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Reconstructing the interaction between dark energy and dark matter using
Gaussian Processes: We present a nonparametric approach to reconstruct the interaction between
dark energy and dark matter directly from SNIa Union 2.1 data using Gaussian
processes, which is a fully Bayesian approach for smoothing data. In this
method, once the equation of state ($w$) of dark energy is specified, the
interaction can be reconstructed as a function of redshift. For the decaying
vacuum energy case with $w=-1$, the reconstructed interaction is consistent
with the standard $\Lambda$CDM model, namely, there is no evidence for the
interaction. This also holds for the constant $w$ cases from $-0.9$ to $-1.1$
and for the Chevallier-Polarski-Linder (CPL) parametrization case. If the
equation of state deviates obviously from $-1$, the reconstructed interaction
exists at $95\%$ confidence level. This shows the degeneracy between the
interaction and the equation of state of dark energy when they get constraints
from the observational data. | Measuring Gravitational Lensing Flexions in Abell 1689 Using an Analytic
Image Model: Measuring dark matter substructure within galaxy cluster haloes is a
fundamental probe of the Lambda-CDM model of structure formation. Gravitational
lensing is a technique for measuring the total mass distribution which is
independent of the nature of the gravitating matter, making it a vital tool for
studying these dark-matter dominated objects. We present a new method for
measuring weak gravitational lensing flexions, the gradients of the lensing
shear field, to measure mass distributions on small angular scales. While
previously published methods for measuring flexions focus on measuring derived
properties of the lensed images, such as shapelet coefficients or surface
brightness moments, our method instead fits a
mass-sheet-transformation-invariant Analytic Image Model (AIM) to the each
galaxy image. This simple parametric model traces the distortion of lensed
image isophotes and constrains the flexion fields. We test the AIM method using
simulated data images with realistic noise and a variety of unlensed image
properties, and show that it successfully reproduces the input flexion fields.
We also apply the AIM method for flexion measurement to Hubble Space Telescope
observations of Abell 1689, and detect mass structure in the cluster using
flexions measured with the AIM method. |
Searching for Cooling Signatures in Strong Lensing Galaxy Clusters:
Evidence Against Baryons Shaping the Matter Distribution in Cluster Cores: The process by which the mass density profile of certain galaxy clusters
becomes centrally concentrated enough to produce high strong lensing (SL)
cross-sections is not well understood. It has been suggested that the baryonic
condensation of the intra-cluster medium (ICM) due to cooling may drag dark
matter to the cores and thus steepen the profile. In this work, we search for
evidence of ongoing ICM cooling in the first large, well-defined sample of
strong lensing selected galaxy clusters in the range 0.1 < z < 0.6. Based on
known correlations between the ICM cooling rate and both optical emission line
luminosity and star formation, we measure, for a sample of 89 strong lensing
clusters, the fraction of clusters that have [OII]3727 emission in their
brightest cluster galaxy (BCG). We find that the fraction of line-emitting BCGs
is constant as a function of redshift for z > 0.2 and shows no statistically
significant deviation from the total cluster population. Specific star
formation rates, as traced by the strength of the 4000 angstrom break, D_4000,
are also consistent with the general cluster population. Finally, we use
optical imaging of the SL clusters to measure the angular separation, R_arc,
between the arc and the center of mass of each lensing cluster in our sample
and test for evidence of changing [OII] emission and D_4000 as a function of
R_arc, a proxy observable for SL cross-sections. D_4000 is constant with all
values of R_arc, and the [OII] emission fractions show no dependence on R_arc
for R_arc > 10" and only very marginal evidence of increased weak [OII]
emission for systems with R_arc < 10". These results argue against the ability
of baryonic cooling associated with cool core activity in the cores of galaxy
clusters to strongly modify the underlying dark matter potential, leading to an
increase in strong lensing cross-sections. | The Zeldovich approximation: key to understanding Cosmic Web complexity: We describe how the dynamics of cosmic structure formation defines the
intricate geometric structure of the spine of the cosmic web. The Zeldovich
approximation is used to model the backbone of the cosmic web in terms of its
singularity structure. The description by Arnold et al. (1982) in terms of
catastrophe theory forms the basis of our analysis.
This two-dimensional analysis involves a profound assessment of the
Lagrangian and Eulerian projections of the gravitationally evolving
four-dimensional phase-space manifold. It involves the identification of the
complete family of singularity classes, and the corresponding caustics that we
see emerging as structure in Eulerian space evolves. In particular, as it is
instrumental in outlining the spatial network of the cosmic web, we investigate
the nature of spatial connections between these singularities.
The major finding of our study is that all singularities are located on a set
of lines in Lagrangian space. All dynamical processes related to the caustics
are concentrated near these lines. We demonstrate and discuss extensively how
all 2D singularities are to be found on these lines. When mapping this spatial
pattern of lines to Eulerian space, we find a growing connectedness between
initially disjoint lines, resulting in a percolating network. In other words,
the lines form the blueprint for the global geometric evolution of the cosmic
web. |
Impact of Galactic polarized emission on B-mode detection at low
multipoles: We use a model of polarized Galactic emission developed by the the Planck
collaboration to assess the impact of foregrounds on B-mode detection at low
multipoles. Our main interest is to applications of noisy polarization data and
in particular to assessing the feasibility of B-mode detection by Planck. This
limits the complexity of foreground subtraction techniques that can be applied
to the data. We analyze internal linear combination techniques and show that
the offset caused by the dominant E-mode polarization pattern leads to a
fundamental limit of r approximately 0.1 for the tensor-scalar ratio even in
the absence of instrumental noise. We devise a simple, robust, template fitting
technique using multi-frequency polarization maps. We show that template
fitting using Planck data alone offers a feasible way of recovering primordial
B-modes from dominant foreground contamination, even in the presence of noise
on the data and templates. We implement and test a pixel-based scheme for
computing the likelihood function of cosmological parameters at low multipoles
that incorporates foreground subtraction of noisy data. | The Subluminous Supernova 2007qd: A Missing Link in a Family of
Low-Luminosity Type Ia Supernovae: We present multi-band photometry and multi-epoch spectroscopy of the peculiar
Type Ia supernova (SN Ia) 2007qd, discovered by the SDSS-II Supernova Survey.
It possesses physical properties intermediate to those of the peculiar SN
2002cx and the extremely low-luminosity SN 2008ha. Optical photometry indicates
that it had an extraordinarily fast rise time of <= 10 days and a peak absolute
B magnitude of -15.4 +/- 0.2 at most, making it one of the most subluminous SN
Ia ever observed. Follow-up spectroscopy of SN 2007qd near maximum brightness
unambiguously shows the presence of intermediate-mass elements which are likely
caused by carbon/oxygen nuclear burning. Near maximum brightness, SN 2007qd had
a photospheric velocity of only 2800 km/s, similar to that of SN 2008ha but
about 4000 and 7000 km/s less than that of SN 2002cx and normal SN Ia,
respectively. We show that the peak luminosities of SN 2002cx-like objects are
highly correlated with both their light-curve stretch and photospheric
velocities. Its strong apparent connection to other SN 2002cx-like events
suggests that SN 2007qd is also a pure deflagration of a white dwarf, although
other mechanisms cannot be ruled out. It may be a critical link between SN
2008ha and the other members of the SN 2002cx-like class of objects. |
Synthetic light cone catalogues of modern redshift and weak lensing
surveys with AbacusSummit: The joint analysis of different cosmological probes, such as galaxy
clustering and weak lensing, can potentially yield invaluable insights into the
nature of the primordial Universe, dark energy and dark matter. However, the
development of high-fidelity theoretical models that cover a wide range of
scales and redshifts is a necessary stepping-stone. Here, we present public
high-resolution weak lensing maps on the light cone, generated using the
$N$-body simulation suite AbacusSummit in the Born approximation, and
accompanying weak lensing mock catalogues, tuned via fits to the Early Data
Release small-scale clustering measurements of the Dark Energy Spectroscopic
Instrument (DESI). Available in this release are maps of the cosmic shear,
deflection angle and convergence fields at source redshifts ranging from $z =
0.15$ to 2.45 with $\Delta z = 0.05$ as well as CMB convergence maps ($z
\approx 1090$) for each of the 25 ${\tt base}$-resolution simulations ($L_{\rm
box} = 2000\,h^{-1}{\rm Mpc}$, $N_{\rm part} = 6912^3$) as well as for the two
${\tt huge}$ simulations ($L_{\rm box} = 7500\,h^{-1}{\rm Mpc}$, $N_{\rm part}
= 8640^3$) at the fiducial AbacusSummit cosmology ($Planck$ 2018). The pixel
resolution of each map is 0.21 arcmin, corresponding to a HEALPiX $N_{\rm
side}$ of 16384. The sky coverage of the ${\tt base}$ simulations is an octant
until $z \approx 0.8$ (decreasing to about 1800 deg$^2$ at $z \approx 2.4$),
whereas the ${\tt huge}$ simulations offer full-sky coverage until $z \approx
2.2$. Mock lensing source catalogues are sampled matching the ensemble
properties of the Kilo-Degree Survey, Dark Energy Survey, and Hyper-Suprime Cam
weak lensing datasets. The produced mock catalogues are validated against
theoretical predictions for various clustering and lensing statistics such as
galaxy clustering multipoles, galaxy-shear and shear-shear, showing excellent
agreement. | On cosmological bias due to the magnification of shear and position
samples in modern weak lensing analyses: The magnification of galaxies in modern galaxy surveys induces additional
correlations in the cosmic shear, galaxy-galaxy lensing and clustering
observables used in modern lensing "3x2pt" analyses, due to sample selection.
In this paper, we emulate the magnification contribution to all three
observables utilising the SLICS simulations suite, and test the sensitivity of
the cosmological model, galaxy bias and redshift distribution calibration to
un-modelled magnification in a Stage-IV-like survey using Monte-Carlo sampling.
We find that magnification cannot be ignored in any single or combined
observable, with magnification inducing $>1\sigma$ biases in the $w_0-\sigma_8$
plane, including for cosmic shear and 3x2pt analyses. Significant cosmological
biases exist in the 3x2pt and cosmic shear from magnification of the shear
sample alone. We show that magnification induces significant biases in the mean
of the redshift distribution where a position sample is analysed, which may
potentially be used to identify contamination by magnification. |
Abundance matching analysis of the emission line galaxy sample in the
extended Baryon Oscillation Spectroscopic Survey: We present the measurements of the small-scale clustering for the emission
line galaxy (ELG) sample from the extended Baryon Oscillation Spectroscopic
Survey (eBOSS) in the Sloan Digital Sky Survey IV (SDSS-IV). We use conditional
abundance matching method to interpret the clustering measurements from
$0.34h^{-1}\textrm{Mpc}$ to $70h^{-1}\textrm{Mpc}$. In order to account for the
correlation between properties of emission line galaxies and their environment,
we add a secondary connection between star formation rate of ELGs and halo
accretion rate. Three parameters are introduced to model the ELG [OII]
luminosity and to mimic the target selection of eBOSS ELGs. The parameters in
our models are optimized using Markov Chain Monte Carlo (MCMC) method. We find
that by conditionally matching star formation rate of galaxies and the halo
accretion rate, we are able to reproduce the eBOSS ELG small scale clustering
within 1$\sigma$ error level. Our best fit model shows that the eBOSS ELG
sample only consists of $\sim 12\%$ of all star-forming galaxies, and the
satellite fraction of eBOSS ELG sample is 19.3\%. We show that the effect of
assembly bias is $\sim20\%$ on the two-point correlation function and $\sim5\%$
on the void probability function at scale of $r\sim 20 h^{-1}\rm Mpc$. | Constraining the intergalactic medium at $z\approx$ 9.1 using LOFAR
Epoch of Reionization observations: We derive constraints on the thermal and ionization states of the
intergalactic medium (IGM) at redshift $\approx$ 9.1 using new upper limits on
the 21-cm power spectrum measured by the LOFAR radio-telescope and a prior on
the ionized fraction at that redshift estimated from recent cosmic microwave
background (CMB) observations. We have used results from the reionization
simulation code GRIZZLY and a Bayesian inference framework to constrain the
parameters which describe the physical state of the IGM. We find that, if the
gas heating remains negligible, an IGM with ionized fraction $\gtrsim 0.13$ and
a distribution of the ionized regions with a characteristic size $\gtrsim 8
~h^{-1}$ comoving megaparsec (Mpc) and a full width at the half maximum (FWHM)
$\gtrsim 16 ~h^{-1}$ Mpc is ruled out. For an IGM with a uniform spin
temperature $T_{\rm S} \gtrsim 3$ K, no constraints on the ionized component
can be computed. If the large-scale fluctuations of the signal are driven by
spin temperature fluctuations, an IGM with a volume fraction $\lesssim 0.34$ of
heated regions with a temperature larger than CMB, average gas temperature
7-160 K and a distribution of the heated regions with characteristic size
3.5-70 $h^{-1}$ Mpc and FWHM of $\lesssim 110$ $h^{-1}$ Mpc is ruled out. These
constraints are within the 95 per cent credible intervals. With more stringent
future upper limits from LOFAR at multiple redshifts, the constraints will
become tighter and will exclude an increasingly large region of the parameter
space. |
On the origin of the Cold Spot: In a concordant $\Lambda$ Cold Dark Matter ($\Lambda$CDM) model, large-angle
Cosmic Microwave Background (CMB) temperature anisotropy due to linear
perturbations in the local universe is not negligible. We explore a possible
role of an underdense region (void) that may cause an anomalous Cold Spot (CS)
in the CMB sky. Although the observed anomalous cold region with a surrounding
hot ring can be produced by an underdense region surrounded by a massive wall,
a decrement in the CMB temperature in the line-of-sight is suppressed because
of blueshift of CMB photons that pass the wall. Therefore, undercompensated
models give better agreement with the observed data in comparison with
overcompensated or compensated models. We find that it is likely that $\sim$90
per cent of the CMB fluctuation is generated due to an overdense region
surrounded by an underdense region at the last scattering surface, and the
remaining $\sim 10$ per cent is produced due to a single spherical underdense
region with a radius $r\sim 6\times 10^2 h^{-1}$Mpc and a density contrast
$\delta_m\sim -0.009$ ($2 \sigma$) at redshift $z\sim 1$ in the line-of-sight
to the CS. The probability of chance alignment of such two structures is $\sim
0.7$ per cent if the perturbation with an underdense region at $z\sim 1$ is
moderately undercompensated. | Understanding Dwarf Galaxies in order to Understand Dark Matter: Much progress has been made in recent years by the galaxy simulation
community in making realistic galaxies, mostly by more accurately capturing the
effects of baryons on the structural evolution of dark matter halos at high
resolutions. This progress has altered theoretical expectations for galaxy
evolution within a Cold Dark Matter (CDM) model, reconciling many earlier
discrepancies between theory and observations. Despite this reconciliation, CDM
may not be an accurate model for our Universe. Much more work must be done to
understand the predictions for galaxy formation within alternative dark matter
models. |
Probing the Gamma-Ray Burst Rate with Trigger Simulations of the Swift
Burst Alert Telescope: The long gamma-ray burst (GRB) rate is essential for revealing the connection
between GRBs, supernovae and stellar evolution. Additionally, the GRB rate at
high redshift provides a strong probe of star formation history in the early
universe. While hundreds of GRBs are observed by Swift, it remains difficult to
determine the intrinsic GRB rate due to the complex trigger algorithm of Swift.
Current studies usually approximate the Swift trigger algorithm by a single
detection threshold. However, unlike the previously flown GRB instruments,
Swift has over 500 trigger criteria based on photon count rate and additional
image threshold for localization. To investigate possible systematic biases and
explore the intrinsic GRB properties, we developed a program that is capable of
simulating all the rate trigger criteria and mimicking the image trigger
threshold. We use this program to search for the intrinsic GRB rate. Our
simulations show that adopting the complex trigger algorithm of Swift increases
the detection rate of dim bursts. As a result, we find that either the GRB rate
is much higher than previously expected at large redshift, or the luminosity
evolution is non-negligible. We will discuss the best results of the GRB rate
in our search, and their impact on the star-formation history. | Multi-Wavelength Properties of Barred Galaxies in the Local Universe. I:
Virgo Cluster: We study in detail how the barred galaxy fraction varies as a function of
luminosity, HI gas mass, morphology and color in the Virgo cluster in order to
provide a well defined, statistically robust measurement of the bar fraction in
the local universe spanning a wide range in luminosity (factor of ~100) and HI
gas mass. We combine multiple public data-sets (UKIDSS near-infrared imaging,
ALFALFA HI gas masses, GOLDMine photometry). After excluding highly inclined
systems, we define three samples where galaxies are selected by their B-band
luminosity, H-band luminosity, and HI gas mass. We visually assign bars using
the high resolution H-band imaging from UKIDSS. When all morphologies are
included, the barred fraction is ~17-24% while for morphologically selected
discs, we find that the barred fraction in Virgo is ~29-34%: it does not depend
strongly on how the sample is defined and does not show variations with
luminosity or HI gas mass. The barred fraction depends most strongly on the
morphological composition of the sample: when the disc populations are
separated into lenticulars (S0--S0/a), early-type spirals (Sa--Sb), and
late-type spirals (Sbc--Sm), we find that the early-type spirals have a higher
barred fraction (~45-50%) compared to the lenticulars and late-type spirals
(~22-36%). This difference may be due to the higher baryon fraction of
early-type discs which makes them more susceptible to bar instabilities. We do
not find any evidence of barred galaxies being preferentially blue. |
Coincidences between OVI and OVII Lines: Insights from High Resolution
Simulations of the Warm-Hot Intergalactic Medium: With high resolution (0.46kpc/h), adaptive mesh-refinement Eulerian
cosmological hydrodynamic simulations we compute properties of O VI and O VII
absorbers from the warm-hot intergalactic medium (WHIM). Our new simulations
are in broad agreement with previous simulations, with ~40% of the
intergalactic medium being in the WHIM at z=0. It is found (1) The amount of
gas in the WHIM at temperature below and above 10^6K is about equal within
uncertainties. (1) Our simulations are in excellent agreement with observed
properties of O VI absorbers, with respect to the line incidence rate and
Doppler width-column density relation. (2) Velocity structures within absorbing
regions are a significant, and for large Doppler width clouds, a dominant
contributor to the Doppler widths of both O VI and O VII absorbers. A
non-negligible fraction (in number and mass) of O VI and O VII clouds can arise
from gas of temperature lower than 10^5, until the Doppler width is well in
excess of 100km/s. (3) Strong O VI absorbers are predominantly collisionally
ionized. About (61%, 57%, 39%) of O VI absorbers in the column density ranges
of log N(OVI) cm^2=(12.5-13,13-14,>14) have temperature lower than 10^5K. (4)
Quantitative prediction is made for the presence of broad and shallow O VI
lines, which current observations may have largely missed. Upcoming
observations by COS may be able to provide a test. (5) The reported 3 sigma
upper limit on the mean column density of coincidental O VII lines at the
location of detected O VI lines by Yao et al is above the predicted value by a
factor of 2.5-4. (6) The claimed observational detection of O VII lines by
Nicastro et al, if true, is 2 sigma above what our simulations predict. | Far Infrared Luminosity Function of Local Galaxies in the AKARI Deep
Field South: We present the first far-infrared luminosity function in the AKARI Deep Field
South, a premier deep field of the AKARI Space Telescope, using spectroscopic
redshifts obtained with AAOmega. To date, we have found spectroscopic redshifts
for 389 galaxies in this field and have measured the local (z < 0.25) 90 micron
luminosity function using about one-third of these redshifts. The results are
in reasonable agreement with recent theoretical predictions. |
Producing a BOSS-CMASS sample with DES imaging: We present a sample of galaxies with the Dark Energy Survey (DES) photometry
that replicates the properties of the BOSS CMASS sample. The CMASS galaxy
sample has been well characterized by the Sloan Digital Sky Survey (SDSS)
collaboration and was used to obtain the most powerful redshift-space galaxy
clustering measurements to date. A joint analysis of redshift-space distortions
(such as those probed by CMASS from SDSS) and a galaxy-galaxy lensing
measurement for an equivalent sample from DES can provide powerful cosmological
constraints. Unfortunately, the DES and SDSS-BOSS footprints have only minimal
overlap, primarily on the celestial equator near the SDSS Stripe 82 region.
Using this overlap, we build a robust Bayesian model to select CMASS-like
galaxies in the remainder of the DES footprint. The newly defined DES-CMASS
(DMASS) sample consists of 117,293 effective galaxies covering $1,244 {\rm
deg}^2$. Through various validation tests, we show that the DMASS sample
selected by this model matches well with the BOSS CMASS sample, specifically in
the South Galactic cap (SGC) region that includes Stripe 82. Combining
measurements of the angular correlation function and the clustering-z
distribution of DMASS, we constrain the difference in mean galaxy bias and mean
redshift between the BOSS CMASS and DMASS samples to be $\Delta b =
0.010^{+0.045}_{-0.052}$ and $\Delta z = \left( 3.46^{+5.48}_{-5.55} \right)
\times 10^{-3}$ for the SGC portion of CMASS, and $\Delta b =
0.044^{+0.044}_{-0.043} $ and $\Delta z= ( 3.51^{+4.93}_{-5.91}) \times
10^{-3}$ for the full CMASS sample. These values indicate that the mean bias of
galaxies and mean redshift in the DMASS sample is consistent with both CMASS
samples within $1\sigma$. | Dark Energy Survey Year 1 results: Detection of Intra-cluster Light at
Redshift $\sim$ 0.25: Using data collected by the Dark Energy Survey (DES), we report the detection
of intracluster light (ICL) with $\sim300$ galaxy clusters in the redshift
range of 0.2-0.3. We design methods to mask detected galaxies and stars in the
images and stack the cluster light profiles, while accounting for several
systematic effects (sky subtraction, instrumental point-spread function,
cluster selection effects and residual light in the ICL raw detection from
background and cluster galaxies). The methods allow us to acquire high
signal-to-noise measurements of the ICL and central galaxies (CGs), which we
separate with radial cuts. The ICL appears as faint and diffuse light extending
to at least 1 Mpc from the cluster center, reaching a surface brightness level
of 30 mag arcsec$^{-2}$. The ICL and the cluster CG contribute to $44\%\pm17$\%
of the total cluster stellar luminosity within 1 Mpc. The ICL color is overall
consistent with that of the cluster red sequence galaxies, but displays the
trend of becoming bluer with increasing radius. The ICL demonstrates an
interesting self-similarity feature -- for clusters in different richness
ranges, their ICL radial profiles are similar after scaling with cluster
$R_\mathrm{200m}$, and the ICL brightness appears to be a good tracer of the
cluster radial mass distribution. These analyses are based on the DES redMaPPer
cluster sample identified in the first year of observations. |
Testing the isotropy of the Universe with type Ia supernovae in a
model-independent way: In this paper, we study an anisotropic universe model with Bianchi-I metric
using Joint Light-curve Analysis (JLA) sample of type Ia supernovae (SNe Ia).
Because light-curve parameters of SNe Ia vary with different cosmological
models and SNe Ia samples, we fit the SNe Ia light-curve parameters and
cosmological parameters simultaneously employing Markov Chain Monte Carlo
method. Therefore, the results on the amount of deviation from isotropy of the
dark energy equation of state ($\delta$), and the level of anisotropy of the
large-scale geometry ($\Sigma_0$) at present, are totally model-independent.
The constraints on the skewness and cosmic shear are $-0.101<\delta<0.071$ and
$-0.007<\Sigma_0<0.008$. This result is consistent with a standard isotropic
universe ($\delta=\Sigma_0=0$). However, a moderate level of anisotropy in the
geometry of the Universe and the equation of state of dark energy, is allowed.
Besides, there is no obvious evidence for a preferred direction of anisotropic
axis in this model. | Quantifying the statistics of CMB-lensing-derived galaxy cluster mass
measurements with simulations: CMB lensing is a promising, novel way to measure galaxy cluster masses that
can be used, e.g., for mass calibration in galaxy cluster counts analyses.
Understanding the statistics of the galaxy cluster mass observable obtained
with such measurements is essential if their use in subsequent analyses is not
to lead to biased results. We study the statistics of a CMB lensing galaxy
cluster mass observable for a Planck-like experiment with mock observations
obtained from an N-body simulation. We quantify the bias and intrinsic scatter
associated with this observable following two different approaches, one in
which the signal due to the cluster and nearby correlated large-scale structure
is isolated, and another one in which the variation due to uncorrelated
large-scale structure is also taken into account. For our first approach we
also quantify deviations from log-normality in the scatter, finding them to
have a negligible impact on mass calibration for our Planck-like experiment. We
briefly discuss how some of our results change for experiments with higher
angular resolution and lower noise levels, such as the current generation of
surveys obtained with ground-based, large-aperture telescopes. |
GMRT 150 MHz follow up of diffuse steep spectrum radio emission in
galaxy clusters: It has been recently found that a few galaxy clusters host diffuse radio halo
emission with very steep synchrotron spectra ($\alpha$ > 1.6), which may be
classified as Ultra Steep Spectrum Radio Halos (USSRHs). USSRHs are expected in
the turbulence re-acceleration model for the origin of cluster radio halos, and
are best discovered and studied at low frequencies. We performed GMRT follow up
observations of three galaxy clusters at 150MHz, selected from the GMRT radio
halo survey, which are known to host an USSRH or candidate very steep spectrum
diffuse emission. This project is aimed to characterize the low frequency
spectrum of USSRHs for a detailed study of their origin and connection with
cluster mergers. We present preliminary results at 150 MHz of the cluster A697. | Understanding Shape and Centroid Deviations in 39 Strong Lensing Galaxy
Clusters in Various Dynamical States: Through observational tests of strong lensing galaxy clusters, we can test
simulation derived structure predictions that follow from $\Lambda$ Cold Dark
Matter ($\Lambda$CDM) cosmology. The shape and centroid deviations between the
total matter distribution, stellar matter distributions, and hot intracluster
gas distribution serve as an observational test of these theoretical structure
predictions. We measure the position angles, ellipticities, and
locations/centroids of the brightest cluster galaxy (BCG), intracluster light
(ICL), the hot intracluster medium (ICM), and the core lensing mass for a
sample of strong lensing galaxy clusters from the SDSS Giant Arcs Survey
(SGAS). We utilize HST WFC3/IR imaging data to measure the shapes/centroids of
the ICL and BCG distributions and use Chandra ACIS-I X-ray data to measure the
shapes/centroids of ICM. Additionally, we measure the concentration parameter c
and asymmetry parameter A to incorporate cluster dynamical state into our
analysis. Using this multicomponent approach, we attempt to constrain the
astrophysics of our strong lensing cluster sample and evaluate the different
components in terms of their ability to trace out the DM halo of clusters in
various dynamical states. |
Is there Correlation between Fine Structure and Dark Energy Cosmic
Dipoles?: We present a detailed analysis (including redshift tomography) of the cosmic
dipoles in the Keck+VLT quasar absorber and in the Union2 SnIa samples. We show
that the fine structure constant cosmic dipole obtained through the Keck+VLT
quasar absorber sample at $4.1\sigma$ level is anomalously aligned with the
corresponding dark energy dipole obtained through the Union2 sample at
$2\sigma$ level. The angular separation between the two dipole directions is
$11.3^\circ \pm 11.8^\circ$. We use Monte Carlo simulations to find the
probability of obtaining the observed dipole magnitudes with the observed
alignment, in the context of an isotropic cosmological model with no
correlation between dark energy and fine structure constant $\alpha$. We find
that this probability is less than one part in $10^6$. We propose a simple
physical model (extended topological quintessence) which naturally predicts a
spherical inhomogeneous distribution for both dark energy density and fine
structure constant values. The model is based on the existence of a recently
formed giant global monopole with Hubble scale core which also couples
non-minimally to electromagnetism. Aligned dipole anisotropies would naturally
emerge for an off-centre observer for both the fine structure constant and for
dark energy density. This model smoothly reduces to \lcdm for proper limits of
its parameters. Two predictions of this model are (a) a correlation between the
existence of strong cosmic electromagnetic fields and the value of $\alpha$ and
(b) the existence of a dark flow on Hubble scales due to the repulsive gravity
of the global defect core (`Great Repulser') aligned with the dark energy and
$\alpha$ dipoles. The direction of the dark flow is predicted to be towards the
spatial region of lower accelerating expansion. Existing data about the dark
flow are consistent with this prediction. | Gravitational Lensing of the Cosmic Neutrino Background: We study gravitational lensing of the cosmic neutrino background. This signal
is undetectable for the foreseeable future, but there is a rich trove of
information available. At least some of the neutrinos from the early universe
will be non-relativistic today, with a closer surface of last scattering
(compared to the cosmic microwave background) and with larger angles of
deflection. Lensing of massive neutrinos is strongly chromatic: both the
amplitude of lensing and the cosmic time at which the potential is traversed
depend on neutrino momentum, in principle giving access to our entire causal
volume, not restricted to the light cone. As a concrete example, we focus on
the case where the cosmic neutrino background would be strongly lensed when
passing through halos of galaxy clusters and galaxies. We calculate the
Einstein radius for cosmic neutrinos and investigate the impact of neutrino
mass. |
Numerical evaluation of the tensor bispectrum in two field inflation: We evaluate the dimensionless non-Gaussianity parameter $h_{_{\rm NL}}$, that
characterizes the amplitude of the tensor bispectrum, numerically for a class
of two field inflationary models such as double inflation, hybrid inflation and
aligned natural inflation. We compare the numerical results with the slow roll
results which can be obtained analytically. In the context of double inflation,
we also investigate the effects on $h_{_{\rm NL}}$ due to curved trajectories
in the field space. We explicitly examine the validity of the consistency
relation governing the tensor bispectrum in the squeezed limit. Lastly, we
discuss the contribution to $h_{_{\rm NL}}$ due to the epoch of preheating in
two field models. | Probing Neutrino Hierarchy and Chirality via Wakes: The relic neutrinos are expected to acquire a bulk relative velocity with
respect to the dark matter at low redshifts, and neutrino wakes are expected to
develop downstream of the dark matter halos. We propose a method of measuring
the neutrino mass based on this mechanism. This neutrino wake will cause a
dipole distortion of the galaxy-galaxy lensing pattern. This effect could be
detected by combining upcoming lensing surveys with a low redshift galaxy
survey or a 21 cm intensity mapping survey, which can map the neutrino flow
field. The data obtained with LSST and Euclid should enable us to make a
positive detection if the three neutrino masses are quasidegenerate with each
neutrino mass of $\sim$0.1 eV, and a future high precision 21 cm lensing survey
would allow the normal hierarchy and inverted hierarchy cases to be
distinguished, and even the right-handed Dirac neutrinos may be detectable. |
Nonconservation of lepton current and asymmetry of relic neutrinos: The neutrino asymmetry in the early universe plasma, $n_\nu - n_{\bar \nu}$,
is calculated both before and after the electroweak phase transition (EWPT).
