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Constraints and tensions in testing general relativity from Planck and
CFHTLenS including intrinsic alignment systematics: We present constraints on testing general relativity (GR) at cosmological
scales using recent data sets and assess the impact of galaxy intrinsic
alignment (IA) in the CFHTLenS lensing data on those constraints. We consider
CMB temperature data from Planck, the galaxy power spectrum from WiggleZ, weak
lensing tomography from the CFHTLenS, ISW-galaxy cross correlations, and BAO
data from 6dF, SDSS DR7, and BOSS DR9. We use a parameterization of the
modified gravity (MG) that is binned in redshift and scale, a parameterization
that evolves monotonically in scale but is binned in redshift, and a functional
parameterization that evolves only in redshift. We present the results in terms
of the MG parameters $Q$ and $\Sigma$. We employ an IA model with an amplitude
$A_{CFHTLenS}$ that is included in the parameter analysis. We find an
improvement in the constraints on the MG parameters corresponding to $40-53\%$
increase on the figure of merit compared to previous studies, and GR is found
consistent with the data at the $95\%$ CL. The bounds found on $A_{CFHTLenS}$
are sensitive to the MG parameterization used, and the correlations between
$A_{CFHTLenS}$ and MG parameters are found to be weak to moderate. For all 3 MG
parameterizations $A_{\rm CFHTLenS}$ is found consistent with zero when the
whole lensing sample is used, however, when using the optimized early-type
galaxy sample a significantly non-zero $A_{\rm CFHTLenS}$ is found for GR and
the third MG parameterization. We find that the tensions observed in previous
studies persist, and there is an indication that CMB data and lensing data
prefer different values for MG parameters, particularly for the parameter
$\Sigma$. The analysis of the confidence contours and probability distributions
suggest that the bimodality found follows that of the known tension in the
$\sigma_8$ parameter. (Abridged) | Black Holes Constitute All Dark Matter: The dimensionless entropy, ${\cal S} \equiv S/k$, of the visible universe,
taken as a sphere of radius 50 billion light years with the Earth at its
"center", is discussed. An upper limit ($10^{112}$), and a lower limit
($10^{102}$), for ${\cal S}$ are introduced. It is suggested that
intermediate-mass black holes (IMBHs) constitute all dark matter, and that they
dominate ${\cal S}$. |
A comprehensive investigation on the slowing down of cosmic acceleration: Shafieloo ea al. firstly proposed the possibility that the current cosmic
acceleration (CA) is slowing down. However, this is rather counterintuitive
because a slowing down CA cannot be accommodated in most mainstream
cosmological models. In this work, by exploring the evolutionary trajectories
of dark energy equation of state $w(z)$ and deceleration parameter $q(z)$, we
present a comprehensive investigation on the slowing down of CA from both the
theoretical and the observational sides. For the theoretical side, we study the
impact of different $w(z)$ by using six parametrization models, and then
discuss the effects of spatial curvature. For the observational side, we
investigate the effects of different type Ia supernovae (SNe Ia), different
baryon acoustic oscillation (BAO), and different cosmic microwave background
(CMB) data, respectively. We find that (1) The evolution of CA are insensitive
to the specific form of $w(z)$; in contrast, a non-flat Universe more favors a
slowing down CA than a flat Universe. (2) SNLS3 SNe Ia datasets favor a slowing
down CA at 1$\sigma$ confidence level, while JLA SNe Ia samples prefer an
eternal CA; in contrast, the effects of different BAO data are negligible. (3)
Compared with CMB distance prior data, full CMB data more favor a slowing down
CA. (4) Due to the low significance, the slowing down of CA is still a
theoretical possibility that cannot be confirmed by the current observations. | EROSITA Spectro-Imaging Analysis of the Abell 3408 Galaxy Cluster: The X-ray telescope eROSITA onboard the newly launched SRG mission
serendipitously observed the galaxy cluster A3408 ($z=0.0420$) during the PV
observation of the AGN 1H0707-495. Despite its brightness and large extent, it
has not been observed by any modern X-ray observatory. A neighbouring cluster
in NW direction, A3407 ($z=0.0428$), appears to be close at least in projection
($\sim 1.7$ Mpc). This cluster pair could be in a pre- or post-merger state.
We perform a detailed X-ray analysis of A3408. We construct particle
background subtracted and exposure corrected images and surface brightness
profiles in different sectors. The spectral analysis is performed out to
$1.4r_{500}$. Additionally, a temperature map is presented depicting the
distribution of the ICM temperature. Furthermore, we make use of data from the
RASS to estimate some bulk properties of A3408 and A3407, using the growth
curve analysis method and scaling relations.
The imaging analysis shows a complex morphology of A3408 with a strong
elongation in SE-NW direction. This is quantified by comparing the surface
brightness profiles of the NW, SW, SE and NE directions, where the NW and SE
directions show a significantly higher surface brightness compared to the other
directions. We determine a gas temperature ${\rm k_B}T_{500}=(2.23\pm0.09)$
keV. The T-profile reveals a hot core within $2'$ of the emission peak, ${\rm
k_B}T=3.04^{+0.29}_{-0.25}$ keV. Employing a M-T relation, we obtain
$M_{500}=(9.27\pm0.75)\times 10^{13}M_{\odot}$ iteratively. The $r_{200}$ of
A3407 and A3408 are found to overlap in projection which makes ongoing
interactions plausible. The 2d T-map reveals higher temperatures in W than in E
direction.
A3407 and A3408 are likely in a pre-merger state, affecting the ICM
properties, i.e., increased temperatures in the direction of A3407 indicate
adiabatic compression or shocks due to the interaction. |
The Effective Field Theory of Inflation Models with Sharp Features: We describe models of single-field inflation with small and sharp step
features in the potential (and sound speed) of the inflaton field, in the
context of the Effective Field Theory of Inflation. This approach allows us to
study the effects of features in the power-spectrum and in the bispectrum of
curvature perturbations, from a model-independent point of view, by
parametrizing the features directly with modified "slow-roll" parameters. We
can obtain a self-consistent power-spectrum, together with enhanced
non-Gaussianity, which grows with a quantity $\beta$ that parametrizes the
sharpness of the step. With this treatment it is straightforward to generalize
and include features in other coefficients of the effective action of the
inflaton field fluctuations. Our conclusion in this case is that, excluding
extrinsic curvature terms, the only interesting effects at the level of the
bispectrum could arise from features in the first slow-roll parameter
$\epsilon$ or in the speed of sound $c_s$. Finally, we derive an upper bound on
the parameter $\beta$ from the consistency of the perturbative expansion of the
action for inflaton perturbations. This constraint can be used for an
estimation of the signal-to-noise ratio, to show that the observable which is
most sensitive to features is the power-spectrum. This conclusion would change
if we consider the contemporary presence of a feature and a speed of sound $c_s
< 1$, as, in such a case, contributions from an oscillating folded
configuration can potentially make the bispectrum the leading observable for
feature models. | The Effects of Varying Cosmological Parameters on Halo Substructure: We investigate how different cosmological parameters, such as those delivered
by the WMAP and Planck missions, affect the nature and evolution of dark matter
halo substructure. We use a series of flat $\Lambda$ cold dark matter
($\Lambda$CDM) cosmological $N$-body simulations of structure formation, each
with a different power spectrum but the same initial white noise field. Our
fiducial simulation is based on parameters from the WMAP 7th year cosmology. We
then systematically vary the spectral index, $n_s$, matter density, $\Omega_M$,
and normalization of the power spectrum, $\sigma_8$, for 7 unique simulations.
Across these, we study variations in the subhalo mass function, mass fraction,
maximum circular velocity function, spatial distribution, concentration,
formation times, accretion times, and peak mass. We eliminate dependence of
subhalo properties on host halo mass and average over many hosts to reduce
variance. While the "same" subhalos from identical initial overdensity peaks in
higher $\sigma_8, n_s$, and $\Omega_m$ simulations accrete earlier and end up
less massive and closer to the halo center at $z=0$, the process of continuous
subhalo accretion and destruction leads to a steady state distribution of these
properties across all subhalos in a given host. This steady state mechanism
eliminates cosmological dependence on all properties listed above except
subhalo concentration and $V_{max}$, which remain greater for higher $\sigma_8,
n_s$ and $\Omega_m$ simulations, and subhalo formation time, which remains
earlier. We also find that the numerical technique for computing scale radius
and the halo finder used can significantly affect the concentration-mass
relationship computed for a simulation. |
The Jubilee ISW Project II: observed and simulated imprints of voids and
superclusters on the cosmic microwave background: We examine the integrated Sachs-Wolfe (ISW) imprint of voids and
superclusters on the cosmic microwave background. We first study results from
the Jubilee $N$-body simulation. From Jubilee, we obtain the full-sky ISW
signal from structures out to redshift $z=1.4$ and a mock luminous red galaxy
(LRG) catalogue. We confirm that the expected signal in the concordance \Lambda
CDM model is very small and likely to always be much smaller than the
anisotropies arising at the last scattering surface. Any current detections of
such an imprint must, therefore, predominantly arise from something other than
an ISW effect in a \Lambda CDM universe. Using the simulation as a guide, we
then look for the signal using a catalogue of voids and superclusters from the
Sloan Digital Sky Survey. We find a result that is consistent with the \Lambda
CDM model, i.e. a signal consistent with zero. | Exploiting Machine Learning and Disequilibrium in Galaxy Clusters to
Obtain a Mass Profile: We use 3-D K Means clustering to characterize galaxy substructure in the
Abell 2146 cluster of galaxies (z = 0.2343). This method objectively
characterizes the cluster's substructure using projected position and velocity
data for 67 galaxies within a 2.305 Mpc circular region centered on the
clusters optical center. The optimal number of substructures is found to be 4.
Four distinct substructures with RMS velocity typical of galaxy groups or low
mass subclusters, when compared to cosmological simulations of galaxy cluster
formation, suggests that Abell 2146 is in the early stages of formation. We
utilize this disequilibrium, that is so prevalent in galaxy clusters at all
redshifts, to construct a radial mass distribution. Substructures are bound but
not virialized. This method is in contrast to previous kinematical analyses,
which have assumed virialization, and ignored the ubiquitous clumping of
galaxies. The best fitting radial mass profile is much less centrally
concentrated than the well known NFW profile, indicating that the dark matter
dominated mass distribution is flatter pre-equilibrium, becoming more centrally
peaked in equilibrium through merging of substructure. |
The distribution of galaxy morphological types and the morphology-mass
relation in different environments at low redshift: We use \sim 2000 galaxies belonging to different environments to show how the
fractions of different galaxy morphological types vary with global environment
and as function of galaxy stellar mass at low redshift. Considering mass
limited galaxy samples with log10 M\star/M\bigodot>= 10.25, we find a smooth
increase/decline in the fraction of Es-S0s/late type galaxies going from single
galaxies, to binaries, to groups. Considering all environments, the fractional
variation is more conspicuous for S0s and late-types than for ellipticals
solely due to a sharp enhancement/dearth of S0s/late-types in clusters compared
to other environments. The morphological distribution of galaxies in the mass
range 10.25 < log10 M\star/M\bigodot < 11 is rather independent both of galaxy
stellar mass and global environment, except in clusters. The morphologies of
galaxies more massive than log10 M\star/M\bigodot = 11 are instead a function
of both galaxy mass and global environment. The morphology-mass relation
therefore changes with global environment, showing that galaxy stellar mass
cannot be the only parameter driving the morphological distribution of
galaxies. The morphology-mass relations for S0 and late-type galaxies in
clusters are peculiar compared to other environments, and this strongly
suggests that cluster-specific effects act on these two types of galaxies, and
that a significant number of S0s in clusters has a different origin with
respect to S0s in other environments. | Can Non-standard Recombination Resolve the Hubble Tension?: The inconsistent Hubble constant values derived from cosmic microwave
background (CMB) observations and from local distance-ladder measurements may
suggest new physics beyond the standard $\Lambda$CDM paradigm. It has been
found in earlier works that, at least phenomenologically, non-standard
recombination histories can reduce the $\gtrsim 4\sigma$ Hubble tension to
$\sim 2\sigma$. Following this path, we vary physical and phenomenological
parameters in RECFAST, the standard code to compute ionization history of the
universe, to explore possible physics beyond standard recombination. We find
that the CMB constraint on the Hubble constant is sensitive to the Hydrogen
ionization energy and $2s \rightarrow 1s$ two-photon decay rate, both of which
are atomic constants, and is insensitive to other details of recombination.
Thus, the Hubble tension is very robust against perturbations of recombination
history, unless exotic physics modifies the atomic constants during the
recombination epoch. |
Barrow nearly-extensive Gibbs-like entropy favoured by the full
dynamical and geometrical data set in cosmology: We apply the full set of most update dynamical and geometrical data in
cosmology to the nonextensive Barrow entropic holographic dark energy. We show
that the data point towards an extensive Gibbs-like entropic behaviour for the
cosmological horizons, which is the extreme case of the Barrow entropy, with
the entropy parameter being $\Delta > 0.86$, close to the maximum threshold of
$\Delta =1$ where the fractal dimension of the area-horizon becomes almost or
just the volume and the intensivity is recovered. Futhermore, we find that the
standard Bekenstein area-entropy limit ($\Delta = 0$) is excluded by the set of
our data. This contradicts the bounds obtained recently from early universe
tests such as the baryon asymmetry, the big-bang nucleosynthesis, and the
inflation limiting $\Delta< 0.008$ at the most extreme case. | Do dark matter halos explain lensing peaks?: We have investigated a recently proposed halo-based model, Camelus, for
predicting weak-lensing peak counts, and compared its results over a collection
of 162 cosmologies with those from N-body simulations. While counts from both
models agree for peaks with $\mathcal{S/N}>1$ (where $\mathcal{S/N}$ is the
ratio of the peak height to the r.m.s. shape noise), we find $\approx 50\%$
fewer counts for peaks near $\mathcal{S/N}=0$ and significantly higher counts
in the negative $\mathcal{S/N}$ tail. Adding shape noise reduces the
differences to within $20\%$ for all cosmologies. We also found larger
covariances that are more sensitive to cosmological parameters. As a result,
credibility regions in the $\{\Omega_m, \sigma_8\}$ are $\approx 30\%$ larger.
Even though the credible contours are commensurate, each model draws its
predictive power from different types of peaks. Low peaks, especially those
with $2<\mathcal{S/N}<3$, convey important cosmological information in N-body
data, as shown in \cite{DietrichHartlap, Kratochvil2010}, but \textsc{Camelus}
constrains cosmology almost exclusively from high significance peaks
$(\mathcal{S/N}>3)$. Our results confirm the importance of using a
cosmology-dependent covariance with at least a 14\% improvement in parameter
constraints. We identified the covariance estimation as the main driver behind
differences in inference, and suggest possible ways to make Camelus even more
useful as a highly accurate peak count emulator. |
Cosmic magnetic fields and dark energy in extended electromagnetism: We discuss an extended version of electromagnetism in which the usual gauge
fixing term is promoted into a physical contribution that introduces a new
scalar state in the theory. This new state can be generated from vacuum quantum
fluctuations during an inflationary era and, on super-Hubble scales, gives rise
to an effective cosmological constant. The value of such a cosmological
constant coincides with the one inferred from observations as long as inflation
took place at the electroweak scale. On the other hand, the new state also
generates an effective electric charge density on sub-Hubble scales that
produces both vorticity and magnetic fields with coherent lengths as large as
the present Hubble horizon. | A single-merger scenario for the formation of the giant stream and the
warp of M31: We propose that the accretion of a dwarf spheroidal galaxy provides a common
origin for the giant southern stream and the warp of M31. We run about 40 full
N-body simulations with live M31, infalling galaxies with varying masses and
density profiles, and cosmologically-plausible initial orbital parameters.
Excellent agreement with a full range of observational data is obtained for a
model in which a dark-matter-rich dwarf spheroidal, whose trajectory lies on
the thin plane of corotating satellites of M31, is accreted from its turnaround
radius of about 200 kpcs into M31 at approximately 3 Gyrs ago. The satellite is
disrupted as it orbits in the potential well of the galaxy and forms the giant
stream and in return heats and warps the disk of M31. We show that our
cosmologically-motivated model is favoured by the kinematic data over the
phenomenological models in which the satellite starts its infall from a close
distance of M31. Our model predicts that the remnant of the disrupted satellite
resides in the region of the North-Eastern shelf of M31. The results here
suggest that the surviving satellites of M31 that orbit on the same thin plane,
as the disrupted satellite once did, could have all been accreted from an
intergalactic filament. |
The Coma cluster at LOFAR frequencies I: insights into particle
acceleration mechanisms in the radio bridge: Radio synchrotron emission from the bridges of low-density gas connecting
galaxy clusters and groups is a challenge for particle acceleration processes.
In this work, we analyse the Coma radio bridge using new LOw Frequency ARray
(LOFAR) observations at 144 MHz. LOFAR detects the bridge and its substructures
with unprecedented sensitivity and resolution. We find that the radio emission
peaks on the NGC 4839 group. Towards the halo, in front of the NGC 4839 group,
the radio brightness decreases and streams of radio emission connect the NGC
4839 group to the radio relic. Using X-ray observations, we find that thermal
and non-thermal plasma are moderately correlated with a sub-linear scaling. We
use archival radio data at 326 MHz to constrain the spectral index in the
bridge, and quantify the distribution of particles and magnetic field at
different frequencies. We find that the spectrum is steeper than $-1.4 \pm
0.2$, and that the emission could be clumpier at 326 MHz than at 144 MHz. Using
cosmological simulations and a simplified approach to compute particle
acceleration, we derive under which conditions turbulent acceleration of mildly
relativistic electrons could generate the radio emission in the bridge.
Assuming that the initial energy ratio of the seed electrons is $3 \cdot
10^{-4}$ with respect to the thermal gas, we are able to reproduce the observed
luminosity. Our results suggest that the seed electrons released by
radiogalaxies in the bridge and the turbulence generated by the motion of gas
and galaxies are essential to produce the radio emission. | Standard siren cosmology in the era of the 2.5-generation ground-based
gravitational wave detectors: bright and dark sirens of LIGO Voyager and NEMO: The 2.5-generation (2.5G) ground-based gravitational wave (GW) detectors LIGO
Voyager and NEMO are expected to be operational in the late 2020s and early
2030s. In this work, we explore the potential of GW standard sirens observed by
the 2.5G GW detectors in measuring cosmological parameters, especially for the
Hubble constant. Using GWs to measure cosmological parameters is inherently
challenging, especially for 2.5G detectors, given their limited capability,
which results in weaker constraints on cosmological parameters from the
detected standard sirens. However, the measurement of the Hubble constant using
standard siren observations from Voyager and NEMO is still promising. For
example, using bright sirens from Voyager and NEMO can measure the Hubble
constant with an accuracy of about $2\%$ and $6\%$ respectively, and using the
Voyager-NEMO network can improve the accuracy to about $1.6\%$. Moreover,
bright sirens can be used to break the degeneracy of cosmological parameters
generated by CMB data, and to a certain extent, 2.5G detectors can also play a
role in this aspect. Observations of dark sirens by 2.5G detectors can achieve
relatively good results in measuring the Hubble constant, with an accuracy of
within $2\%$, and if combining observations of bright and dark sirens, the
accuracy of the Hubble constant measurement can reach about $1.3\%$. Finally,
we also discussed the impact of the uncertainty in the binary neutron star
merger rate on the estimation of cosmological parameters. We conclude that the
magnificent prospect for solving the Hubble tension is worth expecting in the
era of the 2.5G ground-based GW detectors. |
Resolving conclusions about the early Universe requires accurate nuclear
measurements: Nuclear physics experiments give reaction rates that, via modelling and
comparison with primordial abundances, constrain cosmological parameters. The
error bars of a key reaction, \dpg, were tightened in 2020, bringing to light
discrepancies between different analyses and calling for more accurate
measurements of other reactions. | Constraining large scale HI bias using redshifted 21-cm signal from the
post-reionization epoch: In the absence of complex astrophysical processes that characterize the
reionization era, the 21-cm emission from neutral hydrogen (HI) in the
post-reionization epoch is believed to be an excellent tracer of the underlying
dark matter distribution. Assuming a background cosmology, it is modelled
through (i) a bias function b(k,z), which relates HI to the dark matter
distribution and (ii) a mean neutral fraction (x_{HI}) which sets its
amplitude. In this paper, we investigate the nature of large scale HI bias. The
post-reionization HI is modelled using gravity only N-Body simulations and a
suitable prescription for assigning gas to the dark matter halos. Using the
simulated bias as the fiducial model for HI distribution at z\leq 4, we have
generated a hypothetical data set for the 21-cm angular power spectrum (C_{l})
using a noise model based on parameters of an extended version of the GMRT. The
binned C_{l} is assumed to be measured with SNR \gtrsim 4 in the range 400 \leq
l \leq 8000 at a fiducial redshift z=2.5. We explore the possibility of
constraining b(k) using the Principal Component Analysis (PCA) on this
simulated data. Our analysis shows that in the range 0.2 < k < 2 Mpc^{-1}, the
simulated data set cannot distinguish between models exhibiting different k
dependences, provided 1 \lesssim b(k) \lesssim 2 which sets the 2-sigma limits.
This justifies the use of linear bias model on large scales. The largely
uncertain x_{HI} is treated as a free parameter resulting in degradation of the
bias reconstruction. The given simulated data is found to constrain the
fiducial x_{HI} with an accuracy of \sim 4% (2-sigma error). The method
outlined here, could be successfully implemented on future observational data
sets to constrain b(k,z) and x_{HI} and thereby enhance our understanding of
the low redshift Universe. |
Cosmography and flat $Λ$CDM tensions at high redshift: Risaliti, Lusso \& collaborators have constructed a high-redshift Hubble
diagram of supernovae (SNe); quasars (QSO) and gamma-ray bursts (GRB) that
shows a "$\sim 4 \, \sigma$ tension with the $\Lambda$CDM model" based on a log
polynomial cosmographic expansion (Risaliti et.al 2018, Lusso et.al 2019). In
this work, we demonstrate that the log polynomial expansion generically fails
to recover flat $\Lambda$CDM beyond $z \sim 2$, thus undermining the $\sim 4 \,
\sigma$ tension claim. Moreover, through direct fits of both the flat
$\Lambda$CDM and the log polynomial model to the SNe+QSO+GRB dataset, we
confirm that the flat $\Lambda$CDM model is preferred. Ultimately, we trace the
tension to the QSO data and show that a best-fit of the flat $\Lambda$CDM model
to the QSO data leads to a flat $\Lambda$CDM Universe with no dark energy
within $1 \, \sigma$. This marks an irreconcilable tension between the
Risaliti-Lusso QSOs and flat $\Lambda$CDM. | Testing hydrostatic equilibrium in galaxy cluster MS 2137: We test the assumption of strict hydrostatic equilibrium in galaxy cluster
MS2137.3-2353 (MS 2137) using the latest CHANDRA X-ray observations and results
from a combined strong and weak lensing analysis based on optical observations.
We deproject the two-dimensional X-ray surface brightness and mass surface
density maps assuming spherical and spheroidal dark matter distributions. We
find a significant, 40%-50%, contribution from non-thermal pressure in the core
assuming a spherical model. This non-thermal pressure support is similar to
what was found by Molnar et al. (2010) using a sample of massive relaxed
clusters drawn from high resolution cosmological simulations. We have studied
hydrostatic equilibrium in MS 2137 under the assumption of elliptical cluster
geometry adopting prolate models for the dark matter density distribution with
different axis ratios. Our results suggest that the main effect of ellipticity
(compared to spherical models) is to decrease the non-thermal pressure support
required for equilibrium at all radii without changing the distribution
qualitatively. We find that a prolate model with an axis ratio of 1.25 (axis in
the line of sight over perpendicular to it) provides a physically acceptable
model implying that MS 2137 is close to hydrostatic equilibrium at about
0.04-0.15 Rvir and have an about 25% contribution from non-thermal pressure at
the center. Our results provide further evidence that there is a significant
contribution from non-thermal pressure in the core region of even relaxed
clusters, i.e., the assumption of hydrostatic equilibrium is not valid in this
region, independently of the assumed shape of the cluster. |
Planck Lensing and Cosmic Infrared Background Cross-Correlation with
Fermi-LAT: Tracing Dark Matter Signals in the Gamma-Ray Background: The extragalactic $\gamma$-ray background and its spatial anisotropy could
potentially contain a signature of dark matter (DM) annihilation or particle
decay. Astrophysical foregrounds, such as blazars and star-forming galaxies
(SFGs), however, dominate the $\gamma$-ray background, precluding an easy
detection of the signal associated with the DM annihilation or decay in the
background intensity spectrum. The DM imprint on the $\gamma$-ray background is
expected to be correlated with large-scale structure tracers. In some cases,
such a cross-correlation is even expected to have a higher signal-to-noise
ratio than the auto-correlation. One reliable tracer of the DM distribution in
the large-scale structure is lensing of the cosmic microwave background (CMB),
and the cosmic infrared background (CIB) is a reliable tracer of SFGs. We
analyze Fermi-LAT data taken over 92 months and study the cross-correlation
with Planck CMB lensing, Planck CIB, and Fermi-$\gamma$ maps. We put upper
limits on the DM annihilation cross-section from the cross-power spectra with
the $\gamma$-ray background anisotropies. The unbiased power spectrum
estimation is validated with simulations that include cross-correlated signals.
We also provide a set of systematic tests and show that no significant
contaminations are found for the measurements presented here. Using
$\gamma$-ray background map from data gathered over 92 months, we find the best
constraint on the DM annihilation with a $1\sigma$ confidence level upper limit
of $10^{-25}$-$10^{-24}$ cm$^{3}$ s$^{-1}$, when the mass of DM particles is
between 20 and 100 GeV. | The zCOSMOS 10k-sample: the role of galaxy stellar mass in the
colour-density relation up to z=1: [Abridged] With the first 10000 spectra of the flux limited zCOSMOS sample
(I<=22.5) we study the evolution of environmental effects on galaxy properties
since z=1.0, and disentangle the dependence among galaxy colour, stellar mass
and local density (3D local density contrast `delta', computed with the 5th
nearest neighbour approach). We confirm that within a luminosity-limited sample
(M_B<=-20.5-z) the fraction of red (U-B>=1) galaxies 'f_red' depends on delta
at least up to z=1, with red galaxies residing mainly in high densities. This
trend weakens for increasing z, and it is mirrored by the behaviour of the
fraction of galaxies with D4000A break >=1.4. We also find that up to z=1 the
fraction of galaxies with log(EW[OII]) >=1.15 is higher for lower delta, and
also this dependence weakens for increasing z. Given the triple dependence
among galaxy colours, stellar mass and delta, the colour-delta relation found
in the luminosity-selected sample can be due to the broad range of stellar
masses. Thus, we fix the stellar mass and we find that in this case the
colour-delta relation is flat up to z=1 for galaxies with log(M/M_sun)>=10.7.
This means that for these masses the colour-delta relation found in a
luminosity-selected sample is the result of the combined colour-mass and
mass-delta relations. In contrast, we find that for 0.1<=z<=0.5 and
log(M/M_sun)<=10.7 'f_red' depends on delta even at fixed mass. In these mass
and z ranges, environment affects directly also galaxy colours. We suggest a
scenario in which the colour depends primarily on stellar mass, but for
relatively low mass galaxies the local density modulates this dependence. These
galaxies formed more recently, in an epoch when evolved structures were already
in place, and their longer SFH allowed environment-driven physical processes to
operate during longer periods of time. |
Ram pressure stripping of the cool core of the Ophiuchus Cluster: (abridged) We report results from a Chandra study of the central regions of
the nearby, X-ray bright, Ophiuchus Cluster (z = 0.03), the second-brightest
cluster in the sky. Our study reveals a dramatic, close-up view of the
stripping and potential destruction of a cool core within a rich cluster. The
X-ray emission from the Ophiuchus Cluster core exhibits a comet-like morphology
extending to the north, driven by merging activity, indicative of ram-pressure
stripping caused by rapid motion through the ambient cluster gas. A cold front
at the southern edge implies a velocity of 1000$\pm$200 km/s (M~0.6). The X-ray
emission from the cluster core is sharply peaked. As previously noted, the peak
is offset by 4 arcsec (~2 kpc) from the optical center of the associated cD
galaxy, indicating that ram pressure has slowed the core, allowing the
relatively collisionless stars and dark matter to carry on ahead. The cluster
exhibits the strongest central temperature gradient of any massive cluster
observed to date: the temperature rises from 0.7 keV within 1 kpc of the
brightness peak, to 10 keV by 30 kpc. A strong metallicity gradient is also
observed within the same region. This supports a picture in which the outer
parts of the cool core have been stripped by ram-pressure due to its rapid
motion. The cooling time of the innermost gas is very short, ~5$\times10^7$
yrs. Within the central 10 kpc radius, multiple small-scale fronts and a
complex thermodynamic structure are observed, indicating significant motions.
