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Cosmology on the Largest Scales with the SKA: The study of the Universe on ultra-large scales is one of the major science
cases for the Square Kilometre Array (SKA). The SKA will be able to probe a
vast volume of the cosmos, thus representing a unique instrument, amongst
next-generation cosmological experiments, for scrutinising the Universe's
properties on the largest cosmic scales. Probing cosmic structures on extremely
large scales will have many advantages. For instance, the growth of
perturbations is well understood for those modes, since it falls fully within
the linear regime. Also, such scales are unaffected by the poorly understood
feedback of baryonic physics. On ultra-large cosmic scales, two key effects
become significant: primordial non-Gaussianity and relativistic corrections to
cosmological observables. Moreover, if late-time acceleration is driven not by
dark energy but by modifications to general relativity, then such modifications
should become apparent near and above the horizon scale. As a result, the SKA
is forecast to deliver transformational constraints on non-Gaussianity and to
probe gravity on super-horizon scales for the first time. | Relativistic Fractal Cosmologies: This article reviews an approach for constructing a simple relativistic
fractal cosmology whose main aim is to model the observed inhomogeneities of
the distribution of galaxies by means of the Lemaitre-Tolman solution of
Einstein's field equations for spherically symmetric dust in comoving
coordinates. This model is based on earlier works developed by L. Pietronero
and J.R. Wertz on Newtonian cosmology, whose main points are discussed.
Observational relations in this spacetime are presented, together with a
strategy for finding numerical solutions which approximate an averaged and
smoothed out single fractal structure in the past light cone. Such fractal
solutions are shown, with one of them being in agreement with some basic
observational constraints, including the decay of the average density with the
distance as a power law (the de Vaucouleurs' density power law) and the fractal
dimension in the range 1 <= D <= 2. The spatially homogeneous Friedmann model
is discussed as a special case of the Lemaitre-Tolman solution, and it is found
that once we apply the observational relations developed for the fractal model
we find that all Friedmann models look inhomogeneous along the backward null
cone, with a departure from the observable homogeneous region at relatively
close ranges. It is also shown that with these same observational relations the
Einstein-de Sitter model can have an interpretation where it has zero global
density, a result consistent with the "zero global density postulate" advanced
by Wertz for hierarchical cosmologies and conjectured by Pietronero for fractal
cosmological models. The article ends with a brief discussion on the possible
link between this model and nonlinear and chaotic dynamics. |
Retrieving the three-dimensional matter power spectrum and galaxy
biasing parameters from lensing tomography: With the availability of galaxy distance indicators in weak lensing surveys,
lensing tomography can be harnessed to constrain the three-dimensional (3D)
matter power spectrum over a range of redshift and physical scale. By combining
galaxy-galaxy lensing and galaxy clustering, this can be extended to probe the
3D galaxy-matter and galaxy-galaxy power spectrum or, alternatively, galaxy
biasing parameters. To achieve this aim, this paper introduces and discusses
minimum variance estimators and a more general Bayesian approach to
statistically invert a set of noisy tomography 2-point correlation functions,
measured within a confined opening angle. Both methods are constructed such
that they probe deviations of the power spectrum from a fiducial power
spectrum, thereby enabling both a direct comparison of theory and data, and in
principle the identification of the physical scale and redshift of deviations.
By devising a new Monte Carlo technique, we quantify the measurement noise in
the correlators for a fiducial survey, and test the performance of the
inversion techniques. We conclude that a shear tomography analysis of near
future weak lensing surveys promises fruitful insights into the effect of
baryons on the nonlinear matter power spectrum at z<~0.3 around k~2 h/Mpc, and
into galaxy biasing (z<~0.5). However, a proper treatment of anticipated
systematics -- not included in the mock analysis but discussed here -- is
likely to reduce the signal-to-noise in the analysis so that a robust
assessment of the 3D matter power spectrum probably asks for a survey area of
at least 1000 sdeg. [Abridged] | Comparing approximate methods for mock catalogues and covariance
matrices III: Bispectrum: We compare the measurements of the bispectrum and the estimate of its
covariance obtained from a set of different methods for the efficient
generation of approximate dark matter halo catalogs to the same quantities
obtained from full N-body simulations. To this purpose we employ a large set of
three-hundred realisations of the same cosmology for each method, run with
matching initial conditions in order to reduce the contribution of cosmic
variance to the comparison. In addition, we compare how the error on
cosmological parameters such as linear and nonlinear bias parameters depends on
the approximate method used for the determination of the bispectrum variance.
As general result, most methods provide errors within 10% of the errors
estimated from N-body simulations. Exceptions are those methods requiring
calibration of the clustering amplitude but restrict this to two-point
statistics. Finally we test how our results are affected by being limited to a
few hundreds measurements from N-body simulation, and therefore to the
bispectrum variance, by comparing with a larger set of several thousands
realisations performed with one approximate method. |
Clustering Fossil from Primordial Gravitational Waves in Anisotropic
Inflation: Inflationary models can correlate small-scale density perturbations with the
long-wavelength gravitational waves (GW) in the form of the
Tensor-Scalar-Scalar (TSS) bispectrum. This correlation affects the
mass-distribution in the Universe and leads to the off-diagonal correlations of
the density field modes in the form of the quadrupole anisotropy.
Interestingly, this effect survives even after the tensor mode decays when it
re-enters the horizon, known as the fossil effect. As a result, the
off-diagonal correlation function between different Fourier modes of the
density fluctuations can be thought as a way to probe the large-scale GW and
the mechanism of inflation behind the fossil effect. Models of single field
slow roll inflation generically predict a very small quadrupole anisotropy in
TSS while in models of multiple fields inflation this effect can be observable.
Therefore this large scale quadrupole anisotropy can be thought as a
spectroscopy for different inflationary models. In addition, in models of
anisotropic inflation there exists quadrupole anisotropy in curvature
perturbation power spectrum. Here we consider TSS in models of anisotropic
inflation and show that the shape of quadrupole anisotropy is different than in
single field models. In addition in these models the quadrupole anisotropy is
projected into the preferred direction and its amplitude is proportional to
$g_* N_e$ where $N_e$ is the number of e-folds and $g_*$ is the amplitude of
quadrupole anisotropy in curvature perturbation power spectrum. We use this
correlation function to estimate the large scale GW as well as the preferred
direction and discuss the detectability of the signal in the galaxy surveys
like Euclid and 21 cm surveys. | Pitfalls of a power-law parameterization of the primordial power
spectrum for Primordial Black Hole formation: Primordial Black Holes (PBHs) can form in the radiation dominated early
Universe from the collapse of large density perturbations produced by
inflation. A power-law parameterisation of the primordial power spectrum is
often used to extrapolate from cosmological scales, where the amplitude of the
perturbations is well-measured by Cosmic Microwave Background and Large Scale
Structure observations, down to the small scales on which PBHs may form. We
show that this typically leads to large errors in the amplitude of the
fluctuations on small scales, and hence extremely inaccurate calculations of
the abundance of PBHs formed. |
$i(cm)z$, a semi-analytic model for the thermodynamic properties in
galaxy clusters: calibrations with mass and redshift, and implication for the
hydrostatic bias: In the self-similar scenario for galaxy cluster formation and evolution, the
thermodynamic properties of the X-ray emitting plasma can be predicted in their
dependencies on the halo mass and redshift only. However, several departures
from this simple self-similar scenario have been observed. We show how our
semi-analytic model $i(cm)z$, which modifies the self-similar predictions
through two temperature-dependent quantities, the gas mass fraction $f_g=f_0
T^{f_1} E_z^{f_z}$ and the temperature variation $f_T=t_0 T^{t_1} E_z^{t_z}$,
can be calibrated to incorporate the mass and redshift dependencies. We used a
published set of 17 scaling relations to constrain the parameters of the model.
We were subsequently able to make predictions as to the slope of any observed
scaling relation within a few percent of the central value and about one
$\sigma$ of the nominal error. Contextually, the evolution of these scaling
laws was also determined, with predictions within $1.5 \sigma$ and within 10
percent of the observational constraints. Relying on this calibration, we have
also evaluated the consistency of the predictions on the radial profiles with
some observational datasets. For a sample of high-quality data (X-COP), we were
able to constrain a further parameter of the model, the hydrostatic bias $b$.
By calibrating the model, we have determined that (i) the slopes of the
temperature dependence are $f_1=0.403 (\pm0.009)$ and $t_1=0.144 (\pm0.017)$;
and that (ii) the dependence upon $E_z$ are constrained to be $f_z=-0.004 (\pm
0.023)$ and $t_z=0.349 (\pm 0.059)$. These values permit one to estimate
directly how the normalizations of a given quantity $Q_{\Delta}$ changes as a
function of the mass (or temperature) and redshift halo in the form $Q_{\Delta}
\sim M^{a_M} E_z^{a_z} \sim T^{a_T} E_z^{a_{Tz}}$, in very good agreement with
the current observational constraints. | Early formation of supermassive black holes via dark matter
self-interactions: The existence of supermassive black holes at high redshifts ($z\sim7$) is
difficult to accommodate in standard astrophysical scenarios. It has been shown
that dark matter models with a subdominant self-interacting component are able
to produce early seeds for supermassive black holes through the gravothermal
catastrophe. Previous studies used a fluid equation approach, requiring some
limiting assumptions. Here we reconsider the problem using $N$-body
gravitational simulations starting from the formation of the initial dark
matter halo. We consider both elastic and dissipative scattering, and elucidate
the interplay between the dark matter microphysics and subsequent accretion of
the black hole needed to match the properties of observed high redshift
supermassive black holes. We find a region of parameter space in which a small
component of self-interacting dark matter can produce the observed high
redshift supermassive black holes. |
The Weak Lensing Signal and the Clustering of BOSS Galaxies I:
Measurements: A joint analysis of the clustering of galaxies and their weak gravitational
lensing signal is well-suited to simultaneously constrain the galaxy-halo
connection as well as the cosmological parameters by breaking the degeneracy
between galaxy bias and the amplitude of clustering signal. In a series of two
papers, we perform such an analysis at the highest redshift ($z\sim0.53$) in
the literature using CMASS galaxies in the Sloan Digital Sky Survey-III Baryon
Oscillation Spectroscopic Survey Eleventh Data Release (SDSS-III/BOSS DR11)
catalog spanning 8300~deg$^2$. In this paper, we present details of the
clustering and weak lensing measurements of these galaxies. We define a
subsample of 400,916 CMASS galaxies based on their redshifts and stellar mass
estimates so that the galaxies constitute an approximately volume-limited and
similar population over the redshift range $0.47\le z\le 0.59$. We obtain a
signal-to-noise ratio $S/N\simeq 56$ for the galaxy clustering measurement. We
also explore the redshift and stellar mass dependence of the clustering signal.
For the weak lensing measurement, we use existing deeper imaging data from the
CFHTLS with publicly available shape and photometric redshift catalogs from
CFHTLenS, but only in a 105~deg$^2$ area which overlaps with BOSS. This
restricts the lensing measurement to only 5,084 CMASS galaxies. After careful
systematic tests, we find a highly significant detection of the CMASS weak
lensing signal, with total $S/N\simeq 26$. These measurements form the basis of
the halo occupation distribution and cosmology analysis presented in More et
al. (Paper II). | Metallicities, Age--Metallicity relationships, and Kinematics of Red
Giant Branch Stars in the Outer Disk of the Large Magellanic Cloud: The outer disk of the LMC is studied in order to unveil clues about its
formation and evolution. Complementing our previous studies in innermost fields
(3<R<7 kpc), we obtained deep color magnitude diagrams in 6 fields with radius
from 5.2 to 9.2 kpc. The comparison with isochrones shows that while the oldest
population is approximately coeval in all fields, the age of the youngest
populations increases with increasing radius. Low-resolution spectroscopy in
the infrared CaII triplet region has been obtained for about 150 stars near the
tip red giant branch in the same fields. Radial velocities and stellar
metallicities have been obtained from these spectra. The metallicity
distribution of each field has been analyzed together with those previously
studied. The metal content of the most metal-poor objects, which are also the
oldest according to the derived age-metallicity relationships, is similar in
all fields independently of the radius. However, while the metallicity of the
most metal-rich objects measured, which are the youngest ones, remains constant
in the inner 6 kpc, it decreases with increasing radius from there off. The
same is true for the mean metallicity. According to the derived age-metallicity
relationships, which are consistent with being the same in all fields, this
result may be interpreted as an outside-in formation scheme in opposition with
the inside-out scenario predicted by LCDM cosmology for a galaxy like the LMC.
The analysis of the radial velocities of our sample of giants shows that they
follow a rotational cold disk kinematics. The velocity dispersion increases as
metallicity decreases indicating that the most metal-poor/oldest objects are
distributed in a thicker disk than the most metal-rich/youngest ones in
agreement with the findings in other disks such as that of the Milky Way. They
do not seem to be part of a hot halo, if one exists in the LMC. |
The Herschel Lensing Survey (HLS): overview: The Herschel Lensing Survey (HLS) will conduct deep PACS and SPIRE imaging of
~40 massive clusters of galaxies. The strong gravitational lensing power of
these clusters will enable us to penetrate through the confusion noise, which
sets the ultimate limit on our ability to probe the Universe with Herschel.
Here, we present an overview of our survey and a summary of the major results
from our Science Demonstration Phase (SDP) observations of the Bullet Cluster
(z=0.297). The SDP data are rich, allowing us to study not only the background
high-redshift galaxies (e.g., strongly lensed and distorted galaxies at z=2.8
and 3.2) but also the properties of cluster-member galaxies. Our preliminary
analysis shows a great diversity of far-infrared/submillimeter spectral energy
distributions (SEDs), indicating that we have much to learn with Herschel about
the properties of galaxy SEDs. We have also detected the Sunyaev-Zel'dovich
(SZ) effect increment with the SPIRE data. The success of this SDP program
demonstrates the great potential of the Herschel Lensing Survey to produce
exciting results in a variety of science areas. | The End of the Black Hole Dark Ages, and Warm Absorbers: We consider how the radiation pressure of an accreting supermassive hole
(SMBH) affects the interstellar medium around it. Much of the gas originally
surrounding the hole is swept into a shell with a characteristic radius
somewhat larger than the black hole's radius of influence ($\sim$ 1-100 pc).
The shell has a mass directly comparable to the ($M - \sigma$) mass the hole
will eventually reach, and may have a complex topology. We suggest that
outflows from the central supermassive black holes are halted by collisions
with the shell, and that this is the origin of the warm absorber components
frequently seen in AGN spectra. The shell may absorb and reradiate some of the
black hole accretion luminosity at long wavelengths, implying both that the
bolometric luminosities of some known AGN may have been underestimated, and
that some accreting SMBH may have escaped detection entirely. |
Parameterised free functions and saddle stresses in modified gravity: Building on previous work, we explore the parameter space of free functions
in non-relativistic modified gravity theories more widely, showing that in fact
the two broad regimes present have similar functional forms between different
models. Using different parameterisations, we investigate the effects on
scaling tidal stresses as well as attempt to constrain the (hitherto poorly
understood) deep MONDian scaling C. We also consider a new intermediate MOND
limit in these theories and what it tells us about the transition between these
regimes. Finally we suggest a model independent framework, with the aim of
constraining the MONDian parameter space using future data, such as the
forthcoming LISA Pathfinder mission. | Evidence of nuclear disks in starburst galaxies from their radial
distribution of supernovae: Galaxy-galaxy interactions are expected to be responsible for triggering
massive star formation and possibly accretion onto a supermassive black hole,
by providing large amounts of dense molecular gas down to the central
kiloparsec region. Several scenarios to drive the gas further down to the
central ~100 pc, have been proposed, including the formation of a nuclear disk
around the black hole, where massive stars would produce supernovae. Here, we
probe the radial distribution of supernovae and supernova remnants in the
nuclear regions of the starburst galaxies M82, Arp 299-A, and Arp 220, by using
high-angular resolution (< 0."1) radio observations published in the literature
(for M82 and Arp 220), or obtained by ourselves from the European VLBI Network
(Arp 299-A). Our main goal was to characterize the nuclear starbursts in those
galaxies and thus test scenarios that propose that nuclear disks of sizes ~100
pc form in the central regions of starburst galaxies. We obtained the radial
distribution of supernovae (SNe) in the nuclear starbursts of M82, Arp 299-A,
and Arp 220, and derived scale-length values for the putative nuclear disks
powering the bursts in those central regions. The scale lengths for the
(exponential) disks range from ~20-30 pc for Arp 299-A and Arp 220, up to ~140
pc for M82. The radial distribution of SNe for the nuclear disks in Arp 299-A
and Arp 220 is also consistent with a power-law surface density profile of
exponent gamma=1, as expected from detailed hydrodynamical simulations of
nuclear disks. Our results support scenarios where a nuclear disk of size ~100
pc is formed in (U)LIRGs, and sustained by gas pressure, in which case the
accretion onto the black hole could be lowered by supernova feedback. |
Gravitational wave constraints on extended dark matter structures: We generalise existing constraints on primordial black holes to dark objects
with extended sizes using the aLIGO design sensitivity. We show that LIGO is
sensitive to dark objects with radius $O(10-10^3~{\rm km})$ if they make up
more than $\sim O(10^{-2}-10^{-3})$ of dark matter. | N-body simulations with generic non-Gaussian initial conditions I: Power
Spectrum and halo mass function: We address the issue of setting up generic non-Gaussian initial conditions
for N-body simulations. We consider inflationary-motivated primordial
non-Gaussianity where the perturbations in the Bardeen potential are given by a
dominant Gaussian part plus a non-Gaussian part specified by its bispectrum.
The approach we explore here is suitable for any bispectrum, i.e. it does not
have to be of the so-called separable or factorizable form. The procedure of
generating a non-Gaussian field with a given bispectrum (and a given power
spectrum for the Gaussian component) is not univocal, and care must be taken so
that higher-order corrections do not leave a too large signature on the power
spectrum. This is so far a limiting factor of our approach. We then run N-body
simulations for the most popular inflationary-motivated non-Gaussian shapes.
The halo mass function and the non-linear power spectrum agree with theoretical
analytical approximations proposed in the literature, even if they were so far
developed and tested only for a particular shape (the local one). We plan to
make the simulations outputs available to the community via the non-Gaussian
simulations comparison project web site
http://icc.ub.edu/~liciaverde/NGSCP.html. |
A blind HI survey in the Ursa Major region: We have conducted the first blind HI survey covering 480 deg^2 and a
heliocentric velocity range from 300-1900 km/s to investigate the HI content of
the nearby spiral-rich Ursa Major region and to look for previously
uncatalogued gas-rich objects. Here we present the catalog of HI sources. The
HI data were obtained with the 4-beam receiver mounted on the 76.2-m Lovell
telescope (FWHM 12 arcmin) at the Jodrell Bank Observatory (UK) as part of the
HI Jodrell All Sky Survey (HIJASS). We use the automated source finder DUCHAMP
and identify 166 HI sources in the data cubes with HI masses in the range of
10^7 - 10^{10.5} M_sun. Our Ursa Major HI catalogue includes 10 first time
detections in the 21-cm emission line.
We identify optical counterparts for 165 HI sources (99 per cent). For 54 HI
sources (33 per cent) we find numerous optical counterparts in the HIJASS beam,
indicating a high density of galaxies and likely tidal interactions. Four of
these HI systems are discussed in detail.
We find only one HI source (1 per cent) without a visible optical counterpart
out of the 166 HI detections. Green Bank Telescope (FWHM 9 arcmin) follow-up
observations confirmed this HI source and its HI properties. The nature of this
detection is discussed and compared to similar sources in other HI surveys. | Calculating Non-adiabatic Pressure Perturbations during Multi-field
Inflation: Isocurvature perturbations naturally occur in models of inflation consisting
of more than one scalar field. In this paper we calculate the spectrum of
isocurvature perturbations generated at the end of inflation for three
different inflationary models consisting of two canonical scalar fields. The
amount of non-adiabatic pressure present at the end of inflation can have
observational consequences through the generation of vorticity and subsequently
the sourcing of B-mode polarisation. We compare two different definitions of
isocurvature perturbations and show how these quantities evolve in different
ways during inflation. Our results are calculated using the open source
Pyflation numerical package which is available to download. |
Anti-dark matter: a hidden face of mirror world: B and L violating interactions of ordinary particles with their twin
particles from hypothetical mirror world can co-generate baryon asymmetries in
both worlds in comparable amounts, $\Omega'_B/\Omega_B \sim 5$ or so. On the
other hand, the same interactions induce the oscillation phenomena between the
neutral particles of two sectors which convert e.g. mirror neutrons into our
antineutrons. These oscillations are environment dependent and can have
fascinating physical consequences. | SPIDERS: An Overview of The Largest Catalogue of Spectroscopically
Confirmed X-ray Galaxy Clusters: SPIDERS is the spectroscopic follow-up effort of the Sloan Digital Sky Survey
IV (SDSS-IV) project for the identification of X-ray selected galaxy clusters.
We present our catalogue of 2740 visually inspected galaxy clusters as a part
of the SDSS Data Release 16 (DR16). Here we detail the target selection, our
methods for validation of the candidate clusters, performance of the survey,
the construction of the final sample, and a full description of what is found
in the catalogue. Of the sample, the median number of members per cluster is
approximately 10, with 818 having 15 or greater. We find that we are capable of
validating over 99% of clusters when 5 redshifts are obtained below $z<0.3$ and
when 9 redshifts are obtained above $z>0.3$. We discuss the improvements of
this catalogue's identification of cluster using 33,340 redshifts, with $\Delta
z_{\rm{phot}} / \Delta z_{\rm{spec}} \sim 100$, over other photometric and
spectroscopic surveys, as well as present an update to previous ($\sigma -
L_{X}$) and ($\sigma - \lambda$) relations. Finally, we present our
cosmological constraints derived using the velocity dispersion function. |
The radiation energy component of the Hubble function and a LCDM
cosmological simulation: We study some effects the inclusion of the radiation energy component in the
universe, Omega_r, can have on several quantities of interest for the
large-scale structure of the universe in a LCDM cosmological simulation;
started at a very high redshift (z=500). In particular we compute the power
spectrum density, the halo mass function, and the concentration-mass relation
for haloes. We find that Omega_r has an important contribution in the long-term
nonlinear evolution of structures in the universe. For instance, a lower matter
density power, by approx 50%, in all scales is obtained when compared with a
simulation without the radiation term. Also, haloes formed with the Omega_r
taken into account are approx 20% less concentrated than when not included in
the Hubble function. | Breaking of the equivalence principle in the electromagnetic sector and
its cosmological signatures: This paper proposes a systematic study of cosmological signatures of
modifications of gravity via the presence of a scalar field with a
multiplicative coupling to the electromagnetic Lagrangian. We show that, in
this framework, variations of the fine structure constant, violations of the
distance duality relation, evolution of the cosmic microwave background (CMB)
temperature and CMB distortions are intimately and unequivocally linked. This
enables one to put very stringent constraints on possible violations of the
distance duality relation, on the evolution of the CMB temperature and on
admissible CMB distortions using current constraints on the fine structure
constant. Alternatively, this offers interesting possibilities to test a wide
range of theories of gravity by analysing several datasets concurrently. We
discuss results obtained using current data as well as some forecasts for
future data sets such as those coming from EUCLID or the SKA. |
Searching for radio relics and halos. Their role in the formation and
acceleration of extragalactic cosmic rays: We search for extended regions of radio emission not associated with Active
Galactic Nuclei, known as 'relics', 'halos' and 'mini halo's, in a sample of 70
Abell clusters for which we have radio, optical and X-ray data. AGN can produce
particle bubbles of non-thermal emission, which can restrict cosmic rays. Hence
radio relics and (mini) halos could be forming as a result of the confinement
of cosmic rays by these bubbles. We are probing the role that intracluster mag-
netic fields (using Faraday rotation measure and inverse compton arguments),
mergers (through radio/X-ray interactions), cooling flows (X-ray data), radio
jets/shocks as well as radio (mini) halos/relics play in the formation,
acceleration and propagation of cosmic rays. For the current study we have
selected two powerful nearby radio galaxies from our sample: Hercules A and 3C
388. We report on the work in progress and future plans. | Consistency analysis of a Dark Matter velocity dependent force as an
alternative to the Cosmological Constant: A range of cosmological observations demonstrate an accelerated expansion of
the Universe, and the most likely explanation of this phenomenon is a
cosmological constant. Given the importance of understanding the underlying
physics, it is relevant to investigate alternative models. This article uses
numerical simulations to test the consistency of one such alternative model.
Specifically, this model has no cosmological constant, instead the dark matter
particles have an extra force proportional to velocity squared, somewhat
reminiscent of the magnetic force in electrodynamics. The constant strength of
the force is the only free parameter. Since bottom-up structure formation
creates cosmological structures whose internal velocity dispersions increase in
time, this model may mimic the temporal evolution of the effect from a
cosmological constant. It is shown that models with force linearly proportional
to internal velocites, or models proportional to velocity to power three or
more cannot mimic the accelerated expansion induced by a cosmological constant.
However, models proportional to velocity squared are still consistent with the
temporal evolution of a Universe with a cosmological model. |
Cosmic Magnetic Fields: Observations and Prospects: Synchrotron emission, its polarization and its Faraday rotation at radio
frequencies of 0.2-10 GHz are powerful tools to study the strength and
structure of cosmic magnetic fields. The observational results are reviewed for
spiral, barred and flocculent galaxies, the Milky Way, halos and relics of
galaxy clusters, and for the intergalactic medium. Polarization observations
with the forthcoming large radio telescopes will open a new era in the
observation of cosmic magnetic fields and will help to understand their origin.
At low frequencies, LOFAR (10-250 MHz) will allow us to map the structure of
weak magnetic fields in the outer regions and halos of galaxies and galaxy
clusters. Polarization at higher frequencies (1-10 GHz), as observed with the
EVLA, ASKAP, MeerKAT, APERTIF and the SKA, will trace magnetic fields in the
disks and central regions of nearby galaxies in unprecedented detail. Surveys
of Faraday rotation measures of pulsars will map the Milky Way's magnetic field
with high precision. All-sky surveys of Faraday rotation measures towards a
dense grid of polarized background sources with the SKA and its precursor
telescope ASKAP are dedicated to measure magnetic fields in distant intervening
galaxies, galaxy clusters and intergalactic filaments, and will be used to
model the overall structure and strength of the magnetic field in the Milky
Way. | Thought Experiments on Gravitational Forces: Large contributions to the near closure of the Universe and to the
acceleration of its expansion are due to the gravitation of components of the
stress-energy tensor other than its mass density. To familiarise astronomers
with the gravitation of these components we conduct thought experiments on
gravity, analogous to the real experiments that our forebears conducted on
electricity. By analogy to the forces due to electric currents we investigate
the gravitational forces due to the flows of momentum, angular momentum, and
energy along a cylinder. Under tension the gravity of the cylinder decreases
but the 'closure' of the 3-space around it increases. When the cylinder carries
a torque the flow of angular momentum along it leads to a novel helical
interpretation of Levi-Civita's external metric and a novel relativistic
effect. Energy currents give gravomagnetic effects in which parallel currents
repel and antiparallel currents attract, though such effects must be added to
those of static gravity. The gravity of beams of light give striking
illustrations of these effects and a re-derivation of light bending via the
gravity of the light itself. Faraday's experiments lead us to discuss lines of
force of both gravomagnetic and gravity fields. A serious conundrum arrises if
Landau and Lifshitz's definition of Gravitational force is adopted. |
Chandra X-ray and Hubble Space Telescope Imaging of Optically Selected
kiloparsec-Scale Binary Active Galactic Nuclei I. Nature of the Nuclear
Ionizing Sources: Kiloparsec-scale binary active galactic nuclei (AGNs) signal active
supermassive black hole (SMBH) pairs in merging galaxies. Despite their
significance, unambiguously confirmed cases remain scarce and most have been
discovered serendipitously. In a previous systematic search, we optically
identified four kpc-scale binary AGNs from candidates selected with
double-peaked narrow emission lines at redshifts of 0.1--0.2. Here we present
Chandra and Hubble Space Telescope Wide Field Camera 3 (WFC3) imaging of these
four systems. We critically examine and confirm the binary-AGN scenario for two
of the four targets, by combining high angular resolution X-ray imaging
spectroscopy with Chandra ACIS-S, better nuclear position constraints from WFC3
F105W imaging, and direct starburst estimates from WFC3 F336W imaging; for the
other two targets, the existing data are still consistent with the binary-AGN
scenario, but we cannot rule out the possibility of only one AGN ionizing gas
in both merging galaxies. We find tentative evidence for a systematically
smaller X-ray-to-[O III] luminosity ratio and/or higher Compton-thick fraction
in optically selected kpc-scale binary AGNs than in single AGNs, possibly
caused by a higher nuclear gas column due to mergers and/or a viewing angle
bias related to the double-peak narrow line selection. While our result lends
some further support to the general approach of optically identifying kpc-scale
binary AGNs, it also highlights the challenge and ambiguity of X-ray
confirmation. | A Critical Assessment of CMB Limits on Dark Matter-Baryon Scattering:
New Treatment of the Relative Bulk Velocity: We perform an improved cosmic microwave background (CMB) analysis to search
for dark matter-proton scattering with a momentum-transfer cross section of the
form $\sigma_0 v^n$ for $n=-2$ and $n=-4$. In particular, we present a new and
robust prescription for incorporating the relative bulk velocity between the
dark matter and baryon fluids into the standard linear Boltzmann calculation.
