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Determination of z~0.8 neutral hydrogen fluctuations using the 21 cm
intensity mapping auto-correlation: The large-scale distribution of neutral hydrogen in the Universe will be
luminous through its 21 cm emission. Here, for the first time, we use the
auto-power spectrum of 21 cm intensity fluctuations to constrain neutral
hydrogen fluctuations at z~0.8. Our data were acquired with the Green Bank
Telescope and span the redshift range 0.6 < z < 1 over two fields totalling ~41
deg. sq. and 190 h of radio integration time. The dominant synchrotron
foregrounds exceed the signal by ~10^3, but have fewer degrees of freedom and
can be removed efficiently. Even in the presence of residual foregrounds, the
auto-power can still be interpreted as an upper bound on the 21 cm signal. Our
previous measurements of the cross-correlation of 21 cm intensity and the
WiggleZ galaxy survey provide a lower bound. Through a Bayesian treatment of
signal and foregrounds, we can combine both fields in auto- and cross-power
into a measurement of Omega_HI b_HI = [0.62^{+0.23}_{-0.15}] * 10^{-3} at 68%
confidence with 9% systematic calibration uncertainty, where Omega_HI is the
neutral hydrogen (HI) fraction and b_HI is the HI bias parameter. We describe
observational challenges with the present data set and plans to overcome them. | LIMFAST. I. A Semi-Numerical Tool for Line Intensity Mapping: We present LIMFAST, a semi-numerical code for simulating high-redshift galaxy
formation and cosmic reionization as revealed by multi-tracer line intensity
mapping (LIM) signals. LIMFAST builds upon and extends the 21cmFAST code widely
used for 21 cm cosmology by implementing state-of-the-art models of galaxy
formation and evolution. The metagalactic radiation background, including the
production of various star-formation lines, together with the 21 cm line signal
tracing the neutral intergalactic medium (IGM), are self-consistently described
by photoionization modeling and stellar population synthesis coupled to the
galaxy formation model. We introduce basic structure and functionalities of the
code, and demonstrate its validity and capabilities by showing broad agreements
between the predicted and observed evolution of cosmic star formation, IGM
neutral fraction, and metal enrichment. We also present the LIM signals of 21
cm, Ly$\alpha$, H$\alpha$, H$\beta$, [OII], and [OIII] lines simulated by
LIMFAST, and compare them with results from the literature. We elaborate on how
several major aspects of our modeling framework, including models of star
formation, chemical enrichment, and photoionization, may impact different LIM
observables and thus become testable once applied to observational data.
LIMFAST aims at being an efficient and resourceful tool for intensity mapping
studies in general, exploring a wide range of scenarios of galaxy evolution and
reionization and frequencies over which useful cosmological signals can be
measured. |
10C Survey of Radio Sources at 15.7 GHz: II - First Results: The first results from the Tenth Cambridge (10C) Survey of Radio Sources,
carried out using the AMI Large Array (LA) at an observing frequency of 15.7
GHz, are presented. The survey fields cover an area of approximately 27 sq.
degrees to a flux-density completeness of 1 mJy. Results for some deeper areas,
covering approximately 12 sq. degrees, wholly contained within the total areas
and complete to 0.5 mJy, are also presented. The completeness for both areas is
estimated to be at least 93 per cent.
The source catalogue contains 1897 entries and is available at
www.mrao.cam.ac.uk/surveys/10C. It has been combined with that of the 9C Survey
to calculate the 15.7-GHz source counts. A broken power law is found to provide
a good parameterisation of the differential count between 0.5 mJy and 1 Jy. The
measured count has been compared to that predicted by de Zotti et al. (2005).
The model displays good agreement with the data at the highest flux densities
but under-predicts the integrated count between 0.5 mJy and 1 Jy by about 30
per cent.
Entries from the source catalogue have been matched to those contained in the
catalogues of NVSS and FIRST (both of which have observing frequencies of 1.4
GHz). This matching provides evidence for a shift in the typical
1.4-to-15.7-GHz spectral index of the 15.7-GHz-selected source population with
decreasing flux density towards sub-mJy levels - the spectra tend to become
less steep.
Automated methods for detecting extended sources have been applied to the
data; approximately 5 per cent of the sources are found to be extended relative
to the LA synthesised beam of approximately 30 arcsec. Investigations using
higher-resolution data showed that most of the genuinely extended sources at 16
GHz are classical doubles, although some nearby galaxies and twin-jet sources
were also identified. | Stellar prospects for FRB gravitational lensing: Gravitational lensing of fast radio bursts (FRBs) offers an exciting avenue
for several cosmological applications. However, it is not yet clear how many
such events future surveys will detect nor how to optimally find them. We use
the known properties of FRBs to forecast detection rates of gravitational
lensing on delay timescales from microseconds to years, corresponding to lens
masses spanning fifteen orders of magnitude. We highlight the role of the FRB
redshift distribution on our ability to observe gravitational lensing. We
consider cosmological lensing of FRBs by stars in foreground galaxies and show
that strong stellar lensing will dominate on microsecond timescales. Upcoming
surveys such as DSA-2000 and CHORD will constrain the fraction of dark matter
in compact objects (e.g. primordial black holes) and may detect millilensing
events from intermediate mass black holes (IMBHs) or small dark matter halos.
Coherent all-sky monitors will be able to detect longer-duration lensing events
from massive galaxies, in addition to short time-scale lensing. Finally, we
propose a new application of FRB gravitational lensing that will measure
directly the circumgalactic medium of intervening galaxies. |
Cosmic Tidal Reconstruction with Halo Fields: The gravitational coupling between large-scale perturbations and small-scale
perturbations leads to anisotropic distortions of the small-scale matter
distribution. The measured local small-scale power spectrum can thus be used to
infer the large-scale matter distribution. In this paper, we present a new
tidal reconstruction algorithm for reconstructing large-scale modes using the
full three-dimensional tidal shear information. We apply it to simulated dark
matter halo fields and the reconstructed large-scale density field correlates
well with the original matter density field on large scales, improving upon the
previous tidal reconstruction method which only uses two transverse shear
fields. This has profound implications for recovering lost 21~cm radial modes
due to foreground subtraction and constraining primordial non-Gaussianity using
the multi-tracer method with future cosmological surveys. | High-Entropy Polar Regions Around the First Protostars: We report on simulations of the formation of the first stars in the Universe,
where we identify regions of hot atomic gas (fH2 < 10-6) at densities above
10-14 g/cc, heated to temperatures ranging between 3000 and 8000 K. Within this
temperature range atomic hydrogen is unable to cool effectively. We describe
the kinetic and thermal characteristics of these regions and investigate their
origin. We find that these regions, while small in total mass fraction of the
cloud, may be dynamically important over the accretion timescale for the
central clump in the cloud, particularly as a chemical, rather than radiative,
mechanism for clearing the polar regions of the accretion disk of material and
terminating accretion along these directions. These inherently
three-dimensional effects stress the need for multi-dimensional calculations of
protostellar accretion for reliable predictions of the masses of the very first
stars. |
Directional detection of galactic Dark Matter: Directional detection of galactic Dark Matter is a promising search strategy
for discriminating geniune WIMP events from background ones. We present
technical progress on gaseous detectors as well as recent phenomenological
studies, allowing the design and construction of competitive experiments. | SNEMO: Improved Empirical Models for Type Ia Supernovae: Type Ia supernova cosmology depends on the ability to fit and standardize
observations of supernova magnitudes with an empirical model. We present here a
series of new models of Type Ia Supernova spectral time series that capture a
greater amount of supernova diversity than possible with the models that are
currently customary. These are entitled SuperNova Empirical MOdels
(\textsc{SNEMO}\footnote{https://snfactory.lbl.gov/snemo}). The models are
constructed using spectrophotometric time series from $172$ individual
supernovae from the Nearby Supernova Factory, comprising more than $2000$
spectra. Using the available observations, Gaussian Processes are used to
predict a full spectral time series for each supernova. A matrix is constructed
from the spectral time series of all the supernovae, and Expectation
Maximization Factor Analysis is used to calculate the principal components of
the data. K-fold cross-validation then determines the selection of model
parameters and accounts for color variation in the data. Based on this process,
the final models are trained on supernovae that have been dereddened using the
Fitzpatrick and Massa extinction relation. Three final models are presented
here: \textsc{SNEMO2}, a two-component model for comparison with current
Type~Ia models; \textsc{SNEMO7}, a seven component model chosen for
standardizing supernova magnitudes which results in a total dispersion of
$0.100$~mag for a validation set of supernovae, of which $0.087$~mag is
unexplained (a total dispersion of $0.113$~mag with unexplained dispersion of
$0.097$~mag is found for the total set of training and validation supernovae);
and \textsc{SNEMO15}, a comprehensive $15$ component model that maximizes the
amount of spectral time series behavior captured. |
Massive Neutrinos and Magnetic Fields in the Early Universe: Primordial magnetic fields and massive neutrinos can leave an interesting
signal in the CMB temperature and polarization. We perform a systematic
analysis of general perturbations in the radiation-dominated universe,
accounting for any primordial magnetic field and including leading- order
effects of the neutrino mass. We show that massive neutrinos qualitatively
change the large- scale perturbations sourced by magnetic fields, but that the
effect is much smaller than previously claimed. We calculate the CMB power
spectra sourced by inhomogeneous primordial magnetic fields, from before and
after neutrino decoupling, including scalar, vector and tensor modes, and
consistently modelling the correlation between the density and anisotropic
stress sources. In an appendix we present general series solutions for the
possible regular primordial perturbations. | How common is the Milky Way - satellite system alignment?: The highly flattened distribution of satellite galaxies in the Milky Way
presents a number of puzzles. Firstly, its polar alignment stands out from the
planar alignments commonly found in other galaxies. Secondly, recent proper
motion measurements reveal that the orbital angular momentum of at least 3, and
possibly as many as 8, of the Milky Ways satellites point (within 30 degrees)
along the axis of their flattened configuration, suggesting some form of
coherent motion. In this paper we use a high resolution cosmological simulation
to investigate whether this pattern conflicts with the expectations of the cold
dark matter model of structure formation. We find that this seemingly unlikely
set up occurs often: approximately 35% of the time we find systems in which the
angular momentum of 3 individual satellites point along, or close to, the short
axis of the satellite distribution. In addition, in 30% of the systems we find
that the net angular momentum of the 6 best aligned satellites lies within 35
degrees of the short axis of the satellite distribution, as observed for the
Milky Way. |
Anti-symmetric clustering signals in the observed power spectrum: In this paper, we study how to directly measure the effect of peculiar
velocities in the observed angular power spectra. We do this by constructing a
new anti-symmetric estimator of Large Scale Structure using different dark
matter tracers. We show that the Doppler term is the major component of our
estimator and we show that we can measure it with a signal-to-noise ratio up to
$\sim 50$ using a futuristic SKAO HI galaxy survey. We demonstrate the utility
of this estimator by using it to provide constraints on the Euler equation. | Mass Function of Rich Galaxy Clusters and Its Constraint on sigma_8: The mass function of galaxy clusters is a powerful tool to constrain
cosmological parameters, e.g., the mass fluctuation on the scale of 8 h^{-1}
Mpc, sigma_8, and the abundance of total matter, Omega_m. We first determine
the scaling relations between cluster mass and cluster richness, summed r-band
luminosity and the global galaxy number within a cluster radius. These
relations are then used to two complete volume-limited rich cluster samples
which we obtained from the Sloan Digital Sky Survey (SDSS). We estimate the
masses of these clusters and determine the cluster mass function. Fitting the
data with a theoretical expression, we get the cosmological parameter
constraints in the form of sigma_8(Omega_m/0.3)^{alpha}=beta and find out the
parameters of alpha=0.40-0.50 and beta=0.8-0.9, so that sigma_8=0.8-0.9 if
Omega_m=0.3. Our sigma_8 value is slightly higher than recent estimates from
the mass function of X-ray clusters and the Wilkinson Microwave Anisotropy
Probe (WMAP) data, but consistent with the weak lensing statistics. |
Multi-Dimensional Effective Field Theory Analysis for Direct Detection
of Dark Matter: The scattering of dark matter particles off nuclei in direct detection
experiments can be described in terms of a multidimensional effective field
theory (EFT). A new systematic analysis technique is developed using the EFT
approach and Bayesian inference methods to exploit, when possible, the
energy-dependent information of the detected events, experimental efficiencies,
and backgrounds. Highly dimensional likelihoods are calculated over the mass of
the weakly interacting massive particle (WIMP) and multiple EFT coupling
coefficients, which can then be used to set limits on these parameters and
choose models (EFT operators) that best fit the direct detection data.
Expanding the parameter space beyond the standard spin-independent isoscalar
cross section and WIMP mass reduces tensions between previously published
experiments. Combining these experiments to form a single joint likelihood
leads to stronger limits than when each experiment is considered on its own.
Simulations using two nonstandard operators (3 and 8) are used to test the
proposed analysis technique in up to five dimensions and demonstrate the
importance of using multiple likelihood projections when determining
constraints on WIMP mass and EFT coupling coefficients. In particular, this
shows that an explicit momentum dependence in dark matter scattering can be
identified. | Detecting the Stochastic Gravitational Wave Background from Massive
Gravity with Pulsar Timing Arrays: We explore the potential of Pulsar Timing Arrays (PTAs) such as NANOGrav,
EPTA, and PPTA to detect the Stochastic Gravitational Wave Background (SGWB) in
theories of massive gravity. In General Relativity, the function describing the
dependence of the correlation between the arrival times of signals from two
pulsars on the angle between them is known as the Hellings-Downs curve. We
compute the analogous overlap reduction function for massive gravity, including
the additional polarization states and the correction due to the mass of the
graviton, and compare the result with the Hellings-Downs curve. The primary
result is a complete analytical form for the analog Hellings-Downs curve,
providing a starting point for future numerical studies aimed at a detailed
comparison between PTA data and the predictions of massive gravity. We study
both the massless limit and the stationary limit as checks on our calculation,
and discuss how our formalism also allows us to study the impact of massive
spin-2 dark matter candidates on data from PTAs. |
The evolution of galaxies resolved in space and time: an inside-out
growth view from the CALIFA survey: The growth of galaxies is one of the key problems in understanding the
structure and evolution of the universe and its constituents. Galaxies can grow
their stellar mass by accretion of halo or intergalactic gas clouds, or by
merging with smaller or similar mass galaxies. The gas available translates
into a rate of star formation, which controls the generation of metals in the
universe. The spatially resolved history of their stellar mass assembly has not
been obtained so far for any given galaxy beyond the Local Group. Here we
demonstrate how massive galaxies grow their stellar mass inside-out. We report
the results from the analysis of the first 105 galaxies of the largest to date
three-dimensional spectroscopic survey of galaxies in the local universe
(CALIFA). We apply the fossil record method of stellar population spectral
synthesis to recover the spatially and time resolved star formation history of
each galaxy. We show, for the first time, that the signal of downsizing is
spatially preserved, with both inner and outer regions growing faster for more
massive galaxies. Further, we show that the relative growth rate of the
spheroidal component, nucleus and inner galaxy, that happened 5-7 Gyr ago,
shows a maximum at a critical stellar mass ~10^10 Msun. We also find that
galaxies less massive than ~10^10 Msun show a transition to outside-in growth,
thus connecting with results from resolved studies of the growth of low mass
galaxies. | Can modified gravity models reconcile the tension between CMB anisotropy
and lensing maps in Planck-like observations?: Planck-2015 data seem to favour a large value of the lensing amplitude
parameter, $A_{\rm L}=1.22\pm0.10$, in CMB spectra. This result is in $2\sigma$
tension with the lensing reconstruction result, $A_{\rm
L}^{\phi\phi}=0.95\pm0.04$. In this paper, we simulate several CMB anisotropy
and CMB lensing spectra based on Planck-2015 best-fit cosmological parameter
values and Planck blue book beam and noise specifications. We analyse several
modified gravity models within the effective field theory framework against
these simulations and find that models whose effective Newton constant is
enhanced can modulate the CMB anisotropy spectra in a way similar to that of
the $A_{\rm L}$ parameter. However, in order to lens the CMB anisotropies
sufficiently, like in the Planck-2015 results, the growth of matter
perturbations is substantially enhanced and gives a high $\sigma_8$ value. This
in turn proves to be problematic when combining these data to other probes,
like weak lensing from CFHTLenS, that favour a smaller amplitude of matter
fluctuations. |
Markov Chain Monte Carlo methods applied to measuring the fine structure
constant from quasar spectroscopy: Recent attempts to constrain cosmological variation in the fine structure
constant, alpha, using quasar absorption lines have yielded two statistical
samples which initially appear to be inconsistent. One of these samples was
subsequently demonstrated to not pass consistency tests; it appears that the
optimisation algorithm used to fit the model to the spectra failed.
Nevertheless, the results of the other hinge on the robustness of the spectral
fitting program VPFIT, which has been tested through simulation but not through
direct exploration of the likelihood function. We present the application of
Markov Chain Monte Carlo (MCMC) methods to this problem, and demonstrate that
VPFIT produces similar values and uncertainties for (Delta alpha)/(alpha), the
fractional change in the fine structure constant, as our MCMC algorithm, and
thus that VPFIT is reliable. | A Mass Dependent Density Profile from Dwarfs to Clusters: In this paper, we extend the work of Freundlich et al. 2020 who showed how to
obtain a Dekel-Zhao density profile with mass dependent shape parameters in the
case of galaxies. In the case of Freundlich et al. 2020, the baryonic
dependence was obtained using the NIHAO set of simulations. In our case, we
used simulations based on a model of ours. Following Freundlich et al. 2020, we
obtained the dependence from baryon physics of the two shape parameters,
obtaining in this way a mass dependent Dekel-Zhao profile describing the dark
matter profiles from galaxies to clusters of galaxies. The extension to the
Dekel-Zhao mass dependent profile to clusters of galaxies is the main result of
the paper. In the paper, we show how the Dekel-Zhao mass dependent profile
gives a good description of the density profiles of galaxies, already shown by
Freundlich et al. 2020, but also to a set of clusters of galaxies. |
Variations of cosmic large-scale structure covariance matrices across
parameter space: The likelihood function for cosmological parameters, given by e.g. weak
lensing shear measurements, depends on contributions to the covariance induced
by the nonlinear evolution of the cosmic web. As nonlinear clustering to date
has only been described by numerical $N$-body simulations in a reliable and
sufficiently precise way, the necessary computational costs for estimating
those covariances at different points in parameter space are tremendous. In
this work we describe the change of the matter covariance and of the weak
lensing covariance matrix as a function of cosmological parameters by
constructing a suitable basis, where we model the contribution to the
covariance from nonlinear structure formation using Eulerian perturbation
theory at third order. We show that our formalism is capable of dealing with
large matrices and reproduces expected degeneracies and scaling with
cosmological parameters in a reliable way. Comparing our analytical results to
numerical simulations we find that the method describes the variation of the
covariance matrix found in the SUNGLASS weak lensing simulation pipeline within
the errors at one-loop and tree-level for the spectrum and the trispectrum,
respectively, for multipoles up to $\ell\leq 1300$. We show that it is possible
to optimize the sampling of parameter space where numerical simulations should
be carried out by minimising interpolation errors and propose a corresponding
method to distribute points in parameter space in an economical way. | Correlation of Black Hole-Bulge Masses by AGN Jets: I propose a feedback model to explain the correlation between the
supermassive black hole (SMBH) mass and the host galaxy bulge mass. The
feedback is based on narrow jets that are launched by the central SMBH, and
expel large amounts of mass to large distances. The condition is that the jets
do not penetrate through the inflowing gas, such that they can deposit their
energy in the inner region where the bulge is formed. For that to occur, the
SMBH must move relative to the inflowing gas, such that the jets continuously
encounter fresh gas. Taking into account the relative motion of the SMBH and
the inflowing gas I derive a relation between the mass accreted by the SMBH and
the mass that is not expelled, and is assumed to form the bulge. This relation
is not linear, but rather the SMBH to bulge mass ratio increases slowly with
mass. The same mechanism was applied to suppress star formation in cooling flow
clusters, making a tighter connection between the feedback in galaxy formation
and cooling flows. |
The four leading arms of the Magellanic Cloud system: The Magellanic Cloud System (MCS) interacts via tidal and drag forces with
the Milky Way galaxy. Using the Parkes Galactic All-Sky Survey (GASS) of atomic
hydrogen we explore the role of drag on the evolution of the so-called Leading
Arm (LA). We present a new image recognition algorithm that allows us to
differentiate features within a 3-D data cube (longitude, latitude, radial
velocity) and to parameterize individual coherent structures. We compiled an HI
object catalog of LA objects within an area of 70 degr x 85 degr (1.6 sr) of
the LA region. This catalog comprises information of location, column density,
line width, shape and asymmetries of the individual LA objects above the
4-sigma threshold of Delta T_b simeq 200 mK. We present evidence of a fourth
arm segment (LA4). For all LA objects we find an inverse correlation of
velocities v_GSR in Galactic Standard of Rest frame with Magellanic longitude.
High-mass objects tend to have higher radial velocities than low-mass ones.
About 1/4 of all LA objects can be characterized as head-tail (HT) structures.
Using image recognition with objective criteria, it is feasible to isolate most
of LA emission from the diffuse Milky Way HI gas. Some blended gas components
(we estimate 5%) escape detection, but we find a total gas content of the LA
that is about 50% higher than previously assumed. These methods allow the
deceleration of the LA clouds to be traced towards the Milky Way disk by drag
forces. The derived velocity gradient strongly supports the assumption that the
whole LA originates entirely in the Large Magellanic Cloud (LMC). LA4 is
observed opposite to LA1, and we propose that both arms are related, spanning
about 52kpc in space. HT structures trace drag forces even at tens of kpc
altitudes above the Milky Way disk. | Measuring the hydrostatic mass bias in galaxy clusters by combining
Sunyaev-Zel'dovich and CMB lensing data: The cosmological parameters prefered by the cosmic microwave background (CMB)
primary anisotropies predict many more galaxy clusters than those that have
been detected via the thermal Sunyaev-Zeldovich (tSZ) effect. This tension has
attracted considerable attention since it could be evidence of physics beyond
the simplest $\Lambda$CDM model. However, an accurate and robust calibration of
the mass-observable relation for clusters is necessary for the comparison,
which has been proven difficult to obtain so far. Here, we present new
contraints on the mass-pressure relation by combining tSZ and CMB lensing
measurements about optically-selected clusters. Consequently, our galaxy
cluster sample is independent from the data employed to derive cosmological
constrains. We estimate an average hydrostatic mass bias of $b = 0.26 \pm
0.07$, with no significant mass nor redshift evolution. This value greatly
reduces the tension between the predictions of $\Lambda$CDM and the observed
abundance of tSZ clusters while being in agreement with recent estimations from
tSZ clustering. On the other hand, our value for $b$ is higher than the
predictions from hydro-dynamical simulations. This suggests the existence of
mechanisms driving large departures from hydrostatic equilibrium and that are
not included in state-of-the-art simulations, and/or unaccounted systematic
errors such as biases in the cluster catalogue due to the optical selection. |
On the connection between the intergalactic medium and galaxies: The
HI-galaxy cross-correlation at z < 1: We present a new optical spectroscopic survey of 1777 'star-forming' ('SF')
and 366 'non-star-forming' ('non-SF') galaxies at redshifts z < 1 (2143 in
total), 22 AGN and 423 stars, observed by instruments such as DEIMOS, VIMOS and
GMOS, in 3 fields containing 5 quasi-stellar objects (QSOs) with HST UV
spectroscopy. We also present a new spectroscopic survey of 165 'strong' (10^14
< NHI < 10^17 cm^-2), and 489 'weak' (10^13 < NHI < 10^14 cm^-2) intervening HI
absorption line systems at z < 1 (654 in total), observed in the spectra of 8
QSOs by COS and FOS on the HST. Combining these new data with previously
published galaxy catalogs such as VVDS and GDDS, we have gathered a sample of
654 HI absorption systems and 17509 galaxies at transverse scales < 50 Mpc. We
present observational results on the HI-galaxy and galaxy-galaxy correlations
at transverse scales r < 10 Mpc, and the HI-HI auto-correlation at transverse
scales r < 2 Mpc. The two-point correlation functions are measured both along
and transverse to the line-of-sight. We constrain the HI-galaxy statistical
connection, as a function of both HI column density and galaxy star-forming
activity. Our results are consistent with the following conclusions: (1) the
bulk of HI systems on Mpc scales have little velocity dispersion (<120 km/s)
with respect to the bulk of galaxies; (2) the vast majority of strong HI
systems and SF galaxies are distributed in the same locations, together with
75+-15% of non-SF galaxies, all of which typically reside in dark matter haloes
of similar masses; (3) 25+-15% of non-SF galaxies reside in galaxy clusters and
are not correlated with strong HI systems at scales < 2 Mpc; and (4) 50% of
weak HI systems reside within galaxy voids (hence not correlated with
galaxies), and are confined in dark matter haloes of masses smaller than those
hosting... [abridged] | Preparation to the CMB Planck analysis : contamination due to the
polarized galactic emission: The Planck satellite experiment, which was launched the 14th of may 2009,
will give an accurate measurement of the anisotropies of the Cosmic Microwave
Background (CMB) in temperature and polarization. This measurement is polluted
by the presence of diffuse galactic polarized foreground emissions. In order to
obtain the level of accuracy required for the Planck mission it is necessary to
deal with these foregrounds. In order to do this, have develloped and
implemented coherent 3D models of the two main galactic polarized emissions :
the synchrotron and thermal dust emissions. We have optimized these models by
comparing them to preexisting data : the K-band of the WMAP data, the ARCHEOPS
data at 353 GHz and the 408 MHz all-sky continuum survey. By extrapolation of
these models at the frequencies where the CMB is dominant, we are able to
estimate the contamination to the CMB Planck signal due to these polarized
galactic emissions. |
Analytical model for CMB temperature angular power spectrum from cosmic
(super-)strings: We present a new analytical method to calculate the small angle CMB
temperature angular power spectrum due to cosmic (super-)string segments. In
particular, using our method, we clarify the dependence on the intercommuting
probability $P$. We find that the power spectrum is dominated by
Poisson-distributed string segments. The power spectrum for a general value of
$P$ has a plateau on large angular scales and shows a power-law decrease on
small angular scales. The resulting spectrum in the case of conventional cosmic
strings is in very good agreement with the numerical result obtained by Fraisse
et al.. Then we estimate the upper bound on the dimensionless tension of the
string for various values of $P$ by assuming that the fraction of the CMB power
spectrum due to cosmic (super-)strings is less than ten percents at various
angular scales up to $\ell=2000$. We find that the amplitude of the spectrum
increases as the intercommuting probability. As a consequence, strings with
smaller intercommuting probabilities are found to be more tightly constrained. | A measurement of the mean central optical depth of galaxy clusters via
the pairwise kinematic Sunyaev-Zel'dovich effect with SPT-3G and DES: We infer the mean optical depth of a sample of optically-selected galaxy
clusters from the Dark Energy Survey (DES) via the pairwise kinematic
Sunyaev-Zel'dovich (kSZ) effect. The pairwise kSZ signal between pairs of
clusters drawn from the DES Year-3 cluster catalog is detected at $4.1 \sigma$
in cosmic microwave background (CMB) temperature maps from two years of
observations with the SPT-3G camera on the South Pole Telescope. After cuts,
there are 24,580 clusters in the $\sim 1,400$ deg$^2$ of the southern sky
observed by both experiments. We infer the mean optical depth of the cluster
sample with two techniques. The optical depth inferred from the pairwise kSZ
signal is $\bar{\tau}_e = (2.97 \pm 0.73) \times 10^{-3}$, while that inferred
from the thermal SZ signal is $\bar{\tau}_e = (2.51 \pm 0.55^{\text{stat}} \pm
0.15^{\rm syst}) \times 10^{-3}$. The two measures agree at $0.6 \sigma$. We
perform a suite of systematic checks to test the robustness of the analysis. |
Constraining minimally extended varying speed of light by cosmological
chronometers: At least one dimensionless physical constant (i.e., a physically observable)
must change for the cosmic time to make the varying speed of light (VSL) models
phenomenologically feasible. Various physical constants and quantities also
should be functions of cosmic time to satisfy all known local laws of physics,
including special relativity, thermodynamics, and electromagnetism. Adiabatic
condition is another necessary condition to keep the homogeneity and isotropy
of three-dimensional space. To be a self-consistent theory, one should consider
cosmic evolutions of physical constants and quantities when one derives
Einstein's field equations and their solutions. All these conditions are well
satisfied in the so-called minimally extended varying speed of light (meVSL)
model. Unlike other VSL models, we show that the redshift-drift formula of the
meVSL model is the same as a standard model. Therefore, we cannot use this as
an experimental tool to verify the meVSL. Instead, one can still use the
cosmological chronometers (CC) as a model-independent test of the meVSL. The
current CC data cannot distinguish meVSL from the standard model (SM) when we
adopt the best-fit values (or Gaussian prior) of the present values of $H_0$
and of $\Omega_{m0}$ from the Planck mission. However, the CC data prefer the
meVSL when we choose Pantheon 22 data. | Quantifying and mitigating the effect of snapshot interval in light-cone
Epoch of Reionization 21-cm simulations: The Epoch of Reionization (EoR) neutral Hydrogen (HI) 21-cm signal evolves
significantly along the line-of-sight (LoS) due to the light-cone (LC) effect.
