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Tighter Limits on Dark Matter Explanations of the Anomalous EDGES 21cm
Signal: We investigate the hypothesis that Coulomb-type interactions between dark
matter (DM) and baryons explain the anomalously low 21cm brightness-temperature
minimum at redshift z ~ 17 that was recently measured by the EDGES experiment.
In particular, we reassess the validity of the scenario where a small fraction
of the total DM is millicharged, focusing on newly derived constraints from
Planck 2015 cosmic microwave background (CMB) data. Crucially, the CMB power
spectrum is sensitive to DM-baryon scattering if the fraction of interacting DM
is larger than (or comparable to) the fractional uncertainty in the baryon
energy density. Meanwhile, there is a mass-dependent lower limit on the
fraction for which the required interaction to cool the baryons sufficiently is
so strong that it drives the interacting-DM temperature to the baryon
temperature prior to their decoupling from the CMB. If this occurs as early as
recombination, the cooling saturates. We precisely determine the viable
parameter space for millicharged DM, and find that only a fraction (m_chi/MeV)
0.0115% <~ f <~ 0.4% of the entire DM content, and only for DM-particle masses
between 0.5 MeV - 35 MeV, can be charged at the level needed to marginally
explain the anomaly, without violating limits from SLAC, CMB, Big-Bang
nucleosynthesis (BBN), or stellar and SN1987A cooling. In reality, though, we
demonstrate that at least moderate fine tuning is required to both agree with
the measured absorption profile and overcome various astrophysical sources of
heating. Finally, we point out that a ~0.4% millicharged DM component which is
tightly coupled to the baryons at recombination may resolve the current 2-sigma
tension between the BBN and CMB determinations of the baryon energy density.
Future CMB-S4 measurements will be able to probe this scenario directly. | CMB power spectra induced by primordial cross-bispectra between metric
perturbations and vector fields: We study temperature and polarization anisotropies of the cosmic microwave
background (CMB) radiation sourced from primordial cross-bispectra between
metric perturbations and vector fields, which are generated from the inflation
model where an inflaton and a vector field are coupled. In case the vector
field survives after the reheating, both the primordial scalar and tensor
fluctuations can be enhanced by the anisotropic stress composed of the vector
fields during radiation dominated era. We show that through this enhancement
the primordial cross-bispectra generate not only CMB bispectra but also CMB
power spectra. In general, we can expect such cross-bispectra produce the
non-trivial mode-coupling signals between the scalar and tensor fluctuations.
However, we explicitly show that such mode-coupling signals do not appear in
CMB power spectra. Through the numerical analysis of the CMB scalar-mode power
spectra, we find that although signals from these cross-bispectra are smaller
than primary non-electromagnetic ones, these have some characteristic features
such as negative auto-correlations of the temperature and polarization modes,
respectively. On the other hand, signals from tensor modes are almost
comparable to primary non-electromagnetic ones and hence the shape of observed
$B$-mode spectrum may deviate from the prediction in the non-electromagnetic
case. The above imprints may help us to judge the existence of the coupling
between the scalar and vector fields in the early Universe. |
COLD GASS, an IRAM Legacy Survey of Molecular Gas in Massive Galaxies:
III. Comparison with semi-analytic models of galaxy formation: We compare the semi-analytic models of galaxy formation of Fu et al. (2010),
which track the evolution of the radial profiles of atomic and molecular gas in
galaxies, with gas fraction scaling relations derived from the COLD GASS survey
(Saintonge et al 2011). The models provide a good description of how condensed
baryons in galaxies with gas are partitioned into stars, atomic and molecular
gas as a function of galaxy stellar mass and surface density. The models do not
reproduce the tight observed relation between stellar surface density and
bulge-to-disk ratio for this population. We then turn to an analysis of
the"quenched" population of galaxies without detectable cold gas. The current
implementation of radio-mode feedback in the models disagrees strongly with the
data. In the models, gas cooling shuts down in nearly all galaxies in dark
matter halos above a mass of 10**12 M_sun. As a result, stellar mass is the
observable that best predicts whether a galaxy has little or no neutral gas. In
contrast, our data show that quenching is largely independent of stellar mass.
Instead, there are clear thresholds in bulge-to-disk ratio and in stellar
surface density that demarcate the location of quenched galaxies. We propose
that processes associated with bulge formation play a key role in depleting the
neutral gas in galaxies and that further gas accretion is suppressed following
the formation of the bulge, even in dark matter halos of low mass. | Linking the Supermassive Black Hole Growth with the Megamaser Emission: High-resolution observations of the central few 100 pc of the galactic
nuclear environments remain prohibitive for large statistical samples, which
are crucial for tracing the links between central black hole formation, galaxy
formation and AGN activity over cosmic time. With this contribution, we present
novel ways of connecting the physics of black hole accretion with its immediate
environs via a new quantitative evaluation of the degree to which the strength
and spatial configuration of the water maser emission is associated with the
nuclear nebular galactic activity. We discuss possible evolutionary/causal
connections between these two types of emission, together with criteria that
could dramatically enhance our search for mega-maser systems in nearby galactic
centers. These are timely results given the interest in combining
high-resolution observations with extremely large optical telescopes and large
arrays that start to conquer the sub-millimeter window. |
A detection of the integrated Sachs-Wolfe imprint of cosmic
superstructures using a matched-filter approach: We present a new method for detection of the integrated Sachs-Wolfe (ISW)
imprints of cosmic superstructures on the cosmic microwave background, based on
a matched filtering approach. The expected signal-to-noise ratio for this
method is comparable to that obtained from the full cross-correlation, and
unlike other stacked filtering techniques it is not subject to an a posteriori
bias. We apply this method to Planck CMB data using voids and superclusters
identified in the CMASS galaxy data from the Sloan Digital Sky Survey Data
Release 12, and measure the ISW amplitude to be $A_\mathrm{ISW}=1.64\pm0.53$
relative to the $\Lambda$CDM expectation, corresponding to a $3.1\sigma$
detection. In contrast to some previous measurements of the ISW effect of
superstructures, our result is in agreement with the $\Lambda$CDM model. | Non-parametric Lagrangian biasing from the insights of neural nets: We present a Lagrangian model of galaxy clustering bias in which we train a
neural net using the local properties of the smoothed initial density field to
predict the late-time mass-weighted halo field. By fitting the mass-weighted
halo field in the AbacusSummit simulations at z=0.5, we find that including
three coarsely spaced smoothing scales gives the best recovery of the halo
power spectrum. Adding more smoothing scales may lead to 2-5% underestimation
of the large-scale power and can cause the neural net to overfit. We find that
the fitted halo-to-mass ratio can be well described by two directions in the
original high-dimension feature space. Projecting the original features into
these two principal components and re-training the neural net either reproduces
the original training result, or outperforms it with a better match of the halo
power spectrum. The elements of the principal components are unlikely to be
assigned physical meanings, partly owing to the features being highly
correlated between different smoothing scales. Our work illustrates a potential
need to include multiple smoothing scales when studying galaxy bias, and this
can be done easily with machine-learning methods that can take in high
dimensional input feature space. |
Tachyonic Quintessence and a Preferred Direction in the Sky: We show that quintessence, when it is described by a tachyonic field, can
amplify a tiny primordial gradient generating a preferred direction in the sky.
In its simplest realization, this mechanism only affects the Cosmic Microwave
Background fluctuations at the quadrupole level. We briefly discuss how higher
multipoles can also be affected, once the full structure of the quintessence
potential is taken into account. | The Sloan Digital Sky Survey-II: Photometry and Supernova Ia Light
Curves from the 2005 data: We present ugriz light curves for 146 spectroscopically confirmed or
spectroscopically probable Type Ia supernovae from the 2005 season of the
SDSS-II Supernova survey. The light curves have been constructed using a
photometric technique that we call scene modelling, which is described in
detail here; the major feature is that supernova brightnesses are extracted
from a stack of images without spatial resampling or convolution of the image
data. This procedure produces accurate photometry along with accurate estimates
of the statistical uncertainty, and can be used to derive photometry taken with
multiple telescopes. We discuss various tests of this technique that
demonstrate its capabilities. We also describe the methodology used for the
calibration of the photometry, and present calibrated magnitudes and fluxes for
all of the spectroscopic SNe Ia from the 2005 season. |
Constraints on the Dark Matter Particle Mass from the Number of Milky
Way Satellites: We have conducted N-body simulations of the growth of Milky Way-sized halos
in cold and warm dark matter cosmologies. The number of dark matter satellites
in our simulated Milky Ways decreases with decreasing mass of the dark matter
particle. Assuming that the number of dark matter satellites exceeds or equals
the number of observed satellites of the Milky Way we derive lower limits on
the dark matter particle mass. We find with 95% confidence m_s > 13.3 keV for a
sterile neutrino produced by the Dodelson and Widrow mechanism, m_s > 8.9 keV
for the Shi and Fuller mechanism, m_s > 3.0 keV for the Higgs decay mechanism,
and m_{WDM} > 2.3 keV for a thermal dark matter particle. The recent discovery
of many new dark matter dominated satellites of the Milky Way in the Sloan
Digital Sky Survey allows us to set lower limits comparable to constraints from
the complementary methods of Lyman-alpha forest modeling and X-ray observations
of the unresolved cosmic X-ray background and of dark matter halos from dwarf
galaxy to cluster scales. Future surveys like LSST, DES, PanSTARRS, and
SkyMapper have the potential to discover many more satellites and further
improve constraints on the dark matter particle mass. | The SINS survey: modeling the dynamics of z~2 galaxies and the high-z
Tully-Fisher relation: We present the modeling of SINFONI integral field dynamics of 18 star forming
galaxies at z ~ 2 from Halpha line emission. The galaxies are selected from the
larger sample of the SINS survey, based on the prominence of ordered rotational
motions with respect to more complex merger induced dynamics. The quality of
the data allows us to carefully select systems with kinematics dominated by
rotation, and to model the gas dynamics across the whole galaxy using suitable
exponential disk models. We obtain a good correlation between the dynamical
mass and the stellar mass, finding that large gas fractions Mgas~M*) are
required to explain the difference between the two quantities. We use the
derived stellar mass and maximum rotational velocity Vmax from the modeling to
construct for the first time the stellar mass Tully-Fisher relation at z ~ 2.2.
The relation obtained shows a slope similar to what is observed at lower
redshift, but we detect an evolution of the zero point. We find that at z ~ 2.2
there is an offset in log(M*) for a given rotational velocity of 0.41+-0.11
with respect to the local Universe. This result is consistent with the
predictions of the latest N-body/hydrodynamical simulations of disk formation
and evolution, which invoke gas accretion onto the forming disk in filaments
and cooling flows. This scenario is in agreement with other dynamical evidence
from SINS, where gas accretion from the halo is required to reproduce the
observed properties of a large fraction of the z ~ 2 galaxies. |
Detecting sterile neutrinos with KATRIN like experiments: A sterile neutrino with mass in the eV range, mixing with the electron
antineutrino, is allowed and possibly even preferred by cosmology and
oscillation experiments. If such eV-mass neutrinos exist they provide a much
better target for direct detection in beta decay experiments than the active
neutrinos which are expected to have sub-eV masses. Their relatively high mass
would allow for an easy separation from the primary decay signal in experiments
such as KATRIN. | Photometry and Dynamics of the Minor Merger AM1219-430 with Gemini
GMOS-S: We present an observational study of the interaction effect on the dynamics
and morphology of the minor merger AM1219-430. This work is based on r' and g'
images and long-slit spectra obtained with the Gemini Multi-Object Spectrograph
at the Gemini South Telescope. We detected a tidal tail in the main galaxy
(AM1219A) and a bridge of material connecting the galaxies. In luminosity,
AM1219A is about 3.8 times brighter than the secondary (AM1219B). The surface
brightness profile of AM1219A was decomposed into bulge and disc components.
The profile shows a light excess of ~ 53 % due to the contribution of
star-forming regions, which is typical of starburst galaxies. On the other
hand, the surface brightness profile of AM1219B shows a lens structure in
addition to the bulge and disc. The scale lengths and central magnitudes of the
disc structure of both galaxies agree with the average values derived for
galaxies with no sign of ongoing interaction or disturbed morphology. The
S\'ersic index (n<2), the effective and scale radii of the bulge of both
galaxies are typical of pseudo-bulges. The rotation curve of AM1219A derived
from the emission line of ionized gas is quite asymmetric, suggesting a gas
perturbed by interaction. We explore all possible values of stellar and dark
matter masses. The overall best-fitting solution for the mass distribution of
AM1219A was found with M/L for bulge and disc of M/L_b=2.8_-0.4^+0.4 and
M/L_d=2.4_-0.2^+0.3, respectively, and a Navarro, Frenk and White profile of
M_200=2.0_-0.4^+0.5 x10^12 M_sun and c=16.0_-1.1^+1.2. The estimated dynamical
mass is 1.6x10^11 M_sun, within a radius of ~ 10.6 kpc. |
On the multiple supernova population of Arp 299: constraints on
progenitor properties and host galaxy star formation characteristics: Throughout the last 20 years 7 supernovae (SNe) have been discovered within
Arp 299. One of these is unclassified, leaving 6 core-collapse events; 2 type
II, 2 type Ib, a type IIb and one object of indistinct type; Ib/IIb. We analyse
the relative numbers of these types, together with their positions with respect
to host galaxy properties, to investigate implications for both progenitor
characteristics and star formation (SF) properties. Our findings are: 1) the
ratio of 'stripped envelope' (SE) events to other type II is higher than that
found in the local Universe. 2) All SE SNe are more centrally concentrated
within the system than the other type II. 3) All SN environments have similar
metallicities and there are no significant metallicity gradients across the
system. 4) The SE SNe all fall on bright SF regions while the other type II are
found to occur away from bright HII regions. We draw two different -but
non-mutually exclusive- interpretations on the system and its supernovae: 1)
The distribution of SNe, and the relatively high fraction of types Ib and IIb
events over other type II can be explained by the young age of the most recent
SF in the system, where insufficient time has expired for the observed to match
the 'true' relative SN rates. This explanation provides additional independent
evidence that both types Ib and IIb SNe arise from progenitors of shorter
stellar lifetime and hence higher mass than other type II. 2) Given the
assumption that types Ib and IIb trace higher mass progenitor stars, the
relatively high frequency of types Ib and IIb to other type II, and also the
centralisation of the former over the latter with respect to host galaxy light
implies that in the centrally peaked and enhanced SF within this system, the
initial mass function is biased towards the production of high mass stars. | Tests of Dark MACHOs: Lensing, Accretion, and Glow: Dark matter could take the form of dark massive compact halo objects
(dMACHOs); i.e., composite objects that are made up of dark-sector elementary
particles, that could have a macroscopic mass from the Planck scale to above
the solar mass scale, and that also admit a wide range of energy densities and
sizes. Concentrating on the gravitational interaction of dMACHOs with visible
matter, we map out the mass-radius parameter space that is consistent with
gravitational lensing experiments, as well as anisotropies of the cosmic
microwave background (CMB) based on the spherical accretion of matter onto a
dMACHO in the hydrostatic approximation. For dMACHOs with a uniform-density
mass profile and total mass in the range of $\sim 10^{-12} - 10\,M_\odot$, we
find that a dMACHO could explain 100% of the dark matter if its radius is above
$\approx 3$ times the Einstein radius of the lensing system. For a larger mass
above $10\,M_\odot$, a dMACHO with radius above $\sim 1 \times 10^8 \mbox{cm}
\times(M/100\,M_\odot)^{9/2}$ is consistent with CMB observables. For a lighter
dMACHO with mass below $\sim 10^{-12}\,M_\odot$, there still is not a good
experimental probe. Finally, we point out that heavier dMACHOs with masses
$\sim 0.1\,M_\odot$ may be observed by X-ray and optical telescopes if they
reside at rest in a large molecular cloud, nearby to our solar system, and
accrete ordinary matter to emit photons. |
The Atacama Cosmology Telescope: Mitigating the impact of extragalactic
foregrounds for the DR6 CMB lensing analysis: We investigate the impact and mitigation of extragalactic foregrounds for the
CMB lensing power spectrum analysis of Atacama Cosmology Telescope (ACT) data
release 6 (DR6) data. Two independent microwave sky simulations are used to
test a range of mitigation strategies. We demonstrate that finding and then
subtracting point sources, finding and then subtracting models of clusters, and
using a profile bias-hardened lensing estimator, together reduce the fractional
biases to well below statistical uncertainties, with the inferred lensing
amplitude, $A_{\mathrm{lens}}$, biased by less than $0.2\sigma$. We also show
that another method where a model for the cosmic infrared background (CIB)
contribution is deprojected and high frequency data from Planck is included has
similar performance. Other frequency-cleaned options do not perform as well,
incurring either a large noise cost, or resulting in biased recovery of the
lensing spectrum. In addition to these simulation-based tests, we also present
null tests performed on the ACT DR6 data which test for sensitivity of our
lensing spectrum estimation to differences in foreground levels between the two
ACT frequencies used, while nulling the CMB lensing signal. These tests pass
whether the nulling is performed at the map or bandpower level. The
CIB-deprojected measurement performed on the DR6 data is consistent with our
baseline measurement, implying contamination from the CIB is unlikely to
significantly bias the DR6 lensing spectrum. This collection of tests gives
confidence that the ACT DR6 lensing measurements and cosmological constraints
presented in companion papers to this work are robust to extragalactic
foregrounds. | H-ATLAS: The cosmic abundance of dust from the far-infrared background
power spectrum: We present a measurement of the angular power spectrum of the cosmic
far-infrared background (CFIRB) anisotropies in one of the extragalactic fields
of the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) at 250, 350
and 500 \mu m bands. Consistent with recent measurements of the CFIRB power
spectrum in Herschel-SPIRE maps, we confirm the existence of a clear one-halo
term of galaxy clustering on arcminute angular scales with large-scale two-halo
term of clustering at 30 arcminutes to angular scales of a few degrees. The
power spectrum at the largest angular scales, especially at 250 \mu m, is
contaminated by the Galactic cirrus. The angular power spectrum is modeled
using a conditional luminosity function approach to describe the spatial
distribution of unresolved galaxies that make up the bulk of the CFIRB.
Integrating over the dusty galaxy population responsible for the background
anisotropies, we find that the cosmic abundance of dust, relative to the
critical density, to be between \Omega_dust=10^{-6} and 8 x 10^{-6} in the
redshift range z ~ 0-3. This dust abundance is consistent with estimates of the
dust content in the Universe using quasar reddening and magnification
measurements in the SDSS. |
GRB 140515A at z=6.33: Constraints on the End of Reionization From a
Gamma-ray Burst in a Low Hydrogen Column Density Environment: We present the discovery and subsequent spectroscopy with Gemini-North of the
optical afterglow of the Swift gamma-ray burst (GRB) 140515A. The spectrum
exhibits a well-detected continuum at wavelengths longer than 8915 Angs with a
steep decrement to zero flux blueward of 8910 Angs due to Ly-alpha absorption
at redshift z~6.33. Some transmission through the Lyman-alpha forest is present
at 5.2<z<5.733, but none is detected at higher redshift, consistent with
previous measurements from quasars and GRB 130606A. We model the red damping
wing of Lyman-alpha in three ways that provide equally good fits to the data:
(a) a single host galaxy absorber at z=6.327 with log(N_HI)=18.62+/-0.08; (b)
pure intergalactic medium (IGM) absorption from z=6.0 to z=6.328 with a
constant neutral hydrogen fraction of x_HI=0.056+0.011-0.027; and (c) a hybrid
model with a host absorber located within an ionized bubble of radius 10
comoving Mpc in an IGM with x_HI=0.12+/-0.05 (x_HI<0.21 at the 2-sigma level).
Regardless of the model, the sharpness of the dropoff in transmission is
inconsistent with a substantial neutral fraction in the IGM at this redshift.
No narrow absorption lines from the host galaxy are detected, indicating a host
metallicity of [Z/H]<~ -0.8. Even if we assume that all of the hydrogen
absorption is due to the host galaxy, the column is unusually low for a GRB
sightline, similar to two out of the other three highest-redshift bursts with
measured log(N_HI). This is possible evidence that the escape fraction of
ionizing photons from normal star-forming galaxies increases at z>~6. | Cosmological Dynamics of de Sitter Gravity: A new cosmological model based on the de Sitter gravity is investigated by
dynamical analysis and numerical discussions. Via some transformations, the
evolution equations of this model can form an autonomous system with 8 physical
critical points. Among these critical points there exist one positive attractor
and one negative attractor. The positive attractor describes the asymptotic
behavior of late-time universe, which indicates that the universe will enter
the exponential expansion phase, finally. Some numerical calculations are also
carried out, which convince us of this conclusion derived from the dynamical
analysis. |
Regiones HII Gigantes en Galaxias Observables desde el Hemisferio Sur: In this thesis we presented a detailed spectroscopic study in a sample of
Giant HII Regions in galaxies visible from Southern Hemisphere. | Sommerfeld Enhancement of DM Annihilation: Resonance Structure,
Freeze-Out and CMB Spectral Bound: In the last few years there has been some interest in WIMP Dark Matter models
featuring a velocity dependent cross section through the Sommerfeld enhancement
mechanism, which is a nonrelativistic effect due to massive bosons in the dark
sector. In the first part of this article, we find analytic expressions for the
boost factor for three different model potentials, the Coulomb potential, the
spherical well and the spherical cone well and compare with the numerical
solution of the Yukawa potential. We find that the resonance pattern of all the
potentials can be cast into the same universal form. In the second part of the
article we perform a detailed computation of the Dark Matter relic density for
models having Sommerfeld enhancement by solving the Boltzmann equation
numerically. We calculate the expected distortions of the CMB blackbody
spectrum from WIMP annihilations and compare these to the bounds set by FIRAS.
We conclude that only a small part of the parameter space can be ruled out by
the FIRAS observations. |
Environmental imprint on galaxy chemical enrichment: Recent results are presented on the metal enrichment of low-mass star-forming
(SF) galaxies in local Universe clusters. The environmental effects on the
chemical evolution of these galaxies are discussed. We have used spectroscopic
data from the SDSSIII-DR8 and we have derived the gas-phase O/H and N/O
abundances. We have then examined the Mass-Metallicity Relation (MZR) of this
sample of cluster galaxies, and we have found well defined sequences. A
flattening of the slope of these sequences has been observed for galaxies
located in the core of the two more massive clusters of the sample, suggesting
that the effect of the cluster environment depends both on the galaxy mass and
the host cluster mass. Based on these results we explore cluster-specific
effects (e.g. ram-pressure stripping, pressure confinement etc), predicted by
hydrodynamic models, capable of yielding the observed mass-dependent
enhancement of the metallicity. | On the signature of the baryon-dark matter relative velocity in the two
and three-point galaxy correlation functions: We develop a configuration-space picture of the relative velocity between
baryons and dark matter that clearly explains how it can shift the BAO scale in
the galaxy-galaxy correlation function. The shift occurs because the relative
velocity is non-zero only within the sound horizon and thus adds to the
correlation function asymmetrically about the BAO peak. We further show that in
configuration space the relative velocity has a localized, distinctive
signature in the three-point galaxy correlation function (3PCF). In particular,
we find that a multipole decomposition is a favorable way to isolate the
relative velocity in the 3PCF, and that there is a strong signature in the l=1
multipole for triangles with 2 sides around the BAO scale. Finally, we
investigate a further compression of the 3PCF to a function of only one
triangle side that preserves the localized nature of the relative velocity
signature while also nicely separating linear from non-linear bias. We expect
that this scheme will substantially lessen the computational burden of finding
the relative velocity in the 3PCF. The relative velocity's 3PCF signature can
be used to correct the shift induced in the galaxy-galaxy correlation function
so that no systematic error due to this effect is introduced into the BAO as
used for precision cosmology. |
The Covering Factor of Warm Dust in Quasars: View from WISE All-Sky Data
Release: By combining the newly infrared photometric data from the All-Sky Data
Release of the Wide-field Infrared Survey Explorer with the spectroscopic data
from the Seventh Data Release of the Sloan Digital Sky Survey, we study the
covering factor of warm dust ($\CF$) for a large quasar sample, as well as the
relations between $\CF$ and other physical parameters of quasars. We find a
strong correlation between the flux ratio of mid-infrared to near-ultraviolet
and the slope of near-ultraviolet spectra, which is interpreted as the dust
extinction effect. After correcting for the dust extinction utilizing the above
correlation, we examine the relations between $\CF$ and AGN properties:
bolometric luminosity ($\Lbol$), black hole mass ($\MBH$) and Eddington ratio
($L/L_{\rm Edd}$). We confirm the anti-correlation between $\CF$ and $\Lbol$.
Further we find that $\CF$ is anti-correlated with $\MBH$, but is independent
of $L/L_{\rm Edd}$. Radio-loud quasars are found to follow the same
correlations as for radio-quiet quasars. Monte Carlo simulations show that the
anisotropy of UV-optical continuum of the accretion disc can significantly
affect, but is less likely to dominate the $\CF$--$\Lbol$ correlation. | Dark Matter and Gravity Waves from a Dark Big Bang: The Hot Big Bang is often considered as the origin of all matter and
radiation in the Universe. Primordial nucleosynthesis (BBN) provides strong
evidence that the early Universe contained a hot plasma of photons and baryons
with a temperature $T>\text{MeV}$. However, the earliest probes of dark matter
originate from much later times around the epoch of structure formation. In
this work we describe a scenario in which dark matter (and possibly dark
radiation) can be formed around or even after BBN in a second Big Bang which we
dub the ``Dark Big Bang''. The latter occurs through a phase transition in the
dark sector which transforms dark vacuum energy into a hot dark plasma of
particles; in this paper we focus on a first-order phase transition for the
Dark Big Bang. The correct dark matter abundance can be set by dark matter
cannibalism or by pair-annihilation within the dark sector followed by a
thermal freeze-out. Alternatively ultra-heavy ``dark-zilla'' dark matter can
originate directly from bubble collisions during the Dark Big Bang. We will
show that the Dark Big Bang is consistent with constraints from structure
formation and the Cosmic Microwave Background (CMB) if it occurred when the
Universe was less than one month old, corresponding to a temperature in the
visible sector above $\mathcal{O}$(keV). While the dark matter evades direct
and indirect detection, the Dark Big Bang gives rise to striking gravity wave
signatures to be tested at pulsar timing array experiments. Furthermore, the
Dark Big Bang allows for realizations of self-interacting and/or warm dark
matter which suggest exciting discovery potential in future small-scale
structure observations. |
Relic Neutrino Degeneracies and Their Impact on Cosmological Parameters: In the standard $\Lambda$CDM model, neutrinos are treated as radiation, with
their masses and possible degeneracy ignored. In this paper, we compute the
impact of a finite relic neutrino degeneracy $\xi$ on the CMB angular power
spectra, and obtain constraints on $\xi$ using current cosmological data sets.
We find that $\xi \approx O(1)$ is still allowed. We also study the
correlations between $\xi$, the Hubble parameter $H_0$, and the spectral index
$n_s$. Due to these correlations, the CMB constraints on inflation models are
loosened when $\xi$ is fitted together with other cosmological parameters, such
that some models excluded at 95% confidence level by standard fittings without
$\xi$ could be revived. Furthermore, the tension in CMB and local measurements
of $H_0$ is slightly alleviated. Our results suggest that $\xi$ is a
non-negligible physical parameter for cosmological analyses. | Constraining Dust and Molecular Gas Properties in Lyman Alpha Blobs at
z~3: In order to constrain the bolometric luminosities, dust properties and
molecular gas content of giant Lyman alpha nebulae, the so-called Lyman alpha
blobs, we have carried out a study of dust continuum and CO line emission in
two well-studied representatives of this population at z ~ 3: a Lya blob
discovered by its strong Spitzer MIPS 24um detection (LABd05; Dey et al. 2005)
and the Steidel blob 1 (SSA22-LAB01; Steidel et al. 2000). We find that the
spectral energy distribution of LABd05 is well described by an AGN-starburst
composite template with L(FIR) = (4.0 +/- 0.5) x 10^12 Lsun, comparable to
high-z sub-millimeter galaxies and ultraluminous infrared galaxies. New
APEX/LABOCA 870um measurements rule out the reported SCUBA detection of the
SSA22-LAB01 (S[850um] = 16.8 mJy) at the > 4sigma level. Consistent with this,
ultra-deep Plateau de Bure Interferometer (PdBI) observations with ~2arcsec
spatial resolution also fail to detect any 1.2mm continuum source down to
~0.45mJy per beam (3sigma). Combined with the existing (sub)mm observations in
the literature, we conclude that the FIR luminosity of SSA22-LAB01 remains
uncertain. No CO line is detected in either case down to integrated flux limits
of (Snu dV) < 0.25--1.0 Jy km/s, indicating a modest molecular gas reservoir,
M(H_2) < 1--3 x 10^10 Msun. The non-detections exclude, with high significance
(12 sigma), the previous tentative detection of a CO(4-3) line in the
SSA22-LAB01. The increased sensitivity afforded by ALMA will be critical in
studying molecular gas and dust in these interesting systems. |
Testing the Accuracy of Halo Occupation Distribution Modelling using
Hydrodynamic Simulations: Halo models provide a simple and computationally inexpensive way to
investigate the connection between galaxies and their dark matter haloes.
