Sloan Digital Sky Survey IV the extended Baryon Oscillation
Spectroscopic Survey (eBOSS) will improve measurements of the cosmological
distance scale by applying the Baryon Acoustic Oscillation (BAO) method to
quasar samples. eBOSS will adopt two approaches to target quasars over 7500 sq.
deg. First, a "CORE" quasar sample will combine optical selection in ugriz
using a likelihood-based routine called XDQSOz, with a mid-IR-optical
color-cut. eBOSS CORE selection (to g < 22 OR r < 22) should return ~ 70
quasars per sq. deg. at redshifts 0.9 < z < 2.2 and ~7 z > 2.1 quasars per sq.
deg. Second, a selection based on variability in multi-epoch imaging from the
Palomar Transient Factory should recover an additional ~3-4 z > 2.1 quasars per
sq. deg. to g < 22.5. A linear model of how imaging systematics affect target
density recovers the angular distribution of eBOSS CORE quasars over 96.7%
(76.7%) of the SDSS North (South) Galactic Cap area. The eBOSS CORE quasar
sample should thus be sufficiently dense and homogeneous over 0.9 < z < 2.2 to
yield the first few-percent-level BAO constraint near z~1.5. eBOSS quasars at z
> 2.1 will be used to improve BAO measurements in the Lyman-alpha Forest.
Beyond its key cosmological goals, eBOSS should be the next-generation quasar
survey, comprising > 500,000 new quasars and > 500,000 uniformly selected
spectroscopically confirmed 0.9 < z < 2.2 quasars. At the conclusion of eBOSS,
the SDSS will have provided unique spectra of over 800,000 quasars. |
On the non-linear scale of cosmological perturbation theory: We discuss the convergence of cosmological perturbation theory. We prove that
the polynomial enhancement of the non-linear corrections expected from the
effects of soft modes is absent in equal-time correlators like the power or
bispectrum. We first show this at leading order by resumming the most important
corrections of soft modes to an arbitrary skeleton of hard fluctuations. We
derive the same result in the eikonal approximation, which also allows us to
show the absence of enhancement at any order. We complement the proof by an
explicit calculation of the power spectrum at two-loop order, and by further
numerical checks at higher orders. Using these insights, we argue that the
modification of the power spectrum from soft modes corresponds at most to
logarithmic corrections. Finally, we discuss the asymptotic behavior in the
large and small momentum regimes and identify the expansion parameter pertinent
to non-linear corrections. | A manifestly covariant theory of multifield stochastic inflation in
phase space: solving the discretisation ambiguity in stochastic inflation: Stochastic inflation is an effective theory describing the super-Hubble,
coarse-grained, scalar fields driving inflation, by a set of Langevin
equations. We previously highlighted the difficulty of deriving a theory of
stochastic inflation that is invariant under field redefinitions, and the link
with the ambiguity of discretisation schemes defining stochastic differential
equations. In this paper, we solve the issue of these "inflationary stochastic
anomalies" by using the Stratonovich discretisation satisfying general
covariance, and identifying that the quantum nature of the fluctuating fields
entails the existence of a preferred frame defining independent stochastic
noises. Moreover, we derive physically equivalent It\^o-Langevin equations that
are manifestly covariant and well suited for numerical computations. These
equations are formulated in the general context of multifield inflation with
curved field space, taking into account the coupling to gravity as well as the
full phase space in the Hamiltonian language, but this resolution is also
relevant in simpler single-field setups. We also develop a path-integral
derivation of these equations, which solves conceptual issues of the heuristic
approach made at the level of the classical equations of motion, and allows in
principle to compute corrections to the stochastic formalism. Using the
Schwinger-Keldysh formalism, we integrate out small-scale fluctuations, derive
the influence action that describes their effects on the coarse-grained fields,
and show how the resulting coarse-grained effective Hamiltonian action can be
interpreted to derive Langevin equations with manifestly real noises. Although
the corresponding dynamics is not rigorously Markovian, we show the covariant,
phase-space Fokker-Planck equation for the Probability Density Function of
fields and momenta when the Markovian approximation is relevant [...] |
Absorption signatures of warm-hot gas at low redshift: Broad HI
Lyman-Alpha Absorbers: We investigate the physical state of HI absorbing gas at low redshift (z =
0.25) using a subset of cosmological, hydrodynamic simulations from the OWLS
project, focusing in particular on broad (b_HI > 40 km/s) HI Lyman-Alpha
absorbers (BLAs), which are believed to originate in shock-heated gas in the
warm-hot intergalactic medium (WHIM). Our fiducial model, which includes
radiative cooling by heavy elements and feedback by supernovae and active
galactic nuclei, predicts that by z = 0.25 nearly 60 per cent of the gas mass
ends up at densities and temperatures characteristic of the WHIM and we find
that half of this fraction is due to outflows. The standard HI observables
(distribution of HI column densities N_HI, distribution of Doppler parameters
b_HI, b_HI - N_HI correlation) and the BLA line number density predicted by our
simulations are in remarkably good agreement with observations.
BLAs arise in gas that is hotter, more highly ionised and more enriched than
the gas giving rise to typical Lyman-Alpha forest absorbers. The majority of
the BLAs arise in warm-hot (log (T/K) ~ 5) gas at low (log Delta < 1.5)
overdensities. On average, thermal broadening accounts for at least 60 per cent
of the BLA line width, which in turn can be used as a rough indicator of the
thermal state of the gas. Detectable BLAs account for only a small fraction of
the true baryon content of the WHIM at low redshift. In order to detect the
bulk of the mass in this gas phase, a sensitivity at least one order of
magnitude better than achieved by current ultraviolet spectrographs is
required. We argue that BLAs mostly trace gas that has been shock-heated and
enriched by outflows and that they therefore provide an important window on a
poorly understood feedback process. | Data augmentation for machine learning redshifts applied to SDSS
galaxies: We present analyses of data augmentation for machine learning redshift
estimation. Data augmentation makes a training sample more closely resemble a
test sample, if the two base samples differ, in order to improve measured
statistics of the test sample. We perform two sets of analyses by selecting
800k (1.7M) SDSS DR8 (DR10) galaxies with spectroscopic redshifts. We construct
a base training set by imposing an artificial r band apparent magnitude cut to
select only bright galaxies and then augment this base training set by using
simulations and by applying the K-correct package to artificially place
training set galaxies at a higher redshift.
We obtain redshift estimates for the remaining faint galaxy sample, which are
not used during training. We find that data augmentation reduces the error on
the recovered redshifts by 40% in both sets of analyses, when compared to the
difference in error between the ideal case and the non augmented case. The
outlier fraction is also reduced by at least 10% and up to 80% using data
augmentation.
We finally quantify how the recovered redshifts degrade as one probes to
deeper magnitudes past the artificial magnitude limit of the bright training
sample. We find that at all apparent magnitudes explored, the use of data
augmentation with tree based methods provide a estimate of the galaxy redshift
with a negligible bias, although the error on the recovered values increases as
we probe to deeper magnitudes. These results have applications for surveys
which have a spectroscopic training set which forms a biased sample of all
photometric galaxies, for example if the spectroscopic detection magnitude
limit is shallower than the photometric limit. |
CMB-S4: Forecasting Constraints on $f_\mathrm{NL}$ Through
$μ$-distortion Anisotropy: Diffusion damping of the cosmic microwave background (CMB) power spectrum
results from imperfect photon-baryon coupling in the pre-recombination plasma.
At redshift $5 \times 10^4 < z < 2 \times 10^6$, the plasma acquires an
effective chemical potential, and energy injections from acoustic damping in
this era create $\mu$-type spectral distortions of the CMB. These $\mu$
distortions trace the underlying photon density fluctuations, probing the
primordial power spectrum in short-wavelength modes $k_\mathrm{S}$ over the
range $50 \ \mathrm{Mpc}^{-1} \lesssim k \lesssim 10^4 \ \mathrm{Mpc}^{-1}$.
Small-scale power modulated by long-wavelength modes $k_\mathrm{L}$ from
squeezed-limit non-Gaussianities introduces cross-correlations between CMB
temperature anisotropies and $\mu$ distortions. Under single-field inflation
models, $\mu \times T$ correlations measured from an observer in an inertial
frame should vanish up to a factor of $(k_\mathrm{L}/k_\mathrm{S})^2 \ll 1$.
Thus, any measurable correlation rules out single-field inflation models. We
forecast how well the next-generation ground-based CMB experiment CMB-S4 will
be able to constrain primordial squeezed-limit non-Gaussianity, parameterized
by $f_\mathrm{NL}$, using measurements of $C_{\ell}^{\mu T}$ as well as
$C_{\ell}^{\mu E}$ from CMB $E$ modes. Using current experimental
specifications and foreground modeling, we expect $\sigma(f_\mathrm{NL})
\lesssim 1000$. This is roughly four times better than the current limit on
$f_\mathrm{NL}$ using $\mu \times T$ and $\mu \times E$ correlations from
Planck and is comparable to what is achievable with LiteBIRD, demonstrating the
power of the CMB-S4 experiment. This measurement is at an effective scale of $k
\simeq 740 \ \text{Mpc}^{-1}$ and is thus highly complementary to measurements
at larger scales from primary CMB and large-scale structure. | Comparison Of Reionization Models: Radiative Transfer Simulations And
Approximate, Semi-Numeric Models: We compare the predictions of four different algorithms for the distribution
of ionized gas during the Epoch of Reionization. These algorithms are all used
to run a 100 Mpc/h simulation of reionization with the same initial conditions.