Using an iterative procedure, we self-consistently include the effects of the
bulk velocities in a cosmology in which dark matter interacts with baryons.
With this prescription, we derive CMB bounds on the cross section, excluding
$\sigma_0 > 2.3 \times 10^{-33}~\mathrm{cm}^2$ for $n=-2$ and $\sigma_0 > 1.7
\times 10^{-41}~\mathrm{cm}^2$ for $n=-4$ at $95\%$ confidence, for dark matter
masses below 10 MeV. Furthermore, we investigate how these constraints change
when only a subcomponent of dark matter is interacting. We show that Planck
limits vanish if $\lesssim 0.4\%$ of dark matter is tightly coupled to baryons.
We discuss the implications of our results for present and future cosmological
observations. |
Astrophysical bow shocks: An analytical solution for the hypersonic
blunt body problem in the intergalactic medium: Aims: Bow shock waves are a common feature of groups and clusters of galaxies
since they are generated as a result of supersonic motion of galaxies through
the intergalactic medium. The goal of this work is to present an analytical
solution technique for such astrophysical hypersonic blunt body problems.
Methods: A method, developed by Schneider (1968, JFM, 31, 397) in the context
of aeronautics, allows calculation of the galaxy's shape as long as the shape
of the bow shock wave is known (so-called inverse method). In contrast to other
analytical models, the solution is valid in the whole flow region (from the
stagnation point up to the bow shock wings) and in particular takes into
account velocity gradients along the streamlines. We compare our analytical
results with two-dimensional hydrodynamical simulations carried out with an
extended version of the VH-1 hydrocode which is based on the piecewise
parabolic method with a Lagrangian remap. Results: It is shown that the applied
method accurately predicts the galaxy's shape and the fluid variables in the
post-shock flow, thus saving a tremendous amount of computing time for future
interpretations of similar objects. We also find that the method can be applied
to arbitrary angles between the direction of the incoming flow and the axis of
symmetry of the body. We emphasize that it is general enough to be applied to
other astrophysical bow shocks, such as those on stellar and galactic scales. | A Two-Year Time Delay for the Lensed Quasar SDSS J1029+2623: We present 279 epochs of optical monitoring data spanning 5.4 years from 2007
January to 2012 June for the largest image separation (22.6 arcsec)
gravitationally lensed quasar, SDSS J1029+2623. We find that image A leads the
images B and C by dt_AB = (744+-10) days (90% confidence); the uncertainty
includes both statistical uncertainties and systematic differences due to the
choice of models. With only a ~1% fractional error, the interpretation of the
delay is limited primarily by cosmic variance due to fluctuations in the mean
line-of-sight density. We cannot separate the fainter image C from image B, but
since image C trails image B by only 2-3 days in all models, the estimate of
the time delay between image A and B is little affected by combining the fluxes
of images B and C. There is weak evidence for a low level of microlensing,
perhaps created by the small galaxy responsible for the flux ratio anomaly in
this system. Interpreting the delay depends on better constraining the shape of
the gravitational potential using the lensed host galaxy, other lensed arcs and
the structure of the X-ray emission. |
Relation between halo spin and cosmic web filaments at z=3: We investigate the spin evolution of dark matter haloes and their dependence
on the number of connected filaments from the cosmic web at high redshift
(spin-filament relation hereafter). To this purpose, we have simulated $5000$
haloes in the mass range $5\times10^{9}h^{-1}M_{\odot}$ to
$5\times10^{11}h^{-1}M_{\odot}$ at $z=3$ in cosmological N-body simulations. We
confirm the relation found by Prieto et al. 2015 where haloes with fewer
filaments have larger spin. We also found that this relation is more
significant for higher halo masses, and for haloes with a passive (no major
mergers) assembly history. Another finding is that haloes with larger spin or
with fewer filaments have their filaments more perpendicularly aligned with the
spin vector. Our results point to a picture in which the initial spin of haloes
is well described by tidal torque theory and then gets subsequently modified in
a predictable way because of the topology of the cosmic web, which in turn is
given by the currently favoured LCDM model. Our spin-filament relation is a
prediction from LCDM that could be tested with observations. | Constraining neutrino properties with a Euclid-like galaxy cluster
survey: We perform a forecast analysis on how well a Euclid-like photometric galaxy
cluster survey will constrain the total neutrino mass and effective number of
neutrino species. We base our analysis on the Monte Carlo Markov Chains
technique by combining information from cluster number counts and cluster power
spectrum. We find that combining cluster data with CMB measurements from Planck
improves by more than an order of magnitude the constraint on neutrino masses
compared to each probe used independently. For the LCDM+m_nu model the 2 sigma
upper limit on total neutrino mass shifts from M_nu < 0.35 eV using cluster
data alone to M_nu < 0.031 eV when combined with CMB data. When a non-standard
model with N_eff number of neutrino species is considered, we estimate
N_eff<3.14 (95% CL), while the bounds on neutrino mass are relaxed to M_nu <
0.040 eV. This accuracy would be sufficient for a 2 sigma detection of neutrino
mass even in the minimal normal hierarchy scenario. We also consider scenarios
with a constant dark energy equation of state and a non-vanishing curvature.
When these models are considered the error on M_nu is only slightly affected,
while there is a larger impact of the order of ~ 15 % and ~ 20% respectively on
the 2 sigma error bar of N_eff with respect to the standard case. We also treat
the LCDM+m_nu+N_eff case with free nuisance parameters, which parameterize the
uncertainties on the cluster mass determination. In this case, the upper bounds
on M_nu are relaxed by a factor larger than two, M_nu < 0.083 eV (95% CL),
hence compromising the possibility of detecting the total neutrino mass with
good significance. We thus confirm the potential that a large optical/near-IR
cluster survey, like that to be carried out by Euclid, could have in
constraining neutrino properties [abridged]. |
Mapping the large-angle deviation from Gaussianity in simulated CMB maps: [Abridged] In recent works we have proposed two new large-angle
non-Gaussianity indicators based on skewness and kurtosis of patches of CMB
sky-sphere, and used them to find out significant deviation from Gaussianity in
frequency bands and foreground-reduced CMB maps. Simulated CMB maps with
assigned type and amplitude of primordial non-Gaussianity are important tools
to determine the strength, sensitivity and limitations of non-Gaussian
estimators. Here we investigate whether and to what extent our non-Gaussian
indicators have sensitivity to detect non-Gaussianity of local type,
particularly with amplitude within the seven-year WMAP bounds. We make a
systematic study by employing our statistical tools to generate maps of
skewness and kurtosis from several thousands of simulated maps equipped with
non-Gaussianity of local type of various amplitudes. We show that our
indicators can be used to detect large-angle local-type non-Gaussianity only
for relatively large values of the non-linear parameter $f_{\rm NL}^{\rm
local}$. Thus, our indicators have not enough sensitivity to detect deviation
from Gaussianity with the non-linear parameter within the seven-year WMAP
bounds. This result along with the outcomes of frequency bands and
foreground-reduced analyses suggest that non-Gaussianity captured in the
previous works by our indicators is not of primordial origin, although it might
have a primordial component. We have also made a comparative study of
non-Gaussianity of simulated maps and of the full-sky WMAP foreground-reduced
seven-year ILC-7yr map. An outcome of this analysis is that the level of
non-Gaussianity of ILC-7yr map is higher than that of the simulated maps for
$f_{\rm NL}^{\rm local}$ within WMAP bounds. This provides quantitative
indications on the suitability of the ILC-7yr map as a Gaussian reconstruction
of the full-sky CMB. | Non-linear weak lensing forecasts: We investigate the impact of non-linear corrections on dark energy parameter
estimation from weak lensing probes. We find that using halofit expressions,
suited to LCDM models, implies substantial discrepancies with respect to
results directly obtained from N-body simulations, when w(z)\neq-1.
Discrepancies appear strong when using models with w'(z=0)>0, as fiducial
models; they are however significant even in the neighborhood of LCDM, where
neglecting the degrees of freedom associated with the DE state equation can
lead to a misestimate of the matter density parameter \Omega_m. |
Growth of Cosmic Structure: Probing Dark Energy Beyond Expansion: The quantity and quality of cosmic structure observations have greatly
accelerated in recent years. Further leaps forward will be facilitated by
imminent projects, which will enable us to map the evolution of dark and
baryonic matter density fluctuations over cosmic history. The way that these
fluctuations vary over space and time is sensitive to the nature of dark matter
and dark energy. Dark energy and gravity both affect how rapidly structure
grows; the greater the acceleration, the more suppressed the growth of
structure, while the greater the gravity, the more enhanced the growth. While
distance measurements also constrain dark energy, the comparison of growth and
distance data tests whether General Relativity describes the laws of physics
accurately on large scales. Modified gravity models are able to reproduce the
distance measurements but at the cost of altering the growth of structure
(these signatures are described in more detail in the accompanying paper on
Novel Probes of Gravity and Dark Energy). Upcoming surveys will exploit these
differences to determine whether the acceleration of the Universe is due to
dark energy or to modified gravity. To realize this potential, both wide field
imaging and spectroscopic redshift surveys play crucial roles. Projects
including DES, eBOSS, DESI, PFS, LSST, Euclid, and WFIRST are in line to map
more than a 1000 cubic-billion-light-year volume of the Universe. These will
map the cosmic structure growth rate to 1% in the redshift range 0<z<2, over
the last 3/4 of the age of the Universe. | Cosmological Simulations of Decaying Dark Matter: Implications for
Small-scale Structure of Dark Matter Halos: We present a set of N-body simulations of a class of models in which an
unstable dark matter particle decays into a stable non-interacting dark matter
particle, with decay lifetime comparable to the Hubble time. We study the
effects of the kinematic recoil velocity received by the stable dark matter on
the structures of dark matter halos ranging from galaxy-cluster to Milky Way
mass scales. For Milky Way-mass halos, we use high-resolution, zoom-in
simulations to explore the effects of decays on Galactic substructure. In
general, halos with circular velocities comparable to the magnitude of kick
velocity are most strongly affected by decays. We show that decaying dark
matter models with lifetimes comparable to Hubble time and recoil speeds about
20-40 km/s can significantly reduce both the abundance of Galactic subhalos and
the internal densities of the subhalos. We also compare subhalo circular
velocity profiles with observational constraints on the Milky Way dwarf
satellite galaxies. Interestingly, we find that decaying dark matter models
that do not violate current astrophysical constraints, can significantly
mitigate both the well-documented "missing satellites problem" and the more
recent "too big to fail problem" associated with the abundances and densities
of Local Group dwarf satellite galaxies. A relatively unique feature of late
decaying dark matter models is that they predict significant evolution of halos
as a function of time. This is an important consideration because at high
redshifts, prior to decays, decaying models exhibit the same sequence of
structure formation as cold dark matter. We conclude that models of decaying
dark matter make predictions that are relevant for the interpretation of
observations of small galaxies in the Local Group and can be tested or
constrained by the kinematics of Local Group dwarf galaxies as well as by
forthcoming large-scale surveys. |
Scale-dependent bias with higher order primordial non-Gaussianity: Use
of the Integrated Perturbation Theory: We analytically derive a more accurate formula for the power spectrum of the
biased objects with the primordial non-Gaussianity parameterized not only by
the non-linearity parameter fNL, but also by gNL and tauNL which characterize
the trispectrum of the primordial curvature perturbations. We adopt the
integrated perturbation theory which was constructed in Matsubara (2011). We
discuss an inequality between fNL and tauNL in the context of the
scale-dependent bias, by introducing a stochasticity parameter. We also mention
higher order loop corrections into the scale-dependency of the bias parameter. | Does the Corona Borealis Supercluster form a giant binary-like system?: The distribution of local gravitational potentials generated by a complete
volume-limited sample of galaxy groups and clusters filling the Corona Borealis
region has been derived to search for new gravitational hints in the context of
clus-tering analysis unrevealed by alternative methodologies. Mapping such a
distribution as a function of spatial positions, the deepest potential wells in
the sample trace unambiguously the locations of the densest galaxy cluster
clumps providing the physical keys to bring out gravitational features
connected to the formation, composition and evolution of the major clustered
structures filling that region. As expected, the three deepest potential wells
found at Equatorial coordinates: (~ 230{\deg}, ~ 28{\deg}, z ~ 0.075), (~
240{\deg}, ~ 27{\deg}, z ~ 0.09) and, (227{\deg}, 5.8{\deg}, z ~ 0.0788)
correspond to massive superclusters of galaxy groups and clusters identified as
the Corona Borealis, A2142 and Virgo-Serpent, respectively. However, the
deepest isopotential contours around the Corona Borealis and A2142
superclusters seem to suggest a gravitational feature similar to a giant
binary-like system connected by a filamentary structure. To a first
approximation, it seems unlikely that this hypothesized system could be
gravitationally bound. |
Thermodynamic Profiles of Galaxy Clusters from a Joint X-ray/SZ Analysis: We jointly analyze Bolocam Sunyaev-Zeldovich (SZ) effect and Chandra X-ray
data for a set of 45 clusters to derive gas density and temperature profiles
without using spectroscopic information. The sample spans the mass and redshift
range $3 \times 10^{14} M_{\odot} \le M_{500} \le 25 \times 10^{14} M_{\odot}$
and $0.15\le z \le 0.89$. We define cool-core (CC) and non-cool core (NCC)
subsamples based on the central X-ray luminosity, and 17/45 clusters are
classified as CC. In general, the profiles derived from our analysis are found
to be in good agreement with previous analyses, and profile constraints beyond
$r_{500}$ are obtained for 34/45 clusters. In approximately 30% of the CC
clusters our analysis shows a central temperature drop with a statistical
significance of $>3\sigma$; this modest detection fraction is due mainly to a
combination of coarse angular resolution and modest S/N in the SZ data. Most
clusters are consistent with an isothermal profile at the largest radii near
$r_{500}$, although 9/45 show a significant temperature decrease with
increasing radius. The sample mean density profile is in good agreement with
previous studies, and shows a minimum intrinsic scatter of approximately 10%
near $0.5 \times r_{500}$. The sample mean temperature profile is consistent
with isothermal, and has an intrinsic scatter of approximately 50% independent
of radius. This scatter is significantly higher compared to earlier X-ray-only
studies, which find intrinsic scatters near 10%, likely due to a combination of
unaccounted for non-idealities in the SZ noise, projection effects, and sample
selection. | Foreground influence on primordial non-Gaussianity estimates: needlet
analysis of WMAP 5-year data: We constrain the amplitude of primordial non-Gaussianity in the CMB data
taking into account the presence of foreground residuals in the maps. We
generalise the needlet bispectrum estimator marginalizing over the amplitudes
of thermal dust, free-free and synchrotron templates. We apply our procedure to
WMAP 5 year data, finding fNL= 38\pm 47 (1 \sigma), while the analysis without
marginalization provides fNL= 35\pm 42. Splitting the marginalization over each
foreground separately, we found that the estimates of fNL are positively cross
correlated of 17%, 12% with the dust and synchrotron respectively, while a
negative cross correlation of about -10% is found for the free-free component. |
Cosmology with Galaxy Clusters: Systematic Effects in the Halo Mass
Function: We investigate potential systematic effects in constraining the amplitude of
primordial fluctuations \sigma_8 arising from the choice of halo mass function
in the likelihood analysis of current and upcoming galaxy cluster surveys. We
study the widely used N-body simulation fit of Tinker et al. (T08) and, as an
alternative, the recently proposed analytical model of Excursion Set Peaks
(ESP). We first assess the relative bias between these prescriptions when
constraining \sigma_8 by sampling the ESP mass function to generate mock
catalogs and using the T08 fit to analyse them, for various choices of survey
selection threshold, mass definition and statistical priors. To assess the
level of absolute bias in each prescription, we then repeat the analysis on
dark matter halo catalogs in N-body simulations designed to mimic the mass
distribution in the current data release of Planck SZ clusters. This N-body
analysis shows that using the T08 fit without accounting for the scatter
introduced when converting between mass definitions (alternatively, the scatter
induced by errors on the parameters of the fit) can systematically
over-estimate the value of \sigma_8 by as much as 2\sigma\ for current data,
while analyses that account for this scatter should be close to unbiased in
\sigma_8. With an increased number of objects as expected in upcoming data
releases, regardless of accounting for scatter, the T08 fit could over-estimate
the value of \sigma_8 by ~1.5\sigma. The ESP mass function leads to
systematically more biased but comparable results. A strength of the ESP model
is its natural prediction of a weak non-universality in the mass function which
closely tracks the one measured in simulations and described by the T08 fit. We
suggest that it might now be prudent to build new unbiased ESP-based fitting
functions for use with the larger datasets of the near future. | Enhanced Inflation in the Dirac-Born-Infeld framework: We consider the Einstein equations within the DBI scenario for a spatially
flat Friedmann-Robertson-Walker (FRW) spacetime without a cosmological
constant. We derive the inflationary scenario by applying the symmetry
transformations which preserve the form of the Friedmann and conservation
equations. These form invariance transformations generate a symmetry group
parametrized by the Lorentz factor $\ga$. We explicitly obtain an inflationary
scenario by the cooperative effect of adding energy density into the Friedmann
equation. For the case of a constant Lorentz factor, and under the slow roll
assumption, we find the transformation rules for the scalar and tensor power
spectra of perturbations as well as their ratio under the action of the form
invariance symmetry group. Within this case and due to its relevance for the
inflationary paradigm, we find the general solution of the dynamical equations
for a DBI field driven by an exponential potential and show a broad set of
inflationary solutions. The general solution can be split into three subsets
and all these behave asymptotically as a power law solution at early and at
late times. |
The orientation dependence of quasar spectral energy distributions: We investigate the orientation dependence of the spectral energy
distributions in a sample of radio-loud quasars. Selected specifically to study
orientation issues, the sample contains 52 sources with redshifts in the range
0.16<z<1.4 and measurements of radio core dominance, a radio orientation
indicator. Measured properties include monochromatic luminosities at a range of
wavelengths between the infrared and X-rays, integrated infrared luminosity,
spectral slopes, and the covering fraction of the obscuring circumnuclear dust.
We estimate dust covering fraction assuming that the accretion disk emits
anisotropically and discuss the shortcomings and technical difficulties of this
calculation. Luminosities are found to depend on orientation, with face-on
sources factors of a 2-3 brighter than more edge-on sources, depending on
wavelength. The degree of anisotropy varies very little with wavelength such
that the overall shape of the spectral energy distribution does not vary
significantly with orientation. In the infrared, we do not observe a decrease
in anisotropy with increasing wavelength. The spectral slopes and estimates of
covering fraction are not significantly orientation dependent. We construct
composite spectral energy distributions as a function of radio core dominance
and find that these illustrate the results determined from the measured
properties. | No-go guide for the Hubble tension : Late-time solutions: The Hubble tension, if not caused by any systematics, could be relieved or
even resolved from modifying either the early-time or late-time Universe. The
early-time modifications are usually in tension with either galaxy clustering
or galaxy lensing constraints. The late-time modifications are also in conflict
with the constraint from the inverse distance ladder, which, however, is
weakened by the dependence on a sound-horizon prior and some particular
approximation for the late-time expansion history. To achieve a more general
no-go argument for the late-time scenarios, we propose to use a global
parametrizationbased on the cosmic age (PAge) to consistently use the cosmic
chronometers data beyond the Taylor expansion domain and without the input of a
sound-horizon prior. Both the early-time and late-time scenarios are therefore
largely ruled out, indicating the possible ways out of the Hubble tension from
either exotic modifications of our concordance Universe or some unaccounted
systematics. |
Large-scale mass distribution in the Illustris simulation: Observations at low redshifts thus far fail to account for all of the baryons
expected in the Universe according to cosmological constraints. A large
fraction of the baryons presumably resides in a thin and warm-hot medium
between the galaxies, where they are difficult to observe due to their low
densities and high temperatures. Cosmological simulations of structure
formation can be used to verify this picture and provide quantitative
predictions for the distribution of mass in different large-scale structure
components. Here we study the distribution of baryons and dark matter at
different epochs using data from the Illustris simulation. We identify regions
of different dark matter density with the primary constituents of large-scale
structure, allowing us to measure mass and volume of haloes, filaments and
voids. At redshift zero, we find that 49 % of the dark matter and 23 % of the
baryons are within haloes more massive than the resolution limit of $2\times
10^8$ M$_\odot$. The filaments of the cosmic web host a further 45 % of the
dark matter and 46 % of the baryons. The remaining 31 % of the baryons reside
in voids. The majority of these baryons have been transported there through
active galactic nuclei feedback. We note that the feedback model of Illustris
is too strong for heavy haloes, therefore it is likely that we are
overestimating this amount. Categorizing the baryons according to their density
and temperature, we find that 17.8 % of them are in a condensed state, 21.6 %
are present as cold, diffuse gas, and 53.9 % are found in the state of a
warm-hot intergalactic medium. | Interpreting the Evolution of the Size - Luminosity Relation for Disk
Galaxies from Redshift 1 to the Present: A sample of very high resolution cosmological disk galaxy simulations is used
to investigate the evolution of galaxy disk sizes back to redshift 1 within the
Lambda CDM cosmology. Artificial images in the rest frame B band are generated,
allowing for a measurement of disk scale lengths using surface brightness
profiles as observations would, and avoiding any assumption that light must
follow mass as previous models have assumed. We demonstrate that these
simulated disks are an excellent match to the observed magnitude - size
relation for both local disks, and for disks at z=1 in the magnitude/mass range
of overlap. We disentangle the evolution seen in the population as a whole from
the evolution of individual disk galaxies. In agreement with observations, our
simulated disks undergo roughly 1.5 magnitudes/arcsec^2 of surface brightness
dimming since z=1. We find evidence that evolution in the magnitude - size
plane varies by mass, such that galaxies with M* > 10^9 M_sun undergo more
evolution in size than luminosity, while dwarf galaxies tend to evolve
potentially more in luminosity. The disks grow in such a way as to stay on
roughly the same stellar mass - size relation with time. Finally, due to an
evolving stellar mass - SFR relation, a galaxy at a given stellar mass (or
size) at z=1 will reside in a more massive halo and have a higher SFR, and thus
a higher luminosity, than a counterpart of the same stellar mass at z=0. |
Aspects of inflation and the very early universe: Until recently our knowledge of the primordial curvature perturbation was
relatively modest. Ever since COBE delivered its map of data we know the scalar
spectrum of primordial perturbations is approximately flat, with the power
being only slightly stronger at larger scales. Most inflationary models predict
an approximately scale-invariant spectrum, which therefore cannot be used as a
distinctive signature. To distinguish between different inflationary
microphysics we need to study higher point statistics of the primordial
perturbation, which can encode non-gaussian data. In the first part of this
thesis we study the bispectrum in all single-field models with a well-defined
quantum field theory during a quasi-de Sitter inflationary phase. Any
single-field models without ghost-like instabilities fall into this
description: from canonical, to Dirac-Born-Infeld inflation and galileon
inflation theories. We investigate the scale and shape- dependences of the
bispectrum to next-order in the slow-roll approximation. We illustrate our
results by applying them to different models and argue these corrections must
be taken into account to keep the theoretical error below the observational
precision set by the Planck satellite. We then explore the ability of using
bispectrum shapes to distinguish between inflationary models more efficiently.
We further extend the study of the bispectrum of single-field models beyond the
slow-roll approximation, demanding the spectral index to be close to, but not
exactly, unity. In the second part of this thesis we explore the process by
which the universe is repopulated with matter particles at the end of a
Dirac-Born-Infeld inflation phase. We place some mild bounds on the reheating
temperature of these models. We argue that the constraints arising from the
preheating analysis are complementary to those derived from the primordial
perturbation. | Traces of Anisotropic Quasi-Regular Structure in the SDSS Data: The aim of this study is to search for quasi-periodical structures at
moderate cosmological redshifts $z \la 0.5 $. We mainly use the SDSS DR7 data
on the luminous red galaxies (LRGs) with redshifts $0.16 \leq z \leq 0.47$. At
first, we analyze features (peaks) in the power spectra of radial (shell-like)
distributions using separate angular sectors in the sky and calculate the power
spectra within each sector. As a result, we found some signs of a large-scale
anisotropic quasi-periodic structure detectable through 6 sectors out of a
total of 144 sectors. These sectors are distinguished by large amplitudes of
dominant peaks in their radial power spectra at wavenumbers $k$ within a narrow
interval of $0.05 < k < 0.07$~h~Mpc$^{-1}$. Then, passing from a spherical
coordinate system to a Cartesian one, we found a special direction such that
the total distribution of LRG projections on it contains a significant
($\ga$5$\sigma$) quasi-periodical component. We assume that we are dealing with
a signature of a quasi-regular structure with a characteristic scale $116 \pm
10$~h$^{-1}$~Mpc. Our assumption is confirmed by a preliminary analysis of the
SDSS DR12 data. |
Local anomalies around the third peak in the CMB angular power spectrum
of the WMAP 7-year data: We estimate the power spectra of CMB temperature anisotropy in localized
regions on the sky using the WMAP 7-year data. Here, we report that the north
hat and the south hat regions at the high Galactic latitude (|b| >= 30 deg)
show anomaly in the power spectrum amplitude around the third peak, which is
statistically significant up to 3 sigma. We try to figure out the cause of the
observed anomaly by analyzing the low Galactic latitude (|b|< 30 deg) regions
where the galaxy contamination is expected to be stronger, and regions that are
weakly or strongly dominated by the WMAP instrument noise. We also consider the
possible effect of unresolved radio point sources. We found another but less
statistically significant anomaly in the low Galactic latitude north and south
regions whose behavior is opposite to the one at the high latitude. Our
analysis shows that the observed north-south anomaly at high latitude becomes
weaker on the regions with high number of observations (weak instrument noise),
suggesting that the anomaly is significant at sky regions that are dominated by
the WMAP instrument noise. We have checked that the observed north-south
anomaly has weak dependences on the bin-width used in the power spectrum
estimation and the Galactic latitude cut. We have also discussed the
possibility that the detected anomaly may hinge on the particular choice of the
multipole bin around the third peak. We anticipate that the issue of whether
the anomaly is intrinsic one or due to the WMAP instrument noise will be
resolved by the forthcoming Planck data. | Defining the frame of minimum nonlinear Hubble expansion variation: We characterize a cosmic rest frame in which the monopole variation of the
spherically averaged nonlinear Hubble expansion is most uniform, under
arbitrary local Lorentz boosts of the central observer. Using the COMPOSITE
sample of 4534 galaxies, we identify a degenerate set of candidate minimum
nonlinear variation frames, which includes the rest frame of the Local Group
(LG) of galaxies, but excludes the standard Cosmic Microwave Background (CMB)
frame. Candidate rest frames defined by a boost from the LG frame close to the
plane of the galaxy have a statistical likelihood similar to the LG frame. This
may result from a lack of constraining data in the Zone of Avoidance. We extend
our analysis to the Cosmicflows-2 (CF2) sample of 8162 galaxies. While the
signature of a systematic boost offset between the CMB and LG frame averages is
still detected, the spherically averaged nonlinear expansion variation in all
rest frames is significantly larger in the CF2 sample than would be reasonably
expected. We trace this to the CF2 distances being reported without a
correction for inhomogeneous distribution Malmquist bias. Systematic
differences in the inclusion of the large SFI++ subsample into the COMPOSITE
and CF2 catalogues are analysed. Our results highlight the importance of a
careful treatment of Malmquist biases for future peculiar velocities studies,
including tests of the hypothesis of Wiltshire et al [Phys. Rev. D 88 (2013)
083529; arXiv:1201.5371] that a significant fraction of the CMB temperature
dipole may be nonkinematic in origin. |
Primordial blackholes and gravitational waves for an inflection-point
model of inflation: In this article we provide a new closed relationship between cosmic abundance
of primordial gravitational waves and primordial blackholes originated from
initial inflationary perturbations for inflection-point models of inflation
where inflation occurs below the Planck scale. The current Planck constraint on
tensor-to-scalar ratio, running of the spectral tilt, and from the abundance of
dark matter content in the universe, we can deduce a strict bound on the
current abundance of primordial blackholes to be within a range, $9.99712\times
10^{-3}<\Omega_{PBH}h^{2}<9.99736\times 10^{-3}$. | Next Generation Cosmology: Constraints from the Euclid Galaxy Cluster
Survey: We study the characteristics of the galaxy cluster samples expected from the
European Space Agency's Euclid satellite and forecast constraints on
cosmological parameters describing a variety of cosmological models. The method
used in this paper, based on the Fisher Matrix approach, is the same one used
to provide the constraints presented in the Euclid Red Book (Laureijs et
al.2011). We describe the analytical approach to compute the selection function
of the photometric and spectroscopic cluster surveys. Based on the photometric
selection function, we forecast the constraints on a number of cosmological
parameter sets corresponding to different extensions of the standard LambdaCDM
model. The dynamical evolution of dark energy will be constrained to Delta
w_0=0.03 and Delta w_a=0.2 with free curvature Omega_k, resulting in a
(w_0,w_a) Figure of Merit (FoM) of 291. Including the Planck CMB covariance
matrix improves the constraints to Delta w_0=0.02, Delta w_a=0.07 and a
FoM=802. The amplitude of primordial non-Gaussianity, parametrised by f_NL,
will be constrained to \Delta f_NL ~ 6.6 for the local shape scenario, from
Euclid clusters alone. Using only Euclid clusters, the growth factor parameter
\gamma, which signals deviations from GR, will be constrained to Delta
\gamma=0.02, and the neutrino density parameter to Delta Omega_\nu=0.0013 (or
Delta \sum m_\nu=0.01). We emphasise that knowledge of the observable--mass
scaling relation will be crucial to constrain cosmological parameters from a
cluster catalogue. The Euclid mission will have a clear advantage in this
respect, thanks to its imaging and spectroscopic capabilities that will enable
internal mass calibration from weak lensing and the dynamics of cluster
galaxies. This information will be further complemented by wide-area
multi-wavelength external cluster surveys that will already be available when
Euclid flies. [Abridged] |
Bounds on Ultra-Light Hidden-Photon Dark Matter from 21cm at Cosmic Dawn: Ultra-light hidden-photon dark matter produces an oscillating electric field
in the early Universe plasma, which in turn induces an electric current in its
ionized component whose dissipation results in heat transfer from the dark
matter to the plasma. This will affect the global 21cm signal from the Dark
Ages and Cosmic Dawn. In this work we focus on the latter, in light of the
reported detection by the EDGES collaboration of an absorption signal at
frequencies corresponding to redshift z~17. By measuring the 21cm global
signal, a limit can be placed on the amount of gas heating, and thus the
kinetic mixing strength $\varepsilon$ between the hidden and ordinary photons
can be constrained. Our inferred 21cm bounds on $\varepsilon$ in the mass range
$10^{-23}\,{\rm eV}\lesssim m_\chi\lesssim10^{-13}\,{\rm eV}$ are the strongest
to date. | High-redshift cosmography: auxiliary variables versus Padé polynomials: Cosmography becomes non-predictive when cosmic data span beyond the red shift
limit $z\simeq1 $. This leads to a \emph{strong convergence issue} that
jeopardizes its viability. In this work, we critically compare the two main
solutions of the convergence problem, i.e. the $y$-parametrizations of the
redshift and the alternatives to Taylor expansions based on Pad\'e series. In
particular, among several possibilities, we consider two widely adopted
parametrizations, namely $y_1=1-a$ and $y_2=\arctan(a^{-1}-1)$, being $a$ the
scale factor of the Universe. We find that the $y_2$-parametrization performs
relatively better than the $y_1$-parametrization over the whole redshift
domain. Even though $y_2$ overcomes the issues of $y_1$, we get that the most
viable approximations of the luminosity distance $d_L(z)$ are given in terms of
Pad\'e approximations. In order to check this result by means of cosmic data,
we analyze the Pad\'e approximations up to the fifth order, and compare these
series with the corresponding $y$-variables of the same orders. We investigate
two distinct domains involving Monte Carlo analysis on the Pantheon Superovae
Ia data, $H(z)$ and shift parameter measurements. We conclude that the (2,1)
Pad\'e approximation is statistically the optimal approach to explain low and
high-redshift data, together with the fifth-order $y_2$-parametrization. At
high redshifts, the (3,2) Pad\'e approximation cannot be fully excluded, while
the (2,2) Pad\'e one is essentially ruled out. |
Electromagnetic nature of dark energy: Out of the four components of the electromagnetic field, Maxwell's theory
only contains two physical degrees of freedom. However, in an expanding
universe, consistently eliminating one of the "unphysical" states in the
covariant (Gupta-Bleuler) formalism turns out to be difficult to realize. In
this work we explore the possibility of quantization without subsidiary
conditions. This implies that the theory would contain a third physical state.