The leptogenesis before EWPT within the standard model is well known to be
driven by the abelian anomaly in a massless hypercharge field. The generation
of the neutrino asymmetry in the Higgs phase after EWPT, in its turn, has not
been considered previously because of the absence of any quantum anomaly in an
external electromagnetic field for such electroneutral particles as neutrino,
unlike the Adler anomaly for charged left and right polarized massless
electrons in the same electromagnetic field. Using the neutrino Boltzmann
equation, modified by the Berry curvature term in the momentum space, we
establish the violation of the macroscopic neutrino current in plasma after
EWPT and exactly reproduce the nonconservation of the lepton current in the
symmetric phase before EWPT arising in quantum field theory due to the non-zero
lepton hypercharge and corresponding triangle anomaly in an external
hypercharge field. In the last case the violation of the lepton current is
derived through the kinetic approach without the computation of the
corresponding Feynman diagrams. Then the new kinetic equation is applied for
the calculation of the neutrino asymmetry accounting for the the Berry
curvature and the electroweak interaction with background fermions in the Higgs
phase, including the stage after the neutrino decoupling at the absence of
neutrino collisions in plasma. This asymmetry is found to be rather small to be
observed. Thus, a difference of the relic neutrino and antineutrino densities,
if exists, should be acquired mainly in the symmetric phase before EWPT. | A New Hybrid Framework to Efficiently Model Lines of Sight to
Gravitational Lenses: In strong gravitational lens systems, the light bending is usually dominated
by one main galaxy, but may be affected by other mass along the line of sight
(LOS). Shear and convergence can be used to approximate the contributions from
less significant perturbers (e.g. those that are projected far from the lens or
have a small mass), but higher order effects need to be included for objects
that are closer or more massive. We develop a framework for multiplane lensing
that can handle an arbitrary combination of tidal planes treated with shear and
convergence and planes treated exactly (i.e., including higher order terms).
This framework addresses all of the traditional lensing observables including
image positions, fluxes, and time delays to facilitate lens modelling that
includes the non-linear effects due to mass along the LOS. It balances accuracy
(accounting for higher-order terms when necessary) with efficiency (compressing
all other LOS effects into a set of matrices that can be calculated up front
and cached for lens modelling). We identify a generalized multiplane mass sheet
degeneracy, in which the effective shear and convergence are sums over the
lensing planes with specific, redshift-dependent weighting factors. |
Extended Photometry for the DEEP2 Galaxy Redshift Survey: A Testbed for
Photometric Redshift Experiments: This paper describes a new catalog that supplements the existing DEEP2 Galaxy
Redshift Survey photometric and spectroscopic catalogs with ugriz photometry
from two other surveys; the Canada-France-Hawaii Legacy Survey (CFHTLS) and the
Sloan Digital Sky Survey (SDSS). Each catalog is cross-matched by position on
the sky in order to assign ugriz photometry to objects in the DEEP2 catalogs.
We have recalibrated the CFHTLS photometry where it overlaps DEEP2 in order to
provide a more uniform dataset. We have also used this improved photometry to
predict DEEP2 BRI photometry in regions where only poorer measurements were
available previously. In addition, we have included improved astrometry tied to
SDSS rather than USNO-A2.0 for all DEEP2 objects. In total this catalog
contains ~27,000 objects with full ugriz photometry as well as robust
spectroscopic redshift measurements, 64% of which have r > 23. By combining the
secure and accurate redshifts of the DEEP2 Galaxy Redshift Survey with ugriz
photometry, we have created a catalog that can be used as an excellent testbed
for future photo-z studies, including tests of algorithms for surveys such as
LSST and DES. | Interacting dark matter and cosmic acceleration: We study the effect of an explicit interaction between two scalar fields
components describing dark matter in the context of a recent proposal framework
for interaction. We find that, even assuming a very small coupling, it is
sufficient to explain the observational effects of a cosmological constant, and
also overcome the problems of the $\Lambda$CDM model without assuming an exotic
dark energy. |
An alternative singularity-free cosmological scenario from cusp
geometries: We study an alternative geometrical approach on the problem of classical
cosmological singularity. It is based on a generalized function $f (x, y) =
x^{2} + y^{2} = (1 - z)z^{n}$ which consists of a cusped coupled isosurface.
Such a geometry is computed and discussed into the context of Friedmann
singularity-free cosmology where a pre-big bang scenario is considered.
Assuming that the mechanism of cusp formation is described by non-linear
oscillations of a pre-big bang extended very high energy density field ($> 3
\times 10^{94} kg/m^{3} $), we show that the action under the gravitational
field follows a tautochrone of revolution, understood here as the primary
projected geometry that alternatively replaces the Friedmann singularity in the
standard big bang theory. As shown here this new approach allows us to
interpret the nature of both matter and dark energy from first geometric
principles. | Vorticity production and survival in viscous and magnetized cosmologies: We study the role of viscosity and the effects of a magnetic field on a
rotating, self-gravitating fluid, using Newtonian theory and adopting the ideal
magnetohydrodynamic approximation. Our results confirm that viscosity can
generate vorticity in inhomogeneous environments, while the magnetic tension
can produce vorticity even in the absence of fluid pressure and density
gradients. Linearizing our equations around an Einstein-de Sitter cosmology, we
find that viscosity adds to the diluting effect of the universal expansion.
Typically, however, the dissipative viscous effects are confined to relatively
small scales. We also identify the characteristic length bellow which the
viscous dissipation is strong and beyond which viscosity is essentially
negligible. In contrast, magnetism seems to favor cosmic rotation. The magnetic
presence is found to slow down the standard decay-rate of linear vortices, thus
leading to universes with more residual rotation than generally anticipated. |
Radio interferometric observations of two core-dominated triple radio
sources at z>3: Aims. We selected two radio quasars (J1036+1326 and J1353+5725) based on
their 1.4-GHz radio structure, which is dominated by a bright central core and
a pair of weaker and nearly symmetric lobes at ~10" angular separation. They
are optically identified in the Sloan Digital Sky Survey (SDSS) at
spectroscopic redshifts z>3. We investigate the possibility that their
core-dominated triple morphology can be a sign of restarted radio activity in
these quasars, involving a significant repositioning of the radio jet axis.
Methods. We present the results of high-resolution radio imaging observations
of J1036+1326 and J1353+5725, performed with the European Very Long Baseline
Interferometry (VLBI) Network (EVN) at 1.6 GHz. These data are supplemented by
archive observations from the Very Large Array (VLA).We study the large- and
small-scale radio structures and the brightness temperatures, then estimate
relativistic beaming parameters. Results. We show that the central emission
region of these two high-redshift, core-dominated triple sources is compact but
resolved at ~10 milli-arcsecond resolution. We find that it is not necessary to
invoke large misalignment between the VLBI jet and the large-scale radio
structure to explain the observed properties of the sources. | Constraints on Primordial Magnetic Fields from their impact on the
ionization history with Planck 2018: We update and extend our previous CMB anisotropy constraints on primordial
magnetic fields through their dissipation by ambipolar diffusion and MHD
decaying turbulence effects on the post-recombination ionization history. We
derive the constraints using the latest Planck 2018 data release which improves
on the E-mode polarization leading to overall tighter constraints with respect
to Planck 2015. We also use the low-multipole E-mode polarization likelihood
obtained by the SROLL2 map making algorithm and we note how it is compatible
with larger magnetic field amplitudes than the Planck 2018 baseline, especially
for positive spectral indices. The 95% CL constraints on the amplitude of the
magnetic fields from the combination of the effects is $\sqrt{\langle B^2
\rangle} <0.69 (<0.72)$ nG for Planck 2018 (SROLL2) by marginalizing on the
magnetic spectral index. We also investigate the impact of a damping scale
allowed to vary and the interplay between the magnetic field effects and the
lensing amplitude parameter. |
Probing Inflation with Precision Bispectra: Calculating the primordial bispectrum predicted by a model of inflation and
comparing it to what we see in the sky is very computationally intensive,
necessitating layers of approximations and limiting the models which can be
constrained. Exploiting the inherent separability of the tree level in-in
formalism using expansions in separable basis functions provides a means by
which to obviate some of these difficulties. Here, we develop this approach
further into a practical and efficient numerical methodology which can be
applied to a much wider and more complicated range of bispectrum phenomenology,
making an important step forward towards observational pipelines which can
directly confront specific models of inflation. We describe a simple augmented
Legendre polynomial basis and its advantages, then test the method on
single-field inflation models with non-trivial phenomenology, showing that our
calculation of these coefficients is fast and accurate to high orders. | Influence of Low Energy Hadronic Interactions on Air-shower Simulations: Experiments measuring cosmic rays above an energy of 10^14 eV deduce the
energy and mass of the primary cosmic ray particles from air-shower
simulations. We investigate the importance of hadronic interactions at low and
high energies on the distributions of muons and electrons in showers on ground.
In air shower simulation programs, hadronic interactions below an energy
threshold in the range from 80 GeV to 500 GeV are simulated by low energy
interaction models, like Fluka or Gheisha, and above that energy by high energy
interaction models, e.g. Sibyll or QGJSJet. We find that the impact on shower
development obtained by switching the transition energy from 80 GeV to 500 GeV
is comparable to the difference obtained by switching between Fluka and
Gheisha. |
Morphologically-Identified Merging Galaxies in the SWIRE Fields: We investigate the evolutional and environmental effects on star formation
efficiency for more than 400 merging galaxies. The ~400 merging systems, with
photometric redshifts smaller than 0.7, are obtained from a catalog of ~15000
morphologically identified merging galaxies derived from observations of the
Canada-France-Hawaii Telescope. We also obtained the IR data of the merging
galaxies from the Spitzer Wide-area InfraRed Extragalactic Survey (SWIRE). The
redshift differences \Delta z between the member galaxies of these merging
pairs show a large distribution with 0 < \Delta z < 0.4. We divide our merging
pairs into two sub-samples with \Delta z < 0.05 and > 0.05 for further
analyses. We find a statistically significant anti-correlation between the
specific star formation rate (SSFR) and the separation of the merging galaxies
for both sub-samples. Our analyses also show that although most of the merging
systems do have enhanced star formation activity, only very rare ones display
extremely high SFRs. Additionally, the SSFR of the merging galaxies also
decreases when the magnitude difference between two member galaxies becomes
large. However, we find that for the merging pairs with large luminosity
contrast, the fainter components show higher SSFR than the brighter ones.
Finally, there is a higher fraction of gas-poor mergers in galaxy clusters, and
the SSFR of gas-rich mergers is reduced in cluster environments. | Cosmology and Astrophysics Using the Post-reionization HI: We discuss the prospects of using the redshifted 21~cm emission from neutral
hydrogen in the post-reionization epoch to study our universe. The main aim of
the article is to highlight the efforts of Indian scientists in this area with
the SKA in mind. It turns out that the intensity mapping surveys from SKA can
be instrumental in obtaining tighter constraints on the dark energy models.
Cross-correlation of the HI intensity maps with the Ly$\alpha$ forest data can
also be useful in measuring the BAO scale. |
The Effective Field Theory of Large Scale Structures of a Fuzzy Dark
Matter Universe: Ultra-light scalar fields and their non-interacting class, the so-called
fuzzy dark matter (FDM), are candidates for dark matter, introduced to solve
the small-scale problems of the standard cold dark matter. In this paper, we
address whether the small-scale effects, specifically the quantum pressure,
could leave sizable imprints on the large-scale statistics of the matter. For
this purpose, We utilize the Effective Field Theory of Large Scale Structures
(EFT of LSS) wherein small-scale physics is integrated and represented on large
scales by only a set of free parameters. These parameters can be determined by
fitting to the cosmological simulations. We use the \textit{Gadget-2} code to
study the evolution of $512^3$ particles in a box of side length
$250\,h^{-1}\,\mathrm{Mpc}$. Fitting EFT predictions to the simulation data, we
determine the value of the speed of sound. We use the suppressed FDM initial
conditions for the FDM case, sufficient to produce accurate -- enough for our
purpose -- results on large scales. We perform three FDM simulations with
different masses and compare their sound speed with the standard cold dark
matter (CDM) simulation. We found that the FDM sound speed is slightly higher
than CDM's. The deviation of the sound speed for FDM from CDM is larger for
lower FDM masses. We conclude that the impact of the FDM is not limited to the
small scales alone, and we can search for them by studying the matter on large
scales. Though it is beyond the observations' scope today, it is possible to
discriminate it with upcoming observations. | Moving Mesh Cosmology: Properties of Gas Disks: We compare the structural properties of galaxies formed in cosmological
simulations using the smoothed particle hydrodynamics (SPH) code GADGET with
those using the moving-mesh code AREPO. Both codes employ identical gravity
solvers and the same sub-resolution physics but use very different methods to
track the hydrodynamic evolution of gas. This permits us to isolate the effects
of the hydro solver on the formation and evolution of galactic gas disks in
GADGET and AREPO haloes with comparable numerical resolution. In a matching
sample of GADGET and AREPO haloes we fit simulated gas disks with exponential
profiles. We find that the cold gas disks formed using the moving mesh approach
have systematically larger disk scale lengths and higher specific angular
momenta than their GADGET counterparts across a wide range in halo masses. For
low mass galaxies differences between the properties of the simulated galaxy
disks are caused by an insufficient number of resolution elements which lead to
the artificial angular momentum transfer in our SPH calculation. We however
find that galactic disks formed in massive halos, resolved with 10^6
particles/cells, are still systematically smaller in the GADGET run by a factor
of ~2. The reasons for this are: 1) The excessive heating of haloes close to
the cooling radius due to spurious dissipation of the subsonic turbulence in
GADGET; and 2) The efficient delivery of low angular momentum gaseous blobs to
the bottom of the potential well. While this large population of gaseous blobs
in GADGET originates from the filaments which are pressure confined and
fragment due to the SPH surface tension while infalling into hot halo
atmospheres, it is essentially absent in the moving mesh calculation, clearly
indicating numerical rather than physical origin of the blob material. |
The X-ray Spectra of the Luminous LMXBs in NGC 3379: Field and Globular
Cluster Sources: From a deep multi-epoch Chandra observation of the elliptical galaxy NGC 3379
we report the spectral properties of eight luminous LMXBs (LX>1.2E38 erg/s). We
also present a set of spectral simulations, produced to aid the interpretation
of low-count single-component spectral modeling. These simulations demonstrate
that it is possible to infer the spectral states of X-ray binaries from these
simple models and thereby constrain the properties of the source. Of the eight
LMXBs studied, three reside within globular clusters, and one is a confirmed
field source. Due to the nature of the luminosity cut all sources are either
neutron star binaries emitting at or above the Eddington luminosity or black
hole binaries. The spectra from these sources are well described by
single-component models, with parameters consistent with Galactic LMXB
observations, where hard-state sources have a range in photon index of 1.5-1.9
and thermally dominated sources have inner disc temperatures between ~0.7-1.55
keV. The large variability observed in the brightest globular cluster source
(LX>4E38 erg/s) suggests the presence of a black hole binary. At its most
luminous this source is observed in a thermally dominated state with kT=1.5
keV, consistent with a black hole mass of ~4 Msol. This observation provides
further evidence that globular clusters are able to retain such massive
binaries. We also observed a source transitioning from a bright state (LX~1E39
erg/s), with prominent thermal and non-thermal components, to a less luminous
hard state (LX=3.8E38 erg/s, Gamma=1.85). In its high flux emission this source
exhibits a cool-disc component of ~0.14 keV, similar to spectra observed in
some ultraluminous X-ray sources. Such a similarity indicates a possible link
between `normal' stellar mass black holes in a high accretion state and ULXs. | On the sensitivity of weak gravitational lensing to the cosmic expansion
function: We analyse the functional derivative of the cosmic-shear power spectrum
$C_\ell^\gamma$ with respect to the cosmic expansion function. Our interest in
doing so is two-fold: (i) In view of attempts to detect minor changes of the
cosmic expansion function which may be due to a possibly time-dependent
dark-energy density, we wish to know how sensitive the weak-lensing power
spectrum is to changes in the expansion function. (ii) In view of recent
empirical determinations of the cosmic expansion function from distance
measurements, independent of specific cosmological models, we wish to find out
how uncertainties in the expansion function translate to uncertainties in the
cosmic-shear power spectrum. We find the following answers: Relative changes of
the expansion function are amplified by the cosmic-shear power spectrum by a
factor $\approx 2-6$, weakly depending on the scale factor where the change is
applied, and the current uncertainty of one example for an empirically
determined expansion function translates to a relative uncertainty of the
cosmic-shear power spectrum of $\approx10\,\%$. |
On the Detection of CMB B-modes from Ground at Low Frequency: The primordial CMB $B$-mode search is on the spotlight of the scientific
community due to the large amount of cosmological information that is encoded
in the primeval signal. However, the detection of this signal is challenging
from the data analysis point of view, due to the relative low amplitude
compared to the foregrounds, the lensing contamination coming from the leakage
of $E$-modes, and the instrumental noise. Here, we studied the viability of the
detection of the primordial polarization $B$-mode with a ground-based telescope
operating in the microwave low-frequency regime (i.e., from 10GHz-120GHz) in a
handful of different scenarios: i. the instrument's channels distribution and
noise, ii. the tensor-to-scalar ratio ($r$) detectability considering different
possible $r$ values and degrees of delensing, iii. the effect of including a
possible source of polarized anomalous microwave emission (AME), iv. the
strengths and weaknesses of different observational strategies and, v. the
atmospheric and systematic noise impact on the recovery. We focused mainly on
the removal of galactic foregrounds as well as noise contamination by applying
a full-parametric pixel-based maximum likelihood component separation
technique. Moreover, we developed a numerical methodology to estimate the
residuals power spectrum left after component separation, which allow us to
mitigate possible biases introduced in the primordial $B$-mode power spectrum
reconstruction. Among many other results, we found that this sort of experiment
is capable of detecting Starobinsky's $r$ even when no delensing is performed
or, a possible polarized AME contribution is taken into account. Besides, we
showed that this experiment is a powerful complement to other on-ground or
satellite missions, such as LiteBIRD, since it can help significantly with the
low-frequency foregrounds characterization. | Locating Star-Forming Regions in Quasar Host Galaxies: We present a study of the morphology and intensity of star formation in the
host galaxies of eight Palomar-Green quasars using observations with the Hubble
Space Telescope. Our observations are motivated by recent evidence for a close
relationship between black hole growth and the stellar mass evolution in its
host galaxy. We use narrow-band [O II] $\lambda$3727, H$\beta$, [O III]
$\lambda$5007 and Pa$\alpha$ images, taken with the WFPC2 and NICMOS
instruments, to map the morphology of line-emitting regions, and, after
extinction corrections, diagnose the excitation mechanism and infer
star-formation rates. Significant challenges in this type of work are the
separation of the quasar light from the stellar continuum and the
quasar-excited gas from the star-forming regions. To this end, we present a
novel technique for image decomposition and subtraction of quasar light. Our
primary result is the detection of extended line-emitting regions with sizes
ranging from 0.5 to 5 kpc and distributed symmetrically around the nucleus,
powered primarily by star formation. We determine star-formation rates of order
a few tens of M$_\odot$/yr. The host galaxies of our target quasars have
stellar masses of order $10^{11}$ M$_\odot$ and specific star formation rates
on a par with those of M82 and luminous infrared galaxies. As such they fall at
the upper envelope or just above the star-formation mass sequence in the
specific star formation vs stellar mass diagram. We see a clear trend of
increasing star formation rate with quasar luminosity, reinforcing the link
between the growth of the stellar mass of the host and the black hole mass
found by other authors. |
Constraints On Holographic Cosmological Models From Gamma Ray Bursts: We use Gamma Ray Bursts (GRBs) data from Y. Wang (2008) to put additional
constraints on a set of cosmological dark energy models based on the
holographic principle. GRBs are among the most complex and energetic
astrophysical events known in the universe offering us the opportunity to
obtain information from the history of cosmic expansion up to about redshift of
$z\sim 6$. These astrophysical objects provide us a complementary observational
test to determine the nature of dark energy by complementing the information of
data from Supernovas (e.g. Union 2.1 compilation). We found that the $\Lambda
CDM$ model gives the best fit to the observational data, although our
statistical analysis ($\Delta AIC$ and $\Delta BIC$) shows that the models
studied in this work ("Hubble Radius Scale" and "Ricci Scale Q") have a
reasonable agreement with respect to the most successful, except for the "Ricci
Scale CPL" and "Future Event Horizon" models, which can be ruled out by the
present study. However, these results reflect the importance of GRBs
measurements to provide additional observational constraints to alternative
cosmological models, which are mandatory to clarify the way in which the
paradigm of dark energy or any alternative model is correct. | Improving cosmological covariance matrices with machine learning: Cosmological covariance matrices are fundamental for parameter inference,
since they are responsible for propagating uncertainties from the data down to
the model parameters. However, when data vectors are large, in order to
estimate accurate and precise matrices we need huge numbers of observations, or
rather costly simulations - neither of which may be viable. In this work we
propose a machine learning approach to alleviate this problem in the context of
the matrices used in the study of large-scale structure. With only a small
amount of data (matrices built with samples of 50-200 halo power spectra) we
are able to provide significantly improved matrices, which are almost
indistinguishable from the ones built from much larger samples (thousands of
spectra). In order to perform this task we trained convolutional neural
networks to denoise the matrices, using in the training process a data set made
up entirely of spectra extracted from simple, inexpensive halo simulations
(mocks). We then show that the method not only removes the noise in the
matrices of the cheap simulation, but it is also able to successfully denoise
the matrices of halo power spectra from N-body simulations. We compare the
denoised to the other matrices using several metrics, and in all of them they
score better, without any signs of spurious artifacts. With the help of the
Wishart distribution we derive an analytical extrapolation for the effective
sample augmentation allowed by the denoiser. Finally, we show that, by using
the denoised matrices, the cosmological parameters can be recovered with nearly
the same accuracy as when using matrices built with a sample of 30,000 spectra
in the case of the cheap simulations, and with 15,000 spectra in the case of
the N-body simulations. Of particular interest is the bias in the Hubble
parameter $H_0$, which was significantly reduced after applying the denoiser. |
Simulating the Universe with MICE: The abundance of massive clusters: We introduce a new set of large N-body runs, the MICE simulations, that
provide a unique combination of very large cosmological volumes with good mass
resolution. They follow the gravitational evolution of ~ 8.5 billion particles
(2048^3) in volumes covering up to 450 (Gpc/h)^3. Our main goal is to
accurately model and calibrate basic cosmological probes that will be used by
upcoming astronomical surveys. Here we take advantage of the very large volumes
of MICE to make a robust sampling of the high-mass tail of the halo mass
function (MF). We discuss and avoid possible systematic effects in our study,
and do a detailed analysis of different error estimators. We find that
available fits to the local abundance of halos (Warren et al. (2006)) match
well the abundance in MICE up to M ~ 10^{14}\Msun, but significantly deviate
for larger masses, underestimating the mass function by 10% (30%) at M = 3.16 x
10^{14}\Msun (10^{15}\Msun). Similarly, the widely used Sheth & Tormen (1999)
fit, if extrapolated to high redshift assuming universality, leads to an
underestimation of the cluster abundance by 30%, 20% and 15% at z=0, 0.5, 1 for
M ~ [7 - 2.5 - 0.8] x 10^{14}\Msun respectively ($\nu = \delta_c/\sigma ~ 3$).
We provide a re-calibration of the halo MF valid over 5 orders of magnitude in
mass, 10^{10} < M/(\Msun) < 10^{15}, that accurately describes its redshift
evolution up to z=1. We explore the impact of this re-calibration on the
determination of dark-energy, and conclude that using available fits may
systematically bias the estimate of w by as much as 50% for medium-depth (z <=
1) surveys. MICE halo catalogues are publicly available at
http://www.ice.cat/mice | CS, HC3N and CH3CCH multi-line analyses towards starburst galaxies. The
evolution of cloud structures in the central regions of galaxies: We aim to study the properties of the dense molecular gas towards the inner
few 100 pc of four nearby starburst galaxies dominated both by photo
dissociation regions (M82) and large-scale shocks (NGC253, IC342 and Maffei2),
and to relate the chemical and physical properties of the molecular clouds with
the evolutionary stage of the nuclear starbursts. We have carried out
multi-transitional observations and analyses of three dense gas molecular
tracers, CS, HC3N and CH3CCH, using Boltzmann diagrams in order to determine
the rotational temperatures and column densities of the dense gas, and using a
Large Velocity Gradients model to calculate the H2 density structure in the
molecular clouds. The CS and HC3N data indicate the presence of density
gradients in the molecular clouds, showing similar excitation conditions, and
suggesting that they arise from the same gas components. In M82, CH3CCH has the
highest fractional abundance determined in a extragalactic source (10^-8). The
density and the chemical gradients found in all galaxies can be explained in
the framework of the starburst evolution. The young shock-dominatedstarburst
galaxies, like presumably Maffei2, show a cloud structure with a rather uniform
density and chemical composition which suggests low star formation activity.
Molecular clouds in galaxies with starburst in an intermediate stage of
evolution, such as NGC253 and IC342, show clouds with a large density contrast
(two orders of magnitude) between the denser regions (cores) and the less dense
regions (halos) of the molecular clouds and relatively constant chemical
abundance. Finally, the galaxy with the most evolved starburst, M82, has clouds
with a rather uniform density structure, large envelopes of atomic/molecular
gas subjected to UV photodissociating radiation from young star clusters, and
very different chemical abundances of HC3N and CH3CCH. |
Inflationary cosmology with nonlinear dispersion relations: We present a technique, {\em the uniform asymptotic approximation}, to
construct accurate analytical solutions of the linear perturbations of
inflation after quantum effects of the early universe are taken into account,
for which the dispersion relations generically become nonlinear. We construct
explicitly the error bounds associated with the approximations and then study
them in detail. With the understanding of the errors and the proper choice of
the Liouville transformations of the differential equations of the
perturbations, we show that the analytical solutions describe the exact
evolution of the linear perturbations extremely well even only in the
first-order approximations. As an application of the approximate analytical
solutions, we calculate the power spectra and indices of scalar and tensor
perturbations in the slow-roll inflation, and find that the amplitudes of the
power spectra get modified due to the quantum effects, while the power spectrum
indices remain the same as in the linear case. | Cosmological Implications of Axion-Matter Couplings: Axions and other light particles appear ubiquitously in physics beyond the
Standard Model, with a variety of possible couplings to ordinary matter.