Beyond the central 50 kpc, and out to a radius ~150 kpc, the cluster appears
relatively isothermal and has near constant metallicity. The exception is a
large, coherent ridge of enhanced metallicity observed to trail the cool core,
and which is likely to have been stripped from it. | Bayesian Comparison of Interacting Scenarios: We perform a Bayesian model selection analysis for different classes of
phenomenological coupled scenarios of dark matter and dark energy with linear
and non-linear interacting terms. We use a combination of some of the latest
cosmological data such as type Ia supernovae (SNe Ia), cosmic chronometers
(CC), cosmic microwave background (CMB) and two sets of baryon acoustic
oscillations measurements, namely, 2-dimensional angular measurements (BAO2)
and 3-dimensional angle-averaged measurements (BAO3). We find weak and moderate
evidence against two-thirds of the interacting scenarios considered with
respect to $\Lambda$CDM when the full joint analysis is considered. About
one-third of the models provide a description to the data as good as the one
provided by the standard model. Our results also indicate that either SNe Ia,
CC or BAO2 data by themselves are not able to distinguish among interacting
models or $\Lambda$CDM but the standard BAO3 measurements and the combination
with the CMB data are indeed able to discriminate among them. We find that
evidence disfavoring interacting models is weaker when we use BAO2 (data
claimed to be almost model-independent) instead of the standard BAO3
measurements. These results help select classes of viable and non-viable
interacting models in light of current data. |
Properties of type Ia supernovae inside rich galaxy clusters: We used the GMBCG galaxy cluster catalogue and SDSS-II supernovae data with
redshifts measured by the BOSS project to identify 48 SNe Ia residing in rich
galaxy clusters and compare their properties with 1015 SNe Ia in the field.
Their light curves were parametrised by the SALT2 model and the significance of
the observed differences was assessed by a resampling technique. To test our
samples and methods, we first looked for known differences between SNe Ia
residing in active and passive galaxies. We confirm that passive galaxies host
SNe Ia with smaller stretch, weaker colour-luminosity relation [$\beta$ of
2.54(22) against 3.35(14)], and that are $\sim$ 0.1 mag more luminous after
stretch and colour corrections. We show that only 0.02 per cent of random
samples drawn from our set of SNe Ia in active galaxies can reach these values.
Reported differences in the Hubble residuals scatter could not be detected,
possibly due to the exclusion of outliers. We then show that, while most field
and cluster SNe Ia properties are compatible at the current level, their
stretch distributions are different ($\sim3\sigma$): besides having a higher
concentration of passive galaxies than the field, the cluster's passive
galaxies host SNe Ia with an average stretch even smaller than those in field
passive galaxies (at 95 per cent confidence). We argue that the older age of
passive galaxies in clusters is responsible for this effect since, as we show,
old passive galaxies host SNe Ia with smaller stretch than young passive
galaxies ($\sim4\sigma$). | Biased Tracers and Time Evolution: We study the effect of time evolution on galaxy bias. We argue that at any
order in perturbations, the galaxy density contrast can be expressed in terms
of a finite set of locally measurable operators made of spatial and temporal
derivatives of the Newtonian potential. This is checked in an explicit third
order calculation. There is a systematic way to derive a basis for these
operators. This basis spans a larger space than the expansion in gravitational
and velocity potentials usually employed, although new operators only appear at
fourth order. The basis is argued to be closed under renormalization. Most of
the arguments also apply to the structure of the counter-terms in the effective
theory of large-scale structure. |
Did NANOGrav see a signal from primordial black hole formation?: We show that the recent NANOGrav result can be interpreted as a stochastic
gravitational wave signal associated to formation of primordial black holes
from high-amplitude curvature perturbations. The indicated amplitude and power
of the gravitational wave spectrum agrees well with formation of primordial
seeds for supermassive black holes. | HICOSMO - Cosmology with a complete sample of galaxy clusters: II.
Cosmological results: The growth of structure in the Universe is tightly correlated with the
cosmological parameters. Galaxy clusters as tracers of the large scale
structure are the ideal objects to witness this evolution. The X-ray bright,
hot gas in the potential well of a galaxy cluster enables systematic X-ray
studies of samples of galaxy clusters to constrain cosmological parameters.
HIFLUGCS consists of the 64 X-ray brightest clusters in the Universe, building
up a local sample of galaxy clusters. Here we utilize this sample to determine,
for the first time, individual hydrostatic mass estimates for all the clusters
of the sample and, by making use of the completeness of the sample, we quantify
constraints on the two interesting cosmological parameters, OmegaM and sigma8.
In paper I we describe the data analysis procedure and compared the individual
mass estimates with other references. Now we apply the total hydrostatic and
gas mass estimates from the X-ray analysis to a Bayesian cosmological
likelihood analysis and leave several parameters free to be constrained. We
find OmegaM = 0.30+-0.01 and sigma8 = 0.79+-0.03 (statistical uncertainties,
68% credibility level) using our default analysis strategy combining both, a
mass function analysis and the gas mass fraction results. The main sources of
biases that we also correct here are (1) the influence of galaxy groups, (2)
the hydrostatic mass bias, (3) the extrapolation of the total mass, (4) the
theoretical halo mass function and (5) other physical effects. We find that
galaxy groups introduce a strong bias, since their number density seems to be
over predicted by the halo mass function. On the other hand, baryonic effects
as incorporated by recent hydrodynamical simulations do not result in a
significant change in the constraints. The total systematic uncertainties (20%)
clearly dominate the statistical uncertainties on cosmological parameters. |
Reassessing the Constraints from SH0ES Extragalactic Cepheid Amplitudes
on Systematic Blending Bias: The SH0ES collaboration Hubble constant determination is in a ${\sim}5\sigma$
difference with the $Planck$ value, known as the Hubble tension. The accuracy
of the Hubble constant measured with extragalactic Cepheids depends on robust
stellar-crowding background estimation. Riess et al. (R20) compared the light
curves amplitudes of extragalactic and MW Cepheids to constrain an unaccounted
systematic blending bias, $\gamma=-0.029\pm0.037\,\rm{mag}$, which cannot
explain the required, $\gamma=0.24\pm0.05\,\rm{mag}$, to resolve the Hubble
tension. Further checks by Riess et al. demonstrate that a possible blending is
not likely related to the size of the crowding correction. We repeat the R20
analysis, with the following main differences: (1) we limit the extragalactic
and MW Cepheids comparison to periods $P\lesssim50\,\rm{d}$, since the number
of MW Cepheids with longer periods is minimal; (2) we use publicly available
data to recalibrate amplitude ratios of MW Cepheids in standard passbands; (3)
we remeasure the amplitudes of Cepheids in NGC 5584 and NGC 4258 in two HST
filters ($F555W$ and $F350LP$) to improve the empirical constraint on their
amplitude ratio $A^{555}/A^{350}$. We show that the filter transformations
introduce an ${\approx}0.04\,\rm{mag}$ uncertainty in determining $\gamma$, not
included by R20. While our final estimate, $\gamma=0.013\pm0.057\,\rm{mag}$, is
consistent with the value derived by R20 and is consistent with no bias, the
error is somewhat larger, and the best fitting value is shifted by
${\approx}0.04\,\rm{mag}$ and closer to zero. Future observations, especially
with JWST, would allow better calibration of $\gamma$. | Dynamical Friction in fuzzy dark matter: circular orbits: We investigate the dynamical friction (DF) acting on circularly-moving
perturbers in fuzzy dark matter (FDM) backgrounds. After condensation, FDM is
described by a single wave function satisfying a Schr\"odinger-Poisson
equation. An equivalent, hydrodynamic formulation can be obtained through the
Madelung transform. Here, we consider both descriptions and restrict our
analysis to linear response theory. We take advantage of the hydrodynamic
formulation to derive a fully analytic solution to the DF in steady-state and
for a finite time perturbation. We compare our prediction to a numerical
implementation of the wave approach that includes a non-vanishing FDM velocity
dispersion $\sigma$. Our solution is valid for both a single and a binary
perturber in circular motion as long as $\sigma$ does not significantly exceed
the orbital speed $v_\text{circ}$. While the short-distance Coulomb divergence
of the (supersonic) gaseous DF is no longer present, DF in the FDM case
exhibits an infrared divergence which stems from the (also) diffusive nature of
the Schr\"odinger equation. Our analysis of the finite time perturbation case
reveals that the density wake diffuses through the FDM medium until it reaches
its outer boundary. Once this transient regime is over, both the radial and
tangential DF oscillate about the steady-state solution with an exponentially
decaying envelope. Steady-state is thus never achieved. We use our results to
revisit the DF decay timescales of the 5 Fornax globular clusters. We also
point out that the inspiral of compact binary may stall because the DF torque
about the binary center-of-mass sometimes flips sign to become a thrust rather
than a drag (abridged). |
Ricci focusing, shearing, and the expansion rate in an almost
homogeneous Universe: The Universe is inhomogeneous, and yet it seems to be incredibly
well-characterised by a homogeneous relativistic model. One of the current
challenges is to accurately characterise the properties of such a model. In
this paper we explore how inhomogeneities may affect the overall optical
properties of the Universe by quantifying how they can bias the
redshift-distance relation in a number of toy models that mimic the real
Universe. The models that we explore are statistically homogeneous on large
scales. We find that the effect of inhomogeneities is of order of a few
percent, which can be quite important in precise estimation of cosmological
parameters. We discuss what lessons can be learned to help us tackle a more
realistic inhomogeneous universe. | Cosmological constraints on $γ$-gravity models: In this paper we place observational constraints on the well-known
$\gamma$-gravity $f(R)$ model using the latest cosmological data, namely we use
the latest growth rate, Cosmic Microwave Background, Baryon Acoustic
Oscillations, Supernovae type Ia and Hubble parameter data. Performing a joint
likelihood analysis we find that the $\gamma$-gravity model is in very good
agreement with observations. Utilizing the AIC statistical test we
statistically compare the current $f(R)$ model with $\Lambda$CDM cosmology and
find that they are statistically equivalent. Therefore, $\gamma$-gravity can be
seen as a useful scenario toward testing deviations from General Relativity.
Finally, we note that we find somewhat higher values for the $f(R)$ best-fit
values compared to those mentioned in the past in the literature and we argue
that this could potential alleviate the halo-mass function problem. |
Parsec-scale morphology and spectral index distribution in faint high
frequency peakers: We investigate the parsec-scale structure of 17 high frequency peaking radio
sources from the faint HFP sample. VLBA observations were carried out at two
adjacent frequencies, 8.4 and 15.3 GHz, both in the optically-thin part of the
spectrum, to obtain the spectral index information. We found that 64% of the
sources are resolved into subcomponents, while 36% are unresolved even at the
highest frequency. Among the resolved sources, 7 have a morphology and a
spectral index distribution typical of young radio sources, while in other 4
sources, all optically associated with quasars, the radio properties resemble
those of the blazar population. The equipartition magnetic field of the single
components are a few tens milliGauss, similar to the values found in the
hotspots of young sources with larger sizes. Such high magnetic fields cause
severe radiative losses, precluding the formation of extended lobe structures
emitting at centimeter wavelengths. The magnetic fields derived in the various
components of individual source are usually very different, indicating a non
self-similar source evolution, at least during the very first stages of the
source growth. | Metal Lines Associated with the Lyman-alpha Forest from eBOSS Data: We investigate the metal species associated with the Ly$\alpha$ forest in the
eBOSS quasar spectra. Metal absorption lines are revealed in the stacked
spectra from cross-correlating the selected Ly$\alpha$ absorbers in the forest
and the flux fluctuation field. Up to 13 metal species are identified
associated with relatively strong Ly$\alpha$ absorbers (those with flux
fluctuation $-1.0<\delta_{\rm Ly\alpha}<-0.6$ and with neutral hydrogen column
density of ~ $10^{15-16}$ $\rm cm^{-2}$) over absorber redshift range of
$2<z_{\rm abs}<4$. The column densities of these species decrease toward higher
redshift and for weaker Ly$\alpha$ absorbers. From modelling the column
densities of various species, we find that the column density pattern suggests
contributions from multiple gas components both in the circumgalactic medium
(CGM) and in the intergalactic medium (IGM). While the low-ionization species
(e.g., C II, Si II, and Mg II) can be explained by high-density, cool gas ($T
\sim 10^4$ K) from the CGM, the high-ionization species may reside in
low-density or high-temperature gas in the IGM. The measurements provide inputs
to model metal contamination in the Ly$\alpha$ forest baryon acoustic
oscillations measurement. Comparison with metal absorptions in high-resolution
quasar spectra and with hydrodynamic galaxy formation simulations can further
elucidate the physical conditions of these Ly$\alpha$ absorbers. |
The Unchanging Circumgalactic Medium Over the Past 11 Billion Years: This paper examines how the circumgalactic medium (CGM) evolves as a function
of time by comparing results from different absorption-line surveys that have
been conducted in the vicinities of galaxies at different redshifts. Despite
very different star formation properties of the galaxies considered in these
separate studies and different intergalactic radiation fields at redshifts
between z~2.2 and z~0, I show that both the spatial extent and mean absorption
equivalent width of the CGM around galaxies of comparable mass have changed
little over this cosmic time interval. | The bispectrum of single-field inflationary trajectories with $c_{s}
\neq 1$: The bispectrum of single-field inflationary trajectories in which the speed
of sound of the inflationary trajectories $c_s$ is constant but not equal to
the speed of light $c=1$ is explored. The trajectories are generated as random
realisations of the Hubble Slow-Roll (HSR) hierarchy and the bispectra are
calculated using numerical techniques that extends previous work. This method
allows for out-of-slow-roll models with non-trivial time dependence and
arbitrarily low $c_s$. The ensembles obtained using this method yield
distributions for the shape and scale-dependence of the bispectrum and their
relations with the standard inflationary parameters such as scalar spectral
tilt $n_s$ and tensor-to-scalar ratio $r$. The distributions demonstrate the
squeezed-limit consistency relations for arbitrary single-field inflationary
models. |
Determining cosmological growth parameter for stellar-mass black holes: It has recently been suggested that black holes (BHs) may grow with time, so
that their mass is proportional to the cosmological scale factor to the power
$n$, with suggested values $n \approx 3$ for supermassive BHs in elliptical
galaxies. Here we test these predictions with stellar mass BHs in X-ray
binaries using their masses and ages. We perform two sets of tests to assess
the compatible values of $n$. First, we assume that no compact object grows
over the Tolman-Oppenheimer-Volkof limit which marks the borderline between
neutron stars and BHs. We show that half of BHs would be born with a mass below
this limit if $n=3$ applies. The possibility that all BHs were born above the
limit is rejected at $4\,\sigma$ if $n=3$ applies. In the second test, we
assume that masses of BHs at their formation stay the same over cosmic history.
We compare the mass distribution of the youngest BHs, which could have not
grown yet, to their older counterparts. Distributions are compatible for $n =
-0.9^{+1.3}_{-4.6}$, with $n=3$ excluded formally with 87 % confidence. This
result may be biased, because massive BHs tend to have a massive companion.
Correcting for this bias yields $n\approx 0$. We can therefore conclude that
while our results are not a clear rejection of BH scaling with $n=3$, we show
that $n=0$ is much more consistent with the data. | Cosmic variance of the local Hubble flow in large-scale cosmological
simulations: The increasing precision in the determination of the Hubble parameter has
reached a per cent level at which large-scale cosmic flows induced by
inhomogeneities of the matter distribution become non-negligible. Here we use
large-scale cosmological N-body simulations to study statistical properties of
the local Hubble parameter as measured by local observers. We show that the
distribution of the local Hubble parameter depends not only on the scale of
inhomogeneities, but also on how one defines the positions of observers in the
cosmic web and what reference frame is used. Observers located in random dark
matter haloes measure on average lower expansion rates than those at random
positions in space or in the centres of cosmic voids, and this effect is
stronger from the halo rest frames compared to the CMB rest frame. We compare
the predictions for the local Hubble parameter with observational constraints
based on type Ia supernovae (SNIa) and CMB observations. Due to cosmic
variance, for observers located in random haloes we show that the Hubble
constant determined from nearby SNIa may differ from that measured from the CMB
by 0.8 per cent at 1sigma statistical significance. This scatter is too small
to significantly alleviate a recently claimed discrepancy between current
measurements assuming a flat LCDM model. However, for observers located in the
centres of the largest voids permitted by the standard LCDM model, we find that
Hubble constant measurements from SNIa would be biased high by 5 per cent,
rendering this tension inexistent in this extreme case. |
Three-dimensional Multi-probe Analysis of the Galaxy Cluster A1689: We perform a 3D multi-probe analysis of the rich galaxy cluster A1689 by
combining improved weak-lensing data from new BVRi'z' Subaru/Suprime-Cam
observations with strong-lensing, X-ray, and Sunyaev-Zel'dovich effect (SZE)
data sets. We reconstruct the projected matter distribution from a joint
weak-lensing analysis of 2D shear and azimuthally integrated magnification
constraints, the combination of which allows us to break the mass-sheet
degeneracy. The resulting mass distribution reveals elongation with axis ratio
~0.7 in projection. When assuming a spherical halo, our full weak-lensing
analysis yields a projected concentration of $c_{200c}^{2D}=8.9\pm 1.1$
($c_{vir}^{2D}\sim 11$), consistent with and improved from earlier weak-lensing
work. We find excellent consistency between weak and strong lensing in the
region of overlap. In a parametric triaxial framework, we constrain the
intrinsic structure and geometry of the matter and gas distributions, by
combining weak/strong lensing and X-ray/SZE data with minimal geometric
assumptions. We show that the data favor a triaxial geometry with minor-major
axis ratio 0.39+/-0.15 and major axis closely aligned with the line of sight
(22+/-10 deg). We obtain $M_{200c}=(1.2\pm 0.2)\times 10^{15} M_{\odot}/h$ and
$c_{200c}=8.4\pm 1.3$, which overlaps with the $>1\sigma$ tail of the predicted
distribution. The shape of the gas is rounder than the underlying matter but
quite elongated with minor-major axis ratio 0.60+/-0.14. The gas mass fraction
within 0.9Mpc is 10^{+3}_{-2}%. The thermal gas pressure contributes to ~60% of
the equilibrium pressure, indicating a significant level of non-thermal
pressure support. When compared to Planck's hydrostatic mass estimate, our
lensing measurements yield a spherical mass ratio of $M_{Planck}/M_{GL}=0.70\pm
0.15$ and $0.58\pm 0.10$ with and without corrections for lensing projection
effects, respectively. | Contamination of early-type galaxy alignments to galaxy lensing-CMB
lensing cross-correlation: Galaxy shapes are subject to distortions due to the tidal field of the
Universe. The cross-correlation of galaxy lensing with the lensing of the
Cosmic Microwave Background (CMB) cannot easily be separated from the
cross-correlation of galaxy intrinsic shapes with CMB lensing. Previous work
suggested that the intrinsic alignment contamination can be $15\%$ of this
cross-spectrum for the CFHT Stripe 82 (CS82) and Atacama Cosmology Telescope
surveys. Here we re-examine these estimates using up-to-date observational
constraints of intrinsic alignments at a redshift more similar to that of CS82
galaxies. We find a $\approx$ $10\%$ contamination of the cross-spectrum from
red galaxies, with $\approx$ $3\%$ uncertainty due to uncertainties in the
redshift distribution of source galaxies and the modelling of the spectral
energy distribution. Blue galaxies are consistent with being unaligned, but
could contaminate the cross-spectrum by an additional $9.5\%$ within current
$95\%$ confidence levels. While our fiducial estimate of alignment
contamination is similar to previous work, our work suggests that the relevance
of alignments for CMB lensing-galaxy lensing cross-correlation remains largely
unconstrained. Little information is currently available about alignments at
$z>1.2$. We consider the upper limiting case where all $z>1.2$ galaxies are
aligned with the same strength as low redshift luminous red galaxies, finding
as much as $\approx$ $60\%$ contamination. |
Removal of point source leakage from time-order data filtering: Time-ordered data (TOD) from ground-based CMB experiments are generally
filtered before map-making to remove or reduce the contamination from the
ground and the atmospheric emissions. However, when the observation region
contains strong point sources, the filtering process will result in
considerable leakage around the point sources in a measured CMB map, and leave
spurious polarization signals. Therefore, such signals need to be assessed and
removed before CMB science exploitation. In this work, we present a new method
that we call "template fitting" and can effectively remove these leakage
signals in pixel domain, not only satisfying the requirement for measuring
primordial gravitational waves from CMB-$B$ modes, but also avoiding
time-consuming operations on TOD. | A Stringent Upper Limit on Dark Matter Self-Interaction Cross Section
from Cluster Strong Lensing: We analyze strongly lensed images in 8 galaxy clusters to measure their dark
matter density profiles in the radial region between 10 kpc and 150 kpc, and
use this to constrain the self-interaction cross section of dark matter (DM)
particles. We infer the mass profiles of the central DM halos, bright central
galaxies, key member galaxies, and DM subhalos for the member galaxies for all
8 clusters using the Qlens code. The inferred DM halo surface densities are fit
to a self-interacting dark matter (SIDM) model, which allows us to constrain
the self-interaction cross section over mass $\sigma$/m. When our full method
is applied to mock data generated from two clusters in the Illustris-TNG
simulation, we find results consistent with no dark matter self-interactions as
expected. For the eight observed clusters with average relative velocities of
$1458_{-81}^{+80}$ km/s, we infer $\sigma$/m = $0.082_{-0.021}^{+0.027}$
cm$^2$/g and $\sigma$/m < 0.13 cm$^2$/g at the 95% confidence level. |
Evidence for a high-z ISW signal from supervoids in the distribution of
eBOSS quasars: The late-time integrated Sachs-Wolfe (ISW) imprint of $R\gtrsim
100~h^{-1}{\rm Mpc}$ super-structures is sourced by evolving large-scale
potentials due to a dominant dark energy component in the $\Lambda$CDM model.
The aspect that makes the ISW effect distinctly interesting is the repeated
observation of stronger-than-expected imprints from supervoids at
$z\lesssim0.9$. Here we analyze the un-probed key redshift range $0.8<z<2.2$
where the ISW signal is expected to fade in $\Lambda$CDM, due to a weakening
dark energy component, and eventually become consistent with zero in the matter
dominated epoch. On the contrary, alternative cosmological models, proposed to
explain the excess low-$z$ ISW signals, predicted a sign-change in the ISW
effect at $z\approx1.5$ due to the possible growth of large-scale potentials
that is absent in the standard model. To discriminate, we estimated the
high-$z$ $\Lambda$CDM ISW signal using the Millennium XXL mock catalogue, and
compared it to our measurements from about 800 supervoids identified in the
eBOSS DR16 quasar catalogue. At $0.8<z<1.2$, we found an excess ISW signal with
$A_\mathrm{ ISW}\approx3.6\pm2.1$ amplitude. The signal is then consistent with
the $\Lambda$CDM expectation ($A_\mathrm{ ISW}=1$) at $1.2<z<1.5$ where the
standard and alternative models predict similar amplitudes. Most interestingly,
we also detected an opposite-sign ISW signal at $1.5<z<2.2$ that is in
$2.7\sigma$ tension with the $\Lambda$CDM prediction. Taken at face value,
these moderately significant detections of ISW anomalies suggest an alternative
growth rate of structure in low-density environments at $\sim100~h^{-1}{\rm
Mpc}$ scales. | Search for Galaxy Cluster Candidates in the Cosmic Microwave Background
Maps of the Planck Space Mission Using a Convolutional Neural Network Based
on the Method of Tracing the Sunyaev-Zeldovich Effect: We propose a method of searching for radio sources exhibiting the
Sunyaev-Zeldovich effect in the multi-frequency emission maps from the Planck
mission data using a convolutional neural network. A catalog for recognizing
radio sources is compiled using the GLESP pixelation scheme at the frequencies
of 100, 143, 217, 353, and 545 GHz. The quality of the proposed approach is
evaluated and the quality of the dependence of model data on the S/N ratio is
estimated. We show that the presented neural network approach allows the
detection of sources with the Sunyaev-Zeldovich effect. The proposed method can
be used to find the most likely galaxy cluster candidates at large redshifts. |
Results from 730 kg days of the CRESST-II Dark Matter Search: The CRESST-II cryogenic Dark Matter search, aiming at detection of WIMPs via
elastic scattering off nuclei in CaWO$_4$ crystals, completed 730 kg days of
data taking in 2011. We present the data collected with eight detector modules,
each with a two-channel readout; one for a phonon signal and the other for
coincidently produced scintillation light. The former provides a precise
measure of the energy deposited by an interaction, and the ratio of
scintillation light to deposited energy can be used to discriminate different
types of interacting particles and thus to distinguish possible signal events
from the dominant backgrounds. Sixty-seven events are found in the acceptance
region where a WIMP signal in the form of low energy nuclear recoils would be
expected. We estimate background contributions to this observation from four
sources: 1) "leakage" from the e/\gamma-band 2) "leakage" from the
\alpha-particle band 3) neutrons and 4) Pb-206 recoils from Po-210 decay. Using
a maximum likelihood analysis, we find, at a high statistical significance,
that these sources alone are not sufficient to explain the data. The addition
of a signal due to scattering of relatively light WIMPs could account for this
discrepancy, and we determine the associated WIMP parameters. | What do cluster counts really tell us about the Universe?: We study the covariance matrix of the cluster mass function in cosmology. We
adopt a two-line attack: firstly, we employ the counts-in-cells framework to
derive an analytic expression for the covariance of the mass function.
Secondly, we use a large ensemble of N-body simulations in the LCDM framework
to test this. Our theoretical results show that the covariance can be written
as the sum of two terms: a Poisson term, which dominates in the limit of rare
clusters; and a sample variance term, which dominates for more abundant
clusters. Our expressions are analogous to those of Hu & Kravtsov (2003) for
multiple cells and a single mass tracer. Calculating the covariance depends on:
the mass function and bias of clusters, and the variance of mass fluctuations
within the survey volume. The predictions show that there is a strong
bin-to-bin covariance between measurements. In terms of the cross-correlation
coefficient, we find r~0.5 for haloes with M<3e14 Msol at z=0. Comparison of
these predictions with estimates from simulations shows excellent agreement. We
use the Fisher matrix formalism to explore the cosmological information content
of the counts. We compare the Poisson likelihood model, with the more realistic
likelihood model of Lima & Hu (2004), and all terms entering the Fisher
matrices are evaluated using the simulations. We find that the Poisson
approximation should only be used for the rarest objects, M>3e14 Msol,
otherwise the information content of a survey of size V~13.5 [Gpc/h]^3 would be
overestimated, resulting in errors that are ~2 times smaller. As an auxiliary
result, we show that the bias of clusters, obtained from the cluster-mass
cross-variance, is linear on scales >50 Mpc/h, whereas that obtained from the
auto-variance is nonlinear. |
On the Three Primordial Numbers: Cosmological observations have provided us with the measurement of just three
numbers that characterize the very early universe: $ 1-n_{s} $, $ N $ and
$\ln\Delta_R^2$. Although each of the three numbers individually carries
limited information about the physics of inflation, one may hope to extract
non-trivial information from relations among them. Invoking minimality, namely
the absence of ad hoc large numbers, we find two viable and mutually exclusive
inflationary scenarios. The first is the well-known inverse relation between
$1- n_{s} $ and $ N $. The second implies a new relation between $ 1-n_{s} $
and $\ln\Delta_R^2$, which might provide us with a handle on the beginning of
inflation and predicts the intriguing $\textit{lower}$ bound on the
tensor-to-scalar ratio $ r> 0.006 $ ($ 95\% $ CL). | The unphysical character of dark energy fluids: It is well known that, in the context of general relativity, an unknown kind
of matter that must violate the strong energy condition is required to explain
the current accelerated phase of expansion of the Universe. This unknown
component is called dark energy and is characterized by an equation of state
parameter $w=p/\rho<-1/3$. Thermodynamic stability requires that $3w-d\ln
|w|/d\ln a\ge0$ and positiveness of entropy that $w\ge-1$. In this paper we
proof that we cannot obtain a differentiable function $w(a)$ to represent the
dark energy that satisfies these conditions trough the entire history of the
Universe. |
Discovery of Radio Afterglow from the Most Distant Cosmic Explosion: We report the discovery of radio afterglow emission from the gamma-ray burst
GRB 090423, which exploded at a redshift of 8.3, making it the object with the
highest known redshift in the Universe. By combining our radio measurements
with existing X-ray and infrared observations, we estimate the kinetic energy
of the afterglow, the geometry of the outflow and the density of the
circumburst medium. Our best fit model is a quasi-spherical, high-energy
explosion in a low, constant-density medium. \event had a similar energy
release to the other well-studied high redshift GRB 050904 ($z=6.26$), but
their circumburst densities differ by two orders of magnitude. We compare the
properties of \event with a sample of GRBs at moderate redshifts. We find that
the high energy and afterglow properties of \event are not sufficiently
different from other GRBs to suggest a different kind of progenitor, such as a
Population III star. However, we argue that it is not clear that the afterglow
properties alone can provide convincing identification of Population III
progenitors. We suggest that the millimeter and centimeter radio detections of
\event at early times contained emission from a reverse shock component. This
has important implications for the detection of high redshift GRBs by the next
generation of radio facilities. | The cosmological impact of future constraints on $H_0$ from
gravitational-wave standard sirens: Gravitational-wave standard sirens present a novel approach for the
determination of the Hubble constant. After the recent spectacular confirmation
of the method thanks to GW170817 and its optical counterpart, additional
standard siren measurements from future gravitational-wave sources are expected
to constrain the Hubble constant to high accuracy. At the same time, improved
constraints are expected from observations of cosmic microwave background (CMB)
polarization and from baryon acoustic oscillations (BAO) surveys. We explore
the role of future standard siren constraints on $H_0$ in light of expected
CMB+BAO data. Considering a $10$-parameters cosmological model, in which
curvature, the dark energy equation of state, and the Hubble constant are
unbounded by CMB observations, we find that a combination of future CMB+BAO
data will constrain the Hubble parameter to $\sim 1.5 \%$. Further extending
the parameter space to a time-varying dark energy equation of state, we find
that future CMB+BAO constraints on $H_0$ are relaxed to $\sim 3.0 \%$. These
accuracies are within reach of future standard siren measurements from the
Hanford-Livingston-Virgo and the Hanford-Livingston-Virgo-Japan-India networks
of interferometers, showing the cosmological relevance of these sources. If
future gravitational-wave standard siren measurements reach $1\%$ on $H_0$, as
expected, they would significantly improve future CMB+BAO constraints on
curvature and on the dark energy equation of state by up to a factor $\sim 3$.