However, these models rely on the assumption that the role of baryons can be
easily parametrized in the modelling procedure. We aim to examine the ability
of halo occupation distribution (HOD) modelling to reproduce the galaxy
clustering found in two different hydrodynamic simulations, Illustris and
EAGLE. For each simulation, we measure several galaxy clustering statistics on
two different luminosity threshold samples. We then apply a simple five
parameter HOD, which was fit to each simulation separately, to the
corresponding dark matter only simulations, and measure the same clustering
statistics. We find that the halo mass function is shifted to lower masses in
the hydrodynamic simulations, resulting in a galaxy number density that is too
high when an HOD is applied to the dark matter only simulation. However, the
exact way in which baryons alter the mass function is remarkably different in
the two simulations. After applying a correction to the halo mass function in
each simulation, the HOD is able to accurately reproduce all clustering
statistics for the high luminosity sample of galaxies. For the low luminosity
sample, we find evidence that in addition to correcting the halo mass function,
including spatial, velocity, and assembly bias parameters in the HOD is
necessary to accurately reproduce clustering statistics. | Testing Bayesian reconstruction methods from peculiar velocities: Reconstructing the large scale density and velocity fields from surveys of
galaxy distances, is a major challenge for cosmography. The data is very noisy
and sparse. Estimated distances, and thereby peculiar velocities, are strongly
affected by the Malmquist-like lognormal bias. Two algorithms have been
recently introduced to perform reconstructions from such data: the Bias
Gaussian correction coupled with the Wiener filter (BGc/WF) and the HAMLET
implementation of the Hamiltonian Monte Carlo forward modelling. The two
methods are tested here against mock catalogs that mimic the Cosmicflows-3
data. Specifically the reconstructed cosmography and moments of the velocity
field (monopole, dipole) are examined. A comparison is made to the ``exact''
wiener filter as well - namely the Wiener Filter in the unrealistic case of
zero observational errors. This is to understand the limits of the WF method.
The following is found. In the nearby regime ($d \lesssim 40 {\rm Mpc}/h$) the
two methods perform roughly equally well. HAMLET does slightly better in the
intermediate regime ($ 40 \lesssim d \lesssim 120 {\rm Mpc}/h$). The main
differences between the two appear in the most distant regime ($d \gtrsim 120
{\rm Mpc}/h$), close to the edge of the data. The HAMLET outperforms the BGc/WF
in terms of better and tighter correlations, yet in the distant regime the
HAMLET yields a somewhat biased reconstruction. Such biases are missing from
the BGc/WF reconstruction. In sum, both methods perform well and create
reliable reconstructions with significant differences apparent when details are
examined. |
A semi-model-independent approach to describe a cosmological database: A model-independent or non-parametric approach for modeling a database has
been widely used in cosmology. In these scenarios, the data has been used
directly to reconstruct an underlying function. In this work, we introduce a
novel semi-model-independent method to do the task. The new approach not only
removes some drawbacks of previous methods but also has some remarkable
advantages. We combine the well-known Gaussian linear model with a neural
network and introduce a procedure for the reconstruction of an arbitrary
function. In the scenario, the neural network produces some arbitrary base
functions which subsequently are fed to the Gaussian linear model. Given a
prior distribution on the free parameters, the Gaussian linear model provides a
close form for the posterior distribution as well as the Bayesian evidence. In
addition, contrary to other methods, it is straightforward to compute the
uncertainty. | Non-Gaussian CMB and LSS statistics beyond polyspectra: Cosmic inflation may have led to non-Gaussian initial conditions that cannot
be fully parametrised by 3- and/or 4-point functions. In this work, we discuss
various strategies to search for primordial non-Gaussianity beyond polyspectra
with the help of cosmological data. Our starting point is a generalised local
ansatz for the primordial curvature perturbation $\zeta$ of the form $\zeta =
\zeta_{\rm G} + \mathcal{F}_{\rm NG} (\zeta_{\rm G})$, where $\zeta_{\rm G}$ is
a Gaussian random field and $\mathcal{F}_{\rm NG}$ is an arbitrary function
parametrising non-Gaussianity that, in principle, could be reconstructed from
data. Noteworthily, in the case of multi-field inflation, the function
$\mathcal{F}_{\rm NG}$ can be shown to be determined by the shape of
tomographic sections of the landscape potential responsible for driving
inflation. We discuss how this generalised local ansatz leads to a probability
distribution functional that may be used to extract information about inflation
from current and future observations. In particular, we derive various classes
of probability distribution functions suitable for the statistical analysis of
the cosmic microwave background and large-scale structure. |
CMBR Weak Lensing and HI 21-cm Cross-correlation Angular Power Spectrum: Weak gravitational lensing of the CMBR manifests as a secondary anisotropy in
the temperature maps. The effect, quantified through the shear and convergence
fields imprint the underlying large scale structure (LSS), geometry and
evolution history of the Universe. It is hence perceived to be an important
observational probe of cosmology. De-lensing the CMBR temperature maps is also
crucial for detecting the gravitational wave generated B-modes. Future
observations of redshifted 21-cm radiation from the cosmological neutral
hydrogen (HI) distribution hold the potential of probing the LSS over a large
redshift range. We have investigated the correlation between post-reionization
HI signal and weak lensing convergence field. Assuming that the HI follows the
dark matter distribution, the cross-correlation angular power spectrum at a
multipole \ell is found to be proportional to the cold dark matter power
spectrum evaluated at \ell/r, where r denotes the comoving distance to the
redshift where the HI is located. The amplitude of the ross-correlation depends
on quantities specific to the HI distribution, growth of perturbations and also
the underlying cosmological model. In an ideal ituation, we found that a
statistically significant detection of the cross-correlation signal is
possible. If detected, the cross-correlation signal hold the possibility of a
joint estimation of cosmological parameters and also test various CMBR
de-lensing estimators. | Incorporating Photometric Redshift Probability Density Information into
Real-Space Clustering Measurements: The use of photometric redshifts in cosmology is increasing. Often, however
these photo-zs are treated like spectroscopic observations, in that the peak of
the photometric redshift, rather than the full probability density function
(PDF), is used. This overlooks useful information inherent in the full PDF. We
introduce a new real-space estimator for one of the most used cosmological
statistics, the 2-point correlation function, that weights by the PDF of
individual photometric objects in a manner that is optimal when Poisson
statistics dominate. As our estimator does not bin based on the PDF peak it
substantially enhances the clustering signal by usefully incorporating
information from all photometric objects that overlap the redshift bin of
interest. As a real-world application, we measure QSO clustering in the Sloan
Digital Sky Survey (SDSS). We find that our simplest binned estimator improves
the clustering signal by a factor equivalent to increasing the survey size by a
factor of 2-3. We also introduce a new implementation that fully weights
between pairs of objects in constructing the cross-correlation and find that
this pair-weighted estimator improves clustering signal in a manner equivalent
to increasing the survey size by a factor of 4-5. Our technique uses
spectroscopic data to anchor the distance scale and it will be particularly
useful where spectroscopic data (e.g, from BOSS) overlaps deeper photometry
(e.g.,from Pan-STARRS, DES or the LSST). We additionally provide simple,
informative expressions to determine when our estimator will be competitive
with the autocorrelation of spectroscopic objects. Although we use QSOs as an
example population, our estimator can and should be applied to any clustering
estimate that uses photometric objects. |
Discovery of the most isolated globular cluster in the local universe: We report the discovery of two new globular clusters in the remote halos of
M81 and M82 in the M81 Group based on Hubble Space Telescope archive images.
They are brighter than typical globular clusters (MV = -9.34 mag for GC-1 and
M_V = -10.51 mag for GC-2), and much larger than known globular clusters with
similar luminosity in the MilkyWay Galaxy and M81. Radial surface brightness
profiles for GC-1 and GC-2 do not show any features of tidal truncation in the
outer part. They are located much farther from both M81 and M82 in the sky,
compared with previously known star clusters in these galaxies. Color-magnitude
diagrams of resolved stars in each cluster show a well-defined red giant branch
(RGB), indicating that they are metal-poor and old. We derive a low metallicity
with [Fe/H] $\simeq -2.3$ and an old age ~14 Gyr for GC-2 from the analysis of
the absorption lines in its spectrum in the Sloan Digital Sky Survey in
comparison with the simple stellar population models. The I-band magnitude of
the tip of the RGB for GC-2 is 0.26 mag fainter than that for the halo stars in
the same field, showing that GC-2 is ~400 kpc behind the M81 halo along our
line of sight. The deprojected distance to GC-2 from M81 is much larger than
any other known globular clusters in the local universe. This shows that GC-2
is the most isolated globular cluster in the local universe. | Estimate of a non-helical electroweak primordial bootstrap field today: We estimate the magnitude today of the primordial magnetic field originating
at the electroweak phase transition. We find that the field, which at the
electroweak phase transition is originally of order $10^{23}-10^{24}$ G
correlated over the Hubble scale, today is of order $10^{-14}$ G at a scale of
order 2 kpc. This result is consistent with the lower limit on the strength of
intergalactic magnetic fields obtained by Neronov and Vovk from observations of
TeV blazars. The field is non-helical. We compare our results with the helical
case discussed by Field and Carroll. |
The enrichment history of cosmic metals: We use a suite of cosmological, hydrodynamical simulations to investigate the
chemical enrichment history of the Universe. Specifically, we trace the origin
of the metals back in time to investigate when various gas phases were enriched
and by what halo masses. We find that the age of the metals decreases strongly
with the density of the gas in which they end up. At least half of the metals
that reside in the diffuse intergalactic medium (IGM) at redshift zero (two)
were ejected from galaxies above redshift two (three). The mass of the haloes
that last contained the metals increases rapidly with the gas density. More
than half of the mass in intergalactic metals was ejected by haloes with total
masses less than 1e11 solar masses and stellar masses less than 1e9 solar
masses. The range of halo masses that contributes to the enrichment is wider
for the hotter part of the IGM. By combining the `when' and `by what' aspects
of the enrichment history, we show that metals residing in lower density gas
were typically ejected earlier and by lower mass haloes. | The VIMOS Public Extragalactic Redshift Survey (VIPERS): $Ω_{\rm
m_0}$ from the galaxy clustering ratio measured at $z \sim 1$: We use a sample of about 22,000 galaxies at $0.65<z<1.2$ from the VIPERS
PDR-1 catalogue, to constrain the cosmological model through a measurement of
the galaxy {\it clustering ratio} $\eta_{g,R}$. This statistic has favourable
properties, being defined as the ratio of two quantities characterizing the
smoothed density field in spheres of given radius $R$: the value of its
correlation function on a multiple of this scale, $\xi(nR)$, and its variance
$\sigma^2(R)$. For sufficiently large values of $R$, this is a universal
number, capturing 2-point clustering information independently of the linear
bias and linear redshift-space distortions of the specific galaxy tracers. In
this paper we discuss in detail how to extend the application of $\eta_{g,R}$
to quasi-linear scales and how to control and remove observational selection
effects which are typical of redshift surveys as VIPERS. We verify the accuracy
and efficiency of these procedures using mock catalogues that match the survey
selection process. These results evidence the robustness of $\eta_{g,R}$ to
non-linearities and observational effects, which is related to its very
definition as a ratio of quantities that are similarly affected.
We measure $\Omega_{m,0}=0.270_{-0.025}^{+0.029}$. In addition to the great
precision achieved on our estimation of $\Omega_m$ using VIPERS PDR-1, this
result is remarkable because it appears to be in good agreement with a recent
estimate $z\simeq 0.3$, obtained applying the same technique to the SDSS-LRG
catalogue. It, therefore, suports the robustness of the present analysis.
Moreover, the combination of these two measurements at $z\sim 0.3$ and $z\sim
0.9$ provides us with a very precise estimate $\Omega_{m,0}=0.274\pm0.017$
which highlights the great consistency between our estimation and other
cosmological probes such as BAOs, CMB and Supernovae. |
Cool and warm dust emission from M33 (HerM33es): We study the far-infrared emission from the nearby spiral galaxy M33 in order
to investigate the dust physical properties such as the temperature and the
luminosity density across the galaxy. Taking advantage of the unique wavelength
coverage (100, 160, 250, 350 and 500 micron) of the Herschel Space Observatory
and complementing our dataset with Spitzer-IRAC 5.8 and 8 micron and
Spitzer-MIPS 24 and 70 micron data, we construct temperature and luminosity
density maps by fitting two modified blackbodies of a fixed emissivity index of
1.5. We find that the 'cool' dust grains are heated at temperatures between 11
and 28 K with the lowest temperatures found in the outskirts of the galaxy and
the highest ones in the center and in the bright HII regions. The
infrared/submillimeter total luminosity (5 - 1000 micron) is estimated to be
1.9x10^9 Lsun. 59% of the total luminosity of the galaxy is produced by the
'cool' dust grains (~15 K) while the rest 41% is produced by 'warm' dust grains
(~55 K). The ratio of the cool-to-warm dust luminosity is close to unity
(within the computed uncertainties), throughout the galaxy, with the luminosity
of the cool dust being slightly enhanced in the center of the galaxy.
Decomposing the emission of the dust into two components (one emitted by the
diffuse disk of the galaxy and one emitted by the spiral arms) we find that the
fraction of the emission in the disk in the mid-infrared (24 micron) is 21%,
while it gradually rises up to 57% in the submillimeter (500 micron). We find
that the bulk of the luminosity comes from the spiral arm network that produces
70% of the total luminosity of the galaxy with the rest coming from the diffuse
dust disk. The 'cool' dust inside the disk is heated at a narrow range of
temperatures between 18 and 15 K (going from the center to the outer parts of
the galaxy). | Newtonian N-body simulations are compatible with cosmological
perturbation theory: Contrary to recent claims in the literature, Newtonian N-body simulations of
collisionless Dark Matter in a LambdaCDM background are compatible with general
relativity and are not invalidated by general relativistic effects at the
linear level. This verdict is based on four facts. (1) The system of linearized
Einstein equations and conservation laws is well-posed in the gauge invariant
formulation and physically meaningful. (2) Comparing general relativity with
its Newtonian approximation at a given order in perturbation theory is only
meaningful at the level of observables. (3) The dynamics of observables
describing a dust fluid in general relativity and its Newtonian approximation
agree at the linear level. Any disagreement for observables on the lightcone
are well-known, of which the most dominant is gravitational lensing. (4) Large
fluctuations in the Hubble parameter contribute significantly only to
gravitational lensing effects. Therefore, these fluctuations are not in
conflict with Newtonian N-body simulations beyond what has already been
carefully taken into account using ray tracing technology. |
Bias-Limited Extraction of Cosmological Parameters: It is known that modeling uncertainties and astrophysical foregrounds can
potentially introduce appreciable bias in the deduced values of cosmological
parameters. While it is commonly assumed that these uncertainties will be
accounted for to a sufficient level of precision, the level of bias has not
been properly quantified in most cases of interest. We show that the
requirement that the bias in derived values of cosmological parameters does not
surpass nominal statistical error, translates into a maximal level of overall
error $O(N^{-1/2})$ on $|\Delta P(k)|/P(k)$ and $|\Delta C_{l}|/C_{l}$, where
$P(k)$, $C_{l}$, and $N$ are the matter power spectrum, angular power spectrum,
and number of (independent Fourier) modes at a given scale $l$ or $k$ probed by
the cosmological survey, respectively. This required level has important
consequences on the precision with which cosmological parameters are hoped to
be determined by future surveys: In virtually all ongoing and near future
surveys $N$ typically falls in the range $10^{6}-10^{9}$, implying that the
required overall theoretical modeling and numerical precision is already very
high. Future redshifted-21-cm observations, projected to sample $\sim 10^{14}$
modes, will require knowledge of the matter power spectrum to a fantastic
$10^{-7}$ precision level. We conclude that realizing the expected potential of
future cosmological surveys, which aim at detecting $10^{6}-10^{14}$ modes,
sets the formidable challenge of reducing the overall level of uncertainty to
$10^{-3}-10^{-7}$. | KiDS-i-800: Comparing weak gravitational lensing measurements in
same-sky surveys: We present a weak gravitational lensing analysis of 815 square degree of
$i$-band imaging from the Kilo-Degree Survey (KiDS-$i$-800). In contrast to the
deep $r$-band observations, which take priority during excellent seeing
conditions and form the primary KiDS dataset (KiDS-$r$-450), the complementary
yet shallower KiDS-$i$-800 spans a wide range of observing conditions. The
overlapping KiDS-$i$-800 and KiDS-$r$-450 imaging therefore provides a unique
opportunity to assess the robustness of weak lensing measurements. In our
analysis, we introduce two new `null' tests. The `nulled' two-point shear
correlation function uses a matched catalogue to show that the calibrated
KiDS-$i$-800 and KiDS-$r$-450 shear measurements agree at the level of $1 \pm
4$\%. We use five galaxy lens samples to determine a `nulled' galaxy-galaxy
lensing signal from the full KiDS-$i$-800 and KiDS-$r$-450 surveys and find
that the measurements agree to $7 \pm 5$\% when the KiDS-$i$-800 source
redshift distribution is calibrated using either spectroscopic redshifts, or
the 30-band photometric redshifts from the COSMOS survey. |
Kinematics of galaxies in Compact Groups. Studying the B-band
Tully-Fisher relation: We obtained new Fabry-Perot data cubes and derived velocity fields,
monochromatic and velocity dispersion maps for 28 galaxies in the Hickson
compact groups 37, 40, 47, 49, 54, 56, 68, 79 and 93. We find that one third of
the non-barred compact group galaxies have position angle misalignments between
the stellar and gaseous components. This and the asymmetric rotation curves are
clear signatures of kinematic perturbations, probably due to interactions among
compact group galaxies. A comparison between the B-band Tully-Fisher relation
for compact group galaxies and that for the GHASP field-galaxy sample shows
that, despite the high fraction of compact group galaxies with asymmetric
rotation curves, these lie on the Tully-Fisher relation defined by galaxies in
less dense environments, although with more scatter. This is in agreement with
previous results, but now confirmed for a larger sample of 41 galaxies. We
confirm the tendency for compact group galaxies at the low-mass end of the
Tully-Fisher relation (HCG 49b, 89d, 96c, 96d and 100c) to have either a
magnitude that is too bright for its mass (suggesting brightening by star
formation) and/or a low maximum rotational velocity for its luminosity
(suggesting tidal stripping). These galaxies are outside the Tully Fisher
relation, at the 1 sigma level, even when the minimum acceptable values of
inclinations are used to compute their maximum velocities. The inclusion of
such galaxies with v<100 km/s in the determination of the zero point and slope
of the compact group B-band Tully-Fisher relation would strongly change the
fit, making it different from the relation for field galaxies, a fact that has
to be kept in mind when studying scaling relations of interacting galaxies,
specially at high redshifts. | Observed galaxy number counts on the lightcone up to second order: III.
Magnification Bias: We study up to second order the galaxy number over-density that depends on
magnification in redshift space on cosmological scales for a concordance model.
The result contains all general relativistic effects up to second order which
arise from observing on the past light cone, including all redshift and lensing
distortions, contributions from velocities, Sachs-Wolfe, integrated SW and
time-delay terms. We find several new terms and contributions that could be
potentially important for an accurate calculation of the bias on estimates of
non-Gaussianity and on precision parameter estimates. |
Limits on Non-Relativistic Matter During Big-Bang Nucleosynthesis: Big-bang nucleosynthesis (BBN) probes the cosmic mass-energy density at
temperatures $\sim 10$ MeV to $\sim 100$ keV. Here, we consider the effect of a
cosmic matter-like species that is non-relativistic and pressureless during
BBN. Such a component must decay; doing so during BBN can alter the
baryon-to-photon ratio, $\eta$, and the effective number of neutrino species.
We use light element abundances and the cosmic microwave background (CMB)
constraints on $\eta$ and $N_\nu$ to place constraints on such a matter
component. We find that electromagnetic decays heat the photons relative to
neutrinos, and thus dilute the effective number of relativistic species to
$N_{\rm eff} < 3$ for the case of three Standard Model neutrino species.
Intriguingly, likelihood results based on {\em Planck} CMB data alone find
$N_{\nu} = 2.800 \pm 0.294$, and when combined with standard BBN and the
observations of D and \he4 give $N_{\nu} = 2.898 \pm 0.141$. While both results
are consistent with the Standard Model, we find that a nonzero abundance of
electromagnetically decaying matter gives a better fit to these results. Our
best-fit results are for a matter species that decays entirely
electromagnetically with a lifetime $\tau_X = 0.89 \ \rm sec$ and pre-decay
density that is a fraction $\xi = (\rho_X/\rho_{\rm rad})|_{10 \ \rm MeV} =
0.0026$ of the radiation energy density at 10 MeV; similarly good fits are
found over a range where $\xi \tau_X^{1/2}$ is constant. On the other hand,
decaying matter often spoils the BBN+CMB concordance, and we present limits in
the $(\tau_X,\xi)$ plane for both electromagnetic and invisible decays. For
dark (invisible) decays, standard BBN (i.e. $\xi=0$) supplies the best fit. We
end with a brief discussion of the impact of future measurements including
CMB-S4. | The History of Star Formation in Galaxies: If we are to develop a comprehensive and predictive theory of galaxy
formation and evolution, it is essential that we obtain an accurate assessment
of how and when galaxies assemble their stellar populations, and how this
assembly varies with environment. There is strong observational support for the
hierarchical assembly of galaxies, but our insight into this assembly comes
from sifting through the resolved field populations of the surviving galaxies
we see today, in order to reconstruct their star formation histories, chemical
evolution, and kinematics. To obtain the detailed distribution of stellar ages
and metallicities over the entire life of a galaxy, one needs multi-band
photometry reaching solar-luminosity main sequence stars. The Hubble Space
Telescope can obtain such data in the low-density regions of Local Group
galaxies. To perform these essential studies for a fair sample of the Local
Universe, we will require observational capabilities that allow us to extend
the study of resolved stellar populations to much larger galaxy samples that
span the full range of galaxy morphologies, while also enabling the study of
the more crowded regions of relatively nearby galaxies. With such capabilities
in hand, we will reveal the detailed history of star formation and chemical
evolution in the universe. |
Dark energy and dark matter perturbations in singular universes: We discuss the evolution of density perturbations of dark matter and dark
energy in cosmological models which admit future singularities in a finite
time. Up to now geometrical tests of the evolution of the universe do not
differentiate between singular universes and $\Lambda$CDM scenario. We solve
perturbation equations using the gauge invariant formalism. The analysis shows
that the detailed reconstruction of the evolution of perturbations within
singular cosmologies, in the dark sector, exhibit important differences between
the singular universes models and the $\Lambda$CDM cosmology. This is
encouraging for further examination and gives hope for discriminating between
those models with future galaxy weak lensing experiments like the Dark Energy
Survey (DES) and Euclid or CMB observations like PRISM and CoRE. | Ferromagnetic properties of charged vector bosons condensate in the
early universe: Bose-Einstein condensation in the early universe is considered. The magnetic
properties of a condensate of charged vector bosons are studied, showing that a
ferromagnetic state is formed. As a consequence, the primeval plasma may be
spontaneously magnetized inside macroscopically large domains and primordial
magnetic fields can be generated. |
Reanalyzing the upper limit on the tensor-to-scalar perturbation ratio
r_T in a quartic potential inflationary model: We study the polynomial chaotic inflation model with a single scalar field in
a double well quartic potential which has recently been shown to be consistent
with Planck data. In particular, we study the effects of lifting the degeneracy
between the two vacua on the inflationary observables, i.e. spectral index n_s
and tensor-to-scalar perturbation ratio r_T. We find that removing the
degeneracy allows the model to satisfy the upper limit constraints on r_T from
Planck data, provided the field starts near the local maximum. We also
calculate the scalar power spectrum and non-Gaussianity parameter f_NL for the
primordial scalar perturbations in this model. | Designing Future Dark Energy Space Missions: II. Photometric Redshift of
Space Weak Lensing Optimized Survey: Accurate weak-lensing analysis requires not only accurate measurement of
galaxy shapes but also precise and unbiased measurement of galaxy redshifts.
The photometric redshift technique appears as the only possibility to determine
the redshift of the background galaxies used in the weak-lensing analysis.
Using the photometric redshift quality, simple shape measurement requirements,
and a proper sky model, we explore what could be an optimal weak-lensing dark
energy mission based on FoM calculation. We found that photometric redshifts
reach their best accuracy for the bulk of the faint galaxy population when
filters have a resolution R~3.2. We show that an optimal mission would survey
the sky through 8 filters using 2 cameras (visible and near infrared). Assuming
a 5-year mission duration, a mirror size of 1.5m, a 0.5deg2 FOV with a visible
pixel scale of 0.15", we found that a homogeneous survey reaching IAB=25.6
(10sigma) with a sky coverage of ~11000deg2 maximizes the Weak Lensing FoM. The
effective number density of galaxies then used for WL is ~45gal/arcmin2, at
least a factor of two better than ground based survey. This work demonstrates
that a full account of the observational strategy is required to properly
optimize the instrument parameters to maximize the FoM of the future
weak-lensing space dark energy mission. |
Constraining the spatial curvature with cosmic expansion history in a
cosmological model with a non-standard sound horizon: Spatial curvature is one of the most fundamental parameters in our current
concordance flat $\Lambda$CDM model of the Universe. The goal of this work is
to investigate how the constraint on the spatial curvature is affected by an
assumption on the sound horizon scale. The sound horizon is an essential
quantity to use the standard ruler from the Cosmic Microwave Background (CMB)
and Baryon Acoustic Oscillations (BAOs). As an example, we study the curvature
constraint in an axion-like Early Dark Energy (EDE) model in light of recent
cosmological datasets from Planck, the South Pole Telescope (SPT), and the
Atacama Cosmology Telescope (ACT), as well as BAO data compiled in Sloan
Digital Sky Survey Data Release 16. We find that, independent of the CMB
datasets, the EDE model parameters are constrained only by the CMB power
spectra as precisely and consistently as the flat case in previous work, even
with the spatial curvature. We also demonstrate that combining CMB with BAO is
extremely powerful to constrain the curvature parameter even with a reduction
of the sound-horizon scale in an EDE model, resulting in $\Omega_K=-0.0056\pm
0.0031$ in the case of ACT+BAO after marginalizing over the parameters of the
EDE model. This constraint is as competitive as the Planck+BAO result in a
$\Lambda$CDM model, $\Omega_{K}=-0.0001\pm 0.0018$. | Over-constrained Models of Time Delay Lenses Redux: How the Angular Tail
Wags the Radial Dog: The two properties of the radial mass distribution of a gravitational lens
that are well-constrained by Einstein rings are the Einstein radius R_E and xi2
= R_E alpha''(R_E)/(1-kappa_E), where alpha''(R_E) and kappa_E are the second
derivative of the deflection profile and the convergence at R_E. However, if
there is a tight mathematical relationship between the radial mass profile and
the angular structure, as is true of ellipsoids, an Einstein ring can appear to
strongly distinguish radial mass distributions with the same xi2. This problem
is beautifully illustrated by the ellipsoidal models in Millon et al. (2019).