Two of the algorithms are state-of-the-art ray-tracing radiative transfer codes
that use disparate methods to calculate the ionization history. The other two
algorithms are fast but more approximate schemes based on iterative application
of a smoothing filter to the underlying source and density fields. We compare
these algorithms' resulting ionization and 21 cm fields using several different
statistical measures. The two radiative transfer schemes are in excellent
agreement with each other (with the cross-correlation coefficient of the
ionization fields >0.8 for k < 10 h/Mpc and in good agreement with the analytic
schemes (>0.6 for k < 1 h/Mpc). When used to predict the 21cm power spectrum at
different times during reionization, all ionization algorithms agree with one
another at the 10s of percent level. This agreement suggests that the different
approximations involved in the ray tracing algorithms are sensible and that
semi-numerical schemes provide a numerically-inexpensive, yet fairly accurate,
description of the reionization process. |
Warm Gas in the Virgo Cluster: I. Distribution of Lya Absorbers: The first systematic study of the warm gas (T=10^4-5 K) distribution across a
galaxy cluster is presented using multiple background QSOs to the Virgo
Cluster. We detect 25 Lya absorbers (N_HI = 10^13.1-15.4 cm^-2) in the Virgo
velocity range toward 9 of 12 QSO sightlines observed with Cosmic Origin
Spectrograph, with a cluster impact parameter range of 0.36-1.65 Mpc
(0.23-1.05R_vir). Including 18 Lya absorbers previously detected by STIS or
GHRS toward 7 of 11 background QSOs in and around the Virgo Cluster, we
establish a sample of 43 absorbers towards a total of 23 background probes for
studying the incidence of Lya absorbers in and around the Virgo Cluster. With
these absorbers, we find: (1) warm gas is predominantly in the outskirts of the
cluster and avoids the X-ray detected hot ICM. Also, Lya absorption strength
increases with cluster impact parameter. (2) Lya absorbing warm gas traces cold
HI emitting gas in the substructures of the Virgo Cluster. (3) Including the
absorbers associated with the surrounding substructures, the warm gas covering
fraction (100% for N_HI > 10^13.1 cm^-2) is in agreement with cosmological
simulations. We speculate that the observed warm gas is part of large-scale gas
flows feeding the cluster both the ICM and galaxies. | Beyond the growth rate of cosmic structure: Testing modified gravity
models with an extra degree of freedom: In 'modified' gravity the observed acceleration of the universe is explained
by changing the gravitational force law or the number of degrees of freedom in
the gravitational sector. Both possibilities can be tested by measurements of
cosmological structure formation. In this paper we elaborate the details of
such tests using the Galileon model as a case study. We pay attention to the
possibility that each new degree of freedom may have stochastically independent
initial conditions, generating different types of potential well in the early
universe and breaking complete correlation between density and velocity power
spectra. This 'stochastic bias' can confuse schemes to parametrize the
predictions of modified gravity models, such as the use of the growth parameter
f alone. Using data from the WiggleZ Dark Energy Survey we show that it will be
possible to obtain constraints using information about the cosmological-scale
force law embedded in the multipole power spectra of redshift-space
distortions. As an example, we obtain an upper limit on the strength of the
conformal coupling to matter in the cubic Galileon model, giving |1/M| < 200 /
Mp. This allows the fifth-force to be stronger than gravity, but is consistent
with zero coupling. |
Radio jets from stellar tidal disruptions: A star that passes too close to a massive black hole will be torn apart by
tidal forces. The flare of photons emitted during the accretion of the stellar
debris is predicted to be observable and candidates of such events have been
observed at optical to X-ray frequencies. If a fraction of the accreted
material is fed into a jet, tidal flares should be detectable at radio
frequencies too, thus comprising a new class of rare radio transients. Using
the well-established scaling between accretion power and jet luminosity and
basic synchrotron theory, we construct an empirically-rooted model to predict
the jet luminosity for a time-dependent accretion rate. We apply this model to
stellar tidal disruptions and predict the snapshot rate of these events. For a
small angle between the observer and the jet, our model reproduces the observed
radio flux of the tidal flare candidate GRB 110328A. We find that future radio
surveys will be able to test whether the majority of tidal disruptions are
accompanied by a jet. | The observable $E_g$ statistics: Recently Moradinezhad Dizgah & Durrer have shown that the $E_g$ statistics,
useful to test theories of modified gravity, is plagued by additional scale and
bias dependent lensing contributions. In this work we develop and illustrate a
method to remove these lensing terms by using in addition to the galaxy
clustering data also shear data and the correlations of shear and galaxy
clustering. We introduce a truly observable statistics termed $\tilde E_g$
which conserves the properties of scale and bias independence on linear scales.
The method discussed here is best adapted to photometric surveys. It is found
that the corrections to the original $E_g$ statistics are small for the present
DES data, but for future surveys of the quality of Euclid they are very
substantial. |
Modelling narrow-line regions of active galaxies in the Sloan Digital
Sky Survey - I.Sample selection and physical conditions: We systematically determine the electron density and electron temperature of
active galaxies and star-forming galaxies using spectroscopy from the SDSS DR7,
while mainly focusing on the NLRs. Density and temperature are determined
through the I[S II] 6716/6731 and I[O III] 5007/4363 ratios, respectively, in
our [O III] 4363 emission sample of 15 019 galaxies. We find two sequences and
the typical range of density in the NLRs of AGNs is 100-1000 /cm3. The
temperatures in the NLRs range from 10 000 to 20 000 K for Seyferts, and the
ranges were even higher and wider for LINERs and composites. We also propose
that Y_LINER ~ Y_Seyfert > Y_composite > Y_star-forming, where Y is the
characteristic present-day star-formation time-scale. While in the AGN case, we
find several strong lines of evidence suggest that some supplementary energy
source(s) should be responsible for high ionization potential. | Estimation of Inflation parameters for Perturbed Power Law model using
recent CMB measurements: Cosmic Microwave Background (CMB) is an important probe for understanding the
inflationary era of the Universe. We consider the Perturbed Power Law (PPL)
model of inflation which is a soft deviation from Power Law (PL) inflationary
model. This model captures the effect of higher order derivative of Hubble
parameter during inflation, which in turn leads to a non-zero effective mass
$m_{\rm eff}$ for the inflaton field. The higher order derivatives of Hubble
parameter at leading order sources constant difference in the spectral index
for scalar and tensor perturbation going beyond PL model of inflation. PPL
model have two observable independent parameters, namely spectral index for
tensor perturbation $\nu_t$ and change in spectral index for scalar
perturbation $\nu_{st}$ to explain the observed features in the scalar and
tensor power spectrum of perturbation. From the recent measurements of CMB
power spectra by WMAP, Planck and BICEP-2 for temperature and polarization, we
estimate the feasibility of PPL model with standard $\Lambda$CDM model.
Although BICEP-2 claimed a detection of $r=0.2$, estimates of dust
contamination provided by Planck have left open the possibility that only upper
bound on $r$ will be expected in a joint analysis. As a result we consider
different upper bounds on the value of $r$ and show that PPL model can explain
a lower value of tensor to scalar ratio ($r<0.1$ or $r<0.01$) for a scalar
spectral index of $n_s=0.96$ by having a non-zero value of effective mass of
the inflaton field $\frac{m^2_{\rm eff}}{H^2}$. The analysis with WP+ Planck
likelihood shows a non-zero detection of $\frac{m^2_{\rm eff}}{H^2}$ with
$5.7\,\sigma$ and $8.1\,\sigma$ respectively for $r<0.1$ and $r<0.01$. Whereas,
with BICEP-2 likelihood $\frac{m^2_{\rm eff}}{H^2} = -0.0237 \pm 0.0135$ which
is consistent with zero. |
Peeling off the late Universe: Reconstructing the ISW map with galaxy
surveys: The Integrated Sachs-Wolfe (ISW) effect is a large-angle modulation of the
cosmic microwave background (CMB), generated when CMB photons traverse evolving
potential wells associated with large scale structure (LSS). Recent efforts
have been made to reconstruct maps of the ISW signal using information from
surveys of galaxies and other LSS tracers, but investigation into how survey
systematics affect their reliability has so far been limited. Using simulated
ISW and LSS maps, we study the impact of galaxy survey properties and
systematic errors on the accuracy of reconstructed ISW signal. We find that
systematics that affect the observed distribution of galaxies along the line of
sight, such as photo-z and bias-evolution related errors, have a relatively
minor impact on reconstruction quality. In contrast, however, we find that
direction-dependent calibration errors can be very harmful. Specifically, we
find that in order to avoid significant degradation of our reconstruction
quality statistics, direction-dependent number density fluctuations due to
systematics must be controlled so that their variance is smaller than $10^{-6}$
(which corresponds to a 0.1% calibration). Additionally, we explore the
implications of our results for attempts to use reconstructed ISW maps to shed
light on the origin of large-angle CMB alignments. We find that there is only a
weak correlation between the true and reconstructed angular momentum
dispersion, which quantifies alignment, even for reconstructed ISW maps which
are fairly accurate overall. | Next Generation Virgo Cluster Survey. XXI. The weak lensing masses of
the CFHTLS and NGVS RedGOLD galaxy clusters and calibration of the optical
richness: We measured stacked weak lensing cluster masses for a sample of 1325 galaxy
clusters detected by the RedGOLD algorithm in the Canada-France-Hawaii
Telescope Legacy Survey W1 and the Next Generation Virgo Cluster Survey at
$0.2<z<0.5$, in the optical richness range $10<\lambda<70$. After a selection
of our best richness subsample ($20<\lambda<50$), this is the most
comprehensive lensing study of a $\sim 100\%$ complete and $\sim 90\%$ pure
optical cluster catalogue in this redshift range, with a total of 346 clusters
in $\sim164~deg^2$. We test three different mass models, and our best model
includes a basic halo model, with a Navarro Frenk and White profile, and
correction terms that take into account cluster miscentering, non-weak shear,
the two-halo term, the contribution of the Brightest Cluster Galaxy, and an a
posteriori correction for the intrinsic scatter in the mass-richness relation.