It is important to accurately incorporate this in simulations in order to
correctly interpret the signal. 21-cm LC simulations are typically produced by
stitching together slices from a finite number $(N_{\rm RS})$ of ''reionization
snapshot'', each corresponding to a different stage of reionization. In this
paper, we have quantified the errors in the 21-cm LC simulation due to the
finite value of $N_{\rm RS}$. We show that this can introduce large
discontinuities $(> 200 \%)$ at the stitching boundaries when $N_{\rm RS}$ is
small $(= 2,4)$ and the mean neutral fraction jumps by $\delta \bar{x}_{\rm HI}
= 0.2,0.1$ respectively at the stitching boundaries. This drops to $17 \%$ for
$N_{\rm RS} = 13$ where $\delta \bar{x}_{\rm HI}=0.02$. We present and also
validate a method for mitigating this error by increasing $N_{\rm RS}$ without
a proportional increase in the computational costs which are mainly incurred in
generating the dark matter and halo density fields. Our method generates these
fields only at a few redshifts, and interpolates them to generate reionization
snapshots at closely spaced redshifts. We use this to generate 21-cm LC
simulations with $N_{\rm RS} = 26,51,101$ and $201$, and show that the errors
go down as $N_{\rm RS}^{-1}$. |
Increasing the power of survey data with multipole-based intrinsic
alignment estimators: It has long been known that galaxy shapes align coherently with the
large-scale density field. Characterizing this effect is essential to
interpreting measurements of weak gravitational lensing, the deflection of
light from distant galaxies by matter overdensities along the line of sight, as
it produces coherent galaxy alignments that we wish to interpret in terms of a
cosmological model. Existing direct measurements of intrinsic alignments using
galaxy samples with high-quality shape and redshift measurements typically use
well-understood but sub-optimal projected estimators, which do not make good
use of the information in the data when comparing those estimators to
theoretical models. We demonstrate a more optimal estimator, based on a
multipole expansion of the correlation functions or power spectra, for direct
measurements of galaxy intrinsic alignments. We show that even using the lowest
order multipole alone increases the significance of inferred model parameters
using simulated and real data, without any additional modeling complexity. We
apply this estimator to measurements of intrinsic alignments in the Sloan
Digital Sky survey, demonstrating consistent results with a factor of $\sim$2
greater precision in parameter fits to intrinsic alignments models. This result
is functionally equivalent to quadrupling the survey area, but without the
attendant costs -- thereby demonstrating the value in using this new estimator
in current and future intrinsic alignments measurements using spectroscopic
galaxy samples. | X-ray emission from the extended emission-line region of the powerful
radio galaxy 3C171: We present Chandra X-ray observations of the powerful radio galaxy 3C171,
which reveal an extended region of X-ray emission spatially associated with the
well-known 10-kpc scale optical emission-line region around the radio jets. We
argue that the X-ray emission comes from collisionally ionized material,
originally cold gas that has been shock-heated by the passage of the radio jet,
rather than being photoionized by nuclear radiation. This hot plasma is also
responsible for the depolarization at low frequencies of the radio emission
from the jet and hotspots, which allows us to estimate the magnetic field
strength in the external medium. We show that it is likely that both the cold
emission-line gas and the hot plasma in which it is embedded are being driven
out of the host galaxy of 3C171 at supersonic speeds. A significant fraction of
the total energy budget of the central AGN must have been expended in driving
this massive outflow. We argue that 3C171, with its unusual radio morphology
and the strong relation between the jet and large amounts of outflowing
material, is a member of a class of radio galaxies in which there is strong
interaction between the radio jets and cold material in the host galaxy; such
objects may have been very much more common in the early universe. |
Photometric redshifts for galaxies in the Subaru Hyper Suprime-Cam and
unWISE and a catalogue of identified clusters of galaxies: We first present a catalogue of photometric redshifts for 14.68 million
galaxies derived from the 7-band photometric data of Hyper Suprime-Cam Subaru
Strategic Program and the Wide-field Infrared Survey Explorer using the
nearest-neighbour algorithm. The redshift uncertainty is about 0.024 for
galaxies of z<0.7, and steadily increases with redshift to about 0.11 at z~2.
From such a large data set, we identify 21,661 clusters of galaxies, among
which 5537 clusters have redshifts z>1 and 642 clusters have z>1.5,
significantly enlarging the high redshift sample of galaxy clusters. Cluster
richness and mass are estimated, and these clusters have an equivalent mass of
M_{500} > 0.7*10^{14} Msun. We find that the stellar mass of the brightest
cluster galaxies (BCGs) in each richness bin does not significantly evolve with
redshift. The fraction of star-forming BCGs increases with redshift, but does
not depend on cluster mass. | Investigating clustering dark energy with 3d weak cosmic shear: As observational evidence increasingly consolidates the case for a
cosmological constant being the source of the Universe's accelerated expansion,
the question whether, and if so, how well, future experiments could detect
deviations from this standard scenario is raised with urgency. Assuming a dark
energy component different from a cosmological constant, the observable effects
in general include gravitational clustering described by the fluid's
(rest-frame) speed of sound. We employ 3d weak cosmic shear, a proposed method
to take advantage of the full three-dimensional information inherent to the
cosmic shear field, to explore the capability of future surveys to detect dark
energy clustering and the signature of an enhanced amplitude of the matter
power spectrum on large scales. For this purpose, we present adequate numerical
methods facilitating 3d weak cosmic shear calculations. We find that the
possible constraints heavily depend on the dark energy equation of state w. If
w is not very close to -1, constraining the squared sound speed within an order
of magnitude seems possible with a combination of Euclid and Planck data. |
Digging into dark matter with weak gravitational lensing: Ordinary baryonic particles (such as protons and neutrons) account for only
one-sixth of the total matter in the Universe. The remainder is a mysterious
"dark matter" component, which does not interact via the electromagnetic force
and thus neither emits nor reflects light. However, evidence is mounting for
its gravitational influence. The past few years have seen particular progress
in observations of weak gravitational lensing, the slight deflection of light
from distant galaxies due to the curvature of space around foreground mass.
Recent surveys from the Hubble Space Telescope have provided direct proof for
dark matter, and the first measurements of its properties. We review recent
results, then prospects and challenges for future gravitational lensing
surveys. | Mid-Infrared Selection of AGN with the Wide-Field Infrared Survey
Explorer. I. Characterizing WISE-Selected AGN in COSMOS: The Wide-field Infrared Survey Explorer (WISE) is an extremely capable and
efficient black hole finder. We present a simple mid-infrared color criterion,
W1-W2 \geq 0.8 (i.e., [3.4]-[4.6] \geq 0.8, Vega), which identifies 61.9 \pm
5.4 AGN candidates per deg2 to a depth of W2 = 15.0. This implies a much larger
census of luminous AGN than found by typical wide-area surveys, attributable to
the fact that mid-infrared selection identifies both unobscured (type 1) and
obscured (type 2) AGN. Optical and soft X-ray surveys alone are highly biased
towards only unobscured AGN, while this simple WISE selection likely identifies
even heavily obscured, Compton-thick AGN. Using deep, public data in the COSMOS
field, we explore the properties of WISE-selected AGN candidates. At the
mid-infrared depth considered, 160 uJy at 4.6 microns, this simple criterion
identifies 78% of Spitzer mid-infrared AGN candidates according to the criteria
of Stern et al. (2005) and the reliability is 95%. We explore the demographics,
multiwavelength properties and redshift distribution of WISE-selected AGN
candidates in the COSMOS field. |
The X-ray spectral properties of the AGN population in the XMM-Newton
bright serendipitous survey: We present here a detailed X-ray spectral analysis of the AGN belonging to
the XMM-Newton bright survey (XBS) that comprises more than 300 AGN up to
redshift ~ 2.4. We performed an X-ray analysis following two different
approaches: by analyzing individually each AGN X-ray spectrum and by
constructing average spectra for different AGN types. From the individual
analysis, we find that there seems to be an anti correlation between the
spectral index and the sources' hard X-ray luminosity, such that the average
photon index for the higher luminosity sources (> 10E44 erg/s) is significantly
flatter than the average for the lower luminosity sources. We also find that
the intrinsic column density distribution agrees with AGN unified schemes,
although a number of exceptions are found (3% of the whole sample), which are
much more common among optically classified type 2 AGN. We also find that the
so-called "soft-excess", apart from the intrinsic absorption, constitutes the
principal deviation from a power-law shape in AGN X-ray spectra and it clearly
displays different characteristics, and likely a different origin, for
unabsorbed and absorbed AGN. Regarding the shape of the average spectra, we
find that it is best reproduced by a combination of an unabsorbed (absorbed)
power law, a narrow Fe Kalpha emission line and a small (large) amount of
reflection for unabsorbed (absorbed) sources. We do not significantly detect
any relativistic contribution to the line emission and we compute an upper
limit for its equivalent width (EW) of 230 eV at the 3 sigma confidence level.
Finally, by dividing the type 1 AGN sample into high- and low-luminosity
sources, we marginally detect a decrease in the narrow Fe Kalpha line EW and in
the amount of reflection as the luminosity increases, the "so-called"
Iwasawa-Taniguchi effect. | KiDS-1000: Combined halo-model cosmology constraints from galaxy
abundance, galaxy clustering and galaxy-galaxy lensing: We present constraints on the flat $\Lambda$CDM cosmological model through a
joint analysis of galaxy abundance, galaxy clustering and galaxy-galaxy lensing
observables with the Kilo-Degree Survey. Our theoretical model combines a
flexible conditional stellar mass function, to describe the galaxy-halo
connection, with a cosmological N-body simulation-calibrated halo model to
describe the non-linear matter field. Our magnitude-limited bright galaxy
sample combines 9-band optical-to-near-infrared photometry with an extensive
and complete spectroscopic training sample to provide accurate redshift and
stellar mass estimates. Our faint galaxy sample provides a background of
accurately calibrated lensing measurements. We constrain the structure growth
parameter $S_8=\sigma_8\sqrt{\Omega_{\mathrm{m}}/0.3}=0.773^{+0.028}_{-0.030}$,
and the matter density parameter $\Omega_{\mathrm{m}}=0.290^{+0.021}_{-0.017}$.
The galaxy-halo connection model adopted in the work is shown to be in
agreement with previous studies. Our constraints on cosmological parameters are
comparable to, and consistent with, joint $3\times2{\mathrm{pt}}$
clustering-lensing analyses that additionally include a cosmic shear
observable. This analysis therefore brings attention to the significant
constraining power in the often-excluded non-linear scales for galaxy
clustering and galaxy-galaxy lensing observables. By adopting a theoretical
model that accounts for non-linear halo bias, halo exclusion, scale-dependent
galaxy bias and the impact of baryon feedback, this work demonstrates the
potential and a way forward to include non-linear scales in cosmological
analyses. Varying the width of the satellite galaxy distribution with an
additional parameter yields a strong preference for sub-Poissonian variance,
improving the goodness of fit by 0.18 in reduced $\chi^{2}$ value compared to a
fixed Poisson distribution. |
Photometric redshift estimates using Bayesian neural networks in the
CSST survey: Galaxy photometric redshift (photo-$z$) is crucial in cosmological studies,
such as weak gravitational lensing and galaxy angular clustering measurements.
In this work, we try to extract photo-$z$ information and construct its
probability distribution function (PDF) using the Bayesian neural networks
(BNN) from both galaxy flux and image data expected to be obtained by the China
Space Station Telescope (CSST). The mock galaxy images are generated from the
Advanced Camera for Surveys of Hubble Space Telescope ($HST$-ACS) and COSMOS
catalog, in which the CSST instrumental effects are carefully considered. And
the galaxy flux data are measured from galaxy images using aperture photometry.
We construct Bayesian multilayer perceptron (B-MLP) and Bayesian convolutional
neural network (B-CNN) to predict photo-$z$ along with the PDFs from fluxes and
images, respectively. We combine the B-MLP and B-CNN together, and construct a
hybrid network and employ the transfer learning techniques to investigate the
improvement of including both flux and image data. For galaxy samples with
SNR$>$10 in $g$ or $i$ band, we find the accuracy and outlier fraction of
photo-$z$ can achieve $\sigma_{\rm NMAD}=0.022$ and $\eta=2.35\%$ for the B-MLP
using flux data only, and $\sigma_{\rm NMAD}=0.022$ and $\eta=1.32\%$ for the
B-CNN using image data only. The Bayesian hybrid network can achieve
$\sigma_{\rm NMAD}=0.021$ and $\eta=1.23\%$, and utilizing transfer learning
technique can improve results to $\sigma_{\rm NMAD}=0.019$ and $\eta=1.17\%$,
which can provide the most confident predictions with the lowest average
uncertainty. | Power Spectrum Estimation from Peculiar Velocity Catalogues: The peculiar velocities of galaxies are an inherently valuable cosmological
probe, providing an unbiased estimate of the distribution of matter on scales
much larger than the depth of the survey. Much research interest has been
motivated by the high dipole moment of our local peculiar velocity field, which
suggests a large scale excess in the matter power spectrum, and can appear to
be in some tension with the LCDM model. We use a composite catalogue of 4,537
peculiar velocity measurements with a characteristic depth of 33 h-1 Mpc to
estimate the matter power spectrum. We compare the constraints with this
method, directly studying the full peculiar velocity catalogue, to results from
Macaulay et al. (2011), studying minimum variance moments of the velocity
field, as calculated by Watkins, Feldman & Hudson (2009) and Feldman, Watkins &
Hudson (2010). We find good agreement with the LCDM model on scales of k > 0.01
h Mpc-1. We find an excess of power on scales of k < 0.01 h Mpc-1, although
with a 1 sigma uncertainty which includes the LCDM model. We find that the
uncertainty in the excess at these scales is larger than an alternative result
studying only moments of the velocity field, which is due to the minimum
variance weights used to calculate the moments. At small scales, we are able to
clearly discriminate between linear and nonlinear clustering in simulated
peculiar velocity catalogues, and find some evidence (although less clear) for
linear clustering in the real peculiar velocity data. |
Do data favor neutrino mass and a coupling between Cold Dark Matter and
Dark Energy?: We allow simultaneously for a CDM--DE coupling and non--zero neutrino masses
and find that significant coupling and neutrino mass are (slightly)
statistically favoured in respect to a cosmology with no coupling and
negligible neutrino mass (our best fits are: C~1/2m_p, m_\nu~0.12eV each
flavor). We assume DE to be a self--interacting scalar field and use a standard
Monte Carlo Markov Chain approach. | Sub-percent constraints on cosmological temperature evolution: The redshift dependence of the cosmic microwave background temperature is one
of the key cosmological observables. In the standard cosmological model one has
$T(z)=T_0(1+z)$, where $T_0$ is the present-day temperature. Deviations from
this behavior would imply the presence of new physics. Here we discuss how the
combination of all currently available direct and indirect measurements of
$T(z)$ constrains the common phenomenological parametrization
$T(z)=T_0(1+z)^{1-\beta}$, and obtain the first sub-percent constraint on the
$\beta$ parameter, specifically $\beta=(7.6\pm8.0)\times10^{-3}$ at the
$68.3\%$ confidence level. |
Inferring Cosmic String Tension through the Neural Network Prediction of
String Locations in CMB Maps: In previous work, we constructed a convolutional neural network used to
estimate the location of cosmic strings in simulated cosmic microwave
background temperature anisotropy maps. We derived a connection between the
estimates of cosmic string locations by this neural network and the posterior
probability distribution of the cosmic string tension $G\mu$. Here, we
significantly improve the calculation of the posterior distribution of the
string tension $G\mu$. We also improve our previous plain convolutional neural
network by using residual networks. We apply our new neural network and
posterior calculation method to maps from the same simulation used in our
previous work and quantify the improvement. | Schrödinger-Poisson Solitons: Perturbation Theory: Self-gravitating quantum matter may exist in a wide range of cosmological and
astrophysical settings from the very early universe through to present-day
boson stars. Such quantum matter arises in a number of different theories,
including the Peccei-Quinn axion and UltraLight (ULDM) or Fuzzy (FDM) dark
matter scenarios. We consider the dynamical evolution of perturbations to the
spherically symmetric soliton, the ground state solution to the
Schr\"{o}dinger-Poisson system common to all these scenarios. We construct the
eigenstates of the Schr\"{o}dinger equation, holding the gravitational
potential fixed to its ground state value. We see that the eigenstates
qualitatively capture the properties seen in full ULDM simulations, including
the soliton "breathing" mode, the random walk of the soliton center, and
quadrupolar distortions of the soliton. We then show that the time-evolution of
the gravitational potential and its impact on the perturbations can be well
described within the framework of time-dependent perturbation theory. Applying
our formalism to a synthetic ULDM halo reveals considerable mixing of
eigenstates, even though the overall density profile is relatively stable. Our
results provide a new analytic approach to understanding the evolution of these
systems as well as possibilities for faster approximate simulations. |
Neural Network Reconstruction of $H'(z)$ and its application in
Teleparallel Gravity: In this work, we explore the possibility of using artificial neural networks
to impose constraints on teleparallel gravity and its $f(T)$ extensions. We use
the available Hubble parameter observations from cosmic chronometers and baryon
acoustic oscillations from different galaxy surveys. We discuss the procedure
for training a network model to reconstruct the Hubble diagram. Further, we
describe the procedure to obtain $H'(z)$, the first order derivative of $H(z)$,
using artificial neural networks which is a novel approach to this method of
reconstruction. These analyses are complemented with further studies on the
impact of two priors which we put on $H_0$ to assess their impact on the
analysis, which are the local measurements by the SH0ES team ($H_0^{\text{R20}}
= 73.2 \pm 1.3$ km Mpc$^{-1}$ s$^{-1}$) and the updated TRGB calibration from
the Carnegie Supernova Project ($H_0^{\text{TRGB}} = 69.8 \pm 1.9$ km
Mpc$^{-1}$ s$^{-1}$), respectively. Additionally, we investigate the validity
of the concordance model, through some cosmological null tests with these
reconstructed data sets. Finally, we reconstruct the allowed $f(T)$ functions
for different combinations of the observational Hubble data sets. Results show
that the $\Lambda$CDM model lies comfortably included at the 1$\sigma$
confidence level for all the examined cases. | Resolving Small-Scale Dark Matter Structures Using Multi-Source Indirect
Detection: The extragalactic dark matter (DM) annihilation signal depends on the product
of the clumping factor, <\delta^2>, and the velocity-weighted annihilation
cross section, \sigma v. This "clumping factor-\sigma v" degeneracy can be
broken by comparing DM annihilation signals from multiple sources. In
particular, one can constrain the minimum DM halo mass, M_min, which depends on
the mass of the DM particles and the kinetic decoupling temperature, by
comparing observations of individual DM sources to the diffuse DM annihilation
signal. We demonstrate this with careful semi-analytic treatments of the DM
contribution to the diffuse Isotropic Gamma-Ray Background (IGRB), and compare
it with two recent hints of DM from the Galactic Center, namely, ~130 GeV DM
annihilating dominantly in the \chi\chi\ to \gamma\gamma\ channel, and (10-30)
GeV DM annihilating in the \chi\chi\ to b\bar{b} or \chi\chi\ to
\tau^{+}\tau^{-} channels. We show that, even in the most conservative
analysis, the Fermi IGRB measurement already provides interesting sensitivity.
A more detailed analysis of the IGRB, with new Fermi IGRB measurements and
modeling of astrophysical backgrounds, may be able to probe values of M_min up
to 1 M_sun for the 130 GeV candidate and 10^{-6} M_sun for the light DM
candidates. Increasing the substructure content of halos by a reasonable amount
would further improve these constraints. |
Parametrizations of the global 21-cm signal and parameter estimation
from single-dipole experiments: One approach to extracting the global 21-cm signal from total-power
measurements at low radio frequencies is to parametrize the different
contributions to the data and then fit for these parameters. We examine
parametrizations of the 21-cm signal itself, and propose one based on modelling
the Lyman-alpha background, IGM temperature and hydrogen ionized fraction using
tanh functions. This captures the shape of the signal from a physical modelling
code better than an earlier parametrization based on interpolating between
maxima and minima of the signal, and imposes a greater level of physical
plausibility. This allows less biased constraints on the turning points of the
signal, even though these are not explicitly fit for. Biases can also be
alleviated by discarding information which is less robustly described by the
parametrization, for example by ignoring detailed shape information coming from
the covariances between turning points or from the high-frequency parts of the
signal, or by marginalizing over the high-frequency parts of the signal by
fitting a more complex foreground model. The fits are sufficiently accurate to
be usable for experiments gathering 1000 h of data, though in this case it may
be important to choose observing windows which do not include the brightest
areas of the foregrounds. Our assumption of pointed, single-antenna
observations and very broad-band fitting makes these results particularly
applicable to experiments such as the Dark Ages Radio Explorer, which would
study the global 21-cm signal from the clean environment of a low lunar orbit,
taking data from the far side. | Developing a unified pipeline for large-scale structure data analysis
with angular power spectra -- III. Implementing the multi-tracer technique to
constrain neutrino masses: In this paper, we apply the multi-tracer technique to harmonic-space (i.e.\
angular) power spectra with a likelihood-based approach. This goes beyond the
usual Fisher matrix formalism hitherto implemented in forecasts with angular
statistics, opening up a window for future developments and direct application
to available data sets. We also release a fully-operational modified version of
the publicly available code CosmoSIS, where we consistently include all the
add-ons presented in the previous papers of this series. The result is a
modular cosmological parameter estimation suite for angular power spectra of
galaxy number counts, allowing for single and multiple tracers, and including
density fluctuations, redshift-space distortions, and weak lensing
magnification. We demonstrate the improvement on parameter constraints enabled
by the use of multiple tracers on a multi-tracing analysis of luminous red
galaxies and emission line galaxies. We obtain an enhancement of $44\%$ on the
$2\sigma$ upper bound on the sum of neutrino masses. Our code is publicly
available at
https://github.com/ktanidis/Modified_CosmoSIS_for_galaxy_number_count_angular_power_spectra. |
One consistency relation for all single-field inflationary models: In this paper, we present a non-Gaussianity consistency relation that enables
the calculation of the squeezed limit bispectrum of the curvature perturbation
in single-field inflationary models by carefully inspecting the background
evolution and the linear perturbation theory. The consistency relation is more
general than others in the literature since it does not require any specific
symmetry, conservation of the curvature perturbation at large scales, attractor
background evolution or canonical kinetic energy of the inflaton field. We
demonstrate that all known examples of the squeezed limit bispectrum in
single-field models of inflation can be reproduced within this framework. | The cosmological simulation code $\scriptstyle{\rm CO}N{\rm CEPT}\, 1.0$: We present version 1.0 of the cosmological simulation code $\scriptstyle{\rm
CO}N{\rm CEPT}$, designed for simulations of large-scale structure formation.
$\scriptstyle{\rm CO}N{\rm CEPT}\, 1.0$ contains a P$^3$M gravity solver, with
the short-range part implemented using a novel (sub)tiling strategy, coupled
with individual and adaptive particle time-stepping. A primary objective of
$\scriptstyle{\rm CO}N{\rm CEPT}$ is ease of use. To this end, it has built-in
initial condition generation and can produce output in the form of snapshots,
power spectra and direct visualisations. $\scriptstyle{\rm CO}N{\rm CEPT}$ is
the first massively parallel cosmological simulation code written in Python.
Despite of this, excellent performance is obtained, even comparing favourably
to other codes such as $\scriptstyle{\rm GADGET}$ at similar precision, in the
case of low to moderate clustering. By means of power spectrum comparisons we
find extraordinary good agreement between $\scriptstyle{\rm CO}N{\rm CEPT}\,
1.0$ and $\scriptstyle{\rm GADGET}$. At large and intermediate scales the codes
agree to well below the per mille level, while the agreement at the smallest
scales probed ($k \sim 13\, h/{\rm Mpc}$) is of the order of $1\, \%$. The
$\scriptstyle{\rm CO}N{\rm CEPT}$ code is openly released and comes with a
robust installation script as well as thorough documentation. |
Dark energy interactions near the galactic centre: We investigate scalar-tensor theories, motivated by dark energy models, in
the strong gravity regime around the black hole at the centre of our galaxy. In
such theories general relativity is modified since the scalar field couples to
matter. We consider the most general conformal and disformal couplings of the
scalar field to matter to study the orbital behavior of the nearby stars around
the galactic star center $Sgr A^{*}$. Markov Chain Monte Carlo (MCMC)
simulation yields a bound on the parameters of the couplings of the scalar
field to matter. Using Bayesian Analysis yields the first constraints on such
theories in the strong gravity regime. | An extended Herschel drop-out source in the center of AS1063, a 'normal'
dusty galaxy at z=6.1 or SZ substructures?: In the course of our 870um APEX/LABOCA follow up of the Herschel Lensing
Survey we have detected a source in AS1063 (RXC J2248.7-4431), that has no
counterparts in any of the Herschel PACS/SPIRE bands, it is a Herschel
'drop-out' with S_870/S_500>0.5. The 870um emission is extended and centered on
the brightest cluster galaxy suggesting either a multiply imaged background
source or substructure in the Sunyaev-Zel'dovich (SZ) increment due to
inhomogeneities in the hot cluster gas of this merging cluster. We discuss both
interpretations with emphasis on the putative lensed source. Based on the
observed properties and on our lens model we find that this source could be the
first SMG with a moderate far infrared luminosity (L_FIR<10^12 L_sol) detected
so far at z>4. In deep HST observations we identified a multiply imaged z~6
source and we measured its spectroscopic redshift z=6.107 with VLT/FORS. This
source could be associated with the putative SMG but it is most likely offset
spatially by 10-30kpc and they could be interacting galaxies. With a FIR
luminosity in the range [5-15]x10^{11} L_sol corresponding to a star formation
rate in the range [80-260]M_sol/yr, this SMG would be more representative than
the extreme starbursts usually detected at z>4. With a total magnification of
~25 it would open a unique window to the 'normal' dusty galaxies at the end of
the epoch of reionization. |
Reconstruction of the null-test for the matter density perturbations: We systematically study the null-test for the growth rate data first
presented in [S. Nesseris and D. Sapone, arXiv:1409.3697] and we reconstruct it
using various combinations of data sets, such as the $f\sigma_8$ and $H(z)$ or
Type Ia supernovae (SnIa) data. We perform the reconstruction in two different
ways, either by directly binning the data or by fitting various dark energy
models. We also examine how well the null-test can be reconstructed by future
data by creating mock catalogs based on the cosmological constant model, a
model with strong dark energy perturbations, the $f(R)$ and $f(G)$ models, and
the large void LTB model that exhibit different evolution of the matter
perturbations. We find that with future data similar to an LSST-like survey,
the null-test will be able to successfully discriminate between these different
cases at the $5\sigma$ level. | Tracing high redshift cosmic web with quasar systems. Invited talk at
IAU Symposium 308: We study the cosmic web at redshifts 1.0 <= z <= 1.8 using quasar systems
based on quasar data from the SDSS DR7 QSO catalogue. Quasar systems were
determined with a friend-of-friend (FoF) algorithm at a series of linking
lengths. At the linking lengths l <= 30 Mpc/h the diameters of quasar systems
are smaller than the diameters of random systems, and are comparable to the
sizes of galaxy superclusters in the local Universe. The mean space density of
quasar systems is close to the mean space density of local rich superclusters.
At larger linking lengths the diameters of quasar systems are comparable with
the sizes of supercluster complexes in our cosmic neighbourhood. The richest
quasar systems have diameters exceeding 500 Mpc/h. Very rich systems can be
found also in random distribution but the percolating system which penetrate
the whole sample volume appears in quasar sample at smaller linking length than
in random samples showing that the large-scale distribution of quasar systems
differs from random distribution. Quasar system catalogues at our web pages
(http://www.aai.ee/~maret/QSOsystems.html) serve as a database to search for
superclusters of galaxies and to trace the cosmic web at high redshifts. |
Galaxy and Mass Assembly (GAMA): Redshift Space Distortions from the
Clipped Galaxy Field: We present the first cosmological measurement derived from a galaxy density
field subject to a `clipping' transformation. By enforcing an upper bound on
the galaxy number density field in the Galaxy and Mass Assembly survey (GAMA),
contributions from the nonlinear processes of virialisation and galaxy bias are
greatly reduced. This leads to a galaxy power spectrum which is easier to
model, without calibration from numerical simulations.