The presence of such a new (temporal) electromagnetic mode on cosmological
scales is shown to generate an effective cosmological constant which can
account for the accelerated expansion of the universe. This new polarization
state is completely decoupled from charged matter, but can be excited
gravitationally. In fact, primordial electromagnetic quantum fluctuations
produced during electroweak scale inflation could naturally explain the
presence of this mode and also the measured value of the cosmological constant.
The theory is compatible with all the local gravity tests, it is free from
classical or quantum instabilities and reduces to standard QED in the flat
space-time limit. Thus we see that, not only the true nature of dark energy can
be established without resorting to new physics, but also the value of the
cosmological constant finds a natural explanation in the context of standard
inflationary cosmology. Possible signals, discriminating this model from LCDM,
are also discussed. | A search for steep spectrum radio relics and halos with the GMRT: Context: Diffuse radio emission, in the form of radio halos and relics,
traces regions in clusters with shocks or turbulence, probably produced by
cluster mergers. Some models of diffuse radio emission in clusters indicate
that virtually all clusters should contain diffuse radio sources with a steep
spectrum. External accretion shocks associated with filamentary structures of
galaxies could also accelerate electrons to relativistic energies and hence
produce diffuse synchrotron emitting regions. Here we report on Giant Metrewave
Radio Telescope (GMRT) observations of a sample of steep spectrum sources from
the 74 MHz VLSS survey. These sources are diffuse and not associated with
nearby galaxies.
Aims: The main aim of the observations is to search for diffuse radio
emission associated with galaxy clusters or the cosmic web.
Methods: We carried out GMRT 610 MHz continuum observations of unidentified
diffuse steep spectrum sources.
Results: We have constructed a sample of diffuse steep spectrum sources,
selected from the 74 MHz VLSS survey. We identified eight diffuse radio sources
probably all located in clusters. We found five radio relics, one cluster with
a giant radio halo and a radio relic, and one radio mini-halo. By complementing
our observations with measurements from the literature we find correlations
between the physical size of relics and the spectral index, in the sense that
smaller relics have steeper spectra. Furthermore, larger relics are mostly
located in the outskirts of clusters while smaller relics are located closer to
the cluster center. |
The nearest neighbor statistics for X-ray source counts II. Chandra Deep
Field South: It is assumed that the unresolved fraction of the X-ray background (XRB)
consists of a truly diffuse component and a population of the weak sources
below the present detection threshold. Albeit these weak sources are not
observed directly, their collective nature could be investigated by statistical
means. The goal is to estimate the source counts below the conventional
detection limit in the Chandra Deep Field-South 2Ms exposure. The source number
counts are assessed using the nearest neighbor statistics applied to the
distribution of photon counts. The method is described in the first paper of
these series. The source counts down to 3-4 x 10^{-18} cgs in the soft band
(0.5-2 keV) and down to 2-3 x 10^{-17} cgs in the hard band (2-8 keV) are
evaluated. It appears that in the soft band the source counts steepen
substantially below ~10^{-16} cgs. Assuming that the differential slope b =
-1.5 to -1.6 in the range 10^{-16} - 10^{-14} cgs, the number of weaker sources
indicates the slope of approx. -2.0. The steepening is not observed in the hard
band. Steepening of counts in the soft band indicates a new population of
sources. A class of normal galaxies at moderate redshifts is a natural
candidate. | Joint signal extraction from galaxy clusters in X-ray and SZ surveys: A
matched-filter approach: The hot ionized gas of the intra-cluster medium emits thermal radiation in
the X-ray band and also distorts the cosmic microwave radiation through the
Sunyaev-Zel'dovich (SZ) effect. Combining these two complementary sources of
information through innovative techniques can therefore potentially improve the
cluster detection rate when compared to using only one of the probes. Our aim
is to build such a joint X-ray-SZ analysis tool, which will allow us to detect
fainter or more distant clusters while maintaining high catalogue purity. We
present a method based on matched multifrequency filters (MMF) for extracting
cluster catalogues from SZ and X-ray surveys. We first designed an X-ray
matched-filter method, analogous to the classical MMF developed for SZ
observations. Then, we built our joint X-ray-SZ algorithm by combining our
X-ray matched filter with the classical SZ-MMF, for which we used the physical
relation between SZ and X-ray observations. We show that the proposed X-ray
matched filter provides correct photometry results, and that the joint matched
filter also provides correct photometry when the $F_{\rm X}/Y_{500}$ relation
of the clusters is known. Moreover, the proposed joint algorithm provides a
better signal-to-noise ratio than single-map extractions, which improves the
detection rate even if we do not exactly know the $F_{\rm X}/Y_{500}$ relation.
The proposed methods were tested using data from the ROSAT all-sky survey and
from the Planck survey. |
Tensor Squeezed Limits and the Higuchi Bound: We point out that tensor consistency relations-i.e. the behavior of
primordial correlation functions in the limit a tensor mode has a small
momentum-are more universal than scalar consistency relations. They hold in the
presence of multiple scalar fields and as long as anisotropies are diluted
exponentially fast. When de Sitter isometries are approximately respected
during inflation this is guaranteed by the Higuchi bound, which forbids the
existence of light particles with spin: De Sitter space can support scalar hair
but no curly hair. We discuss two indirect ways to look for the violation of
tensor con- sistency relations in observations, as a signature of models in
which inflation is not a strong isotropic attractor, such as solid inflation:
(a) Graviton exchange contribution to the scalar four-point function; (b)
Quadrupolar anisotropy of the scalar power spectrum due to super-horizon tensor
modes. This anisotropy has a well-defined statistics which can be distinguished
from cases in which the background has a privileged direction. | Preparing old and recent radio source tables for the VO age: Current
status: Independent of established data centers, and partly for my own research, I
have been collecting the tabular data from nearly 1500 articles concerned with
radio sources. Optical character recognition (OCR) was used to recover tables
from nearly 600 of these. Tables from only 44 percent of these articles are
available in the CDS or CATS catalog collections. This fraction is 62 percent
for articles with over 100 sources. Surprisingly, these fractions are not
better for articles published electronically since 2001, perhaps partly due to
the fact that often tabular data are published in formats not useful for direct
machine reading. The databases Simbad and NED recognize only about 60 percent
of the bibliographic references corresponding to the existing electronic radio
source lists, and the number of objects associated with these references is
much smaller still. Both, object databases like NED and Simbad, as well as
catalog browsers (VizieR, CATS) need to be consulted to obtain the most
complete information on radio sources. More human resources at the data centers
and better collaboration between authors, referees, editors, publishers, and
data centers are required to improve the flow of tabular data from journals to
public databases. Current efforts within the Virtual Observatory (VO) project,
to provide retrieval and analysis tools for different types of published and
archival data stored at various sites, should be balanced by an equal effort to
recover and include large amounts of published data not currently available in
this way. If human resources can be found, the data sets collected by the
author will be made available for the preparation of metadata necessary for
their ingression into catalog browsers. |
On the accuracy of time-delay cosmography in the Frontier Fields Cluster
MACS J1149.5+2223 with supernova Refsdal: We study possible systematic effects on the values of the cosmological
parameters measured through strong lensing analyses of the HFF galaxy cluster
MACS J1149.5+2223. We use the observed positions of a large set of
spectroscopically selected multiple images, including those of supernova
"Refsdal" with their estimated time delays. Starting from our reference model
in a flat $\Lambda$CDM cosmology, published in Grillo et al. (2018), we confirm
the relevance of the longest measurable time delay, between SX and S1, and an
approximately linear relation between its value and that of $H_{0}$. We perform
true blind tests by considering a range of time delays around its original
estimate of $345 \pm 10$ days, as an accurate measurement of this time delay
was not known at the time of analysis and writing. We investigate separately
the impact of a constant sheet of mass at the cluster redshift, of a power-law
profile for the mass density of the cluster main halo and of some scatter in
the cluster member scaling relations. Remarkably, we find that these systematic
effects do not introduce a significant bias on the inferred values of $H_{0}$
and $\Omega_{\rm m}$ and that the statistical uncertainties dominate the total
error budget: a 3% uncertainty on the time delay of image SX translates into
approximately 6% and 40% (including both statistical and systematic $1\sigma$)
uncertainties for $H_{0}$ and $\Omega_{\rm m}$, respectively. Furthermore, our
model accurately reproduces the extended surface brightness distribution of the
supernova host, covering more than $3 \times 10^{4}$ $HST$ pixels. We also
present the interesting possibility of measuring the value of the
equation-of-state parameter $w$ of the dark energy density, currently with a
30% uncertainty. We conclude that time-delay cluster lenses have the potential
to become soon an alternative and competitive cosmological probe. | Impact of a primordial magnetic field on cosmic microwave background $B$
modes with weak lensing: We discuss the manner in which the primordial magnetic field (PMF) suppresses
the cosmic microwave background (CMB) $B$ mode due to the weak-lensing (WL)
effect. The WL effect depends on the lensing potential (LP) caused by matter
perturbations, the distribution of which at cosmological scales is given by the
matter power spectrum (MPS). Therefore, the WL effect on the CMB $B$ mode is
affected by the MPS. Considering the effect of the ensemble average energy
density of the PMF, which we call "the background PMF," on the MPS, the
amplitude of MPS is suppressed in the wave number range of $k>0.01~h$
Mpc$^{-1}$.The MPS affects the LP and the WL effect in the CMB $B$ mode;
however, the PMF can damp this effect. Previous studies of the CMB $B$ mode
with the PMF have only considered the vector and tensor modes. These modes
boost the CMB $B$ mode in the multipole range of $\ell > 1000$, whereas the
background PMF damps the CMB $B$ mode owing to the WL effect in the entire
multipole range. The matter density in the Universe controls the WL effect.
Therefore, when we constrain the PMF and the matter density parameters from
cosmological observational data sets, including the CMB $B$ mode, we expect
degeneracy between these parameters. The CMB $B$ mode also provides important
information on the background gravitational waves, inflation theory, matter
density fluctuations, and the structure formations at the cosmological scale
through the cosmological parameter search. If we study these topics and
correctly constrain the cosmological parameters from cosmological observations
including the CMB $B$ mode, we need to correctly consider the background PMF. |
On the stellar and baryonic mass fractions of central blue and red
galaxies: By means of the abundance matching technique, we infer the local stellar and
baryonic mass-halo mass (Ms-Mh and Mb-Mh) relation for central blue and red
galaxies separately in the mass range Ms~10^8.5-10^12.0 Msun. The observational
inputs are the SDSS central blue and red Galaxy Stellar Mass Functions reported
in Yang et al. 2009, and the measured local gas mass-Ms relations for blue and
red galaxies. For the Halo Mass Function associated to central blue galaxies,
the distinct LCDM one is used and set up to exclude: (i) the observed
group/cluster mass function (blue galaxies are rare as centers of
groups/clusters), and (ii) halos with a central major merger at resdshifts
z<0.8 (dry late major mergers destroy the disks of blue galaxies). For red
galaxies, we take the complement of this function to the total. The obtained
mean Ms-Mh and Mb-Mh relations of central blue and red galaxies do not differ
significantly from the respective relations for all central galaxies. For
Mh>10^11.5 Msun, the Ms's of red galaxies tend to be higher than those of blue
ones for a given Mh, the difference not being larger than 1.7. For Mh<10^11.5
Msun, this trend is inverted. For blue (red) galaxies: (a) the maximum value of
fs=Ms/Mh is 0.021^{+0.016}_{-0.009} (0.034{+0.026}_{-0.015}) and it is attained
atlog(Mh/Msun)~12.0 (log(Mh/Msun)~11.9); (b) fs\propto Mh (fs\propto Mh^3) at
the low-mass end while at the high-mass end, fs\propto Mh^-0.4 (fs\propto
Mh^-0.6). The baryon mass fractions, fb=Mb/Mh, of blue and red galaxies reach
maximum values of fb=0.028^{+0.018}_{-0.011} and fb=0.034^{+0.025}_{-0.014},
respectively. For Mh<10^11.3 Msun, a much steeper dependence of fb on Mh is
obtained for the red galaxies than for the blue ones. We discuss on the
differences found in the fs-Mh and fb-Mh relations between blue and red
galaxies in the light of of semi-empirical galaxy models. | Impact of the free-streaming neutrinos to the second order induced
gravitational waves: The damping effect of the free-streaming neutrinos on the second order
gravitational waves is investigated in detail. We solve the Boltzmann equation
and give the anisotropic stress induced by neutrinos to second order. The first
order tensor and its coupling with scalar perturbations induced gravitational
waves are considered. We give the analytic equations of the damping kernel
functions and finally obtain the energy density spectrum. The results show that
the free-streaming neutrinos suppress the density spectrum significantly for
low frequency gravitational waves and enlarge the logarithmic slope $n$ in the
infrared region ($k \ll k_*$) of the spectrum. For the spectrum of $k_*\sim
10^{-7}$Hz, the damping effect in the range of $k<k_*$ is significant. The
combined effect of the first and second order could reduce the amplitude by
$30\%$ and make $n$ jump from $1.54$ to $1.63$ at $k\sim 10^{-9}$Hz, which may
be probed by the pulsar timing arrays (PTA) in the future. |
Emission lines in early-type galaxies: active nuclei or stars?: We selected 27244 nearby, red, giant early-type galaxies (RGEs) from the
Sloan Digital Sky Survey (SDSS). In a large fraction (53%) of their spectra the
[O III] emission line is detected, with an equivalent width (EW) distribution
strongly clustered around ~0.75 A. The vast majority of those RGEs for which it
is possible to derive emission line ratios (amounting to about half of the
sample) show values characteristic of LINERs. The close connection between
emission lines and stellar continuum points to stellar processes as the most
likely source of the bulk of the ionizing photons in RGEs, rather than active
nuclei. In particular, the observed EW and optical line ratios are consistent
with the predictions of models in which the photoionization comes from to hot
evolved stars. Shocks driven by supernovae or stellar ejecta might also
contribute to the ionization budget. A minority, ~4%, of the galaxies show
emission lines with an equivalent that is width a factor of ~2 greater than the
sample median. Only among them are Seyfert-like spectra found. Furthermore, 40%
of this subgroup have a radio counterpart, compared to ~6% of the rest of the
sample. These characteristics argue in favor of an AGN origin for their
emission lines. Emission lines diagnostic diagrams do not reveal a distinction
between the AGN subset and the other members of the sample, and consequently
they are not a useful tool for establishing the dominant source of the ionizing
photons, which is better predicted by the EW of the emission lines. | Inflation in the closed FLRW model and the CMB: Recent cosmic microwave background (CMB) observations put strong constraints
on the spatial curvature via estimation of the parameter $\Omega_k$ assuming an
almost scale invariant primordial power spectrum. We study the evolution of the
background geometry and gauge-invariant scalar perturbations in an inflationary
closed FLRW model and calculate the primordial power spectrum. We find that the
inflationary dynamics is modified due to the presence of spatial curvature,
leading to corrections to the nearly scale invariant power spectrum at the end
of inflation. When evolved to the surface of last scattering, the resulting
temperature anisotropy spectrum ($C_{\ell}^{TT}$) shows deficit of power at low
multipoles ($\ell<20$). By comparing our results with the recent Planck data we
discuss the role of spatial curvature in accounting for CMB anomalies and in
the estimation of the parameter $\Omega_k$. Since the curvature effects are
limited to low multipoles, the Planck estimation of cosmological parameters
remains robust under inclusion of positive spatial curvature. |
Detection of a luminous hot X-ray corona around the massive spiral
galaxy NGC266: The presence of luminous hot X-ray coronae in the dark matter halos of
massive spiral galaxies is a basic prediction of galaxy formation models.
However, observational evidence for such coronae is very scarce, with the first
few examples having only been detected recently. In this paper, we study the
large-scale diffuse X-ray emission associated with the massive spiral galaxy
NGC266. Using ROSAT and Chandra X-ray observations we argue that the diffuse
emission extends to at least ~70 kpc, whereas the bulk of the stellar light is
confined to within ~25 kpc. Based on X-ray hardness ratios, we find that most
of the diffuse emission is released at energies <1.2 keV, which indicates that
this emission originates from hot X-ray gas. Adopting a realistic gas
temperature and metallicity, we derive that in the (0.05-0.15)r_200 region
(where r_200 is the virial radius) the bolometric X-ray luminosity of the hot
gas is (4.3 +/- 0.8) x 10^40 erg/s and the gas mass is (9.1 +/- 0.9) x 10^9
M_sun. These values are comparable to those observed for the two other
well-studied X-ray coronae in spiral galaxies, suggesting that the physical
properties of such coronae are similar. This detection offers an excellent
opportunity for comparison of observations with detailed galaxy formation
simulations. | Massive prompt cusps: A new signature of warm dark matter: Every dark matter halo and subhalo is expected to have a prompt $\rho\propto
r^{-1.5}$ central density cusp, which is a relic of its condensation out of the
smooth mass distribution of the early universe. The sizes of these prompt cusps
are linked to the scales of the peaks in the initial density field from which
they formed. In warm dark matter (WDM) models, the smoothing scale set by free
streaming of the dark matter can result in prompt cusps with masses of order
$10^7$ M$_\odot$. We show that WDM models with particle masses ranging from 2
to 6 keV predict prompt cusps that could detectably alter the observed
kinematics of Local Group dwarf galaxies. Thus, prompt cusps present a viable
new probe of WDM. A prompt cusp's properties are highly sensitive to when it
formed, so prospects can be improved with a better understanding of when the
haloes of the Local Group dwarfs originally formed. Tidal stripping can also
affect prompt cusps, so constraints on satellite galaxy orbits can further
tighten WDM inferences. |
Influence of cosmological models on the GZK horizon of ultrahigh energy
protons: We investigate how the density of baryonic and cold dark matter, the density
of dark energy and the value of the Hubble parameter at the present time
influence the propagation of ultrahigh energy protons in the nearby Universe.
We take into account energy losses in the cosmic microwave radiation, the only
one relevant for protons above $10^{18}$ eV, and we explore the dependence of
Greisen-Zatsepin-Kuz'min (GZK) horizon on the cosmology. We investigate several
cosmological scenarios, from matter dominated to energy dominated ones, and we
consider the impact of uncertainties in the Hubble parameter in a
$\Lambda-$Cold Dark Matter (CDM) Universe, estimated from recent observations,
on the GZK horizon. The impact of the (unknown) extragalactic magnetic field on
our study is discussed, as well as possible probes of the Hubble parameter
attainable by current and future experiments. | Implications of Symmetry and Pressure in Friedmann Cosmology. II.
Stellar Remnant Black Hole Mass Function: We consider some observational consequences of replacing all black holes
(BHs) with a class of non-singular solutions that mimic BHs but with Dark
Energy (DE) interiors; GEneric Objects of Dark Energy (GEODEs). We focus on the
BH mass function and chirp-mass redshift distribution of mergers visible to
gravitational wave observatories. We incorporate the GEODE blueshift into an
initially Salpeter stellar remnant distribution, and model the binary
population by evolving synthesized binary remnant distributions, published
before LIGO's first measurements. We find that a GEODE produced between $20
\lesssim z \lesssim 40$, and observed at $z \sim 7$, will have its initial mass
amplified by $\sim 20-140\times$. This can relieve tension between
accretion-only growth models and the inferred masses of BHs in quasars at $z
\gtrsim 6$. Moreover, we find that merger rates of GEODE binaries increase by a
factor of $\sim 2\times$ relative to classical BHs. The resulting GEODE mass
function is consistent with the most recent LIGO constraints at $< 0.5\sigma$.
In contrast, a Salpeter stellar distribution that evolves into classical
remnants is in tension at $\gtrsim 2\sigma$. This agreement occurs without
low-metallicity regions, abnormally massive progenitor stars, novel formation
channels, or primordial object formation at extreme rates. In particular, we
find that solar metallicity progenitors, which produce
$1.1-1.8\mathrm{M}_\odot$ remnants, overlap with many LIGO observations when
evolved as GEODEs. |
Cosmological and Astrophysical Neutrino Mass Measurements: Cosmological and astrophysical measurements provide powerful constraints on
neutrino masses complementary to those from accelerators and reactors. Here we
provide a guide to these different probes, for each explaining its physical
basis, underlying assumptions, current and future reach. | BE-HaPPY: Bias Emulator for Halo Power Spectrum including massive
neutrinos: We study the clustering properties of dark matter halos in real- and
redshift-space in cosmologies with massless and massive neutrinos through a
large set of state-of-the-art N-body simulations. We provide quick and
easy-to-use prescriptions for the halo bias on linear and mildly non-linear
scales, both in real and redshift space, which are valid also for massive
neutrinos cosmologies. Finally we present a halo bias
emulator,$\textbf{BE-HaPPY}$, calibrated on the N-body simulations, which is
fast enough to be used in the standard Markov Chain Monte Carlo approach to
cosmological inference. For a fiducial standard $\Lambda$CDM cosmology
$\textbf{BE-HaPPY}$ provides percent or sub-percent accuracy on the scales of
interest (linear and well into the mildly non-linear regime), meeting therefore
for the halo-bias the accuracy requirements for the analysis of next-generation
large--scale structure surveys. |
Measurements of Degree-Scale B-mode Polarization with the BICEP/Keck
Experiments at South Pole: The BICEP and Keck Array experiments are a suite of small-aperture refracting
telescopes observing the microwave sky from the South Pole. They target the
degree-scale B-mode polarization signal imprinted in the Cosmic Microwave
Background (CMB) by primordial gravitational waves. Such a measurement would
shed light on the physics of the very early universe. While BICEP2 observed for
the first time a B-mode signal at 150 GHz, higher frequencies from the Planck
satellite showed that it could be entirely due to the polarized emission from
Galactic dust, though uncertainty remained high. Keck Array has been observing
the same region of the sky for several years, with an increased detector count,
producing the deepest polarized CMB maps to date. New detectors at 95 GHz were
installed in 2014, and at 220 GHz in 2015. These observations enable a better
constraint of galactic foreground emissions, as presented here. In 2015, BICEP2
was replaced by BICEP3, a 10 times higher throughput telescope observing at 95
GHz, while Keck Array is now focusing on higher frequencies. In the near
future, BICEP Array will replace Keck Array, and will allow unprecedented
sensitivity to the gravitational wave signal. High resolution observations from
the South Pole Telescope (SPT) will also be used to remove the lensing
contribution to B-modes. | The Quest for the Inflationary Spectral Runnings in the Presence of
Systematic Errors: Cosmological inflation predicts that the scalar spectral index "runs" with
scale. Constraints on the values of the spectral runnings, $\alpha_s\equiv
\textrm{d} n_s/\textrm{d}\ln k$ and $\beta_s\equiv
\textrm{d}\alpha_s/\textrm{d}\ln k$, therefore provide a fundamental test of
the physics of inflation. Here we study the feasibility of measuring the
runnings when information from upcoming large-volume galaxy surveys is used to
supplement the information provided by a CMB-S4 experiment, particularly
focusing on the effect of including high-$k$, nonlinear scales. Since these
measurements will be sensitive to modeling uncertainties for the nonlinear
power spectrum, we examine how three different ways of parameterizing those
systematics---introducing zero, two, or several hundred nuisance
parameters---affect constraints and protect against parameter biases.
Considering statistical errors alone, we find that including strongly nonlinear
scales can substantially tighten constraints. However, these constraints weaken
to levels not much better than those from a CMB-S4 experiment alone when we
limit our analysis to scales where estimates are not strongly affected by
systematic biases. Given these considerations, near-future large-scale
structure surveys are unlikely to add much information to the CMB-S4
measurement of the first running $\alpha_s$. There is more potential for
improvement for the second running, $\beta_s$, for which large-scale structure
information will allow constraints to be improved by a factor of 3--4 relative
to using the CMB alone. Though these constraints are still above the value
predicted by slow roll inflation, they do probe regions of parameter space
relevant to nonstandard inflationary models with large runnings, for example
those that can generate an appreciable abundance of primordial black holes. |
Axion minicluster power spectrum and mass function: When Peccei-Quinn (PQ) symmetry breaking happens after inflation, the axion
field takes random values in causally disconnected regions. This leads to
fluctuations of order one in the axion energy density around the QCD epoch.
These over-densities eventually decouple from the Hubble expansion and form
so-called miniclusters. We present a semi-analytical method to calculate the
average axion energy density, as well as the power spectrum, from the
re-alignment mechanism in this scenario. Furthermore, we develop a modified
Press & Schechter approach, suitable to describe the collapse of non-linear
density fluctuations during radiation domination, which is relevant for the
formation of axion miniclusters. It allows us to calculate the double
differential distribution of gravitationally collapsed miniclusters as a
function of their mass and size. For instance, assuming a PQ scale of $10^{11}$
GeV, minicluster masses range from about $5 \times 10^{-16}$ to $3 \times
10^{-13}$ solar masses and have sizes from about $4\times 10^4$ to $7\times
10^5$ km at the time they start to collapse. | The Formation of Spheroids in Early-Type Spirals: Clues From Their
Globular Clusters: We use deep Hubble Space Telescope images taken with the Advanced Camera for
Surveys (ACS) in the F475W and F814W filters to investigate the globular
cluster systems in four edge-on Sa spiral galaxies covering a factor of 4 in
luminosity. The specific frequencies of the blue globular clusters in the
galaxies in our sample fall in the range 0.34 -- 0.84, similar to typical
values found for later-type spirals. The number of red globular clusters
associated with the bulges generally increases with the bulge luminosity,
similar to what is observed for elliptical galaxies, although the specific
frequency of bulge clusters is a factor of 2-3 lower for the lowest luminosity
bulges than for the higher luminosity bulges. We present a new empirical
relation between the fraction of red globular clusters and total bulge
luminosity based on the elliptical galaxies studied by ACSVCS (ACS Virgo
Cluster Survey), and discuss how this diagram can be used to assess the
importance that dissipative processes played in building spiral bulges. Our
results suggest a picture where dissipative processes, which are expected
during gas-rich major mergers, were more important for building luminous bulges
of Sa galaxies, whereas secular evolution may have played a larger role in
building lower-luminosity bulges in spirals. |
The REFLEX galaxy cluster survey. VIII. Spectroscopic observations and
optical atlas: We present the final data from the spectroscopic survey of the ROSAT-ESO
Flux-Limited X-ray (REFLEX) catalog of galaxy clusters. The REFLEX survey
covers 4.24 steradians (34% of the entire sky) below a declination of 2.5 deg
and at high Galactic latitude (|b| > 20 deg). The REFLEX catalog includes 447
entries with a median redshift of 0.08 and is better than 90% complete to a
limiting flux fx = 3x10^{-12} erg s^{-1} cm^{-2} (0.1 to 2.4 keV), representing
the largest statistically homogeneous sample of clusters drawn from the ROSAT
All-Sky Survey (RASS) to date. Here we describe the details of the
spectroscopic observations carried out at the ESO 1.5 m, 2.2 m, and 3.6 m
telescopes, as well as the data reduction and redshift measurement techniques.