When using Einstein rings to constrain the radial mass distribution, the
angular structure of the models must contain all the degrees of freedom
expected in nature (e.g., external shear, different ellipticities for the stars
and the dark matter, modest deviations from elliptical structure, modest twists
of the axes, modest ellipticity gradients, etc.) that work to decouple the
radial and angular structure of the gravity. Models of Einstein rings with too
few angular degrees of freedom will lead to strongly biased likelihood
distinctions between radial mass distributions and very precise but inaccurate
estimates of H0 based on gravitational lens time delays. |
Investigating the Hubble Tension: Effect of Cepheid Calibration: Recent observations of Type Ia supernovae (SNe) by SH0ES collaboration (R11
and R16) diverge from the value reported by recent CMBR observations utilising
the Planck satellite and application of the $\Lambda CDM$ cosmological model by
at least $3 \sigma$. It is among the most challenging problems in contemporary
cosmology and is known as the Hubble tension. The SNe Ia in R11 and R16 were
calibrated through cepheid variables in three distinct galaxies: Milky Way,
LMC, and NGC4258. Carnegie Hubble Program (CHP) observations of type Ia SNe
calibrated using the tip of the red giant approach yielded a somewhat different
estimate for the Hubble constant. This decreased the Hubble tension from over
3$\sigma$ to below 2$\sigma$. It is a legitimate question to answer whether
there are any issues with SNe Ia calibration and to investigate whether the
Hubble tension is real or not. We use statistical techniques namely, ANOVA, K-S
test, and t-test to examine whether the cepheid calibration is host-dependent.
Our analysis shows that (i) both R11 and R16 data suffer from non-Gaussian
systematic effects, (ii) $H_0$ values in the sub-samples (different
anchor-based) in both R11 and R16 groups are significantly different at a 99\%
confidence level, and (iii) neglecting the metal-rich MW sample does not reduce
the $H_0$ value significantly, and thus Hubble tension persists. A small
reduction in the Hubble constant could be linked to the differences in the host
environment. Hence instead of using a single universal relation environment
based slope and zero point should be preferred. | Constraining interacting dark energy models with latest cosmological
observations: The local measurement of $H_0$ is in tension with the prediction of
$\Lambda$CDM model based on the Planck data. This tension may imply that dark
energy is strengthened in the late-time Universe. We employ the latest
cosmological observations on CMB, BAO, LSS, SNe, $H(z)$ and $H_0$ to constrain
several interacting dark energy models. Our results show no significant
indications for the interaction between dark energy and dark matter. The $H_0$
tension can be moderately alleviated, but not totally released. |
PSZSPT: a joint Planck and SPT-SZ cluster catalog: We present the first cluster catalog extracted from combined space-based
(Planck) and ground-based (South Pole Telescope; SPT-SZ) millimeter data. We
developed and applied a matched multi-filter (MMF) capable of dealing with the
different transfer functions and resolutions of the two datasets. We verified
that it produces results consistent with publications from Planck and SPT
collaborations when applied on the datasets individually. We also verified that
Planck and SPT-SZ cluster fluxes are consistent with each other. When applied
blindly to the combined dataset, the MMF generated a catalog of 419 detections
($S/N>5$), of which 323 are already part of the SPT-SZ or PSZ2 catalogs; 54 are
new SZ detections, which have been identified in other catalogs or surveys; and
42 are new unidentified candidates. The MMF takes advantage of the
complementarity of the two datasets, Planck being particularly useful for
detecting clusters at a low redshift ($z<0.3$), while SPT is efficient at
finding higher redshift ($z>0.3$) sources. This work represents a proof of
concept that blind cluster extraction can be performed on combined,
inhomogeneous millimeter datasets acquired from space and ground. This result
is of prime importance for planned ground-based cosmic microwave background
(CMB) experiments (e.g., Simons Observatory, CMB-S4) and envisaged CMB space
missions (e.g., PICO, Backlight) that will detect hundreds of thousands of
clusters in the low mass regime ($M_{500} \leqslant 10^{14} M_\odot$), for
which the various sources of intra-cluster emission (gas, dust, synchrotron)
will be of the same order of magnitude and hence require broad ground and space
frequency coverage with a comparable spatial resolution for adequate
separation. | Translating nano-Hertz gravitational wave background into primordial
perturbations taking account of the cosmological QCD phase transition: The evidence of the nano-Hertz stochastic gravitational wave (GW) background
is reported by multiple pulsar timing array collaborations. While a prominent
candidate of the origin is astrophysical from supermassive black hole binaries,
alternative models involving GWs induced by primordial curvature perturbations
can explain the inferred GW spectrum. Serendipitously, the nano-Hertz range
coincides with the Hubble scale during the cosmological quantum chromodynamics
(QCD) phase transition. The influence of the QCD phase transition can modify
the spectrum of induced GWs within the nano-Hertz frequency range,
necessitating careful analysis. We estimate GWs induced by power-law power
spectra of primordial curvature perturbations taking account of the QCD phase
transition. Then we translate the implication of the NANOGrav data into the
constraint on the power spectrum of the primordial curvature perturbation,
which suggests one would underestimate the amplitude by about $25\%$ and the
spectral index by up to $10\%$ if neglecting the QCD effect. |
Constraining galaxy-halo connection with high-order statistics: We investigate using three-point statistics in constraining the galaxy-halo
connection. We show that for some galaxy samples, the constraints on the halo
occupation distribution parameters are dominated by the three-point function
signal (over its two-point counterpart). We demonstrate this on mock catalogs
corresponding to the Luminous Red Galaxies (LRGs), Emission-Line Galaxies
(ELG), and quasars (QSOs) targeted by the Dark Energy Spectroscopic Instrument
(DESI) Survey. The projected three-point function for triangle sides less up to
20$h^{-1}$ Mpc measured from a cubic Gpc of data can constrain the
characteristic minimum mass of the LRGs with a precision of $0.46$ %. For
comparison, similar constraints from the projected two-point function are
$1.55$ %. The improvements for the ELGs and QSOs targets are more modest. In
the case of the QSOs it is caused by the high shot-noise of the sample, and in
the case of the ELGs, this is caused by the range of halo masses of the host
halos. The most time-consuming part of our pipeline is the measurement of the
three-point functions. We adopt a tabulation method, proposed in earlier works
for the two-point function, to reduce significantly the required compute time
for the three-point analysis. | Parsec-scale Properties of Brightest Cluster Galaxies: We present new VLBI observations at 5 GHz of a complete sample of Brightest
Cluster Galaxies (BCGs) in nearby Abell Clusters (distance class <3). Combined
with data from the literature, this provides parsec-scale information for 34
BCGs. Our analysis of their parsec scale radio emission and cluster X-ray
properties shows a possible dichotomy between BCGs in cool core clusters and
those in non cool core clusters. Among resolved sources, those in cool core
clusters tend to have two-sided parsec-scale jets, while those in less relaxed
clusters have predominantly one-sided parsec-scale jets. We suggest that this
difference could be the result of interplay between the jets and the
surrounding medium. The one-sided structure in non cool core clusters could be
due to Doppler boosting effects in relativistic, intrinsically symmetric jets;
two-sided morphology in cool core clusters is likely related to the presence of
heavy and mildly relativistic jets slowed down on the parsec-scale. Evidence of
recurrent activity are also found in BCGs in cool core clusters. |
Localized correlated features in the CMB power spectrum and primordial
bispectrum from a transient reduction in the speed of sound: The first year of observations by the Planck satellite mission shows that the
cosmic microwave background (CMB) fluctuations are consistent with gaussian
statistics in the primordial perturbations, a key prediction of the simplest
models of inflation. However, there are hints of anomalies in the CMB power
spectrum and bispectrum. We check for the possibility that some of these
anomalous features have a common physical origin in a transient reduction of
the inflaton speed of sound. We do this by exploiting predicted correlations
between the power spectrum and bispectrum. Our results suggest that current
data might already be sensitive enough to detect transient reductions in the
speed of sound as mild as a few percent. Since this is a signature of
interactions, it opens a new window for the detection of extra degrees of
freedom during inflation. | Tension between HST/JWST and $Λ$CDM Cosmology, PBH, and Antimatter
in the Galaxy: Recent data released by James Webb Space Telescope (JWST) and, somewhat
earlier, the data presented by Hubble Space Telescope (HST) are commonly
understood as a strong indication for breaking of the canonical $\Lambda$CDM
cosmology. It is argued in the presented work that massive primordial black
holes (PBH) could seed galaxy and quasar formation in the very young universe
as it has been conjectured in our paper of 1993 and resolve the tension induced
by the JWST and the HST data with the standard cosmology. This point of view is
presently supported by several recent works. The proposed mechanism of PBH
formation leads to the log-normal mass spectrum of PBHs and predicts abundant
antimatter population of our Galaxy, Milky Way. Both these predictions are in
excellent agreement with astronomical observations. |
Termination shock thermal processes as a possible source for the CMB
low-order multipole anomalies: updated with observations: We discuss the possibility that the observed low-order multipole features of
the cosmic microwave background radiation (CMB) all originate in the
termination shock (TS) region of the heliosheath that surrounds the solar
system. If the intrinsic CMB spectrum is assumed to be a pure monopole (2.73K)
then thermodynamic processes occurring within the plasma region of the TS could
imprint the observed power spectrum of the low-order multipoles and their
alignment (the so-called "axis of evil") onto this background isotropic CMB.
Conditions are outlined for the geometric shape of the TS region. A key
requirement of this model is that the TS plasma be characterized as an
optically thin graybody with non-LTE perturbations. Data from the ongoing
Voyager missions is critical to this study. We present four significant recent
observations in support of this ansatz. | Measuring the transition to homogeneity with photometric redshift
surveys: We study the possibility of detecting the transition to homogeneity using
photometric redshift catalogs. Our method is based on measuring the fractality
of the projected galaxy distribution, using angular distances, and relies only
on observable quantites. It thus provides a way to test the Cosmological
Principle in a model-independent unbiased way. We have tested our method on
different synthetic inhomogeneous catalogs, and shown that it is capable of
discriminating some fractal models with relatively large fractal dimensions, in
spite of the loss of information due to the radial projection. We have also
studied the influence of the redshift bin width, photometric redshift errors,
bias, non-linear clustering, and surveyed area, on the angular homogeneity
index H2 ({\theta}) in a {\Lambda}CDM cosmology. The level to which an upcoming
galaxy survey will be able to constrain the transition to homogeneity will
depend mainly on the total surveyed area and the compactness of the surveyed
region. In particular, a Dark Energy Survey (DES)-like survey should be able to
easily discriminate certain fractal models with fractal dimensions as large as
D2 = 2.95. We believe that this method will have relevant applications for
upcoming large photometric redshift surveys, such as DES or the Large Synoptic
Survey Telescope (LSST). |
First Spectroscopic Evidence for High Ionization State and Low Oxygen
Abundance in Lya Emitters: We present results from Keck/NIRSPEC and Magellan/MMIRS follow-up
spectroscopy of Lya emitters (LAEs) at z=2.2 identified in our Subaru
narrowband survey. We successfully detect Ha emission from seven LAEs, and
perform a detailed analysis of six LAEs free from AGN activity, two out of
which, CDFS-3865 and COSMOS-30679, have [OII] and [OIII] line detections. They
are the first [OII]-detected LAEs at high-z, and their [OIII]/[OII] ratios and
R23-indices provide the first simultaneous determinations of ionization
parameter and oxygen abundance for LAEs. CDFS-3865 has a very high ionization
parameter (q_{ion}=2.5^{+1.7}_{-0.8}x10^8 cm s^{-1}) and a low oxygen abundance
(12+log(O/H)=7.84^{+0.24}_{-0.25}) in contrast with moderate values of other
high-z galaxies such as Lyman-break galaxies (LBGs). COSMOS-30679 also
possesses a relatively high ionization parameter (q_{ion}=8^{+10}_{-4}x10^7 cm
s^{-1}) and a low oxygen abundance (12+log(O/H)=8.18^{+0.28}_{-0.28}). Both
LAEs appear to fall below the mass-metallicity relation of z~2 LBGs. Similarly,
a low metallicity of 12+log(O/H)<8.4 is independently indicated for typical
LAEs from a composite spectrum and the [NII]/Ha index. Such high ionization
parameters and low oxygen abundances can be found in local star-forming
galaxies, but this extreme local population occupies only ~0.06% of the SDSS
spectroscopic galaxy sample with a number density ~100 times smaller than that
of LAEs. With their high ionization parameters and low oxygen abundances, LAEs
would represent an early stage of galaxy formation dominated by massive stars
in compact star-forming regions. High-q_{ion} galaxies like LAEs would produce
ionizing photons efficiently with a high escape fraction achieved by
density-bounded HII regions, which would significantly contribute to cosmic
reionization at z>6. | Gravitational Fluctuations as an Alternative to Inflation III. Numerical
Results: Power spectra play an important role in the theory of inflation, and their
ability to reproduce current observational data to high accuracy is often
considered a triumph of inflation, largely because of a lack of credible
alternatives. In previous work we introduced an alternative picture for the
cosmological power spectra based on the nonperturbative features of the quantum
version of Einstein's gravity, instead of currently popular inflation models
based on scalar fields. The key ingredients in this new picture are the
appearance of a nontrivial gravitational vacuum condensate (directly related to
the observed cosmological constant), and a calculable renormalization group
running of Newton's G on cosmological scales. Results obtained previously were
largely based on a semi-analytical treatment, and often suffered from the
limitations of various approximations and simplifying assumptions. In this
work, we extend and refine our previous calculations by laying out an updated
and extended analysis, which now utilizes a set of suitably modified
state-of-the-art numerical programs (ISiTGR, MGCAMB and MGCLASS) developed for
observational cosmology. As a result, we are able to remove some of the
approximations employed in our previous studies, leading to a number of novel
and detailed physical predictions. These should help in potentially distinguish
the vacuum condensate picture of quantum gravity from that of other models such
as scalar field inflation. Here, besides the matter power spectrum P(k), we
work out in detail predictions for what are referred to as the TT, TE, EE, BB
angular spectra, as well as their closely related lensing spectra. However, the
current limited precision of observational data today (especially on large
angular scales) does not allow us yet to clearly prove or disprove either set
of ideas. |
Observational constraints on quantum decoherence during inflation: Since inflationary perturbations must generically couple to all degrees of
freedom present in the early Universe, it is more realistic to view these
fluctuations as an open quantum system interacting with an environment. Then,
on very general grounds, their evolution can be modelled with a Lindblad
equation. This modified evolution leads to quantum decoherence of the system,
as well as to corrections to observables such as the power spectrum of
curvature fluctuations. On one hand, current cosmological observations
constrain the properties of possible environments and place upper bounds on the
interaction strengths. On the other hand, imposing that decoherence completes
by the end of inflation implies lower bounds on the interaction strengths.
Therefore, the question arises of whether successful decoherence can occur
without altering the power spectrum. In this paper, we systematically identify
all scenarios in which this is possible. As an illustration, we discuss the
case in which the environment consists of a heavy test scalar field. We show
that this realises the very peculiar configuration where the correction to the
power spectrum is quasi scale invariant. In that case, the presence of the
environment improves the fit to the data for some inflationary models but
deteriorates it for others. This clearly demonstrates that decoherence is not
only of theoretical importance but can also be crucial for astrophysical
observations. | nIFTy Galaxy Cluster simulations VI: The dynamical imprint of
substructure on gaseous cluster outskirts: Galaxy cluster outskirts mark the transition region from the mildly
non-linear cosmic web to the highly non-linear, virialised, cluster interior.
It is in this transition region that the intra-cluster medium (ICM) begins to
influence the properties of accreting galaxies and groups, as ram pressure
impacts a galaxy's cold gas content and subsequent star formation rate.
Conversely, the thermodynamical properties of the ICM in this transition region
should also feel the influence of accreting substructure (i.e. galaxies and
groups), whose passage can drive shocks. In this paper, we use a suite of
cosmological hydrodynamical zoom simulations of a single galaxy cluster, drawn
from the nIFTy comparison project, to study how the dynamics of substructure
accreted from the cosmic web influences the thermodynamical properties of the
ICM in the cluster's outskirts. We demonstrate how features evident in radial
profiles of the ICM (e.g. gas density and temperature) can be linked to strong
shocks, transient and short-lived in nature, driven by the passage of
substructure. The range of astrophysical codes and galaxy formation models in
our comparison are broadly consistent in their predictions (e.g. agreeing when
and where shocks occur, but differing in how strong shocks will be); this is as
we would expect of a process driven by large-scale gravitational dynamics and
strong, inefficiently radiating, shocks. This suggests that mapping such shock
structures in the ICM in a cluster's outskirts (via e.g. radio synchrotron
emission) could provide a complementary measure of its recent merger and
accretion history. |
Consistency relation and inflaton field redefinition in the delta N
formalism: We compute for general single-field inflation the intrinsic non-Gaussianity
due to the self-interactions of the inflaton field in the squeezed limit. We
recover the consistency relation in the context of the delta N formalism, and
argue that there is a particular field redefinition that makes the intrinsic
non-Gaussianity vanishing, thus improving the estimate of the local
non-Gaussianity using the delta N formalism. | Galactic foregrounds and CMB polarization: The CMB polarization promises to unveil the dawn of time measuring the
gravitational wave background emitted by the Inflation. The CMB signal is
faint, however, and easily contaminated by the Galactic foreground emission,
accurate measurements of which are thus crucial to make CMB observations
successful. We review the CMB polarization properties and the current knowledge
on the Galactic synchrotron emission, which dominates the foregrounds budget at
low frequency. We then focus on the S-Band Polarization All Sky Survey
(S-PASS), a recently completed survey of the entire southern sky designed to
investigate the Galactic CMB foreground. |
Constraining early dark energy with gravitational waves before
recombination: We show that the nonperturbative decay of ultralight scalars into Abelian
gauge bosons, recently proposed as a possible solution to the Hubble tension,
produces a stochastic background of gravitational waves which is constrained by
the cosmic microwave background. We simulate the full nonlinear dynamics of
resonant dark photon production and the associated gravitational wave
production, finding the signals to exceed constraints for the entire parameter
space we consider. Our findings suggest that gravitational wave production from
the decay of early dark energy may provide a unique probe of these models. | Properties of the Intracluster Medium Assuming an Einasto Dark Matter
Profile: I investigate an analytical model of galaxy clusters based on the assumption
that the intracluster medium plasma is polytropic and is in hydrostatic
equilibrium. The Einasto profile is adopted as a model for the spatial-density
distribution of dark matter halos. This model has sufficient degrees of freedom
to simultaneously fit X-ray surface brightness and temperature profiles, with
five parameters to describe the global cluster properties and three additional
parameters to describe the cluster's cool-core feature. The model is tested
with Chandra X-ray data for seven galaxy clusters, including three polytropic
clusters and four cool-core clusters. It is found that the model accurately
reproduces the X-ray data over most of the radial range. For all galaxy
clusters, the data allows to show that the model is essentially as good as that
of Vikhlinin et al and Bulbul et al, as inferred by the reduced $\chi^2$. |
Fisher matrix for multiple tracers: the information in the cross-spectra: We derive general expressions for the multi-tracer Fisher matrix, both
assuming that the cross-spectra are constrained by the auto-spectra, and also
allowing for independent degrees of freedom in the cross-spectra. We show that,
just like the ratios of power spectra, the independent degrees of freedom of
the cross-spectra are also not constrained by cosmic variance. Moreover,
whereas the uncertainties in the ratios of power spectra decrease with the
number density of the tracers as $\sim 1/\sqrt{\bar{n}}$, the uncertainties in
the independent degrees of freedom of the cross-spectra decrease even faster,
as $\sim 1/\bar{n}$. We also derive simple expressions for the optimal number
of tracers in a survey. | Dark matter halo occupation: environment and clustering: We use a large dark matter simulation of a LambdaCDM model to investigate the
clustering and environmental dependence of the number of substructures in a
halo. Focusing on redshift z=1, we find that the halo occupation distribution
is sensitive at the tens of percent level to the surrounding density and to a
lesser extent to asymmetry of the surrounding density distribution. We compute
the autocorrelation function of halos as a function of occupation, building on
the finding of Wechsler et al. (2006) and Gao and White (2007) that halos (at
fixed mass) with more substructure are more clustered. We compute the relative
bias as a function of occupation number at fixed mass, finding a strong
relationship. At fixed mass, halos in the top 5% of occupation can have an
autocorrelation function ~ 1.5-2 times higher than the mean. We also compute
the bias as a function of halo mass, for fixed halo occupation. We find that
for group and cluster sized halos, when the number of subhalos is held fixed,
there is a strong anticorrelation between bias and halo mass. Such a
relationship represents an additional challenge to the halo model. |
Fully relativistic treatment of light neutrinos in $N$-body simulations: Cosmological $N$-body simulations are typically purely run with particles
using Newtonian equations of motion. However, such simulations can be made
fully consistent with general relativity using a well-defined prescription.
Here, we extend the formalism previously developed for $\Lambda$CDM cosmologies
with massless neutrinos to include the effects of massive, but light neutrinos.
We have implemented the method in two different $N$-body codes, CONCEPT and
PKDGRAV, and demonstrate that they produce consistent results. We furthermore
show that we can recover all appropriate limits, including the full GR solution
in linear perturbation theory at the per mille level of precision. | Two Epochs of Globular Cluster Formation from Deep Fields Luminosity
Functions: Implications for Reionization and the Milky Way Satellites: The ages of globular clusters in our own Milky Way are known with precision
of about \pm 1 Gyr, hence their formation at redshifts z>~3 and their role in
hierarchical cosmology and the reionization of the intergalactic medium remain
relatively undetermined. Here we analyze the effect of globular cluster
formation on the observed rest-frame UV luminosity functions (LFs) and UV
continuum slopes of high redshift galaxies in the Hubble Ultra Deep Fields. We
find that the majority of present day globular clusters have formed during two
distinct epochs: at redshifts z ~ 2-3 and at redshifts z>~6. The birth of
proto-GC systems produce the steep, faint-end slopes of the galaxy LFs, and
because the brightness of proto-GCs fades 5 Myrs after their formation, their
blue colors are in excellent agreement with observations.
Our results suggest that: i) the bulk of the old globular cluster population
with estimated ages >~12 Gyr (about 50% of the total population), formed in the
relatively massive dwarf galaxies at redshifts z>~6; ii) proto-GC formation was
an important mode of star formation in those dwarf galaxies, and likely
dominated the reionization process. Another consequence of this scenario is
that some of the most massive Milky Way satellites may be faint and yet
undiscovered because tidal stripping of a dominant GC population precedes
significant stripping of the dark matter halos of these satellites. This
scenario may alleviate some remaining tensions between CDM simulations and
observations. |
Investigating the characteristic shape and scatter of intergalactic
damping wings during reionization: Ly$\alpha$ damping wings in the spectra of bright objects at high redshift
are a useful probe of the ionization state of the intergalactic medium during
the reionization epoch. It has recently been noted that, despite the
inhomogeneous nature of reionization, these damping wings have a characteristic
shape which is a strong function of the volume-weighted average neutral
hydrogen fraction of the intergalactic medium. We present here a closer
examination of this finding using a simulation of patchy reionization from the
Sherwood-Relics simulation suite. We show that the characteristic shape and
scatter of the damping wings are determined by the average neutral hydrogen
density along the line of sight, weighted by its contribution to the optical
depth producing the damping wing. We find that there is a redshift dependence
in the characteristic shape due to the expansion of the Universe. Finally, we
show that it is possible to differentiate between the shapes of damping wings
in galaxies and young (or faint) quasars at different points in the
reionization history at large velocity offsets from the point where the
transmission first reaches zero. | A Dual Narrowband Survey for Hα Emitters at z=2.2: Demonstration
of the Technique and Constraints on the Hα Luminosity Function: We present first results from a narrowband imaging program for intermediate
redshift emission-line galaxies using the newly commissioned FourStar infrared
camera at the 6.5m Magellan telescope. To enable prompt identification of
H\alpha\ emitters, a pair of custom 1% filters, which sample low-airglow
atmospheric windows at 1.19 \mu m and 2.10 \mu m, is used to detect both
H\alpha\ and [OII]\lambda 3727 emission from the same redshift volume at z=2.2.
Initial observations are taken over a 130 arcmin^2 area in the CANDELS-COSMOS
field. The exquisite image quality resulting from the combination of the
instrument, telescope, and standard site conditions (~0.55" FWHM) allows the
1.19 \mu m and 2.10 \mu m data to probe 3\sigma\ emission-line depths down to
1.0e-17 erg/s/cm^2 and 1.2e-17 erg/s/cm^2 respectively, in less than 10 hours
of integration time in each narrowband. For H\alpha\ at z=0.8 and z=2.2, these
fluxes correspond to observed star formation rates of ~0.3 and ~4 Msun/yr
respectively. We find 122 sources with a 1.19 \mu m excess, and 136 with a 2.10
\mu m excess, 41 of which show an excess in both bands. The dual narrowband
technique, as implemented here, is estimated to identify about >80% of z=2.2
H\alpha\ emitters in the narrowband excess population. With the most secure
such sample obtained to-date, we compute constraints on the faint-end slope of
the z=2.2 H\alpha\ luminosity function. These "narrow-deep" FourStar
observations have been obtained as part of the larger NewH\alpha\ Survey, which
will combine the data with "wide-shallow" imaging through a similar narrowband
filter pair with NEWFIRM at the KPNO/CTIO 4m telescopes, to enable study of
both luminous (but rare) and faint emission-line galaxies in the intermediate
redshift universe. [Abridged] |
PArthENoPE reloaded: We describe the main features of a new and updated version of the program
PArthENoPE, which computes the abundances of light elements produced during Big
Bang Nucleosynthesis. As the previous first release in 2008, the new one,
PArthENoPE 2.0, will be soon publicly available and distributed from the code
site, http://parthenope.na.infn.it. Apart from minor changes, which will be
also detailed, the main improvements are as follows. The powerful, but not
freely accessible, NAG routines have been substituted by ODEPACK libraries,
without any significant loss in precision. Moreover, we have developed a
Graphical User Interface (GUI) which allows a friendly use of the code and a
simpler implementation of running for grids of input parameters. Finally, we
report the results of PArthENoPE 2.0 for a minimal BBN scenario with free
radiation energy density. | Scale invariance of the primordial tensor power spectrum: Future cosmic microwave background polarization experiments will search for
evidence of primordial tensor modes at large angular scales, in the multipole
range $4 \leq \ell \leq 50.$ Because in that range there is some mild evidence
of departures from scale invariance in the power spectrum of primordial
curvature perturbations, one may wonder about the possibility of similar
deviations appearing in the primordial power spectrum of tensor modes. Here we
address this issue and analyze the possible presence of features in the tensor
spectrum resulting from the dynamics of primordial fluctuations during
inflation. We derive a general, model independent, relation linking features in
the spectra of curvature and tensor perturbations. We conclude that even with
large deviations from scale invariance in the curvature power spectrum, the
tensor spectrum remains scale invariant for all observational purposes. |
Perturbative Gaussianizing transforms for cosmological fields: Constraints on cosmological parameters from large-scale structure have
traditionally been obtained from two-point statistics. However, non-linear
structure formation renders these statistics insufficient in capturing the full
information content available, necessitating the measurement of higher-order
moments to recover information which would otherwise be lost. We construct
quantities based on non-linear and non-local transformations of weakly
non-Gaussian fields that Gaussianize the full multivariate distribution at a
given order in perturbation theory. Our approach does not require a model of
the fields themselves and takes as input only the first few polyspectra, which
could be modelled or measured from simulations or data, making our method
particularly suited to observables lacking a robust perturbative description
such as the weak-lensing shear. We apply our method to simulated density
fields, finding a significantly reduced bispectrum and an enhanced correlation
with the initial field. We demonstrate that our method reconstructs a large
proportion of the linear baryon acoustic oscillations, improving the
information content over the raw field by 35%. We apply the transform to toy
21cm intensity maps, showing that our method still performs well in the
presence of complications such as redshift-space distortions, beam smoothing,
pixel noise, and foreground subtraction. We discuss how this method might
provide a route to constructing a perturbative model of the fully non-Gaussian
multivariate likelihood function. | Starbursts and High-Redshift Galaxies are Radioactive: High Abundances
of $^{26}$Al and Other Short Lived Radionuclides: Short lived radionuclides (SLRs) like $^{26}$Al are synthesized by massive
stars and are a byproduct of star formation. The abundances of SLRs in the gas
of a star-forming galaxy are inversely proportional to the gas consumption
time. The rapid evolution of specific star formation rate (SSFR) of normal
galaxies implies they had mean SLR abundances ~3--10 times higher at z = 2.
