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Baryon acoustic oscillations with the cross-correlation of spectroscopic
and photometric samples: The baryon acoustic oscillation (BAO) experiment requires a sufficiently
dense sampling of large-scale structure tracers with spectroscopic redshift,
which is observationally expensive especially at high redshifts $z\simgt 1$.
Here we present an alternative route of the BAO analysis that uses the
cross-correlation of sparse spectroscopic tracers with a much denser
photometric sample, where the spectroscopic tracers can be quasars or bright,
rare galaxies that are easier to access spectroscopically. We show that
measurements of the cross-correlation as a function of the transverse comoving
separation rather than the angular separation avoid a smearing of the BAO
feature without mixing the different scales at different redshifts in the
projection, even for a wide redshift slice $\Delta z\simeq 1$. The bias,
scatter, and catastrophic redshift errors of the photometric sample affect only
the overall normalization of the cross-correlation which can be marginalized
over when constraining the angular diameter distance. As a specific example, we
forecast an expected accuracy of the BAO geometrical test via the
cross-correlation of the SDSS and BOSS spectroscopic quasar sample with a dense
photometric galaxy sample that is assumed to have a full overlap with the
SDSS/BOSS survey region. We show that this cross-correlation BAO analysis
allows us to measure the angular diameter distances to a fractional accuracy of
about 10% at each redshift bin over $1\simlt z\simlt 3$, if the photometric
redshift errors of the galaxies, $\sigma_z/(1+z)$, are better than 10-20%
level. | A scaling relation between merger rate of galaxies and their close pair
count: We study how to measure the galaxy merger rate from the observed close pair
count. Using a high-resolution N-body/SPH cosmological simulation, we find an
accurate scaling relation between galaxy pair counts and merger rates down to a
stellar mass ratio of about 1:30. The relation explicitly accounts for the
dependence on redshift (or time), on pair separation, and on mass of the two
galaxies in a pair. With this relation, one can easily obtain the mean merger
timescale for a close pair of galaxies. The use of virial masses, instead of
stellar masses, is motivated by the fact that the dynamical friction time scale
is mainly determined by the dark matter surrounding central and satellite
galaxies. This fact can also minimize the error induced by uncertainties in
modeling star formation in the simulation. Since the virial mass can be read
from the well-established relation between the virial masses and the stellar
masses in observation, our scaling relation can be easily applied to
observations to obtain the merger rate and merger time scale. For major merger
pairs (1:1-1:4) of galaxies above a stellar mass of 4*10^10 M_sun/h at z=0.1,
it takes about 0.31 Gyr to merge for pairs within a projected distance of 20
kpc/h with stellar mass ratio of 1:1, while the time taken goes up to 1.6 Gyr
for mergers with stellar mass ratio of 1:4. Our results indicate that a single
timescale usually used in literature is not accurate to describe mergers with
the stellar mass ratio spanning even a narrow range from 1:1 to 1:4. |
Denoising Weak Lensing Mass Maps with Deep Learning: Weak gravitational lensing is a powerful probe of the large-scale cosmic
matter distribution. Wide-field galaxy surveys allow us to generate the
so-called weak lensing maps, but actual observations suffer from noise due to
imperfect measurement of galaxy shape distortions and to the limited number
density of the source galaxies. In this paper, we explore a deep-learning
approach to reduce the noise. We develop an image-to-image translation method
with conditional adversarial networks (CANs), which learn efficient mapping
from an input noisy weak lensing map to the underlying noise field. We train
the CANs using $30000$ image pairs obtained from $1000$ ray-tracing simulations
of weak gravitational lensing. We show that the trained CANs reproduce the true
one-point probability distribution function (PDF) of the noiseless lensing map
with a bias less than $1\sigma$ on average, where $\sigma$ is the statistical
error. We perform a Fisher analysis to make forecast for cosmological parameter
inference with the one-point lensing PDF. By our denoising method using CANs,
the first derivative of the PDF with respect to the cosmic mean matter density
and the amplitude of the primordial curvature perturbations becomes larger by
$\sim50\%$. This allows us to improve the cosmological constraints by
$\sim30-40\%$ with using observational data from ongoing and upcoming galaxy
imaging surveys. | Could our Universe have begun with Negative Lambda?: In this paper we present an informal description of the Cyclic Inflation
scenario which allows our universe to "start" with a negative potential energy,
inflate, and then gracefully exit to a positive potential energy universe. We
discuss how this scenario fares in comparison with the standard inflationary
paradigm with respect to the classic cosmological puzzles associated with the
horizon, flatness and isotropy of our current universe. We also discuss some of
the most debilitating problems of cyclic cosmologies, Tolman's entropy problem,
and the problem with the overproduction of blackholes. We also sketch the
calculation of the primordial spectrum in these models and possible observable
signatures. We end with a special focus on the exit mechanism where the
universe can transition from the negative to a positive potential region. The
treatise is based on an ongoing collaboration between the authors and closely
follows conference presentations given on the subject by TB. |
The observed $M - σ$ relations imply that SMBHs grow by cold
chaotic accretion: We argue that current observations of $M - \sigma$ relations for galaxies can
be used to constrain theories of super-massive black holes (SMBH) feeding. In
particular, assuming that SMBH mass is limited only by the feedback on the gas
that feeds it, we show that SMBHs fed via a planar galaxy scale gas flow, such
as a disc or a bar, should be much more massive than their counterparts fed by
quasi-spherical inflows. This follows from the relative inefficiency of AGN
feedback on a flattened inflow. We find that even under the most optimistic
conditions for SMBH feedback on flattened inflows, the mass at which the SMBH
expels the gas disc and terminates its own growth is a factor of several higher
than the one established for quasi-spherical inflows. Any beaming of feedback
away from the disc and any disc self-shadowing strengthens this result further.
Contrary to this theoretical expectation, recent observations have shown that
SMBH in pseudobulge galaxies (which are associated with barred galaxies) are
typically under- rather than over-massive when compared with their classical
bulge counterparts at a fixed value of $\sigma$. We conclude from this that
SMBHs are not fed by large (100 pc to many kpc) scale gas discs or bars, most
likely because such planar flows are turned into stars too efficiently to allow
any SMBH growth. Based on this and other related observational evidence, we
argue that most SMBHs grow by chaotic accretion of gas clouds with a small and
nearly randomly distributed direction of angular momentum. | DES Y3 + KiDS-1000: Consistent cosmology combining cosmic shear surveys: We present a joint cosmic shear analysis of the Dark Energy Survey (DES Y3)
and the Kilo-Degree Survey (KiDS-1000) in a collaborative effort between the
two survey teams. We find consistent cosmological parameter constraints between
DES Y3 and KiDS-1000 which, when combined in a joint-survey analysis, constrain
the parameter $S_8 = \sigma_8 \sqrt{\Omega_{\rm m}/0.3}$ with a mean value of
$0.790^{+0.018}_{-0.014}$. The mean marginal is lower than the maximum a
posteriori estimate, $S_8=0.801$, owing to skewness in the marginal
distribution and projection effects in the multi-dimensional parameter space.
Our results are consistent with $S_8$ constraints from observations of the
cosmic microwave background by Planck, with agreement at the $1.7\sigma$ level.
We use a Hybrid analysis pipeline, defined from a mock survey study quantifying
the impact of the different analysis choices originally adopted by each survey
team. We review intrinsic alignment models, baryon feedback mitigation
strategies, priors, samplers and models of the non-linear matter power
spectrum. |
The deepest image of the Universe at a wavelength of 15 microns: We present photometry, photometric redshifts and extra galactic number counts
for ultra deep 15 micron mapping of the gravitational lensing cluster Abell
2218 (A2218), which is the deepest image taken by any facility at this
wavelength. This data resolves the cosmic infrared background (CIRB) beyond the
80% that blank field AKARI surveys aim to achieve. To gain an understanding of
galaxy formation and evolution over the age of the Universe a necessary step is
to fully resolve the CIRB, which represents the dust-shrouded cosmic star
formation history. Observing through A2218 gives magnifications of up to a
factor of 10, thus allowing the sampling of a more representative spread of
high redshift galaxies, which comprise the bulk of the CIRB. 19 pointed
observations were taken by AKARIs IRC MIR-L channel, and a final combined image
with an area of 122.3 square arcminutes and effective integration time of 8460
seconds was achieved. The 5 sigma sensitivity limit is estimated at 41.7 uJy.
An initial 5 sigma catalogue of 565 sources was extracted giving 39 beams per
source, which shows the image is confusion limited. Our 15 micron number counts
show strong evolution consistent with galaxy evolution models that incorporate
downsizing in star formation. | Detection of Dipole Modulation in CMB Temperature Anisotropy Maps from
WMAP and Planck using Artificial Intelligence: Breakdown of rotational invariance of the primordial power spectrum manifests
in the statistical anisotropy of the observed Cosmic Microwave Background (CMB)
radiation. Hemispherical power asymmetry in the CMB may be caused due to a
dipolar modulation, indicating the presence of a preferred direction.
Appropriately re-scaled local variance maps of the CMB temperature anisotropy
data effectively encapsulate this dipolar pattern. As a first-of-its-kind
method, we train Artificial Neural Networks (ANNs) with such local variances as
input features to distinguish statistically isotropic CMB maps from dipole
modulated ones. Our trained ANNs are able to predict components of the
amplitude times the unit vector of the preferred direction for mixed sets of
modulated and unmodulated maps, with goodness of fit ($R^2$) scores $>0.97$ for
full sky, and $>0.96$ for partial sky coverage. On all observed
foreground-cleaned CMB maps, the ANNs detect the dipolar modulation signal with
overall consistent values of amplitudes and directions. This detection is
significant at $97.21\%-99.38\%$ C.L. for all full sky maps, and at
$98.34\%-100\%$ C.L. for all partial sky maps. Robustness of the signal holds
across full and partial skies, various foreground cleaning methods, inpainting
algorithms, instruments and all the different periods of observation for Planck
and WMAP satellites. The significant and robust detection of the signal, in
addition to the consistency of values of amplitude and directions, as found
independent of any pre-existing methods, further mitigates the criticisms of
look-elsewhere effects and a posteriori inferences for the preferred dipole
direction in the CMB. |
The power spectrum from the angular distribution of galaxies in the
CFHTLS-Wide fields at redshift ~0.7: We measure the real-space galaxy power spectrum on large scales at redshifts
0.5 to 1.2 using optical colour-selected samples from the CFHT Legacy Survey.
With the redshift distributions measured with a preliminary ~14000
spectroscopic redshifts from the VIMOS Public Extragalactic Redshift Survey
(VIPERS), we deproject the angular distribution and directly estimate the
three-dimensional power spectrum. We use a maximum likelihood estimator that is
optimal for a Gaussian random field giving well-defined window functions and
error estimates. This measurement presents an initial look at the large-scale
structure field probed by the VIPERS survey. We measure the galaxy bias of the
VIPERS-like sample to be b_g=1.38 +- 0.05 (sigma_8=0.8) on scales k<0.2h/mpc
averaged over 0.5<z<1.2. We further investigate three photometric redshift
slices, and marginalising over the bias factors while keeping other LCDM
parameters fixed, we find the matter density Omega_m=0.30+-0.06. | A Spitzer-IRS Spectroscopic atlas of early-type galaxies in the Revised
Shapley-Ames Catalog: We produce an atlas of homogeneously reduced and calibrated low resolution
IRS spectra of the nuclear regions of nearby early-type galaxies (i.e. Es and
S0s, ETGs), in order to build a reference sample in the mid-infrared window.
From the Spitzer Heritage Archive we extract ETGs in the "Revised Shapley-Ames
Catalog of Bright Galaxies" having an IRS SL and/or LL spectrum. We recover 91
spectra out of 363 galaxies classified as ETGs in the catalog: 56 E (E0-E6), 8
mixed E/S0+S0/E, 27 S0 (both normal and barred - SB0) plus mixed types
SB0/Sa+SB0/SBa. For each galaxy, we provide the fully reduced and calibrated
spectrum, the intensity of nebular and molecular emission lines as well as of
the Polycyclic Aromatic Hydrocarbons (PAHs) after a template spectrum of a
passively evolving ETG has been subtracted. Spectra are classified into five
mid-infrared classes, ranging from AGN (class-4) and star forming nuclei
(class-3), transition class-2 (with PAHs) and class-1 (no-PAHs) to passively
evolving nuclei (class-0). A demographic study of mid-infrared spectra shows
that Es are significantly more passive than S0s: 46^{+11}_{-10}% of Es and
20^{+11}_{-7}% of S0s have a spectrum of class-0. Emission lines are revealed
in 64^{+12}_{-6}% of ETGs. The H_2-S(1) line is found with similar rate in Es
(34^{+10}_{-8}%) and in S0s (51^{+15}_{-12}%). PAHs are detected in
47^{+8}_{-7}% of ETGs, but only 9^{+4}_{-3}% have PAHs ratios typical of star
forming galaxies. Several indicators, such as peculiar morphologies and
kinematics, dust--lane irregular shape, radio and X-ray properties, suggest
that mid-infrared spectral classes are connected to phases of
accretion/feedback phenomena occurring in the nuclei of ETGs. |
Global 21cm signal experiments: A designer's guide: [Abridged] The spatially averaged global spectrum of the redshifted 21cm line
has generated much experimental interest, for it is potentially a direct probe
of the Epoch of Reionization and the Dark Ages. Since the cosmological signal
here has a purely spectral signature, most proposed experiments have little
angular sensitivity. This is worrisome because with only spectra, the global
21cm signal can be difficult to distinguish from foregrounds such as Galactic
synchrotron radiation, as both are spectrally smooth and the latter is orders
of magnitude brighter. We establish a mathematical framework for global signal
data analysis in a way that removes foregrounds optimally, complementing
spectra with angular information. We explore various experimental design
trade-offs, and find that 1) with spectral-only methods, it is impossible to
mitigate errors that arise from uncertainties in foreground modeling; 2)
foreground contamination can be significantly reduced for experiments with fine
angular resolution; 3) most of the statistical significance in a positive
detection during the Dark Ages comes from a characteristic high-redshift trough
in the 21cm brightness temperature; and 4) Measurement errors decrease more
rapidly with integration time for instruments with fine angular resolution. We
show that if observations and algorithms are optimized based on these findings,
an instrument with a 5 degree beam can achieve highly significant detections
(greater than 5-sigma) of even extended (high Delta-z) reionization scenarios
after integrating for 500 hrs. This is in contrast to instruments without
angular resolution, which cannot detect gradual reionization. Abrupt ionization
histories can be detected at the level of 10-100's of sigma. The expected
errors are also low during the Dark Ages, with a 25-sigma detection of the
expected cosmological signal after only 100 hrs of integration. | A little inflation at the cosmological QCD phase transition: We reexamine the recently proposed "little inflation" scenario that allows
for a strong first order phase-transition of QCD at non-negligible baryon
number in the early universe and its possible observable consequences. The
scenario is based on the assumptions of a strong mechanism for baryogenesis and
a quasistable QCD-medium state which triggers a short inflationary period of
inflation diluting the baryon asymmetry to the value observed today. The
cosmological implications are reexamined, namely effects on primordial density
fluctuations up to dark matter mass scales of $M_{max} \sim 1 M_{\astrosun}$,
change in the spectral slope up to $M_{max} \sim 10^6 M_{\astrosun}$,
production of seeds for the present galactic and extragalactic magnetic fields
and a gravitational wave spectrum with a peak frequency around $\nu_{peak} \sim
4 \cdot 10^{-8} Hz$. We discuss the issue of nucleation in more detail and
employ a chiral effective model of QCD to study the impact on small scale
structure formation. |
The Astrophysics of the Intracluster Plasma: [Abridged] Since 1971 observations in X rays of thousands galaxy clusters
have uncovered huge amounts of hot baryons filling up the deep gravitational
potential wells provided by dark matter (DM) halos with sizes of millions
light-years and masses of some 10^15 M_sun. At temperatures T~10^8 K and with
average densities of n~1 particle per liter, such baryons add up to some 10^14
M_sun. With the neutralizing electrons, they constitute the best
proton-electron plasma in the Universe (Intra Cluster Plasma, ICP). A key
physical feature of the ICP is constituted by its good local Thermal
equilibrium, and by its overall hydrostatic condition in the DM wells,
modulated by entropy. The latter is set up in the cluster center by the initial
halo collapse, and is progressively added at the outgrowing cluster boundary by
standing shocks in the supersonic flow of intergalactic gas into the DM wells.
We review these entropy-based models and discuss their outcomes and predictions
concerning the ICP observables in X rays and in microwaves. The results provide
a baseline for disentangling a number of additional and intriguing physical
processes superposed to the general equilibrium. We cover: the central entropy
erosion produced by radiative cooling vs. the intermittent energy inputs mainly
due to active galactic nuclei and mergers; outer turbulent support linked with
weakening shocks and decreasing inflow through the virial boundary, causing
reduced entropy production; the development from high to low entropy levels
throughout a typical cluster; perturbations of the equilibrium up to outright
disruption due to deep impacts of infalling galaxy groups or collisions with
comparable companion clusters; relativistic energy distributions of electrons
accelerated during such events, producing extended radio emission by
synchrotron radiation, and contributing to non-thermal pressure support for the
ICP. | Quantifying and controlling biases in dark matter halo concentration
estimates: We use bootstrapping to estimate the bias of concentration estimates on
N-body dark matter halos as a function of particle number. We find that
algorithms based on the maximum radial velocity and radial particle binning
tend to overestimate the concentration by 15%-20% for halos sampled with 200
particles and by 7% - 10% for halos sampled with 500 particles. To control this
bias at low particle numbers we propose a new algorithm that estimates halo
concentrations based on the integrated mass profile. The method uses the full
particle information without any binning, making it reliable in cases when low
numerical resolution becomes a limitation for other methods. This method
reduces the bias to less than 3% for halos sampled with 200-500 particles. The
velocity and density methods have to use halos with at least 4000 particles in
order to keep the biases down to the same low level. We also show that the
mass-concentration relationship could be shallower than expected once the
biases of the different concentration measurements are taken into account.
These results show that bootstrapping and the concentration estimates based on
the integrated mass profile are valuable tools to probe the internal structure
of dark matter halos in numerical simulations. |
Designing Decisive Detections: We present a general Bayesian formalism for the definition of Figures of
Merit (FoMs) quantifying the scientific return of a future experiment. We
introduce two new FoMs for future experiments based on their model selection
capabilities, called the decisiveness of the experiment and the expected
strength of evidence. We illustrate these by considering dark energy probes,
and compare the relative merits of stage II, III and IV dark energy probes. We
find that probes based on supernovae and on weak lensing perform rather better
on model selection tasks than is indicated by their Fisher matrix FoM as
defined by the Dark Energy Task Force. We argue that our ability to optimize
future experiments for dark energy model selection goals is limited by our
current uncertainty over the models and their parameters, which is ignored in
the usual Fisher matrix forecasts. Our approach gives a more realistic
assessment of the capabilities of future probes and can be applied in a variety
of situations. | Skewness in CMB temperature fluctuations from curved cosmic
(super-)strings: We compute the one-point probability distribution function of small-angle
cosmic microwave background temperature fluctuations due to curved cosmic
(super-)strings with a simple model of string network by performing Monte Carlo
simulations. Taking into account of the correlation between the curvature and
the velocity of string segments, there appear non-Gaussian features,
specifically non-Gaussian tails and a skewness, in the one-point pdf. The
obtained sample skewness for the conventional field-theoretic cosmic strings is
$g_1\approx -0.14$, which is consistent with the result reported by Fraisse et
al.. We also discuss the dependence of the pdf on the intercommuting
probability. We find that the standard deviation of the Gaussian part increases
and non-Gaussian features are suppressed as the intercommuting probability
decreases. For sufficiently small intercommuting probability, the skewness is
given by $\lesssim$ (a\ few) $\times 10^{-2}$. |
Super-solar Metal Abundances in Two Galaxies at z ~ 3.57 revealed by the
GRB 090323 Afterglow Spectrum: We report on the surprisingly high metallicity measured in two absorption
systems at high redshift, detected in the Very Large Telescope spectrum of the
afterglow of the gamma-ray burst GRB 090323. The two systems, at redshift
z=3.5673 and z=3.5774 (separation Delta v ~ 660 km/s), are dominated by the
neutral gas in the interstellar medium of the parent galaxies. From the singly
ionized zinc and sulfur, we estimate oversolar metallicities of [Zn/H]
=+0.29+/-0.10 and [S/H] = +0.67+/- 0.34, in the blue and red absorber,
respectively. These are the highest metallicities ever measured in galaxies at
z>3. We propose that the two systems trace two galaxies in the process of
merging, whose star formation and metallicity are heightened by the
interaction. This enhanced star formation might also have triggered the birth
of the GRB progenitor. As typically seen in star-forming galaxies, the
fine-structure absorption SiII* is detected, both in G0 and G1. From the
rest-frame UV emission in the GRB location, we derive a relatively high, not
corrected for dust extinction, star-formation rate SFR ~ 6 Msun/yr. These
properties suggest a possible connection between some high-redshift GRB host
galaxies and high-z massive sub-millimeter galaxies, which are characterized by
disturbed morphologies and high metallicities. Our result provides additional
evidence that the dispersion in the chemical enrichment of the Universe at high
redshift is substantial, with the existence of very metal rich galaxies less
than two billion years after the Big Bang. | Reconstruction of the neutrino mass as a function of redshift: We reconstruct the neutrino mass as a function of redshift, z, from current
cosmological data using both standard binned priors and linear spline priors
with variable knots. Using cosmic microwave background temperature,
polarization and lensing data, in combination with distance measurements from
baryonic acoustic oscillations and supernovae, we find that the neutrino mass
is consistent with $\sum m_\nu(z)$ = const. We obtain a larger bound on the
neutrino mass at low redshifts coinciding with the onset of dark energy
domination, $\sum m_\nu(z = 0)$ < 1.46 eV (95% CL). This result can be
explained either by the well-known degeneracy between $\sum m_\nu$ and
$\Omega_\Lambda$ at low redshifts, or by models in which neutrino masses are
generated very late in the Universe. We finally convert our results into
cosmological limits for models with non-relativistic neutrino decay and find
$\sum m_\nu$ < 0.21 eV (95% CL), which would be out of reach for the KATRIN
experiment. |
Constraints from Ly-$α$ forests on non-thermal dark matter
including resonantly-produced sterile neutrinos: We use BOSS DR9 quasars to constrain 2 cases of dark matter models:
cold-plus-warm (C+WDM) where the warm component is a thermal relic, and sterile
neutrinos resonantly produced in the presence of a lepton asymmetry (RPSN). We
establish constraints on the relic mass m_x and its relative abundance
$F=\Omega_{wdm}/\Omega_{dm}$ using a suite of hydrodynamical simulations in 28
C+WDM configurations. We find that the 3 sigma bounds approximately follow F ~
$0.35 (keV/m_x)^{-1.37}$ from BOSS alone. We also establish constraints on
sterile neutrino mass and mixing angle by producing the non-linear flux power
spectrum of 8 RPSN models, where the input linear power spectrum is computed
directly from the particles distribution functions. We find values of lepton
asymmetries for which sterile neutrinos as light as 6.5 keV (resp. 3.5 keV) are
consistent with BOSS at the 2 sigma (resp. 3sigma) level. These limits tighten
by close to a factor of 2 for lepton asymmetries departing from those yielding
the coolest distribution functions.
Our Ly-a forest bounds can be strengthened if we include higher-resolution
data from XQ-100, HIRES and MIKE. At these smaller scales, the flux power
spectrum exhibits a suppression that can be due to Doppler broadening, IGM
pressure smoothing or free-streaming of WDM particles. In the current work, we
show that if one extrapolates temperatures from lower redshifts via broken
power laws in T_0 and gamma, then our 3 sigma C+WDM bounds strengthen to F~
$0.20 (keV/m_x)^{-1.37}$, and the lightest RPSN consistent with our extended
data set have masses of 7.0 keV at the 3 sigma level. Using dedicated
hydrodynamical simulations, we show that a 7 keV sterile neutrino produced in a
lepton asymmetry $L = 8 \times 10^{-6}$ is consistent at 1.9 sigma (resp. 3.1
sigma) with BOSS (resp. BOSS + higher-resolution), for the thermal history
models tested in this work. | M94 As A Unique Testbed for Black Hole Mass Estimates and AGN Activity
At Low Luminosities: We discuss the peculiar nature of the nucleus of M94 (NGC 4736) in the
context of new measurements of the broad H_alpha emission from HST-STIS
observations. We show that this component is unambiguously associated with the
high-resolution X-ray, radio, and variable UV sources detected at the optical
nucleus of this galaxy. These multi-wavelength observations suggest that NGC
4736 is one of the least luminous broad-line (type 1) LINERs, with Lbol = 2.5
\times 10^40 erg/s. This LINER galaxy has also possibly the least luminous
broad line region known (LH_alpha =2.2\times10^37 erg/s). We compare black hole
mass estimates of this system to the recently measured ~7 \times 10^6 M_sun
dynamical black hole mass measurement. The fundamental plane and M-sigma
relationship roughly agree with the measured black hole mass, while other
accretion based estimates (the M-FWHM(H_alpha) relation, empirical correlation
of BH mass with high-ionization mid IR emission lines, and the X-ray excess
variance) provide much lower estimates (~10^5 M_sun). An energy budget test
shows that the AGN in this system may be deficient in ionizing radiation
relative to the observed emission-line activity. This deficiency may result
from source variability or the superposition of multiple sources including
supernovae. |
Gravitational hydrodynamics vs observations of voids, Jeans clusters and
MACHO dark matter: Gravitational hydrodynamics acknowledges that hydrodynamics is essentially
nonlinear and viscous. In the plasma, at $z=5100$, the viscous length enters
the horizon and causes fragmentation into plasma clumps surrounded by voids.
The latter have expanded to 38 Mpc now, explaining the cosmic void scale
$30/h=42$ Mpc. After the decoupling the Jeans mechanism fragments all matter in
clumps of ca 40,000 solar masses. Each of them fragments due to viscosity in
millibrown dwarfs of earth weight, so each Jeans cluster contains billions of
them. The Jeans clusters act as ideal gas particles in the isothermal model,
explaining the flattening of rotation curves. The first stars in old globular
clusters are formed by aggregation of milli brown dwarfs, without dark period.
Star formation also happens when Jean clusters come close to each other and
agitate and heat up the cooled milli brown dwarfs, which then expand and
coalesce to form new stars. This explains the Tully-Fischer and Jackson-Faber
relations, and the formation of young globular clusters in galaxy mergers.
Thousand of milli brown dwarfs have been observed in quasar microlensing and
some 40,000 in the Helix planetary nebula.
While the milli brown dwarfs, i.e., dark baryons, constitute the galactic
dark matter, cluster dark matter consists probably of 1.5 eV neutrinos, free
streaming at the decoupling. These two types of dark matter explain a wealth of
observations. | NIR spectroscopy of SDSS J0303-0019: a low luminosity, high Eddington
ratio quasar at z~6: We present sensitive near--infrared VLT ISAAC spectroscopic observations of
the z=6.08 quasar SDSS J030331.40-001912.9. This QSO is more than a magnitude
fainter than other QSOs at z~6 for which NIR spectroscopy has been obtained to
date and is therefore presumably more representative of the QSO population at
the end of Cosmic Reionization. Combining rest--frame UV continuum luminosity
with the width measurements of the Mg II and C IV lines, we derive a black hole
mass of 2(+1.0/-0.5) x 10^8 solar masses, the lowest mass observed for z~6 QSOs
to date, and derive an Eddington ratio of 1.6(+0.4/-0.6), amongst the highest
value derived for QSOs at any redshift. The Spitzer 24 micron non--detection of
this QSO does not leave space for a significant hot dust component in its
optical/near--infrared SED, in common with one other faint QSO at z=6, but in
contrast to more than twenty more z=6 QSOs and all known lower redshift QSOs
with sufficiently deep multi-wavelength photometry. We conclude that we have
found evidence for differences in the intrinsic properties of at least one z~6
QSO as compared to the lower--redshift population. |
Masked areas in shear peak statistics: a forward modeling approach: The statistics of shear peaks have been shown to provide valuable
cosmological information beyond the power spectrum, and will be an important
constraint of models of cosmology with the large survey areas provided by
forthcoming astronomical surveys. Surveys include masked areas due to bright
stars, bad pixels etc, which must be accounted for in producing constraints on
cosmology from shear maps. We advocate a forward-modeling approach, where the
impact of masking (and other survey artifacts) are accounted for in the
theoretical prediction of cosmological parameters, rather than removed from
survey data. We use masks based on the Deep Lens Survey, and explore the impact
of up to 37% of the survey area being masked on LSST and DES-scale surveys. By
reconstructing maps of aperture mass, the masking effect is smoothed out,
resulting in up to 14% smaller statistical uncertainties compared to simply
reducing the survey area by the masked area. We show that, even in the presence
of large survey masks, the bias in cosmological parameter estimation produced
in the forward-modeling process is ~1%, dominated by bias caused by limited
simulation volume. We also explore how this potential bias scales with survey
area and find that small survey areas are more significantly impacted by the
differences in cosmological structure in the data and simulated volumes, due to
cosmic variance. | Constraining Dark Energy with Clusters: Complementarity with Other
Probes: The Figure of Merit Science Working Group (FoMSWG) recently forecast the
constraints on dark energy that will be achieved prior to the Joint Dark Energy
Mission (JDEM) by ground-based experiments that exploit baryon acoustic
oscillations, type Ia supernovae, and weak gravitational lensing. We show that
cluster counts from on-going and near-future surveys should provide robust,
complementary dark energy constraints. In particular, we find that optimally
combined optical and Sunyaev-Zel'dovich effect cluster surveys should improve
the Dark Energy Task Force (DETF) figure of merit for pre-JDEM projects by a
factor of two even without prior knowledge of the nuisance parameters in the
cluster mass-observable relation. Comparable improvements are achieved in the
forecast precision of parameters specifying the principal component description
of the dark energy equation of state parameter as well as in the growth index
gamma. These results indicate that cluster counts can play an important
complementary role in constraining dark energy and modified gravity even if the
associated systematic errors are not strongly controlled. |
ΛCDM with baryons vs. MOND: the time evolution of the universal
acceleration scale in the Magneticum simulations: MOdified Newtonian Dynamics (MOND) is an alternative to the standard Cold
Dark Matter (CDM) paradigm which proposes an alteration of Newton's laws of
motion at low accelerations, characterized by a universal acceleration scale
a_0. It attempts to explain observations of galactic rotation curves and
predicts a specific scaling relation of the baryonic and total acceleration in
galaxies, referred to as the Rotational Acceleration Relation (RAR), which can
be equivalently formulated as a Mass Discrepancy Acceleration Relation (MDAR).