The spectra typically cover the wavelength range 3600-7500 A at a FWHM
resolution of ~14 A, and the measured redshifts have a total rms error of ~100
km s^{-1}. In total we present 1406 new galaxy redshifts in 192 clusters, most
of which previously did not have any redshift measured. Finally, the
luminosity/redshift distributions of the cluster sample and a comparison to the
no-evolution expectations from the cluster X-ray luminosity function are
presented. | Self-Similarity of $k$-Nearest Neighbor Distributions in Scale-Free
Simulations: We use the $k$-nearest neighbor probability distribution function ($k$NN-PDF,
Banerjee & Abel 2021) to assess convergence in a scale-free $N$-body
simulation. Compared to our previous two-point analysis, the $k$NN-PDF allows
us to quantify our results in the language of halos and numbers of particles,
while also incorporating non-Gaussian information. We find good convergence for
32 particles and greater at densities typical of halos, while 16 particles and
fewer appears unconverged. Halving the softening length extends convergence to
higher densities, but not to fewer particles. Our analysis is less sensitive to
voids, but we analyze a limited range of underdensities and find evidence for
convergence at 16 particles and greater even in sparse voids. |
Big Bang Nucleosynthesis: As the early universe expands and cools the rates of the weak interactions
that keep neutrinos in thermal equilibrium with the matter and the related
rates of the reactions that inter-convert neutrons and protons decrease.
Eventually, these rates fall below the expansion rate -- they freeze out.
Likewise, the rates of the strong and electromagnetic nuclear reactions that
build up and tear down nuclei, though fast enough to maintain equilibrium early
on, slow down and ultimately lead to freeze out. Together these freeze out
processes comprise the epoch of Big Bang Nucleosynthesis (BBN). The relics
emerging from this early time include the light element abundances, for example
of helium and deuterium, and a background of decoupled neutrinos, a "C$\nu$B" ,
roughly analogous to the Cosmic Microwave Background, the CMB. These fossil
relics encode the history of the physics operating in the early universe.
Consequently, BBN has emerged as a key tool for constraining new,
beyond-standard-model (BSM) physics. BBN may become an even finer probe of BSM
physics, given the anticipated higher precision in measurements of the
primordial abundances of deuterium and helium afforded by the advent of large
optical telescopes and Stage-4 CMB experiments. The latter experiments will
also provide higher precision determinations of $N_{\rm eff}$, a measure of the
relativistic energy density at the photon decoupling epoch and, hence, an
important probe of the C$\nu$B. | Mid-infrared spectroscopy of candidate AGN-dominated submillimeter
galaxies: Spitzer spectroscopy has revealed that ~80% of submm galaxies (SMGs) are
starburst (SB) dominated in the mid-infrared. Here we focus on the remaining
~20% that show signs of harboring powerful active galactic nuclei (AGN). We
have obtained Spitzer-IRS spectroscopy of a sample of eight SMGs which are
candidates for harboring powerful AGN on the basis of IRAC color-selection
(S8/S4.5>2; i.e. likely power-law mid-infrared SEDs). SMGs with an AGN
dominating (>50%) their mid-infrared emission could represent `missing link'
sources in an evolutionary sequence involving a major merger. First of all, we
detect PAH features in all of the SMGs, indicating redshifts from 2.5-3.4,
demonstrating the power of the mid-infrared to determine redshifts for these
optically faint dusty galaxies. Secondly, we see signs of both star-formation
(from the PAH features) and AGN activity (from continuum emission) in our
sample: 62% of the sample are AGN-dominated in the mid-infrared with a median
AGN content of 56%, compared with <30% on average for typical SMGs, revealing
that our IRAC color selection has successfully singled out sources with
proportionately more AGN emission than typical SB-dominated SMGs. However, we
find that only about 10% of these AGN dominate the bolometric emission of the
SMG when the results are extrapolated to longer infrared wavelengths, implying
that AGN are not a significant power source to the SMG population overall, even
when there is evidence in the mid-infrared for substantial AGN activity. When
existing samples of mid-infrared AGN-dominated SMGs are considered, we find
that S8/S4.5>1.65 works well at selecting mid-infrared energetically dominant
AGN in SMGs, implying a duty cycle of ~15% if all SMGs go through a subsequent
mid-infrared AGN-dominated phase in the proposed evolutionary sequence. |
Hamilton's Object -- a clumpy galaxy straddling the gravitational
caustic of a galaxy cluster : Constraints on dark matter clumping: We report the discovery of a 'folded' gravitationally lensed image,
'Hamilton's Object', found in a HST image of the field near the AGN SDSS
J223010.47-081017.8 ($z=0.62$). The lensed images are sourced by a galaxy at a
spectroscopic redshift of 0.8200$\pm0.0005$ and form a fold configuration on a
caustic caused by a foreground galaxy cluster at a photometric redshift of
0.526$\pm0.018$ seen in the corresponding Pan-STARRS PS1 image and marginally
detected as a faint ROSAT All-Sky Survey X-ray source. The lensed images
exhibit properties similar to those of other folds where the source galaxy
falls very close to or straddles the caustic of a galaxy cluster. The folded
images are stretched in a direction roughly orthogonal to the critical curve,
but the configuration is that of a tangential cusp. Guided by morphological
features, published simulations and similar fold observations in the
literature, we identify a third or counter-image, confirmed by spectroscopy.
Because the fold-configuration shows highly distinctive surface brightness
features, follow-up observations of microlensing or detailed investigations of
the individual surface brightness features at higher resolution can further
shed light on kpc-scale dark matter properties. We determine the local lens
properties at the positions of the multiple images according to the
observation-based lens reconstruction of Wagner et al. (2019). The analysis is
in accordance with a mass density which hardly varies on an arc-second scale (6
kpc) over the areas covered by the multiple images. | An Optimized Ly$α$ Forest Inversion Tool Based on a Quantitative
Comparison of Existing Reconstruction Methods: We present a same-level comparison of the most prominent inversion methods
for the reconstruction of the matter density field in the quasi-linear regime
from the Ly$\alpha$ forest flux. Moreover, we present a pathway for refining
the reconstruction in the framework of numerical optimization. We apply this
approach to construct a novel hybrid method. The methods which are used so far
for matter reconstructions are the Richardson-Lucy algorithm, an iterative
Gauss-Newton method and a statistical approach assuming a one-to-one
correspondence between matter and flux. We study these methods for high
spectral resolutions such that thermal broadening becomes relevant. The
inversion methods are compared on synthetic data (generated with the lognormal
approach) with respect to their performance, accuracy, their stability against
noise, and their robustness against systematic uncertainties. We conclude that
the iterative Gauss-Newton method offers the most accurate reconstruction, in
particular at small S/N, but has also the largest numerical complexity and
requires the strongest assumptions. The other two algorithms are faster,
comparably precise at small noise-levels, and, in the case of the statistical
approach, more robust against inaccurate assumptions on the thermal history of
the intergalactic medium (IGM). We use these results to refine the statistical
approach using regularization. Our new approach has low numerical complexity
and makes few assumptions about the history of the IGM, and is shown to be the
most accurate reconstruction at small S/N, even if the thermal history of the
IGM is not known. Our code will be made publicly available under
https://github.com/hmuellergoe/reglyman. |
Identifying Supermassive Black Hole Binaries with Broad Emission Line
Diagnosis: Double-peaked broad emission lines in Active Galactic Nuclei (AGNs) may
indicate the existence of a bound supermassive black hole (SMBH) binary where
two distinct broad line regions (BLRs) contribute together to the line profile.
An alternative interpretation is a disk emitter origin for the double-peaked
line profile. Using simple BLR models, we calculate the expected broad line
profile for a SMBH binary at different separations. Under reasonable
assumptions that both BLRs are illuminated by the two active SMBHs and that the
ionizing flux at the BLR location is roughly constant, we confirm the emergence
of double-peaked features and radial velocity drifts of the two peaks due to
the binary orbital motion. However, such a clear double-peaked feature only
arises in a particular stage of the binary evolution when the two BHs are close
enough such that the line-of-sight orbital velocity difference is larger than
the FWHM of the individual broad components, while the two BLRs are still
mostly distinct. Prior to this stage, the velocity splitting due to the orbit
motion of the binary is too small to separate the emission from the two BLRs,
leading to asymmetric broad line profiles in general. When the two BHs are even
closer such that the two BLRs can no longer be distinct, the line profile
becomes more complex and the splitting of the peaks does not correspond to the
orbital motion of the binary. In this regime there are no coherent radial
velocity drifts in the peaks with time. Asymmetric line profiles are probably a
far more common signature of binary SMBHs than are double-peaked profiles. We
discuss the temporal variations of the broad line profile for binary SMBHs and
highlight the different behaviors of reverberation mapping in the binary and
disk emitter cases, which may serve as a feasible tool to disentangle these two
scenarios. | Dependence of Nebular Heavy-Element Abundance on H I Content for Spiral
Galaxies: We analyze the galactic H I content and nebular log(O/H) for 60 spiral
galaxies in the Moustakas et al. (2006) spectral catalog. After correcting for
the mass-metallicity relationship, we show that the spirals in cluster
environments show a positive correlation for log(O/H) on DEF, the galactic H I
deficiency parameter, extending the results of previous analyses of the Virgo
and Pegasus I clusters. Additionally, we show for the first time that galaxies
in the field obey a similar dependence. The observed relationship between H I
deficiency and galactic metallicity resembles similar trends shown by
cosmological simulations of galaxy formation including inflows and outflows.
These results indicate the previously observed metallicity-DEF correlation has
a more universal interpretation than simply a cluster's effects on its member
galaxies. Rather, we observe in all environments the stochastic effects of
metal-poor infall as minor mergers and accretion help to build giant spirals. |
A new light boson from MAGIC observations?: Recent detection of blazar 3C279 by MAGIC has confirmed previous indications
by H.E.S.S. that the Universe is more transparent to very-high-energy gamma
rays than currently thought. This circumstance can be reconciled with
observations of nearby blazars provided that photon oscillations into a very
light Axion-Like Particle occur in extragalactic magnetic fields. The emerging
"DARMA scenario" can be tested in the near future by the satellite-borne Fermi
LAT detector as well as by the ground-based Imaging Atmospheric Cherenkov
Telescopes H.E.S.S., MAGIC, CANGAROO III, VERITAS and by the Extensive Air
Shower arrays ARGO-YBJ and MILAGRO. | The stellar populations of massive galaxies in the local Universe: I present a brief review of the stellar population properties of massive
galaxies, focusing on early-type galaxies in particular, with emphasis on
recent results from the ATLAS3D Survey. I discuss the occurrence of young
stellar ages, cold gas, and ongoing star formation in early-type galaxies, the
presence of which gives important clues to the evolutionary path of these
galaxies. Consideration of empirical star formation histories gives a
meaningful picture of galaxy stellar population properties, and allows accurate
comparison of mass estimates from populations and dynamics. This has recently
provided strong evidence of a non-universal IMF, as supported by other recent
evidences. Spatially-resolved studies of stellar populations are also crucial
to connect distinct components within galaxies to spatial structures seen in
other wavelengths or parameters. Stellar populations in the faint outer
envelopes of early-type galaxies are a formidable frontier for observers, but
promise to put constraints on the ratio of accreted stellar mass versus that
formed 'in situ' - a key feature of recent galaxy formation models. Galaxy
environment appears to play a key role in controlling the stellar population
properties of low mass galaxies. Simulations remind us, however, that current
day galaxies are the product of a complex assembly and environment history,
which gives rise to the trends we see. This has strong implications for our
interpretation of environmental trends. |
Effects of Coupled Dark Energy on the Milky Way and its Satellites: We present the first numerical simulations in coupled dark energy cosmologies
with high enough resolution to investigate the effects of the coupling on
galactic and sub-galactic scales. We choose two constant couplings and a
time-varying coupling function and we run simulations of three Milky-Way-size
halos ($\sim$10$^{12}$M$_{\odot}$), a lower mass halo
(6$\times$10$^{11}$M$_{\odot}$) and a dwarf galaxy halo
(5$\times$10$^{9}$M$_{\odot}$). We resolve each halo with several millions dark
matter particles. On all scales the coupling causes lower halo concentrations
and a reduced number of substructures with respect to LCDM. We show that the
reduced concentrations are not due to different formation times, but they are
related to the extra terms that appear in the equations describing the
gravitational dynamics. On the scale of the Milky Way satellites, we show that
the lower concentrations can help in reconciling observed and simulated
rotation curves, but the coupling values necessary to have a significant
difference from LCDM are outside the current observational constraints. On the
other hand, if other modifications to the standard model allowing a higher
coupling (e.g. massive neutrinos) are considered, coupled dark energy can
become an interesting scenario to alleviate the small-scale issues of the LCDM
model. | The Impact of Magnification and Size Bias on Weak Lensing Power Spectrum
and Peak Statistics: The weak lensing power spectrum is a powerful tool to probe cosmological
parameters. Additionally, lensing peak counts contain cosmological information
beyond the power spectrum. Both of these statistics can be affected by the
preferential selection of source galaxies in patches of the sky with high
magnification, as well as by the dilution in the source galaxy surface density
in such regions. If not accounted for, these biases introduce systematic errors
for cosmological measurements. Here we quantify these systematic errors, using
convergence maps from a suite of ray-tracing N-body simulations. At the cut-off
magnitude m of on-going and planned major weak lensing surveys, the logarithmic
slope of the cumulative number counts s = dlog[n(>m)]/dlog(m) is in the range
0.1 < s < 0.5. At s = 0.2, expected in the I band for LSST, the inferred values
of Omega_m, w and sigma_8 are biased by many sigma (where sigma denotes the
marginalized error) and therefore the biases will need to be carefully modeled.
We also find that the parameters are biased differently in the (Omega_m, w,
sigma_8) parameter space when the power spectrum and when the peak counts are
used. In particular, w derived from the power spectrum is less affected than w
derived from peak counts, while the opposite is true for the best-constrained
combination of [sigma_8 Omega_m^gamma] (with gamma=0.62 from the power spectrum
and gamma = 0.48 from peak counts). This suggests that the combination of the
power spectrum and peak counts can help mitigate the impact of magnification
and size biases. |
The ionization mechanism of NGC 185: how to fake a Seyfert galaxy?: NGC 185 is a dwarf spheroidal satellite of the Andromeda galaxy. From
mid-1990s onwards it was revealed that dwarf spheroidals often display a varied
and in some cases complex star formation history. In an optical survey of
bright nearby galaxies, NGC 185 was classified as a Seyfert galaxy based on its
emission line ratios. However, although the emission lines in this object
formally place it in the category of Seyferts, it is probable that this galaxy
does not contain a genuine active nucleus. NGC 185 was not detected in radio
surveys either in 6 or 20 cm, or X-ray observations, which means that the
Seyfert-like line ratios may be produced by stellar processes. In this work, we
try to identify the possible ionization mechanisms for this galaxy. We
discussed the possibility of the line emissions being produced by planetary
nebulae (PNe), using deep spectroscopy observations obtained with GMOS-N, at
Gemini. Although the fluxes of the PNe are high enough to explain the
integrated spectrum, the line ratios are very far from the values for the
Seyfert classification. We then proposed that a mixture of supernova remnants
and PNe could be the source of the ionization, and we show that a composition
of these two objects do mimic Seyfert-like line ratios. We used chemical
evolution models to predict the supernova rates and to support the idea that
these supernova remnants should be present in the galaxy. | Pantheon update on a model-independent analysis of cosmological
supernova data: We present an update of our previous work, necessitated by availability of a
significantly improved dataset. The work is a model-independent analysis of the
cosmological supernova (Type Ia) data, where function families are fit to the
data in form of luminosity distance as function of redshift, that is,
$d_{L}(z)$; and subsequently time-derivatives of the scale function $a(t)$ are
$analytically$ derived, but as functions of $z$, without making assumptions
about of gravity or the contents of the universe. This gives, e.g. the redshift
value at which the universe goes over from deceleration to acceleration, as
$z_{t}=0.54 \pm 0.04$ for a flat universe. In the update, we switch to a more
modern fit criterion and also take into account the uncertainty in the
calibration of the SNIa luminosities.
If a theory of gravity $is$ assumed, our results allow determination of the
density of the universe as function of $z$, from which conclusions about the
contents of the universe can be drawn. We update the previous work's result
where this was done for Einstein gravity, finding a lower-limit on the dark
energy fraction, $\Omega_{DE}>0.46$; and here we do this also for Starobinsky
gravity, where we can find a Starobinsky parameter that can eliminate the need
for dark energy. |
A 2D multiwavelength study of the ionized gas and stellar population in
the Giant HII Region NGC 588: (ABRIDGED) We present an analysis of NGC588 based on IFS data with PMAS,
together with Spitzer images at 8 mi and 24 mi. The extinction distribution in
the optical shows complex structure, with maxima correlating in position with
those of the emission at 24 mi and 8 mi. The Ha luminosity absorbed by the dust
within the GHIIR reproduces the structure observed in the 24 mi image,
supporting the use of this band as a tracer of recent star formation. A
velocity difference of ~50 km/s was measured between the areas of high and low
surface brightness, which would be expected if NGC588 were an evolved GHIIR.
Line ratios used in the BPT diagnostic diagrams show a larger range of
variation in the low surface brightness areas. The ranges are ~0.5 to 1.2 dex
for [NII]/Ha, 0.7 to 1.7 dex for [SII]/Ha, and 0.3 to 0.5 dex for [OIII]/Hb.
Ratios corresponding to large ionization parameter (U) are found between the
peak of the emission in Hb and the main ionizing source decreasing radially
outwards within the region. Differences between the integrated and local values
of the U tracers can be as high as ~0.8 dex. [OII]/Hb and [OIII]/[OII] yield
similar local values for U and consistent with those expected from the
integrated spectrum of an HII region ionized by a single star. The ratio
[SII]/Ha departs significantly from the range predicted by this scenario,
indicating the complex ionization structure in GHIIRs. There is a significant
scatter in derivations of Z using strong line tracers as a function of
position, caused by variations in the degree of ionization. The scatter is
smaller for N2O3 which points to this tracer as a better Z tracer than N2. The
comparison between integrated and local line ratio values indicates that
measurements of the line ratios of GHIIR in galaxies at distances >~25 Mpc may
be dominated by the ionization conditions in their low surface brightness
areas. | Neutrino emission from dark matter annihilation/decay in light of cosmic
$e^{\pm}$ and $\bar{p}$ data: A self-consistent global fitting method based on the Markov Chain Monte Carlo
technique to study the dark matter (DM) property associated with the cosmic ray
electron/positron excesses was developed in our previous work. In this work we
further improve the previous study to include the hadronic branching ratio of
DM annihilation/decay. The PAMELA $\bar{p}/p$ data are employed to constrain
the hadronic branching ratio. We find that the 95% ($2\sigma$) upper limits of
the quark branching ratio allowed by the PAMELA $\bar{p}/p$ data is $\sim
0.032$ for DM annihilation and $\sim 0.044$ for DM decay respectively. This
result shows that the DM coupling to pure leptons is indeed favored by the
current data. Based on the global fitting results, we further study the
neutrino emission from DM in the Galactic center. Our predicted neutrino flux
is some smaller than previous works since the constraint from $\gamma$-rays is
involved. However, it is still capable to be detected by the forth-coming
neutrino detector such as IceCube. The improved points of the present study
compared with previous works include: 1) the DM parameters, both the particle
physical ones and astrophysical ones, are derived in a global fitting way, 2)
constraints from various species of data sets, including $\gamma$-rays and
antiprotons are included, and 3) the expectation of neutrino emission is fully
self-consistent. |
Modified holographic dark energy in DGP brane world: In this paper, the cosmological dynamics of a modified holographic dark
energy which is derived from the UV/IR duality by considering the black hole
mass in higher dimensions as UV cutoff, is investigated in
Dvali-Gabadaze-Porrati (DGP) brane world model. We choose Hubble horizon and
future event horizon as IR cutoff respectively. And the two branches of the DGP
model are both taken into account. When Hubble horizon is considered as IR
cutoff, the modified holographic dark energy (HDE) behaves like an effect dark
energy that modification of gravity in pure DGP brane world model acts and it
can drive the expansion of the universe speed up at late time in $\epsilon=-1$
branch which in pure DGP model can not undergo an accelerating phase. When
future event horizon acts as IR cutoff, the equation of state parameter of the
modified HDE can cross the phantom divide. | The Very Young Type Ia Supernova 2012cg: Discovery and Early-Time
Follow-Up Observations: On 2012 May 17.2 UT, only 1.5 +/- 0.2 d after explosion, we discovered SN
2012cg, a Type Ia supernova (SN Ia) in NGC 4424 (d ~ 15 Mpc). As a result of
the newly modified strategy employed by the Lick Observatory SN Search, a
sequence of filtered images was obtained starting 161 s after discovery.
Utilizing recent models describing the interaction of SN ejecta with a
companion star, we rule out a ~1 M_Sun companion for half of all viewing angles
and a red-giant companion for nearly all orientations. SN 2012cg reached a
B-band maximum of 12.09 +/- 0.02 mag on 2012 June 2.0 and took ~17.3 d from
explosion to reach this, typical for SNe Ia. Our pre-maximum brightness
photometry shows a narrower-than-average B-band light curve for SN 2012cg,
though slightly overluminous at maximum brightness and with normal color
evolution (including some of the earliest SN Ia filtered photometry ever
obtained). Spectral fits to SN 2012cg reveal ions typically found in SNe Ia at
early times, with expansion velocities >14,000 km/s at 2.5 d past explosion.
Absorption from C II is detected early, as well as high-velocity components of
both Si II 6355 Ang. and Ca II. Our last spectrum (13.5 d past explosion)
resembles that of the somewhat peculiar SN Ia 1999aa. This suggests that SN
2012cg will have a slower-than-average declining light curve, which may be
surprising given the faster-than-average rising light curve. |
Dark Stars: a new look at the First Stars in the Universe: We have proposed that the first phase of stellar evolution in the history of
the Universe may be Dark Stars (DS), powered by dark matter heating rather than
by nuclear fusion, and in this paper we examine the history of these DS. The
power source is annihilation of Weakly Interacting Massive Particles (WIMPs)
which are their own antiparticles. These WIMPs are the best motivated dark
matter (DM) candidates and may be discovered by ongoing direct or indirect
detection searches (e.g. FERMI /GLAST) or at the Large Hadron Collider at CERN.
A new stellar phase results, powered by DM annihilation as long as there is DM
fuel, from millions to billions of years. We build up the dark stars from the
time DM heating becomes the dominant power source, accreting more and more
matter onto them. We have included many new effects in the current study,
including a variety of particle masses and accretion rates, nuclear burning,
feedback mechanisms, and possible repopulation of DM density due to capture.
Remarkably, we find that in all these cases, we obtain the same result: the
first stars are very large, 500-1000 times as massive as the Sun; as well as
puffy (radii 1-10 A.U.), bright ($10^6-10^7 L_\odot$), and cool ($T_{surf} <
$10,000 K) during the accretion. These results differ markedly from the
standard picture in the absence of DM heating. Hence DS should be
observationally distinct from standard Pop III stars. In addition, DS avoid the
(unobserved) element enrichment produced by the standard first stars. Once the
dark matter fuel is exhausted, the DS becomes a heavy main sequence star; these
stars eventually collapse to form massive black holes that may provide seeds
for the supermassive black holes and intermediate black holes, and explain
ARCADE data. | Seeding Supermassive Black Holes with Self-Interacting Dark Matter: A
Unified Scenario with Baryons: Observations show that supermassive black holes (SMBHs) with a mass of
$\sim10^9 M_\odot$ exist when the Universe is just $6\%$ of its current age. We
propose a scenario where a self-interacting dark matter halo experiences
gravothermal instability and its central region collapses into a seed black
hole. The presence of baryons in protogalaxies could significantly accelerate
the gravothermal evolution of the halo and shorten collapse timescales. The
central halo could dissipate its angular momentum remnant via viscosity induced
by the self-interactions. The host halo must be on high tails of density
fluctuations, implying that high-$z$ SMBHs are expected to be rare in this
scenario. We further derive conditions for triggering general relativistic
instability of the collapsed region. Our results indicate that self-interacting
dark matter can provide a unified explanation for diverse dark matter
distributions in galaxies today and the origin of SMBHs at redshifts
$z\sim6-7$. |
Scalar-Scalar, Scalar-Tensor, and Tensor-Tensor Correlators from
Anisotropic Inflation: We compute the phenomenological signatures of a model (Watanabe et al' 09) of
anisotropic inflation driven by a scalar and a vector field. The action for the
vector is U(1) invariant, and the model is free of ghost instabilities. A
suitable coupling of the scalar to the kinetic term of the vector allows for a
slow roll evolution of the vector vev, and hence for a prolonged anisotropic
expansion; this provides a counter example to the cosmic no hair conjecture. We
compute the nonvanishing two point correlation functions between physical modes
of the system, and express them in terms of power spectra with angular
dependence. The anisotropy parameter g_* for the scalar-scalar spectrum
(defined as in the Ackerman et al '07 parametrization) turns out to be negative
in the simplest realization of the model, which, therefore, cannot account for
the angular dependence emerged in some analyses of the WMAP data. A g_* of
order -0.1 is achieved when the energy of the vector is about 6-7 orders of
magnitude smaller than that of the scalar during inflation. For such values of
the parameters, the scalar-tensor correlation (which is in principle a
distinctive signature of anisotropic spaces) is smaller than the tensor-tensor
correlation. | New Constraints on Anisotropic Expansion from Supernovae Type Ia: We re-examine the contentious question of constraints on anisotropic
expansion from Type Ia supernovae (SNIa) in the light of a novel determination
of peculiar velocities, which are crucial to test isotropy with supernovae out
to distances $\lesssim 200/h$ Mpc. We re-analyze the Joint Light-Curve Analysis
(JLA) Supernovae (SNe) data, improving on previous treatments of peculiar
velocity corrections and their uncertainties (both statistical and systematic)
by adopting state-of-the-art flow models constrained independently via the
2M$++$ galaxy redshift compilation. We also introduce a novel procedure to
account for colour-based selection effects, and adjust the redshift of low-$z$
SNe self-consistently in the light of our improved peculiar velocity model.
We adopt the Bayesian hierarchical model \texttt{BAHAMAS} to constrain a
dipole in the distance modulus in the context of the $\Lambda$CDM model and the
deceleration parameter in a phenomenological Cosmographic expansion. We do not
find any evidence for anisotropic expansion, and place a tight upper bound on
the amplitude of a dipole, $|D_\mu| < 5.93 \times 10^{-4}$ (95\% credible
interval) in a $\Lambda$CDM setting, and $|D_{q_0}| < 6.29 \times 10^{-2}$ in
the Cosmographic expansion approach. Using Bayesian model comparison, we obtain
posterior odds in excess of 900:1 (640:1) against a constant-in-redshift dipole
for $\Lambda$CDM (the Cosmographic expansion). In the isotropic case, an
accelerating universe is favoured with odds of $\sim 1100:1$ with respect to a
decelerating one. |
Phenomenology of fermion production during axion inflation: We study the production of fermions through a derivative coupling with a
pseudoscalar inflaton and the effects of the produced fermions on the scalar
primordial perturbations. We present analytic results for the modification of
the scalar power spectrum due to the produced fermions, and we estimate the
amplitude of the non-Gaussianities in the equilateral regime. Remarkably, we
find a regime where the effect of the fermions gives the dominant contribution
to the scalar spectrum while the amplitude of the bispectrum is small and in
agreement with observation. We also note the existence of a regime in which the
backreaction of the fermions on the evolution of the zero-mode of the inflaton
can lead to inflation even if the potential of the inflaton is steep and does
not satisfy the slow-roll conditions. | On the Primordial Black Hole Mass Function for Broad Spectra: We elaborate on the mass function of primordial black holes in the case in
which the power spectrum of the curvature perturbation is broad. For the case
of a broad and flat spectrum, we argue that such a mass function is peaked at
the smallest primordial black mass which can be formed and possesses a tail
decaying like $M^{-3/2}$, where $M$ is the mass of the primordial black hole. |
Investigating the effect of cosmic opacity on standard candles: Standard candles can probe the evolution of dark energy in a large redshift
range. But the cosmic opacity can degrade the quality of standard candles. In
this paper, we use the latest observations, including type Ia supernovae (SNe
Ia) from JLA sample and Hubble parameters, to probe the opacity of the
universe. In order to avoid the cosmological dependence of SNe Ia luminosity
distances, a joint fitting of the SNe Ia light-curve parameters, cosmological
parameters and opacity is used. In order to explore the cosmic opacity at high
redshifts, the latest gamma-ray bursts (GRBs) are used. At high redshifts,
cosmic reionization process is considered. We find that the sample supports an
almost transparent universe for flat $\Lambda$CDM and XCDM models. Meanwhile,
free electrons deplete photons from standard candles through the (inverse)
Compton scattering, known as an important component of opacity. This Compton
dimming may paly an important role in future supernova surveys. From analysis,
we find that about a few percent cosmic opacity is caused by Compton dimming in
the two models, which can be correctable. | GMRT 610 MHz observations of galaxy clusters in the ACT equatorial
sample: We present Giant Metrewave Radio Telescope 610 MHz observations of 14 Atacama
Cosmology Telescope (ACT) clusters, including new data for nine. The sample
includes 73\% of ACT equatorial clusters with $M_{500} > 5 \times
10^{14}\;M_\odot$. We detect diffuse emission in three of these
(27$^{+20}_{-14}$\%): we detect a radio mini-halo in ACT-CL J0022.2$-$0036 at
$z=0.8$, making it the highest-redshift mini-halo known; we detect potential
radio relic emission in ACT-CL J0014.9$-$0057 ($z=0.533$); and we confirm the
presence of a radio halo in low-mass cluster ACT-CL J0256.5+0006, with flux
density $S_{610} = 6.3\;\pm\;0.4$ mJy. We also detect residual diffuse emission
in ACT-CL J0045.9$-$0152 ($z=0.545$), which we cannot conclusively classify.