With this model, we obtain a mass-richness relation of $\log{M_{\rm
200}/M_{\odot}}=(14.48\pm0.04)+(1.14\pm0.23)\log{(\lambda/40)}$ (statistical
uncertainties). This result is consistent with other published lensing
mass-richness relations. When compared to X-ray masses and mass proxies, we
find that on average weak lensing masses are $\sim 10\%$ higher than those
derived in the X-ray in the range $2\times10^{13}M_{\rm \odot}<E(z) M^{X}_{\rm
200}<2\times10^{14}M_{\rm \odot}$, in agreement with most previous results and
simulations. We also give the coefficients of the scaling relations between the
lensing mass and X-ray mass proxies, $L_X$ and $T_X$, and compare them with
previous results. |
Higher-order statistics of the large-scale structure from photometric
redshifts: The large-scale structure is a major source of cosmological information.
However, next-generation photometric galaxy surveys will only provide a
distorted view of cosmic structures due to large redshift uncertainties. To
address the need for accurate reconstructions of the large-scale structure in
presence of photometric uncertainties, we present a framework that constrains
the three-dimensional dark matter density jointly with galaxy photometric
redshift probability density functions (PDFs), exploiting information from
galaxy clustering. Our forward model provides Markov Chain Monte Carlo
realizations of the primordial and present-day dark matter density, inferred
jointly from data. Our method goes beyond 2-point statistics via field-level
inference. It accounts for all observational uncertainties and the survey
geometry. We showcase our method using mock catalogs that emulate
next-generation surveys with a worst-case redshift uncertainty, equivalent to
${\sim}300$ Mpc. On scales $150$ Mpc, we improve the cross-correlation of the
photometric galaxy positions with the ground truth from $28\%$ to $86\%$. The
improvement is significant down to $13$ Mpc. On scales $150$ Mpc, we achieve a
cross-correlation of $80-90\%$ with the ground truth for the dark matter
density, radial peculiar velocities, tidal shear and gravitational potential. | Cosmokinetics: A joint analysis of Standard Candles, Rulers and Cosmic
Clocks: We study the accelerated expansion of the universe by using the kinematic
approach. In this context, we parameterize the deceleration parameter, q(z), in
a model independent way. Assuming three simple parameterizations we reconstruct
q(z). We do the joint analysis with combination of latest cosmological data
consisting of standard candles (Supernovae Union2 sample), standard ruler
(CMB/BAO), cosmic clocks (age of passively evolving galaxies) and Hubble (H(z))
data. Our results support the accelerated expansion of the universe. |
Quantifying the $S_8$ tension with the Redshift Space Distortion data
set: One problem of the $\Lambda$CDM model is the tension between the $S_8$ found
in Cosmic Microwave Background (CMB) experiments and the smaller one obtained
from large-scale observations in the late Universe. The $\sigma_8$ quantifies
the relatively high level of clustering. Bayesian Analysis of the Redshift
Space Distortion (RSD) selected data set yields: $S_8 =
0.700^{+0.038}_{-0.037}$. The fit has $3\sigma$ tension with the Planck 2018
results. With Gaussian processes method a model-independent reconstructions of
the growth history of matter in-homogeneity is studied. The fit yields $S_8 =
0.707^{+0.085}_{-0.085}, 0.701^{+0.089}_{-0.089}$, and $
0.731^{+0.063}_{-0.062}$ for different kernels. The tension reduces and being
smaller then $1.5\, \sigma$. With future measurements the tension may be
reduced, but the possibility the tension is real is a plausible situation. | On the radio and NIR jet of PKS 2155-304 and its close environment: PKS 2155-304 is one of the brightest BL Lac object in the sky and a very well
studied target from radio to TeV bands. We report on high-resolution (~ 0.12
arcsec) direct imaging of the field of PKS 2155-304 using adaptive optics
near-IR observations in J and Ks bands obtained with the ESO multi-conjugate
adaptive optic demonstrator (MAD) at the Very Large Telescope. These data are
complemented with archival VLA images at various frequencies to investigate the
properties of the close environment of the source. We characterized the faint
galaxies that form the poor group associated to the target. No radio emission
is present for these galaxies, while an old radio jet at ~ 20 kpc from the
nucleus of PKS 2155-304 and a jet-like structure of ~ 2 kpc (~ 1 arcsec) in the
eastern direction are revealed. No counterparts of these radio jets are found
in the NIR or in archival Chandra observations. |
Statistical Anisotropy in Inflationary Models with Many Vector Fields
and/or Prolonged Anisotropic Expansion: We study the most general contributions due to scalar field perturbations,
vector field perturbations, and anisotropic expansion to the generation of
statistical anisotropy in the primordial curvature perturbation \zeta. Such a
study is done using the \delta N formalism where only linear terms are
considered. Here, we consider two specific cases that lead to determine the
power spectrum P_\zeta(k) of the primordial curvature perturbation. In the
first one, we consider the possibility that the n-point correlators of the
field perturbations in real space are invariant under rotations in space
(statistical isotropy); as a result, we obtain as many levels of statistical
anisotropy as vector fields present and, therefore, several preferred
directions. The second possibility arises when we consider anisotropic
expansion, which leads us to obtain I+a additional contributions to the
generation of statistical anisotropy of \zeta compared with the former case,
being I and a the number of scalar and vector fields involved respectively. | The Cosmological Impact of Luminous TeV Blazars II: Rewriting the
Thermal History of the Intergalactic Medium: The Universe is opaque to extragalactic very high-energy gamma rays (VHEGRs,
E>100 GeV) because they annihilate and pair produce on the extragalactic
background light. The resulting ultra-relativistic pairs are assumed to lose
energy through inverse Compton scattering of CMB photons. In Broderick et al.
(2011, Paper I of this three paper series), we argued that instead powerful
plasma instabilities in the ultra-relativistic pair beam dissipate the kinetic
energy of the TeV-generated pairs locally, heating the intergalactic medium
(IGM). Here, we explore the effect of this heating upon the thermal history of
the IGM. We collate the observed extragalactic VHEGR sources to determine a
local VHEGR heating rate and correct for the pointed nature of VHEGR
observations using Fermi observations of high and intermediate peaked BL Lacs.
Because the local extragalactic VHEGR flux is dominated by TeV blazars, we tie
the TeV blazar luminosity density to the quasar luminosity density, and produce
a VHEGR heating rate as a function of redshift. This heating is relatively
homogeneous for z<~4 with increasing spatial variation at higher redshift
(order unity at z~6). This new heating process dominates photoheating at low
redshift and the inclusion of TeV blazar heating qualitatively and
quantitatively changes the structure and history of the IGM. TeV blazars
produce a uniform volumetric heating rate that is sufficient to increase the
temperature of the mean density IGM by nearly an order of magnitude, and at low
densities by substantially more, naturally producing an inverted equation of
state inferred by observations of the Ly-alpha forest, a feature that is
difficult to reconcile with standard reionization models. Finally, we close
with a discussion on the possibility of detecting this hot low-density IGM, but
find that such measurements are currently not feasible. (abridged) |
21cm fluctuations from primordial magnetic fields: Recent observations of magnetic fields in intergalactic void regions and in
high redshift galaxies may indicate that large scale magnetic fields have a
primordial origin. If primordial magnetic fields were present soon after the
recombination epoch, they would have induced density fluctuations on the one
hand and dissipated their energy into the primordial gas on the other, and
thereby significantly alter the thermal history of the Universe. Here we
consider both the effects and calculate the brightness temperature fluctuations
of the 21cm line using simple Monte Carlo simulations. We find that the
fluctuations of the 21cm line from the energy dissipation appear only on very
small scales and those from the density fluctuations always dominate on
observationally relevant angular scales. | Halo Gas and Galaxy Disk Kinematics of a Volume-Limited Sample of MgII
Absorption-Selected Galaxies at z~0.1: We have directly compared MgII halo gas kinematics to the rotation velocities
derived from emission/absorption lines of the associated host galaxies. Our
0.096<z<0.148 volume-limited sample comprises 13 ~L* galaxies, with impact
parameters of 12-90 kpc from background quasars sight-lines, associated with 11
MgII absorption systems with MgII equivalent widths 0.3< W_r(2796)<2.3A. For
only 5/13 galaxies, the absorption resides to one side of the galaxy systemic
velocity and trends to align with one side of the galaxy rotation curve. The
remainder have absorption that spans both sides of the galaxy systemic
velocity. These results differ from those at z~0.5, where 74% of the galaxies
have absorption residing to one side of the galaxy systemic velocity. For all
the z~0.1 systems, simple extended disk-like rotation models fail to reproduce
the full MgII velocity spread, implying other dynamical processes contribute to
the MgII kinematics. In fact 55% of the galaxies are "counter-rotating" with
respect to the bulk of the MgII absorption. These MgII host-galaxies are
isolated, have low star formation rates (SFRs) in their central regions (<1
Msun/yr), and SFRs per unit area well below those measured for galaxies with
strong winds. The galaxy NaID (stellar+ISM) and MgIb (stellar) absorption line
ratios are consistent with a predominately stellar origin, implying
kinematically quiescent interstellar media. These facts suggest that the
kinematics of the MgII absorption halos for our sample of galaxies are not
influenced by galaxy--galaxy environmental effects, nor by winds intrinsic to
the host galaxies. For these low redshift galaxies, we favor a scenario in
which infalling gas accretion provides a gas reservoir for low-to-moderate star
formation rates and disk/halo processes. |
Cosmic Chronometers with Photometry: a new path to $H(z)$: We present a proof-of-principle determination of the Hubble parameter $H(z)$
from photometric data, obtaining a determination at an effective redshift of
$z=0.75$ ($0.65<z<0.85$) of $H(0.75) =105.0\pm 7.9(stat)\pm 7.3(sys)$ km
s$^{-1}$ Mpc$^{-1}$, with 7.5\% statistical and 7\% systematic (10\% with
statistical and systematics combined in quadrature) accuracy. This is obtained
in a cosmology model-independent fashion, but assuming a linear age-redshift
relation in the relevant redshift range, as such, it can be used to constrain
arbitrary cosmologies as long as $H(z)$ can be considered slowly varying over
redshift. In particular, we have applied a neural network, trained on a
well-studied spectroscopic sample of 140 objects, to the {\tt COSMOS2015}
survey to construct a set of 19 thousand near-passively evolving galaxies and
build an age-redshift relation. The Hubble parameter is given by the derivative
of the red envelope of the age-redshift relation. This is the first time the
Hubble parameter is determined from photometry at $\lesssim 10$\% accuracy.