The appearance of these relations in observational data such as SPARC has lead
to investigations into the existence of similar relations in cosmological
simulations using the standard {\Lambda}CDM model. Here, we report the
existence of an RAR and MDAR similar to that predicted by MOND in {\Lambda}CDM
using a large sample of galaxies extracted from a cosmological, hydrodynamical
simulation (Magneticum). Furthermore, by using galaxies in Magneticum at
different redshifts, a prediction for the evolution of the inferred
acceleration parameter a_0 with cosmic time is derived by fitting a MOND force
law to these galaxies. In Magneticum, the best fit for a_0 is found to increase
by a factor of approximately 3 from redshift z = 0 to z = 2. This offers a
powerful test from cosmological simulations to distinguish between MOND and
{\Lambda}CDM observationally. | A redshift distortion free correlation function at third order in the
nonlinear regime: The zeroth-order component of the cosine expansion of the projected
three-point correlation function is proposed for clustering analysis of cosmic
large scale structure. These functions are third order statistics but can be
measured similarly to the projected two-point correlations. Numerical
experiments with N-body simulations indicate that the advocated statistics are
redshift distortion free within 10% in the non-linear regime on scales
~0.2-10Mpc/h. Halo model prediction of the zeroth-order component of the
projected three-point correlation function agrees with simulations within ~10%.
This lays the ground work for using these functions to perform joint analyses
with the projected two-point correlation functions, exploring galaxy clustering
properties in the framework of the halo model and relevant extensions. |
Measuring the growth of matter fluctuations with third-order galaxy
correlations: Measurements of the linear growth factor $D$ at different redshifts $z$ are
key to distinguish among cosmological models. One can estimate the derivative
$dD(z)/d\ln(1+z)$ from redshift space measurements of the 3D anisotropic galaxy
two-point correlation $\xi(z)$, but the degeneracy of its transverse (or
projected) component with galaxy bias $b$, i.e. $\xi_{\perp}(z) \propto\ D^2(z)
b^2(z)$, introduces large errors in the growth measurement. Here we present a
comparison between two methods which break this degeneracy by combining second-
and third-order statistics. One uses the shape of the reduced three-point
correlation and the other a combination of third-order one- and two-point
cumulants. These methods use the fact that, for Gaussian initial conditions and
scales larger than $20$ $h^{-1}$Mpc, the reduced third-order matter
correlations are independent of redshift (and therefore of the growth factor)
while the third-order galaxy correlations depend on $b$. We use matter and halo
catalogs from the MICE-GC simulation to test how well we can recover $b(z)$ and
therefore $D(z)$ with these methods in 3D real space. We also present a new
approach, which enables us to measure $D$ directly from the redshift evolution
of second- and third-order galaxy correlations without the need of modelling
matter correlations. For haloes with masses lower than $10^{14}$
$h^{-1}$M$_\odot$, we find $10%$ deviations between the different estimates of
$D$, which are comparable to current observational errors. At higher masses we
find larger differences that can probably be attributed to the breakdown of the
bias model and non-Poissonian shot noise. | Comparing galaxy populations in compact and loose groups of galaxies: We perform a comparison of the properties of galaxies in compact groups,
loose groups and in the field to deepen our understanding of the physical
mechanisms acting upon galaxy evolution in different environments. We select
samples of galaxies in compact groups identified by McConnachie et al., loose
groups identified by Zandivarez and Martinez, and field galaxies from the Sloan
Digital Sky Survey. We compare properties of the galaxy populations in these
different environments: absolute magnitude, colour, size, surface brightness,
stellar mass and concentration. We also study the fraction of red and early
type galaxies, the luminosity function, the colour-luminosity and
luminosity-size relations. The population of galaxies in compact groups differ
from that of loose groups and the field. The fraction of read and early type
galaxies is higher in compact groups. On average, galaxies in compact groups
are systematically smaller, more concentrated and have higher surface
brightness than galaxies in the field and in loose groups. For fixed absolute
magnitude, or fixed surface brightness, galaxies in compact groups are smaller.
The physical mechanisms that transform galaxies into earlier types could be
more effective within compact groups given the high densities and low velocity
dispersion that characterise that particular environment, this could explain
the large fraction of red and early type galaxies we found in compact groups.
Galaxies inhabiting compact groups have undergone a major transformation
compared to galaxies that inhabit loose groups. |
New Constraints on Cosmic Polarization Rotation from B-Mode Polarization
in Cosmic Microwave Background: STPpol, POLARBEAR and BICEP2 have recently measured the cosmic microwave
background (CMB) B-mode polarization in various sky regions of several tens of
square degrees and obtained BB power spectra in the multipole range 20-3000,
detecting the components due to gravitational lensing and to inflationary
gravitational waves. We analyze jointly the results of these three experiments
and propose modifications of their analysis of the spectra to include in the
model, in addition to the gravitational lensing and the inflationary
gravitational waves components, also the effects induced by the cosmic
polarization rotation (CPR), if it exists within current upper limits. Although
in principle our analysis would lead also to new constraints on CPR, in
practice these can only be given on its fluctuations <{\delta}{\alpha}^2>,
since constraints on its mean angle are inhibited by the de-rotation which is
applied by current CMB polarization experiments, in order to cope with the
insufficient calibration of the polarization angle. The combined data fits from
all three experiments (with 29% CPR-SPTpol correlation, depending on
theoretical model) gives constraint <{\delta}{\alpha}^2>^1/2 < 27.3 mrad
(1.56{\deg}) with r = 0.194 \pm 0.033. These results show that the present data
are consistent with no CPR detection and the constraint on CPR fluctuation is
about 1.5{\deg}. This method of constraining the cosmic polarization rotation
is new, is complementary to previous tests, which use the radio and optical/UV
polarization of radio galaxies and the CMB E-mode polarization, and adds a new
constraint for the sky areas observed by SPTpol, POLARBEAR and BICEP2. | Relation Between Globular Clusters and Supermassive Black Holes in
Ellipticals as a Manifestation of the Black Hole Fundamental Plane: We analyze the relation between the mass of the central supermassive black
hole (Mbh) and the number of globular clusters (Ngc) in elliptical galaxies and
bulges as a ramification of the black hole fundamental plane, the theoretically
predicted and observed multi-variable correlation between Mbh and bulge binding
energy. Although the tightness of the Mbh-Ngc correlation suggests an unlikely
causal link between supermassive black holes and globular clusters, such a
correspondence can exhibit small scatter even if the physical relationship is
indirect. We show that the relatively small scatter of the Mbh-Ngc relation
owes to the mutual residual correlation of Mbh and Ngc with stellar mass when
the velocity dispersion is held fixed. Thus, present observations lend evidence
for feedback-regulated models in which the bulge binding energy is most
important; they do not necessarily imply any `special' connection between
globular clusters and Mbh. This raises the question of why Ngc traces the
formation of ellipticals and bulges sufficiently well to be correlated with
binding energy. |
The Trispectrum as a Diagnostic of Primordial Orthogonal
non-Gaussianities: In single-field inflationary models with a low sound speed, the orthogonal
shape of the primordial bispectrum arises due to partial cancellations between
equilateral-type shapes. This fact allows for a speed of sound c_s as low as
about 0.01, which is actually weakly preferred by WMAP data. For such values,
the trispectrum, scaling like 1/c_s^4, is of order 10^8 and is therefore
comparable to, and greater than, the 1 sigma observational bound t_NL^eq=(-3.11
+- 7.5)*10^6. Hence, the trispectrum is already constraining inflationary
mechanisms candidates for generating an orthogonal bispectrum at the level
hinted in WMAP data. If this signal persists in imminent Planck data, most of
the parameter space of the simplest effective field theory of inflation will be
under observational pressure, while a dedicated analysis will be needed for the
substantial fraction of parameter space where we show that a qualitatively new,
orthogonal, trispectrum naturally arises. | Probing correlations of early magnetic fields using mu-distortion: The damping of a non-uniform magnetic field between the redshifts of about
$10^4$ and $10^6$ injects energy into the photon-baryon plasma and causes the
CMB to deviate from a perfect blackbody spectrum, producing a so-called
$\mu$-distortion. We can calculate the correlation $\langle\mu T\rangle$ of
this distortion with the temperature anisotropy $T$ of the CMB to search for a
correlation $\langle B^2\zeta\rangle$ between the magnetic field $B$ and the
curvature perturbation $\zeta$; knowing the $\langle B^2\zeta\rangle$
correlation would help us distinguish between different models of
magnetogenesis. Since the perturbations which produce the $\mu$-distortion will
be much smaller scale than the relevant density perturbations, the observation
of this correlation is sensitive to the squeezed limit of $\langle
B^2\zeta\rangle$, which is naturally parameterized by $b_{\text{NL}}$ (a
parameter defined analogously to $f_{\text{NL}}$). We find that a PIXIE-like
CMB experiments has a signal to noise $S/N\approx 1.0 \times b_{\text{NL}}
(\tilde B_\mu/10\text{ nG})^2$, where $\tilde B_\mu$ is the magnetic field's
strength on $\mu$-distortion scales normalized to today's redshift; thus, a 10
nG field would be detectable with $b_{\text{NL}}=\mathcal{O}(1)$. However, if
the field is of inflationary origin, we generically expect it to be accompanied
by a curvature bispectrum $\langle\zeta^3\rangle$ induced by the magnetic
field. For sufficiently small magnetic fields, the signal $\langle B^2
\zeta\rangle$ will dominate, but for $\tilde B_\mu\gtrsim 1$ nG, one would have
to consider the specifics of the inflationary magnetogenesis model.
We also discuss the potential post-magnetogenesis sources of a $\langle
B^2\zeta\rangle$ correlation and explain why there will be no contribution from
the evolution of the magnetic field in response to the curvature perturbation. |
Primordial black holes from second order density perturbations as probes
of the small-scale primordial power spectrum: We investigate the second order energy density perturbation $\delta^{(2)}$
induced by small-scale Gaussian and local-type non-Gaussian primordial
curvature perturbations. The relative abundance of primordial black hole is
calculated in terms of the probability density function of total energy density
perturbation $\delta_r=\delta^{(1)}+\frac{1}{2}\delta^{(2)}$. The effects of
second order density perturbation greatly reduce the upper bounds of
small-scale power spectra of primordial curvature perturbations by one to two
orders of magnitude. For log-normal primordial power spectrum, its amplitude
$A_{\zeta}$ is constrained to be about $A_{\zeta}\sim 3\times10^{-3}$. And for
local-type non-Gaussianity with $f_{\mathrm{NL}}=10$, the upper bound of
$A_{\zeta}$ is about $2.5\times10^{-4}$. | Dynamics of the NGC 4636 globular cluster system II. Improved
constraints from a large sample of globular cluster velocities: We present new radial velocities for 289 globular clusters around NGC 4636,
the southernmost giant elliptical galaxy of the Virgo cluster. The data were
obtained with FORS2/MXU at the Very Large Telescope. Together with data
analysed in an earlier study (Schuberth et al. 2006), we now have a sample of
460 globular cluster velocities out to a radius of 12 arcmin (60 kpc) available
- one of the largest of its kind. This new data set also provides a much more
complete angular coverage. Moreover, we present new kinematical data of the
inner stellar population of NGC 4636. We perform an updated Jeans analysis,
using both stellar and GC data, to better constrain the dark halo properties.
We find a stellar M/L-ratio of 5.8 in the R-band, higher than expected from
single stellar population synthesis. We model the dark halo by cored and cuspy
analytical halo profiles and consider different anisotropies for the tracer
populations. Properties of NFW halos lie well within the expected range of
cosmological simulations. Cored halos give central dark matter densities, which
are typical for elliptical galaxies of NGC 4636's luminosity. The surface
densities of the dark matter halos are higher than those of spiral galaxies. We
compare the predictions of Modified Newtonian Dynamics with the derived halo
properties and find satisfactory agreement. Therefore NGC 4636 therefore falls
onto the baryonic Tully-Fisher relation for spiral galaxies. The comparison
with the X-ray mass profile of Johnson et al. (2009) reveals satisfactory
agreement only, if the abundance gradient of hot plasma has been taken into
account. This might indicate a general bias towards higher masses for X-ray
based mass profiles in all systems, including galaxy clusters, with strong
abundance gradients. |
One-loop Corrections in Power Spectrum in Single Field Inflation: We revisit the one-loop correction in curvature perturbation power spectrum
in models of single field inflation which undergo a phase of ultra slow-roll
(USR) inflation. We include the contributions from both the cubic and quartic
interaction Hamiltonians and calculate the one-loop corrections on the spectrum
of the CMB scale modes from the small scale modes which leave the horizon
during the USR phase. It is shown that the amplitude of one-loop corrections
depends on the sharpness of the transition from the USR phase to the final
slow-roll phase. For an arbitrarily sharp transition, the one-loop correction
becomes arbitrarily large, invalidating the perturbative treatment of the
analysis. We speculate that for a mild transition, the large one-loop
corrections are washed out during the subsequent evolution after the USR phase.
The implications for primordial black holes formation are briefly reviewed. | Exploring Hot Gas at Junctions of Galaxy Filaments with Suzaku: We performed five pointing observations with Suzaku to search for hot gases
associated with the junctions of galaxy filaments where no significant diffuse
X-ray sources were detected so far. We discovered X-ray sources successfully in
all five regions and analyzed two bright sources in each field. Spectral
analysis indicates that three sources originate from X-ray diffuse halos
associated with optically bright galaxies or groups of galaxies with kT~0.6-0.8
keV. Other three sources are possibly group- and cluster-scale X-ray halos with
temperatures of ~1 keV and ~4 keV, respectively while the others are compact
object origins such as AGNs. All the three observed intracluster media within
the junctions of the galaxy filaments previously found are involved in ongoing
mergers. Thus, we demonstrate that deep X-ray observations at the filament
junctions identified by galaxy surveys are a powerful mean to explore growing
halos in a hierarchical structure undetected so far. |
Radio halos in a mass-selected sample of 75 galaxy clusters. I. Sample
selection and data analysis: Radio halos are synchrotron diffuse sources at the centre of a fraction of
galaxy clusters. The study of large samples of clusters with adequate radio and
X-ray data is necessary to investigate the origin of radio halos and their
connection with the cluster dynamics and formation history. The aim of this
paper is to compile a well-selected sample of galaxy clusters with deep radio
observations to perform an unbiased statistical study of the properties of
radio halos. We selected 75 clusters with M > = 6e14 Msun at z=0.08-0.33 from
the Planck Sunyaev-Zel'dovich catalogue. Clusters without suitable radio data
were observed with the Giant Metrewave Radio Telescope (GMRT) and/or the Jansky
Very Large Array (JVLA) to complete the information about the possible presence
of diffuse emission. We used archival Chandra X-ray data to derive information
on the clusters' dynamical states. This observational campaign led to the
detection of several cluster-scale diffuse radio sources and candidates that
deserve future follow-up observations. Here we summarise their properties and
add information resulting from our new observations. For the clusters where we
did not detect any hint of diffuse emission, we derived new upper limits to
their diffuse flux. We have built the largest mass-selected (> 80 per cent
complete in mass) sample of galaxy clusters with deep radio observations
available to date. The statistical analysis of the sample, which includes the
connection between radio halos and cluster mergers, the radio power-mass
correlation, and the occurrence of radio halos as a function of the cluster
mass, will be presented in paper II. | A First Detection of the Acoustic Oscillation Phase Shift Expected from
the Cosmic Neutrino Background: The unimpeded relativistic propagation of cosmological neutrinos prior to
recombination of the baryon-photon plasma alters gravitational potentials and
therefore the details of the time-dependent gravitational driving of acoustic
oscillations. We report here a first detection of the resulting shifts in the
temporal phase of the oscillations, which we infer from their signature in the
Cosmic Microwave Background (CMB) temperature power spectrum. |
Intervening BLR Clouds' Effects on Optical/UV Spectrum: Recent x-ray observations of Mrk 766 suggest that broad emission line region
clouds cross our line of sight and produce variable x-ray absorption. Here we
investigate what optical/ultraviolet spectroscopic features would be produced
by such "Intervening BLR Clouds" (IBC) crossing our line of sight to the
accretion disk, the source of the optical/UV continuum. Although the emission
spectrum produced by intervening clouds is identical to the standard BLR model,
they may produce absorption features on the optical or UV continuum. Single
clouds will have little effect on the optical/UV spectrum because BLR clouds
are likely to be much smaller than the accretion disk. This is unlike the X-ray
case, where the radiation source is considerably smaller. However, an ensemble
of intervening clouds will produce spectroscopic features in the FUV including
a strong depression between the Lyman limit and Ly{\alpha}. The amount of the
depression will indicate the line-of-sight covering factor of clouds, an
unknown quantity that is important for the ionization of the intergalactic
medium and the energy budget of AGN. Comparison with observations suggests that
the SED of Mrk 766 may be affected by intervening BLR clouds and IBC may exist
in most of AGNs. | The Formation and Fragmentation of Disks around Primordial Protostars: The very first stars to form in the Universe heralded an end to the cosmic
dark ages and introduced new physical processes that shaped early cosmic
evolution. Until now, it was thought that these stars lived short, solitary
lives, with only one extremely massive star, or possibly a very wide binary
system, forming in each dark matter minihalo. Here we describe numerical
simulations that show that these stars were, to the contrary, often members of
tight multiple systems. Our results show that the disks that formed around the
first young stars were unstable to gravitational fragmentation, possibly
producing small binary and higher-order systems that had separations as small
as the distance between the Earth and the Sun. |
Chemo-Archaeological Downsizing in a Hierarchical Universe: Impact of a
Top Heavy IGIMF: We make use of a semi-analytical model of galaxy formation to investigate the
origin of the observed correlation between [a/Fe] abundance ratios and stellar
mass in elliptical galaxies. We implement a new galaxy-wide stellar initial
mass function (Top Heavy Integrated Galaxy Initial Mass Function, TH-IGIMF) in
the semi-analytic model SAG and evaluate its impact on the chemical evolution
of galaxies. The SFR-dependence of the slope of the TH-IGIMF is found to be key
to reproducing the correct [a/Fe]-stellar mass relation. Massive galaxies reach
higher [a/Fe] abundance ratios because they are characterized by more top-heavy
IMFs as a result of their higher SFR. As a consequence of our analysis, the
value of the minimum embedded star cluster mass and of the slope of the
embedded cluster mass function, which are free parameters involved in the
TH-IGIMF theory, are found to be as low as 5 solar masses and 2, respectively.
A mild downsizing trend is present for galaxies generated assuming either a
universal IMF or a variable TH-IGIMF. We find that, regardless of galaxy mass,
older galaxies (with formation redshifts > 2) are formed in shorter time-scales
(< 2 Gyr), thus achieving larger [a/Fe] values. Hence, the time-scale of galaxy
formation alone cannot explain the slope of the [a/Fe]-galaxy mass relation,
but is responsible for the big dispersion of [a/Fe] abundance ratios at fixed
stellar mass.We further test the hyphothesis of a TH-IGIMF in elliptical
galaxies by looking into mass-to-light ratios, and luminosity functions. Models
with a TH-IGIMF are also favoured by these constraints. In particular,
mass-to-light ratios agree with observed values for massive galaxies while
being overpredicted for less massive ones; this overprediction is present
regardless of the IMF considered. | Phenomenology of Horndeski Gravity under Positivity Bounds: A set of conditions that any effective field theory needs to satisfy in order
to allow for the existence of a viable UV completion has recently gained
attention in the cosmological context under the name of $\textit{positivity
bounds}$. In this paper we revisit the derivation of such bounds for Horndeski
gravity and translate them into a complete set of viability conditions in the
language of effective field theory of dark energy. We implement the latter into
$\texttt{EFTCAMB}$ and explore the large scale structure phenomenology of
Horndeski gravity under positivity bounds. We build a statistically significant
sample of viable Horndeski models, and derive the corresponding predictions for
the background evolution, in terms of $w_{\rm DE}$, and the dynamics of linear
perturbations, in terms of the phenomenological functions $\mu$ and $\Sigma$,
associated to clustering and weak lensing, respectively. We find that the
addition of positivity bounds to the traditional no-ghost and no-gradient
conditions considerably tightens the theoretical constraints on all these
functions. The most significant feature is a strengthening of the correlation
$\mu\simeq\Sigma$, and a related tight constraint on the luminal speed of
gravitational waves $c^2_T\simeq1$. In anticipation of a more complete
formulation of positivity conditions in cosmology, this work demonstrates the
strong potential of such bounds in shaping the viable parameter space of
scalar-tensor theories. |
The Massive Star Clusters in the Dwarf Merger ESO 185-IG13: is the Red
Excess Ubiquitous in Starbursts?: We have investigated the starburst properties of the luminous blue compact
galaxy ESO 185-IG13. The galaxy has been imaged with the high resolution
cameras onboard to the Hubble Space Telescope. From the UV to the IR, the data
reveal a system shaped by hundreds of young star clusters, and fine structures,
like a tidal stream and a shell. The presence of numerous clusters and the
perturbed morphology indicate that the galaxy has been involved in a recent
merger event. Using previous simulations of shell formation in galaxy mergers
we constrain potential progenitors of ESO 185-IG13. The analysis of the star
cluster population is used to investigate the properties of the present
starburst and to date the final merger event, which has produced hundreds of
clusters younger than 100 Myr. We have found a peak of cluster formation only
3.5 Myr old. A large fraction of these clusters will not survive after 10-20
Myr, due to the "infant mortality" caused by gas expulsion. However, this
sample of clusters represents an unique chance to investigate the youngest
phases of cluster evolution. As already observed in the analog blue compact
galaxy Haro 11, a fraction of young clusters are affected by a flux excess at
wavelengths longer than 8000 \AA. Ages, masses, and extinctions of clusters
with this NIR excess are estimated from UV and optical data. We discuss
similarities and differences of the observed NIR excess in ESO 185-IG13
clusters with other cases in the literature. The cluster ages and masses are
used to distinguish among the potential causes of the excess. We observe, as in
Haro 11, that the use of the IR and the (commonly used) I band data results in
overestimates of age and mass in clusters affected by the NIR excess. This has
important implications for a number of related studies of star clusters. | Probing the integrated Sachs-Wolfe effect using embedded lens models: The photometry profile of the integrated Sachs-Wolfe (ISW) effect recently
obtained by the Planck consortium by stacking patches of Cosmic Microwave
Background (CMB) sky maps around a large number of cosmic voids, contains a
cold ring at about half the void's effective radius surrounded by a hot ring
near the void's boundary. The source of the temperature structure is assumed to
be the ISW effect but the exact cause of the ringed structure is not currently
well understood, particularly the outer hot ring. Numerical simulations have
suggested that hot/cold ring structures can be produced by motions associated
with nonlinear growths of cosmic structures whose gravitational potentials
produce the ISW effect. We have recently developed the embedded lens theory and
the Fermat potential formalism which can be used to model the ISW effect caused
by intervening individual lens inhomogeneities evolving arbitrarily. This
theory only requires knowledge of the void's projected mass profile as a
function of the passing CMB photons' impact radius and the rate of change of
that mass distribution at passage. We present two simple embedded void lens
models with evolving mass densities and investigate the ISW effect caused by
these lenses. Both models posses expanding mass shells which produce hot rings
around central cold regions, consistent with the recent observations. By adding
a small over-density at the void's center we can produce the slight positive
temperature excess hinted at in Planck's photometric results. We conclude that
the embedded lens theory and the Fermat potential formalism is well suited for
modeling the ISW effect. |
The Quantum Origin of Cosmic Structure: In this concise, albeit subjective review of structure formation, I shall
introduce the cosmological standard model and its theoretical and observational
underpinnings. I will focus on recent results and current issues in theoretical
cosmology, in particular in cosmological perturbation theory and its
applications. | The quantum gravity connection between inflation and quintessence: Inflation and quintessence can both be described by a single scalar field.
The cosmic time evolution of this cosmon field realizes a crossover from the
region of an ultraviolet fixed point in the infinite past to an infrared fixed
point in the infinite future. This amounts to a transition from early inflation
to late dynamical dark energy, with intermediate radiation and matter
domination. The scaling solution of the renormalization flow in quantum gravity
connects the two fixed points. It provides for the essential characteristics of
the scalar potential needed for the crossover cosmology and solves the
cosmological constant problem dynamically. The quantum scale symmetry at the
infrared fixed point protects the tiny mass of the cosmon and suppresses the
cosmon coupling to atoms without the need of a non-linear screening mechanism,
thereby explaining apparent issues of fine tuning. For a given content of
particles the scaling solution of quantum gravity is a predictive framework for
the properties of inflation and dynamical dark energy. |
Fast Shape Estimation for Galaxies and Stars: Model fitting is frequently used to determine the shape of galaxies and the
point spread function, for examples, in weak lensing analyses or morphology
studies aiming at probing the evolution of galaxies. However, the number of
parameters in the model, as well as the number of objects, are often so large
as to limit the use of model fitting for future large surveys. In this article,
we propose a set of algorithms to speed up the fitting process. Our approach is
divided into three distinctive steps: centroiding, ellipticity measurement, and
profile fitting. We demonstrate that we can derive the position and ellipticity
of an object analytically in the first two steps and thus leave only a small
number of parameters to be derived through model fitting. The position,
ellipticity, and shape parameters can then used in constructing orthonomal
basis functions such as s\'ersiclets for better galaxy image reconstruction. We
assess the efficiency and accuracy of the algorithms with simulated images. We
have not taken into account the deconvolution of the point spread function,
which most weak lensing analyses do. | Simulations of momentum feedback by black hole winds: The observed super-massive black hole (SMBH) mass -- galaxy velocity
dispersion ($M_{\rm bh} - \sigma$) correlation may be established when
winds/outflows from the SMBH drive gas out of the potential wells of classical
bulges. Here we present numerical simulations of this process in a static
isothermal potential. Simple spherically symmetric models of SMBH feedback at
the Eddington luminosity can successfully explain the $M_{\rm bh} - \sigma$ and
nuclear cluster mass $M_{\rm NC}-\sigma$ correlations, as well as why larger
bulges host SMBHs while smaller ones host nuclear star clusters. However these
models do not specify how SMBHs feed on infalling gas whilst simultaneously
producing feedback that drives gas out of the galaxy.
More complex models with rotation and/or anisotropic feedback allow SMBHs to
feed via a disc or regions not exposed to SMBH winds, but in these more
realistic cases it is not clear why a robust $M_{\rm bh} - \sigma$ relation
should be established. In fact, some of the model predictions contradict
observations. For example, an isotropic SMBH wind impacting on a disc (rather
than a shell) of aspect ratio $H/R \ll 1$ requires the SMBH mass to be larger
by a factor $\sim R/H$, which is opposite to what is observed. We conclude that
understanding how a SMBH feeds is as important a piece of the puzzle as
understanding how its feedback affects its host galaxy.
Finally, we note that in aspherical cases the SMBH outflows induce
differential motions in the bulge. This may pump turbulence that is known to
hinder star formation in star forming regions. SMBH feedback thus may not only
drive gas out of the bulge but also reduce the fraction of gas turned into
stars. |
The Maximum Angular-Diameter Distance in Cosmology: Unlike other observational signatures in cosmology, the angular-diameter
distance d_A(z) uniquely reaches a maximum (at z_max) and then shrinks to zero
towards the big bang. The location of this turning point depends sensitively on
the model, but has been difficult to measure. In this paper, we estimate and
use z_max inferred from quasar cores: (1) by employing a sample of 140 objects
yielding a much reduced dispersion due to pre-constrained limits on their
spectral index and luminosity, (2) by reconstructing d_A(z) using Gaussian
processes, and (3) comparing the predictions of seven different cosmologies and
showing that the measured value of z_max can effectively discriminate between
them. We find that z_max=1.70 +\- 0.20---an important new probe of the
Universe's geometry. The most strongly favoured model is R_h=ct, followed by
Planck LCDM. Several others, including Milne, Einstein-de Sitter and Static
tired light are strongly rejected. According to these results, the R_h=ct
universe, which predicts z_max=1.718, has a ~92.8% probability of being the
correct cosmology. For consistency, we also carry out model selection based on
d_A(z) itself. This test confirms that R_h=ct and Planck LCDM are among the few
models that account for angular-size data better than those that are
disfavoured by z_max. The d_A(z) comparison, however, is less discerning than
that with z_max, due to the additional free parameter, H_0. We find that
H_0=63.4 +\- 1.2 km/s/Mpc for R_h=ct, and 69.9 +\- 1.5 km/s/Mpc for LCDM. Both
are consistent with previously measured values in each model, though they
differ from each other by over 4 sigma. In contrast, model selection based on
z_max is independent of H_0. | An Empirical Study of the Relationship between Lyα and UV
selected Galaxies: Do Theorists and Observers `Select' the Same Objects?: Lyman Alpha Emitters (LAEs) are galaxies that have been selected on the basis
of a strong Ly{\alpha} emission line in their spectra. Observational campaigns
have dramatically increased the sample of known LAEs, which now extends out to
z=7. These discoveries have motivated numerous theoretical studies on the
subject, which usually define LAEs in their models based on sharp Ly{\alpha}
luminosity and equivalent width (EW) cuts. While broadly representative, this
procedure does not mimic the selection from observational programs in detail,
which instead use cuts in various colour-spaces. We investigate what
implications this disjoint may have for studies that aim to model LAEs. We
construct an empirical model for the number density of star forming galaxies as
a function of their UV and Ly{\alpha} luminosity, utilising measured
constraints on the luminosity functions (LFs) of drop-out galaxies, and their
luminosity dependent probability distribution function of Ly{\alpha} EW. In
particular, we investigate whether the LAE LFs can be reproduced by defining
LAEs using a (z-dependent) Ly{\alpha} luminosity and EW threshold. While we are
able to reproduce the observed distribution of Ly{\alpha} EW among LAEs out to
restframe EW 200 A, we find that our formalism over-predicts both the UV and
Ly{\alpha} LFs of LAEs by a factor of 2-3, and is inconsistent with
observations at the ~95% level. This tension is partially resolved if we assume
the Ly{\alpha} EW-distribution of drop-out galaxies to be truncated at
restframe EW>150 A. However the overprediction indicates that modeling LAEs
with simple REW and luminosity cuts does not accurately mimic observed
selection criteria, and can lead to uncertainties in the predicted number
density of LAEs. On the other hand, the predicted z-evolution is not affected.