During the epoch of Solar system formation, the background SLR abundances of
the Galaxy were up to twice as high as at present, if SLR yields from massive
stars do not depend on metallicity. If SLRs are homogenized in the gas of
galaxies, the high SSFRs of normal galaxies can partly explain the elevated
abundance of SLRs like $^{60}$Fe and $^{26}$Al in the early Solar system.
Starburst galaxies have much higher SSFRs still, and have enormous mean
abundances of $^{26}$Al ($^{26}$Al/$^{27}$Al ~ $10^{-3}$ for Solar metallicity
gas). The main uncertainty is whether the SLRs are mixed with the star-forming
molecular gas: they could be trapped in hot gas and decay before entering the
colder phases, or be blown out by starburst winds. I consider how variability
in star-formation rate affects the SLR abundances, and I discuss how SLR
transport may differ in these galaxies. The enhanced $^{26}$Al of starbursts
might maintain moderate ionization rates ($10^{-18}$ -- $10^{-17}$ s$^{-1}$),
possibly dominating ionization in dense clouds not penetrated by cosmic rays.
Similar ionization rates would be maintained in protoplanetary discs of
starbursts, if the SLRs are well-mixed, and the radiogenic heating of
planetesimals would likewise be much higher. In this way, galaxy evolution can
affect the geological history of planetary systems. |
Gravitational microlensing by dark matter in extended structures: Dark matter may be in the form of non-baryonic structures such as compact
subhalos and boson stars. Structures weighing between asteroid and solar masses
may be discovered via gravitational microlensing, an astronomical probe that
has in the past helped constrain the population of primordial black holes and
baryonic MACHOs. We investigate the non-trivial effect of the size of and
density distribution within these structures on the microlensing signal, and
constrain their populations using the EROS-2 and OGLE-IV surveys. Structures
larger than a solar radius are generally constrained more weakly than
point-like lenses, but stronger constraints may be obtained for structures with
mass distributions that give rise to caustic crossings or produce larger
magnifications. | The stellar, molecular gas and dust content of the host galaxies of two
z~2.8 dust obscured quasars: We present optical through radio observations of the host galaxies of two
dust obscured, luminous quasars selected in the mid-infrared, at z=2.62 and
z=2.99, including a search for CO emission. Our limits on the CO luminosities
are consistent with these objects having masses of molecular gas <~10^10 solar
masses, several times less than those of luminous submillimeter-detected
galaxies (SMGs) at comparable redshifts. Their near-infrared spectral energy
distributions, however, imply that these galaxies have high stellar masses
(~10^11-12 solar masses). The relatively small reservoirs of molecular gas and
low dust masses are consistent with them being relatively mature systems at
high-z. |
A sample of Seyfert-2 galaxies with ultra-luminous galaxy-wide NLRs --
Quasar light echos?: We report the discovery of Seyfert-2 galaxies in SDSS-DR8 with galaxy-wide,
ultra-luminous narrow-line regions (NLRs) at redshifts z=0.2-0.6. With a space
density of 4.4 per cubic Gpc at z~0.3, these "Green Beans" (GBs) are amongst
the rarest objects in the Universe. We are witnessing an exceptional and/or
short-lived phenomenon in the life cycle of AGN. The main focus of this paper
is on a detailed analysis of the GB prototype galaxy J2240-0927 (z=0.326). Its
NLR extends over 26x44 kpc and is surrounded by an extended narrow-line region
(ENLR). With a total [OIII]5008 luminosity of (5.7+/-0.9)x10e43 erg/s, this is
one of the most luminous NLR known around any type-2 galaxy. Using VLT/XSHOOTER
we show that the NLR is powered by an AGN, and we derive resolved extinction,
density and ionization maps. Gas kinematics is disturbed on a global scale, and
high velocity outflows are absent or faint. This NLR is unlike any other NLR or
extended emission line region (EELR) known. Spectroscopy with Gemini/GMOS
reveals extended, high luminosity [OIII] emission also in other GBs. WISE
24micron luminosities are 5-50 times lower than predicted by the [OIII] fluxes,
suggesting that the NLRs reflect earlier, very active quasar states that have
strongly subsided in less than a galaxies' light crossing time. These light
echos are about 100 times more luminous than any other such light echo known to
date. X-ray data are needed for photo-ionization modeling and to verify the
light echos. | Laboratory search for a quintessence field: A cosmic scalar field evolving very slowly in time can account for the
observed dark energy of the Universe. Unlike a cosmological constant, an
evolving scalar field also has local spatial gradients due to gravity. If the
scalar field has a minimal derivative coupling to electromagnetism, it will
cause modifications of Maxwell's equations. In particular, in the presence of a
scalar field gradient generated by Earth's gravity, regions with a magnetic
field appear to be electrically charged and regions with a static electric
field appear to contain electric currents. We propose experiments to detect
such effects with sensitivity exceeding current limits on scalar field
interactions from measurements of cosmological birefringence. If the scalar
field has derivative couplings to fermions, it would also generate observable
effects in precision spin precession experiments. |
Population Gradients in the SDSS Galaxy Catalog. The role of merging: We investigate the role of the environment on the colour and stellar
population gradients in a local sample of ~3500 central and ~1150 satellite
SDSS early-type galaxies (ETGs). The environment is parameterized in terms of
the number of satellite galaxies, N_gal in each group. For central galaxies, we
find that both optical colour and mass-to-light (M/L) ratio gradients are
shallower in central galaxies residing in denser environments (higher N_gal).
This trend is driven by metallicity gradients, while age gradients appear to be
less dependent on the environment and to have a larger scatter. On the other
hand, satellites do not show any differences in terms of the environment. The
same results are found if galaxies are classified by central age, and both
central and satellite galaxies have shallower gradients if they are older and
steeper gradients if younger, satellites being independent of ages. In central
galaxies, we show that the observed trends can be explained with the occurrence
of dry mergings, which are more numerous in denser environments and producing
shallower colour gradients because of more uniform metallicity distributions
due to the mixing of stellar populations, while no final clues about merging
occurrence can be obtained for satellites. Finally we discuss all systematics
on stellar population fitting and their impact on the final results. | Global fitting analysis on cosmological models after BICEP2: Recently, BICEP2 collaboration has released their results on the measurements
of the CMB polarizations. In the framework of the $\Lambda$CDM with a power law
form of the scalar primordial power spectrum, this new measurement on the
B-mode puts a tight constraint on tensor/scalar ratio
$r=0.2^{+0.07}_{-0.05}~(1\sigma)$, which however is in tension with the Planck
limit, $r<0.11$ (95% C.L.). In this paper, we consider various extensions of
the $\Lambda$CDM model by introducing extra cosmological parameters such as the
equation state of dark energy $w$, the curvature of the universe $\Omega_k$,
the running of the scalar power spectrum index $\alpha_s$, the sum of the
neutrino mass $\Sigma m_{\nu}$, the effective number of neutrinos $N_{eff}$,
the tensor power spectrum index $n_{t}$, then perform the global fit to the
BICEP2, Planck and also the SN and BAO data. Our results show the cosmological
parameters $\alpha_s$ and $n_t$ are highly and directly correlated with the
tensor/scalar ratio $r$. However indirectly the parameters $\Omega_k$ and
$N_{eff}$ are also correlated with $r$. We will in this paper give the
numerical values on the parameters introduced and show explicitly how the
tension between the BICEP2 and Planck is effectively alleviated by the
inclusion of the parameters $\Omega_k$, $\alpha_s$, $N_{eff}$ and $n_{t}$
separately. |
Globular Cluster Candidates in NGC 891: We use deep images taken with the Advanced Camera for Surveys on board the
Hubble Space Telescope of the disk galaxy NGC 891, to search for globular
cluster candidates. This galaxy has long been considered to be a close analog
in size and structure to the Milky Way and is nearly edge-on, facilitating
studies of its halo population. These extraplanar ACS images, originally
intended to study the halo field-star populations, reach deep enough to reveal
even the faintest globular clusters that would be similar to those in the Milky
Way. From the three pointings we have identified a total of 43 candidates after
culling by object morphology, magnitude, and colour. We present (V,I)
photometry for all of these, along with measurements of their effective radius
and ellipticity. The 16 highest-rank candidates within the whole sample are
found to fall in very much the same regions of parameter space occupied by the
classic Milky Way globular clusters. Our provisional conclusion from this
survey is that the total globular cluster population in NGC 891 as a whole may
be almost as large as that of the Milky Way. | Metallicity of high stellar mass galaxies with signs of merger events: We focus on an analysis of galaxies of high stellar mass and low metallicity.
We cross-correlated the Millenium Galaxy Catalogue (MGC) and the Sloan Digital
Sky Survey (SDSS) galaxy catalogue to provide a sample of MGC objects with high
resolution imaging and both spectroscopic and photometric information available
in the SDSS database. For each galaxy in our sample, we conducted a systematic
morphological analysis by visual inspection of MGC images using their
luminosity contours. The galaxies are classified as either disturbed or
undisturbed objects. We divide the sample into three metallicity regions,
within wich we compare the properties of disturbed and undisturbed objects. We
find that the fraction of galaxies that are strongly disturbed, indicative of
being merger remnants, is higher when lower metallicity objects are considered.
The three bins analysed consist of approximatively 15%, 20%, and 50% disturbed
galaxies (for high, medium, and low metallicity, respectively). Moreover, the
ratio of the disturbed to undisturbed relative distributions of the population
age indicator, Dn(4000), in the low metallicity bin, indicates that the
disturbed objects have substantially younger stellar populations than their
undisturbed counterparts. In addition, we find that an analysis of colour
distributions provides similar results, showing that low metallicity galaxies
with a disturbed morphology are bluer than those that are undisturbed. The
bluer colours and younger populations of the low metallicity, morphologically
disturbed objects suggest that they have experienced a recent merger with an
associated enhanced star formation rate. [abridged] |
Cosmological constraints from the BOSS DR12 void size function: We present the first cosmological constraints derived from the analysis of
the void size function. This work relies on the final BOSS DR12 data set, a
large spectroscopic galaxy catalog, ideal for the identification of cosmic
voids. We extract a sample of voids from the distribution of galaxies and we
apply a cleaning procedure aimed at reaching high levels of purity and
completeness. We model the void size function by means of an extension of the
popular volume-conserving model, based on two additional nuisance parameters.
Relying on mock catalogs specifically designed to reproduce the BOSS DR12
galaxy sample, we calibrate the extended size function model parameters and
validate the methodology. We then apply a Bayesian analysis to constrain the
$\Lambda$CDM model and one of its simplest extensions, featuring a constant
dark energy equation of state parameter, $w$. Following a conservative
approach, we put constraints on the total matter density parameter and the
amplitude of density fluctuations, finding $\Omega_{\rm m}=0.29 \pm 0.06$ and
$\sigma_8=0.79^{+0.09}_{-0.08}$. Testing the alternative scenario, we derive
$w=-1.1\pm 0.2$, in agreement with the $\Lambda$CDM model. These results are
independent and complementary to those derived from standard cosmological
probes, opening up new ways to identify the origin of potential tensions in the
current cosmological paradigm. | Viscosity in a Lepton-Photon Universe: We look at viscosity production in a universe consisting purely of leptons
and photons. This is quite close to what the Universe actually look like when
the temperature was between $10^{10}$ K and $10^{12}$ K ($1$ -- $100$ MeV). By
taking the strong force and the hadronic particles out of the equation, we can
examine how the viscous forces behave with all the 12 leptons present. By this
we study how shear- and (more interestingly) bulk viscosity is affected during
periods with particle annihilation. We use the theory given by Hoogeveen et.
al. from 1986, replicate their 9-particle results and expanded it to include
the muon and tau particles as well. This will impact the bulk viscosity
immensely for high temperatures. We will show that during the beginning of the
lepton era, when the temperature is around 100 MeV, the bulk viscosity will be
roughly 100 million times larger with muons included in the model compared to a
model without. |
A Near-Infrared Period-Luminosity Relation for Miras in NGC 4258, an
Anchor for a New Distance Ladder: We present year-long, near-infrared Hubble Space Telescope WFC3 observations
of Mira variables in the water megamaser host galaxy NGC 4258. Miras are AGB
variables that can be divided into oxygen- (O-) and carbon- (C-) rich
subclasses. Oxygen-rich Miras follow a tight (scatter $\sim 0.14$ mag)
Period-Luminosity Relation (PLR) in the near-infrared and can be used to
measure extragalactic distances. The water megamaser in NGC 4258 gives a
geometric distance to the galaxy accurate to 2.6% that can serve to calibrate
the Mira PLR. We develop criteria for detecting and classifying O-rich Miras
with optical and NIR data as well as NIR data alone. In total, we discover 438
Mira candidates that we classify with high confidence as O-rich. Our most
stringent criteria produce a sample of 139 Mira candidates that we use to
measure a PLR. We use the OGLE-III sample of O-rich Miras in the LMC to obtain
a relative distance modulus, $\mu_{4258} - \mu_{LMC} = 10.95 \pm 0.01 $
(statistical) $\pm 0.06 $ (systematic) mag in good agreement with the relative
distance determined using Cepheids. These results demonstrate the feasibility
of discovering and characterizing Miras using the near-infrared with the Hubble
Space Telescope and the upcoming James Webb Space Telescope and using them to
measure extragalactic distances and determine the Hubble constant. | Constraints on Spatial Variations in the Fine-Structure constant from
Planck: We use the Cosmic Microwave Background (CMB) anisotropy data from Planck to
constrain the spatial fluctuations of the fine-structure constant \alpha.
Through Thompson scattering of CMB photons, spatial anisotropies of \alpha lead
to higher-order correlations in the CMB anisotropies. We use a quadratic
estimator based on the four-point correlation function of the CMB temperature
anisotropy to extract the angular power spectrum of the spatial variation of
the fine-structure constant projected along the line of sight at the last
scattering surface. At tens of degree angular scales and above, we constrain
the rms fluctuations of the fine structure constant to be \delta
\alpha/\alpha_0= (1.34 +/- 5.82) x 10^-2 at the 95% confidence level with
respect to the standard value \alpha_0. We find no evidence for a spatially
varying \alpha at a redshift of 10^3. |
Weak lensing magnification of SpARCS galaxy clusters: Measuring and calibrating relations between cluster observables is critical
for resource-limited studies. The mass-richness relation of clusters offers an
observationally inexpensive way of estimating masses. Its calibration is
essential for cluster and cosmological studies, especially for high-redshift
clusters. Weak gravitational lensing magnification is a promising and
complementary method to shear studies, that can be applied at higher redshifts.
We employed the weak lensing magnification method to calibrate the
mass-richness relation up to a redshift of 1.4. We used the Spitzer Adaptation
of the Red-Sequence Cluster Survey (SpARCS) galaxy cluster candidates
($0.2<z<1.4$) and optical data from the Canada France Hawaii Telescope (CFHT)
to test whether magnification can be effectively used to constrain the mass of
high-redshift clusters. Lyman-Break Galaxies (LBGs) selected using the $u$-band
dropout technique and their colours were used as a background sample of
sources. LBG positions were cross-correlated with the centres of the sample of
SpARCS clusters to estimate the magnification signal measured for cluster
sub-samples, binned in both redshift and richness. We detected a weak lensing
magnification signal for all bins at a detection significance of
2.6-5.5$\sigma$. In particular, the significance of the measurement for
clusters with $z>1.0$ is 4.1$\sigma$; for the entire cluster sample we obtained
an average M$_{200}$ of $1.28^{+0.23}_{-0.21}$ $\times 10^{14} \,
\textrm{M}_{\odot}$. Our measurements demonstrated the feasibility of using
weak lensing magnification as a viable tool for determining the average halo
masses for samples of high redshift galaxy clusters. The results also
established the success of using galaxy over-densities to select massive
clusters at $z > 1$. Additional studies are necessary for further modelling of
the various systematic effects we discussed. | A strong broadband 21 cm cosmological signal from dark matter spin-flip
interactions: In the standard cosmology, it is believed that there are two relatively weak
and distinct band-limited absorption features, with the first absorption minima
near 20 MHz ($z\sim70$) and the other minima at higher frequencies between
50-110 MHz ($z\sim12-27$) in the global cosmological 21cm signal, which are
signatures of collisional gas dynamics in the cosmic dark ages and
Lyman-$\alpha$ photons from the first stars at cosmic dawn, respectively. A
similar prediction of two distinct band-limited, but stronger, absorption
features is expected in models with excess gas cooling, which have been invoked
to explain the EDGES signal. In this work, we explore a novel mechanism, where
dark matter spin-flip interactions with electrons through a light axial-vector
mediator could directly induce a 21cm absorption signal which is
characteristically different from either of these. We find generically, that
our model predicts a strong, broadband absorption signal extending from
frequencies as low as 1.4 MHz ($z\sim1000$), from early in the cosmic dark ages
where no conventional signal is expected, all the way up to higher frequencies
where star formation and X-ray heating effects are expected to terminate the
absorption signal. In the standard cosmology and in excess gas cooling models
it is expected that the gas spin temperature as inferred from the absorption
signal is a tracer of the gas kinetic temperature. However, in our model we
find in certain regions of parameter space that the spin temperature and
kinetic temperature of the gas evolve differently, and the absorption signal
only measures the spin temperature evolution. Large swathes of our model
parameter space of interest are safe from existing constraints, however future
searches for short range spin-dependent forces between electrons on the mm to
nm scale have the potential to discover the light mediator responsible for our
predicted signal. |
Which galaxy property is the best indicator of its host dark matter halo
properties?: In this work we investigate the link between galaxy velocity dispersion, mass
and other properties (color, morphology) with the properties of dark matter
halos by comparing the clustering of galaxies at both fixed mass and velocity
dispersion. We use the Sloan Digital Sky Survey to define a volume limited
sample of massive galaxies complete in both stellar mass (>6e10 Msun) and
velocity dispersion (>75 km/s). Using this sample we show that at fixed
velocity dispersion there is no dependence of the clustering amplitude on
stellar or dynamical mass. Conversely when stellar or dynamical mass are fixed
there is a clear dependence of the clustering amplitude on velocity dispersion
with higher dispersion galaxies showing a higher clustering amplitude. We also
show that whilst when stellar or dynamical mass are fixed there remains a
dependence of clustering amplitude on morphology, there is no such dependency
when dispersion is fixed. However, we do see a dependence of the clustering
amplitude on color when both mass and dispersion are fixed. Despite this, even
when we restrict our samples to only elliptical or red galaxies the
relationship between dispersion and clustering amplitude at fixed mass remains.
It seems likely that the residual correlation with color is driven by satellite
galaxies in massive halos being redder at fixed dispersion. The lack of a
similar morphology dependence implies that the mechanism turning satellites red
is not changing their morphology. Our central result is that velocity
dispersion is more closely related to the clustering amplitude of galaxies than
either stellar or dynamical mass. This implies that velocity dispersion is more
tightly correlated with the halo properties that determine clustering, either
halo mass or age, and supports the notion that the star formation history of a
galaxy is more closely related to its halo properties than its overall mass. | Cylindrical model for the dark matter halo of disk galaxies: A cylindrical model for the dark matter halo of disk galaxies is developed.
At the center of the cylinder, in the plane perpendicular to the long axis, the
rotation curve is constant for distances much less than the cylinder length and
Keplerian at much greater distances. The rotation curve is equivalent to the
spherical truncated flat (TF) profile, a model derived empirically from the
radial velocity dispersion of the Milky Way dark halo. It is shown that an
isothermal, self-gravitating cylinder of length 89 kpc can account for the
observed radial velocity dispersion of the Milky Way dark halo with less mass
than the NFW profile. Moreover, a cylindrical model of the Milky Way dark halo
is consistent with free-streaming neutrinos of mass 1.1 eV. |
Radio Properties of Low Redshift Broad Line Active Galactic Nuclei
Including Extended Radio Sources: We present a study of the extended radio emission in a sample of 8434 low
redshift (z < 0.35) broad line active galactic nuclei (AGN) from the Sloan
Digital Sky Survey (SDSS). To calculate the jet and lobe contributions to the
total radio luminosity, we have taken the 846 radio core sources detected in
our previous study of this sample and performed a systematic search in the
Faint Images of the Radio Sky at Twenty-centimeters (FIRST) database for
extended radio emission that is likely associated with the optical
counterparts. We found 51 out of 846 radio core sources have extended emission
(> 4" from the optical AGN) that is positively associated with the AGN, and we
have identified an additional 12 AGN with extended radio emission but no
detectable radio core emission. Among these 63 AGN, we found 6 giant radio
galaxies (GRGs), with projected emission exceeding 750 kpc in length, and
several other AGN with unusual radio morphologies also seen in higher redshift
surveys. The optical spectra of many of the extended sources are similar to
that of typical broad line radio galaxy spectra, having broad H$\alpha$
emission lines with boxy profiles and large M_BH. With extended emission taken
into account, we find strong evidence for a bimodal distribution in the
radio-loudness parameter R, where the lower radio luminosity core-only sources
appear as a population separate from the extended sources, with a dividing line
at log(R) $\approx 1.75$. This dividing line ensures that these are indeed the
most radio-loud AGN, which may have different or extreme physical conditions in
their central engines when compared to the more numerous radio quiet AGN. | On a class of scaling FRW cosmological models: We study Friedmann-Robertson-Walker cosmological models with matter content
composed of two perfect fluids $\rho_1$ and $\rho_2$, with barotropic pressure
densities $p_1/ \rho_1=\omega_1=const$ and $p_2/ \rho_2=\omega_2=const$, where
one of the energy densities is given by $\rho_1=C_1 a^\alpha + C_2 a^\beta$,
with $C_1$, $C_2$, $\alpha$ and $\beta$ taking constant values. We solve the
field equations by using the conservation equation without breaking it into two
interacting parts with the help of a coupling interacting term $Q$.
Nevertheless, with the found solution may be associated an interacting term
$Q$, and then a number of cosmological interacting models studied in the
literature correspond to particular cases of our cosmological model.
Specifically those models having constant coupling parameters $\tilde{\alpha}$,
$\tilde{\beta}$ and interacting terms given by $Q=\tilde{\alpha} H
\rho_{_{DM}}$, $Q=\tilde{\alpha} H \rho_{_{DE}}$, $Q=\tilde{\alpha} H
(\rho_{_{DM}}+ \rho_{_{DE}})$ and $Q=\tilde{\alpha} H
\rho_{_{DM}}+\tilde{\beta} H \rho_{_{DE}}$, where $\rho_{_{DM}}$ and
$\rho_{_{DE}}$ are the energy densities of dark matter and dark energy
respectively. The studied set of solutions contains a class of cosmological
models presenting a scaling behavior at early and at late times. On the other
hand the two-fluid cosmological models considered in this paper also permit a
three fluid interpretation which is also discussed. In this reinterpretation,
for flat Friedmann-Robertson-Walker cosmologies, the requirement of positivity
of energy densities of the dark matter and dark energy components allows the
state parameter of dark energy to be in the range $-1.37 \lesssim
\omega_{_{DE}}<-1/3$. |
On the connection between shape and stellar population in early-type
galaxies: We report on the discovery of a relation between the stellar mass $M^*$ of
early-type galaxies (hereafter ETGs), their shape, as parametrized by the
Sersic index $n$, and their stellar mass-to-light ratio $M^*/L$. In a 3D log
space defined by these variables the ETGs populate a plane surface with small
scatter. This relation tells us that galaxy shape and stellar population are
not independent physical variables, a result that must be accounted for by
theories of galaxy formation and evolution. | Evolution of X-ray galaxy Cluster Properties in a Representative Sample
(EXCPReS). Optimal binning for temperature profile extraction: We present XMM-Newton observations of a representative X-ray selected sample
of 31 galaxy clusters at moderate redshift $(0.4<z<0.6)$, spanning the mass
range $10^{14} < M_{\textrm 500} < 10^{15}$~M$_\odot$. This sample, EXCPRES
(Evolution of X-ray galaxy Cluster Properties in a Representative Sample), is
used to test and validate a new method to produce optimally-binned cluster
X-ray temperature profiles. The method uses a dynamic programming algorithm,
based on partitioning of the soft-band X-ray surface brightness profile, to
obtain a binning scheme that optimally fulfills a given signal-to-noise
threshold criterion out to large radius. From the resulting optimally-binned
EXCPRES temperature profiles, and combining with those from the local REXCESS
sample, we provide a generic scaling relation between the relative error on the
temperature and the [0.3-2] keV surface brightness signal-to-noise ratio, and
its dependence on temperature and redshift. We derive an average scaled 3D
temperature profile for the sample. Comparing to the average scaled 3D
temperature profiles from REXCESS, we find no evidence for evolution of the
average profile shape within the redshift range that we probe. |
A joint measurement of galaxy luminosity functions and large-scale field
densities during the Epoch of Reionization: One of the most exciting advances of the current generation of telescopes has
been the detection of galaxies during the epoch of reionization, using deep
fields that have pushed these instruments to their limits. It is essential to
optimize our analyses of these fields in order to extract as much information
as possible from them. In particular, standard methods of measuring the galaxy
luminosity function discard information on large-scale dark matter density
fluctuations, even though this large-scale structure drives galaxy formation
and reionization during the Cosmic Dawn. Measuring these densities would
provide a bedrock observable, connecting galaxy surveys to theoretical models
of the reionization process and structure formation. Here, we use existing
Hubble deep field data to simultaneously fit the universal luminosity function
and measure large-scale densities for each Hubble deep field at $z =$ 6--8 by
directly incorporating priors on the large-scale density field and galaxy bias.
Our fit of the universal luminosity function is consistent with previous
methods but differs in the details. For the first time, we measure the
underlying densities of the survey fields, including the most over/under-dense
Hubble fields. We show that the distribution of densities is consistent with
current predictions for cosmic variance. This analysis on just 17 fields is a
small sample of what will be possible with the James Webb Space Telescope,
which will measure hundreds of fields at comparable (or better) depths and at
higher redshifts. | Cosmology from weak lensing alone and implications for the Hubble
tension: We investigate the origin of $\Lambda$CDM parameter constraints in weak
lensing, with a focus on the Hubble constant. We explain why current cosmic
shear data are sensitive to the parameter combination $S_8 \propto \sigma_8
\Omega_m^{0.5}$, improving upon previous studies through use of the halo model.
Motivated by the ongoing discrepancy in measurements of the Hubble constant
from high and low redshift, we explain why cosmic shear provides almost no
constraint on $H_0$ by showing how the lensing angular power spectrum depends
on physical length scales in the dark matter distribution. We derive parameter
constraints from galaxy lensing in KiDS and cosmic microwave background weak
lensing from Planck and SPTpol, separately and jointly, showing how
degeneracies between $\sigma_8$ and $\Omega_m$ can be broken. Using lensing and
Big Bang Nucleosynthesis to calibrate the sound horizon measured in projection
by baryon acoustic oscillations gives $H_0 = 67.4 \pm 0.9 \; \mathrm{km} \,
\mathrm{s}^{-1} \, \mathrm{Mpc}^{-1}$, consistent with previous results from
Planck and the Dark Energy Survey. We find that a toy Euclid-like lensing
survey provides only weak constraints on the Hubble constant due to
degeneracies with other parameters that affect the shape of the lensing
correlation functions. If external priors on $n_s$, the baryon density, and the
amplitude of baryon feedback are available then sub-percent $H_0$ constraints
are achievable with forthcoming lensing surveys. |
On the anisotropies of the cosmological gravitational-wave background
from pulsar timing array observations: Significant evidence for a stochastic gravitational-wave background has
recently been reported by several Pulsar Timing Array observations. These
studies have shown that, in addition to astrophysical explanations based on
supermassive black hole binaries (SMBHBs), cosmological origins are considered
equally important sources for these signals. To further explore these
cosmological sources, in this study, we discuss the anisotropies in the
cosmological gravitational wave background (CGWB) in a model-independent way.