Accurate $H(z)$ determinations could help shed light on the Hubble tension;
this study shows that photometry, with a reduction of only a factor of two in
the uncertainty, could provide a new perspective on the tension. | Observables for moving, stupendously charged and massive primordial
black holes: Stupendously large black holes exceeding $10^{11} M_\odot$ could exist,
supported by recent observations of unexpectedly massive black holes at high
redshifts. These objects may constitute a part of dark matter or even dark
energy. One possibility to explain the cosmic accelerated expansion could be to
consider charged black holes whose mutual repulsion overcomes their
gravitational attraction. However, the extreme charge required turns these
black holes into naked singularities, whose existence is questioned by the
cosmic censorship hypothesis. Since the latter is driven by theoretical
assumptions, we work out the most promising observables which are least
cosmology-dependent to test their existence. We derive the electro-magnetic and
gravitational lensing effects caused by such extreme objects at distances much
larger than their extent to investigate possible ways for a discovery.
Restricting searches to black holes between $10^{12}$ to $10^{14} M_\odot$, we
show that such objects do not cause totally disruptive catastrophes, like
dissociation of neutral hydrogen clouds or proton decay induced by strong
electro-magnetic fields. Einstein rings of the order of 10" and rotation
measures of plasma clouds subject to the magnetic fields induced by the moving
black holes are identified as optimum observable signatures for now. Future
space-based black-hole telescopes will follow up on these candidates and
finally check the cosmic censorship hypothesis by their strong-field
strong-lensing signatures, like an additional sub-arcsecond inner Einstein
ring. Observable effects are so surprisingly moderate that a violation of
cosmic censorship is hard to detect and even explaining cosmic expansion with
moving naked singularities might be possible. |
Measuring the Homogeneity of the Universe Using Polarization Drift: We propose a method to probe the homogeneity of a general universe, without
assuming symmetry. We show that isotropy can be tested at remote locations on
the past lightcone by comparing the line-of-sight and transverse expansion
rates, using the time dependence of the polarization of Cosmic Microwave
Background photons that have been inverse-Compton scattered by the hot gas in
massive clusters of galaxies. This probes a combination of remote transverse
and parallel components of the expansion rate of the metric, and we may use
radial baryon acoustic oscillations or cosmic clocks to measure the parallel
expansion rate. Thus we can test remote isotropy, which is a key requirement of
a homogeneous universe. We provide explicit formulas that connect observables
and properties of the metric. | Testing Gravity on Cosmic Scales: A Case Study of Jordan-Brans-Dicke
Theory: We provide an end-to-end exploration of a distinct modified gravitational
theory in Jordan-Brans-Dicke (JBD) gravity, from an analytical and numerical
description of the background expansion and linear perturbations, to the
nonlinear regime captured with a hybrid suite of $N$-body simulations, to the
parameter constraints from existing cosmological probes. The nonlinear
corrections to the matter power spectrum due to baryons, massive neutrinos, and
modified gravity are simultaneously modeled and propagated in the cosmological
analysis for the first time. In the combined analysis of the Planck CMB
temperature, polarization, and lensing reconstruction, Pantheon supernova
distances, BOSS measurements of BAO distances, the Alcock-Paczynski effect, and
the growth rate, along with the joint ($3\times2$pt) dataset of cosmic shear,
galaxy-galaxy lensing, and overlapping redshift-space galaxy clustering from
KiDS and 2dFLenS, we constrain the JBD coupling constant, $\omega_{\rm
BD}>1540$ (95% CL), the effective gravitational constant, $G_{\rm
matter}/G=0.997\pm0.029$, the sum of neutrino masses, $\sum m_{\nu}<0.12$ eV
(95% CL), and the baryonic feedback amplitude, $B<2.8$ (95% CL), all in
agreement with the standard model expectation. We show that the uncertainty in
the gravitational theory alleviates the tension between KiDS$\times$2dFLenS and
Planck to below $1\sigma$ and the tension in the Hubble constant between Planck
and the direct measurement of Riess et al. (2019) down to ~$3\sigma$; however,
we find no substantial model selection preference for JBD gravity relative to
$\Lambda$CDM. We further show that the neutrino mass bound degrades by up to a
factor of three as the $\omega_{\rm BD}$ parameterization becomes more
restrictive and that a positive shift in $G_{\rm matter}/G$ suppresses the CMB
damping tail in a way that might complicate future inferences of small-scale
physics. (Abridged) |
The Luminosity Function at z~8 from 97 Y-band dropouts: Inferences About
Reionization: [Abbreviated] We present the largest search to date for $z\sim8$ Lyman break
galaxies (LBGs) based on 350 arcmin$^2$ of HST observations in the V-, Y-, J-
and H-bands from the Brightest of Reionizing Galaxies (BoRG) survey. The BoRG
dataset includes $\sim$50 arcmin$^2$ of new data and deeper observations of two
previous BoRG pointings, from which we present 9 new $z\sim8$ LBG candidates,
bringing the total number of BoRG LBGs to 38 with $25.5\leqslant m_{J}
\leqslant 27.6$ (AB system). We introduce a new Bayesian formalism for
estimating the galaxy luminosity function (LF), which does not require binning
(and thus smearing) of the data and includes a likelihood based on the formally
correct binomial distribution as opposed to the often used approximate Poisson
distribution. We demonstrate the utility of the new method on a sample of $97$
LBGs that combines the bright BoRG galaxies with the fainter sources published
in Bouwens et al. (2012) from the HUDF and ERS programs. We show that the
$z\sim8$ LF is well described by a Schechter function with a characteristic
magnitude $M^\star = -20.15^{+0.29}_{-0.38}$, a faint-end slope of $\alpha =
-1.87^{+0.26}_{-0.26}$, and a number density of $\log_{10} \phi^\star
[\textrm{Mpc}^{-3}] = -3.24^{+0.25}_{-0.24}$. Integrated down to $M=-17.7$ this
LF yields a luminosity density, $\log_{10} \epsilon
[\textrm{erg}/\textrm{s/Hz/Mpc}^{3}] = 25.52^{+0.05}_{-0.05}$. Our LF analysis
is consistent with previously published determinations within 1$\sigma$. We
discuss the implication of our study for the physics of reionization. By
assuming theoretically motivated priors on the clumping factor and the photon
escape fraction we show that the UV LF from galaxy samples down to $M=-17.7$
can ionize only 10-50% of the neutral hydrogen at $z\sim8$. Full reionization
would require extending the LF down to $M=-15$. | 21cm signal sensitivity to dark matter decay: The redshifted 21cm signal from the Cosmic Dawn is expected to provide
unprecedented insights into early Universe astrophysics and cosmology. Here we
explore how dark matter can heat the intergalactic medium before the first
galaxies, leaving a distinctive imprint in the 21cm power spectrum. We provide
the first dedicated Fisher matrix forecasts on the sensitivity of the Hydrogen
Epoch of Reionization Array (HERA) telescope to dark matter decays. We show
that with 1000 hours of observation, HERA has the potential to improve current
cosmological constraints on the dark matter decay lifetime by up to three
orders of magnitude. Even in extreme scenarios with strong X-ray emission from
early-forming, metal-free galaxies, the bounds on the decay lifetime would be
improved by up to two orders of magnitude. Overall, HERA shall improve on
existing limits for dark matter masses below $2$ GeV$/c^2$ for decays into
$e^+e^-$ and below few MeV$/c^2$ for decays into photons. |
The Effect of Absorption Systems on Cosmic Reionization: We use large-scale simulations to investigate the morphology of reionization
during the final, overlap phase. Our method uses an efficient three-dimensional
smoothing technique which takes into account the finite mean free path due to
absorption systems, lambda, by only smoothing over scales R_s<lambda. The large
dynamic range of our calculations is necessary to resolve the neutral patches
left at the end of reionization within a representative volume; we find that
simulation volumes exceeding several hundred Mpc on a side are necessary in
order to properly model reionization when the neutral fraction is ~0.01-0.3.