We apply our formalism to drop-out galaxies at z>6, and predict the LFs of LAEs
at z=7-9. |
Integral field spectroscopy with SINFONI of VVDS galaxies. II. The
mass-metallicity relation at 1.2 < z < 1.6: This work aims to provide a first insight into the mass-metallicity (MZ)
relation of star-forming galaxies at redshift z~1.4. To reach this goal, we
present a first set of nine VVDS galaxies observed with the NIR integral-field
spectrograph SINFONI on the VLT. Oxygen abundances are derived from empirical
indicators based on the ratio between strong nebular emission-lines (Halpha,
[NII]6584 and [SII]6717,6731). Stellar masses are deduced from SED fitting with
Charlot & Bruzual (2007) population synthesis models, and star formation rates
are derived from [OII]3727 and Halpha emission-line luminosities. We find a
typical shift of 0.2-0.4 dex towards lower metallicities for the z~1.4
galaxies, compared to the MZ-relation in the local universe as derived from
SDSS data. However, this small sample of eight galaxies does not show any clear
correlation between stellar mass and metallicity, unlike other larger samples
at different redshift (z~0, z~0.7, and z~2). Indeed, our galaxies lie just
under the relation at z~2 and show a small trend for more massive galaxies to
be more metallic (~0.1 logarithmic slope). There are two possible explanations
to account for these observations. First, the most massive galaxies present
higher specific star formation rates when compared to the global VVDS sample
which could explain the particularly low metallicity of these galaxies as
already shown in the SDSS sample. Second, inflow of metal-poor gas due to tidal
interactions could also explain the low metallicity of these galaxies as two of
these three galaxies show clear signatures of merging in their velocity fields.
Finally, we find that the metallicity of 4 galaxies is lower by ~0.2 to 0.4 dex
if we take into account the N/O abundance ratio in their metallicity estimate. | CMB anisotropies at all orders: the non-linear Sachs-Wolfe formula: We obtain the non-linear generalization of the Sachs-Wolfe + integrated
Sachs-Wolfe (ISW) formula describing the CMB temperature anisotropies. Our
formula is valid at all orders in perturbation theory, is also valid in all
gauges and includes scalar, vector and tensor modes. A direct consequence of
our results is that the maps of the logarithmic temperature anisotropies are
much cleaner than the usual CMB maps, because they automatically remove many
secondary anisotropies. This can for instance, facilitate the search for
primordial non-Gaussianity in future works. It also disentangles the non-linear
ISW from other effects. Finally, we provide a method which can iteratively be
used to obtain the lensing solution at the desired order. |
Mapping dark matter and finding filaments: calibration of lensing
analysis techniques on simulated data: We quantify the performance of mass mapping techniques on mock imaging and
gravitational lensing data of galaxy clusters. The optimum method depends upon
the scientific goal. We assess measurements of clusters' radial density
profiles, departures from sphericity, and their filamentary attachment to the
cosmic web. We find that mass maps produced by direct (KS93) inversion of shear
measurements are unbiased, and that their noise can be suppressed via filtering
with MRLens. Forward-fitting techniques, such as Lenstool, suppress noise
further, but at a cost of biased ellipticity in the cluster core and
over-estimation of mass at large radii. Interestingly, current searches for
filaments are noise-limited by the intrinsic shapes of weakly lensed galaxies,
rather than by the projection of line-of-sight structures. Therefore,
space-based or balloon-based imaging surveys that resolve a high density of
lensed galaxies, could soon detect one or two filaments around most clusters. | A comparative study of cosmological constraints from weak lensing using
Convolutional Neural Networks: Weak Lensing (WL) surveys are reaching unprecedented depths, enabling the
investigation of very small angular scales. At these scales, nonlinear
gravitational effects lead to higher-order correlations making the matter
distribution highly non-Gaussian. Extracting this information using traditional
statistics has proven difficult, and Machine Learning based summary statistics
have emerged as a powerful alternative. We explore the capabilities of a
discriminative, Convolutional Neural Networks (CNN) based approach, focusing on
parameter constraints in the ($\Omega_m$, $\sigma_8$) cosmological parameter
space. Leveraging novel training loss functions and network representations on
WL mock datasets without baryons, we show that our models achieve $\sim 5$
times stronger constraints than the power spectrum, $\sim 3$ stronger
constraints than peak counts, and $\sim 2$ stronger constraints than previous
CNN-learned summary statistics and scattering transforms, for noise levels
relevant to Rubin or Euclid. For WL convergence maps with baryonic physics, our
models achieve $\sim 2.3$ times stronger constraining power than the power
spectrum at these noise levels, also outperforming previous summary statistics.
To further explore the possibilities of CNNs for this task, we also discuss
transfer learning where we adapt pre-trained models, trained on different tasks
or datasets, for cosmological inference, finding that these do not improve the
performance. |
The Orthogonally Aligned Dark Halo of an Edge-on Lensing Galaxy in the
Hubble Frontier Fields: A Challenge for Modified Gravity: We examine a well resolved 8 arcsec lensed image that is symmetrically bent
in the middle by an edge-on lenticular galaxy, in the Hubble Frontier Field
(HFF) data of MACSJ0416.1-20403. The lengthy image is generated primarily by
the large tangential shear of the cluster with a local secondary deflection by
the member galaxy out to a limiting radius of about 18 kpc. The lensing
lenticular galaxy is also well resolved and evidently lies nearly edge-on in
projection. This fortuitous combination of a long arc intersecting an edge on
galaxy provides us with an opportunity to place relatively strong constraints
on the lensing effect of this galaxy. We can model the stellar lensing
contribution using the observed pixels belonging to the galaxy, in 2D, and we
add to this a standard parameterised dark halo component. Irrespective of the
detailed choice of parameters we obtain a combined total mass of about 3E11
Msun. Depending on the dark halo parameters, the stellar contribution to this
is limited to the range 5-15E10 Msun or 20-50 percent of the total mass, in
good agreement with the independent stellar mass computed from the photometry
of 5E10 Msun for a Chabrier IMF, or 8E10Msun for a Salpeter IMF. The major axis
of the DM halo is constrained to be nearly orthogonal to the plane of the
galaxy, within a range of about 15 degrees, and with an ellipticity e=015
corresponding to an axis ratio a/c=0.54. We show that these conclusions are
very weakly dependent on the model of the cluster, or the additional influence
of neighbouring galaxies or the properties of the lensed source. Alternative
theories of gravity where the radial dependence is modified to avoid the need
for DM are challenged by this finding since generically these must be tied to
the baryonic component which here is a stellar disk oriented nearly
orthogonally to the lensed image deflection. | NANOGrav signal as mergers of Stupendously Large Primordial Black Holes: We give an explanation for the signal detected by NANOGrav as the stochastic
gravitational wave background from binary mergers of primordial "Stupendously
Large Black Holes" (SLABs) of mass $M\sim(10^{11}-10^{12})M_{\odot}$, and
corresponding to roughly $0.1\%$ of the dark matter. We show that the stringent
bounds coming from $\mu$ distortions of the CMB can be surpassed if the
perturbations resulting in these BHs arise from the non-Gaussian distribution
of fluctuations expected in single field models of inflation generating a spike
in the power spectrum. While the tail of the stochastic background coming from
binaries with $M\lesssim 10^{11}M_{\odot}$ could both fit NANOGrav and respect
$\mu$ distortions limits, they become excluded from large scale structure
constraints. |
Radiative Regulation of Population III Star Formation: We explore the impact of ultraviolet (UV) radiation from massive Population
III (Pop III) stars of 25, 40, 80, and 120 M_sun on the subsequent Pop III star
formation. In this paper, particular attention is paid to the dependence of
radiative feedback on the mass of source Pop III star. UV radiation from the
source star can work to impede the secondary star formation through the
photoheating and photodissociation processes. Recently, Susa & Umemura (2006)
have shown that the ionizing radiation alleviates the negative effect by
H_2-dissociating radiation from 120$M_sun PopIII star, since an H_2 shell
formed ahead of an ionizing front can effectively shield H_2-dissociating
radiation. On the other hand, it is expected that the negative feedback by
H_2-dissociating radiation can be predominant if a source star is less massive,
since a ratio of the H_2-dissociating photon number to the ionizing photon
number becomes higher. In order to investigate the radiative feedback effects
from such less massive stars, we perform three-dimensional radiation
hydrodynamic simulations, incorporating the radiative transfer effect of
ionizing and H_2-dissociating radiation. As a result, we find that if a source
star is less massive than ~25M_sun, the ionizing radiation cannot suppress the
negative feedback of H_2-dissociating radiation. Therefore, the fate of the
neighboring clouds around such less massive stars is determined solely by the
flux of H_2-dissociating radiation from source stars. With making analytic
estimates of H_2 shell formation and its shielding effect, we derive the
criteria for radiation hydrodynamic feedback depending on the source star mass. | The Geometrodynamical Origin of Equilibrium Gravitational Configurations: The origin of equilibrium gravitational configurations is sought in terms of
the stability of their trajectories, as described by the curvature of their
Lagrangian configuration manifold. We focus on the case of spherical systems,
which are integrable in the collisionless (mean field) limit despite the
apparent persistence of local instability of trajectories even as $N
\rightarrow \infty$. It is shown that when the singularity in the potential is
removed, a null scalar curvature is associated with an effective, averaged,
equation of state describing dynamically relaxed equilibria with marginally
stable trajectories. The associated configurations are quite similar to those
of observed elliptical galaxies and simulated cosmological halos. This is the
case because a system starting far from equilibrium finally settles in a state
which is integrable when unperturbed, but where it can most efficiently wash
out perturbations. We explicitly test this interpretation by means of direct
simulations. |
Unveiling the Intrinsic Alignment of Galaxies with Self-Calibration and
DECaLS DR3 data: Galaxy intrinsic alignment (IA) is both a source of systematic contamination
to cosmic shear measurement and its cosmological applications, and a source of
valuable information on the large scale structure of the universe and galaxy
formation. The self-calibration (SC) method \citep{SC2008} was designed to
separate IA from cosmic shear, free of IA modeling. It was first successfully
applied to the KiDS450 and KV450 data \citep{Yao2019}. We apply the SC method
to the DECaLS DR3 shear + photo-z catalog and significantly improve the IA
detection to $\sim 14\sigma$. We find a strong dependence of IA on galaxy
color, with strong IA signal ($\sim17.6\sigma$) for red galaxies, while the IA
signal for blue galaxies is consistent with zero. The detected IA for red
galaxies are in reasonable agreement with the non-linear tidal alignment model
and the inferred IA amplitude increases with redshift. We address the
systematics in the SC method carefully and performed several sanity checks. We
discuss various caveats and possible improvements in the measurement, theory
and parameter fitting that will be addressed in future works. | A $f(R)$-gravity model of the Sunyaev-Zeldovich profile of the Coma
cluster compatible with {\it Planck} data: In the weak field limit, analytic $f(R)$ models of gravity introduce a
Yukawa-like correction to the Newtonian gravitational potential. These models
have been widely tested at galactic scales and provide an alternative
explanation to the dynamics of galaxies without Dark Matter. We study if the
temperature anisotropies due to the thermal Sunyaev-Zeldovich effect are
compatible with these Extended Theories of Gravity. We assume that the gas is
in hydrostatic equilibrium within the modified Newtonian potential and it is
well described by a polytropic equation of state. We particularize the model
for the Coma cluster and the predicted anisotropies are compared with those
measured in the foreground cleaned maps obtained using the Planck Nominal maps
released in 2013. We show that the computed $f(R)$ pressure profile fits the
data giving rise to competitive constraints of the Yukawa scale length
$L=(2.19\pm1.02) \rm{\, Mpc}$, and of the deviation parameter $
\delta=-0.48\pm0.22$. Those are currently the tightest constraints at galaxy
cluster scale, and support the idea that Extended Theories of Gravity provide
an alternative explanation to the dynamics of self-gravitating systems without
requiring Dark Matter. |
Slepian Spatial-Spectral Concentration Problem on the Sphere: Analytical
Formulation for Limited Colatitude-Longitude Spatial Region: In this paper, we develop an analytical formulation for the Slepian
spatial-spectral concentration problem on the sphere for a limited
colatitude-longitude spatial region on the sphere, defined as the Cartesian
product of a range of positive colatitudes and longitudes. The solution of the
Slepian problem is a set of functions that are optimally concentrated and
orthogonal within a spatial or spectral region. These properties make them
useful for applications where measurements are taken within a spatially limited
region of the sphere and/or a signal is only to be analyzed within a region of
the sphere. To support localized spectral/spatial analysis, and estimation and
sparse representation of localized data in these applications, we exploit the
expansion of spherical harmonics in the complex exponential basis to develop an
analytical formulation for the Slepian concentration problem for a limited
colatitude-longitude spatial region. We also extend the analytical formulation
for spatial regions that are comprised of a union of rotated limited
colatitude-longitude subregions. By exploiting various symmetries of the
proposed formulation, we design a computationally efficient algorithm for the
implementation of the proposed analytical formulation. Such a reduction in
computation time is demonstrated through numerical experiments. We present
illustrations of our results with the help of numerical examples and show that
the representation of a spatially concentrated signal is indeed sparse in the
Slepian basis. | It's Always Darkest Before the Cosmic Dawn: Early Results from Novel
Tools and Telescopes for 21 cm Cosmology: 21 cm cosmology, the statistical observation of the high redshift universe
using the hyperfine transition of neutral hydrogen, has the potential to
revolutionize our understanding of cosmology and the astrophysical processes
that underlie the formation of the first stars, galaxies, and black holes
during the "Cosmic Dawn." By making tomographic maps with low frequency radio
interferometers, we can study the evolution of the 21 cm signal with time and
spatial scale and use it to understand the density, temperature, and ionization
evolution of the intergalactic medium over this dramatic period in the history
of the universe.
For my Ph.D. thesis, I explore a number of advancements toward detecting and
characterizing the 21 cm signal from the Cosmic Dawn, especially during its
final stage, the epoch of reionization. In seven different previously published
papers, I explore new techniques for the statistical analysis of
interferometric measurements, apply them to data from current generation
telescopes like the Murchison Widefield Array, and look forward to what we
might measure with the next generation of 21 cm observatories. I focus in
particular on estimating the power spectrum of 21 cm brightness temperature
fluctuations in the presence enormous astrophysical foregrounds and how those
measurements may constrain the physics of the Cosmic Dawn.
Thesis Supervisor: Max Tegmark |
Gas inflows, star formation and metallicity evolution in galaxy pairs: It has been known since many decades that galaxy interactions can induce star
formation (hereafter SF) enhancements and that one of the driving mechanisms of
this enhancement is related to gas inflows into the central galaxy regions,
induced by asymmetries in the stellar component, like bars. In the last years
many evidences have been accumulating, showing that interacting pairs have
central gas-phase metallicities lower than those of field galaxies, by {\sim}
0.2-0.3 dex on average. These diluted ISM metallicities have been explained as
the result of inflows of metal-poor gas from the outer disk to the galaxy
central regions. A number of questions arises: What's the timing and the
duration of this dilution? How and when does the SF induced by the gas inflow
enrich the circumnuclear gas with re-processed material? Is there any
correlation between the timing and strength of the dilution and the timing and
intensity of the SF? By means of Tree-SPH simulations of galaxy major
interactions, we have studied the effect that gas inflows have on the ISM
dilution, and the effect that the induced SF has, subsequently, in re-enriching
the nuclear gas. In this contribution, we present the main results of this
study. | Robust bounds on ALP dark matter from dwarf spheroidal galaxies in the
optical MUSE-Faint survey: Nearby dwarf spheroidal galaxies are ideal targets in the search for indirect
dark matter (DM) signals. In this work, we analyze MUSE spectroscopic
observations of a sample of five galaxies, composed of both classical and
ultra-faint dwarf spheroidals. The goal is to search for radiative decays of
axion-like particles (ALPs) in the mass range of 2.7-5.3 eV. After taking into
account the uncertainties associated with the DM spatial distribution in the
galaxies, we derive robust bounds on the effective ALP-two-photon coupling.
They lie well below the QCD axion band and are significantly more constraining
than limits from other probes, in the relevant mass range. We also test the
possible presence of a positive signal, concluding that none of the channels
selected for this analysis, i.e., not affected by large background
contamination, is exhibiting such evidence. |
Systematic or Signal? How dark matter misalignments can bias strong
lensing models of galaxy clusters: We explore how assuming that mass traces light in strong gravitational
lensing models can lead to systematic errors in the predicted position of
multiple images. Using a model based on the galaxy cluster MACSJ0416 (z =
0.397) from the Hubble Frontier Fields, we split each galactic halo into a
baryonic and dark matter component. We then shift the dark matter halo such
that it no longer aligns with the baryonic halo and investigate how this
affects the resulting position of multiple images. We find for physically
motivated misalignments in dark halo position, ellipticity, position angle and
density profile, that multiple images can move on average by more than 0.2"
with individual images moving greater than 1". We finally estimate the full
error induced by assuming that light traces mass and find that this assumption
leads to an expected RMS error of 0.5", almost the entire error budget observed
in the Frontier Fields. Given the large potential contribution from the
assumption that light traces mass to the error budget in mass reconstructions,
we predict that it should be possible to make a first significant detection and
characterisation of dark halo misalignments in the Hubble Frontier Fields with
strong lensing. Finally, we find that it may be possible to detect ~1kpc
offsets between dark matter and baryons, the smoking gun for self-interacting
dark matter, should the correct alignment of multiple images be observed. | The All-Sky SignAl Short-Spacing INterferometer (ASSASSIN) I: Global sky
measurements with the Engineering Development Array-2: Aiming to fill a crucial gap in our observational knowledge of the early
Universe, experiments around the world continue to attempt to verify the
claimed detection of the redshifted 21-cm signal from Cosmic Dawn by the EDGES
experiment. This sky-averaged or 'global' signal from neutral hydrogen should
be detectable at low radio frequencies (50-200 MHz), but is difficult to
measure due to bright foreground emission and difficulties in reaching the
required levels of instrumental-calibration precision. In this paper we outline
our progress toward using a novel new method to measure the global redshifted
21-cm signal. Motivated by the need to use alternative methods with very
different systematic errors to EDGES for an independent result, we employ an
array of closely-spaced antennas to measure the global sky signal
interferometrically, rather than using the conventional approach with a single
antenna. We use simulations to demonstrate our newly-developed methods and show
that, for an idealised instrument, a 21-cm signal could theoretically be
extracted from the visibilities of an array of closely-spaced dipoles. We
verify that our signal-extraction methods work on real data using observations
made with a Square Kilometre-Array-like prototype; the Engineering Development
Array-2. Finally, we use the lessons learned in both our simulations and
observations to lay out a clear plan for future work, which will ultimately
lead to a new global redshifted 21-cm instrument: the All-Sky SignAl
Short-Spacing INterferometer (ASSASSIN). |
Constraining inflationary magnetogenesis and reheating via GWs in light
of PTA data: Utilizing the bounds on primordial magnetic fields (PMFs), their
contributions to secondary gravitational waves (GWs) and the results from the
pulsar timing arrays (PTAs), we arrive at constraints on the epoch of
reheating. We find that the combined spectral density of primary and secondary
GWs (generated by the PMFs) can, in general, be described as a broken power law
with five different indices. We show that the PMFs that have a blue tilt and
satisfy the other observational constraints can generate secondary GWs of
strengths suggested by the PTA data. | Foreground Separation and Constraints on Primordial Gravitational Waves
with the PICO Space Mission: PICO is a concept for a NASA probe-scale mission aiming to detect or
constrain the tensor to scalar ratio $r$, a parameter that quantifies the
amplitude of inflationary gravity waves. We carry out map-based component
separation on simulations with five foreground models and input $r$ values
$r_{in}=0$ and $r_{in} = 0.003$. We forecast $r$ determinations using a
Gaussian likelihood assuming either no delensing or a residual lensing factor
$A_{\rm lens}$ = 27%. By implementing the first full-sky, post
component-separation, map-domain delensing, we show that PICO should be able to
achieve $A_{\rm lens}$ = 22% - 24%. For four of the five foreground models we
find that PICO would be able to set the constraints $r < 1.3 \times 10^{-4}
\,\, \mbox{to} \,\, r <2.7 \times 10^{-4}\, (95\%)$ if $r_{in}=0$, the
strongest constraints of any foreseeable instrument. For these models,
$r=0.003$ is recovered with confidence levels between $18\sigma$ and
$27\sigma$. We find weaker, and in some cases significantly biased, upper
limits when removing few low or high frequency bands. The fifth model gives a
$3\sigma$ detection when $r_{in}=0$ and a $3\sigma$ bias with $r_{in} = 0.003$.
However, by correlating $r$ determinations from many small 2.5% sky areas with
the mission's 555 GHz data we identify and mitigate the bias. This analysis
underscores the importance of large sky coverage. We show that when only low
multipoles $\ell \leq 12$ are used, the non-Gaussian shape of the true
likelihood gives uncertainties that are on average 30% larger than a Gaussian
approximation. |
Buoyant Bubbles in Intracluster Gas: Effects of Magnetic Fields and
Anisotropic Viscosity: Recent observations by Chandra and XMM-Newton indicate there are complex
structures at the cores of galaxy clusters, such as cavities and filaments. One
plausible model for the formation of such structures is the interaction of
radio jets with the intracluster medium (ICM). To investigate this idea, we use
three-dimensional magnetohydrodynamic simulations including anisotropic
(Braginskii) viscosity to study the effect of magnetic fields on the evolution
and morphology of buoyant bubbles in the ICM. We investigate a range of
different initial magnetic field geometries and strengths, and study the
resulting x-ray surface brightness distribution for comparison to observed
clusters. Magnetic tension forces and viscous transport along field lines tend
to suppress instabilities parallel, but not perpendicular, to field lines.
Thus, the evolution of the bubble depends strongly on the initial field
geometry. We find toroidal field loops initially confined to the interior of
the bubble are best able reproduce the observed cavity structures. | Lagrangian bias in the local bias model: It is often assumed that the halo-patch fluctuation field can be written as a
Taylor series in the initial Lagrangian dark matter density fluctuation field.
We show that if this Lagrangian bias is local, and the initial conditions are
Gaussian, then the two-point cross-correlation between halos and mass should be
linearly proportional to the mass-mass auto-correlation function. This
statement is exact and valid on all scales; there are no higher order
contributions, e.g., from terms proportional to products or convolutions of
two-point functions, which one might have thought would appear upon truncating
the Taylor series of the halo bias function. In addition, the auto-correlation
function of locally biased tracers can be written as a Taylor series in the
auto-correlation function of the mass; there are no terms involving, e.g.,
derivatives or convolutions. Moreover, although the leading order coefficient,
the linear bias factor of the auto-correlation function is just the square of
that for the cross-correlation, it is the same as that obtained from expanding
the mean number of halos as a function of the local density only in the
large-scale limit. In principle, these relations allow simple tests of whether
or not halo bias is indeed local in Lagrangian space. We discuss why things are
more complicated in practice. We also discuss our results in light of recent
work on the renormalizability of halo bias, demonstrating that it is better to
renormalize than not. We use the Lognormal model to illustrate many of our
findings. |
Cosmological backreaction: This work summarises some of the attempts to explain the phenomenon of dark
energy as an effective description of complex gravitational physics and the
proper interpretation of observations. Cosmological backreaction has been shown
to be relevant for observational (precision) cosmology, nevertheless no
convincing explanation of dark energy by means of backreaction has been given
so far. | Exact treatment of weak dark matter-baryon scattering for
linear-cosmology observables: Elastic scattering of dark matter (DM) particles with baryons induce
cosmological signals that may be detectable with modern or future telescopes.
For DM-baryon scattering cross sections scaling with negative powers of
relative velocity, $\sigma_{\chi b}(v) \propto v^{-2}, v^{-4}$, such
interactions introduce a momentum-exchange rate that is nonlinear in DM-baryon
bulk relative velocities, thus not amenable for inclusion as-is into standard
linear cosmological Boltzmann codes. Linear ansatzes have been adopted in past
works, but their accuracy is unknown as they do not arise from first-principles
derivations. In this work, for the first time, we construct a rigorous
framework for computing linear-cosmology observables as a perturbative
expansion in $\sigma_{\chi b}$. We argue that this approach is accurate for
Cosmic Microwave Background (CMB) angular power spectra when most or all of the
DM is scattering with baryons with cross section $\sigma_{\chi b}(v) \propto
v^{-2}, v^{-4}$. We derive exact formal expressions for CMB power spectra at
linear order in $\sigma_{\chi b}$, and show that they only depend on a specific
velocity integral of the momentum-exchange rate. Consequently, we can obtain
the exact power spectra at linear order in $\sigma_{\chi b}$ by substituting
the original nonlinear momentum-exchange rate with a uniquely specified linear
rate. Serendipitously, we find that the exact substitution we derive from first
principles precisely coincides with the most widely used linear ansatz, thus
placing previous CMB-anisotropy upper bounds on a more solid footing. In
addition to finally providing an exact cosmological solution to the DM-baryon
scattering problem in a well-defined region of parameter space, the framework
we construct opens the way to computing higher-order correlation functions,
beyond power spectra, which are promising yet unexplored probes of DM-baryon
scattering. |
Constraints on the time variation of the speed of light using Pantheon
dataset: Both the absolute magnitude of type Ia supernovae (SNe Ia) and the luminosity
distance of them are modified in the context of the minimally extended varying
speed of light (meVSL) model compared to those of general relativity (GR). We
have analyzed the likelihood of various dark energy models under meVSL by using
the Pantheon SNe Ia data. Both $\omega$CDM and CPL parameterization dark energy
models indicate a cosmic variation of the speed of light at the 1-$\sigma$
level. For $\Omega_{\text{m} 0} = 0.30, 0.31$, and 0.32 with $(\omega_0 \,,
\omega_a) = (-1 \,, 0)$, 1-$\sigma$ range of $\dot{\tilde{c}}_0/\tilde{c}_0 \,
(10^{-13} \, \text{yr}^{-1}) $ are (-8.76 \,, -0.89), (-11.8 \,, 3.93), and
(-14.8 \,, -6.98), respectively. Meanwhile, 1-$\sigma$ range of
$\dot{\tilde{c}}_0/\tilde{c}_0 (10^{-12} \, \text{yr}^{-1}) $ for the CPL dark
energy models with $-1.05 \leq \omega_{0} \leq -0.95$ and $0.28 \leq
\Omega_{\text{m} 0} \leq 0.32$, are (-6.31\,, -2.98). The value of $\tilde{c}$
at $z = 3$ can be larger than that of the present by $0.2 \sim 3$ \% for
$\omega$CDM models and $5 \sim 13$ \% for CPL models. We also obtain $-25.6
\leq \dot{\tilde{G}}_0/\tilde{G}_0 \, (10^{-12} \, \text{yr}^{-1}) \leq -0.36$
for viable models except for CPL model for $\Omega_{\text{m} 0} = 0.28$. We
obtain the increasing rate of the gravitational constant as $1.65 \leq
\dot{\tilde{G}}_0/\tilde{G}_0 \, (10^{-12} \, \text{yr}^{-1}) \leq 3.79$ for
that model. | Detecting Features in the Dark Energy Equation of State: A Wavelet
Approach: We study the utility of wavelets for detecting the redshift evolution of the
dark energy equation of state w(z) from the combination of supernovae, CMB and
BAO data. We show that local features in w, such as bumps, can be detected
efficiently using wavelets. To demonstrate, we first generate a mock supernovae
(SNe) data sample for a SNAP-like survey with a bump feature in w(z) hidden in,
then successfully discover it by performing a blind wavelet analysis. We also
apply our method to analyze the recently released "Constitution" SNe data,
combined with WMAP and BAO from SDSS, and find weak hints of dark energy
dynamics. Namely, we find that models with w(z) < -1 for 0.2 < z < 0.5, and
w(z)> -1 for 0.5 < z <1, are mildly favored at 95% confidence level. This is in
good agreement with several recent studies using other methods, such as
redshift binning with principal component analysis (PCA) (e.g. Zhao and Zhang,
arXiv:0908.1568) |
IM3SHAPE: A maximum-likelihood galaxy shear measurement code for cosmic
gravitational lensing: We present and describe im3shape, a new publicly available galaxy shape
measurement code for weak gravitational lensing shear. im3shape performs a
maximum likelihood fit of a bulge-plus-disc galaxy model to noisy images,
incorporating an applied point spread function. We detail challenges faced and
choices made in its design and implementation, and then discuss various
limitations that affect this and other maximum likelihood methods. We assess
the bias arising from fitting an incorrect galaxy model using simple noise-free
images and find that it should not be a concern for current cosmic shear
surveys.