Taking the North American Nanohertz Observatory for Gravitational Waves
(NANOGrav) 15-year dataset as a benchmark, we estimate the angular power
spectra of the CGWB and their cross-correlations with cosmic microwave
background (CMB) fluctuations and weak gravitational lensing. We find that the
NANOGrav 15-year data implies suppressed Sachs-Wolf (SW) effects in the CGBW
spectrum, leading to a marginally negative cross-correlation with the CMB at
large scales. This procedure is applicable to signals introduced by different
early universe processes and is potentially useful for identifying unique
features about anisotropies of CGWB from future space-based interferometers and
astrometric measurements. | The Formation of the First Galaxies: The primary concern of this thesis is to understand the formation and
properties of the first galaxies, as well as the influence of the first stars
in terms of radiative, mechanical and chemical feedback. In particular, we
elucidate the role of turbulence, ionizing radiation by massive Population III
stars, mechanical feedback by highly energetic supernovae, and chemical
enrichment. In light of the next generation of ground- and space based
telescopes, we derive their observational signature in terms of recombination
radiation, bremsstrahlung and 21 cm emission. We find that the cumulative 21 cm
signal of the first H II regions will likely be observable by the planned SKA,
while the recombination radiation from the first starbursts might be observable
by JWST. These probes are essential to test the theoretical framework of the
first stars and galaxies and shed some light on this elusive period of cosmic
history. |
Non-Parametric Analysis for the Dark Matter Density Evolution: In this paper, we investigate a potential departure in the standard dark
matter density evolution law, $\rho_{dm} = \rho_{dm,0}(1+z)^3$. The method
involves considering a deformed evolution model, denoted as $\rho_{dm} =
\rho_{dm,0}(1+z)^3f(z)$, and searching the presence of any deviation ($f(z)\neq
1$). As one may see, $f(z)$ is a general function that parametrizes a
digression from the standard law. We use data of baryon acoustic oscillations,
type I Supernovae luminosity distances, and galaxy cluster gas mass fraction
observations to reconstruct $f(z)$ by Gaussian process regression. Unlike
previous works, it enables us to investigate a possible deviation without using
a specific function to describe it. We have obtained $f(z)=1$, the standard
model scenario, within $2\sigma$ c.l. in all the considered cases. | On the first crossing distributions in fractional Brownian motion and
the mass function of dark matter haloes: We construct an integral equation for the first crossing distributions for
fractional Brownian motion in the case of a constant barrier and we present an
exact analytical solution. Additionally we present first crossing distributions
derived by simulating paths from fractional Brownian motion. We compare the
results of the analytical solutions with both those of simulations and those of
some approximated solutions which have been used in the literature. Finally, we
present multiplicity functions for dark matter structures resulting from our
analytical approach and we compare with those resulting from N-body
simulations.
We show that the results of analytical solutions are in good agreement with
those of path simulations but differ significantly from those derived from
approximated solutions. Additionally, multiplicity functions derived from
fractional Brownian motion are poor fits of the those which result from N-body
simulations. We also present comparisons with other models which exist in the
literature and we discuss different ways of improving the agreement between
analytical results and N-body simulations. |
The Faraday Rotation Measure Grid of the LOFAR Two-metre Sky Survey:
Data Release 2: A Faraday rotation measure (RM) catalogue, or RM Grid, is a valuable resource
for the study of cosmic magnetism. Using the second data release (DR2) from the
LOFAR Two-metre Sky Survey (LoTSS), we have produced a catalogue of 2461
extragalactic high-precision RM values across 5720 deg$^{2}$ of sky
(corresponding to a polarized source areal number density of $\sim$0.43
deg$^{-2}$). The linear polarization and RM properties were derived using RM
synthesis from the Stokes $Q$ and $U$ channel images at an angular resolution
of 20'' across a frequency range of 120 to 168 MHz with a channel bandwidth of
97.6 kHz. The fraction of total intensity sources ($>1$ mJy beam$^{-1}$) found
to be polarized was $\sim$0.2%. The median detection threshold was 0.6 mJy
beam$^{-1}$ ($8\sigma_{QU}$), with a median RM uncertainty of 0.06 rad m$^{-2}$
(although a systematic uncertainty of up to 0.3 rad m$^{-2}$ is possible, after
the ionosphere RM correction). The median degree of polarization of the
detected sources is 1.8%, with a range of 0.05% to 31%. Comparisons with
cm-wavelength RMs indicate minimal amounts of Faraday complexity in the LoTSS
detections, making them ideal sources for RM Grid studies. Host galaxy
identifications were obtained for 88% of the sources, along with redshifts for
79% (both photometric and spectroscopic), with the median redshift being 0.6.
The focus of the current catalogue was on reliability rather than completeness,
and we expect future versions of the LoTSS RM Grid to have a higher areal
number density. In addition, 25 pulsars were identified, mainly through their
high degrees of linear polarization. | The simplest model of galaxy formation I: A formation history model of
galaxy stellar mass growth: We introduce a simple model to self-consistently connect the growth of
galaxies to the formation history of their host dark matter haloes. Our model
is defined by two simple functions: the "baryonic growth function" which
controls the rate at which new baryonic material is made available for star
formation, and the "physics function" which controls the efficiency with which
this material is converted into stars. Using simple, phenomenologically
motivated forms for both functions that depend only on a single halo property,
we demonstrate the model's ability to reproduce the z=0 red and blue stellar
mass functions. Furthermore, by adding redshift as a second input variable to
the physics function we show that the reproduction of the global stellar mass
function out to z=3 is improved. We conclude by discussing the general utility
of our new model, highlighting its usefulness for creating mock galaxy samples
which have a number of key advantages over those generated by other techniques. |
Planck intermediate results. XXXVII. Evidence of unbound gas from the
kinetic Sunyaev-Zeldovich effect: By looking at the kinetic Sunyaev-Zeldovich effect (kSZ) in Planck nominal
mission data, we present a significant detection of baryons participating in
large-scale bulk flows around central galaxies (CGs) at redshift $z\approx
0.1$. We estimate the pairwise momentum of the kSZ temperature fluctuations at
the positions of the CGC (Central Galaxy Catalogue) samples extracted from
Sloan Digital Sky Survey (DR7) data. For the foreground-cleaned maps, we find
$1.8$-$2.5\sigma$ detections of the kSZ signal, which are consistent with the
kSZ evidence found in individual Planck raw frequency maps, although lower than
found in the WMAP-9yr W band ($3.3\sigma$). We further reconstruct the peculiar
velocity field from the CG density field, and compute for the first time the
cross-correlation function between kSZ temperature fluctuations and estimates
of CG radial peculiar velocities. This correlation function yields a
$3.0$-$3.7$$\sigma$ detection of the peculiar motion of extended gas on Mpc
scales, in flows correlated up to distances of 80-100 $h^{-1}$ Mpc. Both the
pairwise momentum estimates and kSZ temperature-velocity field correlation find
evidence for kSZ signatures out to apertures of 8 arcmin and beyond,
corresponding to a physical radius of $> 1$ Mpc, more than twice the mean
virial radius of halos. This is consistent with the predictions from hydro
simulations that most of the baryons are outside the virialized halos. We fit a
simple model, in which the temperature-velocity cross-correlation is
proportional to the signal seen in a semi-analytic model built upon N-body
simulations, and interpret the proportionality constant as an "effective"
optical depth to Thomson scattering. We find $\tau_T=(1.4\pm0.5)\times
10^{-4}$; the simplest interpretation of this measurement is that much of the
gas is in a diffuse phase, which contributes little signal to X-ray or thermal
SZ observations. | Global fits of axion-like particles to XENON1T and astrophysical data: The excess of electron recoil events seen by the XENON1T experiment has been
interpreted as a potential signal of axion-like particles (ALPs), either
produced in the Sun, or constituting part of the dark matter halo of the Milky
Way. It has also been explained as a consequence of trace amounts of tritium in
the experiment. We consider the evidence for the solar and dark-matter ALP
hypotheses from the combination of XENON1T data and multiple astrophysical
probes, including horizontal branch stars, red giants, and white dwarfs. We
briefly address the influence of ALP decays and supernova cooling. While the
different datasets are in clear tension for the case of solar ALPs, all
measurements can be simultaneously accommodated for the case of a sub-dominant
fraction of dark-matter ALPs. Nevertheless, this solution requires the tuning
of several a priori unknown parameters, such that for our choices of priors a
Bayesian analysis shows no strong preference for the ALP interpretation of the
XENON1T excess over the background hypothesis. |
Topology and Dark Energy: Testing Gravity in Voids: Modified gravity has garnered interest as a backstop against dark matter and
dark energy (DE). As one possible modification, the graviton can become
massive, which introduces a new scalar field - here with a Galileon-type
symmetry. The field can lead to a nontrivial equation of state (EOS) of DE
which is density-and-scale-dependent. Tension between Type Ia supernovae and
Planck could be reduced. In voids the scalar field dramatically alters the EOS
of DE, induces a soon-observable gravitational slip between the two metric
potentials, and develops a topological defect (domain wall) due to a nontrivial
vacuum structure for the field. | Domain of validity for pseudo-elliptical NFW lens models: Models with elliptical potentials (pseudo-elliptical) are often used in
gravitational lensing applications. Nevertheless, they generally lead to
nonphysical mass distributions in some regions. In this paper we revisit the
physical limitations of the pseudo-elliptical Navarro-Frenk-White (PNFW) model,
for a broad range of the potential ellipticity parameter \epsilon\ and
characteristic convergence \kappa_s focusing on the behavior of the mass
distribution close to the tangential critical curve, where tangential arcs are
expected to be formed. We investigate the shape of the mass distribution on
this region and the presence of negative convergence. We obtain a mapping from
the PNFW to the NFW model with elliptical mass distribution (ENFW) and provide
fitting formulae for connecting the parameters of both models. We compare the
arc cross section for these models using the "infinitesimal circular source
approximation". We find that the PNFW model is well-suited to model an
elliptical mass distribution on a larger \epsilon\ - \kappa_s parameter space
than previously expected. In particular values as large as \epsilon\ ~ 0.65 are
allowed for small \kappa_s. However, if we require the PNFW model to reproduce
the arc cross section of the ENFW well, the ellipticity is more restricted. We
also find that the negative convergence regions occur far from the arc
formation region and should therefore not be a problem for studies with
gravitational arcs. The determination of a domain of validity for the PNFW
model and the mapping to ENFW models could have implications for the use of
PNFW models for the inverse modeling of lenses and for fast arc simulations. |
The Helmholtz Hierarchy: Phase Space Statistics of Cold Dark Matter: We present a new formalism to study large-scale structure in the universe.
The result is a hierarchy (which we call the "Helmholtz Hierarchy") of
equations describing the phase space statistics of cold dark matter (CDM). The
hierarchy features a physical ordering parameter which interpolates between the
Zel'dovich approximation and fully-fledged gravitational interactions. The
results incorporate the effects of stream crossing. We show that the Helmholtz
hierarchy is self-consistent and obeys causality to all orders. We present an
interpretation of the hierarchy in terms of effective particle trajectories. | Accurate determination of halo velocity bias in simulations and its
cosmological implications: A long-standing issue in peculiar velocity cosmology is whether the
halo/galaxy velocity bias $b_v=1$ at large scale. The resolution of this
important issue must resort to high precision cosmological simulations.
However, this is hampered by another long-standing `sampling artifact' problem
in volume weighted velocity measurement. We circumvent this problem with a
hybrid approach. We first measure statistics free of sampling artifact, then
link them to volume weighted statistics in theory, finally solve for the
velocity bias. $b_v$ determined by our method is not only free of sampling
artifact, but also free of cosmic variance. We apply this method to a
$\Lambda$CDM N-body simulation of $3072^3$ particles and $1200 Mpc/{\rm h}$ box
size. For the first time, we determine the halo velocity bias to $0.1\%$-$1\%$
accuracy. Our major findings are as follows: (1) $b_v\neq 1$ at $k>0.1 h/{\rm
Mpc}$. The deviation from unity ($|b_v-1|$) increases with $k$. Depending on
halo mass and redshift, it may reach $\mathcal{O}(0.01)$ at $k=0.2 h/{\rm Mpc}$
and $\mathcal{O}(0.05)$ at $k\sim 0.3 h/{\rm Mpc}$. The discovered $b_v\neq 1$
has statistically significant impact on structure growth rate measurement by
spectroscopic redshift surveys, including DESI, Euclid and SKA. (2) Both the
sign and the amplitude of $b_v-1$ depend on mass and redshift. These results
disagree with the peak model prediction in that $b_v$ has much weaker deviation
from unity, varies with redshift, and can be bigger than unity. (3) Most of the
mass and redshift dependences can be compressed into a single dependence on the
halo density bias. Based on this finding, we provide an approximate
two-parameter fitting formula. |
Observational Constraint on Heavy Element Production in Inhomogeneous
Big Bang Nucleosynthesis: Based on a scenario of the inhomogeneous big-bang nucleosynthesis (IBBN), we
investigate the detailed nucleosynthesis that includes the production of heavy
elements beyond Li-7. From the observational constraints on light elements of
He4 and D for the baryon-to-photon ratio given by WMAP, possible regions found
on the plane of the volume fraction of the high density region against the
ratio between high- and low-density regions.
In these allowed regions, we have confirmed that the heavy elements beyond Fe
can be produced appreciably, where p- and/or r-process elements are produced
well simultaneously compared to the solar system abundances. We suggest that
recent observational signals such as He4 overabundance in globular clusters and
high metallicity abundances in quasars could be partly due to the results of
IBBN. Possible implications are given for the formation of the first generation
stars | The Keck+Magellan Survey for Lyman Limit Absorption III: Sample
Definition and Column Density Measurements: We present an absorption-line survey of optically thick gas clouds -- Lyman
Limit Systems (LLSs) -- observed at high dispersion with spectrometers on the
Keck and Magellan telescopes. We measure column densities of neutral hydrogen
NHI and associated metal-line transitions for 157 LLSs at z=1.76-4.39
restricted to 10^17.3 < NHI < 10^20.3. An empirical analysis of ionic ratios
indicates an increasing ionization state of the gas with decreasing NHI and
that the majority of LLSs are highly ionized, confirming previous expectations.
The Si^+/H^0 ratio spans nearly four orders-of-magnitude, implying a large
dispersion in the gas metallicity. Fewer than 5% of these LLSs have no positive
detection of a metal transition; by z~3, nearly all gas that is dense enough to
exhibit a very high Lyman limit opacity has previously been polluted by heavy
elements. We add new measurements to the small subset of LLS (~5-10) that may
have super-solar abundances. High Si^+/Fe^+ ratios suggest an alpha-enhanced
medium whereas the Si^+/C^+ ratios do not exhibit the super-solar enhancement
inferred previously for the Lya forest. |
The 2-loop matter power spectrum and the IR-safe integrand: Large scale structure surveys are likely the next leading probe of
cosmological information. It is therefore crucial to reliably predict their
observables. The Effective Field Theory of Large Scale Structures (EFTofLSS)
provides a manifestly convergent perturbation theory for the weakly non-linear
regime, where dark matter correlation functions are computed in an expansion of
the wavenumber k over the wavenumber associated to the non-linear scale knl. To
push the predictions to higher wavenumbers, it is necessary to compute the
2-loop matter power spectrum. For equal-time correlators, exactly as with
standard perturturbation theory, there are IR divergences present in each
diagram that cancel completely in the final result. We develop a method by
which all 2-loop diagrams are computed as one integral, with an integrand that
is manifestly free of any IR divergences. This allows us to compute the 2-loop
power spectra in a reliable way that is much less numerically challenging than
standard techniques. We apply our method to scaling universes where the linear
power spectrum is a single power law of k, and where IR divergences can
particularly easily interfere with accurate evaluation of loop corrections if
not handled carefully. We show that our results are independent of IR cutoff
and, after renormalization, of the UV cutoff, and comment how the method
presented here naturally generalizes to higher loops. | The Redshift Evolution of the Relation between Stellar Mass, Star
Formation Rate, and Gas Metallicity of Galaxies: We investigate the relation between stellar mass ($M_\star$), star formation
rate (SFR), and metallicity ($Z$) of galaxies, so called the fundamental
metallicity relation, in the galaxy sample of the Sloan Digital Sky Survey Data
Release 7. We separate the galaxies into narrow redshift bins and compare the
relation at different redshifts, and find statistically significant ($> 99$%)
evolution. We test various observational effects that might cause seeming $Z$
evolution, and find it difficult to explain the evolution of the relation only
by the observational effects. In the current sample of low redshift galaxies,
galaxies with different $M_\star$ and SFR are sampled from different redshifts,
and there is degeneracy between $M_\star$/SFR and redshift. Hence it is not
straightforward to distinguish a relation between $Z$ and SFR from a relation
between $Z$ and redshift. The separation of the intrinsic relation from the
redshift evolution effect is a crucial issue to understand evolution of
galaxies. |
The Three Hundred-NIKA2 Sunyaev-Zeldovich Large Program twin samples:
Synthetic clusters to support real observations: The simulation database of THE THREE HUNDRED Project has been used to pick
synthetic clusters of galaxies with properties close to the observational
targets of the NIKA2 camera Sunyaev-Zeldovich (SZ) Large Program.
Cross-matching of cluster parameters such as mass and redshift of the cluster
in the two databases has been implemented to generate the so-called twin
samples for the Large Program. This SZ Large Program is observing a selection
of galaxy clusters at intermediate and high redshift $\left( 0.5 < z < 0.9
\right)$, covering one order of magnitude in mass. These are SZ-selected
clusters from the Planck and Atacama Cosmology Telescope catalogs, wherein the
selection is based on their integrated Compton parameter values, $Y_{500}$: the
value of the parameter within the characteristics radius $R_{500}$.
THE THREE HUNDRED hydrodynamical simulations provide us with hundreds of
clusters satisfying these redshift, mass, and $Y_{500}$ requirements. In
addition to the standard post-processing analysis of the simulation, mock
observational maps are available mimicking X-ray, optical, gravitational
lensing, radio, and SZ observations of galaxy clusters. The primary goal of
employing the twin samples is to compare different cluster mass proxies from
synthetic X-ray, SZ effect and optical maps (via the velocity dispersion of
member galaxies and lensing $\kappa$-maps) of the clusters. Eventually, scaling
laws between different mass proxies and the cluster mass will be
cross-correlated to reduce the scatter on the inferred mass and the mass bias
will be related to various physical parameters. | Evolution of intermediate mass galaxies up to z~0.7 and studies of SNe
Ia hosts: In the first part of this manuscript, I present the results on the properties
of the interstellar medium and the stellar content of galaxies at z=0.6, from a
representative sample of distant galaxies observed with the long slit
spectrograph VLT/FORS2. This study has been realized in the framework of the
ESO large program IMAGES "Intermediate MAss Galaxy Evolution Sequences", which
aims to investigate the evolution of the main global properties of galaxies up
to z~0.9. I discuss the implications of the observed chemical enrichment of the
gas on the scenarios of galaxy formation. I also propose a new method to
estimate reliable stellar masses in starburst galaxies using broadband
photometry and their total star-formation rate.
In a second part, I present a new method to extract, with high accuracy, the
sky in spectra acquired with a fiber-fed instrument. I have developed this code
in the Framework of the phase A of an instrument proposed for the E-ELT:
OPTIMOS-EVE. This is a multi-fiber spectrograph able to observe at optical and
infrared wavelengths simultaneously.
In the third part, I show preliminary results from the CENTRA GEPI- survey at
Calar Alto Observatory to study nearby galaxies, hosts of type Ia supernovae,
using integral field spectroscopy. I present the first 2D maps of the gas and
stellar populations of SNe Ia hosts. The results allow us to directly access
the host properties in the immediate vicinity of the SNe Ia. This is a crucial
step to investigate eventual correlations between galaxy properties and SNe Ia
events and evolution, leading to systematic effects on the derivation of the
cosmological parameters. |
Impact of the primordial fluctuation power spectrum on the reionization
history: We argue that observations of the reionization history can be used as a probe
of primordial density fluctuations, particularly on small scales. Although the
primordial curvature perturbations are well constrained from measurements of
cosmic microwave background (CMB) anisotropies and large-scale structure, these
observational data probe the curvature perturbations only on large scales, and
hence its information on smaller scales will give us further insight on
primordial fluctuations. Since the formation of early galaxies is sensitive to
the amplitude of small-scale perturbations, and then, in turn, gives an impact
on the reionization history, one can probe the primordial power spectrum on
small scales through observations of reionization. In this work, we focus on
the running spectral indices of the primordial power spectrum to characterize
the small-scale perturbations, and investigate their impact on the reionization
history using the numerical code \texttt{21cmFAST}, which adopts a simple but
commonly used reionization model. We also derive the constraints on the running
spectral indices from observations of the reionization history indicated by the
luminosity function of the Lyman-$\alpha$ emitters. We show that the
reionization history, in combination with large-scale observations such as CMB,
would be a useful tool to investigate primordial density fluctuations. | Threshold Clustering Functions and Thermal Inhomogeneities in the
Lyman-Alpha Forest: We introduce to astrophysics the threshold probability functions S_2, C_2,
and D_2 first derived by \citet{torq+88}, which effectively samples the flux
probability distribution (PDF) of the Lya forest at different spatial scales.
These statistics are tested on mock Lya forest spectra based on various toy
models for HeII reionization, with homogeneous models with various
temperature-density relations as well as models with temperature
inhomogeneities. These mock samples have systematics and noise added to
simulate the latest Sloan Digital Sky Survey Data Release 7 (SDSS DR7) data. We
find that the flux PDF from SDSS DR7 can be used to constrain the
temperature-density relation $\gamma$ (where $T \propto (1 +
\Delta)^{\gamma-1}$) of the intergalactic medium (IGM) at z=2.5 to a precision
of $\Delta \gamma = 0.2$ at $\sim 4\sigma$ confidence. The flux PDF is
degenerate to temperature inhomogeneities in the IGM arising from HeII
reionization, but we find S_2 can detect these inhomogeneities at $\sim 3
\sigma$, with the assumption that the flux continuum of the Lya forest can be
determined to 9% accuracy, approximately the error from current fitting
methods. If the quasar continuum can be determined to 3% accuracy, then S_2 is
capable of constraining the characteristic scale of temperature
inhomogeneities, with $\sim 4 \sigma$ differentiation between toy models with
hot bubble radii of 50 Mpc/h and 25 Mpc/h, comoving. |
SUGAR: An improved empirical model of Type Ia Supernovae based on
spectral features: Type Ia Supernovae (SNe Ia) are widely used to measure the expansion of the
Universe. Improving distance measurements of SNe Ia is one technique to better
constrain the acceleration of expansion and determine its physical nature. This
document develops a new SNe Ia spectral energy distribution (SED) model, called
the SUpernova Generator And Reconstructor (SUGAR), which improves the spectral
description of SNe Ia, and consequently could improve the distance
measurements. This model is constructed from SNe Ia spectral properties and
spectrophotometric data from The Nearby Supernova Factory collaboration. In a
first step, a PCA-like method is used on spectral features measured at maximum
light, which allows us to extract the intrinsic properties of SNe Ia. Next, the
intrinsic properties are used to extract the average extinction curve. Third,
an interpolation using Gaussian Processes facilitates using data taken at
different epochs during the lifetime of a SN Ia and then projecting the data on
a fixed time grid. Finally, the three steps are combined to build the SED model
as a function of time and wavelength. This is the SUGAR model. The main
advancement in SUGAR is the addition of two additional parameters to
characterize SNe Ia variability. The first is tied to the properties of SNe Ia
ejecta velocity, the second is correlated with their calcium lines. The
addition of these parameters, as well as the high quality the Nearby Supernova
Factory data, makes SUGAR an accurate and efficient model for describing the
spectra of normal SNe Ia as they brighten and fade. The performance of this
model makes it an excellent SED model for experiments like ZTF, LSST or WFIRST. | New polarimetric constraints on axion-like particles: We show that the parameter space of axion-like particles can be severly
constrained using high-precision measurements of quasar polarisations. Robust
limits are derived from the measured bounds on optical circular polarisation
and from the distribution of linear polarisations of quasars. As an outlook,
this technique can be improved by the observation of objects located behind
clusters of galaxies, using upcoming space-borne X-ray polarimeters. |
The SWELLS survey. IV. Precision measurements of the stellar and dark
matter distributions in a spiral lens galaxy: We construct a fully self-consistent mass model for the lens galaxy J2141 at
z=0.14, and use it to improve on previous studies by modelling its
gravitational lensing effect, gas rotation curve and stellar kinematics
simultaneously. We adopt a very flexible axisymmetric mass model constituted by
a generalized NFW dark matter halo and a stellar mass distribution obtained by
deprojecting the MGE fit to the high-resolution K'-band LGSAO imaging data of
the galaxy, with the (spatially constant) M/L ratio as a free parameter. We
model the stellar kinematics by solving the anisotropic Jeans equations. We
find that the inner logarithmic slope of the dark halo is weakly constrained
(gamma = 0.82^{+0.65}_{-0.54}), and consistent with an unmodified NFW profile.