Our results indicate a strong dependence of percolation morphology on a large
and uncertain region of model parameter space. The single most important
parameter is the mean free path to absorption systems, which serve as opaque
barriers to ionizing radiation. If these absorption systems were as abundant as
some realistic estimates indicate, the spatial structure of the overlap phase
is considerably more complex than previously predicted. In view of the lack of
constraints on the mean free path at the highest redshifts, current theories
that do not include absorption by Lyman-limit systems, and in particular
three-dimensional simulations, may underestimate the abundance of neutral
clouds at the end of reionization. This affects predictions for the 21 cm
signal associated with reionization, interpretation of absorption features in
quasar spectra at z ~5-6, the connection between reionization and the local
universe, and constraints on the patchiness and duration of reionization from
temperature fluctuations measured in the cosmic microwave background arising
from the kinetic Sunyaev-Zel'dovich effect. | Possible Implications of Asymmetric Fermionic Dark Matter for Neutron
Stars: We consider the implications of fermionic asymmetric dark matter for a "mixed
neutron star" composed of ordinary baryons and dark fermions. We find examples,
where for a certain range of dark fermion mass -- when it is less than that of
ordinary baryons -- such systems can reach higher masses than the maximal
values allowed for ordinary ("pure") neutron stars. This is shown both within a
simplified, heuristic Newtonian analytic framework with non-interacting
particles and via a general relativistic numerical calculation, under certain
assumptions for the dark matter equation of state. Our work applies to various
dark fermion models such as mirror matter models and to other models where the
dark fermions have self interactions. |
Squeezing the Axion: We apply the squeezed state formalism to scalar field dark matter (e.g.
axion) perturbations generated during inflation. As for the inflationary
perturbations, the scalar field state becomes highly squeezed as modes exit the
horizon. For as long as $H>m_\phi$ (with $H$ the Hubble rate and $m_\phi$ the
scalar mass) the scalar field field does not interact during reheating, and we
follow its evolution exactly as modes re-enter the horizon. We find that the
quantum state remains squeezed after horizon re-entry during the hot big bang.
This demonstrates a fact well-known in the theory of inflation: cosmological
observables for scalar dark matter are accurately modelled by a classical
stochastic field with a fixed phase. Our calculation covers all modes smaller
than the present-day cosmic de Broglie wavelength. Larger scale modes mix
gravitationally with the environment when $H<m_\phi$, and are thus expected to
decohere. | Induced Gravitational Waves via Warm Natural Inflation: We analyze the spectrum of gravitational waves generated by the induced
spectrum of tensor fluctuation during warm natural inflation. In our previous
work it has been demonstrated that an epoch of warm natural inflation can lead
to cosmologically relevant dark matter production in the form of primordial
black holes. Here we show that models which solve the dark-matter production
also produce a contribution to the cosmic gravitational wave background that
satisfies current constraints from pulsar timing and big bang nucleosynthesis.
More importantly, this gravitational wave background may be observable in the
next generation of space-based and ground-based gravitational wave
interferometers. |
The clustering of the SDSS-IV extended Baryon Oscillation Spectroscopic
Survey DR14 quasar sample: First measurement of Baryon Acoustic Oscillations
between redshift 0.8 and 2.2: We present measurements of the Baryon Acoustic Oscillation (BAO) scale in
redshift-space using the clustering of quasars. We consider a sample of 147,000
quasars from the extended Baryon Oscillation Spectroscopic Survey (eBOSS)
distributed over 2044 square degrees with redshifts $0.8 < z < 2.2$ and measure
their spherically-averaged clustering in both configuration and Fourier space.
Our observational dataset and the 1400 simulated realizations of the dataset
allow us to detect a preference for BAO that is greater than 2.8$\sigma$. We
determine the spherically averaged BAO distance to $z = 1.52$ to 3.8 per cent
precision: $D_V(z=1.52)=3843\pm147 \left(r_{\rm d}/r_{\rm d, fid}\right)\ $Mpc.
This is the first time the location of the BAO feature has been measured
between redshifts 1 and 2. Our result is fully consistent with the prediction
obtained by extrapolating the Planck flat $\Lambda$CDM best-fit cosmology. All
of our results are consistent with basic large-scale structure (LSS) theory,
confirming quasars to be a reliable tracer of LSS, and provide a starting point
for numerous cosmological tests to be performed with eBOSS quasar samples. We
combine our result with previous, independent, BAO distance measurements to
construct an updated BAO distance-ladder. Using these BAO data alone and
marginalizing over the length of the standard ruler, we find $\Omega_{\Lambda}
> 0$ at 6.6$\sigma$ significance when testing a $\Lambda$CDM model with free
curvature. | Redshift weighted galaxy number counts: In this paper we introduce the `redshift fluctuation' as a gauge-invariant
cosmological observable and give its fully relativistic expression at first
order in cosmological perturbation theory. We show that this corresponds
effectively to number counts with a radial window function with vanishing mean
which therefore resolve smaller scale radial modes than standard number counts.
In a detailed analysis of the angular power spectrum of this new variable, we
study the relevance of different relativistic contributions, and how it differs
from the conventional observable galaxy number count fluctuations. In order to
investigate its utility for future spectroscopic surveys, we perform Fisher
forecasts for a Euclid-like and an SKAII-like configuration, as examples.
Particular focus is placed on the dependence of the results on the size of the
redshift bins and on the cutoff in $\ell$ adopted in the analysis. |
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. | Lagrangian displacement field estimators in cosmology: The late-time nonlinear Lagrangian displacement field is highly correlated
with the initial field, so reconstructing it could enable us to extract
primordial cosmological information. Our previous work [1] carefully studied
the displacement field reconstructed from the late time density field using the
iterative method proposed by Ref. [2] and found that it does not fully converge
to the true, underlying displacement field (e.g., $\sim 8\%$ offset at $k\sim
0.2 \ihMpc$ at $z=0.6$). We also constructed the Lagrangian perturbation theory
model for the reconstructed field, but the model could not explain the
discrepancy between the true and the reconstructed fields in the previous work.
The main sources of the discrepancy were speculated to be a numerical artifact
in the displacement estimator due to the discreteness of the sample. In this
paper, we develop two new estimators of the displacement fields to reduce such
numerical discreteness effect, the normalized momentum estimator~(NME) and the
rescaled resumed estimator~(RRE). We show that the discrepancy Ref. [1]
reported is not due to the numerical artifacts. We conclude that the method
from Ref. [2] cannot fully reconstruct the shape of the nonlinear displacement
field at the redshift we studied, while it is still an efficient BAO
reconstruction method. In parallel, by properly accounting for the UV-sensitive
term in a reconstruction procedure with an effective field theory approach, we
improve the theoretical model for the reconstructed displacement field, by
almost five times, from $\sim 15\%$ to the level of a few \% at $k\sim
0.2\ihMpc$ at the redshift $z=0.6$. |
The PdBI Arcsecond Whirlpool Survey (PAWS). I. A
Cloud-Scale/Multi-Wavelength View of the Interstellar Medium in a
Grand-Design Spiral Galaxy: The PdBI (Plateau de Bure Interferometer) Arcsecond Whirlpool Survey (PAWS)
has mapped the molecular gas in the central ~9kpc of M51 in its 12CO(1-0) line
emission at cloud-scale resolution of ~40pc using both IRAM telescopes. We
utilize this dataset to quantitatively characterize the relation of molecular
gas (or CO emission) to other tracers of the interstellar medium (ISM), star
formation and stellar populations of varying ages. Using 2-dimensional maps, a
polar cross-correlation technique and pixel-by-pixel diagrams, we find: (a)
that (as expected) the distribution of the molecular gas can be linked to
different components of the gravitational potential, (b) evidence for a
physical link between CO line emission and radio continuum that seems not to be
caused by massive stars, but rather depend on the gas density, (c) a close
spatial relation between the PAH and molecular gas emission, but no predictive
power of PAH emission for the molecular gas mass,(d) that the I-H color map is
an excellent predictor of the distribution (and to a lesser degree the
brightness) of CO emission, and (e) that the impact of massive (UV-intense)
young star-forming regions on the bulk of the molecular gas in central ~9kpc
can not be significant due to a complex spatial relation between molecular gas
and star-forming regions that ranges from co-spatial to spatially offset to
absent. The last point, in particular, highlights the importance of galactic
environment -- and thus the underlying gravitational potential -- for the
distribution of molecular gas and star formation. | Bayesian correction of $H(z)$ data uncertainties: We compile 41 $H(z)$ data from literature and use them to constrain
O$\Lambda$CDM and flat $\Lambda$CDM parameters. We show that the available
$H(z)$ suffers from uncertainties overestimation and propose a Bayesian method
to reduce them. As a result of this method, using $H(z)$ only, we find, in the
context of O$\Lambda$CDM, $H_0=69.5\pm2.5\mathrm{\,km\,s^{-1}Mpc^{-1}}$,
$\Omega_m=0.242\pm0.036$ and $\Omega_\Lambda=0.68\pm0.14$. In the context of
flat $\Lambda$CDM model, we have found
$H_0=70.4\pm1.2\mathrm{\,km\,s^{-1}Mpc^{-1}}$ and $\Omega_m=0.256\pm0.014$.