We test im3shape on the GREAT08 Challenge image simulations, and meet the
requirements for upcoming cosmic shear surveys in the case that the simulations
are encompassed by the fitted model, using a simple correction for image noise
bias. For the fiducial branch of GREAT08 we obtain a negligible additive shear
bias and sub-two percent level multiplicative bias, which is suitable for
analysis of current surveys. We fall short of the sub-percent level requirement
for upcoming surveys, which we attribute to a combination of noise bias and the
mis-match between our galaxy model and the model used in the GREAT08
simulations. We meet the requirements for current surveys across all branches
of GREAT08, except those with small or high noise galaxies, which we would cut
from our analysis. Using the GREAT08 metric we we obtain a score of Q=717 for
the usable branches, relative to the goal of Q=1000 for future experiments. The
code is freely available from https://bitbucket.org/joezuntz/im3shape | The Dark Matter Density in the Solar Neighborhood reconsidered: Both the gas flaring and the dip in the rotation curve, which was recently
reconfirmed with precise measurements using the VERA VLBI array in Japan,
suggest doughnut-like substructure in the dark matter (DM) halo. A global fit
to all available data shows that the data are indeed best described by an NFW
DM profile complemented by two doughnut-like DM substructures with radii of 4.2
and 12.4 kpc, which coincide with the local dust ring and the Monocerus ring of
stars, respectively. Both regions have been suggested as regions with tidal
streams from "shredded" satellites. If real, the radial extensions of these
nearby ringlike structures enhance the local dark matter density by a factor of
four to about 1.3$\pm0.3$ GeV/cm$^3$.
It is shown that i) this higher DM density is perfectly consistent with the
local gravitational potential determining the surface density and the local
matter density (Oort limit), ii) previous determinations of the surface density
were biased by the assumption of a smoothly varying DM halo and iii) the
s-shaped gas flaring is explained. Such a possible enhancement of the local DM
density is of great interest for direct DM searches and would change the
directional dependence for indirect DM searches. |
Extending the $L_{\mathrm{X}}-T$ relation from clusters to groups-Impact
of cool core nature, AGN feedback, and selection effects: We aim to investigate the bolometric $L_{\mathrm{X}}-T$ relation for galaxy
groups, and study the impact of gas cooling, feedback from supermassive black
holes, and selection effects on it. With a sample of 26 galaxy groups we
obtained the best fit $L_{\mathrm{X}}-T$ relation for five different cases
depending on the ICM core properties and central AGN radio emission, and
determined the slopes, normalisations, intrinsic and statistical scatters for
both temperature and luminosity. Simulations were undertaken to correct for
selection effects (e.g. Malmquist bias) and the bias corrected relations for
groups and clusters were compared. The slope of the bias corrected
$L_{\mathrm{X}}-T$ relation is marginally steeper but consistent with clusters
($\sim 3$). Groups with a central cooling time less than 1 Gyr (SCC groups)
show indications of having the steepest slope and the highest normalisation.
For the groups, the bias corrected intrinsic scatter in $L_{\mathrm{X}}$ is
larger than the observed scatter for most cases, which is reported here for the
first time. Lastly, we see indications that the groups with an extended central
radio source have a much steeper slope than those groups which have a CRS with
only core emission. Additionally, we also see indications that the more
powerful radio AGN are preferentially located in NSCC groups rather than SCC
groups. | Satellite Alignment: I. Distribution of Substructures and Their
Dependence On Assembly History From N-Body Simulations: Observations have shown that the spatial distribution of satellite galaxies
is not random, but aligned with the major axes of central galaxies. This
alignment is dependent on galaxy properties, such that red satellites are more
strongly aligned than blue satellites. Theoretical work done to interpret this
phenomena has found that it is due to the non-spherical nature of dark matter
halos. However, most studies over-predict the alignment signal under the
assumption that the central galaxy shape follows the shape of the host halo. It
is also not clear whether the color dependence of alignment is due to an
assembly bias or an evolution effect. In this paper we study these problems
using a cosmological N-body simulation. Subhalos are used to trace the
positions of satellite galaxies. It is found that the shape of dark matter
halos are mis-aligned at different radii. If the central galaxy shares the same
shape as the inner host halo, then the alignment effect is weaker and agrees
with observational data. However, it predicts almost no dependence of alignment
on the color of satellite galaxies, though the late accreted subhalos show
stronger alignment with the outer layer of the host halo than their early
accreted counterparts. We find that this is due to the limitation of pure
N-body simulations that satellites galaxies without associated subhalos
('orphan galaxies') are not resolved. These orphan (mostly red) satellites
often reside in the inner region of host halos and should follow the shape of
the host halo in the inner region. |
RR Lyrae stars in the inner LMC: Where did they form?: RR Lyrae stars (RRLS) belong to population II and are generally used as a
tracer of the host galaxy halo. The surface as well as vertical distribution of
RRLS in the inner Large Magellanic Cloud (LMC) are studied to understand
whether these stars are actually formed in the halo. RRLS identified by the
OGLE III survey are used to estimate their number density distribution. The
scale-height of their distribution is estimated using extinction corrected
average magnitudes of ab type stars. The density distribution mimics the bar,
confirming results in the literature. The distribution of their scale height
indicates that there may be two populations, one with smaller scale-height,
very similar to the red clump stars and the other, much larger. The
distribution of the reddening-corrected magnitude along the minor axis shows
variation, suggesting an inclination. The inclination is estimated to be i =
31.3 (3.5) degrees, very similar to the inclination of the disk. Thus, the RRLS
in the inner LMC mimic the bar and inclination of the disk, suggesting that a
major fraction of RRLS is formed in the disk of the LMC. The results indicate
that the RRLS in the inner LMC trace the disk and probably the inner halo. They
do not trace the extended metal-poor halo of the LMC. We suggest that a major
star formation event happened in the LMC at 10-12 Gyrs ago, resulting in the
formation of most of the inner RRLS, as well as probably the globular clusters,
inner halo and the disk of the LMC. | Revisiting CFHTLenS cosmic shear: Optimal E/B mode decomposition using
COSEBIs and compressed COSEBIs: We present a re-analysis of the CFHTLenS weak gravitational lensing survey
using Complete Orthogonal Sets of E/B-mode Integrals, known as COSEBIs. COSEBIs
provide a complete set of functions to efficiently separate E-modes from
B-modes and hence allow for robust and stringent tests for systematic errors in
the data. This analysis reveals significant B-modes on large angular scales
that were not previously seen using the standard E/B decomposition analyses. We
find that the significance of the B-modes is enhanced when the data is split by
galaxy type and analysed in tomographic redshift bins. Adding tomographic bins
to the analysis increases the number of COSEBIs modes, which results in a less
accurate estimation of the covariance matrix from a set of simulations. We
therefore also present the first compressed COSEBIs analysis of survey data,
where the COSEBIs modes are optimally combined based on their sensitivity to
cosmological parameters. In this tomographic CCOSEBIs analysis we find the
B-modes to be consistent with zero when the full range of angular scales are
considered. |
Formation of Dwarf Spheroidal Galaxies Via Mergers of Disky Dwarfs: We perform collisionless N-body simulations to investigate whether binary
mergers between rotationally-supported dwarfs can lead to the formation of
dwarf spheroidal galaxies (dSphs). Our simulation campaign is based on a hybrid
approach combining cosmological simulations and controlled numerical
experiments. We select merger events from a Constrained Local UniversE (CLUES)
simulation of the Local Group (LG) and record the properties of the interacting
dwarf-sized halos. This information is subsequently used to seed controlled
experiments of binary encounters between dwarf galaxies consisting of
exponential stellar disks embedded in cosmologically-motivated dark matter
halos. These simulations are designed to reproduce eight cosmological merger
events, with initial masses of the interacting systems in the range ~ (5-60) x
10^7 Mo, occurring quite early in the history of the LG, more than 10 Gyr ago.
We compute the properties of the merger remnants as a distant observer would
and demonstrate that at least three of the simulated encounters produce systems
with kinematic and structural properties akin to those of the classic dSphs in
the LG. Tracing the history of the remnants in the cosmological simulation to
z=0, we find that two dSph-like objects remain isolated at distances larger
than 800 kpc from either the Milky Way or M31. These systems constitute
plausible counterparts of the remote dSphs Cetus and Tucana which reside in the
LG outskirts, far from the tidal influence of the primary galaxies. We conclude
that merging of rotationally-supported dwarfs represents a viable mechanism for
the formation of dSphs in the LG and similar environments. | Constraints on ultracompact minihalos from extragalactic γ-ray
background: It has been proposed that ultracompact minihalos (UCMHs) might be formed in
earlier epoch. If dark matter consists of Weakly Interacting Massive Particles
(WIMPs), UCMHs can be treated as the {\gamma}-ray sources due to dark matter
annihilation within them. In this paper, we investigate the contributions of
UCMHs formed during three phase transi- tions (i.e., electroweak symmetry
breaking, QCD confinement and e+ e- annihilation) to the extragalactic
{\gamma}-ray background. Moreover, we use the Fermi-LAT observation data of the
extragalactic {\gamma}-ray background to get the constraints on the current
abundance of UCMHs produced during these phase transitions. We also compare
these results with those obtained from Cosmic Microwave Background (CMB)
observations and find that the constraints from the Fermi-LAT are more
stringent than those from CMB |
Determination of the Cosmic Infrared Background from COBE/FIRAS and
Planck HFI Observations: New determinations are presented of the cosmic infrared background monopole
brightness in the Planck HFI bands from 100 GHz to 857 GHz. Planck was not
designed to measure the monopole component of sky brightness, so
cross-correlation of the 2015 HFI maps with COBE/FIRAS data is used to
recalibrate the zero level of the HFI maps. For the HFI 545 and 857 GHz maps,
the brightness scale is also recalibrated. Correlation of the recalibrated HFI
maps with a linear combination of Galactic H I and H alpha data is used to
separate the Galactic foreground emission and determine the cosmic infrared
background brightness in each of the HFI bands. We obtain CIB values of 0.007
+- 0.014, 0.010 +- 0.019, 0.060 +- 0.023, 0.149 +- 0.017, 0.371 +- 0.018, and
0.576 +- 0.034 MJy/sr at 100, 143, 217, 353, 545, and 857 GHz, respectively.
The estimated uncertainties for the 353 to 857 GHz bands are about 3 to 6 times
smaller than those of previous direct CIB determinations at these frequencies.
Our results are compared with integrated source brightness results from
selected recent submillimeter and millimeter wavelength imaging surveys. | Detecting Dark Energy Fluctuations with Gravitational Waves: Luminosity distance estimates from electromagnetic and gravitational wave
sources are generally different in models of dynamical dark energy and gravity
beyond the standard cosmological scenario. We show that this leaves a unique
imprint on the angular power-spectrum of fluctuations of the luminosity
distance of gravitational-wave observations which tracks inhomogeneities in the
dark energy field. Exploiting the synergy in supernovae and gravitational wave
distance measurements, we build a joint estimator that directly probes dark
energy fluctuations, providing a conclusive evidence for their existence in
case of detection. Moreover, such measurement would also allow to probe the
running of the Planck mass. We discuss experimental requirements to detect
these signals. |
Cosmic Initial Conditions for a Habitable Universe: Within the framework of an eternal inflationary scenario, a natural question
regarding the production of eternal bubbles is the essential condition requires
to have a universe capable of generating life. In either an open or a closed
universe, we find an anthropic lower bound on the amount of e-folding in the
order of $60$ for the inflationary epoch, which results in the formation of
large-scale structures in both linear and non-linear regimes. We extend the
question of the initial condition of the universe to the sufficient condition
in which we have enough initial dark matter and baryonic matter asymmetry in
the early universe for the formation of galactic halos, stars, planets and
consequently life. We show that the probability of a habitable universe is
proportional to the asymmetry of dark matter and baryonic matter, while the
cosmic budget of baryonic matter is limited by the astrophysical constrains. | Primordial black holes and oscillating gravitational waves in slow-roll
and slow-climb inflation with an intermediate non-inflationary phase: We propose a new single field inflation model in which the usual slow-roll
inflation is joined to a new period of slow-climb and slow-roll inflation
through a short intermediate non-inflationary phase. We then show that
primordial curvature perturbations can be enhanced at small scales, a sizable
amount of primordial black holes (PBHs) can be produced which make up most of
dark matter, the gravitational waves (GWs) induced by scalar metric
perturbations that accompany with the formation of PBHs can be detectable by
future GW experiments, and last but not least, our model is compatible with the
latest cosmic microwave background observations. Remarkably, the GW spectrum
displays a unique oscillating character in the ultraviolet regions which
originates from the short non-inflationary phase. A detection of such
oscillations in the GW spectrum may suggest the existence of such a
non-inflationary phase in the whole inflation, thus providing us a chance to
reveal an interesting period in the evolution of the early Universe and
distinguish our model from others. |
Emulating galaxy clustering and galaxy-galaxy lensing into the deeply
nonlinear regime: methodology, information, and forecasts: The combination of galaxy-galaxy lensing (GGL) with galaxy clustering is one
of the most promising routes to determining the amplitude of matter clustering
at low redshifts. We show that extending clustering+GGL analyses from the
linear regime down to $\sim 0.5 \, h^{-1}$ Mpc scales increases their
constraining power considerably, even after marginalizing over a flexible model
of non-linear galaxy bias. Using a grid of cosmological N-body simulations, we
construct a Taylor-expansion emulator that predicts the galaxy autocorrelation
$\xi_{\text{gg}}(r)$ and galaxy-matter cross-correlation $\xi_{\text{gm}}(r)$
as a function of $\sigma_8$, $\Omega_m$, and halo occupation distribution (HOD)
parameters, which are allowed to vary with large scale environment to represent
possible effects of galaxy assembly bias. We present forecasts for a fiducial
case that corresponds to BOSS LOWZ galaxy clustering and SDSS-depth weak
lensing (effective source density $\sim 0.3$ arcmin$^{-2}$). Using tangential
shear and projected correlation function measurements over $0.5 \leq r_p \leq
30 \, h^{-1}$ Mpc yields a 1.8% constraint on the parameter combination
$\sigma_8\Omega_m^{0.58}$, a factor of two better than a constraint that
excludes non-linear scales ($r_p > 2 \, h^{-1}$ Mpc, $4 \, h^{-1}$ Mpc for
$\gamma_t,w_p$). Much of this improvement comes from the non-linear clustering
information, which breaks degeneracies among HOD parameters that would
otherwise degrade the inference of matter clustering from GGL. Increasing the
effective source density to $3$ arcmin$^{-2}$ sharpens the constraint on
$\sigma_8\Omega_m^{0.58}$ by a further factor of two. With robust modeling into
the non-linear regime, low-redshift measurements of matter clustering at the
1-percent level with clustering+GGL alone are well within reach of current data
sets such as those provided by the Dark Energy Survey. | Self-similar growth of Bose stars: We analytically solve the problem of Bose star growth in the bath of
gravitationally interacting particles. We find that after nucleation of this
object the bath is described by a self-similar solution of kinetic equation.
Together with the conservation laws, this fixes mass evolution of the Bose
star. Our theory explains, in particular, the slowdown of the star growth at a
certain "core-halo" mass, but also predicts formation of heavier and lighter
objects in magistral dark matter models. The developed "adiabatic" approach to
self-similarity may be of interest for kinetic theory in general. |
Generation of magnetic fields in Einstein-Aether gravity: Recently the lower bounds of the intergalactic magnetic fields $10^{-16} \sim
10^{-20}$ Gauss are set by gamma-ray observations while it is unlikely to
generate such large scale magnetic fields through astrophysical processes. It
is known that large scale magnetic fields could be generated if there exist
cosmological vector mode perturbations in the primordial plasma. The vector
mode, however, has only a decaying solution in General Relativity if the plasma
consists of perfect fluids. In order to investigate a possible mechanism of
magnetogenesis in the primordial plasma, here we consider cosmological
perturbations in the Einstein-Aether gravity model, in which the aether field
can act as a new source of vector metric perturbations and thus of magnetic
fields. We estimate the angular power spectra of temperature and B-mode
polarization of the Cosmic Microwave Background (CMB) Anisotropies in this
model and put a rough constraint on the aether field parameters from latest
observations. We then estimate the power spectrum of associated magnetic fields
around the recombination epoch within this limit. It is found that the spectrum
has a characteristic peak at $k=0.1 h{\rm Mpc^{-1}}$, and at that scale the
amplitude can be as large as $B\sim 10^{-22}$ Gauss where the upper bound comes
from CMB temperature anisotropies. The magnetic fields with this amplitude can
be seeds of large scale magnetic fields observed today if the sufficient dynamo
mechanism takes place. Analytic interpretation for the power spectra is also
given. | Gravitational potential and X-ray luminosities of early-type galaxies
observed with XMM-Newton and Chandra: We study dark matter content in early-type galaxies and investigate whether
X-ray luminosities of early-type galaxies are determined by the surrounding
gravitational potential. We derived gravitational mass profiles of 22
early-type galaxies observed with XMM-Newton and Chandra. Sixteen galaxies show
constant or decreasing radial temperature profiles, and their X-ray
luminosities are consistent with kinematical energy input from stellar mass
loss. The temperature profiles of the other 6 galaxies increase with radius,
and their X-ray luminosities are significantly higher. The integrated
mass-to-light ratio of each galaxy is constant at that of stars within 0.5-1
r_e, and increases with radius, where r_e is the effective radius of a galaxy.
The scatter of the central mass-to-light ratio of galaxies was less in K-band
light. At 3r_e, the integrated mass-to-light ratios of galaxies with flat or
decreasing temperature profiles are twice the value at 0.5r_e, where the
stellar mass dominates, and at 6r_e, these increase to three times the value at
0.5r_e. This feature should reflect common dark and stellar mass distributions
in early-type galaxies: Within 3r_e, the mass of dark matter is similar to the
stellar mass, while within 6r_e, the former is larger than the latter by a
factor of two. By contrast, X-ray luminous galaxies have higher gravitational
mass in the outer regions than X-ray faint galaxies. We describe these X-ray
luminous galaxies as the central objects of large potential structures; the
presence or absence of this potential is the main source of the large scatter
in the X-ray luminosity. |
Light on Dark Matter with Weak Gravitational Lensing: This paper reviews statistical methods recently developed to reconstruct and
analyze dark matter mass maps from weak lensing observations. The field of weak
lensing is motivated by the observations made in the last decades showing that
the visible matter represents only about 4-5% of the Universe, the rest being
dark. The Universe is now thought to be mostly composed by an invisible,
pressureless matter -potentially relic from higher energy theories- called
"dark matter" (20-21%) and by an even more mysterious term, described in
Einstein equations as a vacuum energy density, called "dark energy" (70%). This
"dark" Universe is not well described or even understood, so this point could
be the next breakthrough in cosmology. Weak gravitational lensing is believed
to be the most promising tool to understand the nature of dark matter and to
constrain the cosmological model used to describe the Universe. Gravitational
lensing is the process in which light from distant galaxies is bent by the
gravity of intervening mass in the Universe as it travels towards us. This
bending causes the image of background galaxies to appear slightly distorted
and can be used to extract significant results for cosmology. Future weak
lensing surveys are already planned in order to cover a large fraction of the
sky with large accuracy. However this increased accuracy also places greater
demands on the methods used to extract the available information. In this
paper, we will first describe the important steps of the weak lensing
processing to reconstruct the dark matter distribution from shear estimation.
Then we will discuss the problem of statistical estimation in order to set
constraints on the cosmological model. We review the methods which are
currently used especially new methods based on sparsity. | The angle-averaged squeezed limit of nonlinear matter N-point functions: We show that in a certain, angle-averaged squeezed limit, the $N$-point
function of matter is related to the response of the matter power spectrum to a
long-wavelength density perturbation,
$P^{-1}d^nP(k|\delta_L)/d\delta_L^n|_{\delta_L=0}$, with $n=N-2$. By performing
N-body simulations with a homogeneous overdensity superimposed on a flat
Friedmann-Robertson-Lema\^itre-Walker (FRLW) universe using the \emph{separate
universe} approach, we obtain measurements of the nonlinear matter power
spectrum response up to $n=3$, which is equivalent to measuring the fully
nonlinear matter $3-$ to $5-$point function in this squeezed limit. The
sub-percent to few percent accuracy of those measurements is unprecedented. We
then test the hypothesis that nonlinear $N$-point functions at a given time are
a function of the linear power spectrum at that time, which is predicted by
standard perturbation theory (SPT) and its variants that are based on the ideal
pressureless fluid equations. Specifically, we compare the responses computed
from the separate universe simulations and simulations with a rescaled initial
(linear) power spectrum amplitude. We find discrepancies of 10\% at $k\simeq
0.2 - 0.5 \,h\,{\rm Mpc}^{-1}$ for $5-$ to $3-$point functions at $z=0$. The
discrepancy occurs at higher wavenumbers at $z=2$. Thus, SPT and its variants,
carried out to arbitrarily high order, are guaranteed to fail to describe
matter $N$-point functions ($N>2$) around that scale. |
Cyclic and Ekpyrotic Universes in Modified Finsler Osculating Gravity on
Tangent Lorentz Bundles: We consider models of accelerating Universe elaborated for Finsler like
gravity theories constructed on tangent bundles to Lorentz manifolds. In the
osculating approximation, certain locally anisotropic configurations are
similar to those for f(R) gravity. This allows us to generalize a proposal (by
Nojiri, Odintsov and Saez-Gomez, arXiv: 1108.0767) in order to reconstruct and
compare two classes of Einstein-Finsler gravity, EFG, and f(R) gravity theories
using modern cosmological data and realistic physical scenarios. We conclude
that EFG provides inflation, acceleration and little rip evolution scenarios
with realistic alternatives to standard Lambda CDM cosmology. The approach is
based on a proof that there is a general decoupling property of gravitational
field equations in EFG and modified theories which allows us to generate
off-diagonal cosmological solutions. | Possible interaction between baryons and dark-matter particles revealed
by the first stars: The cosmic radio-frequency spectrum is expected to show a strong absorption
signal corresponding to the 21-centimetre-wavelength transition of atomic
hydrogen around redshift 20, which arises from Lyman-alpha radiation from some
of the earliest stars. By observing this 21-centimetre signal - either its
sky-averaged spectrum or maps of its fluctuations, obtained using radio
interferometers - we can obtain information about cosmic dawn, the era when the
first astrophysical sources of light were formed. The recent detection of the
global 21-centimetre spectrum reveals a stronger absorption than the maximum
predicted by existing models, at a confidence level of 3.8 standard deviations.
Here we report that this absorption can be explained by the combination of
radiation from the first stars and excess cooling of the cosmic gas induced by
its interaction with dark matter. Our analysis indicates that the spatial
fluctuations of the 21-centimetre signal at cosmic dawn could be an order of
magnitude larger than previously expected and that the dark-matter particle is
no heavier than several proton masses, well below the commonly predicted mass
of weakly interacting massive particles. Our analysis also confirms that dark
matter is highly non-relativistic and at least moderately cold, and primordial
velocities predicted by models of warm dark matter are potentially detectable.
These results indicate that 21-centimetre cosmology can be used as a
dark-matter probe. |
Global Optimization methods for Gravitational Lens Systems with
Regularized Sources: Several approaches exist to model gravitational lens systems. In this study,
we apply global optimization methods to find the optimal set of lens parameters
using a genetic algorithm. We treat the full optimization procedure as a
two-step process: an analytical description of the source plane intensity
distribution is used to find an initial approximation to the optimal lens
parameters. The second stage of the optimization uses a pixelated source plane
with the semilinear method to determine an optimal source. Regularization is
handled by means of an iterative method and the generalized cross validation
(GCV) and unbiased predictive risk estimator (UPRE) functions that are commonly
used in standard image deconvolution problems. This approach simultaneously
estimates the optimal regularization parameter and the number of degrees of
freedom in the source. Using the GCV and UPRE functions we are able to justify
an estimation of the number of source degrees of freedom found in previous
work. We test our approach by applying our code to a subset of the lens systems
included in the SLACS survey. | Constraints on mass loss and self-enrichment scenarios for the globular
clusters of the Fornax dSph: Recently, high-dispersion spectroscopy has demonstrated conclusively that
four of the five globular clusters (GCs) in the Fornax dwarf spheroidal galaxy
are very metal-poor with [Fe/H]<-2. The remaining cluster, Fornax 4, has
[Fe/H]=-1.4. This is in stark contrast to the field star metallicity
distribution which shows a broad peak around [Fe/H]=-1 with only a few percent
of the stars having [Fe/H]<-2. If we only consider stars and clusters with
[Fe/H]<-2 we thus find an extremely high GC specific frequency, SN=400,
implying by far the highest ratio of GCs to field stars known anywhere. We
estimate that about 1/5-1/4 of all stars in the Fornax dSph with [Fe/H]<-2
belong to the four most metal-poor GCs. These GCs could, therefore, at most
have been a factor of 4-5 more massive initially. Yet, the Fornax GCs appear to
share the same anomalous chemical abundance patterns known from Milky Way GCs,
commonly attributed to the presence of multiple stellar generations within the
clusters. The extreme ratio of metal-poor GC- versus field stars in the Fornax
dSph is difficult to reconcile with scenarios for self-enrichment and early
evolution of GCs in which a large fraction (90%-95%) of the first-generation
stars have been lost. It also suggests that the GCs may not have formed as part
of a larger population of now disrupted clusters with an initial power-law mass
distribution. The Fornax dSph may be a rosetta stone for constraining theories
of the formation, self-enrichment and early dynamical evolution of star
clusters. |
Analytical halo models of cosmic tidal fields: The non-linear cosmic web environment of dark matter haloes plays a major
role in shaping their growth and evolution, and potentially also affects the
galaxies that reside in them. We develop an analytical (halo model) formalism
to describe the tidal field of anisotropic halo-centric density distributions,
as characterised by the halo-centric tidal tensor $\langle T_{ij} \rangle(<R)$
spherically averaged on scale $R\sim4R_{\rm vir}$ for haloes of virial radius
$R_{\rm vir}$. We focus on axisymmetric anisotropies, which allows us to
explore simple and intuitive toy models of (sub)halo configurations that
exemplify some of the most interesting anisotropies in the cosmic web. We build
our models around the spherical Navarro-Frenk-White (NFW) profile after
describing it as a Gaussian mixture, which leads to almost fully analytical
expressions for the `tidal anisotropy' scalar $\alpha(<4R_{\rm vir})$ extracted
from the tidal tensor. Our axisymmetric examples include (i) a spherical halo
at the axis of a cylindrical filament, (ii) an off-centred satellite in a
spherical host halo and (iii) an axisymmetric halo. Using these, we demonstrate
several interesting results. For example, the tidal tensor at the axis of a
pure cylindrical filament gives $\alpha^{\rm (fil)}(<R)=1/2$ exactly, for any
$R$. Also, $\alpha(<4R_{\rm vir,sat})$ for a satellite of radius $R_{\rm
vir,sat}$ as a function of its host-centric distance is a sensitive probe of
dynamical mass loss of the satellite in its host environment. Finally, we
discuss a number of potentially interesting extensions and applications of our
formalism that can deepen our understanding of the multi-scale phenomenology of
the cosmic web. | Constraints on the birth of the universe and origin of cosmic dark flow: We summarize three recent efforts to constrain the first few moments of
cosmic creation before and during the epoch of inflation. We consider two means
to explain a slight dip in the power spectrum of the cosmic microwave
background for multipoles in the range of $\ell= 10-30$ from both the {\it
Planck} and {\it WMAP} data. We show that such a dip could be the result of
resonant creation of a massive particle that couples to the inflaton field. For
best-fit models, the epoch of resonant particle creation reenters the horizon
at wave numbers of $k_* \sim 0.00011 \pm 0.0004 $ ($h$ Mpc$^{-1}$). The
amplitude and location of these features correspond to the creation of a number
of degenerate fermion species of mass $\sim 15/\lambda^{3/2} $ $m_{pl}$ during
inflation where $\lambda$ is the coupling constant between the inflaton field
and the created fermion species. Alternatively, one can explain the existence
of such a dip as due to a jump in the inflation generating potential. We show
that such a jump can also resolve the excessively large dark flow predicted
from the M-theory landscape. Finally, we summarize our efforts to quantify
constraints on the cosmic dark flow from a new analysis of the Type Ia
supernova distance-redshift relation. |
Pure kinetic k-essence as the cosmic speed-up: In this paper, we consider three types of k-essence. These k-essence models
were presented in the parametric forms. The exact analytical solutions of the
corresponding equations of motion are found. It is shown that these k-essence
models for the presented solutions can give rise to cosmic acceleration. | Consistency of dark matter interpretations of the 3.5 keV X-ray line: Tentative evidence of a 3.5 keV X-ray line has been found in the stacked
spectra of galaxy clusters, individual clusters, the Andromeda galaxy and the
galactic center, leading to speculation that it could be due to decays of
metastable dark matter such as sterile neutrinos. However searches for the line
in other systems such as dwarf satellites of the Milky Way have given negative
or ambiguous results. We reanalyze both the positive and negative searches from
the point of view that the line is due to inelastic scattering of dark matter
to an excited state that subsequently decays---the mechanism of excited dark
matter (XDM). Unlike the metastable dark matter scenario, XDM gives a stronger
signal in systems with higher velocity dispersions, such as galaxy clusters. We
show that the predictions of XDM can be consistent with null searches from
dwarf satellites, while the signal from the closest individual galaxies can be
detectable having a flux consistent with that from clusters. We discuss the
impact of our new fits to the data for two specific realizations of XDM. |
Further constraining galaxy evolution models through the Size Function
of SDSS Early-type galaxies: We discuss how the effective radius Phi(Re) function (ERF) recently worked
out by Bernardi et al. (2009) represents a new testbed to improve the current
understanding of Semi-analytic Models of Galaxy formation. In particular, we
here show that a detailed hierarchical model of structure formation can broadly
reproduce the correct peak in the size distribution of local early-type
galaxies, although it significantly overpredicts the number of very compact and
very large galaxies. This in turn is reflected in the predicted size-mass
relation, much flatter than the observed one, due to too large (~3 kpc)
low-mass galaxies (<10^11 \msun), and to a non-negligible fraction of compact
(< 0.5-1 kpc) and massive galaxies (> 10^11 \msun). We also find that the
latter discrepancy is smaller than previously claimed, and limited to only
ultracompact (Re < 0.5 kpc) galaxies when considering elliptical-dominated
samples. We explore several causes behind these effects. We conclude that the
former problem might be linked to the initial conditions, given that large and
low-mass galaxies are present at all epochs in the model. The survival of
compact and massive galaxies might instead be linked to their very old ages and
peculiar merger histories. Overall, knowledge of the galactic stellar mass {\em
and} size distributions allows a better understanding of where and how to
improve models. | The First Billion Years Project: The escape fraction of ionizing photons
in the epoch of reionization: Proto-galaxies forming in low-mass dark matter haloes are thought to provide
the majority of ionizing photons needed to reionize the Universe, due to their
high escape fractions of ionizing photons. We study how the escape fraction in
high-redshift galaxies relates to the physical properties of the halo in which
the galaxies form, by computing escape fractions in more than 75000 haloes
between redshifts 27 and 6 that were extracted from the First Billion Years
project, high-resolution cosmological hydrodynamics simulations of galaxy
formation. We find that the main constraint on the escape fraction is the gas
column density in a radius of 10 pc around the stellar populations, causing a
strong mass dependence of the escape fraction. The lower potential well in
haloes with virial mass below 1e8 solar mass results in low column densities
that can be penetrated by radiation from young stars (age < 5 Myr). In haloes
with virial mass above 1e8 solar mass supernova feedback is important, but only
30% of the haloes in this mass range have an escape fraction higher than 1%. We
find a large range of escape fractions in haloes with similar properties,
caused by different distributions of the dense gas in the halo. This makes it
very hard to predict the escape fraction on the basis of halo properties and
results in a highly anisotropic escape fraction. The strong mass dependence,
the large spread and the large anisotropy of the escape fraction may strongly
affect the topology of reionization and is something current models of cosmic
reionization should strive to take into account. |
Stellar Oscillations in Modified Gravity: Starting from the equations of modified gravity hydrodynamics, we derive the
equ tions of motion governing linear, adiabatic, radial perturbations of stars
in scalar-tensor theories. There are two new features: first, the eigenvalue
equation for the period of stellar oscillations is modified such that the
eigenfrequencies are always larger than predicted by General Relativity.