For systems lacking diffuse radio emission, we determine radio halo upper
limits in two ways and find via survival analysis that these limits do not
significantly affect radio power scaling relations. Several clusters with no
diffuse emission detection are known or suspected mergers, based on archival
X-ray and/or optical measures; given the limited sensitivity of our
observations, deeper observations of these disturbed systems are required in
order to rule out the presence of diffuse emission consistent with known
scaling relations. In parallel with our diffuse emission results, we present
catalogs of individual radio sources, including a few interesting extended
sources. Our study represents the first step towards probing the occurrence of
diffuse emission in high-redshift ($z\gtrsim0.5$) clusters, and serves as a
pilot for statistical studies of larger cluster samples with the new radio
telescopes available in the pre-SKA era. |
Scalar Weak Gravity Conjecture in Super Yang-Mills Inflationary Model: In this article, we want to check four inflation models, such as composite
NJL inflation (NJLI), Glueball inflation(GI), super Yang-Mills inflation
(SYMI), and Orientifold inflation (OI), with two conjectures of the swampland
program: scalar weak gravity conjecture (SWGC) and strong scalar weak gravity
conjecture (SSWGC) since all these models violate the dS swampland
conjecture(DSC) but are compatible with further refining de Sitter swampland
conjecture (FRDSSC) through manual adjustment of free parameters of the
mentioned conjecture. We want to study the simultaneous compatibility of each
model with these two new conjectures. Despite being consistent with (FRDSSC),
we find that all models are not compatible with the other conjectures of the
Swampland program in all regions, and these conjectures are only satisfied in a
specific area. Also, due to the presence of constant parameter $(\phi_{0})$ in
the higher orders derivatives, the (SYMI) and (OI) among all the models are
more compatible with all conjectures of the swampland program. These models can
provide a more significant amount of satisfaction with all of them. They can be
suitable and accurate inflation models for a more profound examination of
universe developments. We determined a particular region for these models is
compatible with (FRDSSC), (SWGC), and (SSWGC) simultaneously | One-electron atoms in screened modified gravity: In a large class of scalar-tensor theories that are potential candidates for
dark energy, a nonminimal coupling between the scalar and the photon is
possible. The presence of such an interaction grants us the exciting prospect
of directly observing dark sector phenomenology in the electromagnetic
spectrum. This paper investigates the behavior of one-electron atoms in this
class of modified gravity models, exploring their viability as probes of
deviations from general relativity in both laboratory and astrophysical
settings. Building heavily on earlier studies, our main contribution is
threefold: A thorough analysis finds additional fine-structure corrections
previously unaccounted for, which now predict a contribution to the Lamb shift
that is larger by nearly 4 orders of magnitude. In addition, they also predict
a scalar-mediated photon-photon interaction, which now constrains the scalar's
coupling to the photon independently of the matter coupling. This was not
previously possible with atomic precision tests. Our updated constraints are
$\log_{10}\beta_m \lesssim 13.4$ and $\log_{10}\beta_\gamma \lesssim 19.0$ for
the matter and photon coupling, respectively, although these remain
uncompetitive with bounds from other experiments. Second, we include the
effects of the nuclear magnetic moment, allowing for the study of hyperfine
structure and the 21 cm line, which hitherto have been unexplored in this
context. Finally, we also examine how a background scalar leads to equivalence
principle violations. |
Gas Condensation in the Galactic Halo: Using adaptive mesh refinement (AMR) hydrodynamic simulations of vertically
stratified hot halo gas, we examine the conditions under which clouds can form
and condense out of the hot halo medium to potentially fuel star formation in
the gaseous disk. We find that halo clouds do not develop from linear isobaric
perturbations. This is a regime where the cooling time is longer than the
Brunt-Vaisala time, confirming previous linear analysis. We extend the analysis
into the nonlinear regime by considering mildly or strongly nonlinear
perturbations with overdensities up to 100, also varying the initial height,
the cloud size, and the metallicity of the gas. Here, the result depends on the
ratio of cooling time to the time required to accelerate the cloud to the sound
speed (similar to the dynamical time). If the ratio exceeds a critical value
near unity, the cloud is accelerated without further cooling and gets disrupted
by Kelvin-Helmholtz and/or Rayleigh-Taylor instabilities. If it is less than
the critical value, the cloud cools and condenses before disruption. Accreting
gas with overdensities of 10-20 is expected to be marginally unstable; the
cooling fraction will depend on the metallicity, the size of the incoming
cloud, and the distance to the galaxy. Locally enhanced overdensities within
cold streams have a higher likelihood of cooling out. Our results have
implications on the evolution of clouds seeded by cold accretion that are
barely resolved in current cosmological hydrodynamic simulations and absorption
line systems detected in galaxy halos. | Characterisation of the non-Gaussianity of radio and IR point-sources at
CMB frequencies: This study, using publicly available simulations, focuses on the
characterisation of the non-Gaussianity produced by radio point sources and by
infrared (IR) sources in the frequency range of the cosmic microwave background
from 30 to 350 GHz. We propose a simple prescription to infer the angular
bispectrum from the power spectrum of point sources considering independent
populations of sources, with or without clustering. We test the accuracy of our
prediction using publicly available all-sky simulations of radio and IR sources
and find very good agreement. We further characterise the configuration
dependence and the frequency behaviour of the IR and radio bispectra. We show
that the IR angular bispectrum peaks for squeezed triangles and that the
clustering of IR sources enhances the bispectrum values by several orders of
magnitude at scales l \sim 100. At 150 GHz the bispectrum of IR sources starts
to dominate that of radio sources on large angular scales, and it dominates
over the whole multipole range at 350 GHz. Finally, we compute the bias on f_NL
induced by radio and IR sources. We show that the positive bias induced by
radio sources is significantly reduced by masking the sources. We also show,
for the first time, that the form of the IR bispectrum mimics a primordial
'local' bispectrum f_NL. The IR sources produce a negative bias which becomes
important for Planck-like resolution and at high frequencies (Delta f_NL ~ -6
at 277 GHz and Delta f_NL \sim -60-70 at 350 GHz). Most of the signal being due
to the clustering of faint IR sources, the bias Delta f_NL^IR is not reduced by
masking sources above a flux limit and may, in some cases, even be increased
due to the reduction of the shot-noise term. |
Gamma-ray cosmology and fundamental physics with TeV blazars: results
from 20 years of observations: Gamma rays from TeV blazars have been detected by ground-based experiments
for more than two decades. We have collected the most extensive set of archival
spectra from these sources in order to constrain the processes affecting
gamma-ray propagation on cosmological distances. We discuss our results on the
diffuse photon field that populates universe, called the extragalactic
background light, on the expansion rate of the Universe, and on fundamental
physics in the form of axion-like particles and Lorentz-invariance violation.
Specifically, we present a spectrum of the extragalactic background light from
0.26 to 105 microns constructed from the gamma-ray observations, we measure a
value of the Hubble constant compatible with other estimates, and we constrain
the energy scale at which Lorentz-invariance violation impacts gamma-ray
absorption by the extragalactic background light to be larger than sixty
percent of the Planck scale. | A WFC3 study of globular clusters in NGC 4150 - an early-type minor
merger: We combine near-ultraviolet (NUV; 2250 {\AA}) and optical (U, B, V, I)
imaging from the Wide Field Camera 3 (WFC3), on board the Hubble Space
Telescope (HST), to study the globular cluster (GC) population in NGC 4150, a
sub-L* (M_B ~ -18.48 mag) early-type minor-merger remnant in the Coma I cloud.
We use broadband NUV-optical photometry from the WFC3 to estimate individual
ages, metallicities, masses and line-of-sight extinctions [E_(B-V)] for 63
bright (M_V < -5 mag) GCs in this galaxy. In addition to a small GC population
with ages greater than 10 Gyr, we find a dominant population of clusters with
ages centred around 6 Gyr, consistent with the expected peak of stellar mass
assembly in faint early-types residing in low-density environments. The old and
intermediate-age GCs in NGC 4150 are metal-poor, with metallicities less than
0.1 ZSun, and reside in regions of low extinction (E_(B-V) < 0.05 mag). We also
find a population of young, metal-rich (Z > 0.3 ZSun) clusters that have formed
within the last Gyr and reside in relatively dusty (E_(B-V) > 0.3 mag) regions
that are coincident with the part of the galaxy core that hosts significant
recent star formation. Cluster disruption models (in which ~80-90% of objects
younger than a few 10^8 yr dissolve every dex in time) suggest that the bulk of
these young clusters are a transient population. |
Systematic X-ray Analysis of Radio Relic Clusters with SUZAKU: We perform a systematic X-ray analysis of six giant radio relics in four
clusters of galaxies using the Suzaku satellite. The sample includes CIZA
2242.8-5301, Zwcl 2341.1-0000, the South-East part of Abell 3667 and previously
published results of the North-West part of Abell 3667 and Abell 3376.
Especially we first observed the narrow (50 kpc) relic of CIZA 2242.8-5301 by
Suzaku satellite, which enable us to reduce the projection effect. We report
X-ray detections of shocks at the position of the relics in CIZA2242.8-5301 and
Abell 3667 SE. At the position of the two relics in ZWCL2341.1-0000, we do not
detect shocks. From the spectroscopic temperature profiles across the relic, we
find that the temperature profiles exhibit significant jumps across the relics
for CIZA 2242.8-5301, Abell 3376, Abell 3667NW, and Abell 3667SE. We estimated
the Mach number from the X-ray temperature or pressure profile using the
Rankine-Hugoniot jump condition and compared it with the Mach number derived
from the radio spectral index. The resulting Mach numbers (M=1.5-3) are almost
consistent with each other, while the Mach number of CIZA2242 derived from the
X-ray data tends to be lower than that of the radio observation. These results
indicate that the giant radio relics in merging clusters are related to the
shock structure, as suggested by previous studies of individual clusters. | The Outer Rim Simulation: A Path to Many-Core Supercomputers: We describe the Outer Rim cosmological simulation, one of the largest
high-resolution N-body simulations performed to date, aimed at promoting
science to be carried out with large-scale structure surveys. The simulation
covers a volume of (4.225Gpc)^3 and evolves more than one trillion particles.
It was executed on Mira, a BlueGene/Q system at the Argonne Leadership
Computing Facility. We discuss some of the computational challenges posed by a
system like Mira, a many-core supercomputer, and how the simulation code, HACC,
has been designed to overcome these challenges. We have carried out a large
range of analyses on the simulation data and we report on the results as well
as the data products that have been generated. The full data set generated by
the simulation totals more than 5PB of data, making data curation and data
handling a large challenge in of itself. The simulation results have been used
to generate synthetic catalogs for large-scale structure surveys, including
DESI and eBOSS, as well as CMB experiments. A detailed catalog for the LSST
DESC data challenges has been created as well. We publicly release some of the
Outer Rim halo catalogs, downsampled particle information, and lightcone data. |
The part and the whole: voids, supervoids, and their ISW imprint: The integrated Sachs-Wolfe imprint of extreme structures in the cosmic web
probes the dynamical nature of dark energy. Looking through typical cosmic
voids, no anomalous signal has been reported. On the contrary, supervoids,
associated with large-scale fluctuations in the gravitational potential, have
shown potentially disturbing excess signals. In this study, we used the Jubilee
ISW simulation to demonstrate how the stacked signal depends on the void
definition. We found that large underdensities, with at least $\approx5$ merged
sub-voids, show a peculiar ISW imprint shape with central cold spots and
surrounding hot rings, offering a natural way to define supervoids in the
cosmic web. We then inspected the real-world BOSS DR12 data using the simulated
imprints as templates. The imprinted profile of BOSS supervoids appears to be
more compact than in simulations, requiring an extra $\alpha \approx 0.7$
re-scaling of filter sizes. The data reveals an excess ISW-like signal with
$A_{\rm ISW}\approx9$ amplitude at the $\approx2.5\sigma$ significance level,
unlike previous studies that used isolated voids and reported good consistency
with $A_{\rm ISW}=1$. The tension with the Jubilee-based $\Lambda$CDM
predictions is $\sim 2\sigma$, in consistency with independent analyses of
supervoids in Dark Energy Survey data. We show that such a very large
enhancement of the $A_{\rm ISW}$ parameter hints at a possible causal relation
between the CMB Cold Spot and the Eridanus supervoid. The origin of these
findings remains unclear. | Relic gravitational waves from the chiral magnetic effect: Relic gravitational waves (GWs) can be produced by primordial magnetic
fields. However, not much is known about the resulting GW amplitudes and their
dependence on the details of the generation mechanism. Here we treat magnetic
field generation through the chiral magnetic effect (CME) as a generic
mechanism and explore its dependence on the speed of generation (the product of
magnetic diffusivity and characteristic wavenumber) and the speed
characterizing the maximum magnetic field strength expected from the CME. When
the latter exceeds the former (regime I), the regime applicable to the early
universe, we obtain an inverse cascade with moderate GW energy that scales with
the third power of the magnetic energy. When the generation speed exceeds the
CME limit (regime II), the GW energy continues to increase without a
corresponding increase of magnetic energy. In the early kinematic phase, the GW
energy spectrum (per linear wavenumber interval) has opposite slopes in both
regimes and is characterized by an inertial range spectrum in regime I and a
white noise spectrum in regime II. The occurrence of these two slopes is shown
to be a generic consequence of a nearly monochromatic exponential growth of the
magnetic field. The resulting GW energy is found to be proportional to the
fifth power of the limiting CME speed and the first power of the generation
speed. |
Co-evolution of the Brightest Cluster Galaxies and their Host Clusters
in IllustrisTNG: We use the IllustrisTNG simulations to explore the dynamic scaling relation
between massive clusters and their central galaxies (BCGs). The Illustris
TNG300-1 simulation we use includes 280 massive clusters with $M_{200} >
10^{14}$ M$_{\odot}$ enabling a robust statistical analysis. We derive the
line-of-sight velocity dispersion of the stellar particles of the BCGs
($\sigma_{*, BCG}$), analogous to the observed BCG stellar velocity dispersion.
We also compute the subhalo velocity dispersion to measure the cluster velocity
dispersion ($\sigma_{cl}$). Both $\sigma_{*, BCG}$ and $\sigma_{cl}$ are
proportional to the cluster halo mass, but the slopes differ slightly. Thus
like the observed relation, $\sigma_{*, BCG} / \sigma_{cl}$ declines as a
function of $\sigma_{cl}$, but the scatter is large. We explore the redshift
evolution of $\sigma_{*, BCG} - \sigma_{cl}$ scaling relation for $z \lesssim
1$ in a way that can be compared directly with observations. The scaling
relation has a similar slope at high redshift, but the scatter increases
because of the large scatter in $\sigma_{*, BCG}$. The simulations imply that
high redshift BCGs are dynamically more complex than their low redshift
counterparts. | Warm Decaying Dark Matter and the Hubble Tension: If a fraction of the dark matter is unstable and decays into dark radiation
at around the time of matter-radiation equality, it could impact the expansion
history of the universe in a way that helps to ameliorate the long-standing
tension between the locally measured value of the Hubble constant and the value
inferred from measurements of the cosmic microwave background and baryon
acoustic oscillations (assuming standard $\Lambda$CDM cosmology). If this
component of decaying dark matter is cold, however, it will modify the
evolution of the gravitational potentials, leading to inconsistencies with
these same data sets. With this in mind, we consider here a component of
decaying warm dark matter, with a free-streaming length that is long enough to
remain consistent with existing data. We study the background and perturbation
evolution of warm decaying dark matter, and use cosmological data to constrain
the mass, abundance and decay rate of such a particle. We find that a component
of warm decaying dark matter can significantly reduce the tension between local
and cosmological determinations of the Hubble constant. |
The Point of Origin of the Radio Radiation from the Unresolved Cores of
Radio-Loud Quasars: Locating the exact point of origin of the core radiation in active galactic
nuclei (AGN) would represent important progress in our understanding of
physical processes in the central engine of these objects. However, due to our
inability to resolve the region containing both the central compact object and
the jet base, this has so far been difficult. Here, using an analysis in which
the lack of resolution does not play a significant role, we demonstrate that it
may be impossible even in most radio loud sources for more than a small
percentage of the core radiation at radio wavelengths to come from the jet
base. We find for 3C279 that $\sim85$ percent of the core flux at 15 GHz must
come from a separate, reasonably stable, region that is not part of the jet
base, and that then likely radiates at least quasi-isotropically and is
centered on the black hole. The long-term stability of this component also
suggests that it may originate in a region that extends over many Schwarzschild
radii. | A Universe without Dark Energy and Dark Matter: The universe has evolved to be a filamentary web of galaxies and large
inter-galactic zones of space without matter. The Euclidian nature of the
universe indicates that it is not a 3D manifold within space with an extra
spatial dimension. This justifies our assumption that the FRW space-time
evolves in the inter-galactic zones like separate FRW universes. Thus we do not
necessarily have to consider the entirety of the universe. Our assumption
enables us to prove that: -In the current epoch, space in the intergalactic
zones expands at a constant rate. -In and around galaxies, space expansion is
inhibited. With these results, and an extended Gauss Theorem for a deformed
space, we show that there is no need for the hypothetical Dark Energy (DE) and
Dark Matter (DM) to explain phenomena attributed to them. |
Constraining neutrino mass and extra relativistic degrees of freedom in
dynamical dark energy models using Planck 2015 data in combination with
low-redshift cosmological probes: basic extensions to $Λ$CDM cosmology: We investigate how the properties of dark energy affect the cosmological
measurements of neutrino mass and extra relativistic degrees of freedom. We
limit ourselves to the most basic extensions of $\Lambda$ cold dark matter
(CDM) model, i.e. the $w$CDM model with one additional parameter $w$, and the
$w_{0}w_{a}$CDM model with two additional parameters, $w_{0}$ and $w_{a}$. In
the cosmological fits, we employ the 2015 cosmic microwave background
temperature and polarization data from the Planck mission, in combination with
low-redshift measurements such as the baryon acoustic oscillations, Type Ia
supernovae and the Hubble constant ($H_{0}$). Given effects of massive
neutrinos on large-scale structure, we further include weak lensing, redshift
space distortion, Sunyaev--Zeldovich cluster counts and Planck lensing data. We
show that, though the cosmological constant $\Lambda$ is still consistent with
the current data, a phantom dark energy ($w<-1$) or an early phantom dark
energy (i.e. quintom evolving from $w<-1$ to $w>-1$) is slightly more favoured
by current observations, which leads to the fact that in both $w$CDM and
$w_0w_a$CDM models we obtain a larger upper limit of $\sum m_\nu$. We also show
that in the three dark energy models, the constraints on $N_{\rm eff}$ are in
good accordance with each other, all in favour of the standard value 3.046,
which indicates that the dark energy parameters almost have no impact on
constraining $N_{\rm eff}$. Therefore, we conclude that the dark energy
parameters can exert a significant influence on the cosmological weighing of
neutrinos, but almost cannot affect the constraint on dark radiation. | Locations of Accretion Shocks around Galaxy Clusters and the ICM
properties: insights from Self-Similar Spherical Collapse with arbitrary mass
accretion rates: Accretion shocks around galaxy clusters mark the position where the infalling
diffuse gas is significantly slowed down, heated up, and becomes a part of the
intracluster medium (ICM). They play an important role in setting the ICM
properties. Hydrodynamical simulations have found an intriguing result that the
radial position of this accretion shock tracks closely the position of the
`splashback radius' of the dark matter, despite the very different physical
processes that gas and dark matter experience. Using the self-similar spherical
collapse model for dark matter and gas, we find that an alignment between the
two radii happens only for a gas with an adiabatic index of $\gamma \approx
5/3$ and for clusters with moderate mass accretion rates. In addition, we find
that some observed ICM properties, such as the entropy slope and the effective
polytropic index lying around $\sim 1.1-1.2$, are captured by the self-similar
spherical collapse model, and are insensitive to the mass accretion history. |
Newly-quenched galaxies as the cause for the apparent evolution in
average size of the population: Abridged. We use COSMOS to study in a self-consistent way the change in the
number densities of quenched early-type galaxies (Q-ETGs) of a given size over
the interval 0.2 < z < 1.0 to study the claimed size evolution of these
galaxies. At 10^10.5<Mgalaxy<10^11 Msun, we see no change in the number density
of compact Q-ETGs, while at >10^11 Msun we find a decrease by 30%. In both mass
bins, the increase of the median sizes of Q-ETGs with time is primarily caused
by the addition to the size function of larger and more diffuse Q-ETGs. At all
masses, compact Q-ETGs become systematically redder towards later epochs, with
a (U-V) difference consistent with passive evolution of their stellar
populations, indicating that they are a population that does not appreciably
evolve in size. At all epochs, the larger Q-ETGs (at least in the lower mass
bin) have average rest-frame colors systematically bluer than those of the more
compact Q-ETGs, suggesting that the former are younger than the latter. The
idea that new, large, Q-ETGs are responsible for the observed growth in the
median size of the population at a given mass is supported by the sizes and
number of the star-forming galaxies that are expected to be progenitors of the
new Q-ETGs over the same period. In the low mass bin, the new Q-ETG have 30%
smaller sizes than their star-forming progenitors. This is likely due to the
fading of their disks after they cease star-formation. Comparison with higher z
shows that the median size of newly-quenched galaxies roughly scales, at
constant mass, as (1+z)^-1. The dominant cause of the size evolution seen in
the Q-ETG population is thus that the average sizes of individual Q-ETGs scale
with the average density of the Universe at the time when they were quenched,
with subsequent size changes in individual objects through eg merging of
secondary importance, especially at masses <10^11 Msun. | Galaxy triplets in Sloan Digital Sky Survey Data Release 7: II. A
connection with compact groups?: We analyse a sample of 71 triplets of luminous galaxies derived from the work
of O'Mill et al. (2012). We compare the properties of triplets and their
members with those of control samples of compact groups, the ten brightest
members of rich clusters, and galaxies in pairs. The triplets are restricted to
have members with spectroscopic redshifts in the range 0.01<z<0.14 and
Mr<-20.5. We analyse the stellar mass (SM) content, the star formation rates,
the Dn(4000) parameter and colour index and also analyse different global
properties of these systems as total star formation activity and global
colours. We calculate the probability that the properties of galaxies in
triplets are strongly correlated. We define the triplet compactness as a
measure of the percentage of the system total area that is filled by the light
of member galaxies. Our analysis suggest that triplet galaxy members behave
similarly to compact group members and galaxies in rich clusters. We also find
that systems comprising 3 blue, star-forming, young stellar population galaxies
(blue triplets) are most probably real systems and not a chance configuration
of interloping galaxies. The same holds for triplets composed by 3 red, non
star-forming galaxies, showing the correlation of galaxy properties in these
systems. From the analysis of the triplet as a whole, we conclude that, at a
given total SM content, triplets show a total star formation activity and
global colours similar to compact groups. However, blue triplets show a high
total star formation activity with a lower SM content. From an analysis of the
compactness parameter of the systems we find that light is even more
concentrated in triplets than in compact groups. We propose that triplets
composed by 3 luminous galaxies, should not be considered as an analogous of
galaxy pairs with an extra member, but rather they are a natural extension of
compact groups. |
Constraining stochastic gravitational wave background from weak lensing
of CMB B-modes: A stochastic gravitational wave background (SGWB) will affect the CMB
anisotropies via weak lensing. Unlike weak lensing due to large scale structure
which only deflects photon trajectories, a SGWB has an additional effect of
rotating the polarization vector along the trajectory. We study the relative
importance of these two effects, deflection \& rotation, specifically in the
context of E-mode to B-mode power transfer caused by weak lensing due to SGWB.
Using weak lensing distortion of the CMB as a probe, we derive constraints on
the spectral energy density ($\Omega_{GW}$) of the SGWB, sourced at different
redshifts, without assuming any particular model for its origin. We present
these bounds on $\Omega_{GW}$ for different power-law models characterizing the
SGWB, indicating the threshold above which observable imprints of SGWB must be
present in CMB. | Dark Matter Axions Revisited: We study for what specific values of the theoretical parameters the axion can
form the totality of cold dark matter. We examine the allowed axion parameter
region in the light of recent data collected by the WMAP5 mission plus baryon
acoustic oscillations and supernovae, and assume an inflationary scenario and
standard cosmology. If the Peccei-Quinn symmetry is restored after inflation,
we recover the usual relation between axion mass and density, so that an axion
mass $m_a =67\pm2{\rm \mu eV}$ makes the axion 100% of the cold dark matter. If
the Peccei-Quinn symmetry is broken during inflation, the axion can instead be
100% of the cold dark matter for $m_a < 15{\rm meV}$ provided a specific value
of the initial misalignment angle $\theta_i$ is chosen in correspondence to a
given value of its mass $m_a$. Large values of the Peccei-Quinn symmetry
breaking scale correspond to small, perhaps uncomfortably small, values of the
initial misalignment angle $\theta_i$. |
The outskirts of globular clusters as modified gravity probes: In the context of theories of gravity modified to account for the observed
dynamics of galactic systems without the need to invoke the existence of dark
matter, a prediction often appears regarding low acceleration systems: wherever
$a$ falls below $a_{0}$ one should expect a transition from the classical to
the modified gravity regime.This modified gravity regime will be characterised
by equilibrium velocities which become independent of distance, and which scale
with the fourth root of the total baryonic mass, $V^{4} \propto M$. The two
above conditions are the well known flat rotation curves and Tully-Fisher
relations of the galactic regime. Recently however, a similar phenomenology has
been hinted at, at the outskirts of Galactic globular clusters, precisely in
the region where $a<a_{0}$. Radial profiles of the projected velocity
dispersion have been observed to stop decreasing along Keplerian expectations,
and to level off at constant values beyond the radii where $a<a_{0}$. We have
constructed gravitational equilibrium dynamical models for a number of globular
clusters for which the above gravitational anomaly has been reported, using a
modified Newtonian force law which yields equilibrium velocities equivalent to
MOND. We find models can be easily constructed having an inner Newtonian region
and an outer modified gravity regime, which reproduce all observational
constraints, surface brightness profiles, total masses and line of sight
velocity dispersion profiles. Through the use of detailed single stellar
population models tuned individually to each of the globular clusters in
question, we derive estimates of the total masses for these systems.
Interestingly, we find that the asymptotic values of the velocity dispersion
profiles are consistent with scaling with the fourth root of the total masses,
as expected under modified gravity scenarios. | Observational Evidence for Primordial Black Holes: A Positivist
Perspective: We review numerous arguments for primordial black holes (PBHs) based on
observational evidence from a variety of lensing, dynamical, accretion and
gravitational-wave effects. This represents a shift from the usual emphasis on
PBH constraints and provides what we term a positivist perspective.
Microlensing observations of stars and quasars suggest that PBHs of around
$1\,M_{\odot}$ could provide much of the dark matter in galactic halos, this
being allowed by the Large Magellanic Cloud microlensing observations if the
PBHs have an extended mass function. More generally, providing the mass and
dark matter fraction of the PBHs is large enough, the associated Poisson
fluctuations could generate the first bound objects at a much earlier epoch
than in the standard cosmological scenario. This simultaneously explains the
recent detection of high-redshift dwarf galaxies, puzzling correlations of the
source-subtracted infrared and X-ray cosmic backgrounds, the size and the
mass-to-light ratios of ultra-faint-dwarf galaxies, the dynamical heating of
the Galactic disk, and the binary coalescences observed by LIGO/Virgo/KAGRA in
a mass range not usually associated with stellar remnants. Even if PBHs provide
only a small fraction of the dark matter, they could explain various other
observational conundra, and sufficiently large ones could seed the supermassive
black holes in galactic nuclei or even early galaxies themselves. We argue that
PBHs would naturally have formed around the electroweak, quantum chromodynamics
and electron-positron annihilation epochs, when the sound-speed inevitably
dips. This leads to an extended PBH mass function with a number of distinct
bumps, the most prominent one being at around $1\,M_{\odot}$, and this would
allow PBHs to explain many of the observations in a unified way. |
Is the Sunyaev-Zeldovich effect responsible for the observed steepening
in the spectrum of the Coma radio halo ?: The spectrum of the radio halo in the Coma cluster is measured over almost
two decades in frequency. The current radio data show a steepening of the
spectrum at higher frequencies, which has implications for models of the radio
halo origin. There is an on-going debate on the possibility that the observed
steepening is not intrinsic to the emitted radiation, but is instead caused by
the SZ effect. Recently, the Planck satellite measured the SZ signal and its
spatial distribution in the Coma cluster allowing to test this hypothesis.