Cosmology offers a unique probe of these particles as they can thermalize in
the hot environment of the early universe for any such coupling. For sub-MeV
particles, their entropy must leave a measurable cosmological signal, usually
via the effective number of relativistic particles, $N_\mathrm{eff}$. In this
paper, we will revisit the cosmological constraints on the couplings of axions
and other pseudo-Nambu-Goldstone bosons to Standard Model fermions from
thermalization below the electroweak scale, where these couplings are marginal
and give contributions to the radiation density of $\Delta N_\mathrm{eff} >
0.027$. We update the calculation of the production rates to eliminate
unnecessary approximations and find that the cosmological bounds on these
interactions are complementary to astrophysical constraints, e.g. from
supernova SN 1987A. We additionally provide quantitative explanations for these
bounds and their relationship. |
Constraints on the cosmological coupling of black holes from Gaia: Recent work has suggested that black holes (BHs) could be cosmologically
coupled to the accelerated expansion of the universe, potentially becoming a
candidate for dark energy. This would imply BH mass growth following the
cosmological expansion, with the masses of individual BHs growing as $M_{\rm
BH}\propto (1+z)^3$. In this letter, we discuss the binary systems Gaia BH1 and
Gaia BH2, which contain $\sim 9\,M_{\odot}$ BHs orbited by $\sim 1\,M_{\odot}$
stars in widely-separated orbits. The ages of both systems can be constrained
by the properties of the luminous stars. If BH masses are indeed growing as
$(1+z)^3$, the masses of both BHs at formation would have been significantly
smaller than today. We find a 77% probability that the mass of the BH in Gaia
BH2 would have been below $2.2M_\odot$ at formation. This is below the
classical Tolman-Oppenheimer-Volkov limit, though it is not yet clear if BHs
subject to cosmological coupling should obey this limit. For Gaia BH1, the same
probability is 70%. This analysis is consistent with results from two BHs in
the globular cluster NGC3201, but unlike the NGC3201 BHs, the Gaia BHs have
well-constrained inclinations and thus firm upper mass limits. The discovery of
more BHs in binary systems with Gaia astrometry in the coming years will allow
us to test the cosmological coupling hypothesis decisively. | A Stable Finite-Volume Method for Scalar-Field Dark Matter: We describe and test a family of new numerical methods to solve the
Schrodinger equation in self-gravitating systems, e.g. Bose-Einstein
condensates or 'fuzzy'/ultra-light scalar field dark matter. The methods are
finite-volume Godunov schemes with stable, higher-order accurate gradient
estimation, based on a generalization of recent mesh-free finite-mass Godunov
methods. They couple easily to particle-based N-body gravity solvers (with or
without other fluids, e.g. baryons), are numerically stable, and
computationally efficient. Different sub-methods allow for manifest
conservation of mass, momentum, and energy. We consider a variety of test
problems and demonstrate that these can accurately recover solutions and remain
stable even in noisy, poorly-resolved systems, with dramatically reduced noise
compared to some other proposed implementations (though certain types of
discontinuities remain challenging). This is non-trivial because the "quantum
pressure" is neither isotropic nor positive-definite and depends on
higher-order gradients of the density field. We implement and test the method
in the code GIZMO. |
Deep Chandra observation of the galaxy cluster WARPJ1415.1+3612 at z=1:
an evolved cool-core cluster at high-redshift: Using the deepest (370 ksec) Chandra observation of a high-redshift galaxy
cluster, we perform a detailed characterization of the intra-cluster medium
(ICM) of WARPJ1415.1+3612 at z=1.03. We also explore the connection between the
ICM core properties and the radio/optical properties of the brightest cluster
galaxy (BCG). We perform a spatially resolved analysis of the ICM to obtain
temperature, metallicity and surface brightness profiles. Using the deprojected
temperature and density profiles we accurately derive the cluster mass at
different overdensities. In addition to the X-ray data, we use archival radio
VLA imaging and optical GMOS spectroscopy of the central galaxy to investigate
the feedback between the central galaxy and the ICM. The X-ray spectral
analysis shows a significant temperature drop towards the cluster center, with
a projected value of Tc = 4.6 \pm 0.4 keV, and a remarkably high central iron
abundance peak, Zc= 3.6 Zsun. The central cooling time is shorter than 0.1 Gyr
and the entropy is equal to 9.9 keV cm2. We detect a strong [OII] emission line
in the optical spectra of the BCG with an equivalent width of -25 \AA, for
which we derive a star formation rate within the range 2 - 8 Msun/yr. The VLA
data reveals a central radio source coincident with the BCG and a faint
one-sided jet-like feature with an extent of 80 kpc. The analysis presented
shows that WARPJ1415 has a well developed cool core with ICM properties similar
to those found in the local Universe. Its properties and the clear sign of
feedback activity found in the central galaxy in the optical and radio bands,
show that feedback processes are already established at z~1. In addition, the
presence of a strong metallicity peak shows that the central regions have been
promptly enriched by star formation processes in the central galaxy already at
z > 1. | AMiBA Wideband Analog Correlator: A wideband analog correlator has been constructed for the Yuan-Tseh Lee Array
for Microwave Background Anisotropy. Lag correlators using analog multipliers
provide large bandwidth and moderate frequency resolution. Broadband IF
distribution, backend signal processing and control are described. Operating
conditions for optimum sensitivity and linearity are discussed. From
observations, a large effective bandwidth of around 10 GHz has been shown to
provide sufficient sensitivity for detecting cosmic microwave background
variations. |
Constraints on the low-mass end of the mass-metallicity relation at
z=1-2 from lensed galaxies: We present multi-wavelength imaging and near-IR spectroscopy for ten
gravitationally lensed galaxies at 0.9<z<2.5 selected from a new, large sample
of strong lens systems in the Sloan Digital Sky Survey (SDSS) DR7. We derive
stellar masses from the rest-frame UV to near-IR spectral energy distributions,
star formation rates (SFR) from the dust-corrected Ha flux, and metallicities
from the [N II]/Ha flux ratio. We combine the lensed galaxies with a sample of
sixty star-forming galaxies from the literature in the same redshift range for
which measurements of [N II]/Ha have been published. Due to the lensing
magnification, the lensed galaxies probe intrinsic stellar masses that are on
average a factor of 11 lower than have been studied so far at these redshifts.
They have specific star formation rates that are an order of magnitude higher
than seen for main-sequence star-forming galaxies at z~2. We measure an
evolution of 0.16+/-0.06 dex in the mass-metallicity relation between z~1.4 and
z~2.2. In contrast to previous claims, the redshift evolution is smaller at low
stellar masses. We do not see a correlation between metallicity and SFR at
fixed stellar mass. The combined sample is in general agreement with the local
fundamental relation between metallicity, stellar mass and SFR from Mannucci et
al. (2010, 2011). Using the Kennicutt-Schmidt law to infer gas fractions, we
investigate the importance of gas inflows and outflows on the shape of the
mass-metallicity relation using simple analytical models. This suggests that
the Maiolino et al.(2008) calibration of the [N II]/Ha flux ratio is biased
high. We conclude that both an absolute metallicity calibration and direct
measurements of the gas mass are needed to use the observed mass-metallicity
relation to gain insight into the impact of gas flows on the chemical evolution
of galaxies. | Cross-Correlation of Cosmological Birefringence with CMB Temperature: Theories for new particle and early-Universe physics abound with
pseudo-Nambu-Goldstone fields that arise when global symmetries are
spontaneously broken. The coupling of these fields to the Chern-Simons term of
electromagnetism may give rise to cosmological birefringence (CB), a
frequency-independent rotation of the linear polarization of photons as they
propagate over cosmological distances. Inhomogeneities in the CB-inducing field
may yield a rotation angle that varies across the sky. Here we note that such a
spatially-varying birefringence may be correlated with the cosmic microwave
background (CMB) temperature. We describe quintessence scenarios where this
cross-correlation exists and other scenarios where the scalar field is simply a
massless spectator field, in which case the cross-correlation does not exist.
We discuss how the cross-correlation between CB-rotation angle and CMB
temperature may be measured with CMB polarization. This measurement may improve
the sensitivity to the CB signal, and it can help discriminate between
different models of CB. |
Intermediate inflation under the scrutiny of recent data: We use the flow equations to determine the different hierarchy Hubble
parameters as a function of the number of e-folds for intermediate models in
single-field inflation. The obtained expressions allow us to determine at
second order in the hierarchy Hubble parameters different observational
parameters. We distinguish the scalar spectral index, its running and the
tensor-to-scalar ratio, among others. Recently, it has been noticed that
measurements released by Planck, combined with the WMAP large-angle
polarization are in tension with this sort of model. Here, we show in detail
why this occur. The conclusions do not change even when the recent BICEP2 data
are included. | The VIMOS Public Extragalactic Redshift Survey (VIPERS). Exploring the
dependence of the three-point correlation function on stellar mass and
luminosity at 0.5<z<1.1: The three-point correlation function (3PCF) is a powerful probe to
investigate the clustering of matter in the Universe in a complementary way
with respect to lower-order statistics, providing additional information with
respect to the two-point correlation function and allowing us to shed light on
biasing, nonlinear processes, and deviations from Gaussian statistics. In this
paper, we analyse the first data release of the VIMOS Public Extragalactic
Redshift Survey (VIPERS), determining the dependence of the three-point
correlation function on luminosity and stellar mass at $z=[0.5,1.1]$. We
exploit the VIPERS Public Data Release 1, consisting of more than 50,000
galaxies with B-band magnitudes in the range $-21.6\lesssim M_{\rm
B}-5\log(h)\lesssim-19.9$ and stellar masses in the range
$9.8\lesssim\log(M_\star[h^{-2}\,M_\odot])\lesssim 10.7$. We measure both the
connected 3PCF and the reduced 3PCF in redshift space, probing different
configurations and scales, in the range $2.5<r\,$[Mpc/h]$<20$. We find a
significant dependence of the reduced 3PCF on scales and triangle shapes, with
stronger anisotropy at larger scales ($r\sim10$ Mpc/h) and an almost flat trend
at smaller scales, $r\sim2.5$ Mpc/h. Massive and luminous galaxies present a
larger connected 3PCF, while the reduced 3PCF is remarkably insensitive to
magnitude and stellar masses in the range we explored. These trends, already
observed at low redshifts, are confirmed for the first time to be still valid
up to $z=1.1$, providing support to the hierarchical scenario for which massive
and bright systems are expected to be more clustered. The possibility of using
the measured 3PCF to provide independent constraints on the linear galaxy bias
$b$ has also been explored, showing promising results in agreement with other
probes. |
Detecting coalescences of intermediate-mass black holes in globular
clusters with the Einstein Telescope: We discuss the capability of a third-generation ground-based detector such as
the Einstein Telescope to detect mergers of intermediate-mass black holes that
may have formed through runaway stellar collisions in globular clusters. We
find that detection rates of 500 events per year are plausible. | A Big Ring on the Sky: We present the discovery of `A Big Ring on the Sky' (BR), the second
ultra-large-scale structure (uLSS) found in MgII-absorber catalogues, following
the previously reported Giant Arc (GA). In cosmological terms the BR is close
to the GA - at the same redshift $z \sim 0.8$ and with a separation on the sky
of only $\sim 12^\circ$. Two extraordinary uLSSs in such close configuration
raises the possibility that together they form an even more extraordinary
cosmological system. The BR is a striking circular, annulus-like, structure of
diameter $\sim 400$ Mpc (proper size, present epoch). The method of discovery
is as described in the GA paper, but here using the new MgII-absorber
catalogues restricted to DR16Q quasars. Using the Convex Hull of Member Spheres
(CHMS) algorithm, we estimate that the annulus and inner absorbers of the BR
have departures from random expectations, at the density of the control field,
of up to $5.2\sigma$. We present the discovery of the BR, assess its
significance using the CHMS, Minimal Spanning Tree (MST), FilFinder and Cuzick
& Edwards (CE) methods, show it in the context of the GA+BR system, and suggest
some implications for the origins of uLSS and for our understanding of
cosmology. For example, it may be that unusual geometric patterns, such as
these uLSSs, have an origin in cosmic strings. |
Further evidence for large central mass-to-light ratios in massive
early-type galaxies: We studied the stellar populations, distribution of dark matter, and
dynamical structure of a sample of 25 early-type galaxies in the Coma and Abell
262 clusters. We derived dynamical mass-to-light ratios and dark matter
densities from orbit-based dynamical models, complemented by the ages,
metallicities, and \alpha-elements abundances of the galaxies from single
stellar population models. Most of the galaxies have a significant detection of
dark matter and their halos are about 10 times denser than in spirals of the
same stellar mass. Calibrating dark matter densities to cosmological
simulations we find assembly redshifts z_{DM} \approx 1-3. The dynamical mass
that follows the light is larger than expected for a Kroupa stellar initial
mass function, especially in galaxies with high velocity dispersion
\sigma_{eff} inside the effective radius r_{eff}. We now have 5 of 25 galaxies
where mass follows light to 1-3 r_{eff}, the dynamical mass-to-light ratio of
all the mass that follows the light is large (\approx 8-10 in the Kron-Cousins
R band), the dark matter fraction is negligible to 1-3 r_{eff}. This could
indicate a "massive" initial mass function in massive early-type galaxies.
Alternatively, some of the dark matter in massive galaxies could follow the
light very closely suggesting a significant degeneracy between luminous and
dark matter. | Cosmic String Loop Microlensing: Cosmic superstring loops within the galaxy microlens background point sources
lying close to the observer-string line of sight. For suitable alignments,
multiple paths coexist and the (achromatic) flux enhancement is a factor of
two. We explore this unique type of lensing by numerically solving for
geodesics that extend from source to observer as they pass near an oscillating
string. We characterize the duration of the flux doubling and the scale of the
image splitting. We probe and confirm the existence of a variety of fundamental
effects predicted from previous analyses of the static infinite straight
string: the deficit angle, the Kaiser-Stebbins effect, and the scale of the
impact parameter required to produce microlensing. Our quantitative results for
dynamical loops vary by O(1) factors with respect to estimates based on
infinite straight strings for a given impact parameter. A number of new
features are identified in the computed microlensing solutions. Our results
suggest that optical microlensing can offer a new and potentially powerful
methodology for searches for superstring loop relics of the inflationary era. |
Lyman-Alpha Emitting Galaxies as a Probe of Reionization: Large-Scale
Bubble Morphology and Small-Scale Absorbers: The visibility of LyA emitting galaxies during the Epoch of Reionization is
controlled by both diffuse HI patches in large-scale bubble morphology and
small-scale absorbers. To investigate the impact on LyA photons, we apply a
novel combination of analytic and numerical calculations to three scenarios:
(i) the `bubble' model, where only diffuse HI outside ionized bubbles is
present; (ii) the `web' model, where HI exists only in overdense self-shielded
gas; and (iii) the more realistic 'web-bubble' model, which contains both. Our
analysis confirms that there is a degeneracy between the ionization structure
of the intergalactic medium (IGM) and the HI fraction inferred from LyA
surveys, as the three models suppress LyA flux equally with very different HI
fractions. We argue that a joint analysis of the LyA luminosity function and
the rest-frame equivalent width distribution/LyA fraction can break this
degeneracy and provide constraints on the reionization history and its
topology. We further show that constraints can improve if we consider the full
shape of the M_UV-dependent redshift evolution of the LyA fraction of Lyman
break galaxies. Contrary to conventional wisdom, we find that (i) a drop of LyA
fraction larger for UV-faint than for UV-bright galaxies can be reproduced with
web and web-bubble models and therefore does not provide exclusive evidence of
patchy reionization, and (ii) the IGM-transmission PDF is unimodal for bubble
models and bimodal in web models. We further highlight the importance of
galaxy-absorber cross-correlation. Comparing our models to observations, the
neutral fraction at z~7 is likely to be of order of tens of per cent when
interpreted with bubble or web-bubble models. Alternatively, we obtain a
conservative lower limit ~1% in the web models, if we allow for a drop in the
photoionization rate by a factor of ~100 from the post-reionized universe.
[abridged] | Newtonian Hydrodynamics with General Relativistic Pressure: We present the general relativistic pressure correction terms in Newtonian
hydrodynamic equations to the nonlinear order: these are equations
(\ref{mass-conservation-Mink})-(\ref{Poisson-eq-Mink}). The derivation is made
in the zero-shear gauge based on the fully nonlinear formulation of
cosmological perturbation in Einstein's gravity. The correction terms {\it
differ} from many of the previously suggested forms in the literature based on
hand-waving manners. We confirm our results by comparing with (i) the nonlinear
perturbation theory, (ii) the first order post-Newtonian approximation, and
(iii) the special relativistic limit, and by checking (iv) the consistency with
full Einstein's equation. |
Small Angular Scale Measurements of the CMB Temperature Power Spectrum
from QUaD: We present measurements of the cosmic microwave background (CMB) radiation
temperature anisotropy in the multipole range 2000<ell<3000 from the QUaD
telescope's second and third observing seasons. After masking the brightest
point sources our results are consistent with the primary LCDM expectation
alone. We estimate the contribution of residual (un-masked) radio point sources
using a model calibrated to our own bright source observations, and a full
simulation of the source finding and masking procedure. Including this
contribution slightly improves the chi^2. We also fit a standard SZ template to
the bandpowers and see no strong evidence of an SZ contribution, which is as
expected for sigma_8 approx 0.8. | Machine-learning computation of distance modulus for local galaxies: Quickly growing computing facilities and an increasing number of
extragalactic observations encourage the application of data-driven approaches
to uncover hidden relations from astronomical data. In this work we raise the
problem of distance reconstruction for a large number of galaxies from
available extensive observations. We propose a new data-driven approach for
computing distance moduli for local galaxies based on the machine-learning
regression as an alternative to physically oriented methods. We use key
observable parameters for a large number of galaxies as input explanatory
variables for training: magnitudes in U, B, I, and K bands, corresponding
colour indices, surface brightness, angular size, radial velocity, and
coordinates. We performed detailed tests of the five machine-learning
regression techniques for inference of $m-M$: linear, polynomial, k-nearest
neighbours, gradient boosting, and artificial neural network regression. As a
test set we selected 91 760 galaxies at $z<0.2$ from the NASA/IPAC
extragalactic database with distance moduli measured by different independent
redshift methods. We find that the most effective and precise is the neural
network regression model with two hidden layers. The obtained root-mean-square
error of 0.35 mag, which corresponds to a relative error of 16\%, does not
depend on the distance to galaxy and is comparable with methods based on the
Tully-Fisher and Fundamental Plane relations. The proposed model shows a 0.44
mag (20\%) error in the case of spectroscopic redshift absence and is
complementary to existing photometric redshift methodologies. Our approach has
great potential for obtaining distance moduli for around 250 000 galaxies at
$z<0.2$ for which the above-mentioned parameters are already observed. |
Primordial Non-Gaussianity in Models with Dark Matter Isocurvature
Fluctuations: We investigate primordial non-Gaussianity and dark matter isocurvature
fluctuations in the modulated reheating and the curvaton scenarios. In these
scenarios, large non-Gaussianity can be generated, on the other hand, depending
on how dark matter is produced, too large isocurvature fluctuations can also
arise, which is inconsistent with current observations. In this paper, we study
this issue in a mixed scenario where the curvature fluctuations can also be
produced from the inflaton fluctuations as well as those from a light scalar
field such as the modulus and the curvaton. We show that primordial
fluctuations can be highly non-Gaussian without conflicting the current
constraint on isocurvature fluctuations for such mixed scenarios. However, if
the constraint on isocurvature fluctuations becomes severer as expected by the
Planck satellite, $f_{\rm NL}$, a nonlinearity parameter for adiabatic
fluctuations, should be very small as $f_{\rm NL} \lesssim 3$, which would give
interesting implications for the generation mechanism of dark matter.
Non-Gaussianity from isocurvature fluctuations is also discussed in these
scenarios. | Origin and Modelling of Cold Dark Matter Halo Properties: IV. Triaxial
Ellipticity: This paper has been withdrawn owing a re-arrangement of two previously
submitted papers. The new version of the theoretical work on the triaxial shape
of dark matter haloes can be found at the ArXiv astro-ph list (CO) as article
1104.2905 |
GECO: Galaxy Evolution COde - A new semi-analytical model of galaxy
formation: We present a new semi-analytical model of galaxy formation, GECO (Galaxy
Evolution COde), aimed at a better understanding of when and how the two
processes of star formation and galaxy assembly have taken place. Our model is
structured into a Monte Carlo algorithm based on the Extended Press-Schechter
theory, for the representation of the merging hierarchy of dark matter halos,
and a set of analytic algorithms for the treatment of the baryonic physics,
including classical recipes for the gas cooling, the star formation
time-scales, galaxy mergers and SN feedback. Together with the galaxies, the
parallel growth of BHs is followed in time and their feedback on the hosting
galaxies is modelled. We set the model free parameters by matching with data on
local stellar mass functions and the BH-bulge relation at z=0. Based on such
local boundary conditions, we investigate how data on the high-redshift
universe constrain our understanding of the physical processes driving the
evolution, focusing in particular on the assembly of stellar mass and on the
star formation history. Since both processes are currently strongly constrained
by cosmological near- and far-IR surveys, the basic physics of the Lambda CDM
hierarchical clustering concept of galaxy formation can be effectively tested
by us by comparison with the most reliable set of observables. Our
investigation shows that when the time-scales of the stellar formation and mass
assembly are studied as a function of dark matter halo mass and the single
galaxy stellar mass, the 'downsizing' fashion of star formation appears to be a
natural outcome of the model, reproduced even in the absence of the AGN
feedback. On the contrary, the stellar mass assembly history turns out to
follow a more standard hierarchical pattern progressive in cosmic time, with
the more massive systems assembled at late times mainly through dissipationless
mergers. | Multiwavelength campaign on Mrk 509 VII. Relative abundances of the warm
absorber: Context. The study of abundances in the nucleus of active galaxies allows us
to investigate the evolution of abundance by comparing local and higher
redshift galaxies. However, the methods used so far have substantial drawbacks
or rather large uncertainties. Some of the measurements are at odds with the
initial mass function derived from the older stellar population of local
elliptical galaxies. Aims. We determine accurate and reliable abundances of C,
N, Ne, and Fe relative to O from the narrow absorption lines observed in the
X-ray spectra of Mrk 509. Methods. We use the stacked 600 ks XMM-Newton RGS and
180 ks Chandra LETGS spectra. Thanks to simultaneous observations with INTEGRAL
and the optical monitor on-board XMM-Newton for the RGS observations and
HST-COS and Swift for the LETGS observations, we have an individual spectral
energy distribution for each dataset. Owing to the excellent quality of the RGS
spectrum, the ionisation structure of the absorbing gas is well constrained,
allowing for a reliable abundance determination using ions over the whole
observed range of ionisation parameters. Results. We find that the relative
abundances are consistent with the proto-solar abundance ratios: C/O =
1.19$\pm$0.08, N/O = 0.98$\pm$0.08, Ne/O = 1.11$\pm$0.10, Mg/O = 0.68$\pm$0.16,
Si/O = 1.3$\pm$0.6, Ca/O = 0.89$\pm$0.25, and Fe/O = 0.85$\pm$0.06, with the
exception of S, which is slightly under-abundant, S/O = 0.57$\pm$0.14. Our
results, and their implications, are discussed and compared to the results
obtained using other techniques to derive abundances in galaxies. |
A Uniform Type Ia Supernova Distance Ladder with the Zwicky Transient
Facility: Absolute Calibration Based on the Tip of the Red Giant Branch
(TRGB) Method: The current Cepheid-calibrated distance ladder measurement of $H_0$ is
reported to be in tension with the values inferred from the cosmic microwave
background (CMB), assuming standard cosmology. However, some tip of the red
giant branch (TRGB) estimates report $H_0$ in better agreement with the CMB.
Hence, it is critical to reduce systematic uncertainties in local measurements
to understand the Hubble tension. In this paper, we propose a uniform distance
ladder between the second and third rungs, combining SNe~Ia observed by the
Zwicky Transient Facility (ZTF) with a TRGB calibration of their absolute
luminosity. A large, volume-limited sample of both calibrator and Hubble flow
SNe~Ia from the \emph{same} survey minimizes two of the largest sources of
systematics: host-galaxy bias and non-uniform photometric calibration. We
present results from a pilot study using existing TRGB distance to the host
galaxy of ZTF SN~Ia SN 2021rhu (aka ZTF21abiuvdk) in NGC7814. Combining the ZTF
calibrator with a volume-limited sample from the first data release of ZTF
Hubble flow SNe~Ia, we infer $H_0 = 76.94 \pm 6.4\, {\rm km}\,{\rm
s^{-1}}\,{\rm Mpc^{-1}}$, an $8.3 \%$ measurement. The error budget is
dominated by the single object calibrating the SN~Ia luminosity in this pilot
study. However, the ZTF sample includes already five other SNe~Ia within $\sim$
20 Mpc for which TRGB distances can be obtained with HST. Finally, we present
the prospects of building this distance ladder out to 80 Mpc with JWST
observations of more than one hundred ZTF SNe~Ia. | Spatially Resolved Emission of a High Redshift DLA Galaxy with the
Keck/OSIRIS IFU: We present the first Keck/OSIRIS infrared IFU observations of a high redshift
damped Lyman-alpha (DLA) galaxy detected in the line of sight to a background
quasar. By utilizing the Laser Guide Star Adaptive Optics (LGSAO) to reduce the
quasar PSF to FWHM~0.15 arcsec, we were able to search for and map the
foreground DLA emission free from the quasar contamination. We present maps of
the H-alpha and [OIII] $\lambda \lambda$ 5007, 4959 emission of DLA 2222-0946
at a redshift of z ~ 2.35. From the composite spectrum over the H-alpha
emission region we measure a star formation rate of 9.5 $\pm$ 1.0 M$_{\odot}$
year$^{-1}$ and a dynamical mass, M$_{dyn}$ = 6.1 x 10$^9$ M$_{\odot}$. The
average star formation rate surface density is < \Sigma_{SFR} > = 0.55
M$_{\odot}$ yr$^{-1}$ kpc$^{-2}$, with a central peak of 1.7 M$_{\odot}$
yr$^{-1}$ kpc$^{-2}$. Using the standard Kennicutt-Schmidt relation, this
corresponds to a gas mass surface density of $\Sigma_{gas}$ = 243 M$_{\odot}$
pc$^{-2}$. Integrating over the size of the galaxy we find a total gas mass of
M$_{gas}$ = 4.2 x 10$^9$ M$_{\odot}$. We estimate the gas fraction of DLA
2222-0946 to be $f_{gas}$ ~ 40%. We detect [NII]$\lambda$6583 emission at 2.5
sigma significance with a flux corresponding to a metallicity of 75% solar.
Comparing this metallicity with that derived from the low-ion absorption gas ~6
kpc away, ~30% solar, indicates possible evidence for a metallicity gradient or
enriched in/outflow of gas. Kinematically, both H-alpha and [OIII] emission
show relatively constant velocity fields over the central galactic region.
While we detect some red and blueshifted clumps of emission, they do not
correspond with rotational signatures that support an edge-on disk
interpretation. |
Crossing the phantom divide with a classical Dirac field: In this paper we consider a spatially flat Friedmann-Robertson-Walker (FRW)
cosmological model with cosmological constant, containing a stiff fluid and a
classical Dirac field. The proposed cosmological scenario describes the
evolution of effective dark matter and dark energy components reproducing, with
the help of that effective multifluid configuration, the quintessential
behavior. We find the value of the scale factor where the effective dark energy
component crosses the phantom divide. The model we introduce, which can be
considered as a modified $\Lambda$CDM one, is characterized by a set of
parameters which may be constrained by the astrophysical observations available
up to date. | The nuclear starburst in Arp 299-A: From the 5.0 GHz VLBI radio
light-curves to its core-collapse supernova rate: The nuclear region of the Luminous Infra-red Galaxy Arp 299-A hosts a recent
($\simeq 10$ Myr), intense burst of massive star formation which is expected to
lead to numerous core-collapse supernovae (CCSNe). Previous VLBI observations,
carried out with the EVN at 5.0 GHz and with the VLBA at 2.3 and 8.4 GHz,
resulted in the detection of a large number of compact, bright, non-thermal
sources in a region $\lsim$150 pc in size. We aim at establishing the nature of
all non-thermal, compact components in Arp 299-A, as well as estimating its
core-collapse supernova rate. We use multi-epoch European VLBI Network (EVN)
observations taken at 5.0 GHz to image with milliarcsecond resolution the
compact radio sources in the nuclear region of Arp 299-A. We also use one
single-epoch 5.0 GHz Multi-Element Radio Linked Interferometer Network (MERLIN)
observation to image the extended emission in which the compact radio sources
--traced by our EVN observations-- are embedded. Twenty-six compact sources are
detected, 8 of them are new objects not previously detected. The properties of
all detected objects are consistent with them being a mixed population of CCSNe
and SNRs. We find clear evidence for at least two new CCSNe, implying a lower
limit to the CCSN rate of $\nu_{\rm SN}\gsim$0.80 SN/yr indicating that the
bulk of the current star formation in Arp 299-A is taking place in the
innermost $\sim 150$ pc. Our MERLIN observations trace a region of diffuse,
extended emission which is co-spatial to the region where all compact sources
are found. From this diffuse, non-thermal radio emission we obtain an
independent estimate for the core-collapse supernova rate, which is in the
range $\nu_{\rm SN}=0.40$ - 0.65 SN/yr, roughly in agreement with previous
estimates and our direct estimate of the CCSN rate from the compact radio
emission. |
Magnetic Fields from QCD Phase Transitions: We study the evolution of QCD phase transition-generated magnetic fields in
freely decaying MHD turbulence of the expanding Universe. We consider a
magnetic field generation model that starts from basic non-perturbative QCD
theory and predicts stochastic magnetic fields with an amplitude of the order
of 0.02 $\mu$G and small magnetic helicity. We employ direct numerical
simulations to model the MHD turbulence decay and identify two different
regimes: "weakly helical" turbulence regime, when magnetic helicity increases
during decay, and "fully helical" turbulence, when maximal magnetic helicity is
reached and an inverse cascade develops. The results of our analysis show that
in the most optimistic scenario the magnetic correlation length in the comoving
frame can reach 10 kpc with the amplitude of the effective magnetic field being
0.007 nG. We demonstrate that the considered model of magneto-genesis can
provide the seed magnetic field for galaxies and clusters. | Cosmic bulk flows on 50 {h}^{-1}Mpc scales: A Bayesian hyper-parameter
method and multishells likelihood analysis: It has been argued recently that the galaxy peculiar velocity field provides
evidence of excessive power on scales of $50\hmpc$, which seems to be
inconsistent with the standard $\Lambda$CDM cosmological model. We discuss
several assumptions and conventions used in studies of the large-scale bulk
flow to check whether this claim is robust under a variety of conditions.