We develop a theoretical model for the power spectrum of a clipped field in
redshift space, which is exact for the case of anisotropic Gaussian fields.
Clipping is found to extend the applicability of the conventional Kaiser
prescription by more than a factor of three in wavenumber, or a factor of
thirty in terms of the number of Fourier modes. By modelling the galaxy power
spectrum on scales k < 0.3 h/Mpc and density fluctuations $\delta_g < 4$ we
measure the normalised growth rate $f\sigma_8(z = 0.18) = 0.29 \pm 0.10$. | The VIRUS-P Exploration of Nearby Galaxies (VENGA): Survey Design and
First Results: VENGA is a large-scale extragalactic IFU survey, which maps the bulges, bars
and large parts of the outer disks of 32 nearby normal spiral galaxies. The
targets are chosen to span a wide range in Hubble types, star formation
activities, morphologies, and inclinations, at the same time of having vast
available multi-wavelength coverage from the far-UV to the mid-IR, and
available CO and 21cm mapping. The VENGA dataset will provide 2D maps of the
SFR, stellar and gas kinematics, chemical abundances, ISM density and
ionization states, dust extinction and stellar populations for these 32
galaxies. The uniqueness of the VIRUS-P large field of view permits these
large-scale mappings to be performed. VENGA will allow us to correlate all
these important quantities throughout the different environments present in
galactic disks, allowing the conduction of a large number of studies in star
formation, structure assembly, galactic feedback and ISM in galaxies. |
Multiscale Phenomenology of the Cosmic Web: We analyze the structure and connectivity of the distinct morphologies that
define the Cosmic Web. With the help of our Multiscale Morphology Filter (MMF),
we dissect the matter distribution of a cosmological $\Lambda$CDM N-body
computer simulation into cluster, filaments and walls. The MMF is ideally
suited to adress both the anisotropic morphological character of filaments and
sheets, as well as the multiscale nature of the hierarchically evolved cosmic
matter distribution. The results of our study may be summarized as follows:
i).- While all morphologies occupy a roughly well defined range in density,
this alone is not sufficient to differentiate between them given their overlap.
Environment defined only in terms of density fails to incorporate the intrinsic
dynamics of each morphology. This plays an important role in both linear and
non linear interactions between haloes. ii).- Most of the mass in the Universe
is concentrated in filaments, narrowly followed by clusters. In terms of
volume, clusters only represent a minute fraction, and filaments not more than
9%. Walls are relatively inconspicous in terms of mass and volume. iii).- On
average, massive clusters are connected to more filaments than low mass
clusters. Clusters with $M \sim 10^{14}$ M$_{\odot}$ h$^{-1}$ have on average
two connecting filaments, while clusters with $M \geq 10^{15}$ M$_{\odot}$
h$^{-1}$ have on average five connecting filaments. iv).- Density profiles
indicate that the typical width of filaments is 2$\Mpch$. Walls have less well
defined boundaries with widths between 5-8 Mpc h$^{-1}$. In their interior,
filaments have a power-law density profile with slope ${\gamma}\approx -1$,
corresponding to an isothermal density profile. | Axion Miniclusters in Modified Cosmological Histories: If the symmetry breaking leading to the origin of the axion dark matter field
occurs after the end of inflation and is never restored, then overdensities in
the axion field collapse to form dense objects known in the literature as axion
miniclusters. The estimates of the typical minicluster mass and radius strongly
depend on the details of the cosmology at which the onset of axion oscillations
begin. In this work we study the properties and phenomenology of miniclusters
in alternative cosmological histories and find that they can change by many
orders of magnitude. Our findings have direct implications on current and
future experimental searches and, in the case of discovery, could be used to
learn something about the universe expansion prior to Big-Bang-Nucleosynthesis. |
An inventory of the stellar initial mass function in early-type galaxies: Given a flurry of recent claims for systematic variations in the stellar
initial mass function (IMF), we carry out the first inventory of the
observational evidence using different approaches. This includes literature
results, as well as our own new findings from combined stellar-populations
synthesis (SPS) and Jeans dynamical analyses of data on $\sim$~4500 early-type
galaxies (ETGs) from the SPIDER project. We focus on the mass-to-light ratio
mismatch relative to the Milky Way IMF, \dimf, correlated against the central
stellar velocity dispersion, \sigs. We find a strong correlation between \dimf\
and \sigs, for a wide set of dark matter (DM) model profiles. These results are
robust if a uniform halo response to baryons is adopted across the sample. The
overall normalization of \dimf, and the detailed DM profile, are less certain,
but the data are consistent with standard cold-DM halos, and a central DM
fraction that is roughly constant with \sigs. For a variety of related studies
in the literature, using SPS, dynamics, and gravitational lensing, similar
results are found. Studies based solely on spectroscopic line diagnostics agree
on a Salpeter-like IMF at high \sigs, but differ at low \sigs. Overall, we find
that multiple independent lines of evidence appear to be converging on a
systematic variation in the IMF, such that high-\sigs\ ETGs have an excess of
low-mass stars relative to spirals and low-\sigs\ ETGs. Robust verification of
super-Salpeter IMFs in the highest-\sigs\ galaxies will require additional
scrutiny of scatter and systematic uncertainties. The implications for the
distribution of DM are still inconclusive. | Impact of neutrino properties on the estimation of inflationary
parameters from current and future observations: We study the impact of assumptions about neutrino properties on the
estimation of inflationary parameters from cosmological data, with a specific
focus on the allowed contours in the $n_s/r$ plane. We study the following
neutrino properties: (i) the total neutrino mass $ M_\nu =\sum_i m_i$; (ii) the
number of relativistic degrees of freedom $N_{eff}$; and (iii) the neutrino
hierarchy: whereas previous literature assumed 3 degenerate neutrino masses or
two massless neutrino species (that do not match neutrino oscillation data), we
study the cases of normal and inverted hierarchy. Our basic result is that
these three neutrino properties induce $< 1 \sigma$ shift of the probability
contours in the $n_s/r$ plane with both current or upcoming data. We find that
the choice of neutrino hierarchy has a negligible impact. However, the minimal
cutoff on the total neutrino mass $M_{\nu,{min}}=0 $ that accompanies previous
works using the degenerate hierarchy does introduce biases in the $n_s/r$ plane
and should be replaced by $M_{\nu,min}= 0.059$ eV as required by oscillation
data. Using current CMB data from Planck and Bicep/Keck, marginalizing over $
M_\nu$ and over $r$ can lead to a shift in the mean value of $n_s$ of
$\sim0.3\sigma$ towards lower values. However, once BAO measurements are
included, the standard contours in the $n_s/r$ plane are basically reproduced.
Larger shifts of the contours in the $n_s/r$ plane (up to 0.8$\sigma$) arise
for nonstandard values of $N_{eff}$. We also provide forecasts for the future
CMB experiments COrE and Stage-IV and show that the incomplete knowledge of
neutrino properties, taken into account by a marginalization over $M_\nu$,
could induce a shift of $\sim0.4\sigma$ towards lower values in the
determination of $n_s$ (or a $\sim 0.8\sigma$ shift if one marginalizes over
$N_{eff}$). Comparison to specific inflationary models is shown. |
Relieve the $H_0$ tension with a new coupled generalized three-form dark
energy model: In this work we propose a new coupled generalized three-form dark energy
model, in which dark energy are represented by a three-form field and other
components are represented by ideal fluids. We first perform a dynamical
analysis on the new model and obtain four fixed points, including a saddle
point representing a radiation dominated Universe, a saddle point representing
a matter dominated Universe, and two attractors representing two dark energy
dominated Universes. We then use the observational data, including cosmic
microwave background (CMB) data, baryon acoustic oscillations (BAO) data, and
Type Ia supernovae (SN Ia) data to constrain the model parameters of the
coupled generalized three-form dark energy model. For comparison, we also
consider the coupled three-form dark energy model, generalized three-form dark
energy model, and $\Lambda$CDM model, we find that the coupled generalized
three-form dark energy model is the only one model that can reduce the $H_0$
tension to a more acceptable level, with $H_0=70.1_{-1.5}^{+1.4}$ km/s/Mpc,
which is consistent with R19 at $2.0\sigma$ confidence level. We also
investigate the best-fit dynamical behavior of the coupled generalized
three-form dark energy model, and show that our model is equivalent to a
quintom dark energy model, in which dark energy, at early epoch, behaves like
some form of early dark energy with a small positive equation of state. | Non-Gaussian inference from non-linear and non-Poisson biased
distributed data: We study the statistical inference of the cosmological dark matter density
field from non-Gaussian, non-linear and non-Poisson biased distributed tracers.
We have implemented a Bayesian posterior sampling computer-code solving this
problem and tested it with mock data based on N-body simulations. |
Smoothing expansion rate data to reconstruct cosmological matter
perturbations: The existing degeneracy between different dark energy and modified gravity
cosmologies at the background level may be broken by analysing quantities at
the perturbative level. In this work, we apply a non-parametric smoothing (NPS)
method to reconstruct the expansion history of the Universe ($H(z)$) from
model-independent cosmic chronometers and high-$z$ quasar data. Assuming a
homogeneous and isotropic flat universe and general relativity (GR) as the
gravity theory, we calculate the non-relativistic matter perturbations in the
linear regime using the $H(z)$ reconstruction and realistic values of
$\Omega_{m0}$ and $\sigma_8$ from Planck and WMAP-9 collaborations. We find a
good agreement between the measurements of the growth rate and $f\sigma_8(z)$
from current large-scale structure observations and the estimates obtained from
the reconstruction of the cosmic expansion history. Considering a recently
proposed null test for GR using matter perturbations, we also apply the NPS
method to reconstruct $f\sigma_8(z)$. For this case, we find a $\sim 2\sigma$
tension (good agreement) with the standard relativistic cosmology when the
Planck (WMAP-9) priors are used. | Isobaric Reconstruction of the Baryonic Acoustic Oscillation: In this paper, we report a significant recovery of the linear baryonic
acoustic oscillation (BAO) signature by applying the isobaric reconstruction
algorithm to the non-linear matter density field. Assuming only the
longitudinal component of the displacement being cosmologically relevant, this
algorithm iteratively solves the coordinate transform between the Lagrangian
and Eulerian frames without requiring any specific knowledge of the dynamics.
For dark matter field, it produces the non-linear displacement potential with
very high fidelity. The reconstruction error at the pixel level is within a few
percent, and is caused only by the emergence of the transverse component after
the shell-crossing. As it circumvents the strongest non-linearity of the
density evolution, the reconstructed field is well-described by linear theory
and immune from the bulk-flow smearing of the BAO signature. Therefore this
algorithm could significantly improve the measurement accuracy of the sound
horizon scale. For a perfect large-scale structure survey at redshift zero
without Poisson or instrumental noise, the fractional error is reduced by a
factor of 2.7, very close to the ideal limit with linear power spectrum and
Gaussian covariance matrix. |
Machine Learning improved fits of the sound horizon at the baryon drag
epoch: The baryon acoustic oscillations (BAO) have proven to be an invaluable tool
in constraining the expansion history of the Universe at late times and are
characterized by the comoving sound horizon at the baryon drag epoch
$r_\mathrm{s}(z_\mathrm{d})$. The latter quantity can be calculated either
numerically using recombination codes or via fitting functions, such as the one
by Eisenstein and Hu (EH), made via grids of parameters of the recombination
history. Here we quantify the accuracy of these expressions and show that they
can strongly bias the derived constraints on the cosmological parameters using
BAO data. Then, using a machine learning approach, called the genetic
algorithms, we proceed to derive new analytic expressions for
$r_\mathrm{s}(z_\mathrm{d})$ which are accurate at the $\sim0.003\%$ level in a
range of $10\sigma$ around the Planck 2018 best-fit or $\sim0.018\%$ in a much
broader range, compared to $\sim 2-4\%$ for the EH expression, thus obtaining
an improvement of two to three orders of magnitude. Moreover, we also provide
fits that include the effects of massive neutrinos and an extension to the
concordance cosmological model assuming variations of the fine structure
constant. Finally, we note that our expressions can be used to ease the
computational cost required to compute $r_\mathrm{s}(z_\mathrm{d})$ with a
Boltzmann code when deriving cosmological constraints using BAO data from
current and upcoming surveys. | Imprint of DESI fiber assignment on the anisotropic power spectrum of
emission line galaxies: The Dark Energy Spectroscopic Instrument (DESI), a multiplexed fiber-fed
spectrograph, is a Stage-IV ground-based dark energy experiment aiming to
measure redshifts for 29 million Emission-Line Galaxies (ELG), 4 million
Luminous Red Galaxies (LRG), and 2 million Quasi-Stellar Objects (QSO). The
survey design includes a pattern of tiling on the sky and the locations of the
fiber positioners in the focal plane of the telescope, with the observation
strategy determined by a fiber assignment algorithm that optimizes the
allocation of fibers to targets. This strategy allows a given region to be
covered on average five times for a five-year survey, but with coverage varying
between zero and twelve, which imprints a spatially-dependent pattern on the
galaxy clustering. We investigate the systematic effects of the fiber
assignment coverage on the anisotropic galaxy clustering of ELGs and show that,
in the absence of any corrections, it leads to discrepancies of order ten
percent on large scales for the power spectrum multipoles. We introduce a
method where objects in a random catalog are assigned a coverage, and the mean
density is separately computed for each coverage factor. We show that this
method reduces, but does not eliminate the effect. We next investigate the
angular dependence of the contaminated signal, arguing that it is mostly
localized to purely transverse modes. We demonstrate that the cleanest way to
remove the contaminating signal is to perform an analysis of the anisotropic
power spectrum $P(k,\mu)$ and remove the lowest $\mu$ bin, leaving $\mu>0$
modes accurate at the few-percent level. Here, $\mu$ is the cosine of the angle
between the line-of-sight and the direction of $\vec{k}$. We also investigate
two alternative definitions of the random catalog and show they are comparable
but less effective than the coverage randoms method. |
Constraining the interaction between dark matter and dark energy with
CMB data: We briefly discuss the intriguing case of a phenomenological
non-gravitational coupling in the dark sector, where the interaction is
parameterized as an energy transfer either from dark matter to dark energy or
the opposite. We show that a non-zero coupling with an energy flow from the
latter to the former leads to a full reconciliation of the tension between
high- and low-redshift observations present in the standard cosmological model. | Alleviating the Tension in the Cosmic Microwave Background using
Planck-Scale Physics: Certain anomalies in the CMB bring out a tension between the six-parameter
flat $\Lambda$CDM model and the CMB data. We revisit the PLANCK analysis with
loop quantum cosmology (LQC) predictions and show that LQC alleviates both the
large-scale power anomaly and the tension in the lensing amplitude. These
differences arise because, in LQC, the primordial power spectrum is scale
dependent for small $k$, with a specific power suppression. We conclude with a
prediction of larger optical depth and power suppression in the $B$-mode
polarization power spectrum on large scales. |
What does strong gravitational lensing? The mass and redshift
distribution of high-magnification lenses: Many distant objects can only be detected, or become more scientifically
valuable, if they have been highly magnified by strong gravitational lensing.
We use EAGLE and BAHAMAS, two recent cosmological hydrodynamical simulations,
to predict the probability distribution for both the lens mass and lens
redshift when point sources are highly magnified by gravitational lensing. For
sources at a redshift of two, we find the distribution of lens redshifts to be
broad, peaking at z=0.6. The contribution of different lens masses is also
fairly broad, with most high-magnification lensing due to lenses with halo
masses between 10^12 and 10^14 solar masses. Lower mass haloes are inefficient
lenses, while more massive haloes are rare. We find that a simple model in
which all haloes have singular isothermal sphere density profiles can
approximately reproduce the simulation predictions, although such a model
over-predicts the importance of haloes with mass <10^12 solar masses for
lensing. We also calculate the probability that point sources at different
redshifts are strongly lensed. At low redshift, high magnifications are
extremely unlikely. Each z=0.5 source produces, on average, 5x10^-7 images with
magnification greater than ten; for z =2 this increases to about 2x10^-5. Our
results imply that searches for strongly lensed optical transients, including
the optical counterparts to strongly lensed gravitational waves, can be
optimized by monitoring massive galaxies, groups and clusters rather than
concentrating on an individual population of lenses. | Ultra-local models of modified gravity without kinetic term: We present a class of modified-gravity theories which we call ultra-local
models. We add a scalar field, with negligible kinetic terms, to the
Einstein-Hilbert action. We also introduce a conformal coupling to matter. This
gives rise to a new screening mechanism which is not entirely due to the
non-linearity of the scalar field potential or the coupling function but to the
absence of the kinetic term. As a result this removes any fifth force between
isolated objects in vacuum. The predictions of these models only depend on a
single free function, as the potential and the coupling function are
degenerate, with an amplitude given by a parameter $\alpha \lesssim 10^{-6}$,
whose magnitude springs from requiring a small modification of Newton's
potential astrophysically and cosmologically. This singles out a redshift
$z_{\alpha} \sim \alpha^{-1/3} \gtrsim 100$ where the fifth force is the
greatest. The cosmological background follows the $\Lambda$-CDM history within
a $10^{-6}$ accuracy, while cosmological perturbations are significantly
enhanced (or damped) on small scales, $k \gtrsim 2 h {\rm Mpc}^{-1}$ at $z=0$.
The spherical collapse and the halo mass function are modified in the same
manner. We find that the modifications of gravity are greater for galactic or
sub-galactic structures. We also present a thermodynamic analysis of the
non-linear and inhomogeneous fifth-force regime where we find that the Universe
is not made more inhomogeneous before $z_\alpha$ when the fifth force
dominates, and does not lead to the existence of clumped matter on extra small
scales inside halos for large masses while this possibility exists for masses
$M\lesssim 10^{11} M_\odot$ where the phenomenology of ultra-local models would
be most different from $\Lambda$-CDM. |
The Atacama Cosmology Telescope: Combined kinematic and thermal
Sunyaev-Zel'dovich measurements from BOSS CMASS and LOWZ halos: The scattering of cosmic microwave background (CMB) photons off the
free-electron gas in galaxies and clusters leaves detectable imprints on high
resolution CMB maps: the thermal and kinematic Sunyaev-Zel'dovich effects (tSZ
and kSZ respectively). We use combined microwave maps from the Atacama
Cosmology Telescope (ACT) DR5 and Planck in combination with the CMASS and LOWZ
galaxy catalogs from the Baryon Oscillation Spectroscopic Survey (BOSS DR10 and
DR12), to study the gas associated with these galaxy groups. Using individual
reconstructed velocities, we perform a stacking analysis and reject the no-kSZ
hypothesis at 6.5$\sigma$, the highest significance to date. This directly
translates into a measurement of the electron number density profile, and thus
of the gas density profile. Despite the limited signal to noise, the
measurement shows at high significance that the gas density profile is more
extended than the dark matter density profile, for any reasonable baryon
abundance (formally $>90\sigma$ for the cosmic baryon abundance). We
simultaneously measure the tSZ signal, i.e. the electron thermal pressure
profile of the same CMASS objects, and reject the no-tSZ hypothesis at
10$\sigma$. We combine tSZ and kSZ measurements to estimate the electron
temperature to 20% precision in several aperture bins, and find it comparable
to the virial temperature. In a companion paper, we analyze these measurements
to constrain the gas thermodynamics and the properties of feedback inside
galaxy groups. We present the corresponding LOWZ measurements in this paper,
ruling out a null kSZ (tSZ) signal at 2.9 (13.9)$\sigma$, and leave their
interpretation to future work. Our stacking software ThumbStack is publicly
available at https://github.com/EmmanuelSchaan/ThumbStack and directly
applicable to future Simons Observatory and CMB-S4 data. | An X-ray Detected Group of Quiescent Early-type Galaxies at z=1.6 in the
Chandra Deep Field South: (Abridged) We report the discovery of an X-ray group of galaxies located at a
high redshift of z=1.61 in the Chandra Deep Field South. The group is first
identified as an extended X-ray source. We use a wealth of deep
multi-wavelength data to identify the optical counterpart -- our red sequence
finder detects a significant over-density of galaxies at z~1.6 and the
brightest group galaxy is spectroscopically confirmed at z=1.61. We measure an
X-ray luminosity of L_{0.1-2.4 keV}= 1.8\pm0.6 \times 10^{43} erg/s, which then
translates into a group mass of 3.2\pm0.8 \times 10^{13} M_sun. This is the
lowest mass group ever confirmed at z>1.5. The deep optical-nearIR images from
CANDELS reveal that the group exhibits a surprisingly prominent red sequence. A
detailed analysis of the spectral energy distributions of the group member
candidates confirms that most of them are indeed passive galaxies. Furthermore,
their structural parameters measured from the near-IR CANDELS images show that
they are morphologically early-type. The newly identified group at z=1.61 is
dominated by quiescent early-type galaxies and the group appears similar to
those in the local Universe. One possible difference is the high fraction of
AGN (38^{+23}_{-20}%), which might indicate a role for AGN in quenching. But, a
statistical sample of high-z groups is needed to draw a general picture of
groups at this redshift. Such a sample will hopefully be available in near
future surveys. |
GRB 130606A as a Probe of the Intergalactic Medium and the Interstellar
Medium in a Star-forming Galaxy in the First Gyr After the Big Bang: We present high signal-to-noise ratio Gemini and MMT spectroscopy of the
optical afterglow of the gamma-ray burst (GRB) 130606A at redshift z=5.913,
discovered by Swift. This is the first high-redshift GRB afterglow to have
spectra of comparable quality to those of z~6 quasars. The data exhibit a
smooth continuum at near-infrared wavelengths that is sharply cut off blueward
of 8410 Angs due to absorption from Ly-alpha at redshift z~5.91, with some flux
transmitted through the Ly-alpha forest between 7000-7800 Angs. We use column
densities inferred from metal absorption lines to constrain the metallicity of
the host galaxy between a lower limit of [Si/H]>-1.7 and an upper limit of
[S/H]<-0.5 set by the non-detection of S II absorption. We demonstrate
consistency between the dramatic evolution in the transmission fraction of
Ly-alpha seen in this spectrum over the redshift range z=4.9 to 5.85 with that
previously measured from observations of high-redshift quasars. There is an
extended redshift interval of Delta-z=0.12 in the Ly-alpha forest at z=5.77
with no detected transmission, leading to a 3-sigma upper limit on the mean
Ly-alpha transmission fraction of <0.2% (or tau_eff(Ly-alpha) > 6.4). This is
comparable to the lowest-redshift Gunn-Peterson troughs found in quasar
spectra. We set a 2-sigma upper limit of 0.11 on the neutral fraction of the
IGM at the redshift of the GRB from the lack of a Ly-alpha red damping wing,
assuming a model with a constant neutral density. Some Ly-beta and Ly-gamma
transmission is detected in this redshift window, indicating that it is not
completely opaque, and hence that the IGM is nonetheless mostly ionized at
these redshifts. GRB 130606A thus for the first time realizes the promise of
GRBs as probes of the first galaxies and cosmic reionization. | Phase decoherence of gravitational wave backgrounds: Metric perturbations affect the phase of gravitational waves as they
propagate through the inhomogeneous universe. This effect causes Stochastic
Gravitational Wave Backgrounds (SGWBs) to lose any phase coherence that may
have been present at emission or horizon entry. We show that, for a standard
cosmological model, this implies complete loss of coherence above frequencies
$f \sim 10^{-12}$ Hz. The result is that any attempts to map SGWBs using
phase-coherent methods have no foreseeable applications. Incoherent methods
that solve directly for the intensity of the SGWBs are the only methods that
can reconstruct the angular dependence of any SGWB. |
Practical tools for third order cosmological perturbations: We discuss cosmological perturbation theory at third order, deriving the
gauge transformation rules for metric and matter perturbations, and
constructing third order gauge invariant quantities. We present the Einstein
tensor components, the evolution equations for a perfect fluid, and the
Klein-Gordon equation at third order, including scalar, vector and tensor
perturbations. In doing so, we also give all second order tensor components and
evolution equations in full, exhilarating generality. | High precision simulations of weak lensing effect on Cosmic Microwave
Background polarization: We study accuracy, robustness and self-consistency of pixel-domain
simulations of the gravitational lensing effect on the primordial CMB
anisotropies due to the large-scale structure of the Universe. In particular,
we investigate dependence of the results precision on some crucial parameters
of such techniques and propose a semi-analytic framework to determine their
values so the required precision is a priori assured and the numerical workload
simultaneously optimized. Our focus is on the B-mode signal but we discuss also
other CMB observables, such as total intensity, T, and E-mode polarization,
emphasizing differences and similarities between all these cases. Our
semi-analytic considerations are backed up by extensive numerical results.
Those are obtained using a code, nicknamed lenS2HAT -- for Lensing using
Scalable Spherical Harmonic Transforms (S2HAT) -- which we have developed in
the course of this work. The code implements a version of the pixel-domain
approach of Lewis (2005) and permits performing the simulations at very high
resolutions and data volumes, thanks to its efficient parallelization provided
by the S2HAT library -- a parallel library for a calculation of the spherical
harmonic transforms. The code is made publicly available. |
Anisotropy of phase transition gravitational wave and its implication
for primordial seeds of the Universe: We quantitatively study how the primordial density fluctuations are imprinted
on the anisotropy of the phase transition gravitational wave (PTGW). Generated
long before recombination and free from Silk damping, the anisotropic PTGW
might reveal the density perturbation seeded from inflation or alternatives. We
find new behaviors of the PTGW anisotropy power spectrum. The PTGW anisotropy
is stronger than the anisotropy of the cosmic microwave background temperature
at all scales, and the high-$\ell$ multiples are enhanced about 1 order due to
the early integrated Sachs-Wolfe effect. Furthermore, differences in primordial
power spectra at small scales manifest themselves more significantly on the
angular power spectrum of PTGW anisotropy compared to that of the cosmic
microwave background. These properties might provide a novel clue to
understanding the primordial density perturbation of our early Universe and
thereby complete our understanding of inflation theory. Taking nanohertz PTGW
from dark matter models as a typical example, we obtain amplitudes of PTGW
anisotropy which are about 4 or 3 orders weaker than the isotropic PTGW energy
spectra. | The WiggleZ Dark Energy Survey: constraining galaxy bias and cosmic
growth with 3-point correlation functions: Higher-order statistics are a useful and complementary tool for measuring the
clustering of galaxies, containing information on the non-gaussian evolution
and morphology of large-scale structure in the Universe. In this work we
present measurements of the three-point correlation function (3PCF) for 187,000
galaxies in the WiggleZ spectroscopic galaxy survey. We explore the WiggleZ
3PCF scale and shape dependence at three different epochs z=0.35, 0.55 and
0.68, the highest redshifts where these measurements have been made to date.