Using the Planck results, we calculated the modification of the radio halo
spectrum by the SZ effect in three different ways. With the first two methods
we measured the SZ-decrement within the aperture radii used for flux
measurements of the halo at the different frequencies. First we adopted the
global compilation of data from Thierbach et al. and a reference aperture
radius consistent with those used by the various authors. Second we used the
available brightness profiles of the halo at different frequencies to derive
the spectrum within two fixed apertures, and derived the SZ-decrement using
these apertures. As a third method we used the quasi-linear correlation between
the y and the radio-halo brightness at 330 MHz discovered by Planck to derive
the modification of the radio spectrum by the SZ-decrement in a way that is
almost independent of the adopted aperture radius. We found that the spectral
modification induced by the SZ-decrement is 4-5 times smaller than that
necessary to explain the observed steepening. Consequently a break or cut-off
in the spectrum of the emitting electrons is necessary to explain current data.
We also show that, if a steepening is absent from the emitted spectrum, future
deep observations at 5 GHz with single dishes are expected to measure a halo
flux in a 40 arcmin radius that would be 7-8 times higher than currently seen. | Bias in low-multipole CMB reconstructions: The large-angle, low multipole cosmic microwave background (CMB) provides a
unique view of the largest angular scales in the Universe. Study of these
scales is hampered by the facts that we have only one Universe to observe, only
a few independent samples of the underlying statistical distribution of these
modes, and an incomplete sky to observe due to the interposing Galaxy.
Techniques for reconstructing a full sky from partial sky data are well known
and have been applied to the large angular scales. In this work we critically
study the reconstruction process and show that, in practise, the reconstruction
is biased due to leakage of information from the region obscured by foregrounds
to the region used for the reconstruction. We conclude that, despite being
suboptimal in a technical sense, using the unobscured region without
reconstructing is the most robust measure of the true CMB sky. We also show
that for noise free data reconstructing using the usual optimal, unbiased
estimator may be employed without smoothing thus avoiding the leakage problem.
Unfortunately, directly applying this to real data with noise and residual,
unmasked foregrounds yields highly biased reconstructions requiring further
care to apply this method successfully to real-world CMB. |
Primordial black hole formation in $α$-attractor models: an
analysis using optimized peaks theory: In this paper, the formation of primordial black holes (PBHs) is
reinvestigated using inflationary $\alpha$-attractors. Instead of using the
conventional Press-Schechter theory to compute the abundance, the optimized
peaks theory is used, which was developed in Ref.
\cite{Yoo:2018kvb,Yoo:2020dkz}. This method takes into account how curvature
perturbations play a r\^{o}le in modifying the mass of primordial black holes.
Analyzing the model proposed in \cite{Mahbub:2019uhl} it is seen that the
horizon mass of the collapsed Hubble patch is larger by $\mathcal{O}(10)$
compared to the usual computation. Moreover, PBHs can be formed from curvature
power spectrum, $\mathcal{P}_{\zeta}(k)$, peaked at lower values using
numerically favored threshold overdensities. As a result of the generally
larger masses predicted, the peak of the power spectrum can be placed at larger
$k$ modes than that is typical with which potential future constraints on the
primordial power spectrum through gravitational waves (GWs) can be evaded. | Testing the equivalence principle on cosmological scales: The equivalence principle, that is one of the main pillars of general
relativity, is very well tested in the Solar system; however, its validity is
more uncertain on cosmological scales, or when dark matter is concerned. This
article shows that relativistic effects in the large-scale structure can be
used to directly test whether dark matter satisfies Euler's equation, i.e.
whether its free fall is characterised by geodesic motion, just like baryons
and light. After having proposed a general parametrisation for deviations from
Euler's equation, we perform Fisher-matrix forecasts for future surveys like
DESI and the SKA, and show that such deviations can be constrained with a
precision of order 10%. Deviations from Euler's equation cannot be tested
directly with standard methods like redshift-space distortions and
gravitational lensing, since these observables are not sensitive to the time
component of the metric. Our analysis shows therefore that relativistic effects
bring new and complementary constraints to alternative theories of gravity. |
Spectral Distortion in a Radially Inhomogeneous Cosmology: The spectral distortion of the cosmic microwave background blackbody spectrum
in a radially inhomogeneous spacetime, designed to exactly reproduce a
LambdaCDM expansion history along the past light cone, is shown to exceed the
upper bound established by COBE-FIRAS by a factor of approximately 3700. This
simple observational test helps uncover a slew of pathological features that
lie hidden inside the past light cone, including a radially contracting phase
at decoupling and, if followed to its logical extreme, a naked singularity at
the radially inhomogeneous Big Bang. | Inflation After False Vacuum Decay: New Evidence from BICEP2: Last year we argued that if slow-roll inflation followed the decay of a false
vacuum in a large landscape, the steepening of the scalar potential between the
inflationary plateau and the barrier generically leads to a potentially
observable suppression of the scalar power spectrum at large distances. Here we
revisit this analysis in light of the recent BICEP2 results. Assuming that both
the BICEP2 B-mode signal and the Planck analysis of temperature fluctuations
hold up, we find that the data now discriminate more sharply between our
scenario and $\Lambda$CDM. Nonzero tensor modes exclude standard $\Lambda$CDM
with notable but not yet conclusive confidence: at $\sim 3.8\,\sigma$ if
$r\approx0.2$, or at $\sim 3.5\,\sigma$ if $r=0.15$. Of the two steepening
models of our previous work, one is now ruled out by existing bounds on spatial
curvature. The other entirely reconciles the tension between BICEP2 and Planck.
Upcoming $EE$ polarization measurements have the potential to rule out
unmodified $\Lambda$CDM decisively. Next generation Large Scale Structure
surveys can further increase the significance. More precise measurements of
$BB$ at low $\ell$ will help distinguish our scenario from other explanations.
If steepening is confirmed, the prospects for detecting open curvature increase
but need not be large. |
The Wall of Fundamental Constants: We consider the signatures of a domain wall produced in the spontaneous
symmetry breaking involving a dilaton-like scalar field coupled to
electromagnetism. Domains on either side of the wall exhibit slight differences
in their respective values of the fine-structure constant, alpha. If such a
wall is present within our Hubble volume, absorption spectra at large redshifts
may or may not provide a variation in alpha relative to the terrestrial value,
depending on our relative position with respect to the wall. This wall could
resolve the ``contradiction'' between claims of a variation of alpha based on
Keck/Hires data and of the constancy of alpha based on VLT data. We derive the
properties of the wall and the parameters of the underlying microscopic model
required to reproduce the possible spatial variation of alpha. We discuss the
constraints on the existence of the low-energy domain wall and describe its
observational implications concerning the variation of the fundamental
constants. | Reheating dynamics affects non-perturbative decay of spectator fields: The behaviour of oscillating scalar spectator fields after inflation depends
on the thermal background produced by inflaton decay. Resonant decay of the
spectator is often blocked by large induced thermal masses. We account for the
finite decay width of the inflaton and the protracted build-up of the thermal
bath to determine the early evolution of a homogeneous spectator field, \sigma,
coupled to the Higgs Boson, \Phi, through the term g^2 \sigma^2 \Phi^2, the
only renormalisable coupling of a new scalar to the Standard Model. We find
that for very large higgs-spectator coupling g > 10^{-3}, the resonance is not
always blocked as was previously suggested. As a consequence, the oscillating
spectator can decay quickly. For other parameter values, we find that although
qualitative features of the thermal blocking still hold, the dynamics are
altered compared to the instant decay case. These findings are important for
curvaton models, where the oscillating field must be relatively long lived in
order to produce the curvature perturbation. They are also relevant for other
spectator fields, which must decay sufficiently early to avoid spoiling the
predictions of baryogenesis and nucleosynthesis. |
SICRET: Supernova Ia Cosmology with truncated marginal neural Ratio
EsTimation: Type Ia supernovae (SNae Ia), standardisable candles that allow tracing the
expansion history of the Universe, are instrumental in constraining
cosmological parameters, particularly dark energy. State-of-the-art
likelihood-based analyses scale poorly to future large datasets, are limited to
simplified probabilistic descriptions, and must explicitly sample a
high-dimensional latent posterior to infer the few parameters of interest,
which makes them inefficient.
Marginal likelihood-free inference, on the other hand, is based on forward
simulations of data, and thus can fully account for complicated redshift
uncertainties, contamination from non-SN Ia sources, selection effects, and a
realistic instrumental model. All latent parameters, including instrumental and
survey-related ones, per-object and population-level properties, are implicitly
marginalised, while the cosmological parameters of interest are inferred
directly.
As a proof of concept, we apply truncated marginal neural ratio estimation
(TMNRE), a form of marginal likelihood-free inference, to BAHAMAS, a Bayesian
hierarchical model for SALT parameters. We verify that TMNRE produces unbiased
and precise posteriors for cosmological parameters from up to 100 000 SNae Ia.
With minimal additional effort, we train a network to infer simultaneously the
O(100 000) latent parameters of the supernovae (e.g. absolute brightnesses). In
addition, we describe and apply a procedure that utilises local amortisation of
the inference to convert the approximate Bayesian posteriors into frequentist
confidence regions with exact coverage. Finally, we discuss the planned
improvements to the model that are enabled by using a likelihood-free inference
framework, like selection effects and non-Ia contamination. | Deep Herschel view of obscured star formation in the Bullet cluster: We use deep, five band (100-500um) data from the Herschel Lensing Survey
(HLS) to fully constrain the obscured star formation rate, SFR_FIR, of galaxies
in the Bullet cluster (z=0.296), and a smaller background system (z=0.35) in
the same field. Herschel detects 23 Bullet cluster members with a total SFR_FIR
= 144 +/- 14 M_sun yr^-1. On average, the background system contains brighter
far-infrared (FIR) galaxies, with ~50% higher SFR_FIR (21 galaxies; 207 +/- 9
M_sun yr^-1). SFRs extrapolated from 24um flux via recent templates (SFR_24)
agree well with SFR_FIR for ~60% of the cluster galaxies. In the remaining
~40%, SFR_24 underestimates SFR_FIR due to a significant excess in observed
S_100/S_24 (rest frame S_75/S_18) compared to templates of the same FIR
luminosity. |
On signatures of spontaneous collapse dynamics modified single field
inflation: The observed classicality of primordial perturbations, despite their quantum
origin during inflation, calls for a mechanism for quantum-to-classical
transition of these initial fluctuations. As literature suggests a number of
plausible mechanisms which try to address this issue, it is of importance to
seek for concrete observational signatures of these several approaches in order
to have a better understanding of the early universe dynamics. Among these
several approaches, it is the spontaneous collapse dynamics of Quantum
Mechanics which is most viable of leaving discrete observational signatures as
collapse mechanism inherently changes the generic Quantum dynamics. We observe
in this study that the observables from the scalar sector, i.e. scalar tilt
$n_s$, running of scalar tilt $\alpha_s$ and running of running of scalar tilt
$\beta_s$, can not potentially distinguish a collapse modified inflationary
dynamics in the realm of canonical scalar field and $k-$inflationary scenarios.
The only distinguishable imprint of collapse mechanism lies in the observables
of tensor sector in the form of modified consistency relation and a blue-tilted
tensor spectrum only when the collapse parameter $\delta$ is non-zero and
positive. | Calibrating the standard candles with strong lensing: We propose a new model-independent strategy to calibrate the distance
relation in Type Ia supernova (SN) observations and to probe the intrinsic
properties of SNe Ia, especially the absolute magnitude $M_B$, basing on strong
lensing observations in the upcoming Large Synoptic Survey Telescope (LSST)
era. The strongly lensed quasars can provide the Time Delay Distances (TDD) and
the Angular Diameter Distances (ADD) to the lens galaxies. These absolute
distance measurements can model-independently anchor the SNe Ia at cosmological
distances. We simulated 55 high-quality lensing systems with $5\%$
uncertainties for both TDD and ADD measurements basing on future observation
conditions. For the time delay distances and the angular diameter distances as
the calibration standards, the calibrated $1\sigma$ uncertainties of $M_{B}$
are approximately 0.24 mag and 0.03 mag, respectively. Besides, we also
consider an evolving distance relation, for example, caused by the cosmic
opacity. In this case, the $1\sigma$ uncertainties of $M_B$ calibrated with TDD
and ADD are approximately 0.31 mag and 0.06 mag, respectively. The results show
that the ADD method will be a promising tool for calibrating supernovae. |
Analyzing H(z) Data using Two-point Diagnostics: Measurements of the Hubble constant H(z) are increasingly being used to test
the expansion rate predicted by various cosmological models. But the recent
application of 2-point diagnostics, such as Om(z_i,z_j) and Omh^2(z_i,z_j), has
produced considerable tension between LCDM's predictions and several
observations, with other models faring even worse. Part of this problem is
attributable to the continued mixing of truly model-independent measurements
using the cosmic-chronomter approach, and model-dependent data extracted from
BAOs. In this paper, we advance the use of 2-point diagnostics beyond their
current status, and introduce new variations, which we call Delta h(z_i,z_j),
that are more useful for model comparisons. But we restrict our analysis
exclusively to cosmic-chronometer data, which are truly model independent. Even
for these measurements, however, we confirm the conclusions drawn by earlier
workers that the data have strongly non-Gaussian uncertainties, requiring the
use of both "median" and "mean" statistical approaches. Our results reveal that
previous analyses using 2-point diagnostics greatly underestimated the errors,
thereby misinterpreting the level of tension between theoretical predictions
and H(z) data. Instead, we demonstrate that as of today, only Einstein-de
Sitter is ruled out by the 2-point diagnostics at a level of significance
exceeding ~ 3 sigma. The R_h=ct universe is slightly favoured over the
remaining models, including LCDM and Chevalier-Polarski-Linder, though all of
them (other than Einstein-de Sitter) are consistent to within 1 sigma with the
measured mean of the Delta h(z_i,z_j) diagnostics. | The Evolution of the Stellar Mass Functions of Star-Forming and
Quiescent Galaxies to z = 4 from the COSMOS/UltraVISTA Survey: We present measurements of the stellar mass functions (SMFs) of star-forming
and quiescent galaxies to z = 4 using a sample of 95 675 galaxies in the
COSMOS/UltraVISTA field. Sources have been selected from the DR1 UltraVISTA
K_{s}-band imaging which covers a unique combination of a wide area (1.62
deg^2), to a significant depth (K_{s,tot} = 23.4). The SMFs of the combined
population are in good agreement with previous measurements and show that the
stellar mass density of the universe was only 50%, 10% and 1% of its current
value at z ~ 0.75, 2.0, and 3.5, respectively. The quiescent population drives
most of the overall growth, with the stellar mass density of these galaxies
increasing by 2.71^{+0.93}_{-0.22} dex since z = 3.5. At z > 2.5, star-forming
galaxies dominate the total SMF at all stellar masses, although a nonzero
population of quiescent galaxies persists to z = 4. Comparisons of the
K_{s}-selected star-forming galaxy SMFs to UV-selected SMFs at 2.5 < z < 4 show
reasonable agreement and suggests UV-selected samples are representative of the
majority of the stellar mass density at z > 3.5. We estimate the average mass
growth of individual galaxies by selecting galaxies at fixed cumulative number
density. The average galaxy with Log(M_{*}/M_{sun}) = 11.5 at z = 0.3 has grown
in mass by only 0.2 dex (0.3 dex) since z = 2.0(3.5), whereas those with
Log(M_{*}/M_{sun}) = 10.5 have grown by > 1.0 dex since z = 2. At z < 2, the
time derivatives of the mass growth are always larger for lower-mass galaxies,
which demonstrates that the mass growth in galaxies since that redshift is
mass-dependent and primarily bottom-up. Lastly, we examine potential sources of
systematic uncertainties on the SMFs and find that those from photo-z
templates, SPS modeling, and the definition of quiescent galaxies dominate the
total error budget in the SMFs. |
Soliton Merger Rates and Enhanced Axion Dark Matter Decay: Solitons are observed to form in simulations of dark matter (DM) halos
consisting of bosonic fields. We use the extended Press-Schechter formalism to
compute the mass function of solitons, assuming various forms for the
relationship between halo mass and soliton mass. We further provide a new
calculation of the rate of soliton major mergers. Solitons composed of axion DM
are unstable above a critical mass, and decay to either relativistic axions or
photons, depending on the values of the coupling constants. We use the computed
soliton major merger rate to predict the enhanced DM decay rate due to soliton
instability. For certain values of currently allowed axion parameters, the
energy injection into the intergalactic medium from soliton decays to photons
is comparable to or larger than the energy injection due to core collapse
supernovae at $z>10$. A companion paper explores the phenomenology of such an
energy injection. | Constraining symmetron fields with atom interferometry: We apply the new constraints from atom-interferometry searches for screening
mechanisms to the symmetron model, finding that these experiments exclude a
previously unexplored region of parameter space. We discuss the possibility of
networks of domain walls forming in the vacuum chamber, and how this could be
used to discriminate between models of screening. |
Cosmological constraints on holographic dark energy models under the
energy conditions: We study the holographic and agegraphic dark energy models without
interaction using the latest observational Hubble parameter data (OHD), the
Union2.1 compilation of type Ia supernovae (SNIa), and the energy conditions.
Scenarios of dark energy are distinguished by the cut-off of cosmic age,
conformal time, and event horizon. The best-fit value of matter density for the
three scenarios almost steadily located at $\Omega_{m0}=0.26$ by the joint
constraint. For the agegraphic models, they can be recovered to the standard
cosmological model when the constant $c$ which presents the fraction of dark
energy approaches to infinity. Absence of upper limit of $c$ by the joint
constraint demonstrates the recovery possibility. Using the fitted result, we
also reconstruct the current equation of state of dark energy at different
scenarios, respectively. Employing the model criteria
$\chi^2_{\textrm{min}}/dof$, we find that conformal time model is the worst,
but they can not be distinguished clearly. Comparing with the observational
constraints, we find that SEC is fulfilled at redshift $0.2 \lesssim z \lesssim
0.3$ with $1\sigma$ confidence level. We also find that NEC gives a meaningful
constraint for the event horizon cut-off model, especially compared with OHD
only. We note that the energy condition maybe could play an important role in
the interacting models because of different degeneracy between $\Omega_m$ and
constant $c$. | Are 3C249.1 and 3C334 restarted quasars?: This Research Note follows up a Letter in which I posit that J1211+743 is a
restarted radio source. This means that its structure, where the jet points to
the relic lobe, is only apparently paradoxical. Here, I propose the same
scenario and apply the same mathematical model to 3C249.1 and 3C334. The
ultimate result of my investigation is that these two well-known radio-loud
quasars can be understood best so far if it was assumed that they, too, had
been restarted. |
Fast computation of non-linear power spectrum in cosmologies with
massive neutrinos: We compute 1-loop corrections to the redshift space galaxy power spectrum in
cosmologies containing additional scales, and hence kernels different from
Einstein-de Sitter (EdS). Specifically, our method is tailored for cosmologies
in the presence of massive neutrinos and some modified gravity models; in this
article we concentrate on the former case. The perturbative kernels have
contributions that we notice appear either from the logarithmic growth factor
$f(k,t)$, which is scale-dependent because of the neutrino free-streaming, or
from the failure of the commonly used approximation $f^2=\Omega_m$. The latter
contributions make the computation of loop corrections quite slow, precluding
full-shape analyses for parameter estimation. However, we identify that the
dominant pieces of the kernels come from the growth factor, allowing us to
simplify the kernels but retaining the characteristic free-streaming scale
introduced by the neutrinos' mass. Moreover, with this simplification one can
exploit FFTLog methods to speed up the computations even more. We validate our
analytical modeling and numerical method with halo catalogs extracted from the
Quijote simulations finding good agreement with the, a priori, known
cosmological parameters. We make public our Python code FOLPS$\nu$ to compute
the redshift space power spectrum in a fraction of second. Code available at
https://github.com/henoriega/FOLPS-nu. | The formation of disks in massive spiral galaxies: The flatness of the rotation curve inside spiral galaxies is interpreted as
the imprint of a halo of invisible matter. Using the deepest observations of
distant galaxies, we have investigated how large disks could have been formed.
Observations include spatially resolved kinematics, detailed morphologies and
photometry from UV to mid-IR. Six Giga-years ago, half of the present-day
spirals had anomalous kinematics and morphologies that considerably affect the
scatter of the Tully Fisher relation. All anomalous galaxies can be modelled
through gas-rich, major mergers that lead to a rebuilt of a new disk. The
spiral-rebuilding scenario is proposed as a new channel to form large disks in
present-day spirals and it accounts for all the observed evolutions since the
last 6 Giga-years. A large fraction of the star formation is linked to merging
events during their whole durations. |
Preliminary results of a WIMP search with EDELWEISS-II cryogenic
detectors: The EDELWEISS-II experiment uses cryogenic heat-and-ionization detectors in
order to detect the rare interactions from possible WIMP dark matter particles
on Germanium nuclei. Recently, new-generation detectors with an interleaved
electrode geometry were developped and validated, enabling an outstanding
rejection of gamma-rays and surface interactions. We present here preliminary
results of a one-year WIMP search carried out with ten of such detectors in the
Laboratoire Souterrain de Modane. A sensitivity to the spin-independent
WIMP-nucleon cross-section of 5 \times 10-8 pb was achieved using a 322 kg | Good and Proper: Self-similarity of N-body Simulations with Proper Force
Softening: Analysis of self-similarity in scale-free $N$-body simulations reveals the
spatial and temporal scales for which statistics measured in cosmological
simulations are converged to the physical continuum limit. We examine how the
range of scales in which the two-point correlation function is converged
depends on the force softening length and whether it is held constant in
comoving or proper coordinates. We find that a proper softening that reaches
roughly 1/30th of the inter-particle spacing by the end of the simulation
resolves the same spatial and temporal scales as a comoving softening of the
same length while using a third fewer time steps, for a range of scale factors
typical to $\Lambda$CDM simulations. We additionally infer an inherent
resolution limit, set by the particle mass and scaling as $a^{-1/2}$, beyond
which reducing the softening does not improve the resolution. We postulate a
mapping of these results with spectral index $n=-2$ to $\Lambda$CDM
simulations. |
The value of the Hubble-Lemaître constant queried by Type Ia
Supernovae: A journey from the Calán-Tololo Project to the Carnegie
Supernova Program: We assess the robustness of the two highest rungs of the "cosmic distance
ladder" for Type Ia supernovae and the determination of the Hubble-Lema\^itre
constant. In this analysis, we hold fixed Rung 1 as the distance to the LMC
determined to 1 % using Detached Eclipsing Binary stars. For Rung 2 we analyze
two methods, the TRGB and Cepheid distances for the luminosity calibration of
Type Ia supernovae in nearby galaxies. For Rung 3 we analyze various modern
digital supernova samples in the Hubble flow, such as the Cal\'an-Tololo, CfA,
CSP, and Supercal datasets. This metadata analysis demonstrates that the TRGB
calibration yields smaller $H_0$ values than the Cepheid calibration, a direct
consequence of the systematic difference in the distance moduli calibrated from
these two methods. Selecting the three most independent possible
methodologies/bandpasses ($B$, $V$, $J$), we obtain $H_{0}=69.9 \pm 0.8$ and
$H_{0} =73.5 \pm 0.7$ km s$^{-1}$ Mpc$^{-1}$ from the TRGB and Cepheid
calibrations, respectively. Adding in quadrature the systematic uncertainty in
the TRGB and Cepheid methods of 1.1 and 1.0 km s$^{-1}$ Mpc$^{-1}$,
respectively, this subset reveals a significant 2.0 $\sigma$ systematic
difference in the calibration of Rung 2. If Rung 1 and Rung 2 are held fixed,
the different formalisms developed for standardizing the supernova peak
magnitudes yield consistent results, with a standard deviation of 1.5 km
s$^{-1}$ Mpc$^{-1}$, that is, Type Ia supernovae are able to anchor Rung 3 with
2 % precision. This study demonstrates that Type Ia supernovae have provided a
remarkably robust calibration of R3 for over 25 years. | Spectroscopy of "Big Trio" objects using the "Scorpio" spectrograph of
the 6-m telescope of the Special astrophysical observatory: We present the results of spectroscopy of 71 objects with steep and
ultra-steep spectra ($\alpha<-0.9$, $S\propto\nu^\alpha$) from the "Big Trio"
(RATAN-600-VLA-BTA) project, performed with the "Scorpio" spectrograph on the
6-m telescope of the Special Astrophysical Observatory (Russian Academy of
Sciences). Redshifts were determined for these objects. We also present several
other parameters of the sources, such as their R-magnitudes, maximum radio
sizes in seconds of arc, flux densities at 500, 1425, and 3940 MHz, radio
luminosities at 500 and 3940 MHz, and morphology. Of the total number of radio
galaxies studied, four have redshifts 1<z<2, three have 2<z<3, one has 3<z<4,
and one has z=4.51. Thirteen sources have redshifts 0.7<z<1 and 15 have
0.2<z<0.7. Of all the quasars studied, five have redshifts 0.7<z<1, seven have
1<z<2, four have 2<z<3, and one has z=3.57. We did not detect any spectral
lines for 17 objects. |
Effective picture of bubble expansion: Recently the thermal friction on an expanding bubble from the cosmic
first-order phase transition has been calculated to all orders of the
interactions between the bubble wall and thermal plasma, leading to a
$\gamma^2$-scaling instead of the previously estimated $\gamma^1$-scaling for
the thermal friction exerted on a fast-moving bubble wall with a Lorentz factor
$\gamma$. We propose for the first time the effective equation of motion (EOM)
for an expanding bubble wall in the presence of an arbitrary $\gamma$-scaling
friction to compute the efficiency factor from bubble collisions, which, in the
case of $\gamma^2$-scaling friction, is found to be larger than the recently
updated estimation when the bubble walls collide after starting to approach a
constant terminal velocity, leading to a slightly larger signal of the
gravitational waves background from bubble collisions due to its quadratic
dependence on the bubble collision efficiency factor, although the
$\gamma^2$-scaling friction itself has already suppressed the contribution from
bubble collisions compared to that with $\gamma^1$-scaling friction. We also
suggest a phenomenological parameterization for the out-of-equilibrium term in
the Boltzmann equation that could reproduce the recently found
$(\gamma^2-1)$-scaling of the friction term in the effective EOM of an
expanding bubble wall, which merits further study in future numerical
simulations of bubble expansion and collisions. | A survey of molecular gas in luminous sub-millimetre galaxies: We present the results from a survey for 12CO emission in 40 luminous
sub-millimetre galaxies (SMGs), with 850um fluxes of S850 = 4 - 20 mJy,
conducted with the Plateau de Bure Interferometer. We detect 12CO emission in
32 SMGs at z~1.2 - 4.1, including 16 SMGs not previously published. Using
multiple 12CO line (J_up =2 - 7) observations, we derive a median spectral line
energy distribution for luminous SMGs and use this to estimate a mean gas mass
of (5.3 +/- 1.0) \times 10^10 Msun. We report the discovery of a fundamental
relationship between 12CO FWHM and 12CO line luminosity in high-redshift
starbursts, which we interpret as a natural consequence of the baryon-dominated
dynamics within the regions probed by our observations. We use far-infrared
luminosities to assess the star-formation efficiency in our SMGs, finding a
steepening of the L'CO-LFIR relation as a function of increasing 12CO J_up
transition. We derive dynamical masses and molecular gas masses, and use these
to determine the redshift evolution of the gas content of SMGs, finding that
they do not appear to be significantly more gas rich than less vigorously
star-forming galaxies at high redshifts. Finally, we collate X-ray
observations, and study the interdependence of gas and dynamical properties of
SMGs with their AGN activity and supermassive black hole masses (MBH), finding
that SMGs lie significantly below the local M_BH-sigma relation. We conclude
that SMGs represent a class of massive, gas-rich ultraluminous galaxies with
somewhat heterogeneous properties, ranging from starbursting disc-like systems
with L~10^12 L_sun, to the most highly star-forming mergers in the Universe. |
The Morphological Type Dependence of K-band Luminosity Functions: Differential 2.2um (K-band) luminosity functions are presented for a complete
sample of 1570 nearby Vgsr < 3000 km/s, where Vgsr is the velocity measured
with respect to the Galactic standard of rest), bright (K < 10 mag), galaxies
segregated by visible morphology. The K-band luminosity function for late-type
spirals follows a power law that rises towards low luminosities whereas the
K-band luminosity functions for ellipticals, lenticulars and bulge-dominated
spirals are peaked with a fall off at both high and low luminosities. However,
each morphological type (E, S0, S0/a-Sab, Sb-Sbc, Sc-Scd) contributes
approximately equally to the overall K-band luminosity density in the local
universe, and by inference, the stellar mass density as well. | The Impact of Tomographic Redshift Bin Width Errors on Cosmological
Probes: Systematic errors in the galaxy redshift distribution $n(z)$ can propagate to
systematic errors in the derived cosmology. We characterize how the degenerate
effects in tomographic bin widths and galaxy bias impart systematic errors on
cosmology inference using observational data from the Deep Lens Survey. For
this we use a combination of galaxy clustering and galaxy-galaxy lensing. We
present two end-to-end analyses from the catalogue level to parameter
estimation. We produce an initial cosmological inference using fiducial
tomographic redshift bins derived from photometric redshifts, then compare this
with a result where the redshift bins are empirically corrected using a set of
spectroscopic redshifts. We find that the derived parameter $S_8 \equiv
\sigma_8 (\Omega_m/.3)^{1/2}$ goes from $.841^{+0.062}_{-.061}$ to