This corresponds to an uncertainty reduction of up to 30\% when compared to the
uncorrected analysis in both cases. |
Proper-Time Hypersurface of Non-Relativistic Matter Flows: Galaxy Bias
in General Relativity: We compute the second-order density fluctuation in the proper-time
hypersurface of non-relativistic matter flows and relate it to the galaxy
number density fluctuation in general relativity. At the linear order, it is
equivalent to the density fluctuation in the comoving synchronous gauge, in
which two separate gauge conditions coincide. However, at the second order, the
density fluctuations in these gauge conditions differ, while both gauge
conditions represent the proper-time hypersurface. Compared to the density
fluctuation in the temporal comoving and the spatial C-gauge conditions, the
density fluctuation in the commonly used gauge condition ($N=1$ and
$N^\alpha=0$) violates the mass conservation at the second order. We provide
their physical interpretations in each gauge condition by solving the geodesic
equation and the nonlinear evolution equations of non-relativistic matter. We
apply this finding to the second-order galaxy biasing in general relativity,
which complements the second-order relativistic description of galaxy
clustering in Yoo & Zaldarriaga (2014). | SOMBI: Bayesian identification of parameter relations in unstructured
cosmological data: This work describes the implementation and application of a correlation
determination method based on Self Organizing Maps and Bayesian Inference
(SOMBI). SOMBI aims to automatically identify relations between different
observed parameters in unstructured cosmological or astrophysical surveys by
automatically identifying data clusters in high-dimensional datasets via the
Self Organizing Map neural network algorithm. Parameter relations are then
revealed by means of a Bayesian inference within respective identified data
clusters. Specifically such relations are assumed to be parametrized as a
polynomial of unknown order. The Bayesian approach results in a posterior
probability distribution function for respective polynomial coefficients. To
decide which polynomial order suffices to describe correlation structures in
data, we include a method for model selection, the Bayesian Information
Criterion, to the analysis. The performance of the SOMBI algorithm is tested
with mock data. As illustration we also provide applications of our method to
cosmological data. In particular, we present results of a correlation analysis
between galaxy and AGN properties provided by the SDSS catalog with the cosmic
large-scale-structure (LSS). The results indicate that the combined galaxy and
LSS dataset indeed is clustered into several sub-samples of data with different
average properties (for example different stellar masses or web-type
classifications). The majority of data clusters appear to have a similar
correlation structure between galaxy properties and the LSS. In particular we
revealed a positive and linear dependency between the stellar mass, the
absolute magnitude and the color of a galaxy with the corresponding cosmic
density field. A remaining subset of data shows inverted correlations, which
might be an artifact of non-linear redshift distortions. |
Modified Einstein versus Modified Euler for Dark Matter: Modifications of General Relativity generically contain additional degrees of
freedom that can mediate forces between matter particles. One of the common
manifestations of a fifth force in alternative gravity theories is a difference
between the gravitational potentials felt by relativistic and non-relativistic
particles, also known as "the gravitational slip". In contrast, a fifth force
between dark matter particles, due to dark sector interaction, does not cause a
gravitational slip, making the latter a possible smoking gun of modified
gravity. In this article, we point out that a force acting on dark matter
particles, as in models of coupled quintessence, would also manifest itself as
a measurement of an effective gravitational slip by cosmological surveys of
large-scale structure. This is linked to the fact that redshift-space
distortions due to peculiar motion of galaxies do not provide a measurement of
the true gravitational potential if dark matter is affected by a fifth force.
Hence, it is extremely challenging to distinguish a dark sector interaction
from a modification of gravity with cosmological data alone. Future
observations of gravitational redshift from galaxy surveys can help to break
the degeneracy between these possibilities, by providing a direct measurement
of the distortion of time. We discuss this and other possible ways to resolve
this important question. | The massive black hole-velocity dispersion relation and the halo baryon
fraction: a case for positive AGN feedback: Force balance considerations put a limit on the rate of AGN radiation
momentum output, $L/c$, capable of driving galactic superwinds and reproducing
the observed $\mbh -\sigma $ relation between black hole mass and spheroid
velocity dispersion. We show that black holes cannot supply enough momentum in
radiation to drive the gas out by pressure alone. Energy-driven winds give a
$\mbh -\sigma $ scaling favoured by a recent analysis but also fall short
energetically once cooling is incorporated. We propose that outflow-triggering
of star formation by enhancing the intercloud medium turbulent pressure and
squeezing clouds can supply the necessary boost, and suggest possible tests of
this hypothesis. Our hypothesis simultaneously can account for the observed
halo baryon fraction. |
Improved Constraints on the 21 cm EoR Power Spectrum and the X-Ray
Heating of the IGM with HERA Phase I Observations: We report the most sensitive upper limits to date on the 21 cm epoch of
reionization power spectrum using 94 nights of observing with Phase I of the
Hydrogen Epoch of Reionization Array (HERA). Using similar analysis techniques
as in previously reported limits (HERA Collaboration 2022a), we find at 95%
confidence that $\Delta^2(k = 0.34$ $h$ Mpc$^{-1}$) $\leq 457$ mK$^2$ at $z =
7.9$ and that $\Delta^2 (k = 0.36$ $h$ Mpc$^{-1}) \leq 3,496$ mK$^2$ at $z =
10.4$, an improvement by a factor of 2.1 and 2.6 respectively. These limits are
mostly consistent with thermal noise over a wide range of $k$ after our data
quality cuts, despite performing a relatively conservative analysis designed to
minimize signal loss. Our results are validated with both statistical tests on
the data and end-to-end pipeline simulations. We also report updated
constraints on the astrophysics of reionization and the cosmic dawn. Using
multiple independent modeling and inference techniques previously employed by
HERA Collaboration (2022b), we find that the intergalactic medium must have
been heated above the adiabatic cooling limit at least as early as $z = 10.4$,
ruling out a broad set of so-called "cold reionization" scenarios. If this
heating is due to high-mass X-ray binaries during the cosmic dawn, as is
generally believed, our result's 99% credible interval excludes the local
relationship between soft X-ray luminosity and star formation and thus requires
heating driven by evolved low-metallicity stars. | Parameter constraints from weak lensing tomography of galaxy shapes and
cosmic microwave background fluctuations: Recently, it has been shown that cross-correlating CMB lensing and 3D cosmic
shear allows to considerably tighten cosmological parameter constraints. We
investigate whether similar improvement can be achieved in a conventional
tomographic setup. We present Fisher parameter forecasts for a Euclid-like
galaxy survey in combination with different ongoing and forthcoming CMB
experiments. In contrast to a fully three-dimensional analysis we find only
marginal improvement. Assuming Planck-like CMB data we show that including the
full covariance of the combined CMB and cosmic shear data improves the dark
energy figure of merit by only three per cent. The marginalized error on the
sum of neutrino masses is reduced at the same level. For a next generation CMB
satellite mission such as Prism the predicted improvement of the dark energy
figure of merit amounts to approximately 25 per cent. Furthermore, we show that
the small improvement is contrasted by an increased bias in the dark energy
parameters when the intrinsic alignment of galaxies is not correctly accounted
for in the full covariance matrix. |
Constraining the stochastic gravitational wave from string cosmology
with current and future high frequency detectors: Pre-Big-Bang models in string cosmology predict a relic background of
gravitational wave radiation in the early universe. The spectrum of this
background shows that the energy density rises rapidly with frequency, which is
an interesting target for high-frequency (i.e., kilohertz) detectors. In this
paper, we discussed the constraining power of multiple configurations of
current and future gravitational wave detector (GWD) networks to the stochastic
background predicted in string cosmology. The constraining power is jointly
determined by the overlap reduction function and the sensitivity curves of
multiple detectors. And we further elaborated on the possible contribution of a
future Chinese detector and a kilohertz detector to the constraining power of
detector network for stochastic background in string cosmology. Our results
show that the detectability of the GWD network for the string cosmology
gravitational wave background will improve considerably with the joining of a
Chinese detector. This is because a Chinese detector (e.g. located at Wuhan )
together with KAGRA, has a better overlap reduction function than the laser
interferometer gravitational wave observatory detector pair, and therefore lead
to more stringent limits for stochastic background detection. And with ideal
overlap reduction function, namely, colocated detectors, a kilohertz
sensitivity curve has better performance than previous detectors for stochastic
background detection. Finally, the results are compared with the limitations
given by the observational constraint of the Big Bang nucleosynthesis bound. | Foreground modelling via Gaussian process regression: an application to
HERA data: The key challenge in the observation of the redshifted 21-cm signal from
cosmic reionization is its separation from the much brighter foreground
emission. Such separation relies on the different spectral properties of the
two components, although, in real life, the foreground intrinsic spectrum is
often corrupted by the instrumental response, inducing systematic effects that
can further jeopardize the measurement of the 21-cm signal. In this paper, we
use Gaussian Process Regression to model both foreground emission and
instrumental systematics in $\sim 2$ hours of data from the Hydrogen Epoch of
Reionization Array. We find that a simple co-variance model with three
components matches the data well, giving a residual power spectrum with white
noise properties. These consist of an "intrinsic" and instrumentally corrupted
component with a coherence-scale of 20 MHz and 2.4 MHz respectively (dominating
the line of sight power spectrum over scales $k_{\parallel} \le 0.2$ h
cMpc$^{-1}$) and a baseline dependent periodic signal with a period of $\sim 1$
MHz (dominating over $k_{\parallel} \sim 0.4 - 0.8$h cMpc$^{-1}$) which should
be distinguishable from the 21-cm EoR signal whose typical coherence-scales is
$\sim 0.8$ MHz. |
Shear Measurement with Poorly Resolved Images: Weak lensing studies typically require excellent seeing conditions for the
purpose of maximizing the number density of well-resolved galaxy images. It is
interesting to ask to what extent the seeing size limits the usefulness of the
astronomical images in weak lensing. In this work, we study this issue with the
data of the DECam Legacy Survey (DECaLS), which is a part of the target
selection program for the Dark Energy Spectroscopic Instrument (DESI). Using
the Fourier Quad shear measurement pipeline, we demonstrate that images with
relatively poor seeing conditions (around 1.5 arcsec) can still yield accurate
shear estimators. We do not find any correlation between systematic shear error
and the image resolution. | The Swift AGN and Cluster Survey. II. Cluster Confirmation with SDSS
Data: We study 203 (of 442) Swift AGN and Cluster Survey extended X-ray sources
located in the SDSS DR8 footprint to search for galaxy over-densities in three
dimensional space using SDSS galaxy photometric redshifts and positions near
the Swift cluster candidates. We find 104 Swift clusters with a >3sigma galaxy
over-density. The remaining targets are potentially located at higher redshifts
and require deeper optical follow-up observations for confirmation as galaxy
clusters. We present a series of cluster properties including the redshift, BCG
magnitude, BCG-to-X-ray center offset, optical richness, and X-ray luminosity.