Using N-body simulations to predict the clustering of dark matter, we constrain
the linear and non-linear bias parameters of WiggleZ galaxies with respect to
dark matter, and marginalise over them to obtain constraints on sigma_8(z), the
variance of perturbations on a scale of 8 Mpc/h and its evolution with
redshift. These measurements of sigma_8(z), which have 10-20% accuracies, are
consistent with the predictions of the LCDM concordance cosmology and test this
model in a new way. |
Quasisteady Configurations of Conductive Intracluster Media: The radial distributions of temperature, density, and gas entropy among
cool-core clusters tend to be quite similar, suggesting that they have entered
a quasi-steady state. If that state is regulated by a combination of thermal
conduction and feedback from a central AGN, then the characteristics of those
radial profiles ought to contain information about the spatial distribution of
AGN heat input and the relative importance of thermal conduction. This paper
addresses those topics by deriving steady-state solutions for clusters in which
radiative cooling, electron thermal conduction, and thermal feedback fueled by
accretion are all present, with the aim of interpreting the configurations of
cool-core clusters in terms of steady-state models. It finds that the core
configurations of many cool-core clusters have entropy levels just below those
of conductively balanced solutions in which magnetic fields have suppressed
electron thermal conduction to ~1/3 of the full Spitzer value, suggesting that
AGN feedback is triggered when conduction can no longer compensate for
radiative cooling. And even when feedback is necessary to heat the central ~30
kpc, conduction may still be the most important heating mechanism within a
cluster's central ~100 kpc. | Efficient exploration of cosmology dependence in the EFT of LSS: The most effective use of data from current and upcoming large scale
structure~(LSS) and CMB observations requires the ability to predict the
clustering of LSS with very high precision. The Effective Field Theory of Large
Scale Structure (EFTofLSS) provides an instrument for performing analytical
computations of LSS observables with the required precision in the mildly
nonlinear regime. In this paper, we develop efficient implementations of these
computations that allow for an exploration of their dependence on cosmological
parameters. They are based on two ideas. First, once an observable has been
computed with high precision for a reference cosmology, for a new cosmology the
same can be easily obtained with comparable precision just by adding the
difference in that observable, evaluated with much less precision. Second, most
cosmologies of interest are sufficiently close to the Planck best-fit cosmology
that observables can be obtained from a Taylor expansion around the reference
cosmology. These ideas are implemented for the matter power spectrum at two
loops and are released as public codes. When applied to cosmologies that are
within 3$\sigma$ of the Planck best-fit model, the first method evaluates the
power spectrum in a few minutes on a laptop, with results that have 1\% or
better precision, while with the Taylor expansion the same quantity is
instantly generated with similar precision. The ideas and codes we present may
easily be extended for other applications or higher-precision results. |
Nonlocal Models of Cosmic Acceleration: I review a class of nonlocally modified gravity models which were proposed to
explain the current phase of cosmic acceleration without dark energy. Among the
topics considered are deriving causal and conserved field equations, adjusting
the model to make it support a given expansion history, why these models do not
require an elaborate screening mechanism to evade solar system tests, degrees
of freedom and kinetic stability, and the negative verdict of structure
formation. Although these simple models are not consistent with data on the
growth of cosmic structures many of their features are likely to carry over to
more complicated models which are in better agreement with the data. | Searching for bias and correlations in a Bayesian way: A range of Bayesian tools has become widely used in cosmological data
treatment and parameter inference (see Kunz, Bassett & Hlozek (2007), Trotta
(2008), Amendola, Marra & Quartin (2013)). With increasingly big datasets and
higher precision, tools that enable us to further enhance the accuracy of our
measurements gain importance. Here we present an approach based on internal
robustness, introduced in Amendola, Marra & Quartin (2013) and adopted in
Heneka, Marra & Amendola (2014), to identify biased subsets of data and hidden
correlation in a model independent way. |
Cosmological simulations with disformally coupled symmetron fields: We investigate statistical properties of the distribution of matter at
redshift zero in disformal gravity by using N-body simulations. The disformal
model studied here consists of a conformally coupled symmetron field with an
additional exponential disformal term. We conduct cosmological simulations to
discover the impact of the new disformal terms in the matter power spectrum,
halo mass function, and radial profile of the scalar field. We calculated the
disformal geodesic equation and the equation of motion for the scalar field. We
then implemented these equations into the N-body code ISIS, which is a modified
gravity version of the code RAMSES. The presence of a conformal symmetron field
increases both the power spectrum and mass function compared to standard
gravity on small scales. Our main finding is that the newly added disformal
terms tend to counteract these effects and can make the evolution slightly
closer to standard gravity. We finally show that the disformal terms give rise
to oscillations of the scalar field in the centre of the dark matter haloes. | The MicroJy and NanoJy Radio Sky: Source Population and Multi-wavelength
Properties: I present simple but robust estimates of the types of sources making up the
faint, sub-microJy radio sky. These include, not surprisingly, star-forming
galaxies and radio-quiet AGN but also two "new" populations, that is low radio
power ellipticals and dwarf galaxies, the latter likely constituting the most
numerous component of the radio sky. I then estimate for the first time the
X-ray, optical, and mid-infrared fluxes these objects are likely to have, which
are very important for source identification and the synergy between the
upcoming SKA and its various pathfinders with future missions in other bands.
On large areas of the sky the SKA, and any other radio telescope producing
surveys down to at least the microJy level, will go deeper than all currently
planned (and past) sky surveys, with the possible exception of the optical ones
from PAN-STARRS and the LSST. SPICA, JWST, and in particular the Extremely
Large Telescopes (ELTs) will be a match to the next generation radio telescopes
but only on small areas and above ~ 0.1 - 1 microJy (at 1.4 GHz), while even
IXO will only be able to detect a small (tiny) fraction of the microJy (nanoJy)
population in the X-rays. On the other hand, most sources from currently
planned all-sky surveys, with the likely exception of the optical ones, will
have a radio counterpart within the reach of the SKA. JWST and the ELTs might
turn out to be the main, or perhaps even the only, facilities capable of
securing optical counterparts and especially redshifts of microJy radio
sources. Because of their sensitivity, the SKA and its pathfinders will have a
huge impact on a number of topics in extragalactic astronomy including
star-formation in galaxies and its co-evolution with supermassive black holes,
radio-loudness and radio-quietness in AGN, dwarf galaxies, and the main
contributors to the radio background.[ABRIDGED] |
Evolution of String-Wall Networks and Axionic Domain Wall Problem: We study the cosmological evolution of domain walls bounded by strings which
arise naturally in axion models. If we introduce a bias in the potential, walls
become metastable and finally disappear. We perform two dimensional lattice
simulations of domain wall networks and estimate the decay rate of domain
walls. By using the numerical results, we give a constraint for the bias
parameter and the Peccei-Quinn scale. We also discuss the possibility to probe
axion models by direct detection of gravitational waves produced by domain
walls. | Using inpainting to construct accurate cut-sky CMB estimators: The direct evaluation of manifestly optimal, cut-sky CMB power spectrum and
bispectrum estimators is numerically very costly, due to the presence of
inverse-covariance filtering operations. This justifies the investigation of
alternative approaches. In this work, we mostly focus on an inpainting
algorithm that was introduced in recent CMB analyses to cure cut-sky
suboptimalities of bispectrum estimators. First, we show that inpainting can
equally be applied to the problem of unbiased estimation of power spectra. We
then compare the performance of a novel inpainted CMB temperature power
spectrum estimator to the popular apodised pseudo-$C_l$ (PCL) method and
demonstrate, both numerically and with analytic arguments, that inpainted power
spectrum estimates significantly outperform PCL estimates. Finally, we study
the case of cut-sky bispectrum estimators, comparing the performance of three
different approaches: inpainting, apodisation and a novel low-l leaning scheme.
Providing an analytic argument why the local shape is typically most affected
we mainly focus on local type non-Gaussianity. Our results show that inpainting
allows to achieve optimality also for bispectrum estimation, but interestingly
also demonstrate that appropriate apodisation, in conjunction with low-l
cleaning, can lead to comparable accuracy. |
Observational constraints on Yukawa cosmology and connection with black
hole shadows: We confront Yukawa modified cosmology, proposed in arXiv:2304.11492 [Jusufi
et al. arXiv:2304.11492], with data from Supernovae Type Ia (SNe Ia) and Hubble
parameter (OHD) observations. Yukawa cosmology is obtained from a Yukawa-like
gravitational potential, with coupling parameter $\alpha$ and wavelength
parameter $\lambda$, which gives rise to modified Friedmann equations. We show
that the agreement with observations is very efficient, and within $1\sigma$
confidence level we find the best-fit parameters
$\lambda=\left(2693_{-1262}^{+1191}\right)\, \rm Mpc$,
$\alpha=0.416_{-0.326}^{+1.137}$, and a graviton mass of
$m_{g}=\left(2.374_{-0.728}^{+2.095}\right)\times 10^{-42}\, \text{GeV}$.
Additionally, we establish a connection between the effective dark matter and
dark energy density parameters and the angular radius of the black hole shadow
of the SgrA and M87 black holes in the low-redshift limit, consistent with the
Event Horizon Telescope findings. | CMB-GAN: Fast Simulations of Cosmic Microwave background anisotropy maps
using Deep Learning: Cosmic Microwave Background (CMB) has been a cornerstone in many cosmology
experiments and studies since it was discovered back in 1964. Traditional
computational models like CAMB that are used for generating CMB temperature
anisotropy maps are extremely resource intensive and act as a bottleneck in
cosmology experiments that require a large amount of CMB data for analysis. In
this paper, we present a new approach to the generation of CMB temperature maps
using a specific class of neural networks called Generative Adversarial Network
(GAN). We train our deep generative model to learn the complex distribution of
CMB maps and efficiently generate new sets of CMB data in the form of 2D
patches of anisotropy maps without losing much accuracy. We limit our
experiment to the generation of 56$^{\circ}$ and 112$^{\circ}$ square patches
of CMB maps. We have also trained a Multilayer perceptron model for estimation
of baryon density from a CMB map, we will be using this model for the
performance evaluation of our generative model using diagnostic measures like
Histogram of pixel intensities, the standard deviation of pixel intensity
distribution, Power Spectrum, Cross power spectrum, Correlation matrix of the
power spectrum and Peak count. We show that the GAN model is able to
efficiently generate CMB samples of multiple sizes and is sensitive to the
cosmological parameters corresponding to the underlying distribution of the
data. The primiary advantage of this method is the exponential reduction in the
computational time needed to generate the CMB data, the GAN model is able to
generate the samples within seconds as opposed to hours required by the CAMB
package with an acceptable value to error and loss of information. We hope that
future iterations of this methodology will replace traditional statistical
methods of CMB data generation and help in large scale cosmological
experiments. |
Inhomegeneous cosmological models and fine-tuning of the initial state: Inhomogeneous cosmological models are often reported to suffer from a
fine-tuning problem because of the observer's location. We study if this is a
generic feature in the Lema\^{i}tre-Tolman (LT) models, by investigating if
there are models with freedom in the initial state. In these cases, the present
fine-tuned location would be evolved from a non-fine-tuned initial state and
thus vanishing the problem. In this paper, we show that this is not a generic
problem and we give the condition when the LT models do not have fine-tuned
initial state. The physical meaning of this condition, however, requires more
investigation. We investigate if this condition can be found from a special
case: homogeneous models with matter, dark, and curvature density as
parameters. We found that with any reasonable density values, these models do
not satisfy this condition and thus do not have freedom in the initial state.
We interpret this to be linked with the fine-tuning problem of the initial
state of the homogeneous models, when the early time inflation is not included
to them. We discuss of the condition in the context of non-homogeneous models. | B-mode Detection with an Extended Planck Mission: The Planck satellite has a nominal mission lifetime of 14 months allowing two
complete surveys of the sky. Here we investigate the potential of an extended
Planck mission of four sky surveys to constrain primordial B-mode anisotropies
in the presence of dominant Galactic polarized foreground emission. An extended
Planck mission is capable of powerful constraints on primordial B-modes at low
multipoles, which cannot be probed by ground based or sub-orbital experiments.
A tensor-scalar ratio of r=0.05 can be detected at a high significance level by
an extended Planck mission and it should be possible to set a 95% upper limit
on r of 0.03 if the tensor-scalar ratio is vanishingly small. Furthermore,
extending the Planck mission to four sky surveys offers better control of
polarized Galactic dust emission, since the 217 GHz frequency band can be used
as an effective dust template in addition to the 353 GHz channel. |
Nearest Neighbor distributions: new statistical measures for
cosmological clustering: The use of summary statistics beyond the two-point correlation function to
analyze the non-Gaussian clustering on small scales is an active field of
research in cosmology. In this paper, we explore a set of new summary
statistics -- the $k$-Nearest Neighbor Cumulative Distribution Functions
($k{\rm NN}$-${\rm CDF}$). This is the empirical cumulative distribution
function of distances from a set of volume-filling, Poisson distributed random
points to the $k$-nearest data points, and is sensitive to all connected
$N$-point correlations in the data. The $k{\rm NN}$-${\rm CDF}$ can be used to
measure counts in cell, void probability distributions and higher $N$-point
correlation functions, all using the same formalism exploiting fast searches
with spatial tree data structures. We demonstrate how it can be computed
efficiently from various data sets - both discrete points, and the
generalization for continuous fields. We use data from a large suite of
$N$-body simulations to explore the sensitivity of this new statistic to
various cosmological parameters, compared to the two-point correlation
function, while using the same range of scales. We demonstrate that the use of
$k{\rm NN}$-${\rm CDF}$ improves the constraints on the cosmological parameters
by more than a factor of $2$ when applied to the clustering of dark matter in
the range of scales between $10h^{-1}{\rm Mpc}$ and $40h^{-1}{\rm Mpc}$. We
also show that relative improvement is even greater when applied on the same
scales to the clustering of halos in the simulations at a fixed number density,
both in real space, as well as in redshift space. Since the $k{\rm NN}$-${\rm
CDF}$ are sensitive to all higher order connected correlation functions in the
data, the gains over traditional two-point analyses are expected to grow as
progressively smaller scales are included in the analysis of cosmological data. | Sommerfeld-enhanced dark matter searches with dwarf spheroidal galaxies: We study observable signals from dark matter that self-annihilates via the
Sommerfeld effect in dwarf spheroidal galaxies (dSphs). Since the effect of the
Sommerfeld enhancement depends on the velocity of dark matter, it is crucial to
determine the profile of dSphs to compute the J-factor, i.e., the line-of-sight
integral of density squared. In our study we use the prior distributions of the
parameters for satellite density profiles in order to determine the J-factor,
making most out of the recent developments in the N-body simulations and
semi-analytical modeling for the structure formation. As concrete models, we
analyze fermionic dark matter that annihilates via a light scalar and Wino dark
matter in supersymmetric models. We find that, with the more realistic prior
distributions that we adopt in this study, the J-factor of the most promising
dSphs is decreased by a factor of a few, compared with earlier estimates based
on non-informative priors. Nevertheless, the Cherenkov Telescope Array should
be able to detect the thermal Wino dark matter by pointing it toward best
classical or ultrafaint dSphs for 500 hours. |
On Preferred Axes in WMAP Cosmic Microwave Background Data after
Subtraction of the Integrated Sachs-Wolfe Effect: There is currently a debate over the existence of claimed statistical
anomalies in the cosmic microwave background (CMB), recently confirmed in
Planck data. Recent work has focussed on methods for measuring statistical
significance, on masks and on secondary anisotropies as potential causes of the
anomalies. We investigate simultaneously the method for accounting for masked
regions and the foreground integrated Sachs-Wolfe (ISW) signal. We search for
trends in different years of WMAP CMB data with different mask treatments. We
reconstruct the ISW field due to the 2 Micron All-Sky Survey (2MASS) and the
NRAO VLA Sky Survey (NVSS) up to l=5, and we focus on the Axis of Evil (AoE)
statistic and even/odd mirror parity, both of which search for preferred axes
in the Universe. We find that removing the ISW reduces the significance of
these anomalies in WMAP data, though this does not exclude the possibility of
exotic physics. In the spirit of reproducible research, all reconstructed maps
and codes will be made available for download at
http://www.cosmostat.org/anomaliesCMB.html. | Magneto-reheating constraints from curvature perturbations: As additional perturbative degrees of freedom, it is known that magnetic
fields of inflationary origin can source curvature perturbations on
super-Hubble scales. By requiring the magnetic generated curvature to remain
smaller than its inflationary adiabatic counterpart during inflation and
reheating, we derive new constraints on the maximal field value today, the
reheating energy scale and its equation of state parameter. These bounds end up
being stronger by a few order of magnitude than those associated with a
possible backreaction of the magnetic field onto the background. Our results
are readily applicable to any slow-roll single field inflationary models and
any magnetic field having its energy density scaling as a^gamma during
inflation. As an illustrative example, massive inflation is found to remain
compatible with a magnetic field today Bo = 5 x 10^(-15) G for some values of
gamma only if a matter dominated reheating takes place at energies larger than
10^5 GeV. Conversely, assuming gamma=-1, massive inflation followed by a matter
dominated reheating cannot explain large scale magnetic fields larger than
10^(-20) G today. |
Model-independent confirmation of a constant speed of light over
cosmological distances: Recent attempts at measuring the variation of $c$ using an assortment of
standard candles and the redshift-dependent Hubble expansion rate inferred from
the currently available catalog of cosmic chronometers have tended to show that
the speed of light appears to be constant, at least up to $z\sim 2$. A notable
exception is the use of high-redshift UV $+$ X-ray quasars, whose Hubble
diagram seems to indicate a $\sim 2.7\sigma$ deviation of c from its value
$c_0$ ($\equiv 2.99792458 \times 10^{10}$ cm s$^{-1}$) on Earth. We show in
this paper, however, that this anomaly is due to an error in the derived
relation between the luminosity distance, $D_L$, and $H(z)$ when $c$ is allowed
to vary with redshift, and an imprecise calibration of the quasar catalog. When
these deficiences are addressed correctly, one finds that $c/c_0=0.95 \pm 0.14$
in the redshift range $0\lesssim z\lesssim 2$, fully consistent with zero
variation within the measurement errors. | Suzaku X-ray Follow-up Observation of Weak-lensing-detected Halos in the
Field around ZwCl0823.2+0425: We present the results of Suzaku X-ray follow-up observation of
weak-lensing-detected halos in the field around galaxy cluster ZwCl0823.2+0425.
We clearly detected X-ray emission associated with most of these halos and
determined their detailed physical parameters such as X-ray luminosity,
temperature, and metal abundance, for the first time. We find that the X-ray
luminosity - temperature relation for these halos agrees with former typical
results. With mass determined from the weak gravitational lensing data, the
mass-temperature relation for them is also investigated and found to be
consistent with the prediction from a simple self-similar model and results of
the previous studies with both lensing and X-ray data. We would like to
emphasize that the self-similar scaling relation of mass and temperature is
shown here for the first time using a weak-lensing selected sample, whereas
previous studies of the mass scaling relation used X-ray-selected samples of
clusters. Therefore, our study demonstrates importance of X-ray follow-up
observations of shear-selected clusters, and shows that a joint X-ray and
lensing analysis will be crucial for clusters discovered by the forthcoming
weak-lensing surveys, such as the one planned with Subaru/Hyper-Suprime-Cam. |
Importance of far-infrared mapping in a spiral galaxy: AKARI observation
of M81: The importance of the far-infrared (FIR) mapping is demonstrated for a
face-on spiral galaxy, M81, by analyzing its imaging data at 65, 90, and 140
{\mu}m taken by AKARI. Basic products are the dust temperature map, the dust
optical depth map, and the colour-colour diagram. The main features are as
follows. (i) The dust temperature derived from the total fluxes at 90 {\mu}m
and 140 {\mu}m reflects the relatively low temperatures seen in the interarm
and spiral arms excluding the warm spots, rather than the high temperatures in
warm spots and the centre. This indicates that the total FIR luminosity is
dominated by the dust heated by the general interstellar radiation field. (ii)
The galaxy is more extended at 140 {\mu}m than at the other shorter
wavelengths, which reflects the radial dust temperature gradient. (iii) The
dust optical depth derived from the FIR mapping is broadly consistent with that
estimated from the FIR-to-ultraviolet luminosity ratio. (iv) The FIR
colour-colour diagramis useful to identify a 'contamination' of warm dust. The
existence of small-scale warm star-forming regions is supported in the bright
spots along the spiral arms. This contamination also leads to an underestimate
of dust optical depth (or dust column density). | Confirmation of Faint Dwarf Galaxies in the M81 Group: We have followed up on the results of a 65 square degree CFHT/MegaCam imaging
survey of the nearby M81 Group searching for faint and ultra-faint dwarf
galaxies. The original survey turned up 22 faint candidate dwarf members. Based
on two-color HST ACS/WFC and WFPC2 photometry, we now confirm 14 of these as
dwarf galaxy members of the group. Distances and stellar population
characteristics are discussed for each. To a completeness limit of M_r' = -10,
we find a galaxy luminosity function slope of -1.27+-0.04 for the M81 group. In
this region, there are now 36 M81 group members known, including 4 blue compact
dwarfs, 8 other late types including the interacting giants M81, NGC 3077, and
M82, 19 early type dwarfs, and at least 5 potential tidal dwarf galaxies. We
find that the dSph galaxies in M81 appear to lie in a flattened distribution,
similar to that found for the Milky Way and M31. One of the newly discovered
dSph galaxies has properties similar to the ultra-faint dwarfs being found in
the Local Group with a size R_e ~ 100 pc and total magnitude estimates M_r' =
-6.8 and M_I ~ -9.1. |
Is PLANCK consistent with primordial deuterium measurements ?: The recent measurements of the Cosmic Microwave Background Anisotropies
provided by the Planck satellite experiment have significantly improved the
constraints on several cosmological parameters. In this brief paper we point
out a small but interesting tension present between recent values of the
primordial deuterium measured from quasar absorption line systems and the same
value inferred, albeit indirectly, from the Planck measurements assuming
{\Lambda}CDM and Big Bang Nucleosynthesis. Here we discuss this tension in
detail investigating the possible new physics that could be responsible for the
tension. We found that, among 8 extra parameters, only an anomalous lensing
component and a closed universe could change the Planck constraint towards a
better consistency with direct deuterium measurements. | Discovery of periodic modulations in the optical spectra of galaxies,
possibly due to ultra-rapid light bursts from their massive central black
hole: A Fourier transform analysis of 2.5 million spectra in the SDSS survey was
carried out to detect periodic modulations contained in their intensity versus
frequency spectrum. A statistically significant signal was found for 223
galaxies while the spectra of 0.9 million galaxies were observed. A plot of the
periods as a function of redshift clearly shows that the effect is real without
any doubt, because they are quantized at two base periods that increase with
redshift in two very tight parallel linear relations. I suggest that it could
be caused by light bursts separated by times of the order of 10-13 seconds
because it was the original reason for searching for the spectral periodicity
but other causes may be possible. As another possible cause, I investigate the
hypothesis that the modulation is generated by the Fourier transform of
spectral lines, concluding that it is not valid. Although the light bursts
suggestion implies absurdly high temperatures, it is supported by the fact that
the Crab pulsar also has extremely short unresolved pulses (<0.5 nanosecond)
that also imply absurdly high temperatures. Furthermore, the radio spectrum of
the Crab pulsar also has spectral bands similar to those that have been
detected. Finally, decreasing the signal to noise threshold of detection gave
results consistent with beamed signals having a small beam divergence, as
expected from non-thermal sources that send a jet, like those seen in pulsars.
Considering that galaxy centers contain massive black holes, exotic black hole
physics may be responsible for the spectral modulation. However, at this stage,
this is only a hypothesis to be confirmed with further work. |
First measurement of projected phase correlations and large-scale
structure constraints: Phase correlations are an efficient way to extract astrophysical information
that is largely independent from the power spectrum. We develop an estimator
for the line correlation function (LCF) of projected fields, given by the
correlation between the harmonic-space phases at three equidistant points on a
great circle. We make a first, 6.5$\sigma$ measurement of phase correlations on
data from the 2MPZ survey. Finally, we show that the LCF can significantly
improve constraints on parameters describing the galaxy-halo connection that
are typically degenerate using only two-point data. | On holographic dark-energy models: Different holographic dark-energy models are studied from a unifying point of
view. We compare models for which the Hubble scale, the future event horizon or
a quantity proportional to the Ricci scale are taken as the infrared cutoff
length. We demonstrate that the mere definition of the holographic dark-energy
density generally implies an interaction with the dark-matter component. We
discuss the relation between the equation-of-state parameter and the energy
density ratio of both components for each of the choices, as well as the
possibility of non-interacting and scaling solutions. Parameter estimations for
all three cutoff options are performed with the help of a Bayesian statistical
analysis, using data from supernovae type Ia and the history of the Hubble
parameter. The $\Lambda$CDM model is the clear winner of the analysis.
According to the Bayesian Information Criterion ($BIC$), all holographic models
should be considered as ruled out, since the difference $\Delta BIC$ to the
corresponding $\Lambda$CDM value is $> 10$. According to the Akaike Information
Criterion ($AIC$), however, we find $\Delta AIC$ $< 2$ for models with
Hubble-scale and Ricci-scale cutoffs, indicating, that they may still be
competitive. As we show for the example of the Ricci-scale case, also the use
of certain priors, reducing the number of free parameters to that of the
$\Lambda$CDM model, may result in a competitive holographic model. |
Modelling high redshift Lyman-alpha Emitters: We present a new model for high redshift Lyman-Alpha Emitters (LAEs) in the
cosmological context which takes into account the resonant scattering of Ly-a
photons through expanding gas. The GALICS semi-analytic model provides us with
the physical properties of a large sample of high redshift galaxies. We
implement a gas outflow model for each galaxy based on simple scaling
arguments. The coupling with a library of numerical experiments of Ly-a
transfer through expanding or static dusty shells of gas allows us to derive
the Ly-a escape fractions and profiles. The predicted distribution of Ly-a
photons escape fraction shows that galaxies with a low star formation rate have
a f_esc of the order of unity, suggesting that, for those objects, Ly-a may be
used to trace the star formation rate assuming a given conversion law. In
galaxies forming stars intensely, the escape fraction spans the whole range
from 0 to 1. The model is able to get a good match to the UV and Ly-a
luminosity function (LF) data at 3 < z < 5. We find that we are in good
agreement with both the bright Ly-a data and the faint population observed by
Rauch et al. (2008) at z=3. Most of the Ly-a profiles of our LAEs are
redshifted by the diffusion in the outflow which suppresses IGM absorption. The
bulk of the observed Ly-a equivalent width (EW) distribution is recovered by
our model, but we fail to obtain the very large values sometimes detected.
Predictions for stellar masses and UV LFs of LAEs show a satisfactory agreement
with observational estimates. The UV-brightest galaxies are found to show only
low Ly-a EWs in our model, as it is reported by many observations of high
redshift LAEs. We interpret this effect as the joint consequence of old stellar
populations hosted by UV-bright galaxies, and high HI column densities that we
predict for these objects, which quench preferentially resonant Ly-a photons
via dust extinction. | Nonstandard cosmology: Considering radial geodesics in the Robertson-Walker metric leads us to
abandon the co-moving coordinates. Instead we work in the cosmic rest frame.
Since then the matter is in motion, the solution of Einstein's equations is
more complicated. We calculate the first correction to standard cosmology which
has an off-diagonal term b dt dr in the metric. It describes the late universe.
We then solve Maxwell's equations in the new metric and discuss redshift and
luminosities. We obtain the correct age of the universe T=14 Gyr= 1/H, without
assuming a cosmological constant. |
Growth index and statefinder diagnostic of Oscillating Dark Energy: We study is some detail the Cosmology of Oscillating Dark Energy described by
concrete equations-of-state investigated recently in the literature. In
particular, at the background level we compute the statefinder parameters,
while at the level of linear cosmological perturbations we compute the growth
index $\gamma$ as well as the combination parameter $A=f \sigma_8$. The
comparison with $\Lambda$CDM is made as well. | A Polarisation Survey of Bright Extragalactic AT20G Sources: We present polarisation data for 180 extragalactic sources extracted from the
Australia Telescope 20 GHz (AT20G) survey catalog, and observed with the
Australia Telescope Compact Array during a dedicated, high sensitivity run. For
the sake of completeness we extracted the polarisation information for 7
extended sources from the 9-yr WMAP coadded maps at 23 GHz. The full sample of
187 sources constitutes a 99% complete sample of extragalactic sources brighter
than S(20 GHz)=500mJy at the selection epoch with declination <-30 deg. The
sample has a 91.4% detection rate in polarisation at 20GHz (94% if considering
the sub-sample of point like sources). We have measurements also at 4.8 and 8.6
GHz within 1 month of the 20GHz observations for 172 sources to reconstruct the
spectral properties of the sample in total intensity and in polarisation: 143
of them have a polarisation detection at all three frequencies. We find that
there is no statistically significant evidence of a relationship either between
the fraction of polarisation and frequency or between the fraction of
polarisation and the total intensity flux density. This indicates that Faraday
depolarisation is not very important above 4.8 GHz and that the magnetic field
is not substantially more ordered in the regions dominating the emission at
higher frequencies (up to 20 GHz). We estimate the distribution of the
polarisation fraction and the polarised flux density source counts at 20GHz. |
Can we overcome the neutrino floor at high masses?: The neutrino floor is a barrier in the parameter space of weakly interacting
massive particles (WIMPs) below which discovery is impeded due to an almost
irreducible background of neutrinos. Directional gas time projection chambers
could discriminate against solar neutrinos, relevant for WIMP masses
$\lesssim$10 GeV. At higher masses $\gtrsim$100 GeV the floor is set by the
background of atmospheric neutrinos. Probing below this part of the floor would
require very large target exposures. Since gas-based detectors would be
prohibitively large at this scale, we instead reevaluate the prospects for
liquid noble experiments to probe below the neutrino floor. We combine all
potential methods of subtracting the neutrino background to determine how much
of this difficult to reach, but well-motivated, parameter space it is feasible
to reach. Most notably, we quantify whether a proposed directional signal in
xenon and argon experiments called "columnar recombination" can help in this
task. We find that even if the strength of this effect is amplified beyond
current experimental results, the quantity of directional information contained
in the recombination signal is too low to realistically discriminate against
the atmospheric neutrino background. Instead, benefiting from the refined
measurements of neutrino fluxes by experiments such as DUNE and JUNO will be
the most practical means to push direct WIMP searches below the neutrino floor.