We infer the galaxy to have (i) a dark matter fraction within 2.2 disk radii of
0.28^{+0.15}_{-0.10}, independent of the galaxy stellar population, implying a
maximal disk for J2141; (ii) an apparently uncontracted dark matter halo, with
concentration c_{-2} = 7.7_{-2.5}^{+4.2} and virial velocity v_{vir} =
242_{-39}^{+44} km/s, consistent with LCDM predictions; (iii) a slightly oblate
halo (q_h = 0.75^{+0.27}_{-0.16}), consistent with predictions from
baryon-affected models. Comparing the stellar mass inferred from the combined
analysis (log_{10} Mstar/Msun = 11.12_{-0.09}^{+0.05}) with that inferred from
SPS modelling of the galaxies colours, and accounting for a cold gas fraction
of 20+/-10%, we determine a preference for a Chabrier IMF over Salpeter IMF by
a Bayes factor of 5.7 (substantial evidence). We infer a value beta_{z} = 1 -
sigma^2_{z}/sigma^2_{R} = 0.43_{-0.11}^{+0.08} for the orbital anisotropy
parameter in the meridional plane, in agreement with most studies of local disk
galaxies, and ruling out at 99% CL that the dynamics of this system can be
described by a two-integral distribution function. [Abridged] | Unveiling $ν$ secrets with cosmological data: neutrino masses and mass
hierarchy: Using some of the latest cosmological datasets publicly available, we derive
the strongest bounds in the literature on the sum of the three active neutrino
masses, $M_\nu$, within the assumption of a background flat $\Lambda$CDM
cosmology. In the most conservative scheme, combining Planck cosmic microwave
background (CMB) temperature anisotropies and baryon acoustic oscillations
(BAO) data, as well as the up-to-date constraint on the optical depth to
reionization ($\tau$), the tightest $95\%$ confidence level (C.L.) upper bound
we find is $M_\nu<0.151$~eV. The addition of Planck high-$\ell$ polarization
data, which however might still be contaminated by systematics, further
tightens the bound to $M_\nu<0.118$~eV. A proper model comparison treatment
shows that the two aforementioned combinations disfavor the IH at $\sim
64\%$~C.L. and $\sim 71\%$~C.L. respectively. In addition, we compare the
constraining power of measurements of the full-shape galaxy power spectrum
versus the BAO signature, from the BOSS survey. Even though the latest BOSS
full shape measurements cover a larger volume and benefit from smaller error
bars compared to previous similar measurements, the analysis method commonly
adopted results in their constraining power still being less powerful than that
of the extracted BAO signal. Our work uses only cosmological data; imposing the
constraint $M_\nu>0.06\,{\rm eV}$ from oscillations data would raise the quoted
upper bounds by ${\cal O}(0.1\sigma)$ and would not affect our conclusions. |
The Cosmic Equation of State: The cosmic spacetime is often described in terms of the FRW metric, though
the adoption of this elegant and convenient solution to Einstein's equations
does not tell us much about the equation of state, p=w rho, in terms of the
total energy density rho and pressure p of the cosmic fluid. LCDM and the
R_h=ct Universe are both FRW cosmologies that partition rho into (at least)
three components, matter rho_m, radiation rho_r, and a poorly understood dark
energy rho_de, though the latter goes one step further by also invoking the
constraint w=-1/3. This condition is required by the simultaneous application
of the Cosmological principle and Weyl's postulate. Model selection tools in
one-on-one comparisons favor R_h=ct with a likelihood of ~90% versus only ~10%
for LCDM. Nonetheless, the predictions of LCDM often come quite close to those
of R_h=ct, suggesting that its parameters are optimized to mimic the w=-1/3
equation of state. In this paper, we demonstrate that the equation of state in
R_h=ct helps us to understand why the optimized fraction Omega_m=rho_m/rho in
LCDM must be ~0.27, an otherwise seemingly random variable. We show that when
one forces LCDM to satisfy the equation of state w=(rho_r/3-rho_de)/rho, the
value of the Hubble radius today, c/H_0, can equal its measured value ct_0 only
with Omega_m~0.27 when the equation of state for dark energy is w_de=-1. This
peculiar value of Omega_m therefore appears to be a direct consequence of
trying to fit the data with the equation of state w=(rho_r/3-rho_de)/rho in a
Universe whose principal constraint is instead R_h=ct or, equivalently, w=-1/3. | Gamma-ray induced cascades and magnetic fields in intergalactic medium: We present the results of Monte-Carlo simulations of three-dimensional
electromagnetic cascade initiated by interactions of the multi-TeV gamma-rays
with the cosmological infrared/optical photon background in the intergalactic
medium. Secondary electrons in the cascade are deflected by the intergalactic
magnetic fields before they scatter on CMB photons. This leads to extended
0.1-10 degree scale emission at multi-GeV and TeV energies around extragalactic
sources of very-high-energy gamma-rays. The morphology of the extended emission
depends, in general, on the properties of magnetic fields in the intergalactic
medium. Using Monte-Carlo simulated data sets, we demonstrate that the decrease
of the size of extended source with the increase of energy allows to measure
weak magnetic fields with magnitudes in the range from < 1e-16 G to 1e-12 G if
they exist in the voids of the Large Scale Structure. |
Snowmass2021 Cosmic Frontier: Report of the CF04 Topical Group on Dark
Energy and Cosmic Acceleration in the Modern Universe: Cosmological observations in the new millennium have dramatically increased
our understanding of the Universe, but several fundamental questions remain
unanswered. This topical group report describes the best opportunities to
address these questions over the coming decades by extending observations to
the $z<6$ universe. The greatest opportunity to revolutionize our understanding
of cosmic acceleration both in the modern universe and the inflationary epoch
would be provided by a new Stage V Spectroscopic Facility (Spec-S5) which would
combine a large telescope aperture, wide field of view, and high multiplexing.
Such a facility could simultaneously provide a dense sample of galaxies at
lower redshifts to provide robust measurements of the growth of structure at
small scales, as well as a sample at redshifts $2<z<5$ to measure cosmic
structure at the largest scales, spanning a sufficient volume to probe
primordial non-Gaussianity from inflation, to search for features in the
inflationary power spectrum on a broad range of scales, to test dark energy
models in poorly-explored regimes, and to determine the total neutrino mass and
effective number of light relics. A number of compelling opportunities at
smaller scales should also be pursued alongside Spec-S5. The science
collaborations analyzing DESI and LSST data will need funding for a variety of
activities, including cross-survey simulations and combined analyses. The
results from these experiments can be greatly improved by smaller programs to
obtain complementary data, including follow-up studies of supernovae and
spectroscopy to improve photometric redshift measurements. The best future use
of the Vera C. Rubin Observatory should be evaluated later this decade after
the first LSST analyses have been done. Finally, investments in pathfinder
projects could enable powerful new probes of cosmology to come online in future
decades. | Eternal Hilltop Inflation: We consider eternal inflation in hilltop-type inflation models, favored by
current data, in which the scalar field in inflation rolls off of a local
maximum of the potential. Unlike chaotic or plateau-type inflation models, in
hilltop inflation the region of field space which supports eternal inflation is
finite, and the expansion rate $H_{EI}$ during eternal inflation is almost
exactly the same as the expansion rate $H_*$ during slow roll inflation.
Therefore, in any given Hubble volume, there is a finite and calculable
expectation value for the lifetime of the "eternal" inflation phase, during
which quantum flucutations dominate over classical field evolution. We show
that despite this, inflation in hilltop models is nonetheless eternal in the
sense that the volume of the spacetime at any finite time is exponentially
dominated by regions which continue to inflate. This is true regardless of the
energy scale of inflation, and eternal inflation is supported for inflation at
arbitrarily low energy scale. |
Exploring the Intergalactic Magnetic Field by Means of Faraday
Tomography: Unveiling the intergalactic magnetic field (IGMF) in filaments of galaxies is
a very important and challenging subject in modern astronomy. In order to probe
the IGMF from rotation measures (RMs) of extragalactic radio sources, we need
to separate RMs due to other origins such as the source, intervening galaxies,
and our Galaxy. In this paper, we discuss observational strategies for the
separation by means of Faraday tomography (Faraday RM Synthesis). We consider
an observation of a single radio source such as a radio galaxy or a quasar
viewed through the Galaxy and the cosmic web. We then compare the observation
with another observation of a neighbor source with a small angular separation.
Our simulations with simple models of the sources suggest that it would be not
easy to detect the RM due to the IGMF of order ~ 1 rad/m/m, an expected value
for the IGMF through a single filament. Contrary to it, we find that the RM of
at least ~10 rad/m/m could be detected with the SKA or its
pathfinders/precursors, if we achieve selections of ideal sources. These
results would be improved if we incorporate decomposition techniques such as
RMCLEAN and QU-fitting. We discuss feasibility of the strategies for cases with
complex Galactic emissions as well as with effects of observational noise and
radio frequency interferences. | Long-term variability of radio-bright BL Lacertae objects: Radio-bright BL Lacertae objects (BLOs) are typically variable and exhibit
prominent flaring. We use a sample of 24 BLOs to get a clear idea of their
flaring behavior and to find possible commonalities in their variability
patterns. Our goal was to compare the results given by computational time
scales and the observed variability parameters determined directly from the
flux curves. Also, we wanted to find out if the BLO flares adhere to the
generalized shock model. We use long-term monitoring data from 4.8, 8, 14.5,
22, 37, 90 and 230 GHz. The structure function, discrete correlation function
and Lomb-Scargle periodogram time scales, calculated in a previous study, are
analyzed in more detail. We determine flare durations, rise and decay times,
absolute and relative peak fluxes from the monitoring data. We find that BLOs
demonstrate a wide range of variability behavior. BLOs include sources with
fast and strong variability, such as OJ 287, PKS 1749+096 and BL Lac, but also
sources with more rolling fluctuations like PKS 0735+178. The most extreme
flares can last for up to 13 years or have peak fluxes of approximately 12 Jy
in the observer's frame. When the Doppler boosting effect is taken into
account, the peak flux of a flare does not depend on the duration of the flare.
A rough analysis of the time lags and peak flux evolution indicates that BLO
flares in the mm - cm wavelengths are high-peaking, i.e., are in the adiabatic
stage. Thus, the results concur with the generalized shock model. |
A new approach to cosmological structure formation with massive
neutrinos: We show how Newtonian cosmological simulations can be employed to investigate
the non-linear evolution of two particle species in a relativistic context. We
discuss the application for massive neutrinos and other multi-species systems
such as Cold Dark Matter (CDM) plus baryons or Warm Dark Matter (WDM). We
propose a method that allows us to perform simulations including massive
neutrinos and general relativistic effects at almost the same computational
cost as ordinary CDM only N-body simulations, employing tailor-made initial
conditions and a dictionary for the interpretation of the simulation output. | Minding the MeV Gap: the Indirect Detection of Low Mass Dark Matter: We consider the prospects for the indirect detection of low mass dark matter
which couples dominantly to quarks. If the center of mass energy is below about
280 MeV, the kinematically allowed final states will be dominated by photons
and neutral pions, producing striking signatures at gamma ray telescopes. In
fact, an array of new instruments have been proposed, which would greatly
improve sensitivity to photons in this energy range. We find that planned
instruments can improve on current sensitivity to dark matter models of this
type by up to a few orders of magnitude. |
Non-Gaussianity from Self-Ordering Scalar Fields: The Universe may harbor relics of the post-inflationary epoch in the form of
a network of self-ordered scalar fields. Such fossils, while consistent with
current cosmological data at trace levels, may leave too weak an imprint on the
cosmic microwave background and the large-scale distribution of matter to allow
for direct detection. The non-Gaussian statistics of the density perturbations
induced by these fields, however, permit a direct means to probe for these
relics. Here we calculate the bispectrum that arises in models of self-ordered
scalar fields. We find a compact analytic expression for the bispectrum,
evaluate it numerically, and provide a simple approximation that may be useful
for data analysis. The bispectrum is largest for triangles that are aligned
(have edges $k_1\simeq 2 k_2 \simeq 2 k_3$) as opposed to the local-model
bispectrum, which peaks for squeezed triangles ($k_1\simeq k_2 \gg k_3$), and
the equilateral bispectrum, which peaks at $k_1\simeq k_2 \simeq k_3$. We
estimate that this non-Gaussianity should be detectable by the Planck satellite
if the contribution from self-ordering scalar fields to primordial
perturbations is near the current upper limit. | Dynamo in the Intra-Cluster Medium: Simulation of CGL-MHD Turbulent
Dynamo: The standard magnetohydrodynamic (MHD) description of the plasma in the hot,
magnetized gas of the intra-cluster (ICM) medium is not adequate because it is
weakly collisional. In such collisionless magnetized gas, the microscopic
velocity distribution of the particles is not isotropic, giving rise to kinetic
effects on the dynamical scales. These kinetic effects could be important in
understanding the turbulence, as so as the amplification and maintenance of the
magnetic fields in the ICM. It is possible to formulate fluid models for
collisonless or weakly collisional gas by introducing modifications in the MHD
equations. These models are often referred as kinetic MHD (KMHD). Using a KMHD
model based on the CGL-closure, which allows the adiabatic evolution of the two
components of the pressure tensor (the parallel and perpendicular components
with respect to the local magnetic field), we performed 3D numerical
simulations of forced turbulence in order to study the amplification of an
initially weak seed magnetic field. We found that the growth rate of the
magnetic energy is comparable to that of the ordinary MHD turbulent dynamo, but
the magnetic energy saturates in a level smaller than of the MHD case. We also
found that a necessary condition for the dynamo works is to impose limits to
the anisotropy of the pressure. |
Studying the interstellar medium of HII/BCD galaxies using IFU
spectroscopy: We review the results from our studies, and previous published work, on the
spatially resolved physical properties of a sample of HII/BCD galaxies, as
obtained mainly from integral-field unit spectroscopy with Gemini/GMOS and
VLT/VIMOS. We confirm that, within observational uncertainties, our sample
galaxies show nearly spatially constant chemical abundances, similar to other
low-mass starburst galaxies. They also show He II 4686 emission with properties
being suggestive of a mix of excitation sources, with Wolf-Rayet stars being
excluded as the primary one. Finally, in this contribution we include a list of
all HII/BCD galaxies studied thus far with integral-field unit spectroscopy. | Hubble Hullabaloo and String Cosmology: The discrepancy in measurements of the Hubble constant indicates new physics
in dark energy, dark matter, or both. Drawing inspiration from string theory,
we explore possible solutions to overcome the $H_0$ problem. We investigate the
interplay between the cosmological determination of $\Delta N_{\rm eff}{}$ and
$Z'{}$ searches at the LHC Run3. |
Scale-invariant Helical Magnetic Fields from Inflation: We discuss a model which can generate scale-invariant helical magnetic fields
on large scales ($\lesssim 1$Mpc) in the primordial universe. It is also shown
that the electric conductivity becomes significant and terminates
magnetogenesis even before reheating is completed. By solving the
electromagnetic dynamics taking conductivity into account, we find that
magnetic fields with amplitude $B\simeq 10^{-15}{\rm G}$ at present can be
generated without encountering a backreaction or strong coupling problem. | The duration of reionization constrains the ionizing sources: We investigate how the nature of the galaxies that reionized the Universe
affects the duration of reionization. We contrast two sets of models: one in
which galaxies on the faint side of the luminosity function dominate the
ionizing emissivity, and a second in which the galaxies on the bright side of
the luminosity function dominate. The faint-end of the luminosity function
evolves slowly, therefore the transition from mostly neutral to mostly ionized
state takes a much longer time in the first set of models compared to the
second. Existing observational constraints on the duration of this transition
are relatively weak, but taken at face value prefer the model in which galaxies
on the bright side play a major role. Measurements of the kinetic Sunyaev
Zeldovich effect in the cosmic microwave background from the epoch of
reionization also point in the same direction. |
Kinematics of the intermediate mass black hole candidate HLX-1: We studied the optical spectrum of HLX-1 during its latest outburst, using
the FORS2 spectrograph on the Very Large Telescope. We detect an Halpha
emission line centered at lambda = (6718.9 +/- 0.9) Ang and find that its
projected radial velocity with respect to the nucleus of ESO243-49 is (424 +/-
27) km/s, while the maximum rotational velocity of the stars in that galaxy is
~209 km/s. This suggests that HLX-1 and its surrounding stars were not formed
in situ, but came either from a disrupted dwarf galaxy or from a nuclear
recoil. We also find that the Halpha emission line is resolved with full width
at half maximum ~400 km/s, suggesting a nebular rather than disk origin for the
emission. Its luminosity (L_{Halpha} ~ a few 10^{37} erg/s, equivalent width
~70 Ang) is also consistent with emission from a nebula photo-ionized by HLX-1. | Probing Ultralight Tensor Dark Matter with the Stochastic
Gravitational-Wave Background from Advanced LIGO and Virgo's First Three
Observing Runs: Ultralight bosons are attractive dark-matter candidates and appear in various
scenarios beyond standard model. They can induce superradiant instabilities
around spinning black holes (BHs), extracting the energy and angular momentum
from BHs, and then dissipated through monochromatic gravitational radiation,
which become promising sources of gravitational wave detectors. In this letter,
we focus on massive tensor fields coupled to BHs and compute the stochastic
gravitational wave backgrounds emitted by these sources. We then undertake a
search for this background within the data from LIGO/Virgo O1$\sim$ O3 runs.
Our analysis reveals no discernible evidence of such signals, allowing us to
impose stringent limits on the mass range of tensor bosons. Specifically, we
exclude the existence of tensor bosons with masses ranging from
$4.0\times10^{-14}$ to $2.0\times10^{-12}$ eV at $95\%$ confidence level. |
Non-Extensive Statistics, New Solution to the Cosmological Lithium
Problem: In the primordial Big Bang nucleosynthesis (BBN), only the lightest nuclides
(D, $^3$He, $^4$He, and $^7$Li) were synthesized in appreciable quantities, and
these relics provide us a unique window on the early universe. Currently, BBN
simulations give acceptable agreement between theoretical and observed
abundances of D and $^4$He, but it is still difficult to reconcile the
predicted $^7$Li abundance with the observation for the Galactic halo stars.
The BBN model overestimates the primordial $^7$Li abundance by about a factor
of three, so called the cosmological lithium problem, a long-lasting pending
issue in BBN. Great efforts have been paid in the past decades, however, the
conventional nuclear physics seems unable to resolve such problem. It is
well-known that the classical Maxwell-Boltzmann (MB) velocity distribution has
been usually assumed for nuclei in the Big-Bang plasma. In this work, we have
thoroughly investigated the impact of non-extensive Tsallis statistics
(deviating from the MB) on thermonuclear reaction rates involved in standard
models of BBN. It shows that the predicted primordial abundances of D, $^4$He,
and $^7$Li agree very well with those observed ones by introducing a
non-extensive parameter $q$. It is discovered that the velocities of nuclei in
a hot Big-Bang plasma indeed violate the classical Maxwell-Boltzmann (MB)
distribution in a very small deviation of about 6.3--8.2%. Thus, we have for
the first time found a new solution to the cosmological lithium problem without
introducing any mysterious theories. Furthermore, the implications of
non-extensive statistics in other exotic high-temperature and density
astrophysical environments should be explored, which might offer new insight
into the nucleosynthesis of heavy elements. | Cosmology with Standard Sirens at Cosmic Noon: Gravitational waves (GWs) directly measure the luminosity distance to the
merger, which, when combined with an independent measurement of the source's
redshift, provides a novel probe of cosmology. The proposed next generation of
ground-based GW detectors, Einstein Telescope and Cosmic Explorer, will detect
tens of thousands of binary neutron stars (BNSs) out to cosmological distances
($z>2$), beyond the peak of the star formation rate (SFR), or "cosmic noon." At
these distances, it will be challenging to measure the sources' redshifts by
observing electromagnetic (EM) counterparts or statistically marginalizing over
a galaxy catalog. In the absence of an EM counterpart or galaxy catalog, Ding
et al. showed that theoretical priors on the merger redshift distribution can
be used to infer parameters in a $w$CDM cosmology. We argue that in the BNS
case, the redshift distribution will be measured by independent observations of
short gamma ray bursts (GRBs), kilonovae, and known BNS host galaxies. We show
that, in addition to measuring the background cosmology, this method can
constrain the effects of dark energy on modified GW propagation. We consider
the simple case in which the BNS rate is \textit{a priori} known to follow the
SFR. If the SFR is perfectly known, $\mathcal{O}(10,000)$ events (to be
expected within a year of observation with Cosmic Explorer) would yield a
sub-tenth percent measurement of the combination $H_0^{2.8}\Omega_M$. Fixing
$H_0$ and $\Omega_M$, this method may enable a 5\% measurement of the dark
energy equation of state parameter. Fixing the background cosmology and probing
modified GW propagation, the running of the Planck mass parameter $c_M$ may be
measured to $\pm0.02$. Although realistically, the redshift evolution of the
merger rate will be uncertain, prior knowledge of the peak redshift will
provide valuable information for standard siren analyses. |
A torsion-balance search for ultra low-mass bosonic dark matter: We used a stationary torsion balance with a beryllium-aluminum composition
dipole to search for ultra low-mass bosonic dark matter coupled to baryon minus
lepton number. We set 95% confidence limits on the coupling constant $g_{\rm
B-L}$ for bosons with masses between $10^{-18}$ and $10^{-16}$ eV/$c^2$ with
the best performance at $m_{\rm DM} = 8\times 10^{-18}$ eV/$c^2$ constraining
$g_{B-L}(\hbar c)^{-1/2} < 1 \times 10^{-25}$. This provides a complimentary
limit to equivalence-principle experiments that search for ultra low-mass
bosons as force-mediating particles. | The eccentricity distribution of compact binaries: The current gravitational wave detectors have reached their operational
sensitivity and are nearing detection of compact object binaries. In the coming
years, we expect that the Advanced LIGO/VIRGO will start taking data. At the
same time, there are plans for third generation ground-based detectors such as
the Einstein Telescope, and space detectors such as DECIGO. We discuss the
eccentricity distribution of inspiral compact object binaries during they
inspiral phase. We analyze the expected distributions of eccentricities at
three frequencies that are characteristic of three future detectors: Advanced
LIGO/VIRGO (30 Hz), Einstein Telescope (3 Hz), and DECIGO (0.3 Hz). We use the
StarTrack binary population code to investigate the properties of the
population of compact binaries in formation. We evolve their orbits until the
point that they enter a given detector sensitivity window and analyze the
eccentricity distribution at that time. We find that the eccentricities of
BH-BH and BH-NS binaries are quite small when entering the Advanced LIGO/VIRGO
detector window for all considered models of binary evolution. Even in the case
of the DECIGO detector, the typical eccentricities of BH-BH binaries are below
10^{-4}, and the BH-NS eccentricities are smaller than 10^{-3}. Some fraction
of NS-NS binaries may have significant eccentricities. Within the range of
considered models, we found that a fraction of between 0.2% and 2% NS-NS
binaries will have an eccentricity above 0.01 for the Advanced LIGO/VIRGO
detectors. For the ET detector, this fraction is between 0.4% and 4%, and for
the DECIGO detector it lies between 2% and 27%. |
The Atacama Cosmology Telescope: Weighing distant clusters with the most
ancient light: We use gravitational lensing of the cosmic microwave background (CMB) to
measure the mass of the most distant blindly-selected sample of galaxy clusters
on which a lensing measurement has been performed to date. In CMB data from the
the Atacama Cosmology Telescope (ACT) and the Planck satellite, we detect the
stacked lensing effect from 677 near-infrared-selected galaxy clusters from the
Massive and Distant Clusters of WISE Survey (MaDCoWS), which have a mean
redshift of $ \langle z \rangle = 1.08$. There are no current optical weak
lensing measurements of clusters that match the distance and average mass of
this sample. We detect the lensing signal with a significance of $4.2 \sigma$.
We model the signal with a halo model framework to find the mean mass of the
population from which these clusters are drawn. Assuming that the clusters
follow Navarro-Frenk-White density profiles, we infer a mean mass of $\langle
M_{500c}\rangle = \left(1.7 \pm 0.4 \right)\times10^{14}\,\mathrm{M}_\odot$. We
consider systematic uncertainties from cluster redshift errors, centering
errors, and the shape of the NFW profile. These are all smaller than 30% of our
reported uncertainty. This work highlights the potential of CMB lensing to
enable cosmological constraints from the abundance of distant clusters
populating ever larger volumes of the observable Universe, beyond the
capabilities of optical weak lensing measurements. | Testing cosmological models using relative mass-redshift abundance of SZ
clusters: Recent detection of high-redshift, massive clusters through
Sunyaev-Zel'dovich observations has opened up a new way to test cosmological
models. It is known that detection of a single supermassive cluster at a very
high redshift can rule out many cosmological models all together. However,
since dealing with different observational biases makes it difficult to test
the likeliness of the data assuming a cosmological model, most of the cluster
data (except those with high mass-redshift) stays untouched in confronting
cosmological models with cluster observations. We propose here that one can use
the relative abundance of the clusters with different masses at different
redshifts to test the likeliness of the data in the context of cosmological
models. For this purpose we propose a simple parametric form for the efficiency
of observing clusters at different mass-redshift and we test if the standard
LCDM model can explain the observed abundance of the clusters using this
efficiency parameterization. We argue that one cannot expect an unusual and
highly parametric form of the efficiency function to fit the observed data
assuming a theoretical model. Using many realizations of Monte Carlo
simulations we show that the standard spatially flat LCDM model is barely
consistent with the SPT cluster data using a simple and plausible
two-dimensional efficiency function for detection of the clusters. More cluster
data are needed to make any strong conclusion. |
Eternal Inflation and the Refined Swampland Conjecture: I apply recently proposed "Swampland" conjectures to eternal inflation in
single-scalar field theories. Eternal inflation is a phase of infinite
self-reproduction of a quasi-de Sitter universe which has been argued to be a
generic consequence of cosmological inflation. The originally proposed de
Sitter swampland conjectures were shown by Matsui and Takahashi and by
Dimopoulos to be generically incompatible with eternal inflation. However, the
more recently proposed "refined" swampland conjecture imposes a slightly weaker
criterion on the scalar field potential in inflation, and is consistent with
the existence of a tachyonic instability. In this paper, I show that eternal
inflation is marginally consistent with the refined de Sitter swampland
conjecture. Thus, if the refined conjecture is correct, the existence of a
landscape-based "multiverse" in string theory is not incompatible with a
self-consistent ultraviolet completion, with significant consequences for model
building in string theory. | Metal Abundances in the Cool-Cores of Galaxy Clusters: We use XMM-Newton data to carry out a detailed study of the Si, Fe and Ni
abundances in the cool cores of a representative sample of 26 local clusters.
We have performed a careful evaluation of the systematic uncertainties related
to the instruments, the plasma codes and the spectral modeling finding that the
major source of uncertainty is in the plasma codes. Our Si, Fe, Ni, Si/Fe and
Ni/Fe distributions feature only moderate spreads (from 20% to 30%) around
their mean values strongly suggesting similar enrichment processes at work in
all our cluster cores. Our sample averaged Si/Fe ratio is comparable to those
measured in samples of groups and high luminosity ellipticals implying that the
enrichment process in ellipticals, dominant galaxies in groups and BCGs in
clusters is quite similar. Although our Si/Fe and Ni/Fe abundance ratios are
fairly well constrained, the large uncertainties in the supernovae yields
prevent us from making a firm assessment of the relative contribution of type
Ia and core-collapsed supernovae to the enrichment process. All that can really
be said with some certainty is that both contribute to the enrichment of
cluster cores. |
Constraining primordial black hole masses with the isotropic gamma ray
background: Primordial black holes can represent all or most of the dark matter in the
window $10^{17}-10^{22}\,$g. Here we present an extension of the constraints on
PBHs of masses $10^{13}-10^{18}\,$g arising from the isotropic diffuse gamma
ray background. Primordial black holes evaporate by emitting Hawking radiation
that should not exceed the observed background. Generalizing from monochromatic
distributions of Schwarzschild black holes to extended mass functions of Kerr
rotating black holes, we show that the lower part of this mass window can be
closed for near-extremal black holes. | Fine-structure constant constraints on dark energy: We use astrophysical and atomic clock tests of the stability of the
fine-structure constant $\alpha$, together with Type Ia supernova and Hubble
parameter data, to constrain the simplest class of dynamical dark energy models
where the same degree of freedom is assumed to provide both the dark energy and
(through a dimensionless coupling, $\zeta$, to the electromagnetic sector) the
$\alpha$ variation. We show how current data tightly constrains a combination
of $\zeta$ and the dark energy equation of state $w_0$. At the $95\%$
confidence level and marginalizing over $w_0$ we find $|\zeta|<5\times10^{-6}$,
with the atomic clock tests dominating the constraints. The forthcoming
generation of high-resolution ultra-stable spectrographs will enable
significantly tighter constraints. |
Dynamically generated inflationary two-field potential via
non-Riemannian volume forms: We consider a simple model of modified gravity interacting with a single
scalar field $\varphi$ with weakly coupled exponential potential within the
framework of non-Riemannian spacetime volume-form formalism. The specific form
of the action is fixed by the requirement of invariance under global Weyl-scale
symmetry. Upon passing to the physical Einstein frame we show how the
non-Riemannian volume elements create a second canonical scalar field $u$ and
dynamically generate a non-trivial two-scalar-field potential $U_{\rm
eff}(u,\varphi)$ with two remarkable features: (i) it possesses a large flat
region for large $u$ describing a slow-roll inflation; (ii) it has a stable
low-lying minimum w.r.t. $(u,\varphi)$ representing the dark energy density in
the "late universe". We study the corresponding two-field slow-roll inflation
and show that the pertinent slow-roll inflationary curve $\varphi = \varphi(u)$
in the two-field space $(u,\varphi)$ has a very small curvature, i.e.,
$\varphi$ changes very little during the inflationary evolution of $u$ on the
flat region of $U_{\rm eff}(u,\varphi)$. Explicit expressions are found for the
slow-roll parameters which differ from those in the single-field inflationary
counterpart. Numerical solutions for the scalar spectral index and the
tensor-to-scalar ratio are derived agreeing with the observational data. | Cosmological Implications of the CMB Large-scale Structure: WMAP and Planck may have uncovered several anomalies in the full CMB sky that
could indicate possible new physics driving the growth of density fluctuations
in the early Universe. These include an unusually low power at the largest
scales and an apparent alignment of the quadrupole and octopole moments. In
LCDM, the quadrupole and octopole moments should be statistically independent.