We also detect red sequences in ~85% of the 104 confirmed clusters. The X-ray
luminosity and optical richness for the SDSS confirmed Swift clusters are
correlated and follow previously established relations. The distribution of the
separations between the X-ray centroids and the most likely BCG is also
consistent with expectation. We compare the observed redshift distribution of
the sample with a theoretical model, and find that our sample is complete for z
<~ 0.3 and is still 80% complete up to z ~= 0.4, consistent with the SDSS
survey depth. These analysis results suggest that our Swift cluster selection
algorithm has yielded a statistically well-defined cluster sample for further
studying cluster evolution and cosmology. We also match our SDSS confirmed
Swift clusters to existing cluster catalogs, and find 42, 23 and 1 matches in
optical, X-ray and SZ catalogs, respectively, so the majority of these clusters
are new detections. |
Future CMB Constraints on Early, Cold, or Stressed Dark Energy: We investigate future constraints on early dark energy (EDE) achievable by
the Planck and CMBPol experiments, including cosmic microwave background (CMB)
lensing. For the dark energy, we include the possibility of clustering through
a sound speed c_s^2 <1 (cold dark energy) and anisotropic stresses
parameterized with a viscosity parameter c_vis^2. We discuss the degeneracies
between cosmological parameters and EDE parameters. In particular we show that
the presence of anisotropic stresses in EDE models can substantially undermine
the determination of the EDE sound speed parameter c_s^2. The constraints on
EDE primordial energy density are however unaffected. We also calculate the
future CMB constraints on neutrino masses and find that they are weakened by a
factor of 2 when allowing for the presence of EDE, and highly biased if it is
incorrectly ignored. | Estimating Photometric Redshift from Mock Flux for CSST Survey by using
Weighted Random Forest: Accurate estimation of photometric redshifts (photo-$z$) is crucial in
studies of both galaxy evolution and cosmology using current and future large
sky surveys. In this study, we employ Random Forest (RF), a machine learning
algorithm, to estimate photo-$z$ and investigate the systematic uncertainties
affecting the results. Using galaxy flux and color as input features, we
construct a mapping between input features and redshift by using a training set
of simulated data, generated from the Hubble Space Telescope Advanced Camera
for Surveys (HST-ACS) and COSMOS catalogue, with the expected instrumental
effects of the planned China Space Station Telescope (CSST). To improve the
accuracy and confidence of predictions, we incorporate inverse variance
weighting and perturb the catalog using input feature errors. Our results show
that weighted RF can achieve a photo-$z$ accuracy of $\rm \sigma_{NMAD}=0.025$
and an outlier fraction of $\rm \eta=2.045\%$, significantly better than the
values of $\rm \sigma_{NMAD}=0.043$ and $\rm \eta=6.45\%$ obtained by the
widely used Easy and Accurate Zphot from Yale (EAZY) software which uses
template-fitting method. Furthermore, we have calculated the importance of each
input feature for different redshift ranges and found that the most important
input features reflect the approximate position of the break features in galaxy
spectra, demonstrating the algorithm's ability to extract physical information
from data. Additionally, we have established confidence indices and error bars
for each prediction value based on the shape of the redshift probability
distribution function, suggesting that screening sources with high confidence
can further reduce the outlier fraction. |
Distinguishing cosmological models through quantum signatures of
primordial perturbations: We study the evolution of various measures of quantumness of the curvature
perturbation by integrating out the inaccessible entropic fluctuations in the
multi-field models of inflation. In particular, we discuss the following
measures of quantumness, namely purity, entanglement entropy and quantum
discord. The models being considered in this work are ones that produce large
scale curvature power spectra similar to those produced by single-field models
of inflation. More specifically, we consider different multi-field models which
generate nearly scale invariant and oscillatory curvature power spectrum and
compare their quantum signatures in the perturbations with the corresponding
single-field models. We find that, even though different models of inflation
may produce the same observable power spectrum on large scales, they have
distinct quantum signatures arising from the perturbation modes. This may allow
for a way to distinguish between different models of inflation based on their
quantum signatures. Intriguingly, this result generalizes to bouncing scenarios
as well. | An effective fluid description of scalar-vector-tensor theories under
the sub-horizon and quasi-static approximations: We consider scalar-vector-tensor (SVT) theories with second-order equations
of motion and tensor propagation speed equivalent to the speed of light. Under
the sub-horizon and the quasi-static approximations we find analytical formulae
for an effective dark energy fluid, i.e., sound speed, anisotropic stress as
well as energy density and pressure. We took advantage of our general,
analytical fluid description and showed that it is possible to design SVT
cosmological models which are degenerate with $\Lambda$CDM at the background
level while having gravity strength $G_{\rm eff}<G_{\rm N}$ at late-times as
well as non-vanishing dark energy perturbations. We implemented SVT designer
models in the widely used Boltzmann solver CLASS thus making it possible to
test SVT models against astrophysical observations. Our effective fluid
approach to SVT models reveals non trivial behaviour in the sound speed and the
anisotropic stress well worth an investigation in light of current
discrepancies in cosmological parameters such as $H_0$ and $\sigma_8$. |
The Planck clusters in the LOFAR sky VI. LoTSS-DR2: Properties of radio
relics: Context. It is well-established that shock waves in the intracluster medium
launched by galaxy cluster mergers can produce synchrotron emission, which is
visible to us at radio frequencies as radio relics. However, the particle
acceleration mechanism producing these relics is still not fully understood. It
is also unclear how relics relate to radio halos, which trace merger-induced
turbulence in the intracluster medium. Aims. We aim to perform the first
statistical analysis of radio relics in a mass-selected sample of galaxy
clusters, using homogeneous observations. Methods. We analysed all relics
observed by the Low Frequency Array Two Metre Sky Survey Data Release 2 (LoTSS
DR2) at 144 MHz, hosted by galaxy clusters in the second Planck catalogue of SZ
sources (PSZ2). We measured and compared the relic properties in a uniform,
unbiased way. In particular, we developed a method to describe the
characteristic downstream width in a statistical manner. Additionally, we
searched for differences between radio relic-hosting clusters with and without
radio halos. Results. We find that, in our sample, $\sim$ 10% of galaxy
clusters host at least one radio relic. We confirm previous findings, at higher
frequencies, of a correlation between the relic-cluster centre distance and the
longest linear size, as well as the radio relic power and cluster mass.
However, our findings suggest that we are still missing a population of
low-power relics. We also find that relics are wider than theoretically
expected, even with optimistic downstream conditions. Finally, we do not find
evidence of a single property that separates relic-hosting clusters with and
without radio halos. | Halo Scale Predictions of Symmetron Modified Gravity: We offer predictions of symmetron modified gravity in the neighborhood of
realistic dark matter halos. The predictions for the fifth force are obtained
by solving the nonlinear symmetron equation of motion in the spherical NFW
approximation. In addition, we compare the three major known screening
mechanisms: Vainshtein, Chameleon, and Symmetron around such dark matter
sources, emphasizing the significant differences between them and highlighting
observational tests which exploit these differences. Finally, we demonstrate
the host halo environmental screening effect ("blanket screening") on smaller
satellite halos by solving for the modified forces around a density profile
which is the sum of satellite and approximate host components. |
Bayesian analysis of $f(T)$ gravity using $fσ_8$ data: We use observational data from Supernovae (SNIa) Pantheon sample, from direct
Hubble constant measurements with cosmic chronometers (CC), from the Cosmic
Microwave Background shift parameter $\text{CMB}_{\text{shift}}$, and from
redshift space distortion ($f\sigma_8$) measurements, in order to constrain
$f(T)$ gravity. We do not follow the common $\gamma$ parameterization within
the semi-analytical approximation of the growth rate, in order to avoid
model-dependent uncertainties. Up to our knowledge this is the first time that
$f(T)$ gravity is analyzed within a Bayesian framework, and with background and
perturbation behaviour considered jointly. We show that all three examined
$f(T)$ models are able to describe adequately the $f\sigma_8$ data.
Furthermore, applying the Akaike, Bayesian and Deviance Information Criteria,
we conclude that all considered models are statistically equivalent, however
the most efficient candidate is the exponential model, which additionally
presents a small deviation from $\Lambda$CDM paradigm. | Modeling the Images of Relativistic Jets Lensed by Galaxies with
Different Mass Surface Density Distributions: The images of relativistic jets from extragalactic sources produced by
gravitational lensing by galaxies with different mass surface density
distributions are modeled. In particular, the following models of the
gravitational lens mass distribution are considered: a singular isothermal
ellipsoid, an isothermal ellipsoid with a core, two- and three-component models
with a galactic disk, halo, and bulge. The modeled images are compared both
between themselves and with available observations. Different sets of
parameters are shown to exist for the gravitationally lensed system B0218+357
in multicomponent models. These sets allow the observed geometry of the system
and the intensity ratio of the compact core images to be obtained, but they
lead to a significant variety in the Hubble constant determined from the
modeling results. |
Verifications of scaling relations useful for the intrinsic alignment
self-calibration: The galaxy intrinsic alignment (IA) is a major challenge of weak lensing
cosmology. To alleviate this problem, Zhang (2010, MNRAS, 406, L95) proposed a
self-calibration method, independent of IA modeling. This proposal relies on
several scaling relations between two-point clustering of IA and matter/galaxy
fields, which were previously only tested with analytical IA models. In this
paper, these relations are tested comprehensively with an $N$-body simulation
of $3072^3$ simulation particles and boxsize 600 $h^{-1} \, \mathrm{Mpc}$. They
are verified at the accuracy level of $\mathcal{O}(1)\%$ over angular scales
and source redshifts of interest. We further confirm that these scaling
relations are generic, insensitive to halo mass, weighting in defining halo
ellipticities, photo-$z$ error, and misalignment between galaxy ellipticities
and halo ellipticities. We also present and verify three new scaling relations
on the B-mode IA. These results consolidate and complete the theory side of the
proposed self-calibration technique. | Alpha Shape Topology of the Cosmic Web: We study the topology of the Megaparsec Cosmic Web on the basis of the Alpha
Shapes of the galaxy distribution. The simplicial complexes of the alpha shapes
are used to determine the set of Betti numbers ($\beta_{\rm k},k=1,...,D$),
which represent a complete characterization of the topology of a manifold. This
forms a useful extension of the geometry and topology of the galaxy
distribution by Minkowski functionals, of which three specify the geometrical
structure of surfaces and one, the Euler characteristic, represents a key
aspect of its topology. In order to develop an intuitive understanding for the
relation between Betti numbers and the running $\alpha$ parameter of the alpha
shapes, and thus in how far they may discriminate between different topologies,
we study them within the context of simple heuristic Voronoi clustering models.