Second, the General Relativity condition for stellar instability is altered so
that the adiabatic index can fall below 4/3 before unstable modes appear. Stars
are more stable in modified gravity theories. Specialising to the case of
chameleon-like theories, we investigate these effects numerically using both
polytropic Lane-Emden stars and models coming from modified gravity stellar
structure simulations. The change in the oscillation period can be as large as
50% and the critical adiabatic index for instability falls by a composition
dependent amount of order 10^(-1). By solving the new equation for Cepheid
models, it is found that the change in the inferred distance using the
period-luminosity relation can be up to three times larger than if one had only
considered the modified equilibrium structure. We discuss the implications of
these results for recent and up-coming astrophysical tests and estimate that
previous methods can produce new constraints such that the modifications are
screened in regions of Newtonian potential of order 10^(-8). | Multiple measurements of quasars acing as standard probes: exploring the
cosmic distance duality relation at higher redshift: General relativity reproduces main current cosmological observations,
assuming the validity of cosmic distance duality relation (CDDR) at all scales
and epochs. However, CDDR is poorly tested in the redshift interval between the
farthest observed Type Ia supernovae (SN Ia) and that of the Cosmic Microwave
background (CMB). We present a new idea of testing the validity of CDDR,
through the multiple measurements of high-redshift quasars. Luminosity
distances are derived from the relation between the UV and X-ray luminosities
of quasars, while angular diameter distances are obtained from the compact
structure in radio quasars. This will create a valuable opportunity where two
different cosmological distances from the same kind of objects at high
redshifts are compared. Our constraints are more stringent than other currently
available results based on different observational data and show no evidence
for the deviation from CDDR at $z\sim 3$. Such accurate model-independent test
of fundamental cosmological principles can become a milestone in precision
cosmology. |
Effect of dark energy sound speed and equation of state on CDM power
spectrum: We study the influence of equation of state $w$ and effective sound speed
$c_e$ of the dark energy perturbations on the cold dark matter(CDM) power
spectrum.We consider different cases of the equation of state and the effective
sound speed, the cold dark matter power spectrum is found to be generically
suppressed in these cases as compared to the $\Lambda$CDM model. The
suppression at different length scales depends on the value of $w$ and $c_e$,
and the effect of different $w$ is profoundly seen at all length scales. The
influence of sound speed is significantly seen only at the intermediate length
scales and is negligible at scales very much larger and smaller than the Hubble
scale. | Measuring the equation of state of the high-z intergalactic medium using
curvature statistics: Using hydrodynamical simulations, we explore the use of the mean and
percentiles of the curvature distribution function to recover the equation of
state of the high-$z$ ($2 < z < 4$) intergalactic medium (IGM). We find that
the mean and percentiles of the absolute curvature distribution exhibit tight
correlation with the temperatures measured at respective characteristic
overdensities $\bar{\Delta}_i$'s at each redshift. Hence, they provide
complementary probes of the same underlying temperature-density distribution,
and can in principle be used to simultaneously recover both parameters $T_0$
and $\gamma$ of the IGM effective equation of state. We quantify the associated
errors in the recovered parameters $T_0$ and $\gamma$ from the intrinsic
scatter in the characteristic overdensities and the uncertainties in the
curvature measurement. |
Expected number of massive galaxy relics in the present-day Universe: The number of present-day massive galaxies that has survived untouched since
their formation at high-z is an important observational constraint to the
hierarchical galaxy formation models. Using three different semianalytical
models based on the Millenium simulation, we quantify the expected fraction and
number densities of the massive galaxies form at z>2 which have evolved in
stellar mass less than 10% and 30%. We find that only a small fraction of the
massive galaxies already form at z~2 have remained almost unaltered since their
formation (<2% with Delta_M*/M*<0.1 and <8% with Delta_M*/M*<0.3). These
fractions correspond to the following number densities of massive relics in the
present-day Universe: ~1.2x10^-6 Mpc^-3 for Delta_M*/M*<0.1 and ~5.7x10^-6
Mpc^-3 for Delta_M*/M*<0.3. The observed number of relic candidates found in
the nearby Universe is today pretty uncertain (with uncertainties up to a
factor of ~100) preventing to establish a firm conclusion about the goodness of
current theoretical expectations to predict such important number. | A first model-independent radial BAO constraint from the final BOSS
sample: Using almost one million galaxies from the final Data Release 12 of the
SDSS's Baryon Oscillation Spectroscopic Survey, we have obtained, albeit with
low significance, a first model-independent determination of the radial BAO
peak with 9% error: $\Delta z_{\rm BAO}(z_{\rm eff}=0.51)= 0.0456 \pm 0.0042$.
In order to obtain this measurement, the radial correlation function was
computed in 7,700 angular pixels, from which mean correlation function and
covariance matrix were obtained, making the analysis completely model
independent. This novel method of obtaining the covariance matrix was validated
via the comparison with 500 BOSS mock catalogs. This $\Delta z_{\rm BAO}$
determination can be used to constrain the background expansion of exotic
models for which the assumptions adopted in the standard analysis cannot be
satisfied. Future galaxy catalogs from J-PAS, DESI and Euclid are expected to
significantly increase the quality and significance of model-independent
determinations of the BAO peak, possibly determined at various redshift and
angular positions. We stress that it is imperative to test the standard
paradigm in a model-independent way in order to test its foundations, maximize
the extraction of information from the data, and look for clues regarding the
poorly understood dark energy and dark matter. |
Minkowski functionals and the nonlinear perturbation theory in the
large-scale structure: second-order effects: The second-order formula of Minkowski functionals in weakly non-Gaussian
fields is compared with the numerical $N$-body simulations. Recently, weakly
non-Gaussian formula of Minkowski functionals is extended to include the
second-order effects of non-Gaussianity in general dimensions. We apply this
formula to the three-dimensional density field in the large-scale structure of
the Universe. The parameters of the second-order formula include several kinds
of skewness and kurtosis parameters. We apply the tree-level nonlinear
perturbation theory to estimate these parameters. First we compare the
theoretical values with those of numerical simulations on the basis of
parameter values, and next we test the performance of the analytic formula
combined with the perturbation theory. The second-order formula outperforms the
first-order formula in general. The performance of the perturbation theory
depends on the smoothing radius applied in defining the Minkowski functionals.
The quantitative comparisons are presented in detail. | The ATLAS 5.5 GHz survey of the Extended Chandra Deep Field South:
Catalogue, Source Counts and Spectral Indices: Star forming galaxies are thought to dominate the sub-mJy radio population,
but recent work has shown that low luminosity AGN can still make a significant
contribution to the faint radio source population. Spectral indices are an
important tool for understanding the emission mechanism of the faint radio
sources. We have observed the extended Chandra Deep Field South at 5.5 GHz
using a mosaic of 42 pointings with the Australia Telescope Compact Array
(ATCA). Our image reaches an almost uniform sensitivity of ~12 microJy rms over
0.25 deg^2 with a restoring beam of 4.9 x 2.0 arcsec, making it one of the
deepest 6cm surveys to date. We present the 5.5 GHz catalogue and source counts
from this field. We take advantage of the large amounts of ancillary data in
this field to study the 1.4 to 5.5 GHz spectral indices of the sub-mJy
population. For the full 5.5 GHz selected sample we find a flat median spectral
index, alpha_med = -0.40, which is consistent with previous results. However,
the spectral index appears to steepen at the faintest flux density levels
(S_{5.5 GHz} < 0.1 mJy), where alpha_med = -0.68. We performed stacking
analysis of the faint 1.4 GHz selected sample (40 < S_{1.4 GHz} < 200 microJy)
and also find a steep average spectral index, alpha = -0.8, consistent with
synchrotron emission. We find a weak trend of steepening spectral index with
redshift. Several young AGN candidates are identified using spectral indices,
suggesting Gigahertz Peaked Spectrum (GPS) sources are as common in the mJy
population as they are at Jy levels. |
Two-body collapse model for self-gravitating flow of dark matter and
generalized stable clustering hypothesis for pairwise velocity: Analytical tools are extremely hard to find for non-linear gravitational
collpase. Only a few simple but powerful tools exist so far. Two examples are
the spherical collapse model (SCM) and stable clustering hypothesis (SCH). We
present a new analytical tool, a two-body collapse model (TBCM), that plays the
same fundamental role as harmonic oscillator in dynamics. For convenience, TBCM
is formulated for gravity with any potential exponent $n$ in a static
background with a fixed damping ($n$=-1 for Newtonian gravity). The competition
between gravity, expanding background (or damping), and angular momentum
classifies two-body collapse into: 1) free fall collapse, where free fall time
is greater if same system starts to collapse at earlier time; 2) equilibrium
collapse that persists longer in time, whose perturbative solutions lead to
power-law evolution of system energy and momentum. Two critical values
$\beta_{s1}=1$ and $\beta_{s2}=1/3\pi$ are identified that quantifies the
competition between damping and gravity. Value $\beta_{s2}$ only exists for
discrete values of potential exponent $n=(2-6m)/(1+3m)=$ -1,-10/7... for
integer $m$. Critical density ratio ($\Delta_c=18\pi^2$) is obtained for $n$=-1
that is consistent with SCM. TBCM predicts angular velocity $\propto Hr^{-3/2}$
for two-body system of size $r$. The isothermal density is a result of
extremely fast mass accretion. TBCM is able to demonstrate SCH, i.e. mean
pairwise velocity (first moment) $\langle\Delta u\rangle=-Hr$. A generalized
SCH is developed for higher order moments $\langle\Delta
u^{2m+1}\rangle=-(2m+1)\langle\Delta u^{2m}\rangle Hr$ that is validated by
N-body simulation. Energy evolution in TBCM is independent of particle mass and
energy equipartition does not apply. TBCM can be considered as a non-radial
SCM. Both models predict the same critical density ratio, while TBCM contains
much richer information. | Modeling the Anisotropic Two-Point Galaxy Correlation Function on Small
Scales and Improved Measurements of H(z), D_A(z), and f(z)sigma_8(z) from the
Sloan Digital Sky Survey DR7 Luminous Red Galaxies: We present a simple and efficient phenomenological model for the
two-dimensional two-point galaxy correlation function that works well over a
wide range of scales, from large scales down to scales as small as 25Mpc/h. Our
model incorporates nonlinear effects, a scale-dependent galaxy bias on small
scales, and allows the redshift-space distortions to be scale and direction
dependent. We validate our model using LasDamas mock catalogs, and apply it to
the Sloan Digital Sky Survey (SDSS) DR7 Luminous Red Galaxies (LRGs). Using
only the monopole and quadrupole of the correlation function measured from the
SDSS DR7 LRGs, we obtain improved measurements H(z)r_s(z_d)/c=0.0433\pm 0.0042,
D_A(z)/r_s(z_d)=6.59\pm 0.46, and f(z)sigma_8(z)=0.429\pm 0.089 at z=0.35,
using the scale range of 25<s<120Mpc/h. We expect our results and model to be
useful in tightening dark energy and gravity constraints from the full analysis
of current and future galaxy clustering data. |
$μ$-Distortions or Running: A Guaranteed Discovery from CMB
Spectrometry: We discuss the implications of a PIXIE-like experiment, which would measure
$\mu$-type spectral distortions of the CMB at a level of
$\sigma_{\mu}=(1/n)\times 10^{-8}$, with $n\geq1$ representing an improved
sensitivity (e.g. $n=10$ corresponds to PRISM). Using Planck data and
considering the six-parameter $\Lambda$CDM model, we compute the posterior for
$\mu_8\equiv\mu\times 10^{8}$ and find $\mu_8=1.57^{+0.11}_{-0.13}$
($68\%\,\mathrm{CL}$). This becomes $\mu_{8} = 1.28^{+0.30}_{-0.52}$
($68\%\,\mathrm{CL}$) when the running $\alpha_\mathrm{s}$ of the spectral
index is included. We point out that a sensitivity of about $3\times$ PIXIE
implies a guaranteed discovery: $\mu$-distortion is detected or
$\alpha_\mathrm{s}\geq 0$ is excluded (both at $95\%\,\mathrm{CL}$ or higher).
This threshold sensitivity sets a clear benchmark for CMB spectrometry. For a
combined analysis of PIXIE and current Planck data, we discuss the improvement
on measurements of the tilt $n_\mathrm{s}$ and the running $\alpha_\mathrm{s}$
and the dependence on the choice of the pivot. A fiducial running of
$\alpha_\mathrm{s}=-0.01$ (close to the Planck best-fit) leads to a detection
of negative running at $2\sigma$ for $5\times$ PIXIE. A fiducial running of
$\alpha_\mathrm{s}=-0.02$, still compatible with Planck, requires $3\times$
PIXIE to rule out $\alpha_\mathrm{s} = 0$ (at $95\%\,\mathrm{CL}$). We propose
a convenient and compact visualization of the improving constraints on the
tilt, running and tensor-to-scalar ratio. | A joint analysis of AMI and CARMA observations of the recently
discovered SZ galaxy cluster system AMI-CL J0300+2613: We present CARMA observations of a massive galaxy cluster discovered in the
AMI blind SZ survey. Without knowledge of the cluster redshift a Bayesian
analysis of the AMI, CARMA and joint AMI & CARMA uv-data is used to quantify
the detection significance and parameterise both the physical and observational
properties of the cluster whilst accounting for the statistics of primary CMB
anisotropies, receiver noise and radio sources. The joint analysis of the AMI &
CARMA uv-data was performed with two parametric physical cluster models: the
{\beta}-model; and the model described in Olamaie et al. 2012 with the pressure
profile fixed according to Arnaud et al. 2010. The cluster mass derived from
these different models is comparable but our Bayesian evidences indicate a
preference for the {\beta}-profile which we, therefore, use throughout our
analysis. From the CARMA data alone we obtain a Bayesian probability of
detection ratio of 12.8:1 when assuming that a cluster exists within our search
area; alternatively assuming that Jenkins et al. 2001 accurately predicts the
number of clusters as a function of mass and redshift, the Bayesian probability
of detection is 0.29:1. From the analysis of the AMI or AMI & CARMA data the
probability of detection ratio exceeds 4.5x10^3:1. Performing a joint analysis
of the AMI & CARMA data with a physical cluster model we derive the total mass
internal to r200 as MT,200 = 4.1x10^14Msun. Using a phenomenological
{\beta}-model to quantify the temperature decrement as a function of angular
distance we find a central SZ temperature decrement of 170{\mu}K in the AMI &
CARMA data. The SZ decrement in the CARMA data is weaker than expected and we
speculate that this is a consequence of the cluster morphology. In a
forthcoming study we will assess the impact of cluster morphology on the SZ
decrements that are observed with interferometers such as AMI and CARMA. |
Can Neutrino Self-interactions Save Sterile Neutrino Dark Matter?: Sterile neutrinos only interact with the Standard Model through the neutrino
sector, and thus represent a simple dark matter (DM) candidate with many
potential astrophysical and cosmological signatures. Recently, sterile
neutrinos produced through self-interactions of active neutrinos have received
attention as a particle candidate that can yield the entire observed DM relic
abundance without violating the most stringent constraints from X-ray
observations. We examine consistency of this production mechanism with the
abundance of small-scale structure in the universe, as captured by the
population of ultra-faint dwarf galaxies orbiting the Milky Way, and derive a
lower bound on the sterile-neutrino particle mass of $37$ keV. Combining these
results with previous limits from particle physics and astrophysics excludes
$100\%$ sterile neutrino DM produced by strong neutrino self-coupling, mediated
by a heavy ($\gtrsim 1~\mathrm{GeV}$) scalar particle; however, data permits
sterile-neutrino DM production via a light mediator. | Determination of the large scale volume weighted halo velocity bias in
simulations: A profound assumption in peculiar velocity cosmology is $b_v=1$ at
sufficiently large scales, where $b_v$ is the volume weighted halo(galaxy)
velocity bias with respect to the matter velocity field. However, this
fundamental assumption has not been robustly verified in numerical simulations.
Furthermore, it is challenged by structure formation theory (BBKS, 1986, ApJ;
Desjacques and Sheth, 2010, PRD), which predicts the existence of velocity bias
(at least for proto-halos) due to the fact that halos reside in special regions
(local density peaks). The major obstacle to measure the volume weighted
velocity from N-body simulations is an unphysical sampling artifact. It is
entangled in the measured velocity statistics and becomes significant for
sparse populations. With recently improved understanding of the sampling
artifact (Zhang, Zheng and Jing, 2015, PRD; Zheng, Zhang and Jing, 2015, PRD),
for the first time we are able to {\it appropriately correct this sampling
artifact and then robustly measure the volume weighted halo velocity bias}. (1)
We verify $b_v=1$ within $2\%$ model uncertainty at $k\lesssim 0.1h/$Mpc and
$z=0$-$2$ for halos of mass $\sim 10^{12}$-$10^{13} h^{-1} M_\odot$, and,
therefore, consolidates a foundation of the peculiar velocity cosmology. (2) We
also find statistically significant signs of $b_v\neq 1$ at $k\gtrsim
0.1h/$Mpc. Unfortunately, whether this is real or caused by residual sampling
artifact requires further investigation. Nevertheless, cosmology based on
$k\gtrsim 0.1h/$Mpc velocity data shall be careful this potential velocity
bias. |
Gravitational wave background from mergers of large primordial black
holes: The Peters formula, which tells how the coalescence time of a binary system
emitting gravitational radiation is determined by the initial size and shape of
the elliptic orbit, is often used in estimating the merger rate of primordial
black holes and the gravitational wave background from the mergers. Valid as it
is in some interesting scenarios, such as the analysis of the LIGO-Virgo
events, the Peters formula fails to describe the coalescence time if the
orbital period of the binary exceeds the value given by the formula. This could
underestimate the event rate of mergers that occur before the cosmic time
$t\sim 10^{13}\ \text{s}$. As a result, the energy density spectrum of the
gravitational wave background could develop a peak, which is from mergers
occurring at either $t\sim 10^{13}\ \text{s}$ (for black holes with mass
$M\gtrsim 10^8 M_\odot$) or $t\sim 10^{26}(M/M_\odot)^{-5/3}\ \text{s}$ (for
$10^5 M_\odot \lesssim M\lesssim 10^8 M_\odot$). This can be used to constrain
the fraction of dark matter in primordial black holes (denoted by $f$) if
potential probes (such as SKA and U-DECIGO) do not discover such a background,
with the result $f\lesssim 10^{-6}\text{-}10^{-4}$ for the mass range
$10\text{-} 10^9M_\odot$. We then consider the effect of mass accretion onto
primordial black holes at redshift $z\sim 10$, and find that the merger rate
could drop significantly at low redshifts. The spectrum of the gravitational
wave background thus gets suppressed at the high-frequency end. This feature
might be captured by future detectors such as ET and CE for initial mass $M=
\mathcal{O}(10\text{-}100) M_\odot$ with $f\gtrsim 10^{-4}$. | Voids in cosmological simulations over cosmic time: We study evolution of voids in cosmological simulations using a new method
for tracing voids over cosmic time. The method is based on tracking watershed
basins (contiguous regions around density minima) of well developed voids at
low redshift, on a regular grid of density field. It enables us to construct a
robust and continuous mapping between voids at different redshifts, from
initial conditions to the present time. We discuss how the new approach
eliminates strong spurious effects of numerical origin when voids evolution is
traced by matching voids between successive snapshots (by analogy to halo
merger trees). We apply the new method to a cosmological simulation of a
standard LambdaCDM cosmological model and study evolution of basic properties
of typical voids (with effective radii between 6Mpc/h and 20Mpc/h at redshift
z=0) such as volumes, shapes, matter density distributions and relative
alignments. The final voids at low redshifts appear to retain a significant
part of the configuration acquired in initial conditions. Shapes of voids
evolve in a collective way which barely modifies the overall distribution of
the axial ratios. The evolution appears to have a weak impact on mutual
alignments of voids implying that the present state is in large part set up by
the primordial density field. We present evolution of dark matter density
profiles computed on iso-density surfaces which comply with the actual shapes
of voids. Unlike spherical density profiles, this approach enables us to
demonstrate development of theoretically predicted bucket-like shape of the
final density profiles indicating a wide flat core and a sharp transition to
high-density void walls. |
A high-resolution cosmological simulation of a strong gravitational lens: We present a cosmological hydrodynamical simulation of a 10^13 Msun galaxy
group and its environment (out to 10 times the virial radius) carried out using
the EAGLE model of galaxy formation. Exploiting a novel technique to increase
the resolution of the dark matter calculation independently of that of the gas,
the simulation resolves dark matter haloes and subhaloes of mass 5x10^6 Msun .
It is therefore useful for studying the abundance and properties of the haloes
and subhaloes targeted in strong lensing tests of the cold dark matter model.
We estimate the halo and subhalo mass functions and discuss how they are
affected both by the inclusion of baryons in the simulation and by the
environment. We find that the halo and subhalo mass functions have lower
amplitude in the hydrodynamical simulation than in its dark matter only
counterpart. This reflects the reduced growth of haloes in the hydrodynamical
simulation due to the early loss of gas by reionisation and galactic winds and,
additionally, in the case of subhaloes, disruption by enhanced tidal effects
within the host halo due to the presence of a massive central galaxy. The
distribution of haloes is highly anisotropic reflecting the filamentary
character of mass accretion onto the cluster. As a result, there is significant
variation in the number of structures with viewing direction. The median number
of structures near the centre of the halo, when viewed in projection, is
reduced by a factor of two when baryons are included. | An Estimator for the lensing potential from galaxy number counts: We derive an estimator for the lensing potential from galaxy number counts
which contains a linear and a quadratic term. We show that this estimator has a
much larger signal-to-noise ratio than the corresponding estimator from
intensity mapping. We show that this is due to the additional lensing term in
the number count angular power spectrum which is present already at linear
order. We estimate the signal-to-noise ratio for future photometric surveys. We
find that particularly at high redshifts, $z\gtrsim 1.5$, the signal to noise
ratio can become of order 30. We therefore claim that number counts in
photometric surveys are an excellent means to measure tomographic lensing
spectra. |
Highly Eccentric Kozai Mechanism and Gravitational-Wave Observation for
Neutron Star Binaries: The Kozai mechanism for a hierarchical triple system could reduce the merger
time of inner eccentric binary emitting gravitational waves (GWs), and has been
qualitatively explained with the secular theory that is derived by averaging
short-term orbital revolutions. However, with the secular theory, the minimum
value of the inner pericenter distance could be excessively limited by the
averaging operation. Compared with traditional predictions, the actual
evolution of an eccentric inner binary could be accompanied by (i) a higher
characteristic frequency of the pulse-like GWs around its pericenter passages,
and (ii) a larger residual eccentricity at its final inspiral phase. These
findings would be important for GW astronomy with the forthcoming advanced
detectors. | Three fluid cosmological model using Lie and Noether symmetries: We employ a three fluid model in order to construct a cosmological model in
the Friedmann Robertson Walker flat spacetime, which contains three types of
matter dark energy, dark matter and a perfect fluid with a linear equation of
state. Dark matter is described by dust and dark energy with a scalar field
with potential V({\phi}). In order to fix the scalar field potential we demand
Lie symmetry invariance of the field equations, which is a model-independent
assumption. The requirement of an extra Lie symmetry selects the exponential
scalar field potential. The further requirement that the analytic solution is
invariant under the point transformation generated by the Lie symmetry
eliminates dark matter and leads to a quintessence and a phantom cosmological
model containing a perfect fluid and a scalar field. Next we assume that the
Lagrangian of the system admits an extra Noether symmetry. This new assumption
selects the scalar field potential to be exponential and forces the perfect
fluid to be stiff. Furthermore the existence of the Noether integral allows for
the integration of the dynamical equations. We find new analytic solutions to
quintessence and phantom cosmologies which contain all three fluids. Using
these solutions one is able to compute analytically all main cosmological
functions, such as the scale factor, the scalar field, the Hubble expansion
rate, the deceleration parameter etc. |
Galaxy UV-luminosity function and reionization constraints on axion dark
matter: If the dark matter (DM) were composed of axions, then structure formation in
the Universe would be suppressed below the axion Jeans scale. Using an analytic
model for the halo mass function of a mixed DM model with axions and cold dark
matter, combined with the abundance-matching technique, we construct the
UV-luminosity function. Axions suppress high-$z$ galaxy formation and the
UV-luminosity function is truncated at a faintest limiting magnitude. From the
UV-luminosity function, we predict the reionization history of the universe and
find that axion DM causes reionization to occur at lower redshift. We search
for evidence of axions using the Hubble Ultra Deep Field UV-luminosity function
in the redshift range $z=6$-$10$, and the optical depth to reionization,
$\tau$, as measured from cosmic microwave background polarization. All probes
we consider consistently exclude $m_a\lesssim 10^{-23}\text{ eV}$ from
contributing more than half of the DM, with our strongest constraint ruling
this model out at more than $8\sigma$ significance. In conservative models of
reionization a dominant component of DM with $m_a=10^{-22}\text{ eV}$ is in
$3\sigma$ tension with the measured value of $\tau$, putting pressure on an
axion solution to the cusp-core problem. Tension is reduced to $2\sigma$ for
the axion contributing only half of the DM. A future measurement of the
UV-luminosity function in the range $z=10$-$13$ by JWST would provide further
evidence for or against $m_a=10^{-22}\text{ eV}$. Probing still higher masses
of $m_a=10^{-21}\text{ eV}$ will be possible using future measurements of the
kinetic Sunyaev-Zel'dovich effect by Advanced ACTPol to constrain the time and
duration of reionization. | The imprint of $f(R)$ gravity on weak gravitational lensing II :
Information content in cosmic shear statistics: We investigate the information content of various cosmic shear statistics on
the theory of gravity. Focusing on the Hu-Sawicki-type $f(R)$ model, we perform
a set of ray-tracing simulations and measure the convergence bispectrum, peak
counts and Minkowski functionals. We first show that while the convergence
power spectrum does have sensitivity to the current value of extra scalar
degree of freedom $|f_{\rm R0}|$, it is largely compensated by a change in the
present density amplitude parameter $\sigma_{8}$ and the matter density
parameter $\Omega_{\rm m0}$. With accurate covariance matrices obtained from
1000 lensing simulations, we then examine the constraining power of the three
additional statistics. We find that these probes are indeed helpful to break
the parameter degeneracy, which can not be resolved from the power spectrum
alone. We show that especially the peak counts and Minkowski functionals have
the potential to rigorously (marginally) detect the signature of modified
gravity with the parameter $|f_{\rm R0}|$ as small as $10^{-5}$ ($10^{-6}$) if
we can properly model them on small ($\sim 1\, \mathrm{arcmin}$) scale in a
future survey with a sky coverage of 1,500 squared degrees. We also show that
the signal level is similar among the additional three statistics and all of
them provide complementary information to the power spectrum. These findings
indicate the importance of combining multiple probes beyond the standard power
spectrum analysis to detect possible modifications to General Relativity. |
Relaxing constraints on dark matter annihilation: The relic abundance of thermal dark matter particles is generally assumed to
be inversely proportional to their annihilation rate, which is therefore
constrained by the present matter density, <sigma v> ~ 10^{-26} Omega_{dm}^{-1}
cm^3 sec^{-1}. Here we point out that much lower values of <sigma v> are
possible for heavy dark matter candidates (m < 10 TeV) that couple to other
particle species through the electroweak force. With heavy dark matter
particles present the early universe may evolve according to the following
scenario. After an early entry into matter-dominated phase, dark matter
particles form self-gravitating microhalos. Collisional interaction between
dark matter particles and the surrounding radiation field eventually leads to
microhalos gravothermal collapse and annihilation of most dark matter
particles. For sufficiently heavy dark matter candidates (m < 10 TeV) the
universe can return to radiation-dominated phase before the nucleosynthesis and
thereafter follow the "standard" scenario. | First Light Sources at the End of the Dark Ages: Direct Observations of
Population III Stars, Proto-Galaxies, and Supernovae During the Reionization
Epoch: The cosmic dark ages are the mysterious epoch during which the pristine gas
began to condense and ultimately form the first stars. Although these
beginnings have long been a topic of theoretical interest, technology has only
recently allowed the beginnings of observational insight into this epoch. Many
questions surround the formation of stars in metal-free gas and the history of
the build-up of metals in the intergalactic medium: (1) What were the
properties of the first stellar and galactic sources to form in pristine
(metal-free) gas? (2) When did the epoch of Population III (metal-free) star
formation take place and how long did it last? (3) Was the stellar initial mass
function dramatically different for the first stars and galaxies? These
questions are all active areas of theoretical research. However, new
observational constraints via the direct detection of Population III star
formation are vital to making progress in answering the broader questions
surrounding how galaxies formed and how the cosmological properties of the
universe have affected the objects it contains. |
Inferences from surface brightness fluctuations of Zwicky 3146 via the
Sunyaev-Zeldovich effect and X-ray observations: The galaxy cluster Zwicky 3146 is a sloshing cool core cluster at $z{=}0.291$
that in SZ imaging does not appear to exhibit significant pressure substructure
in the intracluster medium (ICM). We perform a surface brightness fluctuation
analysis via Fourier amplitude spectra on SZ (MUSTANG-2) and X-ray (XMM-Newton)
images of this cluster. These surface brightness fluctuations can be
deprojected to infer pressure and density fluctuations from the SZ and X-ray
data, respectively. In the central region (Ring 1, $r < 100^{\prime\prime} =
440$ kpc, in our analysis) we find fluctuation spectra that suggest injection
scales around 200 kpc ($\sim 140$ kpc from pressure fluctuations and $\sim 250$
kpc from density fluctuations). When comparing the pressure and density
fluctuations in the central region, we observe a change in the effective
thermodynamic state from large to small scales, from isobaric (likely due to
the slow sloshing) to adiabatic (due to more vigorous motions). By leveraging
scalings from hydrodynamical simulations, we find an average 3D Mach number
$\approx0.5$. We further compare our results to other studies of Zwicky 3146
and, more broadly, to other studies of fluctuations in other clusters. | Propagation of the burst of radiation in expanding and recombining
Universe: Thomson scattering: Within the framework of a flat cosmological model a propagation of an
instantaneous burst of nonpolarized isotropic radiation is considered from the
moment of its beginning at some initial redshift z0 to the moment of its
registration now (at z=0). Thomson (Rayleigh) scattering by free electrons is
considered as the only source of opacity. Spatial distributions of the mean
(over directions) radiation intensity are calculated as well as angular
distributions of radiation intensity and polarization at some different
distances from the center of the burst. It is shown that for redshifts z0 large
enough (z0 > 1400) the profile of the mean intensity normalized to the total
number of photons emitted during the burst weakly depends on initial conditions
(say the moment z0 of the burst, the width and shape of initial radiation
distribution in space). As regards angular distributions of intensity and
polarization they turn to be rather narrow (3 - 5 arcmin) while polarization
can reach 70%. On the average an expected polarization can be about 15%. |
Baryon isocurvature constraints on the primordial hypermagnetic fields: It has been pointed out that hypermagnetic helicity decay at the electroweak
symmetry breaking may have produced the observed baryon asymmetry of the
Universe through the chiral anomaly in the standard model of particle physics.