$.739^{+.054}_{-.050}$ upon correcting the n(z) errors in the second method. |
Modelling the evolution of galaxies as a function of environment: In this review, I provide an overview of theoretical aspects related to the
evolution of galaxies as a function of environment. I discuss the main physical
processes at play, their characteristic time-scales and environmental
dependency, and comment on their treatment in the framework of hierarchical
galaxy formation models. I briefly summarize recent results and the main open
issues. | The interacting generalized Ricci dark energy model in non-flat universe: We extend our previous analysis and consider the interacting holographic
Ricci dark energy (IRDE) model in non-flat universe. We study astrophysical
constraints on this model using the recent observations including the type Ia
supernovae (SNIa), the baryon acoustic oscillation (BAO), the cosmic microwave
background (CMB) anisotropy, and the Hubble parameter. It is shown that the
allowed parameter range for the fractional energy density of the curvature is
$-0.005$ $\lesssim$ $\Omega_{k0}$ $\lesssim$ $0.015$ in the presence of the
interactions between dark energy and matter. Without the interaction, the flat
universe is observationally disfavored in this model. |
Constraint on a varying proton-to-electron mass ratio from molecular
hydrogen absorption toward quasar SDSS J123714.60+064759.5: Molecular hydrogen transitions in the sub-damped Lyman alpha absorber at
redshift z = 2.69, toward the background quasar SDSS J123714.60+064759.5, were
analyzed in order to search for a possible variation of the proton-to-electron
mass ratio mu over a cosmological time-scale. The system is composed of three
absorbing clouds where 137 H2 and HD absorption features were detected. The
observations were taken with the Very Large Telescope/Ultraviolet and Visual
Echelle Spectrograph with a signal-to-noise ratio of 32 per 2.5 km/s pixel,
covering the wavelengths from 356.6 to 409.5 nm. A comprehensive fitting method
was used to fit all the absorption features at once. Systematic effects of
distortions to the wavelength calibrations were analyzed in detail from
measurements of asteroid and `solar twin' spectra, and were corrected for. The
final constraint on the relative variation in mu between the absorber and the
current laboratory value is dmu/mu = (-5.4 \pm 6.3 stat \pm 4.0 syst) x
10^(-6), consistent with no variation over a look-back time of 11.4 Gyrs. | Compton rockets and the minimum power of relativistic jets: The power of a relativistic jet depends on the number of leptons and protons
carried by the jet itself. We have reasons to believe that powerful gamma-ray
flat spectrum radio sources emit most of their radiation where radiative
cooling is severe. This helps to find the minimum number of emitting leptons
needed to explain the radiation we see. The number of protons is more
uncertain. If there is one proton per electron, they dominate the jet power,
but they could be unimportant if the emission is due to electron-positron
pairs. In this case the total jet power could be much smaller. However, if the
gamma-ray flux is due to inverse Compton scattering with seed photons produced
outside the jet, the radiation is anisotropic also in the comoving frame,
making the jet to recoil. This Compton rocket effect is strong for light,
electron-positron jets, and negligible for heavy, proton dominated jets. No
significant deceleration, required by fast superluminal motion, requires a
minimum number of protons per lepton, and thus a minimum jet power. We apply
these ideas to the blazar 3C 454.3, to find a robust lower limit to its total
jet power: if the viewing angle theta_v ~ 1/Gamma the jet power is larger than
the accretion luminosity L_d for any bulk Lorentz factor Gamma. For theta_v =0,
instead, the minimum jet power can be smaller than L_d for Gamma<25. No more
than ~10 pairs per proton are allowed. |
Probing the Dark Matter density with gravitational waves from
super-massive binary black holes: Supermassive black hole binaries source gravitational waves measured by
Pulsar Timing Arrays. The frequency spectrum of this stochastic background is
predicted more precisely than its amplitude. We argue that Dark Matter friction
can suppress the spectrum around nHz frequencies, where it is measured,
allowing to derive robust and significant bounds on the Dark Matter density,
which, in turn, controls indirect detection signals from galactic centers. A
precise spectrum of gravitational waves would translate in a tomography of the
DM density profile, potentially probing DM particle-physics effects that induce
a characteristic DM density profile, such as DM annihilations or de Broglie
wavelength. | Deep Multi-object Spectroscopy to Enhance Dark Energy Science from LSST: Community access to deep (i ~ 25), highly-multiplexed optical and
near-infrared multi-object spectroscopy (MOS) on 8-40m telescopes would greatly
improve measurements of cosmological parameters from LSST. The largest gain
would come from improvements to LSST photometric redshifts, which are employed
directly or indirectly for every major LSST cosmological probe; deep
spectroscopic datasets will enable reduced uncertainties in the redshifts of
individual objects via optimized training. Such spectroscopy will also
determine the relationship of galaxy SEDs to their environments, key
observables for studies of galaxy evolution. The resulting data will also
constrain the impact of blending on photo-z's. Focused spectroscopic campaigns
can also improve weak lensing cosmology by constraining the intrinsic
alignments between the orientations of galaxies. Galaxy cluster studies can be
enhanced by measuring motions of galaxies in and around clusters and by testing
photo-z performance in regions of high density. Photometric redshift and
intrinsic alignment studies are best-suited to instruments on large-aperture
telescopes with wider fields of view (e.g., Subaru/PFS, MSE, or GMT/MANIFEST)
but cluster investigations can be pursued with smaller-field instruments (e.g.,
Gemini/GMOS, Keck/DEIMOS, or TMT/WFOS), so deep MOS work can be distributed
amongst a variety of telescopes. However, community access to large amounts of
nights for surveys will still be needed to accomplish this work. In two
companion white papers we present gains from shallower, wide-area MOS and from
single-target imaging and spectroscopy. |
Detailed study of B037 based on {\sl HST} images: B037 is of interest because it is both the most luminous and the most highly
reddened cluster known in M31. Images of deep observations and of highly
spatial resolutions with the Advanced Camera for Surveys on the {\sl HST}
firstly show that this cluster is crossed by a dust lane. Photometric data in
the F606W and F814W filters obtained in this paper provide that, colors of
($\rm {F606W-F814W}$) in the dust lane are redder $\sim 0.4$ mags than ones in
the other regions of B037. The {\sl HST} images show that, this dust lane seems
to be contained in B037, not from the M31 disk or the Milky Way. As we know,
the formation of dust requires gas with a rather high metallicity. However,
B037 has a low metallicity to be $\rm [Fe/H]=-1.07\pm 0.20$. So, it seems
improbable that the observed dust lane is physically associated with B037. It
is clear that the origin of this dust lane is worthy of future study. In
addition, based on these images, we present the precise variation of
ellipticity and position angle, and of surface brightness profile, and
determine the structural parameters of B037 by fitting a single-mass isotropic
King model. In the F606W filter, we derive the best-fitting scale radius,
$r_0=0.56\pm0.02\arcsec~(=2.16\pm0.08~\rm{pc})$, a tidal radius,
$r_t=8.6\pm0.4\arcsec~(=33.1\pm1.5~\rm{pc})$, and a concentration index $c=\log
(r_t/r_0)=1.19\pm0.02$. In the F814W filter, we derive
$r_0=0.56\pm0.01\arcsec~(=2.16\pm0.04~\rm{pc})$,
$r_t=8.9\pm0.3\arcsec~(=34.3\pm1.2~\rm{pc})$, and $c=\log
(r_t/r_0)=1.20\pm0.01$. The extinction-corrected central surface brightness is
$\mu_0=13.53\pm 0.03~{\rm mag~arcsec^{-2}}$ in the F606W filter, and $12.85\pm
0.03~{\rm mag~arcsec^{-2}}$ in the F814W filter, respectively. | NIR imaging spectroscopy of the inner few arcseconds of NGC 4151 with
OSIRIS at Keck: We present H- and K-band data from the inner arcsecond of the Seyfert 1.5
galaxy NGC 4151 obtained with the adaptive optics assisted near-infrared
imaging field spectrograph OSIRIS at the Keck Observatory. We present the
morphology and dynamics of most species detected but focus on the morphology
and dynamics of the narrow line region (as traced by emission of [FeII] \lambda
1.644\mu m), the interplay between plasma ejected from the nucleus (as traced
by 21 cm continuum radio data) and hot H2 gas and characterize the detected
nuclear HeI$\lambda 2.058 \mu m absorption feature as a narrow absorption line
(NAL) phenomenon. |
On the ICS interpretation of the Hard X-Ray Excesses in Galaxy Clusters:
the case of Ophiuchus: (Abridged) High-E electrons produce Hard X-Ray (HXR) emission in galaxy
clusters by via Inverse Compton Scattering (ICS) of CMB photons. We derive the
ICS HXR emission of Ophiuchus under various scenarios: primary cosmic ray
model, secondary cosmic rays model and neutralino DM annihilation scenario. We
further discuss the predictions of the Warming Ray model for the cluster
atmosphere. Under the assumption to fit the observed HXR emission, we find that
the high-E electrons induce various consequences on the cluster atmosphere: i)
primary electrons can be marginally consistent with the data provided that
their spectrum is cutoff at E~30(90) MeV for spectral index of 3.5 (4.4); ii)
secondary electron models from pp collisions are inconsistent with gamma-ray
limits, cosmic ray protons produce too much heating of the IC gas and their
pressure at the cluster center largely exceeds the thermal one; iii) secondary
electron models from DM annihilation are inconsistent with gamma-ray and radio
limits and electrons produce too much heating of the IC gas at the cluster
center, unless the neutralino annihilation cross section is much lower than the
proposed value. We conclude that ICS by secondary electrons from both
neutralino DM annihilation and pp collisions cannot be the mechanism
responsible for the HXR excess emission; primary electrons are still a
marginally viable solution provided that their spectrum has a low-energy cutoff
at E~30-90 MeV. The WR model offers, so far, the best description of the
cluster in terms of temperature distribution, heating, pressure and spectral
energy distribution. Fermi observations of Ophiuchus will set further
constraints to this model. | Early dark energy is not excluded by current large-scale structure data: We revisit the impact of early dark energy (EDE) on galaxy clustering using
BOSS galaxy power spectra, analyzed using the effective field theory (EFT) of
large-scale structure (LSS), and anisotropies of the cosmic microwave
background (CMB) from Planck. Recent studies found that these data place
stringent constraints on the maximum abundance of EDE allowed in the Universe.
We argue here that their conclusions are a consequence of their choice of
priors on the EDE parameter space, rather than any disagreement between the
data and the model. For example, when considering EFT-LSS, CMB, and
high-redshift supernovae data we find the EDE and $\Lambda$CDM models can
provide statistically indistinguishable fits ($\Delta \chi^2 = 0.12$) with a
relatively large value for the maximum fraction of energy density in the EDE
($f_{\rm ede} = 0.09$) and Hubble constant ($H_0 = 71$ km/s/Mpc) in the EDE
model. Moreover, we demonstrate that the constraining power added from the
inclusion of EFT-LSS traces to the potential tension between the power-spectrum
amplitudes $A_s$ derived from BOSS and from Planck that arises even within the
context of $\Lambda$CDM. Until this is better understood, caution should be
used when interpreting EFT-BOSS+Planck constraints to models beyond
$\Lambda$CDM. These findings suggest that EDE still provides a potential
resolution to the Hubble tension and that it is worthwhile to test the
predictions of EDE with future data-sets and further study its theoretical
possibilities. |
The First Galaxies: Assembly of Disks and Prospects for Direct Detection: The James Webb Space Telescope (JWST) will enable observations of galaxies at
redshifts z > 10 and hence allow to test our current understanding of structure
formation at very early times. Previous work has shown that the very first
galaxies inside halos with virial temperatures T < 10^4 K and masses M < 10^8
M_sun at z > 10 are probably too faint, by at least one order of magnitude, to
be detected even in deep exposures with JWST. The light collected with JWST may
therefore be dominated by radiation from galaxies inside ten times more massive
halos. We use cosmological zoomed smoothed particle hydrodynamics simulations
to investigate the assembly of such galaxies and assess their observability
with JWST. We compare two simulations that are identical except for the
inclusion of non-equilibrium H/D chemistry and radiative cooling by molecular
hydrogen. In both simulations a large fraction of the halo gas settles in two
nested, extended gas disks which surround a compact massive gas core. The
presence of molecular hydrogen allows the disk gas to reach low temperatures
and to develop marked spiral structure but does not qualitatively change its
stability against fragmentation. We post-process the simulated galaxies by
combining idealized models for star formation with stellar population synthesis
models to estimate the luminosities in nebular recombination lines as well as
in the ultraviolet continuum. We demonstrate that JWST will be able to
constrain the nature of the stellar populations in galaxies such as simulated
here based on the detection of the He1640 recombination line. Extrapolation of
our results to halos with masses both lower and higher than those simulated
shows that JWST may find up to a thousand star-bursting galaxies in future deep
exposures of the z > 10 universe. | MC^2: Mapping the Dark Matter Distribution of the "Toothbrush" Cluster
RX J0603.3+4214 with Hubble Space Telescope and Subaru Weak-lensing: The galaxy cluster RX J0603.3+4214 at z=0.225 is one of the rarest clusters
boasting an extremely large (~2 Mpc) radio-relic. Because of the remarkable
morphology of the relic, the cluster is nicknamed "Toothbrush Cluster".
Although the cluster's underlying mass distribution is one of the critical
pieces of information needed to reconstruct the merger scenario responsible for
the puzzling radio-relic morphology, its proximity to the Galactic plane b~10
deg has imposed significant observational challenges. We present a
high-resolution weak-lensing study of the cluster with Subaru/Suprime Cam and
Hubble Space Telescope imaging data. Our mass reconstruction reveals that the
cluster is comprised of complicated dark matter substructures closely tracing
the galaxy distribution, however in contrast with the relatively simple binary
X-ray morphology. Nevertheless, we find that the cluster mass is still
dominated by the two most massive clumps aligned north-south with a ~3:1 mass
ratio (M_{200}=6.29_{-1.62}^{+2.24} x 10^{14} Msun and 1.98_{-0.74}^{+1.24} x
10^{14} Msun for the northern and southern clumps, respectively). The southern
mass peak is ~2' offset toward the south with respect to the corresponding
X-ray peak, which has a "bullet"-like morphology pointing south. Comparison of
the current weak-lensing result with the X-ray, galaxy, and radio-relic
suggests that perhaps the dominant mechanism responsible for the observed relic
may be a high-speed collision of the two most massive subclusters, although the
peculiarity of the morphology necessitates involvement of additional
sub-clusters. Careful numerical simulations should follow in order to obtain
more complete understanding of the merger scenario utilizing all existing
observations. |
Cosmological perturbations during the Bose-Einstein condensation of dark
matter: In the present work, we analyze the evolution of the scalar and tensorial
perturbations and the quantities relevant for the physical description of the
Universe, as the density contrast of the scalar perturbations and the
gravitational waves energy density during the Bose-Einstein condensation of
dark matter. The behavior of these parameters during the Bose-Einstein phase
transition of dark matter is analyzed in details. To study the cosmological
dynamics and evolution of scalar and tensorial perturbations in a Universe with
and without cosmological constant we use both analytical and numerical methods.
The Bose-Einstein phase transition modifies the evolution of gravitational
waves of cosmological origin, as well as the process of large-scale structure
formation. | Gamma-Ray Constraints on Maximum Cosmogenic Neutrino Fluxes and UHECR
Source Evolution Models: The dip model assumes that the ultra-high energy cosmic rays (UHECRs) above
10$^{18}$ eV consist exclusively of protons and is consistent with the spectrum
and composition measure by HiRes. Here we present the range of cosmogenic
neutrino fluxes in the dip-model which are compatible with a recent
determination of the extragalactic very high energy (VHE) gamma-ray diffuse
background derived from 2.5 years of Fermi/LAT data. We show that the largest
fluxes predicted in the dip model would be detectable by IceCube in about 10
years of observation and are within the reach of a few years of observation
with the ARA project. In the incomplete UHECR model in which protons are
assumed to dominate only above 10$^{19}$ eV, the cosmogenic neutrino fluxes
could be a factor of 2 or 3 larger. Any fraction of heavier nuclei in the UHECR
at these energies would reduce the maximum cosmogenic neutrino fluxes. We also
consider here special evolution models in which the UHECR sources are assumed
to have the same evolution of either the star formation rate (SFR), or the
gamma-ray burst (GRB) rate, or the active galactic nuclei (AGN) rate in the
Universe and found that the last two are disfavored (and in the dip model
rejected) by the new VHE gamma-ray background. |
Galaxy and Mass Assembly (GAMA): The halo mass of galaxy groups from
maximum-likelihood weak lensing: We present a maximum-likelihood weak lensing analysis of the mass
distribution in optically selected spectroscopic Galaxy Groups (G$^3$Cv5) in
the Galaxy And Mass Assembly (GAMA) survey, using background Sloan Digital Sky
Survey (SDSS) photometric galaxies. The scaling of halo mass, $M_h$, with
various group observables is investigated. Our main results are: 1) the
measured relations of halo mass with group luminosity, virial volume and
central galaxy stellar mass, $M_\star$, agree very well with predictions from
mock group catalogues constructed from a GALFORM semi-analytical galaxy
formation model implemented in the Millennium $\Lambda$CDM N-body simulation;
2) the measured relations of halo mass with velocity dispersion and projected
half-abundance radius show weak tension with mock predictions, hinting at
problems in the mock galaxy dynamics and their small scale distribution; 3) the
median $M_h|M_\star$ measured from weak lensing depends more sensitively on the
lognormal dispersion in $M_\star$ at fixed $M_h$ than it does on the median
$M_\star|M_h$. Our measurements suggest an intrinsic dispersion of
$\sigma_{\log(M_\star)}\sim 0.15$; 4) Comparing our mass estimates with those
in the catalogue, we find that the G$^3$Cv5 mass can give biased results when
used to select subsets of the group sample. Of the various new halo mass
estimators that we calibrate using our weak lensing measurements, group
luminosity is the best single-proxy estimator of group mass. | The Scale Invariant Vacuum Paradigm: Main Results plus the Current BBNS
Progress: We summarize the main results within the Scale Invariant Vacuum (SIV)
paradigm as related to the Weyl Integrable Geometry (WIG) as an extension to
the standard Einstein General Relativity (EGR). After a short sketch of the
mathematical framework, the main results until 2023 [1] are highlighted in
relation to: the inflation within the SIV [2], the growth of the density
fluctuations [3], the application of the SIV to scale-invariant dynamics of
galaxies, MOND, dark matter, and the dwarf spheroidals [4],and the most recent
results on the BBNS light-elements' abundances within the SIV [5]. Keywords:
cosmology: theory, dark matter, dark energy, inflation, BBNS; galaxies:
formation, rotation; Weyl integrable geometry; Dirac co-calculus. |
The RWST, a comprehensive statistical description of the non-Gaussian
structures in the ISM: The interstellar medium (ISM) is a complex non-linear system governed by
gravity and magneto-hydrodynamics, as well as radiative, thermodynamical, and
chemical processes. Our understanding of it mostly progresses through
observations and numerical simulations, and a quantitative comparison between
these two approaches requires a generic and comprehensive statistical
description. The goal of this paper is to build such a description, with the
purpose to permit an efficient comparison independent of any specific prior or
model. We start from the Wavelet Scattering Transform (WST), a low-variance
statistical description of non-Gaussian processes, developed in data science,
that encodes long-range interactions through a hierarchical multiscale approach
based on the Wavelet transform. We perform a reduction of the WST through a fit
of its angular dependencies, allowing to gather most of the information it
contains into a few components whose physical meanings are identified, and that
describe, e.g., isotropic and anisotropic behaviours. The result of this paper
is the Reduced Wavelet Scattering Transform (RWST), a statistical description
with a small number of coefficients that characterizes complex structures
arising from non-linear phenomena, free from any specific prior. The RWST
coefficients encode moments of order up to four, have reduced variances, and
quantify the couplings between scales. To show the efficiency and generality of
this description, we apply it successfully to three kinds of processes:
fractional Brownian motions, MHD simulations, and Herschel observations in a
molecular cloud. With fewer than 100 coefficients when probing 6 scales and 8
angles on 256*256 maps, we were able with the RWST to perform quantitative
comparisons, to infer relevant physical properties, and to produce realistic
synthetic fields. | Tensor perturbations during inflation in a spatially closed Universe: In a recent paper [17], we studied the evolution of the background geometry
and scalar perturbations in an inflationary, spatially closed
Friedmann-Lema\^itre-Robertson-Walker (FLRW) model having constant positive
spatial curvature and spatial topology $\mathbb S^3$. Due to the spatial
curvature, the early phase of slow-roll inflation is modified, leading to
suppression of power in the scalar power spectrum at large angular scales. In
this paper, we extend the analysis to include tensor perturbations. We find
that --- similarly to the scalar perturbations --- the tensor power spectrum
also shows power suppression for long wavelength modes. The correction to the
tensor spectrum is limited to the very long wavelength modes, therefore the
resulting observable CMB B-mode polarization spectrum remains practically the
same as in the standard scenario with flat spatial sections. However, since
both the tensor and scalar power spectra are modified, there are scale
dependent corrections to the tensor-to-scalar ratio that lead to violation of
the standard slow-roll consistency relation. |
The impact of the SZ effect on cm-wavelength (1-30 GHz) observation of
galaxy cluster radio relics: (Abridged) Radio relics in galaxy clusters are believed to be associated with
powerful shock fronts that originate during cluster mergers, and are a testbed
for the acceleration of relativistic particles in the intracluster medium.
Recently, radio relic observations have pushed into the cm-wavelength domain
(1-30 GHz) where a break from the standard synchrotron power-law spectrum has
been found, most noticeably in the famous 'Sausage' relic. In this paper, we
point to an important effect that has been ignored or considered insignificant
while interpreting these new high-frequency radio data, namely the
contamination due to the Sunyaev-Zel'dovich (SZ) effect that changes the
observed synchrotron flux. Even though the radio relics reside in the cluster
outskirts, the shock-driven pressure boost increases the SZ signal locally by
roughly an order of magnitude. The resulting flux contamination for some
well-known relics are non-negligible already at 10 GHz, and at 30 GHz the
observed synchrotron fluxes can be diminished by a factor of several from their
true values. Interferometric observations are not immune to this contamination,
since the change in the SZ signal occurs roughly at the same length scale as
the synchrotron emission, although there the flux loss is less severe than
single-dish observations. We present a simple analytical approximation for the
synchrotron-to-SZ flux ratio, based on a theoretical radio relic model that
connects the non-thermal emission to the thermal gas properties, and show that
by measuring this ratio one can potentially estimate the relic magnetic fields
or the particle acceleration efficiency. | On the insufficiency of arbitrarily precise covariance matrices:
non-Gaussian weak lensing likelihoods: We investigate whether a Gaussian likelihood, as routinely assumed in the
analysis of cosmological data, is supported by simulated survey data. We define
test statistics, based on a novel method that first destroys Gaussian
correlations in a dataset, and then measures the non-Gaussian correlations that
remain. This procedure flags pairs of datapoints which depend on each other in
a non-Gaussian fashion, and thereby identifies where the assumption of a
Gaussian likelihood breaks down. Using this diagnostic, we find that
non-Gaussian correlations in the CFHTLenS cosmic shear correlation functions
are significant. With a simple exclusion of the most contaminated datapoints,
the posterior for $s_8$ is shifted without broadening, but we find no
significant reduction in the tension with $s_8$ derived from Planck Cosmic
Microwave Background data. However, we also show that the one-point
distributions of the correlation statistics are noticeably skewed, such that
sound weak lensing data sets are intrinsically likely to lead to a
systematically low lensing amplitude being inferred. The detected
non-Gaussianities get larger with increasing angular scale such that for future
wide-angle surveys such as Euclid or LSST, with their very small statistical
errors, the large-scale modes are expected to be increasingly affected. The
shifts in posteriors may then not be negligible and we recommend that these
diagnostic tests be run as part of future analyses. |
A study of the remarkable galaxy system AM 546-324 (the core of Abell
S0546): We report first results of an investigation of the tidally disturbed galaxy
system AM\,546-324, whose two principal galaxies 2MFGC 04711 and AM\,0546-324
(NED02) were previously classified as interacting doubles. This system was
selected to study the interaction of ellipticals in a moderately dense
environment. We provide spectral characteristics of the system and present an
observational study of the interaction effects on the morphology, kinematics,
and stellar population of these galaxies. The study is based on long-slit
spectrophotometric data in the range of $\sim$ 4500-8000 $\AA$ obtained with
the Gemini Multi-Object Spetrograph at Gemini South (GMOS-S). We have used the
stellar population synthesis code STARLIGHT to investigate the star formation
history of these galaxies. The Gemini/GMOS-S direct r-G0303 broad band pointing
image was used to enhance and study fine morphological structures. The main
absorption lines in the spectra were used to determine the radial velocity.
Along the whole long-slit signal, the spectra of the Shadowy galaxy (discovered
by us), 2MFGC 04711, and AM\,0546-324 (NED02) resemble that of an early-type
galaxy. We estimated redshifts of z= 0.0696, z= 0.0693 and z= 0.0718,
corresponding to heliocentric velocities of 20\,141 km s$^{-1}$, 20\,057 km
s$^{-1}$, and 20\,754 km s$^{-1}$ for the Shadowy galaxy, 2MFGC 04711 and
AM\,0546-324 (NED02), respectively. ... | Microlensing and the type Ia supernova iPTF16geu: The observed magnifications and light curves of the quadruply-imaged
iPTF16geu supernova (SN) offers a unique opportunity to study a lens system
with a variety of independent constraints. The four observed positions can be
used to constrain the macrolens model. The magnifications and light curves at
the four SN positions are more useful to constrain microlensing models. We
define the macrolens model as a combination of a baryonic component that traces
the observed light distribution, and a dark matter halo component. We constrain
the macrolens model using the positional constraints given by the 4 observed
images, and compare it with the best model obtained when magnification
constraints are included. We find that the magnification can not be explained
by a macrolens model alone, and that contributions from substructures such as
microlenses are needed to explain the observed magnifications. We consider
microlens models based on the inferred stellar mass from the baryonic component
of the macrolens model, and use the observed magnification and light curves to
constrain the contribution from microlenses. We compute the likelihood of a
variety of macro+micro lens models where we vary the dark matter halo, baryonic
component, and microlens configurations. We use information about the position,
magnification and, for the first time, the lightcurves of the four observed SN
images. We combine macrolens and microlens models in order to reproduce the
observations; the four SN positions, magnifications, and lack of fluctuations
in the light curves. After marginalizing over the model parameters, we find
that larger stellar surface mass densities are preferred. This result suggests
that the mass of the baryonic component is dominated by its stellar component.
We conclude that microlensing from the baryonic component suffices to explain
the observed flux ratios and light curves. |
Constraints on f_nl and g_nl from the analysis of the N-pdf of the CMB
large scale anisotropies: [Abridged] In this paper we explore a local non-linear perturbative model up
to third order as a general characterization of the CMB anisotropies. We focus
our analysis in large scale anisotropies. At these angular scales, the
non-Gaussian description proposed in this work defaults (under certain
conditions) to an approximated local form of the weak non-linear coupling
inflationary model. In particular, quadratic and cubic terms are governed by
the non-linear coupling parameters f_nl and g_nl, respectively. The extension
proposed in this paper allows us to directly constrain these non-linear
parameters. Applying the proposed methodology to WMAP 5-yr data, we obtain -5.6
x 10^5 < g_nl < 6.4 x 10^5, at 95% CL. This result is in agreement with
previous findings obtained for equivalent non-Gaussian models and with
different non-Gaussian estimators. A model selection test is performed,
indicating that a Gaussian model is preferred to the non-Gaussian scenario.
When comparing different non-Gaussian models, we observe that a pure f_nl model
is the most favoured case, and that a pure g_nl model is more likely than a
general non-Gaussian scenario. Finally, we have analyzed the WMAP data in two
independent hemispheres, in particular the ones defined by the dipolar pattern
found by Hoftuft et al. 2009. We show that, whereas g_nl is still compatible
with zero for both hemispheres, it is not the case for f_nl (with a p-value
0.04). However, if anisotropy of the data is assumed, the distance between the
likelihood distributions for each hemisphere is larger than expected from
Gaussian and anisotropic simulations, also for g_nl (with a p-value of 0.001 in
the case of this parameter). This result is an extra evidence for the CMB
asymmetries previously reported in WMAP data. | Non-Gaussianities, early Universe, and GRBs. Tracing the primeval state
of the Universe with number counts of Gamma-Ray Bursts: We investigate the effects of primordial non-Gaussianities in the primordial
Universe on the baryonic structure formation process. By relating the cosmic
star formation rate in Gaussian and non-Gaussian scenarios to the detectability
of high-redshift sources of reionization, we derive the expected Gamma-Ray
Burst rate in the different models. We find that counts of high-redshift
Gamma-Ray Bursts can be used as cosmological probes of non-Gaussianities and
that they are suitable candidates to distinguish non-Gaussian effects at early
epochs. |
Geometrical destabilization, premature end of inflation and Bayesian
model selection: By means of Bayesian techniques, we study how a premature ending of
inflation, motivated by geometrical destabilization, affects the observational
evidences of typical inflationary models. Large field models are worsened, and
inflection point potentials are drastically improved for a specific range of
the field-space curvature characterizing the geometrical destabilization. For
other models we observe shifts in the preferred values of the model parameters.