We also show that the inclusion of $H_0$ constraints from gravitational-wave
standard sirens could result in a reduction of the dark energy figure-of-merit
(i.e., the cosmological parameter volume) by up to a factor of $\sim 400$. |
Ultra-Light Dark Matter in Ultra-Faint Dwarf Galaxies: Cold Dark Matter (CDM) models struggle to match the observations at galactic
scales. The tension can be reduced either by dramatic baryonic feedback effects
or by modifying the particle physics of CDM. Here, we consider an ultra-light
scalar field DM particle manifesting a wave nature below a DM particle
mass-dependent Jeans scale. For DM mass $m\sim10^{-22}{\rm eV}$, this scenario
delays galaxy formation and avoids cusps in the center of the dark matter
haloes. We use new measurements of half-light mass in ultra-faint dwarf
galaxies Draco II and Triangulum II to estimate the mass of the DM particle in
this model. We find that if the stellar populations are within the core of the
density profile then the data are in agreement with a wave dark matter model
having a DM particle with $m\sim 3.7-5.6\times 10^{-22}{\rm eV}$. The presence
of this extremely light particle will contribute to the formation of a central
solitonic core replacing the cusp of a Navarro-Frenk-White profile and bringing
predictions closer to observations of cored central density in dwarf galaxies. | Nonlinear spherical perturbations in Quintessence Models of Dark Energy: Observations have confirmed the accelerated expansion of the universe. The
accelerated expansion can be modelled by invoking a cosmological constant or a
dynamical model of dark energy. A key difference between these models is that
the equation of state parameter $w$ for dark energy differs from $-1$ in
dynamical dark energy (DDE) models. Further, the equation of state parameter is
not constant for a general DDE model. Such differences can be probed using the
variation of scale factor with time by measuring distances. Another significant
difference between the cosmological constant and DDE models is that the latter
must cluster. Linear perturbation analysis indicates that perturbations in
quintessence models of dark energy do not grow to have a significant amplitude
at small length scales. In this paper we study the response of quintessence
dark energy to non-linear perturbations in dark matter. We use a fully
relativistic model for spherically symmetric perturbations. In this study we
focus on thawing models. We find that in response to non-linear perturbations
in dark matter, dark energy perturbations grow at a faster rate than expected
in linear perturbation theory. We find that dark energy perturbation remains
localised and does not diffuse out to larger scales. The dominant drivers of
the evolution of dark energy perturbations are the local Hubble flow and a
supression of gradients of the scalar field. We also find that the equation of
state parameter $w$ changes in response to perturbations in dark matter such
that it also becomes a function of position. The variation of $w$ in space is
correlated with density contrast for matter. Variation of $w$ and perturbations
in dark energy are more pronounced in response to large scale perturbations in
matter while the dependence on the amplitude of matter perturbations is much
weaker. |
Pressure from dark matter annihilation and the rotation curve of spiral
galaxies: The rotation curves of spiral galaxies are one of the basic predictions of
the cold dark matter paradigm, and their shape in the innermost regions has
been hotly debated over the last decades. The present work shows that dark
matter annihilation into electron-positron pairs may affect the observed
rotation curve by a significant amount. We adopt a model-independent approach,
where all the electrons and positrons are injected with the same initial energy
E_0 ~ m_dm*c^2 in the range from 1 MeV to 1 TeV and the injection rate is
constrained by INTEGRAL, Fermi, and HESS data. The pressure of the relativistic
electron-positron gas is determined by solving the diffusion-loss equation,
considering inverse Compton scattering, synchrotron radiation, Coulomb
collisions, bremsstrahlung, and ionization. For values of the gas density and
magnetic field that are representative of the Milky Way, it is estimated that
pressure gradients are strong enough to balance gravity in the central parts if
E_0 < 1 GeV. The exact value depends somewhat on the astrophysical parameters,
and it changes dramatically with the slope of the dark matter density profile.
For very steep slopes, as those expected from adiabatic contraction, the
rotation curves of spiral galaxies would be affected on ~kpc scales for most
values of E_0. By comparing the predicted rotation curves with observations of
dwarf and low surface brightness galaxies, we show that the pressure from dark
matter annihilation may improve the agreement between theory and observations
in some cases, but it also imposes severe constraints on the model parameters
(most notably, the inner slope of halo density profile, as well as the mass and
the annihilation cross-section of dark matter particles into electron-positron
pairs). | Scale-dependent CMB power asymmetry from primordial speed of sound and a
generalized $δ$N formalism: We explore a plausible mechanism that the hemispherical power asymmetry in
the CMB is produced by the spatial variation of the primordial sound speed
parameter. We suggest that in a generalized approach of the $\delta N$
formalism the local e-folding number may depend on some other primordial
parameters besides the initial values of inflaton. Here the $\delta N$
formalism is extended by considering the effects of a spatially varying sound
speed parameter caused by a super-Hubble perturbation of a light field. Using
this generalized $\delta N$ formalism, we systematically calculate the
asymmetric primordial spectrum in the model of multi-speed inflation by taking
into account the constraints of primordial non-Gaussianities. We further
discuss specific model constraints, and the corresponding asymmetry amplitudes
are found to be scale-dependent, which can accommodate current observations of
the power asymmetry at different length scales. |
Non-thermal emission and dynamical state of massive galaxy clusters from
CLASH sample: Massive galaxy clusters are the most violent large scale structures
undergoing merger events in the Universe. Based upon their morphological
properties in X-rays, they are classified as un-relaxed and relaxed clusters
and often host (a fraction of them) different types of non-thermal radio
emitting components, viz., haloes, mini-haloes, relics and phoenix within their
Intra Cluster Medium (ICM). The radio haloes show steep (alpha = -1.2) and
ultra steep (alpha < -1.5) spectral properties at low radio frequencies, giving
important insights on the merger (pre or post) state of the cluster. Ultra
steep spectrum radio halo emissions are rare and expected to be the dominating
population to be discovered via LOFAR and SKA in the future. Further, the
distribution of matter (morphological information), alignment of hot X-ray
emitting gas from the ICM with the total mass (dark + baryonic matter) and the
bright cluster galaxy (BCG) is generally used to study the dynamical state of
the cluster. We present here a multi wavelength study on 14 massive clusters
from the CLASH survey and show the correlation between the state of their
merger in X-ray and spectral properties (1.4 GHz - 150 MHz) at radio
wavelengths. Using the optical data we also discuss about the gas-mass
alignment, in order to understand the interplay between dark and baryonic
matter in massive galaxy clusters. | The UV continua and inferred stellar populations of galaxies at z ~ 7 -
9 revealed by the Hubble Ultra Deep Field 2012 campaign: We use the new ultra-deep, near-infrared imaging of the Hubble Ultra-Deep
Field (HUDF) provided by our UDF12 HST WFC3/IR campaign to explore the
rest-frame UV properties of galaxies at redshifts z > 6.5. We present the first
unbiased measurement of the average UV power-law index, beta, for faint
galaxies at z ~ 7, the first meaningful measurements of beta at z ~ 8, and
tentative estimates for a new sample of galaxies at z ~ 9. Utilising galaxy
selection in the new F140W imaging to minimize colour bias, and applying both
colour and power-law estimators of beta, we find beta = -2.1 (+/-0.2) at z ~ 7
for galaxies with M_UV ~ -18. This means that the faintest galaxies uncovered
at this epoch have, on average, UV colours no more extreme than those displayed
by the bluest star-forming galaxies at low redshift. At z ~ 8 we find a similar
value, beta = -1.9 (+/-0.3). At z ~ 9, we find beta = -1.8 (+/-0.6),
essentially unchanged from z ~ 6 - 7 (albeit highly uncertain). Finally, we
show that there is as yet no evidence for a significant intrinsic scatter in
beta within our new, robust z ~ 7 galaxy sample. Our results are most easily
explained by a population of steadily star-forming galaxies with either ~ solar
metallicity and zero dust, or moderately sub-solar (~ 10-20%) metallicity with
modest dust obscuration (A_V ~ 0.1-0.2). This latter interpretation is
consistent with the predictions of a state-of-the-art galaxy-formation
simulation, which also suggests that a significant population of very-low
metallicity, dust-free galaxies with beta ~ -2.5 may not emerge until M_UV >
-16, a regime likely to remain inaccessible until the James Webb Space
Telescope. |
Accelerating Approximate Bayesian Computation with Quantile Regression:
Application to Cosmological Redshift Distributions: Approximate Bayesian Computation (ABC) is a method to obtain a posterior
distribution without a likelihood function, using simulations and a set of
distance metrics. For that reason, it has recently been gaining popularity as
an analysis tool in cosmology and astrophysics. Its drawback, however, is a
slow convergence rate. We propose a novel method, which we call qABC, to
accelerate ABC with Quantile Regression. In this method, we create a model of
quantiles of distance measure as a function of input parameters. This model is
trained on a small number of simulations and estimates which regions of the
prior space are likely to be accepted into the posterior. Other regions are
then immediately rejected. This procedure is then repeated as more simulations
are available. We apply it to the practical problem of estimation of redshift
distribution of cosmological samples, using forward modelling developed in
previous work. The qABC method converges to nearly same posterior as the basic
ABC. It uses, however, only 20\% of the number of simulations compared to basic
ABC, achieving a fivefold gain in execution time for our problem. For other
problems the acceleration rate may vary; it depends on how close the prior is
to the final posterior. We discuss possible improvements and extensions to this
method. | Resolved Near-Infrared Stellar Populations in Nearby Galaxies: We present near-infrared (NIR) color-magnitude diagrams (CMDs) for the
resolved stellar populations within 26 fields of 23 nearby galaxies (<4 Mpc),
based on F110W and F160W images from Wide Field Camera 3 (WFC3) on the Hubble
Space Telescope (HST). The CMDs sample both old dormant and young star-forming
populations. We match key NIR CMD features with their counterparts in optical
CMDs, and identify the red core Helium burning (RHeB) sequence as a significant
contributor to the NIR flux in stellar populations younger than a few 100 Myrs
old, suggesting that star formation can drive surprisingly rapid variations in
the NIR mass-to-light ratio. The NIR luminosity of star forming galaxies is
therefore not necessarily proportional to the stellar mass. We note that these
individual bright RHeB stars may be misidentified as old stellar clusters in
low resolution imaging. We also discuss the CMD location of asymptotic giant
branch (AGB) stars, and the separation of AGB sub-populations using a
combination of optical and NIR colors. We empirically calibrate the NIR
magnitude of the tip of the red giant branch (TRGB) as a function of color,
allowing this widely adopted filter to be used for distance measurements. We
find a clear trend between NIR RGB color and metallicity. However, it appears
unlikely that the slope of the NIR RGB can be used as a metallicity indicator
in extragalactic systems with comparable data. Finally, we discuss scattered
light in the WFC3, which becomes significant for exposures taken close to a
bright earth limb. |
Dark matter axion detection in the radio/mm-waveband: We discuss axion dark matter detection via two mechanisms: spontaneous decays
and resonant conversion in neutron star magnetospheres. For decays, we show
that the brightness temperature signal, rather than flux, is a less ambiguous
measure for selecting candidate objects. This is owing principally to the
finite beam width of telescopes which prevents one from being sensitive to the
total flux from the object. With this in mind, we argue that the large
surface-mass-density of the galactic centre or the Virgo cluster centre offers
the best chance of improving current constraints on the axion-photon coupling
via spontaneous decays. For the neutron star case, we first carry out a
detailed study of mixing in magnetised plasmas. We derive transport equations
for the axion-photon system via a controlled gradient expansion, allowing us to
address inhomogeneous mass-shell constraints for arbitrary momenta. We then
derive a non-perturbative Landau-Zener formula for the conversion probability
valid across the range of relativistic and non-relativistic axions and show
that the standard perturbative resonant conversion amplitude is a truncation of
this result in the non-adiabatic limit. Our treatment reveals that that
infalling dark matter axions typically convert non-adiabatically in
magnetospheres. We describe the limitations of one-dimensional mixing equations
and explain how three-dimensional effects activate new photon polarisations,
including longitudinal modes and illustrate these arguments with numerical
simulations in higher dimensions. We find that the bandwidth of the radio
signal is dominated by Doppler broadening from the relative motion of the
neutron star with respect to the observer. Therefore, we conclude that the
radio signal from the resonant decay is weaker than previously thought, which
means one relies on local density peaks to probe weaker axion-photon couplings. | The phenomenology of beyond Horndeski gravity: We study the phenomenology of the beyond Horndeski class of scalar-tensor
theories of gravity, which on cosmological scales can be characterised in terms
of one extra function of time, $\alpha_{\rm H}$, as well as the usual four
Horndeski set of free functions. We show that $\alpha_{\rm H}$ can be directly
related to the the damping of the matter power spectrum on both large and small
scales. We also find that the temperature power spectrum of the cosmic
microwave background (CMB) is enhanced at low multipoles and the lensing
potential is decreased, as a function of $\alpha_{\rm H}$. We find constraints
on $\alpha_{\rm H}$ of order ${\cal O}(1)$ using measurements of the
temperature and polarisation of the CMB, as well as the lensing potential
derived from it, combined with large scale structure data. We find that
redshift space distortion measurements can play a significant role in
constraining these theories. Finally, we comment on the recent constraints from
the observation of an electromagnetic counterpart to a gravitational wave
signal; we find that these constraints reduce the number of free parameters of
the model but do not significantly change the constraints on the remaining
parameters. |
The Cluster HEritage project with XMM-Newton: Mass Assembly and
Thermodynamics at the Endpoint of structure formation. I. Programme overview: The Cluster HEritage project with XMM-Newton - Mass Assembly and
Thermodynamics at the Endpoint of structure formation (CHEX-MATE) is a three
mega-second Multi-Year Heritage Programme to obtain X-ray observations of a
minimally-biased, signal-to-noise limited sample of 118 galaxy clusters
detected by Planck through the Sunyaev-Zeldovich effect. The programme,
described in detail in this paper, aims to study the ultimate products of
structure formation in time and mass. It is composed of a census of the most
recent objects to have formed (Tier-1: 0.05 < z < 0.2; 2 x 10e14 M_sun < M_500
< 9 x 10e14 M_sun), together with a sample of the highest-mass objects in the
Universe (Tier-2: z < 0.6; M_500 > 7.25 x 10e14 M_sun). The programme will
yield an accurate vision of the statistical properties of the underlying
population, measure how the gas properties are shaped by collapse into the dark
matter halo, uncover the provenance of non-gravitational heating, and resolve
the major uncertainties in mass determination that limit the use of clusters
for cosmological parameter estimation. We will acquire X-ray exposures of
uniform depth, designed to obtain individual mass measurements accurate to
15-20% under the hydrostatic assumption. We present the project motivations,
describe the programme definition, and detail the ongoing multi-wavelength
observational (lensing, SZ, radio) and theoretical effort that is being
deployed in support of the project. | A tidal disruption-like X-ray flare from the quiescent galaxy SDSS
J120136.02+300305.5: SDSS J120136.02+300305.5 was detected in an XMM-Newton slew from June 2010
with a flux 56 times higher than an upper limit from ROSAT, corresponding to
Lx~3x10^44 ergs/s. It has the optical spectrum of a quiescent galaxy (z=0.146).
Overall the X-ray flux has evolved consistently with the canonical t^-5/3
model, expected for returning stellar debris from a tidal disruption event,
fading by a factor ~300 over 300 days. In detail the source is very variable
and became invisible to Swift between 27 and 48 days after discovery, perhaps
due to self-absorption. The X-ray spectrum is soft but is not the expected tail
of optically thick thermal emission. It may be fit with a Bremsstrahlung or
double-power-law model and is seen to soften with time and declining flux.
Optical spectra taken 12 days and 11 months after discovery indicate a deficit
of material in the broad line and coronal line regions of this galaxy, while a
deep radio non-detection implies that a jet was not launched during this event. |
Stellar mass map and dark matter distribution in M31: Stellar mass distribution in M31 is estimated using optical and infrared
imaging data. Combining the derived stellar mass model with various kinematical
data, properties of the DM halo of the galaxy are constrained.
SDSS observations through the ugriz filters and the Spitzer imaging at 3.6
microns are used to sample the SED of the galaxy at each imaging pixel.
Intrinsic dust extinction effects are taken into account by using far-infrared
observations. Synthetic SEDs created with different stellar population
synthesis models are fitted to the observed SEDs, providing estimates for the
stellar mass surface density. The stellar mass distribution of the galaxy is
described with a 3D model consisting of a nucleus, a bulge, a disc, a young
disc and a halo component, each following the Einasto density distribution
(relations between different functional forms of the Einasto density
distribution are given in App. B). By comparing the stellar mass distribution
to the observed rotation curve and kinematics of outer globular clusters and
satellite galaxies, the DM halo parameters are estimated.
Stellar population synthesis models suggest that M31 is dominated by old
stars throughout the galaxy. The total stellar mass is (10-15)10^10Msun, 30% of
which is in the bulge and 56% in the disc. None of the tested DM distribution
models can be falsified on the basis of the stellar matter distribution and the
rotation curve of the galaxy. The virial mass of the DM halo is
(0.8-1.1)10^12Msun and the virial radius is 189-213kpc, depending on the DM
distribution. The central density of the DM halo is comparable to that of
nearby dwarf galaxies, low-surface-brightness galaxies and distant massive disc
galaxies, thus the evolution of central DM halo properties seems to be
regulated by similar processes for a broad range of halo masses, environments,
and cosmological epochs. | On the occupation of X-ray selected galaxy groups by radio AGN since
z=1.3: Previous clustering analysis of low-power radio AGN has indicated that they
preferentially live in massive groups. The X-ray surveys of the COSMOS field
have achieved a sensitivity at which these groups are directly detected out to
z=1.3. Making use of Chandra-, XMM- and VLA-COSMOS surveys we identify radio
AGN members (10**23.6 < L_1.4GHz/(W/Hz) < 10**25) of galaxy groups (10**13.2 <
M_200/M_sun < 10**14.4; 0.1<z<1.3) and study i) the radio AGN -- X-ray group
occupation statistics as a function of group mass, and ii) the distribution of
radio AGN within the groups. We find that radio AGN are preferentially
associated with galaxies close to the center (< 0.2r_200). Compared to our
control sample of group members matched in stellar mass and color to the radio
AGN host galaxies, we find a significant enhancement of radio AGN activity
associated with 10**13.6 < M_200/M_sun < 10**14 halos. We present the first
direct measurement of the halo occupation distribution (HOD) for radio AGN,
based on the total mass function of galaxy groups hosting radio AGN. Our
results suggest a possible deviation from the usually assumed power law HOD
model. We also find an overall increase of the fraction of radio AGN in galaxy
groups (<1r_200), relative to that in all environments. |
Structure and Morphologies of z~7-8 Galaxies from ultra-deep WFC3/IR
Imaging of the HUDF: We present a first morphological study of z~7-8 Lyman Break galaxies (LBGs)
from Oesch et al. 2009 and Bouwens et al. 2009 detected in ultra-deep
near-infrared imaging of the Hubble Ultra Deep field (HUDF) by the HUDF09
program. With an average intrinsic size of 0.7+-0.3 kpc these galaxies are
found to be extremely compact having an average observed surface brightness of
mu_J ~= 26 mag arcsec^(-2), and only two out of the full sample of 16 z~7
galaxies show extended features with resolved double cores. By comparison to
lower redshift LBGs it is found that only little size evolution takes place
from z~7 to z~6, while galaxies between z~4-5 show more extended wings in their
apparent profiles. The average size scales as (1+z)^(-m) with m=1.12+-0.17 for
galaxies with luminosities in the range (0.3-1)L*_{z=3} and with m=1.32+-0.52
for (0.12-0.3)L*_{z=3}, consistent with galaxies having constant comoving
sizes. The peak of the size distribution changes only slowly from z~7 to z~4.
However, a tail of larger galaxies (>~ 1.2 kpc) is gradually built up towards
later cosmic times, possibly via hierarchical build-up or via enhanced
accretion of cold gas. Additionally, the average star-formation surface density
of LBGs with luminosities (0.3-1)L*_{z=3} is nearly constant at Sigma_{SFR}=1.9
Msun/yr/kpc^2 over the entire redshift range z~4-7 suggesting similar
star-formation efficiencies at these early epochs. The above evolutionary
trends seem to hold out to z~8 though the sample is still small and possibly
incomplete. | The analysis of the hydrogen broad Balmer line ratios: possible
implications to the physical properties of the BLR of AGN: We analyze the ratios of the broad hydrogen Balmer emission lines (from
H\alpha to H\epsilon) in the context of estimating the physical conditions in
the broad line region (BLR) of active galactic nuclei (AGN). The Balmer
emission lines are obtained in three ways: i) using photoionization models
obtained by a spectral synthesis code CLOUDY; ii) calculated using the
recombination theory for hydrogenic ions; iii) measured from the sample of
observed spectra taken from the Sloan Digital Sky Survey database. We
investigate the Balmer line ratios in the frame of the so called Boltzmann-plot
(BP), analyzing physical conditions of the emitting plasma for which we could
use the BP method. The BP considers the ratio of Balmer lines normalized to the
atomic data of the corresponding line transition, and is in that way different
from the Balmer decrement. We found that for a certain range of thermodynamic
parameters, there are objects that follow the BP. These AGN may have a BLR
consisting of mostly high density plasma. |
Difficulties Distinguishing Dark Energy from Modified Gravity via
Redshift Distortions: The bulk motion of galaxies induced by the growth of cosmic structure offers
a rare opportunity to test the validity of general relativity across
cosmological scales. However, modified gravity can be degenerate in its effect
with the unknown values of cosmological parameters. More seriously, even the
`observed' value of the RSD (redshift-space distortions) used to measure the
fluctuation growth rate depends on the assumed cosmological parameters (the
Alcock-Paczynski effect). We give a full analysis of these issues, showing how
to combine RSD with BAO (baryon acoustic oscillations) and CMB (Cosmic
Microwave Background) data, in order to obtain joint constraints on deviations
from general relativity and on the equation of state of dark energy whilst
allowing for factors such as non-zero curvature. In particular we note that the
evolution of Omega_m(z), along with the Alcock-Paczynski effect, produces a
degeneracy between the equation of state w and the modified growth parameter
gamma. Typically, the total marginalized error on either of these parameters
will be larger by a factor ~ 2 compared to the conditional error where one or
other is held fixed. We argue that future missions should be judged by their
Figure of Merit as defined in the w_p - gamma plane, and note that the
inclusion of spatial curvature can degrade this value by an order of magnitude. | Asymmetries in the Type IIn SN2010jl: Aims: We study possible signs of asymmetry in the luminous Type IIn SN2010jl,
to obtain independent information on the explosion geometry. Methods: We
obtained optical linear spectropolarimetry of SN2010jl two weeks after the
discovery, in the spectral range 3700-8800 A. Results: The object exhibits a
continuum polarization at a very significant and almost constant level
(1.7-2.0%). Marked line depolarization is seen at the positions of the
strongest emission features, like Halpha and Hbeta. This implies that the line
forming region is well above the photosphere. The continuum polarization level
(1.7-2.0%) indicates a substantial asphericity, of axial ratio <=0.7. The
almost complete depolarization seen at Halpha suggests a very low level of
interstellar polarization (<=0.3%). This rules out the presence of relevant
amounts of dust in the progenitor environment at the time of our observations.
From a polarimetric point of view, SN2010jl appears to be very similar to the
two other well studied Type IIn SNe 1997eg and 1998S, establishing a strong
link within this class of objects. |
Star Formation in the First Galaxies I: Collapse Delayed by Lyman-Werner
Radiation: We investigate the process of metal-free star formation in the first galaxies
with a high-resolution cosmological simulation. We consider the cosmologically
motivated scenario in which a strong molecule-destroying Lyman-Werner (LW)
background inhibits effective cooling in low-mass haloes, delaying star
formation until the collapse or more massive haloes. Only when molecular
hydrogen (H2) can self-shield from LW radiation, which requires a halo capable
of cooling by atomic line emission, will star formation be possible. To follow
the formation of multiple gravitationally bound objects, at high gas densities
we introduce sink particles which accrete gas directly from the computational
grid. We find that in a 1 Mpc^3 (comoving) box, runaway collapse first occurs
in a 3x10^7 M_sun dark matter halo at z~12 assuming a background intensity of
J21=100. Due to a runaway increase in the H2 abundance and cooling rate, a
self-shielding, supersonically turbulent core develops abruptly with ~10^4
M_sun in cold gas available for star formation. We analyze the formation of
this self-shielding core, the character of turbulence, and the prospects for
star formation. Due to a lack of fragmentation on scales we resolve, we argue
that LW-delayed metal-free star formation in atomic cooling haloes is very
similar to star formation in primordial minihaloes, although in making this
conclusion we ignore internal stellar feedback. Finally, we briefly discuss the
detectability of metal-free stellar clusters with the James Webb Space
Telescope. | Chandra X-ray observations of Abell 1835 to the virial radius: We report the first Chandra detection of emission out to the virial radius in
the cluster Abell 1835 at z=0.253. Our analysis of the soft X-ray surface
brightness shows that emission is present out to a radial distance of 10 arcmin
or 2.4 Mpc, and the temperature profile has a factor of ten drop from the peak
temperature of 10 keV to the value at the virial radius. We model the Chandra
data from the core to the virial radius and show that the steep temperature
profile is not compatible with hydrostatic equilibrium of the hot gas, and that
the gas is convectively unstable at the outskirts. A possible interpretation of
the Chandra data is the presence of a second phase of warm-hot gas near the
cluster's virial radius that is not in hydrostatic equilibrium with the
cluster's potential. The observations are also consistent with an alternative
scenario in which the gas is significantly clumped at large radii. |
Magnetic Energy Injection in GRB 080913: GRB 080913, with a spectroscopically determined redshift of z=6.7, was the
record holder of the remotest stellar object before the discovery of the recent
gamma-ray burst GRB 090423, whose redshift is about 8.2. The gradually
accumulated high redshift GRB sample has shed light on the origin and physics
of GRBs during the cosmic re-ionization epoch. We here present a detailed
numerical fit to the multi-wavelength data of the optical afterglow of GRB
080913 and then constrain its circum-burst environment and the other model
parameters. We conclude that the late optical/X-ray plateau at about one day
since the burst is due to the Poynting-flux dominated injection from the
central engine which is very likely a massive spinning black hole with super
strong magnetic fields. | A Nonminimal Coupling Model and its Short-Range Solar System Impact: The objective of this work is to present the effects of a nonminimally
coupled model of gravity on a Solar System short range regime. For this reason,
this study is only valid when the cosmological contribution is considered
irrelevant. The action functional of the model involves two functions $f^1(R)$
and $f^2(R)$ of the Ricci scalar curvature $R$, where the last one multiplies
the matter Lagrangian.
Using a Taylor expansion around $R=0$ for both functions $f^1(R)$ and
$f^2(R)$, it was found that the metric around a spherical object is a
perturbation of the weak-field Schwarzschild metric. The $tt$ component of the
metric, a Newtonian plus a Yukawa perturbation term, is constrained using the
available observational results.