For an ultimate global coordination of xenon and argon experiments, we show
that the neutrino floor is a surmountable barrier. The direct detection of 100
GeV-scale supersymmetric WIMPs may, eventually, be within reach. | Heavily Obscured AGN in Star-Forming Galaxies at z~2: We study the properties of a sample of 211 heavily-obscured Active Galactic
Nucleus (AGN) candidates in the Extended Chandra Deep Field-South selecting
objects with f_24/f_R>1000 and R-K>4.5. Of these, 18 were detected in X-rays
and found to be obscured AGN with neutral hydrogen column densities of ~10^23
cm^-2. In the X-ray undetected sample, the following evidence suggests a large
fraction of heavily-obscured (Compton Thick) AGN: (i) The stacked X-ray signal
of the sample is strong, with an observed ratio of soft to hard X-ray counts
consistent with a population of ~90% heavily obscured AGN combined with 10%
star-forming galaxies. (ii) The X-ray to mid-IR ratios for these sources are
significantly larger than that of star-forming galaxies and ~2 orders of
magnitude smaller than for the general AGN population, suggesting column
densities of N_H>5x10^24 cm^-2. (iii) The Spitzer near- and mid-IR colors of
these sources are consistent with those of the X-ray-detected sample if the
effects of dust self-absorption are considered. Spectral fitting to the
rest-frame UV/optical light (dominated by the host galaxy) returns stellar
masses of ~10^11 M_sun and <E(B-V)> =0.5, and reveals evidence for a
significant young stellar population, indicating that these sources are
experiencing considerable star-formation. This sample of heavily-obscured AGN
candidates implies a space density at z~2 of ~10^-5 Mpc^-3, finding a strong
evolution in the number of L_X>10^44 erg/s sources from z=1.5 to 2.5, possibly
consistent with a short-lived heavily-obscured phase before an unobscured
quasar is visible. |
Mapping the Chevallier-Polarski-Linder parametrization onto Physical
Dark Energy Models: We examine the Chevallier-Polarski-Linder (CPL) parametrization, in the
context of quintessence and barotropic dark energy models, to determine the
subset of such models to which it can provide a good fit. The CPL
parametrization gives the equation of state parameter $w$ for the dark energy
as a linear function of the scale factor $a$, namely $w = w_0 + w_a(1-a)$. In
the case of quintessence models, we find that over most of the $w_0$, $w_a$
parameter space the CPL parametrization maps onto a fairly narrow form of
behavior for the potential $V(\phi)$, while a one-dimensional subset of
parameter space, for which $w_a = \kappa (1+w_0)$, with $\kappa$ constant,
corresponds to a wide range of functional forms for $V(\phi)$. For barotropic
models, we show that the functional dependence of the pressure on the density,
up to a multiplicative constant, depends only on $w_i = w_a + w_0$ and not on
$w_0$ and $w_a$ separately. Our results suggest that the CPL parametrization
may not be optimal for testing either type of model. | The clustering of galaxies in the completed SDSS-III Baryon Oscillation
Spectroscopic Survey: a tomographic analysis of structure growth and
expansion rate from anisotropic galaxy clustering: We perform a tomographic analysis of structure growth and expansion rate from
the anisotropic galaxy clustering of the combined sample of Baryon Oscillation
Spectroscopic Survey (BOSS) Data Release 12, which covers the redshift range of
$0.2<z<0.75$. In order to extract the redshift information of anisotropic
galaxy clustering, we analyse this data set in nine overlapping redshift slices
in configuration space and perform the joint constraints on the parameters
$(D_V, F_{\mathrm{AP}}, f\sigma_8)$ using the correlation function multipoles.
The analysis pipeline is validated using the MultiDark-Patchy mock catalogues.
We obtain a measurement precision of $1.5\%-2.9\%$ for $D_V$, $5.2\%-9\%$ for
$F_{\mathrm{AP}}$ and $13.3\%-24\%$ for $f \sigma_8$, depending on the
effective redshift of the slices. We report a joint measurement of $(D_V,
F_{\mathrm{AP}}, f\sigma_8)$ with the full covariance matrix in nine redshift
slices. We use our joint BAO and RSD measurement combined with external
datasets to constrain the gravitational growth index $\gamma$, and find
$\gamma=0.656 \pm 0.057$, which is consistent with the $\Lambda$CDM prediction
within 95\% CL. |
Refined Study of Isocurvature Fluctuations in the Curvaton Scenario: We revisit the generation of dark matter isocurvature perturbations in the
curvaton model in greater detail, both analytically and numerically. As
concrete examples, we investigate the cases of thermally decoupled dark matter
and axionic dark matter. We show that the radiation produced by the decay of
the curvaton, which has not been taken into account in previous analytical
studies, can significantly affect the amplitude of isocurvature perturbations.
In particular, we find that they are drastically suppressed even when the dark
matter freeze-out (or the onset of the axion oscillations for axionic dark
matter) occurs before the curvaton decays, provided the freeze-out takes place
deep in the curvaton-dominated Universe. As a consequence, we show that the
current observational isocurvature constraints on the curvaton parameters are
not as severe as usually thought. | Radiative transport of relativistic species in cosmology: We review the general construction of distribution functions for gases of
fermions and bosons (photons), emphasizing the similarities and differences
between both cases. The central object which describes polarization for photons
is a tensor-valued distribution function, whereas for fermions it is a
vector-valued one. The collision terms of Boltzmann equations for fermions and
bosons also possess the same general structure and differ only in the quantum
effects associated with the final state of the reactions described. In
particular, neutron-proton conversions in the early universe, which set the
primordial Helium abundance, enjoy many similarities with Compton scattering
which shapes the cosmic microwave background and we show that both can be
handled with a Fokker-Planck type expansion. For neutron-proton conversions,
this allows to obtain the finite nucleon mass corrections, required for precise
theoretical predictions, whereas for Compton scattering it leads to the thermal
and recoil effects which enter the Kompaneets equation. We generalize the
latter to the general case of anisotropic and polarized photon distribution
functions. Finally we discuss a parameterization of the photon spectrum based
on logarithmic moments which allows for a neat separation between temperature
shifts and spectral distortions. |
Possible structure in the GRB sky distribution at redshift two: Context. Research over the past three decades has revolutionized cosmology
while supporting the standard cosmological model. However, the cosmological
principle of Universal homogeneity and isotropy has always been in question,
since structures as large as the survey size have always been found each time
the survey size has increased. Until 2013, the largest known structure in our
Universe was the Sloan Great Wall, which is more than 400 Mpc long located
approximately one billion light years away.
Aims. Gamma-ray bursts are the most energetic explosions in the Universe. As
they are associated with the stellar endpoints of massive stars and are found
in and near distant galaxies, they are viable indicators of the dense part of
the Universe containing normal matter. The spatial distribution of gamma-ray
bursts can thus help expose the large scale structure of the Universe.
Methods. As of July 2012, 283 GRB redshifts have been measured. Subdividing
this sample into nine radial parts, each containing 31 GRBs, indicates that the
GRB sample having 1.6 < z < 2.1 differs significantly from the others in that
14 of the 31 GRBs are concentrated in roughly 1/8 of the sky. A two-dimensional
Kolmogorov-Smirnov test, a nearest-neighbour test, and a Bootstrap Point-Radius
Method explore the significance of this clustering.
Results. All tests used indicate that there is a statistically significant
clustering of the GRB sample at 1.6 < z < 2.1. Furthermore, this angular excess
cannot be entirely attributed to known selection biases, making its existence
due to chance unlikely.
Conclusions. This huge structure lies ten times farther away than the Sloan
Great Wall, at a distance of approximately ten billion light years. The size of
the structure defined by these GRBs is about 2000-3000 Mpc, or more than six
times the size of the Sloan Great Wall. | The Cosmic Large-Scale Structure in X-rays (CLASSIX) Cluster Survey III:
The Perseus-Pisces supercluster and the Southern Great Wall as traced by
X-ray luminous galaxy clusters: The Perseus-Pisces supercluster is known as one of the largest structures in
the nearby Universe that has been charted by the galaxy and galaxy cluster
distributions. For the latter mostly clusters from the Abell catalogue have
been used. Here we take a new approach to a quantitative characterisation of
the Perseus-Pisces supercluster using a statistically complete sample of X-ray
luminous galaxy groups and clusters from our CLASSIX galaxy cluster redshift
survey. We used a friends-of-friends technique to construct the supercluster
membership. We also studied the structure of the Southern Great Wall, which
merges with the Perseus-Pisces supercluster with a slightly increased
friends-of-friends linking length. In this work we discuss the geometric
structure of the superclusters, compare the X-ray luminosity distribution of
the members with that of the surroundings, and provide an estimate of the
supercluster mass. These results establish Perseus-Pisces as the largest
superstructure in the Universe at redshifts z <= 0.03. With the new data this
supercluster extends through the zone of avoidance, which has also been
indicated by some studies of the galaxy distribution by means of HI
observations. We investigated whether the shapes of the member groups and
clusters in X-rays are aligned with the major axis of the supercluster. We find
no evidence for a pronounced alignment, except for the ellipticities of Perseus
and AWM7, which are aligned with the separation vector of the two systems and
weakly with the supercluster. |
The splashback radius of halos from particle dynamics. I. The SPARTA
algorithm: Motivated by the recent proposal of the splashback radius as a physical
boundary of dark matter halos, we present a parallel computer code for Subhalo
and PARticle Trajectory Analysis (SPARTA). The code analyzes the orbits of all
simulation particles in all host halos, billions of orbits in the case of
typical cosmological N-body simulations. Within this general framework, we
develop an algorithm that accurately extracts the location of the first
apocenter of particles after infall into a halo, or splashback. We define the
splashback radius of a halo as the smoothed average of the apocenter radii of
individual particles. This definition allows us to reliably measure the
splashback radii of 95% of host halos above a resolution limit of 1000
particles. We show that, on average, the splashback radius and mass are
converged to better than 5% accuracy with respect to mass resolution, snapshot
spacing, and all free parameters of the method. | Are group- and cluster-scale dark matter halos over-concentrated?: We investigate the relationship between the halo mass, M_200, and
concentration, c, for a sample of 26 group- and cluster-scale strong
gravitational lenses. In contrast with previous results, we find that these
systems are only ~ 0.1 dex more over-concentrated than similar-mass halos from
dark matter simulations; the concentration of a halo with M_200 = 10^14 M_sun
is log c = 0.78\pm0.05, while simulations of halos with this mass at similar
redshifts (z ~ 0.4) predict log c ~ 0.56 - 0.71. We also find that we are
unable to make informative inference on the slope of the M_200-c relation in
spite of our large sample size; we note that the steep slopes found in previous
studies tend to follow the slope in the covariance between M_200 and c,
indicating that these results may be measuring the scatter in the data rather
than the intrinsic signal. Furthermore, we conclude that our inability to
constrain the M_200-c slope is due to a limited range of halo masses, as
determined by explicitly modelling our halo mass distribution, and we suggest
that other studies may be producing biased results by using an incorrect
distribution for their halo masses. |
Continuum Halos in Nearby Galaxies -- an EVLA Survey (CHANG-ES) -- I:
Introduction to the Survey: We introduce a new survey to map the radio continuum halos of a sample of 35
edge-on spiral galaxies at 1.5 GHz and 6 GHz in all polarization products. The
survey is exploiting the new wide bandwidth capabilities of the Karl G. Jansky
Very Large Array (i.e. the Expanded Very Large Array, or EVLA) in a variety of
array configurations (B, C, and D) in order to compile the most comprehensive
data set yet obtained for the study of radio halo properties. This is the first
survey of radio halos to include all polarization products.
In this first paper, we outline the scientific motivation of the survey, the
specific science goals, and the expected improvements in noise levels and
spatial coverage from the survey. Our goals include investigating the physical
conditions and origin of halos, characterizing cosmic ray transport and wind
speed, measuring Faraday rotation and mapping the magnetic field, probing the
in-disk and extraplanar far-infrared - radio continuum relation, and
reconciling non-thermal radio emission with high-energy gamma-ray models. The
sample size allows us to search for correlations between radio halos and other
properties, including environment, star formation rate, and the presence of
AGNs. In a companion paper (Paper II) we outline the data reduction steps and
present the first results of the survey for the galaxy, NGC 4631. | Multiple scattering Sunyaev-Zeldovich signal I: lowest order effect: Future high-resolution, high-sensitivity Sunyaev-Zeldovich (SZ) observations
of individual clusters will allow us to study the dynamical state of the intra
cluster medium (ICM). To exploit the full potential of this new observational
window, it is crucial to understand the different contributions to the total SZ
signal. Here, we investigate the signature caused by multiple scatterings at
lowest order of the electron temperature. Previous analytic discussions of this
problem used the isotropic scattering approximation (ISA), which even for the
simplest cluster geometries is rather rough. We take a step forward and
consistently treat the anisotropy of the ambient radiation field caused by the
first scattering. We show that the multiple scattering SZ signal directly
probes line of sight anisotropies of the ICM, thereby delivering a new set of
SZ observables which could be used for 3D cluster-profile reconstruction. The
multiple scattering signal should furthermore correlate spatially with the
cluster's X-ray and SZ polarization signals, an effect that could allow
enhancing the detectability of this contribution. |
GALEX selected Lyman Break Galaxies at z~2: Comparison with other
Populations: We present results of a search for bright Lyman break galaxies at 1.5<=z<=2.5
in the GOODS-S field using a NUV-dropout technique in combination with
color-selection. We derived a sample of 73 LBG candidates. We compare our
selection efficiencies to BM/BX- and BzK methods (techniques solely based on
ground-based data sets), and find the NUV data to provide greater efficiency
for selecting star-forming galaxies. We estimate LBG candidate ages, masses,
star formation rates, and extinction from fitting PEGASE synthesis evolution
models. We find about 20% of our LBG candidates are comparable to infrared
luminous LBGs or sub-millimeter galaxies which are thought to be precursors of
massive elliptical galaxies today. Overall, we can show that although BM/BX and
BzK methods do identify star-forming galaxies at z~2, the sample they provide
biases against those star-forming galaxies which are more massive and contain
sizeable red stellar populations. A true Lyman break criterion at z~2 is
therefore more directly comparable to the populations found at z~3, which does
contain a red fraction. | Exploring the potentiality of standard sirens to probe cosmic opacity at
high redshifts: In this work, using the Gaussian process, we explore the potentiality of
future gravitational wave (GW) measurements to probe cosmic opacity at high
redshifts through comparing its opacity-free luminosity distance (LD) with the
opacity-dependent one from the combination of Type Ia supernovae (SNIa) and
gamma-ray bursts (GRBs). The GW data, SNIa and GRB data are simulated from the
measurements of the future Einstein Telescope, the actual Pantheon compilation
and the latest observation of GRBs compiled by L. Amati {\it et al},
respectively. A nonparametric method is proposed to probe the spatial
homogeneity of cosmic transparency at high redshift by comparing the LD
reconstructed from the GW data with
that reconstructed from the Pantheon and GRB data. In addition, the cosmic
opacity is tested by using the parametrization for the optical depth, and the
results show that the constraints on cosmic opacity are more stringent than the
previous ones. It shows that the future GW measurements may be used as an
important tool to probe the cosmic opacity in the high redshift region. |
A new method to break the mass sheet degeneracy using aperture moments: Mass determinations from gravitational lensing shear and the higher order
estimator flexion are both subject to the mass sheet degeneracy. Mass sheet
degeneracy refers to a transformation that leaves the reduced shear and flexion
invariant. In general, this transformation can be approximated by the addition
of a constant surface mass density sheet. We propose a new technique to break
the mass sheet degeneracy. The method uses mass moments of the shear or flexion
fields in combination with convergence information derived from number counts
which exploit the magnification bias. The difference between the measured mass
moments provides an estimator for the magnitude of the additive constant that
is the mass-sheet. For demonstrating this, we derive relations that hold true
in general for n-th order moments and show how they can be employed effectively
to break the degeneracy. We investigate the detectability of this degeneracy
parameter from our method and find that the degeneracy parameter can be
feasibly determined from stacked galaxy-galaxy lensing data and cluster lensing
data. Furthermore, we compare the signal-to-noise ratios of convergence
information from number counts with shear and flexion for SIS and NFW models.
We find that the combination of shear and flexion performs best on galaxy and
cluster scales and the convergence information can therefore be used to break
the mass sheet degeneracy without quality loss in the mass reconstruction. In
summary, there is power in the combination of shear, flexion, convergence and
their higher order moments. With the anticipated wealth of lensing data from
upcoming and future satellite missions - EUCLID and WFIRST - this technique
will be feasible. | The Evolution of Our Local Cosmic Domain: Effective Causal Limits: The causal limit usually considered in cosmology is the particle horizon,
delimiting the possibilities of causal connection in the expanding universe.
However it is not a realistic indicator of the effective local limits of
important interactions in spacetime. We consider here the matter horizon for
the Solar System, that is,the comoving region which has contributed matter to
our local physical environment. This lies inside the effective domain of
dependence, which (assuming the universe is dominated by dark matter along with
baryonic matter and vacuum-energy-like dark energy) consists of those regions
that have had a significant active physical influence on this environment
through effects such as matter accretion and acoustic waves. It is not
determined by the velocity of light c, but by the flow of matter perturbations
along their world lines and associated gravitational effects. We emphasize how
small a region the perturbations which became our Galaxy occupied, relative to
the observable universe -- even relative to the smallest-scale perturbations
detectable in the cosmic microwave background radiation. Finally, looking to
the future of our cosmic domain, we suggest simple dynamical criteria for
determining the present domain of influence and the future matter horizon. The
former is the radial distance at which our local region is just now separating
from the cosmic expansion. The latter represents the limits of growth of the
matter horizon in the far future. |
Testing a Phenomenologically Extended DGP Model with Upcoming Weak
Lensing Surveys: A phenomenological extension of the well-known brane-world cosmology of
Dvali, Gabadadze and Porrati (eDGP) has recently been proposed. In this model,
a cosmological-constant-like term is explicitly present as a non-vanishing
tension sigma on the brane, and an extra parameter alpha tunes the cross-over
scale r_c, the scale at which higher dimensional gravity effects become non
negligible. Since the Hubble parameter in this cosmology reproduces the same
LCDM expansion history, we study how upcoming weak lensing surveys, such as
Euclid and DES (Dark Energy Survey), can confirm or rule out this class of
models. We perform Markov Chain Monte Carlo simulations to determine the
parameters of the model, using Type Ia Supernov\ae, H(z) data, Gamma Ray Bursts
and Baryon Acoustic Oscillations. We also fit the power spectrum of the
temperature anisotropies of the Cosmic Microwave Background to obtain the
correct normalisation for the density perturbation power spectrum. Then, we
compute the matter and the cosmic shear power spectra, both in the linear and
non-linear regimes. The latter is calculated with the two different approaches
of Hu and Sawicki (2007) (HS) and Khoury and Wyman (2009) (KW). With the eDGP
parameters coming from the Markov Chains, KW reproduces the LCDM matter power
spectrum at both linear and non-linear scales and the LCDM and eDGP shear
signals are degenerate. This result does not hold with the HS prescription:
Euclid can distinguish the eDGP model from LCDM because their expected power
spectra roughly differ by the 3sigma uncertainty in the angular scale range
700<l<3000; on the contrary, the two models differ at most by the 1sigma
uncertainty over the range 500<l<3000 in the DES experiment and they are
virtually indistinguishable. | The Correspondence between Convergence Peaks from Weak Lensing and
Massive Dark Matter Haloes: The convergence peaks, constructed from galaxy shape measurement in weak
lensing, is a powerful probe of cosmology as the peaks can be connected with
the underlined dark matter haloes. However the capability of convergence peak
statistic is affected by the noise in galaxy shape measurement, signal to noise
ratio as well as the contribution from the projected mass distribution from the
large-scale structures along the line of sight (LOS). In this paper we use the
ray-tracing simulation on a curved sky to investigate the correspondence
between the convergence peak and the dark matter haloes at the LOS. We find
that, in case of no noise and for source galaxies at $z_{\rm s}=1$, more than
$65\%$ peaks with $\text{SNR} \geq 3$ (signal to noise ratio) are related to
more than one massive haloes with mass larger than $10^{13} {\rm M}_{\odot}$.
Those massive haloes contribute $87.2\%$ to high peaks ($\text{SNR} \geq 5$)
with the remaining contributions are from the large-scale structures. On the
other hand, the peaks distribution is skewed by the noise in galaxy shape
measurement, especially for lower SNR peaks. In the noisy field where the shape
noise is modelled as a Gaussian distribution, about $60\%$ high peaks
($\text{SNR} \geq 5$) are true peaks and the fraction decreases to $20\%$ for
lower peaks ($ 3 \leq \text{SNR} < 5$). Furthermore, we find that high peaks
($\text{SNR} \geq 5$) are dominated by very massive haloes larger than $10^{14}
{\rm M}_{\odot}$. |
Constraining stellar properties of intervening damped Lyα and
MgII absorbing galaxies toward GRB 050730: We performed multi-band deep imaging of the field around GRB 050730 to
identify the host galaxies of intervening absorbers, which consist of a damped
Ly{\alpha} absorption (DLA) system at zabs=3.564, a sub-DLA system at
zabs=3.022, and strong MgII absorption systems at zabs=1.773 and 2.253. Our
observations were performed after the gamma-ray burst afterglow had
disappeared. Thus, our imaging survey has a higher sensitivity to the host
galaxies of the intervening absorbers than the normal imaging surveys in the
direction of QSOs, for which the QSO glare tends to hide the foreground
galaxies. In this deep imaging survey, we could not detect any unambiguous
candidates for the host galaxies of the intervening absorbers. Using the 3sigma
upper limit of the flux in the optical to mid-infrared observing bands, which
corresponds to the UV to optical bands in the rest-frame of the intervening
absorbers, we constrained the star-formation rates and stellar masses of the
hosts. We estimated the star-formation rates for the intervening absorbers as <
2.5 Msun/yr for z>3 DLAs and < 1.0 Msun/yr for z~2 MgII systems. Their stellar
masses are estimated to be several times 10^9 Msun or smaller for all
intervening galaxies. These properties are comparable to dwarf galaxies, rather
than the massive star-forming galaxies commonly seen in the z>2 galaxy surveys
based on emission-line selection or color selection. | Gravitational fluctuations of the galaxy distribution: We study the statistical properties of the gravitational field generated by
galaxy distribution observed bythe Sloan Digital Sky Survey (DR7). We
characterize the probability density function of gravitational force
fluctuations and relate its limiting behaviors to the correlation properties of
the underlying density field. In addition, we study whether the PDF converges
to an asymptotic shape within sample volumes. We consider several
volume-limited samples of the Sloan Digital Sky Survey and we compute the
gravitational force probability density function (PDF). The gravitational force
is computed in spheres of varying radius as is its PDF. We find that (i) the
PDF of the force displays features that can be understood in terms of galaxy
two-point correlations and (ii) density fluctuations on the largest scales
probed, i.e. r~100 Mpc/h, still contribute significantly to the amplitude of
the gravitational force. Our main conclusion is that fluctuations in the
gravitational force field generated by galaxy structures are also relevant on
scales ~ 100 Mpc/h. By assuming that the gravitational fluctuations in the
galaxy distribution reflect those in the whole matter distribution, and that
peculiar velocities and accelerations are simply correlated, we may conclude
that large-scale fluctuations in the galaxy density field may be the source of
the large-scale flows recently observed. |
Joint cluster reconstructions: Combining free-form lensing and X-rays: Galaxy clusters provide a multitude of observational data across wavelengths
and their structure and morphology are of considerable interest in cosmology as
well as astrophysics. We develop a framework that allows the combination of
lensing and non-lensing observations in a free-form and mesh-free approach to
infer the projected mass distribution of individual galaxy clusters. This
method can be used to test common assumptions on the morphology of clusters in
parametric models. We make use of the lensing reconstruction code SaWLens2 and
expand its capabilities by incorporating an estimate of the projected
gravitational potential based on X-ray data that are deprojected using the
local Richardson-Lucy method and used to infer the Newtonian potential of the
cluster and we discuss how potentially arising numerical artefacts can be
treated. We demonstrate the feasibility of our method on a simplified mock NFW
halo and on a cluster from a realistic hydrodynamical simulation and show how
the combination of X-ray and weak lensing data can affect a free-form
reconstruction, improving the accuracy in the central region in some cases by a
factor of two. | Improving Small-Scale CMB Lensing Reconstruction: Over the past decade, the gravitational lensing of the Cosmic Microwave
Background (CMB) has become a powerful tool for probing the matter distribution
in the Universe. The standard technique used to reconstruct the CMB lensing
signal employs the quadratic estimator (QE) method, which has recently been
shown to be suboptimal for lensing measurements on very small scales in
temperature and polarization data. We implement a simple, more optimal method
for the small-scale regime, which involves taking the direct inverse of the
background gradient. We derive new techniques to make continuous maps of
lensing using this "Gradient-Inversion" (GI) method and validate our method
with simulated data, finding good agreement with predictions. For idealized
simulations of lensing cross- and autospectra that neglect foregrounds, we
demonstrate that our method performs significantly better than previous
quadratic estimator methods in temperature; at $L=5000-9000$, it reduces errors
on the lensing auto-power spectrum by a factor of $\sim 4$ for both idealized
CMB-S4 and Simons Observatory-like experiments and by a factor of $\sim 2.6$
for cross-correlations of CMB-S4-like lensing reconstruction and the true
lensing field. We caution that the level of the neglected small-scale
foreground power, while low in polarization, is very high in temperature;
though we briefly outline foreground mitigation methods, further work on this
topic is required. Nevertheless, our results show the future potential for
improved small-scale CMB lensing measurements, which could provide stronger
constraints on cosmological parameters and astrophysics at high redshifts. |
Lensing Model of MACS J1149.5+2223 - I. Cluster mass reconstruction: Measurements of the total logarithmic central slope of the mass profile in
galaxy clusters constrain their evolution and assembly history and that of
their brightest cluster galaxies. We report the first full surface brightness
distribution modelling of the inner region of the galaxy cluster MACS
J1149.5+2223. We compare these results with a position-based modelling approach
for which we employ more than twice the previously known positional
constraints. This is the first time that the detailed lensed image
configuration of two non-central cluster galaxies with Einstein rings has been
mapped. Due to the extended radial coverage provided by the multiple images in
this system, we are able to determine the slope $\partial \log{ \kappa
}/\partial \log{R} = -0.33$ of the total projected mass distribution from $8$
to $80~\mathrm{kpc}$. This is within the cluster-to-cluster scatter estimates
from previous cluster measurements. Our reconstruction of the image surface
brightness distribution of the large central spiral galaxy has a root mean
square residual for all image pixels of $1.14~\sigma$, where $\sigma$ is the
observational background noise. This corresponds to a reconstruction of the
positions of bright clumps in the central galaxy with an rms of
$0.063~\mathrm{arcsec}$. | Understanding black hole mass assembly via accretion and mergers at late
times in cosmological simulations: Accretion is thought to primarily contribute to the mass accumulation history
of supermassive black holes throughout cosmic time. While this may be true at
high redshifts, at lower redshifts and for the most massive black holes mergers
themselves might add significantly to the mass budget. We evolve SMBHs from $4
> z > 0$ using merger trees derived from hydrodynamical cosmological
simulations of a cluster and void region, scaled to the observed value of the
stellar mass fraction to account for overcooling. Mass gains from gas accretion
proportional to bulge growth and BH-BH mergers are tracked, as are black holes
that remain "orbiting" due to insufficient dynamical friction in a merger
remnant, as well as those that are ejected due to gravitational recoil. We find
that gas accretion remains the dominant source of mass accumulation in almost
all SMBHs; mergers contribute $2.5\pm0.1\%$ for all SMBHs in the cluster and
$1.0\pm0.1\%$ in the void since $z = 4$. However, mergers are significant for
massive SMBHs. The fraction of mass accumulated from mergers for central BHs
generally increases for larger values of the host bulge mass: in the void, the
fraction is $2\%$ at $M_{*, bul} = 10^{10} M_{\odot}$, increasing to $4\%$ at
$M_{*, bul} \gtrsim 10^{11} M_{\odot}$, and in the cluster it is $4\%$ at
$M_{*, bul} = 10^{10} M_{\odot}$ and $23\%$ at $10^{12} M_{\odot}$. We find
that $40\%$ of SMBHs and $\approx 8\%$ of the total SMBH mass is found orbiting
in the cluster region at $z = 0$. The existence of orbiting and ejected SMBHs
requires modification of the Soltan argument. We estimate this correction to
the integrated accreted mass density of SMBHs to be in the range $6-21\%$, with
a mean value of $11\pm3\%$. We also calculate the total energy output and
strain from gravitational waves emitted by merging SMBHs, and obtain a signal
potentially detectable by pulsar timing arrays. |
Joint reconstructions of growth and expansion histories from stage-IV
surveys with minimal assumptions. II. Modified gravity and massive neutrinos: Based on a formalism introduced in our previous work, we reconstruct the
phenomenological function $G_{\rm eff}(z)$ describing deviations from General
Relativity (GR) in a model-independent manner. In this alternative approach, we
model $\mu\equiv G_\mathrm{eff}/G$ as a Gaussian process and use forecasted
growth-rate measurements from a stage-IV survey to reconstruct its shape for
two different toy models. We follow a two-step procedure: (i) we first
reconstruct the background expansion history from Supernovae (SNe) and Baryon
Acoustic Oscillation (BAO) measurements; (ii) we then use it to obtain the
growth history $f\sigma_8$, that we fit to redshift-space distortions (RSD)
measurements to reconstruct $G_\mathrm{eff}$. We find that upcoming surveys