Rather than using a composite catalogue we select samples from the SN, ENEAR,
SFI++ and A1SN catalogues, and correct for Malmquist bias in each according to
the IRAS PSCz density field. We also use slightly different assumptions about
the small-scale velocity dispersion and the parameterisation of the matter
power spectrum when calculating the variance of the bulk flow. By combining the
likelihood of individual catalogues using a Bayesian hyper-parameter method, we
find that the joint likelihood of the amplitude parameter gives
$\sigma_8=0.65^{+0.47}_{-0.35}(\pm 1 \sigma)$, which is entirely consistent
with the $\Lambda$CDM model. In addition, the bulk flow magnitude ($v \sim 310
\kms$) and direction, $(l,b)\sim (280^{\circ} \pm 8^{\circ}, 5.1^{\circ} \pm
6^{\circ})$, found by each of the catalogues are all consistent with each
other, and with the bulk flow results from most previous studies. Furthermore,
the bulk flow velocities in different shells of the surveys constrain
$\sigma_{8}$--$\Omega_{\rm{m}}$ to be
($1.01^{+0.26}_{-0.20},0.31^{+0.28}_{-0.14}$, SFI++) and
($1.04^{+0.32}_{-0.24},0.28^{+0.30}_{-0.14}$, ENEAR), which is consistent with
{\it WMAP} 7-year best-fit values. We finally discuss the differences between
our conclusions and those of the studies claiming the largest bulk flows. |
Blue E/S0 galaxies: merger remnants or disk rebuilding galaxies?: This paper has been withdrawn A new version is in preparation and will be
soon available. | Star forming galaxies in the Hercules cluster: Halpha imaging of A2151: This paper presents the first results of an Halpha imaging survey of galaxies
in the central regions of the A2151 cluster. A total of 50 sources were
detected in Halpha. The morphologies of the 43 H$\alpha$ selected galaxies
range from grand design spirals and interacting galaxies to blue compacts and
tidal dwarfs or isolated extragalactic HII regions, spanning a range of
magnitudes of -21 <= MB <= -12.5 mag. A comparison with the clusters Coma and
A1367 and a sample of field galaxies has shown the presence of cluster galaxies
with L(Halpha) lower than expected for their MB, a consecuence of the cluster
environment. This fact results in differences in the
L(Halpha) vs. EW(Halpha) and L(H\alpha) distributions of the clusters with
respect to the field, and in cluster to cluster variations of these quantities,
which we propose are driven by a global cluster property as the total mass.
Overall, we conclude that both, the global cluster environment as well as the
cluster merging history play a non negligible role in the integral star
formation properties of clusters of galaxies. |
Inelastic Dark Matter and DAMA/LIBRA: An Experimentum Crucis: The DAMA/LIBRA collaboration has detected an annual modulation of the recoil
rate in NaI crystals with the phase expected for WIMP scattering events. This
signal is dramatically inconsistent with upper limits from other experiments
for elastically scattering weak-scale WIMPs. However, the results are
compatible for the case of inelastic dark matter (iDM). The iDM theory, as
implemented by Tucker-Smith and Weiner, constrains the WIMP to a tight contour
in sigma_n-delta space, where delta is the mass difference between the ground
state and excited WIMPs. An urgent priority in direct detection is to test this
scenario. The crucial test of the iDM explanation of DAMA -- an "experimentum
crucis" -- is an experiment with directional sensitivity, which can measure the
daily modulation in direction. Because the contrast can be 100%, it is a
sharper test than the much smaller annual modulation in the rate. We estimate
the significance of such an experiment as a function of the WIMP mass, cross
section, background rate, and other parameters. The proposed experiment
severely constrains the DAMA/iDM scenario even with modest exposure (~1000 kg
day) on gaseous xenon. | Impact of the Relative Motion between the Dark Matter and Baryons on the
First Stars: Recently the initial supersonic relative velocity between the dark matter and
baryons was shown to have an important effect on galaxy formation at high
redshift. We study the impact of this relative motion on the distribution of
the star-forming halos and on the formation redshift of the very first star. We
include a new aspect of the relative velocity effect found in recent
simulations by fitting their results to obtain the spatially-varying minimum
halo mass needed for molecular cooling. Thus, the relative velocities have
three separate effects: suppression of the halo abundance, suppression of the
gas content within each halo, and boosting of the minimum cooling mass. We show
that the two suppressions (of gas content and of halo abundance) are the
primary effects on the small minihalos that cannot form stars, while the
cooling mass boost combines with the abundance suppression to produce order
unity fluctuations in stellar density. We quantify the large-scale
inhomogeneity of galaxies, finding that 68% of the star formation (averaged on
a 3 Mpc scale) is confined to 35% of the volume at z=20 (and just 18% at z=40).
In addition, we estimate the redshift of the first star to be z ~ 65, which
includes a delay of Dz ~ 5 due to the relative velocity. |
Multi-field inflation with large scalar fluctuations: non-Gaussianity
and perturbativity: Recently multi-field inflation models that can produce large scalar
fluctuations on small scales have drawn a lot of attention, primarily because
they could lead to primordial black hole production and generation of large
second-order gravitational waves. In this work, we focus on models where the
scalar fields responsible for inflation live on a hyperbolic field space. In
this case, geometrical destabilisation and non-geodesic motion are responsible
for the peak in the scalar power spectrum. We present new results for scalar
non-Gaussianity and discuss its dependence on the model's parameters. On scales
around the peak, we typically find that the non-Gaussianity is large and close
to local in form. We validate our results by employing two different numerical
techniques, utilising the transport approach, based on full cosmological
perturbation theory, and the $\delta N$ formalism, based on the separate
universe approximation. We discuss implications of our results for the
perturbativity of the underlying theory, focusing in particular on versions of
these models with potentially relevant phenomenology at interferometer scales. | Electromagnetic plasma waves in dark energy cosmology: We explore electromagnetic wave modes that can exist in a cosmological plasma
dominated by dark energy due to a cosmological constant. It is found that, in
the cold and hot plasma cases, electromagnetic plasma wave modes can be found
exactly. The effect of this cosmology appears as a time-dependent potential in
the wave equation for the electromagnetic modes, that effectively modify the
frequency response of the plasma. This potential depends on the metric of the
spacetime and on the thermodynamical properties of the plasma. For both cases,
cold and hot, the solutions are found in terms of Airy and Bessel functions,
respectively. When those solutions are required to have vanishing initial
conditions, a discretization on the wavelengths of the electromagnetic plasma
waves is imposed. Thus, only some specific wave modes can exist in this dark
energy cosmology. Relaxing those conditions, we obtain other solutions that
approximate to plane waves only in the very hot plasma limit. |
Testing the EoS of dark matter with cosmological observations: We explore the cosmological constraints on the parameter w_dm of the dark
matter barotropic equation of state (EoS) to investigate the "warmness" of the
dark matter fluid. The model is composed by the dark matter and dark energy
fluids in addition to the radiation and baryon components. We constrain the
values of w_dm using the latest cosmological observations that measure the
expansion history of the Universe. When w_dm is estimated together with the
parameter w_de of the barotropic EoS of dark energy we found that the
cosmological data favor a value of w_dm = 0.006 +- 0.001, suggesting a -warm-
dark matter, and w_de= -1.11 +- 0.03$ that corresponds to a phantom dark
energy, instead of favoring a cold dark matter and a cosmological constant
(w_dm = 0, w_de = -1). When w_dm is estimated alone but assuming w_de = -1,
-1.1, -0.9, we found w_dm = 0.009 +- 0.002, 0.006 +- 0.002, 0.012 +- 0.002
respectively, where the errors are at 3 sigma (99.73%), i.e., w_dm > 0 with at
least 99.73% of confidence level. When (w_dm, \Omega_dm0) are constrained
together, the best fit to data corresponds to (w_dm=0.005 +- 0.001, \Omega_dm0
= 0.223 +- 0.008) and with the assumption of w_de = -1.1 instead of a
cosmological constant (i.e., w_de = -1). With these results we found evidence
of w_dm > 0 suggesting a -warm- dark matter, independent of the assumed value
for w_{\rm de}, but where values w_de < -1 are preferred by the observations
instead of the cosmological constant. These constraints on w_dm are consistent
with perturbative analyses done in previous works. | The Canada-France High-z Quasar Survey: nine new quasars and the
luminosity function at redshift 6: We present discovery imaging and spectroscopy for nine new z ~ 6 quasars
found in the Canada-France High-z Quasar Survey (CFHQS) bringing the total
number of CFHQS quasars to 19. By combining the CFHQS with the more luminous
SDSS sample we are able to derive the quasar luminosity function from a sample
of 40 quasars at redshifts 5.74 < z < 6.42. Our binned luminosity function
shows a slightly lower normalisation and flatter slope than found in previous
work. The binned data also suggest a break in the luminosity function at M_1450
approx -25. A double power law maximum likelihood fit to the data is consistent
with the binned results. The luminosity function is strongly constrained (1
sigma uncertainty < 0.1 dex) over the range -27.5 < M_1450 < -24.7. The
best-fit parameters are Phi(M_1450^*) = 1.14 x 10^-8 Mpc^-3 mag^-1, break
magnitude M_1450^* = -25.13 and bright end slope beta = -2.81. However the
covariance between beta and M_1450^* prevents strong constraints being placed
on either parameter. For a break magnitude in the range -26 < M_1450^* < -24 we
find -3.8 < beta < -2.3 at 95% confidence. We calculate the z = 6 quasar
intergalactic ionizing flux and show it is between 20 and 100 times lower than
that necessary for reionization. Finally, we use the luminosity function to
predict how many higher redshift quasars may be discovered in future near-IR
imaging surveys. |
Forecast constraints on Anisotropic Stress in Dark Energy using
gravitational-waves: It is always interesting to investigate how well can a future experiment
perform with respect to others (present or future ones). Cosmology is really an
exciting field where a lot of puzzles are still unknown. In this article we
consider a generalized dark energy (DE) scenario where anisotropic stress is
present. We constrain this generalized cosmic scenario with an aim to
investigate how gravitational waves standard sirens (GWSS) may constrain the
anisotropic stress, which according to the standard cosmological probes,
remains unconstrained. In order to do this, we generate the luminosity distance
measurements from $\mathcal{O} (10^3)$ mock GW events which match the expected
sensitivity of the Einstein Telescope. Our analyses report that, first of all,
GWSS can give better constraints on various cosmological parameters compared to
the usual cosmological probes, but the viscous sound speed appearing due to the
dark energy anisotropic stress, is totally unconstrained even after the
inclusion of GWSS. | Using Spectral Flux Ratios to Standardize SN Ia Luminosities: We present a new method to standardize Type Ia supernova (SN Ia) luminosities
to ~<0.13 magnitudes using flux ratios from a single flux-calibrated spectrum
per SN. Using Nearby Supernova Factory spectrophotomery of 58 SNe Ia, we
performed an unbiased search for flux ratios which correlate with SN Ia
luminosity. After developing the method and selecting the best ratios from a
training sample, we verified the results on a separate validation sample and
with data from the literature. We identified multiple flux ratios whose
correlations with luminosity are stronger than those of light curve shape and
color, previously identified spectral feature ratios, or equivalent width
measurements. In particular, the flux ratio R(642/443) = F(642 nm) / F(443 nm)
has a correlation of 0.95 with SN Ia absolute magnitudes. Using this single
ratio as a correction factor produces a Hubble diagram with a residual scatter
standard deviation of 0.125 +- 0.011 mag, compared with 0.161 +- 0.015 mag when
fit with the SALT2 light curve shape and color parameters x1 and c. The ratio
R(642/443) is an effective correction factor for both extrinsic dust reddening
and instrinsic variations such as those of SN 1991T-like and SN 1999aa-like
SNe. When combined with broad-band color measurements, spectral flux ratios can
standardize SN Ia magnitudes to ~0.12 mag. These are the first spectral metrics
that improve over the standard normalization methods based upon light curve
shape and color and they provide among the lowest scatter Hubble diagrams ever
published. |
Discovery of z~8 Galaxies in the HUDF from ultra-deep WFC3/IR
Observations: We utilize the newly-acquired, ultra-deep WFC3/IR observations over the HUDF
to search for star-forming galaxies at z~8-8.5, only 600 million years from
recombination, using a Y_{105}-dropout selection. The new 4.7 arcmin**2 WFC3/IR
observations reach to ~28.8 AB mag (5 sigma) in the Y_{105}J_{125}H_{160}
bands. These remarkable data reach ~1.5 AB mag deeper than the previous data
over the HUDF, and now are an excellent match to the HUDF optical ACS data. For
our search criteria, we use a two-color Lyman-Break selection technique to
identify z~8-8.5 Y_{105}-dropouts. We find 5 likely z~8-8.5 candidates. The
sources have H_{160}-band magnitudes of ~28.3 AB mag and very blue UV-continuum
slopes, with a median estimated beta of <~-2.5 (where f_{\lambda}\propto
\lambda^{\beta}). This suggests that z~8 galaxies are not only essentially dust
free but also may have very young ages or low metallicities. The observed
number of Y_{105}-dropout candidates is smaller than the 20+/-6 sources
expected assuming no evolution from z~6, but is consistent with the 5 expected
extrapolating the Bouwens et al. 2008 LF results to z~8. These results provide
evidence that the evolution in the LF seen from z~7 to z~3 continues to z~8.
The remarkable improvement in the sensitivity of WFC3/IR has enabled HST to
cross a threshold, revealing star-forming galaxies at z~8-9. | Particle reacceleration by compressible turbulence in galaxy clusters:
effects of reduced mean free path: Direct evidence for in situ particle acceleration mechanisms in the
inter-galactic-medium (IGM) is provided by the diffuse Mpc--scale synchrotron
emissions observed from galaxy clusters. It has been proposed that MHD
turbulence, generated during cluster-cluster mergers, may be a source of
particle reacceleration in the IGM. Calculations of turbulent acceleration must
account self-consistently for the complex non--linear coupling between
turbulent waves and particles. This has been calculated in some detail under
the assumption that turbulence interacts in a collisionless way with the IGM.
In this paper we explore a different picture of acceleration by compressible
turbulence in galaxy clusters, where the interaction between turbulence and the
IGM is mediated by plasma instabilities and maintained collisional at scales
much smaller than the Coulomb mean free path. In this regime most of the energy
of fast modes is channeled into the reacceleration of relativistic particles
and the acceleration process approaches a universal behaviour being
self-regulated by the back-reaction of the accelerated particles on turbulence
itself. Assuming that relativistic protons contribute to several percent (or
less) of the cluster energy, consistent with the FERMI observations of nearby
clusters, we find that compressible turbulence at the level of a few percent of
the thermal energy can reaccelerate relativistic electrons at GeV energies,
that are necessary to explain the observed diffuse radio emission in the form
of giant radio halos. |
A dearth of dark matter in strong gravitational lenses: I show that the lensing masses of the SLACS sample of strong gravitational
lenses are consistent with the stellar masses determined from population
synthesis models using the Salpeter IMF. This is true in the context of both
General Relativity and modified Newtonian dynamics, and is in agreement with
the expectation of MOND that there should be little classical discrepancy
within the high surface brightness regions probed by strong gravitational
lensing. There is also dynamical evidence from this sample supporting the claim
that the mass-to-light ratio of the stellar component increases with the
velocity dispersion. | Hunting Axion Dark Matter with Protoplanetary Disk Polarimetry: We find that the polarimetric observations of protoplanetary disks are useful
to search for ultra-light axion dark matter. Axion dark matter predicts the
rotation of the linear polarization plane of propagating light, and
protoplanetary disks are ideal targets to observe it. We show that a recent
observation puts the tightest constraint on the axion-photon coupling constant
for axion mass $m\lesssim10^{-21}$eV. |
Preheating after multifield inflation with nonminimal couplings, II:
Resonance Structure: This is the second in a series of papers on preheating in inflationary models
comprised of multiple scalar fields coupled nonminimally to gravity. In this
paper, we work in the rigid-spacetime approximation and consider field
trajectories within the single-field attractor, which is a generic feature of
these models. We construct the Floquet charts to find regions of parameter
space in which particle production is efficient for both the adiabatic and
isocurvature modes, and analyze the resonance structure using analytic and
semi-analytic techniques. Particle production in the adiabatic direction is
characterized by the existence of an asymptotic scaling solution at large
values of the nonminimal couplings, $\xi_I \gg 1$, in which the dominant
instability band arises in the long-wavelength limit, for comoving wavenumbers
$k \rightarrow 0$. However, the large-$\xi_I$ regime is not reached until
$\xi_I \geq {\cal O} (100)$. In the intermediate regime, with $\xi_I \sim {\cal
O}(1 - 10)$, the resonance structure depends strongly on wavenumber and
couplings. The resonance structure for isocurvature perturbations is distinct
and more complicated than its adiabatic counterpart. An intermediate regime,
for $\xi_I \sim {\cal O} (1 - 10)$, is again evident. For large values of
$\xi_I$, the Floquet chart consists of densely spaced, nearly parallel
instability bands, suggesting a very efficient preheating behavior. The
increased efficiency arises from features of the nontrivial field-space
manifold in the Einstein frame, which itself arises from the fields' nonminimal
couplings in the Jordan frame, and has no analogue in models with minimal
couplings. Quantitatively, the approach to the large-$\xi_I$ asymptotic
solution for isocurvature modes is slower than in the case of the adiabatic
modes. | Modelling the large scale structure of the Universe as a function of
cosmology and baryonic physics: We present and test a framework that models the three-dimensional
distribution of mass in the Universe as a function of cosmological and
astrophysical parameters. Our approach combines two different techniques: a
rescaling algorithm that modifies the cosmology of gravity-only N-body
simulations, and a baryonification algorithm which mimics the effects of
astrophysical processes induced by baryons, such as star formation and AGN
feedback. We show how this approach can accurately reproduce the effects of
baryons on the matter power spectrum of various state-of-the-art
hydro-dynamical simulations (EAGLE, Illustris, Illustris-TNG, Horizon-AGN, and
OWLS,Cosmo-OWLS and BAHAMAS), to percent level from very large down to small,
highly nonlinear scales, k= 5 h/Mpc, and from z=0 up to z=2. We highlight that,
thanks to the heavy optimisation of the algorithms, we can obtain these
predictions for arbitrary baryonic models and cosmology (including massive
neutrinos and dynamical dark energy models) with an almost negligible CPU cost.
Therefore, this approach is efficient enough for cosmological data analyses.
With these tools in hand we explore the degeneracies between cosmological and
astrophysical parameters in the nonlinear mass power spectrum. Our findings
suggest that after marginalising over baryonic physics, cosmological
constraints inferred from weak gravitational lensing should be moderately
degraded. |
Probing solutions to the $S_8$ tension with galaxy clustering: The current discrepancy between the CMB and weak lensing measurements of the
amplitude of matter fluctuations, the so-called $S_8$ tension, has attracted a
great deal of recent attention, as it may show a crack in the $\Lambda$CDM
model of cosmology. We review the evidence for this tension and describe
potential solutions, focusing on extensions of the standard cosmological model,
including interacting dark energy and modified gravity. We present a likelihood
analysis of the BOSS DR12 data, probing these alternative models as well as
$\Lambda$CDM. From this analysis, we show hints of non-standard cosmology
compatible with those seen in weak lensing observations, demonstrating that
interacting dark energy or modified gravity can explain them successfully. We
then discuss the robustness of these results to analysis choices, as well as
future paths to confirm them with additional data and further distinguish
between models. | Four direct measurements of the fine-structure constant 13 billion years
ago: Observations of the redshift z=7.085 quasar J1120+0641 have been used to
search for variations of the fine structure constant, alpha, over the redshift
range 5.5 to 7.1. Observations at z=7.1 probe the physics of the universe when
it was only 0.8 billion years old. These are the most distant direct
measurements of alpha to date and the first measurements made with a near-IR
spectrograph. A new AI analysis method has been employed. Four measurements
from the X-SHOOTER spectrograph on the European Southern Observatory's Very
Large Telescope (VLT) directly constrain any changes in alpha relative to the
value measured on Earth (alpha_0). The weighted mean strength of the
electromagnetic force over this redshift range in this location in the universe
is da/a = (alpha_z - alpha_0)/alpha_0 = (-2.18 +/- 7.27) X 10^{-5}, i.e. we
find no evidence for a temporal change from the 4 new very high redshift
measurements. When the 4 new measurements are combined with a large existing
sample of lower redshift measurements, a new limit on possible spatial
variation of da/a is marginally preferred over a no-variation model at the 3.7
sigma level. |
Predictions for the 21cm-galaxy cross-power spectrum observable with
LOFAR and Subaru: The 21cm-galaxy cross-power spectrum is expected to be one of the promising
probes of the Epoch of Reionization (EoR), as it could offer information about
the progress of reionization and the typical scale of ionized regions at
different redshifts. With upcoming observations of 21cm emission from the EoR
with the Low Frequency Array (LOFAR), and of high redshift Lyalpha emitters
(LAEs) with Subaru's Hyper Suprime Cam (HSC), we investigate the observability
of such cross-power spectrum with these two instruments, which are both
planning to observe the ELAIS-N1 field at z=6.6. In this paper we use N-body +
radiative transfer (both for continuum and Lyalpha photons) simulations at
redshift 6.68, 7.06 and 7.3 to compute the 3D theoretical 21cm-galaxy
cross-power spectrum, as well as to predict the 2D 21cm-galaxy cross-power
spectrum expected to be observed by LOFAR and HSC. Once noise and projection
effects are accounted for, our predictions of the 21cm-galaxy cross-power
spectrum show clear anti-correlation on scales larger than ~ 60 h$^{-1}$ Mpc
(corresponding to k ~ 0.1 h Mpc$^{-1}$), with levels of significance p=0.04 at
z=6.6 and p=0.048 at z=7.3. On smaller scales, instead, the signal is
completely contaminated. | Very Large Array observations of the 8 o'clock arc lens system: Radio
emission and a limit on the star-formation rate: The 8 o'clock arc is a gravitationally lensed Lyman Break Galaxy (LBG) at
redshift z=2.73 that has a star-formation rate (SFR) of 270 solar-mass/year
(derived from optical and near-infrared spectroscopy). Taking the magnification
of the system ~12 and the SFR into account, the expected flux density of any
associated radio emission at 1.4 GHz is predicted to be just 0.1 mJy. However,
the lens system is found to be coincident with a radio source detected in the
NRAO Very Large Array (VLA) Sky Survey with a flux density of ~5 mJy. If this
flux density is attributed to the lensed LBG then it would imply a SFR ~11000
solar-mass/year, in contrast with the optical and near-infrared derived value.
We want to investigate the radio properties of this system, and independently
determine the SFR for the LBG from its lensed radio emission. We have carried
out new high resolution imaging with the VLA ain A and B-configurations at 1.4
and 5 GHz. We find that the radio emission is dominated by a radio-loud AGN
associated with the lensing galaxy. The radio-jet from the AGN partially covers
the lensed arc of the LBG, and we do not detect any radio emission from the
unobscured region of the arc down to a 3 sigma flux-density limit of 108
micro-Jy/beam. Using the radio data, we place a limit of <750 solar-mass/year
for the SFR of the LBG, which is consistent with the results from the optical
and near-infrared spectroscopy. We expect that the sensitivity of the Expanded
VLA will be sufficient to detect many high redshift LBGs that are
gravitationally lensed after only a few hours of observing time. The high
angular resolution provided by the EVLA will also allow detailed studies of the
lensed galaxies and determine if there is radio emission from the lens. |
Constraints on cosmic hemispherical power anomalies from quasars: Recent analyses of the cosmic microwave background (CMB) maps from the WMAP
satellite have uncovered evidence for a hemispherical power anomaly, i.e. a
dipole modulation of the CMB power spectrum at large angular scales with an
amplitude of +/-14 percent. Erickcek et al have put forward an inflationary
model to explain this anomaly. Their scenario is a variation on the curvaton
scenario in which the curvaton possesses a large-scale spatial gradient that
modulates the amplitude of CMB fluctuations. We show that this scenario would
also lead to a spatial gradient in the amplitude of perturbations sigma_8, and
hence to a dipole asymmetry in any highly biased tracer of the underlying
density field. Using the high-redshift quasars from the Sloan Digital Sky
Survey, we find an upper limit on such a gradient of |nabla
sigma_8|/sigma_8<0.027/r_{lss} (99% posterior probability), where r_{lss} is
the comoving distance to the last-scattering surface. This rules out the
simplest version of the curvaton spatial gradient scenario. | Galaxy pairs in the Sloan digital sky survey - VII: The merger --
luminous infra-red galaxy connection: We use a sample of 9397 low z galaxies with a close companion to investigate
the connection between mergers and luminous infra-red (IR) galaxies (LIRGs).
The pairs are selected from the SDSS and have projected separations rp < 80
kpc, relative velocities dv < 300 km/s and stellar mass ratios within a factor
1:10. The IR luminosities (LIR) of galaxies in the pair and (mass, z and
environment-matched) control samples are determined from the SDSS -- IRAS
matched catalog of Hwang et al. (2010). We find a trend for increasing LIRG
fraction towards smaller pair separations, peaking at a factor of ~ 5--10 above
the median control fraction at the smallest separations (rp < 20 kpc), but
remaining elevated by a factor ~ 2--3 even out to 80 kpc (the widest
separations in our sample). We also find that LIRGs are most likely to be found
in high mass galaxies which have an approximately equal mass companion. We
confirm the results of previous studies that both the active galactic nucleus
(AGN) fraction and merger fraction increase strongly as a function of IR
luminosity. About 7% of LIRGs are associated with major mergers, as defined
within the criteria and mass completion of our sample. Finally, we quantify a
SFR offset (Delta SFR) as the enhancement (or decrement) relative to
star-forming galaxies of the same mass and redshift. We demonstrate that there
is a clear connection between the Delta SFR and the classification of a galaxy
as a LIRG that is mass dependent. Most of the LIRGs in our merger sample are
relatively high mass galaxies (log M* > 10.5), likely because the SFR
enhancement required to produce LIRG luminosities is more modest than at low
masses. The Delta SFR offers a redshift-independent metric for the
identification of the galaxies with the most enhanced star forming rates that
does not rely on fixed LIR boundaries. |
Clustering dark energy and halo abundances: Within the standard paradigm, dark energy is taken as a homogeneous fluid
that drives the accelerated expansion of the universe and does not contribute
to the mass of collapsed objects such as galaxies and galaxy clusters. The
abundance of galaxy clusters -- measured through a variety of channels -- has
been extensively used to constrain the normalization of the power spectrum: it
is an important probe as it allows us to test if the standard $\Lambda$CDM
model can indeed accurately describe the evolution of structures across
billions of years. It is then quite significant that the Planck satellite has
detected, via the Sunyaev-Zel'dovich effect, less clusters than expected
according to the primary CMB anisotropies. One of the simplest generalizations
that could reconcile these observations is to consider models in which dark
energy is allowed to cluster, i.e., allowing its sound speed to vary. In this
case, however, the standard methods to compute the abundance of galaxy clusters
need to be adapted to account for the contributions of dark energy. In
particular, we examine the case of clustering dark energy -- a dark energy
fluid with negligible sound speed -- with a redshift-dependent equation of
state. We carefully study how the halo mass function is modified in this
scenario, highlighting corrections that have not been considered before in the
literature. We address modifications in the growth function, collapse
threshold, virialization densities and also changes in the comoving scale of
collapse and mass function normalization. Our results show that clustering dark
energy can impact halo abundances at the level of 10\%--30\%, depending on the
halo mass, and that cluster counts are modified by about 30\% at a redshift of
unity. | Metal Transport to the Gaseous Outskirts of Galaxies: We present a search for outlying HII regions in the extended gaseous
outskirts of nearby (D < 40 Mpc) galaxies, and subsequent multi-slit
spectroscopy used to obtain the HII region nebular oxygen abundances. The
galaxies in our sample have extended HI disks and/or interaction-related HI
features that extend well beyond their primary stellar components. We report
oxygen abundance gradients out to 2.5 times the optical radius for these
galaxies which span a range of morphologies and masses. We analyze the
underlying stellar and neutral HI gas distributions in the vicinity of the HII
regions to understand the physical processes that give rise to the observed
metal distributions in galaxies. These measurements, for the first time,
convincingly show flat abundance distributions out to large radii in a wide
variety of systems, and have broad implications for galaxy chemodynamical
evolution. |
Asymmetric condensed dark matter: We explore the viability of a boson dark matter candidate with an asymmetry
between the number densities of particles and antiparticles. A simple thermal
field theory analysis confirms that, under certain general conditions, this
component would develop a Bose-Einstein condensate in the early universe that,
for appropriate model parameters, could survive the ensuing cosmological
evolution until now. The condensation of a dark matter component in equilibrium
with the thermal plasma is a relativistic process, hence the amount of matter
dictated by the charge asymmetry is complemented by a hot relic density frozen
out at the time of decoupling. Contrary to the case of ordinary WIMPs, dark
matter particles in a condensate must be lighter than a few tens of eV so that
the density from thermal relics is not too large. Big-Bang nucleosynthesis
constrains the temperature of decoupling to the scale of the QCD phase
transition or above. This requires large dark matter-to-photon ratios and very
weak interactions with standard model particles. | A simplified structure for the second order cosmological perturbation
equations: Increasingly accurate observations of the cosmic microwave background and the
large scale distribution of galaxies necessitate the study of nonlinear
perturbations of Friedmann-Lemaitre cosmologies, whose equations are
notoriously complicated. In this paper we present a new derivation of the
governing equations for second order perturbations within the framework of the
metric-based approach that is minimal, as regards amount of calculation and
length of expressions, and flexible, as regards choice of gauge and
stress-energy tensor. Because of their generality and the simplicity of their
structure our equations provide a convenient starting point for determining the
behaviour of nonlinear perturbations of FL cosmologies with any given
stress-energy content, using either the Poisson gauge or the uniform curvature
gauge. |
Mapping the properties of blue compact dwarf galaxies: integral field
spectroscopy with PMAS: (Abridged) We perform integral field spectroscopy of a sample of Blue compact
dwarf (BCD) galaxies with the aim of analyzing their morphology, the spatial
distribution of some of their physical properties (excitation, extinction, and
electron density) and their relationship with the distribution and evolutionary
state of the stellar populations. Integral field spectroscopy observations of
the sample galaxies were carried out with the Potsdam Multi-Aperture
Spectrophotometer (PMAS) at the 3.5 m telescope at Calar Alto Observatory. An
area 16 arcsec x 16 arcsec in size was mapped with a spatial sampling of 1
arcsec x 1 arcsec. We obtained data in the 3590-6996 Angstroms spectral range,
with a linear dispersion of 3.2 Angstroms per pixel. From these data we built
two-dimensional maps of the flux of the most prominent emission lines, of two
continuum bands, of the most relevant line ratios, and of the gas velocity
field. Integrated spectra of the most prominent star-forming regions and of
whole objects within the FOV were used to derive their physical parameters and
the gas metal abundances. Six galaxies display the same morphology both in
emission line and in continuum maps; only in two objects, Mrk 32 and Tololo
1434+032, the distributions of the ionized gas and of the stars differ
considerably. In general the different excitation maps for a same object
display the same pattern and trace the star-forming regions, as expected for
objects ionized by hot stars; only the outer regions of Mrk 32, I Zw 123 and I
Zw 159 display higher [SII]/Halpha values, suggestive of shocks. Six galaxies
display an inhomogeneous dust distribution. Regarding the kinematics, Mrk 750,
Mrk 206 and I Zw 159 display a clear rotation pattern, while in Mrk 32, Mrk 475
and I Zw 123 the velocity fields are flat. | AMICO galaxy clusters in KiDS-DR3: the impact of estimator statistics on
the luminosity-mass scaling relation: As modern-day precision cosmology aims for statistical uncertainties of the
percent level or lower, it becomes increasingly important to reconsider
estimator assumptions at each step of the process, and their consequences on
the statistical variability of the scientific results.