First it is shown that this effect is null when the characteristic mass
scales of each function $f^1(R)$ and $f^2(R)$ are identical. Besides, the
conclusion is that the nonminimal coupling only affects the Yukawa contribution
strength and not its range and that the Starobinsky model for inflation is not
experimentally constrained. Moreover, the geodetic precession effect, obtained
also from the radial perturbation of the metric, reveals to be of no relevance
for the constraints. |
Observational constraints on decaying vacuum dark energy model: The decaying vacuum model (DV), treating dark energy as a varying vacuum, has
been studied well recently. The vacuum energy decays linearly with the Hubble
parameter in the late-times, $\rho_\Lambda(t) \propto H(t)$, and produces the
additional matter component. We constrain the parameters of the DV model using
the recent data-sets from supernovae, gamma-ray bursts, baryon acoustic
oscillations, CMB, the Hubble rate and x-rays in galaxy clusters. It is found
that the best fit of matter density contrast $\Omega_m$ in the DV model is much
lager than that in $\Lambda$CDM model. We give the confidence contours in the
$\Omega_m-h$ plane up to $3\sigma$ confidence level. Besides, the normalized
likelihoods of $\Omega_m$ and $h$ are presented, respectively. % | Detecting warm DM in the $MeV/c^2$ range: Some tension exists between present experimental data and models which
comprise only the three light neutrino mass eigenstates necessary to explain
solar and atmospheric oscillation results. Hence the revival of the idea that
additional more massive states might enter the active neutrino superpositions
produced and observed in charged current reactions. Such 'heavy' neutrinos with
masses in the keV or MeV range might also be of interest as dark matter
candidates. A state with mass larger than 1022 keV could decay into an $e^+
e^-$ pair and a light mass state, leaving an easily recognizable signature. The
aim of this paper is to estimate the possible signal rate. |
Correlation Analysis of a Large Sample of Narrow-Line Seyfert 1
Galaxies: Linking Central Engine and Host Properties: We present a statistical study of a large, homogeneously analyzed sample of
narrow-line Seyfert 1 (NLS1) galaxies, accompanied by a comparison sample of
broad-line Seyfert 1 (BLS1) galaxies. Optical emission-line and continuum
properties are subjected to correlation analyses, in order to identify the main
drivers of active galactic nuclei (AGN) correlation space, and of NLS1 galaxies
in particular. For the first time, we have established the density of the
narrow-line region as a key parameter in Eigenvector 1 space, as important as
the Eddington ratio L/Ledd. This is important because it links the properties
of the central engine with the properties of the host galaxy; i.e., the
interstellar medium (ISM). We also confirm previously found correlations
involving the line width of Hbeta, and the strength of the FeII and [OIII]5007
emission lines, and we confirm the important role played by L/Ledd in driving
the properties of NLS1 galaxies. A spatial correlation analysis shows that
large-scale environments of the BLS1 and NLS1 galaxies of our sample are
similar. If mergers are rare in our sample, accretion-driven winds on the one
hand, or bar-driven inflows on the other hand, may account for the strong
dependence of Eigenvector 1 on ISM density. | Relic neutrinos: Antineutrinos of Primordial Nucleosynthesis: For the first time the antineutrino spectrum formed as a result of neutron
and tritium decays during the epoch of primordial nucleosynthesis is
calculated. This spectrum is a non-thermal increase in addition to the standard
cosmic neutrino background (C$\nu$B) whose thermal spectrum was formed before
the beginning of primordial nucleosynthesis. For energy larger than
$10^{-2}\,$eV the calculated non-thermal antineutrino flux exceeds the C$\nu$B
spectrum and there are no other comparable sources of antineutrino in this
range. The observations of these antineutrinos will allow us to look directly
at the very early Universe and non-equilibrium processes taken place before,
during, and some time after primordial nucleosynthesis. |
Modelling the dusty universe I: Introducing the artificial neural
network and first applications to luminosity and colour distributions: We introduce a new technique based on artificial neural networks which allows
us to make accurate predictions for the spectral energy distributions (SEDs) of
large samples of galaxies, at wavelengths ranging from the far-ultra-violet to
the sub-millimetre and radio. The neural net is trained to reproduce the SEDs
predicted by a hybrid code comprised of the GALFORM semi-analytical model of
galaxy formation, which predicts the full star formation and galaxy merger
histories, and the GRASIL spectro-photometric code, which carries out a
self-consistent calculation of the SED, including absorption and emission of
radiation by dust. Using a small number of galaxy properties predicted by
GALFORM, the method reproduces the luminosities of galaxies in the majority of
cases to within 10% of those computed directly using GRASIL. The method
performs best in the sub-mm and reasonably well in the mid-infrared and the
far-ultra-violet. The luminosity error introduced by the method has negligible
impact on predicted statistical distributions, such as luminosity functions or
colour distributions of galaxies. We use the neural net to predict the overlap
between galaxies selected in the rest-frame UV and in the observer-frame sub-mm
at z=2. We find that around half of the galaxies with a 850um flux above 5 mJy
should have optical magnitudes brighter than R_AB < 25 mag. However, only 1% of
the galaxies selected in the rest-frame UV down to R_AB < 25 mag should have
850um fluxes brighter than 5 mJy. Our technique will allow the generation of
wide-angle mock catalogues of galaxies selected at rest-frame UV or mid- and
far-infrared wavelengths. | The Role of Mergers in Early-type Galaxy Evolution and Black Hole Growth: Models of galaxy formation invoke the major merger of gas-rich progenitor
galaxies as the trigger for significant phases of black hole growth and the
associated feedback that suppresses star formation to create red spheroidal
remnants. However, the observational evidence for the connection between
mergers and active galactic nucleus (AGN) phases is not clear. We analyze a
sample of low-mass early-type galaxies known to be in the process of migrating
from the blue cloud to the red sequence via an AGN phase in the green valley.
Using deeper imaging from SDSS Stripe 82, we show that the fraction of objects
with major morphological disturbances is high during the early starburst phase,
but declines rapidly to the background level seen in quiescent early-type
galaxies by the time of substantial AGN radiation several hundred Myr after the
starburst. This observation empirically links the AGN activity in low-redshift
early-type galaxies to a significant merger event in the recent past. The large
time delay between the merger-driven starburst and the peak of AGN activity
allows for the merger features to decay to the background and hence may explain
the weak link between merger features and AGN activity in the literature. |
From haloes to Galaxies - I. The dynamics of the gas regulator model and
the implied cosmic sSFR history: We explore the basic parameters that drive the evolution of the fundamental
properties of star forming galaxies within the gas regulator model, or
bathtub-model. We derive the general analytic form of the evolution of the key
galaxy properties, i.e. gas mass, star formation rate (SFR), stellar mass,
specific SFR, gas fraction, gas phase metallicity and stellar metallicity,
without assuming that galaxies live in the equilibrium state. We find that the
timescale required to reach equilibrium, tau_eq, which is determined by the
product of star-formation efficiency and mass-loading factor, is the central
parameter that is essentially in control of the evolution of all key galaxy
properties. The scatters in most of the key scaling relations, such as the
mass-SFR relation and mass-metallicity relation, are primarily governed by
tau_eq. Most strikingly, the predicted sSFR evolution is controlled solely by
tau_eq (apart from the cosmic time). Although the precise evolution of the sSFR
depends on tau_eq, the sSFR history is largely insensitive to different values
of tau_eq. The difference between the minimum and maximum sSFR at any epoch is
less than a factor of four. The shape of the predicted sSFR history simply
mimics that of the specific mass increase rate of the dark matter halos
(sMIR_DM) with the typical value of the sSFR around 2*sMIR_DM, in good
agreement with the predictions from typical Semi-Analytic Models (SAMs), but
both are fundamentally different from the observed sSFR history. This clearly
implies that some key process is missing in both typical SAMs and gas regulator
model, and we hint at some possible culprit. We emphasize the critical role of
tau_eq in controlling the evolution of the galaxy population, especially for
gas rich low mass galaxies that are very unlikely to live around the
equilibrium state at any epoch and this has been largely ignored in many
similar studies. | Signatures of Cosmic Reionization on the 21cm 2- and 3-point Correlation
Function I: Quadratic Bias Modeling: The three-point correlation function (3PCF) of the 21cm brightness
temperature from the Epoch of Reionization (EoR) probes complementary
information to the commonly studied two-point correlation function (2PCF) about
the morphology of ionized regions. We investigate the 21cm 2PCF and 3PCF in
configuration space using semi-numerical simulations and test whether they can
be described by the local quadratic bias model. We find that fits of bias model
predictions for the 2PCF and 3PCF deviate from our measurements by $\sim 20\%$
at scales above the typical size of ionized regions ($\simeq 30$ Mpc) and at
early times with global neutral fractions of $\langle x_{\rm HI} \rangle
\gtrsim 0.7$. At later times and smaller scales these deviations increase
strongly, indicating a break down of the bias model. The 2PCF and 3PCF fits of
the linear bias parameter agree at the $10\%$ level for different EoR model
configurations. This agreement holds, when adding redshift space distortions to
the simulations. The relation between spatial fluctuations in the matter
density and the 21cm signal, as predicted by the bias model, is consistent with
direct measurements of this relation in simulations for large smoothing scales
($\gtrsim 30$ Mpc). From this latter test we conclude that negative amplitudes
of the 21cm 3PCF result from negative bias parameters, which describe the
anti-correlation between the matter over-densities and the 21cm signal during
the EoR. However, a more detailed interpretation of the bias parameters may
require a description of non-local contributions to the bias model. |
Rayleigh scattering: blue sky thinking for future CMB observations: Rayleigh scattering from neutral hydrogen during and shortly after
recombination causes the CMB anisotropies to be significantly frequency
dependent at high frequencies. This may be detectable with Planck, and would be
a strong signal in any future space-based CMB missions. The later peak of the
Rayleigh visibility compared to Thomson scattering gives an increased
large-scale CMB polarization signal that is a greater than 4% effect for
observed frequencies greater than 500GHz. There is a similar magnitude
suppression on small scales from additional damping. Due to strong correlation
between the Rayleigh and primary signal, measurement of the Rayleigh component
is limited by noise and foregrounds, not cosmic variance of the primary CMB,
and should observable over a wide range of angular scales at frequencies
between roughly 200GHz and 800GHz. I give new numerical calculations of the
temperature and polarization power spectra, and show that future CMB missions
could measure the temperature Rayleigh cross-spectrum at high precision, detect
the polarization from Rayleigh scattering, and also accurately determine the
cross-spectra between the Rayleigh temperature signal and primary polarization.
The Rayleigh scattering signal may provide a powerful consistency check on
recombination physics. In principle it can be used to measure additional
horizon-scale primordial perturbation modes at recombination, and distinguish a
significant tensor mode B-polarization signal from gravitational lensing at the
power spectrum level. | The eROSITA view of the Abell 3391/95 field: The Northern Clump. The
largest infalling structure in the longest known gas filament observed with
eROSITA, XMM-Newton, and Chandra: SRG/eROSITA PV observations revealed the A3391/95 cluster system and the
Northern Clump (MCXC J0621.7-5242 galaxy cluster) are aligning along a cosmic
filament in soft X-rays, similarly to what has been seen in simulations before.
We aim to understand the dynamical state of the Northern Clump as it enters the
atmosphere ($3\times R_{200}$) of A3391. We analyzed joint eROSITA, XMM-Newton,
and Chandra observations to probe the morphological, thermal, and chemical
properties of the Northern Clump from its center out to a radius of 988 kpc
($R_{200}$). We utilized the ASKAP/EMU radio data, DECam optical image, and
Planck y-map to study the influence of the WAT radio source on the Northern
Clump central ICM. From the Magneticum simulation, we identified an analog of
the A3391/95 system along with an infalling group resembling the Northern
Clump. The Northern Clump is a WCC cluster centered on a WAT radio galaxy. The
gas temperature over $0.2-0.5R_{500}$ is $k_BT_{500}=1.99\pm0.04$ keV. We
employed the $M-T$ scaling relation and obtained a mass estimate of
$M_{500}=(7.68\pm0.43)\times10^{13}M_{\odot}$ and $R_{500}=(636\pm12)$ kpc. Its
atmosphere has a boxy shape and deviates from spherical symmetry. We identify a
southern surface brightness edge, likely caused by subsonic motion relative to
the filament gas. At $\sim\! R_{500}$, the southern atmosphere appears to be
42% hotter than its northern atmosphere. We detect a downstream tail pointing
toward the north with a projected length of $\sim318$ kpc, plausibly the result
of ram pressure stripping. The analog group in the Magneticum simulation is
experiencing changes in its gas properties and a shift between the position of
the halo center and that of the bound gas while approaching the main cluster
pair. |
On minor black holes in galactic nuclei: Small and intermediate mass black holes should be expected in galactic nuclei
as a result of stellar evolution, minor mergers and gravitational dynamical
friction. If these minor black holes accrete as X-ray binaries or
ultra-luminous X-ray sources, and are associated with star formation, they
could account for observations of many low luminosity AGN or LINERs. Accreting
and inspiralling intermediate mass black holes could provide a crucial
electromagnetic counterpart to strong gravitational wave signatures, allowing
tests of strong gravity. Here we discuss observational signatures of minor
black holes in galactic nuclei and we demonstrate that optical line ratios
observed in LINERs or transition-type objects can be produced by an ionizing
radiation field from ULXs. We conclude by discussing constraints from existing
observations as well as candidates for future study. | Constraints on interacting dark energy models from time-delay
cosmography with seven lensed quasars: Measurements of time-delay cosmography of lensed quasars can provide an
independent probe to explore the expansion history of the late-time Universe.
In this paper, we employ the time-delay cosmography measurements from seven
lenses (here abbreviated as the TD data) to constrain interacting dark energy
(IDE) models. We mainly focus on the scenario of vacuum energy (with $w=-1$)
interacting with cold dark matter, and consider four typical cases of the
interaction form $Q$. When the TD data alone are employed, we find that the IDE
models with $Q\propto \rho_{\rm de}$ seem to have an advantage in relieving the
$H_{0}$ tension between the cosmic microwave background (CMB) and TD data. When
the TD data are added to the CMB$+$BAO$+$SN$+H_0$ data, we find that: (i) the
coupling parameter $\beta$ in all the considered IDE models is positive within
1$\sigma$ range, implying a mild preference for the case of cold dark matter
decaying into dark energy; (ii) the IDE model with $Q = \beta H_{0} \rho_{\rm
c}$ slightly relieves the $S_8$ tension, but the other considered IDE models
further aggravate this tension; (iii) the Akaike information criteria of the
IDE models with $Q \propto \rho_{\rm c}$ are lower than that of the
$\Lambda$CDM model, indicating that these IDE models are more preferred by the
current mainstream data. We conclude that the considered IDE models have their
own different advantages when the TD data are employed, and none of them can
achieve good scores in all aspects. |
Perturbative description of bias tracers using consistency relations of
LSS: We develop a simple formalism of biased tracers that we dub $\mathit{Monkey\
bias}$. In this formalism, a biased tracer field is constructed directly in
terms of the linear matter fluctuation field and the set of derivative
operators acting on it. Such bias expansion is first organized based on the
general structure of non-linear dynamical equations for the biased tracers.
Further physical conditions, like the equivalence principle, are imposed on
tree-level correlators utilising the consistency relations. We obtain the bias
expansion up to the third-order in linear matter fluctuation in the generalized
$\Lambda$CDM background, which reproduces the previous results in the limit of
the EdS universe. This algorithmic construction of our bias operator basis is
well suited for extensions towards higher-order bias fields. Moreover, this
formalism reveals that biased tracer dynamics in generalized $\Lambda$CDM
background is not entirely degenerate with the rest of bias parameters, thus
opening a possibility of testing the background cosmology through the
observations of biased tracers. | Star Formation in the XMMU J2235.3-2557 Galaxy Cluster at z=1.39: We present the first results of a narrow-band photometric study of the
massive galaxy cluster XMMU J2235.3-2557 at z=1.39. We obtained deep $H$
narrow-band imaging with NIRI on Gemini North, corresponding to H-alpha
emission at the cluster's redshift. Our sample consists of 82 galaxies within a
radius of ~500 kpc, ten of which are spectroscopically confirmed cluster
members. Sixteen galaxies are identified as excess line-emitters. Among just
the excess line-emitting galaxies we find an average SFR of 3.6 +/- 1.3
Msun/yr. For spectroscopically confirmed cluster members we find a correlation
between H broad-band magnitude and SFR such that brighter galaxies have lower
SFRs. The probability that SFR and magnitude of confirmed members are
uncorrelated is 0.7%. We also find a correlation between SFR and distance from
the cluster centre for both confirmed and excess line-emitting candidate
members, with a probability of 5% for there to be no correlation among
confirmed members. All excess line-emitting candidate cluster members are
located outside a radius of 200 kpc. We conclude that star formation is
effectively shut off within the central 200 kpc radius (R_QUENCH ~ 200 kpc) of
this massive galaxy cluster at z=1.39, when the universe was only 4.5 Gyr old. |
Interaction of radio jets with clouds in the ambient medium: Numerical
simulations: Hydrodynamical simulations of jets interacting with clouds moving in the
ambient medium of the host galaxy are presented. Clouds with sizes of the order
of the jet diameter and smaller, crossing the path of the jet with different
speeds are considered. In the case of slow moving clouds the jet is stopped
over the brief period of time taken by the cloud to cross the jet. The jet
maintains its general morphology in the case of fast moving clouds. Erosion of
the clouds leads to redistribution of cloud material to large distances. Such
interaction may explain the large outflow velocities observed from pc to kpc
scales in the compact radio sources. | A Possible Large-scale Alignment of Galaxy Spin Directions -- Analysis
of 10 Datasets from SDSS, Pan-STARRS, and HST: Multiple observations made by several different telescopes have shown
asymmetry between the number of spiral galaxies rotating in opposite directions
in different parts of the sky. One of the immediate questions regarding the
possible asymmetry of the spin directions is whether the distribution forms a
cosmological-scale axis. This paper analyzes and compares 10 different datasets
published in the past decade, collected by SDSS, Pan-STARRS, and Hubble Space
Telescope. The datasets contain spiral galaxies separated by their spin
direction, and the distribution can show dipole axes. The analysis shows that
the directions of the most probable dipole axes are consistent in datasets that
have similar average redshift, but different between datasets that have
different average redshift. The analysis also shows that the location of the
most probable axis correlates with the average redshift of the galaxies in the
datasets. That is, the location of the most probable axis shifts when the
redshift gets higher, and the correlation is statistically significant. This
provides a certain indication of a drift in a possible axis formed by the
distribution of galaxy spin directions, or a cosmological scale structure that
peaks at a certain distance from Earth. |
13CO and C18O emission from a dense gas disk at z=2.3: abundance
variations, cosmic rays and the initial conditions for star formation: We analyse the SLEDs of 13CO and C18O for the J=1-0 up to J=7-6 transitions
in the gravitationally lensed ultraluminous infrared galaxy SMMJ2135-0102 at
z=2.3. This is the first detection of 13CO and C18O in a high-redshift
star-forming galaxy. These data comprise observations of six transitions taken
with PdBI and we combine these with 33GHz JVLA data and our previous 12CO and
continuum emission information to better constrain the properties of the ISM
within this system. We study both the velocity-integrated and kinematically
decomposed properties of the galaxy and coupled with an LVG model we find that
the star-forming regions in the system vary in their cold gas properties. We
find strong C18O emission both in the velocity-integrated emission and in the
two kinematic components at the periphery of the system, where the C18O line
flux is equivalent to or higher than the 13CO. We derive an average
velocity-integrated flux ratio of 13CO/C18O~1 suggesting a [13CO]/[C18O]
abundance ratio at least 7x lower than that in the Milky Way. This may suggest
enhanced C18O abundance, perhaps indicating star formation preferentially
biased to high-mass stars. We estimate the relative contribution to the ISM
heating from cosmic rays and UV of (30-3300)x10^(-25)erg/s and 45x10^(-25)erg/s
per H2 molecule respectively and both are comparable to the total cooling rate
of (0.8-20)x10^(-25)erg/s from the CO. However, our LVG models indicate high
(>100K) temperatures and densities (>10^(3))cm^(-3) in the ISM which may
suggest that cosmic rays play a more important role than UV heating in this
system. If cosmic rays dominate the heating of the ISM, the increased
temperature in the star forming regions may favour the formation of massive
stars and so explain the enhanced C18O abundance. This is a potentially
important result for a system which may evolve into a local elliptical galaxy. | Probing the anisotropic expansion history of the universe with cosmic
microwave background: We propose a simple technique to detect any anisotropic expansion stage in
the history of the universe starting from the inflationary stage to the surface
of last scattering from the CMBR data. We use the property that any anisotropic
expansion in the universe would deform the shapes of the primordial density
perturbations and this deformation can be detected in a shape analysis of
superhorizon fluctuations in CMBR. Using this analysis we obtain the constraint
on any previous anisotropic expansion of the universe to be less than about
35%. |
Detecting the neutral IGM in filaments with the SKA: The intergalactic medium (IGM) plays an important role in the formation and
evolution of galaxies. Recent developments in upcoming radio telescopes are
starting to open up the possibility of making a first direct detection of the
21 cm signal of neutral hydrogen (HI) from the warm gas of the IGM in
large-scale filaments. The cosmological hydrodynamical EAGLE simulation is used
to estimate the typical IGM filament signal. Assuming the same average signal
for all filaments, a prediction is made for the detectability of such a signal
with the upcoming mid-frequency array of the Square Kilometer Array (SKA1-mid)
or the future upgrade to SKA2. The signal-to-noise (S/N) then only depends on
the size and orientation of each filament. With filament spines inferred from
existing galaxy surveys as a proxy for typical real filaments, we find hundreds
of filaments in the region of the sky accessible to the SKA that can be
detected. Once the various phases of the SKA telescope become operational,
their own surveys will be able to find the galaxies required to infer the
position of even more filaments within the survey area. We find that in 120 h,
SKA1-mid/SKA2 will detect HI emission from the strongest filaments in the field
with a S/N of the order of 10 to $\sim$150 for the most pessimistic model
considered here. Some of the brighter filaments can be detected with an
integration time of a few minutes with SKA1-mid and a few seconds with SKA2.
Therefore, SKA2 will be capable of not only detecting but also mapping a large
part of the IGM in these filaments. | Gamma-Ray Burst Groups Observed by Different Satellites: Two classes of gamma-ray bursts have been identified in the BATSE catalogs
characterized by durations shorter and longer than about 2 seconds. There are,
however, some indications for the existence of a third one. Swift satellite
detectors have different spectral sensitivity than pre-Swift ones for gamma-ray
bursts. Therefore it is worth to reanalyze the durations and their distribution
and also the classification of GRBs. In this paper we are going to analyze the
bursts' duration distribution and also the duration-hardness bivariate
distribution, published in The First BAT Catalog, whether it contains two,
three or maybe more groups. Similarly to the BATSE data, to explain the BAT
GRBs duration distribution three components are needed. Although, the relative
frequencies of the groups are different than they were in the BATSE GRB sample,
the difference in the instrument spectral sensitivities can explain this bias
in a natural way. This means theoretical models may have to explain three
different type of gamma-ray bursts. |
Cosmological scalar fields and Big-Bang nucleosynthesis: The nature of dark matter and of dark energy which constitute more than
$95\%$ of the energy in the Universe remains a great and unresolved question in
cosmology. Cold dark matter can be made of an ultralight scalar field dominated
by its mass term which interacts only gravitationally. The cosmological
constant introduced to explain the recent acceleration of the Universe
expansion can be easily replaced by a scalar field dominated by its potential.
More generally, scalar fields are ubiquitous in cosmology: inflaton, dilatons,
moduli, quintessence, fuzzy dark matter, dark fluid, etc. are some examples.
One can wonder whether all these scalar fields are independent. The dark fluid
model aims at unifying quintessence and fuzzy dark matter models with a unique
scalar field. One step futher is to unify the dark fluid model with inflation.
In the very early Universe such scalar fields are not strongly constrained by
direct observations, but Big-Bang nucleosynthesis set constraints on scalar
field models which lead to a modification on the abundance of the elements. In
this talk we will present a scalar field model unifying dark matter, dark
energy and inflation, and study constraints from Big-Bang nucleosynthesis on
primordial scalar fields. | Beyond standard models in cosmology (In French): The current description of fundamental interactions is based on two theories
with the status of standard models. The electromagnetic and nuclear
interactions are described at a quantum level by the Standard Model of particle
physics, using tools like gauge theories and spontaneous symmetry breaking by
the Higgs mechanism. The gravitational interaction is described on the other
hand by general relativity, based on a dynamical description of space-time at a
classical level.
Although these models are verified to high precision in the solar system
experiments, they suffer from several theoretical weaknesses and a lack of
predictive power at the Planck scale as well as at cosmological scales; they
are thus not viewed anymore as fundamental theories. As its phenomenology
involves both these extreme scales, cosmology is then a good laboratory to
probe theories going beyond these standard models.
The first part of this thesis focus on cosmic strings, topological defects
forming during the spontaneous symmetry breaking of grand unified theories in
the early universe. I show especially how to study these defects while taking
into account the complete structure of the particles physics models leading to
their formation, going beyond the standard descriptions in terms of simplified
toy-models. The second part is devoted to the construction and the examination
of different theories of modified gravity related to the Galileon model, a
model which tries in particular to explain the dark energy phenomenology. |
The snapshot distance method: estimating the distance to a Type Ia
supernova from minimal observations: We present the snapshot distance method (SDM), a modern incarnation of a
proposed technique for estimating the distance to a Type Ia supernova (SN Ia)
from minimal observations. Our method, which has become possible owing to
recent work in the application of deep learning to SN Ia spectra (we use the
deepSIP package), allows us to estimate the distance to an SN Ia from a single
optical spectrum and epoch of $2+$ passband photometry -- one night's worth of
observations (though contemporaneity is not a requirement). Using a compilation
of well-observed SNe Ia, we generate snapshot distances across a wide range of
spectral and photometric phases, light-curve shapes, photometric passband
combinations, and spectrum signal-to-noise ratios. By comparing these estimates
to the corresponding distances derived from fitting all available photometry
for each object, we demonstrate that our method is robust to the relative
temporal sampling of the provided spectroscopic and photometric information,
and to a broad range of light-curve shapes that lie within the domain of
standard width-luminosity relations. Indeed, the median residual (and
asymmetric scatter) between SDM distances derived from two-passband photometry
and conventional light-curve-derived distances that utilise all available
photometry is $0.013_{-0.143}^{+0.154}$ mag. Moreover, we find that the time of
maximum brightness and light-curve shape (both of which are spectroscopically
derived in our method) are only minimally responsible for the observed scatter.
In a companion paper, we apply the SDM to a large number of sparsely observed
SNe Ia as part of a cosmological study. | Localization accuracy of compact binary coalescences detected by the
third-generation gravitational-wave detectors and implication for cosmology: We use the Fisher information matrix to investigate the angular resolution
and luminosity distance uncertainty for coalescing binary neutron stars (BNSs)
and neutron star-black hole binaries (NSBHs) detected by the third-generation
(3G) gravitational-wave (GW) detectors. Our study focuses on an individual 3G
detector and a network of up to four 3G detectors at different locations
including the US, Europe, China and Australia for the proposed Einstein
Telescope (ET) and Cosmic Explorer (CE) detectors. We in particular examine the
effect of the Earth's rotation, as GW signals from BNS and low mass NSBH
systems could be hours long for 3G detectors. We find that, a time-dependent
antenna beam-pattern function can help better localize BNS and NSBH sources,
especially those edge-on ones. The medium angular resolution for one ET-D
detector is around 150 deg$^2$ for BNSs at a redshift of $z=0.1$. The medium
angular resolution for a network of two CE detectors in the US and Europe
respectively is around 20 deg$^2$ at $z=0.2$ for the simulated BNS and NSBH
samples. While for a network of two ET-D detectors, the similar angular
resolution can be achieved at a much higher redshift of $z=0.5$. The angular
resolution of a network of three detectors is mainly determined by the
baselines between detectors regardless of the CE or ET detector type. We
discuss the implications of our results to constrain the Hubble constant $H_0$,
the deceleration parameter $q_0$ and the equation-of-state (EoS) of dark
energy. We find that in general, if 10 BNSs or NSBHs at $z=0.1$ with known
redshifts are detected, $H_0$ can be measured with an accuracy of $0.9\%$. If
1000 face-on BNSs at $z<2$ are detected with known redshifts, we are able to
achieve $\Delta q_0=0.002$, or $\Delta w_0=0.03$ and $\Delta w_a=0.2$ for dark
energy.(Abridged version). |
Gravitational Microlensing Time Delays at High Optical Depth: Image
Parities and the Temporal Properties of Fast Radio Bursts: Due to differing gravitational potentials and path lengths, gravitational
lensing induces time delays between multiple images of a source which, for
solar mass objects, is of order $\sim10^{-5}$ seconds. If an astrophysically
compact source, such as a Fast Radio Burst (FRB), is observed through a region
with a high optical depth of such microlensing masses, this gravitational
lensing time delay can be imprinted on short timescale transient signals. In
this paper, we consider the impact of the parity of the macroimage on the
resultant microlensing time delays. It is found that this parity is directly
imprinted on the microlensing signal, with macroimages formed at minima of the
time arrival surface beginning with the most highly magnified microimages and
then progressing to the fainter microimages. At macroimages at the maxima of
the time arrival surface, this situation is reversed, with fainter images
observed first and finishing with the brightest microimages. For macroimages at
saddle-points, the signal again begins with fainter images, followed by
brighter images before again fading through the fainter microimages. The
growing populations of cosmologically distant bursty transient sources will
undoubtedly result in the discovery of strong lensed, multiply imaged FRBs,
which will be susceptible to microlensing by compact masses. With the temporal
resolution being offered my modern and future facilities, the detection of
microlensing induced time delays will reveal the parities of the gravitational
lens macroimages, providing additional constraints on macrolensing mass models
and improving the efficacy of these transient sources as a cosmological probes. | Spectrum of Galactic Cosmic Rays Accelerated in Supernova Remnants: The spectra of high-energy protons and nuclei accelerated by supernova
remnant shocks are calculated taking into account magnetic field amplification
and Alfvenic drift both upstream and downstream of the shock for different
types of supernova remnants during their evolution. The maximum energy of
accelerated particles may reach $5\cdot10^{18}$ eV for Fe ions in Type IIb
SNRs. The calculated energy spectrum of cosmic rays after propagation through
the Galaxy is in good agreement with the spectrum measured at the Earth. |
Model-Independent Test for Gravity using Intensity Mapping and Galaxy
Clustering: We propose a novel method to measure the $E_G$ statistic from clustering
alone. The $E_G$ statistic provides an elegant way of testing the consistency
of General Relativity by comparing the geometry of the Universe, probed through
gravitational lensing, with the motion of galaxies in that geometry. Current
$E_G$ estimators combine galaxy clustering with gravitational lensing, measured
either from cosmic shear or from CMB lensing. In this paper, we construct a
novel estimator for $E_G$, using only clustering information obtained from two
tracers of the large-scale structure: intensity mapping and galaxy clustering.