Although fully helical magnetic field that can adequately produce the observed
baryon asymmetry is not strong enough to explain the origin of the
intergalactic magnetic field inferred by the Fermi satellite, the mixture of
helical and nonhelical primordial magnetic fields may explain both baryogenesis
and the intergalactic magnetic fields simultaneously. We first show that such a
scenario is ruled out by the constraint on the amplitude of baryon isocurvature
perturbations produced by the primordial magnetic fields to avoid
overproduction of deuterium at the big bang nucleosynthesis. Then we show that
any attempt to explain the origin of intergalactic magnetic field by primordial
magnetogenesis before the electroweak symmetry breaking does not work due to
the above constraint irrespective of the helicity and baryogenesis mechanism. | The Needlet CMB Trispesctrum: We propose a computationally feasible estimator for the needlet trispectrum,
which develops earlier work on the bispectrum by Donzelli et al. (2012). Our
proposal seems to enjoy a number of useful properties, in particular a) the
construction exploits the localization properties of the needlet system, and
hence it automatically handles masked regions; b) the procedure incorporates a
quadratic correction term to correct for the presence of instrumental noise and
sky-cuts; c) it is possible to provide analytic results on its statistical
properties, which can serve as a guidance for simulations. The needlet
trispectrum we present here provides the natural building blocks for the
efficient estimation of nonlinearity parameters on CMB data, and in particular
for the third order constants $g_{NL}$ and $\tau_{NL}$. |
SDSSJ2222+2745 A Gravitationally Lensed Sextuple Quasar with Maximum
Image Separation of 15.1" Discovered in the Sloan Giant Arcs Survey: We report the discovery of a unique gravitational lens system,
SDSSJ2222+2745, producing five spectroscopically confirmed images of a z_s=2.82
quasar lensed by a foreground galaxy cluster at z_l=0.49. We also present
photometric and spectroscopic evidence for a sixth lensed image of the same
quasar. The maximum separation between the quasar images is 15.1". Both the
large image separations and the high image multiplicity of the lensed quasar
are in themselves exceptionally rare, and observing the combination of these
two factors is an exceptionally unlikely occurrence in present datasets. This
is only the third known case of a quasar lensed by a cluster, and the only one
with six images. The lens system was discovered in the course of the Sloan
Giant Arcs Survey, in which we identify candidate lenses in the Sloan Digital
Sky Survey and target these for follow up and verification with the 2.56m
Nordic Optical Telescope. Multi-band photometry obtained over multiple epochs
from September 2011 to September 2012 reveal significant variability at the
~10-30% level in some of the quasar images, indicating that measurements of the
relative time delay between quasar images will be feasible. In this lens system
we also identify a bright (g = 21.5) giant arc corresponding to a strongly
lensed background galaxy at z_s=2.30. We fit parametric models of the lens
system, constrained by the redshift and positions of the quasar images and the
redshift and position of the giant arc. The predicted time delays between
different pairs of quasar images range from ~100 days to ~6 years. | The Morphology of Reionization in a Dynamically Clumpy Universe: A recent measurement of the Lyman-limit mean free path at $z = 6$ suggests it
may have been very short, motivating a better understanding of the role that
ionizing photon sinks played in reionization. Accurately modeling the sinks in
reionization simulations is challenging because of the large dynamic range
required if $\sim 10^4-10^8 M_{\odot}$ gas structures contributed significant
opacity. Thus, there is no consensus on how important the sinks were in shaping
reionization's morphology. We address this question with a recently developed
radiative transfer code that includes a dynamical sub-grid model for the sinks
based on radiative hydrodynamics simulations. Compared to assuming a fully
pressure-smoothed IGM, our dynamical treatment reduces ionized bubble sizes by
$10-20\%$ under typical assumptions about reionization's sources. Near
reionization's midpoint, the 21 cm power at $k \sim 0.1$ $h$Mpc$^{-1}$ is
similarly reduced. These effects are more modest than the $30-60\%$ suppression
resulting from the higher recombination rate if pressure smoothing is neglected
entirely. Whether the sinks played a significant role in reionization's
morphology depends on the nature of its sources. For example, if reionization
was driven by bright ($M_{\rm UV} < -17$) galaxies, the sinks reduce the
large-scale 21 cm power by at most $20\%$, even if pressure smoothing is
neglected. Conveniently, when bright sources contribute significantly, the
morphology in our dynamical treatment can be reproduced accurately with a
uniform sub-grid clumping factor that yields the same ionizing photon budget.
By contrast, if $M_{\rm UV} \sim -13$ galaxies drove reionization, the uniform
clumping model can err by up to $40\%$. |
Constraining primordial non-Gaussianity with CMB-21cm
cross-correlations?: We investigate the effect of primordial non-Gaussianity on the
cross-correlation between the CMB anisotropies and the 21 cm fluctuations from
the epoch of reionization. We assume an analytic reionization model and an
ionization fraction with $f_{\rm NL}$ induced scale dependent bias. We estimate
the angular power spectrum of the cross-correlation of the CMB and 21 cm. In
order to evaluate the detectability, the signal-to-noise (S/N) ratio for only a
single redshift slice is also calculated for current and future observations,
such as CMB observations by Planck satellite and 21 cm observations by
Omniscope. The existence of the $f_{\rm NL}$ increases the signal of the
cross-correlation at large scales and the amplification does not depend on the
reionization parameters in our reionization model. However the cosmic variance
is significant on such scales and the S/N ratio is suppressed. The obtained S/N
ratio is 2.8 (2.4) for $f_{\rm NL}=10$ (100) in our fiducial reionization
model. Our work suggests in the absence of significant foregrounds and
systematics, the auto-correlations of 21 cm is a better probe of $f_{\rm NL}$
than the cross-correlations (as expected since it depends on $b^2$), while the
cross-correlations contain only one factor of $b$. Nevertheless, it is
interesting to examine the cross-correlations between 21 cm and CMB, as the
signal-to-noise ratio is not negligible and it is more likely we can rid
ourselves of systematics and foregrounds that are common to both CMB and 21 cm
experiments than completely clean 21 cm of all of the possible foregrounds and
systematics in large scales. | Probing the Cosmological Principle in the counts of radio galaxies at
different frequencies: According to the Cosmological Principle, the matter distribution on very
large scales should have a kinematic dipole that is aligned with that of the
CMB. We determine the dipole anisotropy in the number counts of two all-sky
surveys of radio galaxies. For the first time, this analysis is presented for
the TGSS survey, allowing us to check consistency of the radio dipole at low
and high frequencies by comparing the results with the well-known NVSS survey.
We match the flux thresholds of the catalogues, with flux limits chosen to
minimise systematics, and adopt a strict masking scheme. We find dipole
directions that are in good agreement with each other and with the CMB dipole.
In order to compare the amplitude of the dipoles with theoretical predictions,
we produce sets of lognormal realisations. Our realisations include the
theoretical kinematic dipole, galaxy clustering, Poisson noise, simulated
redshift distributions which fit the NVSS and TGSS source counts, and errors in
flux calibration. The measured dipole for NVSS is $\sim\!2$ times larger than
predicted by the mock data. For TGSS, the dipole is almost $\sim\! 5$ times
larger than predicted, even after checking for completeness and taking account
of errors in source fluxes and in flux calibration. Further work is required to
understand the nature of the systematics that are the likely cause of the
anomalously large TGSS dipole amplitude. |
Future constraints on halo thermodynamics from combined
Sunyaev-Zel'dovich measurements: The improving sensitivity of measurements of the kinetic Sunyaev-Zel'dovich
(SZ) effect opens a new window into the thermodynamic properties of the baryons
in halos. We propose a methodology to constrain these thermodynamic properties
by combining the kinetic SZ, which is an unbiased probe of the free electron
density, and the thermal SZ, which probes their thermal pressure. We forecast
that our method constrains the average thermodynamic processes that govern the
energetics of galaxy evolution like energetic feedback across all redshift
ranges where viable halos sample are available. Current Stage-3 cosmic
microwave background (CMB) experiments like AdvACT and SPT-3G can measure the
kSZ and tSZ to greater than 100$\sigma$ if combined with a DESI-like
spectroscopic survey. Such measurements translate into percent-level
constraints on the baryonic density and pressure profiles and on the feedback
and non-thermal pressure support parameters for a given ICM model. This in turn
will provide critical thermodynamic tests for sub-grid models of feedback in
cosmological simulations of galaxy formation. The high fidelity measurements
promised by the next generation CMB experiment, CMB-S4, allow one to further
sub-divide these constraints beyond redshift into other classifications, like
stellar mass or galaxy type. | Breaking the Single Clock Symmetry: measuring single-field inflation
non-Gaussian features: The Universe is not just cold dark matter and dark energy, it also contains
baryons, radiation and neutrinos. The presence of these components, beyond the
pressure-less cold dark matter and the quasi-uniform dark energy ones, imply
that the single clock assumption from inflation is no longer preserved. Here we
quantify this effect and show that the single-clock symmetry is ensured only on
scales where baryonic effects, neutrinos effects, or sound speed are zero.
These scales depend on the cosmic epoch and the Universe composition. Hence for
all use and purposes of interpreting state-of-the-art and possibly forthcoming
surveys, in the accessible scales, single clock symmetry cannot be said to be
satisfied. Breaking the single-clock symmetry has key consequences for the
study of non-Gaussian features generated by pure single-field inflation which
arise from non-linearities in the metric yielding non-Gaussianities of the
local type: the $n_{s}-1$ and the relativistic $-5/3$ term. |
Gravitation And the Universe from large Scale-Structures: The GAUSS
mission concept: Today, thanks in particular to the results of the ESA Planck mission, the
concordance cosmological model appears to be the most robust to describe the
evolution and content of the Universe from its early to late times. It
summarizes the evolution of matter, made mainly of dark matter, from the
primordial fluctuations generated by inflation around $10^{-30}$ second after
the Big-Bang to galaxies and clusters of galaxies, 13.8 billion years later,
and the evolution of the expansion of space, with a relative slowdown in the
matter-dominated era and, since a few billion years, an acceleration powered by
dark energy. But we are far from knowing the pillars of this model which are
inflation, dark matter and dark energy. Comprehending these fundamental
questions requires a detailed mapping of our observable Universe over the whole
of cosmic time. The relic radiation provides the starting point and galaxies
draw the cosmic web. JAXA's LiteBIRD mission will map the beginning of our
Universe with a crucial test for inflation (its primordial gravity waves), and
the ESA Euclid mission will map the most recent half part, crucial for dark
energy. The mission concept, described in this White Paper, GAUSS, aims at
being a mission to fully map the cosmic web up to the reionization era, linking
early and late evolution, to tackle and disentangle the crucial degeneracies
persisting after the Euclid era between dark matter and inflation properties,
dark energy, structure growth and gravitation at large scale. | Self-Accelerating Universe in Galileon Cosmology: We present a cosmological model with a solution that self-accelerates at
late-times without signs of ghost instabilities on small scales. The model is a
natural extension of the Brans-Dicke (BD) theory including a non-linear
derivative interaction, which appears in a theory with the Galilean shift
symmetry. The existence of the self-accelerating universe requires a negative
BD parameter but, thanks to the non-linear term, small fluctuations around the
solution are stable on small scales. General relativity is recovered at early
times and on small scales by this non-linear interaction via the Vainshtein
mechanism. At late time, gravity is strongly modified and the background
cosmology shows a phantom-like behaviour and the growth rate of structure
formation is enhanced. Thus this model leaves distinct signatures in
cosmological observations and it can be distinguished from standard
$\Lambda$CDM cosmology. |
Primordial black holes in interferometry: If there is a population of black holes distributed randomly in space, light
rays passing in their vicinity will acquire random phases. In the "two-slit"
model of an interferometer this can, for a high density of \bhsn, lead to a
diffusion in the phase difference between the two arms of the interferometer
and thus to a loss of coherence or ``visibility''in interferometric
observations. Hence the existence of "fringe constrast" or "visibility" in
interferometric observations can be used to put a limit on the possible
presence of \bhs along the flight path.
We give a formula for this effect and consider its application, particularly
for observations in cosmology. Under the assumption that the dark matter
consists of black holes, we consider sources at high z, up to the CMB. While
the strongest results are for the CMB as the most remote source, more nearby
sources at high z lead to similar effects.
The effect increases with the baseline, and in the limiting case of the CMB
we find that with earth-size baselines a non-zero "visibility" would limit the
mass of possible primordial black holes, to approximately $M/M_\odot \leq
10^{-1}$. Although such limits would not appear to be as strong as those
obtained, say from microlensing, they involve a much different methodology and
are dominated by very early times (see Table 1).
Longer baselines lead to more stringent limits and in principle with extreme
lengths, the method could possibly find positive evidence for primordial black
holes. In this case, however, all other kinds of phase averaging would have to
be constrained or eliminated. | Observational constraints on one-parameter dynamical dark-energy
parametrizations and the $H_0$ tension: The phenomenological parametrizations of dark-energy (DE) equation of state
can be very helpful, since they allow for the investigation of its cosmological
behavior despite the fact that its underlying theory is unknown. However,
although there has been a large amount of research on DE parametrizations which
involve two or more free parameters, the one-parameter parametrizations seem to
be underestimated. We perform a detailed observational confrontation of five
one-parameter DE models, with observational data from cosmic microwave
background (CMB), Joint light-curve analysis sample from Supernovae Type Ia
observations (JLA), baryon acoustic oscillations (BAO) distance measurements,
and cosmic chronometers (CC). We find that all models favor a phantom DE
equation of state at present time, while they lead to $H_0$ values in perfect
agreement with its direct measurements and therefore they offer an alleviation
to the $H_0$-tension. Finally, performing a Bayesian analysis we show that
although $\Lambda$CDM cosmology is still favored, one-parameter DE models have
similar or better efficiency in fitting the data comparing to two-parameter DE
parametrizations, and thus they deserve a thorough investigation. |
The Hubble constant inferred from 18 time-delay lenses: We present a simultaneous analysis of 18 galaxy lenses with time delay
measurements. For each lens we derive mass maps using pixelated simultaneous
modeling with shared Hubble constant. We estimate the Hubble constant to be
66_{-4}^{+6} km/s/Mpc (for a flat Universe with \Omega_m=0.3,
\Omega_\Lambda=0.7).
We have also selected a subsample of five relatively isolated early type
galaxies and by simultaneous modeling with an additional constraint on
isothermality of their mass profiles we get H_0=76 +/-3 km/s/Mpc. | Deep Chandra Observations of the Extended Gas Sloshing Spiral in A2029: Recent X-ray observations of galaxy clusters have shown that there is
substructure present in the intracluster medium (ICM), even in clusters that
are seemingly relaxed. This substructure is sometimes a result of sloshing of
the ICM, which occurs in cool core clusters that have been disturbed by an
off-axis merger with a sub-cluster or group. We present deep Chandra
observations of the cool core cluster Abell 2029, which has a sloshing spiral
extending radially outward from the center of the cluster to approximately 400
kpc at its fullest extent---the largest continuous spiral observed to date. We
find a surface brightness excess, a temperature decrement, a density
enhancement, an elemental abundance enhancement, and a smooth pressure profile
in the area of the spiral. The sloshing gas seems to be interacting with the
southern lobe of the central radio galaxy, causing it to bend and giving the
radio source a wide-angle tail (WAT) morphology. This shows that WATs can be
produced in clusters that are relatively relaxed on large scales. We explore
the interaction between heating and cooling in the central region of the
cluster. Energy injection from the active galactic nucleus (AGN) is likely
insufficient to offset the cooling, and sloshing may be an important additional
mechanism in preventing large amounts of gas from cooling to very low
temperatures. |
Accretion and Outflow in Active Galaxies: I review accretion and outflow in active galactic nuclei. Accretion appears
to occur in a series of very small--scale, chaotic events, whose gas flows have
no correlation with the large--scale structure of the galaxy or with each
other. The accreting gas has extremely low specific angular momentum and
probably represents only a small fraction of the gas involved in a galaxy
merger, which may be the underlying driver.
Eddington accretion episodes in AGN must be common in order for the
supermassive black holes to grow. I show that they produce winds with
velocities $v \sim 0.1c$ and ionization parameters implying the presence of
resonance lines of helium-- and hydrogenlike iron. The wind creates a strong
cooling shock as it interacts with the interstellar medium of the host galaxy,
and this cooling region may be observable in an inverse Compton continuum and
lower--excitation emission lines associated with lower velocities. The shell of
matter swept up by the shocked wind stalls unless the black hole mass has
reached the value $M_{\sigma}$ implied by the $M - \sigma$ relation. Once this
mass is reached, further black hole growth is prevented. If the shocked gas did
not cool as asserted above, the resulting (`energy-driven') outflow would imply
a far smaller SMBH mass than actually observed. Minor accretion events with
small gas fractions can produce galaxy-wide outflows, including fossil outflows
in galaxies where there is little current AGN activity. | Fewer Mocks and Less Noise: Reducing the Dimensionality of Cosmological
Observables with Subspace Projections: Creating accurate and low-noise covariance matrices represents a formidable
challenge in modern-day cosmology. We present a formalism to compress arbitrary
observables into a small number of bins by projection into a model-specific
subspace that minimizes the prior-averaged log-likelihood error. The lower
dimensionality leads to a dramatic reduction in covariance matrix noise,
significantly reducing the number of mocks that need to be computed. Given a
theory model, a set of priors, and a simple model of the covariance, our method
works by using singular value decompositions to construct a basis for the
observable that is close to Euclidean; by restricting to the first few basis
vectors, we can capture almost all the constraining power in a
lower-dimensional subspace. Unlike conventional approaches, the method can be
tailored for specific analyses and captures non-linearities that are not
present in the Fisher matrix, ensuring that the full likelihood can be
reproduced. The procedure is validated with full-shape analyses of power
spectra from BOSS DR12 mock catalogs, showing that the 96-bin power spectra can
be replaced by 12 subspace coefficients without biasing the output cosmology;
this allows for accurate parameter inference using only $\sim 100$ mocks. Such
decompositions facilitate accurate testing of power spectrum covariances; for
the largest BOSS data chunk, we find that: (a) analytic covariances provide
accurate models (with or without trispectrum terms); and (b) using the sample
covariance from the MultiDark-Patchy mocks incurs a $\sim 0.5\sigma$ shift in
$\Omega_m$, unless the subspace projection is applied. The method is easily
extended to higher order statistics; the $\sim 2000$-bin bispectrum can be
compressed into only $\sim 10$ coefficients, allowing for accurate analyses
using few mocks and without having to increase the bin sizes. |
Modeling Dark Photon Oscillations in Our Inhomogeneous Universe: A dark photon may kinetically mix with the Standard Model photon, leading to
observable cosmological signatures. The mixing is resonantly enhanced when the
dark photon mass matches the primordial plasma frequency, which depends
sensitively on the underlying spatial distribution of electrons. Crucially,
inhomogeneities in this distribution can have a significant impact on the
nature of resonant conversions. We develop and describe, for the first time, a
general analytic formalism to treat resonant oscillations in the presence of
inhomogeneities. Our formalism follows from the theory of level crossings of
random fields and only requires knowledge of the one-point probability
distribution function (PDF) of the underlying electron number density
fluctuations. We validate our formalism using simulations and illustrate the
photon-to-dark photon conversion probability for several different choices of
PDFs that are used to characterize the low-redshift Universe. | Cosmological constraints on the velocity-dependent baryon-dark matter
coupling: We present the cosmological constraints on the cross section of baryon-dark
matter interactions for the dark matter mass below the MeV scale from the
Planck CMB (cosmic microwave background) and SDSS (Sloan Digital Sky Survey)
Lyman-$\alpha$ forest data. To explore the dark matter mass $m_{\chi}\lesssim
1$ MeV for which the dark matter's free-streaming effect can suppress the
observable small scale density fluctuations, in addition to the acoustic
oscillation damping in existence of the baryon-dark matter coupling, we apply
the approximated treatment of dark matter free-streaming analogous to that of
the conventional warm dark matter. We also demonstrate the mass dependence of
the baryon-dark matter cross section bounds (for the dark matter mass down to
$m_{\chi} \sim 5~{\rm keV}$), in contrast to the dark matter mass independence
of the cross section constraints for the light dark matter below the MeV scale
claimed in the previous literature. |
Galaxy Formation in Heavily Overdense Regions at z~10: the Prevalence of
Disks in Massive Halos: Using a high-resolution cosmological numerical simulation, we have analyzed
the evolution of galaxies at z~10 in a highly overdense region of the universe.
These objects could represent the high redshift galaxies recently observed by
the Hubble's WFC3, and be as well possible precursors of QSOs at z~6-7. To
overcome the sampling and resolution problems in cosmological simulations, we
have used the Constrained Realizations method. Our main result for z~10 shows
the region of 3.5h^{-1}Mpc radius in comoving coordinates completely dominated
by disk galaxies in the total mass range of >=10^9h^{-1}Mo. We have verified
that the gaseous and stellar disks we identify are robust morphological
features, capable of surviving the ongoing merger process at these redshifts.
Below this mass range, we find a sharp decline in the disk fraction to
negligible numbers. At this redshift, the disks appear to be gas-rich and the
dark matter halos baryon-rich, by a factor of ~2-3 above the average fraction
of baryons in the universe. The prevalence of disk galaxies in the high density
peaks during the epoch of reionization is contrary to the morphology-density
trend observed at low redshifts. | Calibration of the Mid-Infrared Tully-Fisher Relation: Distance measures on a coherent scale around the sky are required to address
the outstanding cosmological problems of the Hubble Constant and of departures
from the mean cosmic flow. The correlation between galaxy luminosities and
rotation rates can be used to determine distances to many thousands of galaxies
in a wide range of environments potentially out to 200 Mpc. Mid-infrared (3.6
microns) photometry with the Spitzer Space Telescope is particularly valuable
as the source of the luminosities because it provides products of uniform
quality across the sky. From a perch above the atmosphere, essentially the
total magnitude of targets can be registered in exposures of a few minutes.
Extinction is minimal and the flux is dominated by the light from old stars
which is expected to correlate with the mass of the targets.
In spite of the superior photometry, the correlation between mid-infrared
luminosities and rotation rates extracted from neutral hydrogen profiles is
slightly degraded from the correlation found with I band luminosities. A color
correction recovers a correlation that provides comparable accuracy to that
available at I band (~20% 1sigma in an individual distance) while retaining the
advantages identified above. Without the color correction the relation between
linewidth and [3.6] magnitudes is M^{b,i,k,a}_{[3.6]} = -20.34 - 9.74 (log
W_{mx}^{i} -2.5). This description is found with a sample of 213 galaxies in 13
clusters that define the slope and 26 galaxies with Cepheid or tip of the red
giant branch distances that define the zero point. A color corrected parameter
M_{C_{[3.6]}} is constructed that has reduced scatter: M_{C_{[3.6]}} = -20.34 -
9.13 (log W_{mx}^{i} -2.5). Consideration of the 7 calibration clusters beyond
50 Mpc, outside the domain of obvious peculiar velocities, provides a
preliminary Hubble Constant estimate of H_0=74+/-5 km/s/Mpc. |
Photometric and Morphological Analysis of Fornax Galaxies through S-PLUS: The photometric and morphological analysis of galaxies in clusters provides
invaluable information regarding the evolutionary stage of the cluster itself.
In addition, it helps to understand how the environment affects the properties
of the galaxies and, as a consequence, their evolutionary path. In this
contribution we present the first steps on the photometric and morphological
analysis of galaxies in the Fornax cluster using S-PLUS data. We expect that
the S-PLUS novel filter set and wide field coverage allow us to obtain new
information about Fornax and its galaxy population. | The broad emission-line region: the confluence of the outer accretion
disc with the inner edge of the dusty torus: (Abridged) We investigate the observational characteristics of BLR geometries
in which the BLR clouds bridge the gap, both in distance and scale height,
between the outer accretion disc and the hot dust, forming an effective surface
of a "bowl". The gas dynamics are dominated by gravity, and we include the
effects of transverse Doppler shift, gravitational redshift and scale-height
dependent macro-turbulence. Our simple model reproduces many of the phenomena
observed in broad emission-line variability studies, including (i) the absence
of response in the core of the optical recombination lines on short timescales,
(ii) the enhanced red-wing response on short timescales, (iii) differences
between the measured delays for the HILs and LILs, and (iv) identifies
turbulence as a means of producing Lorentzian profiles (esp. for LILs) in low
inclination systems, and for suppressing significant continuum--emission-line
delays between the line wings and line core (esp. in LILs). A key motivation of
this work was to reveal the physical underpinnings of the reported measurements
of SMBH masses and their uncertainties. We find that SMBH masses derived from
measurements of the fwhm of the mean and rms profiles show the closest
correspondence between the emission lines in a single object, even though the
emission line fwhm is a more biased mass indicator with respect to inclination.