We compare $L^1$ regression statistics to the weighted mean, the canonical
$L^2$ method based on Gaussian assumptions, for inference of the weak
gravitational shear signal from a catalog of background ellipticity
measurements around a sample of clusters, in many recent analyses a standard
step in the process.
We use the shape measurements of background sources around 6925 AMICO
clusters detected in the KiDS 3rd data release. We investigate the robustness
of our results and the dependence of uncertainties on the signal-to-noise
ratios of the background source detections. Using a halo model approach, we
derive lensing masses from the estimated excess surface density profiles.
The highly significant shear signal allows us to study the scaling relation
between the $r$-band cluster luminosity $L_{200}$, and the derived lensing mass
$M_{200}$. We show the results of the scaling relations derived in 13 bins in
$L_{200}$, with a tightly constrained power law slope of $\sim 1.24\pm 0.08$.
We observe a small, but significant relative bias of a few percent in the
recovered excess surface density profiles between the two regression methods,
which translates to a $1\sigma$ difference in $M_{200}$. The efficiency of
$L^1$ is at least that of the weighted mean, relatively increasing with higher
signal-to-noise shape measurements.
Our results indicate the relevance of optimizing the estimator for infering
the gravitational shear from a distribution of background ellipticities. The
interpretation of measured relative biases can be gauged by deeper
observations, while increased computation times remain feasible. |
Evolution and Distribution of Magnetic Fields from AGNs in Galaxy
Clusters II. The Effects of Cluster Size and Dynamical State: Theory and simulations suggest that magnetic fields from radio jets and lobes
powered by their central super massive black holes can be an important source
of magnetic fields in the galaxy clusters. This is paper II in a series of
studies where we present self-consistent high-resolution adaptive mesh
refinement cosmological magnetohydrodynamic (MHD) simulations that
simultaneously follow the formation of a galaxy cluster and evolution of
magnetic fields ejected by an active galactic nucleus (AGN). We studied 12
different galaxy clusters with virial masses ranging from 1 $\times$ 10$^{14}$
to 2 $\times$ 10$^{15}$ M$_{\odot}$. In this work we examine the effects of the
mass and merger history on the final magnetic properties. We find that the
evolution of magnetic fields is qualitatively similar to those of previous
studies. In most clusters, the injected magnetic fields can be transported
throughout the cluster and be further amplified by the intra-cluster medium
(ICM) turbulence during the cluster formation process with hierarchical
mergers, while the amplification history and the magnetic field distribution
depend on the cluster formation and magnetism history. This can be very
different for different clusters. The total magnetic energies in these clusters
are between 4 $\times$ 10$^{57}$ and $10^{61}$ erg, which is mainly decided by
the cluster mass, scaling approximately with the square of the total mass.
Dynamically older relaxed clusters usually have more magnetic fields in their
ICM. The dynamically very young clusters may be magnetized weakly since there
is not enough time for magnetic fields to be amplified. | Search for dark energy potentials in quintessence theory: The time evolution of the equation of state $w$ for quintessence models with
a scalar field as dark energy is studied up to the third derivative
($d^3w/da^3$) with respect to the scale factor $a$, in order to predict the
future observations and specify the scalar potential parameters with the
observables. The third derivative of $w$ for general potential $V$ is derived
and applied to several types of potentials. They are the inverse power-law
($V=M^{4+\alpha}/Q^{\alpha}$), the exponential ($V=M^4\exp{(\beta M/Q)}$), the
mixed ( $V=M^{4+\gamma}\exp{(\beta M/Q)}/Q^{\gamma}$), the cosine ($V=M^4(\cos
(Q/f)+1)$) and the Gaussian types ($V=M^4\exp(-Q^2/\sigma^2)$), which are
prototypical potentials for the freezing and thawing models.
If the parameter number for a potential form is $ n$, it is necessary to find
at least for $n+2$ independent observations to identify the potential form and
the evolution of the scalar field ($Q$ and $ \dot{Q} $).
Such observations would be the values of $ \Omega_Q, w, dw/da. \cdots $, and
$ dw^n/da^n$.
From these specific potentials, we can predict the $ n+1 $ and higher
derivative of $w$ ; $ dw^{n+1}/da^{n+1}, \cdots$.
Since four of the above mentioned potentials have two parameters, it is
necessary to calculate the third derivative of $w$ for them to estimate the
predict values.
If they are tested observationally, it will be understood whether the dark
energy could be described by the scalar field with this potential.
At least it will satisfy the necessary conditions.
Numerical analysis for $d^3w/da^3$ are made under some specified parameters
in the investigated potentials, except the mixed one.
It becomes possible to distinguish the potentials by the accurate observing
$dw/da$ and $d^2w/da^2$ in some parameters. |
A Method for 21cm Power Spectrum Estimation in the Presence of
Foregrounds: 21cm tomography promises to be a powerful tool for estimating cosmological
parameters, constraining the epoch of reionization, and probing the so-called
dark ages. However, realizing this promise will require the extraction of a
cosmological power spectrum from beneath overwhelmingly large sources of
foreground contamination. In this paper, we develop a unified matrix-based
framework for foreground subtraction and power spectrum estimation, which
allows us to quantify the errors and biases that arise in the power spectrum as
a result of foreground subtraction. We find that existing line-of-sight
foreground subtraction proposals can lead to substantial mode-mixing as well as
residual noise and foreground biases, whereas our proposed inverse variance
foreground subtraction eliminates noise and foreground biases, gives smaller
error bars, and produces less correlated measurements of the power spectrum. We
also numerically confirm the intuitive belief in the literature that 21cm
foreground subtraction is best done using frequency rather than angular
information. | Supernovae without host galaxy? - Hypervelocity stars in foreign
galaxies: Harvesting the SAI supernova catalog, we search for SNe that apparently do
not occur within a distinct host galaxy but lie a great distance apart from
their assigned host galaxy. Assuming two possible explanations for this
host-lessness of a fraction of reported SNe, namely (i) a host galaxy which is
too faint to be detected within the limits of currently available surveys or
(ii) a hypervelocity star (HVS) as progenitor of the SN,we want to distinguish
between these two cases. To do so, we use deep imaging to test explanation (i).
If within our detection limit of 27 mag/arcsec^2, the central surface
brightness of the faintest known LSB galaxy so far, no galaxy could be
identified, we discard this explanation and regard the SN, after several other
checks, to have had a hypervelocity star progenitor. Analyzing a selected
subsample of five host-less SNe we find one, SN 2006bx in UGC5434, to be put in
the hypervelocity progenitor category with a high probability, exhibiting a
projected velocity of > 800 km/s. SN 1969L in NGC1058 is most likely an example
for a very extended star-forming disk visible only in the far-UV, not in the
optical wavebands. Therefore this SN is clearly due to in situ star formation.
This mechanism may also apply for two other SNe we investigated (SN 1970L and
SN 1997C), but this cannot be determined with final certainty. Another one, SN
2005nc associated with a gamma-ray burst (GRB 050525), is a special case not
covered by our initial assumptions. Even with deep Hubble data, a host galaxy
could not be unambiguously identified. |
Galaxy Zoo: A sample of blue early-type galaxies at low redshift: We report the discovery of a population of nearby, blue early-type galaxies
with high star formation rates (0.5 < SFR < 50 Msun/yr). They are identified by
their visual morphology as provided by Galaxy Zoo for SDSS DR6 and their u-r
colour. We select a volume-limited sample in the redshift range 0.02 < z <
0.05, corresponding to luminosities of approximately L* and above, and with u-r
colours significantly bluer than the red sequence. We confirm the early-type
morphology of the objects in this sample and investigate their environmental
dependence and star formation properties. Blue early-type galaxies tend to live
in lower-density environments than `normal' red sequence early-types and make
up 5.7 +/-0.4% of the low-redshift early-type galaxy population. We find that
such blue early-type galaxies are virtually absent at high velocity dispersions
above 200 km/s. Our analysis uses emission line diganostic diagrams and we find
that ~25% of them are actively starforming, while another ~25% host both star
formation and an AGN. Another ~12% are AGN. The remaining 38% show no strong
emission lines. When present and uncontaminated by an AGN contribution, the
star formation is generally intense. We consider star formation rates derived
from Halpha, u-band and infrared luminosities, and radial colour profiles, and
conclude that the star formation is spatially extended. Of those objects that
are not currently undergoing star formation must have ceased doing so recently
in order to account for their blue optical colours. The gas phase metallicity
of the actively starforming blue early-types galaxies is supersolar in all
cases. We discuss the place of these objects in the context of galaxy
formation. A catalogue of all 204 blue early-type galaxies in our sample,
including star formation rates and emission line classification, is provided. | Novel Adaptive softening for collisionless N-body simulations:
Eliminating spurious halos: We describe a NOVel form of Adaptive softening (NovA) for collisionless
$N$-body simulations, implemented in the Ramses adaptive mesh refinement code.
We introduce a refinement criterion that the particle distribution within each
cell be sufficiently isotropic, as measured by its moment of inertia tensor. In
this way, collapse is only refined if it occurs along all three axes, ensuring
that the softening $\epsilon$ is always of order twice the largest
inter-particle spacing in a cell. This more conservative force softening
criterion is designed to minimise spurious two-body effects, while maintaining
high force resolution in collapsed regions of the flow. We test NovA using an
antisymmetric perturbed plane wave collapse (`Valinia' test) before applying it
to warm dark matter (WDM) simulations. For the Valinia test, we show that --
unlike the standard $N$-body method -- NovA produces no numerical fragmentation
while still being able to correctly capture fine caustics and shells around the
collapsing regions. For the WDM simulations, we find that NovA converges
significantly more rapidly than standard $N$-body, producing little or no
spurious halos on small scales. We show, however, that determining whether or
not halos exist below the free streaming mass $M_{\rm fs}$ is complicated by
the fact that our halo finder (AHF) likely incorrectly labels some caustics and
criss-crossing filaments as halos, while one or two particularly massive
filaments appear to fragment in any version of NovA where refinement is
allowed. Such massive filaments may be physically unstable to collapse, as is
the case for infinite, static, self-gravitating cylinders. We will use NovA in
forthcoming papers to study the issue of halo formation below $M_{\rm fs}$;
filament stability; and to obtain new constraints on the temperature of dark
matter. |
Priors on red galaxy stochasticity from hybrid effective field theory: We investigate the stochastic properties of typical red galaxy samples in a
controlled numerical environment. We use Halo Occupation Distribution (HOD)
modelling to create mock realizations of three separate bright red galaxy
samples consistent with datasets used for clustering and lensing analyses in
modern galaxy surveys. Second-order Hybrid Effective Field Theory (HEFT) is
used as a field-level forward model to describe the full statistical
distribution of these tracer samples, and their stochastic power spectra are
directly measured and compared to the Poisson shot-noise prediction. While all
of the galaxy samples we consider are hosted within haloes with sub-Poisson
stochasticity, we observe that the galaxy samples themselves possess
stochasticities that range from sub-Poisson to super-Poisson, in agreement with
predictions from the halo model. As an application of our methodology, we place
priors on the expected degree of non-Poisson stochasticity in cosmological
analyses using such samples. We expect these priors will be useful in reducing
the complexity of the full parameter space for future analyses using
second-order Lagrangian bias models. More generally, the techniques outlined
here present the first application of hybrid EFT methods to characterize models
of the galaxy--halo connection at the field level, revealing new connections
between once-disparate modelling frameworks. | Stable Heating of Cluster Cooling Flows by Cosmic-Ray Streaming: We study heating of cool cores in galaxy clusters by cosmic-ray (CR)
streaming using numerical simulations. In this model, CRs are injected by the
central active galactic nucleus (AGN) and move outward with Alfven waves. The
waves are excited by the streaming itself and become non-linear. If magnetic
fields are large enough, CRs can prevail in and heat the entire core because of
a large Alfven velocity. We find that the CR streaming can stably heat both
high and low temperature clusters for a long time without the assistance of
thermal conduction, and it can prevent the development of massive cooling
flows. If there is even minor contribution of thermal conduction, the heating
can be more stabilized. We discuss the reason of the stability and indicate
that the CR pressure is insensitive to the change of intracluster medium (ICM),
and that the density dependence of the heating term is similar to that of the
radiative cooling. |
Metallicity as a source of dispersion in the SNIa bolometric light curve
luminosity-width relationship: The recognition that the metallicity of Type Ia supernova (SNIa) progenitors
might bias their use for cosmological applications has led to an increasing
interest in its role on the shaping of SNIa light curves. We explore the
sensitivity of the synthesized mass of 56Ni, M(56Ni), to the progenitor
metallicity starting from Pre-Main Sequence models with masses M0 = 2 - 7 M_sun
and metallicities Z = 1e-5 - 0.10. The interplay between convective mixing and
carbon burning during the simmering phase eventually rises the neutron excess
and leads to a smaller 56Ni yield, but does not change substantially the
dependence of M(56Ni) on Z. Uncertain attributes of the WD, like the central
density, have a minor effect on M(56Ni). Our main results are: 1) a sizable
amount of 56 Ni is synthesized during incomplete Si-burning, which leads to a
stronger dependence of M(56Ni) on Z than obtained by assuming that 56Ni is
produced in material that burns fully to nuclear statistical equilibrium; 2) in
one-dimensional delayed detonation simulations a composition dependence of the
deflagration-to-detonation transition density gives a non-linear relationship
between M(56Ni) and Z, and predicts a luminosity larger than previously thought
at low metallicities (however, the progenitor metallicity alone cannot explain
the whole observational scatter of SNIa luminosities), and 3) an accurate
measurement of the slope of the Hubble residuals vs metallicity for a large
enough data set of SNIa might give clues to the physics of
deflagration-to-detonation transition in thermonuclear explosions. | Influence of Unobservable Modes on Correlation Functions during
Inflation: Coupling between sub- and super-Hubble modes can affect the locally observed
statistics of our universe. In the context of Quasi-Single Field Inflation, we
can compute correlation functions and derive the influence of those
unobservable modes on observed correlation functions as well as on the inferred
cosmological parameters. We study how different classes of diagrams affect the
bispectrum in the squeezed limit; in particular, while contact-like diagrams
leave the scaling between the long and short modes unchanged, exchange-like
diagrams do modify the shape of the bispectrum. We show that the mass of the
hidden sector field can hence be biased by an unavoidable cosmic variance that
can reach a 1-$\sigma$ uncertainty of $\mathcal{O}(10\%)$ for a weakly
non-Gaussian universe. Finally, we go beyond the bispectrum and show how
couplings between unobservable and observable modes can affect generic
correlation functions with arbitrary order non-derivative self-interactions. |
Observational Probes of Cosmic Acceleration: The accelerating expansion of the universe is the most surprising
cosmological discovery in many decades, implying that the universe is dominated
by some form of "dark energy" with exotic physical properties, or that
Einstein's theory of gravity breaks down on cosmological scales. The profound
implications of cosmic acceleration have inspired ambitious experimental
efforts to measure the history of expansion and growth of structure with
percent-level precision or higher. We review in detail the four most well
established methods for making such measurements: Type Ia supernovae, baryon
acoustic oscillations (BAO), weak gravitational lensing, and galaxy clusters.
We pay particular attention to the systematic uncertainties in these techniques
and to strategies for controlling them at the level needed to exploit "Stage
IV" dark energy facilities such as BigBOSS, LSST, Euclid, and WFIRST. We
briefly review a number of other approaches including redshift-space
distortions, the Alcock-Paczynski test, and direct measurements of H_0. We
present extensive forecasts for constraints on the dark energy equation of
state and parameterized deviations from GR, achievable with Stage III and Stage
IV experimental programs that incorporate supernovae, BAO, weak lensing, and
CMB data. We also show the level of precision required for other methods to
provide constraints competitive with those of these fiducial programs. We
emphasize the value of a balanced program that employs several of the most
powerful methods in combination, both to cross-check systematic uncertainties
and to take advantage of complementary information. Surveys to probe cosmic
acceleration produce data sets with broad applications, and they continue the
longstanding astronomical tradition of mapping the universe in ever greater
detail over ever larger scales. | What do observations of the Lyman-alpha fraction tell us about
reionization?: An appealing approach for studying the reionization history of the Universe
is to measure the redshift evolution of the Lyman-alpha fraction, the
percentage of Lyman-break selected galaxies that emit appreciably in the
Ly-alpha line. This fraction is expected to fall-off towards high redshift as
the intergalactic medium becomes significantly neutral, and the galaxies'
Ly-alpha emission is progressively attenuated. Intriguingly, early measurements
with this technique suggest a strong drop in the Ly-alpha fraction near z ~ 7.
Previous work concluded that this requires a surprisingly neutral intergalactic
medium -- with neutral hydrogen filling more than 50 % of the volume of the
Universe -- at this redshift. We model the evolving Ly-alpha fraction using
cosmological simulations of the reionization process. Before reionization
completes, the simulated Ly-alpha fraction has large spatial fluctuations owing
to the inhomogeneity of reionization. Since existing measurements of the
Ly-alpha fraction span relatively small regions on the sky, and sample these
regions only sparsely, they may by chance probe mostly galaxies with above
average Ly-alpha attenuation. We find that this sample variance is not
exceedingly large for existing surveys, but that it does somewhat mitigate the
required neutral fraction at z ~ 7. Quantitatively, in a fiducial model
calibrated to match measurements after reionization, we find that current z = 7
observations require a volume-averaged neutral fraction of x_HI > 0.05 at 95 %
confidence level. Hence, we find that the z ~ 7 Ly-alpha fraction measurements
do likely probe the Universe before reionization completes but that they do not
require a very large neutral fraction. |
Nuclear and Extended Spectra of NGC 1068 - II: Near-Infrared Stellar
Population Synthesis: We performed stellar population synthesis on the nuclear and extended regions
of NGC 1068 by means of near-infrared spectroscopy to disentangle their
spectral energy distribution components. This is the first time that such a
technique is applied to the whole 0.8 - 2.4 micron wavelength interval in this
galaxy. NGC 1068 is one of the nearest and probably the most studied Seyfert 2
galaxy, becoming an excellent laboratory to study the interaction between black
holes, the jets that they can produce and the medium in which they propagate.
Our main result is that traces of young stellar population are found at ~ 100
south of the nucleus. The contribution of a power-law continuum in the centre
is about 25%, which is expected if the light is scattered from a Seyfert 1
nucleus. We find peaks in the contribution of the featureless continuum about
100 - 150 pc from the nucleus on both sides. They might be associated with
regions where the jet encounters dense clouds. Further support to this scenario
is given by the peaks of hot dust distribution found around these same regions
and the H2 emission line profile, leading us to propose that the peaks might be
associate to regions where stars are being formed. Hot dust also has an
important contribution to the nuclear region, reinforcing the idea of the
presence of a dense, circumnuclear torus in this galaxy. Cold dust appears
mostly in the south direction, which supports the view that the southwest
emission is behind the plane of the galaxy and is extinguished very likely by
dust in the plane. Intermediate age stellar population contributes
significantly to the continuum, specially in the inner 200 pc. | Inflating a chain of x-ray deficient bubbles by a single jet activity
episode: We show that a continuous jet with time-independent launching properties can
inflate a chain of close and overlapping X-ray deficient bubbles. Using the
numerical code PLUTO we run 2.5D (i.e. spherical coordinate system with
cylindrical symmetry) hydrodynamic simulations and study the interaction of the
jets with the intra-cluster medium (ICM). A key process is vortex fragmentation
due to several mechanisms, including vortex-shedding and Kelvin-Helmholtz (KH)
instabilities. Our results can account for the structure of two opposite chains
of close bubbles as observed in the galaxy cluster Hydra A. Our results imply
that the presence of multiple pairs of bubbles does not necessarily imply
several jet-launching episodes. This finding might have implications to
feedback mechanisms operating by jets. |
On the stellar populations of massive galaxies: In this Letter, we analyse the predicted physical properties of massive
galaxies, in the framework of recent semi-analytic models of galaxy formation.
All models considered account for winds driven by supernovae explosions and
suppression of gas condensation at the centre of relatively massive haloes by
active galactic nuclei (AGN). We show that, while these models successfully
reproduce the old stellar populations observed for massive galaxies, they fail
in reproducing their observed chemical abundances. This problem is alleviate
but still present if AGN feedback is completely switched off. Moreover, in this
case, model predictions fail in accounting for the old stellar ages of massive
galaxies. We argue that the difficulty of semi-analytical models in
simultaneously reproducing the observed ages and metallicities of massive
galaxies, signals a fundamental problem with the schemes that are currently
adopted to model star formation, feedback, and related recycling of gas and
metals. | Weak lensing measurement of the mass-richness relation using the SDSS
database: We study the mass-richness relation using galaxy catalogues and images from
the Sloan Digital Sky Survey. We use two independent methods, in the first one,
we calibrate the scaling relation with weak-lensing mass estimates. In the
second procedure we apply a background subtraction technique to derive the
probability distribution, $P(M \mid N)$, that groups with $N$-members have a
virialized halo mass $M$. Lensing masses are derived in different richness bins
for two galaxy systems sets: the maxBCG catalogue and a catalogue based on a
group finder algorithm developed by Yang et al. MaxBCG results are used to test
the lensing methodology. The lensing mass-richness relation for the Yang et al.
group sample shows a good agreement with $P(M \mid N)$ obtained independently
with a straightforward procedure. |
Observational constraints of diffusive dark-fluid cosmology: In this work, we consider an interacting dark-fluid cosmological model in
which energy exchange between dark matter and dark energy occurs through
diffusion. After solving the background expansion history for a late-time
universe, we attempt to constrain the cosmological parameters by comparing
simulated values of the model against Supernovae Type 1A data. We consider four
different cases and compare them against the LCDM model as the "true model".
Our results show that the diffusive model in which dark energy flows to dark
matter is the most likely alternative to LCDM model. This model is not only in
line with Planck 2018 observational results but can also give a potential
explanation to the so-called Hubble tension. | Spectroscopy in the Era of LSST: This report summarizes the results of the 'Spectroscopy in the Era of LSST'
workshop held April 11-12, 2013 in Tucson, Arizona. At the workshop, there were
breakout sessions covering four broad science topics. These were: time domain
science, Galactic structure and stellar populations, galaxies and AGN, and dark
energy and cosmology. We present the science cases discussed in these breakout
sessions and provide a synthesis of highly desired capabilities that meet needs
across all four broad topics. We also present a table that will be useful to
characterize the needs of specific science cases in a format that provides a
general framework for discussion of future spectroscopic capabilities. |
Chemical properties in the most distant radio galaxy: We present a deep optical spectrum of TN J0924-2201, the most distant radio
galaxy at z = 5.19, obtained with FOCAS on the Subaru Telescope. We
successfully detect, for the first time, the CIV1549 emission line from the
narrow-line region (NLR). In addition to the emission-line fluxes of Ly alpha
and CIV, we set upper limits on the NV and HeII emissions. We use these line
detections and upper limits to constrain the chemical properties of TN
J0924-2201. By comparing the observed emission-line flux ratios with
photoionization models, we infer that the carbon-to-oxygen relative abundance
is already [C/O] > -0.5 at a cosmic age of ~ 1.1 Gyr. This lower limit on [C/O]
is higher than the ratio expected at the earliest phases of the galaxy chemical
evolution, indicating that TN J0924-2201 has already experienced significant
chemical evolution at z = 5.19. | Lessons from the first multiply imaged supernova: A revised
Light-Traces-Mass strong lensing model for the galaxy cluster MACS
J1149.5+2223: Our light-traces-mass (LTM) strong-lensing model for MACS J1149.5+2223 has
played several key roles over the last decade: it aided the identification of
multiple images in this cluster and the study of MACS1149-JD1 at redshift
$z\simeq9$, it was used to estimate the properties of the first multiply imaged
supernova, Refsdal, in its discovery paper, and of the first caustic crossing
event by a cluster, Lensed Star 1. Supernova Refsdal supplied an invaluable
opportunity to conduct a blind test of the ability of common lens-modeling
techniques to accurately describe the properties of SN Refsdal's images and
predict the reappearance of one of its counter images that was due about a year
post-discovery of the original Einstein cross. Thanks to this practice, in
which our submitted model yielded some outlying results, we located a numerical
artifact in the time delay (TD) calculation part of the code, which was now
fixed. This artifact did not influence the reproduction of multiple images
(i.e., the deflection fields -- which are those constrained directly from the
observations) or the derived mass model, and so it remained unnoticed prior to
supernova Refsdal, emphasizing the importance of blind tests in astronomy. Here
we update our model and present revised LTM measurements for Refsdal. These are
important not only for completing the LTM view of the Refsdal event, but also
because they affect the range of values predicted from different lens-modeling
techniques and thus the range of systematic uncertainties for the TD
calculation and the resulting Hubble constant. |
Signatures of Small-scale Structure of the Pre-reionization
Intergalactic Medium in $z\gtrsim7$ Quasar Proximity Zones: The small-scale structure of baryons in the intergalactic medium is
intimately linked to their past thermal history. Prior to the $\gtrsim10^4$ K
photoheating during the epoch of reionization, cold baryons may have closely
traced the clumpy cosmic web of dark matter down to scales as low as
$\lesssim1$ comoving kpc, depending on the degree of heating by the X-ray
background. After the passage of the ionization front, this clumpy structure
can persist for $\sim10^{8}$ years. The strong Ly$\alpha$ damping wings
detected towards a few of the highest redshift quasars, in addition to their
smaller-than-expected Ly$\alpha$-transmissive proximity zones, suggest that
they have ionized and heated the foreground intergalactic medium less than
$10^7$ years ago. Signatures of the pre-reionization small-scale structure
should thus persist in their intergalactic surroundings. Here we explore how
the persistence of this clumpy structure can affect the statistics of
Ly$\alpha$ transmission inside the transparent proximity zones of $z\gtrsim7$
quasars by post-processing a suite of small-volume hydrodynamical simulations
with 1D ionizing radiative transfer. We find that the Ly$\alpha$ flux power
spectrum and flux PDF statistics of ten $z=7.5$ proximity zones, with realistic
observational parameters, could distinguish the gaseous structure of a $T_{\rm
IGM}\sim2$ K CDM model from warm dark matter models with particle masses
$m_{\rm WDM}>10$ keV and X-ray heated models with $f_{\rm X}f_{\rm abs}>0.1$
($T_{\rm IGM}(z=7.5)\gtrsim275$ K) at the $2\sigma$ level. | Suite of Hydrodynamical Simulations for the Lyman-Alpha Forest with
Massive Neutrinos: The signature left in quasar spectra by the presence of neutral hydrogen in
the Universe allows one to constrain the sum of the neutrino masses with
improved sensitivity, with respect to laboratory experiments, and may shed a
new light on the neutrino mass hierarchy and on the absolute mass scale of
neutrinos. Constraints on cosmological parameters and on the dark energy
equation of state can also be derived, from a joint parameter estimation
procedure. However, this requires a detailed modeling of the line-of-sight
power spectrum of the transmitted flux in the Lyman-Alpha (LyA) forest on
scales ranging from a few to hundreds of Mpcs, which in turns demands the
inclusion and careful treatment of cosmological neutrinos. To this end, we
present here a suite of state-of-the-art hydrodynamical simulations with cold
dark matter, baryons and massive neutrinos, specifically targeted for modeling
the low-density regions of the IGM as probed by the LyA forest at
high-redshift. The simulations span volumes ranging from (25 Mpc/h)^3 to (100
Mpc/h)^3, and are made using either 3 X 192^3~21 millions or 3 X 768^3~1.4
billion particles. The resolution of the various runs can be further enhanced,
so that we can reach the equivalent of 3 X 3072^3~87 billion particles in a
(100 Mpc/h)^3 box size. The chosen cosmological parameters are compatible with
the latest Planck (2013) results, although we also explore the effect of slight
variations in the main cosmological and astrophysical parameters. We adopt a
particle-type implementation of massive neutrinos, and consider three
degenerate species having masses M_nu =0.1, 0.2, 0.3, 0.4 and 0.8 eV,
respectively. We improve on previous studies in several ways, in particular
with updated routines for IGM radiative cooling and heating processes, and
initial conditions based on 2LPT rather than the Zeldovich approximation. |
Massive Primordial Black Holes as Dark Matter and their detection with
Gravitational Waves: Massive Primordial Black Holes (MPBH) can be formed after inflation due to
broad peaks in the primordial curvature power spectrum that collapse
gravitationally during the radiation era, to form clusters of black holes that
merge and increase in mass after recombination, generating today a broad
mass-spectrum of black holes with masses ranging from 0.01 to $10^5~M_\odot$.