In this estimator, both the velocity of galaxies and gravitational lensing are
measured through their impact on clustering. We show that with this estimator,
we can suppress the contaminations that affect other $E_G$ estimators and
consequently test the validity of General Relativity robustly. We forecast that
with the coming generation of surveys like HIRAX and Euclid, we will measure
$E_G$ with a precision of up to 7% (3.9% for the more futuristic SKA2). | The redshift-space galaxy two-point correlation function and baryon
acoustic oscillations: Future galaxy surveys will measure baryon acoustic oscillations (BAOs) with
high significance, and a complete understanding of the anisotropies of BAOs in
redshift space will be important to exploit the cosmological information in
BAOs. Here we describe the anisotropies that arise in the redshift-space galaxy
two-point correlation function (2PCF) and elucidate the origin of features that
arise in the dependence of the BAOs on the angle between the orientation of the
galaxy pair and the line of sight. We do so with a derivation of the
configuration-space 2PCF using streaming model. We find that, contrary to
common belief, the locations of BAO peaks in the redshift-space 2PCF are
anisotropic even in the linear theory. Anisotropies in BAO depend strongly on
the method of extracting the peak, showing maximum 3 % angular variation. We
also find that extracting the BAO peak of $r^2\xi(r,\mu)$ significantly reduces
the anisotropy to sub-percent level angular variation. When subtracting the
tilt due to the broadband behavior of the 2PCF, the BAO bump is enhanced along
the line of sight because of local infall velocities toward the BAO bump.
Precise measurement of the angular dependence of the redshift-space 2PCF will
allow new geometrical tests of dark energy beyond the BAO. |
Unified description of dark energy and dark matter in mimetic matter
model: The existence of dark matter and dark energy in cosmology is implied by
various observations, however, they are still unclear because they have not
been directly detected. In this Letter, an unified model of dark energy and
dark matter that can explain the evolution history of the Universe later than
inflationary era, the time evolution of the growth rate function of the matter
density contrast, the flat rotation curves of the spiral galaxies, and the
gravitational experiments in the solar system is proposed in mimetic matter
model. | Bounds on Dark Matter annihilations from 21 cm data: The observation of an absorption feature in the 21 cm spectrum at redshift
$z\approx 17$ implies bounds on Dark Matter annihilations for a broad range of
masses, given that significant heating of the intergalactic medium would have
erased such feature. The resulting bounds on the DM annihilation cross sections
are comparable to the strongest ones from all other observables. |
Environmental effects in the interaction and merging of galaxies in
zCOSMOS: (Abridged) We analyze the environments and galactic properties (morphologies
and star-formation histories) of a sample of 153 close kinematic pairs in the
redshift range 0.2 < z < 1 identified in the zCOSMOS-bright 10k spectroscopic
sample of galaxies. Correcting for projection effects, the fraction of close
kinematic pairs is three times higher in the top density quartile than in the
lowest one. This translates to a three times higher merger rate because the
merger timescales are shown, from mock catalogues based on the Millennium
simulation, to be largely independent of environment once the same corrections
for projection is applied. We then examine the morphologies and stellar
populations of galaxies in the pairs, comparing them to control samples that
are carefully matched in environment so as to remove as much as possible the
well-known effects of environment on the properties of the parent population of
galaxies. Once the environment is properly taken into account in this way, we
find that the early-late morphology mix is the same as for the parent
population, but that the fraction of irregular galaxies is boosted by 50-75%,
with a disproportionate increase in the number of irregular-irregular pairs
(factor of 4-8 times), due to the disturbance of disk galaxies. Future
dry-mergers, involving elliptical galaxies comprise less than 5% of all close
kinematic pairs. In the closest pairs, there is a boost in the specific
star-formation rates of star-forming galaxies of a factor of 2-4, and there is
also evidence for an increased incidence of post star-burst galaxies. Although
significant for the galaxies involved, the "excess" star-formation associated
with pairs represents only about 5% of the integrated star-formation activity
in the parent sample. Although most pair galaxies are in dense environments,
the effects of interaction appear to be largest in the lower density
environments. | Strongly Coupled Cosmologies: Models including an energy transfer from CDM to DE are widely considered in
the literature, namely to allow DE a significant high-z density. Strongly
Coupled cosmologies assume a much larger coupling between DE and CDM, together
with the presence of an uncoupled warm DM component, as the role of CDM is
mostly restricted to radiative eras. This allows us to preserve small scale
fluctuations even if the warm particle, possibly a sterile neutrino, is quite
light, O(100 eV). Linear theory and numerical simulations show that these
cosmologies agree with LCDM on supergalactic scales; e.g., CMB spectra are
substantially identical. Simultaneously, simulations show that they
significantly ease problems related to the properties of MW satellites and
cores in dwarfs. SC cosmologies also open new perspectives on early black hole
formation, and possibly lead towards unificating DE and inflationary scalar
fields. |
Infall Profiles for Supercluster-Scale Filaments: We present theoretical expectations for infall toward supercluster-scale
cosmological filaments, motivated by the Arecibo Pisces-Perseus Supercluster
Survey (APPSS) to map the velocity field around the Pisces-Perseus Supercluster
(PPS) filament. We use a minimum spanning tree applied to dark matter halos the
size of galaxy clusters to identify 236 large filaments within the Millennium
simulation. Stacking the filaments along their principal axes, we determine a
well-defined, sharp-peaked velocity profile function that can be expressed in
terms of the maximum infall rate $V_{\rm max}$ and the distance $\rho_{\rm
max}$ between the location of maximum infall and the principal axis of the
filament. This simple, two-parameter functional form is surprisingly universal
across a wide range of linear mass densities. $V_{\rm max}$ is positively
correlated with the halo mass per length along the filament, and $\rho_{\rm
max}$ is negatively correlated with the degree to which the halos are
concentrated along the principal axis. We also assess an alternative, single
parameter method using $V_{25}$, the infall rate at a distance of 25 Mpc from
the axis of the filament. Filaments similar to the PPS have $V_{\rm max} = 612
\ \pm$ 116 km s$^{-1}$, $\rho_{\rm max} = 8.9 \pm 2.1$ Mpc, and $V_{25} =329 \
\pm$ 68 km s$^{-1}$. We create mock observations to model uncertainties
associated with viewing angle, lack of three-dimensional velocity information,
limited sample size, and distance uncertainties. Our results suggest that it
would be especially useful to measure infall for a larger sample of filaments
to test our predictions for the shape of the infall profile and the
relationships among infall rates and filament properties. | Evolution of primordial magnetic fields in mean-field approximation: We study the evolution of phase-transition-generated cosmic magnetic fields
coupled to the primeval cosmic plasma in turbulent and viscous free-streaming
regimes. The evolution laws for the magnetic energy density and correlation
length, both in helical and non-helical cases, are found by solving the
autoinduction and Navier-Stokes equations in mean-field approximation.
Analytical results are derived in Minkowski spacetime and then extended to the
case of a Friedmann universe with zero spatial curvature, both in radiation and
matter dominated eras. The three possible viscous free-streaming phases are
characterized by a drag term in the Navier-Stokes equation which depends on the
free-streaming properties of neutrinos, photons, or hydrogen atoms,
respectively. In the case of non-helical magnetic fields, the magnetic
intensity $B$ and the magnetic correlation length $\xi_B$ evolve asymptotically
with the temperature $T$ as $B(T) \simeq \kappa_B (N_i v_i)^{\varrho_1}
(T/T_i)^{\varrho_2}$ and $\xi_B(T) \simeq \kappa_\xi (N_i v_i)^{\varrho_3}
(T/T_i)^{\varrho_4}$. Here, $T_i$, $N_i$, and $v_i$ are, respectively, the
temperature, the number of magnetic domains per horizon length, and the bulk
velocity at the onset of the particular regime. The coefficients $\kappa_B$,
$\kappa_\xi$, $\varrho_1$, $\varrho_2$, $\varrho_3$, and $\varrho_4$, depend on
the index of the assumed initial power-law magnetic spectrum, $p$, and on the
particular regime, with the order-one constants $\kappa_B$ and $\kappa_\xi$
depending also on the cut-off adopted for the initial magnetic spectrum. In the
helical case, the quasi-conservation of the magnetic helicity implies, apart
from logarithmic corrections and a factor proportional to the initial
fractional helicity, power-like evolution laws equal to those in the
non-helical case, but with $p$ equal to zero. |
Chandra Observations of the Planck ESZ Sample: A Re-Examination of
Masses and Mass Proxies: Using Chandra observations, we derive the $Y_{\rm X}$ proxy and associated
total mass measurement, $M_{500}^{\rm Y_X}$, for 147 clusters with $z \leq
0.35$ from the Planck Early Sunyaev-Zel'dovich catalog, and for 80 clusters
with $z \leq 0.30$ from an X-ray flux-limited sample. We re-extract the Planck
$Y_{\rm SZ}$ measurements and obtain the corresponding mass proxy,
$M_{500}^{\rm SZ}$, from the full Planck mission maps, minimizing the Malmquist
bias due to observational scatter. The masses re-extracted using the more
precise X-ray position and characteristic size agree with the published PSZ2
values, but yield a significant reduction in the scatter (by a factor of two)
in the $M_{500}^{\rm SZ}$-$M_{500}^{\rm X}$ relation. The slope is
$0.93\pm0.03$, and the median ratio, $M_{500}^{\rm SZ}/M_{500}^{\rm X}=
0.91\pm0.01$, is within the expectations from known X-ray calibration
systematics. The $Y_{\rm SZ}/Y_{\rm X}$ ratio is $0.88\pm0.02$, in good
agreement with predictions from cluster structure, and implying a low level of
clumpiness. In agreement with the findings of the Planck Collaboration, the
slope of the $Y_{\rm SZ}$-$D_{\rm A}^{-2} Y_{X}$ flux relation is significantly
less than unity ($0.89\pm0.01$). Using extensive simulations, we show that this
result is not due to selection effects, intrinsic scatter, or covariance
between quantities. We demonstrate analytically that changing the $Y_{\rm
SZ}$-$Y_{X}$ relation from apparent flux to intrinsic properties results in a
best-fit slope that is closer to unity and increases the dispersion about the
relation. The redistribution resulting from this transformation implies that
the best fit parameters of the $M_{500}^{\rm SZ}$-$M_{500}^{\rm X}$ relation
will be sample-dependent. | Unravelling the origin of large-scale magnetic fields in galaxy clusters
and beyond through Faraday Rotation Measures with the SKA: We investigate the possibility for the SKA to detect and study the magnetic
fields in galaxy clusters and in the less dense environments surrounding them
using Faraday Rotation Measures. To this end, we produce 3-dimensional magnetic
field models for galaxy clusters of different masses and in different stages of
their evolution, and derive mock rotation measure observations of background
radiogalaxies. According to our results, already in phase I, we will be able to
infer the magnetic field properties in galaxy clusters as a function of the
cluster mass, down to $10^{13}$ solar-masses. Moreover, using cosmological
simulations to model the gas density, we have computed the expected rotation
measure through shock-fronts that occur in the intra-cluster medium during
cluster mergers. The enhancement in the rotation measure due to the density
jump will permit to constraint the magnetic field strength and structure after
the shock passage. SKA observations of polarised sources located behind galaxy
clusters will answer several questions about the magnetic field strength and
structure in galaxy clusters, and its evolution with cosmic time. |
Intermediate evolution using SNIa, and BAO: We study the intermediate evolution model and show that, compared with the
recent study of a power-law evolution, the intermediate evolution is a better
description of the low-redshift regime supported by observations from type Ia
supernovae and BAO. We found also that recent data suggest that the
intermediate evolution is as good a fit to this redshift range as the
$\Lambda$CDM model. | Constraining the evolution of the CMB temperature with SZ measurements
from Planck data: The CMB temperature-redshift relation, T_CMB(z)=T_0(1+z), is a key prediction
of the standard cosmology, but is violated in many non standard models.
Constraining possible deviations to this law is an effective way to test the
LambdaCDM paradigm and to search for hints of new physics. We have determined
T_CMB(z), with a precision up to 3%, for a subsample (104 clusters) of the
Planck SZ cluster catalog, at redshift in the range 0.01-- 0.94, using
measurements of the spectrum of the Sunyaev Zel'dovich effect obtained from
Planck temperature maps at frequencies from 70 to 353 GHz. The method adopted
to provide individual determinations of T_CMB(z) at cluster redshift relies on
the use of SZ intensity change, Delta I_SZ(nu), at different frequencies, and
on a Monte-Carlo Markov Chain approach. By applying this method to the sample
of 104 clusters, we limit possible deviations of the form
T_CMB(z)=T_0(1+z)^(1-beta) to be beta= 0.022 +/- 0.018, at 1 sigma uncertainty,
consistent with the prediction of the standard model. Combining these
measurements with previously published results we get beta=0.016+/-0.012. |
Reconstruction of the remote dipole and quadrupole fields from the
kinetic Sunyaev Zel'dovich and polarized Sunyaev Zel'dovich effects: The kinetic Sunyaev Zel'dovich (kSZ) and polarized Sunyaev Zel'dovich (pSZ)
effects are temperature and polarization anisotropies induced by the scattering
of CMB photons from structure in the post-reionization Universe. In the case of
the kSZ effect, small angular scale anisotropies in the optical depth are
modulated by the cosmic microwave background (CMB) dipole field, i.e. the CMB
dipole observed at each spacetime point, which is sourced by the primordial
dipole and especially the local peculiar velocity. In the case of the pSZ
effect, similar small-scale anisotropies are modulated by the CMB quadrupole
field, which receives contributions from both scalar and tensor modes.
Statistical anisotropies in the cross correlations of CMB temperature and
polarization with tracers of the inhomogeneous distribution of electrons
provide a means of isolating and reconstructing the dipole and quadrupole
fields. In this paper, we present a set of unbiased minimum variance quadratic
estimators for the reconstruction of the dipole and quadrupole fields, and
forecast the ability of future CMB experiments and large scale structure
surveys to perform this reconstruction. Consistent with previous work, we find
that a high fidelity reconstruction of the dipole and quadrupole fields over a
variety of scales is indeed possible, and demonstrate the sensitivity of the
pSZ effect to primordial tensor modes. Using a principle component analysis, we
estimate how many independent modes could be accessed in such a reconstruction.
We also comment on a few first applications of a detection of the dipole and
quadrupole fields, including a reconstruction of the primordial contribution to
our locally observed CMB dipole, a test of statistical homogeneity on large
scales from the first modes of the quadrupole field, and a reconstruction
technique for the primordial potential on the largest scales. | Small field models of inflation that predict a tensor-to-scalar ratio
$r=0.03$: Future observations of the cosmic microwave background (CMB) polarization are
expected to set an improved upper bound on the tensor-to-scalar ratio of
$r\lesssim 0.03$. Recently, we showed that small field models of inflation can
produce a significant primordial gravitational wave signal. We constructed
viable small field models that predict a value of $r$ as high as $0.01$. Models
that predict higher values of $r$ are more tightly constrained and lead to
larger field excursions. This leads to an increase in tuning of the potential
parameters and requires higher levels of error control in the numerical
analysis. Here, we present viable small field models which predict $r=0.03$. We
further find the most likely candidate among these models which fit the most
recent Planck data while predicting $r= 0.03$. We thus demonstrate that this
class of small field models is an alternative to the class of large field
models. The BICEP3 experiment and the Euclid and SPHEREx missions are expected
to provide experimental evidence to support or refute our predictions. |
Delta-N Formalism for Curvaton with Modulated Decay: In this paper, the curvature perturbation generated by the modulated curvaton
decay is studied by a direct application of $\delta N$-formalism. Our method
has a sharp contrast with the {\it non-linear formalism} which may be regarded
as an indirect usage of $\delta N$-formalism. We first show that our method can
readily reproduce results in previous works of modulation of curvaton. Then we
move on to calculate the case where the curvaton mass (and hence also the decay
rate) is modulated. The method can be applied to the calculation of the
modulation in the freezeout model, in which the heavy species are considered
instead of the curvaton. Our method explains curvaton and various modulation on
an equal footing. | Statistical Isotropy of the CMB E-mode signal: We test the statistical isotropy (SI) of the $E$-mode polarization of the
cosmic microwave background (CMB) radiation observed by the Planck satellite
using two statistics, namely, the contour Minkowski Tensor (CMT) and the
Directional statistic ($\mathcal{D}$ statistic). The parameter $\alpha$
obtained from the CMT provides information of the alignment of structures and
can be used to infer statistical properties such as Gaussianity and SI of
random fields. The $\mathcal{D}$ statistic is based on detecting preferred
directionality shown by vectors defined by the field. These two tests are
complementary to each other in terms of sensitivity at different angular
scales. The CMT is sensitive towards small-scale information present in the CMB
map while $\mathcal{D}$ statistic is more sensitive at large-scales. We compute
$\alpha$ and $\mathcal{D}$ statistic for the observed $E$-mode of CMB
polarization, focusing on the SMICA maps, and compare with the values
calculated using FFP10 SMICA simulations which contain both CMB and noise. We
find good agreement between the observed data and simulations. Further, in
order to specifically analyze the CMB signal in the data, we compare the values
of the two statistics obtained from the observed Planck data with the values
obtained from isotropic simulations having the same power spectrum, and from
SMICA noise simulations. We find no statistically significant deviation from SI
using the $\alpha$ parameter. From $\mathcal{D}$ statistic we find that the
data shows slight deviation from SI at large angular scales. |
Photometric and Spectroscopic Evolution of the Type IIP SN 2007it to Day
944: SN 2007it is a bright, Type IIP supernova which shows indications of both
pre-existing and newly formed dust. The visible photometry shows a bright
late-time luminosity, powered by the 0.09 M$_{\sun}$ of $^{56}$Ni present in
the ejecta. There is also a sudden drop in optical brightness after day 339,
and a corresponding brightening in the IR due to new dust forming in the
ejecta. CO and SiO emission, generally thought to be precursors to dust
formation, may have been detected in the mid-IR photometry of SN 2007it. The
optical spectra show stronger than average [O I] emission lines and weaker than
average [Ca II] lines, which may indicate a 16 - 27 M$_{\sun}$ progenitor, on
the higher end of expected Type IIP masses. Multi-component [O I] lines are
also seen in the optical spectra, most likely caused by an asymmetric blob or a
torus of oxygen core material being ejected during the SN explosion.
Interaction with circumstellar material prior to day 540 may have created a
cool dense shell between the forward and reverse shocks where new dust is
condensing. At late times there is also a flattening of the visible lightcurve
as the ejecta luminosity fades and a surrounding light echo becomes visible.
Radiative transfer models of SN 2007it SEDs indicate that up to 10$^{-4}$
M$_{\sun}$ of new dust has formed in the ejecta, which is consistent with the
amount of dust formed in other core collapse supernovae. | Type Ia supernovae, standardisable candles, and gravity: Type Ia supernovae (SNIe) are generally accepted to act as standardisable
candles, and their use in cosmology led to the first confirmation of the as yet
unexplained accelerated cosmic expansion. Many of the theoretical models to
explain the cosmic acceleration assume modifications to Einsteinian General
Relativity which accelerate the expansion, but the question of whether such
modifications also affect the ability of SNIe to be standardisable candles has
rarely been addressed. This paper is an attempt to answer this question. For
this we adopt a semi-analytical model to calculate SNIe light curves in
non-standard gravity. We use this model to show that the average rescaled
intrinsic peak luminosity -- a quantity that is assumed to be constant with
redshift in standard analyses of Type Ia supernova (SNIa) cosmology data --
depends on the strength of gravity in the supernova's local environment because
the latter determines the Chandrasekhar mass -- the mass of the SNIa's white
dwarf progenitor right before the explosion. This means that SNIe are no longer
standardisable candles in scenarios where the strength of gravity evolves over
time, and therefore the cosmology implied by the existing SNIa data will be
different when analysed in the context of such models. As an example, we show
that the observational SNIa cosmology data can be fitted with both a model
where $(\Omega_{\rm M}, \Omega_{\Lambda})=(0.62, 0.38)$ and Newton's constant
$G$ varies as $G(z)=G_0(1+z)^{-1/4}$ and the standard model where $(\Omega_{\rm
M}, \Omega_{\Lambda})=(0.3, 0.7)$ and $G$ is constant, when the Universe is
assumed to be flat. |
Constraining new fundamental physics with multiwavelength astrometry: While the deflection of light is achromatic in General Relativity, it is not
always so in several new-physics models (e.g. certain quantum-gravity and
string-inspired models, models with nonminimal photon-gravity coupling or with
massive photon etc.). We discuss how parameters of these models may be
constrained by precise astrometry at different wavelenghts. From published
observations of the gravitational lens MG J2016+112, we obtain world-best
limits on chromatic gravitational deflection of light (and the unique limit on
the photon mass relevant for distance scales >Mpc). We also outline prospects
for further improvement of these limits. | ARTIST: Fast radiative transfer for large-scale simulations of the epoch
of reionisation: We introduce the "Asymmetric Radiative Transfer In Shells Technique"
(ARTIST), a new method for photon propagation on large scales that explicitly
conserves photons, propagates photons at the speed of light, approximately
accounts for photon directionality, and closely reproduces results of more
detailed radiative transfer (RT) codes. Crucially, it is computationally fast
enough to evolve the large cosmological volumes required to predict the 21cm
power spectrum on scales that will be probed by future experiments targeting
the Epoch of Reionisation (EoR). Most semi-numerical models aimed at predicting
the EoR 21cm signal make use of an excursion set formalism (ESF) approach,
which achieves computational viability by compromising on photon conservation,
constraining ionised regions to be spherical by construction, and not
accounting for light-travel time. By implementing our RT method within the
semi-numerical code SimFast21, we show that ARTIST predicts a significantly
different evolution for the EoR ionisation field compared to the code's native
ESF. In particular, ARTIST predicts a more gradual evolution of the
volume-averaged ionisation fraction, and up to an order-of-magnitude difference
in the ionisation power, depending on the physical parameters assumed. Its
application to large-scale EoR simulations will therefore allow more
physically-motivated constraints to be obtained for key EoR parameters, such as
the escape fraction. |
Higher order spectra from an initially anisotropic universe: In this paper, we present the higher order spectra of a scalar field produced
through the higher derivative interactions in the initially anisotropic
universe. Although we ignore the backreaction of the scalar field on the
geometry, our analysis should have much overlap with the quantum fluctuations
of the inflaton field in the anisotropic universe. We also include the planar
modes whose momenta are along the plane which is perpendicular to the
primordial preferred direction, for which effects of the initial anisotropy are
not suppressed. The presence of a negative frequency mode produces features
distinguishable from the case of the de Sitter inflation. We also show that
richer features appear in the trispectra due to the primordial anisotropy. | Integral field spectroscopy of supernova explosion sites: constraining
mass and metallicity of the progenitors -- II. Type II-P and II-L supernovae: Thirteen explosion sites of type II-P and II-L supernovae in nearby galaxies
have been observed using integral field spectroscopy, enabling both spatial and
spectral study of the explosion sites. We used the properties of the parent
stellar population of the coeval supernova progenitor star to derive its
metallicity and initial mass (c.f. Paper I). The spectrum of the parent stellar
population yields the estimates of metallicity via strong-line method, and age
via comparison with simple stellar population (SSP) models. These metallicity
and age parameters are adopted for the progenitor star. Age, or lifetime of the
star, was used to derive initial (ZAMS) mass of the star by comparing with
stellar evolution models. With this technique, we were able to determine
metallicity and initial mass of the SN progenitors in our sample. Our result
indicates that some type-II supernova progenitors may have been stars with mass
comparable to SN Ib/c progenitors. |
Gravitational waves from self-ordering scalar fields: Gravitational waves were copiously produced in the early Universe whenever
the processes taking place were sufficiently violent. The spectra of several of
these gravitational wave backgrounds on subhorizon scales have been extensively
studied in the literature. In this paper we analyze the shape and amplitude of
the gravitational wave spectrum on scales which are superhorizon at the time of
production. Such gravitational waves are expected from the self ordering of
randomly oriented scalar fields which can be present during a thermal phase
transition or during preheating after hybrid inflation. We find that, if the
gravitational wave source acts only during a small fraction of the Hubble time,
the gravitational wave spectrum at frequencies lower than the expansion rate at
the time of production behaves as $\Omega_{\rm GW}(f) \propto f^3$ with an
amplitude much too small to be observable by gravitational wave observatories
like LIGO, LISA or BBO. On the other hand, if the source is active for a much
longer time, until a given mode which is initially superhorizon ($k\eta_* \ll
1$), enters the horizon, for $k\eta \gtrsim 1$, we find that the gravitational
wave energy density is frequency independent, i.e. scale invariant. Moreover,
its amplitude for a GUT scale scenario turns out to be within the range and
sensitivity of BBO and marginally detectable by LIGO and LISA. This new
gravitational wave background can compete with the one generated during
inflation, and distinguishing both may require extra information. | Lagrangian approach to super-sample effects on biased tracers at field
level: galaxy density fields and intrinsic alignments: It has been recognized that the observables of large-scale structure (LSS) is
susceptible to long-wavelength density and tidal fluctuations whose wavelengths
exceed the accessible scale of a finite-volume observation, referred to as the
super-sample modes. The super-sample modes modulate the growth and expansion
rate of local structures, thus affecting the cosmological information encoded
in the statistics of galaxy clustering data. In this paper, based on the
Lagrangian perturbation theory, we develop a new formalism to systematically
compute the response of a biased tracer of LSS, which is expressed
perturbatively in terms of the matter density field of sub-survey modes, to the
super-sample modes at the field level. The formalism presented here reproduces
the power spectrum responses that have been previously derived, and provides an
alternative way to compute statistical quantities with super-sample modes. As
an application, we consider the statistics of the intrinsic alignments of
galaxies and halos, and derive the field response of the galaxy/halo shape bias
to the super-sample modes. Possible impacts of the long-mode contributions on
the covariance of the three-dimensional power spectra of the intrinsic
alignment are also discussed, and the signal-to-noise ratios are estimated. |
Probing dark matter substructure in the gravitational lens HE0435-1223
with the WFC3 grism: Strong gravitational lensing provides a powerful test of Cold Dark Matter
(CDM) as it enables the detection and mass measurement of low mass haloes even
if they do not contain baryons. Compact lensed sources such as Active Galactic
Nuclei (AGN) are particularly sensitive to perturbing subhalos, but their use
as a test of CDM has been limited by the small number of systems which have
significant radio emission which is extended enough avoid significant lensing
by stars in the plane of the lens galaxy, and red enough to be minimally
affected by differential dust extinction. Narrow-line emission is a promising
alternative as it is also extended and, unlike radio, detectable in virtually
all optically selected AGN lenses. We present first results from a WFC3 grism
narrow-line survey of lensed quasars, for the quadruply lensed AGN HE0435-1223.
Using a forward modelling pipeline which enables us to robustly account for
spatial blending, we measure the [OIII] 5007 \AA~ flux ratios of the four
images. We find that the [OIII] fluxes and positions are well fit by a simple
smooth mass model for the main lens. Our data rule out a $M_{600}>10^{8}
(10^{7.2}) M_\odot$ NFW perturber projected within $\sim$1\farcs0 (0\farcs1)
arcseconds of each of the lensed images, where $M_{600}$ is the perturber mass
within its central 600 pc. The non-detection is broadly consistent with the
expectations of $\Lambda$CDM for a single system. The sensitivity achieved
demonstrates that powerful limits on the nature of dark matter can be obtained
with the analysis of $\sim20$ narrow-line lenses. | Report from the Tri-Agency Cosmological Simulation Task Force: The Tri-Agency Cosmological Simulations (TACS) Task Force was formed when
Program Managers from the Department of Energy (DOE), the National Aeronautics
and Space Administration (NASA), and the National Science Foundation (NSF)
expressed an interest in receiving input into the cosmological simulations
landscape related to the upcoming DOE/NSF Vera Rubin Observatory (Rubin),
NASA/ESA's Euclid, and NASA's Wide Field Infrared Survey Telescope (WFIRST).
The Co-Chairs of TACS, Katrin Heitmann and Alina Kiessling, invited community
scientists from the USA and Europe who are each subject matter experts and are
also members of one or more of the surveys to contribute. The following report
represents the input from TACS that was delivered to the Agencies in December
2018. |
Revised Supernova Rates from the IfA Deep Survey: The IfA Deep survey uncovered ~130 thermonuclear supernovae (TNSNe, i.e. Type
Ia) candidates at redshifts from z=0.1 out to beyond z=1. The TNSN explosion
rates derived from these data have been controversial, conflicting with
evidence emerging from other surveys. This work revisits the IfA Deep survey to
re-evaluate the photometric evidence. Applying the SOFT program to the light
curves of all SN candidates, we derive new classification grades and redshift
estimates. We find a volumetric rate for z~0.5 that is substantially smaller
than the originally published values, bringing the revised IfA Deep rate into
good agreement with other surveys. With our improved photometric analysis
techniques, we are able to confidently extend the rate measurements to higher
redshifts, and we find a steadily increasing TNSN rate, with no indication of a
peak out to z=1.05. | The Role of Self Interactions in the Cosmological Evolution of Warm Dark
Matter: In this work we present a summary of recent studies on the effects of elastic
self interactions in the evolution of Warm Dark Matter models (WDM), focusing
on structure formation and the evolution of cosmological perturbations. We pay
special attention to a particular class of sterile neutrino WDM known as
$\nu$MSM and provide examples for the case of vector field self interactions.