such as the Dark Energy Spectroscopic Instrument (DESI) might be capable of
detecting deviations from GR, provided the dark energy behavior is accurately
determined. We might even be able to constrain the transition redshift from
$G\to G_\mathrm{eff}$ for some particular models. We further assess the impact
of massive neutrinos on the reconstructions of $G_\mathrm{eff}$ (or $\mu$)
assuming the expansion history is given, and only the neutrino mass is free to
vary. Given the tight constraints on the neutrino mass, and for the profiles we
considered in this work, we recover numerically that the effect of such massive
neutrinos does not alter our conclusions. Finally, we stress that incorrectly
assuming a $\Lambda$CDM expansion history leads to a degraded reconstruction of
$\mu$, and/or a non-negligible bias in the
($\Omega_\mathrm{m,0}$,$\sigma_{8,0}$)-plane. | The advantage of Bolometric Interferometry for controlling Galactic
foreground contamination in CMB primordial B-modes measurements: In the quest for the faint primordial B-mode polarization of the Cosmic
Microwave Background, three are the key requirements for any present or future
experiment: an utmost sensitivity, excellent control over instrumental
systematic effects and over Galactic foreground contamination. Bolometric
Interferometry (BI) is a novel technique that matches them all by combining the
sensitivity of bolometric detectors, the control of instrumental systematics
from interferometry and a software-based, tunable, in-band spectral resolution
due to its ability to perform band-splitting during data analysis (spectral
imaging). In this paper, we investigate how the spectral imaging capability of
BI can help in detecting residual contamination in case an over-simplified
model of foreground emission is assumed in the analysis. To mimic this
situation, we focus on the next generation of ground-based CMB experiment,
CMB-S4, and compare its anticipated sensitivities, frequency and sky coverage
with a hypothetical version of the same experiment based on BI, CMB-S4/BI,
assuming that line-of-sight (LOS) frequency decorrelation is present in dust
emission but is not accounted for during component separation. We show results
from a Monte-Carlo analysis based on a parametric component separation method
(FGBuster), highlighting how BI has the potential to diagnose the presence of
foreground residuals in estimates of the tensor-to-scalar ratio $r$ in the case
of unaccounted Galactic dust LOS frequency decorrelation. |
Mitigating Cosmic Microwave Background Shadow Degradation of
Tensor-to-scalar Ratio Measurements through Map-based Studies: It has been pointed out that the spurious Cosmic Microwave Background (CMB)
B-mode polarization signals caused by the absorption of the CMB monopole
component due to the Galactic interstellar matter, called the CMB shadow,
degrade the accuracy of detecting the CMB B-mode polarization signals imprinted
by primordial gravitational waves. We have made a realistic estimation using
simulated sky maps of how the CMB shadow affects forthcoming high-precision CMB
B-mode experiments for the first time. The Delta-map method, an internal
template method taking into account the first-order spatial variation of
foregrounds' spectral parameters, is applied as a foreground removal method. We
show that if the CMB shadow effects are not taken into account in the
foreground removal process, future observations would lead to the false
detection of the CMB B-mode polarization signals originating from primordial
gravitational waves. We also show that the effect of the CMB shadow can be
mitigated by our revised Delta-map method to target the CMB B-mode polarization
signals at the level of tensor-to-scalar ratio r=0.001. | Signature of inflation in the stochastic gravitational wave background
generated by cosmic string networks: A cosmic string network created during an inflationary stage in the early
Universe - here defined as i-string network - is expected to enter a transient
stretching regime during inflation, in which its characteristic length is
stretched to scales much larger than the Hubble radius, before attaining a
standard evolution once the network re-enters the Hubble volume after
inflation. During the stretching regime, the production of cosmic string loops
and consequent emission of gravitational radiation are significantly
suppressed. Here, we compute the power spectrum of the stochastic gravitational
wave background generated by i-string networks using the velocity-dependent one
scale model to describe the network dynamics, and demonstrate that this regime
introduces a high-frequency signature on an otherwise standard spectrum of the
stochastic gravitational wave background generated by cosmic strings. We argue
that, if observed by current or forthcoming experiments, this signature would
provide strong evidence for i-strings and, therefore, for (primordial)
inflation. We also develop a simple single-parameter algorithm for the
computation of the stochastic gravitational wave background generated by
i-strings from that of a standard cosmic string network, which may be useful in
the determination of the observational constraints to be obtained by current
and forthcoming gravitational wave experiments. |
Free-form Grale reconstruction of Abell 2744: robustness of
uncertainties against changes in lensing data: Abell 2744, a massive Hubble Frontier Fields merging galaxy cluster with many
multiple images in the core has been the subject of many lens inversions using
different methods. While most existing studies compare various inversion
methods, we focus on a comparison of reconstructions that use different input
lensing data. Since the quantity and quality of lensing data is constantly
improving, it makes sense to ask if the estimated uncertainties are robust
against changes in the data. We address this question using free-form Grale,
which takes only image information as input, and nothing pertaining to cluster
galaxies. We reconstruct Abell 2744 using two sets of strong lensing data from
the Hubble Frontier Fields community. Our first and second reconstructions use
55 and 91 images, respectively, and only 10 of the 91 images have the same
positions and redshifts as in the first reconstruction. Comparison of the two
mass maps shows that Grale uncertainties are robust against these changes, as
well as small modifications in the inversion routine. Additionally, applying
the methods used in Sebesta et al. (2016) for MACS J0416, we conclude that, in
a statistical sense, light follows mass in Abell 2744, with brighter galaxies
clustering stronger with the recovered mass than the fainter ones. We also show
that the faintest galaxies are anti-correlated with mass, which is likely the
result of light contamination from bright galaxies, and lensing magnification
bias acting on galaxies background to the cluster. | Model independent $H(z)$ reconstruction using the cosmic inverse
distance ladder: Recent distance ladder determinations of the Hubble constant $H_0$ disagree
at about the $3.5\sigma$ level with the value determined from Planck
measurements of the cosmic microwave background (CMB) assuming a $\Lambda$CDM
cosmology. This discrepancy has prompted speculation that new physics might be
required beyond that assumed in the $\Lambda$CDM model. In this paper, we apply
the inverse distance ladder to fit a parametric form of $H(z)$ to baryon
acoustic oscillation (BAO) and Type Ia supernova data together with priors on
the sound horizon at the end of the radiation drag epoch, $r_d$. We apply
priors on $r_d$, based on inferences from either Planck or the Wilkinson
Microwave Anistropy Probe (WMAP), and demonstrate that these values are
consistent with CMB-independent determinations of $r_d$ derived from
measurements of the primordial deuterium abundance, BAO and supernova data
assuming the $\Lambda$CDM cosmology. The $H(z)$ constraints that we derive are
independent of detailed physics within the dark sector at low redshifts,
relying only on the validity of the Friedmann-Robertson-Walker (FRW) metric of
General Relativity. For each assumed prior on $r_d$, we find consistency with
the inferred value of $H_0$ and the Planck $\Lambda$CDM value and corresponding
tension with the distance ladder estimate. |
Testing models of vacuum energy interacting with cold dark matter: We test the models of vacuum energy interacting with cold dark matter and try
to probe the possible deviation from the $\Lambda$CDM model using current
observations. We focus on two specific models, $Q=3\beta H\rho_{\Lambda}$ and
$Q=3\beta H\rho_c$. The data combinations come from the Planck 2013 data, the
baryon acoustic oscillations measurements, the type-Ia supernovae data, the
Hubble constant measurement, the redshift space distortions data and the galaxy
weak lensing data. For the $Q=3\beta H\rho_c$ model, we find that it can be
tightly constrained by all the data combinations, while for the $Q=3\beta
H\rho_{\Lambda}$ model, there still exist significant degeneracies between
parameters. The tightest constraints for the coupling constant are
$\beta=-0.026^{+0.036}_{-0.053}$ (for $Q=3\beta H\rho_{\Lambda}$) and
$\beta=-0.00045\pm0.00069$ (for $Q=3\beta H\rho_c$) at the $1\sigma$ level. For
all the fit results, we find that the null interaction $\beta=0$ is always
consistent with data. Our work completes the discussion on the interacting dark
energy model in the recent Planck 2015 papers. Considering this work together
with the Planck 2015 results, it is believed that there is no evidence for the
models beyond the standard $\Lambda$CDM model from the point of view of
possible interaction. | Directional detection of Dark Matter with MIMAC: WIMP identification and
track reconstruction: Directional detection is a promising Dark Matter search strategy. Indeed,
WIMP-induced recoils present a direction dependence toward the Cygnus
constellation, while background-induced recoils exhibit an isotropic
distribution in the galactic rest frame. Taking advantage on these
characteristic features and even in the presence of a sizeable background, we
show for the first time the possibility to constrain the WIMP properties, both
from particle and galactic halo physics, leading to an identification of
non-baryonic Dark Matter. However, such results need highly accurate track
reconstruction which should be reachable by the MIMAC detector using a
dedicated readout combined with a likelihood analysis of recoiling nuclei. |
Time Evolution of the Large-Scale Tail of Nonhelical Primordial Magnetic
Fields with Back-Reaction of the Turbulent Medium: We present a derivation of the time evolution equations for the energy
content of nonhelical magnetic fields and the accompanying turbulent flows from
first principles of incompressible magnetohydrodynamics in the general
framework of homogeneous and isotropic turbulence. This is then applied to the
early Universe, i.e., the evolution of primordial magnetic fields. Numerically
integrating the equations, we find that most of the energy is concentrated at
an integral wavenumber scale k_I where the turbulence turn over time equals the
Hubble time. At larger length scales L, i.e., smaller wavenumbers q = 2 \pi / L
<< k_I, independent of the assumed turbulent flow power spectrum, mode-mode
coupling tends to develop a small q magnetic field tail with a Batchelor
spectrum proportional to the fourth inverse power of L and therefore a scaling
for the magnetic field of B ~ L^(-5/2). | The Galaxy Zoo survey for giant AGN-ionized clouds: past and present
black-hole accretion events: Some active galactic nuclei (AGN) are surrounded by extended emission-line
regions (EELRs), which trace both the illumination pattern of escaping
radiation and its history over the light-travel time from the AGN to the gas.
From a new set of such EELRs, we present evidence that the AGN in many Seyfert
galaxies undergo luminous episodes 20,000-200,000 years in duration. Motivated
by the discovery of the spectacular nebula known as Hanny's Voorwerp, ionized
by a powerful AGN which has apparently faded dramatically within ~ 100,000
years, Galaxy Zoo volunteers have carried out both targeted and serendipitous
searches for similar emission-line clouds around low-redshift galaxies.We
present the resulting list of candidates and describe spectroscopy identifying
19 galaxies with AGN-ionized regions at projected radii > 10 kpc. This search
recovered known EELRs and identified additional previously unknown cases, one
with detected emission to r = 37 kpc. At least 14/19 are in interacting or
merging systems; tidal tails are a prime source of extraplanar ionized gas. We
see a mix of one- and two-sided structures, with observed cone angles from
23-112 degrees. We consider the energy balance in the ionized clouds, with
lower and upper bounds on ionizing luminosity from recombination and
ionization-parameter arguments, and estimate the luminosity of the core from
the far-infrared data. The implied ratio of ionizing radiation seen by the
clouds to that emitted by the nucleus, for a constant nuclear source, ranges
from 0.02 to > 12; 7/19 exceed unity. Small values imply heavily obscured AGN.
However, large values may require that the AGN has faded over tens of thousands
of years, giving us several examples of systems in which such dramatic
long-period variation has occurred; this is the only current technique for
addressing these timescales in AGN history. (Abridged) |
RascalC: A Jackknife Approach to Estimating Single and Multi-Tracer
Galaxy Covariance Matrices: To make use of clustering statistics from large cosmological surveys,
accurate and precise covariance matrices are needed. We present a new code to
estimate large scale galaxy two-point correlation function (2PCF) covariances
in arbitrary survey geometries that, due to new sampling techniques, runs $\sim
10^4$ times faster than previous codes, computing finely-binned covariance
matrices with negligible noise in less than 100 CPU-hours. As in previous
works, non-Gaussianity is approximated via a small rescaling of shot-noise in
the theoretical model, calibrated by comparing jackknife survey covariances to
an associated jackknife model. The flexible code, RascalC, has been publicly
released, and automatically takes care of all necessary pre- and
post-processing, requiring only a single input dataset (without a prior 2PCF
model). Deviations between large scale model covariances from a mock survey and
those from a large suite of mocks are found to be be indistinguishable from
noise. In addition, the choice of input mock are shown to be irrelevant for
desired noise levels below $\sim 10^5$ mocks. Coupled with its generalization
to multi-tracer data-sets, this shows the algorithm to be an excellent tool for
analysis, reducing the need for large numbers of mock simulations to be
computed. | Velocity-dependent interacting dark energy and dark matter with a
Lagrangian description of perfect fluids: We consider a cosmological scenario where the dark sector is described by two
perfect fluids that interact through a velocity-dependent coupling. This
coupling gives rise to an interaction in the dark sector driven by the relative
velocity of the components, thus making the background evolution oblivious to
the interaction and only the perturbed Euler equations are affected at first
order. We obtain the equations governing this system with the Schutz-Sorkin
Lagrangian formulation for perfect fluids and derive the corresponding
stability conditions to avoid ghosts and Laplacian instabilities. As a
particular example, we study a model where dark energy behaves as a radiation
fluid at high redshift while it effectively becomes a cosmological constant in
the late Universe. Within this scenario, we show that the interaction of both
dark components leads to a suppression of the dark matter clustering at late
times. We also argue the possibility that this suppression of clustering
together with the additional dark radiation at early times can simultaneously
alleviate the $\sigma_8$ and $H_0$ tensions. |
Constraining the mass density of free-floating black holes using
razor-thin lensing arcs: Strong lensing of active galactic nuclei in the radio can result in
razor-thin arcs, with a thickness of less than a milli-arcsecond, if observed
at the resolution achievable with very long baseline interferometry (VLBI).
Such razor-thin arcs provide a unique window on the coarseness of the matter
distribution between source and observer. In this paper, we investigate to what
extent such razor-thin arcs can constrain the number density and mass function
of `free-floating' black holes, defined as black holes that do not, or no
longer, reside at the centre of a galaxy. These can be either primordial in
origin or arise as by-products of the evolution of super-massive black holes in
galactic nuclei. When sufficiently close to the line of sight, free-floating
black holes cause kink-like distortions in the arcs, which are detectable by
eye in the VLBI images as long as the black hole mass exceeds $\sim 1000$ Solar
masses. Using a crude estimate for the detectability of such distortions, we
analytically compute constraints on the matter density of free-floating black
holes resulting from null-detections of distortions along a realistic, fiducial
arc, and find them to be comparable to those from quasar milli-lensing. We also
use predictions from a large hydrodynamical simulation for the demographics of
free-floating black holes that are not primordial in origin, and show that
their predicted mass density is roughly four orders of magnitude below the
constraints achievable with a single razor-thin arc. | Disc Heating: Comparing the Milky Way with Cosmological Simulations: We present the analysis of a suite of simulations run with different
particle-and grid-based cosmological hydrodynamical codes and compare them with
observational data of the Milky Way. This is the first study to make
comparisons of properties of galaxies simulated with particle and grid-based
codes. Our analysis indicates that there is broad agreement between these
different modelling techniques. We study the velocity dispersion - age relation
for disc stars at z=0 and find that four of the simulations are more consistent
with observations by Holmberg et al. (2008) in which the stellar disc appears
to undergo continual/secular heating. Two other simulations are in better
agreement with the Quillen & Garnett (2001) observations that suggest a
"saturation" in the heating profile for young stars in the disc. None of the
simulations have thin discs as old as that of the Milky Way. We also analyse
the kinematics of disc stars at the time of their birth for different epochs in
the galaxies' evolution and find that in some simulations old stars are born
cold within the disc and are subsequently heated, while other simulations
possess old stellar populations which are born relatively hot. The models which
are in better agreement with observations of the Milky Way's stellar disc
undergo significantly lower minor-merger/assembly activity after the last major
merger - i.e. once the disc has formed. All of the simulations are
significantly "hotter" than the Milky Way disc; on top of the effects of
mergers, we find a "floor" in the dispersion that is related to the underlying
treatment of the heating and cooling of the interstellar medium, and the low
density threshold which such codes use for star formation. This finding has
important implications for all studies of disc heating that use hydrodynamical
codes. |
Multiphase Signatures of AGN Feedback in Abell 2597: We present new Chandra X-ray observations of the brightest cluster galaxy
(BCG) in the cool core cluster Abell 2597. The data reveal an extensive
kpc-scale X-ray cavity network as well as a 15 kpc filament of soft-excess gas
exhibiting strong spatial correlation with archival VLA radio data. In addition
to several possible scenarios, multiwavelength evidence may suggest that the
filament is associated with multiphase (10^3 - 10^7 K) gas that has been
entrained and dredged-up by the propagating radio source. Stemming from a full
spectral analysis, we also present profiles and 2D spectral maps of modeled
X-ray temperature, entropy, pressure, and metal abundance. The maps reveal an
arc of hot gas which in projection borders the inner edge of a large X-ray
cavity. Although limited by strong caveats, we suggest that the hot arc may be
(a) due to a compressed rim of cold gas pushed outward by the radio bubble or
(b) morphologically and energetically consistent with cavity-driven active
galactic nucleus (AGN) heating models invoked to quench cooling flows, in which
the enthalpy of a buoyant X-ray cavity is locally thermalized as ambient gas
rushes to refill its wake. If confirmed, this would be the first observational
evidence for this model. | A CO J=3-2 map of M51 with HARP-B: Radial properties of the spiral
structure: We present the first complete CO J=3-2 map of the nearby grand-design spiral
galaxy M51 (NGC 5194), at a spatial resolution of ~600 pc, obtained with the
HARP-B instrument on the James Clerk Maxwell Telescope. The map covers the
entire optical galaxy disk and out to the companion NGC 5195, with CO J=3-2
emission detected over an area of ~9'x6' (~21x14 kpc). We describe the CO J=3-2
integrated intensity map and combine our results with maps of CO J=2-1, CO
J=1-0 and other data from the literature to investigate the variation of the
molecular gas, atomic gas and polycyclic aromatic hydrocarbon (PAH) properties
of M51 as a function of distance along the spiral structure on sub-kpc scales.
We find that for the CO J=3-2 and CO J=2-1 transitions there is a clear
difference between the variation of arm and inter-arm emission with
galactocentric radius, with the inter-arm emission relatively constant with
radius and the contrast between arm and inter-arm emission decreasing with
radius. For CO J=1-0 and HI the variation with radius shows a similar trend for
the arm and inter-arm regions, and the arm-inter-arm contrast appears
relatively constant with radius. We investigate the variation of CO line ratios
(J=3-2/2-1, J=2-1/1-0 and J=3-2/1-0) as a function of distance along the spiral
structure. Line ratios are consistent with the range of typical values for
other nearby galaxies in the literature. The highest CO J=3-2/2-1 line ratios
are found in the central ~1 kpc and in the spiral arms and the lowest line
ratios in the inter-arm regions.We find no clear evidence of a trend with
radius for the spiral arms but for the inter-arm regions there appears to be a
trend for all CO line ratios to increase with radius. We find a strong
relationship between the ratio of CO J=3-2 intensity to stellar
continuum-subtracted 8mu PAH surface brightness and the CO J=3-2 intensity that
appears to vary with radius. |
The Dark Energy Cosmic Clock: A New Way to Parametrise the Equation of
State: We propose a completely new parametrisation of the dark energy equation of
state, which uses the dark energy density, $\Omega_e$ as a cosmic clock. We
expand the equation of state in a series of orthogonal polynomials, with
$\Omega_e$ as the expansion parameter and determine the expansion coefficients
by fitting to SNIa and $H(z)$ data. Assuming that $\Omega_e$ is a monotonic
function of time, we show that our parametrisation performs better than the
popular Chevallier--Polarski--Linder (CPL) and Gerke and Efstathiou (GE)
parametrisations, and we demonstrate that it is robust to the choice of prior.
Expanding in orthogonal polynomials allows us to relate models of dark energy
directly to our parametrisation, which we illustrate by placing constraints on
the expansion coefficients extracted from two popular quintessence models.
Finally, we comment on how this parametrisation could be modified to
accommodate high redshift data, where any non--monotonicity of $\Omega_e$ would
need to be accounted for. | A CO emission line from the optical and near-IR undetected submillimeter
galaxy GN10: We report the detection of a CO emission line from the submillimiter galaxy
(SMG) GN10 in the GOODS-N field. GN10 lacks any counterpart in extremely deep
optical and near-IR imaging obtained with the Hubble Space Telescope and
ground-based facilities. This is a prototypical case of a source that is
extremely obscured by dust, for which it is practically impossible to derive a
spectroscopic redshift in the optical/near-IR. Under the hypothesis that GN10
is part of a proto-cluster structure previously identified at z~4.05 in the
same field, we searched for CO[4-3] at 91.4 GHz with the IRAM Plateau de Bure
Interferometer, and successfully detected a line. We find that the most likely
redshift identification is z=4.0424+-0.0013, based on: 1) the very low chance
that the CO line is actually serendipitous from a different redshift; 2) a
radio-IR photometric redshift analysis; 3) the identical radio-IR SED, within a
scaling factor, of two other SMGs at the same redshift. The faintness at
optical/near-IR wavelengths requires an attenuation of A_V~5-7.5 mag. This
result supports the case that a substantial population of very high-z SMGs
exists that had been missed by previous spectroscopic surveys. This is the
first time that a CO emission line has been detected for a galaxy that is
invisible in the optical and near-IR. Our work demonstrates the power of
existing and planned facilities for completing the census of star formation and
stellar mass in the distant Universe by measuring redshifts of the most
obscured galaxies through millimeter spectroscopy. |
Revealing the z~2.5 Cosmic Web With 3D Lyman-Alpha Forest Tomography: A
Deformation Tensor Approach: Studies of cosmological objects should take into account their positions
within the cosmic web of large-scale structure. Unfortunately, the cosmic web
has only been extensively mapped at low-redshifts ($z<1$), using galaxy
redshifts as tracers of the underlying density field. At $z>1$, the required
galaxy densities are inaccessible for the foreseeable future, but 3D
reconstructions of Lyman-$\alpha$ forest absorption in closely-separated
background QSOs and star-forming galaxies already offer a detailed window into
$z\sim2-3$ large-scale structure. We quantify the utility of such maps for
studying the cosmic web by using realistic $z=2.5$ Ly$\alpha$ forest
simulations matched to observational properties of upcoming surveys. A
deformation tensor-based analysis is used to classify voids, sheets, filaments
and nodes in the flux, which is compared to those determined from the
underlying dark matter field. We find an extremely good correspondence, with
$70\%$ of the volume in the flux maps correctly classified relative to the dark
matter web, and $99\%$ classified to within 1 eigenvalue. This compares
favorably to the performance of galaxy-based classifiers with even the highest
galaxy densities at low-redshift. We find that narrow survey geometries can
degrade the cosmic web recovery unless the survey is $\gtrsim
60\,h^{-1}\,\mathrm{Mpc}$ or $\gtrsim 1\,\mathrm{deg}$ on the sky. We also
examine halo abundances as a function of the cosmic web, and find a clear
dependence as a function of flux overdensity, but little explicit dependence on
the cosmic web. These methods will provide a new window on cosmological
environments of galaxies at this very special time in galaxy formation, "high
noon", and on overall properties of cosmological structures at this epoch. | Improved Constraints on Type Ia Supernova Host Galaxy Properties using
Multi-Wavelength Photometry and their Correlations with Supernova Properties: We improve estimates of stellar mass and mass-weighted average age of Type Ia
supernova (SN Ia) host galaxies by combining UV and near-IR photometry with
optical photometry in our analysis. Using 206 SNe Ia drawn from the full
three-year SDSS-II Supernova Survey (median redshift of z {\approx} 0.2) and
multi-wavelength host-galaxy photometry from SDSS, GALEX, and UKIDSS, we
present evidence of a correlation (1.9{\sigma} confidence level) between the
residuals of SNe Ia about the best-fit Hubble relation and the mass-weighted
average age of their host galaxies. The trend is such that older galaxies host
SNe Ia that are brighter than average after standard light-curve corrections
are made. We also confirm, at the 3.0{\sigma} level, the trend seen by previous
studies that more massive galaxies often host brighter SNe Ia after light-curve
correction. |
Testing scale-invariant inflation against cosmological data: There is solid theoretical and observational motivation behind the idea of
scale-invariance as a fundamental symmetry of Nature. We consider a recently
proposed classically scale-invariant inflationary model, quadratic in curvature
and featuring a scalar field non-minimally coupled to gravity. We go beyond
earlier analytical studies, which showed that the model predicts inflationary
observables in qualitative agreement with data, by solving the full two-field
dynamics of the system -- this allows us to corroborate previous analytical
findings and set robust constraints on the model's parameters using the latest
Cosmic Microwave Background (CMB) data from Planck and BICEP/Keck. We
demonstrate that scale-invariance constrains the two-field trajectory such that
the effective dynamics are that of a single field, resulting in vanishing
entropy perturbations and protecting the model from destabilization effects. We
derive tight upper limits on the non-minimal coupling strength, excluding
conformal coupling at high significance. By explicitly sampling over them, we
demonstrate an overall insensitivity to initial conditions. We argue that the
model \textit{predicts} a minimal level of primordial tensor modes set by $r
\gtrsim 0.003$, well within the reach of next-generation CMB experiments. These
will therefore provide a litmus test of scale-invariant inflation, and we
comment on the possibility of distinguishing the model from Starobinsky and
$\alpha$-attractor inflation. Overall, we argue that scale-invariant inflation
is in excellent health, and possesses features which make it an interesting
benchmark for tests of inflation from future CMB data. | Curvaton Decay by Resonant Production of the Standard Model Higgs: We investigate in detail a model where the curvaton is coupled to the
Standard Model higgs. Parametric resonance might be expected to cause a fast
decay of the curvaton, so that it would not have time to build up the curvature
perturbation. However, we show that this is not the case, and that the resonant
decay of the curvaton may be delayed even down to electroweak symmetry
breaking. This delay is due to the coupling of the higgs to the thermal
background, which is formed by the Standard Model degrees of freedom created
from the inflaton decay. We establish the occurrence of the delay by
considering the curvaton evolution and the structure of the higgs resonances.
We then provide analytical expressions for the delay time, and for the
subsequent resonant production of the higgs, which ultimately leads to the
curvaton effective decay width. Contrary to expectations, it is possible to
obtain the observed curvature perturbation for values of the curvaton-higgs
coupling as large as 0.1. Our calculations also apply in the general case of
curvaton decay into any non Standard Model species coupled to the thermal
background. |
Modelling injection and feedback of Cosmic Rays in grid-based
cosmological simulations: effects on cluster outskirts: We present a numerical scheme, implemented in the cosmological adaptive mesh
refinement code ENZO, to model the injection of Cosmic Ray (CR) particles at
shocks, their advection and their dynamical feedback on thermal baryonic gas.
We give a description of the algorithms and show their tests against analytical
and idealized one-dimensional problems. Our implementation is able to track the
injection of CR energy, the spatial advection of CR energy and its feedback on
the thermal gas in run-time. This method is applied to study CR acceleration
and evolution in cosmological volumes, with both fixed and variable mesh
resolution. We compare the properties of galaxy clusters with and without CRs,
for a sample of high-resolution clusters with different dynamical states. At
variance with similar simulations based on Smoothed Particles Hydrodynamics, we
report that the inclusion of CR feedback in our method decreases the central
gas density in clusters, thus reducing the X-ray and Sunyaev-Zeldovich effect
from the clusters centre, while enhancing the gas density and its related
observables near the virial radius. | Size bias and differential lensing of strongly lensed, dusty galaxies
identified in wide-field surveys: We address two selection effects that operate on samples of gravitationally
lensed dusty galaxies identified in millimeter- and submillimeter-wavelength
surveys. First, we point out the existence of a "size bias" in such samples:
due to finite source effects, sources with higher observed fluxes are
increasingly biased towards more compact objects. Second, we examine the effect
of differential lensing in individual lens systems by modeling each source as a
compact core embedded in an extended diffuse halo. Considering the ratio of
magnifications in these two components, we find that at high overall
magnifications the compact component is amplified by a much larger factor than
the diffuse component, but at intermediate magnifications (~10) the probability
of a larger magnification for the extended region is higher. Lens models
determined from multi-frequency resolved imaging data are crucial to correct
for this effect. |
ISW-Galaxy Cross Correlation:A probe of Dark Energy clustering and
distribution of Dark Matter tracers: Cross correlation of the Integrated Sachs-Wolfe signal (ISW) with the galaxy
distribution in late time is a promising tool for constraining the dark energy
properties. Here, we study the effect of dark energy clustering on the
ISW-galaxy cross correlation and demonstrate the fact that the bias parameter
between the distribution of the galaxies and the underlying dark matter
introduces a degeneracy and complications. We argue that as the galaxy's host
halo formation time is different from the observation time, we have to consider
the evolution of the halo bias parameter. It will be shown that any deviation
from $\Lambda$CDM model will change the evolution of the bias as well.