These MPBH could act as seeds for galaxies and quick-start structure formation,
initiating reionization, forming galaxies at redshift $z>10$ and clusters at
$z>1$. They may also be the seeds on which SMBH and IMBH form, by accreting gas
onto them and forming the centers of galaxies and quasars at high redshift.
They form at rest with zero spin and have negligible cross-section with
ordinary matter. If there are enough of these MPBH, they could constitute the
bulk of the Dark Matter today. Such PBH could be responsible for the observed
fluctuations in the CIB and X-ray backgrounds. MPBH could be directly detected
by the gravitational waves emitted when they merge to form more massive black
holes, as recently reported by LIGO. Their continuous merging since
recombination could have generated a stochastic background of gravitational
waves that could eventually be detected by LISA and PTA. MPBH may actually be
responsible for the unidentified point sources seen by Fermi, Magic and
Chandra. Furthermore, the ejection of stars from shallow potential wells like
those of Dwarf Spheroidals (DSph), via the gravitational slingshot effect,
could be due to MPBH, thus alleviating the substructure and too-big-to-fail
problems of standard collisionless CDM. Their mass distribution peaks at a few
tens of $M_\odot$ today, and could be detected also with long-duration
microlensing events, as well as by the anomalous motion of stars in GAIA. Their
presence as CDM in the Universe could be seen in the time-dilation of lensed
images of quasars. | The Dark Energy Spectroscopic Instrument: One-dimensional power spectrum
from first Lyman-$α$ forest samples with Fast Fourier Transform: We present the one-dimensional Lyman-$\alpha$ forest power spectrum
measurement using the first data provided by the Dark Energy Spectroscopic
Instrument (DESI). The data sample comprises $26,330$ quasar spectra, at
redshift $z > 2.1$, contained in the DESI Early Data Release and the first two
months of the main survey. We employ a Fast Fourier Transform (FFT) estimator
and compare the resulting power spectrum to an alternative likelihood-based
method in a companion paper. We investigate methodological and instrumental
contaminants associated to the new DESI instrument, applying techniques similar
to previous Sloan Digital Sky Survey (SDSS) measurements. We use synthetic data
based on log-normal approximation to validate and correct our measurement. We
compare our resulting power spectrum with previous SDSS and high-resolution
measurements. With relatively small number statistics, we successfully perform
the FFT measurement, which is already competitive in terms of the scale range.
At the end of the DESI survey, we expect a five times larger Lyman-$\alpha$
forest sample than SDSS, providing an unprecedented precise one-dimensional
power spectrum measurement. |
Narrowband Lyman-Continuum Imaging of Galaxies at z ~ 2.85: We present results from a survey for z~2.85 Lyman-Continuum (LyC) emission in
the HS1549+1933 field and place constraints on the amount of ionizing radiation
escaping from star-forming galaxies. Using a custom narrowband filter (NB3420)
tuned to wavelengths just below the Lyman limit at z>=2.82, we probe the LyC
spectral region of 49 Lyman break galaxies (LBGs) and 91 Lya-emitters (LAEs)
spectroscopically confirmed at z>=2.82. Four LBGs and seven LAEs are detected
in NB3420. Using V-band data probing the rest-frame non-ionizing UV, we observe
that many NB3420-detected galaxies exhibit spatial offsets between their LyC
and non-ionizing UV emission and are characterized by extremely blue NB3420-V
colors, corresponding to low ratios of non-ionizing to ionizing radiation
(F_UV/F_LyC) that are in tension with current stellar population synthesis
models. We measure average values of F_UV/F_LyC for our LBG and LAE samples,
correcting for foreground galaxy contamination and HI absorption in the IGM. We
find (F_UV/F_LyC)_corr^LBG=82 +/- 45 and (F_UV/F_LyC)_corr^LAE=7.4 +/- 3.6.
These flux-density ratios correspond respectively to relative LyC escape
fractions of f_esc,rel^LBG=5-8% and f_esc,rel^LAE=18-49%, absolute LyC escape
fractions of f_esc^LBG=1-2% and f_esc^LAE=5-15%, and a comoving LyC emissivity
from star-forming galaxies of 8.8-15.0 x 10^24 ergs/s/Hz/Mpc^3. In order to
study the differential properties of galaxies with and without LyC detections,
we analyze narrowband Lya imaging and rest-frame near-infrared imaging, finding
that while LAEs with LyC detections have lower Lya equivalent widths on
average, there is no substantial difference in the rest-frame near-infrared
colors of LBGs or LAEs with and without LyC detections. These preliminary
results are consistent with an orientation-dependent model where LyC emission
escapes through cleared paths in a patchy ISM. | Constraining the Halo Mass of Damped Ly$α$ Absorption Systems
(DLAs) at $z=2-3.5$ using the Quasar-CMB Lensing Cross-correlation: We study the cross correlation of damped Ly$\alpha$ systems (DLAs) and their
background quasars, using the most updated DLA catalog and the Planck 2018 CMB
lensing convergence field. Our measurement suggests that the DLA bias $b_{\rm
DLA}$ is smaller than $3.1$, corresponding to $\log(M/M_\odot h^{-1})\leq 12.3$
at a confidence of $90\%$. These constraints are broadly consistent with Alonso
et al. (2018) and previous measurements by cross-correlation between DLAs and
the Ly$\alpha$ forest (e.g. Font-Ribera et al. 2012; Perez-Rafols et al. 2018).
Further, our results demonstrate the potential of obtaining a more precise
measurement of the halo mass of high-redshift sources using next generation CMB
experiments with a higher angular resolution. The python-based codes and data
products of our analysis are available at
https://github.com/LittleLin1999/CMB-lensingxDLA. |
The Effects of Dark Matter Annihilation on Cosmic Reionization: We revisit the possibility of constraining the properties of dark matter (DM)
by studying the epoch of cosmic reionization. Previous studies have shown that
DM annihilation was unlikely to have provided a large fraction of the photons
that ionized the universe, but instead played a subdominant role relative to
stars and quasars. The DM, however, begins to efficiently annihilate with the
formation of primordial microhalos at $z\sim100-200$, much earlier than the
formation of the first stars. Therefore, if DM annihilation ionized the
universe at even the percent level over the interval $z \sim 20-100$, it can
leave a significant imprint on the global optical depth, $\tau$. Moreover, we
show that cosmic microwave background (CMB) polarization data and future 21 cm
measurements will enable us to more directly probe the DM contribution to the
optical depth. In order to compute the annihilation rate throughout the epoch
of reionization, we adopt the latest results from structure formation studies
and explore the impact of various free parameters on our results. We show that
future measurements could make it possible to place constraints on the dark
matter's annihilation cross section that are at a level comparable to those
obtained from the observations of dwarf galaxies, cosmic ray measurements, and
studies of recombination. | Discovery of a giant HI tail in the galaxy group HCG 44: We report the discovery of a giant HI tail in the intra-group medium of HCG
44 as part of the Atlas3D survey. The tail is ~300 kpc long in projection and
contains ~5x10^8 M_sun of HI. We detect no diffuse stellar light at the
location of the tail down to ~28.5 mag/arcsec^2 in g band. We speculate that
the tail might have formed as gas was stripped from the outer regions of NGC
3187 (a member of HCG 44) by the group tidal field. In this case, a simple
model indicates that about 1/3 of the galaxy's HI was stripped during a time
interval of <1 Gyr. Alternatively, the tail may be the remnant of an
interaction between HCG 44 and NGC 3162, a spiral galaxy now ~650 kpc away from
the group. Regardless of the precise formation mechanism, the detected HI tail
shows for the first time direct evidence of gas stripping in HCG 44. It also
highlights that deep HI observations over a large field are needed to gather a
complete census of this kind of events in the local Universe. |
A high-dispersion molecular gas component in nearby galaxies: We present a comprehensive study of the velocity dispersion of the atomic
(HI) and molecular (H2) gas components in the disks (R < R25) of a sample of 12
nearby spiral galaxies with moderate inclinations. Our analysis is based on
sensitive high resolution data from the THINGS (atomic gas) and HERACLES
(molecular gas) surveys. To obtain reliable measurements of the velocity
dispersion, we stack regions several kilo-parsecs in size, after accounting for
intrinsic velocity shifts due to galactic rotation and large-scale motions. We
stack using various parameters: the galacto-centric distance, star formation
rate surface density, HI surface density, H2 surface density, and total gas
surface density. We fit single Gaussian components to the stacked spectra and
measure median velocity dispersions for HI of 11.9 +/- 3.1 km/s and for H2 of
12.0 +/- 3.9 km/s. The CO velocity dispersions are thus, surprisingly, very
similar to the corresponding ones of HI, with an average ratio of
sigma(HI)/sigma(CO) = 1.0 +/- 0.2 irrespective of the stacking parameter. The
measured CO velocity dispersions are significantly higher (factor 2) than the
traditional picture of a cold molecular gas disk associated with star
formation. The high dispersion implies an additional thick molecular gas disk
(possibly as thick as the HI disk). Our finding is in agreement with recent
sensitive measurements in individual edge-on and face-on galaxies and points
towards the general existence of a thick disk of molecular gas, in addition to
the well-known thin disk in nearby spiral galaxies. | CIV Emission as a Probe of Accretion Disk Winds: We present a brief description of a model for the broad emission line region
(BELR) in quasars, which is supported by analysis of CIV and other emission
lines in the spectra of high-z SDSS quasars. Specifically we consider a
two-component BELR with a disk and wind where the relative strength of each
component is a function of luminosity. The implications of such a model for our
understanding of quasar outflows and estimates of their black hole masses and
accretion rates are discussed. |
Cosmological constraints on Hořava gravity revised in light of
GW170817 and GRB170817A and the degeneracy with massive neutrinos: We revise the cosmological bounds on Ho\v{r}ava gravity taking into accounts
the stringent constraint on the speed of propagation of gravitational waves
from GW170817 and GRB170817A. In light of this we also investigate the
degeneracy between massive neutrinos and Ho\v{r}ava gravity. We show that a
luminal propagation of gravitational waves suppresses the large-scale Cosmic
Microwave Background (CMB) radiation temperature anisotropies and the presence
of massive neutrinos increases this effect. On the contrary large neutrinos
mass can compensate the modifications induced by Ho\v{r}ava gravity in the
lensing, matter and primordial B-mode power spectra. Another degeneracy is
found, at theoretical level, between the tensor-to-scalar ratio $r$ and massive
neutrinos as well as with the model's parameters. We analyze these effects
using CMB, supernovae type Ia (SNIa), galaxy clustering and weak gravitational
lensing measurements and we show how such degeneracies are removed. We find
that the model's parameters are constrained to be very close to their General
Relativity limits and we get a two orders of magnitude improved upper bound,
with respect to the Big Bang Nucleosynthesis constraint, on the deviation of
the effective gravitational constant from the Newtonian one. The deviance
information criterion suggests that in Ho\v{r}ava gravity $\Sigma m_\nu>0$ is
favored when CMB data only are considered, while the joint analysis of all
datasets prefers zero neutrinos mass. | Ram pressure stripping of disk galaxies in galaxy clusters: While galaxies move through the intracluster medium of their host cluster,
they experience a ram pressure which removes at least a significant part of
their interstellar medium. This ram pressure stripping appears to be especially
important for spiral galaxies: this scenario is a good candidate to explain the
differences observed between cluster spirals in the nearby universe and their
field counterparts. Thus, ram pressure stripping of disk galaxies in clusters
has been studied intensively during the last decade. I review advances made in
this area, concentrating on theoretical work, but continuously comparing to
observations. |
The 3.3 micron PAH Emission as a Star Formation Rate Indicator: Polycyclic Aromatic Hydrocarbon (PAH) emission features dominate the
mid-infrared spectra of star-forming galaxies and can be useful to calibrate
star formation rates and diagnose ionized states of grains. However, the PAH
3.3 micron feature has not been studied as much as other PAH features since it
is weaker than others and resides outside of Spitzer capability. In order to
detect and calibrate the 3.3 micron PAH emission and investigate its potential
as a star formation rate indicator, we carried out an AKARI mission program,
AKARI mJy Unbiased Survey of Extragalactic Survey (AMUSES) and compare its
sample with various literature samples. We obtained 2 ~5 micron low resolution
spectra of 20 flux-limited galaxies with mixed SED classes, which yields the
detection of the 3.3 micron PAH emission from three out of 20 galaxies. For the
combined sample of AMUSES and literature samples, the 3.3 micron PAH
luminosities correlate with the infrared luminosities of star-forming galaxies,
albeit with a large scatter (1.5 dex). The correlation appears to break down at
the domain of ultra-luminous infrared galaxies (ULIRGs), and the power of the
3.3 micron PAH luminosity as a proxy for the infrared luminosity is hampered at
log[L(PAH3.3)/(erg/sec)] > -42.0. Possible origins for this deviation in the
correlation are discussed, including contribution from AGN and strongly
obscured YSOs, and the destruction of PAH molecules in ULIRGs. | Turbulence and Dynamo in Galaxy Cluster Medium: Implications on the
Origin of Cluster Magnetic Fields: We present self-consistent cosmological magnetohydrodynamic (MHD) simulations
that simultaneously follow the formation of a galaxy cluster and the magnetic
field ejection by an active galactic nucleus (AGN). We find that the magnetic
fields ejected by the AGNs, though initially distributed in relatively small
volumes, can be transported throughout the cluster and be further amplified by
the intra-cluster medium (ICM) turbulence during the cluster formation process.
The ICM turbulence is shown to be generated and sustained by the frequent
mergers of smaller halos. Furthermore, a cluster-wide dynamo process is shown
to exist in the ICM and amplify the magnetic field energy and flux. The total
magnetic energy in the cluster can reach $\sim$ $10^{61}$ ergs while micro
Gauss ($\mu$G) fields can distribute over $\sim$ Mpc scales throughout the
whole cluster. This finding shows that magnetic fields from AGNs, being further
amplified by the ICM turbulence through small-scale dynamo processes, can be
the origin of cluster-wide magnetic fields. |
Radio-continuum jets around the peculiar galaxy pair ESO 295-IG022: We report new radio-continuum observations with the Australia Telescope
Compact Array (ATCA) of the region surrounding the peculiar galaxy pair ESO
295-IG022, at the centre of the poor cluster Abell S0102. We observed this
cluster at wavelengths of lambda=20/13 and 6/3 cm with the ATCA 6 km array.
With these configurations, we achieved a resolution of ~2" at 3 cm which is
sufficient to resolve the jet-like structure of ~3' length detected at 20 cm.
From our new high resolution images at 6 and 3 cm we confirm the presence of a
double jet structure, most likely originating from the northern galaxy
(ESO295-IG022-N), bent and twisted towards the south. We found the spectral
index of the jet to be very steep (alpha=-1.32). No point source was detected
that could be associated with the core of ESO 295-IG022-N. On the other hand,
ESO 295-IG022-S does not show any jet structure, but does show a point radio
source. This source has variable flux and spectral index, and appears to be
superposed on the line-of-sight of the jets (seen at 20-cm) originating from
the northern galaxy ESO 295-IG022-N. Finally, regions of very high and somewhat
well ordered polarisation were detected at the level of 70%. | Assessing Radiation Pressure as a Feedback Mechanism in Star-Forming
Galaxies: Radiation pressure from the absorption and scattering of starlight by dust
grains may be an important feedback mechanism in regulating star-forming
galaxies. We compile data from the literature on star clusters, star-forming
subregions, normal star-forming galaxies, and starbursts to assess the
importance of radiation pressure on dust as a feedback mechanism, by comparing
the luminosity and flux of these systems to their dust Eddington limit. This
exercise motivates a novel interpretation of the Schmidt Law, the LIR-L'CO
correlation, and the LIR-L'HCN correlation. In particular, the linear LIR-L'HCN
correlation is a natural prediction of radiation pressure regulated star
formation. Overall, we find that the Eddington limit sets a hard upper bound to
the luminosity of any star-forming region. Importantly, however, many normal
star-forming galaxies have luminosities significantly below the Eddington
limit. We explore several explanations for this discrepancy, especially the
role of "intermittency" in normal spirals - the tendency for only a small
number of subregions within a galaxy to be actively forming stars at any moment
because of the time-dependence of the feedback process and the luminosity
evolution of the stellar population. If radiation pressure regulates star
formation in dense gas, then the gas depletion timescale is 6 Myr, in good
agreement with observations of the densest starbursts. Finally, we highlight
the importance of observational uncertainties - namely, the dust-to-gas ratio
and the CO-H2 and HCN-H2 conversion factors - that must be understood before a
definitive assessment of radiation pressure as a feedback mechanism in
star-forming galaxies. |
The ACS Fornax Cluster Survey VII. Half-Light Radii of Globular Clusters
in Early-Type Galaxies: We measure the half-light radii of globular clusters (GCs) in 43 galaxies
from the ACS Fornax Cluster Survey (ACSFCS). We use these data to extend
previous work in which the environmental dependencies of the half-light radii
of GCs in early type galaxies in the ACS Virgo Cluster Survey (ACSVCS) were
studied, and a corrected mean half-light radius (corrected for the observed
environmental trends) was suggested as a reliable distance indicator. This work
both increases the sample size for the study of the environmental dependencies,
and adds leverage to the study of the corrected half-light radius as a possible
distance indicator (since Fornax lies at a larger distance than the Virgo
cluster). We study the environmental dependencies of the size of GCs using both
a Principal Component Analysis as well as 2D scaling relations. We largely
confirm the environmental dependencies shown in Jordan et al. (2005), but find
evidence that there is a residual correlation in the mean half-light radius of
GC systems with galaxy magnitude, and subtle differences in the other
correlations - so there may not be a universal correction for the half-light
radii of lower luminosity galaxy GC systems. The main factor determining the
size of a GC in an early type galaxy is the GC color. Red GCs have <r_h> =
2.8+/-0.3 pc, while blue GCs have <r_h> = 3.4+/-0.3 pc. We show that for bright
early-type galaxies (M_B < -19 mag), the uncorrected mean half-light radius of
the GC system is by itself an excellent distance indicator (with error ~11%),
having the potential to reach cosmologically interesting distances in the era
of high angular resolution adaptive optics on large optical telescopes. | Radio-emission of axion stars: We study parametric instability of compact axion dark matter structures
decaying to radiophotons. Corresponding objects - Bose (axion) stars, their
clusters, and clouds of diffuse axions - form abundantly in the
postinflationary Peccei-Quinn scenario. We develop general description of
parametric resonance incorporating finite-volume effects, backreaction, axion
velocities and their (in)coherence. With additional coarse-graining, our
formalism reproduces kinetic equation for virialized axions interacting with
photons. We derive conditions for the parametric instability in each of the
above objects, as well as in collapsing axion stars, evaluate photon resonance
modes and their growth exponents. As a by-product, we calculate stimulated
emission of Bose stars and diffuse axions, arguing that the former can give
larger contribution into the radiobackground. In the case of QCD axions, the
Bose stars glow and collapsing stars radioburst if the axion-photon coupling
exceeds the original KSVZ value by two orders of magnitude. The latter
constraint is alleviated for several nearby axion stars in resonance and absent
for axion-like particles. Our results show that the parametric effect may
reveal itself in observations, from FRB to excess radiobackground. |
Large pre-inflationary thermal density perturbations: In some versions of the theory of inflation, it is assumed that before
inflation began the universe was in a Friedmann-Robertson-Walker (FRW) stage,
with the energy density dominated by massless particles. The origin of the
nearly scale-invariant density perturbations is quantum fluctuations in the
inflaton field. Here we point out that under those conditions there would
necessarily also be large thermally induced density perturbations. It is
asserted that inflation would smooth out any pre-existing perturbations. But
that argument relies on linear perturbation theory of the scalar modes, which
would be rendered invalid because of the non-negligibility of the vector and
tensor modes when the perturbation in the total density becomes large. Under
those circumstances the original proof that inflation would have the desired
smoothing effect no longer applies, {\it i.e.} for the theory to be robust an
alternative (and hitherto unavailable) demonstration of the smoothing that
takes account of these non-linear terms is necessary. | Path Integral Marginalization for Cosmology: Scale Dependent Galaxy Bias
& Intrinsic Alignments: We present a path-integral likelihood formalism that extends parameterized
likelihood analyses to include continuous functions. The method finds the
maximum likelihood point in function-space, and marginalizes over all possible
functions, under the assumption of a Gaussian-distributed function-space. We
apply our method to the problem of removing unknown systematic functions in two
topical problems for dark energy research : scale-dependent galaxy bias in
redshift surveys; and galaxy intrinsic alignments in cosmic shear surveys. We
find that scale-dependent galaxy bias will degrade information on cosmological
parameters unless the fractional variance in the bias function is known to 10%.
Measuring and removing intrinsic alignments from cosmic shear surveys with a
flat-prior can reduce the dark energy Figure-of-Merit by 20%, however provided
that the scale and redshift-dependence is known to better than 10% with a
Gaussian-prior, the dark energy Figure-of-Merit can be enhanced by a factor of
two with no extra assumptions. |
Parity-violating and anisotropic correlations in pseudoscalar inflation: A pseudo-scalar inflaton field can have interesting phenomenological
signatures associated with parity violation. The existing analyses of these
signatures typically assume statistical isotropy. In the present work we
instead investigate the possibility that a pseudo-scalar inflaton is coupled to
a vector field carrying a small but non-negligible vacuum expectation value
(vev) coherent over our Hubble patch. We show that, in such case, correlators
involving the primordial curvature perturbations and gravitational waves
violate both statistical isotropy and parity symmetry. We compute the Cosmic
Microwave Background (CMB) temperature anisotropies (T) and polarization (E/B)
generated by these primordial modes. The CMB two-point correlation functions
present distinct signals of broken rotational and parity invariance.
Specifically, we find non-vanishing TT, TE, EE and BB correlators between
$\ell_1$ and $\ell_2 = \ell_1 \pm 1$ multipoles, and non-vanishing TB and EB
correlators between $\ell_1$ and $\ell_2 = \ell_1 \pm 2$ multipoles. Such
signatures are specific of the models under consideration and they cannot be
generated if one of parity and isotropy is preserved. As a specific example we
consider the simple case in which the vector field has just an "electric"
background component decaying in the standard way as $a^{-2}$. In this case a
strong scale-dependent quadrupolar modulation of the primordial power spectra
is generated and we find that almost noiseless data of the large-scale
temperature and E-mode polarization anisotropies (like, e.g., the ones provided
by WMAP or $Planck$) should be able to constrain the quadrupolar amplitude
coefficients $g_{2M}$ of the primordial scalar power spectrum (normalized at
the pivot scale comparable to the present horizon size $k_0^{-1} = 14~{\rm
Gpc}$) down to $g_{2M} = 30$ (68%CL). | Rayleigh-Taylor Instability at Ionization Fronts: Perturbation Analysis: The linear growth rate of the Rayleigh-Taylor instability (RTI) at ionization
fronts is investigated via perturbation analysis in the limit of incompressible
fluids. In agreement with previous numerical studies is found that absorption
of ionizing radiation inside the HII region due to hydrogen recombinations
suppresses the growth of instabilities. In the limit of a large density
contrast at the ionization front the RTI growth rate has the simple analytical
solution n=-nur+(nur^2+gk)^(1/2), where nur is the hydrogen recombination rate
inside the HII region, k is the perturbation's wavenumber and g is the
effective acceleration in the frame of reference of the front. Therefore, the
growth of surface perturbations with wavelengths lambda >> lambda_{cr} = 2\pi
g/nur^2 is suppressed by a factor (lambda_{cr}/4lambda)^(1/2) with respect to
the non-radiative incompressible RTI. Implications on stellar and black hole
feedback are briefly discussed. |
Baryon-photon interactions in Resummed Kinetic Field Theory: We explore how interactions between baryons and photons can be incorporated
into Kinetic Field Theory (KFT), a description of cosmic structure formation
based on classical Hamiltonian particle dynamics. In KFT, baryons are described
as effective mesoscopic particles which represent fluid elements governed by
the hydrodynamic equations. In this paper, we modify the mesoscopic particle
model to include pressure effects exerted on baryonic matter through
interactions with photons. As a proof of concept, we use this extended
mesoscopic model to describe the tightly coupled baryon-photon fluid between
matter-radiation equality and recombination. We show that this model can
qualitatively reproduce the formation of baryon-acoustic oscillations in the
cosmological power spectrum. | Infrared Spectroscopy of Halos of Edge-on Galaxies: We present a study of ionized gas, PAHs, and molecular hydrogen emission in
the halos of three edge-on galaxies, NGC 891, NGC 5775 and NGC 3044, based on
10-20 micron Spitzer Space Telescope spectra. The [Ne III]/[Ne II] ratio, an
excellent measure of radiation hardness, rises with z in the halo of NGC 891.