These low probability features may simply be due to posterior selections from
many such possible effects. If this is not the case, however, their combined
statistical significance would be equal to the product of their individual
significances. Ignoring the biasing due to posterior selection, the missing
large-angle correlations would have a probability as low as ~0.1% and the low-l
multipole alignment would be unlikely at the ~4.9% level; under the least
favourable conditions, their simultaneous observation in the context of the
standard model could then be likely at only the ~0.005% level. In this paper,
we explore the possibility that these features are indeed anomalous, and show
that the corresponding probability of CMB multipole alignment in the R_h=ct
Universe would then be ~7-10%, depending on the number of large-scale
Sachs-Wolfe induced fluctuations. Since the low power at the largest spatial
scales is reproduced in this cosmology without the need to invoke cosmic
variance, the overall likelihood of observing both of these features in the CMB
is > 7%, much more likely than in LCDM. The key physical ingredient responsible
for this difference is the existence in the former of a maximum fluctuation
size at the time of recombination, which is absent in the latter because of
inflation. |
Physical Conditions of the Gas in an ALMA [CII]-identified Submillimetre
Galaxy at z = 4.44: We present CO(2-1) observations of the submillimetre galaxy ALESS65.1
performed with the Australia Telescope Compact Array at 42.3 GHz. A previous
ALMA study of submillimetre galaxies in the Extended Chandra Deep Field South
detected [CII] 157.74 micron emission from this galaxy at a redshift of z =
4.44. No CO(2-1) emission was detected but we derive a firm upper limit to the
cold gas mass in ALESS65.1 of M_gas < 1.7 x 10^10 M_odot. The estimated gas
depletion timescale is <50 Myr, which is similar to other high redshift SMGs,
and consistent with z > 4 SMGs being the likely progenitors of massive
red-and-dead galaxies at z > 2. The ratio of the [CII], CO and far-infrared
luminosities implies a strong far-ultraviolet field of G_0 > 10^3, as seen in
Galactic star forming regions or local ULIRGs. The observed L_[CII]/L_FIR = 2.3
x 10^{-3} is high compared to local ULIRGs and, combined with L_[CII]/L_CO >
2700, it is consistent with ALESS65.1 either having an extended (several kpc)
[CII] emitting region or lower than solar metallicity. | $Euclid$ preparation: XV. Forecasting cosmological constraints for the
$Euclid$ and CMB joint analysis: The combination and cross-correlation of the upcoming $Euclid$ data with
cosmic microwave background (CMB) measurements is a source of great expectation
since it will provide the largest lever arm of epochs, ranging from
recombination to structure formation across the entire past light cone. In this
work, we present forecasts for the joint analysis of $Euclid$ and CMB data on
the cosmological parameters of the standard cosmological model and some of its
extensions. This work expands and complements the recently published forecasts
based on $Euclid$-specific probes, namely galaxy clustering, weak lensing, and
their cross-correlation. With some assumptions on the specifications of current
and future CMB experiments, the predicted constraints are obtained from both a
standard Fisher formalism and a posterior-fitting approach based on actual CMB
data. Compared to a $Euclid$-only analysis, the addition of CMB data leads to a
substantial impact on constraints for all cosmological parameters of the
standard $\Lambda$-cold-dark-matter model, with improvements reaching up to a
factor of ten. For the parameters of extended models, which include a
redshift-dependent dark energy equation of state, non-zero curvature, and a
phenomenological modification of gravity, improvements can be of the order of
two to three, reaching higher than ten in some cases. The results highlight the
crucial importance for cosmological constraints of the combination and
cross-correlation of $Euclid$ probes with CMB data. |
Observational constraints on loop quantum cosmology: In the inflationary scenario of loop quantum cosmology in the presence of
inverse-volume corrections, we give analytic formulas for the power spectra of
scalar and tensor perturbations convenient to compare with observations. Since
inverse-volume corrections can provide strong contributions to the running
spectral indices, inclusion of terms higher than the second-order runnings in
the power spectra is crucially important. Using the recent data of cosmic
microwave background and other cosmological experiments, we place bounds on the
quantum corrections. | New estimates of the deceleration parameter in weak gravity: We consider weak gravity at accelerations $\alpha<a_H$ when Rindler and
cosmological horizon collude at $R_H=c/H$, where $c$ is the velocity of light
and $H$ is the Hubble parameter. This is manifest in reduced inertia $m$, below
the value $m_0$ in Newtonian gravity. Striking evidence for a sharp transition
to weak gravity is found in galaxy rotation curves. Their sensitivity to the
cosmological background is expressed by correlations to the deceleration
parameter $q=1-(4\pi a_0/cH)^{2}$ and $q=-1/2 -3
(\Omega_b/\sqrt{2}\sqrt{\pi})^{1/2}$, where $a_0$ is Milgrom's scale in the
baryonic Tully-Fisher relation of spiral galaxies and $\Omega_b$ is the
baryonic matter density. The Planck value $\Omega_b=0.048$ with $H\simeq 73$ km
s$^{-1}$ Mpc$^{-1}$ shows $q\simeq-0.85$. Future surveys may determine
$Q_0=\left.dq(z)/dz\right|_{z=0}$ to provide a direct test for dynamical dark
energy ($Q_0>2.5$) versus $\Lambda$CDM ($Q_0<1$). |
The Hubble constant and dark energy: The Hubble Constant measured from the anisotropy in the cosmic microwave
background (CMB) is shown to be independent of small changes from the standard
model of the redshift dependence of dark energy. Modifications of the Friedmann
equation to include phantom power (w < -1), textures (w = -2/3) and curvature
are considered, and constraints on these dark energy contributors from
supernova observations are derived. Modified values for the density of matter
inferred from cosmic density perturbations and from the CMB under these
circumstances are also estimated, as exemplified by 2df and SDSS. | Searching for the signature of radiative line driving: On the absence of
Ly-alpha-N V line-locking features in a large sample of BALQSOs: We have searched the hybrid BALQSO catalogue of Scaringi et al. derived from
DR5 of the SDSS in order to compile the largest sample of objects displaying
spectral signatures which may be indicative of radiative line driving. The
feature in question is the "ghost of Ly-alpha", a line-locking feature
previously identified in the broad C IV and Si IV absorption lines of a small
fraction of BALQSOs, and formed via the interaction of Ly-alpha photons with N
V ions. We test, where possible the criteria required to produce an observable
ghost feature and find that these criteria are not met significantly more often
in ghost-candidates than in a comparison sample chosen to exhibit relatively
featureless broad absorption troughs. Indeed, the only significant differences
we find between our ghost-candidate and comparison samples, is that on average,
our ghost-candidate sample displays (i) significantly stronger N V absorption,
and (ii) the onset of absorption occurs at lower velocities in our
ghost-candidate objects. Significantly, we find no evidence for an excess of
objects whose absorption troughs bracket the location of the Ly-alpha-N V
line-locking region, rather the location of ghost-like features appears to be
independent of any systematic velocity. Thus, the majority of objects
identified here as strong ghost-candidates are likely multi-trough interlopers
whose absorption feature simply bracket the region of interest. |
Can giant radio halos probe the merging rate of galaxy clusters?: Radio and X-ray observations of galaxy clusters probe a direct link between
cluster mergers and giant radio halos (RH), suggesting that these sources can
be used as probes of the cluster merging rate with cosmic time. In this paper
we carry out an explorative study that combines the observed fractions of
merging clusters (fm) and RH (fRH) with the merging rate predicted by
cosmological simulations and attempt to infer constraints on merger properties
of clusters that appear disturbed in X-rays and of clusters with RH. We use
morphological parameters to identify merging systems and analyze the currently
largest sample of clusters with radio and X-ray data (M500>6d14 Msun, and
0.2<z<0.33, from the Planck SZ cluster catalogue). We found that in this sample
fm~62-67% while fRH~44-51%. The comparison of the theoretical f_m with the
observed one allows to constrain the combination (xi_m,tau_m), where xi_m and
tau_m are the minimum merger mass ratio and the timescale of merger-induced
disturbance. Assuming tau_m~ 2-3 Gyr, as constrained by simulations, we find
that the observed f_m matches the theoretical one for xi_m~0.1-0.18. This is
consistent with optical and near-IR observations of clusters in the sample
(xi_m~0.14-0.16). The fact that RH are found only in a fraction of merging
clusters may suggest that merger events generating RH are characterized by
larger mass ratio; this seems supported by optical/near-IR observations of RH
clusters in the sample (xi_min~0.2-0.25). Alternatively, RH may be generated in
all mergers but their lifetime is shorter than \tau_m (by ~ fRH/fm). This is an
explorative study, however it suggests that follow up studies using the
forthcoming radio surveys and adequate numerical simulations have the potential
to derive quantitative constraints on the link between cluster merging rate and
RH at different cosmic epochs and for different cluster masses. | Reconstruction of Power Spectrum of Primordial Curvature Perturbations
on small scales from Primordial Black Hole Binaries scenario of LIGO/VIRGO
detection: As a candidate bound for the Binary Black Hole (BBH) merger events detected
by LIGO/Virgo, Primordial Black Holes (PBHs) provide a useful tool to
investigate the primordial curvature perturbations on small scales. Using the
GWTC-1 to GWTC-3 catalogs, under the scenario that PBHs originate from large
primordial curvature perturbations on small scales during inflationary epoch,
we for the first time reconstruct the power spectrum of primordial curvature
perturbations on small scales. It is found that the value of the amplitude of
the primordial power spectrum is enhanced to $\mathcal{O}(10^{-2})$ on scales
$\mathcal{O}(1)$ pc. This may imply the validity of PBH as a possible BBH
merger candidate. |
Galaxy Zoo: The fundamentally different co-evolution of supermassive
black holes and their early- and late-type host galaxies: We use data from the Sloan Digital Sky Survey and visual classifications of
morphology from the Galaxy Zoo project to study black hole growth in the nearby
Universe (z < 0.05) and to break down the AGN host galaxy population by color,
stellar mass and morphology. We find that black hole growth at luminosities
L_OIII >1E40 erg/s in early- and late-type galaxies is fundamentally different.
AGN host galaxies as a population have a broad range of stellar masses
(1E10-1E11 Msun), reside in the green valley of the color-mass diagram and
their central black holes have median masses around 1E6.5 Msun. However, by
comparing early- and late-type AGN host galaxies to their non-active
counterparts, we find several key differences: in early-type galaxies, it is
preferentially the galaxies with the least massive black holes that are
growing, while late-type galaxies, it is preferentially the most massive}black
holes that are growing. The duty cycle of AGN in early-type galaxies is
strongly peaked in the green valley below the low-mass end (1E10 Msun) of the
red sequence at stellar masses where there is a steady supply of blue cloud
progenitors. The duty cycle of AGN in late-type galaxies on the other hand
peaks in massive (1E11 Msun) green and red late-types which generally do not
have a corresponding blue cloud population of similar mass. At high Eddington
ratios (L/L_Edd > 0.1), the only population with a substantial fraction of AGN
are the low-mass green valley early-type galaxies. Finally, the Milky Way
likely resides in the "sweet spot" on the color-mass diagram where the AGN duty
cycle of late-type galaxies is highest. We discuss the implications of these
results for our understanding of the role of AGN in the evolution of galaxies | Japanese Cosmic Dawn/Epoch of Reionization Science with the Square
Kilometre Array: Cosmic reionization is known to be a major phase transition of the gas in the
Universe. Since astronomical objects formed in the early Universe, such as the
first stars, galaxies and black holes, are expected to have caused cosmic
reionization, the formation history and properties of such objects are closely
related to the reionization process. In spite of the importance of exploring
reionization, our understandings regarding reionization is not sufficient yet.
Square Kilometre Array (SKA) is a next-generation large telescope that will be
operated in the next decade. Although several programs of next-generation
telescopes are currently scheduled, the SKA will be the unique telescope with a
potential to directly observe neutral hydrogen up to z~30, and provide us with
valuable information on the Cosmic Dawn (CD) and the Epoch of Reionization
(EoR). The early science with the SKA will start in a few years; it is thus the
time for us to elaborate a strategy for CD/EoR Science with the SKA. The
purpose of this document is to introduce Japanese scientific interests in the
SKA project and to report results of our investigation. |
Concerning the Slope of the Cepheid Period-Luminosity Relation: We discuss the impact of possible differences in the slope of the Cepheid
Period-Luminosity relation on the determination of extragalactic distances in
the context of recent studies that suggest changes in this slope. We show that
the Wesenheit function W = V - R x ((V-I), widely used for the determination of
Cepheid distances, is expected to be highly insensitive to changes in the slope
of the underlying (monochromatic) Period-Luminosity (PL) relations. This occurs
because the reddening trajectories in the color-magnitude plane are closely
parallel to lines of constant period. As a result W-based Period-Luminosity
relations have extremely low residual dispersion, which is because differential
(and total line-of-sight) reddening is eliminated in the definition of W and
the residual scatter due to a star's intrinsic color/position within the
Cepheid is also largely insensitive to W. Basic equations are presented and
graphically illustrated, showing the insensitivity of W to changes in the
monochromatic PL relations. | Discovery of a Rich Cluster at z = 1.63 using the Rest-Frame 1.6um
"Stellar Bump Sequence" Method: We present a new two-color algorithm, the "Stellar Bump Sequence" (SBS), that
is optimized for robustly identifying candidate high-redshift galaxy clusters
in combined wide-field optical and mid-infrared (MIR) data. The SBS algorithm
is a fusion of the well-tested cluster red-sequence method of Gladders & Yee
(2000) with the MIR 3.6um - 4.5um cluster detection method developed by
Papovich (2008). As with the cluster red-sequence method, the SBS identifies
candidate overdensities within 3.6um - 4.5um color slices, which are the
equivalent of a rest-frame 1.6um stellar bump "red-sequence". In addition to
employing the MIR colors of galaxies, the SBS algorithm incorporates an
optical/MIR (z' - 3.6um) color cut. This cut effectively eliminates foreground
0.2 < z < 0.4 galaxies which have 3.6um - 4.5um colors that are similarly red
as z > 1.0 galaxies and add noise when searching for high-redshift galaxy
overdensities. We demonstrate using the z ~ 1 GCLASS cluster sample that
similar to the red sequence, the stellar bump sequence appears to be a
ubiquitous feature of high-redshift clusters, and that within that sample the
color of the stellar bump sequence increases monotonically with redshift and
provides photometric redshifts accurate to dz = 0.05. We apply the SBS method
in the XMM-LSS SWIRE field and show that it robustly recovers the majority of
confirmed optical, MIR, and X-ray-selected clusters at z > 1.0 in that field.
Lastly, we present confirmation of SpARCS J022427-032354 at z = 1.63, a new
cluster detected with the method and confirmed with 12 high-confidence
spectroscopic redshifts obtained using FORS2 on the VLT. We conclude with a
discussion of future prospects for using the algorithm. |
The initial mass function of early-type galaxies: We determine an absolute calibration of the initial mass function (IMF) of
early-type galaxies, by studying a sample of 56 gravitational lenses identified
by the SLACS Survey. Under the assumption of standard Navarro, Frenk & White
dark matter halos, a combination of lensing, dynamical, and stellar population
synthesis models is used to disentangle the stellar and dark matter
contribution for each lens. We define an "IMF mismatch" parameter
\alpha=M*(L+D)/M*(SPS) as the ratio of stellar mass inferred by a joint lensing
and dynamical models (M*(L+D)) to the current stellar mass inferred from
stellar populations synthesis models (M*(SPS)). We find that a Salpeter IMF
provides stellar masses in agreement with those inferred by lensing and
dynamical models (<\log \alpha>=0.00+-0.03+-0.02), while a Chabrier IMF
underestimates them (<\log \alpha>=0.25+-0.03+-0.02). A tentative trend is
found, in the sense that \alpha appears to increase with galaxy velocity
dispersion. Taken at face value, this result would imply a non universal IMF,
perhaps dependent on metallicity, age, or abundance ratios of the stellar
populations. Alternatively, the observed trend may imply non-universal dark
matter halos with inner density slope increasing with velocity dispersion.
While the degeneracy between the two interpretations cannot be broken without
additional information, the data imply that massive early-type galaxies cannot
have both a universal IMF and universal dark matter halos. | The Use of Faraday Rotation Sign Maps as a Diagnostic for Helical Jet
Magnetic Fields: We present maps of the sign of the Faraday Rotation measure [sign(RM)]
obtained from multi-frequency radio observations on the Very Long Baseline
Array (VLBA). Many of the Active Galactic Nuclei (AGN) considered have B-field
structures with a central "spine" of B-field orthogonal to the jet and/or a
longitudinal B-field near one or both edges of the jet. This structure can
plausibly be interpreted as being caused by a helical/toroidal jet magnetic
field. Faraday Rotation is a rotation of the plane of polarization that occurs
when the polarized radiation passes through a magnetized plasma. The sign of
the RM is determined by the direction of the line-of-sight B-Field in the
region causing the Faraday Rotation, and an ordered toroidal or helical
magnetic field associated with an AGN jet will thus produce a distinctive
bilateral distribution of positive and negative RMs across the jet. We present
and discuss sign(RM) maps and their possible interpretation regarding the
magnetic field geometries for several sources. |
Subsonic accretion and dynamical friction for a black hole moving
through a self-interacting scalar dark matter cloud: We investigate the flow around a black hole moving through a cloud of
self-interacting scalar dark matter. We focus on the large scalar mass limit,
with quartic self-interactions, and on the subsonic regime. We show how the
scalar field behaves as a perfect gas of adiabatic index $\gamma_{\rm ad}=2$ at
large radii while the accretion rate is governed by the relativistic regime
close to the Schwarzschild radius. We obtain analytical results thanks to
large-radius expansions, which are also related to the small-scale relativistic
accretion rate. We find that the accretion rate is greater than for
collisionless particles, by a factor $c/c_s \gg 1$, but smaller than for a
perfect gas, by a factor $c_s/c \ll 1$, where $c_s$ is the speed of sound. The
dynamical friction is smaller than for a perfect gas, by the same factor $c_s/c
\ll 1$, and also smaller than Chandrasekhar's result for collisionless
particles, by a factor $c_s/(cC)$, where $C$ is the Coulomb logarithm. It is
also smaller than for fuzzy dark matter, by a factor $v_0/c \ll 1$. | Hubble Constant Measurement from Three Large-Separation Quasars Strongly
Lensed by Galaxy Clusters: Tension between cosmic microwave background-based and distance ladder-based
determinations of the Hubble constant ${\rm H}_{\rm 0}$ motivates pursuit of
independent methods that are not subject to the same systematic effects. A
promising alternative, proposed by Refsdal in 1964, relies on the inverse
scaling of ${\rm H}_{\rm 0}$ with the delay between the arrival times of at
least two images of a strongly-lensed variable source such as a quasar. To
date, Refsdal's method has mostly been applied to quasars lensed by individual
galaxies rather than by galaxy clusters. Using the three quasars strongly
lensed by galaxy clusters (SDSS J1004+4112, SDSS J1029+2623, and SDSS
J2222+2745) that have both multiband Hubble Space Telescope data and published
time delay measurements, we derive ${\rm H}_{\rm 0}$, accounting for the
systematic and statistical sources of uncertainty. While a single time delay
measurement does not yield a well-constrained ${\rm H}_{\rm 0}$ value,
analyzing the systems together tightens the constraint. Combining the six time
delays measured in the three cluster-lensed quasars gives ${\rm H}_{\rm 0}$ =
74.1 $\pm$ 8.0 km s$^{-1}$ Mpc$^{-1}$. To reach 1$\%$ uncertainty in ${\rm
H}_{\rm 0}$, we estimate that a sample size of order of 620 time delay
measurements of similar quality as those from SDSS J1004+4112, SDSS J1029+2623,
and SDSS J2222+2745 would be needed. Improving the lens modeling uncertainties
by a factor of two and a half may reduce the needed sample size to 100 time
delays, potentially reachable in the next decade. |
High Resolution 3D Relativistic MHD Simulations of Jets: Relativistic magnetized jets are key elements in Active Galactic Nuclei and
in other astrophysical environments. Their structure and evolution involves a
complex nonlinear physics that can be approached by numerical studies only.
Still, owing to a number of challenging computational aspects, only a few
numerical investigations have been undertaken so far. In this paper, we present
high-resolution three dimensional numerical simulations of relativistic
magnetized jets carrying an initially toroidal magnetic field. The presence of
a substantial toroidal component of the field is nowadays commonly invoked and
held responsible for the process of jet acceleration and collimation. We find
that the typical nose cone structures, commonly observed in axisymmetric
two-dimensional simulations, are not produced in the 3D case. Rather, the
toroidal field gives rise to strong current driven kink instabilities leading
to jet wiggling. However, it appears to be able to maintain an highly
relativistic spine along its full length. By comparing low and high resolution
simulations, we emphasize the impact of resolution on the jet dynamical
properties. | The Influence of Ram Pressure on the Evolution of Tidal Dwarf Galaxies: The formation mechanism of tidal dwarf galaxies means they are expected to
contain little or no dark matter. As such, they might be expected to be very
sensitive to their environment. We investigate the impact of ram pressure on
tidal dwarf galaxies in a parameter study, varying dwarf galaxy properties and
ram pressures. We submit model tidal dwarf galaxies to wind-tunnel style tests
using a toy ram pressure model. The effects of ram pressure are found to be
substantial. If tidal dwarf galaxies have their gas stripped, they may be
completely destroyed. Ram pressure drag causes acceleration of our dwarf galaxy
models, and this further enhances stellar losses. The dragging can also cause
stars to lie in a low surface brightness stellar stream that points in the
opposite direction to the stripped gas, in a manner distinctive from tidal
streams. We investigate the effects of ram pressure on surface density
profiles, the dynamics of the stars, and discuss the consequences for dynamical
mass measurements. |
Magnetic field and gravitational waves from the first-order Phase
Transition: We perform the three dimensional lattice simulation of the magnetic field and
gravitational wave productions from bubble collisions during the first-order
electroweak phase transition. Except that of the gravitational wave, the
power-law spectrum of the magnetic field strength is numerically calculated for
the first time, which is of a broken power-law spectrum: $B_{\xi}\propto
f^{0.91}$ for low frequency region of $f<f_\star$ and $B_{\xi}\propto
f^{-1.65}$ for high frequency region of $f>f_\star$ in the thin-wall limit,
with the peak frequency being $f_\star\sim 5$ Hz at the phase transition
temperature 100 GeV. When the hydrodynamics is taken into account, the
generated magnetic field strength can reach $B_\xi\sim 10^{-7}$G at a
correlation length $\xi\sim 10^{-7}$pc, which may seed the large scale magnetic
fields. Our study shows that the measurements of cosmic magnetic field strength
and gravitational waves are complementary to probe new physics admitting
electroweak phase transition. | Probing the accelerating Universe with radio weak lensing in the JVLA
Sky Survey: We outline the prospects for performing pioneering radio weak gravitational
lensing analyses using observations from a potential forthcoming JVLA Sky
Survey program. A large-scale survey with the JVLA can offer interesting and
unique opportunities for performing weak lensing studies in the radio band, a
field which has until now been the preserve of optical telescopes. In
particular, the JVLA has the capacity for large, deep radio surveys with
relatively high angular resolution, which are the key characteristics required
for a successful weak lensing study. We highlight the potential advantages and
unique aspects of performing weak lensing in the radio band. In particular, the
inclusion of continuum polarisation information can greatly reduce noise in
weak lensing reconstructions and can also remove the effects of intrinsic
galaxy alignments, the key astrophysical systematic effect that limits weak
lensing at all wavelengths. We identify a VLASS "deep fields" program (total
area ~10-20 square degs), to be conducted at L-band and with high-resolution
(A-array configuration), as the optimal survey strategy from the point of view
of weak lensing science. Such a survey will build on the unique strengths of
the JVLA and will remain unsurpassed in terms of its combination of resolution
and sensitivity until the advent of the Square Kilometre Array. We identify the
best fields on the JVLA-accessible sky from the point of view of overlapping
with existing deep optical and near infra-red data which will provide crucial
redshift information and facilitate a host of additional compelling
multi-wavelength science. |
Radiative and Kinetic Feedback by Low-Mass Primordial Stars: Ionizing UV radiation and supernova flows amidst clustered minihalos at high
redshift regulated the rise of the first stellar populations in the universe.
Previous studies have addressed the effects of very massive primordial stars on
the collapse of nearby halos into new stars, but the absence of the odd-even
nucleosynthetic signature of pair-instability supernovae in ancient metal-poor
stars suggests that Population III stars may have been less than 100
M$_{\odot}$. We extend our earlier survey of local UV feedback on star
formation to 25 - 80 M$_{\odot}$ stars and include kinetic feedback by
supernovae for 25 - 40 M$_{\odot}$ stars. We find radiative feedback to be
relatively uniform over this mass range, primarily because the larger fluxes of
more massive stars are offset by their shorter lifetimes. Our models
demonstrate that prior to the rise of global UV backgrounds, Lyman-Werner
photons from nearby stars cannot prevent halos from forming new stars. These
calculations also reveal that violent dynamical instabilities can erupt in the
UV radiation front enveloping a primordial halo but that they ultimately have
no effect on the formation of a star. Finally, our simulations suggest that
relic H II regions surrounding partially evaporated halos may expel
Lyman-Werner backgrounds at lower redshifts, allowing stars to form that were
previously suppressed. We provide fits to radiative and kinetic feedback on
star formation for use in both semianalytic models and numerical simulations. | A pressure parametric dark energy model: In this paper, we propose a new pressure parametric model of the total cosmos
energy components in a spatially flat Friedmann-Robertson-Walker (FRW) universe
and then reconstruct the model into quintessence and phantom scenarios,
respectively. By constraining with the datasets of the type Ia supernova (SNe
Ia), the baryon acoustic oscillation (BAO) and the observational Hubble
parameter data(OHD), we find that $\Omega_{m0}=0.270^{+0.039}_{-0.034}$ at the
1$\sigma$ level and our universe slightly biases towards quintessence behavior.
Then we use two diagnostics including $Om(a)$ diagnostic and statefinder to
discriminate our model from the cosmology constant cold dark matter
($\Lambda$CDM) model. From $Om(a)$ diagnostic, we find that our model has a
relatively large deviation from the $\Lambda$CDM model at high redshifts and
gradually approaches the $\Lambda$CDM model at low redshifts and in the future
evolution, but they can be easily differentiated from each other at the
1$\sigma$ level all along. By the statefinder, we find that both of
quintessence case and phantom case can be well distinguished from the
$\Lambda$CDM model and will gradually deviate from each other. Finally, we
discuss the fate of universe evolution (named the rip analysis) for the phantom
case of our model and find that the universe will run into a little rip stage. |
Weak lensing study of 16 DAFT/FADA clusters: substructures and filaments: While our current cosmological model places galaxy clusters at the nodes of a
filament network (the cosmic web), we still struggle to detect these filaments
at high redshifts. We perform a weak lensing study for a sample of 16 massive,
medium-high redshift (0.4<z<0.9) galaxy clusters from the DAFT/FADA survey,
that are imaged in at least three optical bands with Subaru/Suprime-Cam or
CFHT/MegaCam. We estimate the cluster masses using an NFW fit to the shear
profile measured in a KSB-like method, adding our contribution to the
calibration of the observable-mass relation required for cluster abundance
cosmological studies. We compute convergence maps and select structures within,
securing their detection with noise re-sampling techniques. Taking advantage of
the large field of view of our data, we study cluster environment, adding
information from galaxy density maps at the cluster redshift and from X-ray
images when available. We find that clusters show a large variety of weak
lensing maps at large scales and that they may all be embedded in filamentary
structures at megaparsec scale. We classify them in three categories according
to the smoothness of their weak lensing contours and to the amount of
substructures: relaxed (~7%), past mergers (~21.5%), recent or present mergers
(~71.5%). The fraction of clusters undergoing merging events observationally
supports the hierarchical scenario of cluster growth, and implies that massive
clusters are strongly evolving at the studied redshifts. Finally, we report the
detection of unusually elongated structures in CLJ0152, MACSJ0454, MACSJ0717,
A851, BMW1226, MACSJ1621, and MS1621. | An Attractive Proposal for Resolving the Hubble Tension: Dynamical
Attractors that Unify Early and Late Dark Energy: Early dark energy is a promising potential resolution of the Hubble tension.