For quartic hilltop models for instance, contrary to the standard case, we find
preference for theoretically natural sub-Planckian hill widths. Eventually, the
Bayesian ranking of models becomes substantially reordered with a premature end
of inflation. Such a phenomenon also modifies the constraints on the reheating
expansion history, which has to be properly accounted for since it determines
the position of the observational window with respect to the end of inflation.
Our results demonstrate how the interpretation of cosmological data in terms of
fundamental physics is considerably modified in the presence of premature end
of inflation mechanisms. | CMB constraints on inflection-point inflation with a pseudo-scalar dark
matter: In this work, we investigate the physical aspects of the inflection-point
inflation scenario and assess its observational viability in light of current
Cosmic Microwave Background (CMB) data. The model we consider encapsulates the
inflaton with a pseudo-scalar (the dark matter candidate) in a complex neutral
scalar singlet. The cosmological constraints on the parameters of inflation
derived at a high energy scale are translated to a low energy scale by running
these parameters. Ensuring the entire Lagrangian to be invariant under a $Z_3$
symmetry with the adequate transformation of the fields, the imaginary part of
the singlet decouples from the other scalars of the model. We then investigate
if the observational viability of inflation is also compatible with this
pseudo-scalar being the dark matter component. We show that the CMB constraints
on the inflationary parameters assure that the pseudo-scalar is stable and
provides the correct relic dark matter abundance, regardless of whether it is
thermally or non-thermally produced. |
Warm-hot gas in groups and galaxies toward H2356-309: We present a detailed analysis of the galaxy and group distributions around
three reported X-ray absorption line systems in the spectrum of the quasar
H2356-309. Previous studies associated these absorbers with known large-scale
galaxy structures (i.e., walls and filaments) along the line of sight. Such
absorption lines typically trace 10^{5-7} K gas, and may be evidence of the
elusive warm-hot intergalactic medium (WHIM) thought to harbor the bulk of the
low-redshift "missing baryons;" alternatively, they may be linked to individual
galaxies or groups in the filaments. Here we combine existing galaxy survey
data with new, multi-object Magellan spectroscopy to investigate the detailed
galaxy distribution near each absorber. All of these three absorption systems
are within the projected virial radii of nearby galaxies and/or groups, and
could therefore arise in these virialized structures rather than (or in
addition to) the WHIM. However, we find no additional galaxies near a fourth
"void" absorber recently found in the spectrum, suggesting that this system may
indeed trace gas unassociated with any individual halo. Though the number of
known systems is still small, spatial coincidences suggest that some X-ray
absorbers lie in galaxy and/or group environments, though others could still
trace the large-scale filamentary WHIM gas predicted by simulations. | The origin of the infrared emission in radio galaxies. III. Analysis of
3CRR objects: We present Spitzer photometric data for a complete sample of 19 low redshift
(z<0.1) 3CRR radio galaxies as part of our efforts to understand the origin of
the prodigious mid- to far-infrared (MFIR) emission from radio-loud AGN. Our
results show a correlation between AGN power (indicated by [OIII] 5007 emission
line luminosity) and 24 micron luminosity. This result is consistent with the
24 micron thermal emission originating from warm dust heated directly by AGN
illumination. Applying the same correlation test for 70 micron luminosity
against [OIII] luminosity we find this relation to suffer from increased
scatter compared to that of 24 micron. In line with our results for the
higher-radio-frequency-selected 2Jy sample, we are able to show that much of
this increased scatter is due to heating by starbursts which boost the
far-infrared emission at 70 micron in a minority of objects (17-35%). Overall
this study supports previous work indicating AGN illumination as the dominant
heating mechanism for MFIR emitting dust in the majority of low to intermediate
redshift radio galaxies (0.03<z<0.7), with the advantage of strong statistical
evidence. However, we find evidence that the low redshift broad-line objects
(z<0.1) are distinct in terms of their positions on the MFIR vs. [OIII]
correlations. |
High Resolution H I Distributions and Multi-Wavelength Analyses of
Magellanic Spirals NGC 4618 and NGC 4625: We present a detailed analysis of high resolution H I observations of the
Magellanic spiral galaxies NGC 4618 and NGC 4625. While the H I disk of NGC
4625 is remarkably quiescent with a nearly uniform velocity dispersion and no
evidence of H I holes, there is a dynamic interplay between star formation and
the distribution of neutral hydrogen in NGC 4618. We calculate the critical
density for widespread star formation in each galaxy and find that star
formation proceeds even where the surface density of the atomic gas is well
below the critical density necessary for global star formation. There are
strong spatial correlations in NGC 4618 between UV emission, 1.4 GHz radio
continuum emission, and peaks in the H I column density. Despite the apparent
overlap of the outer disks of the two galaxies, we find that they are
kinematically distinct, indicating that NGC 4618 and NGC 4625 are not
interacting. The structure of NGC 4618 and, in particular, the nature of its
outer ring, are highly suggestive of an interaction, but the timing and nature
of such an interaction remain unclear. | A census of cool core galaxy clusters in IllustrisTNG: The thermodynamic structure of hot gas in galaxy clusters is sensitive to
astrophysical processes and typically difficult to model with galaxy formation
simulations. We explore the fraction of cool-core (CC) clusters in a large
sample of $370$ clusters from IllustrisTNG, examining six common CC
definitions. IllustrisTNG produces continuous CC criteria distributions, the
extremes of which are classified as CC and non-cool-core (NCC), and the
criteria are increasingly correlated for more massive clusters. At $z=0$, the
CC fractions for $2$ criteria are in reasonable agreement with the observed
fractions but the other $4$ CC fractions are lower than observed. This result
is partly driven by systematic differences between the simulated and observed
gas fraction profiles. The simulated CC fractions with redshift show tentative
agreement with the observed fractions, but linear fits demonstrate that the
simulated evolution is steeper than observed. The conversion of CCs to NCCs
appears to begin later and act more rapidly in the simulations. Examining the
fraction of CCs and NCCs defined as relaxed we find no evidence that CCs are
more relaxed, suggesting that mergers are not solely responsible for disrupting
CCs. A comparison of the median thermodynamic profiles defined by different CC
criteria shows that the extent to which they evolve in the cluster core is
dependent on the CC criteria. We conclude that the thermodynamic structure of
galaxy clusters in IllustrisTNG shares many similarities with observations, but
achieving better agreement most likely requires modifications of the underlying
galaxy formation model. |
Testing for dynamical dark energy models with redshift-space distortions: The red-shift space distortions in the galaxy power spectrum can be used to
measure the growth rate of matter density perturbations delta_m. For dynamical
dark energy models in General Relativity we provide a convenient analytic
formula of f(z) sigma_8(z) written as a function of the redshift z, where f=d
ln delta_m/d ln a (a is the cosmological scale factor) and sigma_8 is the rms
amplitude of over-density at the scale 8 h^{-1} Mpc. Our formula can be applied
to the models of imperfect fluids, quintessence, and k-essence, provided that
the dark energy equation of state w does not vary significantly and that the
sound speed is not much smaller than 1. We also place observational constraints
on dark energy models of constant w and tracking quintessence from the recent
data of red-shift space distortions. | Cosmic Axion Bose-Einstein Condensation: QCD axions are a well-motivated candidate for cold dark matter. Cold axions
are produced in the early universe by vacuum realignment, axion string decay
and axion domain wall decay. We show that cold axions thermalize via their
gravitational self-interactions, and form a Bose-Einstein condensate. As a
result, axion dark matter behaves differently from the other proposed forms of
dark matter. The differences are observable. |
The Hubble Space Telescope Cluster Supernova Survey: III. Correlated
Properties of Type Ia Supernovae and Their Hosts at 0.9 < z < 1.46: Using the sample of Type Ia supernovae (SNe Ia) discovered by the Hubble
Space Telescope (HST) Cluster Supernova Survey and augmented with HST-observed
SNe Ia in the GOODS fields, we search for correlations between the properties
of SNe and their host galaxies at high redshift. We use galaxy color and
quantitative morphology to determine the red sequence in 25 clusters and
develop a model to distinguish passively evolving early-type galaxies from
star-forming galaxies in both clusters and the field. With this approach, we
identify six SN Ia hosts that are early-type cluster members and eleven SN Ia
hosts that are early-type field galaxies. We confirm for the first time at
z>0.9 that SNe Ia hosted by early-type galaxies brighten and fade more quickly
than SNe Ia hosted by late-type galaxies. We also show that the two samples of
hosts produce SNe Ia with similar color distributions. The relatively simple
spectral energy distributions (SEDs) expected for passive galaxies enable us to
measure stellar masses of early-type SN hosts. In combination with stellar mass
estimates of late-type GOODS SN hosts from Thomson & Chary (2011), we
investigate the correlation of host mass with Hubble residual observed at lower
redshifts. Although the sample is small and the uncertainties are large, a hint
of this relation is found at z>0.9. By simultaneously fitting the average
cluster galaxy formation history and dust content to the red-sequence scatters,
we show that the reddening of early-type cluster SN hosts is likely E(B-V) <~
0.06. The similarity of the field and cluster early-type host samples suggests
that field early-type galaxies that lie on the red sequence may also be
minimally affected by dust. Hence, the early-type hosted SNe Ia studied here
occupy a more favorable environment to use as well-characterized high-redshift
standard candles than other SNe Ia. | The SAURON Project - XIX. Optical and near-infrared scaling relations of
nearby elliptical, lenticular and Sa galaxies: [Abridged] We present ground-based MDM V-band and Spitzer/IRAC 3.6um-band
photometric observations of the 72 representative galaxies of the SAURON
Survey. In combination with the SAURON stellar velocity dispersion measured
within an effective radius (se), this allows us to explore the location of our
galaxies in the main scaling relations. We investigate the dependence of these
relations on our recent kinematical classification of early-type galaxies (i.e.
Slow/Fast Rotators) and the stellar populations. Slow Rotator and Fast Rotator
E/S0 galaxies do not populate distinct locations in the scaling relations,
although Slow Rotators display a smaller intrinsic scatter. Surprisingly,
extremely young objects do not display the bluest (V-[3.6]) colours in our
sample, as is usually the case in optical colours. This can be understood in
the context of the large contribution of TP-AGB stars to the infrared, even for
young populations, resulting in a very tight (V-[3.6]) - se relation that in
turn allows us to define a strong correlation between metallicity and velocity
dispersion. Many Sa galaxies appear to follow the Fundamental Plane defined by
E/S0 galaxies. Galaxies that appear offset from the relations correspond mostly
to objects with extremely young populations, with signs of on-going, extended
star formation. We correct for this effect in the Fundamental Plane, by
replacing luminosity with stellar mass using an estimate of the stellar
mass-to-light ratio, so that all galaxies are part of a tight, single relation.
The new estimated coefficients are consistent in both photometric bands and
suggest that differences in stellar populations account for about half of the
observed tilt with respect to the virial prediction. After these corrections,
the Slow Rotator family shows almost no intrinsic scatter around the best-fit
Fundamental Plane. |
Fugacity and Reheating of Primordial Neutrinos: We clarify in a quantitative way the impact that distinct chemical $T_c$ and
kinetic $T_k$ freeze-out temperatures have on the reduction of the neutrino
fugacity $\Upsilon_\nu$ below equilibrium, i.e. $\Upsilon_\nu<1$, and the
increase of the neutrino temperature $T_\nu$ via partial reheating. We
establish the connection between $\Upsilon_\nu$ and $T_k$ via the modified
reheating relation $T_\nu(\Upsilon_\nu)/T_\gamma$, where $T_\gamma$ is the
temperature of the background radiation. Our results demonstrate that one must
introduce the chemical nonequilibrium parameter, i.e., the fugacity,
$\Upsilon_\nu$, as an additional standard cosmological model parameter in the
evaluation of CMB fluctuations as its value allows measurement of $T_k$. | Multi-wavelength GOALS Observations of Star Formation and Active
Galactic Nucleus Activity in the Luminous Infrared Galaxy IC 883: New optical HST, Spitzer, GALEX, and Chandra observations of the
single-nucleus, luminous infrared galaxy (LIRG) merger IC 883 are presented.
The galaxy is a member of the Great Observatories All-sky LIRG Survey (GOALS),
and is of particular interest for a detailed examination of a luminous
late-stage merger due to the richness of the optically-visible star clusters
and the extended nature of the nuclear X-ray, mid-IR, CO and radio emission. In
the HST ACS images, the galaxy is shown to contain 156 optically visible star
clusters distributed throughout the nuclear regions and tidal tails of the
merger, with a majority of visible clusters residing in an arc ~ 3-7 kpc from
the position of the mid-infrared core of the galaxy. The luminosity functions
of the clusters have an alpha_F435W ~ -2.17+/-0.22 and alpha_F814W ~
-2.01+/-0.21. Further, the colors and absolute magnitudes of the majority of
the clusters are consistent with instantaneous burst population synthesis model
ages in the range of a few x10^7 - 10^8 yrs (for 10^5 M_sun clusters), but may
be as low as few x10^6 yrs with extinction factored in. The X-ray and mid-IR
spectroscopy are indicative of predominantly starburst-produced nuclear
emission, and the star formation rate is ~ 80 M_sun / yr. The kinematics of the
CO emission and the morphology of both the CO and radio emission are consistent
with the nuclear starburst being situated in a highly inclined disk 2 kpc in
diameter with an infrared surface brightness mu_IR ~ 2x10^11 L_sun kpc^-2, a
factor of 10 less than that of the Orion star-forming region. Finally, the
detection of the [Ne V] 14.32 um emission line is evidence that an AGN is
present. The faintness of the line (i.e., [Ne V] / [Ne II] um ~ 0.01) and the
small equivalent width of the 6.2 um PAH feature ($= 0.39\mu$m) are both
indicative of a relatively weak AGN. (abridged) |
Cosmological foundations revisited with Pantheon+: We reanalyse the Pantheon+ supernova catalogue to compare a cosmology with
non-FLRW evolution, the "timescape cosmology", with the standard $\Lambda$CDM
cosmology. To this end, we consider the Pantheon+ supernova catalogue, which is
the largest available Type Ia supernova dataset for a geometric comparison
between the two models. We construct a covariance matrix to be as independent
of cosmology as possible, including independence from the FLRW geometry and
peculiar velocity with respect to FLRW average evolution. Within this
framework, which goes far beyond most other definitions of "model
independence", we introduce new statistics to refine Type Ia supernova (SneIa)
light-curve analysis. In addition to conventional galaxy correlation functions
used to define the scale of statistical homogeneity we introduce empirical
statistics which enables a refined analysis of the distribution biases of SneIa
light-curve parameters $\beta c$ and $\alpha x_1$.
For lower redshifts, the Bayesian analysis highlights important features
attributable to the increased number of low-redshift supernovae, the artefacts
of model-dependent light-curve fitting and the cosmic structure through which
we observe supernovae. This indicates the need for cosmology-independent data
reduction to conduct a stronger investigation of the emergence of statistical
homogeneity and to compare alternative cosmologies in light of recent
challenges to the standard model.
"Dark energy" is generally invoked as a place-holder for "new physics". Our
from-first-principles reanalysis of the Pantheon+ catalogue supports future
deeper studies of the interplay of matter and nonlinear spacetime geometry, in
a data-driven setting. For the first time in 25 years, we find evidence that
the Pantheon+ catalogue already contains such a wealth of data that with
further reanalysis, a genuine "paradigm shift" may soon emerge. [Abridged] | Lensing and Dynamics in Two Simple Steps: We present a ready-to-use method to constrain the density distribution in
early-type galaxy lenses. Assuming a power-law density profile, then joint use
of the virial theorem and the lens equation yields simple formulae for the
power-law index (or logarithmic density gradient). Any dependence on orbital
anisotropy can be tightly constrained or even erased completely. Our results
rely just on surface brightnesses and line-of-sight kinematics, making
deprojection unnecessary. We revisit three systems that have already been
examined in the literature (the Cosmic Horseshoe, the Jackpot and B1608+656)
and provide our estimates. Finally, we show that the method yields a good
approximation for the density profile even when the true profile is a broken
power-law, albeit with a mild bias towards isothermality. |
CosmoFlow: Using Deep Learning to Learn the Universe at Scale: Deep learning is a promising tool to determine the physical model that
describes our universe. To handle the considerable computational cost of this
problem, we present CosmoFlow: a highly scalable deep learning application
built on top of the TensorFlow framework. CosmoFlow uses efficient
implementations of 3D convolution and pooling primitives, together with
improvements in threading for many element-wise operations, to improve training
performance on Intel(C) Xeon Phi(TM) processors. We also utilize the Cray PE
Machine Learning Plugin for efficient scaling to multiple nodes. We demonstrate
fully synchronous data-parallel training on 8192 nodes of Cori with 77%
parallel efficiency, achieving 3.5 Pflop/s sustained performance. To our
knowledge, this is the first large-scale science application of the TensorFlow
framework at supercomputer scale with fully-synchronous training. These
enhancements enable us to process large 3D dark matter distribution and predict
the cosmological parameters $\Omega_M$, $\sigma_8$ and n$_s$ with unprecedented
accuracy. | Secular Extragalactic Parallax: Measurement Methods and Predictions for
Gaia: Secular extragalactic parallax caused by the solar system's velocity relative
to the cosmic microwave background rest frame may be observable as a dipole
proper motion field with amplitude $78~\mu$as yr$^{-1}$ Mpc. Nearby galaxies
also exhibit proper motions caused by their transverse peculiar velocities that
prevent detection of secular parallax for any single galaxy, although a
statistical detection may be made instead. Such a detection could constrain the
local Hubble parameter. We present methods to measure secular parallax using
correlated extragalactic proper motions and find a first limit on the secular
parallax amplitude using proper motions of 232 nearby galaxies from Gaia Data
Release 2. The recovered dipole has insignificant upper limit of 3500 $\mu$as
yr$^{-1}$ Mpc. This measurement will be improved by larger sample size and
reduced proper motion uncertainties in future data releases. Using the local
peculiar velocity field derived from Cosmicflows-3, we simulate galaxy proper
motions and predict that a significant detection ($5-10\sigma$) of the secular
parallax amplitude will be possible by Gaia's end of mission. The detection is
contingent on proper motions of nearby ($<5$ Mpc), bright ($G<15$ mag)
galaxies, and corresponds to an insignificant upper limit on the Hubble
parameter. We further investigate the implications of our simulations for the
study of transverse peculiar velocities, which we find to be consistent with
large scale structure theory. The peculiar velocity field additionally results
in low-multipole correlated proper motions on the order of $0.3~\mu$as
yr$^{-1}$ that may be confounded with other cosmological proper motion
measurements, such as limits on the gravitational wave background and the
anisotropy of the Hubble expansion. |
Inflationary magnetic fields spoil the homogeneity and isotropy of the
Universe: This paper has been withdrawn by the authors due to a mistake in the
calculations leading to an erroneous conclusion. | A Study on the Baryon Acoustic Oscillation with Topological Data
Analysis: (abridged) The scale of the acoustic oscillation of baryons at the
baryon-photon decoupling is imprinted on the spatial distribution of galaxies
in the Universe, known as the baryon acoustic oscillation (BAO). The
correlation functions and power spectrum are used as a central tool for the
studies on the BAO analysis. In this work, we analyzed the spatial distribution
of galaxies with a method from the topological data analysis (TDA), in order to
detect and examine the BAO signal in the galaxy distribution. The TDA provides
a method to treat various types of "holes" in point set data, by constructing
the persistent homology (PH) group from the geometric structure of data points
and handling the topological information of the dataset. We can obtain the
information on the size, position, and statistical significance of the holes in
the data. A particularly strong point of the persistent homology is that it can
classify the holes by their spatial dimension, i.e., a 0-dim separation, 1-dim
loop, 2-dim shell, etc. We first analyzed the simulation datasets with and
without the baryon physics to examine the performance of the PH method. We
found that the PH is indeed able to detect the BAO signal: simulation data with
baryon physics present a prominent signal from the BAO, while data without
baryon physics does not show this signal. Then, we applied the PH to a quasar
sample at $z <1.0$ from extended Baryon Oscillation Spectroscopic Survey in
Sloan Digital Sky Survey Data Release 14. We discovered a characteristic hole
(a hollow shell) at a scaler $\sim150\ [{\rm Mpc}]$. This exactly corresponds
to the BAO signature imprinted in the galaxy/quasar distribution. We performed
this analysis on a small subsample of 2000 quasars. This clearly demonstrates
that the PH analysis is very efficient in finding this type of topological
structures even if the sampling is very sparse. |
Linear redshift space distortions for cosmic voids based on galaxies in
redshift space: Cosmic voids found in galaxy surveys are defined based on the galaxy
distribution in redshift space. We show that the large scale distribution of
voids in redshift space traces the fluctuations in the dark matter density
field \delta(k) (in Fourier space with \mu being the line of sight projected
k-vector): \delta_v^s(k) = (1 + \beta_v \mu^2) b^s_v \delta(k), with a beta
factor that will be in general different than the one describing the
distribution of galaxies. Only in case voids could be assumed to be quasi-local
transformations of the linear (Gaussian) galaxy redshift space field, one gets
equal beta factors \beta_v=\beta_g=f/b_g with f being the growth rate, and b_g,
b^s_v being the galaxy and void bias on large scales defined in redshift space.
Indeed, in our mock void catalogs we measure void beta factors being in good
agreement with the galaxy one. Further work needs to be done to confirm the
level of accuracy of the beta factor equality between voids and galaxies, but
in general the void beta factor needs to be considered as a free parameter for
RSD studies. | EAGLE-like simulation models do not solve the entropy core problem in
groups and clusters of galaxies: Recent high-resolution cosmological hydrodynamic simulations run with a
variety of codes systematically predict large amounts of entropy in the
intra-cluster medium at low redshift, leading to flat entropy profiles and a
suppressed cool-core population. This prediction is at odds with X-ray
observations of groups and clusters. We use a new implementation of the EAGLE
galaxy formation model to investigate the sensitivity of the central entropy
and the shape of the profiles to changes in the sub-grid model applied to a
suite of zoom-in cosmological simulations of a group of mass $M_{500} = 8.8
\times 10^{12}~{\rm M}_\odot$ and a cluster of mass $2.9 \times 10^{14}~{\rm
M}_\odot$. Using our reference model, calibrated to match the stellar mass
function of field galaxies, we confirm that our simulated groups and clusters
contain hot gas with too high entropy in their cores. Additional simulations
run without artificial conduction, metal cooling or AGN feedback produce lower
entropy levels but still fail to reproduce observed profiles. Conversely, the
two objects run without supernova feedback show a significant entropy increase
which can be attributed to excessive cooling and star formation. Varying the
AGN heating temperature does not greatly affect the profile shape, but only the
overall normalisation. Finally, we compared runs with four AGN heating schemes
and obtained similar profiles, with the exception of bipolar AGN heating, which
produces a higher and more uniform entropy distribution. Our study leaves open
the question of whether the entropy core problem in simulations, and
particularly the lack of power-law cool-core profiles, arise from incorrect
physical assumptions, missing physical processes, or insufficient numerical
resolution. |
New probe of gravity: strongly lensed gravitational wave multi-messenger
approach: Strong gravitational lensing by galaxies provides us with a unique
opportunity to understand the nature of gravity on galactic and extra-galactic
scales. In this paper, we propose a new multimessenger approach using data from
both gravitational wave (GW) and the corresponding electromagnetic (EM)
counterpart to infer the constraint of the modified gravity (MG) theory denoted
by the scale dependent phenomenological parameter. To demonstrate the
robustness of this approach, we calculate the time-delay predictions by
choosing various values of the phenomenological parameters and then compare
them with that from the general relativity (GR). For the third generation
ground-based GW observatory, with one typical strongly lensed GW+EM event, and
assuming that the dominated error from the stellar velocity dispersions is 5\%,
the GW time-delay data can distinguish an 18\% MG effect on a scale of tens of
kiloparsecs with a $68\%$ confidence level. Assuming GR and a Singular
Isothermal Sphere mass model, there exists a simplified consistency
relationship between time-delay and imaging data. This relationship does not
require for the velocity dispersion measurement, and hence can avoid major
uncertainties. By using this relationship, the multimessenger approach is able
to distinguish an $8\%$ MG effect. Our results show that the GW multimessenger
approach can play an important role in revealing the nature of gravity on the
galactic and extra-galactic scales. | X-ray selected Infrared Excess AGN in the Chandra Deep Fields: a
moderate fraction of Compton-thick sources: We examine the properties of the X-ray detected, Infrared Excess AGN or Dust
Obscured Galaxies (DOGs) in the Chandra Deep Fields (CDF). We find 26 X-ray
selected sources which obey the 24 micron to R-band flux ratio criterion
f_24/f_R>1000. These are at a median redshift of 2.3 while their IR
luminosities are above 10^12 solar. Their X-ray luminosities are all above a
few times 10^42 erg s-1 in the 2-10 keV band unambiguously arguing that these
host AGN. Nevertheless, their IR Spectral Energy Distributions are split
between AGN (Mrk231) and star-forming templates (Arp220). Our primary goal is
to examine their individual X-ray spectra in order to assess whether this X-ray
detected DOG population contains heavily obscured or even Compton-thick
sources. The X-ray spectroscopy reveals a mixed bag of objects. We find that
four out of the 12 sources with adequate photon statistics and hence reliable
X-ray spectra, show evidence for a hard X-ray spectral index (~1) or
harder,consistent with a Compton-thick spectrum. In total 12 out of the 26 DOGs
show evidence for flat spectral indices. However, owing to the limited photon
statistics we cannot differentiate whether these are flat because they are
reflection-dominated or because they show moderate amounts of absorption. Seven
DOGs show relatively steep spectra (>1.4) indicative of small column densities.
All the above suggest a fraction of Compton-thick sources that does not exceed
5%. The average X-ray spectrum of all 26 DOGs is hard (~1.1) or even harder
(~0.6) when we exclude the brightest sources. These spectral indices are well
in agreement with the stacked spectrum of X-ray undetected sources (~0.8 in the
CDFN). This could suggest (but not necessarily prove) that X-ray undetected
DOGs, in a similar fashion to the X-ray detected ones presented here, are
hosting a moderate fraction of Compton-thick sources. |
The Steady State Wind Model for Young Stellar Clusters with an
Exponential Stellar Density Distribution: A hydrodynamic model for steady state, spherically-symmetric winds driven by
young stellar clusters with an exponential stellar density distribution is
presented. Unlike in most previous calculations, the position of the singular
point R_sp, which separates the inner subsonic zone from the outer supersonic
flow, is not associated with the star cluster edge, but calculated
self-consistently. When the radiative losses of energy are negligible, the
transition from the subsonic to the supersonic flow occurs always at R_sp ~ 4
R_c, where R_c is the characteristic scale for the stellar density
distribution, irrespective of other star cluster parameters. This is not the
case in the catastrophic cooling regime, when the temperature drops abruptly at
a short distance from the star cluster center and the transition from the
subsonic to the supersonic regime occurs at a much smaller distance from the
star cluster center. The impact from the major star cluster parameters to the
wind inner structure is thoroughly discussed. Particular attention is paid to
the effects which radiative cooling provides to the flow. The results of the
calculations for a set of input parameters, which lead to different
hydrodynamic regimes, are presented and compared to the results from
non-radiative 1D numerical simulations and to those from calculations with a
homogeneous stellar mass distribution. | BICEP2 I: Detection Of B-mode Polarization at Degree Angular Scales: (abridged for arXiv) We report results from the BICEP2 experiment, a cosmic
microwave background (CMB) polarimeter specifically designed to search for the
signal of inflationary gravitational waves in the B-mode power spectrum around
$\ell\sim80$. The telescope comprised a 26 cm aperture all-cold refracting
optical system equipped with a focal plane of 512 antenna coupled transition
edge sensor 150 GHz bolometers each with temperature sensitivity of
$\approx300\mu\mathrm{K}_\mathrm{CMB}\sqrt{s}$. BICEP2 observed from the South
Pole for three seasons from 2010 to 2012. A low-foreground region of sky with
an effective area of 380 square deg was observed to a depth of 87 nK deg in
Stokes $Q$ and $U$. We find an excess of $B$-mode power over the base
lensed-LCDM expectation in the range $30< \ell< 150$, inconsistent with the
null hypothesis at a significance of $> 5\sigma$. Through jackknife tests and
simulations we show that systematic contamination is much smaller than the
observed excess. We also examine a number of available models of polarized dust
emission and find that at their default parameter values they predict power
$\sim(5-10)\times$ smaller than the observed excess signal. However, these
models are not sufficiently constrained to exclude the possibility of dust
emission bright enough to explain the entire excess signal. Cross correlating
BICEP2 against 100 GHz maps from the BICEP1 experiment, the excess signal is
confirmed and its spectral index is found to be consistent with that of the
CMB, disfavoring dust at $1.7\sigma$. The observed $B$-mode power spectrum is
well fit by a lensed-LCDM + tensor theoretical model with tensor-to-scalar
ratio $r=0.20^{+0.07}_{-0.05}$, with $r=0$ disfavored at $7.0\sigma$.
Accounting for the contribution of foreground dust will shift this value
downward by an amount which will be better constrained with upcoming data sets. |
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