The predicted large discrepancies in the SMBH mass estimates between emission
lines at low inclination, as derived using the line dispersion, we suggest may
be used as a means of identifying near face-on systems. Our general results do
not depend on specific choices in the simplifying assumptions, but are in fact
generic properties of BLR geometries with axial symmetry that span a
substantial range in radially-increasing scale height supported by turbulence,
which then merge into the inner dusty TOR. |
Modeling the Anisotropic Tidal Effect on the Spin-Spin Correlations of
Low-Mass Galactic Halos: The halo spin-spin correlation function, $\eta(r)$, measures how rapidly the
strength of the alignments of the spin directions between the neighbor halos
change with the separation distance, $r$. The previous model based on the tidal
torque theory expresses the halo spin-spin correlation function as a power of
the linear density two-point correlation function, $\eta(r)\propto \xi^{n}(r)$,
predicting $n=2$ in the linear regime and $n=1$ in the non-linear regime. Using
a high-resolution N-body simulation, we show that the halo spin-spin
correlation function in fact drops much less rapidly with $r$ than the
prediction of the previous model, finding $\eta(r)$ to be statistically
significant even at $r\ge 10\,h^{-1}$Mpc on the dwarf galaxy scale. Claiming
that the anisotropic tidal effect is responsible for the failure of the
previous model, we propose a new formula for the halo spin-spin correlation
function expressed in terms of the integrals of $\xi(r)$. The new formula with
the best-fit parameters turns out to agree excellently with the numerical
results in a broad mass range, $0.05\le M/(10^{11}\,h^{-1}\,M_{\odot})\le 50$,
describing well the large-scale tail of $\eta(r)$. We discuss a possibility of
using the large-scale spin-spin correlations of the dwarf galactic halos as a
complementary probe of dark matter. | The Recent Stellar Archeology of M31 - The Nearest Red Disk Galaxy: We examine the star-forming history (SFH) of the M31 disk during the past few
hundred Myr. The luminosity functions (LFs) of main sequence stars at distances
R_GC > 21 kpc (i.e. > 4 disk scale lengths) are matched by models that assume a
constant star formation rate (SFR). However, at smaller R_GC the LFs suggest
that during the past ~10 Myr the SFR was 2 - 3 times higher than during the
preceding ~100 Myr. The rings of cool gas that harbor a significant fraction of
the current star-forming activity are traced by stars with ages ~100 Myr,
indicating that (1) these structures have ages of at least 100 Myr, and (2)
stars in these structures do not follow the same relation between age and
random velocity as their counterparts throughout the disks of other spiral
galaxies, probably due to the inherently narrow orbital angular momentum
distribution of the giant molecular clouds in these structures. The
distribution of evolved red stars is not azimuthally symmetric, in the sense
that their projected density along the north east segment of the major axis is
roughly twice that on the opposite side of the galaxy. The north east arm of
the major axis thus appears to be a fossil star-forming area that dates to
intermediate epochs. Such a structure may be the consequence of interactions
with a companion galaxy. |
Updated Constraints and Forecasts on Primordial Tensor Modes: We present new, tight, constraints on the cosmological background of
gravitational waves (GWs) using the latest measurements of CMB temperature and
polarization anisotropies provided by the Planck, BICEP2 and Keck Array
experiments. These constraints are further improved when the GW contribution
$N^{\rm GW}_{\rm eff}$ to the effective number of relativistic degrees of
freedom $N_{\rm eff}$ is also considered. Parametrizing the tensor spectrum as
a power law with tensor-to-scalar ratio $r$, tilt $n_\mathrm{t}$ and pivot
$0.01\,\mathrm{Mpc}^{-1}$, and assuming a minimum value of $r=0.001$, we find
$r < 0.089$, $n_\mathrm{t} = 1.7^{+2.1}_{-2.0}$ ($95\%\,\mathrm{CL}$, no
$N^{\rm GW}_{\rm eff}$) and $r < 0.082$, $n_\mathrm{t} = -0.05^{+0.58}_{-0.87}$
($95\%\,\mathrm{CL}$, with $N^{\rm GW}_{\rm eff}$). When the recently released
$95\,\mathrm{GHz}$ data from Keck Array are added to the analysis, the
constraints on $r$ are improved to $r < 0.067$ ($95\%\,\mathrm{CL}$, no $N^{\rm
GW}_{\rm eff}$), $r < 0.061$ ($95\%\,\mathrm{CL}$, with $N^{\rm GW}_{\rm
eff}$). We discuss the limits coming from direct detection experiments such as
LIGO-Virgo, pulsar timing (European Pulsar Timing Array) and CMB spectral
distortions (FIRAS). Finally, we show future constraints achievable from a
COrE-like mission: if the tensor-to-scalar ratio is of order $10^{-2}$ and the
inflationary consistency relation $n_\mathrm{t} = -r/8$ holds, COrE will be
able to constrain $n_\mathrm{t}$ with an error of $0.16$ at
$95\%\,\mathrm{CL}$. In the case that lensing $B$-modes can be subtracted to
$10\%$ of their power, a feasible goal for COrE, these limits will be improved
to $0.11$ at $95\%\,\mathrm{CL}$. | Beyond 3$\times$2-point cosmology: the integrated shear and galaxy
3-point correlation functions: We present the integrated 3-point correlation functions (3PCF) involving both
the cosmic shear and the galaxy density fields. These are a set of higher-order
statistics that describe the modulation of local 2-point correlation functions
(2PCF) by large-scale features in the fields, and which are easy to measure
from galaxy imaging surveys. Based on previous works on the shear-only
integrated 3PCF, we develop the theoretical framework for modelling 5 new
statistics involving the galaxy field and its cross-correlations with cosmic
shear. Using realistic galaxy and cosmic shear mocks from simulations, we
determine the regime of validity of our models based on leading-order standard
perturbation theory with an MCMC analysis that recovers unbiased constraints of
the amplitude of fluctuations parameter $A_s$ and the linear and quadratic
galaxy bias parameters $b_1$ and $b_2$. Using Fisher matrix forecasts for a
DES-Y3-like survey, relative to baseline analyses with conventional
3$\times$2PCFs, we find that the addition of the shear-only integrated 3PCF can
improve cosmological parameter constraints by $20-40\%$. The subsequent
addition of the new statistics introduced in this paper can lead to further
improvements of $10-20\%$, even when utilizing only conservatively large scales
where the tree-level models are valid. Our results motivate future work on the
galaxy and shear integrated 3PCFs, which offer a practical way to extend
standard analyses based on 3$\times$2PCFs to systematically probe the
non-Gaussian information content of cosmic density fields. |
Non Gaussianity and Minkowski Functionals: forecasts for Planck: We study Minkowski Functionals as probes of primordial non-Gaussianity in the
Cosmic Microwave Background, specifically for the estimate of the primordial
`local' bi-spectrum parameter f_NL, with instrumental parameters which should
be appropriate for the Planck experiment. We use a maximum likelihood approach,
which we couple with various filtering methods and test thoroughly for
convergence. We included the effect of inhomogeneous noise as well as
astrophysical biases induced by point sources and by the contamination from the
Galaxy. We find that, when Wiener filtered maps are used (rather than simply
smoothed with Gaussian), the expected error on the measurement of f_NL should
be as small as \Delta f_NL \simeq 10 when combining the 3 channels at 100, 143
and 217 GHz in the Planck extended mission setup. This result is fairly
insensitive to the non homogeneous nature of the noise, at least for realistic
hit-maps expected from Planck. We then estimate the bias induced on the
measurement of f_NL by point sources in those 3 channels. With the appropriate
masking of the bright sources, this bias can be reduced to a negligible level
in the 100 and 143 GHz channels. It remains significant in the 217 GHz channel,
but can be corrected for. The galactic foreground biases are quite important
and present a complex dependence on sky coverage: making them negligible will
depend strongly on the quality of the component separation methods. | Baryons, Neutrinos, Feedback and Weak Gravitational Lensing: (Abridged) The effect of baryonic feedback on the dark matter mass
distribution is generally considered to be a nuisance to weak gravitational
lensing. Measurements of cosmological parameters are affected as feedback
alters the cosmic shear signal on angular scales smaller than a few arcminutes.
Recent progress on the numerical modelling of baryon physics has shown that
this effect could be so large that, rather than being a nuisance, the effect
can be constrained with current weak lensing surveys, hence providing an
alternative astrophysical insight on one of the most challenging questions of
galaxy formation. In order to perform our analysis, we construct an analytic
fitting formula that describes the effect of the baryons on the mass power
spectrum. This fitting formula is based on three scenarios of the OWL
hydrodynamical simulations. It is specifically calibrated for $z<1.5$, where it
models the simulations to an accuracy that is better than $2\%$ for scales
$k<10 h\mbox{Mpc}^{-1}$ and better than $5\%$ for $10 < k < 100
h\mbox{Mpc}^{-1}$. Equipped with this precise tool, this paper presents the
first constraint on baryonic feedback models using gravitational lensing data,
from the Canada France Hawaii Telescope Lensing Survey (CFHTLenS). In this
analysis, we show that the effect of neutrino mass on the mass power spectrum
is degenerate with the baryonic feedback at small angular scales and cannot be
ignored. Assuming a cosmology precision fixed by WMAP9, we find that a universe
with no baryon feedback and massless neutrinos is rejected by the CFHTLenS
lensing data with 96\% confidence. Our study shows that ongoing weak
gravitational lensing surveys (KiDS, HSC and DES) will offer a unique
opportunity to probe the physics of baryons at galactic scales, in addition to
the expected constraints on the total neutrino mass. |
Large non-Gaussianities in the Effective Field Theory Approach to
Single-Field Inflation: the Bispectrum: The methods of effective field theory are used to study generic theories of
inflation with a single inflaton field and to perform a general analysis of the
associated non-Gaussianities. We investigate the amplitudes and shapes of the
various generic three-point correlators, the bispectra, which may be generated
by different classes of single-field inflationary models. Besides the
well-known results for the DBI-like models and the ghost inflationary theories,
we point out that curvature-related interactions may give rise to large
non-Gaussianities in the form of bispectra characterized by a flat shape which,
quite interestingly, is independently produced by several interaction terms. In
a subsequent work, we will perform a similar general analysis for the
non-Gaussianities generated by the generic four-point correlator, the
trispectrum. | The Origin and Evolution of the Mass-Metallicity Relation using GalICS: The GalICS (Galaxies in Cosmological Simulations) semi-analytical model of
hierar- chical galaxy formation is used to investigate the effects of different
galactic properties, including star formation rate (SFR) and outflows, on the
shape of the mass metallic- ity relation and to predict the relation for
galaxies at redshift z=2.27 and z=3.54. Our version of GalICS has the chemical
evolution implemented in great detail and is less heavily reliant on
approximations such as instantaneous recycling. We vary the model parameters
controlling both the efficiency and redshift dependence of the SFR as well as
the efficiency of supernova feedback. We find that the factors controlling the
SFR influence the relation significantly at all redshifts and require a strong
redshift dependence, proportional to 1+z, in order to reproduce the observed
relation at the low mass end. Indeed, at any redshift, the predicted relation
flattens out at the high mass end resulting in a poorer agreement with
observations in this regime. We also find that variation of the parameters
associated with outflows has a minimal effect on the relation at high redshift
but does serve to alter its shape in the more recent past. We thus conclude
that the relation is one between SFR and mass and that outflows are only
important in shaping the relation at late times. When the relation is
stratified by SFR it is apparent that the predicted galaxies with increasing
stellar masses have higher SFRs, supporting the view that galaxy downsizing is
the origin of the relation. Attempting to reproduce the observed relation, we
vary the parameters controlling the efficiency of star formation and its
redshift dependence and compare the predicted relations with Erb et al. (2006)
at z=2.27 and Maiolino et al. (2008) at z=3.54 in order to find the
best-fitting parameters. (Abridged) |
Testing the hypothesis of a matter density discrepancy within LCDM model
using multiple probes: We investigate whether the two cosmological discrepancies on the Hubble
constant ($H_0$) and the matter fluctuation parameter ($\sigma_8$) are
suggesting and compatible with the existence of an additional one on the matter
density. Knowing that the latter effects on observables is degenerate with
those coming from $H_0$ and $\sigma_8$, we combined different probes to break
these degeneracies while adopting the agnostic approach of, either relaxing the
calibration parameters in each probe, or by only including priors with the
condition that they are obtained independently from the discrepant parameters.
We also compiled and used a dataset from previous direct measurements of
$\Omega_{\rm{M}}$ obtained in a model independent way using the Oort technique.
We found when combining galaxy cluster counts + cluster gas mass fraction probe
+ cosmic chronometers + direct $\Omega_{\rm{M}}$ + priors from BBN and CMB,
that both parameters, $H_0$ and $\sigma_8$, are consistent with those inferred
from local probes, with $\sigma_8 = 0.745 \pm 0.05$ while $H_0 = 73.8 \pm
3.01$, and that for a value of $\Omega_{\rm{M}} = 0.22 \pm 0.01$ at more than
3$\sigma$ from that determined by the CMB. However discrepancies appeared when
we combined SN in addition to CC suggesting either inconsistencies between the
SN sample and the other probes or a challenge to our hypothesis, while only a
prior on the matter density obtained from the CMB data keeps $\sigma_8$ within
the values usually obtained when adopting the calibration parameters of the low
redshift growth of structures probes. We conclude that, either both tensions
are compatible with the local inferred low values of matter density at odd with
those obtained by CMB, reviving by then an overlooked discrepancy, or that the
$\Lambda$CDM model is facing more difficulties to accommodate simultaneously
all the current available observations.(abridged) | VLBA and Chandra Observations of Jets in FRI radio galaxies: Constraints
on Jet Evolution: (ABRIDGED) We present here the results from new Very Long Baseline Array
observations at 1.6 and 5 GHz of 19 galaxies of a complete sample of 21 UGC FRI
radio galaxies. New Chandra data of two sources, viz., UGC00408 and UGC08433,
are combined with the Chandra archival data of 13 sources. The 5 GHz
observations of ten "core-jet" sources are polarization-sensitive, while the
1.6 GHz observations constitute second epoch total intensity observations of
nine "core-only" sources. Polarized emission is detected in the jets of seven
sources at 5 GHz, but the cores are essentially unpolarized, except in M87.
Polarization is detected at the jet edges in several sources, and the inferred
magnetic field is primarily aligned with the jet direction. This could be
indicative of magnetic field "shearing" due to jet-medium interaction, or the
presence of helical magnetic fields. The jet peak intensity $I_\nu$ falls with
distance $d$ from the core, following the relation, $I_\nu\propto d^a$, where
$a$ is typically -1.5. Assuming that adiabatic expansion losses are primarily
responsible for the jet intensity "dimming", two limiting cases are considered:
[1] the jet has a constant speed on parsec-scales and is expanding gradually
such that the jet radius $r\propto d^0.4$; this expansion is however
unobservable in the laterally unresolved jets at 5 GHz, and [2] the jet is
cylindrical and is accelerating on parsec-scales. Accelerating parsec-scale
jets are consistent with the phenomenon of "magnetic driving" in Poynting flux
dominated jets. Chandra observations of 15 UGC FRIs detect X-ray jets in nine
of them. The high frequency of occurrence of X-ray jets in this complete sample
suggests that they are a signature of a ubiquitous process in FRI jets. |
The Role of Environment on the Formation of Early-Type Galaxies: (Abridged) We present a detailed study of the stellar populations of a
volume-limited sample of early-type galaxies from SDSS, across a range of
environments -- defined as the mass of the host dark matter halo. The stellar
populations are explored through the SDSS spectra, via projection onto a set of
two spectral vectors determined from Principal Component Analysis. We find the
velocity dispersion of the galaxy to be the main driver behind the different
star formation histories of early-type galaxies. However, environmental effects
are seen to play a role (although minor). Galaxies populating the lowest mass
halos have stellar populations on average ~1Gyr younger than the rest of the
sample. The fraction of galaxies with small amounts of recent star formation is
also seen to be truncated when occupying halos more massive than 3E13Msun. The
sample is split into satellite and central galaxies for a further analysis of
environment. Satellites are younger than central galaxies of the same stellar
mass. The younger satellite galaxies in 6E12Msun halos have stellar populations
consistent with the central galaxies found in the lowest mass halos of our
sample (i.e. 1E12Msun). This result is indicative of galaxies in lower mass
halos being accreted into larger halos. | The galaxy power spectrum take on spatial curvature and cosmic
concordance: The concordance of the $\Lambda$CDM cosmological model in light of current
observations has been the subject of an intense debate in recent months. The
2018 Planck Cosmic Microwave Background (CMB) temperature anisotropy power
spectrum measurements appear at face value to favour a spatially closed
Universe with curvature parameter $\Omega_K<0$. This preference disappears if
Baryon Acoustic Oscillation (BAO) measurements are combined with Planck data to
break the geometrical degeneracy, although the reliability of this combination
has been questioned due to the strong tension present between the two datasets
when assuming a curved Universe. Here, we approach this issue from yet another
point of view, using measurements of the full-shape (FS) galaxy power spectrum,
$P(k)$, from the Baryon Oscillation Spectroscopic Survey DR12 CMASS sample. By
combining Planck data with FS measurements, we break the geometrical degeneracy
and find $\Omega_K=0.0023 \pm 0.0028$. This constrains the Universe to be
spatially flat to sub-percent precision, in excellent agreement with results
obtained using BAO measurements. However, as with BAO, the overall increase in
the best-fit $\chi^2$ suggests a similar level of tension between Planck and
$P(k)$ under the assumption of a curved Universe. While the debate on spatial
curvature and the concordance between cosmological datasets remains open, our
results provide new perspectives on the issue, highlighting the crucial role of
FS measurements in the era of precision cosmology. |
Optical observations of Ultra Steep Spectrum radio sources: In this paper we present follow-up optical observations of Ultra Steep
Spectrum sources that were found by matching 150 MHz GMRT sources with either
the 74 MHz VLSS or the 1400 MHz NVSS. These sources are possibly high-redshift
radio galaxies but optical identification is required for clarification. The
follow-up observations were conducted with the Liverpool Telescope; in all
cases no sources are detected down to an R magnitude of ~23. By applying models
and using the K-z relation we are able to suggest that these sources are
possibly at high redshift. We discuss how 2m class telescopes can help with the
identification of HzRGs from large-scale, low-frequency surveys. | Increasing Neff with particles in thermal equilibrium with neutrinos: Recent work on increasing the effective number of neutrino species (Neff) in
the early universe has focussed on introducing extra relativistic species
(`dark radiation'). We draw attention to another possibility: a new particle of
mass less than 10 MeV that remains in thermal equilibrium with neutrinos until
it becomes non-relativistic increases the neutrino temperature relative to the
photons. We demonstrate that this leads to a value of Neff that is greater than
three and that Neff at CMB formation is larger than at BBN. We investigate the
constraints on such particles from the primordial abundance of helium and
deuterium created during BBN and from the CMB power spectrum measured by ACT
and SPT and find that they are presently relatively unconstrained. We forecast
the sensitivity of the Planck satellite to this scenario: in addition to
dramatically improving constraints on the particle mass, in some regions of
parameter space it can discriminate between the new particle being a real or
complex scalar. |
Isotropic Heating of Galaxy Cluster Cores via Rapidly Reorienting AGN
Jets: AGN jets carry more than sufficient energy to stave off catastrophic cooling
of the intracluster medium (ICM) in the cores of cool-core clusters. However,
in order to prevent catastrophic cooling, the ICM must be heated in a
near-isotropic fashion and narrow bipolar jets with $P_{\rm jet}=10^{44-45}$
ergs/s, typical of radio AGNs at cluster centres, are inefficient at heating
the gas in the transverse direction to the jets. We argue that due to existent
conditions in cluster cores, the SMBHs will, in addition to accreting gas via
radiatively inefficient flows, experience short stochastic episodes of enhanced
accretion via thin discs. In general, the orientation of these accretion discs
will be misaligned with the spin axis of the black holes and the ensuing
torques will cause the black hole's spin axis (and therefore, the jet axis) to
slew and rapidly change direction. This model not only explains recent
observations showing successive generations of jet-lobes-bubbles in individual
cool-core clusters that are offset from each other in the angular direction
with respect to the cluster center, but also shows that AGN jets {\it can} heat
the cluster core nearly isotropically on the gas cooling timescale. Our model
{\it does} require that the SMBHs at the centers of cool-core clusters be
spinning relatively slowly. Torques from individual misaligned discs are
ineffective at tilting rapidly spinning black holes by more than a few degrees.
Additionally, since SMBHs that host thin accretion discs will manifest as
quasars, we predict that roughly 1--2 rich clusters within $z<0.5$ should have
quasars at their centers. | The WIMP capture process for dark stars in the early universe: The first stars to form in the universe may have been dark stars, powered by
dark matter annihilation instead of nuclear fusion. The initial amount of dark
matter gathered by the star gravitationally can sustain it only for a limited
period of time. It has been suggested that capture of additional dark matter
from the environment can prolong the dark star phase even to the present day.
Here we show that this capture process is ineffective to prolong the life of
the first generation of dark stars. We construct a Monte-Carlo simulation that
follows each Weakly Interacting Massive Particle (WIMP) in the dark matter halo
as its orbit responds to the formation and evolution of the dark star, as it
scatters off the star's nuclei, and as it annihilates inside the star. A rapid
depletion of the WIMPs on orbits that cross the star causes the demise of the
first generation of dark stars. We suggest that a second generation of dark
stars may in principle survive much longer through capture. We comment on the
effect of relaxing our assumptions. |
Analytical shear and flexion of Einasto dark matter haloes: N-body simulations predict that dark matter haloes are described by specific
density profiles on both galactic- and cluster-sized scales. Weak gravitational
lensing through the measurements of their first and second order properties,
shear and flexion, is a powerful observational tool for investigating the true
shape of these profiles. One of the three-parameter density profiles recently
favoured in the description of dark matter haloes is the Einasto profile. We
present exact expressions for the shear and the first and second flexions of
Einasto dark matter haloes derived using a Mellin-transform formalism in terms
of the Fox H and Meijer G functions, that are valid for general values of the
Einasto index. The resulting expressions can be written as series expansions
that permit us to investigate the asymptotic behaviour of these quantities.
Moreover, we compare the shear and flexion of the Einasto profile with those of
different mass profiles including the singular isothermal sphere, the
Navarro-Frenk-White profile, and the S\'ersic profile. We investigate the
concentration and index dependences of the Einasto profile, finding that the
shear and second flexion could be used to determine the halo concentration,
whilst for the Einasto index the shear and first and second flexions may be
employed. We also provide simplified expressions for the weak lensing
properties and other lensing quantities in terms of the generalized
hypergeometric function. | Constraints on the Mass, Concentration, and Nonthermal Pressure Support
of Six CLASH Clusters from a Joint Analysis of X-ray, SZ, and Lensing Data: We present a joint analysis of Chandra X-ray observations, Bolocam thermal
Sunyaev-Zel'dovich (SZ) effect observations, Hubble Space Telescope (HST)
strong lensing data, and HST and Subaru Suprime-Cam weak lensing data. The
multiwavelength dataset is used to constrain parametric models for the
distribution of dark and baryonic matter in a sample of six massive galaxy
clusters selected from the Cluster Lensing And Supernova survey with Hubble
(CLASH). For five of the six clusters, the multiwavelength dataset is well
described by a relatively simple model that assumes spherical symmetry,
hydrostatic equilibrium, and entirely thermal pressure support. The joint
analysis yields considerably better constraints on the total mass and
concentration of the cluster compared to analysis of any one dataset
individually. The subsample of five galaxy clusters is used to place an upper
limit on the fraction of pressure support in the intracluster medium (ICM) due
to nonthermal processes, such as turbulence and bulk flow of the gas. We
constrain the nonthermal pressure fraction at r500c to be less than 0.11 at 95
percent confidence. This is in tension with state-of-the-art hydrodynamical
simulations, which predict a nonthermal pressure fraction of approximately 0.25
at r500c for clusters of similar mass and redshift. This tension may be
explained by the sample selection and/or our assumption of spherical symmetry. |
The R_h=ct Universe Without Inflation: The horizon problem in the standard model of cosmology (LDCM) arises from the
observed uniformity of the cosmic microwave background radiation, which has the
same temperature everywhere (except for tiny, stochastic fluctuations), even in
regions on opposite sides of the sky, which appear to lie outside of each
other's causal horizon. Since no physical process propagating at or below
lightspeed could have brought them into thermal equilibrium, it appears that
the universe in its infancy required highly improbable initial conditions. In
this paper, we examine this well-known problem by considering photon
propagation through a Friedmann-Robertson-Walker (FRW) spacetime at a more
fundamental level than has been attempted before, demonstrating that the
horizon problem only emerges for a subset of FRW cosmologies, such as LCDM,
that include an early phase of rapid deceleration. We show that the horizon
problem is nonexistent for the recently introduced R_h=ct universe, obviating
the principal motivation for the inclusion of inflation. We demonstrate through
direct calculation that, in the R_h=ct universe, even opposite sides of the
cosmos have remained causally connected to us - and to each other - from the
very first moments in the universe's expansion. Therefore, within the context
of the R_h=ct universe, the hypothesized inflationary epoch from t=10^{-35}
seconds to 10^{-32} seconds was not needed to fix this particular "problem",
though it may still provide benefits to cosmology for other reasons. | Resolving high Reynolds numbers in SPH simulations of subsonic
turbulence: Accounting for the Reynolds number is critical in numerical simulations of
turbulence, particularly for subsonic flow. For Smoothed Particle Hydrodynamics
(SPH) with constant artificial viscosity coefficient alpha, it is shown that
the effective Reynolds number in the absence of explicit physical viscosity
terms scales linearly with the Mach number - compared to mesh schemes, where
the effective Reynolds number is largely independent of the flow velocity. As a
result, SPH simulations with alpha=1 will have low Reynolds numbers in the
subsonic regime compared to mesh codes, which may be insufficient to resolve
turbulent flow. This explains the failure of Bauer and Springel (2011,
arXiv:1109.4413v1) to find agreement between the moving-mesh code AREPO and the
GADGET SPH code on simulations of driven, subsonic (v ~ 0.3 c_s) turbulence
appropriate to the intergalactic/intracluster medium, where it was alleged that
SPH is somehow fundamentally incapable of producing a Kolmogorov-like turbulent
cascade. We show that turbulent flow with a Kolmogorov spectrum can be easily
recovered by employing standard methods for reducing alpha away from shocks. |
Joint constraints from cosmic shear, galaxy-galaxy lensing and galaxy
clustering: internal tension as an indicator of intrinsic alignment modelling
error: In cosmological analyses it is common to combine different types of
measurement from the same survey. In this paper we use simulated DES Y3 and
LSST Y1 data to explore differences in sensitivity to intrinsic alignments (IA)
between cosmic shear and galaxy-galaxy lensing. We generate mock shear,
galaxy-galaxy lensing and galaxy clustering data, contaminated with a range of
IA scenarios. Using a simple 2-parameter IA model (NLA) in a DES Y3 like
analysis, we show that the galaxy-galaxy lensing + galaxy clustering
combination ($2\times2$pt) is significantly more robust to IA mismodelling than
cosmic shear. IA scenarios that produce up to $5\sigma$ biases for shear are
seen to be unbiased at the level of $\sim1\sigma$ for $2\times2$pt. We
demonstrate that this robustness can be largely attributed to the redshift
separation in galaxy-galaxy lensing, which provides a cleaner separation of
lensing and IA contributions. We identify secondary factors which may also
contribute, including the possibility of cancellation of higher-order IA terms
in $2\times2$pt and differences in sensitivity to physical scales.
Unfortunately this does not typically correspond to equally effective
self-calibration in a $3\times2$pt analysis of the same data, which can show
significant biases driven by the cosmic shear part of the data vector. If we
increase the precision of our mock analyses to a level roughly equivalent to
LSST Y1, we find a similar pattern, with considerably more bias in a cosmic
shear analysis than a $2\times2$pt one, and significant bias in a joint
analysis of the two. Our findings suggest that IA model error can manifest
itself as internal tension between $\xi_\pm$ and $\gamma_t + w$ data vectors.