It is also higher in the halo of NGC 5775 than in the disk. NGC 3044 presents a
more confusing situation. To explain the [Ne III]/[Ne II] as well as optical
line ratio behavior in NGC 891, we carry out a simple exploration of parameter
space with CLOUDY, which indicates a large increase in radiation temperature
with height. Illustrative examples of physical models using a Monte Carlo
radiative transfer code show that the rising neon ratio may be explained by
adding a vertically extended, hot stellar source to a thin disk of massive
stars. However, several other sources of hard spectra may be relevant. PAH
features have scale heights of 430--530 pc in NGC 891 and 720--1080 pc in NGC
5775, suggesting they can be transported by disk-halo flows. Within NGC 891 and
NGC 5775, scale heights are similar for all PAHs. For NGC 891, the scale
heights exceed that of 8 micron emission, indicating a transition from more
ionized to more neutral PAHs with height. Most PAH equivalent widths are higher
in the halos. Molecular hydrogen 17.03 micron emission with scale heights of
550-580 pc in NGC 891 and 850 pc in NGC 5775 suggests a molecular component in
a surprisingly thick layer. |
Excursion set peaks: the role of shear: Recent analytical work on the modelling of dark halo abundances and
clustering has demonstrated the advantages of combining the excursion set
approach with peaks theory. We extend these ideas and introduce a model of
excursion set peaks that incorporates the role of initial tidal effects or
shear in determining the gravitational collapse of dark haloes. The model -- in
which the critical density threshold for collapse depends on the tidal
influences acting on protohaloes -- is well motivated from ellipsoidal collapse
arguments and is also simple enough to be analytically tractable. We show that
the predictions of this model are in very good agreement with measurements of
the halo mass function and traditional scale dependent halo bias in N-body
simulations across a wide range of masses and redshift. The presence of shear
in the collapse threshold means that halo bias is naturally predicted to be
nonlocal, and that protohalo densities at fixed mass are naturally predicted to
have Lognormal-like distributions. We present the first direct estimate of
Lagrangian nonlocal bias in N-body simulations, finding broad agreement with
the model prediction. Finally, the simplicity of the model (which has
essentially a single free parameter) opens the door to building efficient and
accurate non-universal fitting functions of halo abundances and bias for use in
precision cosmology. | Seeing the First Supernovae at the Edge of the Universe with JWST: The first stars ended the cosmic Dark Ages and created the first heavy
elements necessary for the formation of planets and life. The properties of
these stars remain uncertain, and it may be decades before individual Pop III
stars are directly observed. Their masses, however, can be inferred from their
supernova explosions, which may soon be found in both deep-field surveys by
JWST and in all-sky surveys by WFIRST. We have performed radiation
hydrodynamical simulations of the near infrared signals of Pop III
pair-instability supernovae in realistic circumstellar environments with Lyman
absorption by the neutral intergalactic medium. We find that JWST and WFIRST
will detect these explosions out to z ~ 30 and 20, respectively, unveiling the
first generation of stars in the universe. |
Stellar mass Primordial Black Holes as Cold Dark Matter: Primordial Black Holes (PBHs) might have formed in the early Universe due to
the collapse of density fluctuations. PBHs may act as the sources for some of
the gravitational waves recently observed. We explored the formation scenarios
of PBHs of stellar mass, taking into account the possible influence of the QCD
phase transition, for which we considered three different models: Crossover
Model (CM), Bag Model (BM), and Lattice Fit Model (LFM). For the fluctuations,
we considered a running-tilt power-law spectrum; when these cross the $\sim
10^{-9}$-$10^{-1}\mathrm{~s}$ Universe horizon they originate
0.05-500~M$_{\odot}$ PBHs which could: i) provide a population of stellar mass
PBHs similar to the ones present on the binaries associated with all known
gravitational wave sources; ii) constitute a broad mass spectrum accounting for
$\sim 76\%$ of all Cold Dark Matter (CDM) in the Universe. | Model-independent constraints on cosmic curvature: implication from the
future gravitational wave observation DECIGO: A model-independent test of the cosmic curvature parameter $\Omega_k$ is very
important in cosmology. In order to estimate cosmic curvature from cosmological
probes like standard candles, one has to be able to measure the luminosity
distance $D_L(z)$, it's derivative with respect to redshift $D'_L(z)$ and
independently know the expansion rate $H(z)$ at the same redshift. In this
paper, we study how such an idea could be implemented with the future
generation of space-based DECi-hertz Interferometer Gravitational-wave
Observatory (DECIGO), in combination with cosmic chronometers providing
cosmology-independent $H(z)$ data. Our results show that for the Hubble diagram
of simulated DECIGO data acting as a new type of standard siren, it would be
able to constrain cosmic curvature with the precision of $\Delta \Omega_k=
0.09$ with the currently available sample of 31 measurements of Hubble
parameters. In the framework of the third generation ground-based gravitational
wave detectors, the spatial curvature is constrained to be $\Delta\Omega_k=
0.13$ for Einstein Telescope (ET). More interestingly, compared to other
approaches aiming for model-independent estimations of spatial curvature, our
analysis also achieves the reconstruction of the evolution of $\Omega_k(z)$, in
the framework of a model-independent method of Gaussian processes (GP) without
assuming a specific form. Therefore, one can expect that the newly emerged
gravitational wave astronomy can become useful in local measurements of cosmic
curvature using distant sources. |
Towards a realistic solution of the cosmological constant fine-tuning
problem by Higgs inflation: Why the cosmological constant $\Lambda$ observed today is so much smaller
than the Planck scale or why the universe is accelerating at present? This is
so-called the cosmological constant fine-tuning problem. In this paper, we find
that this problem is solved with the help of Higgs inflation by simply assuming
a variable cosmological "constant" during the inflation epoch. In the
meanwhile, it could predict a large tensor-to-scalar ratio $r\approx 0.20$ and
a large running of spectral index $n'_s \approx -0.028$ with a red-tilt
spectrum $n_s \approx 0.96$, as well as a big enough number of e-folds
$N\approx 40$ that required to solve the problems in the Big Bang cosmology
with the help of $\Lambda$. | Limits on Second-Order Non-Gaussianity from Minkowski Functionals of
WMAP Data: We analyze non-Gaussianity (NG) due to the primordial bispectrum and
trispectrum using CMB temperature maps of WMAP 7-year data. We first apply the
perturbative formulae of Minkowski functionals up to second-order NG derived by
Matsubara (2010), which enable us to give limits on cubic NG parametrized with
tau_NL and g_NL as well as various types of quadratic NG parametrized with
f_NL. We find no signature of primordial NG in WMAP 7-year data, but give
constraints on the local-type, equilateral-type, orthogonal-type f_NL:
f_NL(loc)=20+-42, f_NL(eq)=-121+-208, f_NL(ort)=-129+-171, respectively, and
tau_NL/10^4=-7.6+-8.7, and g_NL/10^5=-1.9+-6.4. We also find that these
constraints are consistent with the limits from skewness and kurtosis
parameters which characterize the perturbative corrections of MFs. |
The Fundamental Plane of Damped Lyman Alpha Systems: Using a sample of 100 H I - selected damped Lyman alpha (DLA) systems,
observed with the High Resolution Echelle Spectrometer on the Keck I telescope,
we present evidence that the scatter in the well-studied correlation between
the redshift and metallicity of a DLA is largely due to the existence of a
mass-metallicity relationship at each redshift. To describe the fundamental
relations that exist between redshift, metallicity and mass, we use a
fundamental plane description, which is described by the following equation:
[M/H]=(-1.9+-0.5)+(0.74+-0.21)logdv_90-(0.32+-0.06)z. Here, we assert that the
velocity width, dv_90, which is defined as the velocity interval containing 90%
of the integrated optical depth, traces the mass of the underlying dark matter
halo. This description provides two significant improvements over the
individual descriptions of the mass-metallicity correlation and
metallicity-redshift correlation. Firstly, the fundamental equation reduces the
scatter around both relationships by about 20%, providing a more stringent
constraint on numerical simulations modeling DLAs. Secondly, it confirms that
the dark matter halos that host DLAs satisfy a mass-metallicity relationship at
each redshift between redshifts 2 through 5. | Reconstructing inflationary paradigm within Effective Field Theory
framework: In this paper my prime objective is to analyze the constraints on a
sub-Planckian excursion of a single inflaton field within Effective Field
Theory framework in a model independent fashion. For a generic single field
inflationary potential, using the various parameterization of the primordial
power spectrum I have derived the most general expression for the field
excursion in terms of various inflationary observables, applying the
observational constraints obtained from recent Planck 2015 and Planck 2015
+BICEP2/Keck Array data. By explicit computation I have reconstructed the
structural form of the inflationary potential by constraining the Taylor
expansion coefficients appearing in the generic expansion of the potential
within the Effective Field Theory. Next I have explicitly derived, a set of
higher order inflationary consistency relationships, which would help us to
break the degeneracy between various class of inflationary models by
differentiating them. I also provided two simple examples of Effective Theory
of inflation- inflection-point model and saddle-point model to check the
compatibility of the prescribed methodology in the light of Planck 2015 and
Planck 2015 +BICEP2/Keck Array data. Finally, I have also checked the validity
of the prescription by estimating the cosmological parameters and fitting the
theoretical CMB TT, TE and EE angular power spectra with the observed data
within the multipole range $2<l<2500$. |
Dust temperature and CO-to-H2 conversion factor variations in the SFR-M*
plane: Deep Herschel imaging and 12CO(2-1) line luminosities from the IRAM PdBI are
combined for a sample of 17 galaxies at z>1 from the GOODS-N field. The sample
includes galaxies both on and above the main sequence (MS) traced by
star-forming galaxies in the SFR-M* plane. The far-infrared data are used to
derive dust masses, Mdust. Combined with an empirical prescription for the
dependence of the gas-to-dust ratio on metallicity (GDR), the CO luminosities
and Mdust values are used to derive for each galaxy the CO-to-H2 conversion
factor, alpha_co. Like in the local Universe, the value of alpha_co is a factor
of ~5 smaller in starbursts compared to normal star-forming galaxies (SFGs). We
also uncover a relation between alpha_co and dust temperature (Tdust; alpha_co
decreasing with increasing Tdust) as obtained from modified blackbody fits to
the far-infrared data. While the absolute normalization of the alpha_co(Tdust)
relation is uncertain, the global trend is robust against possible systematic
biases in the determination of Mdust, GDR or metallicity. Although we cannot
formally distinguish between a step and a smooth evolution of alpha_co with the
dust temperature, we can conclude that in galaxies of near-solar metallicity, a
critical value of Tdust=30K can be used to determine whether the appropriate
alpha_co is closer to the starburst value (1.0 Msun(K kms pc^2)^-1, if
Tdust>30K) or closer to the Galactic value (4.35 Msun (K kms pc^2)^-1, if
Tdust<30K). This indicator has the great advantage of being less subjective
than visual morphological classifications of mergers/SFGs, which can be
difficult at high z because of the clumpy nature of SFGs. In the absence of
far-infrared data, the offset of a galaxy from the main sequence (i.e.,
log[SSFR(galaxy)/SSFR_MS(M*,z)]) can be used to identify galaxies requiring the
use of an alpha_co conversion factor lower than the Galactic value. | Why are some galaxy clusters underluminous? The very low concentration
of the CL2015 mass profile: Our knowledge of the variety of galaxy clusters has been increasing in the
last few years thanks to our progress in understanding the severity of
selection effects on samples. To understand the reason for the observed
variety, we study CL2015, a cluster easily missed in X-ray selected
observational samples. Its core-excised X-ray luminosity is low for its mass
M500, well below the mean relation for an X-ray selected sample, but only ~1.5
sigma below that derived for an X-ray unbiased sample. We derived thermodynamic
profiles and hydrostatic masses with the acquired deep Swift X-ray data, and we
used archival Einstein, Planck, and SDSS data to derive additional
measurements, such as integrated Compton parameter, total mass, and stellar
mass. The pressure and the electron density profiles of CL2015 are
systematically outside the +/- 2 sigma range of the universal profiles; in
particular the electron density profile is even lower than the one derived from
Planck-selected clusters. CL2015 also turns out to be fairly different in the
X-ray luminosity versus integrated pressure scaling compared to an X-ray
selected sample, but it is a normal object in terms of stellar mass fraction.
CL2015's hydrostatic mass profile, by itself or when is considered together
with dynamical masses, shows that the cluster has an unusual low concentration
and an unusual sparsity compared to clusters in X-ray selected samples. The
different behavior of CL2015 is caused by its low concentration. When
concentration differences are accounted for, the properties of CL2015 become
consistent with comparison samples. CL2015 is perhaps the first known cluster
with a remarkably low mass concentration for which high quality X-ray data
exist. Objects similar to CL2015 fail to enter observational X-ray selected
samples because of their low X-ray luminosity relative to their mass. |
A Spitzer IRAC Measure of the Zodiacal Light: The dominant non-instrumental background source for space-based infrared
observatories is the zo- diacal light. We present Spitzer Infrared Array Camera
(IRAC) measurements of the zodiacal light at 3.6, 4.5, 5.8, and 8.0 {\mu}m,
taken as part of the instrument calibrations. We measure the changing surface
brightness levels in approximately weekly IRAC observations near the north
ecliptic pole (NEP) over the period of roughly 8.5 years. This long time
baseline is crucial for measuring the annual sinusoidal variation in the signal
levels due to the tilt of the dust disk with respect to the ecliptic, which is
the true signal of the zodiacal light. This is compared to both Cosmic
Background Explorer Diffuse Infrared Background Experiment (COBE DIRBE) data
and a zodiacal light model based thereon. Our data show a few percent
discrepancy from the Kelsall et al. (1998) model including a potential warping
of the interplanetary dust disk and a previously detected overdensity in the
dust cloud directly behind the Earth in its orbit. Accurate knowledge of the
zodiacal light is important for both extragalactic and Galactic astronomy
including measurements of the cosmic infrared background, absolute measures of
extended sources, and comparison to extrasolar interplanetary dust models. IRAC
data can be used to further inform and test future zodiacal light models. | Testing galaxy formation scenarios with a new mass estimator: We present the recently derived Wolf et al. (2009) mass estimator, which is
applicable for spherical pressure-supported stellar systems spanning over ten
orders of magnitude in luminosity, as a tool to test galaxy formation theories.
We show that all of the Milky Way dwarf spheroidal galaxies (MW dSphs) are
consistent with having formed within a halo of mass approximately 3 x 10^9 Msun
in LCDM cosmology. The faintest MW dSphs seem to have formed in dark matter
halos that are at least as massive as those of the brightest MW dSphs, despite
the almost five orders of magnitude spread in luminosity. We expand our
analysis to the full range of observed pressure-supported stellar systems and
examine their half-light I-band mass-to-light ratios. The M/L vs. half-light
mass M_1/2 relation for pressure-supported galaxies follows a U-shape, with a
broad minimum near M/L ~ 3 that spans dwarf elliptical galaxies to normal
ellipticals, a steep rise to M/L ~ 3,200 for ultra-faint dSphs, and a more
shallow rise to M/L ~ 800 for galaxy cluster spheroids. |
NGC 1300 Dynamics: III. Orbital analysis: We present the orbital analysis of four response models, that succeed in
reproducing morphological features of NGC 1300. Two of them assume a planar
(2D) geometry with $\Omega_p$=22 and 16 \ksk respectively. The two others
assume a cylindrical (thick) disc and rotate with the same pattern speeds as
the 2D models. These response models reproduce most successfully main
morphological features of NGC 1300 among a large number of models, as became
evident in a previous study. Our main result is the discovery of three new
dynamical mechanisms that can support structures in a barred-spiral grand
design system. These mechanisms are presented in characteristic cases, where
these dynamical phenomena take place. They refer firstly to the support of a
strong bar, of ansae type, almost solely by chaotic orbits, then to the support
of spirals by chaotic orbits that for a certain number of pat tern revolutions
follow an n:1 (n=7,8) morphology, and finally to the support of spiral arms by
a combination of orbits trapped around L$_{4,5}$ and sticky chaotic orbits with
the same Jacobi constant. We have encountered these dynamical phenomena in a
large fraction of the cases we studied as we varied the parameters of our
general models, without forcing in some way their appearance. This suggests
that they could be responsible for the observed morphologies of many
barred-spiral galaxies. Comparing our response models among themselves we find
that the NGC 130 0 morphology is best described by a thick disc model for the
bar region and a 2D disc model for the spirals, with both components rotating
with the same pattern speed $\Omega_p$=16 \ksk !. In such a case, the whole
structure is included inside the corotation of the system. The bar is supported
mainly by regular orbits, while the spirals are supported by chaotic orbits. | Constraining Cosmology with Big Data Statistics of Cosmological Graphs: By utilizing large-scale graph analytic tools implemented in the modern Big
Data platform, Apache Spark, we investigate the topological structure of
gravitational clustering in five different universes produced by cosmological
$N$-body simulations with varying parameters: (1) a WMAP 5-year compatible
$\Lambda$CDM cosmology, (2) two different dark energy equation of state
variants, and (3) two different cosmic matter density variants. For the Big
Data calculations, we use a custom build of stand-alone Spark/Hadoop cluster at
Korea Institute for Advanced Study (KIAS) and Dataproc Compute Engine in Google
Cloud Platform (GCP) with the sample size ranging from 7 millions to 200
millions. We find that among the many possible graph-topological measures,
three simple ones: (1) the average of number of neighbors (the so-called
average vertex degree) $\alpha$, (2) closed-to-connected triple fraction (the
so-called transitivity) $\tau_\Delta$, and (3) the cumulative number density
$n_{s\ge5}$ of subcomponents with connected component size $s \ge 5$, can
effectively discriminate among the five model universes. Since these
graph-topological measures are in direct relation with the usual $n$-points
correlation functions of the cosmic density field, graph-topological statistics
powered by Big Data computational infrastructure opens a new, intuitive, and
computationally efficient window into the dark Universe. |
Deformed Distance Duality Relations and Supernovae Dimming: The basic cosmological distances are linked by the Etherington cosmic
distance duality relation, $\eta (z) = D_{L}(z)(1+z)^{-2}/D_{A}(z) \equiv 1$,
where $D_{L}$ and $D_{A}$ are, respectively, the luminosity and angular
diameter distances. In order to test its validity, some authors have proposed
phenomenological expressions for $\eta(z)$ thereby deforming the original
Etherington's relation and comparing the resulting expressions with the
available and future cosmological data. The relevance of such studies is
unquestionable since any violation of the cosmic distance duality relation
could be the signal of new physics or non-negligible astrophysical effects in
the usually assumed perfectly transparent Universe. In this letter, we show
that under certain conditions such expressions can be derived from a more
fundamental approach with the parameters appearing in the $\eta(z)$ expression
defining the cosmic absorption parameter as recently discussed by Chen and
Kantowski. Explicit examples involving four different parametrizations of the
deformation function are given. Based on such an approach, it is also found
that the latest Supernova data can also be explained in the framework of a pure
cold dark matter model (Einstein-de Sitter). Two different scenarios with
cosmic absorption are discussed. Only if the cosmic opacity is fully
negligible, the description of an accelerating Universe powered by dark energy
or some alternative gravity theory must be invoked. | On the Segregation of Dark Matter Substructure: We present the first comprehensive analysis of the segregation of dark matter
subhaloes in their host haloes. Using numerical simulations, we examine the
segregation of twelve different subhalo properties with respect to both orbital
energy and halo-centric radius (in real space as well as in projection).
Subhaloes are strongly segregated by accretion redshift, which is an outcome of
the inside-out assembly of their host haloes. Since subhaloes that were
accreted earlier have experienced more tidal stripping, subhaloes that have
lost a larger fraction of their mass at infall are on more bound orbits.
Subhaloes are also strongly segregated in their masses and maximum circular
velocities at accretion. We demonstrate that part of this segregation is
already imprinted in the infall conditions. For massive subhaloes it is
subsequently boosted by dynamical friction, but only during their first radial
orbit. The impact of these two effects is counterbalanced, though, by the fact
that subhaloes with larger accretion masses are accreted later. Because of
tidal stripping, subhaloes reveal little to no segregation by present-day mass
or maximum circular velocity, while the corresponding torques cause subhaloes
on more bound orbits to have smaller spin. There is a weak tendency for
subhaloes that formed earlier to be segregated towards the center of their host
halo, which is an indirect consequence of the fact that (sub)halo formation
time is correlated with other, strongly segregated properties. We discuss the
implications of our results for the segregation of satellite galaxies in galaxy
groups and clusters. |
Creating perturbations from a decaying field during inflation: Typically the fluctuations generated from a decaying field during inflation
do not contribute to the large scale structures. In this paper we provide an
example where it is possible for a field which slowly rolls and then decays
during inflation to create all the matter perturbations with a slightly
red-tilted spectral index, with no isocurvature perturbations, and with a
possibility of a departure from Gaussian fluctuations. | Fundamental Physics from Future Weak-Lensing Calibrated
Sunyaev-Zel'dovich Galaxy Cluster Counts: Future high-resolution measurements of the cosmic microwave background (CMB)
will produce catalogs of tens of thousands of galaxy clusters through the
thermal Sunyaev-Zel'dovich (tSZ) effect. We forecast how well different
configurations of a CMB Stage-4 experiment can constrain cosmological
parameters, in particular the amplitude of structure as a function of redshift
$\sigma_8(z)$, the sum of neutrino masses $\Sigma m_{\nu}$, and the dark energy
equation of state $w(z)$. A key element of this effort is calibrating the tSZ
scaling relation by measuring the lensing signal around clusters. We examine
how the mass calibration from future optical surveys like the Large Synoptic
Survey (LSST) compares with a purely internal calibration using lensing of the
CMB itself. We find that, due to its high-redshift leverage, internal
calibration gives constraints on cosmological parameters comparable to the
optical calibration, and can be used as a cross-check of systematics in the
optical measurement. We also show that in contrast to the constraints using the
CMB lensing power spectrum, lensing-calibrated tSZ cluster counts can detect a
minimal $\Sigma m_{\nu}$ at the 3-5$\sigma$ level even when the dark energy
equation of state is freed up. |
Quasar Feedback: More Bang for Your Buck: We propose a two-stage model for the effects of feedback from a bright quasar
on the cold gas in a galaxy. It is difficult for feedback from near the
accretion disk to directly impact dense molecular clouds at ~kpc. But if such
feedback can drive a weak wind or outflow in the hot, diffuse ISM (a relatively
'easy' task), then in the wake of such an outflow passing over a cold cloud, a
combination of instabilities will drive the cloud material to effectively
expand in the direction perpendicular to the outflow. Such expansion
dramatically increases the effective cross section of the cloud material and
makes it more susceptible to ionization and momentum coupling from absorption
of the incident quasar radiation field. Even a moderate effect of this nature
can dramatically alter the ability of clouds at large radii to be fully ionized
and driven into a secondary outflow by radiation pressure. Since the amount of
momentum and volume which can be ionized by observed quasar radiation field is
more than sufficient to affect the entire cold gas supply once it has been
altered in this manner (and the 'initial' feedback need only initiate a
moderate wind in the low-density hot gas), this reduces by an order of
magnitude the required energy budget for feedback to affect a host galaxy.
Instead of ~5% of the radiated energy (~100% momentum) needed if the initial
feedback must directly heat or blow out the galactic gas, if only ~0.5% of the
luminosity (~10% momentum) can couple to drive the initial hot outflow, this
mechanism could be efficient. This amounts to hot gas outflow rates from near
the accretion disk of only 5-10% of the BH accretion rate. | Multifrequency Radio Observations of a SNR in the LMC. The Case of SNR
J0527-6549 (DEM l204): We present a detailed study and results of new Australia Telescope Compact
Array (ATCA) observations of supernova remnant, SNR J0527-6549. This Large
Magellanic Cloud (LMC) ob ject follows a typical supernova remnant (SNR)
horseshoe morphology with a diameter of D=(66x58)+-1 pc which is among the
largest SNRs in the LMC. Its relatively large size indicates older age while a
steeper than expected radio spectral index of aplha=-0.92+-0.11 is more typical
for younger and energetic SNRs. Also, we report detections of regions with a
high order of polarization at a peak value of ~54+-17% at 6 cm. |
Incorporating Astrophysical Systematics into a Generalized Likelihood
for Cosmology with Type Ia Supernovae: Traditional cosmological inference using Type Ia supernovae (SNeIa) have used
stretch- and color-corrected fits of SN Ia light curves and assumed a resulting
fiducial mean and symmetric intrinsic dispersion for the resulting relative
luminosity. As systematics become the main contributors to the error budget, it
has become imperative to expand supernova cosmology analyses to include a more
general likelihood to model systematics to remove biases with losses in
precision. To illustrate an example likelihood analysis, we use a simple model
of two populations with a relative luminosity shift, independent intrinsic
dispersions, and linear redshift evolution of the relative fraction of each
population. Treating observationally viable two-population mock data using a
one-population model results in an inferred dark energy equation of state
parameter $w$ that is biased by roughly 2 times its statistical error for a
sample of N $ \gtrsim$ 2500 SNeIa. Modeling the two-population data with a
two-population model removes this bias at a cost of an approximately $\sim20\%$
increase in the statistical constraint on $w$. These significant biases can be
realized even if the support for two underlying SNeIa populations, in the form
of model selection criteria, is inconclusive. With the current
observationally-estimated difference in the two proposed populations, a sample
of N $ \gtrsim$ 10,000 SNeIa is necessary to yield conclusive evidence of two
populations. | Probing the inflaton: Small-scale power spectrum constraints from
measurements of the CMB energy spectrum: In the early Universe, energy stored in small-scale density perturbations is
quickly dissipated by Silk-damping, a process that inevitably generates mu- and
y-type spectral distortions of the cosmic microwave background (CMB). These
spectral distortions depend on the shape and amplitude of the primordial power
spectrum at wavenumbers k < 10^4 Mpc^{-1}. Here we study constraints on the
primordial power spectrum derived from COBE/FIRAS and forecasted for PIXIE. We
show that measurements of mu and y impose strong bounds on the integrated
small-scale power, and we demonstrate how to compute these constraints using
k-space window functions that account for the effects of thermalization and
dissipation physics. We show that COBE/FIRAS places a robust upper limit on the
amplitude of the small-scale power spectrum. This limit is about three orders
of magnitude stronger than the one derived from primordial black holes in the
same scale range. Furthermore, this limit could be improved by another three
orders of magnitude with PIXIE, potentially opening up a new window to early
Universe physics. To illustrate the power of these constraints, we consider
several generic models for the small-scale power spectrum predicted by
different inflation scenarios, including running-mass inflation models and
inflation scenarios with episodes of particle production. PIXIE could place
very tight constraints on these scenarios, potentially even ruling out
running-mass inflation models if no distortion is detected. We also show that
inflation models with sub-Planckian field excursion that generate detectable
tensor perturbations should simultaneously produce a large CMB spectral
distortion, a link that could potentially be established by PIXIE. |
The Impact of Modeling Errors on Interferometer Calibration for 21 cm
Power Spectra: We study the impact of sky-based calibration errors from source mismodeling
on 21\,cm power spectrum measurements with an interferometer and propose a
method for suppressing their effects. While emission from faint sources that
are not accounted for in calibration catalogs is believed to be spectrally
smooth, deviations of true visibilities from model visibilities are not, due to
the inherent chromaticity of the interferometer's sky-response (the "wedge").
Thus, unmodeled foregrounds, below the confusion limit of many instruments,
introduce frequency structure into gain solutions on the same line-of-sight
scales on which we hope to observe the cosmological signal. We derive analytic
expressions describing these errors using linearized approximations of the
calibration equations and estimate the impact of this bias on measurements of
the 21\,cm power spectrum during the Epoch of Reionization (EoR). Given our
current precision in primary beam and foreground modeling, this noise will
significantly impact the sensitivity of existing experiments that rely on
sky-based calibration. Our formalism describes the scaling of calibration with
array and sky-model parameters and can be used to guide future instrument
design and calibration strategy. We find that sky-based calibration that
down-weights long baselines can eliminate contamination in most of the region
outside of the wedge with only a modest increase in instrumental noise. | SPIDERS: the spectroscopic follow-up of X-ray selected clusters of
galaxies in SDSS-IV: SPIDERS (The SPectroscopic IDentification of eROSITA Sources) is a program
dedicated to the homogeneous and complete spectroscopic follow-up of X-ray AGN
and galaxy clusters over a large area ($\sim$7500 deg$^2$) of the extragalactic
sky. SPIDERS is part of the SDSS-IV project, together with the Extended Baryon
Oscillation Spectroscopic Survey (eBOSS) and the Time-Domain Spectroscopic
Survey (TDSS). This paper describes the largest project within SPIDERS before
the launch of eROSITA: an optical spectroscopic survey of X-ray selected,
massive ($\sim 10^{14}$ to $10^{15}~M_{\odot}$) galaxy clusters discovered in
ROSAT and XMM-Newton imaging. The immediate aim is to determine precise
($\Delta_z \sim 0.001$) redshifts for 4,000-5,000 of these systems out to $z
\sim 0.6$. The scientific goal of the program is precision cosmology, using
clusters as probes of large-scale structure in the expanding Universe. We
present the cluster samples, target selection algorithms and observation
strategies. We demonstrate the efficiency of selecting targets using a
combination of SDSS imaging data, a robust red-sequence finder and a dedicated
prioritization scheme. We describe a set of algorithms and work-flow developed
to collate spectra and assign cluster membership, and to deliver catalogues of
spectroscopically confirmed clusters. We discuss the relevance of line-of-sight
velocity dispersion estimators for the richer systems. We illustrate our
techniques by constructing a catalogue of 230 spectroscopically validated
clusters ($0.031 < z < 0.658$), found in pilot observations. We discuss two
potential science applications of the SPIDERS sample: the study of the X-ray
luminosity-velocity dispersion ($L_X-\sigma$) relation and the building of
stacked phase-space diagrams. |
Simulation-based inference of deep fields: galaxy population model and
redshift distributions: Accurate redshift calibration is required to obtain unbiased cosmological
information from large-scale galaxy surveys. In a forward modelling approach,
the redshift distribution n(z) of a galaxy sample is measured using a
parametric galaxy population model constrained by observations. We use a model
that captures the redshift evolution of the galaxy luminosity functions,
colours, and morphology, for red and blue samples. We constrain this model via
simulation-based inference, using factorized Approximate Bayesian Computation
(ABC) at the image level. We apply this framework to HSC deep field images,
complemented with photometric redshifts from COSMOS2020. The simulated
telescope images include realistic observational and instrumental effects. By
applying the same processing and selection to real data and simulations, we
obtain a sample of n(z) distributions from the ABC posterior. The photometric
properties of the simulated galaxies are in good agreement with those from the
real data, including magnitude, colour and redshift joint distributions. We
compare the posterior n(z) from our simulations to the COSMOS2020 redshift
distributions obtained via template fitting photometric data spanning the
wavelength range from UV to IR. We mitigate sample variance in COSMOS by
applying a reweighting technique. We thus obtain a good agreement between the
simulated and observed redshift distributions, with a difference in the mean at
the 1$\sigma$ level up to a magnitude of 24 in the i band. We discuss how our
forward model can be applied to current and future surveys and be further
extended. The ABC posterior and further material will be made publicly
available at https://cosmology.ethz.ch/research/software-lab/ufig.html. | Gravitational lens candidates in the E-CDFS: We report ten lens candidates in the E-CDFS from the GEMS survey. Nine of the
systems are new detections and only one of the candidates is a known lens
system. For the most promising five systems including the known lens system, we
present results from preliminary lens mass modelling, which tests if the
candidates are plausible lens systems. Photometric redshifts of the candidate
lens galaxies are obtained from the COMBO-17 galaxy catalog. Stellar masses of
the candidate lens galaxies within the Einstein radius are obtained by using
the $z$-band luminosity and the $V-z$ color-based stellar mass-to-light ratios.