Therefore, it is deduced that the halo bias depends strongly on the sub-sample
of galaxies which is chosen for cross correlation and that the joint kernel of
ISW effect and the galaxy distribution has a dominant effect on the observed
signal. In this work, comparison is made specifically between the clustered
dark energy models using two samples of galaxies. The first one is a sub-sample
of galaxies from Sloan Digital Sky Survey, chosen with the r-band magnitude $18
< r < 21$ and the dark matter halo host of mass $M \sim10^{12}M_{\odot}$ and
formation redshift of $z_{f}\sim 2.5$. The second one is the sub-sample of
Luminous Red galaxies with the dark matter halo hosts of mass $M \sim
10^{13}M_{\odot}$ and formation redshift of $z_{f}\sim 2.0$. Using the evolved
bias we improve the $\chi^2$ for the $\Lambda$CDM which reconciles the
$\sim$1$\sigma$-2$\sigma$ tension of the ISW-galaxy signal with $\Lambda$CDM
prediction.[abridged] | A Fast Method for Power Spectrum and Foreground Analysis for 21 cm
Cosmology: We develop and demonstrate an acceleration of the Liu & Tegmark quadratic
estimator formalism for inverse variance foreground subtraction and power
spectrum estimation in 21 cm tomography from O(N^3) to O(N log N), where N is
the number of voxels of data. This technique makes feasible the megavoxel scale
analysis necessary for current and upcoming radio interferometers by making
only moderately restrictive assumptions about foreground models and survey
geometry. We exploit iterative and Monte Carlo techniques and the symmetries of
the foreground covariance matrices to quickly estimate the 21 cm brightness
temperature power spectrum, P(k_parallel, k_perpendicular), the Fisher
information matrix, the error bars, the window functions, and the bias. We also
extend the Liu & Tegmark foreground model to include bright point sources with
known positions in a way that scales as O[(N log N)(N point sources)] <
O(N^5/3). As a first application of our method, we forecast error bars and
window functions for the upcoming 128-tile deployment of the Murchinson
Widefield Array, showing that 1000 hours of observation should prove
sufficiently sensitive to detect the power spectrum signal from the Epoch of
Reionization. |
Ultra large-scale cosmology in next-generation experiments with single
tracers: Future surveys of large-scale structure will be able to measure perturbations
on the scale of the cosmological horizon, and so could potentially probe a
number of novel relativistic effects that are negligibly small on sub-horizon
scales. These effects leave distinctive signatures in the power spectra of
clustering observables and, if measurable, would open a new window on
relativistic cosmology. We quantify the size and detectability of the effects
for the most relevant future large-scale structure experiments: spectroscopic
and photometric galaxy redshift surveys, intensity mapping surveys of neutral
hydrogen, and radio continuum surveys. Our forecasts show that next-generation
experiments, reaching out to redshifts $z\simeq 4$, will not be able to detect
previously-undetected general-relativistic effects by using individual tracers
of the density field, although the contribution of weak lensing magnification
on large scales should be clearly detectable. We also perform a rigorous joint
forecast for the detection of primordial non-Gaussianity through the excess
power it produces in the clustering of biased tracers on large scales, finding
that uncertainties of $\sigma(f_{\rm NL})\sim 1-2$ should be achievable. We
study the level of degeneracy of these large-scale effects with several
tracer-dependent nuisance parameters, quantifying the minimal priors on the
latter that are needed for an optimal measurement of the former. Finally, we
discuss the systematic effects that must be mitigated to achieve this level of
sensitivity, and some alternative approaches that should help to improve the
constraints. The computational tools developed to carry out this study, which
requires the full-sky computation of the theoretical angular power spectra for
$\mathcal{O}(100)$ redshift bins, as well as realistic models of the luminosity
function, are publicly available. | Chameleon dark energy models with characteristic signatures: In chameleon dark energy models, local gravity constraints tend to rule out
parameters in which observable cosmological signatures can be found. We study
viable chameleon potentials consistent with a number of recent observational
and experimental bounds. A novel chameleon field potential, motivated by f(R)
gravity, is constructed where observable cosmological signatures are present
both at the background evolution and in the growth-rate of the perturbations.
We study the evolution of matter density perturbations on low redshifts for
this potential and show that the growth index today gamma_0 can have
significant dispersion on scales relevant for large scale structures. The
values of gamma_0 can be even smaller than 0.2 with large variations of gamma
on very low redshifts for the model parameters constrained by local gravity
tests. This gives a possibility to clearly distinguish these chameleon models
from the Lambda-Cold-Dark-Matter model in future high-precision observations. |
Model-independent constraints in inflationary magnetogenesis: We derive a simple model-independent upper bound on the strength of magnetic
fields obtained in inflationary and post-inflationary magnetogenesis taking
into account the constraints imposed by the condition of weak coupling,
back-reaction and Schwinger effect. This bound turns out to be rather low for
cosmologically interesting spatial scales. Somewhat higher upper bound is
obtained if one assumes that some unknown mechanism suppresses the Schwinger
effect in the early universe. Incidentally, we correct our previous estimates
for this case. | Molecular gas in high redshift galaxies: Recent observations with the IRAM instruments have allowed to explore the
star formation efficiency in galaxies as a function of redshift, in detecting
and mapping their molecular gas. Some galaxies stand on what is called the
"main sequence", forming stars with a rate that can be sustained over
time-scales of 1 Gyr, some are starbursts, with a much shorter depletion time.
Star formation was more active in the past, partly because galaxies contained a
larger gas fraction, and also because the star formation efficiency was higher.
The global Kennicutt-Schmidt relation was however similar until z \sim 2.5.
Magnification by gravitational lenses have been used to explore in details
galaxies at higher redshift up to 6. Herschel has discovered many of these
candidates, and their redshift has been determined through the CO lines. ALMA
is beginning to extend considerably these redshift searches, with its
broad-band receivers, for a large range of objects too obscured to be seen in
the optical. |
Acoustic signatures in the Cosmic Microwave Background bispectrum from
primordial magnetic fields: Using the full radiation transfer function, we numerically calculate the CMB
angular bispectrum seeded by the compensated magnetic scalar density mode. We
find that, for the string inspired primordial magnetic fields characterized by
index $n_B=-2.9$ and mean-field amplitude $B_{\lam}=9{\rm nG}$, the angular
bispectrum is dominated by two primordial magnetic shapes. The first magnetic
shape looks similar to the one from local-type primordial curvature
perturbations, so both the amplitude and profile of the Komatsu-Spergel
estimator (reduced bispectrum) seeded by this shape are almost the same as
those of the primary CMB anisotropies. However, for different parameter sets
($l_1,l_2$), this "local-type" reduced bispectrum oscillates around different
asymptotic values in the high-$l_3$ regime because of the effect of the Lorentz
force, which is exerted by the primordial magnetic fields on the charged
baryons. This feature is different from the standard case where all modes
approach to zero asymptotically in the high-$l$ limit. On the other hand, the
second magnetic shape appears only in the primordial magnetic field model. The
amplitude of the Komatsu-Spergel estimator sourced by the second shape diverges
in the low-$l$ regime because of the negative slope of shape. In the high-$l$
regime, this amplitude is approximately equal to that of the first estimator,
but with a reversal phase. | Polarizing Bubble Collisions: We predict the polarization of cosmic microwave background (CMB) photons that
results from a cosmic bubble collision. The polarization is purely E-mode,
symmetric around the axis pointing towards the collision bubble, and has
several salient features in its radial dependence that can help distinguish it
from a more conventional explanation for unusually cold or hot features in the
CMB sky. The anomalous "cold spot" detected by the Wilkinson Microwave
Anisotropy Probe (WMAP) satellite is a candidate for a feature produced by such
a collision, and the Planck satellite and other proposed surveys will measure
the polarization on it in the near future. The detection of such a collision
would provide compelling evidence for the string theory landscape. |
A 2500 square-degree CMB lensing map from combined South Pole Telescope
and Planck data: We present a cosmic microwave background (CMB) lensing map produced from a
linear combination of South Pole Telescope (SPT) and \emph{Planck} temperature
data. The 150 GHz temperature data from the $2500\ {\rm deg}^{2}$ SPT-SZ survey
is combined with the \emph{Planck} 143 GHz data in harmonic space, to obtain a
temperature map that has a broader $\ell$ coverage and less noise than either
individual map. Using a quadratic estimator technique on this combined
temperature map, we produce a map of the gravitational lensing potential
projected along the line of sight. We measure the auto-spectrum of the lensing
potential $C_{L}^{\phi\phi}$, and compare it to the theoretical prediction for
a $\Lambda$CDM cosmology consistent with the \emph{Planck} 2015 data set,
finding a best-fit amplitude of $0.95_{-0.06}^{+0.06}({\rm Stat.})\!
_{-0.01}^{+0.01}({\rm Sys.})$. The null hypothesis of no lensing is rejected at
a significance of $24\,\sigma$. One important use of such a lensing potential
map is in cross-correlations with other dark matter tracers. We demonstrate
this cross-correlation in practice by calculating the cross-spectrum,
$C_{L}^{\phi G}$, between the SPT+\emph{Planck} lensing map and Wide-field
Infrared Survey Explorer (\emph{WISE}) galaxies. We fit $C_{L}^{\phi G}$ to a
power law of the form $p_{L}=a(L/L_{0})^{-b}$ with $a=2.15 \times 10^{-8}$,
$b=1.35$, $L_{0}=490$, and find $\eta^{\phi G}=0.94^{+0.04}_{-0.04}$, which is
marginally lower, but in good agreement with $\eta^{\phi
G}=1.00^{+0.02}_{-0.01}$, the best-fit amplitude for the cross-correlation of
\emph{Planck}-2015 CMB lensing and \emph{WISE} galaxies over $\sim67\%$ of the
sky. The lensing potential map presented here will be used for
cross-correlation studies with the Dark Energy Survey (DES), whose footprint
nearly completely covers the SPT $2500\ {\rm deg}^2$ field. | Improving precision and accuracy in cosmology with model-independent
spectrum and bispectrum: A new and promising avenue was recently developed for analyzing large-scale
structure data with a model-independent approach, in which the linear power
spectrum shape is parametrized with a large number of freely varying wavebands
rather than by assuming specific cosmological models. We call this method
FreePower.
Here we show, using a Fisher matrix approach, that precision of this method
for the case of the one-loop power spectrum is greatly improved with the
inclusion of the tree-level bispectrum. We also show that accuracy can be
similarly improved by employing perturbation theory kernels whose structure is
entirely determined by symmetries instead of evolution equations valid in
particular models (like in the usual Einstein-deSitter approximation). The main
result is that with the Euclid survey one can precisely measure the Hubble
function, distance and ($k$-independent) growth rate $f(z)$ in seven redshift
bins in the range $z\in [0.6,\, 2.0]$. The typical errors for the lowest
$z$bins are around 1\% (for $H$), 0.5--1\% (for $D$), and 1--3\% (for $f$). The
use of general perturbation theory allows us, for the first time, to study
constraints on the nonlinear kernels of cosmological perturbations, that is,
beyond the linear growth factor, showing that they can be probed at the
10--20\% level. We find that the combination of spectrum and bispectrum is
particularly effective in constraining the perturbation parameters, both at
linear and quadratic order. |
Dark-ages Reionization and Galaxy Formation Simulation - XIV. Gas
accretion, cooling and star formation in dwarf galaxies at high redshift: We study dwarf galaxy formation at high redshift ($z\ge5$) using a suite of
high- resolution, cosmological hydrodynamic simulations and a semi-analytic
model (SAM). We focus on gas accretion, cooling and star formation in this work
by isolating the relevant process from reionization and supernova feedback,
which will be further discussed in a companion paper. We apply the SAM to halo
merger trees constructed from a collisionless N-body simulation sharing
identical initial conditions to the hydrodynamic suite, and calibrate the free
parameters against the stellar mass function predicted by the hydrodynamic
simulations at z = 5. By making comparisons of the star formation history and
gas components calculated by the two modelling techniques, we find that
semi-analytic prescriptions that are commonly adopted in the literature of
low-redshift galaxy formation do not accurately represent dwarf galaxy
properties in the hydrodynamic simulation at earlier times. We propose 3
modifications to SAMs that will provide more accurate high-redshift
simulations. These include 1) the halo mass and baryon fraction which are
overestimated by collisionless N-body simulations; 2) the star formation
efficiency which follows a different cosmic evolutionary path from the
hydrodynamic simulation; and 3) the cooling rate which is not well defined for
dwarf galaxies at high redshift. Accurate semi-analytic modelling of dwarf
galaxy formation informed by detailed hydrodynamical modelling will facilitate
reliable semi-analytic predictions over the large volumes needed for the study
of reionization. | Variation of the baryon-to-photon ratio due to decay of dark matter
particles: The influence of dark matter particle decay on the baryon-to-photon ratio has
been studied for different cosmological epochs. We consider different parameter
values of dark matter particles such as mass, lifetime, the relative fraction
of dark matter particles. It is shown that the modern value of the dark matter
density $\Omega_{\rm CDM}=0.26$ is enough to lead to variation of the
baryon-to-photon ratio up to $\Delta \eta / \eta \sim 0.01 \div 1$ for decays
of the particles with masses 10 GeV $\div$ 1 TeV. However, such processes can
also be accompanied by emergence of an excessive gamma ray flux. The
observational data on the diffuse gamma ray background are used to making
constraints on the dark matter decay models and on the maximum possible
variation of the baryon-to-photon ratio $\Delta\eta/\eta\lesssim10^{-5}$.
Detection of such variation of the baryon density in future cosmological
experiments can serve as a powerful means of studying properties of dark matter
particles. |
On the Origin of Near-Infrared Extragalactic Background Light Anisotropy: Extragalactic background light (EBL) anisotropy traces variations in the
total production of photons over cosmic history, and may contain faint,
extended components missed in galaxy point source surveys. Infrared EBL
fluctuations have been attributed to primordial galaxies and black holes at the
epoch of reionization (EOR), or alternately, intra-halo light (IHL) from stars
tidally stripped from their parent galaxies at low redshift. We report new EBL
anisotropy measurements from a specialized sounding rocket experiment at 1.1
and 1.6 micrometers. The observed fluctuations exceed the amplitude from known
galaxy populations, are inconsistent with EOR galaxies and black holes, and are
largely explained by IHL emission. The measured fluctuations are associated
with an EBL intensity that is comparable to the background from known galaxies
measured through number counts, and therefore a substantial contribution to the
energy contained in photons in the cosmos. | The Acceleration of the Expansion of the Universe: A Brief Early History
of the Supernova Cosmology Project (SCP): It is now about 10 years since the evidence, based on Type Ia supernovae, for
the acceleration of the expansion of the Universe was discovered. I will
discuss some aspects of the work and events in the Supernova Cosmology Project
(SCP), during the period 1988 to 1998, which led to this discovery. |
Spin Alignment of Dark Matter Halos: Mad Halos: We investigate the spin alignment of the dark matter halos by considering a
mechanism somewhat similar to tidal locking. We dubbed it Tidal Locking Theory
(TLT). While Tidal Torque Theory is responsible for the initial angular
momentum of the dark matter halos, the Tidal locking Theory explains the
angular momentum evolution during non-linear ages. Our previous work showed
that close encounters between haloes could drastically change their angular
momentum. The current manuscript argues that the tidal locking theory predicts
partial alignment between speed and the spin direction for the large high-speed
halos. To examine this prediction, we use the IllustrisTNG simulation and look
for the alignment of the halos' rotation axis. We find that the excess
probability of alignment between spin and speed is about 10 percent at $z=0$
for fast haloes; with velocities larger than twice the median. We show that
tidal torque theory predicts that the spin of a halo tends to be aligned with
the middle eigendirection of the tidal tensor. Moreover, we find that the halos
at $z=10$ are preferentially aligned with the middle eigendirection of the
tidal tensor with an excess probability of 15 percent. We show that tidal
torque theory fails to predict correct alignment at $z=0$ while it works almost
flawlessly at $z=10$. | Rms variability properties of the iron K alpha line in Seyfert galaxies: We present an analysis of the rms variability spectra of a sample of 18
observations of 14 Seyfert galaxies observed by XMM-Newton, which exhibit
sufficient variability and signal-to-noise ratio to examine the variations in
the iron K-band. The narrow core of the K alpha line at 6.4 keV, seen
universally in Seyferts, shows minimal evidence for variability and is always
less variable than the continuum, supporting an origin in distant material such
as the torus. At least half the observations do show evidence for variations in
the wider iron K-band, however, and in at least 5 cases the excess line
variations appear to be broad. The simplest prediction -- that the broad
emission line is as variable as the continuum -- is generally not confirmed as
only two observations show this type of behaviour. In four cases, the red wing
of the line is more variable than the power-law continuum and extends down to
energies of ~ 5 keV. Three observations show strong variability blueward of the
line core that could also be from the disk, but alternatively might be due to
emission or absorption by other hot or photoionised gas close to the nucleus.
In cases where this excess blue variability is present, it is not always seen
in the time-averaged spectrum. Six observations possess a broad iron line in
the time-averaged spectra but with an invariant red wing, and three of these
six show no variability across the entire iron line region. This suggests a
decoupling of the continuum and reflection component, perhaps due to light
bending or other anisotropic effects as has been suggested for MCG-6-30-15 and
other narrow-line Seyfert 1s. A key result is that the rms spectra of objects
such as NGC 3516 do not agree with complex absorption effects mimicking the
broad red wing. |
Characterizing Galaxy Clusters with Gravitational Potential: We propose a simple estimator for the gravitational potential of cluster-size
halos using the temperature and density profiles of the intracluster gas based
on the assumptions of hydrostatic equilibrium and spherical symmetry. Using
high resolution cosmological simulations of galaxy clusters, we show that the
scaling relation between this estimator and the gravitational potential has a
small intrinsic scatter of ~8%-15%, and it is insensitive to baryon physics
outside the cluster core. The slope and the normalization of the scaling
relation vary weakly with redshift, and they are relatively independent of the
choice of radial range used and the dynamical states of the clusters. The
results presented here provide a possible way for using the cluster potential
function as an alternative to the cluster mass function in constraining
cosmology using galaxy clusters. | The dilution peak, metallicity evolution, and dating of galaxy
interactions and mergers: Strong inflows of gas from the outer disk to the inner kiloparsecs are
induced during the interaction of disk galaxies. This inflow of relatively
low-metallicity gas dilutes the metallicity of the circumnuclear gas. We have
investigated several aspects of the process as the timing and duration of the
dilution and its correlation with the induced star formation. We analysed major
(1:1) gas-rich interactions and mergers, spanning a range of initial orbital
characteristics. Star formation and metal enrichment from SNe are included in
our model. Our results show that the strongest trend is between the star
formation rate and the dilution of the metals in the nuclear region; i.e., the
more intense the central burst of star formation, the more the gas is diluted.
This trend comes from strong inflows of relatively metal-poor gas from the
outer regions of both disks, which fuels the intense star formation and lowers
the overall metallicity for a time. The strong inflows happen on timescales of
about 10^8 years or less, and the most intense star formation and lowest gas
phase metallicities are seen generally after the first pericentre passage. As
the star formation proceeds and the merger advances, the dilution reduces and
enrichment becomes dominant - ultimately increasing the metallicity of the
circumnuclear gas to a level higher than the initial metallicities of the
merging galaxies. The "fly-bys" - pairs that interact but do not merge - also
cause some dilution. We even see some dilution early in the merger or in the
"fly-bys" and thus do not observe a strong trend between the nuclear
metallicities and separation in our simulations until the merger is well
advanced. We also analyse the O and Fe enrichment of the ISM, and show that the
evolution of the alpha/Fe ratios, as well as the dilution of the central gas
metallicity, can be used as a clock for "dating" the interaction. |
The effect of stellar encounters on the dark matter annihilation signal
from prompt cusps: Prompt cusps are the densest quasi-equilibrium dark matter objects; one forms
at the instant of collapse within every isolated peak of the initial
cosmological density field. They have power-law density profiles, $\rho \propto
r^{-1.5}$ with central phase-space density set by the primordial velocity
dispersion of the dark matter. At late times they account for $\sim 1\%$ of the
dark matter mass but for $>90\%$ of its annihilation luminosity in all but the
densest regions, where they are tidally disrupted. Here we demonstrate that
individual stellar encounters, rather than the mean galactic tide, are the
dominant disruptors of prompt cusps within galaxies. Their cumulative effect is
fully (though stochastically) characterised by an impulsive shock strength $B_*
= 2\pi G\int\rho_*({\bf x}(t))\, \mathrm{d}t$ where $\rho_*$, the total mass
density in stars, is integrated over a cusp's entire post-formation trajectory.
Stellar encounters and mean tides have only a small effect on the halo
annihilation luminosity seen by distant observers, but this is not true for the
Galactic halo because of the Sun's position. For a 100 GeV WIMP, Earth-mass
prompt cusps are predicted, and stellar encounters suppress their mean
annihilation luminosity by a factor of two already at 20 kpc, so that their
annihilation emission is predicted to appear almost uniform over the sky. The
Galactic Center $\gamma$-ray Excess is thus unaffected by cusps. If it is
indeed dark matter annihilation radiation, then prompt cusps in the outer
Galactic halo and beyond must account for 20-80% of the observed isotropic
$\gamma$-ray background in the 1 to 10 GeV range. | The effect of hydrodynamical simulation inspired dark matter velocity
profile on directional detection of dark matter: Directional detection is an important way to detect dark matter. An input to
these experiments is the dark matter velocity distribution. Recent
hydrodynamical simulations have shown that the dark matter velocity
distribution differs substantially from the Standard Halo Model. We study the
impact of some of these updated velocity distribution in dark matter
directional detection experiments. We calculate the ratio of events required to
confirm the forward-backward asymmetry and the existence of the ring of maximum
recoil rate using different dark matter velocity distributions for $^{19}$F and
Xe targets. We show that with the use of updated dark matter velocity profiles,
the forward-backward asymmetry and the ring of maximum recoil rate can be
confirmed using a factor of $\sim$2 - 3 less events when compared to that using
the Standard Halo Model. |
Density Weighted Angular Redshift Fluctuations: a New Cosmological
Observable: We propose the use of angular fluctuations in the galaxy redshift field as a
new way to extract cosmological information in the Universe. This new probe
$\delta z (\hat{n})$ consists on the statistics of sky maps built by projecting
redshifts under a Gaussian window of width $\sigma_z$ centred upon a redshift
$z_{\rm obs}$, and weighted by the galaxy density field. We compute the angular
power spectrum of the $\delta z (\hat{n})$ field in both numerical simulations
and in linear perturbation theory. From these we find that the $\delta z
(\hat{n})$ field: {\it (i)} is sensitive to the underlying density and peculiar
velocity fields; {\it (ii)} is highly correlated, at the $\gtrsim 60\,\%$
level, to the line-of-sight projected peculiar velocity field; {\it (iii)} for
narrow windows $(\sigma_z < 0.03$), it is almost completely uncorrelated to the
projected galaxy angular density field under the same redshift window; and {\it
(iv)} it is largely unaffected by multiplicative and additive systematic errors
on the observed number of galaxies that are redshift-independent over
$\sim\sigma_z$. We conclude that $\delta z (\hat{n})$ is a simple and robust
tomographic measure of the cosmic density and velocity fields, complementary to
angular clustering, that will contribute to more complete exploitations of
current and upcoming galaxy redshift surveys. | A Systematic Search of Distant Superclusters with the Subaru Hyper
Suprime-Cam Survey: Superclusters, encompassing environments across a wide range of
overdensities, can be regarded as unique laboratories for studying galaxy
evolution. Although numerous supercluster catalogs have been published, none of
them goes beyond redshift $z=0.7$. In this work, we adopt a physically
motivated supercluster definition, requiring that superclusters should
eventually collapse even in the presence of dark energy. Applying a
friends-of-friends (FoF) algorithm to the CAMIRA cluster sample constructed
using the Subaru Hyper Suprime-Cam survey data, we have conducted the first
systematic search for superclusters at $z=0.5-1.0$ and identified $633$
supercluster candidates over an area of 1027 deg$^2$. The FoF algorithm is
calibrated by evolving $N$-body simulations to the far future to ensure high
purity. We found that these high-$z$ superclusters are mainly composed of $2-4$
clusters, suggesting the limit of gravitationally bound structures in the
younger Universe. In addition, we studied the properties of the clusters and
brightest cluster galaxies (BCGs) residing in different large-scale
environments. We found that clusters associated with superclusters are
typically richer, but no apparent dependence of the BCG properties on
large-scale structures is found. We also compared the abundance of observed
superclusters with mock superclusters extracted from halo light cones, finding
that photometric redshift uncertainty is a limiting factor in the performance
of superclusters detection. |
Translation and Rotation Equivariant Normalizing Flow (TRENF) for
Optimal Cosmological Analysis: Our universe is homogeneous and isotropic, and its perturbations obey
translation and rotation symmetry. In this work we develop Translation and
Rotation Equivariant Normalizing Flow (TRENF), a generative Normalizing Flow
(NF) model which explicitly incorporates these symmetries, defining the data
likelihood via a sequence of Fourier space-based convolutions and pixel-wise
nonlinear transforms. TRENF gives direct access to the high dimensional data
likelihood p(x|y) as a function of the labels y, such as cosmological
parameters. In contrast to traditional analyses based on summary statistics,
the NF approach has no loss of information since it preserves the full
dimensionality of the data. On Gaussian random fields, the TRENF likelihood
agrees well with the analytical expression and saturates the Fisher information
content in the labels y. On nonlinear cosmological overdensity fields from
N-body simulations, TRENF leads to significant improvements in constraining
power over the standard power spectrum summary statistic. TRENF is also a
generative model of the data, and we show that TRENF samples agree well with
the N-body simulations it trained on, and that the inverse mapping of the data
agrees well with a Gaussian white noise both visually and on various summary
statistics: when this is perfectly achieved the resulting p(x|y) likelihood
analysis becomes optimal. Finally, we develop a generalization of this model
that can handle effects that break the symmetry of the data, such as the survey
mask, which enables likelihood analysis on data without periodic boundaries. | The recursion relation in Lagrangian perturbation theory: We derive a recursion relation in the framework of Lagrangian perturbation
theory, appropriate for studying the inhomogeneities of the large scale
structure of the universe. We use the fact that the perturbative expansion of
the matter density contrast is in one-to-one correspondence with standard
perturbation theory (SPT) at any order. This correspondence has been recently
shown to be valid up to fourth order for a non-relativistic, irrotational and
dust-like component. Assuming it to be valid at arbitrary (higher) order, we
express the Lagrangian displacement field in terms of the perturbative kernels
of SPT, which are itself given by their own and well-known recursion relation.
We argue that the Lagrangian solution always contains more non-linear
information in comparison with the SPT solution, (mainly) if the
non-perturbative density contrast is restored after the displacement field is
obtained. |
Black Hole Mass, Host galaxy classification and AGN activity: We investigate the role of host galaxy classification and black hole mass in
a heterogeneous sample of 276 mostly nearby (z<0.1) X-ray and IR selected AGN.