We calculate the effects of assuming self interacting dark matter in X-Ray
astrophysical observations, in the formation of fermionic DM halos in (quasi)
equilibrium states and in the evolution of DM perturbations in the early
universe, assuming particle masses between $\mathcal{O}(1-100)$ keV. In the
latter topic, we perform simulations using a modification to the public
Boltzmann solver CLASS and compare our results with observations. We find self
interactions to be an interesting addition to WDM models, which can alleviate
tensions both present in standard CDM cosmology and regarding WDM itself, as
well as provide an interesting avenue for DM halo formation. |
Could M31 be the result of a major merger?: We investigated a scenario in which M31 could be the remnant of a gas-rich
major merger. Galaxy merger simulations, highly constrained by observations,
were run using GADGET 2 in order to reproduce M31. We succeeded in reproducing
the global shape of M31, the thin disk and the bulge, and in addition some of
the main M31 large-scale features, such as the thick disk, the 10kpc ring and
the Giant Stream. This lead to a new explanation of the Giant Stream which
could be caused by tidal tail stars that have been captured by the galaxy
potential. | The properties of a large volume-limited sample of face-on low surface
brightness disk galaxies: We select a large volume-limited sample of low surface brightness galaxies
(LSBGs, 2,021) to investigate their statistical properties and their
differences from high surface brightness galaxies (HSBGs, 3,639) in details.
The distributions of stellar masses of LSBGs and HSBGs are nearly the same and
they have the same median values. Thus this volume-limited sample have good
completeness and further remove the effect of stellar masses on their other
properties when we compare LSBGs and HSBGs. We found that LSBGs tend to have
lower stellar metallicities, and lower effect dust attenuations indicating that
they have lower dust, than HSBGs. The LSBGs have relatively higher stellar
mass-to-light ratios, higher gas fraction, lower star forming rates (SFRs), and
lower specific SFRs than HSBGs. Moreover, with the decreasing surface
brightness, gas fraction increase, while the SFRs and specific SFRs decrease
rapidly for the sample galaxies. This could mean that the star formation
histories between LSBGs and HSBGs are different, HSBGs may have stronger star
forming activities than LSBGs. |
Breaking the baryon-dark matter degeneracy in a model-independent way
through the Sunyaev-Zeldovich effect: We propose a model-independent \textit{B\'ezier parametric interpolation} to
alleviate the degeneracy between baryonic and dark matter abundances by means
of intermediate-redshift data. To do so, we first interpolate the observational
Hubble data to extract cosmic bounds over the (reduced) Hubble constant, $h_0$,
and interpolate the angular diameter distances, $D(z)$, of the galaxy clusters,
inferred from the Sunyaev-Zeldovich effect, constraining the spatial curvature,
$\Omega_k$. Through the so-determined Hubble points and $D(z)$, we interpolate
uncorrelated data of baryonic acoustic oscillations bounding the baryon
($\omega_b = h^2_0\Omega_b$) and total matter ($\omega_m = h^2_0\Omega_m$)
densities, reinforcing the constraints on $h_0$ and $\Omega_k$ with the same
technique. Instead of pursuing the usual treatment to fix $\omega_b$ via the
value obtained from the cosmic microwave background to remove the matter sector
degeneracy, we here interpolate the acoustic parameter from correlated baryonic
acoustic oscillations. The results of our Monte Carlo--Markov chain simulations
turn out to agree at $1$--$\sigma$ confidence level with the flat $\Lambda$CDM
model. While our findings are roughly suitable at $1$--$\sigma$ with its
non-flat extension too, the Hubble constant appears in tension up to the
$2$--$\sigma$ confidence level. Accordingly, we also reanalyze the Hubble
tension with our treatment and find our expectations slightly match local
constraints. | A convolutional-neural-network estimator of CMB constraints on dark
matter energy injection: We show that the impact of energy injection by dark matter annihilation on
the cosmic microwave background power spectra can be apprehended via a residual
likelihood map. By resorting to convolutional neural networks that can fully
discover the underlying pattern of the map, we propose a novel way of
constraining dark matter annihilation based on the Planck 2018 data. We
demonstrate that the trained neural network can efficiently predict the
likelihood and accurately place bounds on the annihilation cross-section in a
$\textit{model-independent}$ fashion. The machinery will be made public in the
near future. |
Structure formation in a $Λ$ $viscous$ CDM universe: The possibility of dark matter being a dissipative component represents an
option for the standard view where cold dark matter (CDM) particles behave on
large scales as an ideal fluid. By including a physical mechanism to the dark
matter description like viscosity we construct a more realistic model for the
universe. Also, the known small scale pathologies of the standard CDM model
either disappear or become less severe. We study clustering properties of a
$\Lambda$CDM-like model in which dark matter is described as a bulk viscous
fluid. The linear power spectrum, the nonlinear spherical "top hat" collapse
and the mass functions are presented. We use the analysis with such structure
formation tools in order to place an upper bound on the magnitude of the dark
matter's viscosity. | Vector Fuzzy Dark Matter, Fifth Forces, and Binary Pulsars: We study the secular effects that an oscillating background ultralight
(fuzzy) cosmological vector field has on the dynamics of binary systems; such
effects appear when the field and the binary are in resonance. We first
consider the gravitational interaction between the field and the systems, and
quantify the main differences with an oscillating background scalar field. If
the energy density of such a field is sufficiently large, as required if it is
supposed to be all of the dark matter, we show that the secular effects could
yield potentially observable signatures in high precision time of arrival
measurements of binary pulsars. We then analyse the secular effects that arise
when the field is directly coupled to the bodies in the binary. We show that
this study is particularly relevant for models where fuzzy dark matter mediates
a baryonic force $B$ (or $B-L$, with $L$ the lepton number), due to the stellar
amount of nucleons present in the stars. The constraints we obtain from current
data are already competitive with (or even more constraining than) laboratory
tests of the equivalence principle. |
Ambiguity in running spectral index with an extra light field during
inflation: At the beginning of inflation there could be extra dynamical scalar fields
that will soon disappear (become static) before the end of inflation. In the
light of multi-field inflation, those extra degrees of freedom may alter the
time-dependence of the original spectrum of the curvature perturbation. It is
possible to remove such fields introducing extra number of e-foldings prior to
$N_e\sim 60$, however such extra e-foldings may make the trans-Planckian
problem worse due to the Lyth bound. We show that such extra scalar fields can
change the running of the spectral index to give correction of $\pm 0.01$
without adding significant contribution to the spectral index. The corrections
to the spectral index (and the amplitude) could be important in considering
global behavior of the corrected spectrum, although they can be neglected in
the estimation of the spectrum and its spectral index at the pivot scale. The
ambiguity in the running of the spectral index, which could be due to such
fields, can be used to nullify tension between BICEP2 and Planck experiments. | Area spectrum of near-extremal SdS black holes via the new
interpretation of quasinormal modes: Motivated by the recent work about a new physical interpretation of
quasinormal modes by Maggiore, we investigate the quantization of near-extremal
Schwarzschild-de Sitter black holes in the four dimensional spacetime.
Following Kunstatter's method, we derive the area and entropy spectrum of
near-extremal Schwarzschild-de Sitter black holes which differs from Setare's
result. Furthermore, we find that the derived a universal area spectrum is
$2\pi n$ which is equally spaced. |
Star Formation and Substructure in Galaxy Clusters: We investigate the relationship between star formation (SF) and substructure
in a sample of 107 nearby galaxy clusters using data from the Sloan Digital Sky
Survey (SDSS). Several past studies of individual galaxy clusters have
suggested that cluster mergers enhance cluster SF, while others find no such
relationship. The SF fraction in multi-component clusters (0.228 +/- 0.007) is
higher than that in single-component clusters (0.175 +/- 0.016) for galaxies
with M^0.1_r < -20.5. In both single- and multi-component clusters, the
fraction of star-forming galaxies increases with clustercentric distance and
decreases with local galaxy number density, and multi-component clusters show a
higher SF fraction than single-component clusters at almost all clustercentric
distances and local densities. Comparing the SF fraction in individual clusters
to several statistical measures of substructure, we find weak, but in most
cases significant at greater than 2 sigma, correlations between substructure
and SF fraction. These results could indicate that cluster mergers may cause
weak but significant SF enhancement in clusters, or unrelaxed clusters exhibit
slightly stronger SF due to their less evolved states relative to relaxed
clusters. | Precision growth index using the clustering of cosmic structures and
growth data: We use the clustering properties of Luminous Red Galaxies (LRGs) and the
growth rate data provided by the various galaxy surveys in order to constrain
the growth index ($\gamma$) of the linear matter fluctuations. We perform a
standard $\chi^2$-minimization procedure between theoretical expectations and
data, followed by a joint likelihood analysis and we find a value of
$\gamma=0.56\pm 0.05$, perfectly consistent with the expectations of the
$\Lambda$CDM model, and $\Omega_{m0} =0.29\pm 0.01$, in very good agreement
with the latest Planck results. Our analysis provides significantly more
stringent growth index constraints with respect to previous studies, as
indicated by the fact that the corresponding uncertainty is only $\sim 0.09
\gamma$. Finally, allowing $\gamma$ to vary with redshift in two manners
(Taylor expansion around $z=0$, and Taylor expansion around the scale factor),
we find that the combined statistical analysis between our clustering and
literature growth data alleviates the degeneracy and obtain more stringent
constraints with respect to other recent studies. |
Improvements in cosmological constraints from breaking growth degeneracy: The key probes of the growth of large-scale structure are its rate $f$ and
amplitude $\sigma_8$. Redshift space distortions in the galaxy power spectrum
allow us to measure only the combination $f\sigma_8$, which can be used to
constrain the standard cosmological model or alternatives. By using
measurements of the galaxy-galaxy lensing cross-correlation spectrum or of the
galaxy bispectrum, it is possible to break the $f\sigma_8$ degeneracy and
obtain separate estimates of $f$ and $\sigma_8$ from the same galaxy sample.
Currently there are only a handful of such separate measurements, but even this
allows for improved constraints on cosmological models. We explore how having a
larger and more precise sample of such measurements in the future could
constrain further cosmological models. We consider what can be achieved by a
future nominal sample that delivers a $\sim 1\%$ constraint on $f$ and
$\sigma_8$ separately, compared to the case with a similar precision on the
combination $f\sigma_8$. For the six cosmological parameters of $\Lambda$CDM,
we find improvements of $\sim\! 5$--$50\%$ on their constraints. For modified
gravity models in the Horndeski class, the improvements on these standard
parameters are $\sim\! 0$--$15\%$. However, the precision on the sum of
neutrino masses improves by 65\% and there is a significant increase in the
precision on the background and perturbation Horndeski parameters. | The integrated 3-point correlation function of cosmic shear: We present the integrated 3-point shear correlation function $i\zeta_{\pm}$
-- a higher-order statistic of the cosmic shear field -- which can be directly
estimated in wide-area weak lensing surveys without measuring the full 3-point
shear correlation function, making this a practical and complementary tool to
2-point statistics for weak lensing cosmology. We define it as the 1-point
aperture mass statistic $M_{\mathrm{ap}}$ measured at different locations on
the shear field correlated with the corresponding local 2-point shear
correlation function $\xi_{\pm}$. Building upon existing work on the integrated
bispectrum of the weak lensing convergence field, we present a theoretical
framework for computing the integrated 3-point function in real space for any
projected field within the flat-sky approximation and apply it to cosmic shear.
Using analytical formulae for the non-linear matter power spectrum and
bispectrum, we model $i\zeta_{\pm}$ and validate it on N-body simulations
within the uncertainties expected from the sixth year cosmic shear data of the
Dark Energy Survey. We also explore the Fisher information content of
$i\zeta_{\pm}$ and perform a joint analysis with $\xi_{\pm}$ for two
tomographic source redshift bins with realistic shape-noise to analyse its
power in constraining cosmological parameters. We find that the joint analysis
of $\xi_{\pm}$ and $i\zeta_{\pm}$ has the potential to considerably improve
parameter constraints from $\xi_{\pm}$ alone, and can be particularly useful in
improving the figure of merit of the dynamical dark energy equation of state
parameters from cosmic shear data. |
Estimation of the masses in the Local Group by Gradient Boosted Decision
Trees: Our goal is to estimate the mass of the Local Group (LG) and the individual
masses of its primary galaxies, the M31 and the Milky Way (MW). We do this by
means of a supervised machine learning algorithm, the gradient boosted decision
trees (GBDT) and using the observed distance and relative velocity of the two
as input parameters. The GBDT is applied to a sample of 2148 mock LGs drawn
from a set of 5 dark matter (DM)-only simulations, ran within the standard
$\Lambda$CDM\ cosmological model. The selection of the mock LGs is guided by a
LG model, which defines such objects. The role of the observational
uncertainties of the input parameters is gauged by applying the model to an
ensemble of mock LGs pairs whose observables are these input parameters
perturbed by their corresponding observational errors. Finally the
observational data of the actual LG is used to infer its relevant masses. Our
main results are the sum and the individual masses of the MW and M31: $M_{tot}
= 3.31 ^{+0.79}_{-0.67} $, $M_{MW}=1.15^{+0.25}_{-0.22}$ and
$M_{M31}=2.01^{+0.65}_{-0.39} \ \ \times 10^{12}M_{\odot}$ (corresponding to
the median and the 1st and 3rd quartiles). The ratio of the masses is
$M_{M31}/M_{MW}=1.75^{+0.54}_{-0.28}$, where by convention the M31 is defined
here to be the more massive of the two halos. | New MGCAMB tests of gravity with CosmoMC and Cobaya: We present a new version of MGCAMB, a patch for the Einstein-Boltzmann solver
CAMB for cosmological tests of gravity. New features include a new cubic-spline
parameterization allowing for a simultaneous reconstruction of $\mu$, $\Sigma$
and the dark energy density fraction $\Omega_X$ as functions of redshift, the
option to work with a direct implementation of $\mu$, $\Sigma$ (instead of
converting to $\mu$, $\gamma$ first), along with the option to test models with
a scalar field coupled only to dark matter, and the option to include dark
energy perturbations when working with $w\ne -1$ backgrounds, to restore
consistency with CAMB in the GR limit. This version of MGCAMB comes with a
Python wrapper to run it directly from the Python interface, an implementation
in the latest version of CosmoMC, and can be used with Cobaya. |
Redshift drift test of exotic singularity universes: We discuss how dynamical dark energy universes with exotic singularities may
be distinguished from the standard $\Lambda$CDM model on the basis of their
redshift drift signal, for which measurements both in the acceleration phase
and in the deep matter era will be provided by forthcoming astrophysical
facilities. Two specific classes of exotic singularity models are studied:
sudden future singularity models and finite scale factor singularity models. In
each class we identify the models which can mimic $\Lambda$CDM and play the
role of dark energy as well as models for which redshift drift signals are
significantly different from $\Lambda$CDM and the test can differentiate
between them. | A Bayesian ILC method for CMB B-mode posterior estimation and
reconstruction of primordial gravity wave signal: The Cosmic Microwave Background (CMB) radiation B mode polarization signal
contains the unique signature of primordial metric perturbations produced
during the inflation. The separation of the weak CMB B-mode signal from strong
foreground contamination in observed maps is a complex task, and proposed new
generation low noise satellite missions compete with the weak signal level of
this gravitational background. In this article, for the first time, we employ a
foreground model-independent internal linear combination (ILC) method to
reconstruct the CMB B mode signal using simulated observations over large
angular scales of the sky of 6 frequency bands of future generation CMB mission
Probe of Inflation and Cosmic Origins (PICO). We estimate the joint CMB B mode
posterior density following the interleaving Gibbs steps of B mode angular
power spectrum and cleaned map samples using the ILC method. We extend and
improve the earlier reported Bayesian ILC method to analyze weak CMB B mode
reconstruction by introducing noise bias corrections at two stages during the
ILC weight estimation. By performing $200$ Monte Carlo simulations of the
Bayesian ILC method, we find that our method can reconstruct the CMB signals
and the joint posterior density accurately over large angular scales of the
sky. We estimate Blackwell-Rao statistics of the marginal density of CMB B mode
angular power spectrum and use them to estimate the joint density of scalar to
tensor ratio $r$ and a lensing power spectrum amplitude $A^{\textrm{lens}}$.
Using $200$ Monte Carlo simulations of the delensing approach, we find that our
method can achieve an unbiased detection of the primordial gravitational wave
signal $r$ with more than 8$\sigma$ significance for levels of $r \geqslant
0.01$. |
The Deep SWIRE Field III. WIYN Spectroscopy: We present the results of spectroscopy using HYDRA on the WIYN 3.5m telescope
of objects in the deep SWIRE radio field. The goal of the project was to
determine spectroscopic redshifts for as many of the brighter objects in the
field as possible, especially those detected in the radio and at 24 microns.
These redshifts are primarily being used in studies of galaxy evolution and the
connection of that evolution to AGN and star-formation. Redshifts measured for
365 individual objects are reported. The redshifts range from 0.03 to 2.5,
mostly with z < 0.9. The sources were selected to be within the WIYN HYDRA
field of approximately 30' in radius from the center of the SWIRE deep field,
10h46m00s, 59d 01'00" (J2000). Optical sources for spectroscopic observation
were selected from a r-band image of the field. A priority list of
spectroscopic targets was established in the following order: 20cm detections,
24 micron detections, galaxies with r < 20 and the balance made up of fainter
galaxies in the field. We provide a table listing the galaxy positions,
measured redshift and error, and note any emission lines that were visible in
the spectrum. In practice almost all the galaxies with r < 19 were observed
including all of the radio sources and most of the 24 microns sources with r <
20 and a sample of radio sources which had fainter optical counterparts on the
r-band image. | Slowly rotating gas-rich galaxies in modified Newtonian dynamics (MOND): We have carried out a search for gas-rich dwarf galaxies that have lower
rotation velocities in their outskirts than MOdified Newtonian Dynamics (MOND)
predicts, so that the amplitude of their rotation curves cannot be fitted by
arbitrarily increasing the mass-to-light ratio of the stellar component or by
assuming additional undetected matter. With presently available data, the
gas-rich galaxies UGC 4173, Holmberg II, ESO 245-G05, NGC 4861 and ESO 364-G029
deviate most from MOND predictions and, thereby, provide a sample of promising
targets in testing the MOND framework. In the case of Holmberg II and NGC 4861,
we find that their rotation curves are probably inconsistent with MOND, unless
their inclinations and distances differ significantly from the nominal ones.
The galaxy ESO 364-G029 is a promising target because its baryonic mass and
rotation curve are similar to Holmberg II but presents a higher inclination.
Deeper photometric and HI observations of ESO 364-G029, together with further
decreasing systematic uncertainties, may provide a strong test to MOND. |
A 325-MHz GMRT survey of the Herschel-ATLAS/GAMA fields: We describe a 325-MHz survey, undertaken with the Giant Metrewave Radio
Telescope (GMRT), which covers a large part of the three equatorial fields at
9, 12 and 14.5 h of right ascension from the Herschel-Astrophysical Terahertz
Large Area Survey (H-ATLAS) in the area also covered by the Galaxy And Mass
Assembly survey (GAMA). The full dataset, after some observed pointings were
removed during the data reduction process, comprises 212 GMRT pointings
covering ~90 deg^2 of sky. We have imaged and catalogued the data using a
pipeline that automates the process of flagging, calibration, self-calibration
and source detection for each of the survey pointings. The resulting images
have resolutions of between 14 and 24 arcsec and minimum rms noise (away from
bright sources) of ~1 mJy/beam, and the catalogue contains 5263 sources
brighter than 5 sigma. We investigate the spectral indices of GMRT sources
which are also detected at 1.4 GHz and find them to agree broadly with
previously published results; there is no evidence for any flattening of the
radio spectral index below S_1.4=10 mJy. This work adds to the large amount of
available optical and infrared data in the H-ATLAS equatorial fields and will
facilitate further study of the low-frequency radio properties of star
formation and AGN activity in galaxies out to z~1. | Radio structure of the blazar 1156+295 with sub-pc resolution: 1156+295 is a flat-spectrum quasar which is loud at radio and gamma-ray.
Previous observations of the source revealed a radio morphology on pc to kpc
scales consistent with a helical jet model. In our present research, this
source was observed with the VLBA at 86, 43 and 15 GHz on four epochs from 10
May 2003 to 13 March 2005 aiming at studying the structure of the innermost jet
in order to understand the relation between the helical structure and the
astrophysical processes in the central engine. A core-jet structure with six
jet components is identified. The apparent transverse velocities of the six jet
components derived from proper motion measurements are in the range between 3.6
c and 11.6 c. The overall jet shape shows oscillatory morphology with multiple
curvatures on pc scales which might be indicative of a helical pattern. Models
of helical jet are discussed on the basis of both Kelvin-Helmholtz (K-H)
instability and jet precession. The K-H instability model shows better
agreement with the observed data. The overall radio structure on the scale from
sub-pc to kpc appears to be fitted with a hydrodynamic model with the
fundamental helical mode in Kelvin-Helmholtz (K-H) instability. This helical
mode with an initial characteristic wavelength of 0.2 pc is excited at the base
of the jet on the scale of 0.005 pc (or 1000R_s, the typical size of the broad
line region for a super massive black hole of $4.3\times10^8M_{\odot}$). A
presessing jet model can also fit the observed jet structure on the scale
between 10 pc and 300 pc. However, additional astrophysical processes may be
required for the presessing jet model in order to explain the bendings on the
inner jet structure (1 to 10 pc) and re-collimation of the large scale jet
outflow (>300 pc). |
The Frequency of Tidal Features Associated with Nearby Luminous
Elliptical Galaxies from a Statistically Complete Sample: We present a deep broadband optical imaging study of a complete sample of
luminous elliptical galaxies (M_B<-20) at distances 15 Mpc - 50 Mpc, selected
from the Tully catalog of nearby galaxies. The images are flat to ~0.35% across
the 20' field and reach a V band depth of 27.7 mag arcsec^-2. We derive an
objective tidal interaction parameter for all galaxies and find that 73% of
them show tidal disturbance signatures in their stellar bodies. This is the
first time that such an analysis is done on a statistically complete sample and
it confirms that tidal features in ellipticals are common even in the local
Universe. From the dynamical time of the sample galaxies at the innermost
radius where tidal features are detected we estimate the mass assembly rate of
nearby ellipticals to be dM/M 0.2 per Gyr with large uncertainty. We explore
the relation between gravitational interaction signatures and the galaxy
environment and find that galaxies in clusters are less disturbed than group
and field galaxies. We also study how these interactions affect the broadband
colors of ellipticals and find a moderate correlation, suggesting that the
mergers are not accompanied by significant star-formation. Lastly, we find no
correlation between AGN activity, as measured by 6cm radio emission, and large
scale tidal distortions. This implies that gravitational interactions are not
the only, and perhaps not the most important, trigger of nuclear activity. In
summary, we find that elliptical galaxies in groups and low density
environments continue to grow at the present day through mostly "dry" mergers
involving little star formation. | The 21-cm signature of the first stars during the Lyman-Werner feedback
era: The formation of the first stars is an exciting frontier area in astronomy.
Early redshifts z ~ 20 have become observationally promising as a result of a
recently recognized effect of a supersonic relative velocity between the dark
matter and gas. This effect produces prominent structure on 100 comoving Mpc
scales, which makes it much more feasible to detect 21-cm fluctuations from the
epoch of first heating. We use semi-numerical hybrid methods to follow for the
first time the joint evolution of the X-ray and Lyman-Werner radiative
backgrounds, including the effect of the supersonic streaming velocity on the
cosmic distribution of stars. We incorporate self-consistently the negative
feedback on star formation induced by the Lyman-Werner radiation, which
dissociates molecular hydrogen and thus suppresses gas cooling. We find that
the feedback delays the X-ray heating transition by a Delta z ~ 2, but leaves a
promisingly large fluctuation signal over a broad redshift range. The
large-scale power spectrum is predicted to reach a maximal signal-to-noise
ratio of S/N ~ 3-4 at z ~ 18 (for a projected first-generation instrument),
with S/N > 1 out to z ~ 22-23. We hope to stimulate additional numerical
simulations as well as observational efforts focused on the epoch prior to
cosmic reionization. |
Gravity-driven magnetogenesis: Structure formation heralds the era of deviation of the matter content of the
Universe away from thermal equilibrium, so the gravitational contribution to
entropy, in the form of Weyl curvature, must become active in order for the
overall entropy of the Universe to remain increasing. The tidal and frame
dragging sectors of the Weyl tensor must inevitably both be present in this
dynamic environment, as they mutually induce each other. The frame dragging
effect is able to impress vorticity onto the plasma current arising due to the
mass disparity between electrons and protons, which in turn begets a magnetic
field from none. We show that this gravity-driven magnetogenesis mechanism,
besides being able to operate outside of galaxies, thus facilitate large
coherence length scales, may be able to generate the field strength necessary
to seed dynamo processes. | The effect of inhomogeneities on the distance to the last scattering
surface and the accuracy of the CMB analysis: The standard analysis of the CMB data assumes that the distance to the last
scattering surface can be calculated using the distance-redshift relation as in
the Friedmann model. However, in the inhomogeneous universe, even if
<\delta\rho> =0, the distance relation is not the same as in the unperturbed
universe. This can be of serious consequences as a change of distance affects
the mapping of CMB temperature fluctuations into the angular power spectrum. In
addition, if the change of distance is relatively uniform no new temperature
fluctuations are generated. It is therefore a different effect than the lensing
or ISW effects which introduce additional CMB anisotropies. This paper shows
that the accuracy of the CMB analysis can be impaired by the accuracy of
calculation of the distance within the cosmological models. Since this effect
has not been fully explored before, to test how the inhomogeneities affect the
distance-redshift relation, several methods are examined: the Dyer-Roeder
relation, lensing approximation, and non-linear Swiss-Cheese model. In all
cases, the distance to the last scattering surface is different than when
homogeneity is assumed. The difference can be as low as 1% and as high as 80%.
Excluding extreme cases, the distance changes by about 20-30%. Since the
distance to the last scattering surface is set by the position of the CMB
peaks, in order to have a good fit, the distance needs to be adjusted. After
correcting the distance, the cosmological parameters change. Therefore, a not
properly estimated distance to the last scattering surface can be a major
source of systematics. This paper shows that if inhomogeneities are taken into
account when calculating the distance then models with positive spatial
curvature and with \Omega_\Lambda ~ 0.8-0.9 are preferred. The \Lambda CDM
model in most cases, is at odds with the current data. |
Intermediate-Age Stellar Populations in Classical QSO Host Galaxies: Although mergers and starbursts are often invoked in the discussion of QSO
activity in the context of galaxy evolution, several studies have questioned
their importance or even their presence in QSO host galaxies. Accordingly, we
are conducting a study of z~0.2 QSO host galaxies previously classified as
passively evolving elliptical galaxies. We present deep Keck LRIS spectroscopy
of a sample of 15 hosts and model their stellar absorption spectra using
stellar synthesis models. The high S/N of our spectra allow us to break various
degeneracies that arise from different combinations of models, varying
metallicities, and contamination from QSO light. We find that none of the host
spectra can be modeled by purely old stellar populations and that the majority
of the hosts (14/15) have a substantial contribution from intermediate-age
populations with ages ranging from 0.7 to 2.4 Gyr. An average host spectrum is
strikingly well fit by a combination of an old population and a 2.1 (+0.5,
-0.7) Gyr population. The morphologies of the host galaxies suggest that these
aging starbursts were induced during the early stages of the mergers that
resulted in the elliptical-shaped galaxies that we observe. The current AGN
activity likely corresponds to the late episodes of accretion predicted by
numerical simulations, which occur near the end of the mergers, whereas earlier
episodes may be more difficult to observe due to obscuration. Our off-axis
observations prevent us from detecting any current star formation or young
stellar populations that may be present in the central few kiloparsecs. | The CMB lensing bi-spectrum as a probe of modified gravity theories: Cosmological structures grow differently in theories of gravity which are
modified as compared to Einstein's General relativity (GR). Cosmic microwave
background (CMB) fluctuation patterns at the last scattering surface are lensed
by these structures along the photon path to the observer. The observed CMB
pattern therefore keeps trace of the growth history of structures. We show that
observations of the CMB lensing bi-spectrum offer an interesting way to
constrain deviations from GR in a broad class of scalar-tensor theories of
gravity called "beyond Horndeski". We quantify how the constraints on generic
parameters describing the deviations from GR depend on the effective multipole
range of the analysis. Our results further indicate that an accurate nonlinear
correction of the matter bi-spectrum in the modified gravity considered is
necessary when the bi-spectrum is used to probe scales beyond a multipole
$\ell_{\rm max} \gtrsim 1500$. We also found that the results are insensitive
to details of the implementation of the screening mechanism, at very small
scales. We finally demonstrate the potential of the lensing bi-spectrum to
provide a blind reconstruction of the redshift evolution of our modified
gravity parameters by combining the analysis of CMB and low-z source lensing
data. |
On the Correlations between Galaxy Properties and Supermassive Black
Hole Mass: We use a large sample of upper limits and accurate estimates of supermassive
black holes masses coupled with libraries of host galaxy velocity dispersions,
rotational velocities and photometric parameters extracted from Sloan Digital
Sky Survey i-band images to establish correlations between the SMBH and host
galaxy parameters. We test whether the mass of the black hole, MBH, is
fundamentally driven by either local or global galaxy properties. We explore
correlations between MBH and stellar velocity dispersion sigma, bulge
luminosity, bulge mass Sersic index, bulge mean effective surface brightness,
luminosity of the galaxy, galaxy stellar mass, maximum circular velocity Vc,
galaxy dynamical and effective masses. We verify the tightness of the MBH-sigma
relation and find that correlations with other galaxy parameters do not yield
tighter trends. We do not find differences in the MBH-sigma relation of barred
and unbarred galaxies. The MBH-sigma relation of pseudo-bulges is also coarser
and has a different slope than that involving classical bulges. The MBH-bulge
mass is not as tight as the MBH-sigma relation, despite the bulge mass proving
to be a better proxy of MBH than bulge luminosity. We find a rather poor
correlation between MBH and Sersic index suggesting that MBH is not related to
the bulge light concentration. The correlations between MBH and galaxy
luminosity or mass are not a marked improvement over the MBH sigma relation. If
Vc is a proxy for the dark matter halo mass, the large scatter of the MBH-Vc
relation then suggests that MBH is more coupled to the baryonic rather than the
dark matter. We have tested the need for a third parameter in the MBH scaling
relations, through various linear correlations with bulge and galaxy
parameters, only to confirm that the fundamental plane of the SMBH is mainly
driven by sigma, with a small tilt due to the effective radius. (Abridged) | Comparing halo bias from abundance and clustering: We model the abundance of haloes in the $\sim(3 \ \text{Gpc}/h)^3$ volume of
the MICE Grand Challenge simulation by fitting the universal mass function with
an improved Jack-Knife error covariance estimator that matches theory
predictions. We present unifying relations between different fitting models and
new predictions for linear ($b_1$) and non-linear ($c_2$ and $c_3$) halo
clustering bias. Different mass function fits show strong variations in their
performance when including the low mass range ($M_h \lesssim 3 \ 10^{12} \
M_{\odot}/h$) in the analysis. Together with fits from the literature we find
an overall variation in the amplitudes of around $10$% in the low mass and up
to $50$% in the high mass (galaxy cluster) range ($M_h > 10^{14} \
M_{\odot}/h$). These variations propagate into a $10$% change in $b_1$
predictions and a $50$% change in $c_2$ or $c_3$. Despite these strong
variations we find universal relations between $b_1$ and $c_2$ or $c_3$ for
which we provide simple fits. Excluding low mass haloes, different models
fitted with reasonable goodness in this analysis, show percent level agreement
in their $b_1$ predictions, but are systematically $5-10$% lower than the bias
directly measured with two-point halo-mass clustering. This result confirms
previous findings derived from smaller volumes (and smaller masses).