As expected, the lensing masses are found to be larger than the stellar masses
of the candidate lens galaxies. These candidates have similar dark matter
fractions as compared to lenses in SLACS and COSMOS. They also roughly follow
the halo mass-stellar mass relation predicted by the subhalo abundance matching
technique. One of the candidate lens galaxies qualifies as a LIRG and may not
be a true lens because the arc-like feature in the system is likely to be an
active region of star formation in the candidate lens galaxy. Amongst the five
best candidates, one is a confirmed lens system, one is a likely lens system,
two are less likely to be lenses and the status of one of the candidates is
ambiguous. Spectroscopic follow-up of these systems is still required to
confirm lensing and/or for more accurate determination of the lens masses and
mass density profiles. |
Determination of dark matter type by X-ray sources statistics: The current cosmological model includes cold dark matter, which consists of
massive nonrelativistic particles. There are also some observational and
theoretical evidences for warm dark matter. The existence of warm DM can be
examined by measuring of the galaxy clusters density profiles and accurate
counting of dwarf galaxies. In this work I suppose that DM haloes are well
traced by X-ray gas in clusters, groups, pairs and even single galaxies. The
type of DM is inspected with the Xgal sample of 5021 X-ray emitting galaxies
observed by XMM-Newton. The selection bias of this sample is also analyzed. | Nucleosynthetic signatures of primordial origin around supermassive
black holes: If primordial black holes (PBHs) seeded the supermassive black holes (SMBHs)
at the centers of high-redshift quasars, then the gas surrounding these black
holes may reveal nucleosynthetic clues to their primordial origins. We present
predictions of altered primordial abundances around PBHs massive enough to seed
SMBHs at z~6-7.5. We find that if PBHs with initial masses of ~10^5 M$_{\odot}$
are responsible for such SMBHs, they may produce primordial Deuterium and
Helium fractions enhanced by >~ 10%, and Lithium abundance depleted by >~10%,
at distances of up to ~ a comoving kiloparsec away from the black hole after
decoupling. We estimate that ~ 10^8 M$_{\odot}$ of gas is enhanced (or
depleted) by at least one percent. Evidence of these modified primordial
Deuterium, Helium, and Lithium abundances could still be present if this
circum-PBH gas remains unaccreted by the SMBH and in or near the host galaxies
of high-redshift quasars. Measuring the abundance anomalies will be
challenging, but could offer a novel way to reveal the primordial origin of
such SMBH seeds. |
Reconstructing the primordial power spectrum from the CMB: We propose a straightforward and model independent methodology for
characterizing the sensitivity of CMB and other experiments to wiggles,
irregularities, and features in the primordial power spectrum. Assuming that
the primordial cosmological perturbations are adiabatic, we present a function
space generalization of the usual Fisher matrix formalism, applied to a CMB
experiment resembling Planck with and without ancillary data. This work is
closely related to other work on recovering the inflationary potential and
exploring specific models of non-minimal, or perhaps baroque, primordial power
spectra. The approach adopted here, however, most directly expresses what the
data is really telling us. We explore in detail the structure of the available
information and quantify exactly what features can be reconstructed and at what
statistical significance. | Cosmic Topology of Polyhedral Double-Action Manifolds: A special class of non-trivial topologies of the spherical space S^3 is
investigated with respect to their cosmic microwave background (CMB)
anisotropies. The observed correlations of the anisotropies on the CMB sky
possess on large separation angles surprising low amplitudes which might be
naturally be explained by models of the Universe having a multiconnected
spatial space. We analysed in CQG 29(2012)215005 the CMB properties of prism
double-action manifolds that are generated by a binary dihedral group D^*_p and
a cyclic group Z_n up to a group order of 180. Here we extend the CMB analysis
to polyhedral double-action manifolds which are generated by the three binary
polyhedral groups (T^*, O^*, I^*) and a cyclic group Z_n up to a group order of
1000. There are 20 such polyhedral double-action manifolds. Some of them turn
out to have even lower CMB correlations on large angles than the Poincare
dodecahedron. |
Constraining decaying dark energy density models with the CMB
temperature-redshift relation: We discuss the thermodynamic and dynamical properties of a variable dark
energy model with density scaling as $\rho_x \propto (1+z)^{m}$, z being the
redshift. These models lead to the creation/disruption of matter and radiation,
which affect the cosmic evolution of both matter and radiation components in
the Universe. In particular, we have studied the temperature-redshift relation
of radiation, which has been constrained using a recent collection of cosmic
microwave background (CMB) temperature measurements up to $z \sim 3$. We find
that, within the uncertainties, the model is indistinguishable from a
cosmological constant which does not exchange any particles with other
components. Future observations, in particular measurements of CMB temperature
at large redshift, will allow to give firmer bounds on the effective equation
of state parameter $w_{eff}$ for such types of dark energy models. | Large numbers in the Universe and the origin of the Cosmic magnetic
field: The origin of the cosmic magnetic fields is still a mystery. We use current
knowledge of galaxy formation and evolution to estimate that a charge imbalance
of $1$ every $\sim10^{39}$ in protogalaxies would solve this problem. This
imbalance coincides with the ratio of coulomb to gravitational potentials
between protons and electrons which would make the imbalance stable. We show
that this could be produced by Poisson noise in the number of charges left over
by Inflation, or by stellar black holes. This letter describes these remarkable
coincidences that point to simple solutions for this problem. |
The Early Dark Sector, the Hubble Tension, and the Swampland: We consider the interplay of the Early Dark Energy (EDE) model, the Swampland
Distance Conjecture (SDC), and cosmological parameter tensions. EDE is a
proposed resolution of the Hubble tension relying upon a near-Planckian scalar
field excursion, while the SDC predicts an exponential sensitivity of masses of
other fields to such an excursion, $m\propto e^{-c|\Delta \phi|/M_{\rm pl}}$
with $c\sim{\cal O}(1)$. Meanwhile, EDE is in tension with large-scale
structure (LSS) data, due to shifts in the standard $\Lambda$CDM parameters
necessary to fit the cosmic microwave background (CMB). One might hope that a
proper treatment of the model, e.g., accounting for the SDC, may ameliorate the
tension with LSS. Motivated by these considerations, we introduce the Early
Dark Sector (EDS) model, wherein the mass of dark matter is exponentially
sensitive to super-Planckian field excursions of the EDE scalar. The EDS model
exhibits new phenomenology in both the early and late universe, the latter due
to an EDE-mediated dark matter self-interaction. This dark matter-philic "fifth
force", while constrained to be small, remains active in the late universe and
is not screened in virialized halos. We find that the new interaction with dark
matter partially resolves the LSS tension. However, the marginalized posteriors
are nonetheless consistent with $f_{\rm EDE}=0$ at 95$\%$ CL once the Dark
Energy Survey Year 3 measurement of $S_8$ is included. We study constraints on
the model from Atacama Cosmology Telescope data, and find a factor of two
improvement on the error bar on the SDC parameter $c$, along with an increased
preference for the EDE component. We discuss the implications of these
constraints for the SDC, and find the tightest observational constraints to
date on a swampland parameter, suggesting that an EDE description of
cosmological data is in tension with the SDC. | Bulges and discs of spiral galaxies: edge-on perspective: We present a sample of edge-on spiral galaxies both of early and late
types.The sample consists of 175 galaxies in the Ks-filter, 169 galaxies in the
H-filter and 165 galaxies in the J-filter. Bulge and disc decompositions of
each galaxy image, taken from the Two Micron All Sky Survey (2MASS), were
performed. We discuss several scaling relations for bulges and discs which
indicate a tight link between their formation and evolution. We show that
galaxies with bulges fitted by the Sersic index n<2 (pseudobulges) have quite
different distributions of their structural parameters than galaxies with n>=2
bulges (classical bulges). First of all, the distribution of the apparent bulge
axis ratio q_b for the subsample with n<2 can be attributed to triaxial, nearly
prolate bulges, while n>=2 bulges seem to be oblate spheroids with moderate
flattening. Secondly, the Photometric Plane of the sample bulges is not flat
and has a prominent curvature towards small values of n. Thirdly, despite of
the existence of a clear relation between the flattening of stellar discs h/z_0
and the relative mass of a spherical component, the distributions over both
parameters are quite different for galaxies possesing bulges and pseudobulges. |
The Herschel Virgo Cluster Survey XIV: transition-type dwarf galaxies in
the Virgo cluster: We use dust scaling relations to investigate the hypothesis that Virgo
cluster transition-type dwarfs are infalling star-forming field galaxies, which
is argued based on their optical features (e.g. disks, spiral arms, bars) and
kinematic properties similar to late-type galaxies. After their infall,
environmental effects gradually transform them into early-type galaxies through
the removal of their interstellar medium and quenching of all star formation
activity. In this paper, we aim to verify whether this hypothesis holds using
far-infrared diagnostics based on Herschel observations of the Virgo cluster
taken as part of the Herschel Virgo Cluster Survey (HeViCS). We select
transition-type objects in the nearest cluster, Virgo, based on spectral
diagnostics indicative for their residual or ongoing star formation. We detect
dust Md ~ 10^{5-6} Msun in 36% of the transition-type dwarfs located on the
high end of the stellar mass distribution. This suggests that the dust
reservoirs present in non-detections fall just below the Herschel detection
limit (< 1.1x10^5 Msun). Dust scaling relations support the hypothesis of a
transformation between infalling late-type galaxies to quiescent low-mass
spheroids governed by environmental effects, with dust-to-stellar mass
fractions for transition-type dwarfs in between values characteristic for
late-type objects and the lower dust fractions observed in early-type galaxies.
Several transition-type dwarfs demonstrate blue central cores, hinting at the
radially outside-in removal of gas and quenching of star formation activity.
The fact that dust is also confined to the inner regions suggests that metals
are stripped in the outer regions along with the gas. In the scenario of most
dust being stripped from the galaxy along with the gas, we argue that...
(abridged) | Solution to Big-Bang Nucleosynthesis in Hybrid Axion Dark Matter Model: Following a recent suggestion of axion cooling of photons between the
nucleosynthesis and recombination epochs in the Early Universe, we investigate
a hybrid model with both axions and relic supersymmetric particles. In this
model we demonstrate that the 7Li abundance can be consistent with observations
without destroying the important concordance of deuterium abundance. |
Encircling the dark: constraining dark energy via cosmic density in
spheres: The recently published analytic probability density function for the mildly
non-linear cosmic density field within spherical cells is used to build a
simple but accurate maximum likelihood estimate for the redshift evolution of
the variance of the density, which, as expected, is shown to have smaller
relative error than the sample variance. This estimator provides a competitive
probe for the equation of state of dark energy, reaching a few percent accuracy
on wp and wa for a Euclid-like survey. The corresponding likelihood function
can take into account the configuration of the cells via their relative
separations. A code to compute one-cell density probability density functions
for arbitrary initial power spectrum, top-hat smoothing and various spherical
collapse dynamics is made available online so as to provide straightforward
means of testing the effect of alternative dark energy models and initial
power-spectra on the low-redshift matter distribution. | Statistical anisotropy of CMB as a probe of conformal rolling scenario: Search for the statistical anisotropy in the CMB data is a powerful tool for
constraining models of the early Universe. In this paper we focus on the
recently proposed cosmological scenario with conformal rolling. We consider two
sub-scenarios, one of which involves a long intermediate stage between
conformal rolling and conventional hot epoch. Primordial scalar perturbations
generated within these sub-scenarios have different direction-dependent power
spectra, both characterized by a single parameter h^2. We search for the
signatures of this anisotropy in the seven-year WMAP data using quadratic
maximum likelihood method, first applied for similar purposes by Hanson and
Lewis. We confirm the large quadrupole anisotropy detected in V and W bands,
which has been argued to originate from systematic effects rather than from
cosmology. We construct an estimator for the parameter h^2. In the case of the
sub-scenario with the intermediate stage we set an upper limit h^2 < 0.045 at
the 95% confidence level. The constraint on h^2 is much weaker in the case of
another sub-scenario, where the intermediate stage is absent. |
The HiZELS/UKIRT large area survey for bright Lyman-alpha emitters at
z~9: We present the largest area survey to date (1.4 deg2) for Lyman-alpha
emitters (LAEs) at z~9, as part of the Hi-z Emission Line Survey (HiZELS). The
survey, which primarily targets H-alpha emitters at z < 3, uses the Wide Field
CAMera on the United Kingdom Infrared Telescope and a custom narrow-band filter
in the J band to reach a Lyman-alpha luminosity limit of ~10^43.8 erg/s over a
co-moving volume of 1.12x10^6 Mpc^3 at z = 8.96+-0.06. Two candidates were
found out of 1517 line emitters, but those were rejected as LAEs after
follow-up observations. This improves the limit on the space density of bright
Lyman-alpha emitters by 3 orders of magnitude and is consistent with
suppression of the bright end of the Lyman-alpha luminosity function beyond
z~6. Combined with upper limits from smaller but deeper surveys, this rules out
some of the most extreme models for high-redshift Lyman-alpha emitters. The
potential contamination of narrow-band Lyman-alpha surveys at z>7 by Galactic
brown dwarf stars is also examined, leading to the conclusion that such
contamination may well be significant for searches at 7.7 < z < 8.0, 9.1 < z <
9.5 and 11.7 < z < 12.2. | Cosmological perturbations without the Boltzmann hierarchy: Calculations of the evolution of cosmological perturbations generally involve
solution of a large number of coupled differential equations to describe the
evolution of the multipole moments of the distribution of photon intensities
and polarization. However, this "Boltzmann hierarchy" communicates with the
rest of the system of equations for the other perturbation variables only
through the photon-intensity quadrupole moment. Here I develop an alternative
formulation wherein this photon-intensity quadrupole is obtained via solution
of two coupled integral equations -- one for the intensity quadrupole and
another for the linear-polarization quadrupole -- rather than the full
Boltzmann hierarchy. This alternative method of calculation provides some
physical insight and a cross-check for the traditional approach. I describe a
simple and efficient iterative numerical solution that converges fairly
quickly. I surmise that this may allow current state-of-the-art
cosmological-perturbation codes to be accelerated. |
Cosmic chronometers constraints on some fast-varying dark energy
equations of state: We consider three `four-parameters' dark energy equations of state allowing
fast transition from the matter dominated decelerating phase to the current
accelerating phase. The fast-varying nature of the dark energy models is
quantified by the transition width $\tau > 0$, a free parameter associated with
the models where lower values of $\tau$ imply faster transition. We impose the
latest observational constraints on these fast-varying dark energy equations of
state, using the latest released cosmic chronometers data along with a series
of standard dark energy probes, namely, the local Hubble constant value at 2.4%
precision measured by the Hubble Space Telescope, the Joint Light Curve
Analysis from Supernovae Type Ia, Baryon acoustic oscillations distance
measurements and finally the cosmic microwave background radiation distance
priors. Our analyses show that the precise measurements of the free parameters,
when a large number of parameters are allowed in a cosmological model become
very hard. Moreover, the analyses do not enable us to make any decisive comment
on the fast-varying nature of the models, at least from the astronomical data
available at current moment. Finally, we close the work with a discussion based
on the information criteria, which do not return favorable results to the
fast-varying models, at least according to the data employed. | Origin of the anti-hierarchical growth of black holes: Observational studies have revealed a "downsizing" trend in black hole (BH)
growth: the number densities of luminous AGN peak at higher redshifts than
those of faint AGN. This would seem to imply that massive black holes formed
before low mass black holes, in apparent contradiction to hierarchical
clustering scenarios. We investigate whether this observed "downsizing" in BH
growth is reproduced in a semi-analytic model for the formation and evolution
of galaxies and black holes, set within the hierarchical paradigm for structure
formation (Somerville et al. 2008; S08). In this model, black holes evolve from
light seeds (\sim100M\odot) and their growth is merger-driven. The original S08
model (baseline model) reproduces the number density of AGN at intermediate
redshifts and luminosities, but underproduces luminous AGN at very high
redshift (z > 3) and overproduces them at low redshift (z < 1). In addition,
the baseline model underproduces low-luminosity AGN at low redshift (z < 1). To
solve these problems we consider several modifications to the physical
processes in the model: (1) a 'heavy' black hole seeding scenario (2) a
sub-Eddington accretion rate ceiling that depends on the cold gas fraction, and
(3) an additional black hole accretion mode due to disk instabilities. With
these three modifications, the models can explain the observed downsizing,
successfully reproduce the bolometric AGN luminosity function and
simultaneously reproduce galaxy and black hole properties in the local
Universe. We also perform a comparison with the observed soft and hard X-ray
luminosity functions of AGN, including an empirical correction for torus-level
obscuration, and reach similar conclusions. Our best-fit model suggests a
scenario in which disk instabilities are the main driver for moderately
luminous Seyfert galaxies at low redshift, while major mergers are the main
trigger for luminous AGN. |
The Dipole of the Pantheon+SH0ES Data: In this paper we determine the dipole in the distance redshift relation from
the Pantheon+ data. We find that, while its amplitude roughly agrees with the
dipole found in the cosmic microwave background which is attributed to the
motion of the solar system with respect to the cosmic rest frame, the direction
is different with a significance of slightly more than $3\si$. While the
amplitude depends on the lower redshift cutoff, the direction is quite stable.
For redshift cuts of order $z_{\rm cut} \simeq 0.05$ and higher, the dipole is
no longer detected with high statistical significance. An important r\^ole
seems to be played by the redshift corrections for peculiar velocities. | The Phoenix Project: the Dark Side of Rich Galaxy Clusters: [abridged] We introduce the Phoenix Project, a set of $\Lambda$CDM
simulations of the dark matter component of nine rich galaxy clusters. Each
cluster is simulated at least at two different numerical resolutions. For eight
of them, the highest resolution corresponds to $\sim 130$ million particles
within the virial radius, while for one this number is over one billion. We
study the structure and substructure of these systems and contrast them with
six galaxy-sized dark matter haloes from the Aquarius Project, simulated at
comparable resolution. This comparison highlights the approximate mass
invariance of CDM halo structure and substructure. We find little difference in
the spherically-averaged mass, pseudo-phase-space density, and velocity
anisotropy profiles of Aquarius and Phoenix haloes. When scaled to the virial
properties of the host halo, the abundance and radial distribution of subhaloes
are also very similar, despite the fact that Aquarius and Phoenix haloes differ
by roughly three decades in virial mass. The most notable difference is that
cluster haloes have been assembled more recently and are thus significantly
less relaxed than galaxy haloes, which leads to decreased regularity, increased
halo-to-halo scatter and sizable deviations from the mean trends. This
accentuates the effects of the strong asphericity of individual clusters on
surface density profiles, which may vary by up to a factor of three at a given
radius, depending on projection. The high apparent concentration reported for
some strong-lensing clusters might very well reflect these effects. A more
recent assembly also explains why substructure in some Phoenix haloes is
slightly more abundant than in Aquarius, especially in the inner regions.
Resolved subhaloes nevertheless contribute only $11 \pm 3%$ of the virial mass
in Phoenix clusters. . |
Testing Parity Symmetry with the Polarized Cosmic Microwave Background: New physics in the early Universe could lead to parity-violation in the late
Universe, sourcing statistics whose sign changes under point reflection. The
best constraints on such phenomena have come from the Planck temperature
fluctuations; however, this is already cosmic-variance-limited down to
relatively small scales, thus only small improvements are expected in the
future. Here, we search for signatures of parity-violation in the polarized
CMB, using the Planck PR4 $T$- and $E$-mode data. We perform both a
simulation-based blind test for any parity-violating signal at $\ell<518$, and
a targeted search for primordial $U(1)$ gauge fields (and the amplitudes of a
generic collapsed model) at $\ell<2000$. In all cases, we find no evidence for
new physics, with the model-independent test finding consistency with the
FFP10/NPIPE simulation suite at $(-)0.4\sigma$, and the gauge field test
constraining the fractional amplitude of gauge fields during inflation to be
below $6\times 10^{-19}$ at $95\%$ confidence level for a fiducial model. The
addition of polarization data can significantly improve the constraints,
depending on the particular model of primordial physics, and the bounds will
tighten significantly with the inclusion of smaller-scale information. | RadioAstron Early Science Program Space-VLBI AGN survey: strategy and
first results: RadioAstron is a project to use the 10m antenna on board the dedicated
SPEKTR-R spacecraft, launched on 2011 July 18, to perform Very Long Baseline
Interferometry from space - Space-VLBI. We describe the strategy and highlight
the first results of a 92/18/6/1.35cm fringe survey of some of the brighter
radio-loud Active Galactic Nuclei (AGN) at baselines up to 25 Earth diameters
(D_E). The survey goals include a search for extreme brightness temperatures to
resolve the Doppler factor crisis and to constrain possible mechanisms of AGN
radio emission, studying the observed size distribution of the most compact
features in AGN radio jets (with implications for their intrinsic structure and
the properties of the scattering interstellar medium in our Galaxy) and
selecting promising objects for detailed follow-up observations, including
Space-VLBI imaging. Our survey target selection is based on the results of
correlated visibility measurements at the longest ground-ground baselines from
previous VLBI surveys. The current long-baseline fringe detections with
RadioAstron include OJ 287 at 10 D_E (18cm), BL Lac at 10 D_E (6cm) and
B0748+126 at 4.3 D_E (1.3 cm). The 18 and 6cm-band fringe detections at 10 D_E
imply brightness temperatures of T_b ~ 10^13 K, about two orders of magnitude
above the equipartition inverse Compton limit. These high values of T_b might
indicate that the jet flow speed is often higher than the jet pattern speed. |
Galaxy orientation with the cosmic web across cosmic time: This work investigates the alignment of galactic spins with the cosmic web
across cosmic time using the cosmological hydrodynamical simulation
Horizon-AGN. The cosmic web structure is extracted via the persistent skeleton
as implemented in the DISPERSE algorithm. It is found that the spin of low-mass
galaxies is more likely to be aligned with the filaments of the cosmic web and
to lie within the plane of the walls while more massive galaxies tend to have a
spin perpendicular to the axis of the filaments and to the walls. The mass
transition is detected with a significance of 9 sigmas. This galactic alignment
is consistent with the alignment of the spin of dark haloes found in pure dark
matter simulations and with predictions from (anisotropic) tidal torque theory.
However, unlike haloes, the alignment of low-mass galaxies is weak and
disappears at low redshifts while the orthogonal spin orientation of massive
galaxies is strong and increases with time, probably as a result of mergers. At
fixed mass, alignments are correlated with galaxy morphology: the high-redshift
alignment is dominated by spiral galaxies while elliptical centrals are mainly
responsible for the perpendicular signal. These predictions for spin alignments
with respect to cosmic filaments and unprecendently walls are successfully
compared with existing observations. The alignment of the shape of galaxies
with the different components of the cosmic web is also investigated. A
coherent and stronger signal is found in terms of shape at high mass. The two
regimes probed in this work induce competing galactic alignment signals for
weak lensing, with opposite redshift and luminosity evolution. Understanding
the details of these intrinsic alignments will be key to exploit future major
cosmic shear surveys like Euclid or LSST. | Consistency of cosmic microwave background temperature measurements in
three frequency bands in the 2500-square-degree SPT-SZ survey: We present an internal consistency test of South Pole Telescope (SPT)
measurements of the cosmic microwave background (CMB) temperature anisotropy
using three-band data from the SPT-SZ survey. These measurements are made from
observations of ~2500 deg^2 of sky in three frequency bands centered at 95,
150, and 220 GHz. We combine the information from these three bands into six
semi-independent estimates of the CMB power spectrum (three single-frequency
power spectra and three cross-frequency spectra) over the multipole range 650 <
l < 3000. We subtract an estimate of foreground power from each power spectrum
and evaluate the consistency among the resulting CMB-only spectra. We determine
that the six foreground-cleaned power spectra are consistent with the null
hypothesis, in which the six cleaned spectra contain only CMB power and noise.
A fit of the data to this model results in a chi-squared value of 236.3 for 235
degrees of freedom, and the probability to exceed this chi-squared value is
46%. |
Distinguishing interacting dark energy from wCDM with CMB, lensing, and
baryon acoustic oscillation data: We employ the Planck 2013 CMB temperature anisotropy and lensing data, and
baryon acoustic oscillation (BAO) data to constrain a phenomenological $w$CDM
model, where dark matter and dark energy interact. We assume time-dependent
equation of state parameter for dark energy, and treat dark matter and dark
energy as fluids whose energy-exchange rate is proportional to the dark-matter
density. The CMB data alone leave a strong degeneracy between the interaction
rate and the physical CDM density parameter today, $\omega_c$, allowing a large
interaction rate $|\Gamma| \sim H_0$. However, as has been known for a while,
the BAO data break this degeneracy. Moreover, we exploit the CMB lensing
potential likelihood, which probes the matter perturbations at redshift $z \sim
2$ and is very sensitive to the growth of structure, and hence one of the tools
for discerning between the $\Lambda$CDM model and its alternatives. However, we
find that in the non-phantom models ($w_{\mathrm{de}}>-1$), the constraints
remain unchanged by the inclusion of the lensing data and consistent with zero
interaction, $-0.14 < \Gamma/H_0 < 0.02$ at 95\% CL. On the contrary, in the
phantom models ($w_{\mathrm{de}}<-1$), energy transfer from dark energy to dark
matter is moderately favoured over the non-interacting model; $-0.57 <
\Gamma/H_0 < -0.10$ at 95\% CL with CMB+BAO, while addition of the lensing data
shifts this to $-0.46 < \Gamma/H_0 < -0.01$. | SDWFS-MT-1: A Self-Obscured Luminous Supernova at z~0.2: We report the discovery of a six-month-long mid-infrared transient,
SDWFS-MT-1 (aka SN 2007va), in the Spitzer Deep, Wide-Field Survey of the NOAO
Deep Wide-Field Survey Bootes field. The transient, located in a z=0.19 low
luminosity (M_[4.5]~-18.6 mag, L/L_MilkyWay~0.01) metal-poor (12+log(O/H)~7.8)
irregular galaxy, peaked at a mid-infrared absolute magnitude of M_[4.5]~-24.2
in the 4.5 micron Spitzer/IRAC band and emitted a total energy of at least
10^51 ergs. The optical emission was likely fainter than the mid-infrared,
although our constraints on the optical emission are poor because the transient
peaked when the source was "behind" the Sun. The Spitzer data are consistent
with emission by a modified black body with a temperature of ~1350 K. We rule
out a number of scenarios for the origin of the transient such as a Galactic
star, AGN activity, GRB, tidal disruption of a star by a black hole and
gravitational lensing. The most plausible scenario is a supernova exploding
inside a massive, optically thick circumstellar medium, composed of multiple
shells of previously ejected material. If the proposed scenario is correct,
then a significant fraction (~10%) of the most luminous supernova may be
self-enshrouded by dust not only before but also after the supernova occurs.
The spectral energy distribution of the progenitor of such a supernova would be
a slightly cooler version of eta Carina, peaking at 20-30 microns. |
Cross-correlation of galaxies and galaxy clusters in the Sloan Digital
Sky Survey and the importance of non-Poissonian shot noise: We present measurements of angular cross power spectra between galaxies and
optically-selected galaxy clusters in the final photometric sample of the Sloan
Digital Sky Survey (SDSS). We measure the auto- and cross-correlations between
galaxy and cluster samples, from which we extract the effective biases and
study the shot noise properties. We model the non-Poissonian shot noise by
introducing an effective number density of tracers and fit for this quantity.
We find that we can only describe the cross-correlation of galaxies and galaxy
clusters, as well as the auto-correlation of galaxy clusters, on the relevant
scales using a non-Poissonian shot noise contribution.
The values of effective bias we finally measure for a volume-limited sample
are $b_{cc}=4.09 \pm 0.47$ for the cluster auto-correlation and $b_{gc}=2.15
\pm 0.09$ for the galaxy-cluster cross-correlation. We find that these results
are consistent with expectations from the auto-correlations of galaxies and
clusters and are in good agreement with previous studies. The main result is
two-fold: firstly we provide a measurement of the cross-correlation of galaxies
and clusters, which can be used for further cosmological analysis, and secondly
we describe an effective treatment of the shot noise. | High Redshift Long Gamma-Ray Bursts Hubble Diagram as a Test of Basic
Cosmological Relations: We examine the prospects of the high redshift Long Gamma Ray Bursts (LGRB)
Hubble Diagram as a test of the basic cosmological principles. Analysis of the
Hubble Diagram allows us to test several fundamental cosmological principles
using the directly observed flux-distance-redshift relation. Modern LGRB data,
together with the correlation between the spectral peak energy and the
isotropic-equivalent radiated energy (the so-called Amati relation) can be used
for construction of the Hubble Diagram at the model-independent level. We
emphasise observational selection effects, which inevitably exist and distort
the theoretically predicted relations. An example is the weak and strong
gravitational lensing bias effect for high redshift LGRB in the presence of
limited observational sensitivity (Malmquist bias). After bias correction,
there is a tendency to vacuum dominated models with $\Omega_\Lambda \rightarrow
0.9$, $\Omega_\text{m} \rightarrow 0.1$. Forthcoming gamma-ray observations by
the space THESEUS mission together with ground and space based multimessenger
facilities will allow us to improve essentially the restrictions on alternative
basic principles of cosmological models. |
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