These may be tuned to consist of a few or even only one specific morphological
element of the Cosmic Web, ie. clusters, filaments or sheets. |
Semianalytic calculation of cosmic microwave background anisotropies
from wiggly and superconducting cosmic strings: We study how the presence of world-sheet currents affects the evolution of
cosmic string networks, and their impact on predictions for the cosmic
microwave background (CMB) anisotropies generated by these networks. We provide
a general description of string networks with currents and explicitly
investigate in detail two physically motivated examples: wiggly and
superconducting cosmic string networks. By using a modified version of the
CMBact code, we show quantitatively how the relevant network parameters in both
of these cases influence the predicted CMB signal. Our analysis suggests that
previous studies have overestimated the amplitude of the anisotropies for
wiggly strings. For superconducting strings the amplitude of the anisotropies
depends on parameters which presently are not well known - but which can be
measured in future high-resolution numerical simulations. | Investigating the relationship between AGN activity and stellar mass in
zCOSMOS galaxies at 0<z<1 using emission line diagnostic diagrams: We investigate the link between AGN activity, star-formation and stellar mass
of the host galaxy at 0<z<1, looking for spectroscopic traces of AGN and aging
of the host. This work provides an extension of the existing studies at z<0.1
and contributes to shed light on galaxy evolution at intermediate redshifts. We
used the zCOSMOS 20k data to create a sample of galaxies at z<1. We divided the
sample in several mass-redshift bins to obtain stacked galaxy spectra with an
improved S/N. We exploited emission-line diagnostic diagrams to separate AGN
from star-forming galaxies. We found indication of a role for the total galaxy
stellar mass in leading galaxy classification. Stacked spectra show AGN
signatures above the log M_*/M_sun>10.2 threshold. Moreover, the stellar
populations of AGN hosts are found to be older with respect to star-forming and
composites galaxies. This could be due to the the tendency of AGN to reside in
massive hosts. The dependence of the AGN classification on the stellar mass is
in agreement with what has been already found in previous studies. It is
consistent with, together with the evidence of older stellar populations
inhabiting the AGN-like galaxies, the downsizing scenario. In particular, our
evidence points to an evolutionary scenario where the AGN-feedback is capable
of quenching the star formation in the most massive galaxies. Therefore, the
AGN-feedback is the best candidate for initiating the passive evolutionary
phase of galaxies. |
Cosmological test using the Hubble diagram of high-z quasars: It has been known for over three decades that the monochromatic X-ray and UV
luminosities in quasars are correlated, though non-linearly. This offers the
possibility of using high-z quasars as standard candles for cosmological
testing. In this paper, we use a recently assembled, high-quality catalog of
1598 quasars extending all the way to redshift ~6, to compare the predictions
of the R_h=ct and LCDM cosmologies. In so doing, we affirm that the parameters
characterizing the correlation depend only weakly on the chosen cosmology, and
that both models account very well for the data. Unlike LCDM, however, the
R_h=ct model has no free parameters for this work, so the Bayesian Information
Criterion favours it over LCDM with a relative likelihood of ~88 % versus ~10
%. This result is consistent with the outcome of other comparative tests, many
of which have shown that R_h=ct is favoured over the standard model based on a
diverse range of observations. | Synthetic Gravitational Waves from a Rolling Axion Monodromy: In string theory inspired models of axion-like fields, sub-leading
non-perturbative effects, if sufficiently large, can introduce steep cliffs and
gentle plateaus onto the underlying scalar potential. During inflation, the
motion of a spectator axion $\sigma$ on this potential becomes temporarily
fast, leading to localized amplification of one helicity state of gauge fields.
In this model, the tensor and scalar correlators sourced by the vector fields
exhibit localized peak(s) in momentum space corresponding to the modes that
exit the horizon while the roll of $\sigma$ is fast. Thanks to the
gravitational coupling of gauge fields with the visible sector and the
localized nature of particle production, this model can generate observable
gravitational waves (GWs) at CMB scales while satisfying the current limits on
scalar perturbations. The resulting GW signal breaks parity and exhibit
sizeable non-Gaussianity that can be probed by future CMB B-mode missions.
Depending on the initial conditions and model parameters, the roll of the
spectator axion can also generate an observably large GW signature at
interferometer scales while respecting the bounds on the scalar fluctuations
from primordial black hole limits. In our analysis, we carefully investigate
bounds on the model parameters that arise through back-reaction and
perturbativity considerations to show that these limits are satisfied by the
implementations of the model that generate GW signals at CMB and sub-CMB
scales. |
Planck 2015 results. XX. Constraints on inflation: We present the implications for cosmic inflation of the Planck measurements
of the cosmic microwave background (CMB) anisotropies in both temperature and
polarization based on the full Planck survey. The Planck full mission
temperature data and a first release of polarization data on large angular
scales measure the spectral index of curvature perturbations to be
$n_\mathrm{s} = 0.968 \pm 0.006$ and tightly constrain its scale dependence to
$d n_s/d \ln k =-0.003 \pm 0.007$ when combined with the Planck lensing
likelihood. When the high-$\ell$ polarization data is included, the results are
consistent and uncertainties are reduced. The upper bound on the
tensor-to-scalar ratio is $r_{0.002} < 0.11$ (95% CL), consistent with the
B-mode polarization constraint $r< 0.12$ (95% CL) obtained from a joint
BICEP2/Keck Array and Planck analysis. These results imply that $V(\phi)
\propto \phi^2$ and natural inflation are now disfavoured compared to models
predicting a smaller tensor-to-scalar ratio, such as $R^2$ inflation. Three
independent methods reconstructing the primordial power spectrum are
investigated. The Planck data are consistent with adiabatic primordial
perturbations. We investigate inflationary models producing an anisotropic
modulation of the primordial curvature power spectrum as well as generalized
models of inflation not governed by a scalar field with a canonical kinetic
term. The 2015 results are consistent with the 2013 analysis based on the
nominal mission data. | Gravity and the Nonlinear Growth of Structure in the
Carnegie-Spitzer-IMACS Redshift Survey: A key obstacle to developing a satisfying theory of galaxy evolution is the
difficulty in extending analytic descriptions of early structure formation into
full nonlinearity, the regime in which galaxy growth occurs. Extant techniques,
though powerful, are based on approximate numerical methods whose Monte
Carlo-like nature hinders intuition building. Here, we develop a new solution
to this problem and its empirical validation. We first derive closed-form
analytic expectations for the evolution of fixed percentiles in the real-space
cosmic density distribution, {\it averaged over representative volumes
observers can track cross-sectionally\}. Using the Lagrangian forms of the
fluid equations, we show that percentiles in $\delta$---the density relative to
the median---should grow as $\delta(t)\propto\delta_{0}^{\alpha}\,t^{\beta}$,
where $\alpha\equiv2$ and $\beta\equiv2$ for Newtonian gravity at epochs after
the overdensities transitioned to nonlinear growth. We then use 9.5 sq. deg. of
Carnegie-Spitzer-IMACS Redshift Survey data to map {\it galaxy\} environmental
densities over $0.2<z<1.5$ ($\sim$7 Gyr) and infer $\alpha=1.98\pm0.04$ and
$\beta=2.01\pm0.11$---consistent with our analytic prediction. These
findings---enabled by swapping the Eulerian domain of most work on density
growth for a Lagrangian approach to real-space volumetric averages---provide
some of the strongest evidence that a lognormal distribution of early density
fluctuations indeed decoupled from cosmic expansion to grow through
gravitational accretion. They also comprise the first exact, analytic
description of the nonlinear growth of structure extensible to (arbitrarily)
low redshift. We hope these results open the door to new modeling of, and
insight-building into, the galaxy growth and its diversity in cosmological
contexts. |
Model independent results for the inflationary epoch and the breaking of
the degeneracy of models of inflation: We address the problem of determining inflationary characteristics in a model
independent way. We start from a recently proposed equation which allows to
accurately calculate the value of the inflaton at horizon crossing $\phi_k$. We
then use an equivalent form of this equation to write a formula that relates
the number of e-folds from horizon crossing to the pivot scale $N_{ke}+N_{ep}$
with the tensor-to-scalar index $r$, hence a general bound for $N_{ke}+N_{ep}$
follows. $N_{ke}$ is the number of e-folds from the scale factor $a_k$ during
inflation to the end of inflation at $a_e$ and $N_{ep}$ is the number of
e-folds from $a_e$ to the pivot scale factor $a_p$. In particular, at present
$r < 0.063$ implies $N_{ke}+N_{ep}< 112.5$ e-folds at $k=k_p$ and 128.1 e-folds
at the present scale with wavenumber mode $k_0$. We also give a lower bound to
the size of the universe during the inflationary epoch that gave rise to the
current observable universe. We also discussed the problem of degeneracy of
inflationary models and argue that this degeneration can only be resolved by
studying model predictions from the reheating epoch. | Cosmological backreaction and the future evolution of an accelerating
universe: We investigate the effect of backreaction due to inhomogeneities on the
evolution of the present universe within the Buchert framework. Our analysis
shows how backreaction from inhomogeneities in the presence of the cosmic event
horizon causes the current acceleration of the Universe to slow down in the
future and even lead in certain cases to the emergence of a future decelerating
epoch. |
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