Inaccuracies in the bias predictions lead to $5-10$% errors in growth
measurements. They also affect any HOD fitting or (cluster) mass calibration
from clustering measurements. |
The Clustering of MgII Absorption Systems at z=0.5 and Detection of Cold
Gas in Massive Halos: We measure the large-scale clustering of MgII \lambda\lambda 2796,2803
absorbers with respect to a population of luminous red galaxies (LRGs) at z
\sim 0.5. From the cross-correlation measurements between MgII absorbers and
LRGs, we calculate the mean bias of the dark matter halos in which the
absorbers reside. We investigate systematic uncertainties in the clustering
measurements due to the sample selection of LRGs and due to uncertainties in
photometric redshifts. First, we compare the cross-correlation amplitudes
determined using a it flux-limited LRG sample and a volume-limited one. The
comparison shows that the relative halo bias of MgII absorbers using a
flux-limited LRG sample can be overestimated by as much as \approx 20%. Next,
we assess the systematic uncertainty due to photometric redshift errors using a
mock galaxy catalog with added redshift uncertainties comparable to the data.
We show that the relative clustering amplitude measured without accounting for
photometric redshift uncertainties is overestimated by \approx 10%. After
accounting for these two main uncertainties, we find a 1-\sigma
anti-correlation between mean halo bias and absorber strength that translates
into a 1-\sigma anti-correlation between mean galaxy mass and W_r(2796). The
results indicate that a significant fraction of the MgII absorber population of
W_r(2796)=1-1.5 \AA are found in group-size dark matter halos of log M_h <
13.4, whereas absorbers of W_r(2796)>1.5 \AA are seen in halos of log M_h
<12.7. A larger dataset would improve the precision of the clustering
measurements and the relationship between W_r and halo mass. Finally, the
strong clustering of MgII absorbers down to \sim 0.3 h^{-1} Mpc indicates the
presence of cool gas inside the virial radii of the halos hosting the LRGs. | Numerical complexity of the joint nulled weak-lensing probability
distribution function: In the context of tomographic cosmic shear surveys, there exists a nulling
transformation of weak lensing observations (also called BNT transform) that
allows us to simplify the correlation structure of tomographic cosmic shear
observations, as well as to build observables that depend only on a localised
range of redshifts and thus independent from the low-redshift/small-scale
modes. This procedure renders possible accurate, and from-first-principles,
predictions of the convergence and aperture mass one-point distributions (PDF).
We here explore other consequences of this transformation on the (reduced)
numerical complexity of the estimation of the joint PDF between nulled bins and
demonstrate how to use these results to make theoretical predictions. |
Cosmology with Rayleigh Scattering of the Cosmic Microwave Background: The cosmic microwave background (CMB) has been a treasure trove for
cosmology. Over the next decade, current and planned CMB experiments are
expected to exhaust nearly all primary CMB information. To further constrain
cosmological models, there is a great benefit to measuring signals beyond the
primary modes. Rayleigh scattering of the CMB is one source of additional
cosmological information. It is caused by the additional scattering of CMB
photons by neutral species formed during recombination and exhibits a strong
and unique frequency scaling ($\propto \nu^4$). We will show that with
sufficient sensitivity across frequency channels, the Rayleigh scattering
signal should not only be detectable but can significantly improve constraining
power for cosmological parameters, with limited or no additional modifications
to planned experiments. We will provide heuristic explanations for why certain
cosmological parameters benefit from measurement of the Rayleigh scattering
signal, and confirm these intuitions using the Fisher formalism. In particular,
observation of Rayleigh scattering allows significant improvements on
measurements of $N_{\rm eff}$ and $\sum m_\nu$. | High-Redshift Cosmography: We constrain the parameters describing the kinematical state of the universe
using a cosmographic approach, which is fundamental in that it requires a very
minimal set of assumptions (namely to specify a metric) and does not rely on
the dynamical equations for gravity. On the data side, we consider the most
recent compilations of Supernovae and Gamma Ray Bursts catalogues. This allows
to further extend the cosmographic fit up to $z = 6.6$, i.e. up to redshift for
which one could start to resolve the low z degeneracy among competing
cosmological models. In order to reliably control the cosmographic approach at
high redshifts, we adopt the expansion in the improved parameter $y = z/(1+z)$.
This series has the great advantage to hold also for $z > 1$ and hence it is
the appropriate tool for handling data including non-nearby distance
indicators. We find that Gamma Ray Bursts, probing higher redshifts than
Supernovae, have constraining power and do require (and statistically allow) a
cosmographic expansion at higher order than Supernovae alone. Exploiting the
set of data from Union and GRBs catalogues, we show (for the first time in a
purely cosmographic approach parametrized by deceleration $q_0$, jerk $j_0$,
snap $s_0$) a definitively negative deceleration parameter $q_0$ up to the
3$\sigma$ confidence level. We present also forecasts for realistic data sets
that are likely to be obtained in the next few years. |
Fast full N-body simulations of generic modified gravity: conformal
coupling models: We present MG-GLAM, a code developed for the very fast production of full
$N$-body cosmological simulations in modified gravity (MG) models. We describe
the implementation, numerical tests and first results of a large suite of
cosmological simulations for three classes of MG models with conformal coupling
terms: the $f(R)$ gravity, symmetron and coupled quintessence models. Derived
from the parallel particle-mesh code GLAM, MG-GLAM incorporates an efficient
multigrid relaxation technique to solve the characteristic nonlinear partial
differential equations of these models. For $f(R)$ gravity, we have included
new variants to diversify the model behaviour, and we have tailored the
relaxation algorithms to these to maintain high computational efficiency. In a
companion paper, we describe versions of this code developed for derivative
coupling MG models, including the Vainshtein- and K-mouflage-type models.
MG-GLAM can model the prototypes for most MG models of interest, and is broad
and versatile. The code is highly optimised, with a tremendous speedup of a
factor of more than a hundred compared with earlier $N$-body codes, while still
giving accurate predictions of the matter power spectrum and dark matter halo
abundance. MG-GLAM is ideal for the generation of large numbers of MG
simulations that can be used in the construction of mock galaxy catalogues and
the production of accurate emulators for ongoing and future galaxy surveys. | Rapid Decline of Lyman-alpha Emission Toward the Reionization Era: The observed deficit of strongly Lyman-alpha emitting galaxies at z>6.5 is
attributed to either increasing neutral hydrogen in the intergalactic medium
(IGM) and/or to the evolving galaxy properties. To investigate this, we have
performed very deep near-IR spectroscopy of z>7 galaxies using MOSFIRE on the
Keck-I Telescope. We measure the Lyman-alpha fraction at z~8 (combined
photometric redshift peak at z=7.7) using two methods. First, we derived
NLy{\alpha}/Ntot directly using extensive simulations to correct for
incompleteness. Second, we used a Bayesian formalism (introduced by Treu et al.
2012) that compares the z>7 galaxy spectra to models of the Lyman-alpha
equivalent width (WLy{\alpha}) distribution at z~6. We explored two simple
evolutionary scenarios: smooth evolution where Lyman-alpha is attenuated in all
galaxies by a constant factor (perhaps owing to processes from galaxy evolution
or a slowly increasing IGM opacity), and patchy evolution where Lyman-alpha is
blocked in some fraction of galaxies (perhaps due to the IGM being opaque along
only some fraction of sightlines). The Bayesian formalism places stronger
constraints compared with the direct method. Combining our data with that in
the literature we find that at z~8 the Lyman-alpha fraction has dropped by a
factor >3(84% confidence interval) using both the smooth and patchy scenarios
compared to the z~6 values. Furthermore, we find a tentative evidence that the
data favor the patchy scenario over smooth (with "positive" Bayesian evidence),
extending trends observed at z~7 to higher redshift. If this decrease is a
result of reionization as predicted by theory, then our data imply the volume
averaged neutral hydrogen fraction in the IGM to be >0.3 suggesting that the
reionization of the universe is in progress at z~8. |
Roles of $^7$Be$(n,p)^7$Li resonances in big bang nucleosynthesis with
time-dependent quark mass and Li reduction by a heavy quark mass: Big bang nucleosynthesis (BBN) has been used as a probe of beyond-standard
physics in the early Universe, which includes a time-dependent quark mass m_q.
We investigate effects of a quark mass variation delta m_q on the cross
sections of the 7Be(n, p)7Li reaction and primordial light element abundances
taking into account roles of 8Be resonances in the reaction during BBN. This
resonant reaction has not been investigated although behaviors of low-lying
resonances are not trivial. It is found that a resonance at the resonance
energy E_r=0.33 MeV enhances the reaction rate and lowers the 7Li abundance
significantly when the quark mass variation is negative. Based upon up-to-date
observational limits on primordial abundances of D, 4He and Li, the quark mass
variation in the BBN epoch are derived. In a model in which the resonance
energies of the reactions 3He(d, p)4He and 3H(d, n)4He are insensitive to the
quark mass, we find that the Li abundance can be consistent with observations
for delta m_q/m_q = (4--8) times 10^{-3}. | Analytic study of the effect of dark energy-dark matter interaction on
the growth of structures: Large-scale structure has been shown as a promising cosmic probe for
distinguishing and constraining dark energy models. Using the growth index
parametrization, we obtain an analytic formula for the growth rate of
structures in a coupled dark energy model in which the exchange of
energy-momentum is proportional to the dark energy density. We find that the
evolution of $f \sigma_8$ can be determined analytically once we know the
coupling, the dark energy equation of state, the present value of the dark
energy density parameter and the current mean amplitude of dark matter
fluctuations. After correcting the growth function for the correspondence with
the velocity field through the continuity equation in the interacting model, we
use our analytic result to compare the model's predictions with large-scale
structure observations. |
Constraining the second half of reionization with the Lyman-$β$
forest: We present an analysis of the evolution of the Lyman-series forest into the
epoch of reionization using cosmological radiative transfer simulations in a
scenario where reionization ends late. We explore models with different
midpoints of reionization and gas temperatures. We find that once the
simulations have been calibrated to match the mean flux of the observed
Lyman-$\alpha$ forest at $4 < z < 6$, they also naturally reproduce the
distribution of effective optical depths of the Lyman-$\beta$ forest in this
redshift range. We note that the tail of the largest optical depths that is
most challenging to match corresponds to the long absorption trough of ULAS
J0148+0600, which we have previously shown to be rare in our simulations. We
consider the evolution of the Lyman-series forest out to higher redshifts, and
show that future observations of the Lyman-$\beta$ forest at $z>6$ will
discriminate between different reionization histories. The evolution of the
Lyman-$\alpha$ and Lyman-$\gamma$ forests are less promising as a tool for
pushing studies of reionization to higher redshifts due to the stronger
saturation and foreground contamination, respectively. | Probing non-tensorial polarizations of stochastic gravitational-wave
backgrounds with ground-based laser interferometers: In a general metric theory of gravitation in four dimensions, six
polarizations of a gravitational wave are allowed: two scalar and two vector
modes, in addition to two tensor modes in general relativity. Such additional
polarization modes appear due to additional degrees of freedom in modified
theories of gravitation or theories with extra dimensions. Thus, observations
of gravitational waves can be utilized to constrain the extended models of
gravitation. In this paper, we investigate detectability of additional
polarization modes of gravitational waves, particularly focusing on a
stochastic gravitational-wave background, with laser-interferometric detectors
on the Earth. We found that multiple detectors can separate the mixture of
polarization modes in detector outputs, and that they have almost the same
sensitivity to each polarization mode of stochastic gravitational-wave
background. |
Is the dark energy equation of state parameter singular?: A dark energy with a negative energy density in the past can simultaneously
address various cosmological tensions, and if it is to be positive today to
drive the observed acceleration of the universe, we show that it should have a
pole in its equation of state parameter. More precisely, in a spatially uniform
universe, a perfect fluid (submitting to the usual continuity equation of local
energy conservation) whose energy density $\rho(z)$ vanishes at an isolated
zero $z=z_p$, necessarily has a pole in its equation of state parameter $w(z)$
at $z_p$, and, $w(z)$ diverges to positive infinity in the limit $z\to z_p^+$
and it diverges to negative infinity in the limit $z\to z_p^-$ -- we assume
that $z_p$ is not an accumulation point for poles of $w(z)$.
However, the converse statement that this kind of a pole of $w(z)$
corresponds to a vanishing energy density at that point is not true as we show
by a counterexample. An immediate implication of this result is that one should
be hesitant to observationally reconstruct the equation of state parameter of
the dark energy directly, and rather infer it from a directly reconstructed
dark energy density. | Intense look at Virgo Southern Extension: We collected data on radial velocities and distances of galaxies to elucidate
structure and kinematics of the filament attached to the Virgo cluster from
south. In the region RA = [12.5 - 13.5]h, Dec = [-20 - 0]deg there are 171
galaxies with radial velocities VLG < 2000 km/s, and 98 of them have distance
estimates. This galaxy cloud, called as "Virgo Southern Extension", is situated
just on the edge of the Virgo "zero-velocity surface". The mean distance to
Virgo SEx, 17pm2 Mpc, and the average radial velocity, 1172pm23 km/s, are very
close to the Virgo cluster ones. In Supergalactic coordinates the Virgo SEx
dimensions are 15x7x2 Mpc, where the major axis is directed along the line of
sight, the second-major axis looks towards the Virgo core and the minor one is
perpendicular to the Supergalactic plane. This flattened cloud consists of a
dozen virialized groups with the total K-band luminosity of 1.7cdot10^12 Lsol
and the total virial mass of 6.3cdot10^13 Msol, having a typical dark
matter-to-stellar matter ratio of 37. The Hubble diagram for Virgo SEx galaxies
exhibits a tendency of Z-shape wave with a velocity amplitude of ~250 km/s that
may be caused by a mass overdensity of ~6cdot10^13 Msol, and in order of
magnitude agrees with the sum of virial masses of the groups. |
The zCOSMOS redshift survey : Influence of luminosity, mass and
environment on the galaxy merger rate: The contribution of major mergers to galaxy mass assembly along cosmic time
is an important ingredient to the galaxy evolution scenario. We aim to measure
the evolution of the merger rate for both luminosity/mass selected galaxy
samples and investigate its dependence with the local environment. We use a
sample of 10644 spectroscopically observed galaxies from the zCOSMOS redshift
survey to identify pairs of galaxies destined to merge, using only pairs for
which the velocity difference and projected separation of both components with
a confirmed spectroscopic redshift indicate a high probability of merging. We
have identified 263 spectroscopically confirmed pairs with r_p^{max} = 100
h^{-1} kpc. We find that the density of mergers depends on luminosity/mass,
being higher for fainter/less massive galaxies, while the number of mergers a
galaxy will experience does not depends significantly on its intrinsic
luminosity but rather on its stellar mass. We find that the pair fraction and
merger rate increase with local galaxy density, a property observed up to
redshift z=1. We find that the dependence of the merger rate on the luminosity
or mass of galaxies is already present up to redshifts z=1, and that the
evolution of the volumetric merger rate of bright (massive) galaxies is
relatively flat with redshift with a mean value of 3*10^{-4} (8*10^{-5}
respectively) mergers h^3 Mpc^{-3} Gyr^{-1}. The dependence of the merger rate
with environment indicates that dense environments favors major merger events
as can be expected from the hierarchical scenario. The environment therefore
has a direct impact in shapping-up the mass function and its evolution
therefore plays an important role on the mass growth of galaxies along cosmic
time. | On the mass mismatch between simulations and weak-lensing measurements: The recently discovered discrepancy between galaxy mass measurements from
weak lensing and predictions from abundance matching questions our
understanding of cosmology, or of the galaxy-halo connection, or of both. We
re-examined this tension by considering, as models, different cosmological
simulations in the Illustris suite. We produced excess profiles $R\Delta\Sigma$
from subhalo snapshots at different redshifts in Illustris-1 and IllustrisTNG
(TNG100 and TNG300) simulations, enabling a direct comparison with weak-lensing
measurements. We separate the individual contributions of stars, dark matter
and gas within $\approx1$ Mpc (comoving length), beyond which correlated
two-halo terms dominate. The mismatch between measurements and predictions is
more severe than in previous studies: $R\Delta\Sigma$ profiles from
IllustrisTNG are $\approx2$ times higher than the measured ones. Contrary to
abundance matching results, the mismatch is mostly unchanged with increasing
redshifts. The contribution of gas to the $R\Delta\Sigma$ profiles is $5-10\%$
over the scales dominated by one-halo terms. Different procedures to link
stellar and halo masses (abundance matching, cosmological simulations) are
still significantly discrepant with weak lensing measurements, but their trends
are different. Therefore, the change in cosmological parameters advocated
through abundance-matching arguments may not resolve this tension. Also,
current criteria to select isolated massive galaxies in simulations are
susceptible to resolution issues and may not correspond to observational
criteria. The (currently subdominant) contribution of gas is non-negligible,
and even if the major discrepancy within stellar and halo masses is resolved,
it will be an appreciable source of systematics in the LSST era, when
uncertainties on the $R\Delta\Sigma$ profiles are expected to be $\approx10$
times smaller. |
Probing the Fundamental Nature of Dark Matter with the Large Synoptic
Survey Telescope: Astrophysical and cosmological observations currently provide the only
robust, empirical measurements of dark matter. Future observations with Large
Synoptic Survey Telescope (LSST) will provide necessary guidance for the
experimental dark matter program. This white paper represents a community
effort to summarize the science case for studying the fundamental physics of
dark matter with LSST. We discuss how LSST will inform our understanding of the
fundamental properties of dark matter, such as particle mass, self-interaction
strength, non-gravitational couplings to the Standard Model, and compact object
abundances. Additionally, we discuss the ways that LSST will complement other
experiments to strengthen our understanding of the fundamental characteristics
of dark matter. More information on the LSST dark matter effort can be found at
https://lsstdarkmatter.github.io/ . | The sizes of mini-voids in the local universe: an argument in favor of a
warm dark matter model?: Using high-resolution simulations within the Cold and Warm Dark Matter models
we study the evolution of small scale structure in the Local Volume, a sphere
of 8 Mpc radius around the Local Group. We compare the observed spectrum of
mini-voids in the Local Volume with the spectrum of mini-voids determined from
the simulations. We show that the \LWDM model can easily explain both the
observed spectrum of mini-voids and the presence of low-mass galaxies observed
in the Local Volume, provided that all haloes with circular velocities greater
than 20 km/s host galaxies. On the contrary within the LCDM model the
distribution of the simulated mini-voids reflects the observed one if haloes
with maximal circular velocities larger than 35 km/s host galaxies. This
assumption is in contradiction with observations of galaxies with circular
velocities as low as 20 km/s in our Local Universe. A potential problem of the
LWDM model could be the late formation of the haloes in which the gas can be
efficiently photo-evaporated. Thus star formation is suppressed and low-mass
haloes might not host any galaxy at all. |
Properties of the HII region populations of M51 and NGC 4449 from Halpha
images with ACS on HST: We have used the images from the ACS on HST in Halpha, and in the neighboring
continuum, to produce flux calibrated images of the large spiral galaxy M51,
and the dwarf irregular NGC 4449. From these images we have derived the
absolute luminosities in Halpha, the areas, and the positions with respect to
the galactic centers as reference points, of over 2600 HII regions in M51 and
over 270 HII regions in NGC 4449. Using this database we have derived
luminosity (L)--volume (V) relations for the regions in the two galaxies,
showing that within the error limits these obey the equation L ~ V^(2/3), which
differs from the linear relation expected for regions of constant uniform
electron density. We discuss briefly possible models which would give rise to
this behavior, notably models with strong density inhomogeneities within the
regions. Plotting the luminosity functions for the two galaxies we find a break
in the slope for M51 at log(L) = 38.5 dex (units in erg s^(-1)) for M51 in good
agreement with the previous ground-based study by Rand, and above this
luminosity NGC 4449 also shows a sharp decline in its luminosity function,
although the number of regions is too small to plot the function well at higher
luminosities. The cumulative diameter distribution for the HII regions of M51
shows dual behaviour, with a break at a radius close to 100 pc, the radius of
regions with the break luminosity. Here too we indicate the possible physical
implications. | Stellar kinematics and populations out to 1.5 effective radius in the
elliptical galaxy NGC4636: We present high quality long slit spectra along the major and minor axes out
to 1.5 effective radius ($R_e$) of the massive galaxy NGC4636 taken by
Hobby-Eberly Telescope (HET). Using Fourier Correlation Quotient (FCQ) method,
we measured the stellar line-of-sight velocity distribution along the axes.
Furthermore, six Lick/IDS indices
($H\beta,Mgb,Fe_{5015},Fe_{5270},Fe_{5335},Fe_{5406}$) are derived from the
clean spectrum. By comparing the measured absorption line strengths with the
predictions of Simple Stellar Populations (SSP) models, we derived ages, total
metallicity and $\alpha$ abundance profiles of the galaxy. This galaxy presents
old and $[\alpha/Fe]$ over abundant stellar populations. Indeed, using the SSP
model, we obtained the broadband color profiles. The theoretical colors match
well with the measured colors and present red sharp peaks at the galaxy center.
The sharp peaks of the colors are mainly shaped by the high metallicity in the
galaxy center. Interestingly, the galaxy has steep negative metallicity
gradients, but trend flattens outwards. This result likly suggests that the
center and outer regions of the galaxy formed through different formation
process. |
The Growth of Supermassive Black Holes Across Cosmic Time: One of the main themes in extragalactic astronomy for the next decade will be
the evolution of galaxies over cosmic time. Many future observatories,
including JWST, ALMA, GMT, TMT and E-ELT will intensively observe starlight
over a broad redshift range, out to the dawn of the modern Universe when the
first galaxies formed. It has, however, become clear that the properties and
evolution of galaxies are intimately linked to the growth of their central
black holes. Understanding the formation of galaxies, and their subsequent
evolution, will therefore be incomplete without similarly intensive
observations of the accretion light from supermassive black holes (SMBH) in
galactic nuclei. To make further progress, we need to chart the formation of
typical SMBH at z>6, and their subsequent growth over cosmic time, which is
most effectively achieved with X-ray observations. Recent technological
developments in X-ray optics and instrumentation now bring this within our
grasp, enabling capabilities fully matched to those expected from flagship
observatories at longer wavelengths. | Optimal Black Holes are the Cosmological Objects, which Minimize Volume
of Information in Areas of the Universe and in the Universe as a Whole: Black hole is called optimal if information content is minimal at the
University region, consisting of usual substance and one(n) black hole(s).
Optimal black hole mass does not depend on the mass of the Universe region.
Optimal black holes can exist when at least the two types of substance are
available in the Universe: with non-linear and linear correspondence between
information content and mass. Information content of optimal black hole is
proportional to squared coefficient correlating information content with mass
in usual substance and in inverse proportion to coefficient correlating
information content with black hole mass. Concentration of mass in optimal
black hole minimizes information content in the system "usual substance - black
holes". Minimal information content of the Universe consisting of optimal black
holes only is twice as less as information content available of the Universe of
the same mass filled with usual substance only. Under the radiation temperature
T \approx 1E + 12 K the mass of optimal black holes that emerged in the systems
"radiation - black hole" is equal to the mass of optimal black holes that
emerged in the systems "hydrogen (protons) - black hole". |
Estimating CDM Particle Trajectories in the Mildly Non-Linear Regime of
Structure Formation. Implications for the Density Field in Real and Redshift
Space: We obtain approximations for the CDM particle trajectories starting from
Lagrangian Perturbation Theory. These estimates for the CDM trajectories result
in approximations for the density in real and redshift space, as well as for
the momentum density that are better than what standard Eulerian and Lagrangian
perturbation theory give. For the real space density, we find that our proposed
approximation gives a good cross-correlation (>95%) with the non-linear density
down to scales almost twice smaller than the non-linear scale, and six times
smaller than the corresponding scale obtained using linear theory. This allows
for a speed-up of an order of magnitude or more in the scanning of the
cosmological parameter space with N-body simulations for the scales relevant
for the baryon acoustic oscillations. Possible future applications of our
method include baryon acoustic peak reconstruction, building mock galaxy
catalogs, momentum field reconstruction. | Galaxy And Mass Assembly (GAMA): Linking Star Formation Histories and
Stellar Mass Growth: We present evidence for stochastic star formation histories in low-mass (M* <
10^10 Msun) galaxies from observations within the Galaxy And Mass Assembly
(GAMA) survey. For ~73,000 galaxies between 0.05<z<0.32, we calculate star
formation rates (SFR) and specific star formation rates (SSFR = SFR/M*) from
spectroscopic Halpha measurements and apply dust corrections derived from
Balmer decrements. We find a dependence of SSFR on stellar mass, such that
SSFRs decrease with increasing stellar mass for star-forming galaxies, and for
the full sample, SSFRs decrease as a stronger function of stellar mass. We use
simple parametrizations of exponentially declining star formation histories to
investigate the dependence on stellar mass of the star formation timescale and
the formation redshift. We find that parametrizations previously fit to samples
of z~1 galaxies cannot recover the distributions of SSFRs and stellar masses
observed in the GAMA sample between 0.05<z<0.32. In particular, a large number
of low-mass (M* < 10^10 Msun) galaxies are observed to have much higher SSFRs
than can be explained by these simple models over the redshift range of
0.05<z<0.32, even when invoking mass-dependent staged evolution. For such a
large number of galaxies to maintain low stellar masses, yet harbour such high
SSFRs, requires the late onset of a weak underlying exponentially declining SFH
with stochastic bursts of star formation superimposed. |
The Simons Observatory: Constraining inflationary gravitational waves
with multi-tracer B-mode delensing: We introduce and validate a delensing framework for the Simons Observatory
(SO), which will be used to improve constraints on inflationary gravitational
waves (IGWs) by reducing the lensing noise in measurements of the $B$-modes in
CMB polarization. SO will initially observe CMB by using three small aperture
telescopes and one large-aperture telescope. While polarization maps from
small-aperture telescopes will be used to constrain IGWs, the internal CMB
lensing maps used to delens will be reconstructed from data from the
large-aperture telescope. Since lensing maps obtained from the SO data will be
noise-dominated on sub-degree scales, the SO lensing framework constructs a
template for lensing-induced $B$-modes by combining internal CMB lensing maps
with maps of the cosmic infrared background from Planck as well as galaxy
density maps from the LSST survey. We construct a likelihood for constraining
the tensor-to-scalar ratio $r$ that contains auto- and cross-spectra between
observed $B$-modes and the lensing $B$-mode template. We test our delensing
analysis pipeline on map-based simulations containing survey non-idealities,
but that, for this initial exploration, does not include contamination from
Galactic and extragalactic foregrounds. We find that the SO survey masking and
inhomogeneous and atmospheric noise have very little impact on the delensing
performance, and the $r$ constraint becomes $\sigma(r)\approx 0.0015$ which is
close to that obtained from the idealized forecasts in the absence of the
Galactic foreground and is nearly a factor of two tighter than without
delensing. We also find that uncertainties in the external large-scale
structure tracers used in our multi-tracer delensing pipeline lead to bias much
smaller than the $1\,\sigma$ statistical uncertainties. | Probing cosmology and gravity with redshift-space distortions around
voids: Cosmic voids in the large-scale structure of the Universe affect the peculiar
motions of objects in their vicinity. Although these motions are difficult to
observe directly, the clustering pattern of their surrounding tracers in
redshift space is influenced in a unique way. This allows to investigate the
interplay between densities and velocities around voids, which is solely
dictated by the laws of gravity. With the help of $N$-body simulations and
derived mock-galaxy catalogs we calculate the average density fluctuations
around voids identified with a watershed algorithm in redshift space and
compare the results with the expectation from general relativity and the
$\Lambda$CDM model. We find linear theory to work remarkably well in describing
the dynamics of voids. Adopting a Bayesian inference framework, we explore the
full posterior of our model parameters and forecast the achievable accuracy on
measurements of the growth rate of structure and the geometric distortion
through the Alcock-Paczynski effect. Systematic errors in the latter are
reduced from $\sim15\%$ to $\sim5\%$ when peculiar velocities are taken into
account. The relative parameter uncertainties in galaxy surveys with number
densities comparable to the SDSS MAIN (CMASS) sample probing a volume of
$1h^{-3}{\rm Gpc}^3$ yield $\sigma_{f/b}\left/(f/b)\right.\sim2\%$ ($20\%$) and
$\sigma_{D_AH}/D_AH\sim0.2\%$ ($2\%$), respectively. At this level of precision
the linear-theory model becomes systematics dominated, with parameter biases
that fall beyond these values. Nevertheless, the presented method is highly
model independent; its viability lies in the underlying assumption of
statistical isotropy of the Universe. |
The Planck legacy - Reinforcing the case for a standard model of
cosmology: $Λ$CDM: We present a brief review of the main results of the Planck 2015 release
describing the new calibration of the data, showing the maps delivered in
temperature and, for the first time, in polarization, the cosmological
parameters and the lensing potential. In addition we present a forecast of the
Galactic foregrounds in polarization. Future satellite experiments will have
the challenge to remove the foregrounds with great accuracy to be able to
measure a tensor-to-scalar ratio of less than 0.01. | Gravitational waves from binary black holes as probes of the structure
formation history: Gravitational-wave detectors on earth have detected gravitational waves from
merging compact objects in the local Universe. In future we will detect
gravitational waves from higher-redshift sources, which trace the high-redshift
structure formation history. That is, by observing high-redshift
gravitational-wave events we will be able to probe structure formation history.