Unfortunately, many models suffer from the need to fine-tune their initial
conditions to ensure that the epoch of early dark energy coincides with
matter-radiation equality. We propose a class of attractive early dark energy
models where this coincidence arises naturally as a saddle point of a dynamical
system that attracts a large volume of phase-space trajectories regardless of
the initial conditions. The system approaches a global dark energy attractor at
late-times. Our framework therefore unifies early and late dark energy using a
single scalar degree of freedom. We analyze a fiducial attractive early dark
energy model and find that it is disfavored by cosmological data due to the
presence of a long-lived saddle point in the matter era where the scalar plays
the role of an additional component of (non-clustering) dark matter. Our
investigations provide lessons for future model-building efforts aimed at
constructing viable attractive early dark energy models. |
On the Effective Equation of State of Dark Energy: In an effective field theory model with an ultraviolet momentum cutoff, there
is a relation between the effective equation of state of dark energy and the
ultraviolet cutoff scale. It implies that a measure of the equation of state of
dark energy different from minus one, does not rule out vacuum energy as dark
energy. It also indicates an interesting possibility that precise measurements
of the infrared properties of dark energy can be used to probe the ultraviolet
cutoff scale of effective quantum field theory coupled to gravity. In a toy
model with a vacuum energy dominated universe with a Planck scale cutoff, the
dark energy effective equation of state is -0.96. | AKARI Infrared Camera Survey of the Large Magellanic Cloud. I. Point
Source Catalog: We present a near- to mid-infrared point source catalog of 5 photometric
bands at 3.2, 7, 11, 15 and 24 um for a 10 deg2 area of the Large Magellanic
Cloud (LMC) obtained with the Infrared Camera (IRC) onboard the AKARI
satellite. To cover the survey area the observations were carried out at 3
separate seasons from 2006 May to June, 2006 October to December, and 2007
March to July.
The 10-sigma limiting magnitudes of the present survey are 17.9, 13.8, 12.4,
9.9, and 8.6 mag at 3.2, 7, 11, 15 and 24 um, respectively. The photometric
accuracy is estimated to be about 0.1 mag at 3.2 um and 0.06--0.07 mag in the
other bands. The position accuracy is 0.3" at 3.2, 7 and 11um and 1.0" at 15
and 24 um. The sensitivities at 3.2, 7, and 24 um are roughly comparable to
those of the Spitzer SAGE LMC point source catalog, while the AKARI catalog
provides the data at 11 and 15 um, covering the mid-infrared spectral range
contiguously. Two types of catalog are provided: a Catalog and an Archive. The
Archive contains all the detected sources, while the Catalog only includes the
sources that have a counterpart in the Spitzer SAGE point source catalog. The
Archive contains about 650,000, 140,000, 97,000, 43,000, and 52,000 sources at
3.2, 7, 11, 15, and 24 um, respectively. Based on the catalog, we discuss the
luminosity functions at each band, the color-color diagram, and the
color-magnitude diagram using the 3.2, 7, and 11 um band data. Stars without
circumstellar envelopes, dusty C-rich and O-rich stars, young stellar objects,
and background galaxies are located at distinct regions in the diagrams,
suggesting that the present catalog is useful for the classification of objects
towards the LMC. |
A new fitting-function to describe the time evolution of a galaxy's
gravitational potential: We present a new simple functional form to model the evolution of a spherical
mass distribution in a cosmological context. Two parameters control the growth
of the system and this is modelled using a redshift dependent exponential for
the scale mass and scale radius. In this new model, systems form inside out and
the mass of a given shell can be made to never decrease, as generally expected.
This feature makes it more suitable for studying the smooth growth of galactic
potentials or cosmological halos than other parametrizations often used in the
literature. This is further confirmed through a comparison to the growth of
dark matter halos in the Aquarius simulations. | Measuring growth index in a universe with massive neutrinos: A revisit
of the general relativity test with the latest observations: We make a consistency test for the general relativity (GR) through measuring
the growth index $\gamma$ in a universe with massive (sterile/active)
neutrinos. We employ the redshift space distortion measurements to do the
analysis. To constrain other cosmological parameters, we also use other
cosmological measurements, including the Planck 2015 cosmic microwave
background temperature and polarization data, the baryon acoustic oscillation
data, the type Ia supernova JLA data, the weak lensing galaxy shear data, and
the Planck 2015 lensing data. In a universe with massive sterile neutrinos, we
obtain $\gamma=0.624^{+0.055}_{-0.050}$, with the tension with the GR
prediction $\gamma=0.55$ at the 1.48$\sigma$ level, showing that the
consideration of sterile neutrinos still cannot make the true measurement of
$\gamma$ be well consistent with the GR prediction. In a universe with massive
active neutrinos, we obtain $\gamma=0.663\pm0.045$ for the normal hierarchy
case, $\gamma=0.661^{+0.044}_{-0.050}$ for the degenerate hierarchy case, and
$\gamma=0.668^{+0.045}_{-0.051}$ for the inverted hierarchy case, with the
tensions with GR all at beyond the 2$\sigma$ level. We find that the
consideration of massive active neutrinos (no matter what mass hierarchy is
considered) almost does not influence the measurement of the growth index
$\gamma$. |
Constraining deceleration, jerk and transition redshift using cosmic
chronometers, Type Ia supernovae and ISW effect: In this study we present constraints on the deceleration (q) and jerk (j)
parameters using the late time integrated Sachs-Wolfe effect, type Ia
supernovae, and H(z) data . We first directly measure the deceleration and jerk
parameters using the cosmic chronometers data with the Taylor series expression
of H(z).However, due to the unusual variations in the deceleration parameter
with slight changes in other parameters like snap (s) and lerk (l), we found
that direct measurements using the series expression of the H(z) is not a
suitable method for non-Lambda-CDM models and so we will need to derive the
deceleration parameter after constraining density parameters and dark energy
equation of state parameters. Then we present derived values of the
deceleration parameter from Lambda CDM, WCDM and CPL models. We also discuss
the transition redshift (zt) in relation with the deceleration parameter. | Robust Constraint on a Drifting Proton-to-Electron Mass Ratio at z=0.89
from Methanol Observation at Three Radio Telescopes: A limit on a possible cosmological variation of the proton-to-electron mass
ratio $\mu$ is derived from methanol (CH$_3$OH) absorption lines in the
benchmark PKS1830$-$211 lensing galaxy at redshift $z = 0.89$ observed with the
Effelsberg 100-m radio telescope, the Institute de Radio Astronomie
Millim\'{e}trique 30-m telescope, and the Atacama Large
Millimeter/submillimeter Array. Ten different absorption lines of CH$_3$OH
covering a wide range of sensitivity coefficients $K_{\mu}$ are used to derive
a purely statistical 1-$\sigma$ constraint of $\Delta\mu/\mu = (1.5 \pm 1.5)
\times 10^{-7}$ for a lookback time of 7.5 billion years. Systematic effects of
chemical segregation, excitation temperature, frequency dependence and time
variability of the background source are quantified. A multi-dimensional linear
regression analysis leads to a robust constraint of $\Delta\mu/\mu = (-1.0 \pm
0.8_{\rm stat} \pm 1.0_{\rm sys}) \times 10^{-7}$. |
On the Nature of Star Formation at Large Galactic Radii: We have compared far-ultraviolet (FUV), near-ultraviolet (NUV), and Halpha
measurements for star forming regions in 21 galaxies, in order to characterise
the properties of their discs at radii beyond the main optical radius (R25). In
our representative sample of extended and non-extended UV discs we find that
half of the extended UV discs also exhibit extended Halpha emission. We find
that extended UV discs fall into two categories, those with a sharp truncation
in the Halpha disc close to the optical edge (R25), and those with extended
emission in Halpha as well as in the ultraviolet. Although most galaxies with
strong Halpha truncations near R25 show a significant corresponding falloff in
UV emission (factor 10--100), the transition tends to be much smoother than in
Halpha, and significant UV emission often extends well beyond this radius,
confirming earlier results by Thilker et al. (2007) and others. After
correcting for dust attenuation the median fraction of total FUV emission from
regions outside of R25 is 1.7%, but it can be as high as 35% in the most
extreme cases. The corresponding fractions of Halpha emission are approximately
half as large on average. This difference reflects both a slightly lower ratio
of Halpha to UV emission in the HII regions in the outer discs, as well as a
lower fraction of star clusters showing HII regions. Most HII regions in the
extended disc have fluxes consistent with small numbers of ionising O-type
stars, and this poor sampling of the upper initial mass function in small
clusters can probably account for the differences in the emission properties,
consistent with earlier conclusions by Zaritsky & Christlein (2007), without
needing to invoke a significant change in the stellar IMF itself. Consistent
Ha/FUV ratios and brightest HII region to total Halpha fluxes in the inner and
extended discs across our whole galaxy sample demonstrate no evidence for a
change in the cluster luminosity function or the IMF in the low gas density
outer disc. | Multiwavelength study of nearly face-on low surface brightness disk
galaxies: We study the ages of a large sample (1,802) of nearly face-on disk low
surface brightness galaxies (LSBGs) by using the evolutionary population
synthesis (EPS) model PEGASE with exponential decreasing star formation rate to
fit their multiwavelength spectral energy distributions (SEDs) from
far-ultraviolet (FUV) to near-infrared (NIR). The derived ages of LSBGs are 1-5
Gyr for most of the sample no matter the constant or varying dust extinction is
adopted, which are similar to most of the previous studies on smaller samples.
This means that these LSBGs formed their majority of stars quite recently.
However, a small part of the sample (~2-3%) have larger ages as 5-8 Gyr,
meaning their major star forming process may occur earlier. At the same time, a
large sample (5,886) of high surface brightness galaxies (HSBGs) are selected
and studied in the same method for comparisons. The derived ages are 1-5 Gyr
for most of the sample (97%) as well. These may mean that probably these LSBGs
have no much different star formation history from their HSBGs counterparts.
But we should notice that the HSBGs are about 0.2 Gyr younger generally, which
could mean that the HSBGs may have more recent star forming activities than the
LSBGs. |
Unavoidable shear from quantum fluctuations in contracting cosmologies: Contracting cosmologies are known to be flawed with a shear instability,
where the contribution from the anisotropic stress to the overall energy
density grows as $a^{-6}$, with $a$ the scale factor. Classically, whether or
not this contribution becomes important before the bounce depends on its
initial value, which can always be sufficiently fine tuned to make it
irrelevant. However, vacuum quantum fluctuations inevitably provide a
non-vanishing source of anisotropic stress. In this work, we compute the
minimum amount of shear that is obtained if one assumes that it vanishes
initially, but lets quantum fluctuations build it up. In practice, we consider
a massless test scalar field, and describe its quantum fluctuations by means of
the stochastic "inflation" (though here applied to a contracting phase)
formalism. We find that, if the equation-of-state parameter of the contraction
satisfies $w>-1/9$, regardless of when the contracting phase is initiated, the
time at which the shear becomes sizeable is always when the Hubble scale
approaches the Planck mass (which is also where the bounce is expected to take
place). However, if $w<-1/9$, the shear backreaction becomes important much
earlier, at a point that depends on the overall amount of contraction. | The Formation of the First Massive Black Holes: Supermassive black holes (SMBHs) are common in local galactic nuclei, and
SMBHs as massive as several billion solar masses already exist at redshift z=6.
These earliest SMBHs may grow by the combination of radiation-pressure-limited
accretion and mergers of stellar-mass seed BHs, left behind by the first
generation of metal-free stars, or may be formed by more rapid direct collapse
of gas in rare special environments where dense gas can accumulate without
first fragmenting into stars. This chapter offers a review of these two
competing scenarios, as well as some more exotic alternative ideas. It also
briefly discusses how the different models may be distinguished in the future
by observations with JWST, (e)LISA and other instruments. |
Primordial Nucleosynthesis: A Cosmological Probe: During its early evolution the Universe provided a laboratory to probe
fundamental physics at high energies. Relics from those early epochs, such as
the light elements synthesized during primordial nucleosynthesis when the
Universe was only a few minutes old, and the cosmic background photons, last
scattered when the protons (and alphas) and electrons (re)combined some 400
thousand years later, may be used to probe the standard models of cosmology and
of particle physics. The internal consistency of primordial nucleosynthesis is
tested by comparing the predicted and observed abundances of the light
elements, and the consistency of the standard models is explored by comparing
the values of the cosmological parameters inferred from primordial
nucleosynthesis with those determined by studying the cosmic background
radiation. | X-ray nuclear activity in S4G barred galaxies: No link between bar
strength and co-occurrent supermassive black hole fueling: Stellar bars can lead to gas inflow toward the center of a galaxy and
stimulate nuclear star formation. However, there is no compelling evidence on
whether they also feed a central supermassive black hole: by measuring the
fractions of barred active and inactive galaxies, previous studies have yielded
conflicting results. In this paper, we aim to understand the lack of
observational evidence for bar-driven active galactic nucleus (AGN) activity by
studying a sample of 41 nearby (d < 35 Mpc) barred galaxies from the Spitzer
Survey for Stellar Structure in Galaxies. We use Chandra observations to
measure nuclear 2--10 keV X-ray luminosities and estimate Eddington ratios,
together with Spitzer 3.6um imaging to quantify the strength of the stellar bar
in two independent ways: (1) from its structure, as traced by its ellipticity
and boxiness, and (2) from its gravitational torque Q_b, taken as the maximum
ratio of the tangential force to the mean background radial force. In this way,
rather than discretizing the presence of both stellar bars and nuclear
activity, we are able to account for the continuum of bar strengths and degrees
of AGN activity. We find nuclear X-ray sources in 31 out of 41 galaxies with
median X-ray luminosity and Eddington ratio of L_X=4.3x10^{38} erg/s and
L_bol/L_Edd=6.9x10^{-6} respectively, consistent with low-luminosity AGN
activity. Including upper limits for those galaxies without nuclear detections,
we find no significant correlation between any of the bar strength indicators
and the degree of nuclear activity, irrespective of galaxy luminosity, stellar
mass, Hubble type, or bulge size. Strong bars do not favor brighter or more
efficient nuclear activity, implying that at least for the low-luminosity
regime, supermassive black hole fueling is not closely connected to large scale
features. |
Testing the gas mass density profile of galaxy clusters with distance
duality relation: In this paper, assuming the validity of distance duality relation,
$\eta=D_L(z)(1+z)^{-2}/D_A(z)=1$, where $D_A(z)$ and $D_L(z)$ are the angular
and the luminosity distance respectively, we explore two kinds of gas mass
density profiles of clusters: the isothermal $\beta$ model and the
non-isothermal double-$\beta$ model. In our analysis, performed on 38 massive
galaxy clusters observed by \textit{Chandra} (within the redshift range of
$0.14<z<0.89$), we use two types of cluster gas mass fraction data
corresponding to different mass density profiles fitted to the X-ray data.
Using two general parameterizations of $\eta(z)$ (phenomenologically allowing
for distance duality violation), we find that the non-isothermal double-$\beta$
model agrees better with the distance duality relation, while the isothermal
$\beta$ model tends to be marginally incompatible with the Etherington theorem
at 68.3% CL. However, current accuracy of the data does not allow to
distinguish between the two models for the gas-density distribution at a
significant level. | Probing the dark-matter halos of cluster galaxies with weak lensing: Context: Understanding the evolution of the dark matter halos of galaxies
after they become part of a cluster is essential for understanding the
evolution of these satellite galaxies. Aims: We investigate the potential of
galaxy-galaxy lensing to map the halo density profiles of galaxies in clusters.
Methods: We propose a method that separates the weak-lensing signal of the
dark-matter halos of galaxies in clusters from the weak-lensing signal of the
cluster's main halo. Using toy cluster models as well as ray-tracing through
N-body simulations of structure formation along with semi-analytic galaxy
formation models, we test the method and assess its performance. Results: We
show that with the proposed method, one can recover the density profiles of the
cluster galaxy halos in the range 30 - 300 kpc. Using the method, we find that
weak-lensing signal of cluster member galaxies in the Millennium Simulation is
well described by an Navarro-Frenk-White (NFW) profile. In contrast,
non-singular isothermal mass distribution (like PIEMD) model provide a poor
fit. Furthermore, we do not find evidence for a sharp truncation of the galaxy
halos in the range probed by our method. Instead, there is an observed overall
decrease of the halo mass profile of cluster member galaxies with increasing
time spent in the cluster. This trend, as well as the presence or absence of a
truncation radius, should be detectable in future weak-lensing surveys like the
Dark Energy Survey (DES) or the Large Synoptic Survey Telescope (LSST) survey.
Such surveys should also allow one to infer the mass-luminosity relation of
cluster galaxies with our method over two decades in mass. Conclusions: It is
possible to recover in a non-parametric way the mass profile of satellite
galaxies and their dark matter halos in future surveys, using our proposed weak
lensing method. |
Cosmic slowing down of acceleration using $f_{gas}$: We investigate the recent - low redshift - expansion history of the universe
using the most recent observational data. Using only data from 42 measurements
of $f_{gas}$ in clusters, we found that cosmic acceleration could have already
peaked and we are witnessing now its slowing down. This effect, found
previously by Shafieloo, Sahni and Starobinsky in 2010 using supernova data (at
that time the Constitution SNIa sample) appears again using an independent
observational probe. We also discuss the result using the most recent Union 2.1
data set. | Dark matter in galaxies: the dark matter particle mass is about 7 keV: Warm dark matter (WDM) means DM particles with mass m in the keV scale. For
large scales, (structures beyond ~ 100 kpc) WDM and CDM yield identical results
which agree with observations. For intermediate scales, WDM gives the correct
abundance of substructures. Inside galaxy cores, below ~ 100 pc, N-body WDM
classical physics simulations are incorrect because at such scales quantum WDM
effects are important. WDM quantum calculations (Thomas-Fermi approach) provide
galaxy cores, galaxy masses, velocity dispersions and density profiles in
agreement with the observations. For a dark matter particle decoupling at
thermal equilibrium (thermal relic), all evidences point out to a 2 keV
particle. Remarkably enough, sterile neutrinos decouple out of thermal
equilibrium with a primordial power spectrum similar to a 2 keV thermal relic
when the sterile neutrino mass is about 7 keV. Therefore, WDM can be formed by
7 keV sterile neutrinos. Excitingly enough, Bulbul et al. (2014) announced the
detection of a cluster X-ray emission line that could correspond to the decay
of a 7.1 keV sterile neutrino and to a neutrino decay mixing angle of \sin^2 2
\theta ~ 7 10^{-11} . This is a further argument in favour of sterile neutrino
WDM. Baryons, represent 10 % of DM or less in galaxies and are expected to give
a correction to pure WDM results. The detection of the DM particle depends upon
the particle physics model. Sterile neutrinos with keV scale mass (the main WDM
candidate) can be detected in beta decay for Tritium and Renium and in the
electron capture in Holmiun. The sterile neutrino decay into X rays can be
detected observing DM dominated galaxies and through the distortion of the
black-body CMB spectrum. So far, not a single valid objection arose against
WDM. |
Identification of Outflows and Candidate Dual Active Galactic Nuclei in
SDSS Quasars at z=0.8-1.6: We present a sample of 131 quasars from the Sloan Digital Sky Survey at
redshifts 0.8<z<1.6 with double peaks in either of the high-ionization narrow
emission lines [NeV]3426 or [NeIII]3869. These sources were selected with the
intention of identifying high-redshift analogs of the z<0.8 active galactic
nuclei (AGN) with double-peaked [OIII]5007 lines, which might represent AGN
outflows or dual AGN. Lines of high-ionization potential are believed to
originate in the inner, highly photoionized portion of the narrow line region
(NLR), and we exploit this assumption to investigate the possible kinematic
origins of the double-peaked lines. For comparison, we measure the [NeV]3426
and [NeIII]3869 double peaks in low-redshift (z<0.8) [OIII]-selected sources.
We find that [NeV]3426 and [NeIII]3869 show a correlation between
line-splitting and line-width similar to that of [OIII]5007 in other studies;
and the velocity-splittings are correlated with the quasar Eddington ratio.
These results suggest an outflow origin for at least a subset of the
double-peaks, allowing us to study the high-ionization gas kinematics around
quasars. However, we find that a non-neligible fraction of our sample show no
evidence for an ionization stratification. For these sources, the outflow
scenario is less compelling, leaving the dual AGN scenario as a viable
possibility. Finally, we find that our sample shows an anti-correlation between
the velocity-offset ratio and luminosity ratio of the components, which is a
potential dynamical argument for the presence of dual AGN. Therefore, this
study serves as a first attempt at extending the selection of candidate dual
AGN to higher redshifts. | Possible signature of distant foreground in the Planck data: By using the Planck map of the cosmic microwave background (CMB) radiation we
have checked and confirmed the existence of a correlation between supernova
(SN) redshifts, $z_{\rm SN}$, and CMB temperature fluctuations at the SNe
locations, $T_{\rm SN}$, which we previously reported for the Wilkinson
Microwave Anisotropy Probe data. The Pearson correlation coefficient for the
Planck data is $r=+0.38\pm 0.08$ which indicates that the correlation is
statistically significant (the signal is about $5\sigma$ above the noise
level). The correlation becomes even stronger for the type Ia subsample of SNe,
$r_{\rm Ia}=+0.45\pm 0.09$, whereas for the rest of the SNe it is vanishing. By
checking the slopes of the regression lines $T_{\rm SN} / z_{\rm SN}$ for
Planck's different frequency bands we have also excluded the possibility of
this anomaly being caused by the Sunyaev-Zeldovich effect. The remaining
possibility is some, unaccounted for, contribution to the CMB from distant
($z>0.3$) foreground through either the integrated Sachs-Wolfe effect or
thermal emission from intergalactic matter. |
The Dynamics of Galaxy Pairs in a Cosmological Setting: We use the Millennium Simulation, and an abundance-matching framework, to
investigate the dynamical behaviour of galaxy pairs embedded in a cosmological
context. Our main galaxy-pair sample, selected to have separations under 250
kpc/h, consists of over 1.3 million pairs at redshift z = 0, with stellar
masses greater than 10^9 Msun, probing mass ratios down to 1:1000. We use dark
matter halo membership and energy to classify our galaxy pairs. In terms of
halo membership, central-satellite pairs tend to be in isolation (in relation
to external more massive galaxies), are energetically- bound to each other, and
are also weakly-bound to a neighbouring massive galaxy. Satellite-satellite
pairs, instead, inhabit regions in close proximity to a more massive galaxy,
are energetically-unbound, and are often bound to that neighbour. We find that
60% of our paired galaxies are bound to both their companion and to a third
external object. Moreover, only 9% of our pairs resemble the kind of systems
described by idealised binary merger simulations in complete isolation. In sum,
we demonstrate the importance of properly connecting galaxy pairs to the rest
of the Universe. | Stochastic fluctuations of bosonic dark matter: Numerous theories extending beyond the standard model of particle physics
predict the existence of bosons that could constitute the dark matter (DM)
permeating the universe. In the standard halo model (SHM) of galactic dark
matter the velocity distribution of the bosonic DM field defines a
characteristic coherence time $\tau_c$. Until recently, laboratory experiments
searching for bosonic DM fields have been in the regime where the measurement
time $T$ significantly exceeds $\tau_c$, so null results have been interpreted
as constraints on the coupling of bosonic DM to standard model particles with a
bosonic DM field amplitude $\Phi_0$ fixed by the average local DM density.
However, motivated by new theoretical developments, a number of recent searches
probe the regime where $T\ll\tau_c$. Here we show that experiments operating in
this regime do not sample the full distribution of bosonic DM field amplitudes
and therefore it is incorrect to assume a fixed value of $\Phi_0$ when
inferring constraints on the coupling strength of bosonic DM to standard model
particles. Instead, in order to interpret laboratory measurements (even in the
event of a discovery), it is necessary to account for the stochastic nature of
such a virialized ultralight field (VULF). The constraints inferred from
several previous null experiments searching for ultralight bosonic DM were
overestimated by factors ranging from 3 to 10 depending on experimental
details, model assumptions, and choice of inference framework. |
The effect of baryons in the cosmological lensing PDFs: Observational cosmology is passing through a unique moment of grandeur with
the amount of quality data growing fast. However, in order to better take
advantage of this moment, data analysis tools have to keep up the pace.
Understanding the effect of baryonic matter on the large-scale structure is one
of the challenges to be faced in cosmology. In this work, we have thoroughly
studied the effect of baryonic physics on different lensing statistics. Making
use of the Magneticum Pathfinder suite of simulations we show that the
influence of luminous matter on the 1-point lensing statistics of point sources
is significant, enhancing the probability of magnified objects with $\mu>3$ by
a factor of $2$ and the occurrence of multiple-images by a factor $5-500$
depending on the source redshift and size. We also discuss the dependence of
the lensing statistics on the angular resolution of sources. Our results and
methodology were carefully tested in order to guarantee that our uncertainties
are much smaller than the effects here presented. | Dark matter vorticity and velocity dispersion from truncated
Dyson$\unicode{x2013}$Schwinger equations: Large-scale structure formation is studied in a kinetic theory approach,
extending the standard perfect pressureless fluid description for dark matter
by including the velocity dispersion tensor as a dynamical degree of freedom.
The evolution of power spectra for density, velocity and velocity dispersion
degrees of freedom is investigated in a non-perturbative approximation scheme
based on the Dyson$\unicode{x2013}$Schwinger equation. In particular, the
generation of vorticity and velocity dispersion is studied and predictions for
the corresponding power spectra are made, which qualitatively agree well with
results obtained from $N$-body simulations. It is found that velocity
dispersion grows strongly due to non-linear effects and at late times its mean
value seems to be largely independent of the initial conditions. By taking this
into account, a rather realistic picture of non-linear large-scale structure
formation can be obtained, albeit the numerical treatment remains challenging,
especially for very cold dark matter models. |
Measurement of Galaxy Cluster Integrated Comptonization and Mass Scaling
Relations with the South Pole Telescope: We describe a method for measuring the integrated Comptonization (YSZ) of
clusters of galaxies from measurements of the Sunyaev-Zel'dovich (SZ) effect in
multiple frequency bands and use this method to characterize a sample of galaxy
clusters detected in South Pole Telescope (SPT) data. We test this method on
simulated cluster observations and verify that it can accurately recover
cluster parameters with negligible bias. In realistic simulations of an
SPT-like survey, with realizations of cosmic microwave background anisotropy,
point sources, and atmosphere and instrumental noise at typical SPT-SZ survey
levels, we find that YSZ is most accurately determined in an aperture
comparable to the SPT beam size. We demonstrate the utility of this method to
measure YSZ and to constrain mass scaling relations using X-ray mass estimates
for a sample of 18 galaxy clusters from the SPT-SZ survey. Measuring YSZ within
a 0.75' radius aperture, we find an intrinsic log-normal scatter of 21+/-11% in
YSZ at a fixed mass. Measuring YSZ within a 0.3 Mpc projected radius
(equivalent to 0.75' at the survey median redshift z = 0.6), we find a scatter
of 26+/-9%. Prior to this study, the SPT observable found to have the lowest
scatter with mass was cluster detection significance. We demonstrate, from both
simulations and SPT observed clusters, that YSZ measured within an aperture
comparable to the SPT beam size is equivalent, in terms of scatter with cluster
mass, to SPT cluster detection significance. | Clustering of quasars in SDSS-IV eBOSS : study of potential systematics
and bias determination: We study the first year of the eBOSS quasar sample in the redshift range
$0.9<z<2.2$ which includes 68,772 homogeneously selected quasars. We show that
the main source of systematics in the evaluation of the correlation function
arises from inhomogeneities in the quasar target selection, particularly
related to the extinction and depth of the imaging data used for targeting. We
propose a weighting scheme that mitigates these systematics. We measure the
quasar correlation function and provide the most accurate measurement to date
of the quasar bias in this redshift range, $b_Q = 2.45 \pm 0.05$ at $\bar
z=1.55$, together with its evolution with redshift. We use this information to
determine the minimum mass of the halo hosting the quasars and the
characteristic halo mass, which we find to be both independent of redshift
within statistical error. Using a recently-measured quasar-luminosity-function
we also determine the quasar duty cycle. The size of this first year sample is
insufficient to detect any luminosity dependence to quasar clustering and this
issue should be further studied with the final $\sim$500,000 eBOSS quasar
sample. |
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