We thus propose that such tension (or the lack thereof) can be employed as a
test of model sufficiency or insufficiency when choosing a fiducial IA model,
alongside other data-driven methods. | Polarized Synchrotron Foreground Assessment for CMB Experiments: Polarized Galactic synchrotron emission is an undesirable foreground for
cosmic microwave background (CMB) experiments observing at frequencies $< 150$
GHz. We perform a combined analysis of observational data at 1.4, 2.3, 23, 30
and 33 GHz to quantify the spatial variation of the polarized synchrotron
spectral index, $\beta^{pol}$, on $\sim3.5^\circ$ scales. We compare results
from different data combinations to address limitations and inconsistencies
present in these public data, and form a composite map of $\beta^{pol}$. Data
quality masking leaves 44% sky coverage (73% for $|b|> 45^\circ$). Generally
$-3.2 < \beta^{pol} \lesssim -3$ in the inner Galactic plane and spurs, but the
Fan Region in the outer Galaxy has a flatter index. We find a clear spectral
index steepening with increasing latitude south of the Galactic plane with
$\Delta \beta^{pol}=0.4$, and a smaller steepening of $0.25$ in the north. Near
the south Galactic pole the polarized synchrotron spectral index is
$\beta^{pol} \approx -3.4$. Longitudinal spectral index variations of $\Delta
\beta^{pol} \sim 0.1$ about the latitudinal mean are also detected. Within the
BICEP2/Keck survey footprint, we find consistency with a constant value,
$\beta^{pol} = -3.25 \pm 0.04$ (statistical) $\pm 0.02$ (systematic). We
compute a map of the frequency at which synchrotron and thermal dust emission
contribute equally to the total polarized foreground. The limitations and
inconsistencies among datasets encountered in this work make clear the value of
additional independent surveys at multiple frequencies, especially between
$10-20$ GHz, provided these surveys have sufficient sensitivity and control of
instrumental systematic errors. |
Broadband study of hard X-ray selected absorbed AGN: [Abridged]We report on the broadband X-ray properties of a complete sample of
absorbed Seyfert galaxies hard X-ray selected with INTEGRAL. The sample is
composed of 33 sources: 15 are newly discovered above 20 keV while 18 are
already known AGN. For 17 sources we have performed a broadband analysis with
XMM and INTEGRAL data. We have complemented the analysis of the 16 remaining
sources with existing broadband studies. The spectra are well reproduced with
an absorbed primary emission with a high energy cutoff and its scattered
fraction below 2-3 keV, plus the Compton reflection features. A high energy
cut-off is found in 30% of the sample, with an average value below 150 keV. The
hard X-ray selection favours the detection of more obscured sources, with the
log NH average value of 23.15. The diagnostic plot NH vs
F(corr)(2-10keV)/F(20-100keV) allowed the isolation of the Compton thick
objects and may represent a useful tool for future hard X-ray observations of
newly discovered AGN. We are unable to associate the reflection components
(continuum and Fe line) with the absorbing gas as a torus, a more complex
scenario being necessary. In the Compton thin sources, a fraction (but not all)
of the Fe line needs to be produced in a gas located closer to the BH than the
thick torus, and this is possibly associated with the optical BLR, responsible
also for the absorption. We still need a Compton thick medium (not intercepting
the line of sight) likely associated to a torus, which contributes to the Fe
line and produces the observed reflection continuum above 10 keV. The
Iwasawa-Taniguchi effect can not be confirmed with our data. Finally, the
comparison with a sample of unobscured AGN shows that, type 1 and type 2 (once
corrected for absorption) Seyfert are characterized by the same
nuclear/accretion properties (luminosity, bolometric luminosity, Eddington
ratio), supporting the unified view. | Beyond consistency test of gravity with redshift-space distortions at
quasi-linear scales: Redshift-space distortions (RSD) offer an attractive method to measure the
growth of cosmic structure on large scales, and combining with the measurement
of the cosmic expansion history, it can be used as cosmological tests of
gravity. With the advent of future galaxy redshift surveys aiming at precisely
measuring the RSD, an accurate modeling of RSD going beyond linear theory is a
critical issue in order to detect or disprove small deviations from general
relativity (GR). While several improved models of RSD have been recently
proposed based on the perturbation theory (PT), the framework of these models
heavily relies on GR. Here, we put forward a new PT prescription for RSD in
general modified gravity models. As a specific application, we present
theoretical predictions of the redshift-space power spectra in f(R) gravity
model, and compare them with N-body simulations. Using the PT template that
takes into account the effects of both modifications of gravity and RSD
properly, we successfully recover the fiducial model parameter in N-body
simulations in an unbiased way. On the other hand, we found it difficult to
detect the scale dependence of the growth rate in a model-independent way based
on GR templates. |
Investigating the presence of 500 um submillimeter excess emission in
local star forming galaxies: Submillimeter excess emission has been reported at 500 microns in a handful
of local galaxies, and previous studies suggest that it could be correlated
with metal abundance. We investigate the presence of an excess submillimeter
emission at 500 microns for a sample of 20 galaxies from the Key Insights on
Nearby Galaxies: a Far Infrared Survey with Herschel (KINGFISH) that span a
range of morphologies and metallicities (12+log(O/H)=7.8-8.7). We probe the
far-infrared (IR) emission using images from the Spitzer Space Telescope and
Herschel Space Observatory in the wavelength range 24-500 microns. We model the
far-IR peak of the dust emission with a two-temperature modified blackbody and
measure excess of the 500 micron photometry relative to that predicted by our
model. We compare the submillimeter excess, where present, with global galaxy
metallicity and, where available, resolved metallicity measurements. We do not
find any correlation between the 500 micron excess and metallicity. A few
individual sources do show excess (10-20%) at 500 microns; conversely, for
other sources, the model overpredicts the measured 500 micron flux density by
as much as 20%, creating a 500 micron "deficit". None of our sources has an
excess larger than the calculated 1-sigma uncertainty, leading us to conclude
that there is no substantial excess at submillimeter wavelengths at or shorter
than 500 microns in our sample. Our results differ from previous studies
detecting 500 micron excess in KINGFISH galaxies largely due to new, improved
photometry used in this study. | Weak lensing deflection of three-point correlation functions: Weak gravitational lensing alters the apparent separations between observed
sources, potentially affecting clustering statistics. We derive a general
expression for the lensing deflection which is valid for any three-point
statistic, and investigate its effect on the three-point clustering correlation
function. We find that deflection of the clustering correlation function is
greatest at around $z=2$. It is most prominent in regions where the correlation
function varies rapidly, in particular at the baryon acoustic oscillation scale
where it smooths out the peaks and troughs, reducing the peak-to-trough
difference by about 0.1 percent at $z=1$ and around 2.3 percent at $z=10$. The
modification due to lensing deflection is typically at the per cent level of
the expected errors in a Euclid-like survey and therefore undetectable. |
Toward a concordance teleparallel Cosmology I: Background Dynamics: Assuming a spatially flat universe, we study the cosmological viability of an
infrared corrected teleparallel gravity model, which accounts for late
acceleration by weakening gravity at later times on cosmological distances. The
theory does not introduce any additional free parameters into the cosmological
model, as is commonly the case with modified gravity based cosmologies. This
feature renders the cosmological model statistically comparable, on equal
footing, with $\Lambda$CDM. In this context, using recent cosmological
observations -- Pantheon supernova Type Ia, Hubble constant $H_0$, Baryon
acoustic oscillation, redshift space distortions, Big Bang nucleosynthesis and
the cosmic microwave background constraint on the decoupling acoustic scale --
we show that, although the exponential infrared-corrected gravity and
$\Lambda$CDM are physically different, they are phenomenologically and
statistically equivalent. However, the former is more adept at fitting
accurately determined observational constraints while decreasing the $H_0$
tension without worsening the $S_8$ tension. This calls for full examination of
the empirical viability of the theory at the linear perturbation level, which
is the subject of paper II. | Observable Signatures of a Classical Transition: Eternal inflation arising from a potential landscape predicts that our
universe is one realization of many possible cosmological histories. One way to
access different cosmological histories is via the nucleation of bubble
universes from a metastable false vacuum. Another way to sample different
cosmological histories is via classical transitions, the creation of pocket
universes through the collision between bubbles. Using relativistic numerical
simulations, we examine the possibility of observationally determining if our
observable universe resulted from a classical transition. We find that
classical transitions produce spatially infinite, approximately open
Friedman-Robertson-Walker universes. The leading set of observables in the
aftermath of a classical transition are negative spatial curvature and a
contribution to the Cosmic Microwave Background temperature quadrupole. The
level of curvature and magnitude of the quadrupole are dependent on the
position of the observer, and we determine the possible range of observables
for two classes of single-scalar field models. For the first class, where the
inflationary phase has a lower energy than the vacuum preceding the classical
transition, the magnitude of the observed quadrupole generally falls to zero
with distance from the collision while the spatial curvature grows to a
constant. For the second class, where the inflationary phase has a higher
energy than the vacuum preceding the classical transition, the magnitude of the
observed quadrupole generically falls to zero with distance from the collision
while the spatial curvature grows without bound. We find that the magnitude of
the quadrupole and curvature grow with increasing centre of mass energy of the
collision, and explore variations of the parameters in the scalar field
lagrangian. |
The impact and mitigation of broad absorption line quasars in
Lyman$-α$ forest correlations: Correlations in and with the flux transmission of the Lyman$-\alpha$
(Ly$\alpha$) forest in the spectra of high-redshift quasars are powerful
cosmological tools, yet these measurements can be compromised if the intrinsic
quasar continuum is significantly uncertain. One particularly problematic case
is broad absorption line (BAL) quasars, which exhibit blueshifted absorption
associated with many spectral features that are consistent with outflows of up
to $\sim0.1c$. As these absorption features can both fall in the forest region
and be difficult to distinguish from Ly$\alpha$ absorption, cosmological
analyses eliminate the 12 - 16% of quasars that exhibit BALs. In this paper we
explore an alternate approach that includes BALs in the Ly$\alpha$ auto
correlation function, with the exception of the expected locations of the BAL
absorption troughs. This procedure returns over 95% of the pathlength that is
lost by the exclusion of BALs, as well as increases the density of sightlines.
We show that including BAL quasars reduces the fractional uncertainty in the
covariance matrix and correlation function and does not significantly change
the shape of the correlation function relative to analyses that exclude BAL
quasars. We also evaluate different definitions of BALs, masking strategies,
and potential differences in the quasar continuum in the forest region for BALs
with different amounts of absorption. | Mirror Matter, Mirror Gravity and Galactic Rotational Curves: We discuss astrophysical implications of the modified gravity model in which
the two matter components, ordinary and dark, couple to separate gravitational
fields that mix to each other through small mass terms. There are two spin-2
eigenstates: the massless graviton that induces universal Newtonian attraction,
and the massive one that gives rise to the Yukawa-like potential which is
repulsive between the ordinary and dark bodies. As a result the distances much
smaller than the Yukawa radius $r_m$ the gravitation strength between the two
types of matter becomes vanishing. If $r_m \sim 10$ kpc, a typical size of a
galaxy, there are interesting implications for the nature of dark matter. In
particular, one can avoid the problem of the cusp that is typical for the cold
dark matter halos. Interestingly, the flat shape of the rotational curves can
be explained even in the case of the collisional and dissipative dark matter
(as e.g. mirror matter) that cannot give the extended halos but instead must
form galactic discs similarly to the visible matter. The observed rotational
curves for the large, medium-size and dwarf galaxies can be nicely reproduced.
We also briefly discuss possible implications for the direct search of dark
matter. |
First dark matter search results from a 4-kg CF$_3$I bubble chamber
operated in a deep underground site: New data are reported from the operation of a 4.0 kg CF$_{3}$I bubble chamber
in the 6800-foot-deep SNOLAB underground laboratory. The effectiveness of
ultrasound analysis in discriminating alpha-decay background events from single
nuclear recoils has been confirmed, with a lower bound of $>$99.3% rejection of
alpha-decay events. Twenty single nuclear recoil event candidates and three
multiple bubble events were observed during a total exposure of 553 kg-days
distributed over three different bubble nucleation thresholds. The effective
exposure for single bubble recoil-like events was 437.4 kg-days. A neutron
background internal to the apparatus, of known origin, is estimated to account
for five single nuclear recoil events and is consistent with the observed rate
of multiple bubble events. This observation provides world best direct
detection constraints on WIMP-proton spin-dependent scattering for WIMP masses
$>$20 GeV/c$^{2}$ and demonstrates significant sensitivity for spin-independent
interactions. | Genus statistics using the Delaunay tessellation field estimation
method: (I) tests with the Millennium Simulation and the SDSS DR7: We study the topology of cosmic large-scale structure through the genus
statistics, using galaxy catalogues generated from the Millennium Simulation
and observational data from the latest Sloan Digital Sky Survey Data Release
(SDSS DR7). We introduce a new method for constructing galaxy density fields
and for measuring the genus statistics of its isodensity surfaces. It is based
on a Delaunay tessellation field estimation (DTFE) technique that allows the
definition of a piece-wise continuous density field and the exact computation
of the topology of its polygonal isodensity contours, without introducing any
free numerical parameter. Besides this new approach, we also employ the
traditional approaches of smoothing the galaxy distribution with a Gaussian of
fixed width, or by adaptively smoothing with a kernel that encloses a constant
number of neighboring galaxies. Our results show that the Delaunay-based method
extracts the largest amount of topological information. Unlike the traditional
approach for genus statistics, it is able to discriminate between the different
theoretical galaxy catalogues analyzed here, both in real space and in redshift
space, even though they are based on the same underlying simulation model. In
particular, the DTFE approach detects with high confidence a discrepancy of one
of the semi-analytic models studied here compared with the SDSS data, while the
other models are found to be consistent. |
CMB Distortions from Damping of Acoustic Waves Produced by Cosmic
Strings: We study diffusion damping of acoustic waves in the photon-baryon fluid due
to cosmic strings, and calculate the induced $\mu$- and $y$-type spectral
distortions of the cosmic microwave background. For cosmic strings with tension
within current bounds, their contribution to the spectral distortions is
subdominant compared to the distortions from primordial density perturbations. | A WDM model for the evolution of galactic halos: It is a well-known fact that the gravitational effect of dark matter in
galaxies is only noticeable when the orbital accelerations drop below $a_0
\simeq 2\times 10^{-8}$ cm s$^{-1}$ (Milgrom's Law). This peculiarity of the
dynamic behaviour of galaxies was initially ascribed to a modification of
Newtonian dynamics (MOND theory) and, consequently, it was used as an argument
to criticize the dark matter hypothesis. In our model, warm dark matter is
composed by collisionless Vlasov particles with a primordial typical velocity
$\simeq 330$ km s$^{-1}$ and, consequently, they evaporated from galactic cores
and reorganized in halos with a cusp at a finite distance from the galactic
center (in contrast with Cold Dark Matter simulations which predict a cusp at
the center of galaxies). This is confirmed by mean-field N-body simulations of
the self-gravitating Vlasov dark matter particles in the potential well of the
baryonic core. The rest mass of these particles, $\mu$, is determined from a
kinetic theory of the early universe with a cosmological constant. We find that
$\mu$ is in the range of a few keV. This result makes sterile neutrinos the
best suited candidates for the main component of dark matter. |
Galaxy-Scale Strong Lensing Tests of Gravity and Geometric Cosmology:
Constraints and Systematic Limitations: Galaxy-scale strong gravitational lenses with measured stellar velocity
dispersions allow a test of the weak-field metric on kiloparsec scales and a
geometric measurement of the cosmological distance-redshift relation, provided
that the mass-dynamical structure of the lensing galaxies can be independently
constrained to a sufficient degree. We combine data on 53 galaxy-scale strong
lenses from the Sloan Lens ACS Survey with a well-motivated fiducial set of
lens-galaxy parameters to find (1) a constraint on the post-Newtonian parameter
gamma = 1.01 +/- 0.05 and (2) a determination of Omega_Lambda = 0.75 +/- 0.17
under the assumption of a flat universe. These constraints assume that the
underlying observations and priors are free of systematic error. We evaluate
the sensitivity of these results to systematic uncertainties in (1) total
mass-profile shape, (2) velocity anisotropy, (3) light-profile shape, and (4)
stellar velocity dispersion. Based on these sensitivities, we conclude that
while such strong-lens samples can in principle provide an important tool for
testing general relativity and cosmology, they are unlikely to yield precision
measurements of gamma and Omega_Lambda unless the properties of the lensing
galaxies are independently constrained with substantially greater accuracy than
at present. | The Size of the Broad Line Region in M84 (NGC 4374): M84 is a giant elliptical galaxy located in the Virgo cluster. Prior imaging
with the Hubble Space Telescope (HST) revealed a small, highly inclined,
nuclear ionized gas disk, the kinematics of which indicate the presence of a
0.4 -1.5 billion solar mass black hole. Two prominent radio jets emerge
perpendicular to the nuclear ionized gas disk terminating in large radio lobes
that extend beyond the visible galaxy. Plausible kinematic models are used to
constrain the size of the broad line region (BLR) in M84 by modeling the shape
of the broad H-alpha emission line profile. The analysis indicates that the
emitting region is large with an outer radius between ~ 7 and 9 pc, depending
on whether the kinematic model is represented by a spherically symmetric inflow
or a Keplerian disk. The inferred size makes the BLR in M84 the largest yet to
be measured. The fact that the BLR in M84 is so large may explain why the AGN
is unable to sustain the ionization seen there. Thus, the BLR in M84 is not
simply that of a scaled down quasar. |
The Spitzer view of FR-I radio galaxies: on the origin of the nuclear
mid-infrared continuum: We present Spitzer MIR spectra of 25 FR-I radio galaxies and investigate the
nature of their MIR continuum emission. MIR spectra of star-forming galaxies
and quiescent elliptical galaxies are used to identify host galaxy
contributions while radio/optical core data are used to isolate the nuclear
non-thermal emission. Out of the 15 sources with detected optical compact
cores, four sources are dominated by emission related to the host galaxy.
Another four sources show signs of warm, nuclear dust emission: 3C15, 3C84,
3C270, and NGC 6251. It is likley that these warm dust sources result from
hidden AGN of optical spectral type 1. The MIR spectra of seven sources are
dominated by synchrotron emission, with no significant component of nuclear
dust emission. In parabolic SED fits of the non-thermal cores FR-Is tend to
have lower peak frequencies and stronger curvature than blazars. This is
roughly consistent with the common picture in which the core emission in FR-Is
is less strongly beamed than in blazars. | VIVA, VLA Imaging of Virgo spirals in Atomic gas: I. The Atlas & The HI
Properties: We present the result of a new VLA HI Imaging survey of Virgo galaxies, VIVA
(the VLA Imaging survey of Virgo galaxies in Atomic gas). The survey includes
high resolution HI data of 53 carefully selected late type galaxies (48 spirals
and 5 irregular systems). The goal is to study environmental effects on HI gas
properties of cluster galaxies to understand which physical mechanisms affect
galaxy evolution in different density regions, and to establish how far out the
impact of the cluster reaches. As a dynamically young cluster, Virgo contains
examples of galaxies experiencing a variety of environmental effects. Its
nearness allows us to study each galaxy in great detail. We have selected Virgo
galaxies with a range of star formation properties in low to high density
regions (at the projected distance from M87, d_87=0.3-3.3 Mpc). Contrary to pr
evious studies, more than half of the galaxies in the sample (~60%) are fainter
than 12 mag in B_T. Overall, the selected galaxies represent the late type
Virgo galaxies (S0/a to Sd/Irr) down to m_p<~14.6 fairly well in morphological
type, systemic velocity, subcluster membership, HI mass and deficiency. In this
paper (VIVA I: the atlas and the HI properties), we present HI maps and
properties, and describe the HI morphology and kinematics of individual
galaxies in detail (abbreviated). |
Results on Low-Mass Weakly Interacting Massive Particles from an 11
kg-day Target Exposure of DAMIC at SNOLAB: We present constraints on the existence of weakly interacting massive
particles (WIMPs) from an 11 kg-day target exposure of the DAMIC experiment at
the SNOLAB underground laboratory. The observed energy spectrum and spatial
distribution of ionization events with electron-equivalent energies $>$200
eV$_{\rm ee}$ in the DAMIC CCDs are consistent with backgrounds from natural
radioactivity. An excess of ionization events is observed above the analysis
threshold of 50 eV$_{\rm ee}$. While the origin of this low-energy excess
requires further investigation, our data exclude spin-independent WIMP-nucleon
scattering cross sections $\sigma_{\chi-n}$ as low as $3\times 10^{-41}$ cm$^2$
for WIMPs with masses $m_{\chi}$ from 7 to 10 GeV$c^{-2}$ . These results are
the strongest constraints from a silicon target on the existence of WIMPs with
$m_{\chi}$$<$9 GeV$c^{-2}$ and are directly relevant to any dark matter
interpretation of the excess of nuclear-recoil events observed by the CDMS
silicon experiment in 2013. | The complex nature of the nuclear star cluster in FCC 277: Recent observations have shown that compact nuclear star clusters (NSCs) are
present in up to 80% of galaxies. However, detailed studies of their dynamical
and chemical properties are confined mainly to spiral galaxy hosts, where they
are more easily observed. In this paper we present our study of the NSC in FCC
277, a nucleated elliptical galaxy in the Fornax cluster. We use a combination
of adaptive optics assisted near-infrared integral field spectroscopy, Hubble
Space Telescope imaging, and literature long slit data. We show that while the
NSC does not appear to rotate within our detection limit of ~6 km/s, rotation
is detected at larger radii, where the isophotes appear to be disky, suggesting
the presence of a nuclear disk. We also observe a distinct central velocity
dispersion drop that is indicative of a dynamically cold rotating sub-system.
Following the results of orbit-based dynamical modelling, co-rotating as well
as counter-rotating stellar orbits are simultaneously needed to reproduce the
observed kinematics. We find evidence for varying stellar populations, with the
NSC and nuclear disk hosting younger and more metal rich stars than the main
body of the galaxy. We argue that gas dissipation and some level of merging
have likely played an important role in the formation of the nucleus of this
intermediate-mass galaxy. This is in contrast to NSCs in low-mass early- type
galaxies, which may have been formed primarily through the infall of star
clusters. |
Eight New Quasar Lenses from the Sloan Digital Sky Survey Quasar Lens
Search: We report the discovery and confirmation of eight new two-image lensed
quasars by the Sloan Digital Sky Survey (SDSS) Quasar Lens Search. The lenses
are
SDSSJ0904+1512 (image separation \theta=1"13, source redshift z_s=1.826),
SDSSJ1054+2733 (\theta=1"27, z_s=1.452),
SDSSJ1055+4628 (\theta=1"15, z_s=1.249),
SDSSJ1131+1915 (\theta=1"46, z_s=2.915),
SDSSJ1304+2001 (\theta=1"87, z_s=2.175),
SDSSJ1349+1227 (\theta=3"00, z_s=1.722),
SDSSJ1455+1447 (\theta=1"73, z_s=1.424), and
SDSSJ1620+1203 (\theta=2"77, z_s=1.158).
Three of them, SDSSJ1055+4628, SDSSJ1455+1447, and SDSSJ1620+1203, satisfy
the criteria for constructing our statistical sample for studying the
cosmological model. Based on galactic absorption lines of the lens galaxies, we
also derive lens redshifts of z_l=0.398 and z_l=0.513 for SDSSJ1620+1203 and
the previously discovered lens SDSSJ0746+4403, respectively. | Detection of the large scale alignment of massive galaxies at z~0.6: We report on the detection of the alignment between galaxies and large-scale
structure at z~0.6 based on the CMASS galaxy sample from the Baryon Oscillation
Spectroscopy Survey data release 9. We use two statistics to quantify the
alignment signal: 1) the alignment two-point correlation function which probes
the dependence of galaxy clustering at a given separation in redshift space on
the projected angle (theta_p) between the orientation of galaxies and the line
connecting to other galaxies, and 2) the cos(2theta)-statistic which estimates
the average of cos(2theta_p) for all correlated pairs at given separation. We
find significant alignment signal out to about 70 Mpc/h in both statistics.
Applications of the same statistics to dark matter halos of mass above 10^12
M_sun/h in a large cosmological simulation show similar scale-dependent
alignment signals to the observation, but with higher amplitudes at all scales
probed. We show that this discrepancy may be partially explained by a
misalignment angle between central galaxies and their host halos, though
detailed modeling is needed in order to better understand the link between the
orientations of galaxies and host halos. In addition, we find systematic trends
of the alignment statistics with the stellar mass of the CMASS galaxies, in the
sense that more massive galaxies are more strongly aligned with the large-scale
structure. |
Torsion driven Inflationary Magnetogenesis: We show that breaking of the conformal invariance of electromagnetic
Lagrangian which is required for inflationary magnetogenesis arises naturally
in the Poincar{\'e} Gauge Theory. We use the minimal coupling prescription to
introduce the electromagnetic gauge fields as well as non-abelian gauge fields
in this theory. Due to the addition of non-abelian gauge fields, we show that
the solar constraints on this model can be naturally evaded. We find that in
the minimal version of this model the generated magnetic field is too small to
explain the observations. We discuss some generalizations of the gravitational
action, including the Starobinsky model and a model with conformal invariance.
We show that such generalizations naturally generate the kinetic energy terms
required for magnetogenesis. We propose a generalization of the minimal model
by adding a potential term, which is allowed within the framework of this
model, and show that it leads to sufficiently large magnetic fields. | Self-similarity of temperature profiles in distant galaxy clusters: the
quest for a Universal law: We present the XMM-Newton temperature profiles of 12 bright clusters of
galaxies at 0.4<z<0.9, with 5<kT<11 keV. The normalized temperature profiles
(normalized by the mean temperature T500) are found to be generally
self-similar. The sample was subdivided in 5 cool-core (CC) and 7 non cool-core
(NCC) clusters, by introducing a pseudo-entropy ratio
sigma=(T_IN/T_OUT)X(EM_IN/EM_OUT)^-1/3 and defining the objects with sigma<0.6
as CC clusters and those with sigma>=0.6 as NCC clusters. The profiles of CC
and NCC clusters differ mainly in the central regions, with the latters
exhibiting a marginally flatter central profile. A significant dependence of
the temperature profiles on the pseudo-entropy ratio sigma is detected by
fitting a function of both r and sigma, showing an indication that the outer
part of the profiles becomes steeper for higher values of sigma (i.e.
transitioning towards the NCC clusters). No significant evidence of redshift
evolution could be found within the redshift range sampled by our clusters
(0.4<z<0.9). A comparison of our high-z sample with intermediate clusters at
0.1<z<0.3, showed how both the CC and NCC clusters temperature profiles have
experienced some sort of evolution. This can be due by the fact that higher z
clusters are at less advanced stage of their formation and did not have enough
time to create a relaxed structure, characterized by a central temperature dip
in CC clusters and by flatter profiles in NCC clusters. This is the first time
that a systematic study of the temperature profiles of galaxy clusters at z>0.4
has been attempted, as we were able to define the closest possible relation to
a Universal law for the temperature profiles of galaxy clusters at 0.1<z<0.9,
showing a dependence on both the state of relaxation of the clusters and the
redshift. |
Multi-wavelength Probes of Obscuration Towards the Narrow Line Region in
Seyfert Galaxies: We present a study of reddening and absorption towards the Narrow Line
Regions (NLR) in active galactic nuclei (AGN) selected from the Revised
Shapley-Ames, 12mu, and Swift/Burst Alert Telescope samples. For the sources in
host galaxies with inclinations of b/a > 0.5, we find that mean ratio of [O
III] 5007A, from ground-based observations, and [O IV] 28.59mu, from
Spitzer/Infrared Spectrograph observations, is a factor of 2 lower in Seyfert
2s than Seyfert 1s. The combination of low [O III]/[O IV] and [O III] 4363/5007
ratios in Seyfert 2s suggests more extinction of emission from the NLR than in
Seyfert 1s. Similar column densities of dusty gas, NH ~ several X 10^21 cm^-2,
can account for the suppression of both [O III] 5007A and [O III] 4363A, as
compared to those observed in Seyfert 1s. Also, we find that the X-ray line
OVII 22.1A is weaker in Seyfert 2s, consistent with absorption by the same gas
that reddens the optical emission. Using a Hubble Space Telescope/Space
Telescope Imaging Spectrograph slitless spectrum of the Seyfert 1 galaxy NGC
4151, we estimate that only ~ 30% of the [O III] 5007A comes from within 30 pc
of the central source, which is insufficient to account for the low [O
III]/[OIV] ratios in Seyfert 2s. If Seyfert 2 galaxies have similar intrinsic
[OIII] spatial profiles, the external dusty gas must extend further out along
the NLR, perhaps in the form of nuclear dust spirals that have been associated
with fueling flows towards the AGN. | Is an obscured AGN at the centre of the disk galaxy IC 2497 responsible
for Hanny's Voorwerp?: We present the results of VLBI and MERLIN observations of the massive disk
galaxy IC 2497. Optical observations of IC 2497 revealed the existence of a
giant emission nebula "Hanny's Voorwerp" in the proximity of the galaxy.
Earlier short-track 18 cm observations with e-VLBI at 18 cm, detected a compact
radio component (C1) at the centre of IC 2497. The brightness temperature of C1
was measured to be greater than 4E5 K. Deeper, long-track e-VLBI observations
presented here, re-confirm the existence of C1 but also reveal the existence of
a second compact component (C2) located about 230 milliarcseconds to the
North-East of C1. The brightness temperature of C2 is measured to be greater
than 1.4E5 K, suggesting that both components may be related to AGN activity
(e.g. a radio core and jet hotspot). Lower resolution 18cm MERLIN observations
show both components. C1 is shown to be compact with a slight elongation along
the direction of Hanny's Voorwerp, and C2 shows a lot of extended emission in
an almost perpendicular direction to the direction of the Voorwerp. Our results
continue to support the hypothesis that IC 2497 contains an Active Galactic
Nucleus (AGN), and that a jet associated with this AGN clears a path that
permits ionising radiation from the AGN to directly illuminate the emission
nebula. |
The spectroscopically confirmed huge cosmic structure at z=0.55: We report on the spectroscopic confirmation of a huge cosmic structure around
the CL0016 cluster at z=0.55. We made wide-field imaging observations of the
surrounding regions of the cluster and identified more than 30 concentrations
of red galaxies near the cluster redshift. The follow-up spectroscopic
observations of the most prominent part of the structure confirmed 14 systems
close to the cluster redshift, roughly half of which have a positive
probability of being bound to the cluster dynamically. We also made an X-ray
follow-up, which detected extended X-ray emissions from 70% of the systems in
the X-ray surveyed region. The observed structure is among the richest ever
observed in the distant Universe. It will be an ideal site for quantifying
environmental variations in the galaxy properties and effects of large-scale
structure on galaxy evolution. | The Stellar Masses of Disk Galaxies and the Calibration of Color-Mass to
Light Ratio Relations: We present new Spitzer 3.6 micron observations of a sample of disk galaxies
spanning over 10 magnitudes in luminosity and ranging in gas fraction from ~10%
to over 90%. We use these data to test population synthesis prescriptions for
computing stellar mass. Many commonly employed models fail to provide
self-consistent stellar masses in the sense that the stellar mass estimated
from the optical luminosity typically exceeds that estimated from the
near-infrared (NIR) luminosity. This problem is present in models both with and
without TP-AGB stars, but is more severe in the former. Self-consistency can be
achieved if NIR mass-to-light ratios are approximately constant with a mean
value near 0.5 Msun/Lsun at 3.6 microns. We use the Baryonic Tully-Fisher
relation calibrated by gas rich galaxies to provide an independent estimate of
the color-mass to light ratio relation. This approach also suggests that the
typical 3.6 micron mass-to-light ratio is 0.5 (0.65 in the K band) for
rotationally supported galaxies. These values are consistent with a Kroupa IMF. |
A Strategy to Measure the Dark Energy Equation of State using the HII
galaxy Hubble Relation & X-ray AGN Clustering: Preliminary Results: We explore the possibility of setting stringent constraints to the Dark
Energy equation of state using alternative cosmic tracers like: (a) the Hubble
relation using HII galaxies, which can be observed at much higher redshifts
(z~3.5) than those currently traced by SNIa samples, and (b) the large-scale
structure using the clustering of X-ray selected AGN,which have a redshift
distribution peaking at z~1.
We use extensive Monte-Carlo simulations to define the optimal strategy for
the recovery of the dark-energy equation of state using the high redshift (z~2)
Hubble relation, but accounting also for the effects of gravitational lensing,
which for such high redshifts can significantly affect the derived cosmological
constraints. Based on a "Figure of Merit" analysis, we provide estimates for
the number of 2<z<3.5 tracers needed to reduce the cosmological solution space,
presently provided by the Constitution SNIa set, by a desired factor. We find
that it is much more efficient to increase the number of tracers than to reduce
their individual uncertainties.
Finally, we propose a framework to put constraints on the dark energy
equation of state by using the joint likelihood of the X-ray AGN clustering and
of the Hubble relation cosmological analyses. A preliminary joint analysis
using the X-ray AGN clustering of the 2XMM survey and the Hubble relation of
the Constitution SNIa set provide: Omega_m= 0.31+-0.01 and w=-1.06+-0.05. We
also find that the joint SNIa-2XMM analysis provides significantly more
stringent cosmological constraints, increasing the Figure of Merit by a factor
~2, with respect to that of the joint SNIa-BAO analysis. | No-go Theorem for Scalar-Trispectrum-Induced Gravitational Waves: We show that the contribution of the primordial trispectrum to the energy
density of the scalar-induced stochastic gravitational wave background cannot
exceed the one from the scalar power spectrum in conventional inflationary
scenarios. Specifically, we prove in the context of scale-invariant theories
that neither regular trispectrum shapes peaking in so-called equilateral
configurations, nor local trispectrum shapes diverging in soft momentum limits,
can contribute significantly. Indeed, those contributions are always bound to
be smaller than an order-one (or smaller) number multiplying the relative
one-loop correction to the scalar power spectrum, necessarily much smaller than
unity in order for the theory to be under perturbative control. Since a no-go
theorem is only worth its assumptions, we also briefly discuss a toy model for
a scale-dependent scalar spectrum, which confirms the robustness of our no-go
result. |
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