This will provide additional insight into the early Universe when primordial
fluctuations are generated and also into the nature of dark matter. |
Orthogonal BipoSH measures : Scrutinizing sources of isotropy violation: The two point correlation function of the CMB temperature anisotropies is
generally assumed to be statistically isotropic (SI). Deviations from this
assumption could be traced to physical or observational artefacts and
systematic effects. Measurement of non-vanishing power in the BipoSH spectra is
a standard statistical technique to search for isotropy violations. Although
this is a neat tool allowing a blind search for SI violations in the CMB sky,
it is not easy to discern the cause of isotropy violation using this measure.
In this article, we propose a novel technique of constructing orthogonal BipoSH
estimators, which can be used to discern between models of isotropy violation. | Forecasts on dark energy from the X-ray cluster survey with eROSITA:
constraints from counts and clustering: We forecast the potential of the forthcoming X-ray galaxy-cluster survey with
eROSITA to constrain dark-energy models. We focus on spatially-flat
cosmological scenarios with either constant or time-dependent dark-energy
equation-of-state parameters. Fisher information is extracted from the number
density and spatial clustering of a photon-count-limited sample of clusters of
galaxies up to z~2. We consider different scenarios for the availability of (i)
X-ray follow-up observations, (ii) photometric and spectroscopic redshifts, and
(iii) accurate knowledge of the observable -- mass relation down to the scale
of galaxy groups. With about 125,000 clusters (detected with more than 50
photons and with mass M500c > $10^{13} h^{-1}$ Msun) from an average all-sky
exposure of 1.6 ks, eROSITA will give marginalized, one-dimensional, 1-$\sigma$
errors of $\Delta \sigma_8 = \pm~0.008$ ($\sim$1 per cent), $\Delta \Omega_{\rm
M} = \pm~0.006$ (2.2 per cent), $\Delta w_0 = \pm~0.07$ (7 per cent), and
$\Delta w_a = \pm~0.25$ (optimistic scenario) in combination with (and largely
improving upon) current constraints from various cosmological probes (cosmic
microwave background, BAOs, Type Ia SNe). Our findings correspond to a
dark-energy figure of merit in the range of $116-162$ (after the four years of
all-sky survey), making eROSITA one of the first Stage IV experiments to come
on line according to the classification of the Dark Energy Task Force. To
secure improved mass calibrations and to include high-redshift clusters (z >
0.5) as well as objects at the group-mass scale (M500c < 5 $\times~ 10^{13}
h^{-1}$ Msun) will be vital to reach such accuracies. |
Dynamical processes in galaxy centers: How does the gas get in nuclear regions to fuel black holes? How efficient is
the feedback? The different processes to cause rapid gas inflow (or outflow) in
galaxy centers are reviewed. Non axisymmetries can be created or maintained by
internal disk instabilities, or galaxy interactions. Simulations and
observations tell us that the fueling is a chaotic and intermittent process,
with different scenarios and time-scales, according to the various radial
scales across a galaxy. | The DESI One-Percent Survey: Modelling the clustering and halo
occupation of all four DESI tracers with Uchuu: We present results from a set of high-fidelity simulated lightcones for the
DESI One-Percent Survey, created from the Uchuu simulation. This 8 (Gpc/h)^3
N-body simulation comprises 2.1 trillion particles and provides high-resolution
dark matter (sub)haloes in the framework of the Planck base-LCDM cosmology.
Employing the subhalo abundance matching (SHAM) technique, we populate the
Uchuu (sub)haloes with all four DESI tracers (BGS, LRG, ELG and QSO) to z =
2.1. Our method accounts for redshift evolution as well as the clustering
dependence on luminosity and stellar mass. The two-point clustering statistics
of the DESI One-Percent Survey align reasonably well with our predictions from
Uchuu across scales ranging from 0.1 Mpc/h to 100 Mpc/h. Some discrepancies
arise due to cosmic variance, incompleteness in the massive end of the stellar
mass function, and a simplified galaxy-halo connection model. We find that the
Uchuu BGS and LRG samples are adequately described using the standard
5-parameter halo occupation distribution model, while the ELGs and QSOs show
agreement with an adopted Gaussian distribution for central halos with a power
law for satellites. We observe a fair agreement in the large-scale bias
measurements between data and mock samples, although the data exhibits smaller
bias values, likely due to cosmic variance. The bias dependence on absolute
magnitude, stellar mass and redshift aligns with that of previous surveys.
These results improve simulated lightcone construction from cosmological models
and enhance our understanding of the galaxy-halo connection, with pivotal
insights from the first DESI data for the success of the final survey. |
Panoramic Survey of Lyman α Emitters at z=3.1: We present the results of the extensive narrow-band survey of Ly\alpha\
emission-line objects at z=3.1 in the 1.38 deg^2 area surrounding the high
density region of star-forming galaxies at z=3.09 in the SSA22 field, as well
as in the 1.04 deg^2 area of the three separated general blank fields. In total
of 2161 Ly\alpha\ emitters, 1394 in the SSA22 fields and 767 in the general
fields, respectively, are detected to the narrow-band AB magnitude limit of
25.73, which corresponds to the line flux of 1.8 x 10^{-17} erg s^{-1} cm^{-2}
or luminosity of 1.5 x 10^{42} erg s^{-1} at z=3.1, above the observed
equivalent width threshold, 190\AA . The average surface number density of the
emitters at z=3.1 in the whole general fields above the thresholds is
0.20+-0.01 arcmin^{-2}. The SSA22 high-density region at z=3.09 whose peak
local density is 6 times the average is found to be the most prominent
outstanding structure in the whole surveyed area and is firmly identified as a
robust `protocluster' with the enough large sample. We also compared the
overdensity of the 100 arcmin^2 and 700 arcmin^2 areas which contain the
protocluster with the expected fluctuation of the dark matter as well as those
of the model galaxies in cosmological simulations. We found that the peak
height values of the overdensity correspond to be 8-10 times and 3-4 times of
the expected standard deviations of the counts of Ly\alpha emitters at z=3.1 in
the corresponding volume, respectively. We conclude that the structure at
z=3.09 in the SSA22 field is a very significant and rare density peak up to the
scale of 60 Mpc. | Shedding light on Dark Matter through 21 cm Cosmology and Reionization
constraints: During the last decades, our understanding of the universe has reached a
remarkable level, being able to test cosmological predictions with an
astonishing precision. Nonetheless, the nature, composition, mass and
interactions of the Dark Matter still remain unknown, presenting one of the
most intriguing conundrums in current cosmology. In this doctoral thesis,
signatures of Dark Matter candidates which can leave an impact on the process
of formation of structures and on the evolution of the Intergalactic Medium are
studied. This thesis is organized in three parts. Part I is devoted to a broad
introduction to the fundamentals, describing the state of the art of the topics
considered. The basics of the $\Lambda$CDM are presented in Chapter 1. Chapter
2 overviews the historical progress of evidences of Dark Matter, followed by a
discussion of the status and small-scale issues of the Cold Dark Matter
paradigm, examining two alternative non-standard scenarios: Warm Dark Matter
and Interacting Dark Matter. Chapter 3 considers Primordial Black Holes as
another Dark Matter candidate, discussing the effects of accretion of
surrounding matter and the enhancement of small-scale fluctuations due to the
Poisson shot noise, both of which could leave an observational impact in the
Intergalactic Medium. The fundamentals of the 21 cm cosmological signal are
reviewed in Chapter 4, summarizing the main processes which drive the
brightness temperature, and discussing its spatial fluctuations via the power
spectrum. Finally, Chapter 5 is dedicated to the ionization and thermal
evolution of the Intergalactic Medium during the Cosmic Dawn and the
Reionization epochs. Part II includes seven original scientific articles
published during the development of the PhD, which constitute the main work of
this thesis. Finally, Part III contains a summary of the main results in
Spanish. |
The influence of the cluster environment on the star formation
efficiency of 12 Virgo spiral galaxies: The influence of the environment on gas surface density and star formation
efficiency of cluster spiral galaxies is investigated. We extend previous work
on radial profiles by a pixel-to pixel analysis looking for asymmetries due to
environmental interactions. The star formation rate is derived from GALEX UV
and Spitzer total infrared data. As in field galaxies, the star formation rate
for most Virgo galaxies is approximately proportional to the molecular gas
mass. Except for NGC 4438, the cluster environment does not affect the star
formation efficiency with respect to the molecular gas. Gas truncation is not
associated with major changes in the total gas surface density distribution of
the inner disk of Virgo spiral galaxies. In three galaxies, possible increases
in the molecular fraction and the star formation efficiency with respect to the
total gas, of factors of 1.5 to 2, are observed on the windward side of the
galactic disk. A significant increase of the star formation efficiency with
respect to the molecular gas content on the windward side of ram
pressure-stripped galaxies is not observed. The ram-pressure stripped
extraplanar gas of 3 highly inclined spiral galaxies shows a depressed star
formation efficiency with respect to the total gas, and one of them (NGC 4438)
shows a depressed rate even with respect to the molecular gas. The
interpretation is that stripped gas loses the gravitational confinement and
associated pressure of the galactic disk, and the gas flow is diverging, so the
gas density decreases and the star formation rate drops. However, the stripped
extraplanar gas in one highly inclined galaxy (NGC 4569) shows a normal star
formation efficiency with respect to the total gas. We propose this galaxy is
different because it is observed long after peak pressure, and its extraplanar
gas is now in a converging flow as it resettles back into the disk. | CMB Anisotropy Due to Filamentary Gas: Power Spectrum and Cosmological
Parameter Bias: Hot gas in filamentary structures induces CMB aniostropy through the SZ
effect. Guided by results from N-body simulations, we model the morphology and
gas properties of filamentary gas and determine the power spectrum of the
anisotropy. Our treatment suggests that power levels can be an appreciable
fraction of the cluster contribution at multipoles $\ell\lesssim 1500$. Its
spatially irregular morphology and larger characteristic angular scales can
help to distinguish this SZ signature from that of clusters. In addition to
intrinsic interest in this most extended SZ signal as a probe of filaments, its
impact on cosmological parameter estimation should also be assessed. We find
that filament `noise' can potentially bias determination of $A_s$, $n_s$, and
$w$ (the normalization of the primordial power spectrum, the scalar index, and
the dark energy equation of state parameter, respectively) by more than the
nominal statistical uncertainty in Planck SZ survey data. More generally, when
inferred from future optimal cosmic-variance-limited CMB experiments, we find
that virtually all parameters will be biased by more than the nominal
statistical uncertainty estimated for these next generation CMB experiments. |
The young stellar population at the center of NGC 205: Context. NGC 205 is a peculiar dwarf elliptical galaxy hosting in its center
a population of young blue stars. Their origin is still matter of debate, the
central fresh star formation activity possibly being related to dynamical
interactions between NGC 205 and M31. Aims. The star formation history in the
central 30\arcsec ($\sim$120 pc) around the NGC 205 central nucleus is
investigated in order to obtain clues to the origin of the young stellar
population. Methods. Deep HST/ACS CCD photometry is compared with theoretical
isochrones and luminosity functions to characterize the stellar content of the
region under study and compute the recent SF rate. Results. Our photometry
reveals a previously undetected blue plume of young stars clearly
distinguishable down to I$\simeq$26. Our analysis suggests that 1.9$\times10^5$
M$_\odot$ were produced between approximately 62 Myr and 335 Myr ago in the NGC
205 inner regions, with a latest minor episode occurring $\sim$25 Myr ago. This
implies a star formation rate of $\sim7\times10^{-4}$ M$_\odot$/yr over this
period. Conclusions. The excellent fit of the observed luminosity function of
young main sequence stars obtained with a model having a constant star
formation rate argues against a tidally triggered star formation activity over
the last $\sim$300 Myr. Rather, a constant SF may be consistent with NGC 205
being on its first interaction with M 31. | Simulated vs. observed UV emission at high redshift: a hint for a clumpy
ISM?: We discuss the rest-frame UV emission between 5< z < 7 from the MareNostrum
High-z Universe, a SPH simulation done with more than 2 billion particles.
Cosmological simulations of galaxy formation generally overpredict the UV
restframe luminosity function at high redshift, both at the bright and faint
ends. In this Letter we explore a dust attenuation model where a larger
extinction is applied to star populations younger than a given age, mimicking
the effect of a clumpy interstellar medium. We show that this scenario fits
reasonably well both the UV luminosity functions and the UV-continuum slopes
derived from observations. The model assumes a large obscuration for stars
younger than 25 Myr from the gas clouds where they should be embedded at their
formation time. We find that the optical depth in these clouds should be
between 30 and 100 times larger than the mean optical depth for the homogeneous
part of the interstellar medium. These values are one order of magnitude larger
than those estimated in local galaxies. Therefore, we conclude that LambdaCDM
predictions for the high-z UV emission can accommodate the current observations
if we consider a dust extinction model based on the assumption of a clumpy
environment at high redshift. |
Study of star-forming galaxies in SDSS up to redshift 0.4 II. Evolution
from the fundamental parameters: mass, metallicity & SFR: To understand the formation and evolution of galaxies, it is important to
have a full comprehension of the role played by the metallicity, star formation
rate (SFR), morphology, and color. The interplay of these parameters at
different redshifts will substantially affect the evolution of galaxies and, as
a consequence, the evolution of them will provide important clues and
constraints on the galaxy evolution models. In this work we focus on the
evolution of the SFR, metallicity of the gas, and morphology of galaxies at low
redshift in search of signs of evolution. We use the S2N2 diagnostic diagram as
a tool to classify star--forming, composite, and AGN galaxies. We analyzed the
evolution of the three principal BPT diagrams, estimating the SFR and specific
SFR (SSFR) for our samples of galaxies, studying the luminosity and
mass-metallicity relations, and analyzing the morphology of our sample of
galaxies through the g-r color, concentration index, and SSFR. We found that
the S2N2 is a reliable diagram to classify star--forming, composite, and AGNs
galaxies. We demonstrate that the three principal BPT diagrams show an
evolution toward higher values of [OIII]5007/Hb due to a metallicity decrement.
We found an evolution in the mass-metallicity relation of ~ 0.2 dex for the
redshift range 0.3 < z < 0.4 compared to our local one. From the analysis of
the evolution of the SFR and SSFR as a function of the stellar mass and
metallicity, we discovered a group of galaxies with higher SFR and SSFR at all
redshift samples, whose morphology is consistent with those of late-type
galaxies. Finally, the comparison of our local (0.04<z<0.1) with our higher
redshift sample (0.3<z<0.4), show that the metallicity, the SFR and morphology,
evolve toward lower values of metallicity, higher SFRs, and late--type
morphologies for the redshift range 0.3<z<0.4 | The WiggleZ Dark Energy Survey: Galaxy Evolution at 0.25 < z < 0.75
Using The Second Red-Sequence Cluster Survey (RCS-2): We study the evolution of galaxy populations around the spectroscopic WiggleZ
sample of starforming galaxies at 0.25 < z < 0.75 using the photometric catalog
from the Second Red-Sequence Cluster Survey (RCS2). We probe the optical
photometric properties of the net excess neighbor galaxies. The key concept is
that the marker galaxies and their neighbors are located at the same redshift,
providing a sample of galaxies representing a complete census of galaxies in
the neighborhood of star-forming galaxies. The results are compared with those
using the RCS WiggleZ Spare-Fibre (RCS-WSF) sample as markers, representing
galaxies in cluster environments at 0.25 < z < 0.45. By analyzing the stacked
color-color properties of the WiggleZ neighbor galaxies, we find that their
optical colors are not a strong function of indicators of star-forming
activities such as EW([OII]) or GALEX NUV luminoisty of the markers. The
galaxies around the WiggleZ markers exhibit a bimodal distribution on the
color-magnitude diagram, with most of them located in the blue cloud. The
optical galaxy luminosity functions (GLF) of the blue neighbor galaxies have a
faint-end slope \alpha of \sim -1.3, similar to that for galaxies in cluster
environments drawn from the RCS-WSF sample. The faint-end slope of the GLF for
the red neighbors, however, is \sim -0.4, significantly shallower than the \sim
-0.7 found for those in cluster environments. This suggests that the build-up
of the faint-end of the red sequence in cluster environments is in a
significantly more advanced stage than that in the star-forming and lower
galaxy density WiggleZ neighborhoods. We find that the red galaxy fraction
(fred) around the star-forming WiggleZ galaxies has similar values from z \sim
0.3 to z \sim 0.6 with fred \sim 0.28, but drops to fred \sim 0.20 at z >
\sim0.7. This change of fred with redshift suggests that (and more...) |
The Type Ia Supernova Color-Magnitude Relation and Host Galaxy Dust: A
Simple Hierarchical Bayesian Model: Conventional Type Ia supernova (SN Ia) cosmology analyses currently use a
simplistic linear regression of magnitude versus color and light curve shape,
which does not model intrinsic SN Ia variations and host galaxy dust as
physically distinct effects, resulting in low color-magnitude slopes. We
construct a probabilistic generative model for the dusty distribution of
extinguished absolute magnitudes and apparent colors as the convolution of a
intrinsic SN Ia color-magnitude distribution and a host galaxy dust
reddening-extinction distribution. If the intrinsic color-magnitude ($M_B$ vs.
$B-V$) slope $\beta_{int}$ differs from the host galaxy dust law $R_B$, this
convolution results in a specific curve of mean extinguished absolute magnitude
vs. apparent color. The derivative of this curve smoothly transitions from
$\beta_{int}$ in the blue tail to $R_B$ in the red tail of the apparent color
distribution. The conventional linear fit approximates this effective curve
near the average apparent color, resulting in an apparent slope $\beta_{app}$
between $\beta_{int}$ and $R_B$. We incorporate these effects into a
hierarchical Bayesian statistical model for SN Ia light curve measurements, and
analyze a dataset of SALT2 optical light curve fits of 248 nearby SN Ia at z <
0.10. The conventional linear fit obtains $\beta_{app} \approx 3$. Our model
finds a $\beta_{int} = 2.3 \pm 0.3$ and a distinct dust law of $R_B = 3.8 \pm
0.3$, consistent with the average for Milky Way dust, while correcting a
systematic distance bias of $\sim 0.10$ mag in the tails of the apparent color
distribution. Finally, we extend our model to examine the SN Ia luminosity-host
mass dependence in terms of intrinsic and dust components. | On the chains of star complexes and superclouds in spiral arms: The relation is studied between occurrence of a regular chain of star
complexes and superclouds in a spiral arm, and other properties of the latter.
A regular string of star complexes is located in the north-western arm of M31;
they have about the same size 0.6 kpc with spacing of 1.1 kpc. Within the same
arm segment the regular magnetic field with the wavelength of 2.3 kpc was found
by Beck et al. (1989). We noted that this wavelength is twice as large as the
spacing between complexes and suggested that they were formed in result of
magneto-gravitational instability developed along the arm. In this NW arm, star
complexes are located inside the gas-dust lane, whilst in the south-western arm
of M31 the gas-dust lane is upstream of the bright and uniform stellar arm.
Earlier, evidence for the age gradient has been found in the SW arm. All these
are signatures of a spiral shock, which may be associated with unusually large
(for M31) pitch-angle of this SW arm segment. Such a shock may prevent the
formation of the regular magnetic field, which might explain the absence of
star complexes there. Anti-correlation between shock wave signatures and
presence of star complexes is observed in spiral arms of a few other galaxies.
Regular chains of star complexes and superclouds in spiral arms are rare, which
may imply that a rather specific mechanism is involved in their formation, and
the most probable one is the Parker-Jeans instability. The spiral pattern of
our Galaxy is briefly discussed; it may be of M101 type in the outer parts. The
regular bi-modal spacing of HI superclouds is found in Carina and Cygnus
(Outer) arms, which may be an indirect evidence for the regular magnetic field
along these arms. |
AEGIS: The Clustering of X-ray AGN Relative to Galaxies at z~1: We measure the clustering of non-quasar X-ray AGN at z=0.7-1.4 in the AEGIS
field. Using the cross-correlation of 113 Chandra-selected AGN, with a median
log L_X=42.8 erg s^-1, with ~5,000 DEEP2 galaxies, we find that the X-ray AGN
are fit by a power law with a clustering scale length of r_0=5.95 +/-0.90 h^-1
Mpc and slope gamma=1.66 +/-0.22. X-ray AGN have a similar clustering amplitude
as red, quiescent and `green' transition galaxies at z~1 and are significantly
more clustered than blue, star-forming galaxies. The X-ray AGN clustering
strength is primarily determined by the host galaxy color; AGN in red host
galaxies are significantly more clustered than AGN in blue host galaxies, with
a relative bias that is similar to that of red to blue DEEP2 galaxies. We
detect no dependence of clustering on optical brightness, X-ray luminosity, or
hardness ratio within the ranges probed here. We find evidence for galaxies
hosting X-ray AGN to be more clustered than a sample of galaxies with matching
joint optical color and magnitude distributions. This implies that galaxies
hosting X-ray AGN are more likely to reside in groups and more massive dark
matter halos than galaxies of the same color and luminosity without an X-ray
AGN. In comparison to optically-selected quasars in the DEEP2 fields, we find
that X-ray AGN at z~1 are more clustered than optically-selected quasars (with
a 2.6-sigma significance) and therefore likely reside in more massive dark
matter halos. Our results are consistent with galaxies undergoing a quasar
phase while in the blue cloud before settling on the red sequence with a
lower-luminosity X-ray AGN, if they are similar objects at different
evolutionary stages. | The velocity field of 2MRS Ks=11.75 galaxies: constraints on beta and
bulk flow from the luminosity function: Using the nearly full sky Ks=11.75 2MASS Redshift Survey [2MRS]of ~45,000
galaxies we reconstruct the underlying peculiar velocity field and constrain
the cosmological bulk flow within ~100. These results are obtained by
maximizing the probability to estimate the absolute magnitude of a galaxy given
its observed apparent magnitude and redshift. At a depth of ~60 Mpc/h we find a
bulk flow Vb=(90\pm65,-230\pm65,50\pm65) km/s in agreement with the theoretical
predictions of the LCDM model. The reconstructed peculiar velocity field that
maximizes the likelihood is characterized by the parameter beta=0.323 +/- 0.08.
Both results are in agreement with those obtained previously using the ~23,000
galaxies of the shallower Ks=11.25 2MRS survey. In our analysis we find that
the luminosity function of 2MRS galaxies is poorly fitted by the Schechter form
and that luminosity evolves such that objects become fainter with increasing
redshift according to L(z)=L(z=0)(1+z)^(+2.7 +/-0.15). |
AIC and BIC for cosmological interacting scenarios: In this work we study linear and non-linear cosmological interactions, which
depend on dark matter and dark energy densities in the framework of General
Relativity. By using the Akaike information criterion (AIC) and the Bayesian
information criterion (BIC) with data from SnIa (Union 2.1 and binned JLA),
H(z), BAO and CMB we compare the interacting models among themselves and
analyze whether more complex interacting models are favored by these criteria.
In this context, we find some suitable interactions that alleviate the
coincidence problem. | An anisotropic universe due to dimension-changing vacuum decay: In this paper we consider the question of observational signatures of a false
vacuum decay event in the early universe followed by a period of inflation; in
particular, motivated by the string landscape, we consider decays in which the
parent vacuum has a smaller number of large dimensions than the current vacuum,
which leads to an anisotropic universe. We go beyond previous studies, and
examine the effects on the CMB temperature and polarisation power spectra, due
to both scalar and tensor modes, and consider not only late-time effects but
also the full cosmological perturbation theory at early times. We find that
whilst the scalar mode behaves as one would expect, and the effects of
anisotropy at early times are sub-dominant to the late-time effects already
studied, for the tensor modes in fact the the early-time effects grow with
multipole and can become much larger than one would expect, even dominating
over the late-time effects. Thus these effects should be included if one is
looking for such a signal in the tensor modes. |
Host galaxies of luminous quasars: population synthesis of optical
off-axis spectra: There is increasing evidence of a connection between AGN activity and galaxy
evolution. To obtain further insight into this potentially important
evolutionary phase, we analyse the properties of quasar host galaxies. In this
paper, we present a population synthesis modeling technique for off-axis
spectra, the results of which constrain host colour and the stellar ages of
luminous quasars (M_V(nuc)<-23). Our technique is similar to well established
quiescent-galaxy models, modified to accommodate scattered nuclear light (a
combination of atmospheric, instrumental and host galaxy scattered light)
observed off axis. In our model, subtraction of residual scattered quasar light
is performed, while simultaneously modeling the constituent stellar populations
of the host galaxy. The reliability of this technique is tested via a
Monte-Carlo routine in which the correspondence between synthetic spectra with
known parameters and the model output is determined. Application of this model
to a preliminary sample of 10 objects is presented and compared to previous
studies. Spectroscopic data was obtained via long-slit and integral-field unit
observations on the Keck and WIYN telescopes. We confirm that elliptical quasar
hosts are distinguishable (bluer) from inactive ellipticals in rest frame B-V
colour. Additionally, we note a trend for radio luminous (L_5GHz > 10^40 erg
s^-1) quasars to be located in redder host galaxies in comparison to their less
luminous radio counterparts. While the host colour and age of our radio
luminous sample is in close proximity to the green valley, our radio faint
sample is consistent with quiescent star-forming galaxies. However, further
observations are needed to confirm these results. Finally, we discuss future
applications for our technique on a larger sample of objects being obtained via
SALT and WIYN telescope observing campaigns. | Dark energy domination in the Virgocentric flow: The standard \LambdaCDM cosmological model implies that all celestial bodies
are embedded in a perfectly uniform dark energy background, represented by
Einstein's cosmological constant, and experience its repulsive antigravity
action. Can dark energy have strong dynamical effects on small cosmic scales as
well as globally? Continuing our efforts to clarify this question, we focus now
on the Virgo Cluster and the flow of expansion around it. We interpret the
Hubble diagram, from a new database of velocities and distances of galaxies in
the cluster and its environment, using a nonlinear analytical model which
incorporates the antigravity force in terms of Newtonian mechanics. The key
parameter is the zero-gravity radius, the distance at which gravity and
antigravity are in balance. Our conclusions are: 1. The interplay between the
gravity of the cluster and the antigravity of the dark energy background
determines the kinematical structure of the system and controls its evolution.
2. The gravity dominates the quasi-stationary bound cluster, while the
antigravity controls the Virgocentric flow, bringing order and regularity to
the flow, which reaches linearity and the global Hubble rate at distances \ga
15 Mpc. 3. The cluster and the flow form a system similar to the Local Group
and its outflow. In the velocity-distance diagram, the cluster-flow structure
reproduces the group-flow structure with a scaling factor of about 10; the
zero-gravity radius for the cluster system is also 10 times larger. The phase
and dynamical similarity of the systems on the scales of 1-30 Mpc suggests that
a two-component pattern may be universal for groups and clusters: a
quasi-stationary bound central component and an expanding outflow around it,
due to the nonlinear gravity-antigravity interplay with the dark energy
dominating in the flow component. |
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