Around 90% of Seyfert 1 AGN in bulge-dominated host galaxies (without disk
contamination) span a very narrow range in the observed 12um to 2-10keV
luminosity ratio (1<R_{IR/X}<7). This narrow dispersion incorporates all
possible variations among AGN central engines, including accretion mechanism
and efficiency, disk opening angle, orientation to sightline, covering fraction
of absorbing material, patchiness of X-ray corona and measured variability. As
a result, all models of X-ray and IR production in AGN are very strongly
constrained. Among Seyfert 1 AGN, median X-ray and IR luminosities increase
with black hole mass at >99% confidence. Using ring morphology of the host
galaxy as a proxy for lack of tidal interaction, we find that AGN luminosity in
host galaxies within 70Mpc is independent of host galaxy interaction for $\sim$
Gyrs, suggesting that the timescale of AGN activity due to secular evolution is
much shorter than that due to tidal interactions. We find that LINER hosts have
lower 12um luminosity than the median 12um luminosity of normal disk- and
bulge-dominated galaxies which may represent observational evidence for past
epochs of feedback that supressed star formation in LINER host galaxies. We
propose that nuclear ULXs may account for the X-ray emission from LINER 2s
without flat-spectrum, compact radio cores. We confirmed the robustness of our
results in X-rays by comparing them with the 14-195keV 22-month BAT survey of
AGN, which is all-sky and unbiased by photoelectric absorption. | Sub-millimetre source identifications and the micro-Jansky source
population at 8.4 GHz in the William Herschel Deep Field: [Abridged] Sub-mm observations of the William Herschel Deep Field using
LABOCA revealed possible counterparts for 2 X-ray absorbed QSOs. The aim here
is to exploit EVLA imaging at 8.4 GHz to establish the QSOs as radio/sub-mm
sources. The challenge in reducing the EVLA data was the presence of a strong
4C source in the field. A new calibration algorithm was applied to the data to
subtract it. The resulting thermal noise limited radio map covers the 16'x16'
Extended WHDF. It contains 41 sources above a 4-sigma limit, 17 of which have
primary beam corrected flux. The radio observations show that the absorbed AGN
with LABOCA detections are coincident with radio sources, confirming the
tendency for X-ray absorbed AGN to be sub-mm bright. These sources show strong
ultraviolet excess (UVX) suggesting the nuclear sightline is gas- but not
dust-absorbed. Of the 3 remaining LABOCA sources within the ~5' half-power beam
width, 1 is identified with a faint nuclear X-ray/radio source in a nearby
galaxy, 1 with a faint radio source and 1 is unidentified in any other band.
More generally, differential radio source counts are in good agreement with
previous observations, showing at S<50 micro-Jy a significant excess over a
pure AGN model. In the full area, of 10 sources fainter than this limit, 6 have
optical counterparts of which 3 are UVX (i.e. likely QSOs) including the 2
absorbed quasar LABOCA sources. The other faint radio counterparts are not UVX
but are only slightly less blue and likely to be star-forming/merging galaxies,
predominantly at lower luminosities and redshifts. The 4 faint, optically
unidentified radio sources may be either dust obscured QSOs or galaxies. These
high-z obscured AGN and lower-z star-forming populations are thus the main
candidates to explain the observed excess in faint source counts and hence the
excess radio background found previously by the ARCADE2 experiment. |
Fixing the U-band photometry of Type Ia supernovae: We present previously unpublished photometry of supernovae 2003gs and 2003hv.
Using spectroscopically-derived corrections to the U-band photometry, we
reconcile U-band light curves made from imagery with the Cerro Tololo 0.9-m,
1.3-m and Las Campanas 1-m telescopes. Previously, such light curves showed a
0.4 mag spread at one month after maximum light. This gives us hope that a set
of corrected ultraviolet light curves of nearby objects can contribute to the
full utilization of rest frame U-band data of supernovae at redshift ~0.3 to
0.8. As pointed out recently by Kessler et al. in the context of the Sloan
Digital Sky Survey supernova search, if we take the published U-band photometry
of nearby Type Ia supernovae at face value, there is a 0.12 mag U-band anomaly
in the distance moduli of higher redshift objects. This anomaly led the Sloan
survey to eliminate from their analyses all photometry obtained in the rest
frame U-band. The Supernova Legacy Survey eliminated observer frame U-band
photometry, which is to say nearby objects observed in the U-band, but they
used photometry of high redshift objects no matter in which band the photons
were emitted. | Magnetic Field of Cosmic Strings in the Early Universe: Cosmic strings are topological defects which can be formed as a result of
phase transitions with a spontaneous symmetry breaking in the early Universe.
The possibility of the generation of a magnetic field around a cosmic string on
the Grand Unification energy scale (GUT scale) in the early Universe
immediately after the termination of the deconfinement-confinement phase
transition has been analyzed. It is found that a circular current and a
magnetic field directed along the string are induced around the string in the
vacuum of a pseudoscalar matter consisting of charged pions. We also have
studied the interaction between the magnetic flux tube surrounding the string
(the string magnetosphere) and the cosmic plasma in the early Universe. A
possibility of magnetization of the cosmic plasma surrounding the string owing
to its interaction with the string magnetic field has been analyzed. |
Cross-Correlation study between CMB lensing and galaxy surveys: Cosmic Microwave Background (CMB) is a powerful probe to study the early
universe and various cosmological models. Weak gravitational lensing affects
the CMB by changing its power spectrum, but meanwhile, it also carries
information about the distribution of lensing mass and hence, the large scale
structure (LSS) of the universe. When studies of the CMB is combined with the
tracers of LSS, one can constrain cosmological models, models of LSS
development and astrophysical parameters simultaneously. The main focus of this
project is to study the cross-correlations between CMB lensing and the galaxy
matter density to constrain the galaxy bias ($b$) and the amplitude scaling
parameter ($A$), to test the validity of $\Lambda$CDM model. We test our
approach for simulations of the Planck CMB convergence field and galaxy density
field, which mimics the density field of the Herschel Extragalactic Legacy
Project (HELP). We use maximum likelihood method to constrain the parameters. | Axion Structure Formation I: The Co-motion Picture: Axions as dark matter is an increasingly important subject in astrophysics
and cosmology. Experimental and observational searches are mounting across the
mass spectrum of axion-like particles, many of which require detailed knowledge
of axion structure over a wide range of scales. Current understanding of axion
structures is far from complete, however, due largely to controversy in
modeling the candidate's highly-degenerate state. The series Axion Structure
Formation seeks to develop a consistent model of QCD axion dark matter dynamics
that follows their highly-degenerate nature to the present using novel modeling
techniques and sophisticated simulations. This inaugural paper presents the
problem of describing many non-relativistic axions with minimal degrees of
freedom and constructs a theory of axion infall for the limit of complete
condensation. The derived model is shown to contain axion-specific dynamics not
unlike the exchange-correlation influences experienced by identical fermions.
Perturbative calculations are performed to explore the potential for imprints
in early universe structures. |
The pseudo-evolution of halo mass: A dark matter halo is commonly defined as a spherical overdensity of matter
with respect to a reference density, such as the critical density or the mean
matter density of the Universe. Such definitions can lead to a spurious
pseudo-evolution of halo mass simply due to redshift evolution of the reference
density, even if its physical density profile remains constant over time. We
estimate the amount of such pseudo-evolution of mass between z=1 to 0 for halos
identified in a large N-body simulation, and show that it accounts for almost
the entire mass evolution of the majority of halos with M200 of about 1E12
solar masses and can be a significant fraction of the apparent mass growth even
for cluster-sized halos. We estimate the magnitude of the pseudo-evolution
assuming that halo density profiles remain static in physical coordinates, and
show that this simple model predicts the pseudo-evolution of halos identified
in numerical simulations to good accuracy, albeit with significant scatter. We
discuss the impact of pseudo-evolution on the evolution of the halo mass
function and show that the non-evolution of the low-mass end of the halo mass
function is the result of a fortuitous cancellation between pseudo-evolution
and the absorption of small halos into larger hosts. We also show that the
evolution of the low mass end of the concentration-mass relation observed in
simulations is almost entirely due to the pseudo-evolution of mass. Finally, we
discuss the implications of our results for the interpretation of the evolution
of various scaling relations between the observable properties of galaxies and
galaxy clusters and their halo masses. | The slowly evolving role of environment in a spectroscopic survey of
star formation in Mstar > 5E8 Msun galaxies since z=1: We present a deep [OII] emission line survey of faint galaxies (22.5<KAB<24)
in the Chandra Deep Field South and the FIRES field. With these data we measure
the star formation rate (SFR) in galaxies in the stellar mass range 8.85 <
log(M*/Msun) < 9.5 at 0.62<z<0.885, to a limit of SFR = 0.1Msun/yr. The
presence of a massive cluster (MS1054-03) in the FIRES field, and of
significant large scale structure in the CDFS field, allows us to study the
environmental dependence of SFRs amongst this population of low-mass galaxies.
Comparing our results with more massive galaxies at this epoch, with our
previous survey (ROLES) at the higher redshift z=1, and with SDSS Stripe 82
data, we find no significant evolution of the stellar mass function of
star-forming galaxies between z=0 and z=1, and no evidence that its shape
depends on environment. The correlation between specific star formation rate
(sSFR) and stellar mass at z=0.75 has a power-law slope of beta=-0.2, with
evidence for a steeper relation at the lowest masses. The normalization of this
correlation lies as expected between that corresponding to z=1 and the present
day. The global SFR density is consistent with an evolution of the form (1+z)^2
over 0<z<1, with no evidence for a dependence on stellar mass. The sSFR of
these star-forming galaxies at z=0.75 does not depend upon the density of their
local environment. Considering just high-density environments, the low-mass end
of the sSFR-M* relation in our data is steeper than that in Stripe 82 at z=0,
and shallower than that measured by ROLES at z=1. Evolution of low-mass
galaxies in dense environments appears to be more rapid than in the general
field. |
Calibrating cosmological radiative transfer simulations with Lyman alpha
forest data: Evidence for large spatial UV background fluctuations at z ~ 5.6
- 5.8 due to rare bright sources: We calibrate here cosmological radiative transfer simulation with ATON/RAMSES
with a range of measurements of the Lyman alpha opacity from QSO absorption
spectra. We find the Lyman alpha opacity to be very sensitive to the exact
timing of hydrogen reionisation. Models reproducing the measured evolution of
the mean photoionisation rate and average mean free path reach overlap at z ~ 7
and predict an accelerated evolution of the Lyman alpha opacity at z > 6
consistent with the rapidly evolving luminosity function of Lyman alpha
emitters in this redshift range. Similar to "optically thin" simulations our
full radiative transfer simulations fail, however, to reproduce the
high-opacity tail of the Lyman alpha opacity PDF at z > 5. We argue that this
is due to spatial UV fluctuations in the post-overlap phase of reionisation on
substantially larger scales than predicted by our source model, where the
ionising emissivity is dominated by large numbers of sub-L* galaxies. We
further argue that this suggests a significant contribution to the ionising UV
background by much rarer bright sources at high redshift. | Cosmological Parameter Estimation Using Current and Future Observations
of Strong Gravitational Lensing: Remarkable development of cosmology is benefited from the increasingly
improved measurements of cosmic distances including absolute distances and
relative distances. In recent years, however, the emerged cosmological tensions
motivate us to explore the independent and precise late-universe probes. The
two observational effects of strong gravitational lensing (SGL), the velocity
dispersions of lens galaxies and the time delays between multiple images, can
provide measurements of relative and absolute distances respectively, and their
combination is possible to break the degeneracies between cosmological
parameters and enable tight constraints on cosmological parameters. In this
paper, we combine the observed 130 SGL systems with velocity-dispersion
measurements and 7 SGL systems with time-delay measurements to constrain
dark-energy cosmological models. It is found that the combination of the two
effects does not significantly break the degeneracies between cosmological
parameters as expected. However, with the simulations of 8000 SGL systems with
well-measured velocity dispersions and 55 SGL systems with well-measured time
delays based on the forthcoming LSST survey, we find that the combination of
two effects can significantly break the parameter degeneracies, and make the
constraint precision of cosmological parameters meet the standard of precision
cosmology. We conclude that the observations of SGL will become a useful
late-universe probe for precisely measuring cosmological parameters. |
The DEHVILS in the Details: Type Ia Supernova Hubble Residual
Comparisons and Mass Step Analysis in the Near-Infrared: Measurements of Type Ia Supernovae (SNe Ia) in the near-infrared (NIR) have
been used both as an alternate path to cosmology compared to optical
measurements and as a method of constraining key systematics for the larger
optical studies. With the DEHVILS sample, the largest published NIR sample with
consistent NIR coverage of maximum light across three NIR bands ($Y$, $J$, and
$H$), we check three key systematics: (i) the reduction in Hubble residual
scatter as compared to the optical, (ii) the measurement of a "mass step" or
lack thereof and its implications, and (iii) the ability to distinguish between
various dust models by analyzing correlations between Hubble residuals in the
NIR and optical. We produce accurate simulations of the DEHVILS sample and
find, contrary to assumptions in the literature, it is $\textit{harder}$ to
differentiate between various dust models than previously understood.
Additionally, we find that fitting with the current SALT3 model does not yield
accurate wavelength-dependent stretch-luminosity correlations, and we propose a
limited solution for this problem. From the data, we see that (i) the standard
deviation of Hubble residual values from NIR bands treated as standard candles
are 0.007-0.042 mag smaller than those in the optical, (ii) the NIR mass step
is not constrainable with the current sample size from DEHVILS, and (iii)
Hubble residuals in the NIR and optical are correlated in both the simulations
and the data. We test a few variations on the number and combinations of
filters and data samples, and we observe that none of our findings or
conclusions are significantly impacted by these modifications. | Cosmology with clustering anisotropies: disentangling dynamic and
geometric distortions in galaxy redshift surveys: We investigate the impact of different observational effects affecting a
precise and accurate measurement of the growth rate of fluctuations from the
anisotropy of clustering in galaxy redshift surveys. We focus on redshift
measurement errors, on the reconstruction of the underlying real-space
clustering and on the apparent degeneracy existing with the geometrical
distortions induced by the cosmology-dependent conversion of redshifts into
distances. We use a suite of mock catalogues extracted from large N-body
simulations, focusing on the analysis of intermediate, mildly non-linear scales
and apply the standard linear dispersion model to fit the anisotropy of the
observed correlation function. We verify that redshift errors up to ~0.2% have
a negligible impact on the precision with which the specific growth rate beta
can be measured. Larger redshift errors introduce a positive systematic error,
which can be alleviated by adopting a Gaussian distribution function of
pairwise velocities. This is, in any case, smaller than the systematic error of
up to 10% due to the limitations of the linear dispersion model, which is
studied in a separate paper. We then show that 50% of the statistical error
budget on beta depends on the deprojection procedure through which the
real-space correlation function is obtained. Finally, we demonstrate that the
degeneracy with geometric distortions can in fact be circumvented. This is
obtained through a modified version of the Alcock-Paczynski test in
redshift-space, which successfully recovers the correct cosmology by searching
for the solution that optimizes the description of dynamical redshift
distortions. For a flat cosmology, we obtain largely independent, robust
constraints on beta and OmegaM. In a volume of 2.4(Gpc/h)^3, the correct OmegaM
is obtained with ~12% error and negligible bias, once the real-space
correlation function is properly reconstructed. |
Measuring the Variance of the Macquart Relation in z-DM Modeling: The Macquart relation describes the correlation between the dispersion
measure (DM) of fast radio bursts (FRBs) and the redshift $z$ of their host
galaxies. The scatter of the Macquart relation is sensitive to the distribution
of baryons in the intergalactic medium (IGM) including those ejected from
galactic halos through feedback processes. The width of the distribution in DMs
from the cosmic web (${\rm DM}_{\rm cosmic}$) is parameterized by a fluctuation
parameter $F$, which is related to the cosmic DM variance by $\sigma_{\rm DM}=
F z^{-0.5}$. In this work, we present a new measurement of $F$ using 78 FRBs of
which 21 have been localized to host galaxies. Our analysis simultaneously fits
for the Hubble constant $H_0$ and the DM distribution due to the FRB host
galaxy. We find that the fluctuation parameter is degenerate with these
parameters, most notably $H_0$, and use a uniform prior on $H_0$ to measure
$\log_{10} F > -0.89$ at the $3\sigma$ confidence interval and a new constraint
on the Hubble constant $H_0 = 85.3_{-8.1}^{+9.4} \, {\rm km \, s^{-1} \,
Mpc^{-1}}$. Using a synthetic sample of 100 localized FRBs, the constraint on
the fluctuation parameter is improved by a factor of $\sim 2$. Comparing our
$F$ measurement to simulated predictions from cosmological simulation
(IllustrisTNG), we find agreement between $0.4 < z < 2$. However, at $z < 0.4$,
the simulations underpredict $F$ which we attribute to the rapidly changing
extragalactic DM excess distribution at low redshift. | The universal multiplicity function: counting halos and voids: We present a novel combination of the excursion-set approach with the peak
theory formalism in Lagrangian space and provide accurate predictions for halo
and void statistics over a wide range of scales. The set-up is based on an
effective moving barrier. Besides deriving the corresponding numerical
multiplicity function, we introduce a new analytical formula reaching the
percent level agreement with the exact numerical solution obtained via Monte
Carlo realizations down to small scales, $\sim 10^{12} h^{-1}\mathrm{M_\odot}$.
In the void case, we derive the dependence of the effective moving barrier on
the void formation threshold, $\delta_{\rm v}$, by comparison against the
Lagrangian void size function measured in the Dark Energy and Massive Neutrinos
Universe simulations. We discuss the mapping from Lagrangian to Eulerian space
for both halos and voids; adopting the spherical symmetry approximation, we
obtain a strong agreement at intermediate and large scales. Finally, using the
effective moving barrier, we derive Lagrangian void density profiles accurately
matching measurements from cosmological simulations, a major achievement
towards using void profiles for precision cosmology with the next generation of
galaxy surveys. |
Quintessence and tachyon dark energy models with a constant equation of
state parameter: In this work we determine the correspondence between quintessence and tachyon
dark energy models with a constant dark energy equation of state parameter,
$w_e$. Although the evolution of both the Hubble parameter and the scalar field
potential with redshift is the same, we show that the evolution of
quintessence/tachyon scalar fields with redshift is, in general, very
different. We explicity demonstrate that if $w_e \neq -1$ the potentials need
to be very fine-tuned for the relative perturbation on the equation of state
parameter, $\Delta w_e/(1+w_e) \ll 1$, to be very small around the present
time. We also discuss possible implications of our results for the
reconstruction of the evolution of $w_e$ with redshift using varying couplings. | Towards the Chalonge 16th Paris Cosmology Colloquium 2012: Highlights
and Conclusions of the Chalonge 15th Paris Cosmology Colloquium 2011: The Chalonge 15th Paris Cosmology Colloquium 2011 was held on 20-22 July in
the historic Paris Observatory's Perrault building, in the Chalonge School
spirit combining real cosmological/astrophysical data and hard theory
predictive approach connected to them in the Warm Dark Matter Standard Model of
the Universe: News and reviews from Herschel, QUIET, Atacama Cosmology
Telescope (ACT), South Pole Telescole (SPT), Planck, PIXIE, the JWST, UFFO,
KATRIN and MARE experiments; astrophysics, particle and nuclear physics warm
dark matter (DM) searches and galactic observations, related theory and
simulations, with the aim of synthesis, progress and clarification. Philippe
Andre, Peter Biermann, Pasquale Blasi, Daniel Boyanovsky, Carlo Burigana,
Hector de Vega, Joanna Dunkley, Gerry Gilmore, Alexander Kashlinsky, Alan
Kogut, Anthony Lasenby, John Mather, Norma Sanchez, Alexei Smirnov, Sylvaine
Turck-Chieze present here their highlights of the Colloquium. Ayuki Kamada and
Sinziana Paduroiu present here their poster highlights. LambdaWDM (Warm Dark
Matter) is progressing impressively over LambdaCDM whose galactic scale crisis
and decline are staggering. The International School Daniel Chalonge issued an
statement of strong support to the James Webb Space Telescope (JSWT). The
Daniel Chalonge Medal 2011 was awarded to John C. Mather, Science PI of the
JWST. Summary and conclusions are presented by H. J. de Vega, M. C. Falvella
and N. G. Sanchez. Overall, LambdaWDM and keV scale DM particles deserve
dedicated astronomical and laboratory experimental searches, theoretical work
and simulations. KATRIN experiment in the future could perhaps adapt its set-up
to look to keV scale sterile neutrinos. It will be a a fantastic discovery to
detect dark matter in a beta decay. Photos of the Colloquium are included.
(Abridged) |
Coupled Early Dark Energy: Early dark energy has emerged as one of the more promising approaches to
address the Hubble tension - the statistically significant disparity between
measurements of the Hubble constant made using data from different epochs in
cosmic history. However, the idea is not without its own set of challenges,
both from the data, in the effects it has on other measurements, such as the
large-scale structure tension, and from theoretical concerns such as technical
naturalness and the introduction of a new coincidence problem in cosmology. In
this brief note, delivered as an invited plenary lecture at the {\it 15th
Frontiers of Fundamental Physics conference}, I discuss how some of the
fine-tuning problems of early dark energy can be ameliorated by using couplings
to other fields already present in cosmology, and for which the epoch of
matter-radiation equality is already a special one. The resulting models -
neutrino assisted early dark energy, and chameleon early dark energy - provide
testable, theoretically robust implementations of this general idea. I will
discuss the formulation and the cosmology of such approaches, including some
constraints arising from both observational and theoretical considerations. | Spatially Resolved Chandra HETG Spectroscopy of the NLR Ionization Cone
in NGC 1068: We present initial results from a new 440-ks Chandra HETG GTO observation of
the canonical Seyfert 2 galaxy NGC 1068. The proximity of NGC 1068, together
with Chandra's superb spatial and spectral resolution, allow an unprecedented
view of its nucleus and circumnuclear NLR. We perform the first spatially
resolved high-resolution X-ray spectroscopy of the `ionization cone' in any
AGN, and use the sensitive line diagnostics offered by the HETG to measure the
ionization state, density, and temperature at discrete points along the ionized
NLR. We argue that the NLR takes the form of outflowing photoionized gas,
rather than gas that has been collisionally ionized by the small-scale radio
jet in NGC 1068. We investigate evidence for any velocity gradients in the
outflow, and describe our next steps in modeling the spatially resolved spectra
as a function of distance from the nucleus. |
Gravitational tests of electroweak relaxation: We consider a scenario in which the electroweak scale is stabilized via the
relaxion mechanism during inflation, focussing on the case in which the
back-reaction potential is generated by the confinement of new strongly
interacting vector-like fermions. If the reheating temperature is sufficiently
high to cause the deconfinement of the new strong interactions, the
back-reaction barrier then disappears and the Universe undergoes a second
relaxation phase. This phase stops when the temperature drops sufficiently for
the back-reaction to form again. We identify the regions of parameter space in
which the second relaxation phase does not spoil the successful stabilization
of the electroweak scale. In addition, the generation of the back-reaction
potential that ends the second relaxation phase can be associated to a strong
first order phase transition. We then study when such transition can generate a
gravitational wave signal in the range of detectability of future
interferometer experiments. | An Anti-halo Void Catalogue of the Local Super-Volume: We construct an anti-halo void catalogue of $150$ voids with radii $R >
10\,h^{-1}\mathrm{\,Mpc}$ in the Local Super-Volume
($<135\,h^{-1}\mathrm{\,Mpc}$ from the Milky Way), using posterior resimulation
of initial conditions inferred by field-level inference with Bayesian Origin
Reconstruction from Galaxies (\codefont{BORG}). We describe and make use of a
new algorithm for creating a single, unified void catalogue by combining
different samples from the posterior. The catalogue is complete out to
$135\,h^{-1}\mathrm{\,Mpc}$, with void abundances matching theoretical
predictions. Finally, we compute stacked density profiles of those voids which
are reliably identified across posterior samples, and show that these are
compatible with $\Lambda$CDM expectations once environmental selection (e.g.,
the estimated $\sim 4\%$ under-density of the Local Super-Volume) is accounted
for. |
Revisit Short Term X-ray Spectral Variability of NGC 4151 with Chandra: We present new X-ray spectral data for the Seyfert 1 nucleus in NGC 4151
observed with Chandra for 200 ks. A significant ACIS pileup is present,
resulting in a non-linear count rate variation during the observation. With
pileup corrected spectral fitting, we are able to recover the spectral
parameters and find consistency with those derived from unpiled events in the
ACIS readout streak and outer region from the bright nucleus. The absorption
corrected 2-10 keV flux of the nucleus varied between 6E-11 and 1E-10 erg
s^{-1} cm^{-2}. Similar to earlier Chandra studies of NGC 4151 at a historical
low state, the photon indices derived from the same absorbed power-law model
are \Gamma~0.7-0.9. However, we show that \Gamma is highly dependent on the
adopted spectral models. Fitting the power-law continuum with a Compton
reflection component gives \Gamma~1.1. By including passage of non-uniform
X-ray obscuring clouds, we can reproduce the apparent flat spectral states with
\Gamma~1.7, typical for Seyfert 1 AGNs. The same model also fits the hard
spectra from previous ASCA "long look" observation of NGC 4151 in the lowest
flux state. The spectral variability during our observation can be interpreted
as variations in intrinsic soft continuum flux relative to a Compton reflection
component that is from distant cold material and constant on short time scale,
or variations of partially covering absorber in the line of sight towards the
nucleus. An ionized absorber model with ionization parameter \log\xi ~ 0.8-1.1
can also fit the low-resolution ACIS spectra. If the partial covering model is
correct, adopting a black hole mass M_{BH} ~ 4.6E+7 Msun we constrain the
distance of the obscuring cloud from the central black hole to be r<~9
light-days, consistent with the size of broad emission line region of NGC 4151
from optical reverberation mapping. | The Structure of a Low-Metallicity Giant Molecular Cloud Complex: To understand the impact of low metallicities on giant molecular cloud (GMC)
structure, we compare far infrared dust emission, CO emission, and dynamics in
the star-forming complex N83 in the Wing of the Small Magellanic Cloud. Dust
emission (measured by Spitzer as part of the S3MC and SAGE-SMC surveys) probes
the total gas column independent of molecular line emission and traces
shielding from photodissociating radiation. We calibrate a method to estimate
the dust column using only the high-resolution Spitzer data and verify that
dust traces the ISM in the HI-dominated region around N83. This allows us to
resolve the relative structures of H2, dust, and CO within a giant molecular
cloud complex, one of the first times such a measurement has been made in a
low-metallicity galaxy. Our results support the hypothesis that CO is
photodissociated while H2 self-shields in the outer parts of low-metallicity
GMCs, so that dust/self shielding is the primary factor determining the
distribution of CO emission. Four pieces of evidence support this view. First,
the CO-to-H2 conversion factor averaged over the whole cloud is very high 4-11
\times 10^21 cm^-2/(K km/s), or 20-55 times the Galactic value. Second, the
CO-to-H2 conversion factor varies across the complex, with its lowest (most
nearly Galactic) values near the CO peaks. Third, bright CO emission is largely
confined to regions of relatively high line-of-sight extinction, A_V >~ 2 mag,
in agreement with PDR models and Galactic observations. Fourth, a simple model
in which CO emerges from a smaller sphere nested inside a larger cloud can
roughly relate the H2 masses measured from CO kinematics and dust. |
Formation and structure of ultralight bosonic dark matter halos: We simulate the formation and evolution of ultralight bosonic dark matter
halos from cosmological initial conditions. Using zoom-in techniques we are
able to resolve the detailed interior structure of the halos. We observe the
formation of solitonic cores and confirm the core-halo mass relation previously
found by Schive et al. The cores exhibit strong quasi-normal oscillations that
remain largely undamped on evolutionary timescales. On the other hand, no
conclusive growth of the core mass by condensation or relaxation can be
detected. In the incoherent halo surrounding the cores, the scalar field
density profiles and velocity distributions show no significant deviation from
collisionless N-body simulations on scales larger than the coherence length.
Our results are consistent with the core properties being determined mainly by
the coherence length at the time of virialization, whereas the
Schr\"odinger-Vlasov correspondence explains the halo properties when averaged
on scales greater than the coherence length. | The evolution of the mass-metallicity relation in galaxies of different
morphological types: By means of chemical evolution models for ellipticals, spirals and irregular
galaxies, we aim at investigating the physical meaning and the redshift
evolution of the mass-metallicity relation as well as how this relation is
connected with galaxy morphology. {abridged} We assume that galaxy morphologies
do not change with cosmic time. We present a method to account for a spread in
the epochs of galaxy formation and to refine the galactic mass grid. (abridged)
We compare our predictions to observational results obtained for galaxies
between redshifts 0.07 and 3.5. We reproduce the mass-metallicity (MZ) relation
mainly by means of an increasing efficiency of star formation with mass in
galaxies of all morphological types, without any need to invokegalactic
outflows favoring the loss of metals in the less massive galaxies. Our
predictions can help constraining the slope and the zero point of the observed
local MZ relation, both affected by uncertainties related to the use of
different metallicity calibrations. We show how, by considering the MZ, the O/H
vs star formation rate (SFR), and the SFR vs galactic mass diagrams at various
redshifts, it is possible to constrain the morphology of the galaxies producing
these relations. Our results indicate that the galaxies observed at z=3.5
should be mainly proto-ellipticals, whereas at z=2.2 the observed galaxies
consist of a morphological mix of proto-spirals and proto-ellipticals. At lower
redshifts, the observed MZ relation is well reproduced by considering both
spirals and irregulars. (abridged) |
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